Skip to main content

Full text of "The Marin County breeding bird atlas : a distributional and natural history of coastal California birds"

See other formats 


Digitized  by  the  Internet  Archive 

in  2013 


http://archive.org/details/marincountybreedOOshuf 


THE  MARIN  COUNTY 
BREEDING  BIRD  ATLAS 


THE  MARIN  COUNTY 
BREEDING  BIRD  ATLAS 

A  Distributional  and  Natural  History 
of  Coastal  California  Birds 


W.  David  Shuford 


Illustrations  by  Keith  Hansen  and  Ane  Rovetta 

Maps  by  Dewey  Livingston 
Photographs  by  Ian  Tait 


California  Avifauna  Series  1 


Bushtit 
Books 


A  Project  of  Point  Reyes  Bird  Observatory 


i 
y       /    / 


Copyright  ©  1993  by  Point  Reyes  Bird  Observatory. 

All  rights  reserved.  No  part  of  this  book  may  be  reproduced 
in  any  manner  whatsoever  without  written  permission  from 
rite  publisher  except  by  a  reviewer  who  wishes  to  quote  brief 
passages  in  a  review  written  for  inclusion  in  a  magazine, 
newspaper,  or  any  electronic  broadcast  media. 


Publisher's  Cataloging-in-Publication  Data 

Shuford,  W.  David,  1949- 

The  Marin  County  breeding  bird  atlas:  a  distributional  and 
natural  history  of  coastal  California  birds, 
p.      cm. 

Includes  bibliographic  references  and  index  (p.       ) 
1.  Birds— California— Marin  County.     2.  Bird  populations- 
California— Marin  County— Geographical  distribution. 
3.  Marin  County  (Calif.)— Natural  history.       I.  Title. 
QL684.C2.S58       1993        598.2'9794'62        92-81834 

ISBN  0-9633050-O-X 

Library  of  Congress  Catalog  Card  Number:  92-81834. 

Published  by      BUSHTIT  BOOKS 
P.O.  Box  233 
Bolinas,  CA  94924 

Printed  in  the  United  States  of  America  by  Braun-Brumfield,  Inc.,  Ann  Arbor,  Michigan. 

Designed  and  typeset  by  Susan  Goldhaber  Murray. 
Cover  design  by  Susan  Claire  Peaslee. 

Printed  with  soy-based  inks  on  acid-free,  recycled  paper. 


The  Marin  County  Breeding  Bird  Adas  is  a  project  of: 

POINT  REYES  BIRD  OBSERVATORY,  4990  Shoreline  Highway,  Stinson  Beach,  CA  94970.  Founded  in 
1965,  Point  Reyes  Bird  Observatory  is  a  nonprofit  membership  organization  dedicated  to  conducting 
ecological  research,  interpreting  research  results  to  the  public,  and  providing  a  scientific  basis  for  conservation 
of  wildlife  and  their  habitats.  Funding  is  supplied  by  research  grants,  contracts,  and  individual  contributions. 
Skilled  volunteer  work  is  the  backbone  of  many  PRBO  projects,  including  die  one  upon  which  this  book  is 
based.  PRBO  provides  credible,  fact-based  information  and  guidelines  for  policy  issues  and  public  and  private 
environmental  stewardship.  Our  studies  of  birds,  marine  mammals,  and  their  habitats  often  involve  issues 
of  national  and  international  significance,  such  as  oil  spill  impacts,  wedands  conservation,  wildlife/fisheries 
conflicts,  and  population  threats  to  neotropical  migrants. 

Suggested  citations  (whole  book  or  individual  species  accounts): 

Shuford,  W.  D.  1993.  The  Marin  County  Breeding  Bird  Atlas:  A  Distributional  and  Natural  History  of 
Coastal  California  Birds.  California  Avifauna  Series  1 .  Bushtit  Books,  Bolinas,  Calif. 

Peake,  H.  1993.  Hooded  Oriole.  In  W.  D.  Shuford.  The  Marin  County  Breeding  Bird  Atlas:  A 
Distributional  and  Natural  History  of  Coastal  California  Birds,  405-408.  California  Avifauna  Series 
1 .  Bushtit  Books,  Bolinas,  Calif. 


To  the  late  David  Gaines, 

my  first  bird  mentor  and  an  inspirational  teacher,  naturalist,  and  conservationist, 


To  Stuart  Johnston, 

a  born  naturalist  who  knows  the  birds  so  well  and  who  lives  as  wild  and  free 

as  any  of  them,  or  us, 


To  Bob  Stewart, 

who  not  only  started  the  Marin  adas  project 

but  as  a  teacher  has  probably  opened  the  eyes  of  more  budding  naturalists  in 

Marin  County  dian  anyone  else, 


and,  of  course, 
To  my  Family. 


Contents 


Contents vii 

List  of  Marin  Breeding  Bird  Atlas  Contributors    .   .   .   xi 
List  of  Marin  Breeding  Bird  Atlas  Participants  .   .   .   .  xii 

Acknowledgments xiii 

Illustrations xiv 

Preface xv 

INTRODUCTION 1 

Historical  Background  of  Breeding  Bird  Adases     .    .     1 
A  Perspective  on  the  History  of  Avian  Distribution 

Studies  in  California 2 

History  of  Breeding  Bird  Studies  in  Marin  County, 

California 3 

Origin  of  the  Marin  County  Breeding  Bird  Adas 
Project 6 

UNDERSTANDING  BIRD  DISTRIBUTION  7 

Marin  County  Topography 7 

Geology  and  Soils      10 

Climate     11 

Seasonality 11 

Temperatures 11 

Precipitation 11 

Pacific  Ocean  Air  and  Current  Cycles 12 

Climatic  Extremes      16 

Coastal  Summer  Fog 16 

MARIN  COUNTY 

BREEDING  BIRD  HABITATS 19 

Marin  County  Plant  Communities     19 

Mixed  Evergreen  Forest 19 

Coast  Live  Oak-California  Bay- 

Madrone  Forest 19 

Tanbark  Oak-Madrone- 

Live  Oak-Douglas  Fir  Forest 19 

Douglas  Fir  Forest      21 

Oak  Woodland  and  Oak  Savannah 21 

Bishop  Pine  Forest 21 

Coast  Redwood  Forest 22 

Grassland     22 

Coastal  Prairie      22 

Valley  Grassland 23 

Coastal  Beach-Dune  Vegetation 23 

Northern  Beach  Association 23 


Northern  Dune  Scrub 24 

Northern  Coastal  Scrub 24 

Coyote  Brush-Sword  Fern  Scrub 24 

Coastal  Sage-Coyote  Brush  Scrub 24 

Chaparral 24 

Chamise  Chaparral 25 

Manzanita  Chaparral      25 

Mixed  Chaparral      25 

Serpentine  Chaparral 25 

Coastal  Salt  Marsh 25 

Coastal  Riparian  Forest 26 

Freshwater  Marsh 26 

Bulrush-Cattail  Marsh 26 

Coastal  Swale 27 

Exotic  Plants      27 

Additional  Breeding  Bird  Habitats 28 

HISTORY  OF  LAND  USE 

IN  MARIN  COUNTY 31 

TIMING  OF  BREEDING 37 

METHODS  EMPLOYED  IN  THE 

MARIN  ATLAS     41 

Grid  System     41 

Participant  Instruction  and  Block  Assignments   .   .  42 

Gathering  Additional  Information 45 

Determining  Adequacy  of  Coverage 46 

Other  Adases 46 

The  Marin  Adas 47 

Data  Summary 48 

Quantitative  Data  on  Abundance 48 

RESULTS  AND  DISCUSSION     51 

Adas  Coverage 51 

Patterns  of  Species  Richness  of  the 

Breeding  Avifauna      51 

Distributional  Highlights  of  Adas  Work 55 

Composition  of  the  Breeding  Avifauna 56 

Marin  County  Breeding  Bird 

Communities 61 

Factors  Limiting  Species  Richness  of  the  Avifauna  61 

CONSERVATION  APPLICATIONS 69 

How  to  Use  This  Book  as  a  Conservation  Tool      .  69 


vi  I 


CONTENTS 


Identification  of  Breeding  Bird  Species  of 

Special  Concern 69 

CONTENT  OF  SPECIES  ACCOUNTS 73 

Adas  Breeding  Distribution  Maps      73 

Key  to  Abundance  and  Distribution  Data 

Accompanying  Atlas  Maps 73 

Seasonal  Status 73 

Breeding  Status      73 

Blocks  Recorded 75 

Fine-Scale  Abundance  Rating  (FSAR) 75 

Relative  Distribution  Index  (RDl) 75 

Overall  Population  Index  (OPI) 75 

Breeding  Criteria  Categories 75 

Confirmation  Index  (CI) 75 

Content  of  Species  Account  Text 76 

Ecological  Requirements 76 

Marin  Breeding  Distribution 76 

Historical  Trends/Population  Threats 76 

Remarks 77 

Observers 77 

Abbreviations 77 

SPECIES  ACCOUNTS 79 

GREBES 
Pied-billed  Grebe 79 

STORM-PETRELS 
Ashy  Storm-Petrel 81 

CORMORANTS 

Double-crested  Cormorant 83 

Brandt's  Cormorant 85 

Pelagic  Cormorant 89 

BITTERNS  AND  HERONS 

American  Bittern 91 

Great  Blue  Heron 92 

Great  Egret 96 

Snowy  Egret 98 

Green-backed  Heron 100 

Black-crowned  Night-Heron 101 

Recent  Population  Trends  of  Marin  County 

Heron  and  Egret  Colonies 103 

WATERFOWL 

Canada  Goose 104 

Wood  Duck 106 

Mallard 109 

Northern  Pintail Ill 

Blue-winged  Teal 113 

Cinnamon  Teal 115 

Northern  Shoveler 116 

Gadwall 118 

Common  Merganser 120 

Ruddy  Duck 122 


NEW  WORLD  VULTURES 

Turkey  Vulture 125 

HAWKS  AND  EAGLES 

Osprey 129 

Black-shouldered  Kite 133 

Northern  Harrier 136 

Sharp-shinned  Hawk 1 39 

Cooper's  Hawk 141 

Red-shouldered  Hawk 144 

Red-tailed  Hawk 146 

Golden  Eagle 148 

FALCONS 

American  Kestrel 151 

Peregrine  Falcon 154 

PHEASANTS  AND  QUAIL 

Ring-necked  Pheasant 158 

California  Quail 161 

RAILS,  GALLINULES,  AND  COOTS 

Black  Rail     164 

Clapper  Rail 166 

Virginia  Rail 169 

Sora 171 

Common  Moorhen 172 

American  Coot 1 74 

PLOVERS 

Snowy  Plover 176 

Killdeer      179 

OYSTERCATCHERS 

Black  Oystercatcher 181 

STILTS  AND  AVOCETS 

Black-necked  Stilt 1 84 

American  Avocet 187 

SANDPIPERS 

Spotted  Sandpiper 189 

GULLS 

Western  Gull 191 

AUKS,  MURRES,  AND  PUFFINS 

Common  Murre 194 

Pigeon  Guillemot 197 

Rhinoceros  Auklet 199 

Tufted  Puffin 201 

PIGEONS  AND  DOVES 

Rock  Dove 203 

Band-tailed  Pigeon 205 

Mourning  Dove      207 

ROADRUNNERS 

Greater  Roadrunner      209 

BARN  OWLS 

Barn  Owl     210 

TYPICAL  OWLS 

Western  Screech-Owl 213 

Great  Horned  Owl 215 

Northern  Pygmy-Owl 217 


vui 


CONTENTS 


Burrowing  Owl 219 

Spotted  Owl 222 

Long-cared  Owl 226 

Short-eared  Owl      229 

Northern  Saw-whet  Owl 231 

POORWILLS 

Common  Poorwill 233 

SWIFTS 

Vaux's  Swift 234 

White-throated  Swift 236 

HUMMINGBIRDS 

Anna's  Hummingbird      237 

Allen's  Hummingbird 240 

KINGFISHERS 

Belted  Kingfisher 241 

WOODPECKERS 

Acorn  Woodpecker 243 

Red-breasted  Sapsucker 245 

Nuttall's  Woodpecker 246 

Downy  Woodpecker 248 

Hairy  Woodpecker 250 

Northern  Flicker 252 

Pileated  Woodpecker 253 

TYRANT  FLYCATCHERS 

Olive-sided  Flycatcher 255 

Western  Wood-Pewee 256 

Pacific-slope  Flycatcher     258 

Black  Phoebe 261 

Say's  Phoebe 262 

Ash-throated  Flycatcher 264 

Cassin's  Kingbird 265 

Western  Kingbird 266 

LARKS 

Horned  Lark 268 

SWALLOWS 

Purple  Martin 269 

Tree  Swallow 272 

Violet-green  Swallow 273 

Northern  Rough-winged  Swallow 275 

Cliff  Swallow 276 

Barn  Swallow 278 

JAYS  AND  CROWS 

Steller'sjay 280 

Scrub  Jay 282 

American  Crow 284 

Common  Raven 286 

TITMICE 

Chestnut-backed  Chickadee 288 

Plain  Titmouse 290 

BUSHTITS 

Bushtit 292 

NUTHATCHES 

Red-breasted  Nuthatch 294 


White-breasted  Nuthatch      296 

Pygmy  Nuthatch 298 

CREEPERS 

Brown  Creeper 301 

WRENS 

Rock  Wren 303 

Bewick's  Wren 305 

House  Wren 307 

Winter  Wren 309 

Marsh  Wren 310 

DIPPERS 

American  Dipper 312 

KINGLETS  AND  GNATCATCHERS 

Golden-crowned  Kinglet 313 

Blue-gray  Gnatcatcher 314 

THRUSHES 

Western  Bluebird 316 

Swainson's  Thrush 318 

Hermit  Thrush 320 

American  Robin 322 

WRENTITS 

Wrentit 324 

MOCKINGBIRDS  AND  THRASHERS 

Northern  Mockingbird      327 

California  Thrasher 329 

SHRIKES 

Loggerhead  Shrike 330 

STARLINGS 

European  Starling 333 

VIREOS 

Solitary  Vireo 337 

Hutton's  Vireo 338 

Warbling  Vireo 340 

WOOD-WARBLERS 

Orange-crowned  Warbler 342 

Northern  Parula 343 

Yellow  Warbler 346 

Yellow-rumped  Warbler 348 

Black-throated  Gray  Warbler 350 

Hermit  Warbler 352 

MacGillivray's  Warbler 353 

Common  Yellowthroat     355 

Wilson's  Warbler 358 

Yellow-breasted  Chat 360 

TANAGERS 

Western  Tanager 362 

CARDINALINE  GROSBEAKS  AND  BUNTINGS 

Black-headed  Grosbeak 364 

Lazuli  Bunting      367 

EMBERIZINE  SPARROWS 

Rufous-sided  Towhee 369 

California  Towhee 371 

Rufous-crowned  Sparrow     372 


IX 


CONTENTS 


Chipping  Sparrow 374 

Black-chinned  Sparrow 376 

Lark  Sparrow      378 

Sage  Sparrow      379 

Savannah  Sparrow 380 

Grasshopper  Sparrow      382 

Song  Sparrow 385 

White-crowned  Sparrow 388 

Dark-eyed  Junco 390 

NEW  WORLD  BLACKBIRDS  AND  ORIOLES 

Red-winged  Blackbird      392 

Tricolored  Blackbird 394 

Western  Meadowlark 397 

Brewer's  Blackbird 398 

Brown-headed  Cowbird      401 

Hooded  Oriole 405 

Northern  Oriole 409 

CARDUELINE  FINCHES 

Purple  Finch 411 

House  Finch 412 

Red  Crossbill     414 

Pine  Siskin 417 

Lesser  Goldfinch 418 

Lawrence's  Goldfinch      420 

American  Goldfinch 422 

OLD  WORLD  SPARROWS 

House  Sparrow 424 

SPECIES  OF  UNCLEAR  BREEDING  STATUS 

OR  POTENTIAL  BREEDERS     429 

Eared  Grebe 429 

Western  Grebe/Clark's  Grebe 429 

Fork-tailed  Storm-Petrel 429 

Leach's  Storm-Petrel 429 

Little  Blue  Heron     429 

Cattle  Egret 430 

Fulvous  Whisding-Duck 430 

Waterfowl 430 

Green-winged  Teal 430 


American  Wigeon      430 

Canvasback 430 

Redhead 430 

Lesser  Scaup 430 

California  Condor 430 

Bald  Eagle 430 

Prairie  Falcon      431 

Wild  Turkey 431 

Wilson's  Phalarope 431 

Heermann's  Gull 432 

California  Gull 432 

Terns 432 

Caspian  Tern 432 

Forster's  Tern      432 

Least  Tern 432 

Marbled  Murrelet      432 

Yellow-billed  Cuckoo 432 

Chimney  Swift 433 

Black-chinned  Hummingbird 433 

Willow  Flycatcher      433 

Bank  Swallow 433 

Cedar  Waxwing 433 

American  Redstart 433 

Bobolink 434 

Yellow-headed  Blackbird 434 

Great-tailed  Grackle 434 

APPENDLXES 435 

A.  Data  from  three  Spring  Bird  Counts  conducted 

in  Marin  County  from  1977  to  1987 435 

B.  Numbers  of  birds  tallied  on  two  USFWS 
Breeding  Bird  Survey  routes  conducted  in  Marin 
County  from  1972  to  1986 443 

C.  A  list  of  Breeding  Bird  Censuses  conducted  in 
Marin  County  from  1951  to  1990 444 

LITERATURE  CITED 445 

INDEX 477 


Marin  Breeding  Bird  Adas 
Contributors 


Cosponsors— Point  Reyes  Bird  Observatory  and  Marin  Audubon  Society 

Overall  Coordinator  1982,  Compiler,  and  Editor— W.  David  Sbuford 

Overall  Coordinator  1976  to  1978— Robert  M.  Stewart 

Area  Coordinators  1982— Betty  Burridge  (Tomales  Area),  Scott  Carey  (Novato  Area),  Bill 
Lenarz  (South  Marin),  Dave  Shuford  (West  Marin) 

Computer  Entry  and  Summary— Bill  Lenarz 

Species  Account  Authors— John  R.  Arnold  (Nordiern  Mockingbird),  Edward  C.  Beedy 
(Tricolored  Blackbird),  A.  Sidney  England  (Black-chinned  Sparrow,  Sage  Sparrow),  Geoftrey  R. 
Geupel  (Wrentit),  Walter  D.  Koenig  (Acorn  Woodpecker),  Holly  Peake  (Hooded  Oriole),  Helen 
M.  Pratt  (History  of  Marin  County  heron  and  egret  colonies),  Stephen  I.  Rothstein  (Brown- 
headed  Cowbird),  W.  David  Shuford  (153  species),  Robert  M.  Stewart  (Wilson's  Warbler),  and 
Pamela  L  Williams  (Northern  Oriole). 

Reviewers— Edward  C.  Beedy  (landbirds,  main  text),  Pete  H.  Bloom  (diurnal  raptors),  Seth 
Bunnell  (Spotted  Owl),  Scott  Carey  (landbirds),  Harry  R.  Carter  (seabirds),  David  F.  DeSante 
(main  text),  Richard  A.  Erickson  (short  species  accounts),  Jules  G.  Evens  (rails,  Osprey),  Sam 
Fitton  (Hooded  Oriole),  Gordon  I.  Gould,  Jr.  (Spotted  Owl),  Stephen  L.  Granholm  (landbirds), 
Roger  D.  Harris  (Pileated  Woodpecker),  Paul  R.  Kelly  (Clapper  Rail),  Bill  Lenarz  (landbirds, 
main  text),  M.  Robert  McLandress  (waterfowl),  Joseph  Morlan  (short  species  accounts),  Gary 
W.  Page  (shorebirds),  Helen  M.  Pratt  (egrets  and  herons),  Steve  Simmons  (Wood  Duck), 
William  J.  Sydeman  (seabirds,  Pygmy  Nuthatch),  Irene  C.  Timossi  (landbirds),  Brian  J.  Walton 
(Peregrine  Falcon),  Jon  Winter  (owls). 


XI 


Marin  Breeding  Bird  Atlas 
Participants 


Debbie  Ablin,  Julia  Allen,  Sarab  Allen,  Jane  Anderson,  Philip  Ashman,  Audubon  Canyon 
Ranch  Research  Associates,  Stephen  F.  Bailey,  Nancy  Barbour,  Steve  Barbour,  Brenda  Barten, 
Jim  Bartholomew,  Joan  Basore,  Dennis  BeaU^-Max  Beckwith,  Gordon  Beebe,  Ted  Beedy,  Lori 
Belton,  Irene  Biagi,  Steve  Bobzien,  Betty  Boyd,  Warren  Bray,  Joan  Breece,  Tony  Briggs,  Patty 
Briggs,  Betty  Burridge,  Leanne  Bynum,  Kurt  Campbell,  Jean  Canepa,  Scott  Carey,  Barbara 
Chase,  Frank  ck  Carolyn  Christian,  Peter  Colasanti,  Carolyn  Corey,  Robin  Dager,  Rosamond 
Day,  Dave  DeSante,  John  Dillon,  Peter  &  Louise  Dolcini,  Doug  Ellis,  Michael  Ellis,  Jules  Evens, 
Carter  Faust,  Mike  Fennell,  Mary  Fishman,  Barbara  Ford,  Carol  Fraker,  Mary  Gillman,  Helen 
ck  Richard  Classman,  Terry  Goldblatt,  Jon  Goodchild,  Steve  Granholm,  Nancy  Hanson,  Tony 
Harrow,  Kristi  Hein,  Luanna  Helfman,  Emmy  Hill,  Bob  Hogan,  Craig  Hohenberger,  David 
Holway,  Joan  Howard,  Ken  Howard,  George  Hugenberg,  Doug  Judell,  Bill  Keener,  John 
Kipping,  Kathy  Kipping,  Gerry  Kleynenberg,  Elsa  Konig,  Bob  Lampee,  Robert  H.  Laws,  Jr.,  Rick 
LeBaudour,  Bill  Lenarz,  R.  A.  Lewis,  Stephen  M.  Long,  Tom  Love,  Shirley  McArdell,  Flora 
Maclise,  Gary  McCurdy,  Grace  McMichael,  Bill  Manolis,  Marie  Mans,  Buck  Marcussen,  Gloria 
Markowitz,  Leah  Marks,  Mary  Mayer,  Sarah  Mayer,  Audrey  Miller,  Stephen  H.  Morrell,  Brenda 
Myron,  Patricia  ck  Anthony  Napolitan,  Adeene  Nelligan,  Dan  Nelson,  Don  Neubacher, 
La  Verne  Nickel,  Marcia  Nute,  Gary  Page,  Carmen  Patterson,  Holly  Peake,  Susan  Claire  Peaslee, 
Treet  Pellitier,  PRBO's  Palomarin  Staff  and  Volunteers,  Charlotte  Poulsen,  Lina  Jane  Prairie, 
Helen  Pratt,  Alton  ("Bob")  Raible,  Elaine  ck  Tom  Reale,  Liza  Riddle,  Inez  Riney,  Mary  Louise 
Rosegay,  Ane  Rovetta,  Allen  Royer,  Corinne  Ryan,  Mary  Ann  Sadler,  Barbara  Salzman,  Susan 
Sanders,  Phil  ck  Margaret  Schaeffer,  Bob  ck  Ruth  Scott,  Bob  Seely,  Sid  ck  Nancy  Shadle, 
Marianne  Shepard,  Dave  Shuford,  Dianne  Sierra,  Sue  Smith,  Vernon  Smith,  Eric  Sorenson, 
Bruce  Sorrie,  Barry  Spitz,  Spring  Bird  Count  Participants  (Even  Cheaper  Thrills,  Pt.  Reyes 
Peninsula,  ck  South  Marin— Appendix  A),  John  A.  Sproul,  Jr.,  Rich  Stallcup,  Jean  Starkweather, 
Lynne  Stenzel,  Robert  M.  Stewart,  Nick  Story,  Helen  Strong,  Tim  Sullivan,  Ian  Tait,  Lynn 
Tennefoss,  Gil  Thomson,  Carol  Thoney,  Noel  Thoney,  Irene  Timossi,  Dorothy  Tobkin, 
Beverly  Treffinger,  Ed  Vine,  Pat  Welsh,  Bette  Wentzel,  Janet  Wessel,  Jack  Whetstone,  Jim 
White,  Diane  Williams,  Pam  Williams,  Summer  Wilson,  Claire  Wolfe,  Michael  Wolfe,  Keiko 
Yamane,  Vincent  S.  Yoder,  Florence  Youngberg,  Bob  ck  Carol  Yutzy,  Mark  Zumsteg.  Many 
other  people  contributed  additional  observations  via  the  above  participants  or  direcdy  to  the 
coordinators. 


xu 


Acknowledgments 


Financial  support  for  the  atlas  project  was  provided  by  generous  contributions  from  an 
anonymous  donor,  Golden  Gate  Audubon  Society,  Marin  Audubon  Society,  Marin  County 
Fish  and  Game  Fund,  Marin  Municipal  Water  District,  Andrea  Meyer,  Sequoia  Audubon 
Society,  Lynne  Stenzel,  and,  especially,  the  general  membership  of  Point  Reyes  Bird  Observatory. 
The  board,  administration,  and  staff  of  Point  Reyes  Bird  Observatory  provided  tremendous 
logistical  and  moral  support  throughout  the  evolution  of  the  project  from  the  initial  stages  of  field 
work  through  the  completion  of  the  book.  Special  thanks  to  Gary  Page  for  granting  me  an 
extended  leave  from  my  duties  in  PRBO's  Coastal  and  Estuarine  Program  to  work  on  this  book. 
Successive  Executive  Directors— Jane  Church,  Burr  Heneman,  and  Don  McCrimmon— lent  their 
full  support  to  the  project,  and  Laurie  Wayburn's  commitment  at  a  crucial  stage  enabled  the 
completion  of  the  final  product  you  hold  in  your  hands. 

Janet  Kjelmyr,  Lisle  Lee,  Michelle  Morris,  Meg  Sanders,  Meg  Simonds,  Janice  Tweedy,  and, 
particularly,  Susan  Goldhaber  Murray  and  Liz  Tuomi  were  invaluable  in  crafting  my  handwrit- 
ten or  hastily  typed  text  and  tables  into  a  polished  manuscript .  .  .  bless  their  souls.  Susan  Claire 
Peaslee  was  a  godsend  in  rising  well  above  the  call  of  duty  to  deftly  manage  the  early  and  middle 
stages  of  book  production  and  copyediting  ...  I  can't  thank  her  enough.  Liz  Tuomi  contributed 
additional  copyediting  skills  and  along  widi  Pam  Williams  and  Susan  Goldhaber  Murray 
proofread  all  of  the  manuscript.  Mary  Anne  Stewart  skillfully  copyedited  the  entire  final  version 
of  the  manuscript.  Edris  Cole,  Dianne  Sierra,  and  Meryl  Sundove  proofread  the  spellings  of 
observer  names.  Thanks  to  Bertha  Rains  for  an  initial  literature  search,  and  to  Karen  Hamilton 
for  locating  and  obtaining  many  hard  to  find  references  and  for  providing  cataloging  data  for 
the  finished  book.  Many  thanks  to  Julia  Gennert  for  pasting  up  the  illustrations  on  the  typeset 
manuscript.  Helen  and  Paul  Green  generously  provided  a  true  home  away  from  home  when  I 
needed  to  spend  innumerable  days  and  nights  researching  literature  at  the  Biology  Library  at 
U.C.  Berkeley.  Special  thanks  to  Scott  Carey,  Doug  Judell,  Bill  Lenarz,  Bob  Stewart,  Irene 
Timossi,  and  Jules  Evens  for  spending  enormous  amounts  of  time  in  die  field  and  sharing  their 
vast  knowledge  of  Marin  County  breeding  birds.  Many  dianks  to  the  numerous  Marin  County 
landowners  whp  provided  access  to  their  lands  without  which  our  field  work  would  have  suffered 
gready. 

Jules  Evens  (rails  and  Osprey),  Allen  Fish  (diurnal  raptors),  Roger  Hothem  (herons  and 
egrets),  John  Kelly  (herons  and  egrets),  Gary  Page  (Snowy  Plovers),  Helen  Pratt  (herons  and 
egrets),  and  Dave  DeSante,  Geoff  Geupel,  and  Bruce  Sorrie  (Palomarin  landbirds)  kindly 
provided  data  from  their  studies.  L  Richard  Mewaldt  provided  much  of  die  material  in  the 
White-crowned  Sparrow  account.  Sheila  Hershon  searched  the  files  of  die  California  Center  for 
Wildlife  for  breeding  records  of  Western  Screech-Owl  in  Marin  County  during  the  adas  period. 
Numerous  odiers  supplied  essential  facts  and  figures.  Dennis  Beall  drew  the  base  map  used  to 
construct  the  adas  map  for  each  species.  Many  dianks  to  Keidi  Hansen,  Dewey  Livingston,  Ane 
Rovetta,  and  Ian  Tait  for  their  patience  in  waiting  for  my  plodding  writing  to  catch  up  with  their 
inspirational  artwork  which  graces  these  pages.  When  all  of  the  above  was  said  and  done,  Susan 
Goldhaber  Murray  used  her  remarkable  blend  of  computer  skills,  problem  solving  abilities, 
artistic  talents,  and  great  patience  to  craft  the  text  into  a  well  organized  and  aesthetically  pleasing 
book,  for  which  she  should  be  duly  proud.  Speaking  for  die  birds  as  well,  I  give  final  and 
heartfelt  thanks  to  all  diose  listed  above,  or  not,  who  in  one  capacity  or  another  volunteered  their 
time  because  of  a  deep  concern  for  birds  and  their  environment. 

xiii 


Illustrations 


Bird  Drawings  —  Keith  Hansen 

Pages  iii,  xvi,  90,  124,  128,  160,  208,  221,  239,  259,  274,  321,  366,  384,  387,  and 


Marin  County  Maps  —  Dewey  Livingston 
Pages  8,  9,  14,  20,  34 

Landscape  and  Habitat  Drawings  —  Ane  Rovetta 

Pages  6,  18,  21,  22,  23,  24,  25,  26,  27,  28,  30,  36,  50,  71,  78,  back  cover,  and  oak 
spray  dingbats/snippets  throughout 

Bird  Photographs  —  Ian  Tait 

Pages  102,  150,  186,  190,  196,  242,  249,  291,  300,  308,  326,  336,  339,  341,  361, 
375,  and  back  cover 


xiv 


Preface 


The  contents  of  this  book  evolved  over  a  long  period,  at  first  expanding  in  scope,  only  later 
to  contract.  Beyond  the  grid-based  distribution  maps,  there  is  no  set  formula  (nor  should 
there  be)  as  to  what  warrants  inclusion  in  a  breeding  bird  adas,  or  as  to  whether  it  even  need  be 
a  book:  some  county  adas  projects  have  been  published  as  short  papers  in  local  ornithological 
journals  (e.g.,  Klimkiewicz  6k  Solem  1978).  State  or  provincial  adas  books  published  in  North 
America  have  ranged  from  compilations  of  computer  data  printouts  (Adamus  1987)  to  full-scale 
books  for  Vermont  (Laughlin  6k  Kibbe  1985),  Ontario  (Cadman  et  al.  1987),  and  New  York 
(Andrle  6k  Carroll  1988).  These  three  books  and  their  counterparts  from  other  countries  include 
extensive  introductory  and  interpretive  material  along  with  species  accounts  accompanying  the 
maps  that  provide  detail  on  such  topics  as  habitat  preferences,  various  aspects  of  the  species' 
breeding  biology,  and  historical  trends  of  populations.  The  increasing  inclination  of  writers  to 
use  natural  history  information  to  provide  a  framework  for  understanding  distributional  patterns 
is  followed  by  this  author  as  well. 

Although  some  would  argue  that  the  maps  should  be  the  highlight  of  an  adas  book— after  all, 
they  are  usually  the  main  data  generated  by  the  field  work— they  are  lifeless  abstractions  without 
an  understandng  of  the  intricate  web  of  niche  requirements  that  each  species  must  meet  for 
survival,  and  without  survival  there  is  no  distribution  or  map.  Hence,  the  reader  will  encounter 
a  strong  ecological  bent  in  the  material  contained  in  this  adas.  The  stage  is  set  for  interpreting 
the  maps,  the  species  accounts,  and  the  facts  and  concepts  elucidated  by  the  adas  project  by  first 
describing  Marin  County's  geographic  and  geologic  setting,  the  seasonal  oceanic  and  climatic 
cycles  affecting  birds  here,  and  the  county's  principal  bird  habitats— the  realm  in  which  the 
mundane,  dramatic,  and  poignant  events  of  the  lives  of  our  breeding  birds  unfold.  Also,  a 
historical  perspective  is  emphasized  in  describing  changing  land  use  practices,  bird  population 
trends,  and  how  the  concept  of  the  bird  adas  has  transformed  the  way  we  approach  distributional 
studies. 

A  great  deal  of  additional  material  written  for  this  book  had  to  be  left  out  because  of  time, 
space,  and  financial  considerations.  The  original  intent  was  to  broaden  the  discussion  of  bird 
distribution  patterns  to  include  all  of  coastal  northern  California,  and  to  provide  additional 
species  accounts  for  other  species  of  birds  that  breed  elsewhere  in  this  region  but  not  in  Marin 
County.  Much  of  this  material  was  contributed  by  others  and  I  lament  its  loss  from  die  present 
publication  and  the  diversion  of  many  peoples'  talents  from  other  projects.  Their  mark  was  left 
on  this  book  nonetheless. 

Ralph  Hoffmann  (1927)  in  his  enchanting,  but  now  underappreciated,  field  guide,  Birds  of 
the  Pacific  States,  remarked  diat  "one  cannot  have  too  many  good  bird  books."  The  author  will 
feel  the  long  effort  of  writing  was  well  wordi  it  if  but  a  few  readers  deem  the  present  book  to  be 
in  that  category.  True  satisfaction,  though,  will  come  only  if  some  acquire,  in  part  dirough 
reading,  a  deeper  appreciation  and  fascination  with  our  winged  companions  that  motivates  them 
to  be  better  stewards  of  the  Eardi.  May  we  be  lucky  enough  to  meet  in  nature's  heardand  and 
share  its  many  pleasures  together. 

Dave  Shuford 
Bolinas,  California 
March  1 993 


xv 


6itf-)  Manser) 


A  tiny  fuss-budget  of  a  Bushtit  scolds  a  prowling  Scrub  fay  while  its  partner  warily  peers  from  the 
nest  hole.    Drawing  by  Keith  Hansen,  I  990. 


INTRODUCTION 


Lest  the  uninitiated  reader  be  led  to  believe  that  the  problems  of  distribution  of  the  birds  of  California  are  in  the  main  solved 
and  fully  presented  in  this  work,  may  we  quickly  disillusion  him. 

—  Joseph  Grinnell  and  Alden  H.  Miller, 
The  Distribution  of  the  Birds  of  California 


UNTIL  THE  LATE  1960s,  bird  distributions  were  tradi- 
tionally mapped  using  random  observations  from 
scattered  sources,  often  collected  over  lengthy  periods  of 
time.  In  addition,  breeding  distribution  maps  usually  did 
not  distinguish  between  records  of  a  species  based  solely 
on  presence  during  the  breeding  season  and  those  backed 
with  positive  proof  of  breeding.  Even  when  aided  by 
knowledge  of  species'  habitat  needs,  this  manner  of  map- 
ping was  largely  a  subjective  process.  Numerous  judgments 
had  to  be  made  when  encountering  the  inevitable  gaps  in 
the  record  in  seemingly  suitable  habitat  or  isolated  occur- 
rences in  habitats  of  questionable  suitability.  Usually  a 
great  deal  of  uncertainty  remained  over  whether  the  pattern 
of  distribution  plotted  was  pardy  an  artifact  of  uneven 
knowledge  of  the  area  in  question,  whether  breeding 
records  were  sufficiendy  documented,  or  whether  the 
actual  distribution  had  changed  over  the  course  of  the 
extended  period  of  data  collection.  These  problems  were 
especially  acute  where  observers  were  few  but  could  not  be 
overcome  even  in  areas,  such  as  Great  Britain,  with  a  very 
high  proportion  of  observers  in  the  population  and  a 
history  of  ornithological  exploration  stretching  back  for 
centuries.  The  lack  of  an  adequately  documented  record  of 
changes  in  the  distribution  and  abundance  of  highly  visi- 
ble species  such  as  birds  has  been  particularly  frustrating 
for  conservationists  and  managers.  With  subjective  map- 
ping methods  using  data  from  the  entire  historical  record, 
only  the  most  dramatic  changes  in  distribution  and  abun- 
dance were  noticeable.  Often  an  awareness  of  a  reduced 
distribution  or  population  decline  was  apparent  only  dur- 
ing the  later  stages,  when  conservation  efforts  were  the 
most  difficult  to  implement. 

All  this  changed  in  the  late  1960s  when  avian  distribu- 
tion studies  were  revolutionized  by  the  simple  concept  of 
the  breeding  bird  adas— a  compilation  of  accurate  distribu- 
tion maps  for  all  the  bird  species  in  a  particular  geographi- 
cal area  under  study.  At  the  outset,  the  area  is  divided  with 
a  uniform  grid  of  equal-sized  adas  blocks  (rectangles  or 
squares).  These  blocks  are  initially  the  basic  units  of  field 
study  and  ultimately  the  mapping  units  for  bird  distribu- 


tion. In  addition  to  noting  presence  or  absence,  field 
workers  record  for  each  species  the  highest  category  of 
breeding  evidence  they  observe,  based  on  well-defined 
criteria  for  possible,  probable,  and  confirmed  breeding.  By 
conducting  thorough  field  work  in  each  of  these  blocks 
during  a  several-year  period  (usually,  five  years),  the  current 
details  of  avian  distribution  can  effectively  be  frozen  in 
time.  Complete  coverage  of  all  blocks  over  a  short  time 
span  avoids  the  main  weaknesses  of  earlier  mapping  stud- 
ies and  enables  changes  in  distribution  to  be  easily  docu- 
mented by  replicating  the  work  in  future  years. 

Historical  Background  of 
Breeding  Bird  Atlases 

Ferguson-Lees  (1976),  Robbins  (1982),  and  Laughlin  et  al. 
(1982)  have  summarized  the  history  of  mapping  bird 
distributions.  Phillips'  (1922-1926)  A  Natural  History  of 
the  Ducks  was  the  first  serious  attempt  to  map  the  distribu- 
tion of  a  large  number  of  birds.  In  North  America,  the  first 
books  to  map  selected  species  were  Birds  of  New  Mexico 
(Bailey  1928),  Florida  Bird  Life  (Howell  1932),  and  The 
Distribution  of  the  Birds  of  California  (Grinnell  6k  Miller 
1944).  In  Europe,  the  first  attempts  to  map  bird  distribu- 
tion over  broad  areas  were  the  Birds  of  the  Soviet  Union 
(Dement'ev  &  Gladkov  1951-1954),  A  Field  Guide  to  the 
Birds  of  Britain  and  Europe  (Peterson  et  al.  1954)  and  the 
Atlas  of  European  Birds  (Voous  1960).  In  North  America, 
The  Birds  of  Canada  (Godfrey  1966)  and  Birds  of  North 
America  (Robbins  et  al.  1966)  were  the  pioneer  works  in 
this  vein. 

The  concept  of  mapping  distribution  with  the  aid  of  a 
grid  had  its  origin  with  a  German  botanist,  Heermann 
Hoffmann,  who  in  1860  published  the  first  grid-derived 
maps  of  certain  plants  in  central  Europe.  Although  orni- 
thologists began  on  a  subjective  basis  to  use  grids  to  plot 
the  distribution  of  certain  bird  species  in  Britain  in  the 
1950s  (Norris  1960,  Prestt  ck  Bell  1966),  the  main 
impetus  for  the  current  adas  movement  was  the  publica- 
tion by  the  Botanical  Society  of  the  British  Isles  of  the  Atlas 


1 


Historical  Background 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Historical  Studies -California 


of  the  British  Flora  (Perring  &.  Walters  1962).  This  work 
systematically  mapped  the  distribution  of  the  British  flora 
by  10-km  squares.  Things  have  never  been  quite  the  same 
since,  as  British  bird  students  jumped  into  die  objective 
comprehensive  adasing  of  breeding  birds  with  a  passion. 
The  pilot  project  covering  three  counties  in  England  began 
in  1966  and  was  published  as  the  Atlas  of  Breeding  Birds  of 
the  West  Midlands  (Lord  &.  Munns  1970).  Following  close 
on  its  heels  was  the  awe-inspiring  effort  of  The  Atlas  of 
Breeding  Birds  of  Britain  and  Ireland  (Sharrock  1976), 
where  over  10,000  observers  completed  field  work  from 
1968  to  1972  in  each  of  the  3682  10-km  adas  squares 
covering  all  of  Britain  and  Ireland!  While  the  British  field 
work  was  still  in  progress,  other  European  atlas  projects 
were  initiated  and  subsequendy  multiplied  profusely  until 
by  1981  at  least  16  European  countries  had  completed  or 
started  atlas  projects  (Robbins  1982).  Avian  adasing  soon 
spread  to  other  continents  as  well,  and  adasing  already  had 
been  applied  to  map  the  distribution  of  other  life  forms 
ranging  from  marine  algae  to  a  host  of  marine  and  terres- 
trial invertebrates.  Not  ones  to  rest  on  their  laurels,  the 
British  soon  began  and  completed  an  adas  of  winter  bird 
distribution  (Lack  1986).  They  are  also  currendy  working 
toward  the  completion  of  dieir  second  breeding  bird  adas 
diat  will  resurvey  all  of  Britain  and  Ireland. 

In  North  America  the  first  recognition  of  the  impor- 
tance of  grid-based  mapping  of  bird  distribution  came  in 
the  1960s  (Skarr  1967,  1969)  and  resulted  in  the  publica- 
tion of  Montana  Bird  Distribution:  Preliminary  Mapping  by 
Latilong  (Skarr  1975).  Montana  was  divided  into  47 
1  °-blocks  of  longitude  and  latitude,  and  maps  were  con- 
structed for  each  species.  Although  different  categories  of 
breeding  evidence  were  presented  where  applicable,  the 
initial  latilong  study  differed  in  several  important  ways 
from  most  other  atlas  projects.  First,  the  size  of  the  blocks 
was  very  large  compared  with  breeding  bird  adas  blocks— a 
latilong  in  Montana  is  nearly  100  times  as  large  as  a  10-km 
square.  Secondly,  species  were  initially  mapped  in  a  lati- 
long if  diey  occurred  in  any  season,  not  just  the  breeding 
season  (see  Skarr  1 980).  Lasdy,  and  perhaps  most  impor- 
tandy,  observations  were  used  from  the  entire  historical 
record  of  Montana  ornithology  rather  than  from  a  fixed 
and  limited  number  of  years.  Preliminary  latilong  projects 
have  also  been  published  for  Colorado  (Kingery  &  Graul 
1978),  Wyoming  (Oakleaf  et  al.  1979),  and  Utah  (Walters 
1983). 

The  first  North  American  adas  work  (patterned  closely 
on  the  European  models)  was  initiated  in  1971  on  a 
county-by-county  basis  by  the  Maryland  Ornithological 
Society,  and  the  first  work  was  published  as  the  Breeding 
Bird  Atlas  of  Montgomery  and  Howard  Counties,  Maryland 
(Klimkiewicz  ck  Solem  1978).  As  in  Europe,  the  idea 
quickly  spread.  The  number  of  full-state  or  provincial  adas 
projects  underway  or  completed  in  North  America  swelled 


from  10  in  1981  (Laughlin  et  al.  1982),  to  26  in  1986 
(Sutcliffe  et  al.  1986),  to  33  in  1990  (Smith  1990).  The 
accuracy  and  conservation  value  of  distribution  studies  has 
increased  dramatically  with  the  ascendancy  of  avian  adas 
projects. 

A  Perspective  on  the  History  of  Avian 
Distribution  Studies  in  California 

The  bulk  of  the  data  on  California's  avifauna— especially  in 
regard  to  breeding  birds— was  collected  in  the  early  to 
mid-1 900s  by  professional  ornidiologists  from  the  Muse- 
um of  Vertebrate  Zoology  at  the  University  of  California, 
Berkeley,  under  the  direction  and  inspiration  of  Joseph 
Grinnell,  his  students,  and  his  associates  in  the  Cooper 
Ornidiological  Society.  A  large  part  of  the  data  collected 
came  from  field  work  organized  to  document  the  distribu- 
tion of  the  vertebrate  fauna  in  less  well  known  areas  of 
California,  particularly  in  areas  in  danger  of  rapid  change 
caused  by  human  encroachment,  but  also  in  protected 
parks.  Most  of  the  important  distributional  studies  were 
published  as  monographs  either  in  the  University  of  Cali- 
fornia Publications  in  Zoology  or  the  Pacific  Coast  Avi- 
fauna series.  The  culmination  of  this  work  resulted  in  the 
publication  of  the  landmark  TKe  Distribution  of  the  Birds  of 
California  (Grinnell  &.  Miller  1944),  supplemented  by  An 
Analysis  of  the  Distribution  of  the  Birds  of  California  (Miller 
1951).  All  subsequent  California  workers  have  owed  an 
enormous  debt  to  the  1 944  publication.  Though  now  out 
of  date  in  many  respects,  it  still  stands  as  the  single  most 
important  reference  on  the  distribution  of  California  birds. 

In  the  last  40  years,  professional  field  ornithology  has 
shifted  away  from  an  emphasis  on  distributional  and 
taxonomic  studies  toward  ecological  and  experimental 
work,  often  on  single  species.  Although  some  professional 
ornithologists  in  California  still  contribute  important  dis- 
tributional studies,  a  host  of  amateur  field  ornithologists 
are  presendy  in  the  forefront  of  updating  and  expanding 
our  knowledge  of  California's  avifauna.  Much  of  the  recent 
distributional  work  has  been  published  in  the  seasonal 
reports  of  both  the  Middle  and  Southern  Pacific  Coast 
regions  of  American  Birds,  in  articles  in  Western  Birds 
(formerly  California  Birds),  or  in  regional  distribution 
books  or  annotated  checklists.  Much  information  is  scat- 
tered in  numerous  papers  in  a  variety  of  scientific  journals; 
and  a  vast  store  of  unpublished  knowledge  is  on  file  with 
the  regional  editors  of  American  Birds,  university  muse- 
ums, government  agencies,  and  in  individual  field  workers' 
notebooks. 

As  with  past  avifaunal  studies  in  California,  most  recent 
work  has  suffered  from  concerted  effort  in  certain  areas  at 
the  expense  of  others.  First,  the  distribution  of  observers 
in  California,  as  elsewhere,  is  very  clumped— most  are 
concentrated  close  to  population  centers  on  the  coast  and 


Historical  Studies-California 


INTRODUCTION 


Historical  Studies -Marin 


in  the  Central  Valley.  Secondly,  recent  amateur  enthusi- 
asm for  searching  for  migrants,  hence  increasing  one's 
chances  for  sighting  rare  birds,  has  further  concentrated 
observers.  The  discovery  in  the  1960s  that  rarities  can  be 
found  relatively  frequendy  in  isolated  habitat  patches  on 
the  coast  or  in  desert  oases  is  the  prime  example  of  this 
phenomenon.  Though  amateur  ornithologists  in  Califor- 
nia have  added  an  enormous  amount  in  recent  years  to  our 
knowledge  of  vagrants  and  to  migrational  phenomena  in 
general,  until  very  recendy  there  has  been  a  notable  lack  of 
interest  in  breeding  birds. 

There  have  been  few  attempts  to  map  bird  distributions 
throughout  California.  Grinnell  and  Miller  (1944)  were 
the  first  to  map  a  selected  number  of  the  state's  breeding 
species  to  elucidate  subspecific  ranges.  Subsequendy,  Gar- 
rett and  Dunn  (1981)  mapped  selected  breeding  species  in 
southern  California,  and  Grenfell  and  Laudenslayer 
(1983)  mapped  the  summer  and/or  winter  distribution  of 
340  species  of  birds  in  all  of  California.  Unitt  (1984)  and 
Roberson  (1985)  mapped  breeding  distributions  in  Cali- 
fornia in  San  Diego  and  Monterey  counties  respectively. 
All  these  authors  relied  on  subjective  methods  to  map 
approximate  breeding  ranges,  using  largely  presumptive 
evidence  of  breeding.  The  Marin  adas  project  is  the  first  to 
objectively  plot  the  distribution  of  all  breeding  species  in 
any  area  of  California  based  on  systematically  collected 
data. 

The  fine-scale  distribution  data  and  supplemental  natu- 
ral history  information  of  die  Marin  County  Breeding  Bird 
Atlas  can  be  used  by  local  conservationists  as  an  aid  to 
preserving  and  protecting  our  remaining  valuable  wildlife 
habitats.  On  a  larger  scale,  perhaps  this  beginning  will 
stimulate  others  to  start  adas  projects  in  other  counties  and 
eventually  all  of  California.  Indications  are  that  the  Marin 
adas  may  already  have  played  that  role— as  of  1991  there 
are  adas  projects  underway  (or  completed)  in  12  other 
California  counties  (Table  1,  Figure  1;  Manolis  1991).  It 
is  to  be  hoped  that  more  bird  students  will  seize  diis 
opportunity  to  conduct  field  work  with  conservation  rami- 
fications foremost  in  their  minds.  The  human  horde 
presses  heavily  on  our  remaining  wildlands,  and  a  basic 
understanding  of  the  distribution,  abundance,  and  habitat 
requirements  of  all  our  native  fauna  is  essential  for  protect- 
ing our  heritage  of  biological  diversity. 

History  of  Breeding  Bird  Studies  in 
Marin  County,  California 

In  the  late  1870s  and  early  1880s,  C.A.  Allen,  living  dien 
in  Nicasio  or  San  Geronimo,  published  several  short  notes 
on  breeding  birds  in  Marin  County  (e.g.,  Allen  1881).  The 
Mailliard  brothers,  Joseph  and  John  W.,  contributed  the 
most  to  the  early  knowledge  of  Marin's  avifauna,  primarily 
from  field  work  near  their  ranch  in  the  San  Geronimo 


Valley.  Their  work  bore  fruit  in  numerous  papers  pub- 
lished from  1881  to  at  least  1938  (see  Grinnell  1909, 
1924,  1939)  and  the  accumulation  of  a  large  specimen  and 
egg  collection  eventually  housed  at  the  California  Academy 
of  Sciences  (Mailliard  1924b).  Records  of  Allen's  and 
earlier  ones  of  the  Mailliards'  attributed  to  Nicasio  may  in 
fact  refer  to  specimens  collected  some  miles  away  (Mail- 
liard 1924b).  J.  Mailliard's  1900  paper  first  summarized 
knowledge  of  the  status  of  landbirds  in  Marin  County.  The 
first  publication  to  report  the  status  of  all  species  of  the 
county's  avifauna  was  Stephens  and  Pringle's  (1933)  Birds 
of  Marin  County.  They  compiled  information  primarily 
from  records  of  the  Audubon  Association  of  the  Pacific 
(now  Golden  Gate  Audubon),  derived  mosdy  from  obser- 
vations from  56  field  trips  to  various  places  in  southern 
Marin  from  1919  to  1933.  They  also  used  information 
from  Grinnell  and  Wythe's  (1927)  Director}  to  the  Bird-life 
of  the  San  Francisco  Bay  Region  and  unpublished  observa- 
tions of  several  active  observers.  Additions  and  corrections 
to  the  Marin  list  were  published  in  1936  (Gull  18,  No.  6). 
Limited  additional  information  on  Marin's  breeding  birds 
has  been  published  in  avifaunal  works  of  broader  geo- 
graphic scope  (e.g.,  Grinnell  &.  Miller  1944,  Miller  1951), 
as  occasional  notes  (e.g.,  Ralph  &  Ralph  1958),  as  part  of 
single-species  studies  (e.g.,  Page  &  Stenzel  1981),  or  as  part 
of  seasonal  field  note  summaries  of  local  or  national 
Audubon  Society  publications  (e.g.,  The  Gull,  Audubon 
Field  Notes,  American  Birds).  Even  as  the  number  of  observ- 
ers in  the  area  grew  gready  from  the  1950s  to  the  early 
1970s,  and  access  improved  with  better  roads  and  the 
establishment  of  numerous  parks,  little  effort  was  focused 
on  breeding  birds.  At  the  time,  observers  focused  much  of 
their  field  work  on  the  coast,  particularly  on  Point  Reyes, 
and  mosdy  on  migrational  phenomena,  seasonal  abun- 
dance patterns,  Christmas  Bird  Counts,  and  single-species 
studies.  Breeding  birds  took  a  back  seat. 

The  picture  of  Marin  County's  breeding  avifauna 
painted  by  work  prior  to  the  adas  project  was  a  sketchy  one. 
Initial  observer  coverage  was  focused  on  central  and  south- 
ern Marin,  with  minimal  field  work  from  Point  Reyes  (see 
Shuford  1986).  Early  records  from  the  drier  portions  of  the 
county  around  Novato  were  almost  unheard  of.  The  small 
geographic  focus,  few  observers,  and  difficulty  of  travel  are 
reflected  in  the  earlier  lists  of  Marin's  breeding  birds. 
Interpretation  of  Mailliard's  (1900)  summary  of  the  status 
of  landbirds  in  Marin  County  indicated  he  had  knowledge 
at  the  time  of  about  89  species  of  landbirds  breeding  here. 
Similar  interpretation  of  Stephens  and  Pringle's  (1933)  list 
suggests  they  knew  then  of  96  species  of  breeding  land- 
birds.  Even  including  4  species  (Purple  Martin,  Violet- 
green  Swallow,  Bank  Swallow,  and  Western  Bluebird) 
considered  as  breeders  in  Marin  by  Mailliard  (1900)  and 
3  species  (Northern  Harrier,  American  Robin,  and  Tricol- 
ored  Blackbird)  by  Grinnell  and  Wythe  (1927),  as  of  1933 


(rt 

a. 

3 

2 
O 
w> 
c 
■c 
o 

CO 

c 

a 

CO 

c 

3 

< 

g 

P 

V 

E 

u 
« 
CO 

o, 
« 
is 

U       P 

—    ^ 

-    < 

CO 

(rt  .= 

c22 

p 

s 
.2 

3 

-d 

3 
< 
V 

c 
o 
-o 

2 

c 

3 
T3 

3 
< 

O 

c 
"3 

GO 

CTJ 

« 
Z 

Sequoia  Audubon 

S.F.  Bay  Bird  Observatory 

Golden  Gate  Audubon 

c 
o 

c 

a 

CO 

e 

rt 
rt 

u 

(J 

8. 

0 

o 

-Q 

3 

o 

CQ 

3 

(J 

a 

e 

CO 

c 

3 

-o 

3 
< 
rt 

i 
'5 

ii 

In 
U 

C 

o 

3    _2 

J  § 

a  a 

°  s 

2  z 

National  Audubon 
Sea  and  Sage  Audubon 

Kerncrest  Audubon 

Pomona  Valley  Audubon 

San  Bernardino  Valley  Audubon 

c 

3 

■a 

3 

< 

>- 
Jj 

"« 

> 

O 

c 
■3 

A 

c 

U 

CQ 

C 
rt 
CO 

</3 

c   c 
a2^ 

(X     o 
O 

u 

1/5 

c 

08 

£ 

-o    « 

I-      c 

yO          « 

3     * 

Jc    B 
co  co 

Q  « 

OX) 

3 
CO 

g" 

V 

CQ 

a;      >» 

£    21 

E  J- 
S  « 

O  J* 

>- 
u 

'« 

CQ 

ul 
c 

x> 

_P 

a 

V 

co 

c 

0 

p 
_c 

o 

_^ 
(J 

c2 

c 

rt 

£ 

3 
O 
CQ 

CQ 

p 

rt 

-5" 
-o 

3 
CO 

'> 

a 

_>- 

V 

u 
-o 

u 
CO 

rt 
u 
Q 

CQ 

rt 

E 

0 

O 

-a 
u 

M 

2 

V     i-      _ 

C     u     C 

o  -c    5 
e    ox)    g> 

C      rt      C 

^  ^  52 

e2  co  Z 

c 

0 

o 

rt 
_Q 

rt 
CQ 

c 
o 

(rt 

u 

« 
rt 
J3 

e^ 
CQ 

-a  £ 

CQ     O 

U 

« 

« 

rt 

rt 

« 

rt 

rt 

rt 

W5 

<j 
o 

-    ^t 

rt      o    'H 

=    -C      0 

o*  a  -c 

O    .*«-     °" 

c^  c 
o 

(-4 

2 
U 

0 

-a    C   .S 

«    0    <- 

3     "C      O 

a-   a  'B 

■*■ 

m 
r-l 

"« 

i?      "3 

o  .2 

^-     u 
r-i     O 

■- Q 

0    _ 

.5    c 

■5.  a 

p    o 

O         U5 

0  -Q 
W>"rt 

a  g 

1  * 

rt      rv 

rj            (rt) 

Z    o 

oo 

r-l 

m 
00 

On 

O 
c-j 

r- 

00 
NO 

NO 

ON 

O 

■<J- 

- 

r-l 

w 

CO 

(J 

o 
pa 

£ 

in 

l/N. 

r-i 

£ 

£ 

£ 

£ 

in 

£ 

E 

in 

£ 

E 
in 

£ 

in 

£ 
in 

£ 

in 

(J           C/5 

O      <U 

C-J 

o 

ON 

1 

00 
00 
On 

CNl 

00 

On 

i 

NO 

r~ 

On 

On 
On 

i 

NO 

00 
On 

ON 
ON 

1 

On 
00 
On 

r-J 
On 
On 

i 

ON 

On 

m 
On 

ON 

1 

ON 
ON 

ON 

On 

i 
00 
00 
ON 

ON 

On 
1 

oo 

ON 

On 
On 

1 
OO 
00 
On 

m 

ON 
On 

t 

ON 

00 
ON 

O 
On 
On 

i 
in 

00 
On 

r-i 
On 

On 

1 
r~ 
00 

ON 

■*■ 
On 
On 

1 
O 

On 
On 

c 

3 
O 

U 

g 

c 

e 

a 

u 

A 

CO 

B 

0 

c 
o 

CO 

rt 

a 

z 

0 
v> 

'o 

p 

rt 
M 
PL, 

c 

rt 
CO 

0 

B 

rt 

2 

c 

rt 
CO 

rt 
1* 

rt 

O 

s 

c 

rt 
CO 

N 

3 
M 

o 

3 

c 

rt 
CO 

>• 

V 

B 

c 

0 

2 

0 

a 

^5 
0 

t/5 

c 

rt 
CO 

oa 

c 

rt 

0 

o 

c 

« 

c 

l-l 

V 

CQ 

c 

rt 
CO 

V 

US 

V 

> 

c2 

& 

c 

3 

c3 


"T3 

5 


2 

~£ 


> 

c 

rt 

i- 


'i 

£ 


-Nil 

u 
_0 

J3 


0  -5 
o 


£ 
o 


^1 

-if  -a 

£    £ 


•— 

a 

M 

3 

£ 

-^ 

o 

pS 

c 

c  .3 

rt      q, 

|3 

■g  J 

a  _o 
—  "« 
|   '§ 

-fi  8. 


-o    o 

rt 

3    " 

°"  2 

1^ 
«  **- 

^.   o 

J2  - 

J    E 
3    2 


n 

>< 

-L, 

rt 
u 

BO 

C 

C 

e  e 

c    c 


=         8 


« 

It 


■a 

c 

3 

o 

u 

8.. 


—  c 
c  « 
o 

c 

"Si 


CO 


s  g 

3      C 

°"  'p 

«  in 

U    CO 

•s  O 

(«    CO 

»D 

O     M 

O   -T3       . 
-S     >   -^ 

ls| 

JJ      3    -O 
U      ->.  "rt 

-5  -a   •£ 


O      rt 

2  w 


P 


i  a 

£  o 

'1  E 

P  V 

3  t- 

0  D 


-o 
p 


"O  v 

T  P 

U  .3 

>  w 

E  o 

-n  ^- 


-P    £r  o 


U  XI 

a  > 

_0  q      rt 

CQ  .o  2 


OX) 
H       rt 


XI     •  — 


a  -o 

p  a 

O     u 

p  _H 


INTRODUCTION 


Figure  I .    Map  of  California  highlighting  tke  1 3  counties  with  breeding  bird  atlas  projects  that  are  completed  or  in  progress  (see 
Table  I). 


Historical  Studies-Mann 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Origin  of  Project 


there  was  knowledge  of  only  103  species  of  breeding 
landbirds  in  Marin  County.  Adding  the  22  species  of 
waterbirds  that  Stephens  and  Pringle  indicated  were  breed- 
ing in  the  county  gives  a  total  of  1  25  species  of  confirmed 
or  suspected  breeding  birds  in  Marin  County  in  1933.  For 
some  species,  breeding  evidence  was  based  largely  on 
assumptions  and  limited  data.  For  example,  the  evidence 
of  California  Thrasher  in  the  county  was  based  solely  on  a 
single  aural  record  (Mailliard  1900,  Stephens  &  Pringle 
1933).  By  1951  there  were  indications  of  at  least  8  addi- 
tional breeders  in  Marin  (Grinnell  6k  Miller  1944,  Miller 
1951)  for  a  total  of  133  breeding  species  in  the  county. 
This  total  is  about  82%  of  the  number  of  breeding  species 
known  from  Marin  County  at  the  time  of  this  writing  (see 
Results  and  Discussion  p.  51).  These  numerical  compari- 
sons tell  only  part  of  the  story.  Initially  many  species  were 
considered  breeders  without  sufficient  documentation, 
and  knowledge  of  the  countywide  distribution  and  abun- 
dance of  most  species  was  fragmentary  at  best. 


Origin  of  the  Marin  County 
Breeding  Bird  Atlas  Project 

In  1976,  Bob  Stewart,  then  the  landbird  biologist  at  Point 
Reyes  Bird  Observatory,  was  inspired  by  the  publication  of 
the  seminal  Atlas  of  ike  Breeding  Birds  of  Britain  and  Ireland 
(Sharrock  1976).  Encouraged  by  Chandler  Robbins  and 
the  progress  of  Maryland's  adas  work,  Bob  initiated  a 
proposed  three-year  project  to  map  the  breeding  distribu- 
tion of  all  bird  species  in  221  adas  blocks  (2.5-km  square 
equivalents)  in  Marin  County,  California.  At  that  time, 
small-scale  breeding  bird  adas  work  was  in  its  formative 
stages.  The  only  other  projects  underway  in  North  Amer- 
ica were  in  Maryland  and  Massachusetts.  There  was  no 
precedent  whatsoever  in  California  or  the  West  The 
initiation  of  adas  work  in  California,  even  on  this  tiny 
scale,  can  be  viewed  as  an  important  landmark  in  light  of 
the  history  of  previous  avifaunal  work  in  the  state. 


Uninterrupted  chaparral,  redwood  forest,  mixed  evergreen  forest,  and  marshland  graced  Mount  Tamalpais  and  die 
Corte  Madera  shoreline  in  ^resettlement  times.  Drawing  £>}  Ane  Rovetta,  1 989. 


UNDERSTANDING  BIRD 
DISTRIBUTION 


Efforts  to  develop  broad  distributional  principles  and  categories  commonly  run  beyond  the  facts  and  violate  the  essentially 
statistical  character  of  distributional  data.  There  is  an  urge  to  create  simplified  concepts,  perhaps  unwittingly  as  paths  of  least 
intellectual  resistance.  These  become  lines  of  escape  from  exhaustive  factual  comprehension. 

-  Alden  H.  Miller, 
An  Analysis  of  the  Distribution  of  the  Birds  of  California 


SINCE  THE  LOCAL  AVIFAUNA  is  a  product  of  thousands  of 
years  of  evolution,  it  stands  to  reason  that  any  study  of 
bird  distribution  must  start  with  a  solid  understanding  of 
each  species'  biology  and  the  environment  to  which  the 
birds  have  adapted.  A  host  of  climatic,  topographic,  and 
geologic  factors  interact  on  a  local  scale  to  provide  a  suite 
of  habitats  available  for  birds.  The  trick  to  unraveling  the 
puzzle  of  bird  distribution  is  to  grasp  the  factors  that 
influence  the  habitat  selection  of  each  species.  This  is  not 
an  easy  task.  All  bird  distributions  are  constandy  changing, 
at  least  on  a  local  scale,  whether  in  response  to  a  varying 
environment  or  in  response  to  varying  competition  and/or 
predation  influences  from  other  species.  In  addition,  a  bird 
may  reach  the  limit  of  its  distribution  though  seemingly 
suitable  habitat  continues  uninterrupted.  Today  biologists 
believe  that  landbirds  generally  select  habitats  according  to 
the  structure  of  plant  communities,  rather  than  selecting 
particular  species  of  plants  (e.g.,  Verner  &.  Larson  1989) 
though  exceptions  exist  and  many  factors  are  at  play. 
Foraging  seabirds  are  generally  distributed  with  respect  to 
various  water  masses  with  characteristic  ranges  of  tempera- 
ture and/or  salinity,  with  the  added  constraint  of  the  need 
for  protected,  isolated  terrestrial  habitat  for  breeding.  For 
these  reasons,  the  overview  below  emphasizes  the  seasonal 
cycles  of  weather  and  ocean  currents  that  interact  with  the 
local  topography  and  geology,  which  in  concert  shape  the 
breeding  habitats  to  which  Marin  County's  avifauna  has 
adapted.  We  will  see  that  Marin  County's  geographic 
position  and  evolutionary  history  place  it  in  an  area  of 
exceptional  oceanic  productivity  and  varied  terrestrial  plant 
communities.  Consequently,  it  is  home  to  a  large  and 
varied  breeding  avifauna. 


Marin  County  Topography 

Marin  County's  setting  and  topography  are  important 
determinants  of  local  weather  patterns  and  plant  distribu- 
tion. Marin  County  lies  at  38°N  along  the  California  coast 
just  north  of  the  Golden  Gate  at  the  mouth  of  San 
Francisco  Bay.  The  county  is  roughly  diamond  shaped  and 
covers  588  square  miles— it  is  the  fourth  smallest  of  Califor- 
nia's 58  counties.  Its  long  axis  runs  northwest  to  southeast, 
and  it  is  bounded  by  the  Pacific  Ocean  on  the  west,  the 
Golden  Gate  on  the  south,  San  Pablo  and  San  Francisco 
bays  on  the  east,  and  the  low  rolling  hills  of  the  Sonoma 
County  "borderlands"  on  the  north  (Figures  2  and  3). 

Though  seemingly  uniform  from  the  surface,  the  Pacific 
Ocean  off  our  shores  can  be  divided  into  several  zones 
useful  for  describing  the  distribution  of  sea-going  birds  (see 
Shuford  et  al.  1989).  Neritic  describes  waters  over  the 
continental  shelf,  which  off  Marin  varies  from  about  20  to 
25  miles  in  width,  extending  just  seaward  of  the  Farallon 
Islands  and  Cordell  Bank.  The  neritic  zone  can  be  subdi- 
vided into  inshore  and  offshore  zones.  The  inshore  zone 
reaches  from  the  shoreline  to  a  line  beyond  which  the 
bottom  is  too  deep  for  a  diving  seabird  to  exploit— a  depth 
of  about  230  feet.  The  offshore  zone  extends  from  that 
depth  to  the  seaward  edge  of  the  continental  shelf.  Oceanic 
describes  waters  of  the  deep  ocean  from  the  continental 
slopes  beyond  the  continental  or  insular  shelves— the  true 
home  of  pelagic  seabirds. 

Marin's  shoreline  is  dissected  by  several  bays,  lagoons, 
and  estuaries:  Tomales  Bay,  Abbott's  Lagoon,  Drake's  and 
Limantour  esteros,  and  Bolinas  Lagoon  on  the  outer  coast; 
and  several  tongues  of  San  Francisco  Bay,  most  notably 
Richardson  Bay,  on  the  east.  On  the  outer  coast  most  of 
the  shoreline  rises  abrupdy  to  steep  cliffs,  except  for  occa- 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


<°^K':\.t<- 


VALLEY  foRP 


Dillon  Beach 


.Petaluma 


Xr.  \  ~fl  Latiuna 


,,y 


">?'»  *nton. 


Creel 


C, 


■fed  Hill 


Mt  Surdell      \0WMm] 


Tomasmi  Pt 

JOl/krton  Pt 
INVERNESS 


.  Sou/ajule 

Three  Peaks  ■       •  *"■ 

-v 

-9 


HiCki 


H 


Petal  urn  a 


W 


-V 


7  .■> ' 

£' 

HtVmm%t*H      \f;  |T<-> 

A/      -?  ■?  ,'  \i  ~J,/, Point 

-*--■  \_*Vreyes 


Stafford 
Lake. 


O 


[NoVATO 


Black  PbiMT 

V  Pay  /s/dnd 


TocalomA 


't     '         ^,-_~-.^I\STAT'-Mt.garmiie\ 
Lmantour 

deaclT<-'~        ^-' 


^  y 

NICASI0'-5V9*lr/,,&' 


*«*£. 


I6NAUO  V  BelMarimKeys      <5. 


'Hamilton 


/>£.  Hesistance* 


•■--.e  (ISO     >      rLTAtmi!                            VS=                                                ^X'-'.r^  Cr      A ~ 

~P      (.  \vv  -    ■ .  >-\ '(  state  '/%  damabt      \                       io™.  N*-^J5=<  /        Mc, 

\-m:  ^     -P'-'^V^      Jti^5IS{S\NGER0NIM0  j>          ,              /             , 

"i     A?  AFi^E      '"-        oVW-LAOINITAS"^       ,  ^          V.  <%            ^ -'•?„,    >,/- 


AW/erls  P£ 


\»*     ftrtop')'      \V     * 


/» 


Wildcats^,  £<       \ 


SAnAnSElMu  (IAFAEL 


P/kW7/^OsJ<ENTFtELD 


Double Pt^."  1     %.         'VNDOOTOWNsoj.^    ^Ijj/Alpiii^h""'^''-,       X't^S^-M ■&**» 


LARKSPUR  Jr 


PR80> 


C 


te*  \ 


,    Bolinas 
Bolrn&s  Pt.  ^_^.    x-^^    5tin^j 

Beaci? 


/>' 


^^^j^fVV  %/Mll.L J 

MuirBeaoN^.'— ,  /!§)  ^_      X    ^SAUSALITOji^ 


&    kilometers 


3       -f       5  miles 


■p&oey  i*v>ny>ton       ©I9?0 


Tenneaee  Point  V^^^ 

^^LaQoon 


Figure  2.    Place  name  map  of  Marin  County  Map  by  Dewey  Livingston,  I  990. 


UNDERSTANDING  BIRD  DISTRIBUTION 


Marin  County 

TOPOGRAPHY 

SOURCE:  U.  S.  TOPOGRAPHIC  SURVEYS 
©  1991  by  Dewey  Livingston 


Figure  3.   Topographic  map  of  Marin  County.  Dark  solid  lines  show  500  foot  topographic  contours;  thin  dotted  lines  mark  stream 
drainages.  Map  by  Dewey  Livingston,  1991. 


Tolwgraphy 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Geology  and  Soils 


sional  small  pocket  beaches  and  the  long  beaches  fronting 
Drake's  Bay  and  the  west  side  of  the  Point  Reyes  peninsula. 
Along  the  eastern  bayshore,  marshlands  and  reclaimed 
former  marshlands  cover  alluvial  plains,  particularly  near 
Novato.  Otherwise  Marin's  uplands  consist  predominant- 
ly of  hilly  and  low  mountainous  terrain.  The  most  promi- 
nent  peak  is  Mount  Tamalpais,  a  sacred  Miwok  refuge 
with  the  famed  profile  of  the  Sleeping  Lady,  which  reaches 
a  height  of  2571  feet  at  its  East  Peak.  Other  high  peaks  are 
Big  Rock  Ridge  (1887  ft.),  Pine  Mountain  (1758  ft.),  Loma 
Alta  (1592  ft.),  Mount  Burdell  (1558  ft.),  Hicks  Mountain 
(1532  ft.),  Mount  Wittenberg  (1407  ft),  and  Black  Moun- 
tain (1280  ft.).  Although  diese  peaks  are  not  impressive  as 
mountains  go,  diey  are  rather  steep;  the  flank  of  Mount 
Tamalpais  rises  2000  feet  in  a  little  over  a  mile  starting  at 
sea  level  at  Stinson  Beach. 

In  the  pattern  typical  of  the  Coast  Range  mountains, 
Marin  County's  major  ridges  run  northwest  to  southeast 
roughly  paralleling  the  coasdine.  Toward  the  coast  these 
ridges  are  clodied  primarily  widi  conifer  forests,  mixed 
hardwood  forests,  and  coastal  scrub.  Inverness  Ridge 
stretches  the  length  of  the  Point  Reyes  peninsula,  reaching 
a  height  of  1407  feet  at  Mount  Wittenberg.  On  the  east, 
the  ridge  rises  rather  steeply  from  Tomales  Bay  and  the 
Olema  Valley.  On  the  west,  the  soudiern  portion  of  the 
ridge  descends  rapidly  to  steep  cliffs  and  rocky  shoreline. 
The  northern  portion  of  the  ridge,  around  Drake's  and 
Limantour  esteros,  descends  to  low  rolling  hills  and  pas- 
tureland,  flanked  by  a  long  beach  and  dune  system  set  off 
by  the  steep  cliffs  and  rocky  shoreline  of  the  Point  Reyes 
headlands  and  Tomales  Point.  From  the  Golden  Gate  low 
grass-  and  brush-covered  hills  of  the  Marin  Peninsula 
ascend  to  the  north  to  Mount  Tamalpais.  The  rest  of  the 
south  central  part  of  the  county  is  dominated  by  several 
roughly  parallel  ridges,  the  most  prominent  being  Bolinas 
Ridge,  Carson  Ridge,  Loma  Alta,  and  Big  Rock  Ridge. 
Smaller  parallel  ridges  emanating  from  those  larger  ridges 
and  from  Mount  Tamalpais  separate  Marin's  larger  towns 
and  cities  lying  in  small  valleys  along  the  San  Francisco 
and  San  Pablo  bayshores.  The  heavily  forested  southern 
ridges  grade  to  the  north  into  much  smaller,  less  well 
defined  ridges  covered  largely  widi  grasslands  and  a  patch- 
work of  brush  and  hardwood  forest.  To  the  extreme 
northwest  along  the  drainages  of  Estero  de  San  Antonio 
and  Estero  del  Americano,  the  low  rolling  hills  are  clothed 
almost  entirely  in  grasslands,  as  are  lowlands  on  outer 
Point  Reyes. 

Unlike  most  of  the  northern  California  coast,  Marin 
has  no  major  rivers  draining  its  landmass.  Instead  the 
numerous  canyons  give  rise  to  many  small  permanent  and 
intermittent  streams  that  flow  into  small  valleys  between 
the  hills  and  then  into  die  ocean.  Natural  freshwater  ponds 
or  lakes  are  very  rare  in  Marin,  as  in  most  of  die  Coast 
Range.  The  largest  of  these  is  Laguna  Lake,  a  seasonal  lake, 


on  the  Marin-Sonoma  border  in  Chileno  Valley.  The  only 
other  notable  natural  freshwater  ponds  are  several  near 
Double  Point  north  of  Palomarin  on  the  Point  Reyes 
peninsula.  Marin  Municipal  Water  District,  however,  has 
impounded  water  in  seven  sizable  reservoirs:  Alpine  Lake, 
Bon  Tempe  Lake,  Kent  Lake,  Lake  Lagunitas,  Nicasio 
Reservoir,  Phoenix  Lake,  and  Soulajoule  Reservoir.  The 
only  other  large  impoundment  is  North  Marin  Water 
District's  Stafford  Lake.  Numerous  small  diked  stock 
ponds  dot  the  grassy  hills  of  the  cattle  and  sheep  ranches, 
mosdy  in  the  central,  northern,  and  western  parts  of  the 
county. 

The  topography  of  the  coastal  ridges  exerts  a  profound 
effect  on  local  weather.  Varied  coastal  relief  influences  local 
rainfall  patterns  countywide,  as  discussed  in  greater  detail 
below.  The  only  major  gaps  in  the  ridge  system  are  in  the 
Estero  lowlands  near  Tomales  (which  connects  with  the 
Petaluma  Valley  of  southern  Sonoma  County),  the  Nicasio 
gap  near  the  reservoir  of  the  same  name,  and  the  Muir 
Woods  gap.  These  gaps  funnel  winds  and  coastal  fog 
eastward,  moderating  the  summer  climate  of  adjoining 
inland  areas  relative  to  other  areas  blocked  from  major  air 
movements  by  high  ridges.  Evidence  of  the  strong  winds 
in  these  gaps  can  be  readily  seen  in  the  wavelike  top  of  the 
wind-sculptured  bay  laurel  forest  below  Nicasio  Reservoir. 
The  influence  of  Marin's  varied  relief  on  microclimate 
reaches  beyond  its  effect  on  large-scale  air  movement  and 
rainfall.  Local  differences  in  slope,  exposure,  temperature 
inversions,  cold  air  drainage,  and  ground  water  levels  also 
have  marked  effects  on  vegetation. 

Geology  and  Soils 

Marin  County's  most  infamous  geologic  feature,  the  San 
Andreas  Fault,  slices  die  earth's  crust  under  Bolinas  La- 
goon, the  Olema  Valley,  and  Tomales  Bay.  This  fault- 
known  chiefly  as  the  source  of  the  great  1906  San 
Francisco  earthquake— separates  two  areas  of  strikingly  dif- 
ferent geologic  history,  now  juxtaposed  by  displacement 
along  the  fault  of  several  hundred  miles  or  more.  To  the 
west  on  the  northward  moving  Pacific  Plate,  the  Point 
Reyes  peninsula  has  a  base  of  Cretaceous  (at  least  84 
million  years  old)  granitic  rock  overlain  with  relatively 
young  (4-26  million  years  old)  marine  sedimentary  depos- 
its of  the  Cenozoic  age.  To  the  east  on  the  North  American 
Plate  lie  the  intensely  folded  and  faulted  rocks  of  the 
Franciscan  complex,  including  Mesozoic  (1 36  million 
years  old)  marine  sandstones  and  shales,  chert,  sea  floor 
volcanic  rocks  (mainly  greenstone),  serpentine,  and 
unusual  metamorphic  rocks. 

As  a  result  of  its  complex  geologic  setting  and  history, 
Marin  County  hosts  many  soil  types  (Kashiwagi  1985). 
Contrasts  in  soil  types  are  most  apparent  on  opposite  sides 
of  die  San  Andreas  Fault  since  their  respective  origins  and 


10 


Geology  and  Soils 


UNDERSTANDING  BIRD  DISTRIBUTION 


Climate 


histories  are  so  different.  The  distribution  of  distinctive  soil 
types  appears  to  explain  much  of  the  overall  distribution  of 
Marin  County's  conifer  forests.  A  thin,  relatively  barren 
soil  derived  from  serpentine  rock  is  one  of  the  exceptional 
types  found  locally  east  of  the  San  Andreas  Fault.  Although 
serpentine  soils  are  extremely  harsh  and  support  few  spe- 
cies, they  harbor  a  number  of  endemic  species  and  geneti- 
cally distinct  populations  of  plants  (Kruckeberg  1984). 
Serpentine  soil  also  supports  a  unique  chaparral  commu- 
nity, with  generally  sparser  and  stunted  shrubs  favored  by 
certain  chaparral  birds.  Although  soils  may  be  important 
determinants  locally,  topography  and  microclimate  gener- 
ally play  a  greater  role  in  influencing  broad  patterns  of 
plant  distribution  and  hence  bird  distribution. 

Climate 

Seasonality 

Many  transplanted  Easterners  bemoan  the  "lack  of  sea- 
sons" in  coastal  lowland  California.  Despite  the  relatively 
low  variation  between  summer  and  winter  temperatures 
along  the  coast,  there  are  marked  seasonal  changes  in 
weather,  though  these  contrast  gready  with  patterns  typical 
of  the  rest  of  temperate  North  America.  Marin  County  and 
much  of  lowland  California  enjoy  what  is  termed  a  Medi- 
terranean climate  because  of  its  similarity  to  that  of  the 
eastern  Mediterranean  region— a  climate  found  in  only  a 
handful  of  areas  in  the  world.  Seasonally  we  experience  "a 
desert  in  summer,  a  sodden,  dripping  landscape  in  winter, 
and  a  glory  of  wildflowers  in  spring"  (Major  1977).  Zonally 
this  is  a  subtropical  climate  combining  some  of  the  worst 
features  of  arid  and  humid  climates.  The  basic  features  of 
this  climate— tempered  significandy  along  the  coasdine  by 
cool  ocean  waters— are  (1)  hot  and  arid  summers  and  cool 
and  humid  winters,  so  that  (2)  the  supply  of  water  and  the 
need  of  water  for  plant  growth  are  exacdy  out  of  phase,  (3) 
the  growing  season  is  limited  by  cool  winter  temperatures 
and  summer  drought,  and  (4)  native  vegetation  is  lush  in 
the  spring  when  higher  temperatures  occur  temporarily 
with  an  adequate  water  supply  and  either  is  desiccated  or 
fails  to  grow  in  summer  (Major  1977).  In  other  words  we 
have  two  major  seasons:  a  distinct  cool,  rainy  season  when 
the  grassy  hills  turn  green  and  a  dry,  hot  summer  when  the 
hills  turn  golden  brown.  Spring  is  characterized  by  increas- 
ing warmdi  at  the  end  of  the  rainy  season  and  a  profusion 
of  wildflowers  that  begin  to  bloom  in  earnest  in  February 
and  March.  Many  people  also  remember  spring,  not  so 
fondly,  by  the  long  stretches  of  intensely  windy  days. 
Summers  on  the  outer  coast  are  generally  characterized  by 
cool  ocean  breezes  and  recurring  overcast  or  fog,  and 
inland  by  clear  skies  and  hot  days.  Fall  is  a  period  of 
relatively  calm  and  prolonged  warmth  grading  into  the 


cooler  rainy  winter.  Here  flowers  bloom  at  almost  any 
season  and  the  limited  fall  color,  from  the  few  deciduous 
trees  and  shrubs,  lingers  into  November  and  December. 

Temperatures 

Winter  temperatures  in  Marin  County  are  generally  mild 
because  warm  air  masses  usually  accompany  the  frequent 
winter  rainstorms.  Nevertheless,  the  pervasive  dampness 
gives  the  impression  of  cooler  temperatures  than  those 
recorded.  Frosts  may  be  frequent  locally,  but  snow  dusts 
the  higher  ridges  only  every  few  years.  Summer  tempera- 
tures can  exceed  100°  F  at  interior  sites.  Mean  monthly 
temperatures  vary  gready  between  sites  in  Marin  County, 
particularly  among  coastal  and  interior  stations  (Table  2). 
The  narrow  zone  along  the  shore  west  of  the  low  coastal 
ridges  has  an  equitable  maritime  climate— that  is,  average 
temperatures  vary  little  from  month  to  month.  For  exam- 
ple, on  outer  Point  Reyes,  mean  January  and  July  tempera- 
tures vary  by  only  about  4°  F  (Table  2).  Winter 
temperatures  on  the  outer  coast  remain  warmer  than  those 
inland  because  of  the  proximity  of  heat-retaining  ocean 
waters,  whereas  summer  temperatures  are  depressed  by 
cool  ocean  breezes  and  to  a  lesser  degree  by  reduced  solar 
radiation  during  frequent  episodes  of  persistent  fog.  Sum- 
mer temperatures  on  the  outer  coast  may  occasionally 
reach  those  of  the  interior,  but  hot  days  are  few  and  cool 
days  abound.  For  perspective,  summer  temperatures  on 
the  coast  in  the  San  Francisco  Bay  Area  "are  among  the 
coldest  within  the  continental  limits  of  the  U.S.,  yet  air 
temperatures  rise  so  rapidly  inland  that  within  60  miles  of 
the  ocean  the  maximum  temperatures  are  comparable  with 
any  in  the  U.S.  outside  the  Sonoran-Mohave  Desert 
region"  (Patton  1956).  With  every  10-mile  increment  from 
the  coast,  mean  monthly  temperature  increases  3°  F  in  July 
and  August,  and  over  the  same  distance  the  daily  maxi- 
mum increases  about  4-5°  F  from  June  through  August.  In 
contrast  to  the  outer  coast,  January  and  July  mean  tempera- 
tures in  the  interior  of  Marin  County  vary  by  almost  20°  F 
(Table  2).  Although  summer  temperatures  in  the  interior 
of  Marin  often  hover  over  90°  F,  they  too  are  moderated 
to  an  extent,  relative  to  inland  lowland  regions  of  the  state, 
by  the  proximity  of  the  ocean  and  San  Francisco  and  San 
Pablo  bays. 

Precipitation 

On  the  central  California  coast,  precipitation  falls  primar- 
ily as  rain,  with  about  95%  of  the  yearly  total  compressed 
into  the  seven-month  period  from  October  through  April 
(Table  3).  Yearly  rainfall  on  the  coast  generally  decreases 
from  north  to  south.  Because  the  moisture-laden  air  of 
ocean-generated  storms  must  rise  when  encountering 
Marin's  broken,  low  mountainous  terrain,  rainfall  varies 
gready  over  the  short  distances  between  recording  stations 
(Table  3,  Figure  4).  Although  rainfall  is  relatively  high  on 
the  coastal  slope,  much  moisture  passes  inland.  In  fact, 


11 


Climate 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Climate 


Table  2.   Air  temperature  (degrees  F)  at  selected  Marin  County  sites. 


MEAN 
Jan 

MEAN 
Jul 

MIN-MAX 

FOR  ALL 

YEARS 

YEARS  OF 
DATA 

Hamilton  Field 

46.5 

65.5 

23-106 

25 

Point  Reyes 

49.5 

53.6 

30-98 

42 

San  Rafael 

49.5 

67.8 

26-110 

30 

Ml  Tamalpais 

43.7 

69.0 

19-100 

25 

Kentfield3 

46.7 

67.0 

17-112 

30 

Cone  Madera 

47 

62 

22-108 

20 

Data  from  U.S.  Air  Force/Air  Weather  Service 


Data  from  U.S.  Weather  Bureau  (1934). 


Data  from  National  Oceanic  and  Atmospheric  Adminisnarion  (1982). 
4  Data  from  Marin  Municipal  Water  District 


some  of  the  wettest  areas  of  Marin  are  on  the  east  side  of 
the  first  or  second  coastal  ridges,  as  exemplified  by  the 
county's  highest  average  precipitation  at  Kent  Lake.  While 
nearly  rain-free  summers  are  expected,  winter  rainfall  may 
vary  dramatically  over  the  course  of  one  rainy  season  or 
among  years.  Even  in  good  rainfall  years,  a  very  dry  early 
winter  can  be  followed  by  an  extremely  wet  late  winter  or 
vice  versa.  The  period  of  atlas  field  work  fortuitously 
encompassed  dramatic  extremes  of  yearly  rainfall.  The  adas 
project  began  with  (up  to  that  time)  the  state's  worst 
recorded  drought  in  1975-76  and  1976-77  and  culmi- 
nated with  the  deluge  of  1981-82,  highlighted  by  the 
now-legendary  flood  of  4  January  1982,  when  almost  the 
whole  county  was  afloat  (Table  3).  Rainfall  in  California 
tends  to  peak  and  dip  on  approximately  a  five-  to  six-year 
cycle,  though  not  usually  reaching  these  extremes  (Michael- 
son  1977).  The  amount  of  rainfall  in  California  is  a 
function  of  anomalies  in  sea  surface  temperature  in  the 
North  Pacific  Ocean  as  discussed  in  greater  detail  below. 

Pacific  Ocean  Air  and  Current  Cycles 
Publications  by  Patton  (1956),  Gilliam  (1962),  Major 
(1977),  and  Ainley  (1990)  portray  a  dynamic  interaction 
between  the  forces  of  air,  sea,  and  land.  Seasonal  (and 
long-term)  changes  in  the  ocean  currents  and  air  masses  of 
the  Pacific  Ocean  drive  the  weather  cycles  in  coastal  Cali- 
fornia. Weather  systems  move  across  the  Pacific  from  west 
to  east  fueled  and  modified  by  the  direction  of  the  rotation 
of  the  earth,  the  overall  clockwise  circulation  of  water  in  the 
North  Pacific  (Gyre),  and  the  presence  of  the  North  Pacific 
High  about  halfway  between  California  and  Hawaii.  This 
large  high  pressure  system,  with  clockwise  circulating 
winds,  moves  northwest  in  the  spring  and  summer  as  the 


Northern  Hemisphere  warms  up  and  southeast  in  fall  and 
winter  as  it  cools.  The  clockwise  circulation  of  water  in  the 
North  Pacific  Gyre  sends  cool  surface  waters  of  the  Califor- 
nia Current  south  along  our  coasdine  year  round.  This 
boundary  current  is  one  of  the  most  productive  stretches 
of  ocean  in  the  world.  It  appears  to  be  responsible  for  the 
largely  temperate  character  of  the  local  breeding  marine 
avifauna  (in  an  otherwise  subtropical  region)  and  the  large 
variety  and  number  of  breeding  seabirds  (Ainley  6k  Boekel- 
heide  1990).  The  main  flow  of  the  California  Current  is 
about  125  to  310  miles  offshore;  another  more  variable 
zone  occurs  close  to  shore  where  flow  of  the  current  is 
altered  by  bottom  and  coastal  topography.  Also  a  deep, 
warmer  countercurrent  (below  650  feet  in  depth)  flows 
northwest  along  our  coast.  On  the  surface  west  of  the 
California  Current  are  found  warm  subtropical  waters  of 
relatively  high  salinity  and  rather  depleted  nutrients. 

Bolin  and  Abbott  (1963)  described  three  phases  of  the 
annual  cycle  of  ocean  circulation  direcdy  off  northern 
California:  the  Davidson  Period  (Nov-Feb),  the  Upwelling 
Period  (Feb-Sep),  and  die  Oceanic  Period  (Sep-Oct).  Tim- 
ing, intensity,  and  duration  of  these  three  phases  varies 
from  year  to  year,  as  do  weather  patterns  and  ocean 
productivity.  The  Davidson  Period  commences  with  the 
cessation  of  northwest  winds  and  upwelling  in  the  fall  (see 
below).  At  this  time  the  deep  countercurrent  reaches  the 
surface  and  flows  northward  along  the  immediate  coast- 
landward  of  the  soudiward-moving  California  Current— in 
a  band  about  50  miles  wide.  Because  the  North  Pacific 
High  has  dropped  southward  at  this  time,  the  rainy  season 
commences  as  storms  are  no  longer  deflected  northward 
and  now  reach  our  coast.  These  counterclockwise-circulat- 
ing low-pressure  storm   systems   bring  prevailing  winds 


12 


UNDERSTANDING  BIRD  DISTRIBUTION 

Table  3.  Average  yearly  rainfall  during  the  California  water-year  (Oct-Sep)  at  selected  Marin  County  stations. 
Seasonality  and  annual  variation  of  rainfall  depicted  by  patterns  at  Kentfield.  Data  primarily  from  California 
Department  of  Water  Resources  (1980). 


Location 

Elev.  (ft.) 

Data  Period 

Average  (in.) 

Range  (in.) 

Pt.  Reyes  Lighthouse 

510 

62  yrs;  1879-1944 

19.57 

9.56-47.45 

Inverness 

150 

14  yrs;  1951-1968 

36.65 

23.80-48.15 

Palomarin* 

240 

17  yrs;  1967-1983 

35.93 

15.82-61.15 

Nicasio 

205 

16  yrs;  1960-1975 

37.16 

21.50-57.85 

Novato  Fire  House 

18 

17  yrs;  1957-1979 

25.08 

10.19-42.20 

Hamilton  Field 

0 

24  yrs;  1934-1963 

25.90 

12.37-47.84 

Kent  Lake 

360 

16  yrs;  1960-1975 

66.00 

36.14-116.20 

Woodacre* 

430 

31  yrs;  1951-1983 

45.45 

17.02-79.12 

San  Rafael  Nad.  Bank 

25 

105  yrs;  1872-1976 

36.85 

15.01-67.43 

Kentfield* 

80 

92  yrs;  1896-1983 

47.86 

21.41-88.63 

Mt.  Tarn  1  mi.  S 

950 

39  yrs;  1898-1958 

35.26 

12.81-74.50 

Muir  Woods* 

170 

15  yrs;  1966-1983 

40.71 

18.26-66.21 

Mill  Valley 

10 

11  yrs;  1957-1975 

33.69 

18.48-58.02 

Tiburon 

400 

13  yrs;  1958-1979 

29.31 

12.81-47.26 

*  Supplemental  data  direcdy  from  recording  station;  all  data  from  PRBO's  Palomarin  Field  Station  courtesy  of  Dave  DeSante  and  Geoff 
Geupel. 


AVERAGE  MONTHLY  AND  YEARLY  RAINFALL  AT  KENTFIELD 


Oct 

Nov 

Dec 

Jan 

Feb 

Mar 

Apr 

May 

jun 

Jul 

Aug 

Sep 

Total 

2.70 

5.58 

8.77 

10.63 

8.37 

6.44 

2.88 

1.33 

0.30 

0.04 

0.04 

0.58 

47.86 

YEARLY  RAINFALL  TOTALS  AT  KENTFIELD 
DURING  YEARS  OF  THE  MARIN  COUNTY  BREEDING  BIRD  ATLAS 


1975-76 

1976-77 

1977-78 

1978-79 

1979-80 

1980-81 

1981-82 

22.54 

23.40 

62.58 

38.42 

56.83 

30.14 

81.75 

13 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


.24" 


V 


£^ 


Marin  County 

RAINFALL 

SOURCE:  MARIN  MUNICIPAL 

WATER  DISTRICT 

©  1991  by  Dewey  Livingston 


Figure  4.    Rainfall  map  of  Marin  County,  Isohyetal  lines  connect  areas  of  similar  average  annual  rainfall  (inches  per  year).  Map 
by  Dewey  Livingston,  1991. 


14 


Climate 


UNDERSTANDING  BIRD  DISTRIBUTION 


Climate 


from  the  south  as  they  approach  the  coast.  The  Davidson 
Current  is  reinforced  by  these  southerly  winds  (and  other 
factors)  until  prevailing  winds  shift  to  the  northwest  in 
February  and  March.  Because  flowing  water  (or  air)  tends 
to  move  to  the  right  in  the  Northern  Hemisphere  (reacting 
to  the  Coriolis  force  caused  by  the  rotation  of  the  earth), 
water  flowing  northward  in  the  Davidson  Current  tends  to 
pile  up  along  the  coast.  This  causes  water  to  sink— a 
phenomena  called  downwelling— and  to  be  replaced  by 
water  from  offshore.  Although  surface  temperatures  are 
relatively  warm  for  winter  time,  they  decline  through  the 
period  because  the  heavy  storms  of  the  season  mix  waters 
to  a  considerable  depth  and  partially  because  solar  radia- 
tion decreases  seasonally.  The  frequent  winter  storms  often 
hit  land  with  high,  gusty  winds.  Between  storms,  weather 
can  vary  from  cool,  clear  days,  to  variable  overcast,  to 
occasional  periods  of  ground  fog— particularly  inland.  Win- 
ter also  occasionally  blesses  us  with  very  warm  springlike 
days. 

The  onset  of  the  Upwelling  Period  coincides  with  the 
northward  movement  in  spring  of  the  North  Pacific  High, 
which  again  deflects  storms  to  the  north.  Exceptionally, 
summer  rain  reaches  us  from  rare  fragments  of  tropical 
storms  that  move  north  from  the  vicinity  of  Baja  California 
or  from  ocean  storms  that  pass  by  an  infrequently  weak- 
ened North  Pacific  High.  Warming  of  the  interior  at  this 
time  sets  up  a  low-pressure  system  inland.  The  resulting 
high-  to  low-pressure  gradient  causes  winds  to  intensify. 
Prevailing  winds  are  from  the  northwest  due  to  their  origin 
from  the  clockwise-rotating  North  Pacific  High  and  deflec- 
tion to  the  right  by  the  Coriolis  force.  Periods  of  intense 
winds  will  alternate  with  calm  spells,  but  high  winds 
dominate  the  weather  of  this  period.  Winds  pick  up  in  the 
morning  to  reach  late  afternoon  maxima;  high  velocities 
often  extend  into  predawn  hours.  From  March  to  August, 
winds  on  nearby  Southeast  Farallon  Island  on  average 
attain  speeds  greater  than  16  mph  on  about  one-third  of 
all  days  and  on  almost  one-half  of  all  days  from  April  to 
June.  Velocities  typically  reach  35-40  mph  and  maxima 
exceed  55  mph  (Ainley  1990).  The  mean  wind  velocities 
from  April  through  June  of  25.7  mph  (n  =  18  yr.)  at  Point 
Reyes  and  18.8  mph  (n  =  4  yr.)  at  Southeast  Farallon 
Island  are  the  highest  values  of  any  three-month  period  at 
these  stations  (Calif.  Dept.  Water  Resources  1978). 
Another  important  characteristic  of  these  winds  is  their 
steadiness.  Winds  flow  continuously  from  the  west  for 
every  hour  from  May  to  September  except  in  die  early 
mornings  of  June  to  August  when  winds  flow  from  the 
south  or  west-southwest  (Patton  1956). 

These  strong  northwesterly  spring  winds  increase  the 
flow  of  the  cool  California  Current  and  move  water  along 
the  immediate  coast  south  and  offshore,  again  because  of 
the  Coriolis  force  causing  movement  to  the  right.  The 
water  moving  offshore  is  replaced  from  below  by  cool 


nutrient  rich  waters.  This  process,  called  upwelling,  is 
restricted  to  within  1 2  to  30  miles  of  the  coast,  along  our 
narrow  continental  shelf.  Surface  temperatures  reach  the 
low  of  the  annual  cycle  during  peak  winds  and  upwelling 
from  April  through  June.  Moist  ocean  air  passing  over  the 
cool  upwelled  waters  gives  rise  to  periods  of  intense  coastal 
summer  fog  described  in  more  detail  below.  Although 
upwelling  continues  through  the  spring  and  summer,  solar 
warming  causes  sea  surface  temperatures  to  rise.  The 
nutrient-rich  surface  waters— supplied  by  both  the  strength- 
ened California  Current  and  local  upwelling— stimulate 
high  productivity  of  the  food  chain  of  algae,  zooplankton, 
fish,  and  ultimately  seabirds  (Ainley  1990).  Marin  County 
lies  within  the  region  of  maximum  upwelling  along  the 
West  Coast  (stretching  from  Cape  Blanco,  Oregon,  to 
Point  Conception,  California),  and  Point  Reyes  is  a  partic- 
ularly important  upwelling  center.  Upwelling  occurs  pro- 
gressively later  in  the  season  from  south  to  north  along  the 
California  coast  (Bakun  1973),  and  ocean  productivity  and 
weather  patterns  lag  as  well.  Breeding  seabirds  time  their 
nesting,  as  do  arriving  migrant  seabirds,  to  take  advantage 
of  this  seasonal  peak  of  food  abundance  in  late  spring  and 
summer.  Although  upwelling  occurs  during  the  same  gen- 
eral period  each  year,  there  is  considerable  year-to-year 
variation  in  timing  and  intensity  (Ainley  1990).  Conse- 
quendy,  the  timing  and  success  of  seabird  breeding  can 
vary  gready— some  years  many  species  do  not  breed  at  all. 
The  processes  affecting  upwelling  are  complex  and  not  well 
understood  (D.G.  Ainley  &  W.J.  Sydeman  pers.  comm.). 
Although  years  classified  as  cold-water  years  generally  sig- 
nify high  ocean  productivity/high  breeding  success  (vice 
versa  for  warm-water  years),  this  is  not  always  the  case.  The 
timing  of  spring  winds  can  be  as  important  as  their 
intensity— prolonged  periods  of  intense  winds  and  upwell- 
ing can  sometimes  be  too  much  of  a  good  thing,  disrupting 
the  productivity  at  the  base  of  the  food  chain.  Even  some 
years  widi  strong  upwelling  can  be  warm-water  years. 

During  July  and  August,  northerly  winds  lessen  as  we 
grade  into  the  relatively  calm,  relatively  fog-free  Oceanic 
Period  of  September  and  October.  With  the  cessation  of 
strong  winds,  upwelling  slackens  and  the  California  Cur- 
rent slows  down.  This  is  a  period  of  rather  passive  onshore 
movement  of  warm  nutrient-depleted  waters  that  raise  sea 
surface  temperatures  sharply  to  their  annual  high.  Skies 
vary  from  clear  to  overcast  during  this  period,  with  rela- 
tively infrequent  coastal  fog,  while  temperatures  remain 
warm  throughout  the  county  and  are  the  warmest  of  the 
year  on  the  immediate  coast.  This  lag  in  the  occurrence  of 
seasonal  high  temperatures  is  another  characteristic  of  the 
equitable  coastal  climate.  This  period  is  the  West  Coast 
equivalent  of  Indian  Summer.  As  fall  progresses  and  air 
temperatures  drop,  the  North  Pacific  High  moves  farther 
south,  setting  the  stage  for  the  return  of  winter  storms  and 
die  start  of  another  yearly  cycle. 


15 


Climate 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Climate 


Climatic  Extremes 

Although  die  preceding  paragraphs  describe  the  typical 
annual  weather  cycle,  extreme  conditions  arise  when  shifts 
in  global  air  and  water  circulation  cause  a  breakdown  in 
the  normal  pattern  (see  Ainley  1 990).  A  classic  example  of 
this  was  the  now  famous  El  Nino  event  of  1982-83.  The 
term  El  Nino  ("the  child")  was  first  applied  to  the  warm 
countercurrent  that  normally  occurs  off  Peru  around 
Christmastime,  heralding  the  end  of  the  fishing  season.  El 
Nino  now  generally  denotes  the  unusually  persistent 
warm-water  conditions  that  occur  every  two  to  seven  years 
in  the  Peru  Current  brought  about  by  atypical  circulation 
patterns  in  the  tropical  South  Pacific.  For  reasons  not 
completely  understood,  the  normally  persistent  easterly 
trade  winds  near  the  equator  slacken  or  reverse.  Instead  of 
warm  water  piling  up  along  the  coast  of  Asia,  as  it  usually 
does,  it  flows  back  in  a  long  period  wave  toward  the  east, 
bringing  unusually  warm  water  to  the  coast  of  South 
America.  In  very  strong  El  Nino  events,  the  warm  water 
moves  up  the  California  coast  with  a  much  strengthened 
countercurrent.  Usually  during  such  events  upwelling 
winds  subside,  summer  fog  is  infrequent,  and  winter 
rainfall  is  extremely  high.  An  El  Nino  event  is  usually 
followed  by  "anti-El  Nino"  weather  that  is  unusually 
windy,  dry,  and  cold.  Other  atypical  meteorological  events 
can  transport  warm  nutrient-poor  waters  northward  along 
the  California  Coast,  strengthening  the  Davidson  Current 
and  simulating  El  Nino-like  conditions  including  high 
rainfall. 

Coastal  Summer  Fog 

Besides  stimulating  the  food  chain,  upwelling  plays  an 
important  part  in  the  cycle  of  summer  fog.  Although  rain 
is  virtually  nonexistent  here  in  the  summer,  humidity 
along  the  shore  is  die  highest  of  the  year.  Most  people  refer 
to  the  condensation  clouds  that  dominate  coastal  summer 
weather  as  "fog,"  though  in  actuality  they  are  low  stratus 
clouds.  Moisture  in  die  air  moving  in  off  the  open  ocean 
condenses  when  it  cools  as  it  passes  over  the  upwelled 
nearshore  waters.  Although  this  fog  can  occur  at  the 
surface  of  the  ocean  or  land,  moving  landward  it  usually 
forms  predominandy  in  a  belt  500  to  2300  feet  above  sea 
level.  Although  summer  fog  can  blanket  virtually  all  of 
Marin  County,  most  of  it  is  blocked  from  penetrating 
inland  by  the  higher  coastal  ridges,  except  where  gaps  or 
low-lying  areas  occur.  Summer  fog  is  a  dominant  seasonal 
feature  of  the  seaward  side  of  the  Marin  Peninsula,  the  west 
slope  of  Bolinas  Ridge  in  the  Mount  Tamalpais  area,  and 
particularly  the  Point  Reyes  peninsula  west  of  Inverness 
Ridge;  to  the  north,  fog  penetrates  through  the  low-lying 
hills  near  Tomales  inland  to  about  Hicks  Valley.  Except 
near  Sausalito  and  Tiburon,  summer  fog  is  infrequent 
along  the  Marin  shoreline  of  San  Francisco  and  San  Pablo 
bays,  though  "tule  fog"— formed  by  the  cooling  of  humid 
air  over  chilled  land— often  envelopes  this  area  in  winter. 


A  characteristic  of  the  coastal  air  column  that  also  gready 
affects  weather  is  an  inversion  layer  usually  lying  at  an 
altitude  of  about  2300  to  4400  feet.  Both  above  and  below 
this  zone  air  gets  cooler  with  increasing  altitude.  In  con- 
trast, within  the  inversion  layer  air  gets  warmer  with 
increasing  altitude.  There  is  also  an  abrupt  transition  from 
moist  to  dry  air  low  in  the  inversion  layer.  As  moist  ocean 
air  moves  onto  land  it  rises,  cools  off,  and  moisture 
condenses  as  stratus  clouds  up  to  the  height  of  the  base  of 
the  inversion  layer,  where  the  air  is  too  warm  to  allow  for 
condensation.  This  phenomenon  explains  why  summer 
views  from  the  top  of  Mount  Tamalpais  frequendy  show 
just  a  few  ridges  peeking  through  a  sea  of  fog  enveloping 
the  rest  of  the  county.  As  a  result,  in  summer  the  tops  of 
Mount  Tamalpais  and  other  high  ridges  experience 
warmer  temperatures  than  nearby  lowlands  because  they 
are  within  the  tempered  inversion  layer  and  bathed  in 
sunny  skies  above  the  stratus  layer. 

Although  upwelling  is  thought  of  as  the  driving  force 
behind  summer  fog,  the  origin  of  the  air  approaching  us  is 
also  critical.  Normally  cool  air  moving  in  from  the  north- 
west over  the  ocean  is  ideal  for  fog  production,  but  occa- 
sionally a  tongue  of  high  pressure  moves  over  land,  and 
warm  air  off  die  continent  reaches  us  from  the  north  or 
northeast.  In  this  situation,  despite  upwelling,  the  ocean 
cannot  cool  the  warm  air  sufficiendy  to  produce  fog,  and 
the  inversion  layer  may  come  down  to  ground  level,  further 
hindering  the  process.  The  inversion  layer  also  explains 
why  we  rarely  have  summer  thunderstorms,  even  with  a 
copious  supply  of  moist  air.  This  layer  blocks  air  move- 
ment to  the  altitudes  necessary  for  the  production  of 
diunderheads,  except  under  the  conditions  mentioned 
above  when  die  inversion  comes  down  to  ground  level. 

Summer  fog  ebbs  and  flows  on  a  daily  cycle.  It  is  most 
intense  at  night,  dissipates  normally  in  the  morning  or 
early  afternoon  as  the  air  warms,  and  increases  again  in  the 
late  afternoon  as  the  air  cools.  It  typically  ebbs  and  flows 
on  a  several-day  cycle  as  well.  While  the  immediate  coast  is 
enjoying  cool  temperatures,  the  interior  of  Marin  may  be 
baking  in  90-plus-degree  weather,  with  temperatures  fre- 
quendy soaring  over  100  degrees  further  inland  in  the 
Central  Valley.  As  temperatures  rise  in  the  interior,  the 
low-pressure  system  there  intensifies,  causing  cool  coastal 
air  to  flow  inland,  bringing  moist  air  off  the  ocean  and 
increasing  fog  along  the  coast.  As  the  interior  cools  over 
several  days,  the  inflow  of  air  slackens,  as  does  the  intensity 
of  coastal  fog,  until  the  interior  heats  up  again,  renewing 
the  cycle.  Although  summer  fog  is  often  credited  with 
keeping  temperatures  on  the  immediate  coast  low,  there  is 
evidence  that  advection  of  cool  air  off  the  ocean  is  five  to 
six  times  more  important  in  lowering  temperatures  than  is 
loss  of  solar  radiation  blocked  by  the  stratus  layer  (Patton 
1956). 


16 


Climate 


UNDERSTANDING  BIRD  DISTRIBUTION 


Climate 


Like  rainfall,  the  intensity  of  summer  fog  increases  from 
south  to  north  along  the  California  coast,  with  a  corre' 
sponding  increase  in  the  extent  of  coast  redwood  forest.  It 
has  been  stated  or  implied  that  coastal  summer  fog  is  the 
crucial  element  that  maintains  coast  redwood  forests  by 
supplying  large  amounts  of  water  in  the  form  of  "fog  drip" 
when  moisture  condenses  as  the  air  collides  with  the  tall, 
massive  trees  and  falls  to  the  ground  like  rain.  In  actuality, 
redwoods  grow  primarily  in  protected  coastal  valleys  where 
ground  fog,  wind,  and  fog  drip  are  not  particularly  com- 
mon. Fog  drip  is  heaviest  along  ridge  crests  at  the  level  of 
maximum  stratus  layer  and  where  trees  are  exposed  to 
moisture-laden  winds.  Fog  drip  per  se  is  not  the  limiting 
factor  in  the  occurrence  of  redwoods.  Rather,  the  combina- 
tion of  high  summer  humidity,  year-round  cool  tempera- 
tures, and  low  evapotranspiration,  along  with  a  high  water 
table  and  the  alluvial  soils  of  coastal  valleys,  all  provide  a 
nourishing  environment  for  these  awesome  trees. 

Locally,  however,  fog  drip  does  provide  significant  addi- 
tional moisture.  Oberlander  (1956)  measured  2  to  60 
inches  of  precipitation  from  fog  drip  at  various  exposures 


on  the  San  Francisco  Peninsula.  The  highest  measure- 
ments, under  an  exposed  tanbark  oak,  showed  more  pre- 
cipitation from  fog  than  is  normally  recorded  in  an  entire 
rainy  season.  Parsons  (1960)  recorded  9.8  inches  beneath 
a  Monterey  pine  in  the  Berkeley  Hills,  and  Azevedo  and 
Morgan  (1974)  recorded  1.4  to  16.7  inches  at  several  sites 
in  the  low  mountains  south  of  the  Eel  River  Valley, 
Humboldt  County.  Much  of  the  precipitation  fell  during  a 
few  heavy  fog  drip  periods.  Since  rainfall  is  next  to  nil  in 
summer,  fog  drip  and  humid  air  are  important  determi- 
nants of  the  types  of  plant  communities  growing  within  the 
coastal  zone.  There  the  importance  of  summer  moisture  is 
reflected  in  the  dense,  rank  ground  cover  beneath  Marin 
County's  Douglas  fir,  Bishop  pine,  and  bay  laurel-domi- 
nated mixed  evergreen  forests.  Forests  in  the  interior  of 
Marin,  away  from  the  consistent  penetration  of  summer 
fog,  usually  have  very  sparse  understories  or  ground  cover 
because  of  the  lack  of  ground  moisture  during  the  summer. 
The  types  and  distribution  of  plant  communities  found  in 
Marin  County  are  described  in  the  pages  that  follow. 


17 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


"*> 


.'", 


% 


sdf*3 


H 


^ 


The  wind-sculpted  California  bay  forest  leaning  inland  at  the  Nicasio  gap.  Drawing  by  Ane  Rovetta,  1989. 


18 


MARIN  COUNTY 
BREEDING  BIRD  HABITATS 


Strip  tKe  world  of  its  blossoms,  and  the  higher  /orms  of  life  must  come  to  a  speedy  tem\ination.  Thus  we  see  the  flower  playing 
a  wonderfully  important  part  in  the  cosmos  around  us  .  .  .  the  instrument  b}  which  Nature  brings  about  the  fullness  of  her 
perfection  in  her  own  good  season. 

—  Mary  Elizabeth  Parsons, 
The  Wild  Flowers  of  California 


MARIN  COUNTY  hosts  a  diverse  array  of  habitats  for 
breeding  birds.  Most  of  these  habitats  equate  with 
the  county's  plant  communities  described  below.  Others 
do  not,  and  these  additional  habitats  are  described  briefly 
in  a  section  following  the  plant  community  descriptions. 

Marin  County  Plant  Communities 

Evolutionary  history,  varied  topography,  unusual  soils  and 
geology,  and  wide  differences  in  local  climate  over  short 
distances  have  combined  to  proyide  Marin  County  with  a 
diverse  flora  and  a  large  number  of  plant  communities 
arranged  in  a  patchy  mosaic  over  the  landscape  (Figure  5). 
Marin  County  hosts  eleven  major  plant  communities,  of 
which  six  can  be  subdivided  into  fifteen  associations. 
Consequendy,  the  county  is  endowed  with  habitat  that 
supports  a  wide  variety  of  breeding  birds.  Because  birds 
generally  base  their  habitat  choice  on  the  structure  of  plant 
communities  rather  than  on  particular  plant  species  (e.g., 
Verner  &  Larson  1989),  the  following  descriptions 
emphasize  structure  over  floristics.  These  descriptions  are 
condensed  from  Shuford  and  Timossi's  (1989)  Plant  Com- 
munities of  Marin  County,  California,  to  which  the  reader 
is  referred  for  greater  detail.  The  communities  and  associ- 
ations described  can,  of  course,  grade  into  one  another  to 
varying  degrees.  The  edges  of  plant  communities  (eco- 
tones)  often  support  a  high  diversity  of  bird  species. 

Mixed  Evergreen  Forest 

This  is  the  predominant  forest  type  in  Marin  County  and 
is  characterized  by  closed-canopy  stands  of  several  species 
of  broadleaved  evergreen  hardwoods.  Conifers  may  occur 
in  varying  numbers  and  in  some  cases  may  dominate. 
Because  it  occupies  a  broad  range  of  slope,  moisture,  and 
elevational  gradients,  this  community  is  quite  variable, 


occurring  in  three  main  associations  that  may  grade  into 
one  another.  Mixed  evergreen  forest  grows  throughout 
most  of  the  hilly  and  mountainous  terrain  of  Marin 
County. 

Coast  Live  Oak-California  Bay-Madrone  Forest.  This 
association  is  dominated  by  one  or  more  of  these  evergreen 
hardwood  species:  coast  live  oak  (Quercus  agrifolia),  Cali- 
fornia bay  (Umbellularia  califomica),  and  madrone  (Arbu- 
tus menziesii).  California  buckeye  (Aesculus  califomica)  and 
black  oak  (Quercus  kellogii)  may  be  important  locally. 
Dominant  trees  at  maturity  average  30  to  80  feet  in  height. 
In  drier  conditions,  a  true  understory  is  reduced  or  lacking 
entirely,  with  scattered  saplings  of  the  dominant  trees 
forming  the  understory  where  it  exists.  In  most  intermedi- 
ate conditions,  poison  oak  (Toxicodendron  diversilobum) 
and  toyon  (Heteromeles  arbutijolia)  are  important  under- 
story components.  In  moister  conditions,  especially  toward 
the  immediate  coast,  this  forest  association  can  have  a 
well-developed  understory  of  sword  fern  (Polystichum  muni- 
tum),  huckleberry  (Vaccinium  ovatum),  California  hazelnut 
(Corylus  califomica),  poison  oak,  and  currant  (Ribes  spp.) 
about  3  to  6  feet  in  height.  This  association  occurs  at  low 
to  moderate  elevations  throughout  most  of  the  county. 

Tanbark  Oak-Madrone-Live  Oak-Douglas  Fir  Forest. 
This  mixed  evergreen  association  is  dominated,  in  varying 
proportions  according  to  site,  by  tanbark  oak  (Lithocarpus 
densiflorus),  madrone,  Douglas  fir  (Pseudotsuga  menziesii), 
coast  live  oak,  and  canyon  live  oak  (Quercus  chrysolepis) . 
California  bay,  coast  redwood  (Sequoia  sempervirens) ,  Cali- 
fornia nutmeg  (Torreya  califomica),  and  chinquapin  (Casta- 
nopsis  chrysophylla  var.  minor)  occur  locally.  At  maturity, 
dominant  trees  average  30  to  80  feet  and  occasionally  reach 
120  feet.  This  forest  is  generally  rather  open  under  the 
canopy  as  the  understory  consists  of  scattered  saplings  of 

19 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Plant  Communities 


Figure  5.    Preliminary  vegetation  map  of  Marin  County.  Map  by  Dave  Shuford  and  Deu/ej  Livingston,  1991. 


20 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  HABITATS 


Plant  Communities 


mwm 

Oak  woodland  and  oak  savannah  stand  watch  on  Mount  Burdell,  Novate  Drawing  b>  Ane  Rovetta,  I 989. 


the  dominant  trees.  This  association  occupies  mid  to  high 
elevations  on  Mount  Tamalpais  and  surrounding  ridges 
and,  to  a  limited  degree,  Inverness  Ridge. 

Douglas  Fir  Forest.  This  closed-canopy  forest  is  domi- 
nated by  Douglas  fir,  which  in  mature  stands  averages  100 
to  1 60  feet  in  height.  There  may  or  may  not  be  a  secondary 
canopy  of  coast  live  oak,  California  bay,  and  blue  blossom 
(Ceanothus  thyrsiflorus)  averaging  25  to  65  feet  in  height. 
In  most  cases  there  is  a  dense  understory  about  4  to  8  feet 
in  height,  consisting  of  huckleberry,  salal  (Gaukheria  shal- 
lon),  sword  fern,  California  hazelnut,  poison  oak,  red 
elderberry  (Sambucus  callicarpa),  and  thimbleberry  (Rubus 
parviflorus) .  In  Marin  County,  Douglas  fir  forest  grows 
mosdy  on  the  southern  and  central  portions  of  Inverness 
Ridge  and  locally  throughout  the  Mount  Tamalpais  and 
Lagunitus  Creek  watersheds.  In  these  latter  areas,  Douglas 
fir  most  frequendy  mixes  with  coast  redwood  or  with  trees 
of  the  tanbark  oak-madrone-live  oak-Douglas  fir  forest 
described  above. 

Oak  Woodland  and  Oak  Savannah 

In  contrast  to  the  mixed  evergreen  forest,  typical  oak 
woodland  and  oak  savannah  have  open  canopies,  grassy 
ground  cover  below  and  between  the  trees,  and  a  predom- 
inance of  deciduous,  rather  than  live  oaks.  Oak  woodland 
is  distinguished  by  tree  cover  greater  than  30%,  whereas 
oak  savannah  consists  of  isolated  trees.  The  characteristic 
tree  of  Marin's  oak  woodlands  and  oak  savannah  is  valley 
oak  (Quercus  lobata).  Although  there  is  no  true  understory, 
scattered  shrubs  such  as  manzanita  (Arctosta^k^Ios  spp.), 
ceanothus  (Ceanothus  spp.),  poison  oak,  and  several  spe- 
cies of  herbaceous  thisdes  may  occur,  especially  on  the 
edges.  The  grassy  ground  cover  consists  of  species  charac- 
teristic of  valley  grassland,  described  below.  On  deeper 


soils  on  valley  floors,  valley  oaks  at  maturity  vary  in  height 
from  30  to  100  feet,  whereas  smaller  oaks  grow  on  shal- 
lower soils  on  steeper  slopes.  Blue  oak  (Quercus  douglasii), 
a  characteristic  tree  of  oak  woodland  and  oak  savannah  in 
hills  of  the  interior  Coast  Range,  grows  locally  in  Marin 
only  in  Novato  on  Mount  Burdell  and  near  Black  Point. 
Oak  woodland  and  oak  savannah  generally  occupy  rela- 
tively dry  areas  in  the  interior  of  Marin  County,  especially 
around  Novato  north  of  Big  Rock  Ridge  and  east  of  Hicks 
Valley.  A  lack  of  recruitment  of  sapling  oaks  threatens  the 
long-term  survival  of  California's  oak  woodlands  and  oak 
savannahs. 

Bishop  Pine  Forest 

This  forest  is  one  of  a  number  of  relict,  fire-adapted, 
closed-cone  pine  communities  that  grow  in  disjunct  stands 
along  the  California  coast.  Bishop  pine  (Pinus  muricata)  is 
the  dominant  tree,  usually  thriving  in  pure,  even-aged 
stands  that  reach  60  to  70  feet  in  height  at  maturity. 
Bordering  the  pines  are  limited  stands  of  live  oak,  Califor- 
nia bay,  tanbark  oak,  madrone,  California  buckeye,  and 
wax-myrtle  (Myrica  calif ornica).  The  understory  of  the 
pines  is  usually  a  dense  shrub  layer  about  4  to  8  feet  high 
consisting  of  huckleberry,  salal,  coffeeberry  (Rhamnus  cali- 
jomica),  chinquapin,  and  two  species  each  of  manzanita 
and  ceanothus.  On  deeper  soils  where  the  pines  reach  their 
greatest  stature,  the  shrub  layer  is  taller  and  often  parklike, 
with  many  grassy  openings  between  the  shrubs  and  pines. 
On  steeper  slopes  and  rockier  soils,  the  shrub  layer  grows 
as  continuous  low  dense  cover.  In  Marin  County,  bishop 
pine  forest  dirives  primarily  on  granitic  soils  on  the  north 
end  of  Inverness  Ridge  on  the  Point  Reyes  peninsula.  Five 

21 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Plant  Communities 


Gnarly  bishop  pine  forest  at  Tomales  Bay  State  Park. 
Drawing  b}  Ane  Rovetta,  1 985. 


small  stands  grow  on  gravelly,  sandstone-derived  soils  east 
of  the  San  Andreas  Fault  on  Bolinas  Ridge  and  in  the 
vicinity  of  Carson  Ridge  (Millar  1986). 

Coast  Redwood  forest 

The  essence  of  the  coast  redwood  forest  is  a  towering 
canopy  of  coast  redwoods  averaging  100  to  130  feet  in 
height,  widi  exceptional  trees  reaching  250  feet.  California 
bay  and  tanbark  oak  may  form  a  subcanopy  50  to  65  feet 
high.  California  bay  is  consistendy  found  along  moist 
drainages,  while  tanbark  oak  is  found  on  die  edges  or  in 
occasional  sunny  openings  in  the  forest.  The  understory 
consists  primarily  of  California  hazelnut,  huckleberry, 
western  azalea  (Rhododendron  occidentale),  wood  rose  (Rosa 
californica),  thimbleberry,  and  patches  of  sword  fern,  and 
is  generally  open  except  where  it  is  locally  dense  along 
streams.  This  forest  occurs  primarily  east  of  the  San 
Andreas  Fault  in  areas  of  high  year-round  humidity,  hence 
mosdy  in  the  zone  of  persistent  summer  fog.  Redwoods  are 
widespread  on  the  Mount  Tamalpais  and  Lagunitas  Creek 
watersheds,  and  are  local  from  there  north  to  the  north 
slopes  of  Big  Rock  Ridge. 

Grassland 

California's  grasslands  were  formerly  dominated  by  peren- 
nial bunch  grasses,  interspersed  with  numerous  annuals. 
Today  these  grasslands  are  dominated  by  introduced  Euro- 
pean annuals  whose  spread  was  aided  and  abetted  by  stock 
grazing  and  dry-land  farming.  Although  overall  introduced 
annual  grasses  now  dominate  our  grasslands,  native  peren- 
nial bunch  grasses  still  persist  locally  on  the  immediate 
coast.  Grasslands  are  widespread  in  Marin,  particularly  in 
the  northwestern  region  of  the  county.  There  are  two  major 
types  of  grassland  in  California  and  in  Marin  County: 
coastal  prairie  and  valley  grassland. 

Coastal  Prairie.  Coastal  prairie  has  also  been  called  the 
Festuca-Danthonia  grassland  after  the  dominant  genera  of 
grasses  in  diis  community  in  California.  The  dominant 
species  in  ungrazed  sites  on  Point  Reyes  are  the  perennial 
bunch  grass  hairgrass  (Deschampsia  holciformis),  the  low- 
growing  form  of  coyote  brush  {Baccharis  pilularis  ssp. 
pilularis),  the  native  biennial  grass  California  brome 
(Bromus  carinatus),  sheep  sorrel  (Rumex  acetosella),  and 
bracken  fern  (Pteridium  aquilinum  var.  pubescens).  Scattered 
bushes  of  the  low-growing  coyote  brush  and  bracken  ferns 
are  characteristic  of  grassland  on  the  immediate  coast  but 
become  scarcer  inland.  The  scattered  brush  and  ferns  and 
the  mix  of  perennial  and  annual  grasses  give  the  coastal 
prairie  a  more  varied  structure  than  that  of  interior  valley 
grasslands.  Typical  stands  of  coastal  prairie  are  less  than 
about  one  and  one-half  feet  high.  There  are  marked  differ- 
ences between  grazed  and  ungrazed  sites.  Grazing 
decreases  the  average  height  of  plants  threefold,  reduces 
the  percent  cover  of  perennial  and  biennial  species,  and 
reduces   the   percentage   of  native   species   (Elliott   <Sl 


22 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  HABITATS 


Plant  Communities 


Wehausen  1974).  Coastal  prairie  flourishes  in  the  moist 
coastal  zone  shrouded  by  persistent  summer  fog,  and  its 
distribution  seems  to  parallel  that  of  breeding  Grasshopper 
Sparrows  (see  species  account). 

Valley  Grassland.  The  perennial  bunch  grass  that 
originally  dominated  the  valley  grassland  was  needlegrass 
(Stipa  pulchra).  Among  others,  two  major  associates  were 
the  rye  grasses  Elymus  glaucus  and  E.  triticoides.  Stipa 
^ulchra-dominated  grassland  now  occurs  very  locally  on 
Mount  Tamalpais.  Valley  grassland  over  most  of  the  rest 
of  the  drier  interior  of  Marin  County  is  dominated  by 
introduced  annual  grasses  and  forbs  such  as  wild  oats 
(Avena  fatua  and  A.  barbata),  soft  chess  (Bromus  mollis), 
ripgut  grass  (B.  diandrus),  fescues  (Festuca  spp.),  and  filaree 
(Erodtum  spp.).  Today  valley  grassland  appears  to  have 
fewer  species  and  a  less  varied  structure  than  coastal 
prairie.  Valley  grassland  has  one  or  two  often  dense  layers 
up  to  about  three  feet  high.  On  very  disturbed  or  over- 
grazed sites,  one  or  a  few  species  may  predominate,  and 
local  patches  of  noxious  introduced  thisdes  often  thrive. 
Valley  grassland  predominates  in  die  drier  portions  of  die 
county. 


Coastal  Beach-Dune  Vegetation 

Dune  communities  here  reside  in  a  narrow  zone  above  the 
wave-washed  beaches,  primarily  on  Point  Reyes.  There  is  a 
noticeable  zonation  of  plants  from  the  beach  inland  as  a 
function  of  both  changing  physical  gradients— exposure  to 
salt  spray  and  sandblasting  by  persistent  onshore  winds— 
and  of  the  length  of  successional  history  on  stabilized 
dunes. 

Northern  Beach  Association.  Close  to  the  beach  the 
dunes  are  covered  mosdy  with  perennial  grasses,  usually 
less  than  two  feet  tall,  and  a  number  of  low-growing 
perennial  herbs.  The  latter  are  generally  prostrate,  ever- 
green, and  succulent  as  adaptations  to  the  salty  air,  strong 
winds,  and  shifting  sands.  The  prominent  grasses  are  the 
perennial  American  dune  grass  (Elymus  mollis)  and  the 
introduced  European  beach  grass,  or  marram  grass  (Ammo- 
phila  arenaria).  Associated  low-growing  herbs  include  sea 
rocket  (Cakile  maritima),  sandA'erbena  (Abronia  latifolia), 
silver  beach  weed  (Ambrosia  chamissonis),  Atriplex  leuco- 
phylla,  beach  morning  glory  (Calystegia  soldanella),  ice 
plant  {Carpobrotus  chilense  and  C.  edulis),  and  lupines 
(Lupinus  spp.),  particularly  moving  landward.  The  amount 


^C^& 


'■^^^J^^ 


^wK, 


mT7p    -   ;■■  ^m-,y^y 


•4Zi. 


Beach  and  dunes  at  Limantour  Estero  strand  lapped  this  day  by  the  gentle  surf  of  Drake's  Bay.  Drawing  fry  Ane  Rovetta,  1984. 


23 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Plant  Communities 


A  mosaic  o/ grassland,  mixed  evergreen  forest,  and  chaparral  clothing  Big  Rock  Ridge  just  east  of  the  Big  Rock. 

Drawing  by  Ane  Rovetta,  1 989. 


of  plant  cover  can  reach  100%  but  generally  averages  about 
10%-25%.  The  introduction  for  "dune  stabilization"  of 
the  European  beach  grass  has  caused  the  development  of 
a  steep-sided  foredune  parallel  to  the  beach  and  abutting  a 
series  of  wind-molded  dunes  and  coastal  swales  oriented 
perpendicular  to  the  beach  and  coast.  Formerly  foredunes 
rose  gradually  to  the  landward  perpendicular  dunes  that 
had  many  openings  among  them  connected  to  the  beach. 

Northern  Dune  Scrub.  Landward,  a  dune  scrub  associa- 
tion about  three  to  five  feet  high  occupies  the  older,  more 
stable  dunes.  This  association  is  characterized  by  a  number 
of  perennial  lupines  {Lupinus  albi}rons,  L  arboreus,  L 
rivularis,  and  L.  chamissonis),  mock  heather  (Haplopappus 
ericoides),  and  the  low-growing,  small-leaved  form  of  coyote 
brush  (Baccharis  pilularis).  These  shrubs,  mixed  with  other 
subshrubs  and  perennial  and  annual  herbs,  usually  form 
an  open  canopy. 

Northern  Coastal  Scrub 

Northern  coastal  scrub  or  "soft  chaparral"  is  a  two-layered, 
herb-rich,  evergreen  shrub  community  that  grows  on  the 
lower  slopes  of  hills  in  the  summer  fog  zone  along  the 
immediate  coast.  It  consists  of  two  major  associations: 

Coyote  Brush-Sword  Fern  Scrub.  Coyote  brush  (Bacch- 
aris pilularis  ssp.  consanguinea)  dominates  this  association, 
which  has  a  closed  or  open  overstory  about  three  to  seven 
feet  tall.  Other  important  overstory  shrubs  depending  on 
site  and  exposure  are  poison  oak,  California  hazelnut,  blue 
blossom,  coffeeberry,  thimbleberry,  and,  in  the  spring  and 
summer,  cow  parsnip  (Heracleum  lanatum).  The  under- 
story  varies  from  a  dense,  tangled  interwoven  thicket  of 
ferns  along  with  low  woody  and  herbaceous  perennials 

24 


and  annuals  to  a  more  open  one  devoid  of  ferns.  Western 
sword  fern  usually  dominates  the  understory  at  denser  and 
moister  sites,  but  California  blackberry  (Rubus  ursinus 
and/or  R.  vitifolius),  salal,  western  bracken  fern,  huckle- 
berry, bush  monkey-flower  (Mimulus  aurantiacus),  and 
Douglasiris  (Iris  douglasiana)  may  be  important  compo- 
nents along  with  grasses,  sedges  (Carex  spp.),  rushes  ()un- 
cus  spp.),  and  other  forbs.  This  association  is  widespread 
on  the  lower  ocean-fronting  hills  the  length  of  the  county, 
particularly  on  north-facing  slopes. 

Coastal  Sage-Coyote  BrusK  Scrub.  This  is  a  one-layered 
coastal  scrub  association  dominated  by  coastal  sage  (Arte- 
misia californica)  about  two  to  four  feet  high  with  lesser 
amounts  of  coyote  brush,  poison  oak,  bush  monkey- 
flower,  California  blackberry,  western  bracken  fern, 
grasses  and  forbs,  and,  in  some  areas,  lupines.  Open  areas 
among  the  bushes  in  many  areas  are  either  bare  or  rocky 
soil  or,  more  frequently,  are  covered  with  grasses  and 
forbs.  Spanning  the  length  of  the  county  on  south-facing 
slopes,  this  association  is  most  widespread  on  the  southern 
end  of  the  Point  Reyes  peninsula  and  east  of  the  San 
Andreas  Fault  from  Bolinas  Lagoon  south  to  the  Golden 
Gate. 

Chaparral 

Dense  chaparral  scrub  arises  from  poor  rocky  soils  on  drier 
inland  hills.  Dominant  chaparral  species  are  evergreen, 
densely  branched,  woody  summer-dormant  shrubs  with 
small  thick  stiff  leaves.  Chaparral  is  highly  adapted  to  fire 
and  regenerates  quickly.  The  shrubs  in  this  community 
generally  form  a  single  dense,  intertwining,  almost  impene- 
trable overstory  layer  with  a  sparse  ground  cover  below. 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  HABITATS 


Plant  Communities 


Chaparral  associations  vary  with  slope,  sun  exposure, 
elevation,  soil,  and  fire  history.  Chaparral  grows  here  only 
east  of  the  San  Andreas  Fault,  primarily  on  Mount  Tamal- 
pais,  Pine  Mountain/Carson  Ridge,  and  Big  Rock  Ridge. 
Marin's  hills  support  four  chaparral  associations: 

Chamise  Chaparral.  Chamise  (Adenostoma  fascicula- 
turn)  dominates  this  association,  forming  almost  unbroken 
stands  on  hot  xeric  sites,  usually  on  south-  or  west-facing 
slopes  and  ridges.  Chamise  here  reaches  a  height  of  three 
to  six  feet  at  maturity.  Manzanita  and  ceanothus  occur 
infrequently  in  this  association. 

Manzanita  Chaparral.  Manzanita  shrubs  three  to  six 
feet  high  dominate  this  association.  Typical  manzanita 
species  of  the  chaparral  are  Cushing  manzanita  (Arcto- 
staphylos  cushingiana),  hoary  manzanita  (A.  canescens),  and 
Marin  manzanita  (A.  virgata).  Manzanita  and  chamise 
chaparral  often  alternate  on  east-  and  west-facing  slopes— 
for  example,  along  the  Old  Railroad  Grade  near  the  West 
Point  Inn  on  Mount  Tamalpais. 

Mixed  Chaparral.  Mixed  chaparral  consists  of  an 
almost  even  mix  of  manzanita,  chamise,  buck  brush  (Cea- 
nothus ramulosus),  and  interior  live  oak  (Quercus  wislizenii 
var.  frutescens)  ranging  from  diree  to  ten  feet  high.  It 
abounds  on  mesic  sites,  where  it  usually  grades  into  mixed 
evergreen  forest  on  shady  slopes  or  in  draws.  Other  shrubs 
of  this  association  are  chaparral  pea  (Pickeringia  montana), 
coffeeberry,  and  ceanothus  (Ceanothus  sorediatus  and  C. 
foliosus). 

Serpentine  Chaparral.  This  association  is  restricted  to 
biologically  harsh  serpentine  soils.  There  the  shrub  canopy 
is  broken  with  bare  ground  and  rock  outcrops,  and  shrubs 


generally  are  dwarfed  or  stunted,  often  reaching  only  about 
one  and  one-half  to  three  feet  in  height.  Characteristic 
shrubs  are  leather  oak  (Quercus  durata),  Jepson's  cea- 
nothus (Ceanothus  jepsonii),  Tamalpais  manzanita  (Arc- 
tostaphylos  montana),  and  Sargent  cypress  (Cupressus 
sargentii).  Elsewhere  it  may  grow  as  a  fairly  large  tree;  but 
on  Carson  Ridge,  Sargent  cypress  grows  amid  the  chapar- 
ral as  a  striking  dwarf  forest  ten  to  fifteen  feet  high. 
Serpentine  chaparral  occupies  extensive  areas  along  the 
Pine  Mountain  Fire  Road  on  Carson  Ridge  and  on  Mount 
Tamalpais  on  Serpentine  Knoll  and  on  the  Benstein  Trail 
above  Potrero  Meadows. 

Coastal  Salt  Marsh 

Salt  marsh  is  restricted  to  the  upper  intertidal  zone  of 
protected  shallow  bays,  estuaries,  and  lagoons.  Vertical 
zonation  of  saltmarsh  plants  reflects  elevational  gradients 
that  affect  the  frequency  and  duration  of  tidal  flooding. 
Bordering  the  mudflats  are  pure  open  stands  of  cordgrass 
(Spartina  foliosa)  about  one  and  one-half  to  three  feet  tall. 
Landward,  cordgrass  is  replaced  at  the  mean  high  water 
level  by  thick  mats  of  low-growing  salt  marsh  dominated 
by  pickleweed  (Salicornia  virginica),  generally  about  four  to 
eighteen  inches  in  height.  Other  characteristic  plants  of  the 
upper  pickleweed  zone  are  alkali  heath  (Frankenia  grandi- 
folia),  marsh  rosemary  (Limonium  calif ornicum),  jaumea 
(faumea  carnosa),  plantain  (Plantago  maritima),  and  salt- 
grass  (Distichlis  spicata).  On  isolated  mounds  or  along 
natural  levees  of  tidal  sloughs  not  subject  to  frequent 
flooding  grow  clumps  of  gumplant  {Grindelia  humilis  or  G. 
stricta)  and  dock  (Rumex  occidentalis)  up  to  about  three  feet 
tall.  In  the  grasslandlike  upper  border  of  the  salt  marsh, 


mmmmi 

A  toe  hold  of  coastal  salt  marsh  on  the  shores  of  San  Pablo  Bay  abutting  the  mixed  evergreen  forest, 

China  Camp  State  Park.  Drawing  by  Ane  Rovetta,  1 989. 


grassland-blended  hills  of 


25 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Plant  Communities 


saltgrass  and  spergularia  (Styergularia  spp.)  mix  with  other 
salt-tolerant  natives  and  introduced  species.  Where  salt 
marshes  historically  graded  primarily  into  brackish  marsh 
and  then  into  freshwater  marsh,  grassland,  or  shnjb  com- 
munities, today  most  salt  marshes  abruptly  abut  dikes  and 
roadsides.  In  brackish  situations  the  marsh  is  dominated 
by  various  forms  of  bulrush  (Scir|)us  spp.)  and  cattails 
(Typha  spp.). 

An  estimated  60%-95%  of  the  marshland  in  the  San 
Francisco  Bay  system  has  been  lost  to  filling  and  diking 
(Nichols  ck  Wright  1971,  Josselyn  1983).  Remnant  stands 
of  salt  marsh  still  persist  in  Marin  County  at  a  number  of 
sites  along  the  shores  of  San  Francisco  and  San  Pablo  bays 
and  on  the  outer  coast  in  the  upper  reaches  of  Tomales 
Bay,  Limantour  and  Drake's  esteros,  and  at  Bolinas  La- 
goon. 

Coastal  Riparian  Forest 

In  Marin  County,  willow-  and  alder-dominated  riparian 
groves  border  small  streams  and  the  edges  of  ponds  and 
freshwater  marshes,  where  the  trees  merge  with  marsh 
vegetation.  Typical  overstory  trees  of  our  riparian  forests 
are  red  alder  (Alnus  oregona),  white  alder  (A.  rhombi folia), 
arroyo  willow  (Salix  lasiolepis),  yellow  willow  (S.  lasiandra), 
big-leaf  maple  (Acer  macrophyllum),  and  box  elder  (A. 
negundo  ssp.  califomicum).  Near  stream  and  marsh  edges 
willows  colonize  recendy  deposited  soils  and  are  tolerant 
of  some  flooding.  Because  they  reproduce  vegetatively, 
willows  often  form  pure  stands  with  overstory  height 
averaging  10  to  15  feet.  Landward,  willows  usually  inter- 
grade  widi  alders,  which  may  provide  an  overstory  canopy 
30  to  40  feet  high  or  may  grow  in  pure  stands  of  similar 
height. 


The  riparian  undcrstory  may  include  saplings  of  die 
overstory  trees  and  thickets  of  California  blackberry  or 
Flimalaya-berry  (Rubus  procerus)  interspersed  with  a  thick 
herbaceous  ground  cover.  Under  natural  conditions,  alder 
groves  may  sometimes  have  little  understory  or  ground 
cover,  but  cattle  often  eliminate  the  low  vegetation  under 
both  alders  and  willows  by  grazing  and  trampling.  Ripar- 
ian forests  may  grade  into  a  number  of  other  communities. 
In  stream  canyons,  moisture-loving,  shade-tolerant  Califor- 
nia bay  trees  may  mix  with  or  replace  die  typical  riparian 
dominants.  With  the  spread  of  human  influence,  riparian 
communities  in  Marin  County,  as  elsewhere,  have  been 
lost  or  degraded  at  an  alarming  rate.  Alder  and  willow 
riparian  thickets  are  still  widespread  in  drainages  on  the 
outer  coast,  but  few  remain  in  the  urbanized  corridor  near 
the  bayshore  of  eastern  Marin. 

Freshwater  Marsh 

Bulrush-Cattail  Marsh.  Typical  freshwater  marsh 
thrives  in  shallow  standing  or  slow-moving  water  on  the 
edges  of  ponds,  lakes,  or  streams.  Cattail  and  California 
bulrush  (Scirpus  californicus)  border  open  water  in  mixed 
association  with  each  other,  or  in  pure  stands,  averaging 
five  to  eight  feet  high.  Assemblages  of  other  marsh  species, 
usually  about  one  and  one-half  to  five  feet  high,  grow  in 
shallower  water  or  damp  soil.  These  include  rushes  (Juncus 
spp.),  sedges  (Cyperus  eragrostis  and  Carex  spp.),  spike  rush 
(Eleocharis  spp.),  curly  dock  (Rumex  crispus),  sheep  sorrel, 
water  parsley  (Oenanthe  sarmentosa),  and  the  bur-reed  Spar- 
ganium  eurycarpum.  The  county's  largest  freshwater  marsh 
and  willow  riparian  stand  is  located  at  Olema  Marsh. 


Riparian  forest  of  Olema  Valley  flanked  by  Douglas  fir  forest,  mixed  evergreen  forest,  and  grassland  on  Inverness  Ridge. 

Drawing  b>  Ane  Rovetta,  1989. 


26 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  HABITATS 


Plant  Communities 


Riparian  growth  Hemming  in  the  view  of  pond  turtles  at  Five  Brooks  Pond.  Drawing  by  Ane  Rovetta,  I  985. 


Coastal  Swale.  Another  type  of  freshwater  marsh 
grows  primarily  along  the  outer  coast  where  water  reaches 
the  surface  in  depressions  in  coastal  prairie  or  among 
dunes.  Water  channels  are  choked  with  water  cress  (Na- 
sturtium officinale),  water  parsley,  and  marsh  pennywort 
(Hydrocotyle  ranunculacea  and  H.  verticillata)  ranging  up  to 
1 V2  feet  in  height.  In  shallower  water  or  on  saturated  mud, 
the  swale  may  be  dominated  by  pure  stands  up  to  4  feet 
high  of  the  bulrush  Scirpus  microcarpus  or  slough  sedge 
(Carex  obnupta).  On  drier  ground  grow  clumps  of  various 
grasses,  interspersed  with  plants  such  as  marsh  checker- 
bloom  (Sidalcea  rhizomata),  bog  lupine  (Lupinus  polyphyllus 
var.  grandifolius),  Siberian  montia  (Montia  sibirica),  the 
monkeyflower  Mimulus  guttatus,  and  poison  hemlock 
(Conium  maculatum).  Riparian-like  patches  of  wax-myrde, 
6  to  12  feet  high,  sometimes  border  swales.  Coastal  swales 
in  damp  meadow  soil  may  be  dominated  by  clumps  of 
rushes  and  sedges  mixed  with  grasses. 

Exotic  Plants 

Exotic  plants  have  been  introduced  widely  in  California 
and  Marin  County.  In  urban  and  suburban  settings, 
ornamental  plants,  whether  alone  or  mixed  with  native 
species,  provide  shade  and  beauty  for  human  inhabitants 
and  food  and  shelter  for  wildlife.  Many  exotics  have 
escaped  and  become  naturalized  in  native  communities 
with  varying  effects.  Some  introduced  plants  are  inconspic- 
uous immigrants  sharing  the  resources  with  dominant 


native  species,  whereas  other  aggressive  exotics  have 
pushed  out  and  replaced  the  rightful  heirs  of  our  plant 
communities.  As  noted  above,  Mediterranean  annual 
grasses  have  entirely  changed  the  character  of  our  native 
grasslands,  and  European  beach  grass  has  altered  both  the 
structure  and  flora  of  dune  communities.  The  range  and 
extent  of  effects  that  introduced  plants  have  had  on  the 
native  flora  and  on  the  birds  and  other  native  wildlife  that 
depend  on  them  are  very  incompletely  known. 

Of  the  many  introduced  species  naturalized  in  the 
county,  only  the  most  conspicuous,  widespread,  or  offen- 
sive ones  are  mentioned  here.  Many  species  of  Eucalyptus 
have  been  introduced  to  California— the  most  common 
and  widespread  is  bluegum  eucalyptus  (E.  globulus).  Exten- 
sive stands,  planted  originally  as  windbreaks  and  woodlots, 
now  grow  as  small  patches  of  forest  in  what  formerly  were 
almost  treeless  expanses  of  grasslands  in  Marin  County. 
Mature  eucalyptus  groves  may  form  towering  canopies 
reaching  over  100  feet  skyward.  The  volatile  oils  produced 
by  eucalypts  preclude  the  establishment  of  a  rich  under- 
story  flora.  The  most  frequent  understory  plants  are  sap- 
ling eucalypts,  blackberries,  and  in  some  areas,  the  exotic 
and  blanketing  German  ivy  (Senecio  mikanioides).  Eucalyp- 
tus groves  have  shown  only  a  limited  ability  to  invade  forest 
edges  and  are  most  successful  in  penetrating  grasslands 
and   brush   communities.    Planted    Monterey   cypress 

27 


Plant  Communities 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Additional  Habitats 


(Cupressus  macrocarpa)  forms  a  similar  (though  infre- 
quently self-generating)  community  of  lesser  stature  around 
farmyards,  mosdy  on  the  outer  coast. 

Scotch  broom  (Census  scoparius)  and  French  broom  (C. 
monspessulanus)  are  widely  naturalized  along  the  county's 
disturbed  roadsides.  French  broom  has  been  especially 
successful  in  invading  native  communities  of  brush,  open 
woodland,  and  grassy  hillsides.  Other  conspicuous  invad- 
ers are  the  showy  white-plumed  jubata  (Andean)  grass— a 
close  relative  of  the  less  invasive  pampas  grass— and  gorse 
(Ulex  europaeus),  a  dense  diorny  shrub  that  is  difficult  to 
eradicate. 

Disturbed  fields  and  roadsides  usually  support  diickets 
of  introduced  annual  weeds,  some  of  which  may  reach  6 
to  10  feet  in  height.  Conspicuous  in  such  areas  are  sweet 
fennel  (Foeniculum  vulgare),  poison  hemlock,  wild  oat 
(Avena  fatua),  teasel  (Dipsacus  sativus),  and  other  weedy 
herbs  and  exotic  grasses  of  disturbed  valley  grassland. 

While  many  exotics  are  here  to  stay,  extensive  monitor- 
ing and  eradication  efforts  are  needed  to  ensure  the  future 
integrity  of  our  distinctive  native  flora  and  plant  communi- 
ties. When  known,  the  extent  of  use  by  breeding  birds  of 
exotic  plant  species  and  communities  is  described  in  the 
species  accounts. 


Additional  Breeding  Bird  Habitats 

Breeding  birds  may  use  a  number  of  habitats  beyond  the 
standard  plant  communities,  but  these  can  usually  be 
described  verbally  without  resort  to  a  formal  classification 
scheme.  For  example,  rocky  cliffs  may  provide  nest  sites  for 
White-throated  Swifts,  Cliff  Swallows,  Common  Ravens, 
and  Rock  Wrens.  Rocky  sea  stacks,  wave-battered  cliffs, 
and  offshore  islands  are  home  to  busding  colonies  of 
storm-petrels,  cormorants,  gulls,  alcids,  and  scattered  pairs 
of  oystercatchers.  Human  structures  may  supply  nesting 
shelter  for  a  variety  of  birds,  including  American  Kestrels, 
Pacific-slope  Flycatchers,  Black  Phoebes,  several  species  of 
swallows,  American  Robins,  European  Starlings,  House 
Finches,  and  House  Sparrows,  among  others.  Although  a 
pair  of  Killdeer  may  select  for  their  nest  site  the  worn 
pebbles  along  a  stream  margin,  they  seem  equally  at  home 
incubating  their  eggs  in  similar  substrate  in  driveways  or 
on  gravel  roofs.  Ponds  may  furnish  the  requisites  for 
species  such  as  Pied-billed  Grebes  or  American  Coots  that 
build  floating  nests. 

For  many  species  of  landbirds  the  nesting  habitat  and 
die  foraging  habitat  are  one  and  the  same.  Other  species 
may  conceal  their  nests  near  the  edge  in  one  plant  commu- 
nity and  forage  in  an  adjoining  community  or  in  the 


Bishop  pines  lean  outward  /rom  Mount  Vision  toward  Tomales  Bay.  Drawing  by  Ane  Rovetta,  1 989. 


28 


Additional  Habitats 


MARIN  COUNTY  BREEDING  BIRD  HABITATS 


Additional  Habitats 


surrounding  air  space.  Different  species  of  swallows  may 
have  distinct  and  faidy  easily  described  structural  require- 
ments for  nest  sites,  as  well  as  presumably  distinct,  but  not 
so  easily  described,  air  space  requirements  for  foraging. 
Most  seabirds  breed  on  islands  or  steep  mainland  cliffs 
and  forage  considerable  distances  at  sea.  Ducks  often  nest 
in  upland  areas  but  forage  in  aquatic  habitats  and  soon 
lead  their  young  there  as  well.  Similarly,  herons  and  egrets 
select  relatively  predator-proof  nesting  sites  high  in  trees, 
on  islands,  or  in  marshes  over  water  and  may  forage  in 
nearby  or  distant  wedands.  Hence  it  is  not  possible  to 
classify  each  species  by  preference  for  one  or  several  habi- 


tats, any  of  which  will  satisfy  all  their  needs  at  a  given  time. 
Not  only  may  a  single  species  be  dependent  on  more  than 
one  habitat  while  nesting,  but  its  habitat  needs  also  may 
change  during  the  course  of  the  breeding  season.  Habitat 
descriptions  and  preferences  beyond  those  portrayed  here 
can  be  found  in  the  individual  species  accounts;  discussion 
of  species  membership  in  various  bird  communities  can  be 
found  in  the  Results  and  Discussion  section  (p.  61). 
Changes  in  land  use  that  may  have  affected  the  suitability 
of  various  habitats  in  Marin  County  for  breeding  birds  are 
discussed  in  the  section  that  follows. 


29 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Grass-covered  Kills  with  mixed  evergreen  forest  filling  draws  above  Nicasio  Reservoir.  Drawing  by  Ane  Rovetta,  1 989. 


30 


HISTORY  OF  LAND  USE 
IN  MARIN  COUNTY 


How  can  you  expect  the  birds  to  sing  when  their  groves  are  cut  down? 


—  Henry  David  Thoreau, 
Walden 


FOR  THOUSANDS  of  years  people  we  now  call  Coast 
Miwoks  lived  lightly  on  the  land  in  Marin  and  part  of 
adjacent  Sonoma  County.  In  aboriginal  times  their  entire 
population  numbered  about  2000  persons  (Kelly  1978). 
These  Native  Americans  subsisted  by  harvesting  the  abun- 
dant sea  life,  stream-dwelling  fish,  upland  game,  and  a 
variety  of  fruits,  berries,  seeds,  and  roots  that  supple- 
mented their  staple  of  acorns.  Although  relatively  little  is 
known  of  their  history,  by  all  accounts  they  lived  in 
harmony  with  nature,  preserving  the  bounty  that  greeted 
them  when  they  first  occupied  these  lands. 

This  way  of  life  was  destined  to  pass  as  the  seeds  of 
enormous  change  were  sown  in  the  late  1 500s  and  early 
1600s  by  the  arrival  of  the  earliest  European  explorers- 
Drake,  Cermeno,  and  Vizcaino— on  Marin's  shores.  In 
1 776  the  Spanish  established  a  mission  and  presidio  in  San 
Francisco,  and  in  the  same  year  traveled  north  to  explore 
parts  of  what  we  now  call  Marin  County  (Munro-Fraser 
1880).  The  next  wave  of  expansionism  broke  with  the 
founding  of  the  San  Rafael  mission  in  1817.  Forced 
evangelization  of  the  native  population  soon  led,  via 
demoralization  and  disease,  to  the  disintegration  of  their 
culture  (Kelly  1978).  By  1851  or  1852  only  about  250 
Coast  Miwoks  remained. 

The  demise  of  native  wildlife  populations— and  even 
whole  ecosystems— at  the  hands  of  the  invading  Europeans 
was  equally  swift.  Exploitation  of  die  forests  began  almost 
as  soon  as  Europeans  visited  these  shores.  The  first  com- 
mercial logging  was  established  in  Larkspur  in  1816  to  cut 
cordwood  for  Spanish  troops  at  the  presidio  (Fairley  1987). 
In  the  1820s  and  1830s  Yankee  whalers  and  trading  ships 
visiting  San  Francisco  Bay  laid  anchor  at  Sausalito  for 
wood  and  water.  Wood  was  needed  in  quantity  to  fuel  the 
whaler's  trypots,  and  the  mission  in  San  Rafael  undoubt- 
edly used  wood  extensively  for  various  activities  during  its 
tenure  from  1817  to  1834. 


With  the  secularization  of  the  missions  in  1834,  timber 
was  a  big  attraction  on  the  new  land  grants  at  Rancho 
Corte  Madera  del  Presidio  (1834)  and  Rancho  Sausalito 
(1836).  Much  of  Marin's  shoreline  along  San  Francisco 
Bay  was  heavily  forested,  and  the  wood  was  quickly  har- 
vested. Early  logging  concentrated  on  the  lower  slopes  of 
Mount  Tamalpais,  in  the  bottoms  of  canyons  where  giant 
redwoods  grew  and  where  timber  could  be  easily  trans- 
ported via  ships  on  the  bay.  Marin's  first  sawmill  was  built 
in  Cascade  Canyon  on  die  Tamalpais  slope  in  about  1836 
(Munro-Fraser  1880,  Mason  6k  Park  1975,  Fairley  1987). 
Although  some  of  the  timber  supplied  local  needs,  such  as 
construction  of  ranch  buildings  and  fuel  for  brick  kilns, 
most  was  shipped  to  San  Francisco— redwood  for  wharf 
pilings  and  warehouses,  other  trees  for  cordwood  to  heat 
city  buildings.  Cordwood  was  also  cut  in  the  Novato  area, 
where  oak  and  bay  were  the  dominant  trees.  Attesting  to 
the  rapidity  of  exploitation,  all  the  choice  redwoods  were 
felled  in  Mill  Valley  by  1852,  when  a  steam  mill  was 
moved  to  Bolinas,  diough  at  the  time  Corte  Madera  was 
still  being  actively  logged  (Fairley  1987). 

Fueled  by  the  boom  of  the  Gold  Rush,  the  1850s  to 
1 870s  were  the  era  of  greatest  timber  exploitation.  Lumber- 
ing concentrated  then  near  Bolinas  and  on  the  north 
slopes  and  ridges  of  Mount  Tamalpais.  Dogtown  became 
a  major  logging  and  lumber  center,  beginning  with  its  first 
mill  in  1851  (Fairley  1987).  By  1880  about  15  million 
board  feet  of  lumber  had  been  cut  near  Bolinas  (Munro- 
Fraser  1880,  Fairley  1987).  Logging  continued  in  the 
Bolinas  area  throughout  the  nineteendi  century.  Much  of 
it  was  to  supply  cordwood  for  San  Francisco  houses  and, 
after  1875,  to  fuel  steam  locomotives.  Large  amounts  of 
cordwood  also  came  from  the  north  slopes  of  Mount 
Tamalpais,  from  which  it  was  shipped  to  Ross  Landing 
(Corte  Madera);  some  was  burned  at  San  Quentin  prison, 
but  most  was  sent  to  San  Francisco.  Tanbark  oak  was  cut 
for  its  bark,  used  to  tan  hides,  and  the  remainder  was  sold 

31 


History  of  Land  Use 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


/  hstory  of  Land  Use 


for  cordwood  (Rothwcll  1959).  Extensive  woodcutting  in 
this  area  also  supplied  railroad  ties  and  heavy  studding  for 
the  White's  Hill  tunnel  of  the  North  Pacific  Coast  Rail- 
road, fence  posts  for  big  ranches  being  subdivided  for  dairy 
farms,  and  cordwood  for  the  steam  engines  of  the  second 
Pioneer  Paper  Mill  on  Papermill  Creek  (Rothwell  1959, 
Fairley  1987). 

Logging  continued  in  the  lower  drainage  of  Lagunitas 
Creek  until  1903,  when  the  supply  of  old'growth  timber 
was  just  about  exhausted  (Fairley  1987).  Except  at  Muir 
Woods,  ultimately  all  the  old-growth  timber  on  Mount 
Tamalpais  fell  to  the  woodsman's  ax  and  saw.  The  intro- 
duction of  oil  (1902),  gas,  and  electricity  ended  the  suprem- 
acy of  cordwood  and  relaxed,  somewhat,  the  intense 
pressure  on  Marin's  forests.  Around  1918,  a  second  round 
of  cutting  occurred  in  the  area  to  be  flooded  by  Alpine 
Dam.  A  mill  operated  in  the  lower  Lagunitas  Creek  drain- 
age until  1951 ;  the  site  was  flooded  with  the  completion  of 
the  Kent  Lake  dam  in  1953.  Between  1946  to  1951  this 
mill  sawed  over  21  million  board  feet  of  lumber  (Fairley 
1987).  Much  timber  was  cut  on  Inverness  Ridge  in  die  late 
1950s  and  1960s,  and  die  last  logging  in  the  county,  on 
Bolinas  Ridge  above  Dogtown,  was  shut  down  by  court 
order  in  1969  (Mason  1981,  D.  Livingston  pers.  comm.). 

We'll  never  know  die  full  effect  of  all  this  logging  on  the 
county's  birdlife,  but  it  must  have  been  tremendous.  The 
loss  of  most  of  the  old-growth  forest  on  the  slopes  of 
Mount  Tamalpais,  largely  in  a  period  of  fifty  years,  must 
have  displaced  great  numbers  of  birds  breeding  in  these 
habitats.  One  can  only  speculate,  but  it  seems  very  likely 
that  the  populations  of  largely  old  growth-dependent  spe- 
cies such  as  the  Spotted  Owl  must  have  plummeted  during 
this  period.  Great  fires  (usually  human  caused),  such  as 
those  in  1929  and  1945,  were  similarly  destructive  (Fairley 
1987),  but  the  return  of  nutrients  to  the  soil  in  these  cases 
undoubtedly  speeded  recovery. 

Logging  also  filled  the  creeks  and  estuaries  in  down- 
stream drainages  with  silt,  altering  these  habitats  pro- 
foundly. Boat  traffic  was  restricted  in  Bolinas  Lagoon, 
Tomales  Bay,  Corte  Madera  Creek,  and  Richardson  Bay 
by  the  silt  from  logging  and  to  a  lesser  degree,  in  most 
cases,  from  plowing  of  fields  (Munro-Fraser  1880,  Rodi- 
well  1959,  Melbostad  1969,  Mason  &  Park  1975,  Fairley 
1987).  Sedimentation  from  these  sources,  dredging  of 
channels  and  harbors,  leveeing  of  tidal  marshes,  and, 
particularly,  the  transport  into  San  Pablo  Bay  of  debris 
from  the  massive  hydraulic  mining  in  the  Sierra  Nevada 
from  1853  to  1884  all  increased  the  amount  of  tidal  marsh 
in  Marin  County  (Atwater  et  al.  1979,  Josselyn  6k  Buch- 
holz  1984).  Nevertheless,  the  extent  of  historic  expansion 
of  tidal  marsh  habitat  has  been  far  outweighed  by  losses. 
In  fact,  tidal  marsh  habitat  in  the  greater  San  Francisco  Bay 
estuary  has  decreased  historically  by  60%  to  95%  (Nichols 
6k  Wright  1971,  Atwater  et  al.  1979).  As  of  1984  only 


about  32%  of  the  tidal  marsh  habitat  diat  existed  in  Marin 
County  in  1850  remained  (Josselyn  6k  Buchholz  1984). 
Large  tracts  of  tidal  marsh  were  first  diked  off  around 
Novato  and  San  Rafael  in  the  late  1800s,  with  diking 
accelerating  in  the  1900s,  particularly  after  1940  (Atwater 
et  al.  1979,  Josselyn  6k  Buchholz  1984).  Since  1974, 
several  projects  have  restored  some  of  these  marshes  to 
tidal  action,  though  the  total  acreage  is  small  compared  to 
habitat  lost. 

The  effect  on  bird  populations  of  these  losses  of  tidal 
marsh  habitat  has  been  great,  though  little  documented 
except  for  certain  species.  Loss  of  salt  marsh  is  the  main 
reason  for  the  decline  of  the  endangered  California  Clap- 
per Rail,  and  marsh  loss  and  fragmentation  currendy 
threaten  populations  of  salt  marsh-breeding  Black  Rails 
and  Song  Sparrows  (see  accounts).  Many  other  birds  that 
use  diese  habitats  for  breeding,  foraging,  or  roosting  have 
likewise  been  affected. 

Fortunately,  many  birds  reside  in  the  seasonal  wedands 
formed  by  the  alteration  of  tidal  marshes.  But  these  wet- 
lands are  also  being  lost  rapidly  to  urban  encroachment 
(Granholm  1989).  Between  1956  and  1988,  61%  of  the 
seasonal  wedands  in  south  San  Francisco  Bay  were  lost. 
From  1975  to  1988,  35%  of  the  remaining  seasonal 
wedands  in  San  Francisco  Bay  were  lost  and  10%  of  those 
in  San  Pablo  Bay.  During  the  latter  period,  Marin  County 
lost  9%  of  its  seasonal  wedands,  and  in  the  foreseeable 
future  it  will  lose  an  additional  1 3%  if  all  currendy  planned 
projects  are  implemented.  The  impact  on  birds  inhabiting 
seasonal  wedands  is  obvious. 

The  damming  of  Marin's  streams  for  municipal  water 
supplies  beginning  in  1873  (Fairley  1987)  may  have 
doomed  breeding  American  Dippers  in  the  Lagunitas 
Creek  watershed  (see  account).  But  on  the  whole,  the  loss 
of  streamside  and  upland  habitat  to  inundation  has  been 
balanced  by  the  expansion  of  aquatic  habitat  and  the 
accretion  of  some  marshland.  Female  Common  Mergan- 
sers and  their  broods  now  ply  the  waters  of  Kent  Lake 
while  Pied-billed  Grebes,  American  Coots,  Marsh  Wrens, 
Red-winged  Blackbirds,  and  Song  Sparrows  suspend  their 
nests  in  marshy  fringes  of  many  of  the  county's  eight  major 
reservoirs.  In  contrast  to  these  upstream  benefits  to  birds, 
it  seems  likely  diat  loss  of  fresh  water  downstream  must 
have  degraded  some  of  Marin's  important  wedands. 

Agricultural  uses  have  also  taken  their  toll  on  the  land. 
Although  various  crops  have  been  grown  in  Marin,  catde 
and,  particularly,  dairy  ranching  have  dominated  the  agri- 
cultural economy  since  the  early  days  of  white  setdement. 
With  the  establishment  of  the  San  Rafael  mission  in  1817, 
large  herds  of  Mexican  longhorn  catde  ranged  freely  on  the 
land,  to  be  annually  slaughtered  for  their  hides  and  tallow 
(Mason  6k  Park  1975,  Fairley  1987).  In  1834  the  San 
Rafael  mission  owned  4500  catde  (Mason  6k  Park  1971). 
With  the  secularization  of  the  missions  that  year,  thou- 


32 


History  of  Land  Use 


HISTORY  OF  LAND  USE  IN  MARIN  COUNTY 


History  of  Land  Use 


sands  of  cattle  soon  roamed  the  large  land  grants  through- 
out the  county.  In  response  to  the  boom  of  the  Gold  Rush 
the  dairy  industry  prospered,  particularly  on  the  lush 
grasslands  of  Point  Reyes.  In  1870  Point  Reyes  boasted  the 
largest  dairy  operation  in  California  (Mason  &.  Park 
1971);  the  assessor's  rolls  reported  25,390  cows— the  high- 
est number  for  any  county  in  the  state  (Fairley  1987). 
Overgrazing  was  noticed  as  early  as  the  1850s  in  coastal 
areas  of  California  (Heady  1977).  The  introduction  of  alien 
grasses,  dry-land  farming  practices,  and  year-round  concen- 
trated grazing  all  combined  to  drastically  alter  native  grass- 
lands from  ones  dominated  by  perennial  bunch  grasses  to 
ones  dominated  by  exotic  annual  grasses  (see  Bird  Habitats 
section  p.  22).  The  effects  of  these  changes  on  bird  popu- 
lations are  undocumented  but  must  have  been  great 

Agricultural  practices  have  also  inadvertendy  fostered 
the  pervasive  expansion  of  species  such  as  the  European 
Starling  (introduced)  and  Brown-headed  Cowbird  (native) 
that  have  adversely  affected  many  native  hole-nesting  and 
cup-nesting  landbirds,  respectively  (see  accounts).  Grazing 
and  land  clearing  (for  various  purposes)  have  reduced  and 
degraded  Marin  County's  riparian  habitat,  though  to  an 
unknown  degree  as  no  inventories  have  been  taken. 

Direct  exploitation  of  the  region's  wildlife  also  exacted  a 
heavy  toll.  In  fact,  Stine  (MS)  concluded  that  the  California 
game  trade  "is  the  foremost  example  of  rapid  commercial 
plunder  of  a  region's  wildlife  to  be  found  on  this  conti- 
nent." The  demise  or  decline  of  coastal  populations  of 
whales;  sea  otters,  fur  seals,  and  other  pinnepeds;  anad- 
romous  fish;  shellfish;  and  upland  game  such  as  tule  elk, 
grizzly  and  black  bears,  and  various  furbearers  has  been 
relatively  well  documented  (Grinnell,  Dixon,  ck  Linsdale 
1937;  Skinner  1962;  Stine  MS).  Less  is  known  of  impacts 
on  bird  populations.  Nevertheless,  Grinnell  et  al.  (1918) 
concluded  that  in  California  "beyond  question  waterfowl 
and  upland  game  birds  have  both  on  the  average  decreased 
by  fully  one-half  within  the  past  forty  years." 

Perhaps  the  first  extensive  exploitation  of  the  region's 
bird  populations  was  at  the  Farallon  Islands,  where  Rus- 
sian sealers  harvested  the  meat  and  eggs  of  breeding 
seabirds.  Between  1812  and  1827  they  annually  killed 
5000  to  10,000  seabirds,  peaking  at  50,000  in  1828  (Stine 
MS).  The  Russians  skinned  the  birds  and  shipped  the 
dried  meat  to  Fort  Ross,  where  it  was  a  highly  prized  food 
item.  Fort  Ross  also  served  as  a  supply  center  for  fur 
operations  in  Alaska  and  Kamchatka.  The  Russians  at  Fort 
Ross  in  1827  and  1828  shipped  nine  sea  lion  bladders 
containing  hundreds  of  pounds  of  insulating  feathers  of 
Farallon  seabirds  to  Nova  Arkangelsk  (Sitka)  in  Russian 
America  (Stine  MS). 

The  intensity  of  exploitation  of  wildlife  resources  accel- 
erated with  the  rapid  increase  of  the  human  population  at 
the  time  of  the  Gold  Rush.  The  commercial  harvest  of 
Common  Murre  eggs  on  the  Farallon  Islands  from  1848 


to  the  early  1900s  had  a  devastating  effect  on  populations 
of  murres  and  most  other  species  of  seabirds  breeding  on 
those  islands  (Ainley  &  Lewis  1974).  There  appears  to  be 
no  record  of  exploitation  of  seabird  colonies  on  the  Marin 
County  coasdine,  but  it  seems  unlikely  that  any  large 
rookery  went  unmolested  at  a  time  of  unrestrained  harvest- 
ing practices.  Market  hunting  rapidly  depleted  populations 
of  waterfowl,  shorebirds,  and  Clapper  Rails  around  San 
Francisco  Bay  (Grinnell  et  al.  1918).  One  observer  thus 
described  the  decline  in  duck  numbers  in  the  Marin 
County  area:  "In  1876  ducks  were  very  plentiful  in  all  the 
marshes  from  Sausalito  north  to  Petaluma,  Napa  and 
Vallejo.  In  those  days  it  was  easy  for  a  boy  to  kill  from 
twenty  to  thirty  ducks  in  a  day  s  shooting  and  very  much 
larger  bags  were  obtained  by  experienced  hunters.  Today 
[1913],  in  the  region  between  Sausalito  and  Novato,  I 
think  it  is  safe  to  say  there  is  not  one  duck  in  the  marsh 
now  where  there  were  a  hundred  then"  (Grinnell  et  al. 
1918).  Egrets  were  also  shot  for  their  feathers,  in  demand 
by  the  millinery  trade,  leading  to  their  near  extinction  in 
the  Bay  Area  at  the  turn  of  the  century  (see  accounts). 
Although  measures  to  protect  wildlife  were  passed  in 
California  as  early  as  1852,  it  was  not  until  1913  with  the 
prohibition  on  the  sale  of  game  in  the  state  and  the  passage 
of  the  Federal  Migratory  Bird  Treaty  Act  that  wildlife  began 
to  be  given  a  semblance  of  the  protection  we  see  today 
(Grinnell  et  al.  1918). 

As  enlightenment  spread  regarding  the  need  to  conserve 
our  exploited  wildlife  resources,  the  "indirect"  impacts  of 
an  expanding  human  population  continued  to  negatively 
affect  the  county's  birdlife.  These  impacts  fall  into  two 
broad  categories:  direct  conversion  of  wildlife  habitat  to 
industrial,  agricultural,  and  residential  uses;  and  indirect 
contamination  or  degradation  of  habitat  from  human 
activities.  Marin  County's  population  is  now  concentrated 
in  the  eastern  urban  corridor  along  Highway  101,  domi- 
nated by  light  industry,  service-oriented  businesses,  resi- 
dential neighborhoods,  and  their  attendant  impacts.  Rural 
West  Marin  has  a  ranching-  and  tourist-based  economy, 
wid^i  much  of  the  land  there  set  aside  in  federal  or  state 
parks  or  protected  by  agricultural  zoning  (Figure  6). 
Throughout  most  of  its  history  the  county's  population 
and  development  have  concentrated  along  the  shores  of 
San  Francisco  and  San  Pablo  bays  because  of  the  easy 
transportation  links  to  nearby  population  centers.  From 
323  inhabitants  at  the  time  of  the  first  census  in  1850,  the 
county's  population  has  grown  exponentially  to  230,096 
people  in  1990  (U.S.  Bureau  of  the  Census).  The  postwar 
boom  saw  the  population  expand  dramatically  from 
52,907  people  in  1940  to  206,038  in  1970.  The  impacts 
on  the  land  have  followed  a  similar  pattern,  as  detailed 
above,  with  regard  to  the  loss  of  tidal  marshes  and  seasonal 
wedands. 


33 


J  iistory  oj  iMnd  Use 


MARIN  COUNTY  BRHHDING  BIRD  ATIAS 


History  of  Land  Use 


Marin  County 

LAND  USE 

SOURCE:  MARIN  COUNTY 

PLANNING  DEPARTMENT 

©  1991  by  Dewey  Livingston 


Figure  6.    Map  of  land  use  patterns  in  Marin  County.  Map  by  Dewey  Livingston,  1991. 


34 


History  of  Land  Use 


HISTORY  OF  LAND  USE  IN  MARIN  COUNTY 


History  of  Land  Use 


The  impact  of  a  human  population  is  a  function  not 
only  of  population  size,  but  also  of  the  affluence  of  that 
population  and  the  disruptiveness  of  the  technologies 
providing  the  goods  consumed  (Ehrlich  6k  Ehrlich  1990). 
The  impacts  of  technology  were  observed  and  decried  early 
in  Marin  County's  history  with  respect  to  logging  (see 
Munro-Fraser  1880).  More  subde  and  insidious  impacts 
soon  began  to  be  noted.  Beginning  in  1884,  the  second 
Pioneer  Paper  Mill  on  Lagunitas  Creek  dumped  the  waste 
water,  laced  with  acid  and  dyes,  from  its  pulp  vats  into  a 
brick  sewer  and  then  direcdy  into  the  creek  below.  These 
wastes  caused  heavy  silt  to  form  in  the  creekbed  from 
Taylorsville  to  Tomales  Bay.  The  mill  owners  expressed 
concern  over  this  problem  but  had  found  no  solution 
when  the  mill  was  forced  to  close  its  doors  in  the  financial 
crisis  of  1893  (Rothwell  1959). 

More  recendy,  our  high  consumption  rates  were  ulti- 
mately responsible  for  major  oil  spills  in  1971,  1984,  and 
1986  that  despoiled  Marin's  coasdine  and  killed  or  debili- 
tated thousands  of  birds  (Smail  et  al.  1972,  PRBO  1985, 
Page  et  al.  1990).  Chemical  contaminants  from  urban, 
agricultural,  and  industrial  activities  have  been  detected  in 
the  tissues  of  many  species  of  waterbirds  in  San  Francisco 
Bay,  often  at  levels  known  to  impair  reproductive  success 


(Ohlendorf  et  al.  1988,  Ohlendorf  6k  Fleming  1988).  The 
demise  of  Peregrine  Falcon  and  Osprey  populations,  here 
and  throughout  the  country,  are  among  the  foremost 
indicators  of  pesticide  pollution  in  our  environment,  warn- 
ing of  the  direct  threats  to  humans  as  well  from  our  misuse 
of  technology.  These  are  but  a  few  examples  of  advanced 
technologies  gone  awry  as  detected  in  birds. 

Fortunately  a  strong  environmental  movement 
coalesced  in  Marin  County  in  the  1960s  and  1970s  to  fight 
unrestricted  development  and  to  preserve  large  (and  small) 
tracts  of  land  such  as  Point  Reyes  National  Seashore  and 
the  Golden  Gate  National  Recreation  Area.  While  our 
local  environmental  victories  are  impressive,  and  should 
be  duly  lauded,  much  remains  to  be  done.  Even  though 
the  county's  population  has  begun  to  stabilize  through 
restrictive  zoning,  traffic  continues  to  increase  from  the 
relendess  population  expansion  of  nearby  counties,  and 
our  as-yet-unchecked  affluent  lifestyle  keeps  on  affecting 
wildlife.  Protecting  land  and  wildlife  here  in  Marin  is  not 
enough  as  the  effects  of  our  lifestyles  range  way  beyond 
county  borders.  What  new  habitat  changes  will  our  breed- 
ing birds  face  as  nesting  time  approaches  yet  again  widi 
each  revolution  of  the  Earth  around  the  sun? 


35 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Turkey  Vultures  lazily  soar  ov^r  grassland  and  mixed  evergreen  forest  on  the  hills  surrounding  Soulajoule  Reservoir. 

Drawing  by  Ane  Rovetta,  1 985. 


36 


TIMING  OF  BREEDING 


Yet  the  coming  and  going  of  the  birds  is  more  or  less  a  mystery  and  a  surprise.  We  go  out  in  the  morning,  and  no  thrush  or 
vireo  is  to  be  heard;  we  go  out  again,  and  every  tree  and  grove  is  musical;  yet  again,  and  all  is  silent.  Who  saw  them  come? 
Who  saw  them  depart? 

—  John  Burroughs, 
Wake-Robin 


THE  BREEDING  SEASONS  of  birds  are  typically  timed  to 
take  advantage  of  periodic  (often  mild)  conditions  so 
that  the  young  hatch  out  when  appropriate  foods  are 
abundandy  available  (Welty  &  Baptista  1988).  The  inher- 
ited rhythms  of  breeding  roughly  match  the  seasonal 
rhythms  of  the  environment  as  adaptions  not  only  to  food 
supply  or  mild  weather,  but  in  some  cases  to  availability  of 
vegetative  cover,  nest  sites,  nest  materials,  or  avoidance  of 
predation  or  competition.  As  ultimate  factors  driving  adap- 
tation, these  necessities  do  not  always  proximally  trigger 
the  unfolding  of  events  in  the  breeding  cycle.  Some  of  the 
more  important  proximate  factors  that  actually  trigger  the 
initiation  or  termination  of  breeding  include  day  length, 
temperature,  rainfall,  and  food  availability.  In  some  cases 
environmental  conditions  may  act  as  both  ultimate  and 
proximate  factors  influencing  the  timing  of  breeding.  Only 
rarely  will  a  single  factor  determine  the  annual  breeding 
schedule  of  a  species. 

The  timing  of  breeding  for  a  single  species  can  vary  with 
latitude  or  altitude,  between  local  populations  breeding  in 
different  habitats,  and  from  year  to  year.  Moreover,  nesting 
phenology  can  vary  gready  among  many  species  in  the 
same  area.  Some  species  may  not  breed  at  all  in  a  given 
year  unless  certain  environmental  conditions  are  met.  An 
understanding  of  variability  in  the  timing  of  breeding, 
though  fascinating  in  its  own  right,  has  practical  value  in 
aiding  the  planning  of  a  strategy  for  a  breeding  bird  adas 
project  and  in  interpreting  its  results.  Widiout  a  knowl- 
edge of  the  timing  of  local  breeding  events  it  is  difficult  to 
know  when  to  concentrate  field  work  to  best  advantage  or 
how  to  interpret  the  significance  of  observations  collected 
during  adas  field  work. 

Patterns  of  variation  in  the  timing  of  breeding  of  birds 
are  generally  attributable  to  variation  in  the  natural  envi- 
ronment, though  the  linkage  between  timing  and  particu- 
lar causative  factors  is  not  often  clear.  In  one  regard,  the 
climate  on  the  central  California  coast  seems  to  exhibit 
little  seasonal  variability  as  we  experience  relatively  mild 
temperatures  year  round.  On  the  other  hand,  we  do  have 


distinct  rainy  and  dry  seasons.  Moreover,  rainfall  patterns 
here  can  vary  gready  both  within  the  rainy  season  and 
among  years,  while  ocean  conditions  can  also  vary  tremen- 
dously from  year  to  year.  Taken  as  a  whole,  our  climate 
influences  not  only  the  timing  and  length  of  the  breeding 
season  but  also  the  annual  variation  in  these  parameters. 

From  his  studies  of  the  timing  of  breeding  in  the 
Sacramento  Valley,  Davis  (1933)  concluded  that  on  the 
whole,  flesh-eating  species  tended  to  start  breeding  before 
omnivorous  and  insectivorous  species,  which  generally 
preceded  vegetable  and  seed-eating  birds.  These  patterns 
seem  to  hold  for  the  coast  as  well,  though  for  either  region 
there  are  numerous  exceptions.  Another  pattern  that 
seems  to  apply  in  most  areas  is  that  year-round  resident 
species  tend  to  breed  before  summer  residents,  though 
again  there  are  exceptions.  For  example,  California  Quail 
tend  to  initiate  egg  laying  here  in  May  (PRBO  files,  D. 
Shuford  pers.  obs.),  well  after  most  other  year-round  resi- 
dents and  after  some  summer  residents  such  as  Allen's 
Hummingbirds,  Orange-crowned  Warblers,  and  Wilson's 
Warblers  do  (see  below). 

Because  Marin  County's  climate  is  so  mild,  the  breed- 
ing season  here  is  lengthy.  Two  of  the  earliest  breeders  are 
hummingbirds.  Anna's  Hummingbirds  (year-round  resi- 
dents) come  into  breeding  condition  in  late  November  and 
early  December  before  the  winter  solstice,  when  day  length 
approaches  the  shortest  of  the  year  (Pitelka  1951a,  Wil- 
liamson 1956).  Nesting  itself  commences  in  December 
and  probably  reaches  a  peak  in  January  and  February,  the 
coldest  and  generally  the  wettest  months  of  the  year. 
Rainfall  seems  to  be  the  main  climatic  factor  influencing 
the  inherent  rhythm  of  die  breeding  cycle.  Once  males 
begin  to  come  into  breeding  condition,  a  period  of  consec- 
utive days  of  rainfall,  rather  than  the  actual  amount,  seems 
to  abrupdy  increase  territorial  establishment  and  the  com- 
mencement of  other  breeding  activities.  These  adaptations 
seemingly  ensure  breeding  in  a  period  when  food  plants 
are  most  numerous.  Allen  s  Hummingbirds  arrive  in  the 
San  Francisco  Bay  area  in  mid-  to  late  January  and  begin 

37 


Timing  of  Breeding 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Timing  of  Breeding 


to  lay  eggs  in  early  to  mid-March  (rarely  by  mid-Feb;  Pitelka 
1951a).  Thus  this  hummingbird  also  begins  nesting  in  the 
rainy  season,  and  its  arrival  here  seems  to  be  timed  to 
coincide  with  the  initiation  of  blooming  of  particular 
nectar-producing  plants,  presumably  stimulated  by  winter 
rains  and  early  spring  warmth  (see  account). 

Great  Horned  Owls  are  also  very  early  nesters  and  begin 
laying  eggs  here  in  February  (M.  Cohen  in  litt.).  Great  Blue 
Herons  commence  egg  laying  at  Audubon  Canyon  ranch 
from  early  to  mid-February,  and  their  initiation  of  first 
clutches  may  peak  from  early  to  late  March  (Pratt  1 974). 
Killdeer  may  lay  eggs  here  in  early  March  (D.  Shuford  pers. 
obs.).  Spotted  Owls,  Red-tailed  Hawks,  and  Red-shoul- 
dered Hawks  all  are  incubating  eggs  at  least  by  mid-  to  late 
March  (PRBO  files).  Clapper  Rails  begin  laying  in  Marin 
County  by  early  March  (Evens  6k  Page  1983),  Scrub  Jays 
at  least  by  mid-March  (PRBO  files),  and  salt  marsh-breeding 
Song  Sparrows  by  late  February  or  early  March  (J  ohnston 
1956a,  D.  Shuford  pers.  obs.).  Many  resident  landbirds 
begin  egg  laying  in  late  March  or  early  April,  including 
Chestnut-backed  Chickadees,  Plain  Titmice,  Bushtits, 
Bewick's  Wrens,  Wrentits,  Savannah  Sparrows,  upland- 
breeding  Song  Sparrows,  and  White-crowned  Sparrows 
(PRBO  files,  Johnston  1956a,  Geupel  6k  DeSante  1990). 
Several  resident  waterbirds— Double-crested  Cormorants, 
Mallards,  and  American  Coots— begin  egg  laying  in  late 
March  to  early  April  (Ainley  6k  Boekelheide  1990,  D. 
Shuford  pers.  obs.).  Overall,  April  and  May  appear  to  be 
the  peak  months  for  egg  laying  here  for  both  landbirds  and 
waterbirds. 

For  summer  residents  (migrants),  die  timing  of  breeding 
in  Marin  County  corresponds  roughly  to  die  timing  of 
spring  arrival  here  (Table  4).  For  most  species  diere  is 
about  a  four-  to  five-week  lag  between  first  arrival  of  males 
and  egg  laying  of  females.  For  example,  Orange-crowned 
Warblers  arrive  here  in  late  February  to  early  March  and 
begin  egg  laying  by  at  least  early  April  (PRBO  files),  and 
Wilson's  Warblers  arrive  in  late  March  and  begin  egg 
laying  in  late  April  (Stewart  6k  Darling  1972,  Stewart 
1973).  There  are  of  course  a  number  of  exceptions  to  this 
rule.  American  Goldfinches,  though  resident  in  the 
county,  are  largely  absent  from  Point  Reyes  until  late 
March.  Despite  this  relatively  early  arrival,  American  Gold- 
finches do  not  begin  to  nest  on  Point  Reyes  until  the  diird 
to  fourth  week  of  May  (PRBO  files),  presumably  because 
nesting  and  hatching  of  young  is  timed  to  coincide  with  the 
maturation  of  abundant  seed  crops.  In  the  Sacramento 
Valley,  American  Goldfinches  can  start  laying  eggs  in  late 
April  (Davis  1933),  presumably  because  seed  maturation 
is  early  in  that  region's  dry,  hot  climate.  Most  species  that 
glean  insects  from  foliage  can  start  breeding  earlier  than 
seed  eaters  because  of  the  relatively  early  bloom  of  insect 
populations.  The  relationship  of  the  arrival  of  aerial  insec- 
tivores  such  as  swallows  to  timing  of  breeding  is  deceptive. 

38 


Tree  Swallows  start  to  arrive  in  Marin  County  in  numbers 
in  mid-  to  late  February  (Table  4),  but  do  not  begin  laying 
eggs  on  Point  Reyes  until  early  May  (PRBO  files).  Although 
adults  can  survive  during  rainy  weather  early  in  the  spring, 
by  subsisting  on  berries  or  perhaps  traveling  some  distance 
to  find  insects  (see  account),  young  can  not;  total  failure  of 
nests  has  been  documented  here  during  unseasonal  rains 
in  June  (Stewart  1972). 

Also  because  of  our  mild  climate,  many  species  here  can 
raise  two  or  even  three  broods  a  year,  particularly  resident 
landbirds  (DeSante  6k  Baptista  1989,  Geupel  6k  DeSante 
1990,  G.R.  Geupel  6k  D.F.  DeSante  pers.  comm.). 
Although  most  landbird  young  have  fledged  by  late  July, 
nests  of  some  species  such  as  Barn  Swallows  may  be  active 
until  late  August  or,  rarely,  early  September  (B.  Baez  6k  D. 
Shuford  pers.  obs.),  and  American  Goldfinches,  rarely,  are 
still  feeding  fledged  young  in  mid-September  (J  .G.  Evens 
pers.  obs.).  Young  of  many  of  our  species  of  breeding 
seabirds  fledge  in  August  and  September  or  even  later 
(Ainley  6k  Boekelheide  1990).  The  Ashy  Storm-Petrel 
provides  an  extreme  example  of  an  extended  breeding 
season.  At  the  Farallon  Islands,  Ashies  lay  eggs  mosdy 
from  early  May  to  late  August  (sometimes  later),  and  young 
fledge  from  early  September  to  mid-November  and,  rarely, 
through  December.  Although  data  are  lacking  for  this 
region,  Red  Crossbills  elsewhere  in  their  breeding  range 
are  known  to  breed  in  any  month  of  the  year  (see  account). 

Given  this  great  variability  in  timing  of  nesting,  what  are 
the  factors  that  initiate  or  terminate  breeding?  Of  the 
proximate  factors,  day  length  seems  to  have  the  greatest 
influence  through  its  effect  on  the  waxing  and  waning  of 
gonadal  development  (Welty  6k  Baptista  1 988).  As  noted 
above  for  the  Anna's  Hummingbird,  rainfall  is  a  contrib- 
uting factor  to  the  initiation  of  breeding.  Mewaldt  and 
King  (1977)  concluded  diat  warm  temperatures  and  dry 
weather  in  the  prenesting  period  advanced  breeding  in 
White-crowned  Sparrows  and  cool  rainy  weather  delayed 
it.  Also  in  White-crowned  Sparrows  the  timing  of  termina- 
tion of  breeding  is  direcdy  related  to  the  amount  of  winter 
rainfall  during  the  previous  year,  such  that  breeding 
extends  later  into  the  summer  after  winters  of  heavy  rainfall 
(DeSante  6k  Baptista  1989).  Presumably  increased  rainfall 
prolongs  the  growing  season  of  green  plants  upon  which 
grazing  insects  depend  and  hence  the  availability  of  these 
insects  for  the  sparrows  to  feed  their  young.  In  arid  parts 
of  dieir  range,  California  Quail  breed  irregularly  depend- 
ing on  the  amount  of  winter  rainfall  preceding  the  spring 
nesting  season  (Leopold  et  al.  1976).  In  dry  years,  quail  are 
inhibited  by  chemicals  (phytoestrogens)  in  stunted  forbs 
and  grasses,  and  few  or  no  young  are  produced  during  the 
short  breeding  season.  In  contrast,  in  wet  years  lush  forb 
growdi  supplies  large  amounts  of  seeds  for  quail  consump- 
tion, stimulating  vigorous  and  extended  breeding  (young 
hatched  as  late  as  September).  Although  the  initiation  of 


TIMING  OF  BREEDING 

Table  4.  Arrival  dates  of  Marin  County  landbirds  with  comparisons  to  other  regions  of  California.  Data  reported  as  average 
arrival  date  (x),  number  of  years  with  data  (n),  and  the  span  of  first  arrival  dates  (range).  Lack  of  data  for  particular  species  may 
reflect  infrequent  records  of  the  species,  poor  coverage  of  appropriate  habitat,  or  difficulty  of  distinguishing  individual  migrants 
from  birds  of  smaller  resident  populations. 


Palomarin  ,  Point  Reyes 

1967-1989 

x      (n)      range 

Marin  County 

-1900-1980 

x      (n)       range 

Berkeley  Area 

1911-1947 

x      (n)       range 

Northern  California 

1972-1984 

x      (n)       range 

Southern  California5 

1972-1984 

x      (n)      range 

Vaux's  Swift 

- 

- 

- 

4/6    (6)   3/26-4/19 

4/12   (15)  4/4-4/19 

Black-chinned  Hummingbird 

- 

- 

- 

3/26  (5)   3/11-4/9 

3/25   (10)   2/25-4/11 

Allen's  Hummingbird 

2/5    (19)   1/24-2/27 

2/5    (27)   1/16-2/28 

2/13  (30)   1/29-2/24 

- 

- 

Olive-sided  Flycatcher 

4/17   (18)  4/13-4/26 

4/18  (23)  4/7-4/30 

4/19  (30)   3/28-5/5 

4/14   (6)  4/9-4/22 

4/12   (14)   3/19-4/29 

Western  Wood-Pewee 

5/15  (11)  4/24-6/7 

(4)  4/14-4/26 

5/1     (13)  4/18-5/8 

4/15  (6)  4/9-4/21 

4/13   (14)  4/3-4/24 

Pacific-slope  Flycatcher 

3/27   (16)   3/18-4/8 

3/25   (16)   3/11-4/5 

3/26  (32)   3/12-4/9 

3/22   (5)   3/12-4/4 

3/14    (5)   3/2-3/22 

Ash-throated  Flycatcher 

4/26  (13)  4/10-5/9 

- 

- 

4/9    (5)  4/2-4/15 

3/31    (15)  3/22-4/9 

Western  Kingbird 

- 

4/5      (5)  4/1-4/11 

- 

3/23  (5)   3/2-3/31 

3/14  (14)   3/5-4/3 

Purple  Martin 

- 

4/7    (13)   3/6-4/30 

- 

- 

- 

Tree  Swallow 

2/13  (19)   1/20-3/8 

2/22   (12)   2/3-3/5 

- 

- 

- 

Violet-green  Swallow 

2/25   (18)   2/9-3/19 

2/21    (11)   2/6-3/13 

- 

- 

- 

N.  Rough-winged  Swallow 

3/19  (15)   3/8-3/31 

3/7      (7)   2/29-3/15 

- 

- 

- 

Cliff  Swallow 

3/24  (18)   3/12-4/10 

3/18  (16)   3/9-3/29 

3/22   (11)   3/5-4/7 

- 

- 

Barn  Swallow 

3/15  (14)   2/24-4/8 

3/11    (14)   3/5-3/19 

- 

- 

- 

House  Wren 

- 

- 

3/21    (21)   3/4-4/6 

- 

- 

Swainson's  Thrush 

4/27   (19)4/19-5/4 

4/26  (20)  4/15-5/4 

4/24   (32)  4/14-5/5 

4/21    (5)  4/18-4/28 

4/21    (15)  4/6-5/1 

Solitary  Vireo 

- 

-       (4)   3/20-4/5 

- 

4/1     (6)   3/22-4/9 

3/27   (15)   3/14-4/10 

Warbling  Vireo 

3/26  (21)   3/15-4/3 

3/25  (20)   3/13-4/6 

3/25  (30)   3/9-4/6 

3/21    (6)   3/13-3/31 

3/11    (15)   3/1-3/20 

Orange-crowned  Warbler 

3/6    (22)   2/27-3/16 

3/4    (15)   2/18-3/16 

3/3    (29)   2/21-3/14 

(4)   2/26-3/8 

- 

Yellow  Warbler 

- 

4/18    (5)  4/8-4/23 

4/16  (30)  4/7-5/2 

4/6    (6)   3/21-4/17 

4/2    (15)   3/24-4/12 

Black-throated  Gray  Warbler 

- 

4/14    (8)   3/31-4/27 

- 

4/4    (5)   3/30-4/14 

3/24   (15)   3/11-4/7 

Hermit  Warbler 

_ 

_ 

_ 

4/16  (5)  4/13-4/20 

4/16  (15)  4/7-4/24 

MacGillivray's  Warbler 

4/20  (12)  4/9-4/30 

4/18    (9)  4/3-4/30 

4/12   (18)  4/3-4/26 

4/11    (6)  4/8-4/14 

4/1     (15)   3/18-4/17 

Wilson's  Warbler 

3/25   (23)   3/16-4/5 

3/24   (27)   3/10-4/8 

3/22  (32)   3/11-4/3 

3/19  (6)   3/17-3/20 

3/13  (15)   3/3-3/23 

Yellow-breasted  Chat 

- 

- 

- 

- 

4/13  (15)  4/4-4/24 

Western  Tanager 

- 

- 

- 

4/13  (5)  4/3-4/22 

4/13  (15)  4/7-4/17 

Black-headed  Grosbeak 

4/14   (18)  4/5-4/21 

4/13   (34)  4/4-4/26 

4/13  (37)  4/4-4/21 

4/3     (6)    3/28-4/8 

3/26  (15)   3/22-4/1 

Lazuli  Bunting 

- 

4/28    (6)  4/21-5/2 

4/22  (30)   3/30-5/7 

4/18  (5)  4/14-4/22 

4/5    (15)  4/1-4/15 

Chipping  Sparrow 

- 

4/14     (7)  4/2-4/24 

4/15  (10)   3/29-4/26 

-    (4)   3/20-4/12 

- 

Black-chinned  Sparrow 

- 

- 

- 

- 

3/28  (15)3/10-4/24 

Grasshopper  Sparrow 

- 

4/21     (5)  4/2-4/30 

- 

•    (3)  4/1-4/18 

- 

Brown-headed  Cowbird 

3/28   (13)   3/3-4/14 

3/30    (6)   3/17-4/14 

- 

- 

- 

Hooded  Oriole 

- 

3/29  (13)   3/16-4/13 

- 

3/19  (6)   3/5-3/30 

3/10  (15)2/27-3/24 

Northern  Oriole 

- 

4/3       (6)   3/24-4/7 

- 

3/16   (6)    3/10-3/20 

3/14  (15)   3/5-3/21 

American  Goldfinch 

3/30   (13)   3/2  3-4/6 

3/24      (8)    3/2-4/6 

- 

- 

- 

Data  from  PRBO's  Palomarin  Field  Station  courtesy  of  Dave  DeSante  and  Geoff  Geupel. 
Data  compiled  by  the  author  from  various  sources  and  personal  field  notes. 
3  Data  from  Weston  (1948). 
Data  from  summaries  in  seasonal  reports  of  the  Middle  Pacific  Coast  Region  of  American  Birds 
Data  from  summaries  in  seasonal  reports  of  the  Southern  Pacific  Coast  Region  of  American  Birds 


39 


Timing  of  Breeding 


MARIN  COUNTY  BRFFDING  BIRD  ATIAS 


Timing  of  Breeding 


breeding  in  Tricolored  Blackbirds  usually  coincides  witb 
rainfall  or  flooding  of  rice  fields  in  the  Central  Valley, 
nesting  appears  to  be  triggered  by  an  abundance  of  food 
(see  account). 

Most  Farallon  seabirds  seem  to  be  primed  by  photo- 
period  to  both  initiate  and  terminate  egg  laying  (Ainley  6k 
Boekelheide  1990).  Food  abundance  still  appears  to  have 
some  effect  on  timing  of  breeding  though.  In  years  when 
initiation  of  egg  laying  is  late,  laying  by  seabirds  may  begin 
en  masse  when  prey  appear.  Also  second  and  replacement 
clutches  of  seabirds  are  most  frequent  in  years  when  a  high 
level  of  breeding  success  indicates  abundant  food.  The  fact 
that  species  with  the  most  similar  diets  breed  at  the  same 
time  also  suggests  prey  availability  strongly  affects  the 
timing  of  breeding  of  seabirds,  though  the  complexities  of 
the  pathways  linking  upwelling,  prey  availability,  and  tim- 
ing of  breeding  are  still  poorly  understood. 

Year-to-year  variability  in  the  timing  of  initiation  or 
termination  of  breeding  differs  greatly  among  species.  At 
Palomarin,  timing  of  initiation  of  breeding  in  Wrentits,  as 
measured  by  mean  clutch  completion  dates  of  first  nesting 
attempts,  varied  only  from  19  to  30  April  over  six  years 
(Geupel  ck  DeSante  1990).  The  timing  there  of  termina- 
tion of  breeding  by  White-crowned  Sparrows,  measured  as 
the  mean  clutch  completion  date  for  the  latest  10%  of 
nests,  ranged  from  25  June  to  20  July  over  seven  years 
(DeSante  6k  Baptista  1989).  Timing  of  breeding  of  Faral- 
lon seabirds  can  vary  gready  from  year  to  year,  and  under 
extreme  conditions  virtually  all  females  of  species  such  as 
Brandt's  Cormorants,   Pelagic  Cormorants,  and  Pigeon 


Guillemots  fail  to  lay  any  eggs  (Ainley  6k  Boekelheide 
1990).  The  variation  in  the  timing  of  commencement  of 
breeding  for  various  Farallon  seabirds  is  indicated  by  the 
range  among  years  of  mean  clutch  initiation  dates: 
Brandt's  Cormorant  (28  April-6  June),  Pelagic  Cormorant 
(22  May-12  June),  Western  Gull  (only  3-14  May),  Com- 
mon Murre  (9  May-9  June),  and  Pigeon  Guillemot  (20 
May- 17  June).  In  addition  to  the  seabirds  mentioned, 
Marin  County  hosts  a  number  of  odier  species  that  will 
not  breed  unless  certain  food  supplies  are  available.  Long- 
eared  Owls,  Short-eared  Owls,  and  Black-shouldered  Kites 
will  not  remain  to  breed  unless  certain  rodents  occur  in 
abundance;  Red  Crossbills  will  only  breed  in  years  of 
plentiful  conifer  seeds;  and  various  dabbling  ducks  may  fail 
to  breed  locally  when  small  wedands  dry  up  during 
droughts. 

These  patterns  of  variation  in  the  timing  of  breeding  of 
a  wide  range  of  species  further  demonstrate  that  most  if  not 
all  species  have  each  adopted  a  different  strategy  to  exploit 
their  environment.  It  is  clear  from  the  length  of  the 
breeding  season  on  the  California  coast,  the  great  year-to- 
year  variation  in  timing  of  breeding  in  certain  species,  and 
the  lack  of  breeding  by  some  species  in  particular  years  that 
efforts  to  document  patterns  of  breeding  distribution  of 
our  avifauna  are  best  spread  each  year  over  many  months 
and  over  enough  years  to  sample  a  broad  range  of  environ- 
mental conditions.  The  Marin  adas  project  was  fortunate 
enough  to  span  some  of  the  wettest  and  driest  years  in  the 
county's  history  and  consequendy  provided  information 
on  how  both  extremes  affected  bird  distribution  here. 


40 


METHODS  EMPLOYED  IN  THE 
MARIN  ATLAS 


The  detection  of  a  pattern  or  test  of  a  hypothesis  can  be  no  better  than  the  data  on  which  it  is  built. 


—  John  A.  Wiens, 
The  Ecology  of  Bird  Communities 


Grid  System 

THE  GRID  SYSTEM  chosen  in  1976  for  the  Marin  County 
Breeding  Bird  Atlas  was  roughly  comparable  to  the 
metric  grids  used  in  Europe  at  that  time.  Following  the  lead 
of  North  America's  first  adas  project  in  Maryland  (Klim- 
kiewicz  &.  Solem  1978),  a  grid  system  was  overlain  on 
7.5-minute  U.S.  Geological  Survey  topographic  maps  of 
Marin  County.  Each  of  the  1 7  topo  maps  covering  Marin 
County  (Figure  7)  were  divided  into  24  equal-sized  blocks. 
Because  some  of  these  topo  maps  included  large  portions 
of  the  ocean,  San  Pablo  or  San  Francisco  bays,  or  land  in 
adjacent  Sonoma  County,  a  total  of  221  blocks  formed  the 
basic  adas  grid  of  Marin  County  (Figure  8).  Each  of  these 
block  was  assigned  a  specific  numerical  code.  Though 
slighdy  rectangular  in  shape  (about  1.4X1.7  miles  on  a 
side),  each  one  of  our  basic  blocks  is  roughly  equivalent  in 
area  to  a  metric  block  2.5  km  on  a  side.  The  basic  blocks 
were  also  lumped  together  for  later  data  analysis  into 
groups  of  four  and  again  into  groups  of  sixteen  to  facilitate 
direct  comparisons  of  the  Marin  adas  data  with  data  from 
other  adas  projects  with  larger  basic  block  sizes.  At  the 
latitude  of  Marin  County  (38°  N)  our  basic  block,  4-block 
units,  and  16-block  units  are  slighdy  larger  in  area  (1.02 
times)  than  2.5-km,  5-km,  and  10-km  squares,  respectively. 
For  all  practical  purposes,  though,  our  block  units  are 
direcdy  comparable  in  size  to  their  respective  metric  equiva- 
lents. Although  comparability  with  other  adas  projects  is 
desirable,  the  comparison  of  die  Marin  adas  that  will  be  of 
most  benefit  will  be  that  with  itself  when  repeated  at  a 
future  date. 

Blocks  along  the  outer  coasdine,  the  shorelines  of  San 
Francisco  and  San  Pablo  bays,  and  the  Sonoma  County 
border  did  not  conform  to  the  basic  grid  system.  Those 
blocks  were  slighdy  larger  or  smaller  than  a  basic  block  and 
were  of  necessity  irregular  in  shape.  Parts  of  blocks  were 
merged  with  adjacent  blocks  to  facilitate  future  data  com- 
parisons among  blocks  of  roughly  equivalent  size.  This 


Figure  1 .  Overlay  of  U.S.  Geological  Survey  topographic  map 
grid  on  a  Marin  County  map,  forming  tKe  basis  for  tke  Marin 
County  Breeding  Bird  Atlas  grid  (Figure  8). 

avoided,  for  example,  a  comparison  of  a  block  comprised 
of  90%  land  and  10%  ocean  with  a  block  that  has  20% 
land  and  80%  ocean.  Merging  of  blocks  in  this  manner 
has  precedence  in  the  first  adas  project,  the  Atlas  of  British 
Flora  (Perring  &  Walters  1962).  Besides  bringing  odd 
blocks  into  closer  conformity  of  size  and  composition,  this 
method  had  the  practical  application,  in  some  cases,  of 
providing  direct  access  to  all  of  a  block  from  one  place.  For 

41 


Grid  System 


MARIN  COUNTY  BRFFDING  BIRD  ATIAS 


Participant  Instruction 


Figure  8.  The  basic  Mflrin  County  Breeding  Bird  Atlas  grid  with  221  numbered  blocks.  Blocks  were  created  by  dividing  each  of 
I  7  7-5-minute  USGS  topo  maps  (see  Figure  7)  into  24  equal-sized  blocks;  parts  of  some  irregular-sized  blocks  were  merged  with 
adjacent  ones  to  bring  blocks  into  closer  conformity  of  size-  A  basic  Marin  block  is  roughly  equivalent  in  area  to  a  metric  block  2.5 
km  on  a  side. 


example,  if  the  grid  system  had  been  applied  rigidly  along 
Tomales  Bay,  either  an  observer  would  have  had  to  drive 
long  distances  around  the  bay  to  get  access  to  parts  of  a 
block  on  the  opposite  side  of  the  bay,  or  else  two  different 
observers  would  have  had  to  cover  the  separate  parts  of  the 
block.  With  our  convoluted  coasdine,  either  method- 
using  a  rigid  grid  system  or  one  that  merged  parts  of 
blocks— would  have  created  blocks  of  different  sizes  or 
shapes.  The  latter  method  was  chosen  as  a  matter  of 
practicality  and  should  pose  no  problem  if  the  same  exact 
grid  is  used  when  the  adas  project  is  repeated  in  the  future. 

Participant  Instruction  and 
Block  Assignments 

From  1976  through  1978,  Bob  Stewart  was  the  sole 
coordinator  of  the  Marin  County  Breeding  Bird  Adas 
Project.  The  adas  was  advertised  in  the  Point  Reyes  Bird 
Observatory  Newsletter  and  widely  in  local  Audubon  Society 
and  conservation  newsletters.  In  1976  and  1977  several 
organizational  workshops  were  held.  Participants  were 
instructed  on  how  to  conduct  field  work  in  their  blocks 
and  were  provided  with  refresher  sessions  on  bird  songs 
and  nest-finding  strategies.  One  or  more  blocks  were 
assigned  to  each  participant  based  on  his  or  her  available 

42 


time  and  ability.  From  1979  through  1981,  there  was  a 
hiatus  in  adas  work.  This  author  became  the  overall 
coordinator  in  1982  for  the  final  field  season  of  the  adas 
project.  In  that  year  workshops  and  advertisements  were 
conducted  in  the  same  manner  as  in  previous  years. 
Likewise,  the  vast  majority  of  participants  that  year  were 
solicited  through  personal  contact.  In  1982,  regional  coor- 
dinators were  solicited  to  organize  participants  in  four 
areas  encompassing  all  of  Marin  County.  Betty  Burridge 
(who  now  organizes  the  Sonoma  County  Breeding  Bird 
Adas  Project)  was  coordinator  for  1 7  blocks  in  the  Tomales 
area,  Scott  Carey  for  43  blocks  in  the  Novato  area,  Bill 
Lenarz  for  61  blocks  in  southern/eastern  Marin,  and  Dave 
Shuford  for  100  blocks  in  the  West  Marin  area.  An  effort 
was  made  to  maintain  contact  with  participants  throughout 
each  field  season. 

In  all  years  each  participant  was  provided  with  the 
following: 

1 .  Instruction  sheets  detailing  the  objects  of  the  adas 
project,  how  and  when  to  conduct  field  work,  and  how  to 
record  the  required  data. 

2.  A  topo  map  (or  photocopy)  of  his  or  her  adas  block(s) 
and  adjacent  blocks;  the  location  of  the  blocks(s)  was 
oudined  on  an  attached  map  of  Marin  County. 


METHODS  EMPLOYED  IN  THE  MARIN  ATLAS 


PRBO  MARIN  COUNTY  BREEDING  BIRD  ATLAS  PROJECT 


NAME      L)OUG 

tuis 

19 

%Z 

ADDRESS  P 6  ,  i^C 

jl  ISS    tUlviJ 

:<j  Co  . 

ZIP 

?iY3» 

BLOCK*     $~*~I3 

Name 

A.O.U.* 

Po 

Pr 

Co 

Name 

A.O.U.» 

Po 

Pr 

Co 

Name 

A.O.U.» 

Po 

Pr 

Co 

Pied-billed  Grebe 

006 

American  Coot 

221 

Hairy  Woodpecker 

393 

Ashy  Petrel  . 

108 

Black  Oystercatcher 

287 

Downy  Woodpecker 

394 

*i 

Double-crested  Cormorant                120 

Snowy  Plover 

278 

Ash-throated  Flycatcher 

454 

FY 

Brandt's  Cormorant 

122 

Killdeer 

273 

P 

Black  Phoebe 

458 

pr 

Pelagic  Cormorant 

123 

Western  Gull 

049 

Western  Flycatcher 

464 

5 

Great  Blue  Heron 

194 

Common  Murre 

030 

Western  Wood  Pewee 

462 

S 

Green  Heron 

201 

Pigeon  Guillemot 

029 

Olive-sided  Flycatcher 

459 

Great  Egret 

196 

Band-tailed  Pigeon 

312 

Horned  Lark 

474 

T 

9 

Snowy  Egret 

197 

Rock  Dove 

313.1 

Violet-green  Swallow 

615 

Mallard 

132 

Mourning  Dove 

316 

r 

Tree  Swallow 

614 

ON 

Pintail 

143 

Barn  Owl 

365 

Rough-winged  Swallow 

617 

Cinnamon  Teal 

141 

Screech  Owl 

373 

-r 

Barn  Swallow 

613 

qki 

Ruddy  Duck 

167 

Great  Horned  Owl 

375 

Cliff  Swallow 

612 

^ 

Turkey  Vulture 

325 

• 

Pygmy  Owl 

379 

Purple  Martin 

611 

Sharp-shinned  Hawk 

332 

Burrowing  Owl 

3  78 

Steller's  Jay 

478 

J> 

Cooper's  Hawk 

333 

Spotted  Owl 

369 

Scrub  Jay 

481 

*V 

Red-tailed  Hawk 

337 

X 

Saw-whet  Owl 

372 

Common  Raven 

486 

FY 

Red  shouldered  Hawk 

339 

s 

Poor-will 

418 

Common  Crow 

488 

•' 

Marsh  Hawk 

331 

White-throated  Swift 

425 

Chestnut-backed  Chickadee 

741 

a/v 

Osprey 

364 

Anna's  Hummingbird 

431 

T 

Plain  Titmouse 

733 

P 

Sparrow  Hawk 

360 

J 

Allen's  Hummingbird 

434 

*f 

Common  Bushtit 

743 

fir 

California  Quail 

294 

r 

Belted  Kingfisher 

390 

j£ 

White-breasted  Nuthatch 

727 

Ring  necked  Pheasant 

309.1 

Red-shafted  Flicker 

413 

Red-breasted  Nuthatch 

728 

Virginia  Rail 

212 

Pileated  Woodpecker 

405 

Pygmy  Nuthatch 

730 

Sora 

214 

Acorn  Woodpecker 

407 

Brown  Creeper 

726 

Black  Rail 

216 

Po=Possit>le;    Pr  =  Probable;  Co=Confirmed      Enter  Criteria  Code  in  Correct  Column 


Name 

A.O.U.* 

Po 

Pr 

Co 

Name 

A.O.U.# 

Po 

Pr 

Co 

Name                                         A.o 

;j.» 

Po 

P', 

Co 

Wrentit 

742 

5 

Purple  Finch 

517 

5 

Rare  Possibilities 

Dipper 

701 

House  Finch 

519 

ft 

Black-crowned  Night  Heron 

202 

House  Wren 

721 

Pine  Siskin 

533 

n 

American  Bittern 

190 

Winter  Wren 

722 

American  Goldfinch 

529 

rL 

Wood  Duck 

144 

Bewick's  Wren 

719 

rT 

Lesser  Goldfinch 

530 

White-tailed  Kite 

328 

Long-billed  Marsh  Wren 

725 

Red  Crossbill 

521 

Swainson's  Hawk 

342 

Rock  Wren 

715 

Rufous-sided  Towhee 

588 

f) 

Golden  Eagle 

349 

Mockingbird 

703 

Brown  Towhee 

591 

P 

Prarie  Falcon 

355 

California  Thrasher 

710 

Savannah  Sparrow 

542 

*> 

Peregrine  Falcon 

356 

Robin 

761 

f> 

Grasshopper  Sparrow 

546 

S 

Clapper  Rail 

210 

Hermit  Thrush 

759 

Lark  Sparrow 

552 

?> 

Common  Gallinule 

219 

Swainson's  Thrush 

758 

T 

Rufous-crowned  Sparrow 

580 

Tufted  Puffin 

12 

Western  Bluebird 

767 

T 

Oregon  Junco 

567.9 

9P 

Long-eared  Owl 

286 

Golden-crowned  Kinglet 

748 

Chipping  Sparrow 

560 

Ft 

Short-eared  Owl 

287 

Loggerhead  Shrike 

622 

White-crowned  Sparrow 

554 

Vaux  Swift 

298 

Starling 

493 

n 

Song  Sparrow 

581 

fr 

Black-chinned  Hummingbird 

429 

Hutton's  Vireo 

632 

s 

Nuttall's  Woodpecker 

328 

Orf 

Warbling  Vireo 

627 

s 

Western  Kingbird 

447 

T 

Orange-crowned  Warbler 

646 

tJ\ 

Cassin's  Kingbird 

448 

Yellow  Warbler 

652 

Willow  Flycatcher 

466 

Black-throated  Gray  War 

bier          665 

Bank  Swallow 

616 

Hermit  Warbler 

669 

Yellow-breasted  Chat 

683 

MacGillivray's  Warbler 

680 

Hooded  Oriole 

505 

Yellowthroat 

681 

Lawrences  Goldfinch 

531 

Wilson's  Warbler 

665 

s 

Black-chinned  Sparrow 

565 

House  Sparrow 

688.2 

Sage  Sparrow 

574 

Western  Meadowlark 

501.1 

fr 

Red-winged  Blackbird 

498 

fr 

Bullock's  Oriole 

508 

ft 

Brewer's  Blackbird 

510 

pp 

Brown-headed  Cowbird 

495 

Black-headed  Grosbeak 

596 

Lazuli  Bunting 

599 

> 

Figure  9.   A  representative  field  recording  card  from  the  Marin  County  Breeding  Bird  Atlas.  See  Table  5  for  various  codes  used  to 
denote  Possible  (Po),  Probable  (Pr),  and  Confirmed  (Co)  breeding  evidence. 


43 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 

Table  5.    CRITERIA  FOR  POSSIBLE,  PROBABLE,  AND  CONFIRMED  BREEDING  CODES  entered  on  Marin 
County  Breeding  Bird  Adas  field  cards  (Figure  9). 

POSSIBLE  BREEDING  -  this  code  should  be  entered  in  die  first  column  (PO)  of  the  Atlas  Card. 

Bird  recorded  in  the  breeding  season  in  possible  nesting  habitat  but  no  other  indication  of  breeding  noted.  Take  1 
May  through  31  July  as  the  breeding  season  for  most  species.  Summering,  nonbreeding  adults  such  as  gulls  in  a 
dump  when  you  know  diere  is  no  gullery  in  your  block,  migrant  shorebirds  and  warblers,  should  NOT  be  included. 

PROBABLE  BREEDING  -  codes  entered  in  second  column  (PR). 

S  Singing  male  present  (or  breeding  calls  heard)  on  more  than  one  date  in  the  same  place.  It  is  a  good  indication  that 

a  bird  has  taken  up  residence  if  the  dates  are  a  week  or  more  apart. 

T  Bird  (or  pair)  apparendy  holding  territory.  In  addition  to  singing,  chasing  of  others  of  the  same  species  often  marks 

territory. 

D  Courtship  and  display;  or  agitated  behavior  or  anxiety  calls  from  adults,  suggesting  probable  presence  of  nest  or 

young  nearby;  brood-patch  on  trapped  female  or  cloacal  protuberance  on  trapped  male. 

N  Visiting  probable  nest-site. 

B  Nest  building  by  wrens  and  woodpeckers.  Wrens  may  build  many  nests  and  woodpeckers,  although  they  usually 

drill  only  one  nesting  cavity,  may  also  drill  roosting  holes. 

CONFIRMED  BREEDING  -  codes  entered  in  diird  column  (CO). 

DD       Distraction  display  or  injury  feigning,  coition.  Agitated  behavior  and/or  anxiety  calls  are  "D"  only. 

NB       Nest  building  by  any  species  except  wrens  and  woodpeckers. 

UN  Used  nest  found.  These  must  be  carefully  identified  if  they  are  to  be  used.  Some  nests  (like  those  of  Northern  Oriole) 
are  persistent  and  very  characteristic.  Others  are  more  difficult  to  identify  correcdy. 

FE         Female  with  egg  in  the  oviduct. 

FL  Recendy  fledged  young  (including  downy  young  of  waterfowl  etc.).  This  code  should  be  used  with  caution  for  species 
such  as  Starlings  and  swallows  that  may  move  some  distance  soon  after  fledging.  Recently  fledged  passerines  are  still 
dependent  on  parents  and  being  fed  by  diem. 

FS         Adult  carrying  fecal  sac. 

FY  Adult(s)  widi  food  for  young.  Some  birds  (gulls,  terns,  and  birds  of  prey)  continue  to  feed  their  young  long  after 
they've  fledged  and  may  move  considerable  distances.  Also  some  birds  (like  terns)  may  carry  food  long  distances  to 
young  in  a  neighboring  block.  Be  careful  especially  on  the  edge  of  a  block.  Care  should  be  taken  to  avoid  confusion 
with  courtship  feeding  (D). 

ON  Adult(s)  entering  or  leaving  nest-site  in  circumstances  indicating  occupied  nest.  Not  generally  used  for  open  nesting 
birds.  The  correct  code  would  be  "N"  if  you  simply  see  a  bird  fly  into  or  out  of  a  bush  or  tree  and  do  not  find  the 
nest.  It  should  be  used  for  hole  nesters  as  when  a  bird  enters  a  hole  and  remains  inside,  changes  over  at  a  hole,  or 
bird  leaves  hole  after  having  been  inside  for  some  time. 

NE  Nest  and  eggs  or  bird  setting  and  not  disturbed  or  egg  shells  found  below  the  nest.  If  you  find  a  cowbird  egg  in  a 
nest,  it's  NE  for  cowbird  and  NE  for  the  host  nest 

NY  Nest  widi  young  or  downy  young  or  downy  young  of  waterfowl,  quail,  waders,  etc.  If  you  find  a  young  cowbird  with 
the  other  young,  it's  NY  for  the  cowbird  and  NY  for  the  host  species.  Since  parents  often  lead  downy  young  for 
considerable  distances,  care  should  be  taken  if  such  records  are  close  to  the  edge  of  the  block. 

44 


Participant  Instruction 


METHODS  EMPLOYED  IN  THE  MARIN  ATLAS 


Additional  Information 


3.  Atlas  recording  card(s)  to  be  filled  out  in  the  field  or 
immediately  afterwards  (Figure  9). 

4.  A  breeding  category  sheet  (Table  5)— a  slighdy  modi- 
fied form  of  the  one  used  in  the  Maryland  county  adas 
project  (Klimkiewicz  &  Solem  1978),  originally  derived 
from  the  British  categories  (Sharrock  1976). 

5.  The  assurance  that  the  locations  of  all  sightings  of 
rare  breeding  birds  would,  at  the  discretion  of  die  observer, 
be  kept  confidential  and  protected  on  maps  (see  Data 
Summary  p.48). 

In  1982— the  final  year  of  fieldwork— participants  were 
provided  with  photocopies  of  the  previous  years'  adas 
card(s)  for  their  block(s)  if  there  had  been  any  prior 
coverage.  They  were  further  instructed  on  how  to  obtain 
adequate  coverage  of  their  blocks  (see  below).  In  addition, 
observers  were  asked  to  keep  records  of  the  total  number 
of  hours  they  spent  in  the  field  collecting  adas  data.  That 
year,  area  coordinators  contacted  all  participants  around  1 
June.  At  that  time,  if  some  observers  already  had  been  able 
to  cover  their  block(s)  adequately,  they  were  encouraged  to 
help  with  other  areas  still  in  need  of  coverage.  If  partici- 
pants felt  they  would  not  have  time  to  finish  the  necessary 
field  work  in  their  block(s),  another  observer  was  assigned 
to  help  complete  the  coverage  that  season.  Adequacy  of 
coverage  was  judged  qualitatively  by  die  overall  coordinator 
as  described  below.  In  addition  to  regular  communication 
between  area  coordinators  and  participants,  close  contact 
was  maintained  between  area  coordinators  and  the  overall 
coordinator. 


Gathering  Additional  Information 

Because  different  methods  work  best  for  gathering  data  on 
certain  groups  of  species,  or  because  a  diversity  of  methods 
can  enhance  data  collection  for  all  species,  a  number  of 
additional  mediods  were  employed  to  gather  data  that 
supplemented  the  standard  adas  procedures.  These  strate- 
gies included  the  following: 

1.  Owling  routes.  With  the  realization  diat  owls  and 
poorwills  would  be  inadequately  covered  compared  with 
other  species,  special  owling  routes  were  drawn  up  in  1977 
and  1982  and  assigned  to  various  nocturnal  enthusiasts. 
These  routes  were  of  varying  length  and  covered  virtually 
all  the  major  roads  in  the  sparsely  inhabited  parts  of  the 
county.  Several  walking  routes  were  also  covered  along 
trails  in  the  Inverness  Ridge  area  of  the  Point  Reyes 
National  Seashore  and  within  the  Mount  Tamalpais  water- 
shed. 

2.  Spring  Bird  Counts.  Following  the  tradition  of  the 
Christmas  Bird  Counts  (CBC)  published  in  the  National 
Audubon  Society  journal  American  Birds,  three  Spring 
Bird  Counts  (SBC)— Southern  Marin,  Point  Reyes  Penin- 


sula, and  Even  Cheaper  Thrills— were  conducted  in  Marin 
County  in  May  or  early  June  in  various  years  beginning  in 
1978  (Appendix  A). 

Aside  from  seasonal  timing,  these  counts  were  con- 
ducted in  an  identical  manner  to  the  CBCs,  except  that,  in 
addition  to  counting  die  number  of  individuals  of  each 
species,  each  area  leader  assigned  the  highest  category  of 
breeding  observed  that  day  (Table  5)  to  each  potential 
breeding  species  in  an  area.  To  channel  some  of  this 
energy  into  the  adas  project,  the  Marin  adas  grid  was 
overlain  on  the  South  Marin  SBC  circle  in  1977  and  over 
all  diree  SBC  circles  in  1 982.  Each  of  the  area  leaders,  many 
of  whom  were  already  adas  participants,  was  provided  with 
all  the  information  given  to  regular  adas  participants  along 
with  adas  cards  for  all  the  blocks  or  partial  blocks  that  fell 
within  his  or  her  normal  SBC  area.  In  addition  to  collecting 
the  standard  numerical  and  breeding  information 
described  above,  area  leaders  were  also  asked  to  fill  in  all 
breeding  evidence  for  each  individual  adas  block  in  their 
area.  This  resulted  in  large  amounts  of  atlas  data  being 
collected  on  single  days,  and  sometimes  parts  of  blocks 
being  covered  by  the  SBC  team  that  otherwise  might  not 
have  been  covered  by  the  adaser  already  assigned  that 
block. 

3.  Casual  observations.  Besides  using  the  systematic  adas 
data  collected  in  specified  blocks  from  1976  through  1978 
and  in  1982,  other  available  data  were  incorporated  in  the 
data  base.  In  advertisements  and  instructions  to  partici- 
pants, everyone  was  encouraged  to  submit  additional  data 
on  breeding  evidence  for  any  species  (especially  rare  or 
unusual  ones)  that  were  observed  in  an  adas  year  but  not 
in  an  assigned  adas  block.  Available  data  were  also  solic- 
ited for  the  intervening  years  of  1979  through  1981,  when 
no  organized  effort  was  made  to  cover  adas  blocks.  Individ- 
uals particularly  active  in  those  years  were  contacted 
direcdy  and  asked  to  submit  from  their  field  notes  and 
memories  any  and  all  specific  breeding  bird  sightings.  All 
such  observations  were  given  the  same  scrutiny  as  adas 
card  data;  a  determination  of  the  exact  location  and  type  of 
breeding  evidence  observed  was  necessary  to  correcdy 
assign  records  to  specific  adas  blocks. 

4-  Breeding  seabirds  surveys.  Fortuitously,  in  1979  and 
1980  personnel  from  die  U.S.  Fish  and  Wildlife  Service 
conducted  censuses  of  breeding  seabirds  along  the  entire 
California  coast  and  subsequendy  published  the  informa- 
tion as  the  Catalog  of  California  Seabird  Colonies  (Sowls  et 
al.  1980).  Breeding  site  data  from  Marin  County  that  had 
not  already  been  confirmed  during  atlas  work  were 
extracted  from  that  publication  (or  field  notes  and  maps  on 
file  at  the  California  Academy  of  Sciences  in  San  Fran- 
cisco) and  assigned  to  die  appropriate  adas  block.  U.S. 
Fish  and  Wildlife  Service  personnel  resurveyed  breeding 
seabirds  on  the  central  and  northern  California  coast  in 
1989  (Carter  et  al.  1990,  1992).  These  1989  data  were  not 


45 


Additional  Information 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Adequacy  of  Coverage 


used  to  construct  the  atlas  maps  but  were  used  to  supple- 
ment the  knowledge  of  distribution  and  abundance  dis- 
cussed in  the  species  accounts. 


Determining  Adequacy  of  Coverage 

Determining  when  data  of  sufficient  quality  have  been 
collected  in  individual  blocks  or  in  all  blocks  in  a  region  is 
a  perplexing  problem  facing  all  adas  projects.  Although  it 
would  be  ideal  to  confirm  breeding  for  all  species  in  each 
block,  that  goal  is  unrealistic.  On  the  other  hand,  adas 
coordinators  must  attempt  to  maximize  the  return  of  field 
effort  given  limitations  in  the  number  and  ability  of  observ- 
ers, time  available,  and  access  problems  or  other  logistical 
constraints. 

On  a  practical  level,  an  adas  coordinator  must  decide 
when  an  observer  should  be  shifted  to  cover  another  block 
because  additional  time  spent  in  the  original  block  will 
yield  few  new  species  or  instances  of  confirmed  breeding 
evidence.  More  importandy,  an  atlas  project  can  establish 
scientific  credibility  only  if  there  is  confidence  that  field 
work  has  documented  a  high  proportion  of  the  species 
actually  breeding  in  each  block.  Otherwise  there  will  always 
be  the  nagging  doubts,  rife  in  preadasing  days,  as  to 
whether  the  distribution  patterns  or  population  trend 
indicated  is  real  or  just  an  artifact  of  insufficient  coverage. 

Other  Atlases 

A  number  of  methods  have  been  used  to  assess  adequacy 
of  coverage  in  other  adases,  and  all  have  their  shortcom- 
ings. Two  popular  measures,  used  singly  or  in  combina- 
tion, assume  adequate  coverage  in  a  block  when  a  certain 
number  of  species  (and  sometimes  confirmed  breeders) 
have  been  recorded  or  when  a  certain  number  of  field 
hours  have  been  logged.  In  Vermont,  the  initial  experience 
of  adas  committee  members  indicated  that  most  of  the 
state's  blocks  contained  100  breeding  species  (Laughlin  ek 
Kibbe  1985,  Kibbe  1986).  With  this  knowledge  they 
selected  75  species  recorded  in  a  block  (and  35  confirmed 
breeders)  as  the  level  of  acceptable  coverage,  assuming  that 
number  would  represent  75%  of  the  species  actually  in 
most  blocks.  In  practice  75  species  was  only  60%-65%  of 
the  1 20  or  more  species  they  later  found  in  some  blocks. 
The  New  York  adas  initially  defined  adequate  coverage  as 
76  breeding  species  per  block  with  half  (38)  confirmed  as 
breeders;  they  later  dropped  the  50%  confirmation  require- 
ment (Andrle  ck  Carroll  1988).  Ontario  originally  set  an 
adequate  coverage  standard  of  1 6  hours  of  field  work  with 
the  expectation  that  the  effort  would  identify  75%  of  the 
breeding  species  in  a  block  (Cadman  et  al.  1987).  Because 
expectations  were  not  met,  coverage  goals  were  modified. 
Based  on  experience  and  estimates  of  habitat  diversity  in 
each  block,  coordinators  estimated  the  total  number  of 

46 


species  breeding  in  each.  Retaining  the  minimum  require- 
ment of  1 6  hours  of  field  work,  adequate  coverage  was  then 
set  at  establishing  breeding  evidence  for  75%  of  the  esti- 
mated number  of  breeding  species. 

Setting  either  an  arbitrary  number  of  species  detected  or 
field  hours  spent  as  the  measure  of  adequate  coverage  is 
problematic.  Because  habitat  diversity,  and  hence  the  num- 
ber of  breeding  species,  may  vary  gready  among  blocks,  a 
preselected  regionwide  goal  of  species  detection  will  set 
unrealistically  high  or  low  expectations  for  many  blocks.  A 
minimum  number  of  hours  of  field  work  is  an  inadequate 
standard  because  observers  varying  in  field  skills  will 
consequendy  differ  in  the  number  of  species  they  can 
detect  in  a  given  time  period.  Even  when  observer  skills  are 
comparable,  the  number  of  hours  needed  to  detect  the 
same  number  of  birds  may  also  vary  gready  among  blocks 
as  habitat  diversity,  ruggedness  of  terrain,  or  ease  of  access 
varies. 

In  combination  with  species  and  field  time  goals,  Smith 
(1982)  suggested  measuring  adequacy  of  coverage  by  plot- 
ting the  number  of  new  species  detected  in  each  of  the 
three  breeding  categories  against  time  spent  in  each  new 
visit  to  a  block.  Termination  of  coverage  was  recom- 
mended when  the  plotted  curves  leveled  off  as  returns 
diminished  with  time  spent.  This  method  relies  on  the 
probably  unrealistic  assumption  that  most  observers  will 
keep  accurate  records,  graph  them,  and  correcdy  interpret 
die  results;  regardless,  this  method,  like  others,  will  falter 
because  of  observer  variability.  No  matter  how  much  time 
is  spent  to  compensate,  observers  with  poor  skills  in 
identifying  bird  songs  will  plateau  at  lower  species  totals 
than  will  more  skilled  observers. 

Kibbe  (1986)  suggested  using  an  ACID  (Adequate  Cov- 
erage Identification)  test  to  evaluate  when  observers'  efforts 
became  ineffective  and  it  was  time  to  move  on  to  another 
block.  Coverage  in  this  scheme  is  scored  by  adding  the 
products  of  three  times  the  number  of  species  with  con- 
firmed breeding  evidence,  two  times  the  number  with 
probable  evidence,  and  one  times  the  number  with  pos- 
sible evidence  (ACID  score  =  [3*CO]  +  [2*PR]  +  PO).  The 
assumption  is  that  as  complete  coverage  is  approached, 
scores  change  less  and  less  between  successive  surveys. 
With  skilled  observers  this  method  may  actually  measure 
"adequate"  coverage,  but  scores  of  some  observers  may 
peak  at  too  low  a  level  because  they  are  not  recording 
difficult-to-detect  species.  Because  the  score  is  most  sensi- 
tive to  increases  in  the  number  of  confirmed  species,  an 
observer  may  detect  most  of  the  breeding  species  long 
before  the  ACID  score  begins  to  level  off.  Thus  practicality 
would  suggest  moving  skilled  observers  to  new  blocks  long 
before  their  scores  peaked,  if  finding  most  breeding  species 
is  a  higher  priority  than  establishing  confirmed  breeding 
evidence  for  all  of  them. 


Adequacy  of  Coverage 


METHODS  EMPLOYED  IN  THE  MARIN  ATLAS 


Adequacy  of  Coverage 


Raynor  (1983)  suggested  assessing  coverage  by  first 
plotting  the  number  of  species  found  in  each  block  against 
an  informed  estimate  of  the  number  of  breeding  species 
probably  present  in  each  block.  The  informed  estimate  is 
made  after  the  first  adas  year  and  is  based  on  identification 
of  habitats  in  each  block  (from  maps  or  other  data), 
knowledge  of  habitat  preferences  of  expected  breeding 
birds,  lists  of  species  in  nearby  blocks  with  similar  habitats, 
and  personal  knowledge  of  the  block  or  similar  habitats  in 
the  same  area.  The  informed  species  estimate  can  be 
revised  or  updated  annually  if  coverage  continues;  also 
results  can  be  evaluated  against  the  estimate  and  can  be 
used  to  revise  it.  Once  the  expected  number  of  species  is 
estimated  for  each  block,  calculations  can  be  made  of  ratios 
of  the  total  number  of  species  (or  confirmed  species) 
recorded  to  expected  species  (l"/EX  or  CO/EX).  These 
ratios  can  be  plotted  as  percentages  and  classified  to  define 
quality  of  coverage.  For  example,  the  range  of  values 
calculated  can  be  partitioned  into  three  equal  categories 
corresponding  to  good,  fair,  and  poor  coverage.  Raynor 
(1983)  proposed  a  very  high  standard  of  listing  95%  of  the 
expected  species  and  confirming  57%  as  a  goal  for  ade- 
quate coverage  of  a  block.  Although  his  method  is  intu- 
itively appealing,  it  is  not  without  pitfalls.  The  main 
drawback  is  that  refining  estimates  over  time— based  on  the 
assumption  that  with  good  coverage,  counts  and  estimates 
will  tend  to  converge— may  lead  to  a  self-fulfilling  prophecy. 
If  the  species  list  exceeds  the  estimate,  the  estimate  will  be 
revised  upward,  but  if  the  list  is  low  and  remains  low  after 
further  work  is  conducted,  the  estimate  will  likely  be 
revised  downward.  In  other  words,  once  coverage  has  been 
qualitatively  deemed  adequate  on  some  level  the  estimate 
will  be  revised  to  fit  the  actual  number  of  species  recorded. 
This  is  not  a  test  of  adequate  coverage.  Rather,  it  fits  data 
to  what  one  assumes  from  past  knowledge  or  current  field 
work  is  the  "real"  number  of  species  breeding  in  a  block. 
Although  scientifically  fortified  with  plots  and  correlations, 
the  linchpin  of  this  method  is  the  accuracy  of  the  estima- 
tion of  breeding  species.  Sophisticated  data  analysis  will 
not  suffice  if  the  estimates  of  expected  species  have  low 
accuracy.  The  people  estimating  must  have  a  very  extensive 
knowledge  of  local  habitat  distribution,  habitat  preferences 
of  expected  breeding  birds,  and  a  fair  amount  of  prior 
distributional  knowledge  of  die  birds  being  studied.  In 
atlases  covering  large  geographical  areas  various  sub- 
coordinators  are  likely  to  make  the  species  estimates  for  the 
blocks  in  their  subregion.  Hence  coverage  standards  may 
vary  with  subregions  as  coordinators  vary  in  knowledge  or 
a  tendency  to  be  conservative  or  liberal  in  their  estimations 
of  expected  breeding  species. 

The  only  way  to  accurately  test  for  adequate  coverage  is 
to  send  a  highly  qualified  observer— well  versed  in  local 
bird  songs  and  willing  to  hike,  if  need  be,  to  all  available 
habitats— to  a  block  with  prior  coverage  and  see  if  he  or  she 


can  add  many  new  species.  If  after  a  day  in  the  field  the 
observer  adds  little  to  the  breeding  list,  it  seems  fair  to 
assume  that  the  block  has  been  adequately  covered. 
Because  of  limits  to  observer  numbers,  ability,  and  time, 
such  a  test  is  usually  not  possible  for  most  blocks.  On  the 
other  hand,  such  a  test  is  advised  for  blocks  with  lower 
species  totals  than  other  adjoining  blocks  with  similar 
habitats  and  even  for  a  certain  percentage  of  randomly 
selected  blocks  in  various  subregions  of  the  adas  area. 

The  Marin  Atlas 

We  did  not  use  any  a  priori  standard  of  coverage  nor  were 
data  from  Marin  adas  blocks  formally  compared  to  a 
standard,  score,  or  test.  Rather,  we  assessed  adequacy  of 
coverage  in  the  Marin  County  Breeding  Bird  Adas  Project 
on  an  empirical  block-by-block  basis  in  a  manner  similar 
to  that  later  used  in  Ohio  (Rice  6k  Peterjohn  1986).  The 
overall  coordinator  carefully  weighed  the  data  for  each 
block  just  prior  to  and  during  the  final  year  of  adas  field 
work  in  1982.  From  the  basis  of  knowledge  of  habitat 
preferences  of  expected  species  and  the  habitats  known  or 
expected  to  be  found  in  each  block,  species  lists  from  data 
cards  for  each  block  widi  some  coverage  were  scrutinized. 
Species  that  were  likely  still  to  be  found  were  highlighted 
on  cards  sent  back  to  observers,  who  were  asked  to  specifi- 
cally look  for  those  species  in  the  appropriate  habitats.  To 
further  ensure  adequate  coverage  of  all  blocks,  and  to 
prioritize  the  assignment  of  blocks  to  participants  in  the 
final  adas  season,  each  area  coordinator  was  given  a  list  of 
all  blocks  in  their  area  qualitatively  divided  into  the  follow- 
ing categories:  (1)  blocks  not  covered  at  all,  (2)  blocks 
needing  much  work,  (3)  blocks  needing  moderate  work, 
and  (4)  blocks  needing  spot  checking.  Blocks  in  the  last 
category  appeared  already  to  have  been  covered  "ade- 
quately." Nevertheless,  considering  that  one  or  more  spe- 
cies are  almost  inevitably  missed  in  every  block,  no  matter 
how  well  covered,  participants  were  asked  to  look  for 
additional  species  in  these  blocks  when  they  had  reason  to 
suspect  that  a  species  had  been  missed. 

Although  throughout  the  project  we  emphasized  to 
observers  the  importance  of  obtaining  as  much  evidence  of 
confirmed  breeding  as  possible,  we  placed  a  higher  priority 
in  the  final  year  of  at  least  establishing  presence  in  each 
block  of  as  many  of  die  expected  species  as  possible.  This 
approach  was  taken  to  ensure  that  our  data  would  best 
represent  the  distribution  of  each  species.  We  did  not  want 
to  miss  the  presence  of  species  in  undercovered  blocks  at 
the  expense  of  spending  too  much  time  confirming  breed- 
ing of  more  species  in  blocks  where  most  expected  species 
had  already  been  found.  We  assumed  that  if  we  spent 
enough  time  to  document  the  presence  of  most  species  that 
die  natural  by-product  would  be  the  observation  of  consid- 
erable evidence  of  confirmed  breeding. 

47 


Data  Summary 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Quantitative  Data 


Mop-up  efforts  were  targeted  for  blocks  in  the  "needing 
moderate  work"  category.  Skilled  observers  sent  to  such 
blocks  for  one-time  intensive  visits  generally  added  only  a 
few  species.  The  use  of  mop-up  observers  to  randomly 
sample  a  small  number  of  blocks  is  highly  recommended 
as  a  true  hands-on  test  of  adequate  coverage.  The  success 
of  mop-up  efforts  also  bolstered  confidence  in  the  lists  of 
expected  species  generated  for  blocks  where  such  observers 
were  not  used. 

In  the  last  year,  many  blocks  were  covered  for  the  first 
time,  basically  by  the  technique  of  block-busting,  now 
widely  promoted  by  most  adas  projects.  Area  coordinators 
or  other  skilled  observers  with  excellent  birdsong  identifi- 
cation skills  and  the  willingness  to  hike  off  the  beaten  path 
covered  these  blocks  on  at  least  two  field  days  separated  by 
about  two  weeks  to  a  month.  For  comparison,  block-bust- 
ing teams  in  some  state  adas  projects  with  larger  block  sizes 
than  those  in  Marin  averaged  about  10  to  20  hours  per 
block  (Laughlin  ck  Kibbe  1985,  Andrle  &  Carroll  1988). 
It  was  felt  diat  our  blocks  were  of  such  small  size  diat  an 
observer  could  easily  hike  to  visit  all  the  major  habitats  in 
one  day.  The  second  visit  ensured  probable  breeding  status 
for  many  species  based  on  hearing  or  seeing  individuals  at 
the  same  site  over  time.  Confirmed  breeding  evidence  was 
usually  found  for  many  species  on  the  second  visit,  which 
we  tried  to  time  for  the  period  when  many  recendy  fledged 
young  were  just  out  of  the  nest  and  still  being  fed  by 
parents. 

Other  methods  noted  above  geared  toward  specific 
groups,  such  as  owls  and  seabirds,  enhanced  our  ability  to 
achieve  adequate  coverage.  Mop-up  efforts  or  Spring  Bird 
Count  help  also  had  the  advantage  of  obtaining  indepen- 
dent coverage  of  many  blocks.  This  enhanced  coverage 
because  observers  with  different  skills  worked  a  block,  and 
some  individuals  were  likely  to  visit  areas  of  the  block  not 
covered  by  another  observer.  Given  the  pitfalls  of  the  many 
methods  of  assessing  coverage  described  above,  there  is  no 
reason  to  suspect  that  our  adas  necessarily  suffered  by  the 
lack  of  an  a  priori  standard  of  coverage. 

Data  Summary 

After  die  completion  of  atlas  field  work  in  1982,  the  overall 
adas  coordinator  made  a  final  check  of  all  adas  cards  for 
accuracy  and  asked  original  observers  for  details  about 
unusual  or  questionable  sightings.  The  most  frequent 
question  asked  was  not  whether  the  observer  felt  the 
species  in  question  was  identified  correcdy,  but  whether 
the  species  was  observed  in  "appropriate  habitat"  at  die 
right  time  of  year.  After  being  satisfied  that  all  observations 
on  the  data  cards  were  correct  to  the  best  of  the 
coordinator's  knowledge,  the  data  were  transferred  from 
the  adas  cards  onto  species  summary  sheets.  Each  sum- 
mary sheet  had  a  listing  of  all  adas  blocks  and  three 

48 


columns  to  check  off  possible,  probable,  or  confirmed 
breeding.  The  number  of  blocks  that  had  evidence  for  the 
three  categories  was  totaled  and  checked.  Bill  Lenarz  then 
entered  all  die  adas  data  from  the  species  sheets  into 
computer  files  and  checked  the  breeding  category  totals 
against  those  done  by  hand.  Data  were  summarized  for  all 
species  and  all  blocks,  including  the  2.5-,  5-,  and  10-km 
block  equivalents.  Data  presented  below  are  from  the 
2.5-km  block  equivalents.  Lenarz  also  wrote  additional 
computer  programs  for  more  detailed  analyses  currendy 
slated  for  future  publication. 

Before  the  1982  field  season,  preliminary  species  maps 
were  made  by  hand,  using  all  the  1976  to  1981  adas  data 
and  the  symbols  of  breeding  evidence  subsequendy  por- 
trayed on  the  final  maps  (see  Content  of  Species  Accounts 
p.  73).  Copies  of  these  maps  were  given  to  the  regional 
coordinators  to  illustrate  the  detail  of  the  final  maps,  to 
point  out  gaps  in  our  knowledge,  and  to  provide  encour- 
agement to  coordinators  and  adas  participants.  After  the 
completion  of  data  collection  in  1982,  final  maps  were 
constructed  by  adding  to  the  preliminary  maps  all  the 
information  from  the  checked  species  sheets.  For  each 
species,  dots  on  the  map  were  counted  and  checked  against 
the  species  sheets  and,  if  necessary,  adjustments  were 
made.  It  is  likely  that  a  very  few  errors  in  mapping  were 
made,  but  this  should  not  affect  the  overall  pattern  of 
distribution  of  common  species.  Maps  of  rarer  species 
were  checked  and  double-checked  against  the  species 
sheets.  For  several  rare  and  sensitive  species,  the  locations 
of  breeding  records  were  protected  by  moving  the  dots  on 
the  map  by  one  to  two  blocks;  such  maps  were  labeled 
accordingly  (see  Content  of  Species  Accounts  p.  73). 

Quantitative  Data  on  Abundance 

Although  no  organized  effort  was  made  to  estimate  the 
abundance  of  each  species  in  each  block  as  part  of  the  adas 
project,  data  on  the  abundance  of  birds  in  Marin  County 
collected  for  other  purposes  were  summarized  or  identi- 
fied. Sources  of  this  data  included  the  following: 

1 .  Spring  Bird  Counts.  Data  from  the  three  SBCs 
described  above  are  presented  in  Appendix  A. 

2.  Breeding  Bird  Survey  routes.  Data  from  the  two  24-5- 
mile  USFWS  Breeding  Bird  Survey  routes  established  in 
Marin  County  are  summarized  in  Appendix  B.  Eleven 
years  of  data  from  the  period  1972  to  1986  were  used  from 
the  Fairfax  083  route;  coverage  dates  ranged  from  8  May 
to  14  June  (median  2  June).  Seven  years  of  data  from  the 
period  1975  to  1986  were  used  from  the  Point  Reyes  071 
route;  coverage  dates  ranged  from  3  to  22  June  (median  1 1 
June). 

3.  Breeding  Bird  Census  plots.  Data  on  abundance  of 
Marin  County  birds  collected  on  Breeding  Bird  Census 
plots  along  the  coast  (1951-1990)  and  published  in  Amer- 


Quantitative  Data 


METHODS  EMPLOYED  IN  THE  MARIN  ATLAS 


Quantitative  Data 


ican  Birds  or  the  journal  of  Field  Ornithology  were  not 
summarized,  but  the  names,  locations,  and  citations  of  the 
published  accounts  of  these  plots  are  listed  in  Appendix 
C. 

4.  Breeding  seabird  colony  surveys.  Numbers  of  seabirds 
estimated  at  various  colonies  in  Marin  County  by  USFWS 
personnel  (Sowls  et  al.  1980;  Carter  et  al.  1990,  1992) 
were  summarized  and  accompany  the  seabird  accounts. 

5.  Heron  and  egret  rookery  surveys.  Data  on  the  numbers 
of  herons  and  egrets  breeding  at  various  Marin  County 
rookeries  (Pratt  1983,  p.  103  this  volume)  are  presented  in 
tabular  form  with  the  appropriate  species  accounts. 

6.  testing  Osprey  surveys.  Data  on  the  number  of 
Ospreys  nesting  at  Kent  Lake  in  the  Marin  Municipal 
Water  District  (Evens  1991)  accompany  the  Osprey 
account. 


7-  Common  Yellowthroat  surveys.  Data  on  numbers  of 
Saltmarsh  Common  Yellowthroats  from  surveys  of  the  San 
Francisco  Bay  area  (Hobson  et  al.  1986)  supplement  the 
Yellowthroat  account 

In  addition,  after  the  adas  work  was  completed,  esti- 
mates were  made  of  the  relative  abundance  of  each  species 
in  an  "average"  block.  These  qualitative  estimates  were 
based  on  the  author's  detailed  field  notes  on  abundance 
gathered  while  exploring  habitats  in  virtually  all  parts  of 
Marin  over  an  eight-year  span  from  1975  to  1982.  These 
abundance  estimates  per  average  block  were  used  in  con- 
junction with  the  adas  distribution  data  to  make  estimates 
of  the  relative  abundance  of  each  species  countywide  as 
presented  in  each  species  account  (see  Content  of  Species 
Accounts  p.  73). 


/ 


jm 


49 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


£&&  «4fc£.4dU 


Coastal  scrub,  grassland,  and  riparian  forest  lend  a  soft-looking  texture  to  the  landforms  of  the  Rodeo  Lagoon  valley  and 
Wolf  Ridge  west  of  "Hawk  Hill."  Drawing  fry  Ane  Rovetta,  1  989. 


50 


RESULTS  AND  DISCUSSION 


all  nature  is  so  full,  that  that  district  produces  the  greatest  variety  which  is  most  examined. 


-  Gilbert  White,  1768 


Atlas  Coverage 

FIELD  WORKERS  covered  all  221  blocks  in  the  Marin 
County  Breeding  Bird  Atlas  grid.  The  amount  of  time 
spent  on  field  work  was  tallied  only  in  1982,  when  about 
92  observers  logged  over  2800  hours  afield.  In  only  a  few 
blocks  was  coverage  considered  unsatisfactory.  In  one  case, 
coverage  was  compromised  because  we  were  denied  access 
to  private  land  comprising  all  of  one  block  along  the  Estero 
del  Americano;  but  observers  were  able  to  at  least  sample 
most  habitats  in  that  block  via  kayak. 

For  all  atlas  blocks  combined,  possible  breeding 
accounted  for  33.4%  of  all  records,  probable  for  34-0%, 
and  confirmed  for  32.6%.  Although  these  data  fall  short 
of  the  ideal  of  confirming  all  species  as  breeders  in  all 
blocks,  they  are  consistent  with  our  efforts  to  obtain 
accurate  distribution  maps  by  documenting  the  presence 
of  most  breeding  species  in  each  block  (see  Adequacy  of 
Coverage  p.  46).  Excluding  nightbirds,  we  probably  found 
some  evidence  of  breeding  for  90%-95%  of  all  species 
actually  breeding  in  most  blocks.  Owls,  poorwills,  and 
other  secretive  species  such  as  rails  were  not  surveyed  as 
well  as  other  species,  but  their  basic  distribution  patterns 
were  established.  For  example,  the  Great  Horned  Owl  was 
recorded  in  about  two-thirds  of  the  potential  blocks  though 
it  likely  occurred  in  almost  all  of  them.  Nonetheless,  the 
owl's  adas  map  clearly  shows  that  it  breeds  throughout  the 
county;  notably,  a  high  proportion  of  the  blocks  without 
documentation  of  Great  Horned  Owl  were  away  from 
roads,  where  coverage  was  scant.  Extraordinary  efforts 
would  have  to  have  been  made  to  bring  the  completeness 
of  data  collection  for  nocturnal  birds  up  to  that  of  diurnal 
species.  Since  the  basic  distribution  patterns  of  nocturnal 
species  were  established,  the  expenditure  of  such  effort 
seems  warranted  only  in  the  case  of  Endangered  or  Threat- 
ened species  such  as  the  Spotted  Owl  (see  account). 

Patterns  of  Species  Richness  of  the 
Breeding  Avifauna 

During  the  field  work  for  the  Marin  County  Breeding  Bird 
Atlas,  we  found  breeding  evidence  for  1 57  species  of  birds. 
For  143  of  these  we  established  confirmed  breeding  evi- 


dence. Of  the  remaining  14  species,  9  species— Blue- 
winged  Teal,  Rhinoceros  Auklet,  Tufted  Puffin,  Northern 
Pygmy-Owl,  Burrowing  Owl,  Vaux's  Swift,  California 
Thrasher,  Yellow-breasted  Chat,  and  Red  Crossbill— still 
lack  confirmed  breeding  evidence.  Currendy,  all  of  these 
species  except  Burrowing  Owl,  Yellow-breasted  Chat,  and 
Red  Crossbill  probably  breed  in  the  county  annually  in 
small  numbers. 

Of  the  14  species  that  remained  unconfirmed  during 
die  years  of  adas  field  work,  5  species  were  confirmed 
breeding  in  the  county  at  other  times:  Northern  Shoveler 
was  confirmed  subsequent  to  atlas  work,  bodi  Common 
Poorwill  and  Rock  Wren  prior  to  adas  work,  and  both 
MacGillivray's  Warbler  and  Black-chinned  Sparrow  both 
before  and  after  the  atlas  period.  An  additional  6  species 
not  recorded  during  adas  field  work  have  been  confirmed 
as  breeders  in  the  county:  Peregrine  Falcon  both  prior  to 
and  after  adas  work;  American  Avocet  after  adas  work; 
Spotted  Sandpiper  both  prior  to  and  after  adas  work;  and 
Greater  Roadrunner,  Cassin's  Kingbird,  and  American 
Dipper  all  prior  to  atlas  work.  Of  these,  Greater  Roadrun- 
ner has  been  entirely  extirpated  from  the  county,  and 
American  Dipper  appears  to  have  been  extirpated  here  as 
a  breeder.  In  recent  years,  Dippers  have  been  recorded  in 
the  county  only  as  irregular  migrants  or  winter  visitants;  it 
is  possible  they  may  still  breed  here  irregularly  in  high 
runoff  years,  though  recent  summer  records  are  lacking. 

In  all,  in  historical  times  Marin  County  has  supported 
at  least  1 63  species  of  breeding  birds— 1 54  based  on 
confirmed  evidence  and  9  based  on  suspected  evidence. 
Including  naturally  irregular/irruptive  breeders  such  as 
Long-eared  Owl,  Black-chinned  Sparrow,  Red  Crossbill, 
and  Lawrence's  Goldfinch,  but  excluding  extirpated  breed- 
ing species  (Greater  Roadrunner  and  American  Dipper), 
extralimital  breeders  (Say's  Phoebe,  Cassin's  Kingbird, 
and  Northern  Parula)  or  otherwise  very  infrequent  breed- 
ers (Double-crested  Cormorant,  American  Avocet,  Spotted 
Sandpiper,  Burrowing  Owl,  Short-eared  Owl,  and  Yellow- 
breasted  Chat),  the  county's  breeding  avifauna  currendy 
numbers  about  152  more  or  less  regularly  breeding  spe- 
cies. 

A  number  of  additional  species  not  mentioned  above 
may  also   have   bred   here   historically  and   either  went 

51 


Patterns  of  Species  Richness 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Patterns  of  Species  Richness 


undetected  or  were  inadequately  documented;  some  of 
these  may  once  have  been  part  of  the  regular  breeding 
avifauna  (see  Species  of  Unclear  Breeding  Status  or  Poten- 
tial Breeders  pp.  429-434)-  Certain  other  species  breeding 
elsewhere  in  die  San  Francisco  Bay  Area  are  the  most  likely 
potential  future  colonizers  to  Marin  County.  One  of  the 
most  likely  species  to  soon  become  established  is  Wild 
Turkey  which  was  introduced  to  die  county  in  1988. 

Based  on  the  number  of  blocks  in  which  they  were 
recorded,  20  of  the  157  breeding  species  during  the  adas 
period  were  classified  as  nearly  ubiquitous  in  their  distri- 
bution here,  15  as  very  widespread,  17  as  widespread,  10 
as  fairly  widespread,  9  as  somewhat  local,  23  as  local,  and 
63  as  very  local  (Table  6).  A  ranking  of  the  157  species  by 
their  Overall  Population  Index  yielded  5  species  with 
extremely  large  populations,  15  with  very  large  popula- 
tions, 12  with  large  populations,  18  with  fairly  large  popu- 
lations, 6  with  moderate-sized  populations,  19  with  small 
populations,  and  82  with  very  small  populations  (Table  7). 
The  two  methods  of  ranking  species— by  distribution  and 
a  combination  of  distribution  and  abundance— each 
showed  a  disproportionate  number  of  species  with  rela- 
tively restricted  distributions  and  relatively  small  popula- 
tions. These  patterns  are  typical  of  many  avifaunal 
assemblages  that  have  been  studied  (e.g.,  Wiens  1989). 

Countywide,  the  number  of  breeding  species  recorded 
per  block  ranged  from  22  to  84  and  averaged  56.7  (SE  =  ± 
0.79)  (Figure  10).  Sixty-two  percent  of  the  blocks  had 
between  50  to  70  species  each.  The  areas  of  the  county  that 
tended  to  have  the  highest  breeding  species  richness  per 
block  were  the  south-central  interior  ridges  (Figure  11)  with 
a  mix  of  hardwood,  conifer,  scrub,  and  grassland  habitats. 
On  the  whole,  blocks  in  the  grassland-dominated  regions 
of  outer  Point  Reyes  and  around  Tomales  supported  the 
lowest  species  richness.  Habitat  diversity  was  not  meas- 
ured, but  it  undoubtedly  would  have  shown  a  positive 
relationship  with  species  richness  per  block. 

Recognizing  that  comparisons  of  species  richness 
between  areas  of  different  size,  or  where  data  were  collected 
differendy,  poses  some  problems  (Wiens  1989),  it  is  still 
instructive  to  compare  the  size  of  Marin's  breeding  avi- 
fauna with  that  of  other  regions.  Preliminary  comparisons 
show  that  the  species  richness  of  the  entire  Marin  County 
breeding  avifauna  is  roughly  similar  to  that  of  most  other 
counties  in  coastal  northern  California  (Shuford  in  prep.). 
Comparisons  also  show  that  the  breeding  avifauna  of 
Marin  County  (latitude  about  38°,  588  square  miles)  is 
greater  than  that  of  interior  areas  at  roughly  the  same 
latitude  of  similar  or  even  much  greater  size.  At  about 
38°45'  latitude,  Yolo  County  encompasses  1034  square 
miles,  ranges  from  about  100  to  3000  feet  in  elevation,  and 
extends  from  the  east  slope  of  the  Interior  Coast  Range 
across  the  west  side  of  the  Sacramento  Valley  floor.  Yolo 
County  has  a  breeding  avifauna  of  about  133  species 

52 


80-1 


60* 


o 
o 


E 
in 

CVJ 


40* 


20- 


"  I     I    I    I    I    I     I 

20    30    40    50    60    70    80    90 

No.    species/block 

Figure  10.  Frequency  distribution  of  the  number  of  species 
found  per  atlas  block. 

(Gaines  &.  Beedy  1987).  At  about  37°45'  latitude,  the  west 
slope  of  the  Yosemite  region  is  roughly  the  size  of  Yolo 
County,  ranges  from  about  1 200  to  over  1 3,000  feet  on  the 
west  slope  of  the  Sierra  Nevada,  and  currendy  supports 
about  141  species  of  breeding  birds  (Gaines  1988).  The 
east  slope  of  the  Yosemite  region,  roughly  equal  in  size  to 
the  west  slope,  ranges  from  the  Sierran  crest  down  the  east 
slope  to  about  6400  feet  in  the  Great  Basin  and  currendy 
sustains  about  149  species  of  breeding  birds.  The  com- 
bined Yosemite  region  spanning  the  west  and  east  slopes 
harbors  about  187  species  of  breeding  birds.  It  is  not 
surprising  that  the  greater  Yosemite  region  supports  a 
more  numerous  breeding  avifauna  than  Marin  County, 
considering  that  the  former  is  much  larger,  ranges  over 
almost  12,000  feet  in  elevation,  and  straddles  two  of 
California  s  major  biogeographical  regions,  the  Sierra 
Nevada  and  the  Great  Basin.  Further  adas  work  in  Califor- 
nia will  provide  needed  insight  into  patterns  of  breeding 
bird  species  richness  in  this  diverse  state. 

The  number  of  breeding  species  in  Marin  County's 
avifauna  compares  favorably  even  with  a  few  states  and 
provinces  in  North  America:  Kentucky  (164  species), 
Arkansas  (157),  Delaware  (157),  Mississippi  (153),  Prince 
Edward  Island  (146),  and  Hawaii  (131)  (DeSante  &  Pyle 
1986).  Clearly,  Marin  County  supports  a  large  avifauna  for 
its  size.  This  can  be  attributed  to  the  county's  diverse  array 


RESULTS  AND  DISCUSSION 

Table  6.  Relative  distribution  ranking  of  all  species  recorded  on  the  Marin  County  Breeding  Bird  Adas.  Species  are  listed 
in  descending  order,  by  the  number  and  percentage  of  total  blocks  (No.  -  %)  in  which  they  were  detected,  with  respect  to 
the  seven  categories  of  the  Relative  Distribution  Index  (RDI);  see  Content  of  Species  of  Accounts  (p.  75). 


NEARLY  UBIQUITOUS 

Scrub  Jay  (214-96.8) 
Turkey  Vulture  (213-96.4) 
Red-tailed  Hawk  (213-96.4) 
Mourning  Dove  (212-95.9) 
California  Quail  (208-94.1) 
Bushtit  (207-93.7) 
House  Finch  (207-93.7) 
Bewick's  Wren  (205-92.8) 
Barn  Swallow  (203-91.8) 
Cliff  Swallow  (202-91.4) 
California  Towhee  (201-91.0) 
Allen's  Hummingbird  (198-89.6) 
American  Robin  (197-89.1) 
Chestnut-backed  Chickadee  (195-88.2) 
Rufous-sided  Towhee  (195-88.2) 
European  Starling  (194-87.8) 
Brewer's  Blackbird  (193-87.3) 
Song  Sparrow  (192-86.9) 
Orange-crowned  Warbler  (191  -86.4) 
Dark-eyed  Junco  (188-85.1) 

VERY  WIDESPREAD 

Hutton's  Vireo  (184-83.2) 
Wrentit  (182-82.4) 
Violet-green  Swallow  (177-80.1) 
Purple  Finch  (177-80.1) 
Brown-headed  Cowbird  (173-78.3) 
American  Goldfinch  (173-78.3) 
Red-winged  Blackbird  (172-77.8) 
Common  Raven  (170-76.9) 
Western  Bluebird  (170-76.9) 
American  Crow  (169-76.5) 
Black  Phoebe  (167-75.6) 
Warbling  Vireo  (164-74-2) 
Anna's  Hummingbird  (163-73.8) 
Pacific-slope  Flycatcher  (163-73.8) 
Wilson's  Warbler  (161-72.8) 

WIDESPREAD 

Steller'sjay  (154-69.7) 
Pine  Siskin  (151-68.3) 
Ash-throated  Flycatcher  (150-67.9) 
Great  Horned  Owl  (149-67.4) 
Killdeer  (146-66.1) 
Downy  Wood  pecker  (145-65.6) 
Lesser  Goldfinch  (145-65.6) 
House  Sparrow  (144-65.2) 
Northern  Flicker  (143-64.7) 
Swainson's  Thrush  (137-62.0) 
Western  Wood-Pewee  (136-61.5) 
Western  Meadowlark  (135-61.1) 
Tree  Swallow  (132-59.7) 
Plain  Titmouse  (129-58.4) 
Black-headed  Grosbeak  (129-58.4) 
Northern  Oriole  (129-58.4) 
Brown  Creeper  (128-57.9) 


FAIRLY  WIDESPREAD 

Lark  Sparrow  (124-56.1) 
Horned  Lark  (123-55.6) 
American  Kestrel   (122-55.2) 
Band-tailed  Pigeon  (117-52.9) 
Lazuli  Bunting  (115-52.0) 
Savannah  Sparrow  (115-52.0) 
Mallard  (110-49.8) 
N.  Rough-winged  Swallow  (104-47.0) 
Olive-sided  Flycatcher  (96-43.4) 
Grasshopper  Sparrow  (96-43.4) 

SOMEWHAT  LOCAL 

Chipping  Sparrow  (93-42.1) 
Rock  Dove  (90-40.7) 
Acorn  Woodpecker  (86-38.9) 
White-crowned  Sparrow  (85-38.5) 
Hairy  Woodpecker  (82-37.1) 
Western  Kingbird  (74-33.5) 
Belted  Kingfisher  (73-33.0) 
Nuttall's  Woodpecker  (72-32.6) 
Northern  Mockingbird  (67-30.3) 

LOCAL 

White-breasted  Nuthatch  (59-26.7) 
American  Coot  (58-26.2) 
Red-shouldered  Hawk  (56-25.3) 
Winter  Wren  (56-25.3) 
Cinnamon  Teal  (52-23.5) 
Rufous-crowned  Sparrow  (52-23.5) 
Osprey  (49-22.2) 
Northern  Harrier  (48-21.7) 
Hermit  Thrush  (48-21.7) 
Western  Screech-Owl   (42-19.0) 
White-throated  Swift  (42-19.0) 
Golden-crowned  Kinglet  (42-19.0) 
Pygmy  Nuthatch  (40-18.1) 
Loggerhead  Shrike  (40-18.1) 
Red-breasted  Nuthatch  (39-17.6) 
Golden  Eagle  (38-17.2) 
Common  Yellowthroat  (38-17.2) 
Cooper's  Hawk  (36-16.3) 
Pied-billed  Grebe  (34-15.4) 
Black-shouldered  Kite  (34-15.4) 
Barn  Owl  (34-15.4) 
Marsh  Wren  (34-15.4) 
Northern  Saw-whet  Owl  (32-14.5) 

VERY  LOCAL 

House  Wren  (29-13.1) 
Pileated  Woodpecker  (28-12.7) 
Green-backed  Heron   (24-10.8) 
Purple  Martin  (24-10.8) 
Black-throated  Gray  Warbler  (23-10.4) 
Yellow  Warbler  (22-10.0) 
Ruddy  Duck  (20-9.0) 
Yellow-rumped  Warbler  (19-8.6) 


Virginia  Rail  (17-7.7) 
Spotted  Owl  (16-7.2) 
Blue-gray  Gnatcatcher  (16-7.2) 
Rock  Wren  (15-6.8) 
California  Thrasher  (15-6.8) 
Tricolored  Blackbird  (15-6.8) 
Hooded  Oriole  (15-6.8) 
Northern  Pintail  (14-6.3) 
Western  Gull  (14-6.3) 
Great  Blue  Heron  (12-5.4) 
Vaux's  Swift  (12-5.4) 
Western  Tanager  (12-5.4) 
Red  Crossbill  (12-5.4) 
Pelagic  Cormorant  (11-5.0) 
Snowy  Plover  (11-5.0) 
Hermit  Warbler  (11-5.0) 
Gadwall  (10-4-5) 
Sora  (10-4.5) 

Black  Oystercatcher  (10-4-5) 
Pigeon  Guillemot  (10-4-5) 
Blue-winged  Teal  (9-4.1) 
Ring-necked  Pheasant  (9-4.1) 
Black-necked  Stilt  (9-4.1) 
Solitary  Vireo  (8-3.6) 
MacGillivray's  Warbler  (8-3.6) 
American  Bittern   (7-3.2) 
Sharp-shinned  Hawk  (7-3.2) 
Black  Rail  (6-2.7) 
Great  Egret  (5-2.3) 
Wood  Duck  (5-2.3) 
Common  Merganser  (5-2.3) 
Clapper  Rail  (5-2.3) 
Red-breasted  Sapsucker  (5-2.3) 
Black-chinned  Sparrow  (5-2.3) 
Brandt's  Cormorant  (4-1-8) 
Northern  Shoveler  (4-1-8) 
Sage  Sparrow  (4-1.8) 
Lawrence's  Goldfinch  (4-1.8) 
Common  Murre  (3-1.4) 
Common  Moorhen   (2-0.9) 
Northern  Pygmy-Owl  (2-0.9) 
Burrowing  Owl  (2-0.9) 
Long-eared  Owl  (2-0.9) 
Common  Poorwill  (2-0.9) 
Yellow-breasted  Chat  (2-0.9) 
Ashy  Storm-Petrel  (1-0.4) 
Double-crested  Cormorant  (1-0.4) 
Snowy  Egret  (1  -0.4) 
Black-crowned  Night-Heron   (1-0.4) 
Canada  Goose   (1-0.4) 
Rhinoceros  Auklet  (1  -0.4) 
Tufted  Puffin  (1  -0.4) 
Short-eared  Owl  (1-0.4) 
Say's  Phoebe  (1  -0.4) 
Northern  Parula  (1-0.4) 


53 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 

Table  7.  Abundance  ranking  of  all  species  recorded  on  the  Marin  County  Breeding  Bird  Adas.  Species  are  listed  in 
descending  order  in  seven  categories  with  respect  to  their  Overall  Population  Index  (OPI);  see  Content  of  Species  Accounts 
(p.  75). 


EXTREMELY  LARGE  POPULATION 

Cliff  Swallow  (1010) 
Warbling  Vireo  (984) 
Song  Sparrow  (960) 
Orange-crowned  Warbler  (955) 
Dark-eyed  Junco  (940) 

VERY  LARGE  POPULATION 

Red-winged  Blackbird  (860) 
Scrub  Jay  (856) 
Mourning  Dove  (848) 
House  Finch  (828) 
Bewick's  Wren  (820) 
Barn  Swallow  (812) 
Wilson's  Warbler  (805) 
California  Towhee  (804) 
Allen's  Hummingbird  (792) 
American  Robin  (788) 
Chestnut-backed  Chickadee  (780) 
Rufous-sided  Towhee   (780) 
European  Starling  (776) 
Brewer's  Blackbird  (772) 
Wrentit  (728) 

LARGE  POPULATION 

Violet-green  Swallow  (708) 
Purple  Finch  (708) 
American  Goldfinch  (692) 
Swainson's  Thrush   (685) 
Pacific-slope  Flycatcher  (652) 
Turkey  Vulture  (639) 
Red-tailed  Hawk  (639) 
California  Quail  (624) 
Bushtit  (621) 
Pine  Siskin  (604) 
Ash-throated  Flycatcher  (600) 
Lesser  Goldfinch  (580) 

FAIRLY  LARGE  POPULATION 

House  Sparrow  (576) 
Savannah  Sparrow  (575) 
Hutton's  Vireo  (552) 
Western  Meadowlark  (540) 
Brown-headed  Cowbird   (519) 
Plain  Titmouse  (516) 
Black-headed  Grosbeak  (516) 
Northern  Oriole  (516) 
Brown  Creeper  (512) 
Western  Bluebird  (510) 
American  Crow  (507) 
Black  Phoebe  (501) 
Lark  Sparrow  (496) 
Horned  Lark  (492) 
Anna's  Hummingbird   (489) 
Steller's  Jay  (462) 
Great  Horned  Owl  (447) 
Killdeer  (438) 


MODERATE-SIZED  POPULATION 

White-crowned  Sparrow   (425) 
Western  Wood-Pewee   (408) 
Band-tailed  Pigeon   (351) 
Lazuli  Bunting  (345) 
Common  Raven   (340) 
Mallard  (330) 

SMALL  POPULATION 

Downy  Woodpecker   (290) 
Olive-sided  Flycatcher  (288) 
Grasshopper  Sparrow   (288) 
Northern   Flicker  (286) 
Chipping  Sparrow  (279) 
Rock  Dove  (270) 
Tree  Swallow  (264) 
Acom  Woodpecker  (258) 
American  Kestrel   (244) 
Winter  Wren  (224) 
Western  Kingbird  (222) 
Nuttall's  Woodpecker  (216) 
N.  Rough-winged  Swallow  (208) 
Northern  Mockingbird   (201) 
White-breasted  Nuthatch  (177) 
American  Coot  (174) 
Hairy  Woodpecker  (164) 
Cinnamon  Teal   (156) 
Common  Yellowthroat  (152) 

VERY  SMALL  POPULATION 

Belted  Kingfisher  (146) 
Hermit  Thrush   (144) 
Marsh  Wren  (136) 
Western  Screech-Owl  (126) 
Pygmy  Nuthatch  (120) 
Red-shouldered  Hawk  (112) 
Rufous-crowned  Sparrow  (104) 
Osprey  (98) 
Northern  Harrier  (96) 
Black-throated  Gray  Warbler  (92) 
White-throated  Swift   (84) 
Golden-crowned  Kinglet  (84) 
Loggerhead  Shrike  (80) 
Red-breasted  Nuthatch  (78) 
Pied-billed  Grebe  (68) 
Black-shouldered  Kite  (68) 
Barn  Owl  (68) 
Yellow  Warbler  (66) 
Northern  Saw-whet  Owl   (64) 
House  Wren  (58) 
Yellow-rumped  Warbler  (57) 
Western  Gull  (56) 
Pileated  Woodpecker  (56) 
Pelagic  Cormorant  (55) 
Green-backed  Heron   (48) 
Purple  Martin    (48) 
Blue-gray  Gnatcatcher  (48) 


Tricolored  Blackbird  (45) 
Hooded  Oriole  (45) 
Pigeon  Guillemot  (40) 
Golden  Eagle  (38) 
Great  Blue  Heron   (36) 
Cooper's  Hawk  (36) 
Virginia  Rail   (34) 
Snowy  Plover  (33) 
Spotted  Owl  (32) 
Rock  Wren  (30) 
California  Thrasher  (30) 
Brandt's  Cormorant  (28) 
Northern  Pintail   (28) 
Black-necked  Stilt  (27) 
Great  Egret  (25) 
Western  Tanager  (24) 
Hermit  Warbler  (22) 
Common  Murre  (21) 
Ruddy  Duck  (20) 
Black  Oystercatcher  (20) 
Ring-necked  Pheasant  (18) 
Black  Rail  (18) 
MacGillivray's  Warbler  (16) 
Solitary  Vireo  (16) 
Clapper  Rail  (15) 
Red  Crossbill   (12) 
Vaux's  Swift  (1 2) 
Gadwall  (10) 
Sora  (10) 

Blue-winged  Teal  (9) 
Sage  Sparrow  (8) 
American  Bittern   (7) 
Snowy  Egret   (7) 
Sharp-shinned  Hawk  (7) 
Black-crowned  Night-Heron   (6) 
Common  Poorwill   (6) 
Wood  Duck  (5) 
Common  Merganser  (5) 
Red-breasted  Sapsucker  (5) 
Black-chinned  Sparrow  (5) 
Northern  Shoveler  (4) 
Lawrence's  Goldfinch  (4) 
Ashy  Storm-Petrel  (3) 
Common  Moorhen   (2) 
Rhinoceros  Auklet  (2) 
Tufted  Puffin  (2) 
Northern  Pygmy-Owl   (2) 
Long-eared  Owl  (2) 
Yellow-breasted  Chat  (2) 
Double-crested  Cormorant  (1) 
Canada  Goose  (1) 
Burrowing  Owl  (1) 
Short-eared  Owl   (1) 
Say's  Phoebe   (1) 
Northern  Parula  (1) 


54 


Patterns  of  Species  Richness 


RESULTS  AND  DISCUSSION 


Distributional  Highlights 


SPECIES      RICHNESS 


Number     of 
Species  per  Block 


73-84 


48-59 


Figure  1 1.    Map  of  countywide  patterns  of  species  richness  of  breeding  birds. 


of  habitats,  resulting  from  varied  topography  and  the  sharp 
moisture  and  temperature  gradients  over  the  short  distance 
from  the  cool,  moist  coast  to  the  hotter,  drier  interior. 

Distributional  Highlights  of  Atlas  Work 

The  adas  field  work  documented  distribution  patterns  for 
a  number  of  Marin  County's  breeding  species  diat  prob- 
ably would  not  have  been  predicted  beforehand.  Foremost 
among  these  was  the  distribution  pattern  here  of  the 
Grasshopper  Sparrow.  McCaskie  et  al.  (1979)  considered 
the  Grasshopper  Sparrow  an  uncommon  to  rare  breeding 
species  in  northern  California  as  a  whole,  and  in  preadas 
days  that  classification  seemed  to  fit  Marin  County  as  well. 
Thorough  coverage  of  our  previously  litde-birded  grass- 
lands revealed  Grasshopper  Sparrows  breeding  in  over 
40%  of  ail  atlas  blocks  and  the  vast  majority  of  blocks  near 
the  coast  with  extensive  grassland  (adas  map  and  Figure  5). 
The  concentration  of  breeding  Grasshopper  Sparrows  in 
the  moister,  less  disturbed  grasslands  toward  the  immedi- 
ate coast  matched  the  pattern  noted  along  the  San  Mateo 
County  coast  in  the  1960s  and  1970s  (D.F.  DeSante  pers. 
comm.);  in  contrast,  Sibley  (1952)  had  reported  most 
nesting  records  in  the  soudi  San  Francisco  Bay  region  were 
from  the  Inner  Coast  Range,  20  to  25  miles  from  the  coast. 
Before  the  atlas  period,  the  Cooper's  Hawk  was  a  species 


very  rarely  reported  in  Marin  County  in  the  breeding 
season,  but  we  now  know  it  is  a  secretive  but  regular 
breeder  here  in  broadleaved  mixed  evergreen  forests. 

Of  course  a  number  of  rare  or  newly  established  breed- 
ers were  documented  nesting  in  the  county  for  the  first 
time  during  the  adas  years.  Among  others,  these  included 
American  Bittern,  Common  Merganser,  Sharp-shinned 
Hawk,  Black  Rail,  Black-necked  Stilt,  Short-eared  Owl, 
Say's  Phoebe,  and  Northern  Parula.  The  first  and  subse- 
quent breeding  records  of  Red-breasted  Sapsucker  in  the 
county  documented  the  existence  of  a  disjunct  breeding 
population  here  (Shuford  1986).  The  adas  also  provided 
documentation  of  the  distribution  of  several  species  that, 
direcdy  or  indirecdy  as  a  result  of  activities  of  an  expanding 
human  population,  have  become  well  established  here  in 
appropriate  habitat  in  the  last  few  decades.  These  include 
Northern  Mockingbird,  European  Starling,  Brown-headed 
Cowbird,  and  Hooded  Oriole.  The  reader  is  encouraged 
to  comb  the  species  accounts  for  other  noteworthy  breed- 
ing records  or  distribution  patterns  uncovered  by  the  adas 
work. 

The  previously  little  surveyed  region  of  the  county 
around  Novato  proved  to  support  radier  widespread  breed- 
ing populations  of  species  characteristic  of  die  Inner  Coast 
Range,  such  as  Nuttall's  Woodpecker,  Western  Kingbird, 
and  Northern  Oriole,  and  a  restricted  population  of  a 
formerly  unknown  breeder  in  the  county— Blue-gray  Gnat- 


55 


Distributional  F/igKfigKts 


MARIN  COUNTY  BREEDING  BIRD  ATLAS  Composition  of  Breeding  Avifauna 


catcher.  That  the  Novato  area  also  supported  populations 
of  such  species  as  Olive-sided  Flycatcher,  Pacific-slope  Ely- 
catcher,  Steller's  Jay,  Chestnut-backed  Chickadee,  Brown 
Creeper,  Wilson's  Warbler,  and  Purple  Finch  indicated 
that  all  of  die  county  is  tempered  to  some  degree  by  die 
cool  and  moist  coastal  climate.  Although  hinted  at  by 
previous  work  (Orr  1937,  Miller  1951),  the  slopes  of 
Mount  Tamalpais  and  some  surrounding  ridges  proved  to 
host  the  county's  only  or  main  breeding  populations  of 
Solitary  Vireo,  Yellow-rumped  Warbler,  Black-throated 
Gray  Warbler,  Hermit  Warbler,  and  Western  Tanager. 
The  chaparral  on  Carson  Ridge  proved  to  be  an  important 
habitat  in  the  county  for  Common  Poorwill,  California 
Thrasher,  Rufous-crowned  Sparrow,  Sage  Sparrow,  and, 
irregularly,  Black-chinned  Sparrow.  A  number  of 
waterbirds  (ducks,  rails,  and  shorebirds)  were  added  to  die 
county's  breeding  list,  but  the  restricted  breeding  distribu- 
tion of  most  of  them  documents  the  limited  extent  of 
freshwater,  brackish,  and  saline  wedands  in  the  county. 

A  number  of  other  studies  conducted  concurrendy  with 
or  subsequendy  to  the  adas  project  have  provided  valuable 
data  for  the  county  on  the  distribution  and  abundance  of 
breeding  seabirds  (Sowls  et  al.  1980,  Carter  et  al.  1990), 
herons  and  egrets  (Pratt  1983,  p.  103  this  volume),  Black 
Rails  (Evens  et  al.  1989),  Snowy  Plovers  (Page  6k  Stenzel 
1981),  Ospreys  (Evens  1989),  and  Common  Yellowdiroats 
(Hobson  et  al.  1986).  Quantitative  data  on  an  array  of 
Marin's  breeding  birds  has  been  contributed  by  Spring 
Bird  Counts,  Breeding  Bird  Plots,  and  Breeding  Bird 
Surveys  (Appendixes  A-C). 

Composition  of  the  Breeding  Avifauna 

The  163  species  of  Marin  County's  breeding  avifauna 
represent  43  families  of  birds.  Of  these,  41  are  aquatic 
species  (including  Osprey,  Belted  Kingfisher,  and  Ameri- 


can Dipper),  and  122  are  landbirds.  All  of  the  waterbirds 
can  be  found  in  Marin  County  year  round,  although  22 
species  have  substantially  greater  populations  in  winter 
and  7  species  have  substantially  greater  populations  in 
summer  (Table  8).  Of  the  landbirds,  30%  (37)  are  summer 
residents  (breeding  migrants)  and  70%  (85)  are  year-round 
residents,  although  at  least  23  of  these  are  generally  more 
numerous  in  winter  (Table  9).  Of  1  54  wintering  landbird 
species  recorded  for  Marin  County  (Shuford  1982),  67% 
(103)  are  year-round  residents  (including  15  species  of 
lingering  summer  residents)  and  33%  (51)  are  wintering 
migrants  (including  lingering  individuals  of  13  species  of 
typically  passage  migrants).  These  patterns  of  a  relatively 
high  percentage  of  resident  species  and  a  moderate  percent- 
age of  summer  and  winter  resident  migrants  are  typical  of 
the  central  and  southern  coast  and  foothill  regions  of 
California  (Tangren  1977).  On  the  whole,  these  regions 
tend  to  have  relatively  moderate  temperatures  and  rainfall. 
Areas  in  California  with  a  high  percentage  of  summer 
residents  and  a  low  percentage  of  winter  residents  (e.g., 
high  mountains)  tend  to  have  relatively  low  June  and 
December  temperatures  and  relatively  high  precipitation. 
Areas  with  a  high  percentage  of  winter  residents  and  a  low 
percentage  of  summer  residents  (e.g.,  Central  Valley  and 
southern  deserts)  tend  to  have  relatively  high  June  and 
December  temperatures  and  relatively  low  precipitation. 
Areas  with  a  high  percentage  of  both  summer  and  winter 
residents  (e.g.,  northern  Sacramento  Valley)  tend  to  have 
large  amounts  of  June  rainfall  coupled  with  mild  winters, 
whereas  areas  with  low  percentages  of  both  of  these  com- 
ponents (e.g.,  some  southern  California  mountains)  tend 
to  have  relatively  low  June  precipitation  and  relatively  more 
severe  winters  (Tangren  1977). 

Miller  (1951)  partitioned  California's  breeding  birds 
into  four  avifaunal  groupings— one  of  Boreal  (conifer)  affin- 
ity and   three  of  Austral   (lowland,   nonboreal)   affinity. 


Table  8.    A  list  of  41  species  of  waterbirds  breeding  in  Marin  County,  California,  with  annotations  on  seasonal  status;  all 
species  occur  year  round  to  some  degree.  List  includes  one  extirpated  breeder— American  Dipper. 


Pied-billed  Grebe* 
Ashy  Storm-Petrel 
Double-crested  Cormorant 
Brandt's  Cormorant 
Pelagic  Cormorant 
American  Bittern* 
Great  Blue  Heron 
Great  Egret*  * 
Snowy  Egret 
Green-backed  Heron  *  * 
Black-crowned  Night-Heron 
Canada  Goose* 
Wood  Duck* 
Mallard 


Northern  Pintail* 

Blue-winged  Teal*  * 

Cinnamon  Teal** 

Northern  Shoveler* 

Gadwall* 

Common  Merganser* 

Ruddy  Duck* 

Osprey*  * 

Black  Rail* 

Clapper  Rail 

Virginia  Rail* 

Sora* 

Common  Moorhen* 

American  Coot* 


Snowy  Plover* 
Killdeer* 

Black  Oystercatcher 
Black-necked  Stilt*  * 
American  Avocet* 
Spotted  Sandpiper* 
Western  Gull 
Common  Murre* 
Pigeon  Guillemot*  * 
Rhinoceros  Auklet* 
Tufted  Puffin* 
Belted  Kingfisher 
American  Dipper* 


*     Relatively  more   numerous  in  winter. 
'*     Relatively  more  numerous  in  summer. 


56 


Composition  of  Breeding  Avifauna 


RESULTS  AND  DISCUSSION 


Composition  of  Breeding  Avifauna 


Table  9.  Classification  of  seasonal  status  of  122  species  of  breeding  landbirds  in  Marin  County,  California.  List  includes 
one  extirpated  breeder— Greater  Roadrunner— and  three  extralimital  breeders— Say's  Phoebe,  Cassin's  Kingbird,  and 
Northern  Parula. 


YEAR-ROUND  RESIDENTS 

(85  Species) 

Turkey  Vulture 
Black-shouldered  Kite 
Northern  Harrier* 
Sharp-shinned  Hawk* 
Cooper's  Hawk* 
Red-shouldered  Hawk 
Red-tailed  Hawk* 
Golden  Eagle 
American  Kestrel* 
Peregrine  Falcon* 
Ring-necked  Pheasant 
California  Quail 
Rock  Dove 
Band-tailed  Pigeon* 
Mourning  Dove 
Greater  Roadrunner 
Barn  Owl 

Western  Screech-Owl 
Great  Horned  Owl 
Northern  Pygmy-Owl 
Burrowing  Owl 
Spotted  Owl 
Long-eared  Owl* 
Short-eared  Owl* 
Northern  Saw-whet  Owl 
White-throated  Swift 
Anna's  Hummingbird 
Acom  Woodpecker 
Red-breasted  Sapsucker* 
Nuttall's  Woodpecker 
Downy  Woodpecker 


Hairy  Woodpecker 

Northern  Flicker* 

Pileated  Woodpecker 

Black  Phoebe 

Say's  Phoebe* 

Homed  Lark 

Steller's  Jay 

Scrub  Jay 

American  Crow 

Common  Raven 

Chestnut-backed  Chickadee 

Plain  Titmouse 

Bushtit 

Red-breasted  Nuthatch* 

White-breasted  Nuthatch 

Pygmy  Nuthatch 

Brown  Creeper 

Rock  Wren 

Bewick's  Wren 

Winter  Wren* 

Marsh  Wren 

Golden-crowned  Kinglet* 

Western  Bluebird 

Hermit  Thrush* 

American  Robin* 

Wrentit 

Northern  Mockingbird 

California  Thrasher 

Loggerhead  Shrike 

European  Starling 

Hutton's  Vireo 

Yellow-rumped  Warbler* 


Common  Yellowthroat 
Rufous-sided  Towhee 
California  Towhee 
Rufous-crowned  Sparrow 
Lark  Sparrow 
Sage  Sparrow 
Savannah  Sparrow 
Song  Sparrow 
White-crowned  Sparrow* 
Dark-eyed  Junco* 
Red-winged  Blackbird 
Tricolored  Blackbird* 
Western  Meadowlark* 
Brewer's  Blackbird 
Brown-headed  Cowbird 
Purple  Finch 
House  Finch 
Red  Crossbill* 
Pine  Siskin 
Lesser  Goldfinch 
American  Goldfinch 
House  Sparrow 


SUMMER  RESIDENTS 
(37  Species) 

Common  Poorwill** 
Vaux's  Swift 
Allen's  Hummingbird 
Olive-sided  Flycatcher 
Western  Wood-Pewee 


Pacific-slope  Hycatcher 
Ash-throated  Hycatcher 
Cassin's  Kingbird 
Western  Kingbird 
Purple  Martin 
Tree  Swallow 
Violet-green  Swallow 
N.  Rough-winged  Swallow 
Cliff  Swallow 
Barn  Swallow 
House  Wren 
Blue-gray  Gnatcatcher 
Swainson's  Thrush 
Solitary  Vireo 
Warbling  Vireo 
Orange-crowned  Warbler*  * 
Northern  Parula 
Yellow  Warbler 
Black-throated  Gray  Warbler 
Hermit  Warbler*  * 
MacGillivray's  Warbler 
Wilson's  Warbler 
Yellow-breasted  Chat 
Western  Tanager 
Black-headed  Grosbeak 
Lazuli  Bunting 
Chipping  Sparrow 
Black-chinned  Sparrow 
Grasshopper  Sparrow 
Hooded  Oriole 
Northern  Oriole 
Lawrence's  Goldfinch 


Relatively  more  numerous  in  winter  than  summer. 
Small  numbers  regularly  winter. 


Members  of  these  avifaunas  have  similar  centers  of  distri- 
bution and  often  similar  areas  of  origin  as  species.  The 
four  avifaunas  are  classified  as  follows: 

1.  Boreal  avifauna.  Species  of  northern  derivation  or 
distribution  centered  in  coniferous  forest  areas  and  habi- 
tats. 

2.  Great  Basin  avifauna.  Chiefly  Great  Basin  and  Great 
Plains  species.  This  avifauna  in  California  is  concentrated 
east  of  the  Sierran  crest  in  grassland,  sagebrush,  pifion- 
juniper  woodland,  riparian  woodland,  and  aquatic  and 
semiaquatic  environments. 

3.  Sonoran  avifauna.  Desert-dwelling  species  and  those 
that  range  into  the  state  from  the  Southwest  and  Mexico. 
In  California,  this  avifauna  occupies  mosdy  Colorado  and 
Mohave  desert  habitats  of  desert  scrub,  arid  woodland, 
riparian  woodland,  and  marshes. 


4-  Cali/ornian  avifauna.  Lowland  species  that  are  essen- 
tially confined  to  the  state  or  are  centered  there  and  have 
their  most  continuous  and  dense  populations  in  Califor- 
nia. These  species  are  found  principally  in  oak  woodlands, 
riparian  forest,  chaparral,  and  marshlands  west  of  the 
Cascade-Sierra  axis. 

In  addition,  California's  breeding  avifauna  hosts  a  large 
list  of  unclassified  forms,  chiefly  species  of  marine  environ- 
ments, species  of  general  continental  or  holarctic  distribu- 
tion, and  species  or  races  of  widespread  western  North 
American  distribution. 

Marin  County's  avifauna  is  generally  dominated  by 
Boreal  and  Californian  forms.  Nonetheless,  the  Boreal 
and  the  combined  Austral  elements  are  of  similar  impor- 
tance here  at  the  species  level,  while  Austral  (mosdy  Cali- 
fornian) elements  predominate  at  the  racial  and  combined 


57 


Composition  of  Breeding  Avifauna  MARIN  COUNTY  BREEDING  BIRD  ATI  AS  Composition  of  Breeding  Avifauna 


(species  and  race)  levels  (Table  10).  The  Boreal  avifauna 
provides  Marin  with  27  species  and  13  races;  the  Califor- 
nian  avifauna,  11  species  and  33  races;  the  Great  Basin 
avifauna,  1 1  species  and  3  races;  and  the  Sonoran  avi- 
fauna, 5  species  and  1  race.  Only  four  Great  Basin  species 
(Western  Meadowlark,  Brewer's  Blackbird,  Northern  Ori- 
ole, and  Brown-headed  Cowbird)  and  no  Sonoran  species 
were  classified  as  having  fairly  large  or  larger  populations 
in  the  county  (cf.  Tables  7  and  10),  further  indicating  the 
minor  contribution  of  these  avifaunas  to  that  of  Marin 
County.  The  27  Boreal  species  of  Marin's  avifauna  are 
matched  by  27  species  of  Austral  origin;  the  13  Boreal 
races  compare  to  37  Austral  races. 

Miller  (1951)  stressed  the  greater  importance  in  Califor- 
nia of  the  strong  west-east  moisture  gradient  versus  the 
weaker  north-south  moisture  and  temperature  gradient  in 
influencing  the  differentiation  of  the  state's  Boreal  avi- 
fauna. Similarly,  the  strong  west-east  (coast-interior)  mois- 
ture and  temperature  gradients  in  Marin  County  are  the 
prime  factors  affecting  regional  distribution  of  die  county's 
avifauna,  Boreal  or  non-Boreal.  As  detailed  above,  die 
county  has  two  main  climate  zones:  (1)  a  coastal  zone  of 
relatively  high  winter  rainfall,  cool  summer  temperatures, 
and  high  summer  humidity  from  summer  fog  and  (2)  an 
interior  zone  with  less  rainfall,  higher  summer  tempera- 
tures, and  lower  summer  humidity.  These  climatic  zones 
correspond  to  two  main  biogeographical  regions  of  the 
county  with  differing  avifaunas  (Figure  1 2).  The  coastal 
zone  has  a  dominant  Boreal  avifaunal  element  and  the 
interior  zone  a  dominant  Austral/Californian  element. 
Inverness  Ridge,  Bolinas  Ridge,  Mount  Tamalpais,  and 
several  other  spur  ridges  in  central  Marin  have  similar 
avifaunas  because  they  share  many  species  that  prefer  the 
conifer  forests  or  dense  mixed  evergreen  forests  that  pre- 
dominate in  the  moist  coastal  zone.  Characteristic 
landbirds  of  the  coastal  zone  are  Band-tailed  Pigeon,  Spot- 
ted Owl,  Northern  Saw-whet  Owl,  Hairy  Woodpecker, 
Pileated  Woodpecker,  Olive-sided  Flycatcher,  Red-breasted 
Nuthatch,  Pygmy  Nuthatch,  Winter  Wren,  Golden- 
crowned  Kinglet,  Hermit  Thrush,  Wilson's  Warbler,  and 
Pine  Siskin.  The  upper  slopes  of  Mount  Tamalpais  and 
nearby  ridges  support  another  subset  of  Boreal  species. 
These  areas  have  relatively  high  winter  rainfall  but  are 
sheltered  from  intense  summer  fogs  by  either  an  inversion 
layer  of  warmer  air  at  higher  elevation  or  by  die  barrier  of 
adjacent  coastal  ridges.  In  these  somewhat  drier  areas,  die 
conifer  and  mixed  conifer  forests  are  more  open  and  hence 
support  such  boreal  species  as  Solitary  Vireo,  Yellow- 
rumped  Warbler,  Western  Tanager,  and  a  non-Boreal  but 
allied  species,  Black-throated  Gray  Warbler.  All  of  these 
are  lacking  from  Inverness  Ridge,  except  Yellow-rumped 
Warbler,  which  breeds  there  in  smaller  numbers  than  on 
Mount  Tamalpais. 


58 


Figure  12.    Preliminary  map  of  the  two  main  biogeographical 
regions  of  Marin  County. 

The  avifaunas  of  outer  Point  Reyes  and  the  Tomales 
area  are  also  similar  to  each  other.  Although  lacking  most 
of  the  true  conifer  birds,  their  combined  avifauna  is  pri- 
marily just  a  depauperate  subset  of  that  of  the 
Boreal/coastal  avifaunal  region  of  Marin  County.  Hence, 
the  Point  Reyes/Tomales  area  should  be  included  in  that 
avifaunal  region  rather  than  in  the  Austral/interior  region 
of  Marin.  The  outer  Point  Reyes/Tomales  area  shares  with 
the  conifer-dominated  coastal  areas  species  such  as 
Swainson's  Thrush,  Savannah  Sparrow,  Grasshopper 
Sparrow,  White-crowned  Sparrow,  Pine  Siskin,  and 
American  Goldfinch  diat  are  lacking  or  breed  in  smaller 
numbers  in  the  drier  interior  of  Marin. 

The  other  true  biogeographical  region  of  Marin  County 
is  die  oak  woodland-dominated  area  from  north  of  San 
Rafael  dirough  Novato  to  the  Sonoma  County  line  and 
west  to  around  Hicks  Valley.  This  Austral/interior  region 
of  Marin  County  supports  a  primarily  Austral/Californian 
avifauna.  Characteristic  members  of  the  avifauna  of  this 
region  are  Western  Screech-Owl,  Nuttall's  Woodpecker, 
Plain  Titmouse,  White-breasted  Nuthatch,  House  Wren, 
Blue-gray  Gnatcatcher,  and  Lesser  Goldfinch.  As  noted 
above,  even  in  this  region  the  coastal  influence  is  felt  as 
such  Boreal  species  as  Steller's  Jay,  Chestnut-backed 
Chickadee,  Brown  Creeper,  Wilson's  Warbler,  Dark-eyed 
Junco,  and  Purple  Finch  are  rather  widely  distributed, 
though  more  locally  than  on  the  immediate  coast. 

Miller  (1951)  divided  California  geographically  into  a 
number  of  faunal  districts,  provinces,  and  areas.  He 
included  the  conifer-dominated  areas  of  Marin  County,  as 
well  as  outer  Point  Reyes,  in  the  Central  Coast  District  of 
the  Coastal  Province  of  Boreal  avifaunal  regions  of  the 
state.  He  included  the  rest  of  Marin,  including  the  Tomales 
area,  in  the  San  Francisco  Bay  District  of  the  Californian 
Province  of  Austral  avifaunal  regions  of  the  state.  His 
inclusion  of  die  Tomales  area  in  the  San  Francisco  Bay 
district,  while  at  the  same  time  including  outer  Point  Reyes 
in  the  coastal  Boreal  province,  seems  unwarranted  because 
of  the  number  of  moist  habitat-adapted  species  found  in 


RESULTS  AND  DISCUSSION 
Table  10.   Avifaunal  affinities  of  Marin  County's  breeding  birds,  after  Miller  (1951). 


BOREAL  AVIFAUNA  (27  species) 

Canada  Goose 
Common  Merganser 
Northern  Pygmy-Owl 
Spotted  Owl 
Northern  Saw-whet  Owl 
Red-breasted  Sapsucker 
Olive-sided  Flycatcher 
Steller's  Jay 

Chestnut-backed  Chickadee 
Red-breasted  Nuthatch 


Pygmy  Nuthatch 
Brown  Creeper 
Winter  Wren 
Golden-crowned  Kinglet 
Swainson's  Thrush 
Hermit  Thrush 
Solitary  Vireo 
Yellow-rumped  Warbler 
Hermit  Warbler 
MacGitlivray's  Warbler 


Wilson's  Warbler 
Western  Tanager 
White-crowned  Sparrow 
Dark-eyed  J  unco 
Purple  Finch 
Red  Crossbill 
Pine  Siskin 


1  A  small  population  probably  of  introduced  stock. 


White-throated  Swift 
Say's  Phoebe 
Rock  Wren 
Western  Meadowlark 


AUSTRAL  AVIFAUNA 

Great  Basin  Avifauna  (1 1  species) 
Blue-winged  Teal 
Black-necked  Stilt 
American  Avocet 
Common  Poorwill 

Race  in  Marin  of  Californian  affinity. 
Single  extralimital  breeding  record. 
Race  in  Marin  of  Sonoran  affinity. 

Sonoran  Avifauna  (5  species) 
Greater  Roadrunner 
Cassin's  Kingbird 

Extirpated. 

Single  extralimital  breeding  record. 

Populations  expanded  into  residential  plantings  in  Marin  in  last  few  decades. 

Race  presumed  in  Marin  of  Californian  affinity. 

Race  in  Marin  of  Californian  affinity. 

Calt/ornian  Avifauna  (11  species) 
California  Quail 


Northern  Mockingbird 
Black-chinned  Sparrow 


Anna's  Hummingbird 
Allen's  Hummingbird 
Nuttall's  Woodpecker 

California  Condor  perhaps  formerly  bred  in  Marin. 
Race  in  Marin  of  Boreal  affinity. 


Plain  Titmouse 
Bushtit 
Wrentit 
California  Thrasher 


Brewer's  Blackbird 
Brown-headed  Cowbird 
Northern  (Bullock's)  Oriole 


Hooded  Oriole 


Hutton's  Vireo 
Tricolored  Blackbird 
Lawrence's  Goldfinch 


UNCLASSIFIED  SPECIES  (109  species) 

Pied-billed  Grebe 
Ashy  Storm-Petrel 
Double-crested  Cormorant 
Brandt's  Cormorant 
Pelagic  Cormorant 
American  Bittern 
Great  Blue  Heron 
Great  Egret 
Snowy  Egret 
Green-backed  Heron 
Black-crowned  Night-Heron 


Wood  Duck 
Mallard 

Northern  Pintail 
Cinnamon  Teal 
Northern  Shoveler 
Gadwall 
Ruddy  Duckb 
Turkey  Vulture 
Osprey 

Black-shouldered  Kite 
Northern  Harrier 


Sharp-shinned  Hawk 
Cooper's  Hawk 
Red-shouldered  Hawk1" 
Red-tailed  Hawk 
Golden  Eagle 
American  Kestrel 
Peregrine  Falcon 
Ring-necked  Pheasant 
Black  Rail0 
Clapper  Riil 
Virginia  Rail 


(Continued) 


59 


MARIN  COUNTY  BREEDING  BIRD  ATI^S 


Table  10.  (Continued) 


UNCLASSIFIED  SPECIES  (Continued) 

Sora 

Common  Moorhen 
American  Coot 
Snowy  Plover 
Killdeer 

Black  Oystercatcher 
Spotted  Sandpiper 
Western  Gull 
Common  Murre 
Pigeon  Guillemot 
Rhinoceros  Auklet 
Tufted  Puffin 
Rock  Dove 
Band-tailed  Pigeon 
Mourning  Dove 
Barn  Owl 

Western  Screech-Owl 
Great  Homed  Owl 
Burrowing  Owl 
Long-eared  Owl 
Short-eared  Owla 
Vaux's  Swift 
Belted  Kingfisher 
Acom  Woodpecker 
Downy  Woodpecker 
Hairy  Woodpecker 


Northern  Flicker 
Pileated  Woodpecker 
Western  Wood-Pewee 
Pacific-slope  Flycatcher 
Black  Phoebe 
Ash-throated  Flycatcher 
Western  Kingbird 
Horned  Lark 
Purple  Martin 
Tree  Swallow 
Violet-green  Swallow 
N.  Rough-winged  Swallow 
Cliff  Swallow 
Barn  Swallow 
Scrub  Jay 
American  Crow 
Common  Raven 
White-breasted  Nuthatch 
Bewick's  Wren 
House  Wren 
Marsh  Wren 
American  Dipper 
Blue-gray  Gnatcatcher 
Western  Bluebird 
American  Robin 
Loggerhead  Shrike 


European  Starling 
Warbling  Vireo 
Orange-crowned  Warbler 
Northern  Parula 
Yellow  Warbler0 
Black-dtroated  Gray  Warbler6 
Common  Yellowthroat 
Yellow-breasted  Chat 
Black-headed  Grosbeak 
Lazuli  Bunting 
Rufous-sided  Towhee 
California  Towhee 
Rufous-crowned  Sparrow 
Chipping  Sparrow 
Lark  Sparrow 
Sage  Sparrow 
Savannah  Sparrow 
Grasshopper  Sparrow 
Song  Sparrow 
Red-winged  Blackbird 
House  Finch 
Lesser  Goldfinch 
American  Goldfinch 
House  Sparrow 


Race  in  Marin  of  Boreal  affinity. 
Race  in  Marin  of  Great  Basin  affinity. 
Race  in  Marin  of  Californian  affinity. 
Race  of  general  western  distribution. 
Species  of  general  western  distribution. 


60 


Breeding  Bird  Communities 


RESULTS  AND  DISCUSSION 


Factors  Limiting  Species  Richness 


both  the  outer  Point  Reyes  and  Tomales  areas.  On  the 
other  hand,  a  number  of  species  with  interior  affinities 
occur  in  the  Tomales  area  to  a  limited  or  greater  extent  but 
are  essentially  lacking  on  outer  Point  Reyes.  These  species 
include  Nuttall's  Woodpecker,  Western  Kingbird,  Lark 
Sparrow,  and  Northern  Oriole.  Quantitative  analyses 
using  matching  coefficients  and  cluster  analysis  (Johnson 
&  Cicero  1986,  Taylor  6k  Smith  1986),  or  other  multi- 
variate techniques,  are  needed  to  refine  the  subjectively 
described  regions  of  avifaunal  similarity  in  Marin  County 
and  perhaps  to  elucidate  others. 

Marin  County  Breeding  Bird 
Communities 

Knowledge  of  the  requirements  of  individual  species  as 
described  in  the  species  accounts  probably  provides  the 
most  insight  into  species'  distribution  patterns.  Looking  at 
species'  relationships  may  stimulate  additional  discussion 
of  both  local  and  broad-scale  distribution  patterns.  For  this 
reason,  the  county's  nesting  avifauna  has  been  grouped 
into  22  main  breeding  bird  communities  (Table  11). 
Wiens  (1989)  has  indicated  that  published  definitions  of 
biotic  communities  range  from  discrete,  closely  integrated 
assemblages  of  species  that  possess  properties  paralleling 
those  of  individuals,  to  the  fortuitous  overlapping  of  spe- 
cies responding  independendy  to  environmental  condi- 
tions, to  any  set  of  organisms  living  near  each  other  about 
which  it  is  interesting  to  talk  (Wiens  1989).  The  listing  of 
species  in  Marin's  bird  communities  implies  no  relation- 
ship among  the  species,  or  lack  diereof,  but  simply  diat 
species  in  a  particular  community  are  likely  to  co-occur  in 
similar  habitats  with  a  fair  degree  of  certainty. 

An  important  lesson  learned  from  the  exercise  of  cate- 
gorizing Marin's  birdlife  into  communities  is  that  it  is  a 
difficult  and  not  entirely  satisfying  task.  Marin  County, 
and  California  in  general,  are  characterized  by  a  diverse 
array  of  habitats  arranged  in  a  patchy  mosaic  over  the 
landscape.  Consequendy,  Marin  hosts  many  single  habitat 
specialists,  many  multihabitat  generalists,  and  many  edge- 
adapted  species.  Because  many  species  may  use  several 
habitats,  linger  on  the  edge  of  two  or  more,  or  fall  any- 
where along  the  continuum  among  these  strategies,  they 
are  difficult  to  categorize  as  to  community  affiliations. 
Hence,  such  species  may  not  be  listed  as  primary  members 
of  any  community,  but  rather  as  secondary  or  tertiary 
members  of  several  communities. 

Most  aquatic  species  of  necessity  use  more  than  one 
habitat  type— one  for  foraging  and  another  for  nest  sites. 
For  these  species  the  foraging  habitat  is  the  community  of 
which  they  are  considered  primary  members.  Among 
landbirds,  raptors  often  use  open  habitats  to  forage  in  and 
nearby  forests  or  cliffs  for  foraging  perches,  shelter  or  roost 
sites,  and  nest  sites.  Such  species  include  Turkey  Vulture, 


Black-shouldered  Kite,  Red-shouldered  Hawk,  Red-tailed 
Hawk,  Golden  Eagle,  American  Kestrel,  Peregrine  Falcon, 
Barn  Owl,  Great  Horned  Owl,  Northern  Pygmy-Owl,  and 
Long-eared  Owl.  Aerial  insectivores  such  as  swifts  and 
swallows  forage  almost  exclusively  on  the  wing  but  must 
come  to  earth  to  nest.  Among  Marin's  landbirds  it  is 
possible  to  list  quite  a  number  of  strongly  edge-adapted 
species  or  multihabitat  generalists.  These  include  Califor- 
nia Quail,  Mourning  Dove,  Common  Poorwill,  Anna's 
and  Allen's  hummingbirds,  Northern  Flicker,  Black 
Phoebe,  Western  Kingbird,  Scrub  Jay,  American  Crow, 
Common  Raven,  Bushtit,  Western  Bluebird,  American 
Robin,  Northern  Mockingbird,  Loggerhead  Shrike,  Euro- 
pean Starling,  Lazuli  Bunting,  California  Towhee,  Rufous- 
crowned  Sparrow,  Lark  Sparrow,  Red-winged  Blackbird, 
Tricolored  Blackbird,  Brewer's  Blackbird,  Brown-headed 
Cowbird,  House  Finch,  Pine  Siskin,  the  three  goldfinch 
species,  and  House  Sparrow.  The  large  number  of  such 
species  and  the  abundance  and  widespread  distribution  of 
many  of  them  attest  to  the  success  of  a  generalist  or 
edge-adapted  lifestyle. 

Factors  Limiting  Species  Richness 
of  the  Avifauna 

A  great  number  of  factors  influence  the  number  of  species 
that  breed  in  a  given  area,  but  several  of  these  are  of 
paramount  importance  (MacArthur  6k  Wilson  1967, 
Wiens  1 989).  The  pool  of  species  available  to  colonize  an 
area  is  a  function  of  the  distance  from  source  populations, 
the  size  of  source  populations,  and  the  dispersal  ability  of 
those  species.  Clearly,  if  populations  of  potential  colonizers 
are  isolated  from  an  area  by  long  distances,  are  small  in 
size,  and  have  poor  dispersal  abilities,  they  are  unlikely  to 
provide  colonizers  or  become  established  if  they  arrive  in 
the  area  in  question.  The  availability  of  suitable  habitat, 
nest  sites,  shelter,  or  odier  resources  also  influences  the 
ability  of  an  area  to  support  colonizers  that  do  reach  the 
area.  Local  extinction  (extirpation)  can  also  reduce  the 
number  of  breeding  species,  whether  by  unpredictable 
chance  events  such  as  volcanic  activity,  forest  fires,  or 
droughts  or  by  competition  with  similar  species  or  from 
predation. 

At  present  the  size  of  the  Marin  County  breeding 
avifauna  seems  limited  largely  by  availability  of  suitable 
breeding  habitats.  Many  species  of  waterbirds  that  have 
bred  elsewhere  in  the  San  Francisco  Bay  Area  and  poten- 
tially could  colonize  Marin  County  (see  Potential  Breeders 
pp.  429-434)  occur  here  on  a  regular  basis  in  winter  or 
during  migratory  periods  (Shuford  et  al.  1989).  Presum- 
ably if  suitable  habitats  were  available  in  the  county,  some 
of  them  would  establish  themselves  as  breeders  here.  On 
die  other  hand,  some  species  may  be  poor  colonizers 
because   of  strong   attachment   to   traditional   breeding 

61 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 

Table  11.  Species  membership  of  twenty-two  Marin  County  breeding  bird  communities.  Primary,  secondary,  and  tertiary 
membership  assigned  by  subjective  assessment  of  species'  relative  abundance  among  habitat  types  and  with  respect  to  other 
members  of  a  particular  community.  Many  additional  species  may  be  found  in  the  Urban/Suburban  Community 
depending  on  the  mix  of  native  and  exotic  vegetation.  Community  use  codes— N  =  nesting,  F  =  foraging,  E  =  use  of  edge 
of  community— may  apply  to  single  species  or  a  whole  community.  Nesting  and  foraging  codes  designate  species  that  use  a 
particular  habitat  for  only  one  of  those  needs;  in  terrestrial  habitats,  all  species  that  lack  N  and  F  codes  satisfy  both  breeding 
and  foraging  needs  in  their  respective  habitats. 

OCEANIC  (PELAGIC)  WATERS  COMMUNITY  (F) 

Primary  Members  Secondary  Members 

Ashy  Storm-Petrel  Western  Gull 

Rhinoceros  Auklet  Common  Murre 

Tufted  Puffin 


NERITIC  (CONTINENTAL  SHELF)  WATERS  COMMUNITY  (F) 
Primary  Members  Common  Murre 

Brandt's  Cormorant  Pigeon  Guillemot 

Pelagic  Cormorant 
Western  Gull 


Ternary  Members 
Rhinoceros  Auklet 
Tufted  Puffin 
Osprey 


ESTUARINE  WATERS  AND  TIDAL  FLAT  COMMUNITY  (F) 

Primary  Members  Secondary  Members 

Great  Blue  Heron  Mallard 

Great  Egret  Northern  Pintail 

Snowy  Egret  Clapper  Rail  (E) 

Black-crowned  Night-Heron  Snowy  Plover 

Osprey  Killdeer  (E) 

Western  Gull  Belted  Kingfisher 

American  Crow  (E) 
Song  Sparrow  (E) 


Tertiary  Members 

Double-crested  Cormorant 
Canada  Goose 
Peregrine  Falcon 
Brewer's  Blackbird  (E) 


COASTAL  SALT  MARSH  COMMUNITY 

Primary  Members 
Mallard 

Northern  Harrier 
Black  Rail 
Clapper  Rail 
Savannah  Sparrow 
Song  Sparrow 


Secondary  Members 
Northern  Pintail 
Cinnamon  Teal 


Tertiary  Members 

Black-necked  Stilt  (N,E) 
Bam  Owl  (F) 
Common  Raven  (F) 


COASTAL  BEACH  AND  DUNE  COMMUNITY 


Primary  Members 
Snowy  Plover 
Western  Gull  (F) 
Common  Raven  (F) 
Horned  Lark 
White-crowned  Sparrow 
House  Finch 
American  Goldfinch 


Secondary  Members 
Northern  Harrier 
Killdeer 
Song  Sparrow 
Brewer's  Blackbird 
Brown-headed  Cowbird 


GRASSLAND  COMMUNITY 

Primary  Members 
Turkey  Vulture  (F) 
Red-tailed  Hawk  (F) 
Mourning  Dove  (F) 
Great  Horned  Owl  (F) 
Western  Kingbird  (F) 


Horned  Lark 
American  Crow  (F) 
Common  Raven  (F) 
Western  Bluebird  (F) 
European  Starling -(F) 
Lirk  Sparrow 


Savannah  Sparrow 
Grasshopper  Sparrow 
Red-winged  Blackbird  (F) 
Western  Meadowlark 
Brewer's  Blackbird  (F) 
Brown-headed  Cowbird  (F) 


(Continued) 


62 


Table  1 1 .  (Continued) 


RESULTS  AND  DISCUSSION 


GRASSLAND  COMMUNITY  (Continued) 
Secondary  Members 

Black-shouldered  Kite  (F) 
Northern  Harrier  (F) 
Golden  Eagle  (F) 
American  Kestrel  (F) 
Rock  Dove  (F) 
Barn  Owl  (F) 
Loggerhead  Shrike  (F) 
Tricolored  Blackbird  (F) 


Tertiary  Members 

California  Quail  (E/F) 
Burrowing  Owl 
Short-eared  Owl 
Black  Phoebe  (E/F) 
Say's  Phoebe  (F) 
Lazuli  Bunting  (E/F) 
California  Towhee  (E/F) 
Rufous-crowned  Sparrow  (E) 


Chipping  Sparrow  (E/F) 
Northern  Oriole  (E/F) 
House  Finch  (E/F) 
Pine  Siskin  (E/F) 
Lesser  Goldfinch  (E/F) 
American  Goldfinch  (E/F) 
Lawrence's  Goldfinch  (E/F) 


NORTHERN  COASTAL  SCRUB  COMMUNITY 


Primary  Members 
California  Quail 
Allen's  Hummingbird 
Scrub  Jay 
Bushtit 

Bewick's  Wren 
Wrentit 

Rufous-sided  Towhee 
Song  Sparrow 
White-crowned  Sparrow 
Brown-headed  Cowbird 
American  Goldfinch 


Secondary  Members 
Great  Horned  Owl  (E) 
Western  Bluebird  (E) 
Swainson's  Thrush 
European  Starling  (F) 
Orange-crowned  Warbler 
Wilson's  Warbler 
California  Towhee  (E) 
Rufous-crowned  Sparrow 
House  Finch  (E) 


Tertiary  Members 
Mourning  Dove  (F) 
Anna's  Hummingbird 
Northern  Flicker  (F) 
American  Robin  (E/F) 
Lazuli  Bunting  (E) 
Black-chinned  Sparrow 
Brewer's  Blackbird  (E) 
Purple  Finch  (E) 
Pine  Siskin  (F) 


FRESHWATER  POND  OR  LAKE  COMMUNITY 

Primary  Members 
Pied-billed  Grebe 
Great  Blue  Heron  (F) 
Mallard  (F) 
Cinnamon  Teal  (F) 
American  Coot 

Secondary  Members 
Great  Egret  (F) 
Snowy  Egret  (F) 
Green-backed  Heron  (F) 
Black-crowned  Night-Heron  (F) 
Wood  Duck  (F) 


Northern  Pintail  (F) 
Gadwall  (F) 
Ruddy  Duck  (F) 
Osprey  (F) 
Virginia  Rail  (E/F) 
Sora  (E/F) 
Killdeer  (E/F) 
Black-necked  Stilt  (F) 
Belted  Kingfisher  (F) 
Black  Phoebe  (E/F) 
Song  Sparrow  (E/F) 
Red-winged  Blackbird  (E/F) 
Brewer's  Blackbird  (E/F) 


Tertiary  Members 
Canada  Goose  (F) 
Blue-winged  Teal  (F) 
Northern  Shoveler  (F) 
Common  Merganser  (F) 
Common  Moorhen  (F) 
American  Avocet  (F) 
Spotted  Sandpiper  (E) 


FRESHWATER  MARSH  COMMUNITY 

Primary  Members 
Northern  Harrier 
Virginia  Rail 
Sora 

Marsh  Wren 
Common  Yellowthroat 
Song  Sparrow 
Red-winged  Blackbird 


Secondary  Members 
Great  Blue  Heron  (F) 
Mallard 

Cinnamon  Teal 
American  Coot 
Black  Phoebe  (E) 
Tricolored  Blackbird 


Tertiary  Members 
American  Bittern 
Black  Rail 
Common  Moorhen 
Short-eared  Owl 


FRESHWATER  STREAM  COMMUNITY  (F) 
Primary  Members 
Great  Blue  Heron 
Belted  Kingfisher 

Secondary  Members 
Green-backed  Heron 


Wood  Duck 
Mallard 

Cinnamon  Teal 
Gadwall 
Killdeer  (E) 
Song  Sparrow  (E) 


Red-winged  Blackbird  (E) 
Brewer's  Blackbird  (E) 

Tertiary  Members 

Common  Merganser 


(Continued,) 

63 


MARIN  COUNTY  BRHLDING  BIRD  ATIAS 


Table  1 1 .  (Continued) 


COASTAL  RIPARIAN  FOREST  COMMUNITY 
Primary  Members 

Red-shouldered  Hawk 
California  Quail  (E) 
Mourning  Dove 
Great  Horned  Owl 
Anna's  Hummingbird 
Allen's  Hummingbird 
Downy  Woodpecker 
Hairy  Woodpecker 
Western  Wood-Pewee 
Pacific-slope  Flycatcher 
Black  Phoebe  (E) 
Tree  Swallow  (N) 
Steller's  Jay 
Scrub  Jay 

Chestnut-backed  Chickadee 
Bushtit 

Bewick's  Wren 
Swainson's  Thrush 
American  Robin 
Wrentit 


European  Starling 
Warbling  Vireo 
Orange-crowned  Warbler 
Yellow  Warbler 
Wilson's  Warbler 
Black-headed  Grosbeak 
Rufous-sided  Towhee 
Song  Sparrow 
Brown-headed  Cowbird 
Purple  Finch 
American  Goldfinch  (E) 

Secondary  Members 
Green-backed  Heron 
Wood  Duck 
Northern  Saw-whet  Owl 
Belted  Kingfisher 
Nunall's  Woodpecker 
Northern  Flicker 
Ash-throated  Flycatcher 
American  Crow  (N) 


Plain  Titmouse 
Winter  Wren 
Western  Bluebird  (E) 
Hutton's  Vireo 
Common  Yellowthroat 
I  .c-i ill  Bunting  (E) 
California  Towhee  (E) 
Red-winged  Blackbird  (E) 
Northern  Oriole 
House  Finch  (E) 
Pine  Siskin 
Lesser  Goldfinch  (E) 

Tertiary  Members 
Cooper's  Hawk 
Red-breasted  Sapsucker 
House  Wren 
MacGillivray's  Warbler 
Yellow-breasted  Chat 


MIXED  EVERGREEN  FOREST  COMMUNITY 

Primary  Members 
Cooper's  Hawk 
Band-tailed  Pigeon 
Great  Horned  Owl 
Northern  Saw-whet  Owl 
Anna's  Hummingbird 
Allen's  Hummingbird 
Downy  Woodpecker 
Hairy  Woodpecker 
Western  Wood-Pewee 
Pacific-slope  Flycatcher 
Ash-throated  Flycatcher 
Steller's  Jay 
Scrub  Jay 

Chestnut-backed  Chickadee 
Bushtit 

Brown  Creeper 
Bewick's  Wren 
Swainson's  Thrush 
American  Robin  (E) 
Hutton's  Vireo 
Warbling  Vireo 
Orange-crowned  Warbler 
Wilson's  Warbler 
Black-headed  Grosbeak 
Dark-eyed  J  unco 
Purple  Finch 


Secondary  Members 

Black-shouldered  Kite  (N,E) 
Red-shouldered  Hawk  (N,E) 
Red-tailed  Hawk  (N,E) 
American  Kestrel  (N,E) 
California  Quail  (E) 
Mourning  Dove  (N,E) 
Western  Screech-Owl 
Spotted  Owl 
Acorn  Woodpecker 
Northern  Flicker  (N,E) 
Olive-sided  Flycatcher 
Violet-green  Swallow  (N) 
Plain  Titmouse 
Red-breasted  Nuthatch 
White-breasted  Nuthatch 
Pygmy  Nuthatch 
Winter  Wren 
Golden-crowned  Kinglet 
Western  Bluebird  (N,E) 
Hermit  Thrush 
Wrentit 

European  Starling  (N) 
Solitary  Vireo 
Yellow-rumped  Warbler 
Black-throated  Gray  Warbler 
Western  Tanager 


Lazuli  Bunting  (E) 
Rufous-sided  Towhee 
California  Towhee  (E) 
Chipping  Sparrow  (N,E) 
Lark  Sparrow  (N,E) 
Song  Sparrow 
Brown-headed  Cowbird  (E) 
House  Finch  (N,E) 
Pine  Siskin 

Tertiary  Members 

Great  Blue  Heron  (N) 
Great  Egret  (N) 
Snowy  Egret  (N) 
Black-crowned  Night-Heron  (N) 
Wood  Duck 
Turkey  Vulture  (N) 
Northern  Pygmy-Owl 
Long-eared  Owl  (N) 
Red-breasted  Sapsucker 
Tree  Swallow  (N) 
American  Crow  (N) 
Common  Raven  (N) 
Northern  Parula 
White-crowned  Sparrow  (E) 
American  Goldfinch  (E) 


(Continued^ 


64 


Table  1 1 .  (Continued) 


RESULTS  AND  DISCUSSION 


BISHOP  PINE  FOREST  COMMUNITY 

Primary  Members 

Northern  Saw-whet  Owl 
Allen's  Hummingbird 
Hairy  Woodpecker 
Pacific-slope  Flycatcher 
Steller's  Jay 

Chestnut-backed  Chickadee 
Pygmy  Nuthatch 
Brown  Creeper 
Bewick's  Wren 
Wrentit 

Wilson's  Warbler 
Rufous-sided  Towhee 
Dark-eyed  Junco 
Purple  Finch 
Pine  Siskin 


Secondary  Members 
Mourning  Dove  (E) 
Spotted  Owl 
Great  Horned  Owl  (E) 
Violet-green  Swallow  (N) 
Bushtit 
Winter  Wren 
Swainson's  Thrush 
European  Starling  (N) 
Hutton's  Vireo 
Song  Sparrow 
White-crowned  Sparrow  (E) 

Tertiary  Members 
Osprey  (N) 
California  Quail  (E) 
Band-tailed  Pigeon 
Anna's  Hummingbird 


Northern  Flicker  (E) 
Pileated  Woodpecker 
Olive-sided  Flycatcher 
Purple  Martin  (N) 
Tree  Swallow  (N) 
Red-breasted  Nuthatch 
Golden-crowned  Kinglet 
Western  Bluebird  (E) 
Hermit  Thrush 
American  Robin  (E) 
Orange-crowned  Warbler 
Yellow-rumped  Warbler 
California  Towhee  (E) 
Chipping  Sparrow 
Brown-headed  Cowbird 
House  Finch  (E) 
Red  Crossbill 
American  Goldfinch  (E) 


COAST  REDWOOD  FOREST  COMMUNITY 

Primary  Members 
Spotted  Owl 
Northern  Saw-whet  Owl 
Allen's  Hummingbird 
Hairy  Woodpecker 
Pileated  Woodpecker 
Pacific-slope  Flycatcher 
Steller's  Jay 

Chestnut-backed  Chickadee 
Red-breasted  Nuthatch 
Brown  Creeper 
Winter  Wren 


Golden-crowned  Kinglet 
Hermit  Thrush 
Wilson's  Warbler 
Dark-eyed  Junco 
Purple  Finch 
Pine  Siskin 

Secondary  Members 
Band-tailed  Pigeon 
Vaux's  Swift  (N) 
Olive-sided  Flycatcher 
American  Robin 


Tertiary  Members 

Great  Blue  Heron  (N) 
Great  Egret  (N) 
Snowy  Egret  (N) 
Turkey  Vulture  (N) 
Osprey  (N) 
Sharp-shinned  Hawk 
Pygmy  Nuthatch 
Hermit  Warbler 
Red  Crossbill 


DOUGLAS  FIR  FOREST  COMMUNITY 
Primary  Members 
Band-tailed  Pigeon 
Spotted  Owl 
Northern  Saw-whet  Owl 
Allen's  Hummingbird 
Hairy  Woodpecker 
Pileated  Woodpecker 
Olive-sided  Flycatcher 
Pacific-slope  Flycatcher 
Steller's  Jay 

Chestnut-backed  Chickadee 
Red-breasted  Nuthatch 
Pygmy  Nuthatch 
Brown  Creeper 
Winter  Wren 
Golden-crowned  Kinglet 
Wilson's  Warbler 


Dark-eyed  Junco 
Purple  Finch 
Pine  Siskin 

Secondary  Members 
Bushtit  (E) 
Hermit  Thrush 
American  Robin 
Wrentit 

European  Starling  (N) 
Yellow-rumped  Warbler 
Lazuli  Bunting  (E) 
Rufous-sided  Towhee 
Chipping  Sparrow  (N,E) 
Song  Sparrow 
Brown-headed  Cowbird  (E) 
Red  Crossbil 


Tertiary  Members 

Great  Blue  Heron  (N) 
Great  Egret  (N) 
Turkey  Vulture  (N) 
Osprey  (N) 
Sharp-shinned  Hawk 
California  Quail  (E) 
Northern  Pygmy-Owl 
Acorn  Woodpecker  (N,E) 
Red-breasted  Sapsucker 
Purple  Martin  (N) 
Bewick's  Wren 
Swainson's  Thrush  (E) 
Orange-crowned  Warbler  (E) 
Northern  Parula 
Hermit  Warbler 
White-crowned  Sparrow  (E) 


(Continued) 


65 


MARIN  COUNTY  BRITDING  BIRD  ATI  AS 


Table  1 1 .  (Continued) 


OAK  WOODLAND  AND  OAK 

Primary  Members 
Red-tailed  Hawk 
Mourning  Dove 
Anna's  Hummingbird 
Western  Screech-Owl 
Great  Horned  Owl 
Acorn  Woodpecker 
Nuttall's  Woodpecker 
Ash-throated  Flycatcher 
Western  Kingbird 
Violet-green  Swallow 
Scrub  Jay 
Plain  Titmouse 
Bushtit 

White-breasted  Nuthatch 
Bewick's  Wren 


SAVANNAH  COMMUNITY 

Western  Bluebird 
European  Starling 
Orange-crowned  Warbler 
Chipping  Sparrow 
Brown-headed  Cowbird 
Northern  Oriole 
Lesser  Goldfinch 

Secondary  Members 
Turkey  Vulture 
Black-shouldered  Kite  (N) 
Red-shouldered  Hawk  (N) 
Golden  Eagle 
American  Kestrel 
California  Quail 
American  Crow  (E) 


House  Wren 
Blue-gray  Gnatcatcher 
I  lutton's  Vireo 
Lazuli  Bunting  (E) 
Rufous-sided  Towhee  (E) 
California  Towhee  (E) 
Lark  Sparrow  (N,E) 
Western  Meadowlark 
House  Finch 

Tertiary  Members 
Long-eared  Owl  (N) 
Lawrence's  Goldfinch 


CHAPARRAL  COMMUNITY 

Primary  Members 

California  Quail  (E) 

Common  Poorwill 

Anna's  Hummingbird 

Scrub  Jay 

Bushtit 

Bewick's  Wren 

Wrentit 

California  Thrasher 

Rufous-sided  Towhee 

Rufous-crowned  Sparrow  (E) 

Sage  Sparrow 


Secondary  Members 
Turkey  Vulture  (E) 
Mourning  Dove  (E) 
Great  Horned  Owl  (E) 
Orange-crowned  Warbler 
Lazuli  Bunting  (E) 
California  Towhee  (E) 
Brown-headed  Cowbird 
Lesser  Goldfinch  (E) 


Tertiary  Members 

Ash-throated  Flycatcher 
Blue-gray  Gnatcatcher  (E) 
Black-chinned  Sparrow 


EUCALYPTUS  GROVE  COMMUNITY 

Primary  Members 
Great  Horned  Owl 
Allen's  Hummingbird 
Olive-sided  Hycatcher 
Chestnut-backed  Chickadee 
Bewick's  Wren 
American  Robin 
Northern  Oriole 
House  Finch 
Pine  Siskin 
American  Goldfinch 

Secondary  Members 

Red-shouldered  Hawk  (N) 
Red-tailed  Hawk  (N) 
Mourning  Dove  (N) 
Downy  Woodpecker 
Northern  Hicker 


Western  Kingbird  (N,E) 
Tree  Swallow  (N) 
Scrub  Jay 

American  Crow  (N) 
Common  Raven  (N) 
Bushtit 

Brown  Creeper 
Western  Bluebird  (N,E) 
Swainson's  Thrush 
European  Starling  (N) 
Lazuli  Bunting  (E) 
California  Towhee 
Song  Sparrow 
Dark-eyed  Junco 
Brown-headed  Cowbird  (E) 
Purple  Finch 
Lesser  Goldfinch 


Tertiary  Members 

Great  Blue  Heron  (N) 
Great  Egret  (N) 
Black-shouldered  Kite  (N) 
California  Quail 
Pacific-slope  Hycatcher 
House  Wren 
Winter  Wren 
Warbling  Vireo 
Chipping  Sparrow 
White-crowned  Sparrow  (E) 


WEEDY  HELD  COMMUNITY 

Primary  Members 
California  Quail 
Mourning  Dove 
European  Starling 
California  Towhee 


66 


Song  Sparrow 
Red-winged  Blackbird 
Brewer's  Blackbird 
Brown-headed  Cowbird 
House  Finch 


Pine  Siskin  (F) 
Lesser  Goldfinch  (F) 
American  Goldfinch 


(Continued,) 


Table  1 1 .  (Continued) 


RESULTS  AND  DISCUSSION 


WEEDY  HELD  COMMUNITY  (Continued) 
Secondary  Members 

Black-shouldered  Kite  (F) 
Northern  Harrier 
Red-tailed  Hawk  (F) 
American  Kestrel  (F) 
Great  Horned  Owl  (F) 
Black  Phoebe  (E/F) 
Bewick's  Wren 
Western  Bluebird  (F) 
Rufous-sided  Towhee 
Western  Meadowlark 
House  Sparrow 


Tertiary  Members 
Mallard  (N) 
Northern  Pintail  (N) 
Cinnamon  Teal  (N) 
Northern  Shoveler  (N) 
Gadwall  (N) 
Ring-necked  Pheasant 
Barn  Owl  (F) 
Northern  Flicker  (F) 
Western  Kingbird  (F) 
Bushrit  (F) 
Loggerhead  Shrike 


Common  Yellowthroat 
Lazuli  Bunting 
Tricolored  Blackbird 


URBAN/SUBURBAN  COMMUNITY 

Primary  Members 
Rock  Dove 
Mourning  Dove 
Anna's  Hummingbird 
Northern  Mockingbird 
European  Starling 


California  Towhee 
Brewer's  Blackbird 
Brown-headed  Cowbird 
House  Finch 
House  Sparrow 


Tertiary  Members 
Hooded  Oriole 


AERIAL  COMMUNITY  (F) 

Primary  Members 

Violet-gTeen  Swallow 
Cliff  Swallow 
Barn  Swallow 


Secondary  Members 
Tree  Swallow 
N.  Rough-winged  Swallow 


Tertiary  Members 
Peregrine  Falcon 
Vaux's  Swift 
White-throated  Swift 
Purple  Martin 


CLIFF,  SLOPE,  BLUFF,  OR  BANK  COMMUNITY  (N) 


Primary  Members 

Brandt's  Cormorant 
Pelagic  Cormorant 
Black  Oystercatcher 
Western  Gull 
Common  Murre 
Pigeon  Guillemot 
Belted  Kingfisher 


Secondary  Members 
White-throated  Swift 
Pacific-slope  Flycatcher 
Black  Phoebe 
N.  Rough-winged  Swallow 
Cliff  Swallow 
Barn  Swallow 
Common  Raven 
Rock  Wren 
Bewick's  Wren 


Tertiary  Members 
Ashy  Storm-Petrel 
Turkey  Vulture 
Peregrine  Falcon 
Rhinoceros  Auklet 
Tufted  Puffin 
Rock  Dove 


67 


Factors  Limiting  Species  Richness 


MARIN  COUNTY  BRFFDING  BIRD  ATI  AS 


Factors  Limiting  Species  Richness 


grounds.  For  example,  Canada  Geese  (apparendy  from 
captive  stock)  have  only  recendy  become  established  as 
breeders  in  the  San  Francisco  Bay  Area  (Lidicker  &  Mc- 
Collum  1979),  including  Marin  County,  although  they 
have  long  wintered  in  the  region  (Grinnell  6k  Wythe  1927, 
Grinnell  &.  Miller  1944). 

Many  species  of  landbirds  that  breed  elsewhere  in 
California  pass  through  Marin  County  as  regular  migrants 
or  strays  (Shuford  1982),  but  the  few  that  have  established 
themselves  in  Marin  in  recent  decades  either  were  formerly 
habitat  limited  or  were  introduced  species  expanding  into 
vacant  niches.  Northern  Mockingbirds  and  Hooded  Ori- 
oles have  both  expanded  their  breeding  ranges  in  Califor- 
nia as  a  whole  during  this  century.  Both  began  to  breed  in 
Marin  County  as  their  statewide  population  numbers 
increased  and  the  residential  plantings  they  favor  in  this 
part  of  their  range  became  available  with  the  expanding 
human  population  (see  accounts).  Brown-headed  Cow- 
birds  also  expanded  into  the  San  Francisco  Bay  Area, 
including  Marin  County,  by  exploiting  habitat  changes 
caused  by  extensive  livestock  grazing  and  other  human 
habitat  modifications.  Introduced  Rock  Doves,  European 
Starlings,  and  House  Sparrows  also  expanded  to  exploit 
unoccupied  niches  (or  were  better  competitors)  in  agricul- 
tural, pastoral,  or  urban/suburban  habitats  made  suitable 
by  human  endeavors. 

Extralimital  breeders  such  as  Cassin's  Kingbird  and 
Say's  Phoebe  have  bred  here  only  once  each,  presumably 
because  of  a  lack  of  suitable  breeding  habitat.  Aldiough  the 
breeding  record  of  Cassin's  Kingbird  is  also  die  only 
record  of  the  species  for  the  county,  the  Say's  Phoebe  is 
fairly  common  here  each  year  in  winter  and  thus  provides 
a  large  pool  of  potential  colonizers.  It  is  unclear  whether 
the  Northern  Parula  is  limited  here  by  a  lack  of  suitable 
habitat  or  by  the  fact  that  few  potential  colonizers  stray 
from  their  eastern  breeding  grounds.  Other  species  with 
small  or  irregular  breeding  populations  in  Marin  such  as 
American  Avocet,  Spotted  Sandpiper,  Burrowing  Owl, 
Short-eared  Owl,  and  Yellow-breasted  Chat  are  probably 
limited  by  suitable  habitat  (e.g.,  lack  of  many  ground 
squirrels  to  provide  burrows  for  Burrowing  Owls);  coloniz- 
ers are  in  short  supply  only  for  die  Chat. 

One  species  that  very  likely  is  absent  as  a  breeder  in 
Marin  County  because  of  its  limited  dispersal  ability  is 
Mountain  Quail.  Mountain  Quail  breed  in  the  outer  Coast 
Range  both  to  the  north  and  south  of  Marin  County 
(Grinnell  &  Miller  1944),  and  seemingly  suitable  habitat 


is  available  on  Mount  Tamalpais  and  elsewhere  in  Marin. 
However,  Mountain  Quail  disperse  on  foot,  and  the  clos- 
est breeding  population  in  Sonoma  County  is  cut  off  from 
Marin  County  by  a  large  stretch  of  unsuitable  grassland 
and  marshland  habitat  along  the  border  of  the  two  coun- 
ties. It  is  not  clear  if  Blue  Grouse,  which  also  breeds  in 
Sonoma  County,  has  not  colonized  Marin  County  because 
of  poor  dispersal  capabilities  or  because  of  unsuitable 
climatic  or  habitat  factors.  Red-breasted  Sapsuckers  for- 
merly were  thought  to  reach  their  breeding  limit  on  the 
California  coast  in  central  Mendocino  County  but  are  now 
known  to  breed  in  small  numbers  in  Sonoma  and  Marin 
counties  (Shuford  1986).  Limited  observer  coverage  of  the 
southern  part  of  the  coastal  breeding  range  suggests  that 
these  small  sapsucker  populations  formerly  may  have  gone 
undetected,  but  then  again  the  species  may  have  colonized 
from  the  regular  wintering  population  in  this  region,  an 
option  not  available  to  Blue  Grouse.  Now  that  it  is  extir- 
pated in  the  county,  the  Greater  Roadrunner  is  as  unlikely 
as  the  Mountain  Quail  to  recolonize  Marin  County.  The 
Roadrunner  appears  to  be  constrained  by  its  limited  dis- 
persal abilities,  the  small  size  of  the  nearest  breeding 
populations,  and  the  inhospitability  of  the  intervening 
habitats  between  Marin  and  source  populations,  rather 
dian  by  lack  of  suitable  breeding  habitats  in  Marin.  The 
American  Dipper,  another  extirpated  breeder  and  cur- 
rendy  an  irregular  winter  visitant  here,  seems  unlikely  to 
recolonize  because  of  habitat  degradation  caused  by  dam- 
ming of  the  one  known  former  breeding  stream. 

The  lack  of  a  breeding  population  of  a  particular  species 
may  also  be  due  to  the  time  lag  between  extirpation  and 
recolonization.  Double-crested  Cormorants  formerly  bred 
on  the  outer  coast  of  Marin  County  and  only  recendy  have 
recolonized  that  area  (see  account),  at  a  time  when  the 
coastal  California  breeding  population  as  a  whole  was 
increasing.  The  potential  pool  of  colonizing  cormorants 
was  large  because  of  the  species'  presence  in  Marin  year 
round,  but  nevertheless  it  took  several  decades  to  become 
reestablished  here  as  a  breeder.  Peregrine  Falcons  formerly 
bred  all  along  the  Marin  County  coasdine  but  were  extir- 
pated when  the  species  population  crashed  in  the  1970s 
from  reproductive  failures  caused  by  pesticide  pollution. 
Peregrines  recolonized  Marin  in  1990.  The  time  lag 
between  extirpation  and  recolonization  may  have  been  a 
function  of  both  a  limited  pool  of  colonizers  and  chance 
factors  that  led  to  reestablishment  of  breeding  populations 
in  odier  counties  before  Marin. 


68 


CONSERVATION  APPLICATIONS 


Come  now,  let  us  make  a  truce  with  tke  children  of  life,  and  share  with  them  the  good  things  which  we  plentifully  enjoy.  There 
is  happiness  enough  for  all;  and  some  of  us  there  are  who  cannot  be  happy  unless  all  are. 

—  William  Leon  Dawson, 
The  Birds  of  California 

The  birds  and  animals,  trees  and  grasses,  rocks,  water  and  wind  are  our  allies.  We  need  to  see  them  with  our  hearts  as  well 
as  our  mind's,  to  let  them  speak  to  us  of  where  we  have  come  and  where  we  are  going,  of  three-and-a-half  billion  years  of  shared 
evolutionary  travel,  of  our  place  on  this  planet. 

—  David  Gaines, 
Birds  of  Yosemite  and  the  East  Slope 


How  to  Use  This  Book  as  a 
Conservation  Tool 

IT  IS  ONE  THING  to  state  that  a  breeding  bird  adas  will  be 
useful  for  conservation  or  management  but  quite 
another  to  articulate  exacdy  how  to  put  it  to  its  best  use. 
Perhaps  it  is  appropriate  to  start  by  stating  what  a  breeding 
bird  adas  will  not  do.  An  adas  will  not  substitute  for 
environmental  impact  statements  and  reports  involving 
studies  of  local  habitat  needs  of  birds  or  potential  human 
impacts  on  birds  at  specific  sites,  particularly  if  local  condi- 
tions have  changed  between  the  time  of  adas  work  and 
these  studies.  Because  an  adas  tries  to  document  the 
distribution,  and  sometimes  abundance,  of  all  species  of 
birds  in  an  area,  it  cannot  be  expected  to  be  as  accurate  as 
similar  studies  that  concentrate  on  single  species  (e.g.,  Page 
&.  Stenzel  1981  for  Snowy  Plovers)  or  small  groups  of 
closely  related  species  of  birds  (e.g.,  Sowls  et  al.  1980  and 
Carter  et  al.  1990  for  seabirds).  An  adas  will,  however,  if 
conducted  and  written  with  care,  serve  as  a  very  important 
reference  tool  to  conservationists,  consultants,  and  manag- 
ers. All  adases  should  first  and  foremost  provide  an  accu- 
rate picture  of  distribution  of  most  bird  species  in  the 
chosen  area  and  thus  should  serve  as  the  primary  reference 
that  defines  which  breeding  species  are  of  restricted  distri- 
bution there.  These  are  the  species  that  should  be  given 
special  consideration  in  any  development,  mitigation,  habi- 
tat enhancement,  or  habitat  acquisition  projects.  Because 
species  of  limited  range  also  often  occur  in  small  numbers, 
it  should  not  be  assumed  that  such  species  were  found 
during  the  adas  years  in  every  atlas  block  in  which  diey 
actually  breed.  Hence,  when  a  habitat  is  direatened  widi 
degradation,  specific  searches  should  be  made  for  relatively 
rare  species  found  in  equivalent  habitats  in  nearby  blocks, 


based  on  the  assumption  that  some  such  species  missed  in 
the  initial  adas  work  may  be  found  if  additional  effort  is 
made. 

The  further  usefulness  of  an  adas  book  will  then  depend 
on  the  types  and  extent  of  additional  information  provided 
to  supplement  the  adas  maps  of  each  breeding  species. 
This  will  of  course  vary  from  adas  to  adas.  Because  the 
present  book  documents  each  species'  current  and  former 
status,  it  lends  a  historical  perspective  to  evaluations  of  the 
need  for  protection  of  species.  For  example,  all  other  things 
being  equal,  greater  consideration  should  be  given  to 
protection  of  a  species  that  has  already  declined  in  num- 
bers, especially  if  it  is  in  trouble  throughout  its  entire  range. 
The  extensive  information  on  habitat,  nesting,  and  food 
requirements  will  not  only  acquaint  the  reader  with  basic 
breeding  needs  of  any  species  but  will  also  direct  them  to 
further,  more  detailed  literature.  Information  on  popula- 
tion threats  will  also  alert  the  reader  to  problems  various 
species  have  faced  in  the  past  or  might  face  in  the  future. 
In  short,  an  adas  book  can  be  most  useful  as  a  source  of 
detailed  information  upon  which  decisions  can  be  based. 
Often  those  decisions  will  require  further  field  work  and 
literature  research,  as  rarely  will  this  or  any  other  atlas  book 
provide  all  the  information  needed  to  understand  and  deal 
with  a  specific  environmental  problem. 

Identification  of  Breeding  Bird  Species 
of  Special  Concern 

A  number  of  birds  diat  breed  in  Marin  County  can  be 
found  on  various  lists  of  species  that  warrant  or  need 
consideration  for  protection  at  the  state  or  national  level 
(Table  12).  Populations  of  these  species  are  declining  to 
various  degrees  and  in  extreme  cases  face  possible  extinc- 
tion. At  present  only  state  and  federally  Threatened  or 

69 


Species  of  Special  Concern 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Species  of  Special  Concern 


Table  12.    Species  or  subspecies  of  birds  that  breed  in  Marin  County  that  are  currendy  listed  as  Endangered,  Threatened, 
or  of  management  concern  in  diis  region  by  state  or  national  organizations. 


FEDERAL  AND  STATE  ENDANGERED1' 2 

American  Peregrine  Falcon 
California  Clapper  Rail 

FEDERAL  THREATENED1 

Northern  Spotted  Owl 

Western  Snowy  Plover  (coastal  population) 

FEDERAL  CANDIDATE3,  Category  2 

Black  Rail 

California  Homed  Lark 

Loggerhead  Shrike 

Saltmarsh  Common  Yellowthroat 

Bell's  Sage  Sparrow 

San  Pablo  Song  Sparrow 

Tricolored  Blackbird 

FEDERAL  MANAGEMENT  CONCERN4,  Region  1 
(California) 

Black  Rail 
Snowy  Plover 
Olive-sided  Flycatcher 
Loggerhead  Shrike 

STATE  THREATENED2 

California  Black  Rail 


SLATE  SPECIES  OF  SPECIAL  CONCERN' 

Ashy  Storm-Petrel 

Double-crested  Cormorant 

Osprey 

Northern  1  larrier 

Sharp-shinned  Hawk 

Cooper's  Hawk 

Golden  Eagle 

Snowy  Plover 

Rhinoceros  Auklet 

Tufted  Puffin 

Burrowing  Owl 

Long-eared  Owl 

Short-eared  Owl 

Purple  Martin 

Yellow  Warbler 

Saltmarsh  Common  Yellowthroat 

Yellow-breasted  Chat 

San  Pablo  Song  Sparrow 

Tricolored  Blackbird 

AUDUBON  BLUE  LIST6 

American  Bittern 
Northern  Harrier 
Sharp-shinned  Hawk 
Cooper's  Hawk 
Red-shouldered  Hawk 
Short-eared  Owl 
Loggerhead  Shrike 
Grasshopper  Spanow 


U.S.  Fish  and  Wildlife  Service  (1989a),  Federal  Register. 

2  Calif.  Dept.  Fish  and  Game  (1991a). 

3  U.S.  Fish  and  Wildlife  Service  (1991). 


4  U.S.  Fish  and  Wildlife  Service  (1987b). 

5  Calif.  Dept.  Fish  and  Game  (1991b). 

6  Tate  (1986). 


Endangered  species  are  afforded  special  legal  protection, 
aldiough  many  Candidate  or  Forest  Service  "sensitive" 
species  are  treated  on  federal  lands  as  if  they  were  "listed." 
Other  management  categories  of  concern  are  just  diat— diey 
express  concern  over  apparent  declines  in  species'  popula- 
tions but  do  little  to  protect  diem  beyond  raising  aware- 
ness, an  important  first  step.  Although  these  protection 
efforts  should  be  lauded,  diey  may  not  do  enough.  Are  the 
state  and  federal  levels  the  only  valid  ones  for  considera- 
tion of  protection  of  species?  Biodiversity  has  recendy 
become  a  fashionable  concept  to  promote,  but  should  we 
try  to  enhance  biodiversity  just  at  the  state  and  federal  level 
and  not  at  the  county  level  or  even  in  our  backyards? 
Should  we  settle  for  small  populations  of  species  in  distant 
parts  of  our  state  and  nation,  when  with  protection  viable 
populations  could  exist  as  well  in  our  own  neighborhoods? 
Preservation  and  enhancement  of  habitats  is  now  also  an 
often  championed  approach  to  retaining  biodiversity,  but 


again  why  not  at  die  local  as  well  as  the  state  and  federal 
levels?  These  topics  will  be  hody  debated  in  the  years  to 
come. 

As  a  starting  point  for  consideration  of  preservation  of 
biodiversity  of  breeding  birds  in  Marin  County,  it  seems 
logical  to  first  promote  protection  of  all  the  species  that 
breed  in  die  county  diat  have  already  been  given  a  state, 
federal,  or  other  national  management  designation  (Table 
1 2).  This  study  also  identifies  an  additional  preliminary  list 
of  Marin  County  Breeding  Bird  Species  of  Special  Con- 
cern (Table  13),  not  on  any  state  or  national  list,  that 
should  at  a  minimum  be  given  consideration  for  protection 
at  the  county  level.  An  emphasis  is  placed  on  the  prelimi- 
nary nature  of  the  Marin  list  and  die  need  for  refining  it, 
as  others  will  undoubtedly  disagree  widi  die  author  over 
which  species  to  include  on  the  list  or  if  such  a  county  list 
is  even  needed.  The  species  in  Table  13  are  regular  native 
breeding  species  widi  overall  population  indices  in  the 


70 


Species  of  Special  Concern 


CONSERVATION  APPLICATIONS 


Species  of  Special  Concern 


lower  25%  of  those  calculated  for  all  species  recorded  in 
the  adas  project  (Table  7).  They  are  vulnerable  because 
they  nest  here  in  very  small  numbers,  generally  in 
restricted,  often  imperiled,  habitats  or  are  colonial  nesting 
species  that  concentrate  at  very  few  sites.  Some  species 
falling  in  the  lower  25%  of  population  indices  were 
excluded  from  the  list  because  they  were  irregular  or 
extralimital  breeders  (Canada  Goose,  Blue-winged  Teal, 
Say's  Phoebe,  Northern  Parula,  Black-chinned  Sparrow, 
Red  Crossbill,  and  Lawrence's  Goldfinch)  or  had  small 
recendy  established  populations  in  human-created  habitat 
(Hooded  Oriole). 

If  we  are  to  maintain  viable  diverse  communities  of 
birds  in  Marin  County,  it  is  clearly  necessary  to  protect 
extensive  areas  of  the  full  range  of  the  county  s  natural 
habitats.  Fortunately  much  of  our  land  has  already  been 
preserved  in  parks  or  open  space  (Figure  6).  The  effect  of 
habitat  fragmentation  on  bird  populations  is  now  a  trendy 
topic  in  ecological  and  conservation  circles,  but  our  knowl- 
edge of  these  effects  is  still  in  its  infancy.  In  that  light,  it 
seems  prudent  to  err  on  the  side  of  caution  and  preserve 


large  rather  than  small  areas  of  habitat.  The  bird  habitats 
in  Marin  County  that  most  deserve  protection  are  ones 
that  conservation  efforts  are  also  currendy  focused  on 
elsewhere  in  the  state  and  nation— wedands,  marshlands, 
and  riparian  forests.  Of  the  63  species  from  the  county  on 
various  management  lists  (Tables  12  and  13),  51%  are 
marsh-dependent  species,  other  waterbirds,  or  seabirds; 
21%  are  miscellaneous  landbirds;  19%  are  raptors  (two 
species  are  also  marsh  dependent);  5%  are  chaparral- 
dependent  species;  and  5%  are  riparian-dependent  species. 
As  discussed  in  the  land  use  section,  loss  or  degradation 
of  important  habitats  in  the  county  is  very  evident.  Many 
of  these  species,  particularly  those  dependent  on  wedands, 
face  uncertain  futures  without  preservation  or  enhance- 
ment of  their  habitats. 

The  knowledge  presented  in  this  and  other  scientific 
studies  can  inform  concerned  citizens,  but  only  if  they 
repeatedly  and  forcefully  express  the  value  and  importance 
that  wildlife  plays  in  enhancing  their  lives  will  habitat 
preservation  and  enhancement  efforts  succeed. 


Trail  winding  through  the  dimly-lit  understory  of  the  Douglas  fir  forest  on  Inverness  Ridge.  Drawing  b}  Ane  Rovetta,  I  986. 


71 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 

Table  13.    A  preliminary  list  of  Breeding  Bird  Species  of  Special  Concern  in  Marin  County.  Does  not  include  species 
already  given  state,  federal,  or  national  protection  or  recognition  (see  Table  1 2). 


BRANDT'S  CORMORANT  —  county  breeding  population  con- 
centrated at  only  six  colonies;  vulnerable  to  disturbance  at  colonies 
and  oil  pollution. 

PELAGIC  CORMORANT  —  breeding  population  well  scattered 
along  the  coast  but  particularly  vulnerable  to  nearshore  oilspills  in 
breeding  season. 

GREAT  BLUE  HERON  —  currently  breeding  at  only  seven  colonies 
and  numbers  breeding  in  county  have  declined  in  recent  years; 
vulnerable  to  loss  of  wetlands,  disturbance  at  colonies,  and  pesticide 
contamination. 

GREAT  EGRET  —  currendy  breeding  at  only  five  colonies;  depend- 
ent on  dwindling  wedands  and  vulnerable  to  pesticide  contamina- 
tion and  disturbance  at  colonies. 

SNOWY  EGRET  —  virtually  entire  county  breeding  population 
concentrated  at  one  colony;  dependent  on  vanishing  wedands  and 
vulnerable  to  disturbance  and  pesticides. 

GREEN-BACKED  HERON  —  a  very  small  population  dependent 
on  overgrown  borders  of  streams  and  marsh  edges;  threatened  by 
degradation  and  loss  of  riparian  and  freshwater  marsh  habitats. 

BLACK-CROWNED  NIGHT-HERON  -  entire  county  breeding 
population  concentrated  at  one  colony;  dependent  on  shrinking 
wedands  and  vulnerable  to  disturbance  at  colonies  and  pesticides. 

WOOD  DUCK  —  very  small  population  dependent  on  freshwater 
ponds  and  streams  with  overgrown  borders;  numbers  apparendy 
reduced  over  former  times. 

NORTHERN  PINTAIL  —  very  small  breeding  population  depend- 
ent on  freshwater,  brackish,  and  saline  wedands  for  breeding. 

NORTHERN  SHOVELER  -  currendy  known  to  breed  in  the 
county  at  only  one  managed  freshwater  wedand. 

GADWALL  —  very  small  breeding  population  dependent  on 
scarce  freshwater  and  brackish  marshes  and  ponds. 

COMMON  MERGANSER  —  very  small  breeding  population  on 
reservoirs  and  streams. 

RUDDY  DUCK  —  very  small  breeding  population  in  freshwater 
ponds  and  marshes. 

VIRGINIA  RAIL  —  very  small  breeding  population  restricted  to 
freshwater  marshes. 

SORA  —  very  small  breeding  population  restricted  to  freshwater 
marshes. 

COMMON  MOORHEN  —very  small  breeding  population  depend- 
ent on  limited  freshwater  ponds,  sloughs,  and  marshes. 

BLACK  OYSTERCATCHER  -  very  small  breeding  population 
restricted  to  rocky  shores  primarily  on  the  outer  coast;  intertidal  food 
supply  vulnerable  to  oil  pollution. 


BLACK-NECKED  STILT  -  very  small  breeding  population 
restricted  to  a  few  freshwater  and  brackish  wedands  along  the  San 
Francisco  and  San  Pablo  bay  shorelines;  vulnerable  to  heavy  metal 
contamination. 

AMERICAN  AVOCET  —  has  attempted  to  breed  a  few  times  in 
brackish  or  freshwater  wedands  along  the  San  Francisco  and  San 
Pablo  bay  shorelines;  vulnerable  to  heavy  metal  contamination. 

COMMON  MURRE  —  currendy  breeding  in  the  county  at  only  four 
colonies;  populations  have  been  severely  reduced  in  recent  years  by 
oil  pollution,  gill  netting,  and  severe  El  Nino. 

PIGEON  GUILLEMOT  —  breeding  population  well  scattered  along 
coast  but  particularly  vulnerable  to  nearshore  oilspills  in  breeding 
season. 

NORTHERN  PYGMY-OWL  -  inexplicably  scarce  as  a  breeding 
bird  in  the  county;  dependent  on  clearings  in  conifer  and  mixed 
evergreen  forests. 

COMMON  POORW1LL  -  very  small  breeding  population 
restricted  to  chaparral-covered  ridges. 

VAUX'S  SWIFT  —  very  small  breeding  population  apparendy 
dependent  on  fire-hollowed  nesting  snags  in  conifer  forests. 

RED-BREASTED  SAPSUCKER  -  very  small  disjunct  breeding 
population  dependent  on  moist  conifer  forests  and  bordering  ripar- 
ian zones. 

PILEATED  WOODPECKER  -  very  small  breeding  population 
dependent  on  old-growdi  or  mature  second-growth  conifer  forests. 

ROCK  WREN  —  very  small  population  breeding  at  few  sites;  may 
be  vulnerable  to  predation  as  is  the  Farallon  population. 

BLUE-GRAY  GNATCATCHER  -  very  small  breeding  population 
restricted  mosdy  to  live  oak  woodlands. 

CALIFORNIA  THRASHER  -  very  small  breeding  population 
restricted  to  a  few  chaparral-covered  ridges. 

SOLITARY  VIREO  —  very  small  breeding  population  restricted  to 
relatively  dry  open  mixed  evergreen  woodlands  on  Mount  Tamalpais 
and  vicinity. 

HERMIT  WARBLER  —  very  small  breeding  population  inhabits 
Douglas  fir  or  mixed  Douglas  fir/redwood  forests  on  Mount 
Tamalpais  and  nearby  ridges. 

MACGILLIVRAY'S  WARBLER  -  very  small  breeding  population 
inhabits  brushy  riparian  borders  mosdy  on  the  coastal  slope. 

WESTERN  TANAGER  —  very  small  population  breeding  in 
relatively  open  Douglas  fir  or  mixed  evergreen  hardwoods  on  Mount 
Tamalpais  and  nearby  ridges. 


72 


CONTENT  OF  SPECIES  ACCOUNTS 


Birds  .  .  .  had  many  magical  properties  .  .  .  they  u/ere  thought  to  know  the  secret  of  all  living  things,  to  have  great  foresight, 
and  to  fill  with  wisdom  the  hearts  of  those  who  took  the  trouble  to  learn  their  language  and  listen. 

—  Laurens  van  der  Post, 
A  Story  Like  the  Wind 


THE  SPECIES  ACCOUNTS  section  of  the  book  provides 
basic,  though  detailed,  information  for  all  of  Marin 
County's  breeding  birds.  The  key  sections  of  each  account 
include  (1)  an  adas  distribution  map,  (2)  adas  data  accom- 
panying the  map,  and  (3)  the  species  account  text.  These 
materials  are  presented  in  a  standardized  format  as 
described  below. 


Atlas  Breeding  Distribution  Maps 

A  distribution  map  is  presented  for  each  species  that  was 
confirmed  or  believed  to  breed  in  Marin  County  during 
the  period  of  adas  field  work,  1976  to  1982.  Species 
lacking  adas  maps  were  found  breeding  in  Marin  County 
prior  to  or  after  the  period  of  adas  field  work.  Each  map 
has  the  adas  grid  of  221  blocks  overlain  on  a  standard  map 
of  Marin  County.  Broken  lines  within  the  county  bound- 
aries denote  major  roads— further  orientation  can  be 
obtained  by  reference  to  the  place  name  map  of  Marin 
County  (Figure  2). 

Three  symbols  are  used  within  the  blocks  of  the  adas 
maps  to  denote  the  three  categories  of  breeding  evidence 
(Table  5): 

O  —     Possible  Breeding 

©  —     Probable  Breeding 

•  —     Confirmed  Breeding 

Blocks  lacking  any  of  the  above  symbols  indicate  that  no 
evidence  of  breeding  was  observed  in  that  block  for  that 
species  during  the  period  of  adas  field  work.  Asterisks  in 
certain  blocks  of  the  map  for  Nuttall's  Woodpecker  denote 
records  of  that  species  in  late  June  and  July  indicative  of 
postbreeding  dispersal;  these  data  demonstrate  the  impor- 
tance of  completing  field  work  before  the  postbreeding 
period  (which  varies  among  species)  to  ensure  that  adas 
maps  accurately  portray  breeding  distribution. 

The  symbol  P  next  to  the  map  of  several  rare  and 
sensitive  species  denotes  diat  locations  of  breeding  records 
have  been  protected  by  moving  dots  on  the  map  by  one  to 
two  blocks  in  any  direction  (see  Data  Summary  p.  48). 


Key  to  Abundance  and  Distribution 
Data  Accompanying  Atlas  Maps 

This  key  describes  the  information  that  accompanies  the 
adas  map  preceding  the  species  account  text,  with  exam- 
ples for  a  colonial  nesting  species— Great  Blue  Heron— and 
a  solitary  nesting  species— Swainson's  Thrush  (Figure  13). 
Accounts  for  former,  or  recendy  documented,  breeding 
species  of  course  lack  adas  maps  or  data  and  therefore  are 
preceded  only  by  information  on  former  or  current  sea- 
sonal status. 

Seasonal  Status 

Information  is  presented  on  whether  a  breeding  species 
occurs  in  Marin  County  as  a  year-round  resident  or  only 
as  a  summer  resident  (Figure  1 3).  For  year-round  residents, 
periods  of  peak  occurrence  (if  any)  are  indicated  and 
whether  the  species  occurs  primarily  in  a  seasonal  role 
other  than  as  a  breeder.  For  example,  the  seasonal  status 
of  the  Sharp-shinned  Hawk  is  "Occurs  year  round,  though 
almost  exclusively  as  a  winter  resident  and  transient  from 
Sep  through  Apr;  numbers  swell  substantially  during  fall 
migration  from  Sep  through  mid-Nov."  Information  is  also 
provided  on  the  periods  when  colonial  waterbirds  gather 
at  their  breeding  colonies  (e.g.,  Great  Blue  Heron,  Figure 
13). 

Breeding  Status 

This  section  gives  a  verbal  description  of  the  relative 
abundance  of  the  species  in  an  average  block  and  its 
distribution  countywide,  based,  respectively,  on  categories 
of  the  Fine-Scale  Abundance  Rating  and  the  Relative  Dis- 
tribution Index  listed  below.  In  addition,  the  overall  popu- 
lation size  of  the  species  in  the  county  is  described  by  the 
verbal  categories  of  the  Overall  Population  Index  also  listed 
below.  For  example,  Swainson's  Thrush  (Figure  13)  is 
termed  "a  very  common  [Fine-Scale  Abundance  Rating  =  5], 
widespread  [Relative  Distribution  Index  =  1 37]  breeder; 
overall  breeding  population  large  [Overall  Population 
Index  =  685]." 

73 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 
Great  Blue  Heron    Ardea  herodias 


A  year-round  resident;  occupies  breeding 
rookeries  mosdy  from  late  Jan  or  early 
Feb  through  late  lun  or  mid-jul. 

ACmirly  commor^(very  locaDbreeder; 
overall^reedingpopuTation^ery  smatt) 

Recorded  in(O)(80)  or  5A%j362%) 
of  221  blocks  (see  Methods). 

O    Possible  68  (85%) 

€    Probable  0  (0%) 

•    Confirmed  =       12   (15%) 


Fine-Scale 
Abundance  Rating 


seasonal 
status 

breeding 
status 


Blocks  recorded/Relative  Distribution  Index  (RDl) 


Number  (and  percentage)  of  blocks  in  which 
the  three  breeding  categories  were  recorded. 


Overall 
Population  Index 
(FSARx  RDl) 


Confirmation  Index 


?o  +  (PT  x  2)  +  (Co  x  3) 
total  blocks  recorded 


Swainson's  Thrush    Catharus  ustulata 


A  summer  resident  from  late  Apr 
mrougliearlyOct. 

A(very  commor)^widespread2breeder; 
overaUbreeding  population(Targe. 

Recorded  in(O7)(62.0%)  6T221 
blocks. 


O  Possible 
€  Probable 
w    Confirmed 


17  (12%) 
95  (69%) 
25  (18%) 


OPI  =  685)    CI  =  2.06 


Fine-Scale 
Abundance  Rating 


seasonal 
status 

breeding 
status 


Blocks  recorded/Relative  Distribution  Index  (RDl) 


Number  (and  percentage)  of  blocks  in  which 
the  three  breeding  categories  were  recorded. 


Overall 
Population  Index 
(TSAR*  RDl) 


Confirmation  Index 


P0  +  (Pr  x  2)  +  (C0  x  3) 
total  blocks  recorded 


Figure  13.  Examples  of  data  presented  with  the  atlas  map  of  each  breeding  species  during  the  Marin  County  Breeding  Bird  Atlas 
project.  Data  presentation  is  sligktl}  different  for  colonial  breeders  (e.g.,  Great  Blue  Heron  above)  than  solitary  breeders  (e.g., 
Swainson's  Thrush  above)  because  most  colonies  have  been  located  and  their  size  determined  (see  textj.  The  circled  abundance  and 
distribution  terms  are  trie  verbal  equivalents  (from  index  scales,  p.  75),  respectively,  of  the  circled  FSAR,  RDl,  and  OP/  values  below 
them. 


74 


Key  To  Atlas  Map  Data 


CONTENT  OF  SPECIES  ACCOUNTS 


Key  to  Atlas  Map  Data 


Blocks  Recorded 

For  each  species,  the  number  of  atlas  blocks  in  which  it 
was  recorded  is  listed  along  with  what  percentage  of  the 
total  number  of  blocks  (221)  that  represents.  Because  we 
felt  we  documented  most,  if  not  all,  heron  and  egret 
colonies,  for  those  species,  data  on  blocks  recorded  is  listed 
first  as  the  number  of  blocks  widi  confirmed  breeding 
based  on  known  active  colonies.  Following  in  parentheses 
is  the  number  of  blocks  in  which  these  wedand-dependent 
species  were  recorded,  as  an  indication  of  the  importance 
of  foraging  habitat  away  from  colonies  and  often  outside 
the  adas  block  where  actual  nesting  activities  were  centered 
(e.g.,  Great  Blue  Heron,  Figure  13).  Similarly,  for  herons 
and  egrets,  the  percentage  of  "total"  blocks  is  listed  first  as 
the  percentage  of  confirmed  to  total  blocks  and  in  parenthe- 
ses as  the  percentage  of  recorded  to  total  blocks.  Since  the 
adas  grid  did  not  sample  most  foraging  habitat  of  breeding 
seabirds,  the  number  of  blocks  recorded  (and  percentage 
of  total  blocks)  for  those  species  is  based  on  only  die 
number  of  blocks  with  active  colonies. 

Fine-Scale  Abundance  Rating  (FSAR) 
For  all  but  colonial  waterbirds,  this  rating  qualitatively 
defines  the  abundance  of  a  species  (based  on  notes  and 
impressions  gathered  by  the  audior  over  a  number  of  years) 
in  an  "average"  adas  block  in  which  it  was  recorded.  The 
scale  from  1  to  7  is  based  on  the  number  of  pairs  an 
observer  would  expect  to  encounter  by  sight  and/or  sound 
while  on  foot  during  four  hours  afield  in  one  block  during 
prime  daily  or  nighdy  hours  of  activity  for  the  species 
during  the  height  of  its  breeding  season.  Because  the 
categories  were  assigned  qualitatively,  diey  may  be  off  by 
plus  or  minus  one  (or  more?)  category.  For  colonial 
waterbirds,  rating  categories  are  assigned  based  on  average 
population  sizes  of  known  colonies  in  Marin  County 
during  the  adas  period  (Tables  14-17).  The  categories 
(numbers  seen/4  hrs)  and  their  verbal  equivalents  are 
based  on  a  log  scale  like  that  used  by  DeSante  and  Ainley 

(1980): 

1  <  1  pair  very  rare  (irregular;  does  not  occur 

every  year) 
rare  (regular;  occurs  yearly) 

2  1-3  pairs         uncommon 

3  4-9  pairs         fairly  common 

4  10-27   pairs       common 

5  28-81    pairs        very  common 

6  82-243  pairs      abundant 

7  >  243  pairs      very  abundant 

Relative  Distribution  Index  (RDl) 

For  all  but  colonial  waterbirds,  this  index  is  a  measure  of 
the  relative  breeding  distribution  of  a  species  in  the  county 
based  simply  on  the  number  of  blocks  in  which  it  was 
recorded  during  the  period  of  atlas  field  work.  The  index 
for  colonial  waterbirds  is  the  number  of  blocks  with  active 


breeding  colonies.  For  example,  the  Great  Blue  Heron 
(Figure  13)  has  a  Relative  Distribution  Index  of  12  (blocks 
with  colonies)  even  though  it  was  recorded  in  a  total  of  80 
blocks.  The  total  number  of  potential  blocks  in  the  county 
(221)  in  which  a  species  could  occur  were  divided  into 
seven  categories  with  verbal  equivalents: 
1-31  blocks  very  local 

32-62  blocks  local 

63-93  blocks  somewhat  local 

94-124  blocks         fairly  widespread 
125-155  blocks         widespread 
156-186  blocks         very  widespread 
187-221  blocks  nearly  ubiquitous 

Overall  Population  Index  (OPl) 

This  index  is  derived  by  multiplying  the  Fine-Scale  Abun- 
dance Rating  for  a  species  times  the  number  of  blocks  in 
which  it  was  recorded  during  die  adas  project  (times  blocks 
with  colonies  for  colonial  waterbirds).  The  range  of  actual 
values— from  1  to  1010— was  divided  into  seven  categories 
with  verbal  descriptions: 

1-146  very  small  population 

147-290  small  population 

291-434  moderate-sized  population 

435-578  fairly  large  population 

579-722  large  population 

723-866  very  large  population 

867-1010  extremely  large  population 

Breeding  Criteria  Categories 

For  each  of  the  three  Breeding  Criteria  Categories  of 
Possible  (O),  Probable  (©),  and  Confirmed  (9)  there  is 
listed  the  number  of  blocks  in  which  that  category  was 
recorded  and,  in  parentheses,  the  percentage  of  the  total 
number  of  recorded  blocks  (of  all  categories)  that  figure 
represents.  Colonial  waterbirds  are  treated  the  same  as 
other  species  even  though  they  probably  were  confirmed  in 
most,  if  not  all,  the  blocks  they  were  breeding  in. 

Confirmation  Index  (Cl) 

This  index  is  a  measure  of  how  difficult  each  species  was, 
relative  to  other  species,  to  confirm  as  a  breeder.  The  index 
for  each  species  was  derived  by  multiplying  the  number  of 
blocks  with  Possible  evidence  of  breeding  by  1 ,  the  number 
of  blocks  with  Probable  evidence  by  2,  and  the  number  of 
blocks  with  Confirmed  evidence  by  3.  These  three  prod- 
ucts were  dien  summed  and  divided  by  the  total  number 
of  blocks  in  which  the  species  was  recorded.  Though  used 
for  a  different  purpose,  our  Confirmation  Index  is  similar 
mathematically  to  die  "ACID  (Adequate  Coverage  Identi- 
fication) test  used  by  some  to  evaluate  whedier  an  adas 
block  has  received  enough  observer  coverage  (Kibbe  1986, 
p.  46  this  volume). 

75 


Content  of  Species  Account  Text 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Content  of  Species  Account  Text 


Content  of  Species  Account  Text 

Although  the  atlas  maps  do  stand  alone  in  documenting 
the  breeding  distribution  of  each  species,  they  do  not 
provide  information  that  might  help  to  explain  the 
observed  distribution  or  a  knowledge  of  habitat  and  forag- 
ing requirements  necessary  for  conservation  efforts.  These 
functions  are  served  by  the  species  account  text.  Selected 
(but  detailed)  biological/ecological,  distributional,  and  his- 
torical information  is  presented  in  three  standard  sections: 
(1)  Ecological  Requirements,  (2)  Marin  Breeding  Distribu- 
tion, (3)  Historical  Trends/Population  Threats  (sometimes 
combined  with  section  2),  and  a  fourth  infrequendy  used 
Remarks  section.  The  accounts  primarily  are  meant  to  be 
informative  and  to  point  the  reader  in  the  right  direction 
when  additional  information  is  needed.  They  are  by  no 
means  meant  to  be  the  last  word  on  the  subject. 

Because  an  attempt  has  been  made  to  standardize  the 
accounts  and  make  them  accessible,  without  sacrificing 
detail,  the  reader  may  be  under  the  illusion  that  most 
aspects  of  each  species'  breeding  ecology  are  well  known. 
This  is  far  from  the  case.  Much  still  needs  to  be  known 
about  the  basic  biology  of  even  the  most  common  and 
well-studied  species.  The  species  accounts  vary  gready  in 
length  for  the  simple  reason  that  the  amount  of  informa- 
tion available  varies  widely  among  species.  The  reader  is 
cautioned  to  interpret  and  use  this  information  carefully. 
If  information  is  critical  for  the  conservation  efforts  of  a 
species,  primary  sources  should  be  consulted  directly  and, 
if  possible,  local  studies  should  be  undertaken. 

Although  an  effort  was  made  to  use  information  from 
local  studies  whenever  possible,  the  data  presented  in  the 
species  accounts  may  have  been  collected  far  from  Marin 
County  or  even  outside  California,  and  its  applicability 
may  suffer  accordingly.  The  reader  may  wonder  why  the 
text  provides  detail  on  aspects  of  a  species  ecology  derived 
from  distant  studies  when  in  fact  local  studies  are  available. 
Such  information  is  presented  because  insight  often  comes 
from  comparing  the  biology  of  die  same  species  in  different 
habitats.  A  classic  example  of  this  is  Bob  Stewart's  compar- 
ative studies  of  Wilson's  Warblers  at  Palomarin  on  the 
Point  Reyes  National  Seashore  and  at  Tioga  Pass  in  the 
Sierra  Nevada  (see  account).  The  comparative  approach 
works  on  the  local  level  as  well.  I  did  not  realize  that  a  basic 
habitat  requirement  of  breeding  Wilson's  Warblers  in 
Marin  County  was  moist,  low  dense  cover  until  I  observed 
them  breeding  here  in  moist  stands  of  coastal  scrub  that 
lacked  the  canopy  of  Douglas  fir,  bishop  pine,  alder,  or 
willow  typically  associated  with  their  more  widespread 
forested  breeding  haunts  here. 

Although  the  accounts  focus  on  the  important  aspects 
of  each  species  ecology,  they  cannot  begin  to  convey  ade- 
quately the  grace,  spirit,  intensity,  drama,  humor,  or  exhil- 
arating beauty  of  our  feathered  friends  and  their  lives. 
Much  of  avian  essence  can  be  captured  in  prose  and 

76 


poetry,  as  such  authors  as  Dawson  (1923)  and  others  have 
so  admirably  demonstrated,  but  much  cannot.  One  has  to 
experience  birds  in  the  raw,  on  their  own  terms.  The 
accounts  that  follow  may  in  some  small  way  transmit  an 
appreciation  for  the  ecological  factors  that  are  important  to 
birds,  but  only  by  spending  time  widi  die  birds  themselves 
can  we  appreciate  their  importance,  and  that  of  the  rest  of 
the  natural  world,  to  our  lives. 

Ecological  Requirements 

The  more  one  knows  about  the  basic  breeding  biology  of 
a  species,  the  better  able  one  is  to  interpret  its  pattern  of 
distribution.  Nevertheless,  an  understanding  of  certain 
aspects  of  the  ecology  of  breeding  birds  appears  more 
crucial  in  this  regard.  Hence,  particular  ecological  require- 
ments have  been  emphasized  here  and  others  have  been 
deliberately  ignored,  even  though  the  latter  factors  might 
provide  additional  insight  as  well.  Each  species  account 
tries  to  describe  the  range  of  local  habitats  the  species 
occupies  for  breeding,  special  features  of  the  habitat(s)  it 
needs,  where  it  locates  its  nest,  what  type(s)  of  nest  it  builds 
and  of  what  materials,  what  kinds  of  food  it  requires,  and 
what  foraging  styles  it  uses  to  obtain  its  food.  For  all  but 
habitat  requirements,  information  on  seasonal,  sex-,  and 
age-related  variation  in  nesting  and  foraging  requirements 
are  presented  when  available.  Various  biological  character- 
istics of  each  species  such  as  types  of  breeding  displays  or 
clutch  size  are  not  presented  because  they  do  not  bear 
direcdy  on  the  issue  of  niche  requirements  and  because 
this  information  is  already  summarized  in  such  standard 
references  as  Harrison  (1978)  and  Ehrlich  et  al.  (1988). 

Marin  Breeding  Distribution 

This  section  gives  a  verbal  description  of  the  species' 
breeding  distribution,  any  geographical  trends  of  distribu- 
tion or  abundance  in  the  county,  and  any  factors  that 
might  help  explain  the  observed  distribution.  Also 
included  are  specific  documented  records  from  the  period 
of  adas  field  work,  though  particularly  noteworthy  records 
from  outside  that  period  are  occasionally  listed  as  well.  The 
format  of  these  "representative"  breeding  records  is  as 
follows:  (breeding  code,  date  of  observation,  and  observer 
initials).  For  example,  a  record  (NY  5/22-28/82  -TO) 
would  read  that  a  nest  with  young  was  under  observation 
from  22  to  28  May  1982  by  Typical  Observer.  Breeding 
codes  (Table  5)  joined  by  a  slash  indicates  that  more  than 
one  type  of  breeding  behavior  was  observed  on  the  same 
date,  whereas  codes  joined  by  a  hyphen  indicates  that 
different  categories  of  breeding  evidence  were  observed 
over  a  period  of  days  or  weeks. 

Historical  Trends/Population  Threats 
Although  the  historical  record  of  changes  in  the  distribu- 
tion and  abundance  of  birds  in  Marin  County  and  Cali- 
fornia as  a  whole  is  incomplete,  any  and  all  apparent 
population  trends  are  discussed,   from  the  local  to  the 


Content  of  Species  Account  Text 


CONTENT  OF  SPECIES  ACCOUNTS 


Content  of  Species  Account  Text 


widespread.  The  main  historic  sources  consulted  were 
Mailliard  (1900)  and  Stephens  and  Pringle  (1933)  for 
Marin  County;  Grinnell  and  Wythe  (1927)  and  Sibley 
(1952)  for  the  San  Francisco  Bay  Area;  and  Grinnell  and 
Miller  (1944)  and  Remsen  (1978)  for  California  as  a 
whole.  Robbins  et  al.  (1986)  and  the  corresponding 
unpublished  Breeding  Bird  Survey  data  for  California 
collected  by  volunteers  of  USFWS  provided  information  on 
recent  bird  population  trends.  Additional  sources  are  other 
avifaunal  works,  published  papers  or  reports  on  particular 
species  or  species  groups,  and  the  published  seasonal 
reports  and/or  unpublished  data  on  file  with  the  editors  of 
the  Middle  and  Southern  Pacific  Coast  regions  of  Ameri- 
can Birds. 

Remarks 

This  section  is  a  catch-all  used  very  infrequendy  and  only 

when  important  or  interesting  material  about  a  species  did 

not  fit  conveniendy  into  any  of  the  three  main  subdivisions 

of  the   species   accounts   (e.g.,   Brown-headed   Cowbird 

account). 

Observers 

The  following  individuals  are  cited  in  the  text  for  their  spe- 
cific observations:  Peg  Abbott  (PA),  Sarah  G.  Allen  (SGA), 
Carol  Annable  (CA),  Bob  Baez  (BoB),  Janice  Barry  (JBa), 
Hal  Barwood  (HBa),  Dennis  Beall  (DnB),  Max  Beckwith 
(MB),  Gordon  Beebe  (GBe),  Edward  C.  Beedy  (ECB),  Lau- 
rence C.  Binford  (LCB),  Barbara  Binger  (BBi),  Tupper 
Ansel  Blake  (TAB),  Gerald  Brady  (GB),  Aubrey  Burns 
(ABu),  Stan  Camiccia  (SCa),  Scott  Carey  (ScC),  Harry  R. 
Carter  (HRC),  Pam  Cleland  (PCI),  Marna  Cohen  (MC), 
Peter  Colasanti  (PCo),  Chris  Cuder  (CCu),  Dave  DeSante 
(DDeS),  Jules  G.  Evens  (J  GE),  Carter  L  Faust  (CLF),  Marc 
Fenner  (MFe),  Shawneen  E.  Finnegan  (SEF),  Richard  Franz 
(RFz),  Steve  Gellman  (SG),  Al  6k  Wilma  Ghiorso 
(A&.WG),  Manuel  ck  Lillian  Gorin  (M6kLG),  Keith  Han- 
sen (KH),  Rob  Hansen  (RH),  Roger  D.  Harris  (RDH), 
Roger  Harshaw  (RHa),  Burr  Heneman  (BHe),  Jim  Higbee 
(J  H),  Emmy  Hill  (EH),  David  A.  Holway  (DAH),  Ken  How- 
ard (KeHo),  Stuart  Johnston  (SJ),  John  P.  Kelly  (JPK),  Shir- 
ley 6k  Mike  Kelly  (SckMK),  John  Kipping  (J  Kip),  Gerry  J. 
Kleynenberg  (GJK),  Rick  LeBaudour  (RLe),  Bill  Lenarz 
(BiL),  Phil  Lenna  (PL),  R  A.  Lewis  (RAL),  John  Lovio  (J  Lo), 
Gary  F.  McCurdy  (GFMc),  Flora  Maclise  (FMa),  Grace 
McMichael  (GMcM),  Eugene  Y.  Makishima  (EYM),  Bill  G. 
Manolis  (BGM),  Gloria  Markowitz  (GMk),  Peter  J. 
Metropulos  (PJM),  Andrea  Meyer  (AM),  Grace  Miller 
(GMi),  Joseph  Morlan  (JM),  Marina  Gera  Nell  (MGN), 
Don  Neubacher  (DNe),  Ed  O'Connor  (EO),  Gary  W.  Page 
(GWP),  Linda  Parker  (LP),  Carmen  J.  Patterson  (CJP), 


Holly  Peake  (HoP),  Susan  Claire  Peaslee  (SCP),  Alan 
Pistorius  (AP),  Point  Reyes  Bird  Observatory  personnel 
(PRBO),  Helen  Pratt  (HPr),  William  M.  Pursell  (WMP), 
Alton  "Bob"  Raible  (ARa),  C.  J.  Ralph  (CJR),  Jean  M.  Rich- 
mond (J  MR),  Ane  Rovetta  (ARo),  David  Ruiz  (DRu),  R.  J. 
Ryder  (RJRy),  Ellen  Sabine  (ESa),  Mary  Ann  Sadler  (MAS), 
Barry  Sauppe  (BS),  Phil  6k  Margaret  Schaeffer  (PckMSh), 
Dave  Shuford  (DS),  David  Sibley  (DaS),  Dianne  Sierra 
(DSi),  Sue  Smith  (SSm),  Bruce  Sorrie  (BSo),  Barry  Spitz 
(BSp),  Rich  Stallcup  (RS),  Jean  Starkweather  (J  St),  Lynne 
E.  Stenzel  (LES),  Robert  M.  Stewart  (RMS),  Roger  Stone 
(RSt),  Helen  Strong  (HS),  Merl  Sturgeon  (MeS),  Meryl  Sun- 
dove  (MSd),  Ian  Tait  (ITa),  Gil  Thomson  (GiT),  Irene 
Timossi  (ITi),  Dorothy  Tobkin  (DT),  Beverly  Treffinger 
(BTr),  Wayne  6k  Susan  Trivelpiece  (W6kST),  Bill  Tyokodi 
(BTy),  Ed  Vine  (EV),  Nils  Warnock  (NW),  Anne  6k  John 
West  (AekJWe),  Ralph  S.  Widrig  (RSW),  Pamela  L  Wil- 
liams (PLW),  Jon  Winter  (J  W),  Peg  Woodin  (PWo),  Keiko 
Yamane  (KY),  Mark  Zumsteg  (MZ),  Clerin  Zumwalt  (CZ). 

Abbreviations 

The  following  abbreviations  are  used  for  frequendy  used 
literature  citations:  AB  =  American  Birds,  formerly  Audubon 
Field  Notes  (AFN);  ABN  =  "American  Birds  Notebooks"— 
data  on  file  with  the  regional  editors  of  the  Middle  Pacific 
Coast  Region  of  American  Birds;  ACR  Report  =  Audubon 
Canyon  Ranch  Report;  JFOs  =  journal  of  Field  Ornithology 
Supplement;  (G6kM  1944)  =  (Grinnell  6k  Miller  1944); 
(G6kW  1927)  =  (Grinnell  6k  Wythe  1927);  (S6kP  1933)  = 
(Stephens  6k  Pringle  1933).  The  following  abbreviations 
are  used  in  the  listing  of  representative  breeding  records  in 
the  Marin  Breeding  Distribution  section  or  elsewhere  in 
parentheses  in  the  text  of  the  species  accounts: 

Ave.  =     Avenue 

CDFG  =     California  Department  of  Fish 

and  Game 

E,  W,  N,  S  =     compass  directions 

ft.  =      foot  (feet) 

in.  =      inch(es) 

km  =     kilometer  (s) 

mi.  =      mile(s) 

Mt.  =      Mount 

PRNS  =      Point  Reyes  National  Seashore 

Rd.  =      Road 

SP  =     State  Park 

St.  =     Street 

USFWS         =      U.S.  Fish  and  Wildlife  Service 

USFS  =      U.S.  Forest  Service 

yd.  =     yard(s) 

yr.  year(s) 


77 


MARIN  COUNTY  BRHHDING  BIRD  ATIAS 


Coast  redwoods  toivering  above  the  lusk,  /em;)  understory  at  Samuel 
P.  Taylor  State  Parle.  Drawing  fc>}  Ane  Rovetta,  1 989. 


78 


SPECIES  ACCOUNTS 


Greb 


es 


Family  Podicipedidae 


PIED-BILLED  GREBE   Podilymbus  podiceps 


Occurs  year  round,  though  primarily  as 

a  winter  resident  from  Sep  through  Mar. 

/•A    liV\\  \^3f 

^VCTS--.                  \                                   VT~ 

An  uncommon  local  breeder;  overall 

~^<i\     ^Sr^\v> 

r^\°3rNL<^-  - 

breeding  population  very  small. 

<r\^\^T\ 

Recorded  breeding  in  34  (15.4%)  of 

'3c\SrsQ?^^^^ 

^V3?n^M 

221  blocks. 

yl^\J^\\^\}^\^' 

^\°3r\  J\ 

hv 

-Vx^-VaSA^— 

O    Possible        =      12  (35%) 

^\>^-''\»  ^c\  '■l-^^^V/Y 

^\              Jf^V              Jr-^\               f 

€    Probable       =         5   (15%) 

^K^\^^^^^P^ 

V^V><^T\^A\i»X  " 

.  -- 

•    Confirmed  =      17   (50%) 

FSAR=2        OPI  =  68         CI  =  2.15 

^^^~^^^kK 

V*n\Mjr^ 

v?0> 

--?"/                                   voV^V 

__/           ^~^~^^^r\^ 

Ecological  Requirements 

These  floating  submersibles  are  breeding  inhabitants  of 
Marin  County's  marshy-edged  freshwater  ponds  and  lakes, 
freshwater  marshes  with  open  water,  and,  sparingly,  brack- 
ish water  impoundments.  In  much  of  their  range,  Pied- 
billed  Grebes  also  nest  on  sloughs  and  marshy  areas  of 
slow-flowing  rivers.  Occasionally,  they  breed  on  estuarine 
waters  with  slight  tidal  fluctuations  (Palmer  1962, 
Johnsgard  1987),  but  there  appear  to  be  no  reports  of 
nesting  in  this  habitat  in  coastal  California.  Infrequent 
sightings  of  birds  on  estuarine  waters  in  summer  (e.g.,  3 
birds  at  Drake's  Estero  23  Jun  1981  — DS)  may  represent 
breeders  foraging  away  from  nesting  ponds  or  perhaps 
oversummering  nonbreeders.  Of  major  importance  in  all 
breeding  habitats  is  the  availability  of  fairly  dense  emergent 
vegetation  used  for  nest  construction,  anchorage,  or  con- 
cealment. Breeding  ponds  range  in  size  from  xh  to  more 


than  100  acres  and  in  depth  from  a  few  inches  to  10  feet 
(usually  less  than  3-5  ft.);  smaller  ponds  (1  -5  acres)  are 
used  most  frequently  (Bent  1919,  Johnsgard  1987). 

Pairs  are  generally  solitary  while  nesting.  They  defend  a 
small  area  around  die  nest  site,  but  they  will  feed  with  other 
nesting  Pied-billeds  in  deeper,  open-water  areas  of  ponds 
and  marshes  (Glover  1 953a).  These  grebes  build  nests  that 
are  sodden  masses  of  decaying  aquatic  vegetation.  They 
usually  conceal  the  nests  in  varying  amounts  of  emergent 
vegetation  but  still  allow  for  underwater  approach;  some- 
times diey  locate  nests  in  open  water  (Miller  1942,  Glover 
1953a,  Stewart  1975).  Nests  are  usually  anchored  to,  or 
built  up  around  or  among,  dead  or  growing  reeds,  rushes, 
or,  infrequendy,  bushes,  logs,  or  dead  trees.  The  nests  are 
not  rigidly  anchored  as  some  rooted  plant  stalks  always 
project   through    them,    preventing   drift,   yet   allowing 

79 


Grebes 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Greh 


a 


enough  up-and-down  play  to  accommodate  changing  water 
levels  (Miller  1942).  In  shallow  water,  Pied-billeds  usually 
build  their  nests  up  from  the  bottom.  Below  water  level, 
the  nest  foundation  is  a  bulky  mass  of  vegetation  culminat- 
ing above  water  in  a  smaller  hollowed  platform  in  which 
the  female  lays  the  eggs.  Nest  materials  are  a  wide  variety 
of  available  dead,  and  sometimes  green,  materials  includ- 
ing cattail  flags,  rushes,  sedges,  grasses,  algae,  and,  if  the 
nest  is  in  shallow  water,  occasionally  mud.  Although  they 
lay  eggs  in  only  one  nest,  Pied-billeds  construct  two  to 
several  nest  structures,  and  they  may  continue  to  add 
considerable  nest  material  during  incubation. 

Pied-billed  Grebes  capture  their  aquatic  prey  in  their 
bills  by  foot-propelled  pursuit  dives  of  short  duration  in 
shallow  water;  by  picking  individual  items  from  the  water's 
surface;  by  skimming  the  surface  for  masses  of  floating 
invertebrates;  or  even  by  snatching  insects  from  the  air 
(Johnsgard  1987).  Overall,  the  North  American  diet  is 
about  46.3%  insects  (especially  damselflies,  dragonflies 
and  nymphs,  grasshoppers,  water  boatmen,  back- 
swimmers,  waterbugs,  predaceous  diving  beetles,  flies,  and 
hymenoptera),  27%  crayfish,  24-2%  fish  (especially  catfish, 
eels,  perch,  and  sunfish),  and  4.1%  other  crustaceans 
(brine  shrimp,  crabs,  shrimp,  etc.)  (Wetmore  in  Palmer 
1962  and  Johnsgard  1987,  n=  174).  Other  food  items 
include  frogs,  salamanders,  snails,  leeches,  spiders,  and 
seeds  and  soft  parts  of  aquatic  plants.  The  stout  bills  and 
heavy  jaw  musculature  of  Pied-billed  Grebes  are  well 
adapted  for  killing  heavy-bodied  fish,  as  well  as  crayfish 
and  frogs,  which  they  eat  in  greater  proportions  than  do 
other  species  of  North  American  grebes  (Zusi  &  Storer 
1969).  For  unknown  reasons,  grebes  ingest  their  own 
feathers.  Perhaps  the  feathers  function  to  prevent  bones  in 
the  stomach  from  passing  into  and  puncturing  the  intes- 


tine, to  retain  bones  in  the  gizzard  until  they  can  be 
digested,  or  to  promote  the  regurgitation  of  pellets  (Jehl 
1988).  Hatching  is  asynchronous.  Initially,  young  often 
ride  on  their  parents'  backs,  where  they  are  sometimes  fed, 
and  remain  there  when  the  adults  dive  at  signs  of  danger 
(Palmer  1962). 

Marin  Breeding  Distribution 

During  the  adas  period,  Pied-billed  Grebes  were  patchily 
distributed  in  Marin  County,  reflecting  the  distribution  of 
suitable  ponds  and  marshes.  Representative  breeding  loca- 
tions were  Nicasio  Reservoir  (NB-FL  5/16-7/17/82  — 
DS);  Phoenix  Lake  (FL  6/16/76  -RMS);  a  brackish  pond 
at  Spinnaker  Point,  San  Rafael  (NE  Jun  1982  — HoP);  and 
a  freshwater  pond  above  Rodeo  Lagoon  (FL  7/27/82 
-DS). 

Historical  Trends/ Population  Threats 

The  number  of  Pied-billed  Grebes  breeding  in  Marin 
County  has  undoubtedly  increased  in  historical  times 
because  of  the  impoundment  of  streams  for  catde  and 
human  water  needs,  since  natural  freshwater  ponds  and 
marshes  are  rare  here  and  in  coastal  California  in  general. 
For  California  as  a  whole,  numbers  of  Pied-billed  Grebes 
have  likely  decreased  because  of  loss  of  most  of  our 
wedands.  Numbers  of  Pied-billed  Grebes  were  relatively 
stable  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989  (USFWS  unpubl.  analyses).  Since  the  early  1980s, 
government  agencies  and  private  groups  in  California  have 
made  management  decisions  leading  to  increasing  areas  of 
permanent  and  summer-flooded  wetlands  for  waterfowl, 
and  Pied-billed  Grebes  will  undoubtedly  benefit  from  these 
new  habitats  (M.R.  McLandress  pers.  comm.). 


80 


Storm-Petrels 


SPECIES  ACCOUNTS 


Storm-Petrels 


Storm-Petrels 

Family  Hydrobatidae 


ASHY  STORM-PETREL    Oceanodroma  homochroa 


A  year-round  resident  on  pelagic  waters 

(peak  Sep-Jan);  petrels  occupy  the  Faral- 

A~^>^^                        \                    jOia 

lon  Island  colony  (and  probably  Bird 

Rock,  Marin  Co.)  almost  year  round 

"3rA^r\3r\^ 

(irregular  late  Nov-early  Dec). 

^^^^^K^K^x^C^^^c^C^, 

A  fairly  common,  very  local  breeder; 

overall  breeding  population  very  small. 

\^~  >><\v \ ~>^r  \  ^-V^\  jV^\    -V^\    \^^\    \--^^**'^i 

Recorded  in  1  (0.4%)  of  221  blocks 

(see  Methods). 

/ti3r'\OcC^5£'v 

O    Possible                  0   (0%) 

j3MYlMPr^^ 

€    Probable       =         0   (0%) 

^p^^"~^^Or^^ 

•    Confirmed   =         1    (100%) 

FSAR  =3         OPI  =  3           CI  =  3.00 

Ecological  Requirements 

Adapted  to  a  lifetime  at  sea,  during  the  breeding  season 
these  diminutive  ocean  waifs  obtain  their  sustenance  from 
the  edge  to  about  1 5  miles  seaward  of  the  continental  shelf 
within  the  cool  waters  of  the  California  Current— waters 
strongly  influenced  by  coastal  upwelling  (Ainley  et  al. 
1974;  Briggs  et  al.  1987;  Ainley  ck  Boekelheide  1990, 
Chap.  4).  From  spring  to  fall,  Ashy  Storm-Petrels  in  this 
region  most  consistendy  frequent  the  warm  side  of  thermal 
fronts  bordering  upwelled  waters  (Briggs  et  al.  1 987). 

Ashy  Storm-Petrels  nest  in  loose  colonies  on  islands  and 
offshore  rocks.  Pairs  occupy  cavities  among  loose  rocks  of 
talus  slopes,  in  stone  walls,  in  caves,  or  under  driftwood 
(Bent  1922,  Dawson  1923,  Ainley  et  al.  1974).  Petrels 
usually  occupy  breeding  sites  for  a  few  days  one  to  two 
weeks  prior  to  egg  laying  before  finally  settling  down  to  the 
chores  of  their  lengthy  breeding  season  (W.J.  Sydeman 
pers.  comm.).  Generally  females  lay  the  single  egg  on  tihe 
floor  of  the  cavity,  though  occasionally  they  place  it  on  a 
rough  foundation  of  weeds  or  pebbles  (Bent  1922).  Char- 
acteristics of  nesting  islands  selected  by  die  petrels  are 
suitable  nest  cavities,  a  lack  of  terrestrial  predators,  and 
reasonable  proximity  to  productive  ocean  feeding  grounds. 
Nonetheless,  the  presence  of  avian  predators,  particularly 


the  Western  Gull,  affects  colony  attendance  patterns  and 
other  aspects  of  the  biology  of  uhese  petrels.  At  the  Farallon 
Islands,  Ashy  Storm-Petrels  approach  their  nesting 
grounds  only  under  the  cloak  of  darkness  and  make  fewer 
visits  on  full-moon  nights  than  on  new  moon-nights 
(Ainley  &  Boekelheide  1990,  Chap.  4).  As  adaptations  to 
avoid  predation,  adults  feed  their  chicks  more  frequendy 
and  chicks  fledge  more  often  during  dark  phases  of  the 
moon;  most  chicks  that  fledge  during  light  phases  of  the 
moon  do  so  on  overcast  nights.  When  disturbed,  storm- 
petrels  also  discharge  foul-smelling  oil  from  the  mouth  and 
nostrils,  presumably  another  antipredator  defense. 

Ashy  Storm-Petrels  usually  occur  solitarily  at  sea,  but 
large  numbers  sometimes  gadier  around  concentrations  of 
food,  which  they  may  locate  by  their  well-developed  sense 
of  smell.  Foraging  birds  hover  on  outstretched  wings  and 
patter  on  the  sea's  surface  with  outspread  webbed  feet,  then 
catch  their  prey  by  dipping,  surface  seizing,  or  shallow 
plunges.  They  forage  during  the  day  and  also  probably 
extensively  at  night  (Ainley  ck  Boekelheide  1 990,  Chap.  3), 
as  suggested  by  their  consumption  of  some  cnjstaceans 
diat  ascend  to  surface  waters  mosdy  at  night  (McChesney 
1988).  While  feeding  chicks,  Ashy  Storm-Petrels  at  the 

81 


Storm-Petrels 


MARIN  COUNTY  BREEDING  BIRD  ATI.AS 


Storm-Petrels 


Farallon  Islands  prey  mainly  on  small  fish  and 
euphausiids,  and  to  a  limited  degree  on  other  crustaceans 
(decapods  and  amphipods)  and  cephalopods  (McChesney 
1988,  n  =  30);  they  are  also  known  to  scavenge  and  con- 
sume fish  oil  (Ainley  et  al.  1974,  Ainley  1984a).  Admirably 
suited  to  the  vagaries  of  finding  food  far  at  sea  or  to  the 
uncertainties  of  returning  landward  during  adverse 
weather,  adults  often  spend  several  days  away  at  sea  during 
nesting.  Upon  returning  to  nesting  sites,  they  feed  small 
young  an  energy-rich  stomach  oil  or,  later  in  the  season, 
partially  digested  prey.  Because  adults  attend  their  eggs  and 
young  infrequendy  and  irregularly,  the  incubation  and 
nesding  phases  are  long  and  variable,  even  by  seabird 
standards. 

Marin  Breeding  Distribution 

Ashy  Storm-Petrels  breed  in  Marin  County  at  Bird  Rock 
off  Tomales  Point,  the  northernmost  locale  in  the  species' 
breeding  range  where  nesting  has  been  confirmed.  These 
petrels  were  first  confirmed  breeding  there  on  3  July  1972 
when  an  adult  was  found  incubating  an  egg  in  a  rock 
crevice;  a  petrel  chick  found  there  on  23  August  1969, 
though  unidentified,  was  undoubtedly  this  species  (Ainley 
&  Osborne  1972).  Sowls  et  al.  (1980)  found  them  still 
breeding  there  during  the  adas  period  as  did  Carter  et  al. 
(1992)  in  1989  (see  below). 

An  adult  Ashy  Storm-Petrel  with  a  brood  patch  was 
captured  in  a  mist  net  on  the  night  of  5-6  August  1989  in 
the  vicinity  of  suitable  crevice-nesting  habitat  on  an  off- 
shore islet  in  Van  Damme  Cove,  Mendocino  County; 
additional  evidence  of  breeding  is  needed  to  substantiate 
this  probable  extension  of  the  breeding  range  85  miles 
north  of  Bird  Rock  (Carter  et  al.  1992). 

Historical  Trends/  Population  Threats 

Although  long-term  data  are  lacking,  the  Marin  County 
breeding  population  of  Ashy  Storm-Petrels  probably  has 
always  been  small.  Ainley  and  Osborne  (1972)  initially 


estimated  a  maximum  of  20  to  24  birds  nesting  on  Bird 
Rock  in  1972,  but  Ainley  and  Whitt  (1973)  later  revised 
the  estimate  downward  to  10  birds.  During  the  adas 
period,  Sowls  et  al.  (1980,  NE  7/1/79)  estimated  the 
breeding  population  on  Bird  Rock  at  14  birds.  A  higher 
estimate  of  74  petrels  breeding  there  in  1 989  was  attributed 
to  greater  effort  expended  that  year  than  in  others  to 
determine  the  size  of  this  colony  (Carter  et  al.  1992). 

Virtually  all  of  the  northern  and  central  California 
breeding  population  of  Ashy  Storm-Petrels  is  concentrated 
on  the  Farallon  Islands  (Sowls  et  al.  1980,  Carter  et  al. 
1992).  A  population  estimate  at  the  Farallones  of  4000 
birds  in  1972  (Ainley  6k  Lewis  1974)  has  also  been 
reported  by  other  workers  (Sowls  et  al.  1980,  Carter  et  al. 
1992),  but  additional  censusing  efforts  are  needed  to  assess 
the  accuracy  of  this  estimate  and  the  trend  of  the  regional 
population  (H.R.  Carter  6k  W.J.  Sydeman  pers.  comm.). 
The  Ashy  Storm-Petrel  is  currendy  a  Bird  Species  of 
Special  Concern  in  California  (Remsen  1978,  CDFG 
1991b). 

Ashy  Storm-Petrels  breeding  at  Bird  Rock  are  vulnerable 
to  disturbance  by  humans  crossing  from  Tomales  Point  at 
low  tide  or  by  boat.  Occasional  intruders,  however,  are 
quite  unlikely  to  even  notice  these  furtive,  nocturnal  cavity- 
dwellers,  though  they  would  undoubtedly  disturb  other 
nesting  seabirds.  Coulter  and  Risebrough  (1973)  detected 
high  pesticide  levels  and  eggshell  thinning  in  Ashy  Storm- 
Petrels  at  the  Farallon  Islands,  but  breeding  biology  studies 
have  not  disclosed  any  adverse  effects  of  this  contamina- 
tion (Ainley  6k  Lewis  1974;  Ainley  6k  Boekelheide  1990, 
Chap.  4).  Perhaps  the  greatest  threat  to  the  species  would 
be  a  catastrophic  event  at  sea.  An  oil  spill  to  the  south  in 
Monterey  Bay,  where  thousands  of  Ashies  concentrate  in 
fall,  could  inflict  severe,  perhaps  irreparable,  damage  to  the 
population  (Ainley  1976,  Sowls  et  al.  1980,  Roberson 
1985). 


82 


Cormorants 


SPECIES  ACCOUNTS 


Cormorants 


Cormorants 

Family  Phalacrocoracidae 


DOUBLE-CRESTED  CORMORANT   Phalacrocorax  auritus 


A  year-round  resident;  numbers  swell  (at 

least  on  Pt.  Reyes  estuaries)  from  Aug 

A>\^$r^^\    N           JC^ 

through  Dec.  At  Farallon  Islands  (and 

xv-^f^^ 

S.F.  Bay  bridges),  birds  occupy  nest  sites 

^Vm^Y^VmJ^  \^\J\^C  \^\l^\  ~ 

mosdy  from  mid-  to  late  Mar  (rarely 

*\s^\X2\\J^^^ 

beginning  early  Apr)  through  Aug  (rarely 

\\^\>)^^\^KX^ 

Sep).  In  poor  food  years,  Farallon  birds 

Vv^c^Cx  >^\\   \^\     \^\\^\\^\\^\ 

desert  colonies  during  midseason. 

\&\*^^^ 

A  very  rare,  very  local  breeder;  overall 

\u<^\^^^ 

breeding  population  very  small. 

^v^a^aA^<v3p^\^^ 

Recorded  in  1  (0.4%)  of  221  blocks 

<35h^^ 

(see  Mediods). 

O    Possible        =         0   (0%) 
©    Probable      =        0  (0%) 

)  s^**                                       ^^\      /       ^-^^^^s^T-  \^^*V*^^\  J*? 

•    Confirmed  =         1    (100%) 

FSAR  =1          OPI  =  1           CI  =  3.00 

Ecological  Requirements 

The  West  Coast  version  of  this  piscivorous  phalacrocorid 
was  originally  dubbed  the  Farallon  Cormorant,  despite 
being  the  only  one  of  our  locally  breeding  cormorants  that 
makes  its  living  in  both  estuarine  or  inshore  waters  and 
inland  lakes,  reservoirs,  and  rivers. 

Farallon  Island  breeders  feed  within  about  20  to  50 
miles  of  the  colony  in  nearshore  coastal  waters  and  in 
estuaries  and  lagoons  on  Point  Reyes  and  in  San  Francisco 
Bay  (Ainley  &  Boekelheide  1990,  Chap.  3).  Although 
most  foraging  waters  are  no  more  than  about  35  feet  deep, 
Double-crests  apparendy  can,  if  need  be,  dive  foot-pro- 
pelled from  65  to  260  feet,  intermediate  depdis  for  diving 
seabirds.  Pelagic  and  Brandt's  cormorants  generally  are 
deeper  divers.  Double-crested  Cormorants  usually  feed 
singly  or  in  small  flocks  of  less  than  20  but  sometimes  up 
to  hundreds  of  birds  (Bartholomew  1942).  Smaller  flocks 
are  often  roughly  circular  in  formation  and  coalesce  by 
swimming  after  diving.  Larger  flocks  arrange  themselves  in 
long,  compact  lines  perpendicular  to  the  direction  of  move- 
ment of  schooling  fish  and  "leapfrog"  (by  swimming  or 
flying)  to  the  front  of  the  flock  after  surfacing  from  dives. 
In  marine  waters  along  die  West  Coast,  Double-crests  feed 


mostly  on  schooling  fish  found  from  the  surface  to  near 
(but  not  on)  flat  sand  or  mud  bottoms  (Ainley  et  al.  1981; 
Ainley  ck  Boekelheide  1990,  Chap.  3).  They  also  feed 
somewhat  over  rocky  or  gravelly  substrates  (Lewis  1929, 
Palmer  1962).  Farallon  breeders  feed  almost  exclusively  on 
neritic  and  estuarine  fish,  predominately  two  species  of 
surfperch  (Embiotocidae')  and  in  particular  the  shiner  surf- 
perch  fC^nuztogaster  aggregata)  (Ainley  et  al.  1981;  Ainley 
&  Boekelheide  1990,  Chap.  3,  n  =  2815).  At  the  Faral- 
lones,  the  diet  of  Double-crests  varies  little  between  years 
and  overlaps  little  widi  that  of  Brandt's  or  Pelagic  cormo- 
rants. Overall  the  Double-crested  Cormorant  feeds  primar- 
ily on  a  wide  variety  of  marine  and  freshwater  fish,  usually 
of  no  commercial  value  (Lewis  1929,  Palmer  1962,  Robert- 
son 1974,  Ainley  et  al.  1981).  Other  dietary  items  include 
shrimp,  squid,  salamanders,  frogs,  and  watersnakes, 
whereas  crayfish  may  be  important  at  some  inland  sites. 
Crabs,  mollusks,  seaworms,  aquatic  insects,  and  odier 
invertebrates  are  likely  first  consumed  by  the  cormorants' 
fish  prey.  The  young  are  fed  by  regurgitation  and,  if 
possible,  they  creche  (gather  together  in  clusters)  after 
leaving  their  nests  but  before  fledging. 

83 


Cormorants 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Cormorants 


On  the  California  coast,  nest  sites  of  Double-crests  are 
more  varied  than  those  of  Pelagic  or  Brandt's  cormorants. 
Double-crests  nest  on  the  moderately  steep,  rocky  slopes  of 
offshore  islands  or  rocks;  on  inaccessible  mainland  cliffs; 
in  trees;  and  on  structures  such  as  bridges,  wharf  pilings, 
abandoned  dredges,  and  electrical  power  towers.  At  inland 
sites  (and  sometimes  coastal  salt  ponds),  birds  nest  near 
fresh  water,  in  trees,  usually  surrounded  by  water,  or  on 
islands,  where  the  nest  may  be  placed  on  the  ground;  on 
rock  ledges  or  pinnacles;  or  in  bushes  or  trees  (Bent  1922, 
Lewis  1929,  Palmer  1962,  D.  Shuford  pers.  obs.).  Tree 
nests  may  be  in  crotches  or  well  out  on  horizontal  limbs 
and  range  to  over  100  feet  above  the  ground.  Double-crests 
are  highly  colonial  except  where  die  availability  of  suitable 
nest  foundations  precludes  closer  spacing.  Where  Double- 
crests  cohabit  nesting  islands  with  Brandt's  Cormorants, 
Double-crests  often  nest  on  the  steeper,  more  broken 
terrain  of  higher  slopes,  crests  of  ridges,  and  summits  of 
rocks  or  islands  (Dawson  1923;  Ainley  6k  Boekelheide 
1990,  Chap.  6).  A  prime  requisite  of  Double-crested  Cor- 
morants' nest  sites  appears  to  be  at  least  one  side  of  die 
ground  or  rock  falling  abrupdy  away  (Bent  1922).  On  the 
other  hand,  Double-crests  tend  to  avoid  the  narrow  shelves 
of  precipitous  cliffs  inhabited  by  Pelagics  (Dawson  1923; 
Ainley  6k  Boekelheide  1990,  Chap.  6). 

The  bulky,  cup-shaped  body  of  a  Double-crested  Cor- 
morant nest  is  composed  primarily  of  coarse  sticks  and 
twigs  when  available.  Otherwise  seaweed,  kelp,  dead  tules, 
and  weed  stalks  are  typical  substitutes.  The  large  stick  nests 
found  in  trees  may  serve  as  much  as  landing  platforms  as 
they  do  egg  baskets  for  diese  heavy,  ungainly  landing  craft 
(Ainley  1984b).  Various  soft  materials  such  as  grasses, 
straw,  seaweed,  moss,  green  leaves  or  conifer  sprays,  bark 
strips,  and  feathers  (along  with  the  odd  bone,  dead  crab, 
or  human  artifact)  are  incorporated  in  the  wall  of  the  nest 
or  form  a  pseudolining  (Bent  1922;  Dawson  1923;  Palmer 
1962;  Ainley  6k  Boekelheide  1990,  Chap.  6).  Items  such 
as  plastic  rope,  packing  tape,  paper,  cigarette  butts,  rags, 
and  even  a  gun  holster  have  been  found  in  nests  on  the 
girders  of  the  San  Rafael-Richmond  Bridge,  Contra  Costa 
County;  one  nest  there  was  built  on  a  hubcap  (R.P. 
Henderson  6k  M.  Rauzon  pers.  coram.)!  Nests  built  on  the 
remains  of  previous  years'  nests  may  become  quite  large 
from  the  addition  of  material  throughout  the  nesting  sea- 
son and  over  the  course  of  many  years. 

Marin  Breeding  Distribution 

The  only  Marin  County  breeding  record  for  Double- 
crested  Cormorants  during  the  adas  period  was  of  a  single 
nest  observed  in  a  California  bay  tree  amidst  a  Great  Blue 
Heron  colony  on  an  island  in  Stafford  Lake,  Novate,  in  the 
breeding  season  of  1978  (ScC).  The  only  two  known 
colonies  of  this  cormorant  in  the  county  were  established 

84 


on  the  outer  coast  prior  to  and  subsequent  to  the  adas 
project  (see  below). 

Historical  Trends/ Population  Threats 

Formerly,  a  nesting  colony  (size  unknown)  was  located  in 
Marin  County  on  a  flat  shelf  of  the  cliff  at  Point  Resistance, 
about  one  mile  north  of  the  ocean  end  of  Bear  Valley;  nests 
with  large  young  were  observed  there  on  30  May  1929 
(Bolander  6k  Bryant  1930).  Surveys  in  1979  and  1980  of 
seabirds  breeding  on  the  outer  coast  of  California  revealed 
no  colonies  of  Double-crested  Cormorants  in  Marin 
County  (Sowls  et  al.  1980),  but  repeat  surveys  in  1989 
found  a  new  colony  of  14  birds  on  5  June  at  Dillon  Beach 
Rocks  (Carter  et  al.  1992). 

Breeding  populations  of  Double-crested  Cormorants  in 
California  declined  during  historical  times  at  the  Farallon 
Islands  because  of  disturbance  from  commercial  collectors 
harvesting  Common  Murre  eggs  and  from  island  occu- 
pants (Ainley  6k  Lewis  1974;  Ainley  6k  Boekelheide  1990, 
Chap.  6),  on  islands  off  southern  California  and  the  west 
coast  of  Baja  California  because  of  pesticide  contamination 
and  human  disturbance  (Gress  et  al.  1973),  and  in  interior 
California  because  of  disturbance  from  lake  development 
and  recreation  (G6kM  1944,  Sowls  et  al.  1980).  Eggshell 
diinning  has  also  been  documented  at  the  Old  Areata 
Wharf,  Humboldt  County  {fide  Sowls  et  al.  1980). 

Ainley  and  Lewis  (1974)  suggested  that  marine  breeding 
populations  of  Double-crested  Cormorants  failed  to  re- 
cover from  their  decline  because  populations  of  their  prey 
base— the  Pacific  sardine  (Sardinops  caerulea)— were  over- 
exploited  by  humans  in  the  late  1940s  at  a  time  of  unfavor- 
able environmental  conditions.  The  sardines  were 
replaced  by  the  northern  anchovy  (Engraulis  mordax),  a 
possibly  less  desirable  prey  of  the  cormorants.  Recent 
dramatic  increases  of  Double-crested  Cormorants  in  Cali- 
fornia, despite  no  rise  in  sardine  populations,  suggest  that 
other  factors  may  also  have  been  limiting  the  cormorants. 
The  Farallon  population  of  this  cormorant  began  to  re- 
cover slighdy  in  the  1970s  (Ainley  6k  Boekelheide  1990, 
Chap.  6),  declined  substantially  after  the  1982-83  El  Nino 
Southern  Oscillation  event,  but  by  1 989  had  increased  to 
about  1140  breeding  birds  (Carter  et  al.  1992).  Channel 
Island  populations,  which  may  have  declined  substantially 
since  die  turn  of  the  century,  now  also  are  increasing 
(Carter  et  al.  1992).  Breeding  numbers  in  San  Francisco 
Bay— swelled  gready  by  the  establishment  (primarily  since 
1984)  of  colonies  on  bridges— totaled  2789  birds  in  1989 
to  1991,  representing  37%  of  the  northern  and  central 
coastal  California  population  (Carter  et  al.  1992,  H.R. 
Carter  pers.  comm.).  Numbers  on  the  outer  coast  of  this 
region  alone  increased  from  1466  birds  in  1979  to  1980, 
to  4785  in  1989,  as  a  result  of  expansion  at  old  colonies 
and  the  establishment  of  1 1  new  ones  (Carter  et  al.  1992). 
Numbers  of  Double-crested  Cormorants  also  increased  on 


Cormorants 


SPECIES  ACCOUNTS 


Cormorants 


Breeding  Bird  Surveys  in  California  from  1968  to  1989, 
though  they  were  relatively  stable  from  1980  to  1989 
(USFWS  unpubl.  analyses).  These  trends  presumably 
reflect  changes  in  the  population  of  the  interior,  where 
most  BBS  routes  are  located. 

Because  of  continentwide  population  declines,  the  Dou- 
ble-crested  Cormorant  was   placed   on   the  Audubon 


Society's  Blue  List  from  1972  to  1981  (Tate  1981)  and  on 
its  Species  with  Special  Concerns  list  in  1982  (Tate  ck  Tate 
1982).  Although  numbers  now  appear  to  be  increasing 
widely  (e.g.,  Tate  1986,  Carter  et  al.  1992),  this  cormorant 
is  still  considered  a  Bird  Species  of  Special  Concern  in 
California  (Remsen  1978,  CDFG  1991b). 


BRANDT'S  CORMORANT    Phalacrocorax  penicillatus 


A  year-round  resident;  numbers 

depressed  somewhat  on  ocean  waters 

from  Dec  through  Apr.  Farallon  Island 

A^\y^A^^                  \                     ypv. 

(and  probably  Marin)  breeders  occupy 

"^^\-^\Ot^v  \^\  \-?^r<:^,^rTV-^\\^^\?t-\(_^' 

nesting  colonies  starting  mid-  to  late  Mar 

J\^A     £c\     y<^\    J^^.     \5t<r\      \^\      \^\      \^r\ 

(extremes  early  Mar  and  early  May) 

\^^^\jr^(^^^^^^^^%^ 

through  Aug  (rarely  through  Sep  and 

Oct).  In  poor  food  years,  few  birds 

V5"  J^x^Ca ~z>^\\  ^\\  ^<r\  ^*c\  y<i\   \^\ 

occupy  nest  sites  and  all  desert  early  in 

\)y<^^-§rx^^\^\j£^ 

the  season. 

\\^*\^^ 

A  very  abundant,  very  local  breeder; 

u^c^A^rj)^^^^                                                    '" 

overall  breeding  population  very  small. 

V^X^Oe^\^}\-^\Jr^\)^^ 

Recorded  in  4  (1.8%)  of  221  blocks 

ix^r/  vVf  v-^r  \^\   \^3T^v^(pi\^\    x>\  s-^ 

(see  Methods). 

■^^^^^^Ps^^i^s^^^^ 

O    Possible        =        0   (0%) 

C    Probable                 0   (0%) 

•    Confirmed  =        4  (100%) 

FSAR  =7        OPI  =  28         CI  =  3.00 

Ecological  Requirements 

Flight  lines  of  Brandt's  Cormorants  merge  with  multi- 
species  feeding  flocks,  alerting  birds  and  humans  alike  to 
the  bountiful  productivity  of  the  ocean  waters  near 
California's  seabird  breeding  colonies.  The  Brandt's  Cor- 
morant is  one  of  two  stricdy  marine  cormorants  breeding 
along  the  California  coast  and  inhabiting  waters  over  the 
continental  shelf.  Of  the  two,  its  distribution  indicates  it  is 
the  most  characteristic  of  the  cool  upwelling  waters  of  the 
California  Current  (Ainley  ck  Boekelheide  1990,  Chap. 
5).  Brandts  feed  primarily  in  nearshore  waters,  but  also 
well  offshore  and  in  deep  coastal  bays.  The  importance  of 
these  different  foraging  areas  to  Farallon  Island  breeders 
varies  seasonally  and  yearly  (Ainley  <St  Boekelheide  1 990, 
Chap.  3).  Although  breeders  range  up  to  50  miles  from  the 
Farallon  colony  on  feeding  trips  (Ainley  ck  Boekelheide 
1990,  Chap.  3),  foraging  birds  seldom  stray  more  than  6 
miles  from  land,  except  in  transit  (Briggs  et  al.  1987). 

Brandt's  Cormorants  make  relatively  deep,  foot- 
propelled  foraging  dives.  Along  die  mainland  coast,  they 
forage  over  sand  and  mud  bottoms  at  depths  of  about  30 


to  200  feet  and  offshore  over  rocky  bottoms,  as  well, 
apparendy  up  to  about  400  feet  in  depth  (Ainley  ck 
Boekelheide  1990,  Chap.  3).  Brandts  use  equal  propor- 
tions of  schooling  and  nonschooling  prey  and  show  great 
dietary  diversity.  A  study  of  their  diet  up  and  down  the 
Pacific  Coast  indicates  that  although  the  majority  of  their 
prey  live  on  or  just  above  the  bottom  over  both  rocky  and 
flat  substrates,  appreciable  numbers  range  from  mid- 
depths  to  the  surface  and  others  hide  in  the  substrate 
(Ainley  et  al.  1981).  Brandts  vary  dieir  feeding  habits  from 
nordi  to  south  along  the  West  Coast.  To  the  north  in  areas 
of  overlap  widi  Pelagics,  Brandts  eat  the  same  prey  as 
Pelagics,  but  they  feed  just  above  rocky  substrate  or  near 
substrate  without  relief,  whereas  Pelagics  feed  primarily  in 
rocky  substrate.  To  the  south,  in  areas  where  Pelagics  are 
absent,  Brandts  feed  almost  exclusively  in  rocky  habitat  or 
near  rocks  on  flat  bottoms  (Ainley  et  al.  1981). 

Brandt's  Cormorants  are  gregarious  foragers.  In  years  of 
high  oceanic  productivity  (rockfish  abundance),  they  tend 
to  feed   in  large  flocks,  often  with   Western  Gulls  and 

85 


Cormorants 


MARIN  C:OUNTY  BRLHDING  BIRD  ATIAS 


Cormorants 


Common  Murres;  in  unproductive  years  they  feed  in 
smaller  flocks  by  themselves  (Ainley  6k  Boekelheide  1990, 
Chap.  3).  Brandts  prey  on  a  wide  variety  of  marine  fish  and 
occasionally  take  octopus  and  market  squid.  At  die  Faral- 
lon  Islands,  the  diet  is  dominated  by  midwater  schooling 
rockfish,  mainly  Sebasles  flavidus  and  S.  jordani.  Other 
important  prey  are  flatfish  (bothids  and  pleuroncctids), 
Pacific  tomcod  (Microgadus  jnoximus),  midshipmen  (Porich- 
thys  notatus),  and  spotted  cuskeels  (Chilara  taylori)  (Ainley 
et  al.  1981;  Ainley  &  Boekelheide  1990,  Chap.  3,  n  = 
11,190).  In  most  years,  dietary  diversity  is  low  because  of 
the  reliance  on  juvenile  rockfish,  but  in  unproductive 
(usually  warm-water)  years  it  is  higher.  In  cool-water  years, 
the  pre-egglaying  diet  is  more  diverse  and  overlaps  little  in 
species  composition  with  the  later-season  diet.  Overlap  of 
the  Brandt's  Cormorant  diet  with  that  of  die  Double- 
crested  Cormorant  is  minimal,  though  slightly  greater  in 
warm-water  years.  At  the  Farallon  Islands,  Brandt's  and 
Pelagic  cormorants  eat  many  of  the  same  prey  species 
(except  in  warm-water  years),  because  they  bodi  rely  heavily 
on  juvenile  rockfish,  though  Pelagics  tend  to  take  smaller- 
sized  prey.  Like  our  other  cormorants,  Brandts  feed  their 
young  by  regurgitation,  and  the  young  creche  (gadier  to- 
gether) before  and  after  leaving  the  nest  and  before  fledging 
(Carter  &  Hobson  1988). 

Brandts  form  the  largest  and  densest  colonies  of  our 
locally  breeding  cormorants  where  they  nest  on  offshore 
islands,  sea  stacks,  and  inaccessible  mainland  cliffs.  Where 
Brandts'  colonies  overlap  with  those  of  Double-crested 
Cormorants,  Brandts  often  prefer  the  gentler  terrain  of 
high,  rounded  shoulders  of  rock;  gradual,  sloping  inclines; 
and  flattops  of  rocky  islands  (Bent  1922,  Williams  1942). 
Aldiough  Brandts  occasionally  nest  on  wide  ledges  or 
niches  on  a  cliff  face,  these  sites  are  never  as  precarious  as 
diose  chosen  by  Pelagic  Cormorants.  Brandt's  Cormo- 
rants build  large,  bulky,  cup-shaped  nests  diat  solidify  from 
compaction  and  the  accumulation  of  fecal  droppings. 
Nests  are  generally  built  on  the  rotted  debris  and  guano  of 
the  previous  year's  effort,  but,  rarely,  diey  expand  to  tall 
cylinders  widi  yearly  additions  of  material.  Typical  nest 
materials  are  land  plants  such  as  Farallon  weed,  grasses, 
and  mosses  and  marine  plants,  including  algae,  eelgrass, 
and  surfgrass  (Bent  1922;  Dawson  1923;  Palmer  1962; 
Ainley  6k  Boekelheide  1990,  Chap.  5). 

Marin  Breeding  Distribution 

During  die  adas  period,  Brandt's  Cormorants  bred  at  six 
colonies  along  the  outer  coast  of  Marin  County  (NE,  Sowls 
et  al.  1 980;  Table  1 4,  Figure  1 4).  In  1 989,  the  total  number 


of  occupied  colonies  remained  the  same,  but  the  small 
colony  at  die  "Sonoma-Marin  County  Line"  was  aban- 
doned and  a  new  colony  was  established  at  Bird  Rock,  off 
Tomales  Point  (Carter  et  al.  1992). 

Historical  Trends/ Population  Threats 

Partial  surveys  in  1969  to  1972  estimated  a  total  of  1330 
Brandt's  Cormorants  were  breeding  at  diree  sites  along  the 
Marin  County  coast  (Ainley  6k  Whitt  1973).  From  com- 
plete surveys,  numbers  of  this  cormorant  breeding  in  the 
county  totaled  3204  birds  in  1979  to  1980  (Sowls  et  al. 
1980)  and  1935  birds  in  1989  (Carter  et  al.  1992).  The 
recent  change  in  local  population  size  may  in  part  reflect 
differences  between  the  two  survey  periods  in  oceano- 
graphic  conditions,  which  can  dramatically  affect  the  num- 
ber of  Brandt's  Cormorants  that  breed  in  a  given  year 
(Ainley  6k  Boekelheide  1990,  Chap.  5).  Also,  because  part 
or  all  of.die  birds  at  a  colony  often  shift  breeding  locations 
among  years,  Carter  et  al.  (1990)  stressed  the  importance 
of  assessing  population  trends  over  large  rather  than  small 
areas. 

During  the  mid-1 880s,  the  Brandt's  Cormorant  popu- 
lation at  the  Farallon  Islands  declined  drastically  from 
disturbance  caused  by  commercial  egg  collectors  gathering 
Common  Murre  eggs,  but  cormorant  numbers  there  have 
since  increased  dramatically  (Ainley  &  Lewis  1974).  Num- 
bers of  Brandt's  Cormorants  attempting  to  breed  at  the 
Farallones  in  the  1970s  and  1980s  have  fluctuated  gready 
from  year  to  year,  reflecting  varying  oceanographic  condi- 
tions and  hence  food  supplies  (Ainley  6k  Boekelheide 
1990,  Chap.  5).  On  the  central  and  northern  California 
coast  as  a  whole,  estimates  of  the  population  size  of  this 
cormorant  varied  from  58,290  breeding  birds  at  61  sites  in 
1979  to  1980  (Sowls  et  al.  1980)  to  54,029  birds  at  71  sites 
in  1989  (Carteret  al.  1992).  Sowls  et  al.  used  a  1979  PRBO 
estimate  for  the  South  Farallon  Islands  of  28,000  Brandt's 
that  Ainley  and  Boekelheide  (1990)  revised  to  about 
19,000. 

Populations  of  Brandt's  Cormorants  on  the  Channel 
Islands  have  also  declined  historically,  first  from  human 
disturbance  and  later  presumably  from  the  accumulation 
of  pesticides  as  indicated  by  eggshell  thinning  (Hunt  et  al. 
1979).  Chick  deformities  that  often  result  from  pollutants 
are  rarely  observed  at  the  Farallon  Islands  (Hobson  6k 
Carter  1988).  Significant  numbers  of  Brandt's  Cormo- 
rants are  caught  in  gill  nets  (H.R.  Carter  pers.  comm.),  but 
few  die  during  oil  spills  (Page  et  al.  1990). 


86 


1 

On 
OO 
On 

00 
rsi 

o 

ro 
rsl 

o 

00 
00 

Tl- 

NO 

r<-> 

NO 

rsi 
r-i 

rO 

r — 

NO 

00 

NO 

1- 

NO 

rsl 

On 

rsl 

NO 

r^ 

o 

ON 
■sf 

CO 
00 

00* 
rsi 

On 
On 

NO 

O 
rsi 

rn 

rM 

00 

00 
rsl 

NO 

o 

On_ 
On" 

' 

NO 

00 

00 
On 

o 

Ti- 
ro 
r*N 

' 

NO 

NO 

m 

NO 

+ 

T|- 

nO 

+ 

r-i 
rsl 

+ 

o 

00 

00 

|s- 

rsf 

"8   c| 

On 
00 
On 

' 

• 

i 

' 

' 

■+■ 

' 

' 

' 

' 

' 

' 

i 

' 

' 

' 

- 

■sf 

On 
On 

' 

• 

' 

' 

' 

NO 

' 

' 

1 

' 

' 

I 

' 

1 

' 

' 

' 

nO 

2 

8  3 

■S  J 

On 
00 
On 

' 

' 

' 

rO 

' 

NO 

' 

■ 

' 

' 

' 

1 

1 

1 

' 

' 

' 

On 

On 
I — 

On 

' 

' 

' 

' 

' 

' 

' 

i 

i 

' 

' 

' 

' 

1 

' 

i 

1 

1 

0     u 

ac  _ 

O 

On 
00 
ON 

to 

rsi 

o 

rsl 

' 

w>. 

00 

NO 
NO 

rO 

o 

r«J 

' 

r-~ 

to 

NO 
NO 

rsl 

1 

00 

o 

On 

On 

O 

o 

00 

o 

rr> 

rsl 

O 

csl 

' 

o 

NO 

O 

O 
■nT 

' 

r-j 

X 

<*- 

X 

X 

X 

NO 

NO 

rr, 

c 

0      V 

£    t 

£  «§ 

c32 

On 
OO 

ON 

■ 

' 

' 

t 

I 

UN 
un" 

' 

OO 
«1 

00 
U-N 

NO 
f 
1- 

' 

' 

' 

1 

' 

' 

i 

u-l 

On 
■sT 
rn 

rsi 

On 
rs_ 

o\ 

i 

i 

1 

1 

1 

o 
o 

U-l 

NO" 

' 

O 
O 
in 

r- 

' 

o 

o 

' 

1 

1 

1 

' 

' 

- 

O 
O 

o_ 

|SsT 

E  _ 

a  "5 

8  O 

On 
00 
On 

■*■ 

rsl 

o 

00 

NO 

00 

00 

• 

00 

o 

CO 

00 

NO 

NO 

O 

O 

\Q 

■st" 

rn 

o 

On 

On 
On 

nO 

csl 

rsi 

00 
Csl 

' 

NO 

' 

o 

rO 

Tl- 

' 

■«■ 

' 

rsi 

■"I" 

rsi 

NO 

NO 

rsi 
•sT 

j: 

6" 

On 
00 
On 

l/N 

r»-N 

rO 

NO 

' 

NO 

' 

' 

- 

' 

' 

- 

- 

- 

' 

• 

' 

rsi 

On 
i — 
On 

■■a- 

NO 

' 

rsl 

• 

o 

' 

rvl 

' 

rsl 

' 

rsl 

rs 

' 

i 

' 

' 

O 

ro 

c 

u      £ 

re    ° 

^    o 

0 

On 
00 
On 

00 

f"N 

TT 

■**■ 

' 

NO 
NO 

rsi 

' 

' 

On 

ON 

1 

0\ 

rsi 

' 

On 

rsi 

in 

rsi 

O 

ON 

On 
On 

Ti- 
ro 

vO 
00 

00 

NO 

00 
O 
00 

' 

■N»- 

o 

O 

NO 

NO 

' 

00 

' 

o 

NO 

O 

-1- 

sO 

rsi 

NO 

•JO         C 

1  § 
ffic3 

On 
00 
On 

1 

oo 

1 

U"l 

u-l 

' 

rsl 
u-i 

' 

NO 

■*■ 

o 
oo 

' 

1 

i 

' 

! 

' 

1 

u-l 

rn 

ON 

On 
ON 

rsi 

o 

ON 

I 

' 

' 

o 

o 

TT 
rs| 

' 

o 

ON 

CO 
rsl 

1 

' 

' 

' 

' 

■ 

' 

■*■ 
o 

rsi 

rn 

Double- 
crested 
Cormorant 

On 
00 
On 

' 

*»■ 

I 

' 

' 

' 

' 

i 

' 

' 

1 

1 

' 

' 

' 

■ 

' 

■«■ 

On 
On 

' 

' 

' 

' 

' 

' 

' 

' 

' 

' 

1 

1 

1 

1 

1 

' 

' 

' 

en 

On 
00 
On 

' 

' 

• 

' 

' 

' 

' 

' 

' 

' 

' 

' 

' 

' 

1 

' 

On 
On 

1 

1 

1 

Tf- 

' 

' 

' 

' 

' 

' 

' 

' 

' 

' 

' 

■ 

' 

TT 

c 
"3 

2r 

c 

3 
0 

0 

c 

rt 

s 

ni 

E 

o 
c 

(J 

s. 

'J 

s 

oa 

c 
_o 

Q 

a 

E 
o 

1 

co 

jg 

a 
E 

6 

C 
n 
_c 
a 

V 

c2 
c 

■fi 

3 
0 
00 

-o 

e 

3 
0 
be 

a 
E 

o 

3 
0 

V 

c 

e 

c 

'J 

c 
5 
c 

V 

J2 

'.J 

c 
'5 

3 

Q 

c 

o 
c 

JS 

0 

_c 

i 

CQ 

c 

0 

c 
□ 
00 

< 

'J 

J 

a 

c 
rt 

-o 

s  « 

I      0 

JJ 

-o 

c 

-a 
p5 

E 
c 

0 
CO 

c 

cu 

V 

i 
u 
g 

c 
3 
CO 

-a 

c 

3 
CO 

S  2 

13 

c2  z 

1 

0 
r- 

o 

o 

On 
On 


U  — 

•"  S. 

2  I, 

.£  -° 

O  (A) 

S  D 

£  c 


C 

M 

CO 

V 

c 

it 

c 

3 

2 


3 

-o 

« 
M 

_o 

C3 

C- 

c 

« 

t/) 

-a 

c 


-o 

c 

3 

.o 


D 

C 

'C 

3 

-o 

to 

-a 
c 


u- 
c 

rt 

u9 

c 


c 
o 

-o 

c 

3 

n£ 

o 


2ro 

c   <*"> 

3      „, 
0      V 

U  "5 

c 

C     C 

rt     •  — 

2S 

rsl    (On 


2      C    -71 


3s     ^ 


^5 


3 

c 


* 


CD 


M 

O 

M 

E 

3 

c 

■a 

0 


MARIN  COUNTY  BRHHDING  BIRD  ATLAS 


Colony  codes  used  are: 

01  =  "Sonoma-Marin  County  Line" 

02  =  "Dillon  Beach  Rocks" 

03  =  Tomales  Point 

04  =  Bird  Rock 

05  =  "Elephant  Rock  Complex" 

06  =  Point  Reyes 

07  =  Coast  Campground  South 

08  =  Point  Resistance 

09  =  Millers  Point  Rocks 

10  =  Double  Point  Rocks 


11=  Stinson  Beach  to  Rocky  Point 
12=  Gull  Rock  Area 

13  =  Muir  Beach  Headlands  to  Tennessee  Cove 

14  =  Bird  Island 

15  =  Point  Bonita 

16  =  Bonita  Cove 

17  =  Point  Diablo  Bluffs  and  Needles 

18  =  Yellow  Bluff 

19  =  Sausalito  Point  Area 

20  =  Peninsula  Point  and  Cone  Rock 


21  =  Angel  Island 

22  =  Bluff  Point  to  Paradise  Cay 

23  =  Richmond-San  Rafael  Bridge 

24  =  Point  San  Quentin 

25  =  Marin  Islands 

26  =  The  Sisters  and  Point  San  Pablo 

27  =  Rat  Rock 

28  =  Southwest  San  Pablo  Bay  Duck  Blinds 

29  =  Marin  County- West  San  Pablo  Bay  Ship 

Channel 


Figure  14-    Map  of  marine  bird  colony  sites  in  Marin  County.  See  Carter  et  al.  (1992)  for  detailed  colony  maps  and  standard 
California  and  USFWS  colony  codes  (not  used  here). 


88 


Cormorants 


SPECIES  ACCOUNTS 


Cormorants 


PELAGIC  CORMORANT    Phalacrocorax  pelagicus 


A  year-round  resident.  Pelagics  occupy 
breeding  cliffs  at  the  Farallon  Islands 
(and  probably  Marin)  in  high  numbers 
mosdy  from  Mar  (extremes  Dec  or  Jan 
and  Apr  or  May)  through  Aug  (rarely  to 
early  Oct).  In  poor  food  years,  birds  fail 
to  lay  eggs  or  desert  nests  as  early  as  Jun 

r\* 

'/'  VatV  L\r"'\  JV""\    \r^\^£T\    \^efC^\^V\Y"-'\ 

or  Jul. 

A  very  common,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  11  (5.0%)  of  221  blocks 
(see  Methods). 

ir^^^      ^^T»  \^\A\Jl)'X\  ^i-V<^    /  rv 

O    Possible                  0   (0%) 

C    Probable       =         0   (0%) 

•    Confirmed   =       11    (100%) 

FSAR  =  5        OPI  =  55         CI  =  3.00 

Ecological  Requirements 

These  sleek  iridescent  cormorants  choose  lofty,  precarious 
nest  sites  free  of  acrophobics.  In  the  watery  realm,  they  are 
exclusively  marine  inhabitants,  but  despite  what  their 
name  implies  they  occupy  nearshore  waters  within  12 
miles  (mosdy  within  6  mi.)  of  mainland  or  island  shores 
(Briggsetal.  1987). 

Like  Brandts,  Pelagic  Cormorants  are  foot-propelled 
divers  that  perhaps  reach  400  feet  in  depth.  In  contrast  to 
Brandts,  Pelagics  typically  feed  alone  on  solitary  nearshore 
prey  that  hide  in  rocky  reef  substrates  (Ainley  et  al.  1981; 
Ainley  6k  Boekelheide  1990,  Chap.  3).  In  years  of  high 
ocean  productivity  and  superabundant  prey,  Pelagics  at  the 
Farallon  Islands  tend  to  feed  in  the  company  of  small 
multispecies  flocks  of  seabirds  on  midwater  schools  of 
rockfish.  The  Brandt's  Cormorant  account  contains  fur- 
ther comparison  of  the  feeding  niches  of  these  two  species. 
The  diet  of  the  Pelagic  Cormorant  is  most  similar  to  the 
Pigeon  Guillemot,  another  species  feeding  mosdy  in  rocky 
substrates  (see  account).  The  predominant  prey  of  Pelagic 
Cormorants  at  the  Farallon  Islands  are  several  species  of 
sculpin  (cottids),  juvenile  rockfish  (mosdy  Sebastes  flavidus 
and  S.  jordani),  and  a  mysid  shrimp  (Spirontocaris  sp.); 
other  fish,  crustaceans,  octopuses,  and  marine  worms  are 
minor  components  of  the  diet  there  (Ainley  et  al.  1981; 
Ainley  6k  Boekelheide  1990,  Chap.  3,  n  =  6839).  Juvenile 
rockfish  are  most  important  in  cold-water  years,  and  scul- 
pins  in  warm-water  years.  Like  our  other  cormorants, 
Pelagics  feed  their  young  by  regurgitation. 


Of  the  California  cormorant  clan,  Pelagics  are  the  dare- 
devils, nesting  on  narrow  ledges  and  niches  of  precipitous 
cliffs  and  sea  caves  on  coastal  bluffs  or  offshore  rocks  and 
islands.  Because  these  sites  are  limited,  Pelagic  Cormorant 
colonies  are  generally  smaller  and  looser  aggregations  than 
diose  of  Brandt's  and  Double-crested  cormorants  (Sowls  et 
al.  1980,  Carter  et  al.  1984).  Presumably  because  of  the 
precariousness  of  cliff  nests,  Pelagics  cement  them  to  the 
ledge  by  their  own  excrement.  Nests  are  often  semicircular, 
radrer  than  round,  where  they  abut  the  cliff  face,  but  like 
Brandts'  nests,  they  rarely  become  large  from  yearly  recon- 
struction and  additions.  Nest  materials  include  seaweeds, 
grasses,  mosses,  and,  rarely,  sticks,  with  dry  grasses  and, 
occasionally,  feadrers  used  as  a  lining  (Bent  1922;  Dawson 
1923;  Palmer  1962;  Ainley  6k  Boekelheide  1990,  Chap. 
6). 

Marin  Breeding  Distribution 

During  the  adas  period,  Pelagic  Cormorants  bred  in  14 
main  colony  sites  along  the  outer  coast  of  Marin  County 
(NE,  Sowls  et  al.  1980;  Table  14,  Figure  14).  In  1989,  the 
number  of  colony  sites  was  reduced  to  12  by  the  abandon- 
ment of  the  "Elephant  Rock  Complex"  and  Point  Resis- 
tance colonies  (Carter  et  al.  1992). 

Historical  Trends/ Population  Threats 

Partial  surveys  in  1969  to  1972  estimated  800  Pelagic 
Cormorants  were  breeding  at  four  sites  along  die  Marin 
County  coast  (Ainley  6k  Whitt  1973).  Based  on  complete 

89 


Cormorants 


MARIN  COUNTY  BRHKDING  BIRD  ATIAS 


Cormorants 


surveys,  numbers  of  this  cormorant  breeding  in  Marin 
declined  from  an  estimated  1672  birds  in  1979  (Sowls  et 
al.  1980)  to  902  in  1989  (Carter  et  al.  1992).  At  the 
Farallon  Islands,  numbers  of  breeding  Pelagic  Cormorants 
vary  greatly  from  year  to  year  depending  on  oceanographic 
conditions  and  food  supply  (Ainley  6k  Boekelbeide  1990, 
Chap.  6).  In  particularly  poor  food  years,  virtually  the 
whole  population  there  may  desert  their  nests  early  in  die 
breeding  season— 1989  was  such  a  year.  Hence,  the  low 
numbers  at  Marin  County  colonies  in  1989  are  probably 
indicative  of  short-term  variation  in  ocean  conditions  in 
die  Gulf  of  the  Farallones  rather  than  a  long-term  decline 
of  the  cormorant  population.  Again,  because  Pelagic  Cor- 
morants, like  Brandts,  frequendy  shift  colony  sites,  popu- 
lation trends  should  be  assessed  for  large  rather  than  small 


areas  (Carter  et  al.  1990).  Sowls  et  al.  (1980)  estimated  a 
breeding  population  of  1  5,458  Pelagic  Cormorants  at  166 
sites  along  the  central  and  northern  California  coast  in 
1979  to  1980,  whereas  Carter  et  al.  (1992)  estimated 
1 1 ,658  birds  at  169  sites  (including  1  in  S.F.  Bay)  in  1989 
to  1990.  Population  trends  between  die  two  surveys  varied 
among  several  large  segments  of  the  coast. 

Numbers  of  Pelagic  Cormorants  breeding  on  the  Faral- 
lon Islands  declined  in  the  late  nineteenth  century  because 
of  disturbance  but  subsequently  increased  (Ainley  6k  Lewis 
1 974).  Pelagic  Cormorants  generally  are  less  vulnerable  to 
disturbance  than  are  Brandt's  or  Double-crested  cormo- 
rants because  they  are  more  widely  dispersed  in  less  acces- 
sible nesting  sites. 


^Ci+h  Anysu.n 


Nesting  cormorants  must  be  ever  watchful  for  the  predatory  shenanigans  of 
Western  Gulls.  Drawing  by  Keith  Hansen,  1989. 


90 


Bitterns  and  Herons 


SPECIES  ACCOUNTS 


Bitterns  and  Herons 


Bitterns  and  Herons 


Family  Ardeidae 


AMERICAN  BITTERN    Botaurus  lentiginosus 


A  year-round  resident;  numbers  swell 

\                         Vr~V, 

slightly  from  Sep  through  Apr. 

-)^\\':.j^\^\    c^^\  J^"""---^ 

A  very  rare  (perhaps  rare),  very  local 

JV\\JV\S-V\SA^ 

(-  - 

breeder;  overall  breeding  population  very 
small. 

^^^ScVw; 

Recorded  in  7  (3.2%)  of  221  blocks. 

O    Possible                  4   (57%) 

\E)^v^^^ 

<r*""^A  • '  \^\      \*^\       \^\       V--" 

€    Probable                2   (29%) 

\^^><^%\j<(\ 

^\>^V •=-' 

•    Confirmed  =         1    (14%) 

j?|y^ 

FSAR=1         OPI  =  7          CI  =  1.57 

>^^P°" 

Ecological  Requirements 

With  their  frozen  sky-pointing  postures,  cryptic  reedlike 
coloration,  and  booming,  ventriloqual  calls,  American 
Bitterns  can  be  difficult  to  spot  in  their  breeding  haunts  of 
freshwater  marshes  and  coastal  swales.  They  prefer  cattail 
and  tule  marshes  over  much  of  the  range,  but  their  main 
requirement  seems  to  be  dense  marsh  vegetation  within 
the  first  two  to  three  feet  of  the  ground.  Although  Ameri- 
can Bitterns  breed  in  brackish  and  saltwater  marshes 
elsewhere  in  North  America  (Bent  1926,  Palmer  1962), 
there  appear  to  be  no  definitive  breeding  records  for  these 
habitats  in  coastal  California;  Bitterns  do  frequent  them  at 
other  seasons,  however. 

American  Bitterns  are  solitary  feeders  that  usually  hunt 
from  a  standing  or  slow  walking  position  (Hancock  6k 
Kushlan  1984).  They  hold  their  bills  low  and  strike  with  a 
quick  jab  while  wading  through  water  or  low  marsh,  or 
while  peering  down  from  a  bank  or  a  perch  in  marsh 
vegetation.  American  Bitterns  also  walk  quickly  or  run  in 
tall  grass,  gleaning  insects  from  grass  stems  or  flycatching 
them  from  the  air.  Overall,  the  diet  includes  about  20.3% 
fish,  19.0%  crayfish,  23.1%  aquatic  and  land  insects, 
20.6%  frogs  and  salamanders,  9.6%  mice  and  shrews, 


5.5%  snakes,  and  2.2%  crabs,  spiders,  and  miscellaneous 
invertebrates  (Palmer  1 962).  Geographic  and  seasonal  vari- 
ation in  the  diet  has  been  noted. 

Unlike  most  of  the  heron  and  egret  clan,  American 
Bitterns  breed  solitarily.  They  usually  locate  their  nests  in 
wet  places  in  a  marsh;  they  build  them  up  as  much  as  eight 
inches  above  shallow  water  or  mud,  or  they  lodge  them  in 
marsh  vegetation  (Bent  1926,  Palmer  1962).  Nests  are  also 
found  occasionally  on  dry  ground  in  grassy  meadows  or 
hayfields  (though  in  proximity  to  marshlands)  or  on  float- 
ing islands  in  lakes.  Concealment  is  provided  by  surround- 
ing vegetation,  but  more  often  than  not  the  nest  is  open 
above  radier  than  screened  by  arched-over  stalks;  new 
growth  may  further  seclude  the  nest  as  the  season  pro- 
gresses. The  nest  is  a  small,  flat  platform  made  of  materials 
such  as  dead  cattail  flags,  bulrushes,  other  sedges,  rushes, 
and  reeds,  as  well  as  grasses,  weeds,  or  small  sticks;  eggs 
may  sometimes  be  laid  practically  on  bare  ground.  Young 
hatch  asynchronously  and  are  fed  by  regurgitation.  Cir- 
cumstantial evidence  suggests  that  young  may  move  to  a 
second  nearby  platform  after  20  days  of  age  and  that 
previous  years'  nests  may  sometimes  be  reused  (Palmer 
1962). 

91 


Bitterns  and  Herons 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Bitterns  and  Herons 


Marin  Breeding  Distribution 

The  only  confirmed  breeding  record  for  American  Bittern 
in  Marin  County  was  a  sighting  of  two  recendy  fledged 
young  at  Abbott's  Lagoon  on  28  July  1981  (DS)  in  an  area 
where  adults  had  been  seen  diroughout  the  breeding 
season.  The  rarity  here  of  Bitterns  in  the  breeding  season 
seems  largely  attributable  to  the  scarcity  of  extensive  fresh- 
water marshes. 


Historical  Trends/Population  Threats 

American  Bitterns  probably  always  have  been  scarce  breed- 
ers in  Marin  County,  but  diey  may  have  declined  with  the 
historic  loss  of  freshwater  marshes,  particularly  around 
San  Pablo  and  San  Francisco  bays.  The  American  Bittern 
was  included  on  die  Audubon  Society's  Blue  List  in  seven 
years  from  1976  to  1986  (Tate  1981,  1986;  Tate  6k  Tate 
1982).  Numbers  of  American  Bitterns  were  relatively  sta- 
ble on  Breeding  Bird  Surveys  in  California  from  1968  to 
1989  (USFWS  unpubl.  analyses). 


GREAT  BLUE  HERON    Ardea  herodias 


A  year-round  resident;  occupies  breeding 

rookeries  mostly  from  late  Jan  or  early 
Feb  through  late  Jun  or  mid-Jul. 

jf-^- 

A  fairly  common,  very  local  breeder; 

<?-A 

overall  breeding  population  very  small. 

\*Z>^       \  A.  A  Jr.    \  w  Jr       \        J^^  \  O   \^Z-\-~    Jt^i*  \        \^^\^      .1 

\vN5rf\  °^c\  9-V\  ^-V\  ■lclV^rA(^V\  °J>^ 

^oj 

Recorded  in  12  (80)  or  5.4%  (36.2%) 

\^-\XA-Jr\0Jr\    A--\    3r^\    3r\ 

of  221  blocks  (see  Methods). 

\^v  >-^h  >A^^\     v-^\  o  V--i\     \^-^\      i^\      v 

O    Possible        =      68  (85%) 
€    Probable       =         0   (0%) 

V^^J^rx^V^V^^A^c^^JV^xS-T 

•    Confirmed  =       12   (15%) 

r-T7                                 ^C\^\°3<>^ 

^54^ 

^& 

FSAR  =  3         OPI  =  36         CI  =  1 .30 

Ecological  Requirements 

Great  Blue  Herons  are  stately  denizens  of  shallow  tidal  and 
freshwater  feeding  grounds  and  adjacent  uplands.  Great 
Blues  have  the  widest  range  of  foraging  habitat  of  Marin's 
breeding  herons  and  egrets.  To  seize  unsuspecting  prey, 
diey  most  commonly  stand  still  or  wade  slowly  in  die 
shallow  waters  or  along  the  shores  of  estuaries,  lagoons, 
bays,  freshwater  ponds,  streams,  and,  less  frequently,  tide 
pools;  they  also  perch  in  nearshore  kelp  beds  in  die 
Monterey  Bay  area,  riding  the  swells  (Roberson  1985). 
Less  frequendy,  in  aquatic  habitats,  they  hover  over  water 
and  stab  at  prey  below,  dive  into  water  from  die  air 
headfirst,  drop  into  water  from  perches  feet  first,  float  or 
swim  on  die  water's  surface  stabbing  at  or  picking  up  prey, 
wing-flick  to  disturb  prey,  and  dash  after  prey  with  dieir 
wings  used  for  balance,  lift,  or  braking  (Hancock  &. 
Kushlan  1984).  Additional  aquatic,  shoreline,  or  terrestrial 

92 


feeding  techniques  include  pecking,  probing,  and  even 
flycatching.  Great  Blues  spend  a  fair  amount  of  time 
stalking,  poised  motionless,  in  pastures  and  fields  in 
search  of  rodents  (especially  pocket  gophers),  lizards,  and 
insects.  Although  dtey  forage  mosdy  during  the  day,  Great 
Blues  also  feed  at  night,  especially  in  tidal  habitats  (Han- 
cock ck  Kushlan  1984).  In  some  areas,  especially  on 
islands,  Great  Blues  visit  human  habitations  for  scraps  of 
food  put  out  for  them.  Great  Blues  forage  singly  or  in 
aggregations  and  in  some  circumstances  defend  feeding 
territories  (Pratt  1 980).  It  has  been  suggested  that  colonial 
nesting  Great  Blues  will  follow  one  anodier  to  exploit  food 
diat  is  unevenly  distributed  and  concentrated  in  areas  of 
temporary  abundance.  However,  adult  birds  at  the 
Audubon  Canyon  Ranch  rookery  on  Bolinas  Lagoon  do 
not  appear  to   follow  odier  herons  on  foraging  flights; 


Bitterns  and  Herons 


SPECIES  ACCOUNTS 


Bitterns  and  Herons 


instead  they  land  where  other  herons  are  already  feeding 
or  go  to  familiar  feeding  grounds  (Pratt  1980).  Long- 
distance foraging  flights  are  common  in  Ciconiformes,  and 
some  authors  believe  Great  Blues  may  fly  up  to  about  50 
miles  to  feeding  areas.  Although  most  adults  departing  the 
Audubon  Canyon  Ranch  rookery  go  to  Bolinas  Lagoon  to 
feed,  many  fly  out  of  sight  in  several  directions  to  unknown 
foraging  areas  (Pratt  1980).  See  Marin  Breeding  Distribu- 
tion section  for  the  extent  of  the  foraging  range  in  the 
county. 

Overall  in  the  U.S.,  this  heron's  diet  is  about  71.6% 
fish,  8.9%  crustaceans,  8.2%  insects,  4.7%  mice  and 
shrews,  4.2%  amphibians  and  reptiles,  and  2.5%  miscel- 
laneous animal  and  vegetable  matter  (Palmer  1962).  Most 
vegetable  fare  is  probably  taken  incidentally,  but  Great 
Blues  apparendy  eat  the  seeds  of  water  lilies.  They  also 
capture  marshbirds  as  large  as  Black-necked  Stilts  and 
Clapper  Rails  (Palmer  1962,  Hancock  6k  Kushlan  1984); 
rails  are  particularly  susceptible  to  herons  and  egrets  when 
forced  out  of  marshes  at  high  tides  (Evens  6k  Page  1986). 

Great  Blues  breed  in  small  to  large  colonies  or,  rarely, 
solitarily.  In  Marin  County,  they  place  their  nests  high  in 
large  trees  such  as  redwoods,  Douglas  fir,  California  bay, 
coast  live  oak,  and  eucalyptus,  often  in  mixed  colonies  with 
Great  Egrets  (Pratt  1983).  In  mixed  heronries,  Great  Blues 
typically,  but  not  invariably,  nest  in  the  highest  parts  of 
trees  (up  to  130  ft.,  Bent  1926),  with  other  species  below 
them  (Palmer  1962).  In  other  areas,  Great  Blues  also  nest 
in  shrubs,  on  the  ground,  on  tule  platforms,  on  rock  ledges 
or  sea  cliffs,  and  on  duck  blinds  or  other  artificial  struc- 
tures. Nests  are  flat  platforms  of  sticks  with  inner  shallow, 
saucer-shaped  depressions.  They  may  vary  considerably  in 
bulk  since  they  are  reused  repeatedly;  nest  material  is 
added  throughout  incubation  and  early  in  the  nesding 
phase.  The  nests  may  be  lined  widi  fine  twigs,  mosses,  pine 


needles,  reeds,  weed  stalks,  marsh  grasses,  or  leaves  (Bent 
1926,  Palmer  1962,  H.M.  Pratt  pers.  comm.).  The  young 
hatch  asynchronously  and  are  fed  by  regurgitation. 

Marin  Breeding  Distribution 

During  the  adas  period,  Great  Blues  were  confirmed  nest- 
ing in  12  colonies  scattered  throughout  Marin  County 
(Pratt  1 983;  Table  1 5,  Figure  1 5,  and  adas  map).  Only  two 
of  these  colonies  (at  Nicasio  Reservoir  and  Drake's  Head) 
were  newly  discovered  by  adasers.  Great  Blues  have  also 
nested  at  several  other  sites  either  prior  to  or  after  the  adas 
period  (Pratt  p.  103  this  volume;  Table  15,  Figure  15). 
Although  most  local  heron  colonies  are  adjacent  to  estuar- 
ies, Great  Blues  forage  throughout  the  lowlands  of  Marin 
in  the  breeding  season.  In  contrast,  the  other  colonial 
breeding  herons  and  egrets  forage  primarily  in  the  estuaries 
and  marshes  along  Marin  County's  bay  and  ocean  shores 
(see  atlas  maps). 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  did  not  list  any  breeding  sites 
for  Great  Blue  Herons  in  Marin  County,  but  this  was 
undoubtedly  because  of  limited  coverage  in  this  area.  Pratt 
(1983)  reported  the  known  history  of  Marin  County  colo- 
nies, noting  that  the  Audubon  Canyon  Ranch  colony  was 
"well  established  and  active  in  1941."  Although  data  are 
lacking,  it  seems  likely  diat  heron  populations  have  been 
reduced  by  die  historic  loss  of  extensive  marshlands  in  the 
San  Francisco  Bay  system.  Pratt  (p.  103  this  volume) 
describes  a  decline  in  Great  Blue  numbers  in  Marin  since 
1968.  For  California  as  a  whole,  numbers  were  relatively 
stable  on  Breeding  Bird  Surveys  from  1968  to  1989 
(USFWS  unpubl.  analyses).  Disturbance  at  nesting  colonies 
can  cause  abandonment  (Werschkul  et  al.  1976),  and 
pesticide  contamination  poses  threats  to  reproductive  suc- 
cess (see  Hancock  6k  Kushlan  1984). 


93 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Table  15.  Numbers  of  breeding  pairs  of  Great  Blue  Herons  at  16  Marin  County  colonies  from  1967  to  1991  (see  Figure  15). 
U  =  Nest  counts  unavailable— herons  may  or  may  not  have  been  nesting.  In  addition,  at  least  one  heron  nest  was  at  an  inaccessible 
site  off  Bel  Marin  Keys  Boulevard,  Novato,  in  1985  (based  on  the  sound  of  large  young  being  fed). 


1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

1977 

1978 

1979 

Audubon  Canyon  Ranch 

50 

62 

55 

50 

44 

46 

58 

48 

45 

40 

41 

43 

35 

De  Silva  Island 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

5 

Drake's  Head 

U 

u 

U 

U 

U 

U 

U 

U 

u 

U 

U 

U 

U 

Home  Bay 

u 

2 

3 

U 

U 

u 

u 

U 

u 

U 

u 

U 

u 

Inverness  Park 

u 

U 

U 

u 

U 

16 

0 

U 

4 

3 

4 

3 

u 

Nicasio  Reservoir 

u 

u 

u 

u 

u 

U 

u 

U 

U 

U 

U 

U 

u 

Nick's  Cove 

u 

u 

u 

23 

u 

u 

u 

23 

28 

23 

24 

16 

u 

North  San  Pedro  Road 

0 

0 

0 

0 

1 

I 

1 

0 

0 

1 

2 

1 

4 

Phoenix  Lake 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Sand  Point 

u 

u 

u 

u 

u 

u 

u 

25 

7 

u 

U 

U 

u 

Schooner  Bay  A  &.  B 

u 

u 

u 

u 

u 

u 

15 

15 

12 

9 

0 

7 

7 

Stafford  Lake 

8 

u 

u 

5 

u 

u 

5 

14 

21 

U 

21 

19 

16 

Olema 

u 

u 

u 

26 

u 

19 

0 

0 

0 

0 

0 

0 

U 

Bolinas-Fairfax  Road 

u 

u 

u 

U 

u 

U 

U 

u 

U 

u 

U 

U 

U 

Smiley's  "Preserve" 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

West  Marin  Island 

u 

u 

u 

U 

u 

u 

u 

u 

u 

u 

U 

u 

0 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

Audubon  Canyon  Ranch 

33 

27 

26 

13 

16 

18 

21 

18 

13 

16 

9 

7 

De  Silva  Island 

5 

3 

0 

0 

1 

4 

3 

3 

7 

6 

9 

9 

Drake's  Head 

U 

U 

11 

3 

4 

1  + 

U 

U 

3 

U 

0 

0 

Home  Bay 

0 

1 

0 

0 

0 

U 

U 

U 

0 

U 

0 

0 

Inverness  Park 

12 

8 

6 

3 

6 

u 

u 

u 

10 

U 

7 

9 

Nicasio  Reservoir 

U 

U 

6 

6 

5 

u 

u 

u 

13 

0 

0 

U 

Nick's  Cove 

18 

15 

15 

19 

16 

u 

12 

0 

0 

0 

0 

0 

North  San  Pedro  Road 

4 

3 

2 

2 

4 

u 

u 

u 

8 

16 

21 

17 

Phoenix  Lake 

0 

0 

0 

1 

U 

u 

u 

u 

0 

u 

0 

U 

Sand  Point 

U 

16 

13 

10 

12 

u 

7 

u 

8 

13 

18 

16 

Schooner  Bay  A  &  B 

7 

3 

0 

0 

0 

u 

u 

u 

0 

U 

0 

0 

Stafford  Lake 

27 

23 

27 

29 

28 

30 

31 

u 

30 

27 

32 

16 

Olema 

U 

U 

U 

U 

U 

U 

U 

u 

U 

U 

U 

U 

Bolinas-Fairfax  Road 

u 

U 

U 

u 

U 

U 

u 

u 

U 

1 

1 

1 

Smiley's  "Preserve" 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

6 

10 

West  Marin  Island 

0 

0 

1 

0 

0 

0 

0 

0 

0 

0 

1 

2 

94 


SPECIES  ACCOUNTS 


Colony  codes  used  are: 

1  =  Audubon  Canyon  Ranch 

2  =  De  Silva  Island 

3  =  Drake's  Head 

4  =  Home  Bay 

5  =  Inverness  Park 

6  =  Nicasio  Reservoir 


7  =  Nick's  Cove 

8  =   North  San  Pedro  Road 

9  =  Phoenix  Lake 
10  =  Sand  Point 

11=  Schooner  Bay  A  6k  B 
12  =  Stafford  Lake 


13  =  Olema 

14  =   Bolinas-Fairfax  Road 

15  =  Smiley's  "Preserve" 

16  =  West  Marin  Island 


Figure  15.    Map  of  heron  and  egret  colony  sites  in  Marin  County.  Rookeries  denoted  b>  bold  numbers  were  known  to  be  active  in 
1991;  all  other  sites  were  active  prior  to  1991  (see  Tables  15  and  16). 


95 


Bitterns  and  Herons 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Bitterns  and  Herons 


GREAT  EGRET   Casmerodius  albus 


'vgtft^ 

^r^-^        ^ 

Occurs  year  round,  though  numbers 
swell  substantially  when  birds  occupy 

X\^V 

T  V^V Jk^\9^ 

\  ^V\  ^V\  ^-V\  °>A ' 

breeding  rookeries,  mosdy  from  mid-Mar 
(rarely  mid-Apr)  until  late  Jul  to  mid-Aug. 

^Y^ 

\^vC \r\  3r\  3r^A^ 

A  very  common,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  5  (37)  or  2.3%  (16.7%)  of 
221  blocks  (see  Methods). 

5\  ^-Y"\  i-'TX  L' 

■>-'\>i  \^\ '    v-"\       )£--"v 

\  '""jsxrv               .— ' 

O    Possible        =      32  (86%) 

■*\ .  3r-^\-J J^T\    JV""\    -A"" 

£rvT' 

©    Probable      =        0  (0%) 

-^SS^t-V^ 

^"\  ^-Ya  clV\.  JVv"- 

IS?0 

•    Confirmed   =          5   (14%) 

^s=> 

t^V^'A'    vx 

FSAR=5         OPI  =  25         CI  =  1.27 

Ecological  Requirements 

Great  Egrets  present  elegant  lines  and  exude  a  ghosdy  aura 
as  they  forage  in  a  variety  of  shallow-water  habitats,  includ- 
ing estuaries;  lagoons;  bays;  saltwater,  brackish,  and  fresh- 
water marshes;  as  well  as  ponds  and  streams,  irrigation 
ditches,  and  wet  meadows.  In  Marin  County,  breeding 
Great  Egrets  prefer  estuarine  and  bay  habitats.  They  use 
inland  freshwater  habitats  and  pasturelands  only  to  a 
limited  degree  compared  with  Great  Blue  Herons  (see  adas 
maps). 

Great  Egrets  feed  singly  or  in  groups  and  form  large 
aggregations  at  concentrations  of  prey.  Solitary  birds  vigor- 
ously defend  foraging  sites.  Aggressive  encounters  occur 
when  gregariously  feeding  birds  attempt  to  steal  prey  cap- 
tured by  other  individuals  (Hancock  &  Kushlan  1984). 
Great  Egrets  forage  primarily  by  slowly  walking  in  shallow 
water,  along  shorelines,  or  in  dry  habitats;  they  also  poise 
motionless  to  dart  out  and  seize  prey  from  a  crouched 
posture  with  their  heads  drawn  in.  Infrequent  foraging 
tactics  include  startling  or  activating  prey  by  vibrating  their 
feet  in  water  (moving  their  feet  up  and  down  on  the 
substrate)  or  by  wing  flicking.  Great  Egrets  also  forage 
actively  by  hovering  over  the  water  and  stabbing  at  prey 
below,  by  flying  along  and  periodically  reaching  into  the 
water  to  pick  up  prey,  or  by  diving  into  the  water  from  the 
air  headfirst.  More  complex  foraging  tactics  include  foot 
paddling  while  flapping  the  wings  violendy  up  and  down; 
and  periodically  hopping  from  the  water,  stabbing  prey 
brought  to  the  surface.  Great  Egrets  also  glean  insects  from 

96 


plants.  They  feed  primarily  on  fish,  frogs,  salamanders, 
snakes,  snails,  crustaceans,  insects,  small  mammals,  and, 
occasionally,  small  birds.  Fish  usually  comprise  the  bulk  of 
the  diet  in  the  wet  season,  but  there  is  considerable  local 
variation  (Palmer  1962,  Hancock  &  Kushlan  1984).  Great 
Egrets  specialize  in  capturing  small  to  medium-sized  rails 
forced  from  cover  at  high  tides  (Evens  &  Page  1986).  Birds 
apparendy  travel  considerable  distances  to  forage.  In  the 
breeding  season,  Great  Egrets  frequendy  fly  along  the 
shoreline  northwest  of  Bolinas,  presumably  commuting 
from  the  nesting  colony  at  Audubon  Canyon  Ranch  on 
Bolinas  Lagoon  to  alternate  feeding  grounds  at  Limantour 
and/or  Drake's  esteros  (Shuford  et  al.  1989). 

Great  Egrets  breed  solitarily  or,  more  often,  in  small  to 
large  colonies,  often  in  association  with  other  species  of 
wading  birds.  In  Marin  County,  they  nest  in  tall  trees 
(redwoods,  Douglas  firs,  eucalyptus,  California  buckeyes), 
often  alongside  Great  Blue  Herons  (Pratt  1983;  see  Great 
Blue  Heron  account).  Elsewhere,  they  sometimes  nest  low 
to  the  ground  in  small  willows  or  on  bent-down  bulrushes 
(Bent  1926,  Palmer  1962).  Nests  are  flat  platforms  of  sticks 
or  rule  stalks  and  are  usually  flimsier  and  flatter  than  those 
of  Great  Blue  Herons;  nests  from  previous  years  may  be 
reused.  Many  nests  lack  a  lining  or  cavity,  but  sometimes 
they  are  considerably  hollowed  and  are  well  lined  with  fine 
twigs,  vines,  or  weed  stems.  The  young  hatch  asynchro- 
nously and  are  fed  by  regurgitation. 


Bitterns  and  Herons 


SPECIES  ACCOUNTS 


Bitterns  and  Herons 


Marin  Breeding  Distribution 

During  the  atlas  period,  Great  Egrets  nested  at  five  colonies 
along  the  Marin  County  shoreline  (Table  16,  Figure  15, 
and  adas  map). 

Historical  Trends/  Population  Threats 

From  the  1880s  to  the  1890s,  Great  Egret  numbers  in 
California  were  gready  reduced  by  hunters  for  the  feather 
trade.  They  began  to  recover  by  1911,  and  by  1943  the 
species  was  "common  in  the  remaining  suitable  portions 
of  its  former  range"  (G&M  1944).  Numbers  probably 
failed  to  reach  historic  levels  because  of  the  extensive  loss 
of  the  state's  wedand  habitat.  Great  Egrets  reappeared  in 
the  San  Francisco  Bay  Area  in  1924  (Stoner  1934),  and  in 
Marin  County  with  seven  birds  at  Bolinas  on  7  May  1929 
(Stoner  1934)  and  one  bird  at  Drake's  Estero  on  7  June 
1931  (Stephens  1931).  The  birds  at  Bolinas  were  likely 
breeding  then  at  what  is  now  known  as  Audubon  Canyon 


Ranch  (Pratt  1983).  Human  insensitivity  was  still  evident 
in  July  1955,  when  53  egrets  (mosdy  Greats,  a  few  Snow- 
ies) were  "wantonly  slaughtered  ...  by  rifle-bearing  target 
shooters"  at  West  Marin  Island;  the  culprits  were  arrested 
(AFN  10:51).  The  West  Marin  Island  rookery  had  been 
active  for  "many  years"  prior  to  this  incident  (Ralph  ck 
Ralph  1958).  Pratt  (p.  103  this  volume)  describes  recent 
trends  in  numbers  of  Great  Egrets  at  Marin  County 
colonies.  On  the  whole,  Great  Egret  numbers  increased  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 

Great  Egrets  reproduced  poorly  in  the  late  1960s  and  early 
1970s  because  of  DDT-induced  eggshell  thinning  (Faber  et 
al.  1972,  Ives  1972,  Pratt  1972),  but  since  then  a  decrease 
in  the  rate  of  egg  loss  during  incubation  suggests  the 
species  is  recovering  (Pratt  1974).  Disturbance  at  colonies 
can,  of  course,  cause  abandonment. 


Table  16.  Numbers  of  breeding  pairs  of  Great  Egrets  at  five  Marin  County  colonies  from  1967  to  1991  (see  Figure  15).  U  = 
Nest  counts  unavailable— egrets  may  or  may  not  have  been  nesting.  See  Pratt  (1983)  for  numbers  of  Great  Egrets  seen  on  or 
feeding  near  West  Marin  Island,  1973  through  1981. 


1967 

1968 

1969 

1970 

1971 

1972 

1973 

1974 

1975 

1976 

1977 

1978 

1979 

Audubon  Canyon  Ranch 

70 

74 

86 

85 

85 

96 

99 

96 

85 

65 

84 

88 

98 

Inverness  Park 

0 

0 

0 

0 

0 

0 

0 

0 

3 

4 

12 

2 

U 

Nick's  Cove 

U 

u 

u 

0 

u 

U 

u 

5 

15 

13 

6 

12 

U 

Sand  Point 

U 

u 

u 

U 

u 

u 

u 

0 

0 

U 

U 

U 

u 

West  Marin  Island 

U 

u 

u 

u 

u 

u 

u 

U 

u 

U 

U 

u 

58 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

Audubon  Canyon  Ranch 

103 

148 

150 

97 

110 

113 

98 

113 

113 

102 

91 

100 

Inverness  Park 

1 

0 

0 

0 

0 

U 

U 

U 

1  + 

U 

0 

0 

Nick's  Cove 

6 

5 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

Sand  Point 

U 

6 

13 

19 

19 

u 

20 

u 

20 

25 

25 

49 

West  Marin  Island 

u 

75 

187 

190 

139 

84 

160 

89 

66 

79 

119 

90 

On-site  counts  found  155  pairs  in  1990  and  131  pairs  in  1991  (R.L.  Hothem/USFWS  pers.  comm.);  counts  from  this  site  reported  in  table  from 
these  and  previous  years  were  taken  from  a  boat 


97 


Bitterns  and  Herons 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Bitterns  and  Herons 


SNOWY  EGRET   Egretta  thula 


xV'YdV' 

A  year-round  resident;  birds  occupy 
breeding  colonies  mosdy  from  mid-Mar 
dirough  mid-Aug. 
A  very  abundant,  very  local  breeder; 

<"\  ^\\  ^-V\  ^&\  J^c\  S^\°^c     \ 

overall  breeding  population  very  small. 

Recorded  in  1  (22)  or  0.4%  (10.0%)  of 
221  blocks  (see  Methods). 

\  V-1 

O    Possible        =      21    (95%) 

\i\^K\^^P^                                    — ■*" 

©    Probable       =         0   (0%) 

.  )b<^\      V^\"     X^S.      V^Y-J  V-'A       \^\      \^-\~P^S 

>"Ak  tfV^C  \^\    J^\    \^df-  v-'V  i^olK" 

•    Confirmed  =         1    (5%) 

FSAR=7         OPI  =  7          CI  =  1.09 

Ecological  Requirements 

These  dashingly  handsome  little  egrets  with  "golden  slip- 
pers" forage  in  a  variety  of  shallow  saltwater,  brackish,  and 
freshwater  habitats  comparable  to  those  frequented  by 
their  larger  cousin  the  Great  Egret.  Snowies  also  occasion- 
ally forage  in  pastures  and  fields  and,  like  Cattle  Egrets,  will 
follow  cattle  and  other  livestock  to  pick  up  insects  dis- 
turbed by  their  grazing  (Palmer  1962,  Hancock  ck  Kushlan 
1984)-  In  the  breeding  season  in  Marin  County,  Snowy 
Egrets  forage  primarily  in  tidelands  and  marshlands  along 
the  San  Francisco  and  San  Pablo  bayshores  near  their  only 
regular  nesting  colony  (see  adas  map). 

Snowies  are  extremely  active  feeders  "moving  about  with 
great  show  of  nervous  energy,  yet  much  poise  and  grace" 
(Palmer  1 962).  They  also  have  the  most  diverse  repertoire 
of  foraging  behaviors  of  any  heron  or  egret  so  far  studied 
(Hancock  ck  Kushlan  1984)-  Snowies  typically  feed  in 
conspecific  or  multispecies  flocks,  principally  while  walk- 
ing slowly  or  quickly  or  while  standing.  They  are  especially 
adept  at  startling  or  attracting  prey  by  vibrating  their  legs 
and  yellow  feet,  by  scratching  their  toes  across  or  inserting 
them  into  the  substrate,  or  by  moving  their  feet  up  and 
down  on  the  substrate.  In  addition,  Snowies  attract  fish  by 
placing  their  bills  in  the  water  and  rapidly  opening  and 
closing  them.  Snowies  are  also  accomplished  aerial  forag- 
ers. From  flight  they  periodically  reach  into  the  water  for 
prey,  trail  their  toes  in  die  water,  and  while  hovering  stab 
at  prey  below  or  pat,  stir,  or  rake  the  water  with  their  feet. 
Snowies  also  dash  about  rapidly,  extending  their  wings  for 
a  few  seconds  at  a  time,  with  short  flights  interspersed. 
Their  gende  looks  belie  their  kleptoparasitic  tendencies.  I 

98 


have  watched  Snowies  chase  White-faced  Ibis  at  Los  Banos 
wildlife  refuge  and  force  them  to  drop  crayfish,  which  the 
Snowies  prompdy  ate.  Their  diet  includes  small  fish, 
crustaceans  (especially  crayfish),  frogs,  lizards,  snakes, 
worms,  snails,  insects,  and,  occasionally,  small  rodents 
(Palmer  1962). 

Breeding  Snowies  are  highly  colonial,  and  they  typically 
nest  widi  other  species  of  egrets  or  herons.  Only  occasion- 
ally do  pairs  breed  alone.  At  the  only  well-established 
Marin  County  colony  at  West  Marin  Island,  Snowies  nest 
at  varying  heights  in  live  oak  and  buckeye  trees,  in  coastal 
scrub,  and  on  the  ground  (Pratt  1983,  H.M.  Pratt  ck  R 
Hothem  pers.  comm.).  Birds  breeding  irregularly  at 
Audubon  Canyon  Ranch  nest  60  to  70  feet  up  in  coast 
redwood  trees  (H.M.  Pratt  pers.  comm.).  Throughout  their 
range,  nests  usually  are  situated  from  the  ground  to  30  feet 
up  (most  5-10  ft.)  in  a  variety  of  trees;  various  bushes, 
cacti,  and  broken-down  reeds  and  bulrushes  also  serve  as 
nest  supports  (Bent  1926,  Palmer  1962).  The  typically 
elliptical,  somewhat  loosely  woven  nest  has  a  foundation 
of  sticks  and  a  rather  flat  body  of  twigs  with  a  shallow 
cavity.  Nests  are  sometimes  lined  with  finer  twigs,  stalks  of 
marsh  plants,  or  roodets.  On  occasion,  birds  construct  no 
nest  and  instead  lay  eggs  in  a  depression  in  the  broken  and 
matted-down  tules  of  the  previous  year.  Dead  canes,  reeds, 
rushes,  tules,  sage,  holly,  birch,  and  other  plants  may  be 
used  in  the  nest  depending  on  availability.  Snowies  prob- 
ably do  not,  or  only  infrequendy,  reuse  former  nests, 
although  they  may  use  the  same  site  and  sticks  from  other 


Bitterns  and  Herons 


SPECIES  ACCOUNTS 


Bitterns  and  Herons 


old  nests  in  construction  of  the  new  one  (Palmer  1962). 
Young  hatch  asynchronously  and  are  fed  by  regurgitation. 

Marin  Breeding  Distribution 

Snowy  Egrets  breed  consistendy  in  Marin  County  in  large 
numbers  only  at  the  West  Marin  Island  rookery  (Table  1 7, 
Figure  15,  and  adas  map).  About  five  pairs  nested  at 
Audubon  Canyon  Ranch  in  1969,  1988,  and  1989;  four 
pairs  nested  there  in  1990  and  1991  (Pratt  1983,  H.M. 
Pratt  pers.  comm.). 

Historical  Trends/ Population  Threats 

Snowy  Egrets  were  locally  common  in  California  prior  to 
1880,  but  because  of  the  ravages  of  plume  hunters  diey 
declined  to  the  brink  of  extinction  by  the  early  1900s 
(G6kM  1944).  By  1908  they  were  recorded  again,  and  by 
1943  they  were  fairly  common  in  favored  places  (G&.M 
1944),  though  as  late  as  1932  a  bird  seen  at  Richardson 
Bay,  Marin  County,  was  still  worthy  of  note  in  the  Condor 
(Swanton  1933).  Snowy  Egrets  probably  have  not  recov- 


ered to  historical  population  levels  because  of  the  extensive 
loss  of  California's  wedands.  At  the  time  of  Ralph  and 
Ralph's  (1958)  visit  to  the  active  Snowy  Egret  colony  at 
West  Marin  Island  in  1957,  local  residents  claimed  that 
Snowies  had  been  established  there  "for  at  least  five  years. 
See  Great  Egret  account  regarding  a  slaughter  of  53  egrets, 
including  a  few  Snowies,  on  West  Marin  Island  in  July 
1955.  Pratt  (p.  103  this  volume)  describes  recent  trends  in 
the  West  Marin  Island  Colony.  On  the  whole,  Snowy 
Egret  numbers  increased  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1989  (USFWS  unpubl.  analyses). 
In  San  Francisco  Bay,  Snowy  Egret  eggs  show  concentra- 
tions of  organochlorine  pesticide  residues  and  mercury, 
but  below  "critical"  levels  that  cause  adverse  effects  on 
reproduction  (Ohlendorf  et  al.  1 988).  Monitoring  of  Bay 
Area  colonies  should  be  continued  as  reproductive  failure 
in  Idaho  colonies  has  been  linked  to  DDE  contamination 
(Findholt  1984).  Like  our  other  colonial  nesting  waders, 
Snowy  Egrets  are  also  highly  susceptible  to  nest  loss  from 
disturbance. 


Table  17.   Estimates  of  the  number  of  breeding  pairs  of  Snowy  Egrets  and  Black-crowned  Night-Herons  on  West  Marin  Island 
from  boat  censuses  from  1979  to  1991. 


1979 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

Snowy  Egrets 

262 

U 

325 

500 

400 

400 

161 

126 

239 

212 

245 

300 

277 

Black-crowned  Night-Herons 

98 

U 

109 

80 

89 

54 

79 

40 

41 

35 

61 

37 

45 

On-site  counts  found  463  pairs  in  1990  and  487  pairs  in  1991  (R.L.  Hothem/USFWS  pers.  comm.). 
On-site  counts  found  306  pairs  in  1990  and  294  pairs  in  1991  (R.L.  Hothem/USFWS  pers.  comm.). 


99 


Bitterns  and  Herons 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Bitterns  and  Herons 


GREEN-BACKED  HERON   Butorides  striatus 


A  year-round  resident;  numbers  swell 
slightly  from  Apr  through  mid-Oct 

An  uncommon,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  24  (10.8%)  of  221  blocks. 

O    Possible        =       20   (83%) 
C    Probable       =         1    (4%) 
•    Confirmed   =         3   (13%) 

FSAR  =  2         OPI  =  48         CI  =  1.29 


Ecological  Requirements 

This  compact,  dapper  heron  blends  in  well  with  the 
forested  margins  of  the  quiet  waters  of  streams,  ponds,  and 
freshwater  marshes.  Green-backed  Herons  use  brackish 
marshes  and  estuarine  borders  to  a  limited  extent  in 
California,  as  they  do  commonly  elsewhere,  but  most 
breeding  birds  here  inhabit  freshwater  habitats.  They  for- 
age mosdy  by  day  but  also  sometimes  at  night;  at  coastal 
sites,  the  timing  of  foraging  bouts  may  vary  with  tidal 
heights  (Hancock  &.  Kushlan  1984).  Green-backs  are 
patient  feeders.  They  usually  stand  crouched  and  motion- 
less on  a  branch  or  rock,  or  they  walk  slowly  along  the 
shoreline  waiting  to  stab  their  prey.  Birds  also  flycatch 
from  a  standing  position  and  startle  prey  by  vibrating  their 
feet  in  water  or  by  raking  their  toes  across  the  substrate. 
More  active  foraging  techniques  include  launching  from  a 
perch  feet  first,  or  from  the  air  headfirst,  into  the  water,  and 
floating  or  swimming  on  the  surface  of  the  water  while 
securing  prey.  They  even  hang  from  branches  while  stab- 
bing in  the  water.  Green-backed  Herons  also  ingeniously 
place  items  such  as  bread  and  feathers  on  the  water's 
surface  to  lure  in  prey  (Lovell  1958,  Sisson  1974).  In  many 
situations  they  vigorously  defend  feeding  territories 
(Palmer  1962,  Hancock  ck  Kushlan  1984).  Their  diet 
includes  small  fish,  crustaceans,  aquatic  and  land  insects, 
amphibians,  reptiles,  other  invertebrates,  and  small  mam- 
mals (Palmer  1962,  Hancock  ck  Kushlan  1984). 

In  Marin  County,  Green-backed  Herons  nest  solitarily. 
Elsewhere,  they  also  nest  in  small  groups  or,  rarely,  large 
colonies;  they  rarely  mix  widi  other  species  for  nesting. 
Nests  are  placed  in  a  variety  of  situations.  These  include 
from  on  the  ground  to  up  to  30  feet  in  trees  in  dry  woods 


or  orchards;  in  low  trees  (most  10-15  ft.)  or  bushes  over 
or  near  water;  or  amid  marsh  vegetation  (Bent  1926, 
Palmer  1 962).  Nests  vary  from  round  to  oval  and  from  very 
flimsy  platforms  (usually  new  nests)  to  very  tighdy  woven, 
bulky  structures  (mostly  old,  reworked  nests).  Green- 
backed  Heron  nests  built  on  the  foundations  of  other 
species'  nests,  such  as  those  of  Black-crowned  Night-Her- 
ons or  crows,  are  usually  rather  flimsy.  The  body  of  the 
nest  is  built  of  twigs  or,  rarely,  of  coarse  weeds,  reeds,  or 
cattails.  It  is  commonly  unlined  or  lined  with  finer  twigs, 
vines,  and  bits  of  reeds  or  other  plant  material.  The  young 
hatch  asynchronously  and  are  fed  by  regurgitation. 

Marin  Breeding  Distribution 

The  spotty  breeding  distribution  of  Green-backed  Herons 
in  Marin  County  during  the  atlas  period  reflected  the 
limited  distribution  of  their  preferred  breeding  habitat. 
Representative  nesting  locations  were  Nicasio  Reservoir 
(NB  5/9/81  — JE)  and  just  north  of  Inverness  Park  (FL 
7/18/82  — DS).  An  earlier  breeding  record  was  of  a  nest 
with  diree  young  observed  at  San  Anselmo  Creek  in  Ross 
on  5  July  1935  (GuIIl  7,  No.  7). 

Historical  Trends/  Population  Threats 

Loss  and  degradation  of  marsh  and  riparian  habitats  must 
have  gready  reduced  the  state's  historic  populations  of  this 
heron.  On  the  whole,  numbers  of  Green-backed  Herons 
increased  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989,  though  numbers  were  relatively  stable  from 
1980  to  1989  (Robbins  et  al.  1986,  USFWS  unpubl. 
analyses). 


100 


Bitterns  and  Herons 


SPECIES  ACCOUNTS 


Bitterns  and  Herons 


BLACK-CROWNED  NIGHT-HERON   Nycticorax  nycticorax 


A  year-round  resident;  birds  occupy 

^v^T-^       N                   PO^~- 

breeding  colonies  mosdy  from  mid-Mar 

j\^\j><^ 

through  mid-Aug. 

\^\  Jk^\  J>r\    \^\   Jk^\   J^\°i^\ 

An  abundant,  very  local  breeder;  over- 

V\Jr 

'^<^^\^\\^^^^\\^\^i^^f°^ 

all  breeding  population  very  small. 

PcjAa^o^^V!^^^ 

Recorded  in  1  (1 7)  or  0.4%  (7.7%)  of 

^X^~ 

^x^t^^^ 

221  blocks  (see  Methods). 

\  \^ 

O    Possible        =      16  (94%) 

—  -r" 

©    Probable       =         0   (0%) 

Ai^TV^pV-^CJ^ 

•    Confirmed  =         1    (6%) 

^ 

FSAR  =  6         OPI  =  6          CI  =  1.12 

!vL,                                                              ^ 7         ^^^"^S^c^X 

Ecological  Requirements 

The  handsome  portly  profiles  of  Black-crowned  Night- 
Herons  appear  posed  for  die  painter  at  their  communal 
daytime  roosts  and  nesting  colonies.  The  seasoned  natural- 
ist need  not  raise  binoculars  in  the  fading  light  of  dusk  to 
identify  their  eerie  silhouettes  as  these  herons  give  their 
characteristic  wok-wok  calls  while  flying  out  to  feed  in  a 
variety  of  shallow  marine  and  freshwater  habitats,  includ- 
ing bays,  estuaries,  tidal  flats,  lagoons,  freshwater  ponds, 
and  marshes. 

Unlike  our  other  herons  and  egrets,  Black-crowned 
Night-Herons  are  primarily  nocturnal  or  crepuscular  forag- 
ers. Although  they  occasionally  come  out  to  feed  in  broad 
daylight,  they  usually  do  so  only  on  overcast  or  foggy  days. 
They  forage  either  solitarily,  maintaining  exclusive  feeding 
territories,  or  in  aggregations,  and  they  usually  hunt  their 
prey  from  a  poised  stance  or  from  a  slow  stalking  gait 
(Hancock  &  Kushlan  1984).  While  standing  or  walking, 
they  sometimes  put  dieir  heads  under  an  opened  wing, 
which  may  reduce  glare,  making  prey  more  visible,  or 
attract  prey  to  the  shade  of  the  wing.  Additionally,  Black- 
crowns  occasionally  hover  over  water,  stabbing  at  prey 
below;  dive  headfirst  into  water;  and  float  or  swim  on  the 
water's  surface,  stabbing  or  picking  up  prey.  On  occasion 
they  also  rapidly  open  and  close  their  bills  in  algae-covered 
water  to  attract  prey  (Palmer  1 962). 

The  diet  is  diverse  and  varies  with  locality.  Overall  in 
the  U.S.  it  consists  roughly  of  51 .5%  fish,  22%  crustaceans 
(shrimp  and  crayfish),  16%  aquatic  insects,  6%  frogs,  3% 
rodents,  and  the  remainder  mosdy  spiders  and  worms; 
other  food  items  include  tadpoles,  snakes,  salamanders, 


mollusks,  marine  annelids,  vegetable  matter,  and  small 
birds  (Palmer  1962,  Wolford  6k  Boag  1971).  While  walk- 
ing around  in  colonies  of  nesting  waterbirds,  Black-crowns 
will  take  the  young  of  terns,  other  herons,  and  ibises 
(Hancock  6k  Kushlan  1984)-  At  one  locale,  Black-crown 
young  were  initially  fed  shrimp,  followed  by  fish  after  the 
young  reached  three  weeks  of  age  (Palmer  1962). 

Black-crowned  Night-Herons  nest  in  small  to  very  large 
colonies,  usually  with  other  herons  or  egrets.  Nest  sites  are 
diverse  and  range  in  height  from  the  ground  to  160  feet  up 
in  trees.  Colonies  are  variously  located  in  trees  or  brush  in 
mainland  or  island  woodlands,  forests,  or  swampland;  in 
old  orchards  or  in  city  parks;  in  stands  of  cattails  and  tules 
and  on  floating  dead  vegetation  anchored  to  emergent 
cattail  stalks;  and  on  the  ground  among  tufts  of  tall  grass 
on  islands  (Bent  1926,  Palmer  1962).  Black-crowns  at 
Marin  County's  West  Marin  Island  colony  build  their 
nests  mostly  in  coastal  scrub  but  also  in  California  buckeye 
trees  (H.M.  Pratt  6k  R.  Hothem  pers.  comm.).  Nests  vary 
from  radier  frail  platforms  to  solid,  bulky  structures  (some- 
times deeply  cupped)  that  are  used  for  several  years.  Coarse 
twigs,  sticks,  reeds,  or  weed  stalks  make  up  the  body  of  the 
nest,  while  finer  materials  such  as  small  twigs  or  rootlets 
form  the  lining  or  are  woven  into  the  top;  sticks  from  old 
nests  are  reused  in  die  construction  of  new  ones. 

Marin  Breeding  Distribution 

Black-crowned  Night-Herons  currently  nest  in  Marin 
County  only  at  West  Marin  Island  (Pratt  1983;  Table  17, 
Figure  1 5,  and  adas  map). 

101 


Bitterns  and  Herons 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Bitterns  and  Herons 


Historical  Trends/ Population  Threats 

Little  information  is  available  on  the  historical  status  of  this 
species  throughout  California,  though  Grinnell  and  Miller 
(1944)  termed  it  "formerly  abundant,  now  greatly  depleted 
locally."  Moffitt  (1939a)  reported  that  about  25  pairs  of 
Black-crowned  Night-Herons  nested  in  Marin  County  in 
live  oaks  and  California  bays  on  die  north  end  of  Belvedere 
Island  from  at  least  1918  to  1938.  He  expressed  concern 
at  that  time  over  the  fate  of  the  colony  because  of  recent 
nearby  house  building  and  brush  clearing.  That  colony  is 
no  longer  extant,  and  the  birds  probably  abandoned  it 
because  of  further  human  encroachment  soon  after 
Moffitt's  report.  Disturbance  to  colonies  can,  of  course, 
cause  abandonment  (Tremblay  6k  Ellison  1979).  Ralph 
and  Ralph  (1958)  observed  Black-crowns  breeding  at  the 
West  Marin  Island  rookery,  which  had  been  active  for 
"many  years."  It  is  unknown  if  all,  part,  or  any  of  that 


colony  was  established  by  emigrants  from  the  Belvedere 
Island  colony.  Pratt  (p.  103  this  volume)  describes  recent 
trends  in  the  West  Marin  Island  colony.  On  the  whole, 
Black-crowned  Night-Heron  numbers  were  relatively  stable 
on  Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 

The  Black-crowned  Night-Heron  was  included  in  the 
Audubon  Society's  Blue  List  from  1972  to  1981  (Tate 
1981)  and  on  its  list  of  Species  with  Special  Concerns  in 
1982  (Tate  &  Tate  1982).  It  was  down-listed  to  a  Species 
of  Local  Concern  in  1986  (Tate  1986).  In  addition  to 
habitat  loss  and  disturbance,  organochlorine  (and  mer- 
cury) contamination  poses  a  widespread  threat  to  Black- 
crowned  Night-Heron  populations,  including  Bay  Area 
colonies,  but  so  far  it  has  had  only  limited  local  effects  on 
their  reproductive  success  (Ohlendorf  et  al.  1978,  1988; 
Custer  et  al.  1983;  Findholt  1984). 


Whether  foraging  or  attending  young,  Black-crowned  Night-Herons  exude  unwavering  concentration.  Photograph  by  Ian  Tait. 


102 


Bitterns  and  Herons 


SPECIES  ACCOUNTS 


Bitterns  and  Herons 


RECENT  POPULATION  TRENDS  OF  MARIN  COUNTY 
HERON  AND  EGRET  COLONIES 

Helen  M.  Pratt 


The  history  of  Marin  County's  heron  and  egret  colonies 
was  previously  chronicled  by  Pratt  (1983).  Ongoing 
monitoring  of  these  colonies  provides  additional  informa- 
tion on  the  population  trends  of  Great  Blue  Herons,  Great 
Egrets,  Snowy  Egrets,  and  Black-crowned  Night-Herons. 
See  Pratt  (1983)  for  census  methods.  The  recent  initiation 
of  a  monitoring  program  of  heron  and  egret  colonies 
throughout  much  of  die  San  Francisco  Bay  Area  (J.  P.  Kelly 
pers.  comm.)  should  provide  a  broader  perspective  with 
which  to  evaluate  future  population  trends  of  the  Marin 
colonies. 

Great  Blue  Heron 

Since  the  high  of  62  pairs  in  1968,  the  Great  Blue  Heron 
population  at  Audubon  Canyon  Ranch  has  declined  by 
about  89%  (Table  15).  During  die  past  25  years,  various 
other  colonies  were  newly  formed,  first  discovered,  aban- 
doned, or  have  increased  or  decreased  in  size.  Preceding 
the  discovery  of  the  Drake's  Head  and  Nicasio  Reservoir 
colonies,  a  countywide  census  in  1974  revealed  125  heron 
nests.  In  1982,  the  first  year  after  all  the  notable  colonies 
were  discovered,  107  nests  were  counted.  In  1989,  the  nest 
count  was  79,  though  additional  birds  were  nesting  then 
at  Inverness  Park,  where  poor  visibility  through  the  trees 
precluded  a  census.  Thus  the  overall  heron  population  in 
Marin  County  has  declined  since  1968,  largely  attributable 
to  the  drop  in  numbers  at  Audubon  Canyon  Ranch  and 
the  abandonment  of  the  Nick's  Cove  and  Schooner  Bay 
colonies.  Recent  events  at  the  Stafford  Lake  colony— die 
county's  largest  in  1990— may  presage  further  declines  of 
the  Marin  heron  population.  The  Stafford  population 
declined  by  50%  from  1990  to  1991.  Also  in  1991,  all 
nests  there  failed  because  a  temporary  lowering  of  the  water 
level  in  the  lake,  to  enable  repair  of  die  irrigation  system  of 
the  neighboring  golf  course,  apparendy  allowed  raccoons 
to  invade  the  colony  (H.M.  Pratt  pers.  obs.). 


Great  Egret 

The  Great  Egret  population  at  Audubon  Canyon  Ranch 
has  increased  since  1967  (Table  16).  In  two  instances, 
sharp  declines  from  one  year  to  the  next— from  85  pairs  in 
1975  to  65  in  1976  and  from  150  pairs  in  1982  to  97  in 
1983— occurred  the  year  following  raccoon  predation  on 
die  colony.  After  installation  of  raccoon  barriers  at  the  base 
of  nesting  trees  prior  to  the  1984  nesting  season,  the 
Audubon  Canyon  Ranch  population  has  since  remained 
at  a  plateau  of  about  100  to  110  pairs.  On  West  Marin 
Island,  the  Great  Egret  population  has  fluctuated  widely 
since  the  first  census  there  in  1979  (Table  16). 

Snowy  Egret 

Like  those  of  Great  Egrets,  Snowy  Egret  numbers  on  West 
Marin  Island  have  fluctuated  widely  since  1979— from  a 
low  of  126  pairs  in  1986  to  a  high  of  500  pairs  in  1982 
(Table  1 7).  Such  fluctuations  are  characteristic  of  Snowy 
Egrets  at  other  colonies  as  well  (e.g.,  Thompson  et  al. 
1979).  Determinations  of  general  population  trends  would 
require  coordinated  censuses  over  a  wide  area. 

Black-crowned  Night-Heron 

Based  on  counts  from  a  boat,  the  Black-crowned  Night- 
Heron  population  on  West  Marin  Island  has  decreased 
since  the  first  census  in  1979  (Table  17).  A  fire  on  the 
island  in  July  1981  may  have  been  responsible  for  a  decline 
from  109  nests  that  year  to  80  in  1982.  Night-heron  nests 
are  hidden  deep  widiin  die  coastal  scrub,  and  probably 
most  of  them  are  impossible  to  see  from  a  boat.  Figures 
from  these  censuses  may  be  too  inaccurate  to  be  useful. 
Recent  on-site  counts  provide  better  population  estimates 
(see  Table  1  7). 


103 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Waterfowl 


Waterfowl 

Family  Anatidae 


CANADA  GOOSE     Branta  canadensis 


J^\\\  3>2*\ 

^C^\      \                  jf\ 

Occurs  year  round,  though  primarily  as  a 
winter  resident  from  Sep  through  early 
Apr. 

A  rare,  very  local  breeder,  overall  breed- 

r>A^oiV^J^ 

ing  population  very  small. 
Recorded  in  1  (0.4%)  of  221  blocks. 

O    Possible        =        0   (0%) 

prO  '  \  .  \^\^~^-^^\"^ r^\  C-A^^  \     ^K^^  \    ^*\        \    ^^^  \     ~^/     o 

C    Probable       =         0   (0%) 

"\:  \^\   Ar^V  ^~^^S^\\^^\jP^C\e^^r —  r' 

•    Confirmed  =         1    (100%) 

0/                                ^-^*^\  2vy^-i^V^\  y^\  ^V^\ 

FSAR  =1          OPI  =  1           CI  =  3.00 

i^^                                                        V-^_i                ^~~^^JO<-'''\  ^r^-. 

Ecological  Requirements 

The  echoing  sounds  of  geese  calling  in  flight  overhead  stir 
nostalgic  feelings  for  times  when  California  was  wilder  and 
untrammeled.  The  only  native  subspecies  of  Canada 
Goose  known  to  breed  in  California  is  the  Western,  or 
Great  Basin,  Canada  Goose,  Branta  canadensis  moffitti  (see 
Bellrose  1980).  As  native  breeders,  "Honkers"  are  pres- 
endy  restricted  in  California  to  the  Modoc  Plateau,  Great 
Basin  Desert,  and  valleys  of  die  adjoining  Klamath,  Cas- 
cade, and  Sierra  Nevada  mountains  (GckM  1944).  There 
they  breed  on  the  marshy  borders  of  freshwater  and  alka- 
line lakes,  reservoirs,  streams,  and  in  extensive  marshes 
and  wet  meadows.  In  recent  years,  birds  (probably  mosdy 
or  entirely  from  plantings)  have  begun  breeding  locally  in 
a  wild  state  in  the  San  Francisco  Bay  region  on  estuarine 
borders  or  islands,  and  at  reservoirs,  where  they  may  also 
mix  with  domestic  birds  (see  below).  Captive  birds  estab- 
lished in  California  are  largely  B.  c.  moffitti,  especially  stock 
from  near  Reno,  Nevada  (M.R.  McLandress  pers.  comm.). 
Canada  Geese  nest  in  a  greater  variety  of  sites  than  all 
other  species  of  waterfowl  (Palmer  1976a,  Bellrose  1980). 
They  sometimes  give  the  appearance  of  being  semicolonial 
nesters,  but  this  seems  to  reflect  the  concentration  of  birds 
at  limited  suitable  nesting  sites  rather  than  inherent  social 

104 


tendencies  of  the  species;  they  do  sometimes  nest  in  or 
near  California  or  Ring-billed  gull  colonies  (Palmer 
1976a).  The  nest  site  must  be  firm  and  dry  and  include 
freedom  from  disturbance,  cover  for  the  nest,  and  unob- 
structed visibility  in  all  directions  for  the  incubating  bird 
(sometimes  island  nests  may  be  in  woods  or  under  scrub). 
Nearby  must  be  a  guard  site  for  the  gander  (up  to  0.25  mi. 
away  on  open  terrain),  a  grazing  area  (usually  close  at  hand, 
but  up  to  1  -5  mi.  away),  and  proximity  to  permanent  water 
(to  which  the  young  are  led).  Nests  are  usually  within  a  few 
feet  of  water,  and  about  90%  are  within  50  yards;  excep- 
tionally, a  nest  may  be  300  yards  from  water.  Canada 
Geese  nest  most  frequendy  on  islands  or  islets.  They  also 
commonly  select  hummocks  on  peninsulas,  lakeshores, 
streamsides,  or  in  marshes  or  fields;  mats  of  bullrushes  in 
marshes,  or  the  tops  of  muskrat  or  beaver  houses;  hay- 
stacks; dikes  and  ditch  banks;  gravel  bars,  talus  slopes, 
river  bluffs,  ledges,  or  cliffs;  clusters  of  low  scrubby  growth, 
stumps,  or  trees  (particularly  in  abandoned  nests  of  her- 
ons, Ospreys,  and  other  hawks);  and  a  variety  of  elevated 
artificial  structures,  including  washtubs,  tires,  wicker  bas- 
kets, wooden  boxes  or  platforms,  and  anchored  floating 
rafts.  The  female  forms  the  nest  scrape  in  the  earth  or  other 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


soft  substrate  by  "wallowing"  and  collects  twigs,  reeds, 
weed  stems,  and  grasses  for  the  base  and  rim  from,  at  most, 
a  few  feet  from  the  nest  (Dawson  1923,  Palmer  1976a, 
Bellrose  1980). 

Canada  Geese  feed  primarily  by  grazing  in  marshes, 
meadows,  and  fields;  they  forage  in  cultivated  fields  more 
often  on  autumn  staging  areas  and  wintering  grounds  than 
on  spring  or  summer  habitats.  Aquatic  feeding  is  inciden- 
tal except  in  coastal  birds.  They  feed  by  tipping  up  in  water, 
mainly  when  grazing  forage  is  scarce,  and,  rarely,  by  diving 
from  the  surface  (Palmer  1976a).  Breeding  birds  feed 
singly  or  in  flocks  away  from  nesting  territories.  They  feed 
mosdy  during  the  day,  but  also  at  night  during  periods  of 
fattening  (McLandress  &  Raveling  1981a)  or  when  they 
are  unable  to  secure  adequate  food  during  daylight  hours 
because  of  shortages  or  excessive  disturbance  while  feeding 
(M.R.  McLandress  pers.  comm.).  The  diet  of  breeding 
birds  includes  mainly  the  shoots,  foliage,  stems,  seeds, 
roots,  and  rhizomes  of  grasses,  sedges,  and  aquatic  plants, 
berries,  and  cultivated  grains  (particularly  succulent,  high 
protein  sprouts  and  mature  seed  heads).  Insects,  crusta- 
ceans, mollusks,  and  fish  form  a  minor  part  of  the  diet, 
and  perhaps  all  but  the  latter  are  consumed  when  attached 
to  food  plants.  Canada  Geese  shift  from  a  winter  diet  of 
mosdy  corn  or  other  carbohydrates  to  a  diversity  of  food 
items  in  spring  before  migrating  (McLandress  6k  Raveling 
1981a,b).  Although  they  still  continue  to  eat  some  corn, 
protein-rich  new-growth  grass  is  important  for  laying  on  fat 
stores  necessary  for  the  migration  and  breeding  effort. 
Females  may  have  to  obtain  minerals  (perhaps  some  from 
snail  shells),  and  possibly  protein,  for  egg  formation  from 
food  sources  on  the  breeding  grounds.  Goslings  also  need 
high-protein  grass  for  growth  (M.R.  McLandress  pers. 
comm.). 

Marin  Breeding  Distribution 

The  only  known  breeding  location  for  Canada  Geese  in 
Marin  County  was  at  West  Marin  Island  near  San  Rafael. 
During  the  adas  period,  an  adult  was  seen  there  from  a 
boat  in  the  spring/summer  of  1982  (HPr).  Goslings  seen 
nearby  at  McNear's  Beach  by  Point  San  Pedro  in  May  or 
June  of  1982  (DT)  may  have  come  from  a  nesting  attempt 
on  West  Marin  Island,  the  Sisters  (small  islets  direcdy  off 
Pt.  San  Pedro),  or  from  any  of  a  number  of  duck  blinds 
along  the  shoreline  to  the  north.  Subsequendy,  nesting 


was  confirmed  on  West  Marin  Island  by  the  observation 
there  of  a  nest  with  eggs  on  27  March  1983  (PCI)  and  two 
adults  with  two  goslings  on  the  water  close  to  the  island  on 
24  May  1 983  (HPr  et  al.).  A  semidomestic  flock  also  lived 
nearby  at  Peacock  Gap  golf  course.  In  recent  years,  non- 
breeding  oversummering  individuals  or  escapees  have 
occasionally  been  seen  during  the  breeding  season  at 
various  Marin  County  locations.  A  flock  of  up  to  35  birds 
at  Bolinas  Lagoon  in  June  and  July  each  year  since  1984 
may  represent  birds  dispersing  after  breeding  at  sites  else- 
where in  Marin  County  or  the  San  Francisco  Bay  Area 
(Shuford  et  al.  1989). 

Historical  Trends/Population  Threats 

The  Canada  Goose  was  first  recorded  nesting  on  the 
California  coast  in  1932  when  two  pair  bred  at  Crystal 
Springs  Reservoir,  San  Mateo  County  (Bird  Lore  35:112, 
Moffitt  1939b).  It  is  now  well  established  as  a  breeder  in 
small  numbers  at  several  sites  around  San  Francisco  Bay 
(Lidicker  6k  McCollum  1979)  and  appears  to  be  increasing 
(ABN).  It  seems  likely  that  most,  if  not  all,  coastal  nesting 
records  pertain  to  birds  of  introduced  stock  for  the  follow- 
ing reasons:  (1)  the  major  gap  in  the  breeding  range 
between  the  main  California  population  in  the  northeast- 
ern corner  of  the  state  and  that  of  the  recendy  established 
population  in  the  Bay  Area,  Suisun  Marsh  (1970s),  the 
Delta  (1980s),  and  Yolo  County  (1970s)  (M.R. 
McLandress  pers.  comm.);  (2)  the  strong  attachment  to 
traditional  breeding  grounds  (Palmer  1976a);  and  (3)  the 
ease  with  which  this  species  adapts  to  captivity.  It  is  also 
possible  that  a  few  winter  residents  pioneered  a  new 
breeding  outpost  on  their  own,  perhaps  as  cripples  from 
hunting  casualties.  The  current  coastal  population  may 
have  originated  from  birds  bred  in  captivity  in  the  Bay  Area 
in  the  early  1900s  from  eggs  collected  at  Lake  Tahoe 
(Grinnell  et  al.  1918);  from  a  semicaptive  flock  of  B.  c. 
moffitti  that  has  bred  at  Lake  Merritt,  Oakland,  since  at 
least  1954  (AFN  10:276,  AB  27:91 3);  or  from  captive  stock 
derived  from  near  Reno,  Nevada,  and  released  in  Suisun 
Marsh,  the  Delta,  or  the  Sacramento  Valley.  Released  birds 
from  captive  stock  from  the  Tahoe-Reno  area  seem  to  adapt 
to  the  mild  conditions  of  Bay  marshes  and  will  probably 
continue  to  increase  until  hunters  perceive  numbers  to  be 
great  enough  to  hunt  (M.R.  McLandress  pers.  comm.). 


105 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Waterfowl 


WOOD  DUCK   Aixsponsa 


A  year-round  resident;  numbers  swell 

\ 

somewhat  from  Sep  th  rough  Apr. 

rAvA 

\^A\3A\ 

[-  - 

A  rare,  very  local  breeder;  overall  breed- 
ing population  very  small. 
Recorded  in  5  (2.3%)  of  221  blocks. 

\<5 

^A^A^ 

O    Possible                 4  (80%) 

p^^v 

*OVAP*fA^ 

€    Probable                 0  (0%) 

V-^V-^>^ 

^V^CvA 

V--^C    " 

•    Confirmed   =         1    (20%) 

VA°^cA^ 

\^s(~\^\\^\ 

Or^^V" — '"r" 

Cm 

\SV\*V 

C3A\Afv3r 

3^5^^ 

FSAR  =1          OPI  =  5          CI  =  1 .40 

J    h^Z> 

Ecological  Requirements 

Gaudily  bedecked  male  Wood  Ducks  and  their  cryptic 
mates  are  wary  recluses  of  the  quiet  waters  of  ponds, 
slow-flowing  streams,  wooded  swamps,  marshes,  and  res- 
ervoirs that  provide  overhanging  secluding,  woody  vegeta- 
tion along  their  margins.  Wood  Ducks  rarely  venture  into 
deep  open  or  fast-flowing  waters.  In  most  cases,  they  seem 
to  prefer  smaller  water  bodies  to  larger  lakes  and  rivers  for 
nesting  (Naylor  1 960).  Wood  Ducks  are  the  most  wood- 
land- and  forest-inhabiting  of  our  local  breeding  ducks. 
Expert  at  flying  between  trees  or  through  their  crowns, 
Woodies  use  tree  trunks  and  branches  for  perches,  nest 
sites,  and  part  of  their  foraging  beat.  In  Marin  County, 
riparian,  broadleaved  evergreen,  mixed  coniferous,  or 
coniferous  forests  surround  the  wedands  used  for  nesting. 
Prime  feeding  areas  are  shallow  (<1  ft.  deep)  or  contain 
much  floating  or  emergent  vegetation  as  substrate  for 
invertebrates  (Drobney  &  Fredrickson  1979).  Decompos- 
ing deciduous  leaves  provide  excellent  substrate  for  the 
midge  larvae  and  other  invertebrates  important  in  the  diet 
of  Wood  Ducks,  particularly  egg-laying  females  and  grow- 
ing ducklings  (M.R.  McLandress  pers.  comm.).  A  diversity 
of  habitats  is  important  to  Wood  Ducks  to  provide  them 
with  a  broad  array  of  plant  and  invertebrate  foods  (Landers 
et  al.  1977).  As  well  as  providing  foraging  needs,  ideal 
habitat  for  brood  rearing  and  summer  molting  should 
include  a  spreading  brushy  overstory  for  concealment  from 
above;  small  open-water  passages;  and  scattered  fallen  dead 
limbs,  trees,  stumps,  exposed  roots,  or  muskrat  houses  for 
perching  (Palmer  1976b). 


Pairs  or  small  groups  of  Wood  Ducks  generally  feed 
from  the  surface  in  shallow  water.  They  prefer  to  forage  in 
wooded  wedands,  though  they  occasionally  feed  along 
nonwooded  shorelines  next  to  open  water  (Drobney  6k 
Fredrickson  1979).  Foraging  birds  move  constandy  and 
rapidly,  using  sizable  areas  during  the  course  of  feeding. 
There  is  no  evidence  that  birds  are  attached  to  specific 
feeding  areas  or  that  they  establish  feeding  territories. 
Woodies  forage  primarily  by  pecking  at  foods  on  the 
surface  or  by  surface  dabbling  and,  infrequendy,  by  sub- 
surface dabbling  or  bottom  feeding  (Drobney  ck  Fredrick- 
son 1979).  Rarely,  they  dive  to  catch  fish  (Palmer  1976b). 
While  afloat  or  ashore,  Wood  Ducks  are  adept  at  catching 
nearby  airborne  insects  (Palmer  1976b)  and  probably 
glean  others  from  emergent  vegetation,  stumps,  logs,  and 
water  margins  (Landers  et  al.  1977).  In  fall  and  winter,  they 
prefer  to  procure  acorns  and  other  mast  from  shallow 
flooded  swamps  and  bottomlands,  but  they  also  search  for 
diese  foods  under  trees,  and  even  among  shrubbery,  in 
upland  forests  (Palmer  1976b,  Bellrose  1980).  At  times 
they  fly  into  trees  twined  with  grapevines  and  snatch  the 
grapes  from  arboreal  perches.  Wood  Ducks  sometimes 
also  feed  in  fields  of  corn,  wheat,  or  other  cereal  grains, 
and,  at  least  in  Ohio,  in  farmers'  hog  lots. 

The  diet  from  fall  di rough  early  spring  is  about  90.2% 
vegetable  matter  and  9.8%  animal  matter  (Mabbott  in 
Palmer  1976b,  n  =  399).  In  South  Carolina,  vegetable 
foods  account  for  over  90%  of  the  diet  in  all  months  except 
March,  when  they  comprise  77%  (Landers  et  al.  1977,  n  = 
200).  In  Missouri,  animal  foods  comprise  about  one-third 


106 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


of  the  diet  of  males  in  spring  (n  =  55)  and  of  males  and 
females  in  fall  (n  =  40)  (Drobney  6k  Fredrickson  1979).  In 
preparation  for  breeding,  females  enter  a  period  of 
hyperphagia,  when  they  concentrate  on  protein-rich  inver- 
tebrates and  spend  twice  as  much  time  feeding  as  do  males 
(Drobney  6k  Fredrickson  1979;  Drobney  1980,  1982). 
During  the  breeding  season  in  Missouri,  consumption  of 
animal  foods  by  females  averages  about  58%  (n  =  60)  and 
reaches  a  peak  of  79%  (n  =  20)  during  laying  (Drobney  6k 
Fredrickson  1979).  Females  of  breeding  pairs  there  eat 
more  invertebrates,  a  greater  diversity  of  invertebrates,  and 
more  aquatic  (vs.  aquatic-associated  and  nonaquatic)  inver- 
tebrates than  do  males.  The  latter  difference  is  perhaps 
attributable  to  the  fact  that  males  are  more  alert  to  their 
surroundings  while  foraging  and  therefore  feed  from  a 
more  erect  posture.  Hence  they  might  be  expected  to  feed 
more  on  fallen  branches  and  tree  trunks  than  do  females, 
which  feed  more  on  or  below  die  water's  surface.  The  shift 
of  Woodies  from  eating  mostly  aquatic  invertebrates  in 
spring  to  mosdy  nonaquatic  invertebrates  in  fall  may  be  a 
result  of  changing  availability  (Drobney  6k  Fredrickson 
1979)  or  perhaps  more  time  spent  foraging  in  upland  areas 
when  mast  and  fruit  crops  have  ripened.  The  young 
initially  eat  almost  exclusively  animal  matter  (mostly 
insects),  but  by  six  weeks  of  age  they  have  gradually 
switched  to  a  diet  comparable  to  that  of  adults  (Palmer 
1976b,  Bellrose  1980). 

The  main  vegetable  fare  includes  the  seeds  and  other 
parts  of  aquatic  plants  and  the  seeds,  nuts,  and  fruits  of 
trees;  fleshy  fruits  may  be  important  in  summer  (Palmer 
1976b,  Landers  et  al.  1977,  Drobney  6k  Fredrickson 
1979).  Acorns  may  be  a  particularly  important  food  in  fall 
and  winter,  depending  on  the  crop.  Animal  foods  consist 
primarily  of  aquatic  and  land  insects  and  other  inverte- 
brates. Important  items  are  adult  and  larval  dragonflies, 
damselflies,  mayflies,  midges,  caddisflies,  crane  flies,  horse 
flies,  beedes,  and  true  bugs;  less  important  are  odier 
insects,  spiders,  snails  and  slugs,  isopods,  crustaceans, 
and,  very  rarely,  amphibians,  fish,  and  mice. 

Wood  Ducks  nest  in  natural  cavities  of  trees,  in  Nordi- 
ern  Flicker  or  Pileated  Woodpecker  cavities  more  or  less 
enlarged  by  the  decay  of  wood,  in  wooden  and  metal  nest 
boxes,  in  barns  (in  hay)  and  abandoned  camps,  and  in 
hollow  trees  (especially  fallen  ones)  (Palmer  1976b).  In 
Merced  County,  Wood  Ducks  use  natural  cavities  in  trees, 
since  woodpecker  (even  flicker)  cavities  there  are  too  small, 
though  most  use  wooden  nest  boxes  erected  in  the  last  16 
years  (S.  Simmons  pers.  comm.).  Exceptionally,  Wood 
Ducks  prospect  for  nests  in  chimneys,  or  nest  in  crevices 
or  fissures  in  rocks;  one  very  unusual  twig  and  leaf  nest 
they  used  was  supported  by  small  branches  high  in  a  tree 
(Palmer  1976b).  No  nest  material  is  added  to  the  nest 
cavity  except  down  (Bellrose  1980).  The  eggs  are  laid  (and 
initially  covered  by  debris)  in  a  depression  hollowed  or 


scratched  out  by  the  female  in  the  soft,  dry  rotted  wood  or 
in  other  bits  of  bark,  twigs,  and  leaves  that  have  fallen  into 
the  cavity  or  have  been  brought  in  by  squirrels  (Bent  1923, 
Dixon  1924,  Palmer  1976b,  Bellrose  1980).  Wood  Ducks 
prefer  nest  boxes  with  sawdust  spread  on  the  bottom  of  the 
cavity  (S.  Simmons  pers.  comm.).  They  also  prefer  nest 
trees  over  water  or  in  open  stands  along  small  streams  or 
ponds,  though  they  sometimes  nest  in  dense  woodlands 
and  up  to  200  yards  from  water  (Dixon  1924,  Naylor 
1960,  Palmer  1976b,  Bellrose  1980).  In  Merced  County, 
Wood  Ducks  most  readily  accept  nest  boxes  close  to  and 
facing  the  water  since  they  typically  fly  along  waterways  and 
are  more  likely  to  see  nest  holes  so  situated  (S.  Simmons 
pers.  comm.).  A  preference  is  shown  for  nest  boxes  on 
vertical  or  forward-leaning  trees.  The  height  of  natural 
cavities  in  trees  ranges  from  2  to  65  feet  above  the  ground 
(Bellrose  1980).  In  California,  12  natural  nest  sites  (in 
willows,  cottonwoods,  or  valley  oaks)  ranged  from  6  to  30 
feet  above  the  ground,  and  10  of  these  were  below  15  feet 
(Dixon  1924).  In  Illinois,  the  height  of  158  nest  cavities 
ranged  from  6  to  55  feet  above  the  ground  (Bellrose  et  al. 
1964).  The  average  height  there  was  25  feet,  but  nests  over 
30  feet  were  actually  preferred,  based  on  occupancy  rates 
relative  to  availability.  Wood  Ducks  will  use  nest  cavities 
year  after  year  and  are  most  likely  to  use  previously  occu- 
pied nests.  Females  prefer  entrance  holes  as  small  as  they 
can  easily  pass  through,  and  there  are  instances  of  females 
cracking  an  egg  still  in  the  oviduct  while  squeezing  through 
a  narrow  crevice  (Dixon  1924)!  Frequendy,  more  than  one 
female  will  "dump"  eggs  in  the  same  cavity  (Palmer  1976b, 
Bellrose  1980).  In  Merced  County,  up  to  62  eggs  have 
been  dumped  in  a  single  nest  box,  and  as  many  as  six 
different  females  have  laid  in  the  same  box  on  the  same 
day  (S.  Simmons  pers.  comm.)!  Egg  dumping  occurs  there 
mostly  from  the  middle  to  the  end  of  the  nesting  season 
and  may  involve  mosdy  juvenile  females.  Only  rarely  will 
two  female  Wood  Ducks  incubate  in  the  same  cavity  or  will 
one  lay  jointly  with  another  species  of  cavity-nesting  duck 
(Palmer  1976b,  Bellrose  1980). 

The  day  after  the  young  hatch,  the  female  coaxes  them 
to  spring  out  of  the  cavity  and  flutter  to  the  ground  or  water 
by  calling  to  them  from  the  entrance  cavity,  a  nearby  limb, 
or  from  below.  After  first  leading  the  young  to  water,  the 
female  is  likely  to  keep  moving  them  (Bellrose  1980). 
Females  and  broods  may  move  to  a  series  of  ponds, 
traveling  as  much  as  1 .5  miles  direcdy  from  an  initial  open 
nest  pond  to  a  vegetated  one.  Before  developing  flight 
capabilities,  they  may  journey  as  far  as  4  miles  to  another 
watershed.  In  areas  of  rivers  and  oxbow  lakes,  broods  may 
move  an  average  of  1 .5  to  3  miles  in  die  first  two  days  after 
leaving  the  nest  and  a  maximum  of  6.5  miles  in  four  days 
(Smith  6k  Flake  1985).  Wood  Ducks  sometimes  produce 
two  broods  in  a  season,  a  rare  phenomenon  in  North 

107 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Waterfowl 


American  waterfowl  (Bellrose  1980).  The  production  of 
two  broods  in  a  season  by  banded  females  has  been  noted 
repeatedly  in  Merced  County  (S.  Simmons  pers.  comm.). 

Marin  Breeding  Distribution 

Although  seen  at  scattered  locations  in  Marin  County 
during  the  atlas  period,  Wood  Ducks  were  confirmed 
breeding  only  once.  A  female  with  two  downy  young  was 
observed  on  5  May  1980  at  Mill  Pond  on  the  Stewart 
Ranch  about  two  miles  south  of  Olema  (DS).  Had  we 
contacted  the  California  Department  of  Fish  and  Game 
during  our  adas  work,  we  undoubtedly  would  have  con- 
firmed nesting  of  more  Wood  Ducks.  Fish  and  Game 
initiated  a  pilot  nest  box  program  by  erecting  1 52  boxes 
throughout  the  state  from  1 952  to  1 956  (Naylor  1 960).  Of 
the  5  boxes  in  Marin  County,  at  least  2  were  occupied 
"immediately"  by  pairs  of  nesting  Wood  Ducks;  on  the 
basis  of  a  photograph  in  Naylor  (1960:247),  these  were 
apparendy  at  Mill  Pond.  Of  1 2  nest  boxes  in  Marin  in  the 
1960s,  Wood  Ducks  "used"  1  at  Mill  Pond  in  1967,  3  of 
7  along  Lagunitas  Creek  (19??),  and  2  of  4  along  Olema 
Creek  in  1966  (MeS  fide  GiT).  California  Department  of 
Fish  and  Game  personnel  also  put  up  3  nest  boxes  at 
Nicasio  Reservoir  in  both  1983  and  1984,  but  as  of  1991 
it  is  not  known  if  Wood  Ducks  have  nested  in  diem  yet. 
In  the  1970s,  females  widi  small  young  were  seen  on  Pine 
Gulch  Creek,  on  Mill  Pond,  and  on  Papermill  Creek  north 
of  Tocaloma  (EO).  Adults  with  small  young  were  seen  at 
Five  Brooks  Pond  in  the  Olema  Valley  from  late  May 
through  July  each  year  from  1987  dirough  1989  (ABN). 


Historical  Trends/ Population  Threats 

In  Marin  County,  Wood  Ducks  formerly  "nested"  on 
Gallinas  Creek  in  1872  or  1873  and  occurred  along 
Papermill  and  Lagunitas  creeks  up  to  about  1886  (GckW 
1927).  Mailliard  (191 1)  observed  that  Wood  Ducks  were 
"plentiful"  in  Marin  County  in  the  1870s  and  1880s,  but 
that  they  were  "extremely  scarce"  there  in  1910.  Grinnell 
and  Wydie  (1927)  considered  them  extirpated  in  the  San 
Francisco  Bay  region.  Numbers  also  declined  throughout 
California,  with  a  low  ebb  in  1915;  thereafter,  numbers 
increased  at  least  through  1943  (G&.M  1944,  Naylor 
1960).  Naylor  (1960)  attributed  the  early  declines  to  over- 
shooting from  sport  hunting,  to  market  hunting  (especially 
for  the  valuable,  highly  colored  feathers  of  the  male),  and 
to  habitat  destruction.  The  latter  included  draining  and 
reclaiming  marshes,  dredging  and  mining  activities,  along 
with  clearing  of  riparian  vegetation  resulting  in  the  loss  of 
nesting  cavities.  Though  recent  nest  box  programs  will 
likely  aid  their  recovery,  it  is  doubtful  that  Wood  Ducks 
will  ever  regain  their  former  "abundance,"  given  the  his- 
tory of  habitat  degradation  and  continuing  increases  in 
human  development  and  recreational  uses  of  waterways. 
Pesticides  from  agricultural  runoff  may  also  be  affecting  the 
supply  of  aquatic  insects  that  are  crucial  during  the  nesting 
season  (S.  Simmons  pers.  comm.).  Numbers  of  Wood 
Ducks  were  relatively  stable  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1989  (USFWS  unpubl.  analyses). 


108 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


MALLARD   Anas  platyrhynchos 


A  year-round  resident. 

A  fairly  common,  fairly  widespread 
breeder;  overall  breeding  population  of 
moderate  size. 

Recorded  in  110  (49.8%)  of  221 
blocks. 


O  Possible 
©  Probable 
•    Confirmed 


43  (39%) 
10  (9%) 
57  (52%) 


FSAR  =  3 


OPI  =  330       CI  =  2.13 


Ecological  Requirements 

Mallards,  our  most  familiar  and  adaptable  ducks,  frequent 
a  wide  variety  of  shallow  freshwater  ponds,  marshes,  sew- 
age ponds,  reservoirs,  slow-moving  streams,  and  brackish 
marshes  and  estuaries.  Mallards  need  wedands  for  resting 
and  loafing,  feeding,  waiting,  and  brood  rearing;  they  also 
require  upland  nesting  sites  with  good  cover  (Dzubin 
1969).  Wedand  feeding  sites  are  generally  near  to,  but  up 
to  five  miles  from,  nesting  areas  (M.R.  McLandress  pers. 
comm.).  An  important  requisite  for  breeding  is  space  and 
freedom  from  interference  from  conspecifics.  Although  the 
home  range  throughout  the  whole  breeding  cycle  may 
include  up  to  six  to  ten  ponds,  the  pair  soon  localizes  its 
activity  to  one  or  two  ponds  (or  a  part  of  a  large  pond).  This 
waiting  area  is  a  temporarily  exclusive  territory  from  which 
the  male  chases  intruding  pairs  (and  pursues  lone  females), 
especially  during  the  brief  period  (1 3-22  days)  just  prior  to 
laying  until  early  incubation  (Titman  1983).  The  male 
defends  his  mate  from  other  males  intent  on  forced  copu- 
lation, and  he  alerts  her  to  the  presence  of  potential 
predators,  allowing  her  to  feed  with  a  minimum  of  inter- 
ruption during  a  period  when  she  has  special  nutrient 
requirements.  An  important  function  of  the  waiting  area  is 
the  reestablishment  of  the  pair  bond  whenever  the  female 
is  away  from  the  nest  (Dzubin  1969).  Territories  some- 
times overlap,  but  more  than  one  pair  are  usually  not  seen 
at  the  same  place  at  the  same  time;  some  males  move 
beyond  the  territory  once  the  female  begins  incubating. 

Breeding  Mallards  feed  primarily  in  shallow  water  by 
tipping  up  for  aquatic  plants  in  marshes  and  for  mast  in 
flooded  swamps.  Although  capable  of  diving  for  food,  they 


rarely  do  so  (Palmer  1976a).  They  also  feed  in  agricultural 
crops  such  as  corn,  rice,  or  waste  grain  in  stubble  fields, 
especially  from  late  summer  dirough  winter.  In  addition, 
they  may  obtain  grain  during  breeding  from  ephemeral 
ponds  in  tilled  land  (Swanson  et  al.  1979).  On  warm 
summer  nights,  hens  and  broods  may  feed  after  dark  on 
concentrations  of  emerging  midges  and  mayflies  (Swanson 
ck  Sargeant  1972).  The  diet  overall  consists  of  about  90% 
vegetable  matter,  including  the  stems  and,  particularly,  the 
seeds  of  aquatic  plants,  cultivated  grains,  and  mast 
(McAtee  in  Palmer  1976a,  n  =  1  578).  Animal  matter  com- 
prises 10%  of  the  diet  in  the  form  of  aquatic  insects 
(caddisfly  larvae,  dragonflies,  damselflies,  predaceous  div- 
ing beedes,  water  boatmen,  mosquito  larvae,  and  midge 
larvae),  earthworms,  snails,  crustaceans,  tadpoles,  fish 
eggs,  and,  rarely,  frogs  and  small  fish  (Palmer  1976a, 
Swanson  et  al.  1979).  Mallards  obtain  a  significant  part  of 
their  energy  and  lipid  (fat)  requirements  for  reproduction 
at  sites  occupied  prior  to  arrival  on  the  breeding  grounds 
(Krapu  1981).  The  protein  for  egg  formation,  however,  is 
obtained  principally  from  the  diet  during  the  nesting 
period.  Females  spend  more  than  twice  as  much  time 
foraging  during  the  laying  period  as  do  males  (Dwyer  et  al. 
1979).  During  laying,  females  increase  their  consumption 
of  animal  matter  to  about  70%;  snails  are  important  dien 
for  both  protein  and  calcium  (Krapu  1979;  Swanson  et  al. 
1979,  n  =  15).  See  Northern  Shoveler  account  regarding 
the  importance  of  fat  reserves  for  egg  formation.  Young 

109 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Waierfowl 


Mallards  switch  from  an  initial  exclusive  dependence  on 
invertebrates  to  vegetable  fare  when  diey  are  about  half 
grown  (M.R.  McLandress  pers.  comm.). 

Mallards  are  catholic  in  dieir  choice  of  nest  sites  but 
generally  prefer  upland  sites  to  marshes  (Bellrose  1980). 
Availability  of  fairly  dense  cover  about  two  feet  high 
appears  to  be  the  main  requirement.  Nests  range  from  a 
few  feet  to  as  much  as  a  mile  and  a  half  away  (Palmer 
1976a,  Bellrose  1980).  Reports  of  most  nests  being  within 
100  to  350  yards  of  water  (Dzubin  6k  Gollop  1972,  Palmer 
1976a,  Bellrose  1980)  are  likely  an  artifact  of  extensive 
research  in  the  pond-studded  prairie  pothole  regions  of  the 
U.S.  and  Canada.  At  Grizzly  Island  in  the  Suisun  Marsh, 
nest  densities  are  highest  about  one-half  mile  (or  as  far  as 
possible)  from  water  (M.R.  McLandress  pers.  comm.).  The 
distance  of  nests  from  the  water  is  related  not  only  to  the 
dispersion  of  water,  but  also  to  the  availability  of  nesting 
cover  close  by  and  the  intensity  of  harassment  of  females 
by  males  as  a  function  of  population  density  (Dzubin  & 
Gollop  1972).  Because  of  these  considerations,  the  closest 
water  to  the  nesting  site  is  not  necessarily  the  pond  used  as 
a  waiting  site  or  the  pond  to  which  the  brood  is  moved  at 
hatching. 

Typical  nest  sites  include  weed  fields,  hayfields  and 
pastures,  grain  stubble  fields,  grassy  and  weedy  edges  of 
roadsides,  weedy  and  brushy  levee  and  ditch  banks,  dense 
marsh  vegetation  (sometimes  over  water),  small  islands, 
under  piles  of  brush,  under  fallen  logs  in  dense  brush, 
under  clusters  of  trees,  and,  less  frequendy,  in  heavy  timber 
at  the  base  of  a  large  tree  (Bent  1923,  Palmer  1976a, 
Bellrose  1980).  Atypical  sites  include  tree  crotches  up  to  25 
feet  above  the  ground,  on  tree  limbs,  in  hollows  of  trees, 
on  stumps,  on  muskrat  houses  or  fallen  logs,  in  old  magpie 
nests,  on  the  understructure  of  a  bridge,  and  in  a  box  on 
a  barn  roof.  Mallards  also  accept  artificial  nest  baskets, 
especially  those  located  three  to  four  feet  over  water  in  areas 
free  of  heavy  vegetation  (Bellrose  1980).  The  female  forms 
the  nest  bowl  in  plant  litter  (already  in  place  or  gathered  at 
the  site)  or  in  moist  earth  and  adds  pieces  of  marsh  plants, 


weeds,  and  grasses  reachable  from  the  nest.  Most  nests 
have  a  distinct  canopy  or  cover,  either  natural  or  bent  over 
die  nest  by  the  female  (M.R.  Mcl^andress  pers.  comm.). 
After  hatching,  the  female  may  lead  the  precocial  young 
overland  to  more  than  one  body  of  water;  distances  trav- 
eled by  hens  and  broods  may  be  up  to  three  and  a  half 
miles  in  two  days,  and  five  miles  in  nine  days  (Dzubin  6k 
Gollop  1972,  Palmer  1976a,  Bellrose  1980).  In  large 
ponds  and  marshes,  several  stretches  of  shoreline  are  used 
during  this  period.  The  factors  responsible  for  brood 
movement  are  unclear  (Dzubin  ck  Gollop  1972).  They 
probably  involve  searching  for  favorable  food  and  cover 
and  moving  to  more  permanent  ponds  and  may  be  influ- 
enced by  drying  of  wetlands,  food  shortage,  and  distur- 
bance. 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Mallard  was  the  most  numer- 
ous and  widespread  duck  nesting  in  Marin  County.  It  bred 
at  freshwater  sites  scattered  throughout  the  interior,  at 
brackish  marshes  along  the  coast,  and  on  the  San  Fran- 
cisco and  San  Pablo  bayshores.  In  urban-suburban  set- 
tings, the  breeding  status  of  free-flying  birds  can  be  difficult 
to  establish  because  of  the  presence  of  domestic  stock  and 
their  hybrids  and  of  "self-tamed,"  unconfined  wild  birds 
on  the  same  ponds  with  truly  wild  stock.  Fortunately,  these 
considerations  did  not  pose  problems  in  establishing 
breeding  in  particular  blocks  because  wild  Mallards  were 
such  widespread  breeders.  Representative  nesting  loca- 
tions were  a  pond  by  the  beach  at  Limantour  Estero  (FL 
4/8/80  — DS);  Bahia  Drive  ponds  near  the  Petaluma  River 
mouth,  Novato  (NE  6/7/80  — DS);  and  Nicasio  Reservoir 
(FL  7/18/82 -DS). 

Historical  Trends/  Population  Threats 

In  the  period  1968  to  1989,  populations  of  breeding 
Mallards  were  increasing  in  California  (Robbins  et  al. 
1986,  USFWS  unpubl.  analyses). 


110 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


NORTHERN  PINTAIL  Anas  acuta 


Occurs  year  round,  though  primarily  as  a 

winter  resident  from  late  Aug  through 

j\^^%^ 

early  Apr. 

N-     \s*\'\    \f^ 

\\\2^XX^c^\^^^i-  - 

An  uncommon,  very  local  breeder; 

r^VVrC 

\^\  \^\  \<v\^\    \^\\^Kio\ 

overall  breeding  population  very  small. 

-"\    Jr\    jx^X    it^-K-  \-<Z\     V^V  o  V"^  \ 

Recorded  in  14  (6.3%)  of  221  blocks. 

^^^X^^X-A^Cl^r^A^A^x^^^CsA^-^ 

O    Possible        =         8   (57%) 

i^y^F^^^^ 

©    Probable       =         2    (14%) 

•    Confirmed  =        4  (29%) 

^J^V^^^ 

FSAR  =  2        OPI  =  28         CI  =  1.71 

Ecological  Requirements 

These  sleek,  elegant  ducks  characteristically  nest  in  open 
country  that  contains  many  scattered  small  bodies  of  water 
(Palmer  1976a)— typically  shallow,  temporarily  flooded 
basins  harboring  an  abundance  of  aquatic  invertebrates  for 
foraging  and  brood-rearing  habitat  (Krapu  1 974a).  Ephem- 
eral spring  ponds,  vernal  pools,  and  flooded  uplands  are 
particularly  attractive  (M.R.  McLandress  pers.  coram.). 
Apparent  adaptations  by  Pintails  to  the  use  of  ephemeral 
wedands  are  smaller  clutches,  shorter  incubation  periods, 
and  shorter  fledging  periods  than  Mallards  and  Gadwalls 
(Bellrose  1980,  M.R.  McLandress  pers.  comm.).  Surpris- 
ingly, open  flooded  areas  are  used,  seldom  near  trees.  In 
Marin  County,  breeding  Pintails  mosdy  frequent  wedands 
in  or  near  extensive  brackish  marshes  along  the  bayshore, 
though  they  sometimes  also  use  inland  bodies  of  water. 
How  the  niches  of  the  Mallard  and  Gadwall  differ  from 
that  of  the  Pintail  in  Marin  County  is  not  clear,  though 
Pintails  are  fussier  in  their  choice  of  wedands  and  appear 
to  choose  larger,  but  shallower  bodies  of  water.  Compared 
with  other  dabbling  ducks,  Pintail  drakes  are  highly  mobile 
and  least  attached  to  their  waiting  sites  or  "activity  centers" 
(Palmer  1976a).  Drakes  will  chase  other  females  and  loaf 
or  feed  with  other  drakes  while  their  mates  are  at  their 
nests.  With  this  low  level  of  aggression,  many  individuals 
can  use  preferred  ponds. 

Pintails  prefer  to  feed  in  very  shallow  water  at  the  surface 
or  by  tipping  up  (Palmer  1976a).  Rarely,  large  numbers  of 
Pintails  will  dive  for  preferred  foods  (Miller  1983).  Their 
long  necks  and  tipping  feeding  style  enable  them  to  sift 
seeds   and  benthic   invertebrates   from  the  detritus   and 


sediments  on  or  near  the  bottoms  of  ponds  (Krapu  1974a). 
They  also  pick  seeds  or  invertebrates  from  concentrations 
on  the  water's  surface  (Krapu  1974a,  Euliss  &  Harris 
1987).  While  foraging,  they  tend  to  spend  more  time 
tipping  up  than  moving,  then  move  quickly  over  short 
distances  between  tip-ups  (Eadie  et  al.  1979).  Pintails  also 
feed  extensively  in  rice,  corn,  and  stubble  fields  on  waste 
grain,  though  primarily  in  fall  and  winter  (Bellrose  1980). 
Pintails  often  feed  in  both  agricultural  fields  and  wedands 
at  night  (Euliss  &  Harris  1987,  Miller  1987). 

The  diet  in  North  America  is  about  87.2%  vegetable 
and  12.8%  animal  (Mabbott  in  Palmer  1976a,  n  =  790), 
but  percentages  vary  and  animal  matter  sometimes  pre- 
dominates geographically  or  seasonally.  For  example,  in 
die  Central  Valley  the  fall  diet  of  Pintails  is  97%  or  more 
vegetable  matter,  but  by  mid-  to  late  winter  it  may  be  about 
30%-85%  animal  matter  (Connelly  ck  Chesemore  1980, 
Euliss  &.  Harris  1987,  Miller  1987).  Vegetable  fare  con- 
sists largely  of  the  seeds  of  pondweeds,  sedges,  alkali 
bulrush,  grasses,  smartweeds,  and  several  species  of  "moist 
soil  plants"  such  as  brass  buttons,  fat  hen,  swamp  timothy, 
and  purslane  (Palmer  1976a,  Miller  1987,  M.R. 
McLandress  pers.  comm.).  Animal  fare  includes  various 
aquatic  insects  (midge  larvae,  water  boatmen,  caddisfly 
larvae,  dragonfly  and  damselfly  larvae  and  nymphs,  preda- 
ceous  diving  beetles,  mosquito  larvae),  earthworms,  snails 
and  other  mollusks,  crustaceans  (brine  shrimp,  crabs, 
crayfish,  shrimp),  and,  very  rarely,  miscellaneous  items 
such  as  frogs  and  fish  (Krapu  1974a,b;  Palmer  1976a; 
Swanson  et  al.  1979;  Miller  1987).  Pintails  arrive  on  the 


111 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


Waterfowl 


breeding  grounds  with  large  fat  reserves  necessary  for  the 
reproductive  effort  (Krapu  1974a).  In  North  Dakota, 
breeding  female  Pintails  in  insect-rich  habitats  consume 
79%  animal  matter  compared  with  30%  by  males  (Krapu 
1974b).  Overall  in  various  habitats,  females  consume  60% 
animal  foods,  reaching  a  peak  of  77%  during  laying,  when 
there  is  the  greatest  need  for  calcium  (from  snails)  and 
protein.  See  Northern  Shoveler  account  regarding  the 
importance  of  fat  reserves  for  egg  formation. 

Pintails  choose  relatively  dry,  open  nest  sites  with  low  or 
sparse  vegetation  and  generally  nest  farther  from  water 
than  other  ground-nesting  ducks  (Duncan  1987).  In 
Alberta,  most  nests  are  from  0.6  to  1.2  miles  from  water, 
with  some  as  far  as  1 .9  miles  from  water;  many  nests  are 
also  on  pond  edges  or  on  islands.  The  low  average  dis- 
tances of  nests  from  water  in  other  studies  (about  200  yds. 
or  less)  may  be  because  nest  searches  were  conducted  close 
to  water  (Duncan  1987)  or  because  studies  were  in  areas 
with  extensive  pond  systems,  where  it  is  difficult  for  birds 
to  nest  far  from  water  (M.R.  McLandress  pers.  comm.). 
Female  Pintails  apparendy  nest  far  from  water  to  reduce  the 
probability  of  predation,  rather  than  to  avoid  harassment 
by  males  near  ponds  as  some  authors  have  suggested 
(Duncan  1987).  Spacing  in  available  upland  areas  seems 
to  be  more  important  than  vegetation  for  nest  site  selection 
(M.R  McLandress  pers.  comm.).  Although  Pintails  may 
select  nest  sites  in  bare  earth,  they  more  often  choose  sites 
near,  or  in,  some  vegetation,  such  as  weeds,  grasses,  brush 
clumps,  low  willows,  or  beds  of  marsh  plants  (Palmer 
1976a,  Bellrose  1980).  They  generally  avoid  timbered  or 
extensive  brushy  areas.  In  the  brackish  Suisun  Marsh, 
Pintails  often  nest  in  the  cover  of  pickleweed  two  to  diree 
feet  high  (M.R.   McLandress  pers.  comm.).   More  than 


other  species  of  waterfowl,  Pintails  use  farmland  habitats 
such  as  stubble  fields,  hayfields  and  pastures,  roadsides, 
fallow  fields,  grain  fields,  and  field  edges  for  nesting 
(Palmer  1976a,  Bellrose  1980).  Females  lay  their  eggs  in  a 
natural  or  hollowed-out  depression  lined  with  grass,  bits  of 
straw,  weed  stems,  leaves,  sticks,  or  mosses  mixed  with 
down  (Bent  1923).  Pintail  hens  usually  lead  their  broods 
farther  overland  to  water  than  other  puddle  ducks,  and 
frequently  from  one  pond  to  another  (Bellrose  1980). 

Marin  Breeding  Distribution 

During  the  adas  period,  most  nesting  Pintails  in  Marin 
County  were  found  in  wedands  along  the  San  Francisco 
and  San  Pablo  bay  shorelines.  Representative  nesting  local- 
ities included  Spinnaker  wedands,  San  Rafael  (FL  5/6/80 
— DS);  Bahia  Drive  ponds  near  the  Petaluma  River  mouth, 
Novato  (FL  6/1 6/79  &  6/14/80  -Gil);  and  fish-breeding 
ponds  near  the  Cheese  Factory,  Hicks  Valley  (FL  6/21  &. 
7/1 4/82  — DS,  ScC).  The  presence  of  a  pair  of  birds  at  a 
freshwater  pond  at  the  head  of  Home  Bay,  Drake's  Estero, 
on  1 7  June  1981  (DS)  suggested  that  Pintails  may  occasion- 
ally breed  along  the  outer  coast  of  Marin  County. 

Historical  Trends/ Population  Threats 

Formerly,  Pintails  were  not  known  to  breed  in  Marin 
County  (GekW  1927,  S&P  1933,  G&lM  1944),  but  they 
were  probably  overlooked  because  of  limited  observer 
coverage  since  small  numbers  were  known  to  breed  then 
around  San  Francisco  Bay  (G&.M  1944).  Numbers  of 
Northern  Pintails  were  relatively  stable  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989  (USFWS  unpubl. 
analyses). 


112 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


BLUE- WINGED  TEAL  Anas  discors 


Occurs  year  round,  though  primarily  as  a 

spring  transient  from  late  Jan  through 

Jun  (mostly  Apr-Jun). 

^K\^\^^^\^3^^C^ 

A  very  rare  (perhaps  rare),  very  local 
breeder;  overall  breeding  population  very 

Y^O\  \zVA^T      \^-^\       \  *a**,"r      \  ^-^\''    \"~><* 

^Vw^cA 

small. 

\^S^^^k\^\v\\. 

^\3r\    3r^C^V^_ 

Recorded  in  9  (4.1%)  of  221  blocks. 

\  uyf^A  ■  i^-^^-^^^i  c-\^\ 

^^p^3^^ 

O    Possible                  8   (89%) 

^pV^V^T^V^^^Or 

C    Probable       =         1    (11%) 

IS^^Tr^vV 

•    Confirmed  =         0   (0%) 

-^^^^^^?(> 

FSAR=1         OPl  =  9            CI  =  1.11 

Ecological  Requirements 

This  dapper  eastern  counterpart  of  the  Cinnamon  Teal 
occurs  irregularly  in  the  breeding  season  in  Marin  County 
in  shallow,  marshy-edged  ponds,  in  freshwater  marshes,  in 
slow-moving  streams  and  sloughs,  and,  sparingly,  in  brack- 
ish water  impoundments.  The  drake  defends  both  his 
waiting  site  and  his  mate  (Palmer  1976a).  Both  the  hen  and 
the  drake  stay  within  a  circumscribed  site,  which  may 
contain  more  than  one  water  area;  the  drake  prefers  to  wait 
at  the  one  nearest  the  nest.  Other  nearby  areas  are  used  for 
communal  feeding.  Blue-winged  and  Cinnamon  teal  over- 
lap broadly  in  habitat  use  and  are  often  found  in  each 
other's  company.  Both  species  prefer  to  feed  in  very  shal- 
low water,  usually  with  much  emergent  or  floating  vegeta- 
tion (Bent  1923,  Palmer  1976a).  Although  bodi  species 
feed  frequendy  in  both  open  water  and  among  emergent 
vegetation,  Blue-wings  feed  more  often  in  open  water  than 
Cinnamons  do;  both  species  feed  to  a  limited  degree  on 
mudflats  on  pond  edges  (Connelly  &  Ball  1984).  At  times, 
Blue-winged  Teal  feed  over  deep  water  on  emerging  aquatic 
insects  or  on  invertebrates  using  the  substrate  of  vascular 
plants  that  extend  to  the  surface  (Swanson  et  al.  1974). 
Blue-wings  sometimes  gather  to  feed  at  night  on  emerging 
insects  that  concentrate  in  large  numbers  on  die  water's 
surface  at  the  approach  of  darkness.  Bodi  of  these  teal 
species  feed  mosdy  near  the  surface  by  prolonged  immer- 
sion of  part  or  all  of  the  bill  below  the  water's  surface  (eye 
above  water)  or  by  picking  items  off  the  surface.  To  a 
limited  degree,  they  feed  by  immersing  the  head  past  the 
eye  or  by  tipping  up,  but  they  seldom  dive  (Swanson  et  al. 


1974,  Palmer  1976a,  Connelly  &  Ball  1984).  They  also 
visit  grain  fields  in  the  fall  (Bent  1923). 

The  Blue-winged  Teal  diet  year  round  is  about  70% 
vegetable  matter  and  30%  animal  matter  (Mabbott  in 
Palmer  1976a,  n  =  319).  Vegetable  food  consists  mainly  of 
seeds  of  grasses  and  sedges,  and  seeds,  stems,  and  leaves 
of  pondweeds.  Animal  foods  include  aquatic  insects 
(midge  larvae,  caddisfly  larvae,  nymphs  of  damselflies  and 
dragonflies,  predaceous  diving  beedes,  water  boatmen, 
mosquito  larvae),  mollusks  (mosdy  snails),  various  small 
crustaceans,  and  a  few  spiders,  water  mites,  and,  very 
rarely,  fish  (Swanson  et  al.  1974,  1979;  Palmer  1976a).  As 
with  other  dabbling  ducks,  dietary  changes  occur  season- 
ally. Animal  matter  is  particularly  important  in  die  breed- 
ing season  when  it  can  amount  to  89%  (increasing  from 
45%  in  spring  to  95%  in  summer)  of  die  diet  of  males  and 
females  combined  (Swanson  et  al.  1974,  n  =  107).  At  that 
time,  females  feed  more  intensely  and  consume  more 
animal  matter  (more  snails,  less  crustaceans)  than  do 
males.  In  North  Dakota,  consumption  of  animal  matter 
(especially  midge  larvae  and  snails)  by  females  (n  =  20) 
peaks  at  99%  of  the  diet  during  laying,  when  calcium  and 
protein  needs  are  high  for  egg  formation  (Swanson  et  al. 
1974,  1979;  Krapu  1979).  See  Northern  Shoveler  account 
regarding  die  importance  of  fat  reserves  for  egg  formation. 
The  Blue-winged  Teal  diet  also  varies  considerably 
between  local  habitats  (Swanson  et  al.  1974).  Compared 
with  Green-winged  Teal,  Blue-wings  feed  more  on  animal 
matter  and  more  heavily  on  vegetative  parts  of  plants  than 
on  seeds  (Bellrose  1980).  Relative  to  Shovelers,  Blue-wings 


113 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Waterfowl 


eat  larger  crustaceans  (Swanson  et  al.  1974).  Unlike  other 
dabbling  clucks,  Blue-winged  Teal  feed  on  amphipods  tbat 
concentrate  on  the  terminal  buds  and  other  parts  of 
vascular  plants. 

Blue-winged  Teal  typically  nest  in  dry  sites  widi  fairly 
tall,  dense  grass,  in  sedge  meadows,  in  brackish  marshes 
of  cord  grass  and  salt  grass,  or  in  hay  or  alfalfa  fields  (Bent 
1923,  Palmer  1976a,  Bellrose  1980).  They  also  occasion- 
ally nest  on  soggy  ground,  on  islands,  in  dense  cattail 
growth,  and  in  cavities  in  and  upon  muskrat  houses.  Nest 
sites  range  from  the  water's  edge  up  to  a  mile  away,  but 
average  roughly  125  feet  from  water  (Bellrose  1980).  The 
nest  may  be  set  well  into  a  dense  clump  of  rank  grass  on 
the  surface  or  may  be  sunk  in  a  cavity  flush  with  the  ground 
(Bent  1923).  The  nest  bowl  is  lined  with  fine  dead  grass 
(less  frequendy  with  cattail  blades  or  other  wedand  vegeta- 
tion in  damp  places)  and  the  obligatory  down;  growing 
grass  often  arches  over  the  nest  cavity.  Females  with  broods 
may  travel  overland  about  100  to  1600  yards  (maximum 
2.25  mi.)  from  the  nest  site  to  water  but  once  established 
are  more  likely  to  remain  at  a  site  than  are  many  other 
species  of  ducks  (Bellrose  1 980). 

Marin  Breeding  Distribution 

Blue-winged  Teal  occur  in  Marin  County  in  small  num- 
bers most  years  in  May  and  June  (DS),  but  die  species  has 
not  yet  been  adequately  documented  to  breed  here.  Docu- 
mentation is  difficult  to  obtain  because  of  the  species' 
relative  scarcity  in  Marin,  the  great  similarity  of  female 
Blue-winged  Teal  and  the  much  commoner  Cinnamon 
Teal,  and  the  tendency  of  these  two  species  to  hybridize  in 
the  wild  (Harris  ck  Wheeler  1965;  relatively  frequent 
sightings  of  males  showing  apparent  hybrid  characters 
— ABN).  During  the  adas  years,  we  obtained  suggestive 
evidence  of  nesting  by  observations  of  a  female  Blue- 
winged/Cinnamon-type  female  and  downy  young  accom- 
panied by  a  male  Blue-winged  Teal  on  Americano  Creek 
on  the  Marin/Sonoma  County  border  near  Valley  Ford, 
Sonoma  County,  on  10  June  1977  (CJP),  and  at  the  Bahia 
Drive  ponds  near  the  Petaluma  River  mouth,  Novato,  on 
14  June  1980  (GiT)  (but  see  comments  below).  During  the 
adas  period,  there  were  also  scattered  sightings  of  male 
Blue-winged  Teal  on  Point  Reyes  and  in  wedands  along  the 
San  Pablo  and  San  Francisco  bay  shorelines. 

Adasers  in  California  should  be  very  cautious  about 
interpreting  the  significance  of  observations  of  male  Blue- 
winged  Teal  accompanying  female  Blue-winged/Cinna- 
mon  Teal  and  young.  First  of  all,  Blue-wings  likely  breed 
one  to  two  months  later  than  Cinnamon  Teal  (M.R. 
McLandress  pers.  comm.).  Secondly,  male  Cinnamon 
Teal  attend  females  with  young  only  infrequendy  (5%- 


10%  of  broods),  and  Blue-winged  Teal  probably  do  so 
even  less  frequently  since  they  are  one  of  the  northern 
ducks,  which  tend  to  have  weak  pair  bonds.  Blue-winged 
Teal  males  in  these  cases  may  be  ready  to  mate,  but  the 
hens  were  likely  mated  earlier  in  the  season  to  Cinnamon 
Teal  males,  hence  the  offspring  would  be  Cinnamon  Teals 
(M.R.  McLandress  pers.  comm.).  Even  the  observation  of 
a  carefully  identified  Blue-winged  Teal  female  with  young, 
even  if  attended  by  a  male  Blue-winged  Teal,  is  not  positive 
proof  of  nesting  of  this  species  because  of  the  uncertainty 
of  parentage.  Nesting  of  Blue-winged  Teal  in  areas  of 
marginal  occurrence  of  that  species  within  the  heart  of  the 
range  of  the  Cinnamon  Teal  can  probably  best  be  consid- 
ered valid  only  after  a  number  of  carefully  identified  Blue- 
winged  Teal  females  have  been  seen  with  broods,  thus 
lessening  the  likelihood  that  all  sightings  represented  off- 
spring of  mixed-species  pairs. 

Historical  Trends/  Population  Threats 

Grinnell  and  Miller  (1944)  did  not  consider  the  Blue- 
winged  Teal  a  breeding  species  in  coastal  northern  Califor- 
nia, although  they  did  list  a  21  June  record  for  Areata, 
Humboldt  County.  Recendy,  McCaskie  et  al.  (1979)  con- 
sidered the  species  a  rare  to  uncommon  breeder  on  the 
northern  California  coast.  This  reported  change  in  status 
may  simply  be  the  result  of  more  thorough  recent  coverage 
of  this  region,  but  odier  evidence  suggests  a  possible  range 
expansion.  Wheeler  (1965)  and  Connelly  (1978)  reported 
that  from  the  1930s  to  the  1960s,  Blue-winged  Teal  pio- 
neered new  breeding  areas  and  increased  in  numbers  on 
the  Pacific  Coast,  especially  north  of  California.  On  the 
other  hand,  the  species'  notorious  tendency  to  abandon 
drought-stricken  areas  to  pioneer  newly  available  habitat 
far  from  the  center  of  its  breeding  range  (Bellrose  1980) 
perhaps  explains  periodic  influxes  that  occur  in  Marin 
County  and  elsewhere  along  the  northern  California  coast 
that  might  be  interpreted  as  a  true  range  expansion.  For 
example,  in  May  and  June  of  1980,  one  observer  (DS)  saw 
23  Blue-winged  Teal  in  Marin  County  compared  with 
about  1  to  4  birds  per  year  in  several  other  years,  with 
roughly  equivalent  time  spent  in  the  field.  Similarly,  John- 
son and  Yocum's  (1966)  report  of  a  ratio  of  42  Blue- 
winged  Teal  males  to  36  Cinnamon  Teal  males  at  Lake 
Earl,  Del  Norte  County,  from  1  June  to  20  July  is  certainly 
not  typical  of  most  years  since  Yocum  and  Harris  (1975) 
considered  Blue-wings  to  be  rare  breeders  in  that  region. 
Numbers  of  Blue-winged  Teal  on  Breeding  Bird  Surveys 
in  California  did  increase  from  1968  to  1989  but  were 
relatively  stable  from  1980  to  1989  (USFWS  unpubl.  anal- 
yses). 


114 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


CINNAMON  TEAL  Anas  cyanoptera 


Occurs  year  round,  though  primarily  as  a 

A^l^>^           N                    «~i 

spring  transient  from  Jan  through  May 

^V^TvJrt^Ow^^-dV- 

^^voj^ 

(especially  Mar  and  Apr)  and  secondarily 

x^^^Pc^^^X^coA 

as  a  summer  resident  from  May  through 

r^Swr^C^\\%^\^r 

A>VO\ 

Sep. 

\VSQcM^^ 

YSkcCi 

A  fairly  common,  local  breeder;  overall 

\^\><v» V-^\    h^\    \/f    \yf    I 
KNjiA^iM  _A"\  Jr\  3f\ 

breeding  population  small. 

r^\     A^A^W— 

Recorded  in  52  (23.5%)  of  221  blocks. 

'lA^x^A^^v^x 

O    Possible        =      23  (44%) 

^\ujV\°JV\^^\  3t^^v 

-V"s  J^c^\  ^Vfe\ — -v 

©    Probable      =        6  (12%) 

^w3^5y\3r\3r€ 

•    Confirmed  =       23   (44%) 

Jj>^                       \^7    ^^LA^>K 

FSAR  =  3        OPI  =  156       CI  =  2.00 

Ecological  Requirements 

The  stunning  Cinnamon  Teal  drakes  and  their  cryptic 
mates  are  studies  in  contrast  in  the  freshwater  and  brackish 
ponds  and  marshes  they  inhabit.  Their  lifestyles,  habitat 
preferences,  and  foraging  methods  are  so  similar  to  those 
of  their  primarily  eastern  congeners,  the  Blue-winged  Teal, 
that  the  reader  is  referred  to  the  descriptions  in  the  preced- 
ing account.  The  Cinnamon  Teal  diet  is  roughly  80% 
vegetable  matter,  mosdy  seeds  and  other  parts  of  sedges, 
pondweeds,  and  grasses;  and  20%  animal  matter,  divided 
about  equally  between  aquatic  insects  (beedes,  true  bugs, 
damselflies,  dragonflies,  larval  midges,  etc.),  and  mollusks 
(snails  and  small  bivalves)  (Martin  et  al.  1951,  n  =  59; 
Mabbott  in  Palmer  1976a,  n  =  41).  Like  other  dabbling 
ducks  (see  accounts),  Cinnamon  Teal  appear  to  change 
their  diet  seasonally  and  consume  more  animal  matter  in 
summer  (especially  females). 

Cinnamon  Teal  usually  select  nest  sites  in  dense  vegeta- 
tion, such  as  grasses,  weeds,  bulrushes,  and  sedges  in 
uncultivated  land,  meadowlands,  marshes,  swales,  and 
grain  fields,  and  on  dikes  and  islands  (Bent  1923,  Dawson 
1923,  Palmer  1976a,  Bellrose  1980).  Females  usually 
scratch  out  a  shallow  depression  on  dry  land  that  they  line 
with  dead  grasses  and  plant  stems.  They  also  frequendy 
establish  marsh  nests  and,  more  commonly  than  other 
species  of  dabbling  ducks,  nests  over  water.  Marsh  nests 
are  bulkier  baskets  or  platforms  made  of  dried  cattails, 
sedges,  or  marsh  grasses.  These  nests  may  be  under  dense 
matted  vegetation  of  the  previous  year's  growth,  may  be 


reached  by  a  tunnel  burrowed  out  by  the  female,  or  may  be 
suspended  over  water  in  emergent  vegetation.  If  threatened 
by  rising  water  levels,  females  sometimes  raise  ground 
nests  by  adding  materials.  Although  nests  range  from 
direcdy  over  water  to  220  yards  away  from  it,  most  are 
widiin  75  yards  of  water.  The  best  brood  habitats  are  small 
bodies  of  water,  such  as  ponds,  ditches,  and  canals,  with 
plentiful  submerged  aquatic  vegetation  for  feeding  and 
emergent  vegetation  for  protective  cover  (Bellrose  1980). 
The  hen  may  move  broods  as  far  as  a  mile  in  a  few  days, 
but,  if  cover  and  feeding  conditions  are  good,  their  activi- 
ties may  involve  only  a  few  acres  (Palmer  1976a). 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Cinnamon  Teal,  next  to  the 
Mallard,  was  the  second  most  widespread  breeding  duck 
in  Marin  County.  Although  some  breeding  Cinnamon 
Teal  were  scattered  throughout  the  county,  most  were 
concentrated  in  coastal  and  bayshore  wedands.  Represen- 
tative breeding  locations  included  the  pond  at  the  Drake's 
Beach  visitor's  center,  PRNS  (FL  5/27/80  -DS);  McGinnis 
Park,  San  Rafael  (FL  6/3/80  -DS);  and  Laguna  Lake, 
Chileno  Valley  (FL  6/28/81  -DS).  Numbers  of  Cinna- 
mon Teal  in  early  spring  belie  actual  breeding  abundance 
since  there  is  a  peak  migratory  period  from  February 
through  April  with  numbers  falling  to  summer  levels  by 
May  (Shuford  et  al.  1989). 


115 


Waterfowl 


MARIN  COUNTY  BRHHDING  BIRD  ATLAS 


Waterfowl 


Historical  Trends/Population  Threats 

Cinnamon  Teal  were  not  reported  historically  from  Marin 
County  as  breeding  birds  (G&W  1927,  SckP  1933, 
G&.M  1944),  probably  because  of  limited  observer  cover- 
age or  an  author's  impression  that  such  records  lacked 


regional  significance.  Numbers  of  Cinnamon  Teal  were 
relatively  stable  on  Breeding  Bird  Surveys  in  California 
from  1968  to  1989  (USFWS  unpubl.  analyses). 


NORTHERN  SHOVELER   Anas  clypeata 


Occurs  year  round,  though  almost  exclu- 

^>-x^^               \                          jr^i. 

sively  as  a  winter  resident  from  late  Aug 

_/  ^^Ai^'A  -t>**k 

through  Apr. 

r^Vv^n 

\r^\  Jk^\°y<r\    V^\OrC 

-••Vb  V\/  s 

A  very  rare  (perhaps  now  rare),  very 
local  breeder;  overall  breeding  popula- 

rX^Ofv^rS^v 

tion  very  small. 

\d~^ 

Of<:v\  >-V^\  ^-V^\  jV^\  J^<^\ 

r\    V^A°A-^ 

Recorded  in  4  (1.8%)  of  221  blocks. 

^^^_V^V^^Va> 

WAj^AprC^^r^^ 

m^\  . '^^"^-^V^A"  C^\^\    3<*^\ 

^^V^ \  ^^^\-J^y  oo 

O    Possible                  4   (100%) 

^C^rC^S^r^wV^ 

^^^^V^v^v <- 

€    Probable       =        0  (0%) 

^Ps^?>^ 

p^^O^^Jo 

•    Confirmed   =         0   (0%) 

FSAR  =1          OPI  =  4           CI  =  1 .00 

i  >^=>                             s , 

Ecological  Requirements 

With  such  an  outsized  bill,  one  might  expect  the  "Spoon- 
bill" to  ply  its  trade  in  waters  of  a  different  ilk,  but,  like 
many  of  the  dabbling  duck  clan,  its  breeding  haunts  are 
shallow  ponds  and  open  marshy  areas  with  shallow  water- 
ways and  abundant  aquatic  vegetation  (along  widi  sur- 
rounding dry  meadows).  Soft,  slimy  mud  is  another 
requisite  (Palmer  1976a).  Shovelers  do  not  appear  to  care 
if  the  water  is  clear,  clean,  muddy,  flowing,  or  stagnant;  and 
they  nest  near  fresh,  alkaline,  brackish,  or  estuarine  waters. 
Breeding  Shovelers  are  the  most  territorial  of  the  prairie- 
nesting  dabbling  ducks,  presumably  because  of  their  need 
to  secure  high-quality  feeding  sites  for  reproduction 
(Ankney  ck  Afton  1988).  Shovelers  select  a  home  range 
with  a  "core  area  or  "waiting  area,'  a  nest  site,  and  several 
(3-13)  "peripheral"  ponds  (Poston  1974)-  Pairs  spend 
60%-90%  of  dieir  time  on  the  core  area,  which  appears  to 
supply  the  basic  resources  for  nesting  and  pair  isolation. 
The  core  area  is  a  restricted  portion  of  the  home  range, 
such  as  a  pond,  a  section  of  a  pond,  or  several  adjacent 
small  ponds.  It  contains  a  loafing  area  (the  waiting  area) 
and  feeding  areas.  The  male  waits  at  the  core  area  for  the 
return  of  the  female  during  incubation  and  defends  it 


against  other  intruding  Shovelers  at  all  times  from  the 
onset  of  laying  until  the  waning  of  the  pair  bond  or  until 
the  female  hatches  the  brood,  whichever  comes  first.  Home 
ranges  overlap,  with  neighboring  pairs  sharing  "neutral" 
areas  of  nesting  cover,  peripheral  ponds,  and  sometimes 
core  areas  in  the  absence  of  the  residents.  Nest  sites  are 
usually  close  to  core  areas  but  may  be  at  some  distance. 

The  Shoveler's  large,  spatulate  bill  with  well-developed 
lamellae  is  designed  for  filter  feeding.  Shovelers  often  feed 
in  very  shallow  water,  continuously  moving  slowly  about 
with  their  heads  and  necks  partly  or  fully  submerged.  Thus 
engaged,  they  sweep  their  bills  from  side  to  side,  skimming 
above  the  bottom  or  filtering  the  water  to  obtain  small 
animal  life  and  seeds  (Palmer  1976a,  Bellrose  1980).  A 
number  of  Shovelers  will  feed  socially  in  this  manner, 
paddling  rapidly  together  in  a  circular  or  elliptical  orbit  on 
the  water,  apparently  stirring  up  the  plankton-laden  waters 
and  straining  it  through  the  lamellae  of  the  bill.  In  breed- 
ing areas  in  Alberta,  Shovelers  prefer  to  feed  in  the  shal- 
lows of  ponds  containing  submergent  and  surface 
vegetation  (Poston  1 974).  They  also  feed  in  deeper  water 
than  most  dabbling  ducks  do,  by  swimming  along,  with 


116 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


the  bill  slightly  submerged,  skimming  and  filtering  the 
surface  waters  (Palmer  1976a,  Bellrose  1980).  Shovelers 
gather  in  large  numbers  to  feed  in  this  manner  on  sewage 
ponds.  They  also  filter  below  the  surface  by  tipping  up,  but 
infrequendy  compared  with  other  dabblers;  they  seldom  go 
to  fields  to  forage.  Like  most  others  dabblers,  they  rarely 
dive.  On  warm  summer  nights,  hens  and  broods  feed  after 
dark  on  emerging  midges  and  mayflies  and  on  water  fleas 
making  vertical  migrations  to  the  water's  surface  (Swanson 
6kSargeantl972). 

The  diet  of  North  American  birds  (fall  to  spring)  is 
roughly  66%-72%  vegetable  matter,  including  seeds  and 
soft  parts  of  grasses,  sedges,  pondweeds,  waterlilies,  algae, 
and  smartweeds.  The  remaining  28%-34%  of  the  diet  is 
animal  matter,  especially  mollusks  (mostly  freshwater  uni- 
valves), insects  (water  boatmen,  backswimmers,  water 
tigers,  dragonfly  nymphs,  flies,  and  caddisfly  and  mayfly 
larvae),  small  crustaceans  (ostracods,  copepods),  and  cray- 
fish and  fish  (probably  rare);  in  certain  areas,  animal  matter 
may  predominate  in  the  diet  (Martin  et  al.  1951,  n  =  101; 
McAtee  in  Palmer  1 976a,  n  =  70).  The  bill  is  particularly 
well  adapted  for  feeding  on  microscopic  phytoplankton 
and  zooplankton,  but  these  food  items  are  rapidly  digested, 
hence  their  importance  is  undoubtedly  underestimated  in 
many  diet  studies  (Bellrose  1980).  In  one  study  of  post- 
breeding  Shovelers,  their  diet  was  78%  animal  matter,  of 
which  90%  was  zooplankton  (Dubowy  1985).  Like  other 
dabbling  ducks,  Shovelers  change  their  diet  seasonally  and 
rely  more  on  animal  matter  in  summer.  In  North  Dakota, 
females  (n  =  1 5)  consume  99%  animal  matter  (mosdy 
microcrustaceans  and  small  snails)  during  laying  when  the 
need  is  high  for  protein  and  calcium  for  egg  formation 
(Swanson  et  al.  1979,  Krapu  1979).  Ankney  and  Afton 
(1988)  reported  that  prelaying  (n  =  14)  and  laying  (n  =  23) 
female  Shovelers  in  Manitoba  ate  over  90%  animal  matter, 
again  mosdy  snails  and  crustaceans.  They  concluded  that 
while  protein  intake  is  important  to  nesting  birds  that  the 
size  of  fat  reserves  is  the  factor  limiting  clutch  size  of 
Shovelers  and  probably  also  other  dabbling  ducks,  such  as 
Wood  Ducks  and  Mallards.  During  the  prelaying  period, 
male  Shovelers  ate  a  similar  proportion  of  animal  matter 
to  that  consumed  by  females  but  only  67%  (n  =  10)  during 
the  laying  period. 

Northern  Shovelers  usually  nest  in  dry  upland  sites, 
sometimes  in  moist  meadowland,  and,  rarely,  in  wet 
marshes.  Nesting  cover  is  typically  grasses  (especially  short 
varieties  and  salt  grass),  sometimes  hay,  and,  rarely,  weeds, 
bulrushes,  sedges,  or  woody  vegetation,  such  as  willows, 


poplars,  or  rosebushes;  concealment  can  be  minimal, 
especially  early  in  the  season  (Bent  1923,  Dawson  1923, 
Poston  1974,  Palmer  1976a,  Bellrose  1980).  The  nest  is  a 
hollow,  lined  with  dead  grasses,  weeds,  or  broken  reeds, 
and,  of  course,  down.  Apparendy  females  sometimes  re- 
locate nests  to  higher  ground  when  threatened  by  rising 
waters  (Poston  1974).  Although  they  may  range  up  to  a 
mile  from  water,  most  nests  are  from  about  75  to  300  feet 
from  water;  nests  immediately  adjacent  to  water  are  usually 
on  islands  or  levees  (Poston  1974,  Palmer  1976a,  Bellrose 
1980).  In  the  prairies  of  Canada,  broods  seldom  remain 
on  one  pond  longer  than  seven  to  ten  days,  and  they  may 
move  with  the  hen  up  to  a  mile  through  a  series  of  ponds 
in  about  two  weeks  (Poston  1974).  Younger  broods  are 
kept  in  shallow  shoreline  areas  near  emergent  vegetation; 
older  broods  prefer  larger  bodies  of  permanent  water 
(Palmer  1976a). 

Marin  Breeding  Distribution 

During  the  atlas  period,  we  obtained  circumstantial  evi- 
dence of  breeding  via  sightings  of  a  male  at  McGinnis 
Park,  San  Rafael,  on  3  June  1980;  a  male  at  the  Bahia  Drive 
ponds  near  the  Petaluma  River  mouth,  Novato,  on  7  June 
1980;  two  to  three  birds  on  outer  Point  Reyes  from  16  to 
18  June  1981;  and  a  female  on  Laguna  Lake,  Chileno 
Valley,  on  19  July  1982  (all  DS).  Subsequendy,  breeding 
was  confirmed  at  the  Las  Gallinas  sewage  ponds,  San 
Rafael,  with  the  observation  of  a  female  with  downy  young 
from  28  May  to  7  July  1985  (DT,  CLF,  DAH);  Shovelers 
also  bred  there  at  least  in  1986,  1987,  and  1988  (ABN). 

Historical  Trends/ Population  Threats 

Formerly,  Northern  Shovelers  were  not  known  to  breed  in 
Marin  County  (GckW  1927,  S&P  1933,  G&M  1944), 
but  they  may  have  gone  undetected  because  of  limited 
observer  coverage  since  small  numbers  did  breed  dien 
nearby  on  San  Francisco  Bay  (G&W  1927,  GckM  1944). 
Recent  increases  in  the  number  of  breeding  Shovelers,  and 
dieir  broods,  at  Grizzly  Island  Wildlife  Area,  Solano 
County,  have  coincided  with  increases  in  the  number  and 
total  acreage  of  summer  ponds  following  extensive  flood- 
ing in  1983  and  subsequent  management  for  summer 
water  (M.R.  McLandress  pers.  comm.).  Shoveler  numbers 
increased  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989  but  were  relatively  stable  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


117 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Waterfowl 


GAD  WALL  Anas  strepera 


Occurs  year  round,  though  primarily  as  a 

^V^r-^      K              ^C2>u. 

winter  resident  from  late  Aug  through 

-V^\\>;;\^ 

Apr. 

A  rare,  very  local  breeder;  overall  breed- 

y<c\JV\ \^\^<r\  yr\\<r\^^\ 

ing  population  very  small. 

\\^<r\ 

\\\\^Qx^D<^ 

Recorded  in  10  (4.5%)  of  221  blocks. 

^\^^\  3rV \±\. \^\  y<^\  \^\°\~-~^ 

O    Possible                 6  (60%) 

n'^\^^^3^^r^v^^\^^V^\^-^^^\^^A\>-^;^  •° 

€    Probable                0  (0%) 

^\      3r^\      A^V^  '■'"•J^\Vi  Jf^/V    "\-^\       Jt-^v       jr-^^>— "*"" 

•    Confirmed   =         4   (40%) 

FSAR=1         OPI  =  10          CI  =  1.80 

Ecological  Requirements 

The  Gadwall's  subde  yet  striking  beauty  graces  Marin 
County's  shallow  freshwater  ponds  and  marshes,  sluggish 
streams,  and  brackish  marshes,  which  abound  in  sub- 
merged aquatic  plants.  During  the  breeding  season,  it 
avoids  woods  or  thick  brush  (and  waters  widi  such  bor- 
ders) and,  along  with  the  Shoveler,  uses  alkaline  or  brack- 
ish waters  more  than  other  dabbling  ducks  do  (Palmer 
1976a).  Breeding  pairs  often  use  areas  that  include  a  broad 
stretch  of  open  water  as  well  as  small  ponds.  Like  odier 
dabbling  ducks  (see  accounts),  Gadwall  usually  occupy  a 
home  range  with  a  nest  site,  waiting  area,  and  feeding  areas 
that  may  overlap  with  those  of  neighboring  pairs;  aggres- 
sion of  the  male  centers  around  a  smaller  defended  area  or 
just  the  mate  (Gates  1962,  Dwyer  1974,  Palmer  1976a). 
When  nesting  densities  are  very  high  on  islands,  intense 
aerial-pursuit  activity  causes  territorial  defense  of  a  female 
or  section  of  habitat  to  break  down  (Duebbert  1966). 
Under  these  conditions,  hens  leaving  nests  for  relief  peri- 
ods may  be  forced  to  fly  more  than  a  mile  to  feed  and  rest 
free  of  pursuing  drakes. 

Gadwall  usually  feed  on  shallowly  submerged  and  float- 
ing vegetation,  and  more  often  in  open  water  than  odier 
dabblers  do  (Palmer  1976a).  They  feed  at  all  hours  of  the 
day  and  after  dark  on  abundant  supplies  of  emerging 
midges  and  water  fleas  making  vertical  migrations  to  open 
surface  waters.  Gadwall  feed  mosdy  by  dabbling,  tipping 
up,  and  picking,  and  by  fdtering  from  the  surface  or  while 
swimming  with  their  heads  immersed;  they  apparendy  do 
not  feed  direcdy  on  the  bottom  (Serie  ck  Swanson  1976). 

118 


Small  planktonic  crustaceans  are  most  frequently  ingested 
by  fdtering  (though  not  as  effectively  as  Shovelers  do),  and 
most  insects  and  fdamentous  algae  are  obtained  by  surface 
picking  or  tipping  up.  Gadwall  are  adept  at  separating 
small  midges  and  beede  larvae  from  a  substrate  of  algae 
and  detritus.  Sometimes  they  feed  from  shore  on 
windrowed  detritus  or  concentrated  plankton.  While  feed- 
ing, Gadwall  spend  more  time  moving  than  tipping  up  and 
move  slowly  over  long  distances  between  bouts  of  tipping 
up  (Eadie  et  al.  1979).  They  also  dive  well  for  food  when 
necessary  (though  infrequendy),  occasionally  forage  in 
grain  stubble,  and,  rarely,  forage  in  woods  for  acorns 
(Palmer  1976a). 

Like  wigeon,  but  unlike  most  dabbling  ducks,  Gadwall 
generally  prefer  the  succulent  leaves  and  stems  rather  than 
the  seeds  of  aquatic  plants.  Filamentous  algae  are  very 
common  in  Gadwall  diets,  making  the  Gadwall  somewhat 
unique  among  ducks  (Serie  ck  Swanson  1976,  Swanson  et 
al.  1979,  M.R.  McLandress  pers.  comm.).  The  North 
American  fall  and  winter  diet  is  about  98%  vegetable 
matter  and  2%  animal  matter  (Martin  et  al.  1951,  n  =  371; 
Mabbott  in  Palmer  1976a,  n  =  362).  Like  odier  dabblers, 
Gadwall  depend  more  on  animal  matter  in  summer.  Dur- 
ing breeding  on  saline  lakes  in  North  Dakota,  the  diet  of 
adults  is  46%  animal  and  54%  vegetable  matter;  females 
consume  more  animal  matter  than  males  do  (Serie  ck 
Swanson  1976,  n=  107).  Consumption  there  of  animal 
matter  (mosdy  aquatic  insects  and  crustaceans)  by  females 
in   both    freshwater   (n  =  35)   and    saline   lakes   (n  =  20) 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


reaches  a  peak  at  72%  of  the  diet  during  laying  when 
demand  is  high  for  calcium  and  protein  for  egg  formation 
(Serie  6k  Swanson  1976,  Krapu  1979,  Swanson  et  al. 
1979).  Throughout  North  America,  animal  matter  con- 
sumed includes  aquatic  insects  (larvae  and  adults  of 
midges,  caddisflies,  beetles,  other  flies,  true  bugs,  dragon- 
flies,  damselflies,  and  grasshoppers),  crustaceans,  mollusks 
(mosdy  snails),  and  a  few  fish.  Vegetable  fare  consists 
primarily  of  leaves,  stems,  rootstocks,  and,  sparingly,  seeds 
(important  locally  or  seasonally)  of  grasses,  sedges,  pond- 
weeds,  and  other  aquatic  plants,  including  algae.  Preflight 
young  initially  eat  chiefly  surface  invertebrates  but  gradu- 
ally switch  to  aquatic  invertebrates  and  plants  until,  by 
three  weeks  of  age,  they  are  essentially  herbivores;  import- 
ant invertebrates  to  young  are  midges,  aquatic  beedes, 
water  fleas,  and  water  boatmen  (Palmer  1 976a). 

Although  widely  distributed  in  nesting  habitat,  Gadwall 
show  a  tendency  toward  colonial  breeding  (on  islands, 
especially  where  surrounded  by  open  water)  (Palmer 
1976a).  Exceptionally,  on  islands,  many  nests  may  be 
within  a  few  feet  of  each  other,  some  less  than  one  foot 
apart  (Duebbert  1 966).  Gadwall  nest  a  month  to  a  month 
and  a  half  later  than  Mallards  (M.R.  McLandress  pers. 
comm.).  This  may  be  related  to  their  dependence  on 
nesting  in  dry  and  dense  upland  herbaceous  vegetation, 
which  becomes  increasingly  available  as  spring  advances 
(Gates  1962).  Late  nesting  may  also  be  due  to  a  depen- 
dence on  insects  that  develop  later  in  the  season  in  semi- 
permanent wedands  (Serie  6k  Swanson  1976).  Gadwall 
usually  select  nest  sites  on  well-drained  or,  occasionally, 
damp  ground,  but  rarely  in  emergent  or  matted  floating 
vegetation.  Reports  of  most  nests  being  within  100  yards 
of  water  (sometimes  nearly  a  mile  from  water)  may  be 
because  of  the  tendency  of  Gadwall  to  nest  on  small 
islands,  dikes,  and  channel  banks  with  requisite  cover 
(Gates  1962,  Palmer  1976a,  Bellrose  1980).  At  Grizzly 
Island  in  the  Suisun  Marsh,  highest  nest  densities  were 
about  one-half  mile  (or  as  far  as  possible)  from  water  (M.R. 
McLandress  pers.  comm.).  For  nesting,  Gadwall  favor 
transitions  in  habitat,  such  as  the  interface  of  water  and 
land,  breaks  or  openings  in  cover,  patches  or  clumps 
within  uniform  stands  of  vegetation,  or  sites  near  mounds, 
stones,  or  other  landmarks  (usually  within  10  ft.).  Gadwall 
generally  seek  taller  and  more  leafy  vegetation  for  nesting 
than  do  other  dabbling  ducks  and  do  not  nest  in  stubble 
fields  unless  other  herbaceous  vegetation  is  growing  there 
(Palmer  1976a,  Bellrose  1980).  The  cover  they  select  is 


usually  dense,  coarse  herbaceous  vegetation  (especially  net- 
des  and  thisdes),  taller  grasses,  alfalfa  or  hay,  sedges, 
bushes,  or  willows.  The  nest  is  a  hollow  lined  with  dry 
grasses,  weed  stems,  or  strips  and  pieces  of  reeds,  and,  of 
course,  down;,  it  is  usually  arched  over  by  vegetation  or  is 
beneath  leafy,  herbaceous  plants  (Bent  1923,  Dawson 
1923,  M.R.  McLandress  pers.  comm.).  Females  sometimes 
build  up  the  nest  to  escape  rising  water  (Palmer  1 976a).  An 
exceptional  nest  site  was  one  in  a  crow's  nest  in  a  tree.  On 
islands,  females  sometimes  lay  their  eggs  in  nest  bowls  of 
the  preceding  year(s?)  (Duebbert  1966).  Broods  do  not 
remain  long  on  small  water  bodies;  instead,  they  prefer 
open-water  areas  of  moderate  to  large  size  having  sub- 
merged aquatic  plants  for  food  and  deep  channels  for 
escape  by  diving  (Palmer  1976a).  Females  may  lead  broods 
as  much  as  500  yards  across  open  water  or  over  a  mile  from 
upland  nest  sites  to  favorable  deep-water  marshes  or 
impoundments  (Gates  1962,  Duebbert  1966).  In  Utah, 
the  distance  that  hens  moved  their  broods  during  the 
rearing  period  averaged  0.56  miles  (range  0.26-1.15  mi.) 
(Gates  1962,  n  =  13). 

Marin  Breeding  Distribution 

During  the  adas  period,  Gadwall  bred  locally  in  Marin 
County  along  the  San  Pablo  Bay  shoreline  and,  occasion- 
ally, on  Point  Reyes  and  in  the  interior  of  the  county. 
Representative  breeding  locations  included  San  Antonio 
Creek,  W  of  Point  Reyes-Petaluma  Rd.  (FL  5/6/79  -SG); 
Bahia  Drive  ponds  near  the  Petaluma  River  mouth, 
Novato  (FL  6/20/80  -DS);  and  Horseshoe  Pond,  E  of  the 
Drake's  Beach  visitor's  center,  PRNS  (FL  7/8  6k  8/15/81 
-DS). 

Historical  Trends/ Population  Threats 

Historically,  Gadwall  were  not  known  to  breed  in  Marin 
County  or  the  San  Francisco  Bay  Area  (G6kW  1927,  S6kP 
1933,  G6kM  1944).  Subsequent  confirmation  of  breeding 
in  these  areas  (Gill  1977,  ABN,  records  above)  may  partly 
reflect  increased  observer  coverage  or  the  dramatic  con- 
tinentwide  post-1 950s  rise  in  breeding  and  wintering  pop- 
ulations (Johnsgard  1978,  Bellrose  1980).  Wintering 
numbers  have  also  increased  on  Point  Reyes  since  the  early 
1970s  (Shuford  et  al.  1989).  Gadwall  numbers  increased 
on  Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


119 


Waterfowl 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Waterfou/l 


COMMON  MERGANSER    Mergus  merganser 


A  year-round  resident;  numbers  swell 

^>-\   v         ^o^^ 

slightly  from  Nov  through  Mar. 

J\^\%^ 

A  rare,  very  local  breeder;  overall  breed- 

A ^K^\.  j^y\  JK     \    3r^^\  ^<i\  xVV •£  -  - 

ing  population  very  small. 

^Vvtv 

o\^\\^\  \r\i\r\  JV^\  JkV>A 

Recorded  in  5  (2.3%)  of  221  blocks. 

OcvVjPrtEV^^^ 

O    Possible                 3  (60%) 

\\  i 

5JvWVa3^ 

€    Probable       =        0  (0%) 

^V\3r\SV^\^V\3cr:>A^^               -' 

•    Confirmed   ■          2    (40%) 

■  i^^vvrv-A^^ 

FSAR=1          OPI  =  5          CI  =  1.80 

^JC<MW»^V() 

Ecological  Requirements 

Along  the  northern  California  coast,  these  "fish-hounds" 
ply  the  cool,  clear  waters  of  rivers,  large  streams,  lakes,  and, 
particularly  toward  the  south,  reservoirs.  Because  visibility 
plays  such  a  large  part  in  the  pursuit  of  their  fish  prey, 
Common  Mergansers  are  generally  absent  from  turbid  or 
weed-choked  waters.  Foraging  birds  work  relatively  shallow 
waters,  varying  from  riverine  rapids  to  quiet  backwaters, 
more  or  less  following  shorelines.  They  feed  mosdy  near 
the  bottom  in  about  6  feet  of  water,  but  their  efforts  may 
take  them  to  40  feet  in  depth  (Palmer  1976b).  Birds  may 
initiate  searches  for  prey  by  swimming  along  widi  their 
heads  submerged.  Mergansers  propel  themselves  under- 
water with  their  feet  only  (stroked  in  unison),  except 
perhaps  in  unusual  circumstances,  and  they  randomly 
search  among,  and  under,  submerged  rocks  or  other 
objects  where  fish  might  hide.  The  diet  of  adults  is  over- 
whelmingly fish,  but  occasionally  they  eat  fish  eggs,  aquatic 
salamanders,  shrimp,  and  mussels  or  other  mollusks  (Pal- 
mer 1976b).  Common  Mergansers  consume  at  least  50 
species  of  North  American  fish,  eating  what  is  locally 
available  roughly  in  proportion  to  their  abundance  and 
vulnerability.  Studies  of  captive  birds  indicate  Mergansers 
first  eat  smaller  fish  if  available.  The  upper  limit  in  size  of 
fish  they  can  eat  probably  ranges  from  5  to  6V2  inches  in 
girth  (Latta  &  Sharkey  1966).  Ducklings  at  first  feed  en- 
tirely on  insects  caught  mosdy  beneath  the  surface  but 
soon  catch  small  fish;  they  will  also  eat  some  green  vegeta- 
tion (Palmer  1976b). 

Common  Mergansers  are  cavity  nesters  and  prefer  hol- 
low trees  when  available;  as  many  as  four  nests  have  been 

120 


found  in  different  cavities  in  the  same  tree  (Palmer  1976b). 
The  height  of  tree  cavities  does  not  appear  to  be  important 
(Palmer  1976b),  but  most  are  at  moderate  heights  and 
range  to  100  feet  or  more  above  the  ground  (Dawson 
1923).  Nest  sites  are  used  repeatedly,  probably  by  the  same 
female  (Palmer  1976b).  When  suitable  tree  cavities  are  in 
short  supply,  Common  Mergansers  will  nest  in  a  variety  of 
well-protected  holes  and  dark  recesses.  Among  the  alter- 
nate sites  reported  are  cavities  on  cliff  faces,  ledges  under 
low  fir  bushes,  among  the  undercut  roots  of  standing  trees, 
in  remote  crevices  among  loose  boulders,  under  dense 
tangles  of  gooseberry  bushes  and  nettles  on  the  tops  of 
islands,  in  old  nests  of  hawks  or  crows,  in  large  nest  boxes, 
and  in  buildings  (Bent  1923,  Dawson  1923,  Palmer 
1976b,  Bellrose  1980).  Common  Mergansers  sometimes 
descend  chimneys  or  otherwise  enter  unoccupied  build- 
ings. Nests  in  human  structures  include  ones  in  between 
loosely  piled  bales  of  hay  in  an  abandoned  ice  house,  in 
depressions  scraped  in  the  dirt  floor  of  an  abandoned 
lighthouse,  and  underneath  the  supports  of  a  covered 
bridge.  In  Sweden,  people  provide  entrance  holes  to  attics, 
and  they  have  noted  up  to  four  nests  in  an  attic.  Some 
authors  have  reported  that,  in  addition  to  a  thick  layer  of 
down,  the  nest  is  also  lined  with  weeds,  grasses,  roodets, 
moss,  or  leaves  (Bent  1923,  Dawson  1923).  However, 
Palmer  (1976b)  claimed  that  no  vegetation  is  added  to  the 
nest.  Perhaps  the  vegetation  reported  in  some  nests  was 
material  already  present  in  the  cavity  before  it  was  occupied 
by  a  Merganser.  The  young  climb  to  the  entrance  of  the 
cavity  and  tumble  to  the  ground  while  the  female  calls  from 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


nearby.  Most  nest  sites  are  situated  near  or  over  water,  but 
females  will  bring  broods  down  small  tributaries  to  main 
waterways  or  will  lead  them  overland  as  much  as  200 
yards;  one  female  and  her  brood  were  found  almost  a  mile 
from  water  (Palmer  1976b).  Once  on  the  water,  part  of  the 
brood  will  sometimes  ride  on  the  mother  s  back.  As  the 
season  progresses,  adults  and  young  tend  to  move  down- 
stream and,  if  available,  to  larger  bodies  of  water,  such  as 
lakes  and  estuaries. 

Marin  Breeding  Distribution 

During  the  atlas  period,  Common  Mergansers  were  con- 
firmed breeding  only  at  Kent  Lake.  A  female  with  a  brood 
was  seen  there  on  27  June  1981,  as  were  two  females  with 
broods  in  the  summer  of  1982  (GFMc).  An  estimated  two 
pairs  have  bred  at  Kent  Lake  in  most  subsequent  years 
through  1988  (JOE).  A  high  count  of  seven  adult  females 
with  10+  chicks  on  7  June  1985  (JGE)  may  have  included 
the  previous  year's  young  as  Mergansers  are  known  to  have 
"gang"  broods,  and  probably  extended  families  and 
delayed  maturation  (M.R.  McLandress  pers.  comm.). 
Sightings  of  four  females  or  immatures  at  Alpine  Lake  on 


1  August  1981  (DS,  ITi),  one  to  three  females  on  Walker 
Creek  about  one  mile  east  of  Hwy.  1  on  1  May  and  1 2  June 
1 982  (DS),  and  one  to  five  birds  on  Papermill  Creek  just 
northwest  of  Tocaloma  on  26  March  and  early  April  1982 
(GMk)  suggest  the  possibility  of  nesting  at  these  sites.  A 
more  recent  nesting  confirmation  came  from  the  discovery 
of  a  two-to-three-week-old  Common  Merganser  (one  eye 
damaged)  near  Bon  Tempe  Lake  on  23  July  1991  QBa  et 
al.  fide  RMS). 

Historical  Trends/  Population  Threats 

Formerly,  Common  Mergansers  were  not  known  to  breed 
in  Marin  County  or  elsewhere  in  the  San  Francisco  Bay 
Area  (GckW  1927,  SckP  1933,  G&M  1944).  Because  of 
their  scarcity  as  breeders  here,  they  may  have  been  over- 
looked. On  the  other  hand,  the  creation  of  large,  forest- 
bordered  reservoirs,  such  as  Kent  and  Alpine  lakes,  may 
have  allowed  wintering  birds  to  pioneer  new  breeding 
habitat.  Numbers  of  Common  Mergansers  increased  on 
Breeding  Bird  Surveys  in  California  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


mrA 


121 


Waterfowl 


MARIN  COUNTY  BRIiMDING  BIRD  ATLAS 


Waterfowl 


RUDDY  DUCK    Oxyura  jamaicensis 


^A\^<\*  3r^vAr^\  3rv  \^\ 

Occurs  year  round,  though  primarily  as  a 
winter  resident  from  mid-Sep  through 
mid-May. 

A  rare,  very  local  breeder;  overall  breed- 
ing population  very  small. 

Recorded  in  20  (9.0%)  of  221  blocks. 

\V^J)^0\a    V«*A    \- 

\^\\^\2A^^ 

O    Possible        =       13  (65%) 

\aX°  A^^-^CV  ^\^K 

©    Probable       =        2   (10%) 

\     ;j&r^\      V--*A^~     \^\      \^Kv~  '  v- 

A^r^r^vB^ 

•    Confirmed  =         5   (25%) 

' 

t^M^y^w 

-'\^-v^>-''\'''  A^^\V^  Jr^*^ — \ 

FSAR=1          OPI  =  20         CI  =  1.60 

J   '>^> 

v^_/                 ^^~'^?V<©'    " 

Ecological  Requirements 

The  rusty  hues  of  male  Ruddy  Ducks  in  breeding  plumage, 
widi  their  brilliant,  sky-blue  bills,  smardy  accent  Marin 
County's  freshwater  marshes  and  marsh-edged  ponds.  For 
breeding,  Ruddies  select  permanent  wedands  in  semiarid 
environments  that  support  rich  concentrations  of  benthic 
invertebrates  for  foraging  and  emergent  vegetation  for  nest 
construction,  support,  and  concealment  (Siegfried  1976a, 
Gray  1 980).  Nesting  habitat  and  food  do  not  appear  to  be 
limiting  factors,  and  breeding  males  do  not  defend  a 
well-defined  territory  or  restrict  themselves  to  discrete  areas 
with  fixed  boundaries.  Instead,  males  are  highly  mobile  in 
search  of  food  and  females  and  defend  an  area  that  extends 
about  ten  feet  around  their  mate,  on  or  off  the  nest.  Males 
tend  to  stay  close  to  their  mates  before  and  during  laying 
but  will  continue  to  court  other  females  and  copulate  with 
them  if  the  opportunity  arises.  During  periods  of  nest 
relief,  paired  females  are  escorted  by  males  to  favorable 
open-water  feeding  areas,  while  unpaired  females  behave 
secredy  and  feed  near  emergent  vegetation  to  avoid  harass- 
ment by  courting  males  (Gray  1980). 

Ruddy  Ducks  procure  their  food  mosdy  by  diving  and 
straining  items  from  the  soft  muddy  ooze  on  the  bottoms 
of  ponds  as  they  move  along  (Siegfried  1973).  They  also 
skim  items  from  the  water's  surface  widi  the  head  and  neck 
stretched  out  and  moving  from  side  to  side,  the  bill  halfway 
immersed,  and  the  tongue  making  rapid  pumping  move- 
ments. Rarely,  they  pick  at  items  on  the  surface.  Ruddy 
Ducks  forage  during  the  day,  but  nonincubating  birds,  at 
least,  also  feed  at  night  (Siegfried  et  al.  1976),  and  perhaps 
females  and  ducklings  do  as  well  (see  Swanson  6k  Sargeant 

122 


1972).  The  year-round  diet  of  Ruddy  Ducks  in  North 
America  is  about  72%  vegetable  and  28%  animal  matter 
(Cottam  in  Palmer  1976b,  n  =  163).  Martin  et  al.  (1951) 
reported  animal  matter  varying  from  a  low  of  21%  of  the 
diet  in  winter  (n  =  60)  to  41%  in  summer  (n  =  25);  but 
others  have  found  almost  complete  dependence  on  animal 
matter  during  breeding  (see  below).  The  vegetable  fare  is 
mosdy  die  seeds,  tubers,  and  leafy  parts  of  pondweeds  and 
sedges,  with  some  wild  celery  and  algae.  Animal  matter 
consists  largely  of  insects  (mainly  midge  larvae;  also  caddis- 
fly  larvae,  water  boatmen,  predaceous  diving  beedes,  and 
nymphs  of  dragonflies  and  damselflies),  along  with  small 
numbers  of  mollusks,  crustaceans  (mosdy  amphipods), 
leeches,  and  miscellaneous  items,  such  as  marine  worms, 
water  mites,  bryozoans,  fish,  sponges,  and  hydroids. 

In  the  breeding  season  in  Manitoba,  animal  matter 
accounts  for  90%  of  the  diet  of  adult  males  (82%  midge 
larvae  and  pupae,  n  =  23),  95%  of  adult  females  (63% 
midges,  22%  mollusks;  n  =  19),  and  88%  of  ducklings 
(73%  midges,  n  =  18)  (Siegfried  1973).  At  Tule  Lake  in 
California,  five  major  invertebrates  represent  94%  (by 
volume)  of  the  diet  of  breeding  adults  (Gray  1980).  Midges 
comprise  79%  of  die  diet  of  males  (n  =  22),  83%  of  females 
(n  =  22),  and  80%  of  ducklings;  snails  are  consumed  only 
by  egg-laying  females  (5%,  n  =  7).  Breeding  females  con- 
sume more  midge  larvae  than  males  at  every  stage  of  the 
breeding  cycle  except  incubation.  At  Tule  Lake,  the  first 
peak,  or  "bloom,"  of  midges  in  open  water  coincides  with 
the  period  of  prereproductive  fattening  of  females.  Most 
clutches  are  initiated  about  two  weeks  after  numbers  of 


Waterfowl 


SPECIES  ACCOUNTS 


Waterfowl 


midge  larvae  reach  a  peak  in  the  nesting  area.  Midge 
densities  decline  in  the  breeding  areas  through  the  incuba- 
tion and  hatching  periods  and  increase  in  open  water. 
Highest  prey  densities  are  in  open  water  immediately 
following  peak  hatching  of  young  and  coincide  with  the 
movement  of  females  with  broods  out  of  the  nesting  area. 
Young  initially  seek  shelter  in  shallow  water  and  emergent 
vegetation  but  usually  within  a  week  move  to  open-water 
areas  of  high  food  availability.  Although  Ruddy  Duck 
broods  generally  do  not  move  overland  to  different  ponds 
(Siegfried  1977)  and  brood  movement  over  water  is  mini- 
mal when  nests  are  located  within  favorable  brood-rearing 
localities  (Joyner  1977a),  in  large  wetlands  broods  may 
move  over  three  miles  from  nesting  areas  to  open  water 
(Gray  1980).  Occasionally,  Ruddy  Ducks  raise  two  broods. 
Females  remain  with  young  only  until  they  are  half  grown; 
males  accompanying  females  with  broods  are  attracted  to 
the  female  rather  than  to  the  young. 

Ruddy  Ducks  preferentially  nest  around  permanent 
marsh  areas  in  the  fringe  of  dense  to  moderately  dense 
emergent  vegetation  of  bulrushes,  cattails,  sedges,  and 
rushes  (Bent  1923,  Low  1941,  Palmer  1976b,  Siegfried 
1976b,  Bellrose  1980).  The  height  of  nests  above  water  or 
distance  of  nests  from  open  water  can,  of  course,  vary 
because  of  seasonal  and  yearly  changes  in  water  levels.  In 
Iowa,  nest  sites  vary  from  1  to  1 33  yards  (av.  32  yds.)  from 
open  water  free  of  emergent  vegetation  (Low  1941).  Nests 
there  also  vary  from  about  l/5  to  3Vi  feet  above  the  mud. 
Average  nest  heights  above  water  in  various  habitats  range 
from  about  1  to  2  feet  (Low  1941,  Siegfried  1976b). 
Ruddies  build  nests  up  from  the  marsh  bottom  to  above 
the  water,  use  broken  and  matted  emergent  vegetation,  or 
attach  the  nests,  floating,  to  surrounding  vegetation.  The 
choice  of  nest  sites  is  governed  to  a  large  extent  by  water 
depth  at  the  time  of  nesting;  therefore,  the  predominant 
species  of  plant  cover  used  varies  from  year  to  year  and 
during  the  course  of  the  nesting  season  (Low  1941,  Sieg- 
fried 1976b).  In  some  studies,  Ruddies  were  found  to  use 
predominantly  green  vegetation  for  nests  (Siegfried 
1976b),  whereas  in  others  they  used  mosdy  dried  residual 
vegetation  from  the  previous  year  (Low  1941,  Joyner 
1977b).  Siegfried  (1976b)  suggested  that  Ruddies  delayed 
breeding  until  there  was  enough  new  plant  growth  to 
satisfy  nesting  requirements,  but  Gray  (1980)  felt  that  food 
availability  played  an  important  role  in  determining  the 
onset  of  breeding. 

The  female  first  constructs  a  flat  platform  of  reeds, 
bulrushes,  cattails,  or  marsh  grasses  on  which  she  lays  her 
outsized  eggs  (largest,  relative  to  body  size,  of  any  water- 
fowl) (Bent  1923,   Low   1941,  Palmer  1976b,  Siegfried 


1976b,  Bellrose  1980).  When  the  clutch  is  complete,  she 
adds  a  rim,  forming  a  bowl-shaped  nest,  and  begins  incu- 
bating. She  may  or  may  not  add  a  sparse  lining  of  finer  bits 
of  marsh  plants  or  down.  Fresh  materials  are  constandy 
being  added  to  the  nests  to  compensate  for  a  gradual 
setding  caused  by  the  decomposition  of  the  underparts  of 
the  nests  (Low  1941).  Varying  numbers  of  nests  are 
equipped  with  overhead  canopies  of  bent  vegetation  for 
concealment  and  ramps  or  runways  of  matted  vegetation 
for  entering  or  leaving  the  nest  (Bent  1923,  Low  1941). 
Alternate  nest  sites  include  abandoned  nests  of  Coots  and 
Redheads,  muskrat  houses  or  feeding  platforms,  and  the 
hollow  side  of  a  floating  log  (Bent  1923). 

Ruddy  Ducks  are  also  noted  for  their  habit  of  sometimes 
parasitically  laying  eggs  in  nests  of  other  Ruddies  and  other 
marsh-nesting  species  (such  as  other  ducks,  grebes,  Amer- 
ican Bitterns,  American  Coots,  and  Common  Moorhens) 
or  dropping  them  on  the  ground  (Bent  1923;  Low  1941; 
Joyner  1973a,b;  Palmer  1976b;  Siegfried  1976b).  Ruddy 
Ducks  may  respond  to  loss  of  nesting  habitat  and  to 
drastically  fluctuating  water  levels  (high  or  low)  by  aban- 
doning nest  sites;  building  up  the  bases  of  their  nests  to 
compensate  for  rising  water  levels;  increasing  rates  of  inter- 
and  intraspecific  nest  parasitism;  and  producing  platform 
nests  (flattened  emergent  vegetation)  into  which  they 
deposit  "unwanted"  eggs  (Joyner  1977b). 

Marin  Breeding  Distribution 

During  the  adas  years,  Ruddy  Ducks  bred  at  scattered  sites 
throughout  Marin  County.  Numbers  of  breeding  birds 
here  are  not  as  large  as  they  might  at  first  seem  because  fair 
numbers  of  birds  oversummer  on  both  salt  and  fresh  water 
(Shuford  et  al.  1989).  Representative  breeding  locations 
included  die  pond  at  Drakes' s  Beach  visitor's  center,  PRNS 
(FL  7/10/82  — JGE);  fish-breeding  ponds  near  the  Cheese 
Factory,  Hicks  Valley  (FL  6/1 5-7/14/82  -ScC,  DS);  and 
Bahia  Drive  ponds  near  the  Petaluma  River  mouth, 
Novate  (FL  6/28/80  -DS). 

Historical  Trends/  Population  Threats 

Grinnell  and  Miller  (1944)  reported  a  decline  in  the 
California  population  caused  by  loss  of  breeding  habitat. 
Numbers  were  relatively  stable  on  Breeding  Bird  Surveys 
in  California  from  1968  to  1989  (USFWS  unpubl.  analy- 
ses). Tule  Lake  was  an  important  area  of  Ruddy  Duck 
production  in  the  1970s,  but  now  few  broods  survive 
(M.R  McLandress  pers.  comm.).  This  loss  of  production 
may  be  die  result  of  large  numbers  of  predators  (raccoons) 
or  perhaps  the  effect  of  pesticides  from  agricultural  runoff. 


123 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


**•/• 


Does  innate  courage  or  naivete  propel  downy  Wood  Ducks,  fluttering,  jrom  their  lofty  nest  holes! 

Drawing  b}  Keith  Hansen,  I  989. 


124 


blew  World  Vultures 


SPECIES  ACCOUNTS 


New  World  Vultures 


New  World  Vultures 


Family  Cathartidae 


TURKEY  VULTURE   Cathartes  aura 


A  year-round  resident. 

HtoiHoV^                   k                          ~^ 
^\°X^\o\>r\ °3rV\o \>A °  V>\o >^o\>JCoO(  ~ 

A  fairly  common,  nearly  ubiquitous 

breeder;  overall  breeding  population 
large. 

JV^\  OjV<\  °3r<\  °A^\  °;A^\ O  V-^A  •  jAiC  O  \J>A 

Recorded  in  213  (96.4%)  of  221 

\^y\  \Jk\^\  °J<^\  °  >-^\o  V^\  o  \>z\Q-  YP<~«  \^\ 

\  NCk^^oX  °Jt<r\  °  Jv^C\0  \-^A  jo  p<A(m^r  o  \>rC  O  J 

blocks. 

\   >r5A    V<C\  °  3A\  °  Jr-'X      \^\  oT^C  O  V^AO'-V^V 

^^°><^0>^9'iV:>\ o V-Ajo V>A«  V-"ao Vi-A  o  \ 

V55^>#7v\'-8>Tn\  °A<\  °Jv^°A<CC  °A^\  °  ><a 

\AJ^H^A^\03c^\0>Ki\o  \^\  o  V-"\  o  \AvTo  \ 
Vvo  3?<1T\P  V'x  o  \^i?^v\-^\  o  v>-a  O  V>JCQA^--^r7>r^>^ 

O    Possible        =     204   (96%) 

\  iV^TX  ®si  t\\  °  V — \  °  i&>5j&  i/A-'J-i^T^j^  o  v>^^ 

\  VJk^X  &^?A^Ki:A"0'J^\  o  V-"\ •  >-<\  o  V^C  o  V-7 

C    Probable       =         1    (0.5%) 

\  ^\<A  °3r<\  cOe^X  90P^o\^'o\^^fijC^^J\ 

-  -r* 

•    Confirmed  =         8   (3.5%) 

To.oP'ao  >-^vO  X>Ko  y^VSA^V o  V>A«  \>^v  P  J7 

l-^skQfV^\  o,'V>a  o  £<-A  o  \>d^n  V>\o  UAoXK 

i:\J^YMJ^\0A^\0A<\o,3^r\  o  i^rtv  o\^\  <sjrr\ 

r*  ? 

FSAR=3        OPI  =  639       CI  =  1.08 

^7                 ^^c^^^c^c^ 

^& 

Ecological  Requirements 

The  "tippy-glider,"  wings  held  in  a  slight  V,  soars  gracefully 
over  virtually  all  of  Marin's  landscape,  circling  and  teeter- 
ing gendy  in  response  to  the  vagaries  of  the  air  currents. 
Once  aloft,  it  flaps  leisurely  but  infrequendy  as  it  exploits 
the  earth's  envelope  in  its  far-ranging  searches  for  animals 
that  have  met  their  fate.  TVs  are  usually  seen  in  the  air 
singly  or  in  small  groups  except  when  congregating  at  or 
leaving  roosts  or  during  migration.  In  Marin  County,  they 
feed  in  virtually  any  habitat  where  they  are  able  to  reach  the 
ground  easily.  Although  TVs,  unlike  other  North  Ameri- 
can vultures,  forage  efficiendy  beneath  the  forest  canopy 
(Houston  1986,  Jackson  1988),  apparendy  they  descend  to 
the  forest  floor  in  Marin  County  only  at  nest  sites.  They 
feed  here  most  often  in  open  agricultural  country  that 
affords  an  abundance  of  grazing  animals  and  easy  sighting 
of  dead  "prey"  from  the  air.  They  also  feed  frequendy  along 
open  road  corridors  on  animals  cut  down  by  fast-moving 
vehicles  and  along  estuarine  shores  and  beaches  on  car- 
casses of  wave-cast  birds  and  marine  mammals. 

Turkey  Vultures  are  primarily  solitary  breeders, 
although  nesting  birds  sometimes  cluster  near  concen- 
trated food  sources  (Jackson  1988).  They  choose  secluded 
nest  sites  consisting  of  little  more  than  a  cleared,  trampled 


area  within  a  relatively  dark  recess.  Although  nest  sites  are 
usually  at  ground  level,  some  are  high  in  tree  cavities,  in 
caves,  under  rocks  on  ledges  of  cliffs,  in  old  tree  nests  of 
other  raptors  or  herons,  or  in  upper  rooms  of  buildings 
(Tyler  1937;  Jackson  1983,  1988).  Prominent  forest  breed- 
ing habitats  are  bottomland  hardwoods  and  thickets. 
When  available,  cliffs  are  also  favored,  primarily  because 
of  cave  nesting  sites  and  perhaps  because  updrafts  make 
departures  from  the  nest  site  easy.  Ground  nests  may  be  in 
podroles,  in  crevices  among  rocks,  under  or  beside  logs, 
inside  hollow  logs,  at  the  base  of  hollowedout  trees,  and 
in  thickets,  tangles  of  vines,  brush  heaps,  and  clumps  of 
chaparral  with  narrow  entrance  ways.  Sometimes  nest  sites 
are  below  ground  in  caves  or  in  hollows  of  rotten  stumps. 
There  appear  to  be  no  records  of  Turkey  Vultures  nesting 
in  old  tree  nests  of  odrer  species  or  in  buildings  in 
California  (P.H.  Bloom  pers.  comm.).  In  the  West,  about 
77%  of  nests  are  in  caves  and  10%  on  cliff  ledges  or  among 
rocks  (Jackson  1983,  1988;  n  =  324).  In  die  East,  nest  sites 
are  more  varied,  with  about  34%  in  hollow  trees,  stumps, 
or  logs;  28%  in  drickets;  1 3%  in  caves;  8%  on  cliff  ledges 
or  among  rocks;  and  5%  in  buildings  (n  =  418).  The 
choice  probably  reflects  site  availability  rather  than  regional 

125 


hleui  World  Vultures 


MARIN  COUNTY  BREEDING  BIRD  ATlJ\S 


New  World  Vultures 


preference.  In  many  heavily  forested  regions  of  the  West, 
nest  sites  probably  are  more  like  those  in  the  East,  and 
Marin  County  is  no  exception  (see  records  below).  Turkey 
Vultures  lay  their  eggs  on  the  ground,  on  bare  stone,  in 
rotten  wood  chips,  or  sometimes  in  other  debris.  Although 
they  usually  make  little  or  no  effort  to  prepare  the  nest  site, 
one  bird  using  a  tree  cavity  pulled  off  dry  rotten  wood  from 
the  walls  of  the  cavity  with  its  beak,  tore  it  into  bits,  and 
spread  it  on  the  floor  (Tyler  1937).  TVs  often  use  nest  sites 
again  in  successive  years  or  at  intervals  (Jackson  1988). 
Since  1920  there  have  been  fewer  nests  found  in  the  East 
in  tree  cavities  and  more  in  thickets,  apparendy  because  of 
changing  forest  management  practices  and  the  prolifera- 
tion of  exotic  vines.  For  obvious  reasons,  nest  sites  in 
buildings  must  have  also  increased  historically. 

Roosting  is  a  ritual  aspect  of  Turkey  Vulture  existence. 
In  spring  and  summer,  some  birds  roost  singly;  others 
roost  in  aggregations  year  round  (Jackson  1988).  Roosting 
congregations  are  generally  near  stable  food  resources  and 
often  near  or  over  water.  Turkey  Vultures  often  remain  at 
roosts  well  past  sunrise,  perhaps  for  thermoregulatory 
reasons  as  well  as  to  await  favorable  winds  or  updrafts  for 
flight.  Departure  time  from  roosts  is  correlated  with  ambi- 
ent wind  speeds,  but  not  with  temperature  or  cloud  cover. 
TVs  can  lower  their  body  temperatures  markedly  at  night, 
thus  reducing  energy  expenditures  (however,  see  Hatch 
1970).  At  or  near  the  roost,  perching  birds  are  statuesque 
with  wings  outspread,  feathers  raised,  and  backs  to  the 
sun.  This  behavior  may  facilitate  a  return  to  normal  diur- 
nal body  temperature.  In  inclement  weather,  they  may 
remain  at  roosts  for  as  long  as  two  days,  foregoing  meals 
until  suitable  flying  conditions  return. 

Communal  roosting  appears  to  be  an  adaptation  for 
increasing  the  efficiency  of  individuals  foraging  on  a  dis- 
persed, unpredictable  food  supply  (Rabenold  1983).  The 
scavenging  lifestyle  is  one  of  extended  search  and  patience, 
since  these  weak-clawed,  weak-billed  raptors  cannot  select 
their  victims.  Birds  forage  widely  and  do  not  patrol  a  fixed 
breeding  range  (Houston  1986).  Most  feeding  is  done 
from  midmorning  to  midday.  Rabenold  (1983)  speculated 
that  birds  circle  to  higher  altitudes  later  in  the  day  to  search 
for  die  next  meal,  to  which  they  return  the  following  day. 
The  degree  to  which  sight  and  smell  guide  Turkey  Vultures 
in  finding  their  meals  has  long  been  the  subject  of  much 
debate.  Unlike  most  birds,  Turkey  Vultures  have  a  well- 
developed  olfactory  sense.  In  tropical  forests,  Turkey  Vul- 
tures mosdy  use  smell  to  locate  carrion.  Vision  plays  a 
minor  role,  for  they  find  completely  hidden  food  as  quickly 
as  visible  bait  (Houston  1986).  Birds  cannot  detect  fresh 
carcasses,  probably  because  they  do  not  yet  give  off  a  strong 
odor,  but  do  prefer  comparatively  fresh  meat  if  given  a 
choice.  Nevertheless,  vision  plays  an  important  role  (Jack- 
son 1988)  and  seems  to  be  of  great  aid  in  very  open 
country.  Turkey  Vultures  also  watch  each  other  and  odier 

126 


scavengers,  such  as  ravens  and  crows,  that  have  located 
food.  They  may  sight  scavengers  on  the  ground  or  other 
vulnires  circling  over  carcasses  in  a  distinct  "verification 
pattern"  (Rabenold  1983).  Having  located  a  seemingly 
dead  animal,  the  Turkey  Vulture  approaches  it  cautiously 
with  a  gawky  gait  to  see  if  it  has  breadied  its  last.  Smaller, 
thin-skinned  carcasses  are  torn  open  immediately.  Vul- 
tures usually  'attack"  carcasses  through  available  orifices- 
eyes,  mouth,  and  anus  (Rabenold  1983).  For  larger, 
thicker-skinned  carcasses,  the  Vultures  gather  in  numbers 
and  wait  patiendy  until  other  scavengers  make  the  first 
incisions  or  until  time  and  decay  make  the  carcasses  soft 
and  ripe.  If  large  animals  are  set  upon  immediately,  they 
usually  cannot  be  finished  while  fresh,  but  purification 
works  fast  and  the  naked  cathartid  head  is  well  adapted  for 
avoiding  disease  while  plunging  into  a  body  in  an 
advanced  state  of  decomposition. 

Turkey  Vultures  are  primarily  carrion  feeders,  and  the 
diet  reflects  what  is  available.  The  main  items  are  mam- 
mals, birds,  turtles,  snakes,  and  fish.  Occasionally  Turkey 
Vultures  eat  insects,  such  as  grasshoppers  and  mormon 
crickets;  dead  tadpoles  in  drying  ponds;  cow  dung  (per- 
haps deriving  benefit  from  the  beedes  it  contains);  and 
seal,  sea  lion,  or  human  excrement  (Tyler  1937,  Jackson 
1988).  Turkey  Vultures  will  also  occasionally  take  live  prey, 
usually  vulnerable  young  or  incapacitated  adults.  They 
have  killed  newborn  pigs,  young  and  weakened  chickens, 
tethered  or  otherwise  entrapped  birds,  and  the  young  of 
colonial  waders.  In  addition,  they  sometimes  batter  nest- 
ling Great  Blue  Herons,  forcing  them  to  disgorge;  wade 
into  water  to  stab  live  fish;  and  peck  out  the  eyes  of  cows 
or  horses  mired  in  bogs.  When  hard  pressed,  Turkey 
Vultures  will  eat  vegetable  matter,  such  as  pumpkins  and 
palm  nuts.  Paterson  (1984)  found  plant  material  in  about 
25%  of  all  pellets  collected  in  Virginia  in  autumn.  Vegeta- 
tion comprised  as  much  as  70%  of  one  pellet,  suggesting 
it  was  consumed  direcdy,  not  inadvertendy.  TVs  will  also 
eat  salt  from  blocks  left  in  pastures  for  cattle. 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Turkey  Vulture  was  perhaps 
the  most  wide  ranging  of  Marin's  breeding  birds,  seen 
soaring  over  virtually  every  square  inch  of  the  county.  But 
because  of  the  difficulty  of  finding  nests,  the  adas  map  of 
this  species  is  one  of  the  least  satisfying  in  terms  of 
documenting  the  details  of  breeding  distribution.  Because 
of  the  limited  numbers  of  stable  cliffs  or  caves  in  Marin 
County,  most  Turkey  Vultures  seem  to  nest  here  in  for- 
ested areas.  Representative  nesting  locations  were  inside  a 
burned  out  hollow  at  the  base  of  a  redwood  (shielded  by 
small  branches  and  debris)  on  the  ridge  north  of  San 
Geronimo  (NY  5/29-7/11/82  -DS);  under  a  rock  over- 
hang among  boulders  in  chaparral  off  the  Yolanda  Trail, 
Mt.  Tamalpais  (NE-NY  4/.?-6/5/82  — ITi);  inside  the  hoi- 


New  World  Vultures 


SPECIES  ACCOUNTS 


New  World  Vultures 


lowed-out  trunk  of  a  living  oak  near  Stafford  Lake,  Novato 
(NE  5/6/79  — KH);  in  a  burned-out  redwood  stump  in  a 
canyon  of  Big  Rock  Ridge  above  Stafford  Lake  (NY  5/?/82 
— ScC);  and  in  a  crack  in  serpentine  rock  under  oaks  on 
ML  Burdell,  Novato  (NE  5/?/79  -ScC).  Prior  to  the  adas 
period,  a  nest  was  found  under  a  horizontal  log  in  a  logged 
bishop  pine  forest  on  Inverness  Ridge  (NE  5/7-11/73 
-RH). 

Historical  Trends/ Population  Threats 

Although  not  well  quantified,  some  population  trends  are 
evident.  Overall,  Turkey  Vultures  seem  to  have  been  wide- 
spread and  numerous  in  North  America  in  the  1800s 
(Wilbur  1983,  Jackson  1988).  Subsequendy,  they  declined 
in  numbers  with  the  depletion  of  populations  of  bison  and 
other  large  herbivores.  They  later  increased  with  the  avail- 
ability of  road-killed  animals  along  our  expanding  highway 
system  but  decreased  again  as  forest  breeding  sites  were 
cleared,  organochloride  pesticide  contamination  increased, 
and  environmental  laws  required  burial  of  animal  wastes. 
Grinnell  and  Miller  (1944)  reported  that  Turkey  Vul- 
tures were  "thought  to  be  less  numerous  now  than  for- 
merly" in  California.  Based  on  Christmas  Bird  Count 
(CBC)  data  from  1950  to  1973,  Brown  (1976)  detected  a 
decline  in  wintering  populations  of  Turkey  Vultures  in  the 
United  States.  California  was  the  only  state  to  show  an 
apparent  increase,  but  this  was  because  of  a  large  popula- 
tion on  CBCs  (Drake's  Bay  and  Pt.  Reyes)  reported  only  in 
later  years.  Garrett  and  Dunn  (1981)  suggested  that  Turkey 
Vultures  have  declined  as  breeders  in  coastal  southern 
California.  Turkey  Vultures  were  on  the  Audubon  Society 


Blue  List  for  1972  and  1980,  with  concern  in  southern 
California  (Tate  1981).  They  were  also  on  their  list  of 
Special  Concern  in  1982  (Tate  &.  Tate  1982),  and  on  their 
list  of  Local  Concern  in  1986  (Tate  1986).  Numbers  of 
Turkey  Vultures  on  Breeding  Bird  Surveys  in  California 
were  relatively  stable  from  1968  to  1989  (USFWS  unpubl. 
analyses). 

Turkey  Vulture  eggshells  were  11%  thinner  in  Califor- 
nia in  the  pesticide  era  (post-1947)  than  previously,  but  this 
degree  of  thinning  is  not  of  the  magnitude  generally  asso- 
ciated with  major  declines  of  productivity  in  other  species 
(Wilbur  1978).  Other  potential  contaminants  that  might 
affect  Vultures  are  systemic  organophosphate  pesticides 
applied  topically  to  livestock  and  ingested  from  carcasses, 
and  perhaps  heavy  metals  (Pattee  ck  Wilbur  1 989).  Turkey 
Vultures  face  additional  threats  today.  Urbanization  may 
limit  food  supplies  and  nest  sites.  Although  road  kills 
provide  supplemental  food,  the  Vultures  themselves  also 
fall  victim  to  speeding  vehicles.  Recent  changes  in  grazing 
practices  and  husbandry  techniques  have  meant  that  fewer 
animal  carcasses  are  left  on  the  range  to  be  eaten  by 
Vultures  (Wilbur  1983).  Tree  cavity  sites,  in  which  birds 
have  high  nesting  success,  may  now  be  limited  by  forest 
management  practices  (Jackson  1983).  Trees  large  enough 
to  harbor  suitable  cavities  are  generally  about  150  to  200 
years  old  and  are  increasingly  rare  today.  Also  these  trees 
must  be  injured  before  fungus  invades  to  rot  out  cavities, 
and  fire  suppression  makes  this  less  likely.  Although  Tur- 
key Vultures  do  not  lead  a  charming  lifestyle,  these  gende 
creatures  deserve  our  admiration  and  protection. 


127 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


ft  mm 

mm 


e  V        Ik  W^ 

'3     \\.  f% 


*K  \ 


Although  the  Turkey  Vulture  is  one  of  Marin  County's  most  widespread  and  conspicuous  birds,  who  among  us  has  been  honored 
with  even  a  glimpse  of  the  intimacies  of  its  home  life?  Drawing  b}  Keith  Hansen,  1989. 


128 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


Hawks  and  Eagles 

Family  Accipitridae 


OSPREY    Pandion  haliaetus 


Uto^ 

Occurs  year  round,  though  primarily  as  a 
summer  resident  from  Feb  through  Sep. 

J^\\\J^< 

An  uncommon,  local  breeder;  overall 

"mA^cT  jL- 

breeding  population  very  small  (numbers 
increasing). 
Recorded  in  49  (22.2%)  of  221  blocks. 

\\{ 

O^v^pv^x 

V"\  JV^\*3r^\  -V' 

3^a2-V^_ 

O    Possible        =      41    (84%) 

i^V^^JtA 

©    Probable       =        0  (0%) 

■^J^vVv^ 

"Y>V^>^C 

. .  -r- 

•    Confirmed  =         8   (16%) 

^^^V^^v- 

<^SX^_j 

^vJV^X^Ar^ 

r^?o 

FSAR  =  2         OPI  =  98        CI  =  1.33 

xi^* 

^\j?7 

Ecological  Requirements 

This  cosmopolitan  raptor  haunts  the  fish-producing  waters 
of  bays,  estuaries,  reservoirs,  and  large  streams  or  rivers. 
Marin  County's  breeding  birds  are  concentrated  within  a 
few  miles  of  the  coast,  where  they  forage  primarily  in 
estuaries,  in  the  ocean  near  the  surf,  and  in  reservoirs. 
Overall,  the  coastal  California  breeding  population  is  con- 
centrated along  rivers,  streams,  and  bays.  Marin  County's 
Kent  Lake  is  the  only  coastal  reservoir  currendy  used  for 
nesting.  In  the  interior  of  the  state,  72%  of  the  birds  nest 
by  lakes  and  reservoirs  and  28%  on  rivers  (Henny  et  al. 
1978). 

Ospreys  nest  solitarily  or  semicolonially.  Most  nests  in 
Marin  County  are  over,  or  within  a  half  mile  of,  water  and 
are  situated  about  40  to  1 20  feet  up  in  Douglas  fir,  coast 
redwood,  or  bishop  pine.  Tree  characteristics,  elevation, 
slope,  distance  from  water,  and  isolation  from  predators 
are  likely  the  main  factors  influencing  the  choice  of  nest 
sites.  From  1981  to  1990,  53  nest  sites  at  Kent  Lake  were 
almost  evenly  split  between  Douglas  fir  (53%)  and  coast 
redwood  (47%)  and  between  dead  (51%)  and  live  (49%) 
trees;  10  of  the  26  live  trees  had  dead  crowns  (Evens  1991 , 
in  press).  Of  25  sites  in  use  from  1981  to  1984,  76%  were 
in  Douglas  firs  and  24%  were  in  redwoods;  of  28  sites 


established  since  1984,  32%  were  in  Douglas  firs  and  68% 
were  in  redwoods.  The  reason  for  this  shift  in  tree  species 
use  is  unclear  (Evens  1991 ,  in  press),  but  it  may  reflect  the 
changing  availability  of  suitable  nest  sites  as  prime  sites 
become  occupied.  In  this  regard,  it  should  be  noted  that 
the  period  of  increasing  use  of  redwoods  as  nest  sites 
coincided  with  the  most  rapid  growth  of  the  Kent  Lake 
Osprey  population  (Evens  1 991 ,  in  press;  Table  1 8).  Of  1 8 
nest  sites  in  1990  in  the  Tomales  Bay  area  (from  Five 
Brooks  north  to  Mt.  Vision),  10  were  in  bishop  pines  (7 
dead,  3  live),  5  in  Douglas  firs  (all  dead),  and  3  on  artificial 
structures.  The  greater  use  of  bishop  pine  reflects  the 
dominance  of  this  pine  along  almost  all  of  Inverness  Ridge 
adjacent  to  Tomales  Bay,  except  at  the  south  end  of  the 
bay,  where  it  is  replaced  by  Douglas  fir. 

Ospreys  may  prefer  dead  trees  with  a  minimum  of 
lateral  branches  because  such  trees  deter  climbing  preda- 
tors (Evens  1985).  Nest  sites  at  Kent  Lake  range  from  over 
water  to  about  0.56  miles  (av.  209  yds.)  from  shore  (Evens 
1987,  n  =  42).  One  Marin  nest  in  the  early  1960s  was  on 
a  rocky  coastal  bluff.  0(  the  three  nests  constructed  on 
artificial  structures  at  Tomales  Bay  in  recent  years,  two 
were  on  duck  blinds  and  one  was  on  an  active  power  pole. 

129 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 

Table  18.  Numbers  of  nests  and  productivity  of  Ospreys  in  Marin  County,  California,  at  Kent  Lake  from  1981  to  1990  and 
at  Tomales  Bay  in  1 989  and  1 990  (Evens  1 991 ,  in  press).  Numbers  for  Kent  Lake  in  parentheses  represent  adjustments  (using 
the  ratio  of  productive  to  occupied  nests  of  1:1.4  in  subsequent  years)  for  1982  data  to  account  for  underestimation  of 
occupied  nests  because  of  late  season  nest  counts  in  that  year. 


KENT  LAKE 


YEAR 

Occupied 
Nests 

Active 
Nests 

Productive 
Nests 

Total 
Young 

Number  of  Fledglings  per/ 

Occupied 

Active 

Productive 

1981 

15 

11 

11 

23 

1.53 

2.09 

2.09 

1982 

16(20) 

15 

14 

20 

1.25(1.0) 

1.33 

1.43 

1983 

20 

14 

13 

24 

1.20 

1.71 

1.85 

1984 

18 

14 

11 

19 

1.06 

1.36 

1.73 

1985 

22 

20 

19 

37 

1.68 

1.85 

1.95 

1986 

24 

22 

19 

37 

1.54 

1.68 

1.95 

1987 

31 

27 

23 

41 

1.32 

1.52 

1.78 

1988 

30 

26 

23 

36 

1.20 

1.38 

1.56 

1989 

32 

28 

26 

48 

1.50 

1.71 

1.85 

1990 

35 

25 

22 

31 

0.89 

1.24 

1.41 

Me 


1.32(1.29) 


1.59 


1.76 


TOMALES  BAY 


YEAR 

Occupied 
Nests 

Active 
Nests 

Productive 
Nests 

Total 
Young 

Number  of  Fledglings  per/ 

Occupied 

Active 

Productive 

1989 

14 

12 

9 

13 

0.93 

1.08 

1.44 

1990 

15 

11 

8 

11 

0.73 

1.00 

1.38 

Me 


0.83 


1.04 


1.41 


Occupied  nest  =  a  large  apparendy  complete  nest  attended  by  one  or  two  Ospreys  during  the  breeding  season. 

Active  nest  =  an  occupied  nest  with  an  incubating  adult. 

Productive  nest  =  an  occupied  nest  from  which  at  least  one  young  fledged. 


130 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


In  1989,  the  latter  nest  was  carefully  moved  during  the 
incubation  period  to  a  platform  specifically  constructed 
about  1 50  feet  away,  but  the  occupants  abandoned  it  Q.G. 
Evens  pers.  comm.).  In  coastal  California  as  a  whole, 
Ospreys  nest  almost  exclusively  in  trees,  whereas  in  the 
interior  of  the  state  about  79%  use  trees  and  21%  use 
artificial  structures  (Henny  et  al.  1978).  Tree  nests  are 
located  at  the  top,  exposed  to  the  sky  (Henny  1988). 
Elsewhere,  Ospreys  nest  in  a  wide  variety  of  sites  in  varying 
proportions,  occasionally  as  much  as  two  to  three  miles 
from  water.  Nest  height  is  not  as  important  as  inaccessibil- 
ity from  mammalian  predators  and  seclusion  from  distur- 
bance. Nests  over  water  are  generally  at  lower  heights  than 
those  over  land,  and  ground  nests,  which  tend  to  be  on  or 
near  a  prominent  object,  are  prevalent  on  small  islands. 
All  nests  have  relatively  unobstructed  views  of  the  sur- 
roundings and  at  least  one  perch  nearby.  Other  nest  sites 
include  power  towers,  unused  chimneys  or  windmills, 
sheds  or  buildings,  channel  markers,  pilings,  road  signs, 
boats  (sunk  or  aground),  piles  of  fence  rails,  fences  or 
walls,  old  stumps,  cacti,  tops  of  rock  pinnacles,  rocks  or 
boulders  (on  land  or  in  water),  piles  of  seaweed,  driftwood, 
or  other  debris  on  beaches,  and  even  the  crossed  poles  of 
a  tepee  and  a  1000-pound  bomb  (Bent  1937,  Henny 
1988)!  Ospreys  readily  adapt  to  nest  sites  provided  for 
them  and  often  have  greater  nesting  success  on  nest  plat- 
forms than  at  natural  sites  (Henny  1988). 

Ospreys  construct  large,  bulky  nests  primarily  of  sticks, 
but  they  also  may  use  sod,  seaweed,  cornstalks,  bird  wings 
or  corpses,  bones,  cow  dung,  and  a  wide  variety  of  odier 
natural  and  human  debris.  They  line  the  nest  widi  materi- 
als such  as  moss,  lichen,  eelgrass,  grass,  bark,  and  even 
mud.  Nests  can  be  very  large  because  sticks  are  added 
throughout  the  breeding  season,  and  old  nests  are  refur- 
bished and  added  to  year  after  year.  In  some  cases,  nests 
have  been  continuously  occupied  for  45  years  or  more 
(Bent  1937).  Pairs  will  sometimes  have  several  alternative 
nests  built  within  the  territory  over  a  period  of  years,  one 
of  which  is  active  at  a  time  (Henny  1988).  Some  birds 
(presumably  subadults)  build  nests  but  do  not  lay  eggs,  and 
adults  often  build  "frustration  nests,"  generally  not  laying 
in  them,  after  failing  to  rear  young  in  their  original  nests. 

The  Osprey's  mode  of  foraging  combines  plunging  and 
grasping  with  its  feet,  the  undersides  of  which  are  covered 
with  pointed,  prickly  scales,  or  spicules,  for  retaining  a 
grasp  on  slippery  fish  (Henny  1988).  Ospreys  generally 
cruise  at  a  height  of  50  to  100  feet  and  look  into  the  water 
at  an  angle  of  45°  or  less.  When  Ospreys  see  fish,  they 
maneuver  into  position  above,  often  hovering,  waiting 
until  the  fish  are  close  to  the  surface.  From  a  long  glide  or 
brief  hover,  they  plunge  feet  first,  strike  the  water  at  about 
20  to  45  mph,  and  penetrate  to  a  maximum  depth  of  about 
three  feet.  Just  before  the  Osprey  enters  the  water,  the  feet 
are  swung  forward  beyond  the  head  and  the  wings  are 


extended  upward  and  back  so  that  their  tips  extend  past 
the  tail.  After  capture,  powerful  forward  and  downward 
strokes  of  the  wings  raise  the  bird  to  the  surface  and  clear 
of  the  water.  Ospreys  sometimes  fly  down  at  an  oblique 
angle  and  catch  fish  while  skimming  along  the  water's 
surface  (J.G.  Evens  pers.  comm.).  In  flight,  Ospreys  adjust 
the  fish  so  that  its  head  points  forward,  and  they  often 
must  fend  off  piratical  forays  from  gulls.  Ospreys  take  fish 
up  to  about  two  pounds,  and,  exceptionally,  they  will 
capture  two  fish,  one  in  each  foot,  on  the  same  dive! 

The  Osprey  diet  is  almost  exclusively  live  fish,  but 
occasionally  dead  ones  are  taken.  A  wide  variety  of  fresh- 
water and  saltwater  species  are  secured,  but  benthic-feeding 
fish  of  shallow  waters  are  easier  to  capture,  suggesting  that 
they  are  selected  over  piscivorous  fish  when  equally  avail- 
able (Swenson  1979).  Larger  fish  are  brought  back  to  the 
nest  later  in  the  nesting  cycle,  not  because  the  larger 
females  first  begin  to  forage  for  young  then,  but  because 
fish  have  grown  in  size  as  the  season  progresses  (DeSante 
6k  Scriven  1977).  The  increase  in  fish  size  is  advantageous 
to  adults  then  feeding  the  older,  more  demanding  Osprey 
young.  In  Marin  County,  the  few  prey  remains  found 
under  Osprey  nests  at  Kent  Lake  were  freshwater  carp 
(W.C.  Follet  fide  GFMc,  Evens  1985),  but  in  fact,  Kent 
Lake  breeders  appear  to  feed  much  more  extensively  on 
saltwater  species  at  Bolinas  Lagoon  and  on  the  outer  coast 
(Evens  1985,  1991,  in  press).  Inverness  Ridge  breeders 
also  appear  to  feed  primarily  in  salt  water.  Ospreys  also 
occasionally  prey  on  small  rodents  or  rabbits,  small  to 
medium-sized  birds,  snakes,  frogs,  turtles,  and  inverte- 
brates (Bent  1937,  Tait  et  al.  1972,  Wiley  6k  Lohrer  1973, 
Henny  1988).  Presumably  such  prey  are  taken  when  fish 
are  scarce;  when  foraging  is  hampered  by  inclement 
weather  or  murky  water;  when  young  Osprey  lack  fishing 
skill;  or  when  crippled,  captive,  or  concentrated  alternative 
prey  are  too  attractive  to  pass  up. 

Historical  Trends/ Population  Threats/Marin 
Breeding  Distribution 

Osprey  populations  have  declined  seriously  in  historic 
times.  In  California,  Grinnell  and  Miller  (1944)  reported 
that  the  species  was  "originally  common  and  widespread," 
but  by  1944  was  "much  reduced  in  number."  Continent- 
wide,  but  most  severely  in  the  East,  a  drastic  population 
reduction  began  to  be  noticed  in  the  1960s  (Ames  6k 
Mersereau  1964).  This  decline  was  attributed  largely  to 
eggshell  thinning  from  the  accumulation  of  pesticide  resi- 
dues, exacerbated  by  encroachment  of  humans  on  nesting 
sites  and  by  shooting  (Henny  1977,  Ogden  1977).  In 
California,  the  Channel  Island  population  disappeared 
from  1917  to  1968,  while  concurrently  the  population  on 
die  central  and  soudiern  mainland  declined  virtually  to 
extinction  (Diamond  1969).  The  southern  California 
population  disappeared  long  before  the  pesticide  era,  and 


131 


Hawks  and  Eagles 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hawks  and  Eagles 


this  decline  may  be  attributable  to  removal  of  nesting  trees, 
degradation  of  lake  and  river  quality,  boating  on  nesting 
lakes,  and  shooting  (Remsen  1978).  With  the  banning  of 
DDT,  dieldrin,  and  other  pesticides,  Ospreys  have  begun  a 
comeback,  though  the  southern  California  population  still 
remains  close  to  extirpation  (I  lenny  et  al.  1978,  Garrett  ck 
Dunn  1981,  Henny  &.  Anthony  1989).  Pesticide  contami- 
nation and  eggshell  diinning  were  still  occurring  in  Cali- 
fornia from  1973  to  1984,  but  apparendy  were  not  major 
mortality  factors  at  that  time  (Littrell  1 986).  Ospreys  appear 
to  have  increased  in  the  West  after  the  creation  of  reser- 
voirs (Swenson  1981,  Henny  1983),  but  it  seems  unlikely 
that  this  has  completely  counterbalanced  the  loss  of  spawn- 
ing beds  of  anadromous  fish  from  reservoir  construction 
or  the  effects  of  pollution,  disturbance,  or  shooting.  In  the 
San  Francisco  Bay  Area,  the  loss  of  anadromous  fish  has 
been  offset  to  some  degree  by  the  introduction,  beginning 
in  the  1870s,  of  fish  from  the  East  and  Midwest  that  now 
make  up  the  bulk  of  our  warm-water  fish  populations 
(Skinner  1962). 

Although  historical  sightings  existed  for  Lake  Lagunitas 
and  Tomales  Bay  (Mailliard  1900,  S&P  1933),  there  were 
no  reports  of  nesting  Ospreys  in  Marin  County  as  of  1943 
(G&.M  1944).  Given  the  limited  historical  coverage  of  the 
area,  the  former  "abundance  of  the  species  in  California, 
and  the  current  breeding  distribution,  it  seems  likely  that 
Ospreys  formerly  bred  here  (though  perhaps  in  smaller 
numbers)  but  were  overlooked.  From  1962  to  1963, 
Ospreys  nested  on  the  cliffs  at  Double  Point  on  the  Point 
Reyes  peninsula  (Chan  1979).  In  1953,  Kent  Lake  was 
constructed  in  the  Lagunitas  Creek  watershed  north  of 
Mount  Tamalpais.  Although  one  of  several  reservoirs  in 
that  area,  it  was  the  largest  and  most  remote.  A  fire  that 
swept  the  slopes  adjoining  Kent  Lake  in  1945  left  many 
large  snags— prime  nesting  habitat— in  an  open  Douglas 
fir-coast  redwood  forest.  Many  dead  redwoods  that  now 
border  the  lakeshore  apparendy  were  drowned  by  the 
rising  of  the  dammed  waters  (Evens  1985).  The  first 
Osprey  nest  was  found  at  Kent  Lake  in  1967  (S. 
Cammiccia  pers.  comm.;  Evens  1991,  in  press).  Ospreys 
may  not  have  nested  there  until  then  because  of  the  time 
necessary  for  colonization  and  because  copper  sulfate  was 
added  to  the  lake  in  1964  to  kill  carp,  thus  reducing  or 
eliminating  the  food  supply.  The  Kent  Lake  population 
increased  rapidly  to  about  8  "active"  nests  in  1973  (C. 
Zumwalt  pers.  comm.),  and  an  estimated  7  occupied  nests 
in  1975  (Henny  et  al.  1978).  Osprey  studies  at  Kent  Lake 
from  1981  to  the  present  have  documented  a  continued 
dramatic  increase  of  the  population  to  35  occupied  nests 
in  1 990  (Evens  1 991 ,  in  press;  Table  1 8).  The  fact  that  the 
Kent  Lake  population  expansion  began  before  die  ban  on 
DDT  in  1972  may  be  because  this  isolated  watershed  was 


free  of  DDT  residues.  Currendy,  breeding  Ospreys  also 
concentrate  in  Marin  County  along  central  and  northern 
Inverness  Ridge  and  the  fringes  of  the  south  end  of 
Tomales  Bay,  where  there  were  1 5  occupied  nests  in  1 990 
(Evens  1991,  in  press).  This  population  expanded  gready 
in  the  last  decade.  A  sighting  of  an  Osprey  in  the  Tomales 
Bay  area  in  the  mid-1970s  was  considered  a  red-letter  day, 
whereas  now  it  is  rare  not  to  see  an  Osprey  in  this  area  on 
a  summer  day.  The  first  known  nest  on  Inverness  Ridge 
was  established  above  the  town  of  Inverness  in  1978,  but 
pairs  had  been  noted  in  the  area  for  two  or  three  years 
before  that  (Evens  1991,  in  press).  Since  most  Ospreys 
nest  within  about  20  miles  of  where  they  were  raised 
(Henny  1977),  the  Inverness  Ridge  population  may  have 
expanded  by  recruitment  from  the  Kent  Lake  population. 

During  the  adas  period,  new  information  was  added  on 
die  distribution  of  Ospreys  breeding  away  from  Kent  Lake. 
Without  a  thorough  systematic  search  just  for  Osprey 
nests,  a  minimum  of  5  occupied  nests  were  located  on 
Inverness  Ridge  in  1982  (DS  et  al.).  In  1981  and  1982, 
there  was  also  a  single  nest  on  top  of  a  duck  blind  over 
water  at  the  southeast  end  of  Tomales  Bay  (NY  each  year 
1981-89  — JGE),  another  on  Big  Rock  Ridge  above  Staf- 
ford Lake  (NY  5/20/82  — ScC),  and  16  occupied  nests  at 
Kent  Lake  (McCurdy  1983).  Because  nest  surveys  at  Kent 
Lake  in  1982  were  not  initiated  until  mid-June,  perhaps 
after  some  nesting  failures  earlier  in  the  season,  there  may 
have  been  up  to  20  occupied  nests  at  Kent  Lake  that  year 
(Evens  1985).  Using  the  conservative  survey  figures  for 
Kent  Lake  and  random  observations  from  elsewhere  in  the 
county,  there  were  a  minimum  of  23  occupied  nests  in 
Marin  County  during  the  last  summer  of  adas  field  work 
in  1982.  The  continued  increase  of  the  Kent  Lake  popula- 
tion (Table  18)  and  more  thorough  searches  on  Inverness 
Ridge,  whose  population  is  perhaps  also  still  increasing, 
have  produced  a  high  count  of  50  occupied  nests  in  Marin 
in  1990  (Evens  1991,  in  press).  The  Marin  County  breed- 
ing population  is  currently  the  most  southerly  stronghold 
for  the  species  in  California,  although  a  sizable  population 
occurs  in  Baja  California  and  the  Gulf  of  California 
(Henny  &.  Anderson  1979,  Henny  &.  Anthony  1989). 

Numbers  of  Ospreys  recorded  on  Breeding  Bird  Sur- 
veys in  California  were  relatively  stable  from  1968  to  1989 
(USFWS  unpubl.  analyses),  but  these  multispecies  surveys 
are  not  well  suited  for  detecting  population  trends  of 
semicolonial  raptors.  Surveys  solely  of  Ospreys  indicate 
that  on  the  whole  their  numbers  are  increasing  and  the 
breeding  range  is  currently  expanding  in  northern  Califor- 
nia (Gould  &  Jurek  1988,  Henny  &.  Anthony  1989). 
Nonetheless,  the  Osprey  is  still  a  Bird  Species  of  Special 
Concern  in  California  (Remsen  1978,  CDFG  1991b). 


132 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


BLACK-SHOULDERED  KITE   Elanus  caeruleus 


A  year-round  resident;  numbers  generally 

^c^x^               K 

swell  from  Sep  through  Mar  but  vary 

jOv'^wV^ 

■^\     -:i>--^                * 

irregularly  between  seasons  and  years, 

^C\ Jk 

A  ^^\      \  -'j^C^'  \  ^\      \ 

depending  on  fluctuating  vole  popula- 
tions. 

\^^\      \  Jt>>^Y~  \^\^~ 

p^A^VO 

An  uncommon,  local  breeder;  overall 

^v^ 

breeding  population  very  small. 

Recorded  in  34  (15.4%)  of  221  blocks. 

o<<\  ®V^\  ®j?\  ,Jri 

.. 

O    Possible        =      20  (59%) 

-^x$k^\°J^r\?y^ 

©    Probable       =         7   (21%) 

2-Mv  >V\    \^\   V^ 

^c^^A^^S 

•    Confirmed   =         7   (21%) 

~\J?/      ^^siv' 

S<y  - 

FSAR  =  2        OPI  =  68         CI  =  1.62 

Ecological  Requirements 

These  elegant  graceful  kites  inhabit  Marin  County's  open 
lowland  valleys  and  low,  rolling  foothills.  They  forage  in 
moist  meadows,  grasslands,  low  marsh  vegetation,  riparian 
edges,  irrigated  pastures,  and  cultivated  fields  or  orchards 
that  provide  the  requisite  prey  base.  Although  the  sur- 
rounding terrain  may  be  semiarid,  Kites  often  reside  near 
water  sources,  where  prey  are  more  abundant.  The  partic- 
ular characteristics  of  the  nesting  site  do  not  appear  to  be 
as  important  as  its  proximity  to  a  suitable  food  source 
(Hawbecker  1942).  With  open  foraging  country  nearby, 
Kites  often  build  nests  in  isolated  trees  or  clumps  of  trees, 
although  they  sometimes  place  them  in  dense  stands  on 
steep  slopes.  They  nest  in  a  wide  variety  of  trees  of 
moderate  height  and  sometimes  in  tall  bushes.  Native  trees 
used  in  California  are  live  and  deciduous  oaks,  willows, 
cottonwoods,  sycamores,  maples,  toyons,  and  Monterey 
cypress  (Pickwell  1930;  Hawbecker  1940,  1942;  Dixon  et 
al.  1957).  Kites  also  use  introduced  trees,  such  as  orchard 
varieties  and  eucalyptus.  Unlike  most  tree-nesting  hawks, 
Kites  do  not  build  their  nests  in  a  firm  crotch  next  to  a 
trunk  or  at  a  limb  fork,  but  instead  among  the  slender 
branches  of  the  crown  of  the  tree  (Pickwell  1930).  The  nest 
is  typically  screened  from  view  from  below  but  is  open 
above,  affording  easy  access  to  the  occupants  and  aerial 
predators.  The  nest  is  usually  deep  enough  in  the  tree, 
however,  to  provide  at  least  dappled  shade  when  the  young 
are  left  for  long  periods  (Hawbecker  1940).  Heights  of  tree 
nests  range  from  15  to  75  feet  (most  20-50  ft.)  above  the 
ground  (Pickwell  1930,  Bent  1937,  Hawbecker  1942).  At 


Grizzly  Island  in  the  Suisun  Marsh  of  Solano  County, 
Kites  nest  commonly  in  coyote  brush  about  6  to  8  feet  high 
(D.  Fortna  pers.  comm.).  In  this  area,  they  nest  in  bushes 
even  though  there  are  many  eucalyptus  groves  nearby  in 
which  Red-tailed  Hawks  and  Great  Horned  Owls  nest. 
Although  sometimes  frail  looking,  most  nests  are  well-built 
platforms  varying  from  a  shallow  to  a  deeply  hollowed 
bowl  (Pickwell  1930,  Bent  1937,  Hawbecker  1942).  Nests 
tend  to  flatten  out  as  the  young  develop  (Hawbecker  1942). 
Kites  build  their  nests  of  dry  sticks  and  twigs  and  line  them 
with  materials  such  as  grass,  straw,  roodets,  stubble,  weed 
stems,  lichen,  moss,  strips  of  inner  bark,  and  perhaps  a  few 
feathers  (Pickwell  1930,  Bent  1937).  Unlike  many  hawks, 
Kites  generally  build  a  new  nest  for  each  clutch.  Occasion- 
ally, they  will  build  on  top  of  old  nests  of  other  birds,  such 
as  Cooper's  Hawks  and  American  Crows  (Dixon  et  al. 
1957).  Rarely,  they  will  rebuild  in  the  exact  spot  in  the 
following  year  after  removal  of  a  nest,  refurbish  the  last 
year's  nest,  re-lay  in  the  same  nest  if  the  eggs  are  taken,  or 
use  one  of  their  nests  from  a  previous  year  for  a  second 
brood  (Barlow  1897,  Hawbecker  1942). 

Kites  traverse  their  foraging  grounds  in  buoyant,  airy 
flight.  They  typically  hunt  while  hovering  at  about  100  feet 
with  legs  dangling  down.  Birds  generally  face  into  the  wind 
and  maintain  their  position  by  slowly  flapping  their 
upstretched  wings  or  remain  aloft,  "kiting,"  by  the  force  of 
the  wind  alone.  When  prey  are  spotted,  they  raise  their 

133 


/  lawks  and  Eagles 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hawks  and  Eagles 


wings  even  higher  in  a  sharp)  V  and  then  slowly  descend, 
accelerating  in  the  last  few  yards  when  actually  making  a 
strike  from  a  diagonal  or  vertical  fall. 

Although  hunting  Kites  may  range  up  to  about  2  miles 
from  perches,  they  forage  mostly  within  100  yards  (primar- 
ily males  near  nest  sites)  and  secondarily  up  to  0.6  miles 
from  perches  (Warner  6k  Rudd  1 975).  At  all  seasons,  Kites 
forage  mosdy  early  and  late  in  die  day.  From  die  initiation 
of  incubation  until  the  young  approach  fledging,  the  male 
provides  food  for  both  his  mate  and  the  young.  (See 
Warner  and  Rudd  1975  for  further  details  of  seasonal, 
temporal,  or  sexual  differences  in  hunting  behavior,  hunt- 
ing success,  and  strike  efficiency.)  Rodents  and  birds  are 
commonly  decapitated  before  delivery  to  the  nest  (Palmer 
1988a).  The  male  usually  transfers  food  to  the  female  at  or 
near  a  perch  or  the  nest.  If  she  declines,  the  male  eats  the 
prey  or  sometimes  stores  it  in  a  shallow  hollow  of  a  limb 
or  in  a  split  limb  of  a  tree  (Dixon  et  al.  1957).  The  female 
may  eat  prey  at  a  perch,  but  when  she  delivers  it  to  the 
young  she  initially  tears  it  into  pieces  to  feed  them  (Palmer 
1988a).  Later  in  the  season,  she  drops  the  prey  at  the  nest, 
and  the  young  are  able  to  dismember  it  themselves. 

Based  on  analysis  of  prey  remains  from  their  relatively 
large,  owllike  pellets,  Kites  in  California  eat  small  mam- 
mals almost  exclusively  (Bond  1940,  1942;  Hawbecker 
1940,  1942;  Moore  6k  Barr  1941;  Stoner  1947;  Cunning- 
ham 1955;  Dixon  et  al.  1957;  Waian  &  Stendell  1970; 
Stendell  6k  Meyers  1973;  Warner  6k  Rudd  1975;  Meserve 
1977;  Palmer  1988a).  Prey  must  be  diurnally  active,  have 
a  minimum  body  weight  (usually  about  1  oz.),  and  occur 
in  some  minimal  abundance  (Meserve  1977).  In  most 
instances,  the  meadow  mouse  (Microtus  californicus)  over- 
whelmingly dominates  the  diet,  accounting  for  50%- 
100%  (usually  70%-90%)  of  the  prey  items  (references 
above).  At  times,  feral  house  mice  (Mus  musculus)  may  be 
equally  important  or  even  the  dominant  prey.  Instances  of 
Mus  accounting  for  85%-90%  of  die  diet  are  from  prey 
remains  of  nonbreeding  groups  of  Kites  or  from  commu- 
nal winter  roosts  (Meserve  1977)-  Because  of  their  much 
smaller  size  (three  times  less  by  weight)  than  Microtus,  Mus 
may  not  provide  sufficient  energy  for  Kites  to  nest  success- 
fully. In  two  California  studies,  numbers  of  Microtus  prey 
were  highest  during  summer  and  lowest  in  winter,  and  vice 
versa  for  Mus  (Warner  6k  Rudd  1975,  Stendell  in  Meserve 
1977).  The  harvest  mouse  (Reithrodontomys  megalotis)  is  a 
distant  third  in  dietary  importance,  occurring  in  about 
5%-10%  of  the  pellets.  Odier  small  mammal  prey  of 
minor  importance  are  pocket  gophers,  pocket  mice,  kanga- 
roo rats,  white-footed  mice,  shrews,  and  die  young  of 
cottontail  rabbits,  woodrats,  and  ground  squirrels.  Rirely, 
small  ground-dwelling  birds,  snakes,  frogs,  lizards,  and 
large  insects  are  taken.  Kites  occasionally  scavenge  (Warner 
6k  Rudd  1975). 

134 


Since  Black-shouldered  Kites  exploit  cyclic  populations 
of  meadow  mice  (Krebs  1966)  and  irregularly  irrupting 
populations  of  house  mice  (Pearson  1963),  they  exhibit 
many  adaptations  to  an  abundant  but  temporally  and 
spatially  fluctuating  food  supply.  Although  Kites  may  nest 
in  an  area  for  many  successive  years,  they  generally  are 
nomadic  seasonally,  and  their  breeding  populations  may 
increase  locally  and  their  nest  spacing  may  decrease  with 
increasing  vole  populations  (Palmer  1988a).  Most  birds 
breed  successfully  in  spring  during  the  peak  of  vole  popu- 
lations, but  some  will  double  brood  during  periods  of 
plentiful  food  (Dixon  et  al.  1957).  In  addition,  clutch  size 
increases  with  prey  density,  and  the  number  of  successful 
nests  and  the  number  of  young  raised  are  related  to  the 
percentage  of  voles  in  the  Kites'  diet  (B.A.  Wright  in 
Palmer  1988a).  Eggs  hatch  asynchronously,  and  the  length 
of  the  nesting  period  varies  with  the  food  supply  (Palmer 
1988a).  Also,  as  noted  above,  food  is  stored  when  plenti- 
ful. 

Marin  Breeding  Distribution 

During  the  adas  years,  breeding  Black-shouldered  Kites 
were  concentrated  in  Marin  County  in  two  general  areas: 
(1)  the  valleys  and  low  hills  in  the  south-central  coastal 
sector  and  (2)  similar  terrain  near  Novato.  This  distribu- 
tion pattern  was  similar  to  that  of  die  Red-shouldered 
Hawk  and  may  reflect  the  productivity  of  lowland  areas  that 
remain  relatively  moist  during  the  summer  dry  season  and 
therefore  support  abundant  prey  in  the  respective  habitats 
used  by  these  two  species.  The  lack  of  adas  breeding 
records  in  the  northern  part  of  the  county  near  Tomales 
may  have  been  because  of  overgrazing,  which  eliminates 
extensive  potential  Microtus  habitat.  The  limited  breeding 
population  on  Point  Reyes  is  puzzling.  Although  much  of 
diis  area  is  overgrazed,  it  supports  extensive  areas  of  seem- 
ingly suitable  marshy  grassland  and  coastal  swale  habitat. 
A  representative  Marin  breeding  locality  was  Bolinas  (NB 
4/14/77 -DS.CA). 

Because  Kites  tend  to  be  nomadic  and  to  decrease  or 
increase  rapidly  with  fluctuating  vole  populations,  future 
adasers  should  be  very  cautious  in  interpreting  any  changes 
they  detect  when  they  repeat  the  Marin  adas  at  a  later  date. 

Historical  Trends/Population  Threats 

Early  historical  breeding  records  for  Marin  County  are 
from  near  Novato  in  1901  and  1902  (Ray  1904,  G6kW 
1927)  and  from  Kentfield  in  1917  (Squires  1917).  Ste- 
phens and  Pringle  (1933)  considered  Kites  "rather  rare"  in 
Marin  County.  However,  diose  audiors  and  Stephens 
(1 945)  together  list  1 5  records  for  the  county  from  1 920  to 
1945.  This  seems  a  rather  respectable  total,  considering 
the  very  limited  observer  coverage  at  that  time. 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


Much  has  been  written  about  historical  population 
decreases,  a  more  recent  dramatic  upswing  in  the  U.S. 
population,  and  a  major  range  extension  into  Central 
America  (Eisenmann  1971).  Grinnell  and  Miller  (1944) 
reported  that  Kites  were  common  and  widespread  in 
appropriate  habitat  in  California  prior  to  1885,  but  by 
1943  they  were  rare  in,  or  extirpated  from,  many  sections, 
despite  a  slight  recent  trend  of  recovery.  Several  audiors 
have  since  speculated  that  the  species  reached  a  nadir  in 
the  late  1920s  and  1930s  and  have  stated  or  implied,  based 
on  limited  evidence,  that  the  species  was  close  to  extinction 
at  the  time  (Waian  &.  Stendell  1970,  Warner  6k  Rudd 
1975,  Larson  1980,  Pruett-Jones  et  al.  1980).  However, 
Williams  (1940)  reviewed  109  published  accounts  and  1 36 
records  from  correspondence  and  interviews  and  con- 
cluded that  "no  statement  as  to  its  actual  increase  or 
decrease  is  justified  at  the  present;  nor  could  we  say 
whether  the  bird  is  holding  its  own."  For  the  period  1935 
to  1939  alone,  Williams  assembled  records  of  32  definite 
and  39  probable  California  breeding  pairs.  Considering 
the  few  observers  then  and  the  lack  of  systematic  surveys, 
these  data  suggest  that  the  species  was  not  in  imminent 
danger  of  extinction  as  a  breeder  in  California  at  that  time, 
despite  its  obvious  serious  decline  earlier  in  the  century. 

Despite  the  problems  of  tracking  population  trends  of  a 
species  tied  to  rapidly  fluctuating  food  supplies,  analyses  of 
Christmas  Bird  Count  data  documented  a  rapid  increase 
of  the  California  population  from  the  mid-1 940s  through 
the  mid-1960s  (Fry  1966,  Waian  &  Stendell  1970, 
Eisenmann  1971,  Larson  1980).  Subsequent  data  suggest 
an  increase  continuing  through  the  mid-1970s  (Larson 
1980,  Pruett-Jones  et  al.  1980),  but  the  population  since 
the  mid-1960s  might  just  have  been  fluctuating  markedly 
from  year  to  year  in  response  to  prey  populations.  Num- 
bers of  Kites  on  Breeding  Bird  Surveys  in  California  were 
relatively  stable  from  1968  to  1989,  diough  data  suggested 


a  slight  decrease  from  1980  to  1989  (USFWS  unpubl. 
analyses). 

Early  declines  were  apparendy  caused  by  shooting,  habi- 
tat loss,  and  perhaps  by  overzealous  egg  collectors.  The 
eggs  were  highly  prized  because  of  their  scarcity,  because  of 
the  variability  between  egg  sets,  and  because  Black-shoul- 
dered Kite  eggs  are  among  the  most  beautiful  of  those  of 
all  North  American  birds.  Illegal  egg  collecting  continued 
until  at  least  1940  despite  laws  passed  in  1905  to  protect 
the  birds  and  their  nests  (Williams  1940);  further  protec- 
tion was  afforded  by  legislation  in  1957.  California's  Kite 
population  has  apparendy  increased  because  of  the  birds' 
ability  to  tolerate  habitat  fragmentation  caused  by  agricul- 
tural practices,  to  exploit  increased  Microtus  populations 
thriving  in  fields  irrigated  year  round  (Eisenmann  1971, 
Warner  6k  Rudd  1975,  Pruett-Jones  et  al.  1980),  and  to 
reproduce  at  a  high  rate.  A  clutch  size  of  four  to  five  eggs 
and  the  ability  to  double  brood  in  a  single  year  are  both 
unusual  adaptations  for  a  hawk  (Hawbecker  1940, 
Eisenmann  1971).  Martin  (1989)  noted  that  the  amount 
of  irrigated  agricultural  land  in  California  increased  by 
42%  from  1944  to  1978,  coinciding  with  the  period  of 
dramatically  increasing  Kite  numbers. 

The  great  year-to-year  fluctuations  in  Kite  numbers 
appear,  at  least  in  part,  to  be  tied  to  similar  changes  in  the 
prey  base  influenced  by  rainfall.  Pruett-Jones  et  al.  (1980) 
found  a  significant  positive  correlation  between  Kite  num- 
bers and  rainfall.  This  perhaps  is  explained  by  the  fact  that 
microtine  rodents  need  standing  water  to  reproduce 
(Church  1966)  and  that  their  numbers  are  usually  reduced 
in  a  drought.  The  decline  in  Kite  numbers  in  California 
during  the  1975-76  to  1976-77  drought  and  the  substan- 
tial increase  in  numbers  in  Oregon  at  that  time,  including 
their  first  breeding  record  (Henny  6k  Annear  1978),  fur- 
ther suggests  a  link  between  rainfall,  vole  populations,  and 
Kite  populations. 


135 


Hawks  and  Eagles 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hawks  and  Eagles 


NORTHERN  HARRIER    Circus  cyaneus 


A  year-round  resident;  numbers  swell 

/"VdYv^V    \ 

\ 

from  Sep  through  mid-Mar. 

\j^\    \^ 

Y^y 

An  uncommon,  local  breeder;  overall 
breeding  population  very  small. 

\*\^\ 

vLV\" 

\pp*0x 

\  VvV 

Recorded  in  48  (21.7%)  of  221  blocks. 

^V^ToV- 

-^\)    V^\  ^-\ 

O    Possible        =      32  (67%) 

^\  o- V^A 

~^^K\''Jk 

X^^ 

C    Probable       =        9  (19%) 
•    Confirmed   =         7   (14%) 

3rwr^ 

"t3<~ 

FSAR  =  2         OPI  =  96         CI  =  1.48 

'z^r'^ 

voV--V" 

i  „  -a<\  J^t^ 

-"■YOrH 

^2o 

b^"^* 

^^<r\ 

Ecological  Requirements 

The  Northern  Harrier  is  quick  to  attract  attention  with  its 
conspicuously  low  foraging  flights  and  the  loop-the-loop 
antics  of  its  roller  coaster-like  breeding  display  dives. 
Marin  County's  breeding  Harriers  inhabit  freshwater 
marshes,  coastal  swales,  wet  meadows,  moist  grasslands, 
salt  marshes,  and  hayfields.  Throughout  their  breeding 
range,  Northern  Harriers  occupy  a  variety  of  open  terrain 
that  typically  has  herbaceous  cover,  often  intermixed  with 
woody  growth  (Palmer  1988a).  They  generally  occur  in 
moist  or  wet  areas,  which  are  more  likely  to  provide 
adequate  nesting  cover  and  a  good  prey  base.  In  addition 
to  marshland,  swampland,  or  grain  field  habitats,  diey 
sometimes  occupy  fallow  weed  fields,  cut  woodlands, 
young  stands  of  planted  conifers,  and  sagebrush  steppe  far 
from  water.  In  general,  however,  they  nest  in  wetter,  less 
exposed  sites  than  their  crepuscular  ecological  equivalent, 
the  Short-eared  Owl. 

Harriers  select  ground  nest  sites  in  grassy  areas,  in 
cattails,  in  mixtures  of  herbaceous  and  woody  growth,  in 
weed  patches,  among  low  brush  or  close  beside  bushes  or 
trees,  or  in  grain  fields  or  other  low  cultivated  croplands. 
They  also  occasionally  nest  on  muskrat  houses  in  water  or 
on  accumulated  floating  vegetation;  exceptionally,  birds 
have  located  their  nests  on  haystacks  or,  once,  20  feet  up 
in  a  willow  in  an  old  Swainson's  Hawk  nest  (Palmer 
1988a).  Ground  nests  tend  to  be  well  concealed,  at  least 
from  the  sides,  in  densely  vegetated  areas  within  a  marsh 
or  field;  rarely,  they  are  fully  exposed. 

136 


The  nest  is  generally  a  shallow,  slightly  hollowed  plat- 
form situated  on  the  ground,  perhaps  in  a  depression,  or 
on  top  of  flattened,  low  vegetation  (Dawson  1923,  Bent 
1937,  Palmer  1988a).  It  may  be  simply  a  hollow  lined  with 
grasses,  or,  particularly  in  damp  places,  it  may  be  built  up 
widi  sticks,  straw,  reeds,  and  weed  stems  and  lined  with 
finer  vegetative  parts  and  perhaps  a  little  moss  or  feathers. 
The  height  of  the  nest  wall  varies  with  the  height  of  water 
in  tidal  areas,  and  nests  in  wet  areas  often  act  as  bulky, 
floating  rafts.  Harriers  sometimes  use  nests  several  years  in 
a  row  and  add  new  materials  annually  (Palmer  1988a). 
Young  over  five  days  old  usually  leave  the  nest  if  disturbed 
or  to  seek  shade  in  covered  portions  of  runways.  The 
young  usually  return  to  the  nest  when  the  female  returns 
with  food.  With  time,  these  hideouts  often  become  crude 
platforms  that  the  female  sometimes  uses  as  a  distribution 
center  for  prey.  At  wet  sites,  the  young  are  less  likely  to 
leave  the  nest  before  they  can  fly. 

Northern  Harriers  may  be  colonial,  even  within  tracts 
of  apparendy  similar  habitat  (Palmer  1988a).  Although 
rather  opportunistic  feeders,  their  distribution  seems  to  be 
tied  closely  to  the  presence  of  small,  diurnal,  primarily 
grassland  rodents  (mostly  microtines)  and  perhaps  birds  to 
some  extent.  In  addition  to  their  tendency  toward  colonial 
nesting,  Harriers  also  exhibit  a  strong  bent  toward  bigamy, 
or  even  harem  polygamy  with  males  sometimes  mated  with 
up  to  seven  females.  Polygamy  tends  to  be  practiced  by 
older  birds,  especially  in  dense  Harrier  populations  when 
voles  are  abundant. 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


The  male  typically  caches  and  delivers  all  the  food 
during  incubation  and  early  brood  life.  About  five  days 
after  the  eggs  hatch,  females  begin  short  hunting  flights, 
which  they  increase  and  extend  throughout  the  remainder 
of  the  nesting  cycle.  Monogamous  males  generally  tend  to 
supply  food  for  nesdings  longer  than  polygamous  males, 
which  often  cease  prey  deliveries  to  less  favored  nests.  This 
can  lead  to  instances  of  female  attempts  to  intercept  and 
snatch  prey  from  the  talons  of  a  male  going  to  feed  another 
female,  and  to  piracy  attempts  between  females  mated  to 
the  same  male.  More  typically,  the  female  flies  up  to  seize 
food  dropped  by  the  male  upon  delivery.  Food  transfers 
usually  occur  within  100  yards  of  the  nest,  though  some 
may  occur  over  0.6  miles  away.  The  altitude  or  method  of 
prey  transfer  may  vary  depending  on  the  stage  of  the 
nesting  cycle,  the  weather,  the  size  of  prey  delivered,  or 
pesticides  accumulated  by  the  adults.  Before  delivery,  die 
male  typically  beheads  the  prey,  sometimes  eviscerates  it, 
and,  if  it  is  a  bird,  more  or  less  plucks  it.  Frogs  are  skinned, 
and  the  fur  of  voles  is  stripped  off  and  discarded.  On 
recovering  the  prey,  the  female  will,  if  need  be,  prepare  it 
and  return  to  the  nest  to  feed  the  young;  she  sometimes 
first  eats  a  portion.  The  talons  of  Harriers  are  best  adapted 
for  seizing  and  holding  prey.  Consequendy,  much  killing 
is  done  with  the  beak,  often  incidentally  as  the  bird  begins 
feeding  on  the  neck  and  throat  of  prey.  Harriers  eat  prey 
piecemeal  and  usually  consume  everything  but  the  gastro- 
intestinal tract. 

Northern  Harriers  exhibit  marked  overlap  in  their 
home  ranges  or  hunting  areas,  especially  away  from  nests 
(Palmer  1988a).  These  areas  are  not  hunted  uniformly,  as 
birds  again  and  again  fly  routes  that  enable  diem  to 
surprise  prey,  sometimes  hunting  as  little  as  20%-30%  of 
their  territory.  This  results  in  particular  prey  species  com- 
posing a  significant  portion  of  the  diet  for  a  short  period, 
and  then  possibly  not  recurring.  In  one  study,  radio-tagged 
birds  had  a  daily  cruising  radius  of  1 .25  x  1 .75  miles;  they 
used  certain  areas  near  the  nest  much  more  than  others, 
and  they  departed  in  the  same  direction  from  which  they 
had  returned  with  prey. 

The  Northern  Harrier  is  our  only  raptor  that  seeks  small 
and  medium-sized  prey  by  low-level,  lineal  scanning 
(Palmer  1988a).  Hearing  is  also  an  integral  aid  to  hunting. 
Harriers  have  angular  acoustic  resolution  within  the  range 
known  for  owls  and  at  least  four  times  as  great  as  that  of 
"typical"  diurnal  raptors  (Palmer  1988a).  Notably,  Harriers 
are  our  only  diurnal  raptor  with  well-developed  facial  discs. 
In  the  field  they  are  able  to  locate  vole  squeaks  accurately 
and  to  attack  prey  successfully  without  the  aid  of  visual  or 
olfactory  cues.  Harriers  typically  hunt  from  buoyant,  sus- 
tained, tilting  flight,  generally  less  dian  ten  feet  above  die 
vegetation.  They  do  not  usually  hunt  while  soaring  or 
gliding.  Harriers  quarter  to  and  fro  over  short  distances 
over  fields  and  marshes,  making  numerous  sharp  turns 


and,  occasionally,  doubling  back  to  reinvestigate  likely 
spots.  While  quartering  over  dense  vegetation,  they  often 
hover  persistendy,  or  stall  midair  and  drop  lower.  In  such 
instances,  they  frequendy  reach  down  with  their  legs  and 
foot-stab  in  an  effort  to  force  prey  from  cover.  This  tech- 
nique is  used  particularly  against  songbirds  in  bushy  vege- 
tation and  against  rails  hiding  in  wracks  of  floating  debris. 
Harriers  will  fly  from  one  stranded  debris  wrack  to 
another,  hovering  and  sometimes  landing  in  apparent 
attempts  to  flush  prey.  Flying  prey  are  usually  taken  on  the 
first  attempt  and  are  not  pursued  if  they  flee.  Another 
common  hunting  technique  is  "border  following,"  in 
which  Harriers  fly  purposefully  along  ridges  and  vegetation 
discontinuities,  such  as  fencerows,  ditches,  or  roadsides,  in 
efforts  to  surprise  mobile  prey. 

Capable  of  remarkably  quick  maneuvering  at  close 
range,  Harriers  pounce  directly  on  prey  from  flight,  after 
hovering,  or  they  "hook-pounce"  in  a  three-quarter  turn 
after  overshooting  prey  (Palmer  1988a).  They  also  make 
slower,  deliberate  pounces  on  microtine  nests.  Males  tend 
to  border-follow  and  nest-pounce  more  and  hook-pounce 
less  than  females  do.  Generally,  males  tend  to  fly  lower  and 
faster  and  catch  more  passerines  than  females,  which  catch 
fewer,  larger  prey.  The  males'  coloration  may  serve  as  an 
advantage  in  hunting  sharp-eyed  prey  in  open  terrain. 

Harriers  also  hunt  while  perched  on  the  ground  or, 
occasionally,  from  stumps  or  fence  posts  (Palmer  1988a). 
Rarely,  they  plunge,  Ospreylike,  to  catch  fish  in  ponds  or 
make  horizontal  passes  along  the  top  of  streams  of  flying 
bats.  It  is  unclear  whether  large  birds  captured  on  the  water 
are  sometimes  drowned  deliberately  or  inadvertendy.  Har- 
riers also  opportunistically  take  advantage  of  songbird 
nests  uncovered  in  newly  mown  hayfields.  Additionally, 
they  hunt  in  association  with  foxes,  along  the  edges  of  fires, 
and  even  near  targets  in  active  bombing  ranges!  Harriers 
also  pirate  food  from  other  species  of  raptors  and  vice 
versa.  Both  sexes  appear  to  hunt  throughout  the  day,  but 
activity  peaks  among  locations  and  years  may  reflect  vari- 
ous activity  periods  of  major  prey  species  taken.  Daily 
hunting  activity  varies  widi  weather,  prey  activity,  competi- 
tion, and  other  factors.  Harriers  perch  more  in  rainy 
weather,  tend  to  hunt  more  birds  when  windy,  and  feed 
on  carrion  and  rob  prey  more  in  severe  winter  weather. 

For  North  America  as  a  whole,  the  yearly  Harrier  diet 
by  weight  is  about  58%  mammals,  34%  birds,  and  8% 
other  prey  (Clark  &  Ward  in  Palmer  1988a).  In  another 
summary  based  on  number  of  prey  items  (n  =  2362), 
Snyder  and  Wiley  (1976)  reported  the  North  American 
diet  was  47.7%  birds,  34.8%  mammals,  15%  inverte- 
brates, and  2.5%  lower  vertebrates.  Harriers,  however, 
exploit  whatever  prey  are  readily  available  to  dieir  hunting 
techniques,  resulting  in  great  dietary  variation  among  sea- 
sons and  localities.  For  examples,  Errington  and 
Breckenridge  (1936),  reporting  on  the  diet  of  nesting  birds 

137 


Hawks  and  Eagles 


MARIN  c:OUNTY  BREEDING  BIRD  ATLAS 


Hawks  and  Eagles 


in  the  Midwest,  found  drat  mammals  accounted  for  96% 
of  the  dietary  items  during  a  vole  outbreak,  but  only  37% 
at  another  site  during  a  drought  year.  Selleck  and  Glading 
(1943)  reported  that  birds  made  up  80.6%,  mammals 
18%,  and  reptiles  1 .4%  of  the  total  prey  items  (n  438)  at 
four  nests  in  San  Luis  Obispo  County,  California.  The 
main  prey  diere  were  blackbirds,  House  Finches,  other 
passerines,  California  Quail,  and  brush  rabbits;  there  was 
considerable  variation  in  the  prey  delivered  to  various 
nests. 

Mammal  prey  may  range  from  shrews  to  skunks  and 
jackrabbits  (especially  voles  and  small  to  medium-sized 
rodents),  but,  except  for  their  young,  larger  species  are 
probably  incapacitated  or  dead.  Bird  prey  range  from  small 
sparrows  to  upland  game  birds,  ducks,  and  American 
Bitterns,  consisting  mosdy  of  small  to  medium-sized  birds 
from  sparrows  to  Mourning  Doves;  again,  larger  species 
taken  are  usually  young  birds  or  those  found  injured  or 
dead.  Short-eared  and  Screech  owls  are  occasional  prey,  as 
are  small  diurnal  raptors  such  as  Sharp-shinned  Hawks 
and  American  Kestrels.  Other  miscellaneous  prey  items 
include  snakes,  lizards,  toads,  frogs,  fish,  crayfish,  large 
insects  (especially  grasshoppers),  and  spiders.  Young  Har- 
riers may  supplement  their  diet  with  slow,  weak  insects  and 
snakes  that  they  themselves  can  catch.  In  some  instances, 
adults  catch  larger  prey  for  older  young.  In  fall  and  winter, 
voles  and  carrion  are  more  important  in  die  diet  (especially 
to  juveniles).  Harriers  take  the  greatest  variety  of  prey  items 
in  spring  and  summer  when  young  mammals,  young  and 
adult  birds,  and  cold-blooded  prey  are  more  prevalent. 

Marin  Breeding  Distribution 

During  the  adas  period,  nesting  Harriers  were  concen- 
trated in  two  sections  of  Marin  County.  The  stronghold 
was  the  coastal  lowlands,  particularly  on  outer  Point  Reyes, 
where  the  extensive  grassland  and  dune  system  are  replete 
with  coastal  swale  marshland.  To  a  lesser  degree,  breeding 
Harriers  concentrated  in  bayshore  marshes  and  reclaimed 
marshland  converted  to  grain  agriculture,  particularly  in 
the  vicinity  of  the  Petaluma  River  near  Novate  Represen- 
tative breeding  localities  were  the  marshy/brushy  border  of 
salt  marsh  at  Limantour  Estero  (NE  4/5/78  —AM);  swale 
near  McClure's  Ranch,  Point  Reyes  (NE  5/11/82  -DS); 
and  swale  near  Brazil  Ranch,  SE  of  Dillon  Beach  (NY 
6/3/82  -DS). 

Historical  Trends/  Population  Threats 

Mailliard  (1900)  and  Stephens  and  Pringle  (1933)  consid- 
ered the  "Marsh  Hawk"  a  winter  resident  in  Marin  Coun- 
ty, but  nesting  had  been  documented  on  Point  Reyes  as 


early  as  1917  (NE  6/20/17  -GckW  1927).  The  earlier 
ascriptions  of  winter  residency  probably  reflected  the  influx 
of  I  larriers  at  drat  season  and  the  limited  exploration  of 
the  favored  breeding  haunts  of  Point  Reyes  and  bayside 
marshes,  radier  than  any  subsequent  change  in  status.  In 
fact,  much  evidence  points  to  declining,  rather  than 
increasing,  populations  of  breeding  Harriers  in  recent 
decades. 

Grinnell  and  Miller  (1944)  noted  that  breeding  Harrier 
populations  had  been  gready  reduced  by  habitat  loss  in 
"late  years."  Although  there  is  no  numerical  documenta- 
tion, Harriers  must  have  continued  to  decline  sharply 
during  the  period  of  great  human  population  growth  and 
intense  diking  and  filling  of  the  greater  San  Francisco  Bay 
marshes  just  before  and  after  World  War  II  (Atwater  et  al. 
1979).  As  much  as  95%  of  that  estuary's  tidal  marshes 
have  been  leveed  or  filled  since  the  Gold  Rush,  and  Harrier 
populations  must  have  plummeted  accordingly.  Using 
Christmas  Bird  Count  data  from  1952  to  1971,  Brown 
(1973)  documented  a  continentwide  decline  in  wintering 
Harrier  numbers  from  the  early  1950s  to  the  early  1960s, 
when  populations  leveled  off  and  then  increased  some- 
what, particularly  in  California.  From  1968  to  1989,  num- 
bers of  Harriers  were  relatively  stable  on  Breeding  Bird 
Surveys  in  California  (USFWS  unpubl.  analyses).  Concern 
over  Harrier  population  declines  has  resulted  in  inclusion 
of  the  species  on  the  Audubon  Society's  Blue  List  every 
year  from  1972  to  1986  (Tate  1981,  1986;  Tate  6k  Tate 
1982);  as  of  1986  Harriers  were  considered  "down  or 
greatly  down  nearly  everywhere."  Similar  concerns  resulted 
in  listing  the  Northern  Harrier  as  a  Bird  Species  of  Special 
Concern  in  California  (Remsen  1978).  Martin  (1989) 
noted  the  mixed  results  of  reports  on  population  trends  of 
Harriers.  Though  cautioning  against  the  difficulty  of  inter- 
preting population  trends  of  the  species,  he  felt  that  Har- 
rier numbers  appeared  to  be  stable  or  increasing  slighdy  in 
die  West.  In  addition  to  habitat  loss,  Harriers  have  also 
been  troubled  by  eggshell  thinning  from  pesticide  accumu- 
lations (Anderson  6k  Hickey  1972).  Although  biocides 
were  implicated  in  declines,  at  least  early  on,  supporting 
evidence  could  be  stronger.  Other  postulated  causes  of 
declines  are  grazing  (Remsen  1978)  and,  at  least  formerly, 
shooting  (Palmer  1988a).  Despite  encouraging  signs  in 
California,  continued  concern  for  the  fate  of  this  species  is 
clearly  warranted,  as  indicated  by  retention  of  the  North- 
ern Harrier  on  the  state's  recent  list  of  Bird  Species  of 
Special  Concern  (CDFG  1991b). 


138 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


SHARP-SHINNED  HAWK  Accipiter  striatus 


Occurs  year  round,  though  almost  exclu- 

^P^-^      N                      j(\ 

sively  as  a  winter  resident  and  transient 

y\^3^ 

from  Sep  through  Apr;  numbers  swell 

^-V\ JkK 

\v-Vv3r\  \r\^\^c\t^\' 

substantially  during  fall  migration  from 
Sep  through  mid-Nov. 

\^\\^C\\^D^                               p 

A  rare,  very  local  breeder;  overall  breed- 

C\^K^\^i\\^>\\ ^V"\  J^\\  J^c\  J^ 

ing  population  very  small. 

^-^X^^nA   l"'  \       \*^\       \£*%*\       \  ^^\-      \-^*^-~-~\z^*\       \  J^>^~^. 

Recorded  in  7  (3.2%)  of  221  blocks. 

ff^\  S^\^-i^^\ ~'c\^\    3r^\    J^T\     \r\      ></ 

O    Possible                 6  (86%) 

*J^\^\^\^^X~J^^ 

€    Probable       =         0   (0%) 

•    Confirmed   =          1    (14%) 

Sr^^^^^^^K^^^^ 

p^*                              \^  i        ^^si\/V  V-^s. 

FSAR=1         OPI  =  7           CI  =  1.29 

Ecological  Requirements 

This  dashing  miniature  bird-hawk  is  such  a  rare  breeder  in 
Marin  County  that  it  is  difficult  to  describe  its  habitat 
preferences  here.  The  only  breeding  confirmation  for  die 
county  was  of  a  family  group  of  adults  and  recently  fledged 
young  residing  in  a  dense  stand  of  second-growth  Douglas 
fir  and  coast  redwood.  This  forest  had  an  understory  of 
mosdy  small  to  medium-sized  tanbark  oaks,  a  few  sapling 
firs  and  redwoods,  and  scattered  ground  cover  of  sword 
ferns.  Regardless  of  the  dominance  of  conifers,  this  habitat 
was  noticeably  denser  than  the  stands  of  mixed  evergreen 
forest  where  Cooper's  Hawks  breed  here. 

Grinnell  and  Miller  (1944)  knew  of  few  actual  nesting 
records  for  California  and  hence,  apparently  based  on 
limited  evidence,  described  breeding  habitat  as  "eidier 
deciduous  or  coniferous  woodland,  not  dense  forest  but  at 
edges  or  where  broken."  Continentwide,  most  birds  nest 
in  stands  of  dense  young  conifers  in  conifer  or  mixed 
conifer-deciduous  forests;  where  deciduous  trees  are  the 
dominant  cover,  they  usually  select  insular  conifer  stands 
for  the  actual  nest  site.  Although  some  authors  mention  a 
preference  for  nesting  sites  near  openings  (Bent  1937, 
GckM  1944,  Palmer  1988a),  Sharp-shins  nest  both  in 
broken  forests,  fragmented  naturally  or  by  timber  harvests, 
and  in  large  blocks  of  continuous  pristine  forests  (Reyn- 
olds 1989).  Based  on  extensive  surveys  in  Oregon's  conifer 
forests,  the  three  species  of  Accipiter  breeding  there  all 
select  dense  stands  that  provide  screening  from  predators 
and  a  shady,  mild  environment  (Reynolds  et  al.  1982, 
Reynolds  1983).  In  contrast  to  Cooper's  Hawks  and  Gos- 
hawks, most  Sharp-shins  in  Oregon  use  denser,  younger 


(25-  to  60-year-old),  even-aged  stands  for  nesting  (see  Coop- 
ers account  for  comparison).  These  stands  have  shallow, 
single-layered,  dense  canopies  (mean  crown  closure  68%- 
80%),  an  abundance  of  dead  limbs  on  trunks  beneath  the 
live  crowns,  and  ground  cover  of  patches  of  ferns,  mosses, 
grasses,  and  low  shrubs.  A  few  Sharp-shins  nest  there  in 
dense  (mean  closure  90%),  old-growth  (200+  years)  stands 
with  multi-layered  canopies  and  sparse  ground  cover;  occa- 
sionally, a  pair  nests  in  a  stand  of  stunted  quaking  aspen. 
Sharp-shins  there  chose  nests  sites  on  gende  to  moderate 
slopes  (av.  25%,  range  8%-47%),  and,  unlike  Coopers 
and  Goshawks,  which  prefer  northerly  facing  slopes,  they 
do  not  prefer  any  particular  slope  aspect.  Nest  sites  tend  to 
be  near  springs  or  quiet  streams,  but  this  may  have  been 
an  artifact  of  choosing  dense  forests  that  tend  to  be  in 
moist  situations. 

In  Oregon,  Sharp-shins  place  their  nests  in  the  denser 
portion  of  the  lower  canopy  on  horizontal  branches  against 
the  trunk  or  in  a  crotch  of  a  double  or  split  trunk  (Reynolds 
et  al.  1982).  Nest  heights  there  range  from  10  to  80  feet 
above  the  ground,  averaging  75  feet  in  mature  sites  and  39 
feet  in  second-growth  sites.  Elsewhere,  nests  are  placed  in 
similar  situations,  ranging  from  6  to  90  feet  above  the 
ground  (Bent  1937).  The  nest  is  a  shallow  platform  of 
interlaced  dead  conifer  twigs  lined  with  finer  twigs  or  outer 
tree  bark  (Bent  1937,  Palmer  1988a).  Sharp-shins  build 
most  nests  in  conifers  but,  occasionally,  select  deciduous 
trees  for  nest  sites.  Unusual  nest  sites  include  an  old  Blue 
Jay  nest  6  feet  up  in  a  sapling;  in  a  hole  in  a  cave;  in  a 
"hollow  prong"  of  a  broken  sycamore  branch;  on  high 

139 


Hawks  and  Eagles 


MARIN  COUNTY  BRHLDING  BIRD  ATLAS 


Hawks  and  Eagles 


rocks;  on  an  old,  collapsed  magpie  nest;  and  on  top  of  a 
pile  of  tnmbleweed  (Bent  1937,  Palmer  1988a,  Reynolds 
1989).  Sharp-shins  sometimes  reoccupy  nest  sites  the  fol- 
lowing year,  usually  building  a  new  nest  or,  rarely,  building 
on  top  of  the  previous  year's  nest  (Reynolds  &.  Wight 
1978,  Reynolds  1983,  Palmer  1988a).  In  Oregon,  Sharp- 
shins  reoccupy  40%  of  nest  sites  the  following  year,  but 
none  thereafter;  they  build  new  nests  within  100  yards  of 
old  nests  (Reynolds  1983). 

Breeding  Sharp-shinned  Hawks  forage  in  a  wide  variety 
of  coniferous,  mixed,  or  deciduous  forests  and  woodlands 
(Reynolds  1989).  In  Oregon,  they  forage  primarily  in  the 
forest  canopy,  but  in  Alaska  they  also  forage  extensively  in 
the  ground-shrub  and  shrub-canopy  zones  (Reynolds 
1989).  Sharp-shinned  Hawks  are  experts  at  reckless  sneak 
attacks  on  unsuspecting  prey.  From  concealing  foliage, 
usually  well  up  in  the  forest  canopy,  diey  dash  out  to  seize 
small  birds  and  vanish  (Bent  1937,  Palmer  1988a);  or  diey 
drop  low  to  the  ground  from  perches  and  alternately  flap 
and  glide,  concealing  themselves  behind  vegetation  or 
landforms,  then  pounce  on  quarry  by  surprise.  Sharp- 
shins  do  not  hesitate  to  dash  fearlessly  through  dense 
tangles  of  trees  and  underbrush  in  pursuit  of  prey.  They 
also  pursue  prey  on  the  ground,  sometimes  jumping  or 
running  in  open  areas  or  through  weeds  and  bushes.  The 
male  captures  all  the  food  for  his  mate  and  offspring  until 
the  midnesding  phase,  when  the  female  resumes  hunting 
(Palmer  1988a).  Males  will  hunt  up  to  nine-tenths  of  a  mile 
from  the  nest  site.  Upon  capturing  prey,  they  begin  tearing 
and  plucking  at  the  base  of  the  skull.  Favored  plucking  sites 
(stumps,  logs,  or  horizontal  limbs)  in  Oregon  average  1 34 
feet  from  nest  trees  (range  69-1 71  ft.;  Reynolds  et  al.  1982, 
Reynolds  1983).  Prey  is  often  beheaded  before  delivery  to 
the  female  or  nesdings. 

The  Sharp-shinned  Hawk  diet  is  over  90%  small  birds, 
the  remainder  small  mammals,  reptiles,  amphibians,  and 
insects  (Palmer  1988a).  Snyder  and  Wiley  (1976)  reported 
that  93.1%  of  prey  items  (n  =  1343)  were  birds,  4.2% 
invertebrates,  2%  mammals,  and  0.6%  lower  vertebrates. 
Sharp-shins  take  birds  up  to  quail  size,  mosdy  sparrows, 
finches,  warblers,  thrushes,  vireos,  and  swallows.  They 
take  mammals  up  to  tree  squirrels  in  size,  mosdy  mice  and 
voles,  small  rabbits,  shrews,  and  bats.  Cold-blooded  prey 
include  frogs,  snakes,  lizards,  and  insects,  especially  grass- 
hoppers, dragonflies,  crickets,  beedes,  large  butterflies  and 
moths,  and  caterpillars.  During  the  breeding  season,  when 
males  forage  for  the  family,  mean  prey  size  for  three  sites 
in  Oregon  and  Utah  ranged  from  0.4  to  1  ounce  (Reynolds 
1989).  On  average,  Sharp-shins  tend  to  take  smaller  prey 
than   Cooper's    Hawks,    but   there   is   controversy   as   to 


whether  female  Sharp-shins  take  larger  prey  than  conspe- 
cific  males  (Balgooyen  1976,  references  in  Palmer  1988a). 

Marin  Breeding  Distribution 

The  few  sightings  of  Sharp-shinned  Hawks  during  the 
breeding  seasons  of  die  adas  period  were  primarily  from 
ridges  in  the  Kent  Lake  area  north  of  Mount  Tamalpais. 
The  only  confirmed  breeding  record  was  of  the  sighting  of 
two  fledglings  accompanied  by  adults  on  the  east  side  of 
Bolinas  Ridge  above  Kent  Lake  on  28  and  30  July  1982 
(GFMc,  DS).  Although  Sharp-shins  are  definitely  localized 
and  very  scarce  breeders  here,  the  true  status  of  the  species 
may  be  masked  by  its  retiring  habits  and  its  preference  for 
remote  areas  during  the  breeding  season. 

Historical  Trends/ Population  Threats 

Mailliard  (1900)  and  Stephens  and  Pringle  (1933)  consid- 
ered the  Sharp-shinned  Hawk  a  winter  resident  in  Marin 
County.  Grinnell  and  Miller  (1944)  reported  only  a  few 
breeding  records  for  the  San  Francisco  Bay  Area,  none  of 
which  were  from  Marin.  Although  the  species  was  scarce 
during  the  period  of  intensive  field  work  during  the  adas 
project,  confirmation  of  breeding  then  suggests  it  was 
overlooked  as  a  nesting  species  in  Marin  County  in  earlier 
times. 

Grinnell  and  Miller  (1944)  did  not  report  any  popula- 
tion declines  in  California.  Based  on  limited  circumstan- 
tial evidence,  Remsen  (1978)  felt  that  breeding  populations 
had  declined  gready  since  that  time,  resulting  in  placement 
of  die  species  on  the  state's  list  of  Bird  Species  of  Special 
Concern,  where  it  still  remains  (CDFG  1991b).  Popula- 
tions were  apparendy  reduced  early  in  the  century  by 
shooting,  particularly  in  the  East  (Palmer  1988a).  Sharp- 
shin  populations  declined  drastically  (mosdy  in  the  East) 
starting  in  the  1940s,  apparendy  from  pesticide  accumula- 
tion and  eggshell  thinning,  documented  in  the  West  (Sny- 
der et  al.  1973).  The  species  was  on  the  Audubon  Society's 
Blue  List  every  year  from  1972  to  1986  (Tate  1981,  1986; 
Tate  &.  Tate  1982).  Based  on  Christmas  Bird  Counts, 
continentwide  declines  leveled  off  in  the  mid-1960s  and 
swung  upward  by  die  late  1960s,  largely  from  increases  in 
California  (Brown  1973).  North  American  breeding  pop- 
ulations were  relatively  stable  from  1965  to  1979  (Robbins 
et  al.  1986).  Numbers  increased  in  California  from  1968 
to  1979,  but  the  trend  was  relatively  stable  when  the 
analysis  was  extended  to  1989  (USFWS  unpubl.  data). 
Currendy,  the  most  important  regional  threat  to  Sharp- 
shinned  Hawks  is  the  reduction  of  nesting  and  foraging 
habitat  from  logging  (Reynolds  1989). 


140 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


COOPER'S  HAWK  Accipiter  cooperii 


Occurs  year  round,  though  primarily  as  a 

^5^-^    N 

winter  resident  and  transient  from  Sep 

fSM^S^ 

^w?-^^ 

through  Apr;  numbers  swell  substantially 

during  fall  migration  from  Sep  through 

r^CVnK 

\2A^VA\^V 

mid-Nov. 

r~\^x 

^QrWTJ 

P 

A  rare,  local  breeder;  overall  breeding 

vs 

\A^>t\x' 

xSOV' 

population  very  small. 

Recorded  in  36  (16.3%)  of  221  blocks. 

v>S 

-y.. 

O    Possible        =      27   (75%) 

'*^%V\°3rO\ 

<Vo 

~q  V^f\o  Y^C     Y><£\- 

€    Probable       =        4  (11%) 

2^KVjCVf^v^\ 

viV 

'^\^air\%V^;A?J^r' 

i^V?0* 

•    Confirmed  =        5  (14%) 

V^X2> 

FSAR=1        OPI  =  36         CI  =  1.39 

Ecological  Requirements 

The  penetrating  red  eyes  and  the  harsh,  cackling  alarm 
calls  of  a  Cooper's  Hawk  defending  its  nest  site  are  not 
quickly  forgotten  by  the  observer  lucky  enough  to  stumble 
upon  such  forest  magic.  In  Marin  County,  most  Cooper's 
Hawks  breed  in  secluded  stands  of  closed-canopied  mixed 
evergreen  hardwoods,  usually  dominated  by  coast  live  oak, 
California  bay  laurel,  and  madrone  (see  records  below); 
rarely,  they  breed  here  in  alder-dominated  riparian  forest 
or  woodland.  Although  Grinnell  and  Miller  (1944) 
emphasized  the  importance  of  riparian-deciduous  habitat, 
Cooper's  Hawks  in  California  breed  primarily  in  live  oak 
woodlands  (mixed  evergreen  forests),  though  they  also 
inhabit  coniferous  forest  to  a  limited  degree  (Asay  1987). 
Most  California  nests  are  in  closed-canopied  stands  of  six 
or  more  trees  (rarely  in  isolated  trees)  with  a  subcanopy  of 
vertical  tree  trunks  and  large  branches  widi  few  small 
branches  or  leaves;  ground  cover  is  absent  or  consists  of 
short  grass  and/or  poison  oak  or  a  few  other  shrubs  (Asay 
1987,  n  =  52).  Dense  canopy  cover  (about  65%-95% 
closure)  is  a  consistent  vegetative  characteristic  of  Cooper's 
Hawk  nest  sites  throughout  their  range;  also,  understories 
at  nest  sites  are  often  relatively  open  (Palmer  1988a).  Marin 
County  nest  sites  resemble  the  structure  of  those  elsewhere 
in  California,  though  the  dominant  trees  and  saplings, 
shrubs,  and  ferns  in  the  sparse  understory/ground  cover 
differ  (see  records  below).  Most  California  nest  trees  (79%) 
are  in  flat  areas,  usually  bottomlands  between  hills,  and  the 
rest  (21%)  are  on  steep  hillsides  (Asay  1987).  The  flat  areas 
appear  most  favorable  for  growth  of  tall  live  oak  trees. 


Cooper's  Hawks  also  breed  in  coniferous  (typically 
second-growth)  or  mixed  forests  (Reynolds  1989).  In 
Oregon's  conifer  forests,  most  pairs  of  three  species  of 
Accipiter  nest  in  dense  stands  on  gende  to  moderate  slopes 
with  northerly  exposures  that  provide  screening  and  pro- 
tection from  predators  and  a  shady,  mild  environment 
(Reynolds  et  al.  1982,  Reynolds  1983).  Most  nest  sites 
there  are  also  near  quiet,  ephemeral  streams  or  springs. 
Cooper's  Hawks  probably  select  for  dense  forest  growth 
rather  than  for  particular  factors  (such  as  water)  that 
promote  it.  These  coexisting  species  use  habitats  with 
different  structures  at  the  nest  site  associated  with  the  age 
of  the  forest  stand  used.  Sharp-shinned  Hawks  use  25-  to 
60-year-old  even-aged  stands;  Cooper's  Hawks  use  30-  to 
80-yearold  even-aged  stands  with  somewhat  larger  and 
more  widely  spaced  trees  and  deeper  crowns;  and  Gos- 
hawks use  1 50+-year-old  mature  stands  ranging  from 
closed  canopies  with  few  shade-tolerant  understory  trees  to 
stands  with  more  open  canopies  with  many  understory 
trees.  Cooper's  Hawk  nest  sites  in  Oregon  have  an  average 
canopy  closure  of  69%  (range  15%-100%,  n  =  9),  many 
dead  limbs  below  the  live  crowns,  and  sparse  to  moderate 
ground  cover.  The  slope  gradient  at  nest  trees  there  aver- 
ages 1 7%  (range  0%-80%).  In  Oregon,  yearling  females 
nest  in  younger  successional  stages  than  older  females  do, 
or  in  stands  that  have  undergone  selective  overstory 
removal  (Moore  ck  Henny  in  Palmer  1988a). 

In  California's  evergreen  hardwood  forests/woodlands, 
Cooper's  Hawks  select  nest  trees  that  are  generally  some  of 
the  most  mature  trees  in  the  stand,  in  an  area  widi  the 


141 


/  lawks  and  Eagles 


MARIN  COUNTY  BRLTDING  BIRD  ATLAS 


Hawks  and  Eagles 


highest  canopy  cover  and  the  sparsest  ground  cover  (Asay 
1987).  Of  California  nests,  75  of  77  were  in  live  oaks 
(Quercus  agrifolia  and  Q.  wislizenii).  Cooper's  Hawks  here 
huild  nests  in  or  just  below  the  canopy  and,  depending  on 
die  growth  form  of  the  tree,  either  in  a  fork  of  the  main 
trunk  or  out  on  a  branch  away  from  the  tnink.  Cooper's 
Hawks  place  their  nests  from  three-quarters  to  four-fifths  of 
the  way  up  the  tree;  the  average  nest  height  of  48  California 
nests  is  33  feet  (range  19-46  ft.).  Estimated  heights  of  5 
Marin  County  nests  ranged  from  about  25  to  50  feet  above 
the  ground  (records  below).  In  Oregon's  conifer  forests, 
Cooper's  Hawks  place  their  nests  either  immediately  below 
the  crown  or  in  the  lower  crown  of  the  nest  tree;  nest 
height  of  33  nests  there  averaged  48  feet  (range  25-100  ft.) 
above  the  ground  (Reynolds  et  al.  1982).  Most  Cooper's 
Hawk  nests  there  are  placed  on  horizontal  limbs  against 
trunks;  and  a  few  are  placed  out  on  limbs  or  in  crotches  of 
double  trunks.  In  eastern  Oregon,  many  of  these  hawks 
nest  in  deformed  trees  infected  with  dwarf  misdetoe  and 
having  heavy  foliage,  "witches  brooms,"  or  double  trunks. 
Yearling  females  in  Oregon  use  misdetoe  as  a  nest  struc- 
ture significandy  less  often  (50%)  than  older  females  (70%) 
do  (Moore  ck  Henny  in  Palmer  1988a).  Throughout 
North  America,  average  nest  heights  range  from  26  to  50 
feet  above  the  ground  (Palmer  1 988a);  nests  may  be  as  low 
as  10  feet  or  perhaps,  exceptionally,  on  the  ground  (Bent 
1937).  Some  nests  are  built  on  squirrel,  crow,  or  woodrat 
nests,  or  on  rubble  in  the  fork  of  a  tree;  others  may  be 
incorporated  in  masses  of  misdetoe,  grapevines,  or  die 
abnormal,  densely  branched  growth  of  a  limb  (Bent  1937, 
Palmer  1988a). 

The  nest  is  a  broad,  shallow  platform  of  clean,  dry  sticks 
and  twigs,  lined  with  flakes  of  bark  added  throughout  egg 
laying  and  incubation.  Greenery,  usually  one  or  two  coni- 
fer sprays,  is  added  to  the  nest  intermittendy.  In  evergreen 
hardwood  habitat  in  California,  the  rate  of  nest  site 
reoccupancy  was  80%  (Asay  1987,  n  =  41).  Birds  reused 
the  previous  year's  nest  in  32%  (1 1  of  34)  of  the  nesting 
areas  occupied  in  consecutive  years;  half  of  all  nesting 
attempts  were  in  rebuilt  nests.  In  conifer  habitat  in  Ore- 
gon, Cooper's  Hawks  reoccupied  27%  of  nest  sites  in  the 
second  year  and  1 1%  in  the  third  year  (Reynolds  1983).  If 
they  reused  a  nest  site,  they  usually  built  a  new  nest;  a  few 
birds  irregularly  used  alternate  nest  sites.  In  another  Ore- 
gon study,  10  of  17  (59%)  nest  sites  were  reused  in  the 
following  year,  and  only  successfully  nesting  females  over 
two  years  old  returned  to  the  same  site  (Moore  ck  Henny 
in  Palmer  1988a). 

Cooper's  Hawks  forage  in  a  variety  of  cover  types— from 
openings  to  dense  forests— though  one  study  in  Utah 
showed  a  preference  for  foraging  in  dense  stands  of  small 
to  medium-sized  trees  (Reynolds  1983,  1989).  A  sugges- 
tion that  these  hawks  forage  mosdy  in  edge  situations  may 
be  an  artifact  of  the  ease  with  which  they  are  seen  in  open 

142 


settings.  On  the  odier  hand,  prey  is  usually  more  abundant 
in  edge  situations  than  deep  in  dense  forests.  In  Oregon, 
at  least,  die  Cooper's  Hawk  is  more  of  a  generalist  than  the 
Sharp-shinned  Hawk  and  captures  prey  in  the  ground- 
shrub,  shrub-canopy,  and  canopy  zones  (Reynolds  1989). 

Cooper's  Hawks  are  efficient  predators,  capable  of  very 
rapid  flight  over  short  distances.  Their  rounded  wings  and 
long  tails  give  them  great  maneuverability,  which  enables 
them  to  fly  dexterously  through  dense  brush  (Brown  ck 
Amadon  1968,  Palmer  1988a).  They  rely  on  concealment 
and  surprise  to  capture  quick  and  agile  prey.  Cooper's 
Hawks  often  hunt  from  a  perch  and  fly  down  with  a 
sudden  burst  of  speed  to  seize  unsuspecting  prey  (Brown 
ck  Amadon  1968,  Palmer  1988a).  Leaving  the  perch,  they 
often  fly  low,  taking  advantage  of  die  contours  of  the  land 
or  vegetation  for  cover,  and  may  fly  higher  after  flying 
quarry.  In  a  typical  strike,  they  stop  flapping  12  to  15  feet 
from  the  prey  and  begin  swinging  the  feet  forward  at  about 
5  feet  (Palmer  1988a).  Just  before  impact,  they  set  their 
wings  in  a  braking  movement,  dirust  the  pelvis  forward, 
and  rapidly  extend  the  feet  chest-high,  seizing  the  prey  with 
both  or,  occasionally,  only  one  foot.  Cooper's  Hawks 
pursue  and  catch  many  birds  that  fly  by  the  trees  in  which 
they  are  perched.  On  occasion,  they  also  fly  through 
swarms  of  bats  leaving  a  cave,  singling  out  one  and  follow- 
ing its  every  twist  and  turn.  Coopers  sometimes  hunt  from 
higher  flight,  stooping  falconlike  at  pigeons  in  the  open. 
They  also  pursue  prey  into  bushes,  stalk  or  pursue  it  on 
the  ground  (by  walking,  hopping,  or  half  running  and  half 
flying),  and  even  attempt  to  flush  it  from  cover.  Cooper's 
Hawks  use  their  hearing  to  stalk  quail.  They  are  known  to 
down  prey  in  water  and  hold  it  underwater  until  it  ceases 
to  move. 

Males  feed  their  mates  occasionally  before  egg  laying 
and  are  their  sole  providers  during  incubation  (Palmer 
1988a);  females  rarely  hunt  during  the  first  three  weeks  of 
the  nesding  period  but  do  hunt  increasingly  thereafter 
(Kennedy  ck  Johnson  1986).  The  amount  of  time  and  the 
time  of  day  the  male  spends  hunting  may  depend  on  the 
activity  patterns  of  the  prey,  and  especially  the  demands  of 
the  young,  which  increase  to  the  point  requiring  hunting 
throughout  the  day.  Males  forage  out  to  one  and  one-half 
to  two  miles  or  more  from  the  nest  (Reynolds  1983,  Palmer 
1988a).  The  male  usually  eats  the  head  and  viscera  and 
does  much  of  the  plucking  at  the  kill  site  (Palmer  1988a). 
He  brings  the  prey  to  stumps,  logs,  or  large  horizontal 
limbs  used  as  plucking  sites,  where  he  continues  to  pluck 
and  partially  dismember  the  prey.  In  Oregon,  the  most 
frequently  used  plucking  site  averaged  177  feet  from  the 
nest  tree  (range  138-282  ft.;  Reynolds  et  al.  1982).  When 
the  young  are  small,  the  prey  is  well  plucked,  headless,  and 
eviscerated,  but  by  the  fourth  or  fifth  week,  the  male  brings 
prey  only  three-quarters  plucked  and  whole  (Palmer 
1988a).  The  female  flies  out  to  receive  the  prey  at  the 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


plucking  site  and  feeds  herself  there  or  at  the  nest.  The 
female  initially  flies  out  to  the  plucking  site  to  retrieve  food 
for  the  young,  but  later,  if  she  is  absent,  the  male  delivers 
prey  to  the  nest.  If  the  male  brings  more  food  than  is 
needed  it  is  stored  for  future  use  on  an  old  nest  nearby 
(Brown  6k  Amadon  1968).  Dead  chicks  may  be  eaten,  but 
probably  larger  young  do  not  attack  smaller  siblings  unless 
they  are  very  hungry  from  a  shortage  of  prey  (Palmer 
1988a). 

The  Cooper's  Hawk  diet  is  about  70.4%  birds  (mosdy 
medium-sized,  such  as  jays,  thrushes,  and  flickers),  17.9% 
small  mammals,  8.9%  reptiles  (mosdy)  and  amphibians, 
and  2.1%  insects  (Jones  m  Palmer  1988a).  In  the  East, 
birds  account  for  over  80%  of  the  diet,  but  in  the  West, 
birds  comprise  only  about  47%-74%  of  the  diet.  Cooper's 
Hawks  capture  larger  birds  than  Sharp-shinned  Hawks  do, 
although  mean  weight  of  birds  in  die  Cooper's  Hawk  diet 
is  highly  variable  among  studies— from  1.5  ounces  in  the 
eastern  U.S.  to  4-3  ounces  in  eastern  Oregon  (Reynolds  & 
Meslow  1984,  Reynolds  1989).  Cooper's  Hawks  take  birds 
as  large  as  pheasants,  grouse,  small  owls,  American  Kes- 
trels, Merlins,  and  crows,  and  as  small  as  nesding  gold- 
finches. Important  mammal  prey  are  chipmunks,  young 
hares,  cottontails,  tree  and  ground  squirrels,  woodrats  (in 
Calif.;  P.H.  Bloom  pers.  comm.),  voles,  deer  mice,  and 
shrews.  Mean  weight  of  mammal  prey  at  three  sites  in 
Oregon  and  Utah  ranged  from  5.2  to  10.4  ounces  (Reyn- 
olds 1989).  Some  Coopers  will  specialize  in  certain  types 
of  prey.  For  example,  in  the  southern  Sierra  foothills,  a 
breeding  pair  brought  to  the  nest  63.4%  lizards,  29.3% 
birds,  and  7.4%  mammals  (Fitch  et  al.  1946,  n  =  41). 
There  is  controversy  as  to  whether  females  do  (e.g.,  Storer 
1966)  or  do  not  (e.g.,  Kennedy  6k  Johnson  1986)  take 
larger  prey  than  males  do. 

Marin  Breeding  Distribution 

During  the  adas  period,  Cooper's  Hawks  were  scattered 
widely  throughout  the  forested  regions  of  Marin  County  in 
the  breeding  season.  The  status  as  indicated  by  the  atlas 
map  is  probably  deceptive,  though,  considering  that 
Cooper's  Hawks  are  very  retiring  while  breeding  and  prefer 
areas  away  from  human  presence.  Observers  equipped 
with  a  knowledge  of  the  species'  habits  and  a  willingness 
to  get  off  the  trail  in  hilly  terrain  would  likely  be  able  to 
discover  many  more  breeding  sites.  For  example,  one  atlas 
observer  stumbled  upon  four  nests  in  one  breeding  sea- 
son—at three  of  them  the  hawks  were  seen  only  at  the 
immediate  nest  site.  Contrary  to  popular  belief,  the 
Cooper's  Hawk  may  be  a  more  numerous  breeder  in 
Marin  and  other  coastal  counties  than  the  Red-shouldered 
Hawk.  The  latter  species  is  much  more  easily  detectable 
than  the  Cooper's  Hawk  because  it  resides  primarily  in 


lowland  areas,  where  observers  are  concentrated,  and 
because  it  is  very  vocal  and  visible  when  displaying  or 
hunting. 

Representative  breeding  records  are  listed  with  fairly 
detailed  nest  site  descriptions  because  of  the  paucity  of 
such  information  for  California  beyond  those  found  in 
Asay  (1987):  (1)  Bolinas  Ridge  near  Bolinas  Lagoon, 
6/2/81  (ARo  et  al.),  NE  about  25  ft.  up  in  coast  live  oak 
in  mixed  forest  of  coast  live  oak,  bay  laurel,  and  coast 
redwood  with  a  brushy  understory  on  the  edge  of  a 
redwood-dominated  canyon  slope;  (2)  N  end  of  Inverness 
Ridge,  4/29/82  (DS),  NE  about  50  ft.  up  in  bishop  pine 
in  a  mixed  coast  live  oak,  bishop  pine,  and  bay  laurel  forest 
with  a  moderate  understory  of  huckleberry,  poison  oak, 
and  hazelnut;  (3)  on  north-facing  slope  off  Marshall- 
Petaluma  Rd.,  6/21/82  (DS),  NY  about  45  ft.  up  in  a  bay 
laurel  in  a  forest  almost  exclusively  of  that  species  with 
sparse  ground  cover  mosdy  of  sword  ferns;  (4)  Chileno 
Valley,  7/2/82  (DS),  NY  about  45  ft.  up  in  a  California 
buckeye,  in  a  buckeye,  bay  laurel,  and  coast  live  oak  forest 
with  sparse  understory/ground  cover;  and  (5)  canyon  off 
Big  Rock  Ridge,  7/4/82  (DS),  NY  about  45  ft.  up  in  a  bay 
laurel  in  a  mixed  forest  of  about  equal  proportions  of  bay 
laurel,  coast  live  oak,  and  madrone  with  a  sparse  under- 
story of  sword  ferns  and  hazelnut. 

Historical  Trends/ Population  Threats 

For  Marin  County,  Mailliard  (1900)  reported  the  Cooper's 
Hawk  was  a  "common  winter  resident";  Grinnell  and 
Wythe  (1927)  listed  Inverness  as  a  station  of  summer 
residence;  and  Stephens  and  Pringle  (1933)  considered  the 
Cooper's  Hawk  a  permanent  resident,  "fairly  common, 
more  numerous  in  winter."  Prior  to  the  adas  work,  sum- 
mer reports  were  few  for  the  county,  and  the  only  breeding 
record  was  of  a  nest  in  an  alder  grove  at  Muddy  Hollow, 
near  Limantour  Estero  in  die  early  1970s  (JH  fide  GWP). 
Prior  data  are  not  sufficient  to  compare  with  the  status  in 
Marin  today.  Since  Grinnell  and  Miller's  (1944)  mono- 
graph on  California's  avifauna,  the  population  of  Cooper's 
Hawks  breeding  in  the  state  has  declined  to  an  unknown 
degree,  resulting  in  its  listing  as  a  Bird  Species  of  Special 
Concern  (Remsen  1978,  CDFG  1991b). 

Based  on  migration  counts,  Christmas  Bird  Counts, 
and  incidental  reports,  Cooper's  Hawk  populations 
declined  continentwide,  but  mosdy  in  the  East,  from  the 
1920s  to  1960s  (Palmer  1988a).  The  Cooper's  Hawk  was 
on  the  Audubon  Society's  Blue  List  from  1972  to  1981 
and  in  1986,  and  on  their  list  of  Species  of  Special 
Concern  in  1982  (Tate  1981,  1986;  Tate  6k  Tate  1982). 
From  1965  to  1979,  Nordi  American  breeding  popula- 
tions were  low  but  relatively  stable  (Robbins  et  al.  1986); 
die  California  Foothills  had  one  of  the  highest  densities. 

143 


Hawks  and  Eagles 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hawks  and  Eagles 


The  California  population  was  relatively  stable  from  1968 
to  1989,  though  data  suggested  a  slight  decrease  from  1980 
to  1989  (USFWS  unpubl.  analyses). 

Early  declines  may  have  been  from  extensive  shooting, 
but  declines  since  the  late  1940s  appear  to  be  caused  by 
DDT  accumulation  (Henny  ck  Wight  1972,  Snyder  et  al. 
1973).  Populations  in  the  East  declined  much  more  dian 
in  the  West.  Eastern  Cooper's  Hawks  carried  higher  con- 
centrations of  DDE  than  those  in  the  West  did,  apparendy 
because  of  the  greater  reliance  of  the  eastern  birds  on  avian 


prey  (see  above).  California  birds  have  been  somewhat 
contaminated  with  pesticides;  the  decline  of  the  California 
breeding  population  probably  was  caused  mosdy  by  habi- 
tat destruction  (Remsen  1978).  Today,  nesting  and  forag- 
ing habitat  loss  from  logging  remains  die  main  threat  to 
breeding  populations  in  the  U.S.,  though  indirect  human 
disturbance  at  nest  sites  and  the  taking  of  nesdings  by 
falconers  pose  additional  threats  (Remsen  1978).  Pesticide 
accumulation,  loss  of  wintering  habitat,  and  shooting  still 
pose  threats  in  Mexico  (Reynolds  1 989). 


RED-SHOULDERED  HAWK   Buteo  lineatus 


A  year-round  resident;  numbers  swell 

slighdy  during  fall  migration  from  Sep 

AdX*rvA 

^^O^^^^qP^^ 

through  mid-Nov. 

\\^?^CX^\^\j^O?>^- 

An  uncommon,  local  breeder;  overall 

Vfl 

breeding  population  very  small. 

\  Jf\    J*r\   Jt-"\  £>  V^AC»  \^\  •  i><T  o  J 

Recorded  in  56  (25.3%)  of  221  blocks. 

3r\  JVA  Jr\  j^^o^>\k\Z^0\>^\ 

^^A^\^\\^-V\  J^c\  J<\  <l\\.  J\ 

v~Cv 

^S*>£^\^\}>^^ 

O    Possible        =      29  (52%) 

"x    \^\     Jr\'*l^  \^\     \^\      \^\     \^^~-y- 

©    Probable                 9   (16%) 
•    Confirmed  =       18   (32%) 

-;  \3vyV  iA^\^-V\^V\  J-*<La  J&$\. \\.  J>A 

-i^/V^^A 11  V^\o\><V^V^\^lL--V^V-A^V. 

FSAR  =  2        OPI  =  112        CI  =  1.80 

rj^^Y^nf^               -<T       \^\       \-^-\       \>*\      \^\       V^A 

^& 

-V/                                              ^C.V-^A*T^S#  \y\       \i^\ 

i                         ^^^--x  v^s^^^zo  \^\   V- 

J*3^                                                                                      \Jtf                   ^^~^rX^\ 

Ecological  Requirements 

This  resplendent  woodland  hawk  inhabits  Marin 
County's  well-timbered  lowland  drainages  and,  secondar- 
ily, adjacent  upland  slopes.  Prime  areas  include  stretches 
of  dense  riparian  forest  or  woodland,  oak-dominated 
mixed  evergreen  forest,  oak  woodland,  or  eucalyptus 
groves,  adjacent  to  or  interspersed  with  openings  clothed 
with  soft  and  luxuriant  but  relatively  low  vegetation  of 
moist  grasslands,  meadows,  swales,  or  marshland.  Forests 
or  woodlands  provide  nest  sites,  shelter,  and  some  foraging 
opportunities.  Although  nesting  habitat  is  usually  near 
open  water,  this  is  not  essential  as  long  as  moist  upland 
openings  are  available  for  foraging.  The  haunts  of  Red- 
shouldered  Hawks  here  contrast  with  die  drier,  more  open 
upland  habitats  frequented  by  Red-tailed  Hawks  (see 
account). 


Red-shouldered  Hawks  place  their  nests  in  large  trees  in 
stands  of  mature  timber,  often  near  openings;  there  may 
or  may  not  be  a  well-developed  understory  at  the  nest  site 
(D.  Shuford  pers.  obs.).  Red-shoulders  generally  situate 
nests  more  than  halfway  up  the  tree,  below  the  canopy 
crown;  Red-tails  generally  build  much  higher  (Palmer 
1988a).  The  average  height  of  274  widespread  nest  records 
is  47  feet,  with  a  range  of  8  to  110  feet  (Apfelbaum  6k 
Seebach  in  Palmer  1988a);  exceptional  nests  have  been 
found  on  the  ground  (Palmer  1988a).  Nests  are  generally 
placed  in  a  main  fork  where  the  trunk  divides  into  three  or 
more  branches  (Bent  1937).  They  are  seldom  built  on  a 
horizontal  branch  against  the  trunk  and  very  rarely  in  the 
fork  of  a  branch.  The  nest  is  a  substantial,  well-built 
structure  fdling  die  crotch  to  a  considerable  depth.  Red- 
shoulder  nests  are  smaller  than  Red-tail  nests  and  contain 


144 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


more  soft  material  than  those  of  accipiters.  Red-shoulders 
sometimes  use  nests  built  by  Cooper's  Hawks  or  nests 
previously  occupied  by  owls;  they  also  will  build  over  old 
squirrel  nests.  Red-shoulders  build  the  nest  from  sticks  or 
twigs  mixed  with  strips  of  bark,  dry  leaves,  lichens,  mosses, 
and  twigs  of  evergreens  with  needles  attached.  They  line  it 
with  fine  shreds  of  bark,  soft  mosses  or  lichens,  fresh 
conifer  sprays,  and,  as  incubation  progresses,  downy  feath- 
ers. Decorative  greenery  or  other  "symbolic"  materials 
added  to  the  nest  (months  before  egg  laying  through  the 
nesding  stage)  may  function  to  indicate  active  attachment 
to  a  site  (Palmer  1988a).  Later,  eggs  and  young  would  seem 
adequate  notice  of  occupation.  An  apparent  increase  in  the 
addition  of  greenery  through  the  nesding  phase  (Portnoy 
6k  Dodge  1979)  may  support  Bent's  (1937)  contention 
that  this  material  may  be  for  sanitary  rather  than  ornamen- 
tal purposes.  Greenery  or  its  substitutes  may  include  coni- 
fer sprays,  green  leaves,  whole  plants,  blades  of  cornstalks, 
dried  tent  caterpillar  webs,  ears  of  corn  or  corncobs,  tissue 
paper,  and  nests  of  various  passerines  (Bent  1937,  Palmer 
1988a).  Red-shoulders  tend  to  build  new  nests  each  year, 
but  occasionally  they  use  them  for  two  or  three  successive 
years  or,  more  often,  return  to  the  old,  alternative  nest  after 
a  lapse  of  two  or  more  years  (Bent  1937). 

The  Red-shouldered  Hawk  sometimes  hunts  by  gliding 
just  over  the  tops  of  the  forest,  through  the  woods,  or  flying 
low  over  marshes  or  meadows  (Bent  1937).  It  can  slip 
upon  prey  at  close  range  in  trees  or  pounce  on  smaller, 
slower  prey  on  the  ground  (Bent  1937),  relying  on  surprise 
more  than  speed  (Palmer  1988a).  Red-shoulders  are  most 
frequendy  observed  waiting  patiendy  on  relatively  low 
perches  on  trees,  utility  poles,  wires,  or  fence  posts,  from 
which  they  drop  or  swoop  down  on  prey.  In  California,  in 
more  than  6000  hours  of  observation  including  over  250 
prey  capture  attempts,  Red-shoulders  always  initiated 
attacks  from  a  perched  position  (P.H.  Bloom  pers.  comm.). 
This  hawk's  hearing  is  extremely  keen,  and  it  may  rely  on 
hearing  as  much  as  sight  for  hunting  (Dixon  in  Bent  1937 
and  Palmer  1988a). 

As  the  moist  habitats  frequented  and  the  hunting  tech- 
niques used  suggest,  the  Red-shouldered  Hawk  concen- 
trates on  cold-blooded  vertebrates  and,  in  some  places, 
seasonally,  on  small  mammals  (Palmer  1988a).  Snyder  and 
Wiley  (1 976)  reported  that  prey  items  (n  =  141 3)  consisted 
of  55.6%  invertebrates,  21.2%  lower  vertebrates,  20.2% 
mammals,  and  2.8%  birds.  In  southern  California,  small 
rodents  are  the  principal  prey  (P.H.  Bloom  pers.  comm.). 
Dietary  items  include  snakes,  toads,  frogs,  or  other 
amphibians  up  to  bullfrog  size;  mammals  mostly  from 
shrew  (more  than  voles)  to  chipmunk  size;  small  lizards 
and  young  turtles;  a  few  small  to  medium-sized  birds;  a  few 
small  fish;  a  few  crayfish;  considerable  numbers  of  insects, 
usually  cricket  and  large-grasshopper  size;  and  the  odd 
centipede,  earthworm,  or  snail.  Red-shoulders  are  able  to 


transport,  sometimes  drag,  or  eat  in  place,  surprisingly 
heavy  prey,  such  as  small  herons,  full-grown  squirrels, 
ducks,  opossums,  and  muskrats.  They  also  occasionally  eat 
carrion. 

Marin  Breeding  Distribution 

During  the  adas  period,  Marin  County's  breeding  Red- 
shouldered  Hawks  were  concentrated  in  two  general  areas: 
in  the  San  Andreas  fault  zone,  primarily  of  the  Olema 
Valley;  and,  more  extensively,  in  the  lowlands  around 
Novato.  The  paucity  of  Red-shoulders  in  the  lowlands  of 
the  northwestern  sector  of  the  county  may  have  reflected 
the  lack  of  appropriate  moist  grassland  and  meadow  edges 
to  riparian  areas  there  caused  by  heavy  grazing.  Represen- 
tative nesting  sites  were  in  a  Douglas  fir  in  Inverness  (NY 
May-early  Jun  1982  -AckJWe);  in  Olema  Marsh  (NB 
2/25/81  — DS);  in  an  alder  grove  at  Stinson  Gulch  (NE 
4/26/82  — DS);  in  a  eucalyptus  along  Novato  Creek  in 
O'Hare  Park,  Novato  (NE  4/26/82  -ScC,  DS);  and  in  a 
valley  oak  along  San  Jose  Creek,  E  of  Hwy.  101,  Novato 
(NB-NY  2/19-6/7/78  -MGN). 

Historical  Trends/Population  Threats 

Mailliard  (1900)  considered  the  "Red-bellied  Hawk"  an 
"occasional  winter  visitant"  in  Marin  County,  and  Ste- 
phens &  Pringle  (1933)  considered  it  a  "rather  rare" 
resident  here.  Compared  with  the  current  status,  this 
would  suggest  an  increase  in  numbers  historically,  whereas 
instead  numbers  have  probably  decreased.  In  earlier  times, 
the  status  of  this  species  was  apparendy  underestimated 
because  of  the  limited  ornithological  attention  focused  on 
the  Point  Reyes  area  or  on  the  northern  sectors  of  the 
county,  including  Novato,  areas  where  the  Red-shouldered 
Hawk  is  most  numerous  today.  Although  information  is 
lacking,  Red-shoulders  have  likely  been  displaced  in  recent 
times  from  former  breeding  areas  in  the  moist  lowlands  of 
the  now  heavily  developed  Highway  101  corridor  in  east- 
ern Marin. 

Grinnell  and  Miller  (1944)  reported  that  the  species  was 
gready  reduced  throughout  California  and  even  extirpated 
locally  "due  to  progressive  human  occupancy  of  the  land." 
In  reviewing  the  recent  status  in  California,  Wilbur 
(1973a)  concluded  that  despite  local  displacement,  extirpa- 
tion had  not  occurred  in  any  major  segment  of  the  original 
range.  A  major  population  decline  in  the  Central  Valley 
(Wilbur  1973a,  Gaines  1974)  has  reversed  itself  recendy 
(S.A.  Laymon  pers.  comm.).  Suggestions  of  increases  in 
some  coastal  counties  (Wilbur  1973a)  may  reflect 
rebounds  from  former  declines  or,  alternatively,  an  artifact 
of  increased  observer  effort.  In  southern  California,  these 
hawks  are  reoccupying  parts  of  the  Los  Angeles  basin 
where  mature  trees  now  provide  nesting  habitat  in  certain 
residential  areas,  parks,  and  cemeteries;  they  have  also 
expanded  into  date  palm  plantations  in  the  Mohave  Desert 

145 


Hawks  and  Eagles 


MARIN  COUNTY  BRFFDING  BIRD  ATLAS 


Hawks  and  Eagles 


(Harlow  6k  Bloom  1989).  On  the  whole,  Red-shouldered 
Hawk  numbers  increased  in  California  from  1968  to  1989 
but  were  relatively  stable  from  1980  to  1989  (USFWS 
unpubl.  analyses).  Caution  is  still  warranted,  though,  as 
the  ongoing  expansion  of  the  human  population  in  low- 
land corridors  puts  additional  pressure  on  this  species 
(despite  its  ability  to  adapt  to  some  residential  situations. 

From  the  late  1950s  to  the  early  1970s,  eggshell  thick- 
ness of  Red-shouldered  Hawk  populations  in  southern 
California  was  reduced  by  3%-14%  from  the  accumula- 


tion of  pesticide  residues  (Anderson  6k  Hickey  1972, 
Wiley  1975).  Reproductive  success  in  southern  California 
between  1972  and  1987  appeared  to  be  normal,  and  the 
eggshell  thinning  is  currcndy  being  investigated  (Harlow 
6k  Bloom  1989).  The  loss  of  riparian  and  oak  woodland 
nesting  habitat  is  die  most  serious  factor  currendy  affecting 
the  species  in  California. 


RED-TAILED  HAWK    Buteo  jamaicensis 


A  year-round  resident;  numbers  swell 

JO 

\^*\  0  j£^\  *-J>P\  0~>\                       _i^_X«  p-<\^r-^ 

Sep  through  Feb. 
A  fairly  common,  nearly  ubiquitous 

'  V^A * JrlA  oV-^A  °Je^Y  *\  r.  \  q  A^CA  °  A^A  •JpV^     - 

breeder;  overall  breeding  population 

\^\  •A^\  °V\o>;^\ovAoVA  ©A^a  •  V-^T  \ 
^\  •  V<5\  •  V^A  o  v-'A  °  Wto  A>A  ©  Y>-A~  o\>-V  °  ^A 

V^k5oo\  #JV<\  °\<\  °A<A  .•3r^*3r\  ° Jr^A  *^ 
\  ^^A   nj^A  o  \^\  •  jr-^A  *  XJaA  o  \^\  o  V-^\     \-^ ' 

large. 
Recorded  in  213  (96.4%)  of  221 

Vso  Ji<?s\  QJirA  •  \^\  o  ,V^\  o  \^\  o  \>\  ©  Y^-A 
VV^-^H^V^A®  \^oWVe\W\o  \A-A  © Y>A; •  \ 

blocks. 

Va  ©  J<<vvP  V"\  ®  A^AeA'V^A  ©  V^  °  Y^A  ©>^AfT^>^ 

X  VV^XonA "tA  oV^-A  ©i&S^A^vvQAp^TDAf-^©  \>^  > 

Vt\  °  Y-^^Ask^x  ©  VTovlfl  V-^A  ©  A^x  »-V^\  ©  r^ 
X  Vj^X  '•;A>aj;v^'Oy>Ao  V--A  ©>>A»  V^x©  V<7 
\-+£v-»  XPa  oA^A© \x\o  Wfo  A>r\  ■©  V-'A  •  \>r(  " 

O    Possible        =     111    (52%) 

^^ 

API^svA'kaPVA     k\o  Y>A'©  X^A-o LA 
\K\  -,©  V--A  •  A^\  '♦  \c--AA©  >^A  ©  V--^\  ©  jaA  o  V-A^A> 

.  r- 

©    Probable       =       56   (26%) 

U^v%>-^\*  V^A  o  XS>Ao  V^dpjjVM-o  wr\  ov^v 

-4"i  VU4-A>»  X  ^--T  n  \^-"A  ».\  ^*T  riSV  ^--\  n  V rVTS  X  ^V  A  X — ~v 

•    Confirmed   =       46   (22%) 

JP<\(OStk^\o  Vw\°  \^.o\^^=b\^%~6\>\o  V>A«^ 

Io^jksjb^ — X°  VA»vA°  X^A©  a^A-®  V-"\  •  V< 
Q^x0^^      ^<o  V>A ©  wo  \£-*\  © -vc\  •  V*C2\ 
■<x<y\^                 ^-<r  o  V-^A  o  v-'A  ®  A-^A  o^A^x^L 

^?& 

FSAR  =3        OPI  =  639       CI  =  1 .70 

IJ^>                                                                \*/               ^^*^\^ 

Ecological  Requirements 

The  Red-tailed  Hawk  is  a  bird  of  myth,  song,  and  legend, 
but  even  more  a  part  of  everyday  reality  as  it  soars  gracefully 
overhead  on  outstretched  wings.  Even  our  jays,  for 
unknown  reasons,  pay  homage  to  the  Red-tail  by  their 
imperfect  screeching  vocal  imitations.  In  Marin  County 
and  elsewhere,  Red-tails  are  primarily  birds  of  forest  or 
woodland  edges.  Here  they  hunt  mosdy  in  open,  relatively 
dry  upland  grasslands  that  host  suitable  foraging  perches, 
which  may  be  exposed  limbs  of  isolated  trees,  trees  in 
clumps,  woodlots,  edges  of  woodland  or  forest,  utility 
poles,  or  large  rock  outcrops.  Foraging  perches  are  usually 
scattered  throughout  the  territory,  though  certain  ones  are 
favored  (Palmer  1988b).  Nest  site  requirements  are  iso- 
lation from  disturbance,  a  commanding  view,  and  un- 
obstructed access.  Red-tails  typically  nest  high  in  the  open 
crown  of  a  tree  taller  than  those  surrounding  it  and 
generally  within  view  of  several  perch  sites.  Chosen  trees 

146 


are  often  well  up  a  slope  or  on  a  ridge  or  hilltop,  in  a  clump 
or  grove  of  trees,  in  a  woodlot,  or,  occasionally,  in  an 
extensive  forest.  Tree  nests  are  usually  situated  at  the 
junction  of  large  limbs  with  the  trunk  or  in  crotches 
formed  by  two  or  more  large  limbs  (Bent  1937).  Red-tails 
also  nest  on  the  crossbeams  of  utility  poles.  Although 
preferring  lofty  views,  Red-tails  select  varying  nest  sites,  and 
in  the  West,  nest  heights  range  from  a  few  feet  (in  desert 
habitats)  to  120  teet  (Bent  1937).  The  average  height  of  22 
nests  in  sycamores  in  San  Diego  County  was  55  feet, 
ranging  from  43  to  75  feet  (Dixon  in  Bent  1937);  this  is 
probably  fairly  typical  of  most  of  die  wooded  sections  of 
California.  Red-tails  use  a  wide  variety  of  trees  for  nesting. 
In  Marin  County,  they  appear  to  prefer  eucalyptus,  particu- 
larly in  open  ranchlands,  and  coast  live  oaks.  Red-tails  also 
use  cliff  ledges  for  nest  sites,  particularly  in  arid  areas  where 
trees  are  scarce.  Red-tails  sometimes  nest  in  unused  aeries 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


of  Golden  Eagles;  in  nests  of  ravens,  crows,  and  other 
species  of  buteos;  and  in  nests  previously  used  by  owls;  or 
they  will  build  on  the  platforms  of  old  squirrel  nests  (Bent 
1937,  Palmer  1988b).  They  may  build  a  nest  each  year  for 
at  least  several  years,  reuse  a  nest  during  successive  years, 
or  leave  a  nest  vacant  for  a  year  or  more  and  then  reuse  it 
(Palmer  1988b).  The  nest  is  a  large,  bulky  affair  made  of 
sticks  and  twigs,  lined  with  items  such  as  strips  of  bark, 
small  twigs,  and  lichens.  For  a  period  of  weeks,  before 
laying  to  late  incubation,  Red-tails  add  greenery  or  "deco- 
ration" to  the  nest  in  the  form  of  conifer  sprays,  deciduous 
twigs  and  leaves,  corncobs,  cornhusks,  cornstalks,  willow 
and  aspen  catkins,  a  variety  of  other  plant  material,  various 
rubbish,  and  even  oriole  nests!  It  is  not  always  clear  what 
is  "decoration"  and  what  is  nest  lining.  The  addition  of 
decorative  material  appears  to  be  a  behavioral  derivation  of 
prey  capture  and  delivery  that  serves  to  indicate  active 
attachment  to  a  site  (Palmer  1 988b). 

As  might  be  expected  for  a  numerous  and  widespread 
species,  Red-tails  are  versatile,  opportunistic  hunters 
(Palmer  1988b).  Most  frequendy  they  hunt  from  an  erect 
or  forward-leaning  stance,  high  on  a  perch,  waiting  for  prey 
to  reveal  itself.  For  close  prey,  Red-tails  glide  downward  at 
an  angle  with  few  wingbeats;  for  more  distant  prey  they 
approach  with  a  few  rapid  wingbeats  alternating  with 
glides.  Watching  for  movements  of  the  intended  prey,  on 
the  final  gliding  approach  at  about  a  ten-foot  distance,  they 
extend  the  legs  forward  and  spread  the  toes.  The  strike  is 
usually  made  with  one  foot  farther  forward.  A  number  of 
aerial  foraging  tactics  are  also  used.  Generally  at  an  altitude 
under  200  feet,  Red-tails  will  flap  and  glide,  quartering  over 
terrain  to  catch  prey  in  the  open;  they  may  dodge  among 
trees,  brush,  or  rock  outcrops,  remaining  concealed  until 
coming  upon  their  prey  at  close  range.  Occasionally,  they 
also  maneuver  through  thick  stands  of  trees,  accipiterlike, 
usually  striking  prey  on  or  near  the  ground.  Red-tails  also 
swoop  down  from  hovering  flight  or  from  an  immobile 
position  while  facing  into  the  wind  on  set  wings  (Dunne 
et  al.  1988).  When  streams  of  bats  are  departing  from 
caves,  Red-tails  sometimes  stoop  downward  on  diem  with 
half-closed  wings  or  fly  parallel  and  veer  sharply  toward 
them  (Palmer  1988b).  Red-tails  may  actually  run  on  the 
ground  when  attacking  (especially  when  the  prey  is  large), 
and  bound  from  one  to  another  in  pursuit  of  grasshop- 
pers, crickets,  or  other  small,  relatively  slow  prey.  Two 
Red-tails,  presumably  paired,  sometimes  hunt  coopera- 
tively with  one  on  each  side  of  a  tree  attempting  to  catch 
tree  squirrels.  Red-tails  will  also  pirate  from  other  hawks, 
such  as  Northern  Harriers,  and  will  eat  fresh  carrion. 
Upon  capture,  they  carry  small  prey  to  a  feeding  perch, 
which  is  lower  than  a  hunting  perch.  Voles  are  swallowed 
whole;  larger  mammals  may  be  beheaded  and  the  fur 
partially  discarded;  small  birds  are  beheaded  and  plucked. 
Heavy  prey,  which  may  struggle  and  crawl  into  cover,  may 


be  dragged  a  short  distance  to  a  suitable  spot,  where  it  is 
plucked  and  fed  on;  the  remains  may  be  carried  to  an 
elevated  perch. 

The  bulk  of  the  Red-tail  diet,  up  to  80%  in  some  studies, 
is  mammals  (Palmer  1988b).  Birds  make  up  much  of  the 
remainder,  but  the  menu  also  includes  snakes,  lizards, 
frogs  and  toads,  salamanders,  fish  (mosdy  dead),  turtles, 
crayfish,  various  insects,  centipedes,  spiders,  and  some 
carrion.  Snyder  and  Wiley  (1976)  reported  that  prey  items 
(n  =  2224)  in  the  North  American  diet  consisted  of  50.5% 
mammals,  36.8%  invertebrates,  8.5%  birds,  and  4-2% 
lower  vertebrates.  The  diet  of  Red-tails  in  the  Sierra  Nevada 
foothills  (excluding  arthropods  probably  taken  acciden- 
tally, n  =  507)  is  73.7%  mammals  (mostly  small  to 
medium-sized  ones,  such  as  ground  squirrels,  pocket 
gophers,  and  rabbits),  21 .6%  snakes  and  lizards,  and  4-7% 
birds  (Fitch  et  al.  1946,  n  =  4l54).  Some  Red-tails  there 
specialize  on  larger  prey  dian  odier  individuals  do. 

Marin  Breeding  Distribution 

During  the  atlas  period,  the  Red-tailed  Hawk  was  the  most 
widespread  of  all  of  Marin  County's  breeding  diurnal 
raptors  and  one  of  our  most  widespread  breeding  birds 
overall.  Red-tails  appeared  to  be  most  numerous  as  breed- 
ers in  the  central  and  northern  sections  of  the  county, 
where  lowland  valleys  and  rolling  hills  are  dominated  by 
grassland  interspersed  with  broken  woodland  and  forest  or 
extensive  tree  plantings.  Representative  breeding  localities 
were  the  eucalyptus  grove  along  Hwy.  1  about  1  mi.  S  of 
Sonoma  County  border  (NB  2/1 1/78  — SJ,  DS);  the  euca- 
lyptus grove  at  Brazil  Ranch,  SE  of  Dillon  Beach  (NE 
4/28/82  — DS);  and  the  eucalyptus  grove  near  SE  corner 
of  Abbott's  Lagoon  (NE  5/11/82  -DS). 

Historical  Trends/  Population  Threats 

The  planting  of  cypresses  and  especially  eucalyptus  (used 
as  hunting  perches  and  nest  sites  by  hawks)  in  the  once 
nearly  treeless  northwestern  part  of  Marin  County  appar- 
endy  has  enabled  breeding  Red-tails  to  expand  locally  in 
historical  times.  This  expansion  has  probably  been  offset 
by  displacement  in  parts  of  the  heavily  developed  areas  of 
Marin,  particularly  along  the  Highway  101  corridor,  as  has 
been  noted  elsewhere  in  California  (G&.M  1944).  Red- 
tailed  Hawk  numbers  appeared  to  increase  slighdy  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
but  were  relatively  stable  from  1980  to  1989  (USFWS 
unpubl.  analyses).  Personnel  of  wildlife  agencies  respond- 
ing to  questionnaires  felt  that  Red-tailed  Hawks  were 
declining  in  California.  The  authors  summarizing  that 
survey  data  indicated  that  most  of  the  state's  populations 
were  stable,  though  local  populations,  such  as  on  die 
southern  coast,  were  declining  rapidly,  primarily  from 
housing  developments  and  fire  (Harlow  6k  Bloom  1989). 


147 


Hawks  and  Eagles 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hawks  and  Eagles 


GOLDEN  EAGLE   Aquila  chrysaetos 

A  year-round  resident. 

A  rare,  local  breeder;  overall  breeding 
population  very  small. 
Recorded  in  38  (17.2%)  of  221  blocks. 

>r\      \^\  O  \--^\     \^\     \^\      \-^\  •  V— "A      V^\ 

\^^vx  j^\»\^\  °  v-^v   V-^A    X^K  v-^V   y^"\ 
\  >c^  >^\   Jr\  JrVoV^A     V^\°Jv^\    V^\ 

P 

O    Possible        -      33  (87%) 

^^^^^^^c^x^ 

€    Probable      =        0  (0%) 

•    Confirmed  =         5   (13%) 

vAi3c\S\^^^ 

^KSp. -r- 

FSAR=1         OPI  =  38         CI  =  1.26 

^^?^ 

b^*                                                                                                   *^^J                                   ^^^^X- 

Ecological  Requirements 

When  watching  soaring  Golden  Eagles  at  close  range  it  is 
easy  to  fathom  why  they  inspire  folklore,  creation  myths, 
and,  most  of  all,  respect.  These  aerial  masters  range  from 
the  arctic  tundra  to  desert  regions.  Breeding  requisites 
include  solitude,  extensive  open-ground  foraging  areas, 
and  suitable  nest  sites  nearby  (Palmer  1988b).  In  Marin 
County,  breeding  Golden  Eagles  inhabit  expansive  interior 
grasslands  and  oak  savannah  interspersed  with  a  mosaic  of 
forests  or  woodlands  in  adjoining  canyons  or  on  nearby 
slopes. 

Depending  on  availability,  Golden  Eagles  build  their 
nests  in  large  trees,  on  niches  or  shelves  of  cliffs  or  steep 
earthen  banks,  on  boulders,  on  human  structures,  or, 
rarely,  on  the  ground  (Bent  1937,  Palmer  1988b).  Tree 
nests  range  from  about  20  (rarely  10)  to  100  feet  above  the 
ground  and  the  species  most  often  used  in  California  are 
pines,  oaks,  sycamores,  eucalyptus,  and  redwoods  (Bent 
1937).  Active  nests  in  Marin  County  during  the  adas 
period  were  in  planted  pines,  Douglas  firs,  and  redwoods. 
Ideally  the  nest  site  should  be  where  an  eagle  burdened 
with  prey  can  arrive  without  hindrance  on  a  favorable  wind 
or  updraft,  and  where  currents  allow  landing  at  slow 
speeds  (Dixon  1937,  Palmer  1988b).  Depending  on  the 
region,  nests  are  often  oriented  to  provide  shelter  from 
excessive  heat  or  cold  (Palmer  1988b).  Pairs  frequendy 
have  additional  nests  (up  to  1 2  total),  and  they  may  nest  in 
one  nest  for  a  number  of  consecutive  years  or  alternate  nest 
sites;  there  is  no  obvious  pattern  of  occupancy  among 

148 


various  pairs  (Palmer  1988b).  Certain  nest  sites  are  mag- 
nets attracting  a  succession  of  owners  over  perhaps  hun- 
dreds of  years  or  more. 

These  eagles'  nests  are  very  large,  bulky  affairs  that  vary 
considerably  in  size,  depending  on  the  amount  of  material 
added  when  reused.  The  body  of  the  nest  consists  of  large, 
dry  sticks;  the  lining  is  typically  of  finer  material,  such  as 
coarse  roots,  leaves,  moss,  lichens,  rabbit  fur,  dry  grass, 
and  sprigs  of  bush  or  tree  greenery.  Some  nest  lining 
oddities  are  cow  bones,  deer  antlers,  barbed  wire,  burlap 
bags,  newspapers,  stockings,  and  other  rubbish,  including 
a  cowboy  hat  (but  no  sign  of  cowboy,  horse,  or  boots)!  As 
is  typical  of  raptors,  Golden  Eagles  bring  small  branches 
or  twigs  of  greenery  (pine,  deciduous,  or  other)  to  the  nest 
throughout  the  reproductive  cycle  (sometimes  to  all  nests 
in  a  territory)  and  at  other  times  (Palmer  1988b).  Greenery 
may  function  to  advertise  ownership  or  reinforce  attach- 
ment to  the  territory. 

Golden  Eagles  usually  hunt  early  and  late  in  the  day, 
mosdy  when  in  flight  (Palmer  1 988b).  Soaring  birds  sweep 
and  circle  high  above  the  ground,  descend  upon  spotting 
prey,  then  fold  their  wings  and  plunge  headfirst.  About 
three  yards  above  ground,  they  check  their  flight,  follow  the 
quarry,  and  grasp  it  with  one  or  both  feet.  These  eagles  also 
fly  low  to  the  contours  of  the  ground,  keeping  out  of  sight, 
seizing  prey  they  surprise  away  from  cover.  Less  frequendy, 
eagles  hunt  from  perches,  swooping  down  on  prey  that 
they  spot  moving  into  the  open.  They  also  stoop  on  or 


Hawks  and  Eagles 


SPECIES  ACCOUNTS 


Hawks  and  Eagles 


chase  birds  in  the  air.  Rarely,  if  an  eagle  misses  a  squirrel, 
it  may  wait  on  the  ground  until  the  squirrel  surfaces  from 
a  burrow,  then  take  wing  and  catch  it.  Birds  also  feint  at 
snakes  to  make  them  uncoil  and  tire,  then  seize  them 
behind  the  head  with  one  foot  and  grasp  them  farther 
behind  with  the  other.  Golden  Eagles  may  hunt  coopera- 
tively in  pairs  (usually  later  in  the  nesting  cycle)  or  in 
groups  of  up  to  four  (Palmer  1988b).  One  member  of  a 
pair  usually  makes  the  initial  attempt  at  capture.  If  unsuc- 
cessful, it  may  flush  the  intended  victim  (during  the  initial 
stoop  or  after  landing  and  walking  about  on  the  ground), 
which  is  then  caught  by  the  other  bird,  which  has  been 
soaring  above  (Carnie  1954,  Palmer  1988b).  Groups  of 
eagles  sometimes  cooperate  to  catch  large  prey,  such  as 
foxes,  Wild  Turkeys,  or  deer  and  antelope  (disabled  by 
snow  or  in  poor  condition)  (Palmer  1988b). 

Overall,  the  Golden  Eagle's  diet  is  about  83.9%  mam- 
mals, 14.7%  birds,  1.0%  reptiles,  and  0.4%  fish 
(Olendorff  in  Palmer  1988b).  In  terms  of  biomass,  the 
main  prey  of  Golden  Eagles  are  rodents  (ground  squirrels, 
prairie  dogs,  marmots),  hares,  and  rabbits  (Palmer  1988b). 
Goldens  sometimes  prey  on  full-grown  deer  or  prong- 
horns,  but  probably  only  when  the  quarry  is  already 
injured  or  handicapped.  They  also  take  deer  fawns  or  the 
young  of  other  large  mammals,  adult  and  young  foxes  and 
coyotes,  and  a  wide  variety  of  small  mammals  (in  addition 
to  those  already  mentioned),  including  opossums,  skunks, 
muskrats,  tree  squirrels,  woodrats,  and  odiers  in  size  down 
to  deer  mice  and  voles.  Locally,  Golden  Eagles  do  occasion- 
ally prey  on  very  young  sheep  (rarely  other  livestock  or 
domestic  animals),  but  consumption  is  mosdy  of  stillborn 
young  or  other  carrion.  Birds  also  eat  carrion  of  a  variety 
of  other  species,  particularly  road-killed  hares  and  rabbits. 
Bird  prey  range  in  size  from  cranes,  swans,  Wild  Turkeys, 
and  Great  Blue  Herons  down  to,  rarely,  larks  and  spar- 
rows. Important  bird  prey  are  open-country  game  birds 
(grouse  and  pheasants)  and  magpies.  Golden  Eagles  also 
eat  small  numbers  of  fish,  snakes,  tortoises  and  turtles, 
large  insects  such  as  grasshoppers  and  Mormon  crickets, 
and  the  odd  frog.  In  the  interior  central  Coast  Range  of 
California,  the  Golden  Eagle's  diet  is  77.3%  mammals 
(mosdy  jackrabbits,  ground  squirrels,  and  black-tailed  deer 
fawns),  1 3.5%  medium-  to  large-sized  birds  (mosdy  Yellow- 
billed  Magpies,  Western  Meadowlarks,  and  Great  Horned 
Owls,  but  also  such  large  species  as  Great  Blue  Heron, 
Mallard,  Turkey  Vulture,  Red-tailed  Hawk,  Greater  Road- 
runner,  and  American  Crow),  5.6%  snakes,  and  3.6%  fish 
(Carnie  1954,  n  =  503).  The  considerable  variation  in  the 
diet  there  of  pairs  hunting  close  together  was  apparendy 
due  to  preference  for,  or  specialization  on,  certain  types  of 
prey. 

Males  feed  females  during  incubation  and,  early  in  the 
nesding  phase,  supply  food  for  both  their  mates  and  the 
nesdings  (Palmer  1988b).  Incubating  females  leave  their 


nests  to  obtain  food  brought  by  their  mates  to  nearby 
plucking  sites.  When  nestlings  hatch,  males  prepare  food 
at  plucking  sites  by  removing  feathers  from  birds  and 
decapitating  or  dismembering  mammals  and  more  or  less 
removing  their  fur.  Males  dien  deliver  food  items  to  their 
nests,  or  females  come  to  get  them.  When  the  young  are 
small,  generally  a  great  excess  of  food  accumulates  at  the 
nest.  Hence  the  aerie  serves  as  a  food  cache  against  possible 
shortage  when  hunting  becomes  difficult  during  prolonged 
periods  of  inclement  weather.  When  the  young  get  inade- 
quate food,  stronger  eaglets  sometimes  attack  weaker  ones, 
eventually  causing  death,  and  they  may  sometimes  eat 
them. 

Marin  Breeding  Distribution 

During  the  adas  period,  Golden  Eagles  nested  only  in  the 
northern  interior  of  Marin  County,  but  the  exact  locations 
are  masked  on  the  adas  map  (see  Content  of  Species 
Accounts  p.  73).  The  relatively  even  spacing  of  nests,  the 
scattered  sightings  between  nest  sites,  and  the  fact  that 
home  ranges  in  San  Diego  County  range  from  19  to  59 
square  miles  (av.  36;  Dixon  1937)  suggest  that  the  total 
breeding  population  in  Marin  County  was  about  five  pairs. 
In  1982,  we  found  four  active  nests  and  a  fifth  unoccupied 
nest  used  in  previous  years,  which  may  have  been  an 
alternative  nest  of  one  of  die  other  four  pairs  (ScC,  DS, 
HBa  —data  on  file).  The  lack  of  breeding  Golden  Eagles  in 
die  extensive  grassland  areas  of  the  Point  Reyes  peninsula 
and  the  Marin  Headlands  may  have  been  because  of  a  lack 
of  ground  squirrels  and  low  numbers  of  jackrabbits  there. 

Historical  Trends/Population  Threats 

Pressure  on  Golden  Eagles,  especially  through  degradation 
or  total  loss  of  habitat,  became  serious  in  the  West  only  in 
the  present  century  (Palmer  1988b).  Grinnell  and  Miller 
(1944)  noted  that  the  species  had  been  reduced  in  num- 
bers or  extirpated  in  areas  of  California  closely  setded  by 
humans,  but  elsewhere  in  the  state  numbers  were  close  to 
normal.  The  Golden  Eagle  is  currendy  listed  in  California 
as  a  Bird  Species  of  Special  Concern  (Remsen  1978,  CDFG 
1991b)  and  as  "Fully  Protected"  (Harlow  ck  Bloom  1989). 
Thelander  (1 974)  estimated  there  were  500  breeding  pairs 
in  California,  and  Olendorff  et  al.  (in  Palmer  1988b) 
estimated  the  state's  wintering  population  at  about  5046 
birds.  Numbers  of  Golden  Eagles  appeared  to  increase 
slighdy  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989  but  were  relatively  stable  from  1980  to  1989 
(USFWS  unpubl.  analyses);  odier  observations  suggest 
declines  in  the  state,  particularly  on  the  southern  coast 
(Harlow  ck  Bloom  1989). 

In  the  West,  ranchers  have  put  intense  pressure  on 
Golden  Eagle  populations  because  of  reputed  extensive 
predation  on  sheep,  though  the  facts  indicate  such  preda- 
tion  is  limited  and  local.  Golden  Eagles  were  shot  from 

149 


Hawks  and  Eagles 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hawks  and  Eagles 


airplanes  as  early  as  fall  to  spring  of  1935-36,  when  over 
200  birds  were  killed  by  "sportsmen"  in  Tehama  County 
(Dale  1936).  At  least  20,000  (perhaps  40,000)  eagles  were 
killed,  mosdy  from  aircraft,  from  1940  to  1962  in  die 
sheep-raising  country  of  west  Texas  and  New  Mexico  alone 
(Spofford  1964,  Palmer  1988b).  Golden  Eagles  were  given 
legal  protection  in  1963.  Permits  were  still  issued  for 
livestock  protection,  though  eagles  could  not  be  taken  from 
aircraft  or  by  poison.  Hundreds  were  still  being  killed 
illegally  in  the  early  1970s,  but  the  enlightened  efforts  of 


Audubon  societies  and  state  and  federal  agencies  have 
greatly  lessened  the  problem.  Accidental  electrocution  on 
power  lines  has  also  been  a  problem  but  has  been  reduced 
in  some  areas  by  the  redesign  of  transmission  structures. 
Golden  Eagles  have  also  experienced  eggshell  thinning, 
deadi,  and  contamination  from  pesticides  (Reichel  et  al. 
1969,  Palmer  1988b)  and  have  picked  up  lead  concentra- 
tions from  the  environment  (Harlow  6k  Bloom  1989). 
Golden  Eagles  are  very  sensitive  to  disturbance;  watching 
of  nests  (even  with  telescopes  at  long  range)  is  best  avoided. 


A  Golden  Eagle  looks  over  its  territory  from  its  formidable  nest.  Photograph  by  Ian  Tait. 


150 


Falc 


SPECIES  ACCOUNTS 


Falcons 

Family  Falconidae 


Falcons 


AMERICAN  KESTREL  Falco  sparverius 


Occurs  year  round,  though  primarily  as  a 
winter  resident  from  mid-Aug  through 
Feb. 

An  uncommon,  fairly  widespread 
breeder;  overall  breeding  population 
small. 

Recorded  in  122  (55.2%)  of  221 
blocks. 

O  Possible  =  71  (58%) 
C  Probable  =  26  (21%) 
•    Confirmed  =      25  (20%) 


FSAR  =2        OPI  =  244 


CI  =  1.62 


Ecological  Requirements 

It  is  common  to  see  these  dainty,  boldly  marked  falcons 
emphatically  pump  their  tails  or  bob  their  heads  after 
alighting  in  hunched  posture  on  perches  in  open  country. 
Elevation,  moisture,  or  particular  plant  communities  exert 
little  influence  on  Kestrel  distribution,  as  they  range  from 
sea  level  to  timberline  and  from  deserts  to  moist  forest 
fringes.  Kestrels  are  edge  adapted  and  inhabit  the  margins 
of  a  wide  variety  of  forests  and  woodlands  bordering  on 
low,  open  vegetation  of  grasslands,  meadows,  and  scattered 
brush;  open  or  burned  forests  or  woodlands;  and  even 
urban-suburban  settings.  In  Marin  County,  American  Kes- 
trels breed  along  the  edges  of,  or  within  extensive  openings 
in,  all  the  major  forest  or  woodland  communities  border- 
ing on  grasslands,  open  weed  fields,  or  meadows;  around 
isolated  woodlots,  windbreaks,  and  ranchyards  in  expan- 
sive pasturelands;  or  in  similar  urban-suburban  environ- 
ments. In  winter,  the  sexes  segregate  by  habitat— females 
mosdy  use  expansive  open  habitats  with  few  trees,  and 
males  mostly  use  clearings  in  habitats  with  more  trees  and 
brush  (Koplin  1973,  Mills  1976,  Stinson  et  al.  1981). 
These  differences  may  reflect  the  dominant  females'  forc- 
ing the  males  into  less  suitable  habitats,  thereby  reducing 
competition  for  food,  or  sexual  differences  in  preferred 


habitats  harboring  preferred  prey.  Smallwood  (1988)  attri- 
buted sexual  habitat  segregation  on  the  wintering  grounds 
to  earlier  migration  of  females,  which  occupy  habitats  of 
superior  foraging  quality  first,  leaving  poor-quality  habitats 
to  later-arriving  males.  A  suggestion  that  habitat  separation 
may  also  be  widespread  in  summer  (to  a  lesser  extent  than 
in  winter;  Mills  1 976)  is  countered  by  the  knowledge  that 
females  initially  center  most  activities  around  the  nest  site 
and  are  fed  by  their  mates,  which  range  widely  throughout 
dieir  territories,  and  that,  in  some  areas  at  least,  there  is  no 
sexual  separation  in  die  foraging  niches  of  breeding  birds 
(Balgooyen  1976).  The  main  requirements  for  breeding 
Kestrels  are  low,  open  vegetation  for  ground  foraging, 
suitable  foraging  perches  (high  preferred  to  low),  an  ade- 
quate prey  base,  and  available  nest  cavities  (Balgooyen 
1976,  Palmer  1988b). 

Nest  sites  in  particular  can  limit  Kestrel  density.  A 
suggestion  diat  Kestrels  breed  almost  colonially  or  socially 
where  there  is  an  abundance  of  cavities  (Palmer  1 988b) 
may  be  an  exaggeration,  as  territoriality  will  limit  Kestrel 
numbers  before  nest  sites  are  exhausted  in  such  a  situation 
(Balgooyen  1976).  Unlike  most  raptors,  Kestrels  prefer 
natural  tree  cavities  or  those  excavated  by  large  woodpeck- 

151 


Falcons 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Falc 


ers  (particularly  Northern  Flickers)  for  nesting  (Bent  1938, 
Balgooyen  1976,  Palmer  1988b).  They  also  use  holes  in 
cliffs  or  eroded  stream  banks  (natural  or  excavated  by 
kingfishers),  cavities  in  buildings,  chimneys,  drainpipes, 
hollowedout  fence  posts,  old  pigeon  boxes,  magpie  nests, 
and  bird  boxes.  Kestrels  add  little,  if  any,  material  to  the 
cavities  and  lay  their  eggs  on  the  bare  door  or  on  whatever 
die  previous  occupant  has  left  behind  (Bent  1938).  Nest 
heights  range  from  less  than  three  feet  above  the  ground  to 
as  high  as  suitable  cavities  exist— in  one  case  over  350  feet 
up  in  a  22-story  building  (Palmer  1988b).  Roest  (1957) 
reported  nest  heights  at  various  locations  in  North  Amer- 
ica ranging  from  4  to  50+  feet  above  the  ground  (most 
10-35  ft.)  and  Balgooyen  (1976)  reported  43  nests  in  the 
Sierra  Nevada  ranging  from  7  to  80  feet  (av.  26  ft.). 

Balgooyen  (1976)  found  most  nests  in  the  eastern  Sierra 
in  the  lower  reaches  of  basins,  presumably  because  these 
sites  were  sheltered  from  weather  and  allowed  easy  flights 
back  to  die  nest  with  food.  In  Marin  County,  most  Kestrels 
nest  in  lowland  areas  because  of  the  greater  availability  of 
open  areas  and,  apparendy,  nests  sites  there,  and  probably 
because  of  a  greater  prey  base  in  fertile  lowland  valleys.  In 
the  Sierra,  Balgooyen  (1976)  found  that  both  the  slope 
exposure  of  the  nest  tree  and  the  nest  entrance  tended  to 
face  east,  providing  protection  from  storms  and  die  advan- 
tage of  early  morning  sun.  Raphael  (1985)  confirmed  the 
easterly  orientation  of  Kestrels'  nest  trees  and  nest  cavities 
in  Balgooyen's  study  area;  Kestrels  there  chose  these  sites 
despite  the  availability  of  cavities  oriented  in  other  direc- 
tions. Interestingly,  woodpeckers  in  the  same  area,  which 
might  similarly  benefit  from  the  thermoregulatory  advan- 
tages of  easterly  oriented  nest  cavities,  tended  to  choose 
northerly  facing  cavities  even  though  suitable  decay  was 
randomly  oriented.  Kestrels  nesting  in  the  tropics  may 
avoid  heat  by  selecting  nest  sites  facing  into  prevailing 
winds  and  away  from  direct  sunlight  (Balgooyen  1990). 

Kestrels  hunt  more  or  less  regularly  and  continuously 
throughout  the  day  and  may  or  may  not  show  peaks  of 
foraging  activity  (Palmer  1988b).  They  seek  visible  and 
vulnerable  prey  in  short,  sparse  vegetation,  where  they 
capture  most  prey  on  or  near  the  ground  and  take  most 
flying  prey  on  the  wing  (Balgooyen  1976,  Palmer  1988b). 
These  falcons  mosdy  hunt  from  perches  (when  available) 
and  secondarily  hover  and  hawk.  Birds  use  a  wide  variety 
of  foraging  perches,  including  dead  branches  and  trees, 
stumps,  rock  outcrops  or  cliffs,  fence  posts,  telephone  and 
power  poles,  transmission  lines,  and  an  array  of  artificial 
structures.  Average  perch  height  in  the  Sierra  Nevada  is  22 
feet  (n  =  328);  birds  forage  from  lower  perches  in  high 
winds  (Balgooyen  1 976).  From  perches,  birds  face  into  the 
wind  and  scan  terrain  for  prey  by  rotating  or  tilting  die 
head,  dien  snap  the  head  into  a  fixed  position  upon 
locating  prey  and  fly  down  to  make  the  capture.  In  the 
Sierra,  effective  capture  distance  from  the  perch  extends  to 

152 


900  feet,  with  86%  of  captures  from  0  to  164  feet  (av.  112 
ft.).  In  areas  lacking  perches,  Kestrels  face  the  wind  with 
their  bodies  angled  head  upwards  and  hover  with  shallow 
wingbeats  and  tail  fanned.  Sometimes  they  hang  motion- 
less, then  plummet  direcdy  down  or  drop  lower  and  hover 
again  before  die  final  attack.  Kestrels  hover  mosdy  from 
heights  of  40  to  100  feet  and  dive  headfirst  after  mammals 
and  feet  first  after  insects  (Balgooyen  1976,  Palmer  1988b). 
During  dives,  the  birds  may  partly  close  their  wings  or 
flutter  downward,  checking  and  controlling  their  descent 
(Palmer  1988b).  Whether  hunting  from  perches  or  hover- 
ing, Kestrels  modify  their  attacks,  depending  on  the  type  of 
prey  (Balgooyen  1976).  They  direcdy  attack  frogs,  lizards, 
and  small  mammals  from  flight.  Kestrels  track  the  flight  of 
grasshoppers,  and  after  they  land,  the  birds  fly  to  the  spot, 
brake,  and  usually  flush  the  insect  and  make  the  kill  on  the 
wing.  If  grasshoppers  remain  still,  Kestrels  land  and  walk 
about,  crisscrossing  the  area  to  attempt  to  raise  the  insect. 
From  flight,  Kestrels  also,  rarely,  pick  large  insects  or 
lizards  deftly  from  tree  trunks  or  rocks  (Balgooyen  1976, 
Palmer  1988b).  Sometimes  they  fly  rapidly,  low  to  the 
ground,  in  pursuit  of  flying  prey  (Palmer  1988b).  Birds 
also  hawk  insects  by  flying  direcdy  out  (up  to  35  ft.)  from 
perches  (Balgooyen  1976)  or  by  soaring  and  flapping 
upward  and  away  from  perches,  then  stalling  and  diving 
abrupdy  at  their  targets  (Palmer  1988b).  They  sometimes 
dart  out  from  a  perch,  tilt  their  bodies,  attempt  to  strike 
down  dragonflies  with  their  wings,  then  drop  to  the 
ground  to  seize  their  prey  (Palmer  1988b).  Birds  may  eat 
prey  at  the  capture  site,  while  transported  aerially,  or  on 
arrival  at  a  nearby  perch. 

Kestrels  sometimes  catch  birds  in  flight  and  secure  bats 
from  the  bark  of  trees  or  by  diving  down  on  them  or  from 
behind  in  straight  flight  (Balgooyen  1976,  Palmer  1988b). 
Rarely,  these  falcons  obtain  small  nonflying  insects,  spi- 
ders, or  worms  with  their  beaks  while  running  (occasion- 
ally flapping  to  gain  speed)  or  jumping  on  the  ground. 
Kestrels  sometimes  persistendy  rob  nests  and  return  to  get 
the  rest  of  a  brood  (Palmer  1988b).  They  have  plundered 
burrows  of  Bank  Swallows  and  nests  of  Cliff  Swallows, 
Barn  Swallows,  phoebes,  bluebirds,  and  House  Sparrows 
by  hanging  upside  down  and  reaching  in  with  one  foot  or 
by  ripping  off  the  top  of  the  nest.  Infrequendy,  Kestrels 
take  birds  captured  in  mist  nests  or  ground  traps  and  hunt 
along  the  smoky  windward  edges  of  fires.  Rarely,  Kestrels 
eat  fresh  or  decayed  carrion.  One  Kestrel  foraged  on  the 
ground  for  bread  (initially  with  feral  pigeons). 

Kestrels  usually  capture  prey  in  the  talons  and  kill  them 
by  biting  them  with  die  beak  in  the  head  or  neck  (Bal- 
gooyen 1976,  Palmer  1988b).  They  usually  crush  the  head 
and  discard  the  wings,  legs,  and  other  extraneous  parts  of 
insects;  pluck  feathers  from  birds;  discard  some  rodent 
hair  and  ingest  much;  and  discard  large  hard  parts  and 
alimentary  canals  of  birds  and  mammals. 


Falcons 


SPECIES  ACCOUNTS 


Falcons 


Kestrels  are  generalized  predators  of  invertebrates  and 
small  vertebrate  animals.  Prey  items  consist  of  95.7% 
invertebrates,  2.4%  mammals,  1.2%  birds,  and  0.7% 
lower  vertebrates  (Snyder  6k  Wiley  1976,  n  =  9242).  Prey 
taken  can  vary  considerably  with  locality,  season,  or  the 
tendency  of  individuals  to  concentrate  on  one  particular 
type  of  prey  (Balgooyen  1976,  Palmer  1988b).  Principal 
prey  are  large  insects  (especially  grasshoppers,  Jerusalem 
crickets,  dragonflies,  beedes,  and  caterpillars);  small  mam- 
mals (from  shrew  to  ground  squirrel  or  rabbit  size— espe- 
cially voles);  birds  (from  hummingbird  to  Mourning  Dove 
or  quail  size,  but  mosdy  moderate,  size);  and  reptiles  and 
amphibians  (small  lizards,  snakes,  frogs,  tadpoles,  and 
toads).  Miscellaneous  prey  items  include  crayfish,  centi- 
pedes, scorpions,  spiders,  earthworms,  and  snails.  The 
Kestrels'  diet  by  weight  in  the  Sierra  Nevada  is  31.7% 
insects  (mostly  grasshoppers),  26.0%  reptiles,  25.7% 
mammals,  and  16.6%  birds;  by  occurrence,  it  is  88.4% 
insects,  8.1%  reptiles,  2.1%  mammals,  and  1.4%  birds 
(Balgooyen  1976).  In  the  early  season  or  during  inclement 
weather,  Kestrels  in  the  Sierra  Nevada  concentrate  on 
birds  and  mammals.  Later  on,  they  rely  more  on  lizards 
and  insects  and  even  more  so  on  insects  from  midseason 
until  fall  departure.  In  Humboldt  County,  Kestrels  feed  on 
voles  and  shrews  in  the  absence  of  insect  prey  (Collopy  in 
Palmer  1988b).  Although  die  sexes  generally  take  the  same 
kinds  of  prey  in  about  the  same  proportions,  there  are 
some  exceptions.  In  the  Sierra  Nevada,  breeding  males 
and  females  choose  similar-sized  prey  (Balgooyen  1976), 
but  in  southern  California,  breeding  males  usually  choose 
smaller  prey  than  breeding  females  (Bryan  in  Palmer 
1988b). 

Males  forage  in  areas  of  the  territory  away  from  the 
immediate  nest  site  and  bring  females  food  from  four  to 
five  weeks  before  egg  laying  until  one  to  two  weeks  after 
hatching  of  the  eggs  (Balgooyen  1976).  Males  transport 
prey  to  perches  near  the  nest  site,  where  they  transfer  the 
food  to  females  with  their  beaks  (Balgooyen  1976,  Palmer 
1988b).  Both  sexes  may  cache  surplus  vertebrate  prey  by 
wedging  or  pushing  it  with  the  beak  into  a  suitable  site. 
Cache  sites  may  range  from  the  ground  up  to  65  feet  and 
include  grass  clumps,  hollow  railroad  ties,  tree  roots, 
bushes,  fence  posts,  building  gutters,  tree  limbs  and  holes, 
and  tops  of  power  poles  or  burned  stumps.  Although  food 
caching  may  serve  to  hide  prey,  the  main  function  is  to 
store  it  as  a  reserve  for  times  of  inclement  weather  or  low 


prey  availability  or  to  meet  the  demands  of  growing  young. 
Cached  food  is  usually  eaten  within  a  few  hours  or  within 
2  or  3  days;  some  food  is  held  as  long  as  6  or  7  days.  The 
young  are  initially  fed  by  the  female  via  the  male  for  7  to 
10  days  after  hatching,  then  by  both  sexes  separately 
(Balgooyen  1976).  Through  the  first  7  to  14  days,  the 
female  initially  removes  all  extraneous  material  from  prey 
and  feeds  the  young  only  flesh.  Thereafter,  prey  are  deliv- 
ered to  the  young  whole  and  unprepared. 

Marin  Breeding  Distribution 

During  the  adas  period,  Kestrels  bred  widely  in  Marin 
County,  though  breeding  numbers  were  substantially 
smaller  than  winter  numbers.  Breeding  Kestrels  were 
sparse  or  lacking  on  much  of  Point  Reyes  because  of  the 
dense  forest  or  scrub  cover  on  most  of  Inverness  Ridge, 
and  perhaps  because  of  limited  nest  sites  and  small  popu- 
lations of  large  insects  in  the  fog-shrouded,  windswept 
grasslands  of  the  outer  Point  Reyes  peninsula.  The  reasons 
for  their  spotty  distribution  elsewhere  in  Marin,  particu- 
larly in  the  grassland-dominated  hills  east  of  Tomales  Bay 
where  large  numbers  of  Kestrels  winter,  is  less  clear.  Nest 
sites  may  be  a  limiting  factor:  40%  of  the  blocks  east  of  the 
Point  Reyes  peninsula  that  lack  breeding  Kestrels  also  lack 
breeding  Northern  Flickers,  which  typically  provide  many 
Kestrel  nest  cavities.  Representative  breeding  localities  of 
American  Kestrels  were  Bear  Valley,  PRNS  (FY  4/22/76 
-RMS);  Ignacio  area  (FY  5/27/77  -RMS);  and  Carson 
Ridge  (DD  3/9/85  -ITi). 

Historical  Trends/  Population  Threats 

Grinnell  and  Miller  (1944)  did  not  comment  on  any 
trends  in  California  populations,  but  Palmer  (1988b) 
reported  that  "widespread  deforestation  and  land  develop- 
ment have  facilitated  a  continentwide  population  increase 
of  this  remarkably  adaptive  species."  Numbers  of  breeding 
Kestrels  decreased  on  Breeding  Bird  Surveys  in  California 
from  1980  to  1989  (USFWS  unpubl.  analyses).  Eggshell 
thinning  in  Kestrels  has  been  correlated  with  increasing 
levels  of  DDE  (Risebrough  ck  Monk  1989),  but  even 
though  chemical  contaminants  have  caused  deaths,  there 
have  been  no  drastic  declines  in  Kestrel  numbers  as  a 
result  (Palmer  1 988b).  There  currendy  are  no  major  threats 
to  western  populations  (Piatt  6k  Enderson  1989). 


153 


Falc 


MARIN  COUNTY  BRFFDING  BIRD  ATI  AS 


Falcons 


PEREGRINE  FALCON    Falco  peregrinus 


Formerly  a  year-round  resident  and  breeder  until  the  1970s,  when  extirpated  as  a  nesting  bird.  Now  occurs  year  round, 
though  primarily  as  a  winter  resident  and  transient  from  mid-Sep  through  mid-Apr.  Following  a  statewide  increase  after  a 
ban  on  DDT  pesticides  and  the  implementation  of  a  captive  breeding  program,  summer  sightings  have  increased  in  Marin 
and  breeding  attempted  in  1990  and  1991  (successfully). 


Ecological  Requirements 

These  swift,  spirited  falcons  inhabit  open  country,  where 
their  speed  and  feather-raising  pursuit  dives  strike  fear  in 
the  hearts  of  the  avian  populace.  Peregrines  hunt  in  the 
air— over  oceans,  forests  and  woodlands,  marshes  and 
wedands,  chaparral,  and  cities— and  very  rarely  take  ground 
prey.  In  coastal  areas,  Peregrines  hunt  a  great  deal  around 
estuaries  and  seabird  colonies.  Ideally,  they  select  nesting 
aeries  that  command  a  wide  view,  are  near  water,  have 
plentiful  bird  prey  in  the  vicinity,  and  are  seldom  disturbed 
(Palmer  1988b).  Peregrine  Falcons  formerly  nested  in 
Marin  County  on  cliffs  overlooking  the  ocean  (see  below). 
In  contrast,  Prairie  Falcons,  which  have  never  nested  here, 
tend  to  inhabit  more  arid  environments,  select  lower,  more 
sheltered  nest  sites,  and  feed  lower  to  the  ground  and 
considerably  more  on  mammals  than  do  Peregrines  (Pal- 
mer 1988b).  Peregrine  Falcons  will  nest  in  deserts  if  near 
marshes,  lakes,  or  rivers,  and  both  Peregrine  and  Prairie 
falcons  may  nest  on  the  same  cliffs  or  switch  ownership  of 
nest  sites  in  different  years. 

Peregrines  typically  select  cavities  or  ledges  on  cliffs, 
often  with  a  sheltering  overhang,  for  nest  sites  (Palmer 
1988b).  They  generally  lay  their  eggs  on  a  fairly  level  spot 
at  least  two  feet  in  diameter— a  larger  space  is  advantageous 
so  the  young  can  move  about  as  they  grow.  Peregrines 
make  a  nest  scrape  in  debris,  such  as  soil  or  rocks,  and 
sitting  birds  may  pull  some  of  tins  material  toward  them  to 
form  a  rim  sufficient  to  keep  the  eggs  from  rolling  away.  In 
North  America,  cliff  nest  sites  are  usually  unmodified  or 
may  contain  old  nests  of  Common  Ravens,  Rough-legged 
Hawks,  Golden  Eagles,  Red-tailed  Hawks,  or  cormorants. 
Historically,  raven  nests  were  often  used  in  Marin  County 
(B.J.  Walton  pers.  comm.).  Substitutes  for  cliff  nests  in- 
clude church  towers,  castle  ruins,  bridges,  quarries,  raised 
platforms,  and  assorted  buildings  (mosdy  urban).  In  very 
open  country,  such  as  tundra,  Peregrines  will  nest  in 
recesses  or  level  spots  at  or  near  the  top  of  eroded  river- 
banks  or  on  boulders,  hills,  slopes,  dunes,  bog  hummocks 
or  islets,  or  even  on  ground  with  no  topographical  relief. 
One  pair  nested  in  the  straw  packing  inside  a  barrel  cast 
up  in  salt  marsh  in  San  Francisco  Bay  near  Redwood  City, 
San  Mateo  County  (Dawson  1923);  other  birds  reportedly 
bred  in  bay  marshes  in  Santa  Clara  County  (G&W  1927). 

154 


Peregrines  will  also  appropriate  solid  (rarely  flimsy)  stick 
nests  (usually  disused)  of  a  variety  of  large  birds  placed  in 
dead  or  living  trees  (Palmer  1988b).  The  use  of  stick  nests 
in  trees  is  only  widespread  in  Australia,  and  there  are  only 
one  or  two  such  records  in  North  America  (occupation  of 
Bald  Eagle  nests  in  British  Columbia).  On  the  whole,  the 
use  of  tree  cavities,  including  hollow  tops  where  limbs  have 
broken  off,  is  even  rarer,  though  slightly  more  frequent  in 
North  America  than  the  use  of  stick  nests  in  trees.  Pere- 
grines often  use  alternative  nest  sites  within  the  same 
territory— one  or  two  is  common,  and  birds  have  used  up 
to  seven  in  16  years.  If  several  sites  or  ledges  are  available 
along  a  cliff,  individual  pairs  may  change  about  in  different 
years  or  shift  to  different  cliffs.  If  alternative  sites  or  ledges 
are  not  available,  pairs  tend  to  stay  put.  Birds  robbed  of 
their  eggs  commonly  move  to  alternate  sites,  and  birds  may 
move  and  re-lay  after  breeding  failure.  Use  of  particular 
sites  may  also  alternate  between  Peregrines  and  other 
species  of  cliff-nesting  raptors.  Despite  birds'  switching  to 
alternative  sites,  some  Peregrine  territories  in  Britain  have 
been  occupied  at  least  since  the  1 3th  century. 

The  Peregrine  Falcon  is  a  very  fast,  extremely  agile,  and 
versatile  raptor  specialized  for  capturing  aerial  prey.  In  level 
flight,  Peregrines  normally  fly  at  25  to  35  mph  and  usually 
do  not  exceed  60  mph;  in  vertical  stoops,  they  usually  make 
strikes  at  about  100  mph  and  from  a  height  of  5000  feet 
would  reach  a  terminal  velocity  of  230  to  240  mph  (Palmer 
1988b).  Breeding  males  may  hunt  throughout  the  day,  but 
mosdy  early  in  the  morning  and  secondarily  toward  eve- 
ning. Timing  of  hunting  may  depend  on  the  activity 
patterns  or  the  size  of  prey.  Peregrines  living  within  colo- 
nies of  nocturnal,  burrowing  seabirds  hunt  such  prey  (and 
bats)  around  their  aeries  in  near  darkness.  Individuals 
specializing  on  waterfowl  must  hunt  two  times  a  day,  and 
diose  hunting  small  shorebirds  must  hunt  three  to  four  or 
even  five  to  six  times  per  day.  Hunting  demands  peak 
when  males  are  feeding  both  females  and  growing  young. 

Often,  probably  when  already  satiated,  Peregrines  pur- 
sue flying  birds  seemingly  for  the  pleasure  of  the  chase 
(Palmer  1 988b)  or  perhaps  to  hone  hunting  skills  or  tactics 
(B.J.  Walton  pers.  comm.).  At  other  times,  they  turn 
deadly  serious  in  their  attempts.  Hunting  birds  launch 


Falcons 


SPECIES  ACCOUNTS 


Falcc 


attacks  from  a  stationary  position  on  a  prominence  or  tall 
tree,  or  from  flight.  If  the  quarry  is  below  them,  they  may 
make  a  shallow  stoop  or  climb  higher  and  stoop  at  tremen- 
dous speed.  If  their  initial  strikes  fail,  Peregrines  rise 
rapidly  and  stoop  again,  making  repeated  attempts  if  nec- 
essary. When  prey  near  cover,  Peregrines  sometimes  get 
beneath  them,  turn  over,  and  seize  them  from  below.  If 
quarry  are  initially  high  overhead  or  are  forced  upward, 
these  falcons  spiral  upward  spectacularly  to  get  above 
them.  Fast  birds  try  to  keep  above  falcons  or  to  outdistance 
them  in  straight-away  flight,  whereas  slower  fliers  try  to 
keep  above  their  pursuers.  As  a  last  resort,  quarry  may 
plummet  earthward,  but  they  are  closely  pursued  and 
generally  captured  quickly.  If  the  prey  reaches  ground  but 
fails  to  find  concealing  cover,  it  may  be  killed.  Peregrines 
may  launch  attacks  from  circling  flight,  stooping  at  lower 
targets  or  spiraling  up  after  higher  prey.  Smaller  prey  are 
often  grasped  in  the  air  and  carried  to  earth.  Larger  victims 
are  often  struck  with  such  speed  (with  either  or  both  feet) 
that  falcons  slash  the  victim  with  the  rear  talon(s)  and  rip 
right  through  without  holding  on.  Feathers  fly,  and  the 
prey  may  be  dead  as  it  falls  earthward.  Peregrines  then 
half-circle  and  alight,  and  whether  the  prey  is  alive  or  not 
they  bite  it  near  the  base  of  the  brain,  breaking  the  neck 
with  their  specialized  double-notched  beak,  adapted  for 
this  purpose.  Mated  pairs  may  hunt  cooperatively  and  may 
stay  together  year  round  in  Marin.  There  is  some  evidence 
that  females  may  maneuver  the  quarry  into  a  favorable 
position  for  the  male  to  strike  from  a  greater  height, 
coming  out  of  the  sun  (B.J.  Walton  pers.  comm.). 

Peregrines  also  hunt  flying  low  to  the  ground,  keeping 
out  of  sight  as  best  they  can  behind  vegetation  and  irregu- 
larities of  the  terrain  (Palmer  1988b).  Some  low  flying  is 
done  deliberately  to  flush  potential  prey  from  vegetation. 
Peregrines  also  seek  the  shelter  of  waves  when  pursuing 
marine  birds  at  sea.  If  the  quarry  escapes  by  diving,  a  falcon 
may  wait  overhead  and  pick  the  prey  from  the  surface  after 
it  emerges  exhausted  after  repeated  dives.  In  forested 
regions,  Peregrines  take  exposed  prey  crossing  water  or 
clearings.  Peregrines  usually  flush  standing  or  swimming 
birds  before  seizing  them,  but,  very  rarely,  they  do  take 
some  prey  from  or  on  the  ground  or  water.  Mammals 
(other  than  bats),  usually  found  in  Peregrine  nests,  are 
probably  those  pirated  from  other  raptors  (B.J.  Walton 
pers.  comm.).  Relatively  large  mammals,  such  as  full-grown 
ground  squirrels,  may  be  killed  by  a  series  of  stoops  at  the 
head  and  neck  that  stun  or  blind  the  individual  or  fracture 
its  skull.  Lemmings  are  reportedly  hunted  afoot,  but  many 
are  probably  snatched  by  flying  falcons.  Ground  hunting 
is  more  frequent  in  inexperienced  young  Peregrines,  which 
catch  insects,  large  slugs,  fiddler  crabs,  and  other  suitable 
prey  by  this  method.  Adults  sometimes  hawk  flying  insects 
leisurely.  These  falcons  also  follow  people,  dogs,  or  harri- 
ers to  catch  birds  they  flush.  Peregrines  capture  bats  by 


cutting  through  flocks  departing  from  caves  or  ambush 
individuals  returning  to  them.  They  also  catch  fish  break- 
ing the  surface,  pirate  them  from  Ospreys,  and  perhaps 
take  stranded  or  dead  ones.  Peregrines  also  pirate  food 
from  other  raptors  of  Harrier  to  Kestrel  size.  Peregrines  eat 
some  smaller  prey  on  the  wing.  They  probably  at  least 
partially  dismember,  then  eat  during  flight,  prey  such  as 
bats,  voles,  and  insects,  which  are  unsuitable  for  plucking. 
Birds  captured  at  sea  may  also  be  eaten  in  flight.  These 
falcons  generally  partially  pluck  and  feed  on  heavy  prey 
where  they  strike  them  down,  though  typically  they  carry 
food  to  one  or  more  plucking  sites  or  perches.  They  pluck 
wings  and  tail  and  eat  the  head  to  make  prey  aerodynami- 
cally  efficient  for  carrying  (B.J.  Walton  pers.  comm.).  The 
beaks  and  feet  of  larger  prey  often  are  not  eaten. 

Peregrines  defend  a  small  area  around  the  aerie.  Food 
supply  probably  determines  the  size  of  the  much  larger 
hunting  range,  which  in  the  breeding  season  may  be  over 
40  square  miles;  the  total  feeding  areas  of  breeding  pairs 
frequendy  overlap  (Palmer  1 988b).  Some  foraging  is  done 
from  die  aerie  or  nearby  perches,  but  foraging  flights 
during  breeding  in  California  range  up  to  4  to  5  miles 
(mosdy  2  to  3  miles).  The  male  feeds  the  female  during 
prelaying  and  incubation.  After  hatching,  he  feeds  both  the 
brood  and  his  mate,  but  the  female  hunts  progressively 
more  as  her  brooding  declines.  The  male  delivers  prey 
(fresh  or  retrieved  from  a  cache)  to  a  nearby  perch,  and  the 
females  gets  it  there;  or  she  may  meet  him  in  the  air  and 
obtain  it  in  an  aerial  food  pass  or  drop.  Females  may 
retrieve  food  cached  by  the  male  and  again  cache  and 
retrieve  any  uneaten  portion.  Food  caching  also  occurs  at 
other  seasons  (B.J.  Walton  pers.  comm.).  Caching  assures 
a  supply  of  food  during  bad  weather  when  hunting  is 
difficult  and  at  least  sometimes  is  triggered  by  an  abun- 
dance of  prey.  Sometimes  the  male  delivers  food  to  the 
young  direcdy,  especially  when  die  female  is  absent.  Avian 
prey  are  almost  always,  and  mammals  are  frequendy, 
headless  when  delivered  to  the  aerie.  Males  may  subsist 
largely  on  heads  at  this  time,  but  they  apparendy  consume 
some  whole  prey  away  from  the  breeding  territory. 

Peregrines  prey  principally  on  fast-flying  birds  in  the 
open  and  worldwide  have  captured  well  over  250  species 
(Palmer  1988b).  These  range  in  size,  rarely,  from  prey 
heavier  than  the  predator  (loons,  herons,  cormorants, 
geese,  and  large  gulls)  down  to  very  small  passerines.  Most 
important  prey  are  usually  small  to  medium-sized  birds- 
blackbirds,  swallows,  shorebirds,  seabirds,  pigeons,  doves, 
etc.  The  bulk  of  the  prey  taken  in  an  area  usually  consists 
of  a  few  common  open-country  species.  Individuals  some- 
times specialize  on  certain  prey  species,  but  less  so  when 
feeding  a  growing  brood.  In  California,  Peregrines  usually 
do  not  deliver  a  predominance  of  any  one  prey  species  to 
a  nest— prey  remains  usually  mirror  the  array  of  the  most 
numerous    species   of  appropriate   size   recorded   in   the 


155 


Fake 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Falc 


territory  (B.J.  Walton  pers.  comm.).  About  25+  prey  spe- 
cies is  typical  at  California  nests,  and  many  prey  items  are 
represented  at  every  nest.  Coastal  Peregrines  often  special- 
ize on  seabirds  during  the  breeding  season  and  on  shore- 
birds  and  waterfowl  in  winter  (Palmer  1988b).  Seasonal 
changes  in  diet  likely  reflect  availability  of  common  prey 
species.  Rock  Doves  are  a  preferred  food,  especially  in 
cities.  Mammals  are  extremely  rare  fare,  but  a  wide  variety 
are  consumed,  including  shrews,  bats,  rabbits  and  young 
hares,  pikas,  tree  squirrels,  chipmunks,  ground  squirrels, 
lemmings,  rats,  and  voles.  In  California,  mammal  prey 
include  only  bats  and  very  small  mammals,  often  pirated 
from  Black-shouldered  Kites  and  Red-tailed  Hawks  (B.J. 
Walton  pers.  comm.).  Extremely  rarely,  Peregrines  eat 
invertebrates,  insects,  and  carrion  (not  recorded  in  Califor- 
nia). Evidendy  males  and  females  eat  prey  of  the  same 
average  size  (Palmer  1988b). 

Historical  Trends/Population  Threats 

Peregrine  Falcons  formerly  nested  in  Marin  County  on 
precipitous  seacliffs  (G6kW  1927,  GckM  1944).  Known 
former  nesting  sites  include  the  cliffs  between  the  Golden 
Gate  Bridge  and  Point  Bonita,  the  north  side  of  Muir 
Beach,  Bear  Valley,  Drake's  Bay,  the  Point  Reyes  head- 
lands, Kehoe  Beach,  McClure's  Beach,  and  Tomales  Point 
(B.J.  Walton  pers.  comm.).  Peregrines  also  formerly  nested 
on  Red  Rock  in  San  Francisco  Bay,  but  it  is  unclear  if  the 
aerie(s)  were  on  the  small  Marin  County  portion  of  that 
island.  In  the  1930s,  there  were  seven  pairs  of  Peregrines 
nesting  in  Marin  County  in  one  year,  but  by  the  1960s 
there  were  only  one  or  two  pairs  (B.J.  Walton  pers. 
comm.).  In  the  1970s,  there  were  no  documented  pairs;  in 
the  1980s,  circumstantial  evidence  suggested  at  least  one 
pair  may  have  nested  here,  though  confirmation  is  lacking. 
In  1990,  a  pair  began  nesting  on  a  cliff  at  the  Marin 
Headlands,  but  the  attempt  failed  soon  after  the  young 
hatched  (Golden  Gate  Raptor  Observatory).  In  1991,  this 
same  pair  apparendy  nested  farther  north  along  the  soudv 
ern  Marin  coast  and,  unassisted  by  humans,  successfully 
fledged  four  young.  Breeding  Peregrines  may  become  re- 
established here  via  management  efforts  or  from  recruit- 
ment from  natural  population  expansion/recovery.  Young 
Peregrines  were  released  at  hack  sites  at  Muir  Beach  from 
1983  to  1988  and  at  Tomales  Point  in  1987  and  1988 
(Linthicum  1988).  One  of  the  birds  released  at  Muir  Beach 
is  now  nesting  on  the  San  Francisco-Oakland  Bay  Bridge 
(B.J.  Walton  pers.  comm.). 

Grinnell  and  Miller  (1944)  noted  for  California  at  the 
time  that  Peregrines  were  "fairly  common  for  a  hawk"  and 
that,  except  locally,  numbers  were  holding  fairly  constant. 
North  American  populations  also  were  relatively  stable  up 
to  that  time,  but  rather  suddenly,  beginning  in  the  late 
1940s,  here  and  in  Europe,  Peregrine  populations  began 
to  decline  dramatically.  This  led  to  a  severe  population 

156 


crash  by  die  early  1960s,  which  bottomed  out  by  1973  to 
1975  (Hickey  1969,  Kiff  1988).  Although  other  factors 
have  affected  Peregrines— mortality  from  collisions  with 
wires,  shooting  on  wintering  grounds,  habitat  loss,  egg 
collecting,  taking  young  for  falconry,  disturbance  at  nest 
sites,  and  human  encroachment  affecting  prey  species— this 
decline  was  clearly  linked  to  pesticide  pollution.  Because  of 
their  position  high  on  the  food  chain,  Peregrines  readily 
concentrate  contaminants  from  their  prey.  Population 
crashes  in  North  America  (and  elsewhere)  were  primarily 
from  reproductive  failure  caused  by  DDE-induced  eggshell 
thinning  (Cade  et  al.  1988,  Peakall  &.  Kiff  1988,  Rise- 
brough  ek  Peakall  1988),  though  adult  mortality  from 
dieldrin  or  other  organochlorines  may  also  have  been  an 
important  factor  (Cade  et  al.  1988,  Nisbet  1988).  In 
California,  Peregrine  eggs  analyzed  to  date  have  extremely 
high  levels  of  DDT,  DDE,  PCBs,  and  dioxin  (B.J.  Walton 
pers.  comm.). 

The  size  of  the  historic  Peregrine  population  in  Califor- 
nia is  unknown.  Herman  et  al.  (1970)  estimated  that  100 
California  aeries  were  producing  young  until  at  least  the 
mid-1 940s.  The  actual  number  of  aeries  active  in  a  given 
year  at  the  turn  of  the  century  may  have  been  as  many  as 
300;  extensive  searching  of  historical  records  has  now 
revealed  about  200  pre-DDT  era  breeding  sites,  and  many 
probably  went  unrecorded  (B.J.  Walton  pers.  comm.). 
From  1 946  to  1 950,  there  were  definite  signs  of  reproduc- 
tive problems,  but  no  evidence  of  serious  population 
decline;  from  1950  to  1960,  there  was  a  precipitous  decline 
in  die  number  of  pairs  producing  young;  and  from  1961 
to  1969,  diere  were  sporadic  nesting  success  and  further 
declines,  leaving  fewer  than  10  known  breeding  pairs  in 
the  state  in  1969  (Herman  et  al.  1970).  By  1970  the  state 
breeding  population  did  not  exceed  5  successful  pairs— a 
reduction  of  95%  from  the  estimated  level  in  the  mid- 
19405  (Herman  1971).  Because  of  these  declines,  Pere- 
grines were  placed  on  both  federal  and  state  Endangered 
species  lists  (USFWS  1989a,  CDFG  1991a).  Use  of  offend- 
ing pesticides  was  gready  restricted  in  the  United  States  in 
1972  (Kiff  1988).  Since  these  bans,  populations  have 
expanded  through  natural  recovery  and  management 
activities,  which  have  included  manipulation  of  eggs  and 
young  at  nest  sites  in  California  beginning  in  1977  (Wal- 
ton <St  Thelander  1988).  Recent  increases  in  the  number 
of  known  active  nest  sites  in  California  are  also,  in  part,  a 
result  of  increased  efforts  to  find  them  (Walton  et  al. 
1988).  Since  the  1970s,  Peregrines  have  reoccupied  only 
35  of  California's  200  known  historic  (pre-DDT  era)  nest 
sites,  though  they  also  have  occupied  over  100  sites  not 
previously  known  (B.J.  Walton  pers.  comm.).  Many  seem- 
ingly suitable  sites  remain  vacant,  and  the  process  of 
population  expansion  has  been  slow  (Walton  et  al.  1988), 
increasing  at  an  average  of  8%  (6.8  breeding  pairs)  per  year 
since  1975  (Monk  et  al.  1989).  As  of  1989,  researchers 


Falcons 


SPECIES  ACCOUNTS 


Falcons 


knew  of  only  90  active  nest  sites  in  the  state  (Monk  et  al. 
1 989).  The  Coast  Ranges  north  of  San  Francisco  to  the 
Oregon  border  currently  support  the  largest  number  of 
nesting  pairs  in  the  western  United  States  and  about 
two-thirds  of  California's  nesting  population  (Walton  et  al. 
1988,  Monk  et  al.  1989).  Between  1971  and  the  mid- 
1980s,  no  Peregrines  were  known  to  have  nested  along  the 
coastline  north  of  San  Francisco,  an  area  with  over  30 
historic  nest  sites.  In  the  late  1980s,  Peregrine  sightings 
along  the  north  coast  increased,  and  at  least  one  pair 
nested  successfully  (B.J.  Walton  pers.  comm.).  With  man- 
agement help,  Peregrine  populations  on  the  central  Cali- 
fornia coast  (from  San  Francisco  to  Santa  Barbara 
counties)  have  increased  from  1  pair  at  Morro  Rock  in  the 
1960s  and  1970s  to  12  pairs,  many  of  which  are  located 
on  the  Big  Sur  coasdine.  The  central  coast  contains  about 
65  historical  nesting  sites.  The  historical  population  of 
over  40  pairs  on  the  southern  California  coast  and  Chan- 
nel Islands  was  extirpated  but  has  since  recovered  to  about 
8  pairs,  3  of  which  were  established  on  large  buildings  or 
bridges  in  the  Los  Angeles  basin  by  release  programs;  the 
island  population  is  expanding  rapidly  (5  pairs  in  1989). 
Interior  populations  have  always  been  less  densely  spaced, 
and  currendy  there  are  fewer  than  6  active  sites  in  river 
canyons  of  the  Cascades  and  Sierra  Nevada,  including  3 
pairs  in  Yosemite  National  Park. 

Although  nesting  productivity  of  wild  pairs  is  improv- 
ing, it  is  still  compromised  by  accumulations  of  pesticides 
remaining  in  the  fatty  tissues  of  these  long-lived  birds, 
augmented  by  further  accumulations  of  pesticides  still 
circulating  in  the  environment  (B.J.  Walton  pers.  comm.). 
Eggshell  thinning  continues  at  critical  or  near  critical  levels 
throughout  California  (Walton  et  al.  1988),  necessitating 
an  aggressive  management  effort  to  maintain  and  increase 


the  rate  of  recovery  of  the  state's  breeding  population 
(Walton  6k  Thelander  1988).  In  fact,  one  or  both  adults  at 
nearly  50%  of  known  nesting  sites  were  born  at  the 
Peregrine  Fund's  facilities  at  Santa  Cruz.  There  are  three 
methods  of  "hands  on"  management  of  Peregrines:  (1) 
fostering— placing  in  active  Peregrine  nests  young  produced 
from  thin-shelled  eggs  removed  from  the  wild  and  incu- 
bated in  captivity,  or  from  eggs  laid  and  hatched  by  captive 
birds;  (2)  cross-fostering— placing  captive  reared  young  in 
the  nests  of  Prairie  Falcons,  which  raise  them  to  indepen- 
dence; and  (3)  hacking— placing  in  a  hack  box  at  an 
appropriate  nest  site  captive-reared  young  that  are  released, 
fed,  and  monitored  through  independence  by  concealed 
biologists. 

Possible  sources  of  currendy  accumulated  DDE  include 
(1)  residues  in  soils,  air,  and  water;  (2)  contaminants  in 
other  legal  pesticides;  (3)  residues  in  migrant  prey  species; 
(4)  illegal  pesticide  use;  and  (5)  legal  use  for  emergency 
applications  (Walton  ck  Thelander  1988,  Risebrough  ck 
Monk  1989).  Scientific  studies  indicate  that  Peregrines  are 
accumulating  pesticides  mosdy  from  the  United  States 
rather  than  from  Mexico  and  South  America,  where  there 
is  little  restriction  of  pesticide  use.  Although  chlorinated 
hydrocarbon  pesticide  use  is  restricted  in  this  country, 
other  toxins,  such  as  dioxin,  still  pose  serious  threats  to 
Peregrines  (B.J.  Walton  pers.  comm.).  Whether  Peregrines 
can  ever  again  maintain  large  natural  populations  in  Cali- 
fornia without  human  assistance  is  an  acid  test  of  our 
resolve  and  ability  to  cope  with  environmental  degradation 
and,  perhaps,  of  the  chances  of  long-term  survival  of  our 
species  on  the  planet.  Even  with  a  complete  solution  to  the 
pollution  problem,  Peregrines  will  never  reach  historical 
levels  because  of  extensive  habitat  loss,  particularly  of 
wedands(Kiffl988). 


157 


Pheasants  and  Quail 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Pheasants  and  Quail 


Pheasants  and  Quail 


Family  Phasianidae 


RING-NECKED  PHEASANT   Phasianus  colchicus 


ok 

A  year-round  resident,  though  popula- 
tions maintained  by  game  farm  releases. 

An  uncommon,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  9  (4.1%)  of  221  blocks. 

\^>^^\^\^ 

O    Possible        =         5   (56%) 

\\^\  '" 

C    Probable       =         3   (33%) 
•    Confirmed  =         1    (11%) 

FSAR  =  2        OPI  =  18         CI  =  1.56 

^^-%5?^ 

Ecological  Requirements 

This  resplendent  native  of  eastern  Asia  has  been  intro- 
duced widely  in  California  and  has  taken  hold  in  fertile, 
irrigated  agricultural  lands.  The  most  important  Pheasant 
habitats  are  cultivated  fields  of  grain,  such  as  rice,  barley, 
and  wheat,  but  irrigated  pastures  and  hayfields  may  also  be 
prominent  locally.  In  Marin  County,  Ring-necked  Pheas- 
ants occupy  areas  dominated  by  hay  and  alfalfa  crops,  but 
their  population  here  is  apparendy  not  self-sustaining,  as 
are  those  in  similar  habitat  in  nearby  Sonoma,  Napa,  and 
Solano  counties  (Calif.  Dept.  Fish  Game).  Irrigated  farm- 
land is  crucial  to  Pheasants  for  food.  It  provides  the  best 
habitat  for  them  when  it  is  interspersed  with  vegetation 
that  also  meets  their  requirements  for  nesting  and  cover 
(Olsen  1977,  Johnsgard  1986). 

In  winter,  birds  form  temporary  mixed  or  unisexual 
flocks.  For  breeding,  the  polygynous  males  break  off  singly 
to  attract  harems  of  about  three  to  ten  females.  The  males 
select  ill-defined  crowing  territories  diat  include  patches  of 
varied,  interspersed  habitat.  They  avoid  all  but  the  edges  of 
large  blocks  of  monotypic  vegetation  and  prefer  a  blending 
of  food  patches  with  herbaceous,  meadow,  marsh,  brush, 
and  tree  clump  habitats.  Pheasants  use  moderately  dense 
herbaceous  and  brushy  cover  for  roosting,  loafing,  and 

158 


nesting.  For  nesting  early  in  spring,  they  prefer  permanent 
residual  cover  of  dry  grasses  and  forbs  persisting  from  the 
previous  year;  with  continued  plant  growth,  birds  shift  to 
farm  crops  and  new  spring  vegetation.  Nesting  habitats 
include  hayfields,  small  grain  crops,  strip  cover,  pastures, 
wetland  and  woodland  edges,  and,  to  a  lesser  extent,  fallow 
fields,  gravel  pits,  lakeshores,  farmyards,  stubble  fields, 
plowed  fields,  and  orchards.  Strip  cover,  which  is  also 
important  for  roosting  and  loafing,  generally  consists  of 
low-growing  vegetation  parallel  to  roadways,  railroads, 
drainage  ditches,  irrigation  canals,  streams,  dikes,  and 
fence  lines.  Pheasants  prefer  wider  strips  to  narrower  ones, 
and  moderate-sized  fields  to  small,  narrow,  or  large  ones. 
Males  apparendy  adjust  their  crowing  territories  to  include 
the  nest  sites  of  females. 

Pheasants  place  most  nests  in  shallow  depressions 
scooped  out  of  the  earth  or  in  natural  hollows.  Occasion- 
ally, they  raise  their  nests  slighdy  above  the  ground,  for 
example,  atop  wind-drifted  cornhusks  or  on  tussocks  in  a 
marsh;  rarely,  diey  locate  nests  well  above  ground  in  straw 
stacks  or  in  the  old  nests  of  other  birds  or  squirrels.  Nests 
are  lined  with  dried  grasses  or  leaves,  weed  stalks,  fine 
twigs,  or  cornhusks  taken  from  the  immediate  vicinity  of 


Pheasants  and  Quail 


SPECIES  ACCOUNTS 


Pheasants  and  Quail 


the  nest;  a  few  feathers  from  the  hen  Pheasant  may  some- 
times be  found  in  the  nest.  The  nest  site  microhabitat 
generally  has  a  greater  density  of  vegetative  cover  (particu- 
larly to  the  side  of  the  nest)  than  does  the  broader  sur- 
rounding nesting  habitat  (Wood  6k  Brotherson  1981). 
The  height  of  vegetative  cover  (within  a  general  range  of 
about  10-100  in.)  does  not  seem  to  be  as  important  as 
vegetative  density  (Olsen  1977,  Wood  6k  Brotherson 
1981);  but  see  Hanson  (1970).  Canopy  cover  can  vary 
from  leaving  the  nest  completely  exposed  from  above  to 
providing  partial  or  complete  concealment.  Although  nest- 
ing cover  appears  to  provide  protection  from  predators, 
perhaps  more  importandy  it  furnishes  a  microclimate  of 
lower  temperature  and  higher  humidity  than  is  found  at 
similar  heights  in  surrounding  vegetation  (Francis  1968, 
Hanson  1970,  Wood  6k  Brotherson  1981).  In  California, 
brood  cover  consists  primarily  of  grain,  rice,  natural  cover 
areas,  and  plowed  fields  (Olsen  1977).  In  the  fall,  Pheas- 
ants tend  to  drift  toward  stream  bottoms,  swales,  and 
swampy  edges;  ungrazed  hayfields,  wild  grass,  weeds, 
brushy  woodlots,  fencerows,  and  stubble  fields  provide 
additional  cover.  At  all  seasons,  Pheasants  require  a  source 
of  water  close  by. 

Ring-necked  Pheasants  are  primarily  grain  eaters, 
though  leafage  can  be  important  in  their  diets  seasonally; 
they  take  animal  matter  in  small  amounts  from  spring 
through  fall.  In  California,  the  diet  varies  greatly  among 
habitat  types,  locally  as  well  as  geographically  and  season- 
ally (Grenfell  et  al.  1980).  In  grain-growing  regions  of  the 
Sacramento  and  San  Joaquin  valleys,  cultivated  grains, 
such  as  rice,  barley,  wheat,  oats,  and  grain  sorghums,  are 
the  most  important  foods  year  round  and  may  constitute 
as  much  as  80%  of  the  whole  diet  in  a  given  season.  In  the 
Sacramento  Valley  grain  regions,  at  least,  Pheasants  in- 
crease their  use  of  green  forb  and  grass  leafage  in  spring 
and  of  forb  and  grass  seeds  in  spring  and  summer;  animal 
foods  account  for  only  about  3%-7%  of  the  spring 
through  fall  diet.  In  contrast,  in  an  area  of  extensive 
irrigated  pastureland  in  the  San  Joaquin  Valley,  the  spring 
to  fall  diet  consists  of  about  60%-90%  grass  and  forb 
seeds.  The  amount  of  green  leafage  in  the  diet  there  shifts 
dramatically  to  over  60%  in  winter  and  drops  to  slighdy 
over  25%  in  spring;  cultivated  crops  reach  a  maximum  of 
only  about  1 7%  of  the  diet  in  summer.  Based  on  limited 
samples,  the  spring  through  fall  diet  in  the  Modoc  Plateau 
and  Great  Basin  regions  varies  seasonally  from  75%-96% 
cultivated  crops;  winter  diet  (data  available  only  from 
Modoc)  is  over  50%  leafage,  secondarily  grass  and  forb 
seeds,  and  lasdy  cultivated  grains.  In  spring,  birds  in  the 
Modoc  region  use  over  85%  cultivated  grain,  whereas 
those  in  the  Great  Basin  rely  on  over  50%  leafage  and 
about  40%  grass  seed;  animal  foods  in  these  areas  account 
for  as  high  as  23%  of  the  diet  in  summer.  Pheasants  also 
eat  limited   amounts  of  corms   and   roots,   fleshy  fruits, 


flower  buds  and  flowers,  and  mast;  additionally,  they  do 
some  damage  to  tomato,  melon,  and  potato  crops  (Ferrel 
et  al.  1949,  Leach  et  al.  1953,  Grenfell  et  al.  1980).  Little 
appears  to  have  been  written  on  the  foraging  tactics  of 
Pheasants,  but  they  are  primarily  ground  foragers  and  must 
uncover  some  items.  Johnsgard  (1 986)  indicated  that  the 
birds'  short  toes,  strong  claws,  and  sharp  bills  are  all  well 
adapted  for  digging  and  scratching.  Edminster  (1954),  on 
the  other  hand,  reported  that  they  pick  and  root  in  the 
ground  better  with  their  beaks  and  do  not  use  their  feet  for 
scratching  out  food.  Pheasants  appear  to  take  most  culti- 
vated grain  as  waste  grain  from  the  ground,  but  they  also 
take  some  from  the  plants  before  harvest  (Ferrel  et  al. 
1949).  The  fact  that  Pheasants  browse  on  flower  buds, 
flowers,  and  leafage  suggests  they  also  procure  some  weed 
seeds  direcdy  from  the  plants.  In  the  Sacramento  Valley, 
Pheasants  consume  18  orders  of  insects  and  other  inverte- 
brates, grasshoppers  being  the  most  important;  occasion- 
ally, they  take  mice  (Ferrel  et  al.  1949).  The  diet  of  week-old 
chicks  is  exclusively  insects;  by  8  weeks  of  age  it  decreases 
to  about  50%  insects;  and  by  1 3  weeks  it  resembles  that  of 
adults.  Chicks  initially  take  small  insects,  such  as  beedes, 
and  later  larger  ones,  such  as  grasshoppers.  Females 
appear  to  eat  more  insects  than  do  males,  and  they  fre- 
quendy  take  calcium-rich  snails,  which  presumably  are 
important  for  egg  formation  (Korschgen  1964). 

Marin  Breeding  Distribution 

Although  there  were  a  few  adas  sightings  toward  the  coast, 
most  were  in  the  vicinity  of  agricultural  hay  and  alfalfa 
fields  near  marshlands  along  San  Pablo  Bay  near  Novate 
The  only  confirmation  of  breeding  was  a  hen  with  a 
half-grown  chick  in  reclaimed  marshlands  east  of  Ignacio 
on  13  May  1979  (Anonymous  fide  DS).  Despite  such 
evidence,  the  Marin  population  is  not  viable  but  depends 
upon  the  release  by  hunt  clubs  of  game  farm-reared  birds 
(G.  Thomsen,  J.R.  Slosson  pers.  comm.). 

Historical  Trends/Population  Threats 

Ring-necked  Pheasants  were  first  introduced  to  California 
in  Santa  Cruz,  San  Mateo,  and  Marin  counties  prior  to 
1889  by  private  parties  (Grinnell  et  al.  1918;  G6kM  1944; 
Hjersman  1947).  Birds  were  first  released  by  the  Fish  and 
Game  Commission  in  1889  in  a  number  of  counties, 
including  coastal  Marin  and  Monterey;  a  year  or  two  after 
1894,  they  were  also  released  in  Humboldt  and  Santa 
Clara  counties.  Introductions  began  in  earnest  in  1908 
from  breeding  stock  from  the  newly  established  State 
Game  Farm.  By  1916,  Pheasants  had  been  released  in  37 
of  the  state's  58  counties,  and  they  appeared  to  be  estab- 
lished in  the  wild  in  coastal  counties  at  Eureka  and 
Fortuna,  Humboldt  County;  Napa,  Napa  County;  Wat- 
sonville,  Santa  Cruz  County;  Pacific  Grove,  Monterey 
County;  and  especially  in  the  Santa  Clara  Valley  north  of 

159 


Pheasants  and  Quail 


MARIN  COUNTY  BREEDING  BIRD  ATlJ\S 


Pheasants  and  Quail 


San  Jose,  Santa  Clara  County.  Based  on  the  current 
distribution  of  Pheasants,  it  is  unclear  whether  viable 
populations  really  existed  in  all  these  areas.  Pheasants  may 
have  been  extirpated  locally  on  the  coast  by  changing 
agricultural  practices  rather  than  by  inherendy  low  fecun- 
dity. A  hunting  season  was  first  opened  in  Inyo  and  Mono 
counties  in  1925  and  then  statewide  in  1933  (Hjersman 
1947,  Nelson  &.  Hooper  1976,  Mallette  6k  Slosson  1987). 
By  1944,  Pheasants  had  been  planted  in  every  county  in 
the  state  except  Alpine,  and  diey  had  been  persistendy 
replanted  in  most  of  the  seemingly  "suitable"  parts  of  the 
state  (GckM  1944,  Hjersman  1947).  It  appears  that  Pheas- 
ants never  established  themselves  in  Marin  County 
(GckW  1927,  SckP  1933,  G&M  1944). 

Although  Pheasants  were  initially  successful  along  cer- 
tain sections  of  the  coast,  their  most  important  populations 
there  (in  the  Santa  Clara  Valley)  declined  in  the  early 
1920s  because  of  changing  farm  practices  (Hjersman 
1947).  The  heart  of  the  state's  Pheasant  population 
switched  to  the  Central  Valley  following  the  introduction 
of  rice  culture  there  during  World  War  I.  Nelson  and 
Hooper  (1976)  and  Mallette  and  Slosson  (1987)  reported 


that  the  state's  Pheasant  populations  have  declined  in 
recent  years  from  die  advent  of  "clean  farming"  practices, 
which  eliminate  bordering  weedy  and  brushy  vegetation, 
and  from  the  continued  encroachment  of  urban-suburban 
sprawl.  Although  many  naturalists  might  not  mourn  the 
decline  of  an  alien  species  such  as  the  Pheasant,  it  should 
be  remembered  that  the  Pheasant's  demise  would  surely  be 
paralleled  by  that  of  native  species  that  also  depend  on  the 
marginal  refuges  in  large  tracts  of  human-manipulated 
habitat.  Breeding  Bird  Surveys,  on  the  other  hand,  suggest 
that  Pheasant  numbers  in  California  were  relatively  stable 
from  1968  to  1989  (USFWS  unpubl.  analyses). 

Remarks 

California  birds  were  first  obtained  from  China  and  Ore- 
gon (where  they  were  first  introduced  in  America  in  1881; 
Bent  1932),  but  thereafter  came  largely  from  game  farms 
(G&M  1944,  Hjersman  1947).  Although  most  California 
birds  are  of  the  race  P.  c.  torquatus,  other  closely  related 
races  have  been  released,  as  well  as  crosses  between  some 
of  them. 


#4 .  #  *^  m 


l\        'Mf$# 


California  Quail  must  be  extreme!}  vigilant  if  tkej  are  to  raise  all  of  their  young  to  maturity.    Draining  by  Keith  Hansen,  1 989. 

160 


Pheasants  and  Quail 


SPECIES  ACCOUNTS 


Pheasants  and  Quail 


CALIFORNIA  QUAIL   Callipepla  californica 


A  year-round  resident. 

A  fairly  common,  nearly  ubiquitous 

breeder;  overall  breeding  population 
large. 

^^^^k^k^^\^kky\ 

Recorded  in  208  (94.1%)  of  221 
blocks. 

O    Possible        =       31    (15%) 

^^^^k^0^^ 

^a 

©    Probable       =      92   (44%) 
•    Confirmed  =      85   (41%) 

FSAR  =  3        OPI  =  624        CI  =  2.26 

Ecological  Requirements 

From  prominent  lookouts,  cocks  stand  sentry  duty  for  wary 
coveys  of  "Valley  Quail"  before  they  break  up  into  pairs  in 
spring  and  scatter  widely  to  breed.  California  Quail  stick 
close  to  the  brushy  edges  of,  or  openings  in,  all  of  Marin 
County's  major  scrub,  woodland,  and  forest  habitats 
where  they  border  on  pasturelands,  weedy  fields,  mead- 
ows, and  unkempt  lawns  and  yards.  In  dense,  extensive 
tracts  of  coastal  scrub  and  chaparral,  Quail  frequent  the 
edges  or  openings  along  trails,  fireroads,  localized  burns, 
or  other  open  disturbed  sites.  California  Quail  prefer  edge 
situations  with  interspersed  low  protective  cover,  open- 
ground  foraging  areas,  and  water  sources  (Sumner  1935, 
Emlen  ck  Glading  1945,  Leopold  1977).  Cover  provides 
shade,  shelter  from  inclement  weather,  and,  perhaps  most 
importandy,  refuge  from  predators  for  adults  and  broods. 
Cover  can  consist  of  small  or  extensive  patches  of  bushes, 
bramble  and  briar  thickets,  trees,  thick  clumps  of  weed 
stalks,  rough  outcrops  of  rock,  or  brush  piles  that  are  dense 
at  ground  level  and  impervious  to  penetration  by  avian 
predators.  Such  cover  provides  a  daytime  loafing  area  and 
a  sanctuary  for  escape.  At  night,  California  Quail  normally 
roost  off  the  ground  in  dense  evergreen  trees  or  tall  shrubs 
out  of  reach  of  ground  predators  and  concealed  from 
hungry  owls.  Quail  foraging  areas  ideally  provide  a  sparse 
to  moderately  dense  growth  of  annual  grasses  and  particu- 
larly forbs,  with  a  duff  or  litter  layer  that  harbors  fallen 
seeds.  California  Quail  generally  forage  within  about  50 
feet  of  escape  cover.  In  dry  areas  in  late  summer  and  fall, 
they  will  venture  several  hundred  yards  into  the  open  to 
forage  until  the  arrival  of  the  first  migrant  Cooper's  Hawks, 


when  they  again  retract  their  foraging  radius  to  the  close 
proximity  of  cover.  For  much  of  the  year,  Quail  can  obtain 
water  from  succulent  greenery,  but  in  the  hot  and  dry 
months  of  summer  and  early  autumn,  they  usually  need  a 
dependable  source  of  water  close  to  cover,  be  it  only  a  drip, 
seep,  or  puddle.  This  is  less  of  a  summertime  problem 
along  the  fog-shrouded  coasdine.  If  hard  pressed,  Quail 
can  live  without  drinking  water,  provided  they  have  at 
hand  heavy  dew,  berries,  or  succulent  vegetation  (Sumner 
1935). 

The  absence  of  Mountain  Quail  in  Marin  County 
appears  to  be  a  fluke  of  geography,  since  suitable  habitat  is 
available  here.  They  occur  in  coastal  counties  to  the  north 
and  south  and  probably  did  not  reach  Marin  because  of 
habitat  barriers  to  foot-powered  dispersal.  In  coastal  Cali- 
fornia, Mountain  Quail  inhabit  coniferous  forest  with  a 
shrubby  understory,  mixed  evergreen  forest,  and  chapar- 
ral. Although  diey  overlap  in  habitat  somewhat  with  Cali- 
fornia Quail,  Mountains  generally  occur  at  higher 
elevations,  on  steeper  slopes,  and  spend  most  of  their  time 
inside  chaparral  thickets  or  beneath  the  forest  canopy 
(Gutierrez  1980). 

California  Quail  generally  prefer  nest  sites  that  are  in 
the  open  away  from  a  continuous  canopy  of  shrubs  or  trees 
(Leopold  1977).  Early-season  nest  sites  may  be  far  from 
water  when  green  vegetation  is  at  a  peak;  even  chicks  can 
derive  their  water  needs  from  succulent  vegetation.  Quail 
may  avoid  nesting  close  to  streams  (fenced  or  unfenced)  or 
water  troughs  where  overgrazing  has  destroyed  nesting 
cover.  Widi  the  diminution  or  disappearance  of  greenery 

161 


Pheasants  and  Quail 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Pheasants  and  Quail 


in  midsummer,  Quail  must  nest  within  about  400  yards 
(the  cruising  radius  of  chicks)  from  water  (Sumner  1935, 
Leopold  1977).  California  Quail  typically  conceal  their 
nests  on  die  ground  in  dense  clumps  of  grass  or  weeds, 
often  sheltered  at  the  base  of  bushes,  fallen  trees  or  limbs, 
vines,  bnash  piles,  or  fencerows.  Other  nests  are  sheltered 
beneath  overhanging  rocks,  in  rock  crannies,  in  niches  in 
narrow  gullies,  or  under  piles  of  scrap  lumber  (Grinnell  et 
al.  1918,  Dawson  1923,  Bent  1932,  Glading  1938,  Leo- 
pold 1977).  The  nest  is  usually  a  hollow  in  the  ground 
lined  sparsely  with  grasses,  leaves,  weed  stems,  and  per- 
haps a  few  feathers;  usually  nests  are  roofed  over,  at  least 
during  the  early  part  of  incubation,  by  vegetation,  or 
sometimes  by  overhanging  rocks.  Occasionally,  birds  build 
a  crude  but  more  substantial  nest  of  the  same  materials  on 
a  log  or  stump,  in  a  brush  pile,  on  a  bale  of  hay  or  the  side 
of  a  haystack,  or  among  vines  on  a  trellis.  Rarely,  they  place 
nests  up  in  trees  at  the  broken  or  decayed  ends  of  limbs  or 
at  an  intersection  of  two  large  branches.  One  pair  nested 
in  a  garden  on  a  rooftop.  Exceptionally,  these  Quail  may 
lay  eggs  in  the  nests  of  other  birds  on  or  above  ground. 

California  Quail  forage  primarily  on  the  ground  by 
grazing  on  annual  plants  and  by  scratching  in  the  soil  and 
litter;  occasionally,  they  jump  to  reach  blossoms  and  climb 
into  shrubbery.  Mountain  Quail  also  forage  by  these  meth- 
ods, jump  for  flowers  and  seeds  more  frequendy,  climb 
trees  and  shrubs  to  procure  berries  and  fruits  more  readily, 
dig  beneath  the  soil  for  bugs,  and  shell  acorns  (Gutierrez 
1980).  Like  other  gallinaceous  birds,  both  species  pick  up 
grit  to  grind  seeds.  California  Quail  generally  forage  mosdy 
right  after  dawn  and  during  a  second  burst  of  activity  in  the 
evening  (Sumner  1935,  Leopold  1977).  In  hot  weather, 
they  usually  go  to  water  daily  and  generally  lead  chicks  to 
drink  after  the  morning  feeding  bout  and  often  at  other 
times.  During  breeding,  adults  subsist  on  short  rations:  the 
male  because  of  time  spent  defending  against  intruders, 
guarding  the  female  and  nest,  and  protecting  the  young; 
the  female  because  of  intermittent  feeding  during  incuba- 
tion and  time  spent  tending  the  young.  When  Quail 
double  brood,  females  desert  their  families  after  about 
three  weeks  to  find  new  mates  and  nest  again,  leaving  the 
original  males  to  rear  the  first  brood  (Leopold  1977). 

California  Quail  eat  primarily  forb  seeds  and  green 
leafage,  but  also  fruits,  berries,  buds,  blossoms,  catkins, 
acorn  fragments,  plant  galls,  and  waste  grain  (Browning 
1977,  Leopold  1977,  Grenfell  et  al.  1980).  They  consume 
about  l%-7%  animal  matter  only  in  spring  and  early 
summer  and  more  in  wet  than  dry  years.  Animal  foods 
include  insects,  millipedes,  mites,  spiders,  snails,  and  sow- 
bugs.  The  seeds  of  annual  broadleaved  forbs  are  a  staple 
throughout  the  year  and,  along  with  minor  amounts  of 
grass  seeds,  constitute  about  95%  of  the  diet  in  summer, 
90%  in  fall,  70%  in  winter,  and  over  55%  in  spring 
(Leopold  1 977).  In  the  Coast  Ranges,  bur  clover  is  perhaps 

162 


the  most  important  single  food  plant,  though  other 
legumes  (various  clovers,  lotuses,  and  lupines)  and  filaree 
can  be  equally  important  locally.  Other  key  seed-bearing 
forbs  are  fiddleneck,  turkey  mullein,  geranium,  vetch, 
various  thistles,  popcorn  flower,  chickweed,  miners  lettuce, 
red  maids,  buttercup,  buckthorn  weed,  windmill  pink, 
tarweeds,  California  poppy,  vinegar  weed,  and  gamble- 
weed  (Browning  1977,  Leopold  1977).  Generally,  the 
annual  grasses  that  now  dominate  California's  grasslands 
are  not  important  Quail  foods  and  in  fact  compete  with  and 
displace  the  more  favored  broadleaved  annuals.  Quail  also 
browse  extensively  on  green  leafage,  mosdy  of  the  seed- 
bearing  annual  forbs  mentioned  above.  They  regularly  eat 
small  amounts  of  green  grasses  but  feed  on  them  exten- 
sively only  when  the  seeds  and  green  foliage  of  forbs  are 
scarce  or  absent.  Consumption  of  greens  begins  with  the 
appearance  of  new  growth  after  the  first  fall  rains  (even  in 
years  of  seed  abundance),  peaks  in  winter  and  spring,  and 
generally  ceases  when  annual  plants  die  in  late  spring  and 
summer  and  the  new  crop  of  seeds  becomes  available. 
Usage  of  greenery  climbs  from  a  low  of  about  2%  in 
summer  and  10%  in  fall  to  a  peak  of  about  30%-44%  in 
winter  and  35%-40%  in  spring  (Browning  1977,  Leopold 
1977).  Use  of  greens  in  winter  may  vary  between  locations 
from  as  much  as  75%  to  as  little  as  0%-3%.  Acorn 
fragments  can  be  an  important  component  of  the  diet  in 
fall  or  winter  (as  much  as  35%)  and  even  in  spring,  in 
some  localities  and  in  certain  years  (Browning  1977).  In 
addition,  Quail  take  limited  amounts  of  the  fruits  of  other 
woody  perennials,  such  as  poison  oak,  manzanita,  cea- 
nothus,  misdetoe,  acacia,  and  black  locust.  In  summer  and 
fall,  Quail  may  eat  some  waste  grains  left  after  harvest, 
especially  wheat,  oats,  barley,  corn,  or  even  rice,  kafir,  or 
safflower. 

Quail  chicks  are  born  with  a  substantial  residue  of 
original  egg  yolk  enclosed  within  the  abdomen.  This  serves 
the  vital  function  of  tiding  over  the  precocial  young  during 
the  critical  period  when  they  are  learning  to  feed,  or  during 
periods  of  rain  or  fog  when  foraging  is  difficult  or  impos- 
sible (Leopold  1977).  Chicks  a  few  days  old  live  mosdy  on 
insects  (Grenfell  et  al.  1980).  At  one  site,  chicks  one  to 
three  weeks  of  age  ate  mosdy  seeds  and  only  about  11% 
insects  (n  =  47)  and  at  four  to  six  weeks  about  9%  insects 
(n  =  66);  thereafter,  insect  consumption  fell  rapidly  to  a 
trace  (Leopold  1977).  Chicks  start  with  small  food  items 
and,  as  they  grow,  graduate  to  larger  ones  (Sumner  1935, 
Grenfell  et  al.  1980). 

Marin  Breeding  Distribution 

The  California  Quail  was  one  of  the  most  widespread  of 
Marin  County's  breeding  birds,  occurring  in  virtually  every 
block  during  the  adas  period.  Quail  were  absent  locally 
only  on  the  tops  of  some  of  the  higher  ridges,  such  as  the 
peak  of  Mount  Tamalpais,  and  in  a  few  areas  without 


Pheasants  and  Quail 


SPECIES  ACCOUNTS 


Pheasants  and  Quail 


brushy  cover.  Representative  breeding  sites  were  Marshall 
(NE  6/15/76  -GJK);  near  Three  Peaks  (FL  6/17/82 
— DS);  and  Pine  Gulch  Creek,  Bolinas  Lagoon  (FL 
6/14/80 -DS). 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  reported  that  the  California 
Quail  had  declined  in  the  state  in  the  previous  35  years, 
though  it  was  still  numerous  in  favorable  territory  where 
not  "shot  out."  Many  authors  attributed  this  decline  pri- 
marily to  intense  market  hunting  (e.g.,  Grinnell  et  al. 
1918).  Settlers  turned  to  Quail  for  food  after  the  Gold 
Rush  depleted  supplies  of  edible  large  mammals  (Leopold 
1977).  Quail  hunting  for  the  San  Francisco  market  began 
in  Marin  County  in  the  1860s  (Welch  1928).  During  the 
late  1880s  and  1890s,  millions  of  Quail  were  shot, 
trapped,  and  sold  in  California.  In  1895-96,  hunters  sold 
177,366  Quail  in  the  open  markets  of  San  Francisco  and 
Los  Angeles  alone.  Because  of  decreases  in  the  Quail 
population,  laws  were  passed  in  1880  that  prohibited 
trapping  and  in  1901  that  fixed  a  bag  limit  and  oudawed 
the  sale  of  Quail  (Welch  1928,  Leopold  1977).  Boodeg 
operations  continued  to  circumvent  the  laws,  and  by  1925 
only  a  pitiful  remnant  of  the  state's  bountiful  supply  of 
Quail  remained. 

Sumner  (1935),  on  the  other  hand,  concluded  diat  the 
decline  was  due  to  a  combination  of  overhunting  and 
various  other  factors,  such  as  '  clean  farming    practices, 


that  eliminate  cover  and  increase  erosion,  overgrazing, 
man's  usurpation  of  water  sources,  fire  control  that  pro- 
motes growth  of  impenetrable  brush  that  chokes  out  Quail 
food,  and  poisons  set  out  for  rodents.  Despite  the  depre- 
dations of  hunters,  Leopold  (1977)  felt  that  the  decline  in 
Quail  numbers  was  mainly  from  a  decrease  in  the  produc- 
tion of  Quail  food  caused  by  changing  land  use.  He 
envisioned  a  population  peak  at  the  start  of  the  market 
hunting  era  that  was  greater  than  in  presettlement  times. 
Quail  numbers  may  have  been  increased  at  the  time  by  the 
breaking  up  of  native  bunch  grasses  allowing  the  intrusion 
of  seed-bearing  forbs;  by  the  planting  of  grains  and  hedge- 
rows; and  by  the  opening  up  of  woods— factors  that  pro- 
vided a  mosaic  of  Quail  habitat  and,  along  with  the  virgin 
fertility  of  the  soils,  fueled  increased  production  of  pre- 
ferred Quail  foods.  Leopold  concluded  that  the  subsequent 
decline  in  numbers  was  caused  by  the  loss  of  soil  fertility 
from  intensive  agriculture  and  overgrazing  and  by  the 
invasion  of  alien  annual  grasses,  which  replaced  the  pre- 
ferred Quail  foods  of  native  and  introduced  forbs.  The 
trend  toward  large  landholdings  and  mechanized  agricul- 
ture has  eliminated  much  cover,  leading  to  further  habitat 
deterioration.  Although  clearing  and  logging  have  opened 
up  some  habitat  in  certain  areas  of  California,  the  overall 
trend  here  has  been  toward  a  reduction  in  the  extent  and 
quality  of  Quail  habitat  (Sumner  1935).  Quail  numbers 
were  relatively  stable  on  Breeding  Bird  Surveys  in  Califor- 
nia from  1968  to  1989  (USFWS  unpubl.  analyses). 


163 


Rails 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Rails 


Rails,  Gallinules,  and  Coots 

Family  Rallidae 


BLACK  RAIL    Laterallus  jamaicensis 


A  year-round  resident;  numbers  swell 

^^^^^JOS 

from  Sep  through  Mar. 

jC^^Q^c 

A  fairly  common,  very  local  breeder; 

\"""\  J&^\    \^\\     \^\     \r\     \^\vy^. 

_ 

overall  breeding  population  very  small. 

^V*\  ^-Pc 

Pc^vV>\^^^Vv^^ 

Recorded  in  6  (2.7%)  of  221  blocks. 

\^\ 

w^cv  -^c\  yc\  \^\  \^\  \^\  V--^ 

O    Possible        =         1    (17%) 

Vu 

^v\\\or  \^\  vp^r>- \^^\--  \^^K^-"\^^\ 

©    Probable       =         4   (67%) 

f^\  i^^^-^-V^^A  wV'X    Jv^\  J^\   3r"\ 

•    Confirmed   =         1    (17%) 

^5POf<i^^ 

V^Sp. T- 

^Vw-v 

FSAR  =  3        OPI  =  18          CI  =  2.00 

J,    jZ^"^                                                                  ^\^^\            \l^V^t^    \^^Y-^'V\^ 

^^5^^ 

>J^>                                                             \L_   /             ^=>-=<5 

Ecological  Requirements 

This  furtive  little  rail  inhabits  tidal  salt  and  brackish 
marshes  and,  to  a  lesser  extent,  freshwater  marshes.  Black 
Rails  prefer  areas  of  high  marsh  at  the  upper  limit  of  tidal 
flooding  with  a  dense  cover,  usually  of  pickleweed  (Sali- 
cornia  virginica)  or  sedges  (Scirpus  spp.)  (Manolis  1978; 
Evens  et  al.  1989,  1991).  The  tidal  marshes  Black  Rails 
inhabit  in  Marin  County  are  either  dominated  by  Sali- 
comia,  have  a  preponderance  of  Salicornia  with  Scirpus  on 
the  borders  or  in  small  patches  within  the  Salicornia 
matrix,  or  are  a  mosaic  of  Salicornia  and  Scirpus  (Evens  et 
al.  1989).  At  Marin  County's  largest  freshwater  marsh, 
Olema  Marsh,  Black  Rails  have  occurred  in  stands  of 
cattail  (Typha)  or  bulrush  (Scirpus)  that  mix  with  other 
freshwater  marsh  or  coastal  swale  plant  species  and  border 
on  willow  or  alder  riparian  forest  (D.  Shuford  pers.  obs.). 
Black  Rails  are  patchily  distributed  in  tidal  marshes.  A 
suite  of  factors  interact  to  determine  the  suitability  of 
habitat,  though  no  single  factor  or  combination  of  factors 
is  sufficient  to  predict  Black  Rail  occurrence  (Evens  et  al. 
1989,  1991).  The  most  important  factors  influencing 
Black  Rail  distribution  are  tidal  regime,  marsh  elevation, 
and  freshwater  influence;  marsh  age  (maturity)  and  size, 
degree  of  channelization,  soil  and  water  salinity,  and  plant 

164 


composition  may  also  bear  on  rail  habitat  preferences 
(Evens  et  al.  1989,  1991).  Black  Rails  are  more  numerous 
in  marshes  with  unrestricted  tidal  flow  than  with  restricted 
tidal  flow;  they  are  extremely  rare  in  diked  marshes.  They 
inhabit  the  upper  reaches  of  marshes  where  there  is  emer- 
gent vegetation  at  high  tides  and  avoid  marshes  dominated 
by  salt  grass  (DisticKIis  spicata).  The  importance  of  a  mix  of 
tidal  and  freshwater  influence  is  suggested  by  the  concen- 
tration of  Black  Rails  in  the  northern  sections  of  the  greater 
San  Francisco  Bay  estuary  where  freshwater  inflow  is 
greatest.  There  Black  Rails  are  most  plentiful  in  large, 
broad  tidal  marshes  bordering  major  rivers.  In  bayshore 
marshes,  these  rails  are  most  numerous  at  the  mouths  of 
sloughs,  creeks,  and  rivers,  and  at  some  Sah'cornia-domi- 
nated  marshes  rails  cluster  at  clumps  of  Scirpus,  indicators 
of  freshwater  influence  (often  from  seeps).  Ultimately, 
Black  Rail  habitat  must  provide  cover,  nest  sites,  and 
suitable  food.  Since  predation  by  natural  enemies  such  as 
Great  Egrets,  Great  Blue  Herons,  and  Northern  Harriers 
can  be  severe  (Evens  &  Page  1986),  dense  cover  is  import- 
ant, especially  during  high  tides.  There  is  also  speculation 
that  Black  Rails  may  avoid  areas  with  large  densities  of 
Clapper  Rails  since  the  latter  species  may  prey  on  small 


Raits 


SPECIES  ACCOUNTS 


Rails 


birds  QM.  fide  JGE).  To  support  Black  Rails,  marshes 
should  grade  gradually  into  weedy  or  brushy  upland  vege- 
tation where  the  rails  can  retreat  at  extremely  high  tides. 

Black  Rails  usually  conceal  their  nests  completely  from 
view  in  the  dense  growth  of  Salicomia,  grasses,  sedges,  or 
other  marsh  vegetation,  which  they  also  use  to  construct 
their  nests;  rarely,  they  leave  them  open  to  view  from  above 
(Bent  1926).  They  place  most  nests  from  one  to  several 
inches  above  the  mud,  but  sometimes  nests  are  built  on 
the  ground  or  up  to  10  to  12  inches  above  ground.  Nests 
vary  gready  in  structure  from  thin,  frail  platforms  to,  rarely, 
ground  nests  five  inches  thick;  they  may  be  flat  or  deeply 
cupped.  Often  the  rails  interweave  surrounding  vegetation 
over  the  nest  to  give  it  the  appearance  of  a  domed-over 
meadowlark  nest  with  a  side  entrance.  Thicker  nests  are 
usually  built  up  from  the  ground,  and  thin  ones  are  usually 
placed  on  convenient  shelves  of  matted  vegetation.  Of  six 
nests  observed  in  the  San  Francisco  Bay  system,  all  were 
of  the  thin,  raised  type  and  lacked  a  dome  of  interwoven 
vegetation  (J-G.  Evens  pers.  comm.). 

Because  of  their  elusive  nature,  very  little  is  known  of 
the  food  habits  of  Black  Rails  (Wilbur  1 974).  Apparendy 
they  feed  on  insects  or  other  arthropods  (Bent  1926); 
presumably  they  pick  or  glean  dieir  meals  from  the  muddy 
substrate  or  from  the  surface  of  marsh  plants.  Black  Rail 
occurrence  is  positively  associated  widi  insect  and  spider 
abundance  and  negatively  associated  with  amphipod  abun- 
dance in  marshes  (Evens  et  al.  1986).  It  is  unclear  whether 
insects  and  spiders  are  a  primary  food  source  for  Black 
Rails  and  whether  these  arthropods  are  more  abundant  in 
tidal  marshes  diluted  by  fresh  water  (Evens  et  al.  1989). 
What  is  clear  is  that  much  still  needs  to  be  learned  of  the 
habitat  preferences  and  lifestyles  of  these  secretive  black 
gnomes. 

Marin  Breeding  Distribution 

In  Marin  County,  Black  Rails  breed  along  the  San  Fran- 
cisco and  San  Pablo  bayshores  from  Corte  Madera  Marsh 
north  to  the  Petaluma  marshes,  and  on  the  outer  coast, 
along  the  fringes  of  Bolinas  Lagoon,  at  the  south  end  of 
Tomales  Bay,  and,  perhaps  sporadically,  at  Olema  Marsh. 
We  recorded  Black  Rails  in  five  adas  blocks  on  the  bayside 
tidal  marshes.  The  adas  work  and  subsequent  more  inten- 
sive rail  censuses  (Evens  et  al.  1986,  1989,  1991)  revealed 
breeding  Black  Rails  at  Corte  Madera  Marsh,  China 
Camp,  Gallinas  Creek,  Novato  Creek,  Day  Island,  Black 
John  Slough,  die  Petaluma  marshes,  in  addition  to  die 
spots  on  the  outer  coast  mentioned  above.  During  die  adas 
period,  breeding  was  confirmed  only  at  China  Camp.  A 
nest  was  located  at  the  upper  edge  of  a  salt  marsh  about 
eight  inches  above  the  mud  in  a  patch  of  arrowgrass 
(Triglochin  sp.,  presumably  T.  maritima)  at  a  freshwater 
seep  (NE  5/20/80  -ITa).  In  1982,  five  additional  nests 
were  found  in  the  same  vicinity  in  Salicomia,  again  at  the 


upper  edge  of  the  marsh  near  freshwater  seeps  (ITa,  JGE, 
GWP).  Subsequendy,  during  extensive  surveys  (Evens  et 
al.  1986),  Black  Rails  were  confirmed  breeding  at  Day 
Island  near  Novato  with  the  observation  of  newly  hatched 
chicks  on  30  May  1986  (JGE)  and  at  Black  John  Slough  in 
the  Petaluma  marshes  with  the  location  of  a  nest  with  egg 
fragments  on  8  May  1986  (GWP,  NW).  During  the  adas 
period,  we  recorded  Black  Rails  away  from  the  bayside 
marshes  only  at  Olema  Marsh  (up  to  four  calling  6/17- 
7/30/80  —JGE,  DS).  Birds  have  not  been  recorded  there 
since  the  early  1980s,  perhaps  because  of  extensive  silt- 
ation  during  the  intense  flooding  of  1982.  Previously, 
breeding  had  been  confirmed  at  a  brackish  marsh  along 
Tomales  Bay  south  of  Inverness  with  the  observation  of  an 
adult  and  chicks  in  the  summer  of  1976  (GB).  A  high 
count  of  seven  calling  birds  was  recorded  at  the  south  end 
of  Tomales  Bay  on  16  May  1986  (JGE).  A  record  of  a  bird 
calling  on  the  west  shore  of  Bolinas  Lagoon  on  10  and  1 1 
March  1979  (RS  et  al.)  may  have  been  a  breeder,  a  winter 
visitant,  or  a  migrant.  Probable  evidence  of  breeding  at 
Bolinas  Lagoon  is  provided  by  records  of  one  to  two  birds 
calling  at  the  Pine  Gulch  Creek  delta  from  2  March  to  20 
May  1 987  (DDeS,  DAH)  and  one  to  two  calling  on  the  east 
shore  on  various  dates  from  29  March  to  1 1  July,  1983  to 
1986  (CCu  et  al.).  Surveys  at  Schooner  Bay,  Drake's 
Estero,  in  spring  1986  and  1988  and  at  Richardson  Bay  in 
spring  1988  did  not  reveal  any  Black  Rails  (Evens  et  al. 
1986,  1989). 

Historical  Trends/Population  Threats 

Until  recently,  the  status  of  breeding  Black  Rails  in  north- 
ern California  was  clouded  by  the  lack  of  adequate  field 
work  needed  to  detect  such  a  secretive  species.  Early 
authorities  had  stated  or  implied  that  the  species  moved 
north  to  northern  California  in  the  fall  after  the  breeding 
season  (Bent  1926,  AOU  1957).  Incidental  sightings  from 
the  late  1 950s  to  the  present  (ABN)  and,  particularly,  recent 
thorough  surveys  (Jurek  1976;  Manolis  1978;  Evens  et  al. 
1 989,  1 991)  have  documented  the  occurrence  of  a  substan- 
tial breeding  population  in  tidal  marshes  around  San 
Pablo  and  Suisun  bays  and  smaller  numbers  in  the  Sacra- 
mento-San Joaquin  Delta  as  far  inland  as  Lodi,  San 
Joaquin  County.  Kiff  (1978)  documented  the  first  breeding 
record  for  northern  California  from  the  reidentification  of 
an  egg  set  collected  on  10  April  191 1  at  Newark,  Alameda 
County,  in  south  San  Francisco  Bay,  where  today  the 
species  is  a  very  rare  or  sporadic  breeder.  The  greater  San 
Francisco  Bay  estuary  supports  the  bulk  (80%)  of  the  Black 
Rail  population  of  the  West,  with  the  remainder  along  the 
lower  Colorado  River  (<1 50  individuals);  at  the  Salton  Sea, 
canals,  and  lakes  of  die  Salton  Trough  (<50  individuals); 
at  Morro  Bay;  and  at  the  Point  Reyes  sites  described  above 
(Evens  et  al.  1991). 

165 


Rails 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Rails 


Because  tidal  marshes  in  the  San  Francisco  Bay  system 
have  been  reduced  by  60%-95%  (Nichols  6k  Wright 
1971,  Josselyn  1983),  Black  Rail  populations  there  must 
also  have  declined  drastically  (Evens  et  al.  1989,  1991). 
Black  Rails  no  longer  breed  in  salt  marshes  on  the  Califor- 
nia coast  south  of  Morro  Bay  (Garrett  &.  Dunn  1981, 
Unitt  1984).  The  California  Black  Rail  (L.  j.  coturniculus) 
is  currently  listed  as  Threatened  in  California  (CDFG 
1991a)  and  is  a  Candidate  (Category  2)  for  listing  as 
federally  Threatened  or  Endangered  (USFWS  1991). 
Saltmarsh  habitat  was  lost  through  diking,  filling,  and 
conversion  to  agricultural  lands,  salt  ponds,  and  urban 
development.  Because  of  its  proximity  to  human  habita- 
tion and  agricultural  land,  high  marsh  habitat  is  most 
susceptible  to  conversion.  Intensive  alteration  of  high 
marsh  habitat  in  south  San  Francisco  Bay  and  apparent 
subsidence  of  remaining  marshes  may  explain  the  near 


absence  of  breeding  Black  Rails  there  (Manolis  1978; 
Evens  et  al.  1989,  1991).  Most  marsh  habitat  in  the  South 
Bay  is  completely  flooded  at  high  tide  since  remaining 
marsh  abuts  directly  on  salt  pond  dikes  and  roadways; 
formerly  the  marsh  graded  gradually  into  upland  habitat. 
Further  loss  or  degradation  of  marshes,  possible  rising  sea 
level,  and  diversion  of  freshwater  inflow  to  the  North  Bay 
potentially  pose  ongoing  threats  to  Black  Rail  habitat 
(Evens  et  al.  1989,  1991).  In  addition,  these  rails  face 
higher  predation  pressures  from  the  lack  of  transitional 
upland  vegetation  in  many  marshes  and  possibly  from 
introduced  Norway  rats,  which  are  known  to  a  be  serious 
threat  to  Clapper  Rail  nests  (Harvey  1 980a).  It  is  unknown 
whether  toxic  substances  are  affecting  Black  Rails,  but 
there  is  increasing  evidence  of  their  effects  on  other  birds 
in  San  Francisco  Bay  (Ohlendorf  6k  Fleming  1988). 


CLAPPER  RAIL    Rallus  longirostris 


"Xv3rv 

>p^^^      \                   jTV 

A  year-round  resident. 

A  fairly  common,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  5  (2.3%)  of  221  blocks. 

^\^ 

O    Possible        =         1    (20%) 
€    Probable       =         2   (40%) 
•    Confirmed   =         2   (40%) 

__■• r- 

FSAR  =  3        OPI  =  15          CI  =  2.20 

Vo 

t 

■J^*                               X1-^j        ^~^"^<^\^\ 

Ecological  Requirements 

California  Clapper  Rails  (Rallus  longirostris  obsoletus)  are  at 
home  in  the  ebb  and  flow  of  salt  marshes  intersected  by 
numerous  tidal  channels.  The  vegetation  of  these  marshes 
is  usually  dominated  by  cord  grass  (Spartina  joliosa),  pickle- 
weed  (Salicomia  spp.),  and  salt  grass  (Distichlis);  gumplant 
(Grindelia)  provides  important  cover  in  some  marshes 
(Gill  1979,  Evens  6k  Page  1984).  During  the  breeding 
season,  Clapper  Rails  also  occupy  brackish  tidal  marshes 
in  those  parts  of  south  San  Francisco,  San  Pablo,  and 
Suisun  bays  that  are  dominated  by  bulrushes  (Scirpus  spp.) 


and  other  low,  salt-tolerant  marsh  plants  (Gill  1979,  Har- 
vey 1980b).  During  die  winter,  Clapper  Rails  leave  brack- 
ish marshes  and  contract  into  favored  areas  of  Spartina  salt 
marsh,  further  suggesting  that  brackish  marshes  may  be 
suboptimal  breeding  habitat  (P.R.  Kelly  pers.  comm.). 
Their  concentration  in  south  San  Francisco  Bay  (see 
below)  also  suggests  they  can  tolerate  higher  salinities  and 
a  wider  tidal  range  than  Black  Rails.  Perhaps  salinities  and 
the  degree  of  tidal  inundation  affect  the  distribution  of 
these  rails  via  vegetation  structure  and/or  food  resources. 


166 


Rails 


SPECIES  ACCOUNTS 


Rails 


Important  factors  for  breeding  Clapper  Rails  are  (1) 
well-developed  sloughs  and  secondary  tidal  channels;  (2) 
extensive  (dense,  tall,  lush)  cord  grass  stands  (though  not 
all  are  used);  (3)  dense  saltmarsh  vegetation  for  cover,  nest 
sites,  and  brooding  areas;  (4)  intertidal  mudflats,  gradually 
sloping  banks  of  tidal  channels,  and  cord  grass  beds  for 
foraging;  (5)  abundant  invertebrate  food  resources;  and  (6) 
transitional  vegetation  at  the  upland  edge  of  the  salt  marsh 
as  a  refuge  during  high  tides  (Evens  &  Page  1984,  Harvey 
1987,  P.R.  Kelly  pers.  comm.).  These  rails  do  occur  where 
there  are  few  stands  of  cord  grass,  as  at  Corte  Madera 
Marsh  in  Marin  County  (J.G.  Evens  pers.  comm.).  At 
Corte  Madera,  the  minimum  channel  size  used  by  Clapper 
Rails  averaged  about  14  inches  deep  by  25  inches  wide 
(Evens  ck  Page  1983,  n  =  8).  They  avoid  large  channels 
that  have  undercut  banks  and  small  channels  that  are 
overgrown  with  vegetation.  Clapper  Rails  may  use  all  parts 
of  the  marsh  during  the  year,  but  in  winter,  at  least  in  the 
South  Bay,  they  tend  not  to  use  extensive  areas  of  pickle- 
weed  and  instead  concentrate  then  in  cord  grass  in  the 
lower  marsh  (P.R.  Kelly  pers.  comm.).  Unlike  Black  Rails, 
they  are  not  restricted  to  high  upper  marsh  for  breeding. 
In  Corte  Madera  Marsh,  all  nests  found  were  in  the  upper 
marsh  Q.G.  Evens  pers.  comm.);  in  the  South  Bay,  many 
nests  are  located  in  both  the  lower  and  higher  marsh 
(Harvey  1980a). 

Although  there  is  much  intersite  variation  in  nest  place- 
ment, Clapper  Rails  generally  tend  to  locate  their  nests  on 
raised  ground  near  the  tidal  sloughs  that  intersect  marshes 
(Harvey  1980a,  1987;  Evens  6k  Page  1984).  Birds  usually 
build  their  nests  under  the  dense,  sheltering  vegetation  of 
pickleweed,  cord  grass,  gumplant,  or  salt  grass;  on  occa- 
sion, or  sometimes  commonly  (in  the  Soudi  Bay),  they  nest 
under  a  canopy  of  wrack  or  debris  stranded  on  top  of  the 
marsh  vegetation.  At  Corte  Madera  Marsh,  14  nests  were 
under  dense  gumplant  bushes  on  the  elevated  natural 
levees  of  tidal  sloughs,  and  3  late-season  nests  were  under 
dense  clumps  of  pickleweed  (Evens  ck  Page  1983).  In  the 
South  Bay,  nest  concentrations  vary  from  areas  dominated 
by  pickleweed  and  tidal  wrack  to  those  dominated  by  cord 
grass;  nests  are  sheltered  by  pickleweed,  cord  grass,  gum- 
plant, salt  grass,  or  tidal  debris;  and  generally  nests  are 
associated  with  sloughs  or  the  open  bay  edge  (Harvey 
1980a,  1987).  Mean  canopy  height  of  nesting  cover  in  the 
South  Bay  is  22  to  23  inches  (Harvey  1980a).  At  Corte 
Madera  Marsh,  most  nests  are  within  5  feet,  and  none 
were  more  than  10  feet,  from  a  tidal  channel  (Evens  ck 
Page  1983,  n  =  17).  In  the  South  Bay,  mean  distances  of 
nests  to  the  nearest  channel  range  from  about  20  to  36  feet 
(Harvey  1980a,  n  =  50).  Clapper  Rails  may  prefer  nesting 
in  the  cord  grass  zone  of  the  lower  marsh  because  nests 
there  are  better  protected  from  terrestrial  predators  and 
because  nests  made  of  Spartina  float  during  high  tide. 
Variations  in  nest  site  distribution  may  reflect  intersite 


differences  in  plant  succession  and  abundance,  tidal  gradi- 
ents, or  predation  pressures.  Nest  placement  may  also  vary 
seasonally  (more  use  of  wrack  or  gumplant  early  in  the 
season  before  Spartina  growth  occurs)  and  yearly  (more  use 
of  Salicornia  nest  sites  in  years  of  severe  high  tides). 

Clapper  Rails  lay  their  eggs  in  the  hollow  of  a  bulky 
platform  of  dry  cord  grass,  pickleweed,  salt  grass,  or  other 
marsh  vegetation  built  up  three  to  six  inches  above  the 
sodden  ground  (Dawson  1923,  Bent  1926,  Harvey  1980a, 
Evens  ck  Page  1984).  Cord  grass  is  the  preferred  nest 
material  in  the  South  Bay,  perhaps  because  the  hollow 
stems  float  and  thus  provide  better  protection  for  eggs 
during  high  tides  (Harvey  1980a).  Rails  usually  approach 
the  nest  site  via  a  runway  or  tunnel  through  the  matted 
vegetation  (Dawson  1923).  While  one  parent  broods 
newly  hatched  chicks  and  incubates  the  remaining  eggs, 
the  other  sometimes  leads  the  first-hatched  chicks  up  to  50 
feet  from  the  nest  (Adams  ck  Quay  1958).  During  their 
first  few  days,  chicks  are  brooded  almost  continually  either 
on  the  original  nest,  on  brood  nests,  or  on  floating  drift. 
In  North  Carolina,  adults  construct  up  to  six  brood  nests 
of  buoyant  Spartina  that  float  with  the  rising  tide  and 
provide  dry  places  for  refuge;  brood  nests  there  are  like  egg 
nests  without  canopies. 

Clapper  Rails  forage  mosdy  when  tidal  flats  and  channel 
banks  are  exposed.  From  widiin  or  near  cover,  they  obtain 
food  by  probing  and  digging  in  the  mud,  picking  from  the 
surface,  or  rapidly  seizing  or  chasing  down  more  mobile 
prey.  They  often  wash  their  food  before  eating  it,  peck  open 
or  dismember  larger  items  before  consuming  them,  and 
usually  swallow  small  items  whole  (Williams  1929).  The 
diet  is  predominandy  invertebrates  and  small  amounts  of 
cord  grass  seeds.  The  main  animal  foods  are  ribbed  mus- 
sels, clams,  amphipods,  shore  crabs,  spiders,  along  with 
occasional  snails,  nereid  worms,  and  insects;  minor  items 
are  small  vertebrates,  such  as  mice,  fish,  frogs,  brush 
rabbits  (probably  carrion),  and  (for  other  races  besides 
obsoletus)  birds  (Moffitt  1941,  Evens  ck  Page  1984).  Stom- 
ach samples  of  18  birds  collected  near  Palo  Alto,  Santa 
Clara  County,  on  4  February  1939  were  composed  (by 
volume)  of  85%  animal  matter  and  14.5%  cord  grass  seeds 
and  hull  fragments  (Moffitt  1941).  The  summer  diet  may 
include  more  insects  and  less  vegetable  matter;  vegetable 
foods  at  any  season  may  be  more  important  during  tidal 
regimes  where  the  mudflats  are  exposed  for  only  limited 
periods.  Parental  care  (including  feeding  of  young)  extends 
into  the  fifth  or  sixth  week  after  hatching  (Adams  ck  Quay 
1958). 

Marin  Breeding  Distribution 

In  Marin  County,  breeding  Clapper  Rails  are  restricted  to 
salt  marshes  along  the  shorelines  of  San  Francisco  and  San 
Pablo  bays.  During  the  adas  period,  Clapper  Rails  were 
confirmed  breeding  at  Corte  Madera  Ecological  Reserve, 


167 


Rai 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Rails 


Greenbrae  (NE  3/25-6/30/82  -JGE,  GWP).  Other 
recent  breeding  records  exist  for  Richardson  Bay  in  1972 
(SFBCDC  &  Harvey  1983)  and  for  Creekside  Park  along 
Corte  Madera  Creek,  Greenbrae  (FL  8/23/84  — HoP). 
Historical  breeding  records  exist  for  Manzanita  in  1930 
and  near  Greenbrae  in  1931  (Gill  1979).  Other  sightings 
for  Marin  are  from  Muzzi  Marsh,  Triangle  Marsh,  and  San 
Clemente  Creek,  Corte  Madera;  Tiscornia  Marsh,  San 
Rafael;  from  the  mouth  of  San  Rafael  Creek  upstream 
approximately  0.6  miles;  China  Camp  SP;  Santa  Venetia 
marshes;  Las  Gallinas  Creek  to  the  mouth  of  Novato 
Creek;  Novato  Creek  upstream  to  1 .2  miles  north  of  Hwy. 
37;  Day  Island;  and  Black  John  Slough  (Evens  6k  Page 
1984,  JG.  Evens  pers.  comm.). 

Gill  (1979)  estimated  that  for  the  period  1971  to  1975, 
the  average  yearly  population  in  Marin  was  153  birds 
(range  102-204),  though  his  estimates  for  the  entire  San 
Francisco  Bay  system  at  that  time  were  probably  much  too 
high  (see  below).  Page  and  Evens  (1987)  estimated  a 
population  of  about  40  birds  at  Corte  Madera  Ecological 
Reserve  in  both  1982  and  1987.  Estimates  from  censuses 
at  other  Corte  Madera  marshes  in  1987  were  15  birds  at 
Muzzi  Marsh,  3  birds  at  San  Clemente  Creek,  and  1  bird 
at  Triangle  Marsh.  The  59  birds  inhabiting  die  Corte 
Madera  marshes  represents  an  unknown  portion  of  the 
entire  Marin  population.  Because  of  continuing  dramatic 
declines  in  the  South  Bay  and  threats  to  the  entire  San 
Francisco  Bay  system  population  (see  below),  periodic 
censuses  should  be  made  of  all  Clapper  Rail  habitat  in 
Marin  County.  With  these  declines,  the  Corte  Madera  and 
Gallinas  Creek  populations,  in  particular,  are  taking  on 
increasing  importance  to  the  California  Clapper  Rail  popu- 
lation as  a  whole  (P.R.  Kelly  pers.  comm.). 

Historical  Trends/  Population  Threats 

The  California  Clapper  Rail  was  formerly  a  resident  of 
coastal  salt  marshes  from  Humboldt  Bay  south  to  Morro 
Bay,  with  the  greatest  population  in  San  Francisco  Bay 
(G6kM  1944,  Gill  1979,  Evens  &  Page  1984).  Populations 
have  declined  drastically  since  the  late  nineteenth  century. 
The  California  Clapper  Rail  is  now  restricted  to  San 
Francisco,  San  Pablo,  and  Suisun  bays  and  is  listed  as 
Endangered  by  both  state  (CDFG  1991a)  and  federal  gov- 
ernments (USFWS  1 989a).  Although  formerly  recorded  in 
Marin  County  at  Tomales  Bay,  it  is  unclear  if  it  ever  bred 
there  (Evens  6k  Page  1984,  Shuford  et  al.  1989).  Intensive 
rail  surveys  from  1984  to  1986  at  the  south  end  of  Tomales 
Bay  failed  to  reveal  any  birds  (JGE,  GWP).  Marin  popula- 
tions along  San  Francisco  and  San  Pablo  bayshores  have 
surely  declined  over  historical  levels. 

Gill  (1979)  estimated  that  4200  to  6000  birds  inhabited 
greater  San  Francisco  Bay,  with  55%  of  the  population  in 
the  South  Bay  and  38%  in  the  Napa  Marsh.  Logistical 
restraints  limited  Gill's  ability  to  census  many  of  the  bay's 

168 


marshes,  and  his  use  of  extrapolations  probably  greatly 
overestimated  the  size  of  the  population  (I  larvey  1987,  P.R 
Kelly  pers.  comm.).  Based  on  more  thorough  high-tide 
censuses  in  winter,  die  population  of  the  entire  San  Fran- 
cisco Bay  system  from  the  time  of  Gill's  work  up  until 
about  1985  was  about  700  Clapper  Rails,  with  approxi- 
mately 90%  in  the  Soudi  Bay  (P.R.  Kelly  pers.  comm.).  As 
of  the  winters  of  1988-89  and  1989-90,  the  population 
had  declined  dramatically  to  under  500  birds,  apparendy 
mosdy  because  of  predation  by  introduced  red  foxes  that 
appeared  in  South  Bay  marshes  by  at  least  1983  (P.R.  Kelly 
pers.  comm.).  Winter  censuses  in  1990-91  revealed  con- 
tinuing declines  that  leave  only  300  to  400  rails  still 
inhabiting  the  Bay  (P.R.  Kelly  pers.  comm.).  Surely  histori- 
cal numbers  gready  exceeded  these  recent  population  esti- 
mates. 

Gill  (1979)  speculated  that  Clapper  Rails  had  colonized 
the  Napa  Marsh  in  numbers  since  the  1930s  because  of 
increasing  salinity  there  from  reduced  freshwater  inflow 
into  the  Bay.  The  lack  of  many  Clapper  Rail  sightings  in 
the  Napa  Marsh  before  1940  parallels  the  absence  of 
records  of  breeding  Black  Rails  in  San  Pablo  Bay  prior  to 
the  late  1950s.  This  is  probably  from  very  limited  observer 
coverage  in  these  areas  radier  than  recent  dramatic  changes 
in  these  populations,  which  is  further  supported  by  the 
small  numbers  of  Clapper  Rails  found  in  the  Napa  Marsh 
in  die  1980s  (P.R.  Kelly  pers.  comm.).  Gill  (1979)  sug- 
gested that  local  population  fluctuations  were  from  changes 
in  production  and  biomass  of  Spartina— in  dry  years,  popu- 
lations were  reduced  because  of  increasing  intraspecific 
competition  for  nesting  territories.  Greater  use  of 
Salicornia  for  nest  sites  in  die  South  Bay  in  recent  years, 
perhaps  because  of  successional  changes  in  marshes,  sug- 
gest other  factors  may  be  responsible  for  population  fluctu- 
ations (Harvey  1980a). 

After,  and  in  concert  with,  initial  reductions  from  mar- 
ket hunting  (Grinnell  et  al.  1918),  habitat  loss  has  been  the 
primary  cause  of  decline  and  failure  to  return  to  historical 
levels  (Gill  1979,  Evens  6k  Page  1984).  Gill  (1979)  sum- 
marized data  on  market  hunting  in  the  South  Bay  around 
the  turn  of  the  century.  At  that  time,  it  was  not  uncommon 
for  individual  hunters  to  kill  30  to  50  rails  a  day.  One 
newspaper  account  referred  to  5000  rails  killed  in  a  one- 
week  period  alone  in  1897— ten  times  today's  total  popula- 
tion in  greater  San  Francisco  Bay!  Outcries  led  to  passage 
of  protective  laws  in  191 3,  and  numbers  began  to  rebound 
with  recolonization  of  areas  of  local  extirpation  (G6kM 
1944).  This  population  resurgence  was  short  lived.  Steady 
habitat  destruction  from  human  development  has  resulted 
in  a  loss  of  60%-95%  of  the  former  saltmarsh  habitat 
around  the  San  Francisco  Bay  estuary  (Nichols  6k  Wright 
1971,  Josselyn  1983)  and  about  90%  around  Humboldt 
Bay  (MacDonald  1977).  Clapper  Rails  face  a  host  of 
problems,  including  further  habitat  loss  and  degradation 


Rails 


SPECIES  ACCOUNTS 


Rails 


from  human  encroachment  as  summarized  for  the  Black 
Rail  (see  account).  Additional  threats  are  recent  losses  of 
potential  habitat  formerly  suitable  for  restoration,  an 
increase  in  brackish  marsh  at  the  expense  of  salt  marsh  in 
the  South  Bay  from  dramatic  increases  in  sewage  outfall 


since  the  early  1970s,  and  the  introduction  of  red  foxes  as 
noted  above  (Harvey  1983,  1987;  P.R.  Kelly  pers.  comm.). 
Restoration  of  large  tracts  of  former  salt  marsh  offers  the 
best  hope  for  offsetting  other  immediate  threats. 


VIRGINIA  RAIL  Rallus  limicola 


A  year-round  resident;  numbers  swell 

^t^\       ^                  ^Cb<u^ 

from  Sep  through  Mar. 

■i^o^Or 

An  uncommon,  very  local  breeder; 

^v    \><\\   y^ 

\^^\    V^**v^  \  ^\    \  i-*V*^\  ^-"V^A  ^\^~^x  —  - 

overall  breeding  population  very  small. 

<^\     \^>\ 

{\j^Kjy^fj^ 

Recorded  in  17  (7.7%)  of  221  blocks. 

V^C^ 

vOt^V^rx  \^\J^\^Jk^\\^\     \ 

O    Possible        =        8  (47%) 

yrt 

^^^^S^X^^S^^^^X^^ 

©    Probable       =        5   (29%) 

#^\  !j(^^V^yV\  3s*^\  J^c\  \^\  \"v 

•    Confirmed  =         4   (24%) 

FSAR  =  2         OPI  =  34         CI  =  1.76 

^^^^^^k^^^f^C^^c^ 

'>[                                 ^-^cTv'5<!^ J4r\J5?\ 

t 

^                                       "w'^^oW 

Ecological  Requirements 

Eerie  cackling  or  hiccupping  calls  betray  die  presence  of 
Virginia  Rails  in  their  Marin  County  breeding  haunts  of 
freshwater  marshes,  coastal  swales,  wet  meadows,  and, 
perhaps,  brackish  marshes.  In  the  winter,  some  Virginias 
disperse  to  tidal  salt  marshes,  which  they  shun  during  the 
breeding  season  here,  but  not  in  some  other  parts  of  the 
range  (Zimmerman  1977).  Important  needs  of  breeding 
birds  are  shallow  standing  water;  dense  marsh  vegetation 
for  cover,  nest  sites,  and  brooding  areas;  and  a  suitable 
supply  of  invertebrate  food.  Virginia  Rails  overlap  consid- 
erably in  habitat  preference  with  Soras.  Virginias  are  more 
widespread  here  and  appear  to  have  less  stringent  nesting 
requirements,  though  the  differences  in  habitat  needs 
between  the  two  species  are  not  easily  explained.  In  Colo- 
rado, both  Virginia  Rails  and  Soras  prefer  breeding 
marshes  widi  water  less  than  6  inches  in  depdi  (Griese  et 
al.  1980).  In  Missouri,  migrant  Virginias,  at  least,  inhabit 
areas  of  marsh  with  shallower  water  than  Soras,  though 
both  species  prefer  similar  vegetation  density  and  height 
(Sayre  6k  Rundle  1984).  Migrant  Virginias  in  Missouri 
prefer  saturated  to  shallowly  flooded  sites  less  than  2 
inches  deep  and  are  usually  flushed  near  the  interface  of 
standing  water  and  soil;  Soras  prefer  water  depths  from  2 


to  6  inches  but  use  saturated  sites  more  often  than  those 
with  18  inches  of  water.  In  Iowa,  breeding  Virginia  Rails 
and  Soras  show  little  evidence  of  distinct  niche  segregation. 
Soras  diere  are  most  numerous  at  nearshore  sites  with 
relatively  shallow  water,  diverse  vegetation,  and  many  seed- 
producing  plants,  while  Virginias  are  more  evenly  distrib- 
uted across  various  marsh  types  (Johnson  &  Dinsmore 
1986).  Marsh  areas  with  floating  residual  plants  may  be 
important  to  Soras  because  such  cover  provides  good 
substrate  for  invertebrates  that  are  kept  near  the  surface 
within  reach  of  these  short-billed  rails.  The  availability  of 
preferred  foods  and  the  species'  ability  to  exploit  them,  as 
reflected  by  bill  shape,  may  be  more  important  than  water 
depdi  per  se  in  explaining  the  difference  in  habitat  prefer- 
ences of  these  two  species. 

Virginia  Rails  conceal  their  nests  in  dense  marsh  vege- 
tation where  they  usually  suspend  them  in,  and  intertwine 
them  with,  emergent  plant  stalks  (Townsend  1926, 
Walkinshaw  1937).  Water  depths  around  nest  sites  at  the 
beginning  of  incubation  range  from  about  3  to  10  inches 
(Walkinshaw  1937,  Berger  1951,  Zimmerman  1977,  Gri- 
ese et  al.  1980).  Sometimes  Virginias  build  nests  from  the 
ground  up  that  may  reach  seven  or  eight  inches  in  height 


169 


Rai 


MARIN  COUNTY  BRFHDING  BIRD  ATlJ\S 


Rails 


(Townsend  1926).  Glahn  (1974)  reported  that  Virginias 
locate  most  of  their  nests  within  tall  vegetation  near  dis- 
continuities with  shorter  vegetation,  water,  or  mud  along 
territory  boundaries.  Virginia  Rails  usually  build  their 
shallow  platform  nests  from  pieces  of  coarse  rushes, 
sedges,  or  grasses  and  line  diem  with  finer  materials  of  the 
same  types  (Townsend  1926,  Walkinshaw  1937).  When 
die  vegetation  allows,  die  nest  is  usually  arched  over  widi 
a  canopy  of  rushes  and  sedges.  Birds  approach  their  nests 
via  a  sloping  runway.  At  die  first  sign  of  rising  water,  these 
rails  add  material  to  raise  die  eggs  above  harm's  way.  The 
eggs  hatch  asynchronously,  and  one  parent  leads  die  first 
chicks  away  from  the  nest  while  the  other  continues  to 
incubate  the  remaining  eggs.  Young  feed  with  parental 
assistance  the  first  day  but  are  self-sufficient  foragers  by  the 
end  of  die  first  week  of  life  (Zimmerman  1977). 

Virginia  Rails  use  their  slender  curved  beaks  to  probe 
and,  presumably,  to  peck  and  glean  for  food  along  the 
muddy  interface  of  standing  water  and  marsh  vegetation 
and  in  openings  between  plants.  Breeding  birds  in  Iowa 
consume  84.6%  animal  matter  and  1 5.4%  vegetable  fare 
(Horak  1970,  n  =  37).  Continentwide,  die  diet  ranges 
from  97%  animal  matter  in  summer  (n  =  20)  to  68%  in 
fall  (n  =  69)  (Martin  et  al.  1 951 ).  Animal  matter  is  predom- 


inantly insects,  along  widi  spiders,  snails,  crayfish,  bryozo- 
ans,  slugs,  small  fish,  frogs,  and  small  snakes  (Townsend 
1926,  Martin  et  al.  1951,  Horak  1970).  Seeds  of  marsh 
plants  and  duckweed  are  important  plant  foods. 

Marin  Breeding  Distribution 

Virginia  Rails  are  patchily  distributed  in  Marin  County, 
reflecting  the  availability  of  suitable  marshes,  found  mosdy 
near  the  outer  coast.  Representative  nesting  sites  were 
Olema  Marsh  (FL  5/1/80  — DS)  and  Cypress  Grove,  near 
Marshall,  Tomales  Bay  (FL  5/23  6k  6/6/78  -FMa,  BTy). 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  noted  a  decline  in  Virginia  Rail 
numbers  in  California  from  habitat  loss.  Subsequendy, 
numbers  must  have  continued  to  decline  for  the  same 
reason.  Because  of  its  proximity  to  human  endeavors, 
freshwater  marsh  habitat  must  have  decreased  to  an  even 
greater  degree  than  tidal  marsh  habitat,  which  has  been 
reduced  in  the  San  Francisco  Bay  system  by  60%-95% 
from  historical  levels  (Nichols  6k  Wright  1971,  Josselyn 
1983). 


170 


Rails 


SPECIES  ACCOUNTS 


Rails 


SORA    Porzana  Carolina 


^<\3cC 

?^^-^  \ 

^P*0f\^rC^ 

A  year-round  resident;  numbers  swell 
from  Sep  through  Apr. 

A  rare,  very  local  breeder;  overall  breed- 
ing population  very  small. 

Recorded  in  10  (4-5%)  of  221  blocks. 

O    Possible                  3   (30%) 

V?\^'  V"\  3^v^ 

zkrZ  \^X^  \^K-^\^*K 

©    Probable       =        6  (60%) 

w2?° 

•    Confirmed  =         1    (10%) 
FSAR=1          OPI  =  10          CI  =  1.80 

Ecological  Requirements 

The  Sora  is  another  shadowy  recluse  of  the  moist  soils  and 
shallow  waters  of  freshwater  marshes,  coastal  swales,  wet 
meadows,  and,  perhaps,  brackish  marshes.  Some  Soras 
disperse  to  winter  in  tidal  salt  marshes,  from  which  they 
are  absent  during  the  breeding  season.  Important  needs  of 
breeding  birds  are  standing  fresh  water;  dense  marsh 
vegetation  for  cover,  nest  sites,  and  brooding  areas;  and  a 
suitable  supply  of  seeds  and  invertebrate  foods.  Differences 
in  habitat  preferences  between  Soras  and  Virginia  Rails  are 
subde,  though  Soras  are  less  widespread  here  and  appear 
to  have  more  stringent  requirements  (see  Virginia  Rail 
account). 

Soras  usually  nest  in  dense  marsh  vegetation  and,  occa- 
sionally, in  somewhat  open  surroundings.  Whether  in  tall 
or  short  vegetation,  Soras  tend  to  locate  their  nests  near 
discontinuities  with  vegetational  borders,  water,  or  mud 
along  territory  boundaries  (Walkinshaw  1940,  Glahn 
1974).  They  build  nest  platforms  or  well-built  baskets  of 
rushes,  sedges,  or  grasses  raised  up  from  the  marsh  floor 
or  suspended  and  interwoven  with  surrounding  vegetation 
(Bent  1926,  Walkinshaw  1940).  Nests  are  lined  widi  finer 
marsh  vegetation  and  are  usually  more  or  less  concealed 
with  an  arched-over  canopy  of  grasses,  reeds,  or  cattails. 
There  is  often  a  slanting  runway  of  nest  materials  leading 
to  and  from  the  nest.  Nests  are  generally  raised  an  average 
of  about  three  to  seven  inches  above  the  water  (Bent  1 926; 
Walkinshaw  1937,  1940;  Berger  1951;  Griese  et  al.  1980). 
Birds  usually  complete  the  nest  after  they  start  laying  and 
will  add  materials  to  raise  the  nest  when  water  levels  rise 


(Walkinshaw  1940).  Eggs  hatch  asynchronously  and  one 
parent  leads  the  first  chicks  away  while  the  other  incubates 
the  remaining  eggs. 

With  their  stubby  bills,  Soras  pick  or  glean  from  the 
marsh  substrate  or  water's  surface  and  strip  seed  heads 
from  marsh  plants  (Bent  1926,  Walkinshaw  1940,  Sayre 
ck  Rundle  1984).  Breeding  birds  in  Iowa  consume  80.8% 
vegetable  matter,  mostly  the  seeds  of  aquatic  plants  (Horak 
1970,  n  =  19).  Continentwide  the  diet  ranges  from  60% 
(n  =  109)  animal  matter  in  spring  and  summer  to  31%- 
32%  (n  =  223)  animal  matter  in  fall  and  winter  (Martin  et 
al.  1951).  In  Missouri,  spring  and  fall  migrants  consumed 
63%  (n  =  18)  and  82.5%  (n  =  20)  vegetable  matter,  respec- 
tively, with  sedge  seeds  predominant  in  spring  and  grass 
seeds  in  fall  (Rundle  <St  Sayre  1983).  In  Connecticut,  the 
fall  diet  was  98%  seeds  in  freshwater  marshes  and  91% 
insects  in  brackish  marshes  (Webster  1964  fide  Odum 
1977).  Animal  foods  are  various  aquatic  insects,  snails, 
crustaceans,  and  small  tadpoles  or  fish  (Bent  1926,  Martin 
et  al.  1951,  Horak  1970,  Odum  1977). 

Marin  Breeding  Distribution 

During  the  adas  period,  Soras  were  found  breeding  at  only 
scattered  sites  in  Marin  County.  Their  distribution  was 
similar  to,  but  more  restricted  than,  that  of  Virginia  Rails. 
Most  Soras  were  found  on  the  outer  coast.  Nevertheless, 
the  only  confirmed  breeding  record  was  of  a  nest  (with  ten 
eggs)  on  the  marshy  edge  of  a  fish-breeding  pond  inland  in 
Hicks  Valley  from  1  to  21  May  1982  (ScC,  ITa). 


171 


Rails 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Rails 


Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  reported  no  change  in  the 
aggregate  numbers  of  Soras  in  California  except  as  caused 
by  reclamation  of  marshes,  which  up  to  that  time  and  since 
must  have  been  great  (see  Virginia  Rail  account). 


COMMON  MOORHEN   Gallinula  chloropus 


Generally  of  irregular  occurrence  year 

^JpOc^>r-^     N             ^O 

round;  slightly  more  numerous  from  Sep 

through  early  Mar. 

^K\ >V^\  Jrv ^V\  %^\J^C\Jk 

3r\iX" 

A  very  rare  (perhaps  rare),  very  local 
breeder;  overall  breeding  population  very 

\§^^VvVvV\>V^V 

^rC^X^I 

small. 

VO\L^  W)    3r\     ie^\     \^\ 

V-^\  ®\^    \ 

Recorded  in  2  (0.9%)  of  221  blocks. 

^^r^^cyp^) 

O    Possible        =         0   (0%) 

xpV^a^A^v^^a^-Vv-A^^ 

J\^\  S-^C\  '^<\^^—  -r" 

€    Probable       =         1    (50%) 

7  \MVurA0r^\^^\3^ 

\^^X       \^cS\\li^\ 

•    Confirmed   =         1    (50%) 

•  i                                       ^"^-^^\  ^ 

^$^^5?^ 

FSAR  =1         OPI  =  2          CI  =  2.50 

Ecological  Requirements 

In  both  appearance  and  habits,  the  Common  Moorhen 
bridges  the  gap  between  our  typical  small  rails  and  their 
cousin  the  American  Coot.  In  Marin  County,  breeding 
Moorhens  inhabit  freshwater  marshes  with  some  open 
water,  natural  or  artificial  ponds,  and  drainage  or  irrigation 
ditches,  though  lakes  or  slow-flowing  streams  edged  with 
emergent  vegetation  suffice  elsewhere  in  California.  The 
main  breeding  requirements  seem  to  be  robust  emergent 
vegetation  for  cover,  nest  sites,  and  brood  rearing;  some 
open  standing  or  slow-moving  fresh  water;  and  an  ade- 
quate food  supply.  Moorhens  typically  use  deeper-water 
marshes  and  prefer  centrally  placed  emergents  rather  than 
the  bordering  vegetation  of  shallow-water  marshes  used  by 
Virginia  Rails  and  Soras  (Weller  6k  Fredrickson  1973, 
Byrd  &  Zeillemaker  1981).  Moorhens  keep  more  to  cover 
and  less  to  open  water  than  do  Coots. 

In  marshes  of  variable  water  depth,  Moorhens  select 
nest  sites  in  areas  of  deeper  water  (Byrd  6k  Zeillemaker 
1981).  In  the  managed  shallow  water  of  irrigated  taro  fields 
in  Hawaii,  Moorhens  choose  nest  sites  where  the  water 
depth  averages  2.6  inches;  elsewhere  in  the  breeding  range, 
they  may  nest  over  waters  1  to  6.5  feet  deep.  Moorhens 

172 


usually  attach  their  nests  to  emergent  or  broken-down 
aquatic  vegetation;  nests  range  from  near  floating  up  to  six 
inches,  or,  rarely,  two  or  three  feet  above  water  (Dawson 
1923,  Bent  1926,  Fredrickson  1971,  Strohmeyer  1977, 
Roselaar  1980,  Byrd  6k  Zeillemaker  1981).  They  may  build 
more  nests  than  they  use  for  egg  laying  (Bent  1926).  Less 
frequendy  used  nest  sites  include  among  scattered  sub- 
merged bushes;  under  weeds  on  a  floating  island;  on 
mobile,  semisubmerged  logs;  high  on  a  mass  of  cattails 
tangled  by  the  wind;  on  top  of  a  dead  stump  two  feet  from 
the  water  and  surrounded  by  willows;  on  banks  amid  thick 
tangles  of  briars,  grasses,  and  vines  within  a  few  feet  of 
water;  and  in  a  low  crotch  of  a  bush  near  water  (Bent 
1926).  Birds  usually  conceal  their  nests  within  stands  of 
vegetation  and  only  rarely  nest  in  exposed  situations.  In 
Iowa,  nests  averaged  1 1  feet  (range  0-59  ft.)  from  an  edge 
of  vegetative  change  or  water  and  15  feet  (range  7-92  ft.) 
from  open  water  (Fredrickson  1971);  easy  access  to  open 
water  is  probably  important. 

Moorhens  build  their  shallow  nest  baskets  from  the 
dead  leaves  and  stalks  of  cattails,  bulrushes,  grasses,  or 
other  coarse  aquatic  plants.  They  may  preferentially  select 


Rails 


SPECIES  ACCOUNTS 


Rails 


for  nest  building  certain  plants  among  those  available 
(Byrd  &  Zeillemaker  1981).  Often  the  nest  is  screened 
from  above  by  a  canopy  of  aquatic  plants.  It  usually  has  an 
inclined  runway  of  nest  material  used  to  leave  or  enter  the 
nest  (Bent  1926).  Nest  building  continues  through  egg 
laying  and  incubation,  and  birds  will  add  additional  nest 
material  to  raise  the  nest  above  rising  water  (Bent  1926, 
Fredrickson  1971).  The  first  clutch  normally  hatches  syn- 
chronously; replacement  and  second  clutches  hatch  asyn- 
chronously (Roselaar  1980).  Within  hours  after  hatching, 
the  young  are  fed  by  the  parents  (Fredrickson  1971). 
Moorhens  brood  their  young  on  brood  platforms  (with 
ramps)  they  build  or  on  platforms  built  by  Coots  or 
muskrats.  One  adult  brings  food  to  die  brooding  mate, 
which  transfers  it  to  the  young.  Groups  of  Moorhens 
occasionally  contain  two  adults  along  with  both  downy  and 
nearly  fledged  young  (Roselaar  1 980,  Byrd  ck  Zeillemaker 
1981).  The  older  chicks  of  these  "multiple  brood  family 
units"  will  sometimes  feed  and  brood  younger  chicks, 
incubate  eggs  if  the  pair  has  not  yet  hatched  die  second 
clutch,  and  make  nest  repairs. 

These  aquatic  rails  feed  while  swimming,  walking  on 
floating  vegetation,  or  walking  on  land,  nodding  their 
heads  and  perking  their  tails  as  they  go  (Dawson  1923, 
Bent  1926,  Roselaar  1980).  They  obtain  food  by  dipping 
the  head  underwater,  by  surface  picking  or  sifting,  and, 
rarely,  by  diving.  Birds  also  up-end  and  snatch  food  from 
other  birds.  In  addition,  they  pick  food  items  off  the 
ground  and  off  plants,  often  by  clambering  over  leaves  and 
balancing  on  stems  by  flapping  their  wings.  Moorhens 
often  feed  in  dense  cover,  threading  their  way  through  the 
reeds,  and  also  range  onto  grass  on  the  dry  borders  of 
marshes,  though  seldom  beyond  easy  reach  of  cover.  The 
diet  is  omnivorous,  with  varying  proportions  of  plant  and 
animal  matter;  little  quantitative  work  has  been  done,  so 
changes  in  diet  with  season  and  locality  are  unknown 
(Bent  1926,  Roselaar  1980).  Animal  matter  in  the  diet 
consists  of  snails  and  other  small  mollusks,  adult  and 


larval  insects,  spiders  and  harvestmen,  earthworms, 
amphibian  tadpoles,  and,  rarely,  small  fish.  Moorhens  also 
eat  carrion  and  birds'  eggs  up  to  those  of  Mallards'  in  size. 
Vegetable  foods  include  die  seeds,  roots,  and  soft  parts  of 
succulent  aquatic  plants,  and  berries  and  fruits.  Birds  also 
feed  on  vegetable  peelings  and  scraps.  Initially,  parents 
apparendy  feed  chicks  mosdy  aquatic  insects,  such  as 
dragonfly  and  mayfly  nymphs  (Fredrickson  1971). 

Marin  Breeding  Distribution 

During  the  adas  period,  Moorhens  were  recorded  in  the 
breeding  season  in  small  marshes  in  only  two  adas  blocks 
near  Novate  Breeding  was  confirmed  at  a  pond  off  High- 
way 37  with  the  presence  of  adults  with  small  young  on  2 
June  1977  (RMS).  There  is  a  prior  breeding  record  from 
Olema  Marsh  (FL  8/31/67  — CJR)  and  more  recent  ones 
from  the  Bolinas  sewage  ponds  (FL  7/12/83  — JGE)  and 
from  a  pond  near  Rush  Creek,  Novato  (FL  7/21/84 
— HoP).  See  Shuford  et  al.  (1989)  for  additional  records 
suggestive  of  breeding  elsewhere  on  Point  Reyes. 

Historical  Trends/  Population  Threats 

Earlier  avifaunal  accounts  lacked  records  of  Moorhens 
breeding  in  Marin  County  (G&W  1927,  S&P  1933)  or, 
for  that  matter,  along  the  coast  north  of  the  Golden  Gate 
(G&M  1944).  The  recent  breeding  records  in  Marin 
County  probably  reflect  greater  observer  coverage  rather 
dian  any  recent  expansion  of  the  breeding  range.  Grinnell 
and  Miller  (1944)  felt  that  numbers  had  declined  because 
of  habitat  loss,  which  was  offset  somewhat  by  the  develop- 
ment of  irrigation.  Continued  destruction  of  marshland 
since  that  time  has  surely  reduced  numbers  substantially 
(see  other  rail  accounts).  Numbers  of  Common  Moorhens 
were  relatively  stable  on  Breeding  Bird  Surveys  in  Califor- 
nia from  1968  to  1989,  a  period  after  most  habitat  destruc- 
tion had  occurred,  though  numbers  increased  from  1980 
to  1989  (USFWS  unpubl.  analyses). 


173 


Rai 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Rails 


AMERICAN  COOT    Fulica  americana 


Occurs  year  round,  though  primarily  as  a 
winter  resident  from  mid-Sep  through 
May. 

A  fairly  common,  local  breeder;  overall 
breeding  population  small. 

Recorded  in  58  (26.2%)  of  221  blocks. 

O    Possible  25   (43%) 

C    Probable  1    (2%) 

•    Confirmed  =       32   (55%) 

FSAR  =  3        OPI  =  174         CI  =  2.12 


Ecological  Requirements 

The  "Mud-hen,"  though  of  humble  mien,  is  perhaps  our 
most  adaptable  nesting  waterbird.  Breeding  Coots  inhabit 
Marin  County's  freshwater  ponds,  lakes,  reservoirs, 
marshes,  sewage  ponds,  and  irrigation  channels.  Prime 
breeding  habitat  has  a  good  mix  of  open  water  and  dense 
emergent  vegetation,  particularly  tules  or  cattails.  Robust 
emergents  provide  nest  sites,  nest  materials,  and  cover  for 
adults  and  broods;  open  water  provides  foraging  habitat. 
Coots  will  nest  where  open  water  is  patchily  or  continu- 
ously edged  with  emergent  vegetation,  but  in  Iowa,  at  least, 
Coots  reach  highest  densities  where  there  is  a  50:50  mix 
of  open  water  and  emergent  cover  (Weller  &.  Fredrickson 
1973).  Coots  tend  to  occupy  microhabitats  with  shallower 
water  than  do  Pied-billed  Grebes  (Nudd  1 982). 

In  the  San  Francisco  Bay  Area,  breeding  Coots  build 
from  seven  to  nine  structures  associated  with  nesting- 
including  display  platforms,  egg  nests,  and  brood  nests 
(Gullion  1954).  Elsewhere,  Coots  build  fewer  structures 
(except  egg  nests)  when  naturally  occurring  platforms,  such 
as  those  built  by  muskrats,  are  available  (Fredrickson 
1970).  Display  platforms  are  composed  of  coarse  cattail 
stems  and  leaves  and  are  built  on  a  foundation  such  as  a 
floating  board  or  stick  or  a  heap  of  broken-down  cattails 
(Gullion  1954).  Display  platforms  are  usually  thoroughly 
water  soaked  and  after  the  copulation  period  are  allowed 
to  disintegrate,  though  up  to  that  point  nonincubating 
birds  may  use  them  as  roost  sites.  Egg  nests  are  shallow 
baskets,  usually  with  a  floating  foundation,  attached  to 
emergent  vegetation  over  various  depths  of  water  (Bent 
1926,  Gullion  1954,  Fredrickson  1970,  Fredrickson  et  al. 

174 


1977).  Most  nests  are  partially  or  well  hidden  in  emergent 
vegetation,  though  sometimes  they  are  in  plain  sight  at  the 
edge  of  vegetation,  in  an  isolated  clump,  or  in  an  entirely 
open  situation  without  concealment  Usually  overhead 
cover  is  naturally  provided.  Coots  do  not  build  canopies 
above  the  nest  (Gullion  1 954).  In  the  Bay  Area,  all  struc- 
tures are  located  close  (usually  2  to  3  ft.,  or  a  maximum  of 
4  ft.)  to  open  water.  Throughout  the  range,  exceptional 
nest  sites  are  on  dry  ground;  two  feet  above  ground  on  a 
platform  of  dead  cattails;  and  four  feet  above  ground  in  the 
lower  branches  of  an  apple  tree  following  receding  flood- 
waters  (Bent  1926).  These  odd  records  suggest  nests  were 
built  at  times  of  unusual  water  conditions  (Gullion  1954). 
Coots  often  build  more  than  one  nest  structure  before 
finally  selecting  one  in  which  to  lay  the  eggs  (Gullion 
1954).  Coots  usually  build  their  nests— starting  with  coarse 
materials  and  progressively  adding  finer  materials— from 
dry  or  green  stems  and  leaves  of  cattails  or  other  marsh 
plants;  they  sometimes  also  use  willow  leaves  and  small 
sticks.  The  cup  is  composed  of  fine  dry  leaves.  Coots  enter 
and  leave  the  nest  via  a  ramp  of  coarse  stems  laid  length- 
wise and  incorporated  into  the  side  of  the  nest  They  may 
begin  laying  eggs  while  the  nest  is  still  under  construction 
but  finish  the  nest  and  line  it  before  the  clutch  is  complete 
(Bent  1926,  Gullion  1954).  Since  egg  nests  are  actually 
elaborate  rafts,  Coots  must  constandy  add  material  to  them 
to  keep  them  from  settling  below  the  surface  (Gullion 
1954).  Pairs  of  Coots  may  either  build  new  egg  nests  or 
reuse  display  platforms  or  brood  nests  used  previously  by 
them  or  other  pairs.  When  the  eggs  hatch,  Coots  usually 


Rails 


SPECIES  ACCOUNTS 


Rails 


construct  a  new,  larger  brood  nest,  or  convert  an  egg  nest 
to  a  brood  nest  Brood  nests  frequendy  lack  a  cup,  or,  if 
present,  it  is  usually  obscured  in  the  restructuring  process. 
Brood  nests  are  distinguished  from  egg  nests  by  the  wet 
materials  worked  into  the  final  lining  and  by  the  presence 
of  feces  in  and  about  the  nest. 

Since  eggs  hatch  asynchronously,  one  parent  takes  over 
the  major  share  of  incubation  while  the  other  seeks  food 
for  the  young  already  hatched  (Gullion  1954).  Initially  one 
adult  collects  food  and  presents  it  to  the  incubating  bird, 
which  in  turn  feeds  the  chicks  (Fredrickson  1970).  Usually 
the  male  incubates  during  this  period  and  also  broods  the 
young  not  feeding  with  the  female  (Gullion  1954).  The 
female  returns  frequendy  to  the  nest  widi  food.  Two-  and 
three-day-old  chicks  leave  the  nest,  swim  out  to  be  fed  by 
the  female,  then  return  to  the  nest  and  the  protection  of 
the  incubating  male.  Three  or  four  days  after  hatching,  the 
female  broods  the  older,  more  active  young  at  night  on  the 
brood  nest  while  the  male  incubates  the  remaining  eggs 
and  the  newly  hatched  young  on  the  egg  nest.  When  a 
sufficient  number  (about  eight)  of  young  have  hatched, 
both  parents  turn  their  attention  to  the  care  of  the  young 
and  either  desert  the  remaining  eggs  or  dump  them  out  of 
the  nest.  At  about  five  days  of  age,  the  young  begin  to 
spend  most  of  the  day  following  their  parents  on  foraging 
excursions  in  the  emergent  vegetation  and  later  in  open 
water.  At  dusk,  when  broods  move  to  platforms,  the  male 
appears  to  assume  the  responsibility  of  caring  for  most 
young  (Fredrickson  1970). 

Coots  obtain  their  food  by  dabbling  and  grazing  from 
or  near  the  surface  of  the  water,  by  grazing  or  picking  items 
from  the  surface  of  moist  or  dry  land  along  or  well  back 
from  the  shore,  and  by  diving  to  moderate  depths  (Bent 
1926).  While  swimming  or  walking,  they  nod  their  heads 
in  rhythm  to  their  foot  movements.  Coots  clip  off  green 
grasses  in  meadows,  pastures,  or  lawns  and  sometimes 
grain  (particularly  rice)  in  cultivated  land.  They  also  steal 
some  aquatic  plant  food  from  ducks  and  eat  grain  set  out 
to  attract  ducks.  Continentwide,  the  annual  diet  is  about 
89.4%  plant  matter  and  10.6%  animal  matter  and  varies 
little  by  region  (Jones  1940,  n  =  792).  Plant  foods  make  up 
about  98%  of  the  diet  in  fall  and  winter  (n  =  658),  84%  in 
spring  (n  =  82),  and  56%  in  summer  (n  =  36)  (Martin  et 
al.  1951).  Coots  prefer  the  foliage,  stems,  fleshy  rootstalks, 
and,  secondarily,  seeds  of  a  wide  variety  of  marsh  and 


aquatic  plants,  especially  pondweeds,  sedges,  algae,  and 
grasses  (Jones  1940,  Martin  et  al.  1951).  The  main  animal 
foods  are  insects  (especially  beedes,  true  bugs,  and  dragon- 
fly and  damselfly  larvae  and  nymphs),  mussels,  and  snails; 
infrequent  items  are  spiders,  crustaceans,  and,  rarely,  small 
fish  and  amphibians.  Initially,  the  young  are  fed  exclusively 
animal  matter,  mosdy  in  the  form  of  aquatic  insect  larvae 
of  dragonflies  and  damselflies;  by  the  time  they  are  eight 
days  old,  young  Coots  consume  considerable  quantities  of 
vegetable  food  (Gullion  1 954). 

Marin  Breeding  Distribution 

During  the  adas  period,  Coots  bred  widely,  though  patch- 
ily,  throughout  the  lowlands  of  Marin  County.  They  were 
somewhat  more  prevalent  breeders  on  the  outer  coast  and 
along  the  San  Pablo  and  San  Francisco  bayshores.  Repre- 
sentative nesting  locations  were  Olema  Valley  (FL  6/1 1/82 
— BiL);  Bolinas  sewage  ponds  (FL  5/5/80  — DS);  pond  at 
ocean  end  of  Tennessee  Valley  (FL  9/1 1/82  — DS);  Hicks 
Valley  (FL  6/21/82  -DS);  and  McGinnis  Park,  San  Rafael 
(FL  6/3/80  -DS). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  reported  that  Coot  numbers 
had  held  up  over  the  years,  but  historically  they  must  have 
declined  dramatically  with  the  drainage  of  most  of  the 
state's  wedands.  Marin  County  has  few  natural  lakes  and 
ponds,  so  Coot  numbers  may  have  increased  here  over  the 
years  because  of  the  impoundment  of  water  in  municipal 
reservoirs,  stock  ponds,  and  sewage  ponds.  On  the  other 
hand,  some  marshes  have  been  drained;  others,  such  as 
Olema  Marsh,  have  been  lost  to  Coots  as  they  have  choked 
with  emergent  vegetation  from  poor  drainage,  apparendy 
caused  by  road  building  and  diking.  Numbers  of  Coots 
wintering  on  Pt.  Reyes  have  declined  since  1976,  appar- 
endy because  of  two  periods  of  widespread  drought  in 
California  (Shuford  et  al.  1989).  On  the  whole,  Coot 
numbers  were  relatively  stable  on  Breeding  Bird  Surveys 
in  California  from  1968  to  1989  (USFWS  unpubl.  analy- 
ses), a  period  after  most  habitat  loss  had  occurred.  Num- 
bers decreased  from  1980  to  1989  (USFWS  unpubl. 
analyses),  perhaps  because  much  habitat  dried  up  during 
the  three  years  of  drought  at  the  end  of  that  period. 


175 


Plovers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


n 


overs 


Plovers 

Family  Charadriidae 


SNOWY  PLOVER    Charadrius  alexandrinus 


Occurs  year  round,  though  numbers 

Ap^s^.           N                    Jf 

swell  considerably  from  Jul  through  early 

Apr. 

\^\,    \^\—^-  ~ 

A  fairly  common,  very  local  breeder; 

C\9\V 

-^V>A^^V\^O^W 

overall  breeding  population  very  small. 

^\\yf^%^&^. 

Recorded  in  11  (5.0%)  of  221  blocks. 

O    Possible        =         1    (9%) 

\    L#F^A     ^t^-^-V^A  X^i\     J*?' 

C    Probable       =         4   (36%) 

\*J^T\  ^C\"^^\-^\\'^ 

Jk^Kj^K^k^^ 

•    Confirmed  =        6  (55%) 

^^¥^^w^?a 

FSAR  =  3        OPI  =  33         CI  =  2.45 

x^'^^^^c^V^^L 

Ecological  Requirements 

An  illusory  movement  is  all  that  betrays  a  tiny  sand-colored 
plover  as  it  stealthily  slips  off  its  nest  amid  coastal  dunes. 
On  the  mainland  California  coast,  Snowy  Plovers  scatter 
widely  to  breed  on  sandspits,  dune-backed  beaches,  lagoon 
and  estuarine  margins,  around  salt  evaporators,  and  on 
small  pocket  beaches  (Stenzel  et  al.  1981).  Sandspits  and 
bars,  with  their  low  topographic  relief  of  well-developed 
hummocks  and  dunes,  separate  the  ocean  from  coastal 
wedands.  Bordering  wedands  enhance  the  spits  as  plover 
habitat.  They  provide  tidal  flats  and  other  barren  open 
areas  in  marshes  that  afford  alternate,  often  productive, 
feeding  areas  and  also  refuge  from  human  disturbance  on 
the  beaches.  Frequent  plover  movements  between  beaches, 
tidal  flats,  and  salt  pans  illustrate  the  attractiveness  of  a 
suite  of  favorable  habitats  close  at  hand.  Dune-backed 
beaches  are  usually  interrupted  by  rivers,  creeks,  ponds, 
lagoons,  or  salt  pans,  and  the  sections  of  these  beaches  that 
abut  such  wedands  hold  disproportionate  numbers  of 
nesting  plovers  relative  to  the  availability  of  the  habitat.  In 
Marin  County,  Snowy  Plovers  nest  primarily  on  spits  or 
on  dune-backed  beaches,  but  also  on  the  margins  of 
Abbott's  Lagoon  and  occasionally  on  bluff-backed  beaches 
(i.e.,  soudi  end  of  Pt.  Reyes  Beach).  Elsewhere  on  the  coast, 

176 


plovers  also  nest  in  or  on  the  margins  of  estuaries  and 
lagoons,  in  naturally  open  or  disturbed  areas,  such  as  salt 
pans  in  salt  marshes  or  bay  fill.  At  a  few  sites,  plovers  breed 
commonly  at  commercial  or  abandoned  salt  evaporators, 
where  they  nest  on  low  dikes  separating  evaporator  ponds 
and  on  the  floors  of  dried  ponds.  Only  small  numbers  of 
plovers  nest  at  the  mouths  of  coastal  creeks  and  lagoons— 
on  small  pocket  beaches  that  are  set  off  by  high  bluffs  or 
rocky  points  and  usually  lacking  in  dunes  or  hummocks. 
Snowies  prefer  to  nest  in  flat  or  gendy  undulating  open 
areas  devoid  of,  or  sparsely  covered  with,  low-growing 
vegetation,  driftwood,  or  odier  debris  (Stenzel  &  Peaslee 
1979,  Stenzel  et  al.  1981).  In  coastal  areas,  these  may 
include  sand  beaches;  sand  flats  among  the  dunes;  salt  or 
alkali  flats  in  marshes,  on  lagoon  or  estuarine  margins,  or 
in  evaporator  ponds;  low,  unvegetated  dikes;  or,  rarely, 
wind-eroded  sandy  bluffs  or  sandy  dredge  islands  (Stenzel 
et  al.  1981,  D.  Shuford  pers.  obs.).  Coastal  nest  sites  are 
usually  within  100  yards  of  water  but  occasionally,  when 
there  is  not  a  formidable  barrier  between  the  nest  and 
water,  are  several  hundred  yards  away  from  it  (Stenzel  et  al. 
1981).  Openness  of  nesting  habitat  seems  a  key  require- 
ment—for  visual  security  from  predators  while  the  birds  are 


P!c 


SPECIES  ACCOUNTS 


Plovers 


incubating  eggs,  for  foraging,  and  for  leading  plover  chicks 
from  nesting  sites  down  to  shoreline  foraging  areas.  For 
breeding,  Snowies  eschew  beach  areas  that  are  heavily 
littered  with  driftwood,  are  back  in  dunes  with  steep  dune 
faces  perpendicular  to  the  shoreline,  or  where  there  is 
moderate  to  dense  vegetation,  since  any  of  these  hinder 
movement  of  chicks  to  low-lying  foraging  grounds.  Snow- 
ies also  avoid  breeding  in  areas  very  heavily  used  by 
humans. 

During  courtship,  a  male  uses  his  belly  and  feet  to  make 
a  series  of  shallow  nest  scrapes  in  soft  substrate,  only  one 
of  which  the  female  selects  for  egg  laying  (Page  et  al.  1985). 
The  nest  scape  may  or  may  not  be  lined  with  bits  of  broken 
shell,  fish  bones,  small  stones,  salt  crystals,  bits  of  wood, 
or  other  debris  (Bent  1929,  D.  Shuford  pers.  obs.).  Snow- 
ies typically  continue  to  add  nest  material  to  the  scrape 
throughout  incubation  (G.W.  Page  pers.  comm.).  They 
often  select  nest  sites  next  to  an  object,  such  as  driftwood, 
kelp,  other  stranded  flotsam  or  jetsam,  or  a  clump  of 
vegetation  (Stenzel  6k  Peaslee  1979,  Stenzel  et  al.  1981, 
Page  et  al.  1985).  In  California,  68%  of  136  nests  were 
within  six  inches  of  such  an  object  (Page  et  al.  1985); 
objects  selected  are  usually  small  radier  than  large  ones 
(G.W.  Page  pers.  comm.).  Nearby  objects  possibly  serve  as 
concealment  for  incubating  plovers,  or  they  may  function 
in  unknown  ways  in  courtship  activities;  observations 
suggest  that  objects  do  not  function  as  windbreaks,  to 
provide  shade,  as  cues  to  nest  location,  or  to  conceal  eggs 
or  adults  coming  from  or  going  to  them  (G.W.  Page  pers. 
comm.).  At  Mono  Lake,  the  disruptive  effects  of  nearby 
objects  did  not  reduce  predation,  as  did  overhead  cover 
(Page  et  al.  1985).  The  situation  there  may  be  anomalous, 
because  objects  are  not  numerous  as  they  are  at  coastal 
sites;  at  the  latter,  searches  by  predators  for  plovers'  nests 
beside  objects  might  prove  fruidess.  In  California,  the 
Snowy  Plover  breeding  system  is  one  of  serial  polyandry— 
that  is,  in  the  same  season,  females  nest  in  succession  with 
different  males  (Warriner  et  al.  1986).  A  few  days  after  the 
hatching  of  the  first  clutch,  the  female  leaves  the  precocial 
young  to  the  care  of  the  male  and  departs  to  search  for  a 
new  mate. 

Snowy  Plovers  forage  in  open  areas  on  outer-coast 
beaches,  from  the  water's  edge  back  to  the  fore  edge  of  die 
dunes,  and  on  tidal,  sand,  or  alkali  flats  of  estuaries, 
lagoons,  salt  marshes,  river  mouths,  and  evaporator 
ponds.  They  forage  on  beaches,  mosdy  on  wet  sand  or 
higher  up  where  invertebrates  concentrate  around  cast-up 
wrack.  Like  most  plovers,  Snowies  are  visual  predators  that 
primarily  search  for  prey  in  a  robinlike  style— by  walking  or 
running  several  steps,  peering  down,  and  then  picking 
items  from  the  surface.  Foraging  birds  run  along  in  a 
halting  zigzag  fashion,  stopping  frequendy  to  peck  at  prey 
items  (Swarth  1983).  Snowies  also  probe  into  the  surface 
of  the  mud  for  wriggling  prey  they  detect  visually.  They 


commonly  charge,  open  mouthed,  into  mats  of  brine  flies 
and  twist  their  heads  and  snap  at  airborne  flies.  Infre- 
quendy,  they  wade  into  shallow  water  to  feed  on  inverte- 
brates. Rarely,  they  vibrate  one  foot  on  a  solid  surface  to 
make  prey  move  and  reveal  themselves  (Johnsgard  1981). 
Snowy  Plovers  breeding  at  inland  sites  feed  on  a  great 
variety  of  ground-dwelling  arthropods,  primarily  flies  and 
beedes  (Swarth  1983).  At  Mono  Lake,  California,  they  feed 
primarily  on  brine  flies  and  a  species  of  carabid  beede; 
brine  flies  are  also  important  at  coastal  salt  evaporation 
ponds.  A  small  stomach-pumped  sample  (n  =  3)  from 
birds  at  Limantour  Estero,  Point  Reyes,  indicates  that 
coastal  birds  eat  polychaete  worms,  insects,  various  small 
crustaceans,  and  an  occasional  clam  (G.W.  Page  unpubl. 
data). 

Marin  Breeding  Distribution 

During  the  adas  period,  Snowy  Plovers  bred  on  the  outer 
coast  of  Point  Reyes  at  the  Seadrift/Stinson  Beach  spit  at 
Bolinas  Lagoon,  Limantour  Estero  spit,  Drake's  Beach 
spit,  Point  Reyes  Beach,  and  Abbott's  Lagoon  (Stenzel  et 
al.  1981).  Occasionally  they  may  also  breed  at  the  mouth 
of  Tomales  Bay,  at  Sand  Point  at  the  south  end  of  Dillon 
Beach,  though  documentation  is  lacking  for  that  site. 

Single-day  surveys  in  the  breeding  season  revealed  40 
Snowies  on  Point  Reyes  in  1977  (Stenzel  et  al.  1981),  24 
in  1989,  and  25  in  1991  (PRBO  unpubl.  data).  These  are 
low  estimates  of  the  total  breeding  population  as  intensive 
studies  of  color-banded  plovers  at  Point  Reyes  in  1989 
documented  that  there  were  at  least  32  adult  Snowies 
breeding  that  year  (Page  et  al.  1991).  Representative  breed- 
ing locations  during  the  adas  period  were  the  spit  at 
Bolinas  Lagoon  (NE  5/11  6k  12/77  -GWP  et  al.);  Ab- 
bott's Lagoon  (NE  4/14-27/77  -LES  et  al.);  and  Liman- 
tour Estero  (NE  4/20-30/77  -SCP  et  al.). 

Historical  Trends/  Population  Threats 

Grinnell  and  Miller  (1944)  noted  declines  in  Snowy  Plover 
numbers  in  the  southern  portion  of  the  state.  Page  and 
Stenzel  (1981)  documented  the  decline  in  California's 
coastal  breeding  population.  During  statewide  surveys 
from  1977  to  1980,  plovers  were  not  found  breeding  at  33 
of  53  coastal  sites  with  breeding  records  prior  to  1970.  It 
seems  unlikely  diat  plovers  will  breed  again  at  28  of  the  33 
sites  because  of  habitat  destruction  or  intense  human  use. 
The  greatest  losses  are  along  the  heavily  urbanized  south- 
ern California  coast;  this  region,  if  left  undisturbed,  pro- 
vides the  best  coastal  breeding  habitat.  The  coastal  Oregon 
breeding  population  has  also  declined  since  1979,  and 
surveys  in  1989  suggest  that  California's  coastal  popula- 
tion may  still  be  declining  (Page  et  al.  1991).  Interior 
breeding  populations  may  be  declining  as  well,  but  popu- 
lation trend  data  for  that  region  are  difficult  to  interpret. 

177 


Pic 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Plovers 


Numbers  of  Snowy  Plovers  wintering  on  the  southern 
California  coast  also  appear  to  have  decreased  since  at  least 
1961  (Pageetal.  1986). 

Plover  habitat  has  been  degraded  by  industrial  and 
residential  development,  intense  recreational  use  by 
humans  and  their  animals,  off-road  vehicle  use,  and 
grooming  of  beaches.  Less  noticeable  but  perhaps  equally 
important  are  the  indirect  effects  resulting  from  the  plant- 
ing for  dune  stabilization,  and  subsequent  naturalization, 
of  the  introduced  European  beachgrass  or  marram  grass 
(Ammophila  arenaria),  which  is  now  well  established  north 
of  Point  Conception.  Natural  dune  systems  along  our 
coasdine  have  a  series  of  dunes  that  run  perpendicular  to 
the  shoreline  and  are  frequently  interspersed  with 
expanses  of  flat  sand  that  extend  back  from  the  beach  and 
provide  excellent  plover  nesting  habitat  (Page  &.  Stenzel 
1981).  Ammo^hila-dominated  dunes  usually  have  a 
continuous  foredune  running  parallel  with  die  shoreline 
diat  restricts  access  to  the  interdune  sand  flats.  Addition- 
ally, Ainmophila  reduces  the  species  diversity  of  native 
plants,  increases  plant  cover,  steepens  the  dunes  (Barbour 
et  al.  1976),  and  markedly  depresses  the  abundance  and 
diversity   of  sand   dune    arthropods   (Slobodchikoff  &. 


Doyen  1977).  This  reduction  in  potential  prey  may 
adversely  affect  the  plovers  since  they  frequendy  feed  on 
insects  well  above  the  tide  line  (Stenzel  et  al.  1981).  In 
northern  California,  degradation  of  plover  habitat  has 
been  balanced  to  a  large  degree  by  the  creation  inside  San 
Francisco  Bay  of  salt  evaporation  ponds,  which  breeding 
plovers  have  used  since  at  least  1918.  For  the  whole  coast, 
habitat  degradation  has  far  outweighed  such  enhancement 
(Page  ck  Stenzel  1981). 

Federal  and  state  agencies  and  private  conservation 
groups  have  expressed  concern  over  the  plover's  declining 
populations.  The  Snowy  Plover  was  on  the  Audubon 
Society's  Blue  List  from  its  inception  in  1972  to  1982  and 
on  its  list  of  Species  with  Special  Concerns  in  1986  (Tate 
1981,  1986;  Tate  ck  Tate  1982).  In  California,  this  plover 
is  currendy  a  Bird  Species  of  Special  Concern  (Remsen 
1978,  CDFG  1991b).  Spurred  by  a  petition  by  Page  and 
Walter  (1988),  the  coastal  population  of  the  Western 
Snowy  Plover  (C.  a.  nivosus)  was  finally  listed  by  the  U.S. 
Fish  and  Wildlife  Service  as  federally  Threatened  in  March 
1993.  Techniques  to  successfully  hand-rear  Snowy  Plovers 
have  been  developed  should  the  need  arise  (Page  et  al. 
1989). 


178 


Plovers 


SPECIES  ACCOUNTS 


Pic 


KILLDEER    Charadrius  vociferus 


Occurs  year  round,  though  numbers 

^^^^rOw^^ci^^ 

swell  gready  from  Sep  through  Mar. 

A  fairly  common,  widespread  breeder; 

^^^k^^^^^^- 

overall  breeding  population  fairly  large. 

j?ZS  «JV<\  °3r<\  °J^\  *K^\o  V^A*  V>^Co  V>A 

Recorded  in  146  (66.1%)  of  221 

V5o\V\**\ "->V\  *tVo\  °A:>\    3r-"\    Jv"\     V^l 

blocks. 

O    Possible        =      51    (35%) 
€    Probable       =       31    (21%) 
•    Confirmed  =      64   (44%) 

,-Pvv  Jk^kX     V\    V^v    V-^^M^OfV^C    V^A*^ 
Pw^JkOiAS — X_    \^\     w^a     V-^\    lkZ^\-    \^\  *  V^: 

FSAR  =  3        OPI  =  438       CI  =  2.09 

^o 

Ecological  Requirements 

Whether  described  as  plaintive  or  petulant,  sonorous  or 
strident,  vociferus  is  apdy  named.  Killdeer  are  the  first  and 
most  persistent  of  birds  to  raise  the  hue  and  cry  when 
intruders  invade  their  nesting  haunts.  Scantily  vegetated 
open  terrain  that  provides  clear  vistas  at  ground  level 
characterizes  both  nesting  and  foraging  areas.  These 
include  pastures;  plowed  or  uncultivated  fields;  roadside 
margins;  lawns  and  playing  fields;  the  fringes  of  quiet 
shallow  waters,  such  as  stock  or  sewage  ponds,  lakes, 
lagoons,  estuaries,  and  streams;  and  other  disturbed  sites. 
Killdeer  select  barren  or  sparsely  vegetated,  often  gravelly 
nesting  sites  with  an  ample  supply  of  nest  material  at  hand 
(Bunni  1959).  Lawns,  even  if  close  cropped,  are  rarely  used 
for  nesting  unless  they  offer  bare  spots.  Preferred  gravelly 
areas  often  arise  from  erosion  or  stream  flooding  or  from 
construction  of  roadsides,  dikes,  or  railroad  right-of-ways. 
Nest  sites  are  usually  in  close  proximity  to  water  used  for 
bathing,  cooling  in  hot  weather,  and  foraging.  Rarely,  nest 
sites  may  be  1.5  to  2  miles  from  water;  irrigated  lawns  or 
fields  may  sometimes  substitute  for  standing  shallow  water 
(Townsend  1929,  GckM  1944,  Bunni  1959).  Nest  sites 
frequendy  are  elevated  slighdy  on  mounds,  knolls,  hills,  or 
slopes,  giving  incubating  birds  a  wide  view  of  their  sur- 
roundings and  affording  protection  from  flooding  by  rain- 
water (Bunni  1959).  Nest  scrapes  and  nests  are  often 
placed  beside  an  object,  such  as  a  stone,  plant,  log,  manure 
pile,  or  dirt  mound,  which  perhaps  provides  concealment 
from  predators.  In  the  absence  of  such  an  object,  the 
cryptically  colored  eggs  blend  with  uneven  surfaces  or  the 


coloration  or  texture  of  the  substrate  to  afford  protection. 
If  these  methods  fail,  Killdeer  often  resort  to  their  classic 
broken-wing  displays  to  lure  potential  predators  away  from 
nests  or  vulnerable  young. 

During  courtship  ceremonies,  males  construct  with 
their  feet  several  shallow  scrapes,  into  the  last  of  which 
their  mates  lay  eggs;  additional  scrapes  sometimes  serve  as 
reserve  nests  when  eggs  are  lost  (Bunni  1959).  Killdeer 
avoid  digging  scrapes  in  hard  substrates  or  in  soft  or 
muddy  substrates  where  the  pits  might  collapse.  Availabil- 
ity close  at  hand  of  small,  loose  objects  for  nest  building  is 
important,  since  Killdeer  obtain  materials  by  tossing  them 
with  their  bills  toward  the  nest,  usually  from  less  than  three 
feet.  Typically,  the  bottom  of  the  nest  scrape  is  formed  of 
stones  that  protect  the  nest  from  flooding  by  allowing  water 
to  percolate  down;  a  fringe  of  nest  material  outside  the  nest 
protects  from  erosion.  Killdeer  prefer  flat  or  angular  stones 
from  0.2  to  0.4  inches  (secondarily  up  to  0.6  in.)  in  length 
that  are  easily  flipped.  Birds  select  weed  stems,  twigs,  and 
wood  or  bark  chips  in  the  0.2-  to  0.8-inch  (secondarily  up 
to  2.4-in.)  size  range  over  stones  for  lining  the  nest.  White 
objects  are  preferred  over  black  ones,  though  size  and 
shape  considerations  will  override  color  in  the  selection 
process.  Almost  any  flat,  lightweight  object  will  do  for  nest 
material;  these  can  include  shells,  lichens,  manure,  small 
bones,  crayfish  armor,  dry  shells  of  melon  seeds,  dead 
leaves,  cornhusks,  and  rubbish  such  as  peanut  shells, 
paper  matches,  cigarette  butts,  dry  chewing  gum,  bits  of 
paper,  plaster  chips,  or  charcoal.  Rarely,  a  nest  on  an  area 

179 


Plovers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Plovers 


of  sparse  grass  on  a  lawn  is  made  mostly  of  grass,  and 
sometimes  eggs  are  laid  in  a  bare  scrape  without  nest 
materials.  Killdeer  sometimes  nest  on  the  gravel  or  crushed 
stone  roofs  of  one-  to  four-story  buildings  (Bunni  1959, 
Demaree  1975).  Chicks  that  don't  succeed  in  tumbling 
safely  from  the  roofs  to  the  ground  often  succumb  to 
dehydration.  Killdeer  have  also  nested  three  feet  off  the 
ground  in  a  depression  of  semidecayed  wood  on  a  log 
(Bunni  1959).  Killdeer  sometimes  begin  to  lay  before  the 
addition  of  much  nest  material,  and  birds  typically  con- 
tinue to  add  nest  material  throughout  incubation.  During 
one  nesting  season,  females  will  sometimes  lay  successive 
clutches  successfully  in  the  same  scrape. 

Killdeer  forage  in  a  variety  of  open  habitats,  particularly 
in  pastures,  plowed  fields,  lawns,  and  on  the  muddy, 
sandy,  or  marshy  margins  of  shallow  still  or  slow-moving 
water.  Like  most  plovers,  Killdeer  are  visual  predators  that 
forage  robinlike  by  walking  or  running  in  a  zigzag  pattern, 
then  stopping  and  peering  intendy  in  search  of  hidden 
prey,  which  they  pick  from  the  ground  (Bunni  1959).  They 
also  pull  earthworms  from  the  ground  and  wade  into 
shallow  water  to  feed.  A  Killdeer  will  sometimes  cleanse  its 
prey  by  dropping  it  into  water  several  times  and  picking  it 
up,  or  by  rinsing  it  with  sideways  movements  of  the  bill. 
After  the  precocial  young  hatch,  adults  lead  them  to  the 
nearest  feeding  area.  The  Killdeer  diet  is  about  97.7% 
insects  and  other  animal  matter  and  2.3%  vegetable  mat- 
ter, chiefly  weed  seeds  (McAtee  &.  Beal  1912,  n  =  228). 
Important  animal  foods  are  beedes,  grasshoppers,  caterpil- 
lars, ants,  true  bugs,  caddisflies,  dragonflies,  flies,  centi- 


pedes, spiders,  ticks,  nereid  worms,  earthworms,  snails, 
crabs,  and  other  crustaceans.  The  diet  of  upland-feeding 
birds  undoubtedly  varies  considerably  from  that  of  birds 
foraging  on  freshwater  margins  or  tidal  flats. 

Marin  Breeding  Distribution 

During  the  adas  period,  Killdeer  bred  widely  throughout 
the  lowlands  of  Marin  County.  Representative  breeding 
locations  were  the  head  of  Schooner  Bay  (NE  3/22- 
4/7/81  — DS);  near  the  mouth  of  Estero  Americano 
(NE/NY  7/12/82  -DS);  near  Chileno  Creek,  Chileno 
Valley,  on  a  gravel  wash  formed  by  the  1982  flood  (NE 
5/5/82  —PA);  and  Bahia  Drive  ponds  near  the  Petaluma 
River  moudi,  Novato  (NE  5/7/78  — DS).  Of  interest  was 
an  earlier  sighting  of  a  pair  that  successfully  raised  two  or 
three  broods  on  the  roof  of  the  Inverness  Motel  (NE-FL 
3/29-8/3/67  -PL). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  felt  that  the  augmentation  of 
favorable  Killdeer  habitat  in  California  because  of  irriga- 
tion had  more  than  compensated  for  reductions  in  "natu- 
ral" territory.  This  may  be  the  case,  but  it  is  difficult  to 
judge  the  skimpy  facts  available  regarding  the  effects  on 
wildlife  of  the  tremendous  changes  brought  by  the  state's 
extensive  agricultural  and  urban  development.  Killdeer 
numbers  decreased  on  Breeding  Bird  Surveys  in  Califor- 
nia from  1968  to  1989  but  were  relatively  stable  from  1980 
to  1989  (USFWS  unpubl.  analyses). 


180 


Oystercatchers 


SPECIES  ACCOUNTS 


Oystercatchers 


Oystercatchers 

Family  Haematopodidae 


BLACK  OYSTERCATCHER   Haematopus  bachmani 


A  year-round  resident. 

/OaVv\ 

\             ^jCV-. 

An  uncommon,  very  local  breeder; 

-C^V^Cip^V^ 

overall  breeding  population  very  small. 

"x^i \^*\\    \^ 

^f>A3^^CVTV 

Recorded  in  10  (4.5%)  of  221  blocks. 
O    Possible                 4   (40%) 

VV^ 

^C\^ 

i^A       \^\       \-- — \        V^\       \^^\       V- 

€    Probable       =        0  (0%) 

\  Je* 

vJV<o> 

^^-^A^^A ^\^\  3s^\  ^-V^\  ^\^ 

•    Confirmed  =         6   (60%) 

i  V^\^     V^\    -V^^x  ^^^\      \^c\\ 

Oi^^V- — ""s" 

FSAR  =2         OPI  =  20        CI  =  2.20 

"TUf/    v 

^^^^ 

JU 

^-->C^\^^^-^fe^o 

Ecological  Requirements 

Boisterous,  effusive  piping  greets  any  meddler  in  Oyster- 
catcher  affairs  along  the  wave-battered,  sea-sprayed  rocky 
shoreline  of  Marin  County's  outer  coast.  Black  Oyster- 
catchers inhabit  rocky  reefs,  offshore  islets,  and  sea  stacks 
on  promontories  and  stretches  of  exposed  coasdine.  Their 
breeding  requisites  include  nest  sites  sheltered  from  high 
tides,  spray  from  crashing  waves,  prevailing  winds  or 
storms,  and  mainland  ground  predators;  and  suitable 
rocky  intertidal  foraging  grounds  (Webster  1941a,  Hart- 
wick  1974).  Oystercatchers  avoid  nesting  near  high  densi- 
ties of  gulls  (Hartwick  1974).  In  British  Columbia,  the 
distance  from  nest  sites  to  foraging  areas  varies  from  about 
40  to  200  feet  (Hartwick  1974).  Nest  sites  and  feeding 
territories  are  usually  contiguous,  but  sometimes  a  nest  site 
is  isolated  from  the  feeding  area  by  water  or  the  territories 
of  other  birds.  Nest  sites  are  often  on  shelves  just  above  the 
sea,  but  they  may  range  up  to  90  feet  or  more  above  the 
tide  line  on  the  exposed  shoulders  of  great  rocks  (Dawson 
1923,  Webster  1941a). 

During  the  ten  days  to  two  weeks  before  egg  laying, 
Oystercatchers  build  several  "play  nests,"  which  are  usually 
inferior  in  construction  to  the  one  finally  chosen  for  the 
eggs  (Webster  1941a).  A  typical  egg  nest  is  a  platform  or 


bowl  of  rock  flakes,  rounded  pebbles,  or  bits  of  shell  placed 
in  a  cranny  of  bare  rock  (Dawson  1923,  Bent  1929, 
Webster  1941a,  Hartwick  1974).  Oystercatchers  also  lay 
their  eggs  in  hollows  scraped  from  soil  pockets  in  irregu- 
larities of  the  rock  or  from  weedy  turf  on  ledges,  lining 
these  nests  with  similar  materials  to  those  in  bare  rock. 
Exceptionally,  they  build  bowls  of  grass  or  dried  moss 
similar  to  a  gull's  nest  or  lay  their  eggs  in  a  hollow  scooped 
in  a  gravel  or  shell  beach.  Birds  add  nest  material  through- 
out incubation  (Webster  1941a).  When  the  nonincubating 
bird  is  not  foraging,  it  stands  on  lookout  on  a  rock 
eminence,  usually  at  or  below  nest  level  and  within  about 
5  to  25  yards  of  the  nest.  After  chick  hatching,  adults  make 
initial  foraging  trips  by  flying,  but  after  a  few  days  they 
begin  to  walk;  occasionally  they  continue  to  fly  to  feeding 
grounds  distant  from  the  defended  territory  (Webster 
1941a,  Hartwick  1974). 

Black  Oystercatchers  forage  mosdy  in  the  rocky  inter- 
tidal zone.  There  they  hop  about  rocks  and  wade  in  tide 
pools,  pounding,  prying,  and  cutting  mollusks  from  their 
protective  armor  and  anchorages  and  picking  or  probing 
in  hiding  places  for  unshelled  prey  (Webster  1941b,  Hart- 
wick 1976).  At  the  Farallon  Islands,  70%-95%  of  feeding 

181 


Oystercatchers 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


Oystercatchers 


activity  occurs  during  the  lower  half  of  the  tidal  cycle, 
depending  on  shoreline  exposure  and  swell  height  (Mor- 
rell  et  al.  1979).  Oystercatchers  there  feed  during  the  high 
half  of  the  tidal  cycle,  mosdy  in  late  summer,  when  adults 
are  feeding  large,  rapidly  growing  chicks,  and  in  fall,  when 
fledglings  require  more  time  to  feed  themselves  until  they 
master  dieir  apprenticeship.  Adults  may  concentrate  in 
particular  areas  of  die  intertidal.  For  example,  adults  feed- 
ing chicks  may  spend  considerahle  time  foraging  at  the 
bottom  edge  of  mussel  beds,  where  a  certain  species  of  crab 
lives  (Harfwick  1976).  At  the  Earallon  Islands,  Oyster- 
catchers also  probe  in  the  soil  of  a  nontidal  marine  terrace 
for  tenebrionid  beede  larvae  (Morrell  et  al.  1979),  and  at 
Vancouver  Island  they  also  feed  in  mussel  beds  on  tidal 
mudflats,    particularly   in   winter  (Hartwick   ck    Blaylock 

1979). 

An  adult  Oystercatcher's  sturdy,  bright  vermillion,  later- 
ally compressed  bill  is  an  essential  tool  for  mining  the 
abundant  (though  tighdy  fastened  and  armored)  inverte- 
brate fauna  of  rocky  reefs.  Birds  seek  recendy  exposed  or 
slighdy  inundated,  hence  partially  relaxed,  mollusks  since 
these  are  the  only  ones  they  have  a  reasonable  chance  of 
opening  (Webster  1941b,  Hartwick  1976).  Because  of  the 
short  period  when  gaping  mussels  are  available,  Oyster- 
catchers move  quickly,  often  pass  over  small  food  items, 
and  appear  to  cover  greater  distances  while  foraging  on 
mussels  than  when  seeking  a  greater  array  of  prey  (Hart- 
wick 1976).  In  search  of  gaping  mussels,  Oystercatchers 
walk  over  reefs  with  their  heads  directed  forward  and  their 
"chisel-tipped"  bills  poised  to  strike  a  sharp  blow  on  the 
dorsal  border  oblique  to  the  long  axis  of  die  mussel 
(Webster  1941b,  Hartwick  1976).  Such  a  blow  depresses 
die  valve,  forming  an  abnormal  gap  diat  will  admit  the  tip 
of  the  bird's  bill.  Birds  also  search  for  mussels  already 
opened  wide  enough  to  permit  entrance  of  dieir  bills.  In 
either  case,  the  bill  is  then  stabbed  down  into  the  mussel 
with  a  number  of  forceful  and  rapid  jerks  until  the  deepest 
part  of  the  bill  lies  lengthwise  between  the  margins  of  the 
valves.  Next  the  mussel  is  opened  by  rapid  levering  and 
biting  that  severs  the  adductor  muscle;  sometimes  the  shell 
is  fractured  in  the  process.  In  rare  instances,  when  a 
mussel  sits  with  its  ventral  byssal  fissure  exposed,  Oyster- 
catchers work  from  that  juncture  to  open  the  mussel  by  the 
above  methods.  Birds  sometimes  detach  the  mussel  after 
opening  it  and  carry  it  to  a  more  convenient  location  to 
remove  the  meat.  Many  mussels  are  also  located  by  prob- 
ing in  die  mud  and  dien  usually  are  opened  from  the 
vulnerable  ventral  side.  Oystercatchers  remove  the  flesh  by 
first  tearing  larger  pieces  and  then  laying  the  bill  flat  on  the 
shell  like  scissors  and  pushing  it  forward  as  the  points  snip 
away  the  adherent  flesh. 

Oystercatchers  loosen  limpets  from  their  moorings  by 
first  delivering  one  or  more  sharp  strokes  of  die  bill  from 
a  low  angle  (Webster  1941b,  Hartwick  1976).  This  will 


remove  small  limpets  but  only  weakens  the  grip  of  larger 
ones  and  sometimes  chips  their  shells.  As  needed,  this  is 
followed  by  firm  pushing,  lateral  head  swaying,  or  to-and- 
fro  rotation  of  the  bill.  If  diis  does  not  complete  the  job, 
die  bird  forces  the  bill  under  the  shell  and  levers  it  free. 
The  Oystercatcher  dien  seizes  the  limpet  and  carries  it  to  a 
niche  or  rock  crevice  to  remove  the  meat.  Placing  the 
limpet  shell  down,  the  bird  rapidly  bites  around  die  edge 
of  the  shell  and  finally  picks  the  body  up,  shakes  the  shell 
off,  and  swallows  the  meat  in  one  gulp.  Oystercatchers 
attack  chitons  in  the  same  way  as  limpets,  but  unless  they 
topple  small  ones  with  the  first  stroke,  further  quick  work 
is  needed  (Webster  1941b).  Birds  push  the  tip  of  the  bill 
under  one  corner  of  die  leathery  shell,  breaking  the  vac- 
uum set  up  by  the  muscular  foot  of  the  mollusk.  Then  they 
usually  slip  the  bill  under,  flat  side  against  the  rock,  and 
cut  the  animal  loose  by  sawing  strokes  of  the  bill.  Oyster- 
catchers obtain  barnacles  by  sharply  tapping  one  valve, 
levering  the  valves  apart  by  circular  leverage,  and  then 
pulling  out  the  bite-sized  body  whole.  Oystercatchers 
obtain  many  smaller  prey,  such  as  small  limpets  and  sea 
cucumbers,  by  probing  and  moving  aside  seaweed  (Hart- 
wick 1976). 

The  Black  Oystercatcher  diet  consists  primarily  of  mus- 
sels, limpets,  and  chitons,  along  with  smaller  amounts  of 
barnacles,  marine  worms  (annelids,  nemerteans,  and 
sipunculids),  crabs,  snails,  young  abalone,  isopods,  echino- 
derms,  and  sometimes  insects  (Webster  1941b,  Hartwick 
1976,  Morrell  et  al.  1979).  At  the  Farallon  Islands,  the  diet 
is  primarily  the  California  mussel  fM^tilus  californianus), 
several  species  of  limpets,  beede  larvae,  and  marine  (ne- 
mertean  and  polychaete)  worms;  crabs  are  also  taken 
(Morrell  et  al.  1979).  The  diet  at  the  Farallones  varies 
among  territories,  depending  on  the  topography  of  the 
shoreline— sloping  shoreline  supports  mussel  beds,  where- 
as steep  shoreline  does  not.  At  nests  where  mussels  com- 
prise 40%  or  more  of  the  prey  remains,  the  diet  is  more 
varied  than  at  nests  where  mussels  comprise  30%  or  less 
of  the  diet.  Presumably  this  reflects  a  greater  diversity  of 
prey  in  mussel  beds.  In  any  case,  when  mussels  are 
available  there,  they  are  preferred  over  limpets  as  a  food  for 
chicks  (Morrell  et  al.  1979). 

Unlike  most  precocial  shorebirds,  Oystercatcher  young 
initially  are  not  able  to  feed  themselves  because  their 
underdeveloped  bills  and  feeding  skills  are  no  match  for 
armored  prey.  Very  young  chicks  usually  remain  close  to 
the  nest,  and  the  parents  take  turns  guarding  the  chicks 
and  carrying  food  items  singly  to  them  from  the  intertidal 
zone  (Webster  1941a,  Hartwick  1974,  Groves  1984). 
Adults  may  hold  food  in  the  bill  before  chicks  or  drop 
items  and  point  to  them  on  the  ground  (Hartwick  1976). 
One  adult  may  also  pass  the  food  to  the  other  adult,  who 
prepares  it  and  presents  it  to  the  chick  while  the  first  adult 
returns  to  foraging  duties.  In  British  Columbia,  adults  feed 


182 


Oystercatchers 


SPECIES  ACCOUNTS 


Oystercatchers 


chicks  at  nests  mostly  mussels  (larger  than  average  sized) 
and  limpets  of  large  size  or  species  (Hartwick  1976). 
Chicks  are  also  fed  quite  large  chitons  and  crabs.  Crabs 
may  be  a  special  part  of  the  chick  diet  since  adults  there  do 
not  prey  on  them  until  they  begin  feeding  their  chicks.  In 
contrast  to  chicks,  adults  then  are  eating  less  profitable 
items— small  to  medium-sized  limpets,  smaller  mussels, 
and  a  lot  of  small  unshelled  food  items.  Chicks  move  with 
foraging  parents  to  the  littoral  zone  in  stages  (Hartwick 
1974).  Young  may  reach  the  feeding  area  as  early  as  two 
days  after  hatching  but  usually  not  until  the  third  to  fifth 
week  (Webster  1941a,  Hartwick  1974),  depending  on  the 
difficulty  of  descent  to  feeding  areas  (Webster  1941a). 
Sometimes  gulls  prevent  adults  from  moving  their  chicks 
to  the  intertidal  zone,  and  so  the  young  remain  near  the 
nest  site  until  fledging  (Hartwick  1974).  Chicks  that 
remain  at  the  nest  for  long  periods  are  fed  an  increasing 
proportion  of  mussels  (Hartwick  1976).  Although  prefledg- 
ing  chicks  that  move  to  the  littoral  zone  are  able  to  capture 
small  prey  items,  they  still  depend  on  adults  for  the  most 
profitable  ones  (Hartwick  1976,  Groves  1984).  When 
young  begin  to  move  to  foraging  areas  with  parents,  one 
adult  often  remains  higher  in  the  intertidal  guarding  the 
chicks  and  feeding  them  smaller  items,  while  the  other 
adult  hunts  farther  down  and  carries  mussel  meat  and 
other  larger  items  to  the  chicks.  It  does  appear,  diough, 
that  feeding  becomes  a  teaching  process,  as  progressively 
more  and  more  work  is  left  to  the  chicks.  The  diet  during 
this  period  shifts  away  from  a  dependence  on  mussels  to 
more  limpets  and  smaller  unshelled  items.  At  the  Farallon 
Islands,  marine  worms  and  beede  larvae  make  up  as  much 
as  57%  (by  number)  of  the  diet  fed  to  1-  to  40-dayold 
chicks  (Morrell  et  al.  1979).  When  chicks  there  are  old 
enough  (67-100  days)  to  forage  with  their  parents  in  the 
littoral  zone,  limpets  are  the  major  prey  item  (60%-85%), 
whether  fed  to  a  chick  by  a  parent  or  captured  by  a  chick 
itself.  The  diet  of  newly  independent  chicks  is  mainly 
limpets,  marine  worms,  and  beede  larvae,  since  the  young 
birds  have  not  yet  developed  the  skill  to  open  mussels. 
Adults  have  been  observed  feeding  adult-sized  young  at 
Point  Lobos,  Monterey  County,  as  late  as  3  November 
(Williams  1927),  and  fledglings  are  not  fully  adept  at 
opening  mussels  or  prying  barnacles  or  chitons  from  rocks 
until  they  are  three  to  four  months  old  (Webster  1941a). 

Marin  Breeding  Distribution 

During  the  adas  period,  Black  Oystercatchers  bred  at  a 
number  of  spots  at  irregular  intervals  along  Marin  Coun- 
ty's outer  coast  where  suitable  stretches  of  rocky  shoreline 


exist  (Table  14,  Figure  14).  Representative  breeding  loca- 
tions were  Double  Point,  PRNS  (NE  summer  1978  — SGA); 
about  V2  mi.  NW  of  the  mouth  of  Bear  Valley,  PRNS  (FL 
7/3/80  — DS);  and  near  the  mouth  of  Estero  de  San 
Antonio  (FL  6/24/82  -DS).  In  1988,  Rauzon  and  Carter 
(1988)  documented  Black  Oystercatchers  breeding  on 
West  Marin  Island  inside  San  Francisco  Bay;  two  Oyster- 
catchers were  also  present  there  during  USFWS  surveys  in 
1990  (Carter  et  al.  1992). 

Historical  Trends/ Population  Threats 

In  surveys  of  selected  sites  in  1969  to  1972,  Ainley  and 
Whitt  (1973)  estimated  14  Oystercatchers  were  breeding  at 
three  sites  on  the  Marin  County  coast.  From  complete 
surveys,  Sowls  et  al.  (1980)  estimated  30  birds  were  breed- 
ing at  eight  sites  on  Marin's  outer  coast  in  1979,  and 
Carter  et  al.  (1992)  estimated  27  birds  were  breeding  at 
nine  sites  there  in  1989.  Even  numbers  from  the  more 
recent  surveys  are  probably  low,  considering  die  difficulty 
of  counting  this  scattered,  solitary-nesting  species  from 
boats. 

From  surveys  in  1979  to  1980,  Sowls  et  al.  (1980) 
estimated  a  total  of  462  Oystercatchers  were  breeding  on 
the  central  and  northern  California  coast.  In  1989,  Carter 
et  al.  (1992)  recorded  575  birds  in  surveys  of  the  same 
region  (plus  6  in  S.F.  Bay  in  1990);  their  numbers  would 
have  been  even  greater  than  those  of  the  prior  survey  if  they 
had  rounded  numbers  to  represent  breeding  pairs  as  was 
done  previously.  They  concluded  that  the  higher  1989 
figures  (rounded  or  not)  may  be  indicative  of  better  viewing 
conditions  during  die  later  survey  and  slighdy  different 
definitions  of  breeding  birds  between  the  surveys,  rather 
than  a  true  population  increase. 

Oystercatchers  have  held  up  well  to  human  pressures  in 
California,  except  locally  at  the  Farallon  Islands  and  at  San 
Pedro,  Los  Angeles  County  (GckM  1944).  Ainley  and 
Lewis  (1974)  claimed  that  Oystercatchers  disappeared  from 
the  Farallones  in  die  1860s,  probably  because  of  too  much 
disturbance  from  humans  and  domestic  animals.  That 
population  has  subsequendy  recovered.  Although  it  seems 
clear  that  the  Farallon  population  did  decline,  it  is  hard  to 
imagine  the  species  totally  disappearing  there  because  the 
island  harbors  inaccessible  intertidal  areas  where  Oyster- 
catchers could  have  taken  refuge  from  disturbance.  Near- 
shore  oil  spills  potentially  could  decimate  the  littoral  food 
resources  upon  which  Oystercatchers  depend  (Sowls  et  al. 
1980). 


183 


Stilts  and  Avocets 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Stilts  and  Avocets 


Stilts  and  Avocets 

Family  Recurvirostridae 


BLACK-NECKED  STILT    Himantopus  mexicanus 


l 

A  year-round  resident;  numbers 

A/Sp%S?^>^^    N 

depressed  from  Oct  through  mid-Mar. 

^-V><AQ^x 

A  fairly  common,  very  local  breeder; 

overall  breeding  population  very  small. 

XAa^Vsa 

Recorded  in  9  (4.1%)  of  221  blocks. 

v^^A^Aj^VA-Air^?^ 

^\^OoC-i 

\^<S^S^tv\^J^\'^ 

O    Possible                  4   (44%) 

\$P^H^rv^^^ 

\  ~^k"^  \   ^-V^^A  ^L-'t'-^ 

C    Probable                 0   (0%) 

\Jl^v*^\  '•^\<^^^l^^i\L\^^\     3* 

•    Confirmed   =         5   (56%) 

—  T- 

^wPsV^P^^^Vv 

FSAR  =  3        OPI  =  27         CI  =  2.11 

Vo 

Ecological  Requirements 

These  dainty  black  and  white  shorebirds  perched  on  out- 
landishly  long  pink  legs  cast  surreal  reflections  in  the 
waters  of  a  variety  of  shallow  freshwater,  brackish,  and 
alkaline  wedands.  In  Marin  County,  Stilts  breed  in  the 
reclaimed  or  altered  bayshore  saltmarsh  habitats  of  diked 
(tidal  and  nontidal)  brackish  ponds,  sewage  ponds,  and 
ephemeral  freshwater  ponds.  Although  they  often  overlap 
in  habitat  preferences  with  American  Avocets,  Stilts  tend 
to  prefer  fresher  water  and  more  emergent  vegetation,  and 
they  feed  more  in  marshes,  than  do  Avocets  (Hamilton 
1975).  Observations  at  agricultural  evaporation  ponds  in 
the  San  Joaquin  Valley  suggest  that  prey  availability  is  die 
primary  limiting  factor  for  both  of  these  shorebirds. 
Regardless  of  salinity  and  alkalinity,  both  Stilts  and  Avo- 
cets are  numerous  in  evaporation  ponds  when  suitable 
invertebrate  prey  are  abundant  and  available  to  them  via 
their  respective  foraging  techniques  (G.  Gerstenberg  pers. 
comm.).  Hence,  the  habitat  choices  of  these  species  seem 
to  reflect  the  likelihood  of  finding  suitable  prey  resources 
rather  than  a  selection  for  particular  water  chemistry. 

Stilts  generally  nest  as  close  as  possible  to  accessible 
feeding  areas.  They  prefer  rather  open  habitat,  where  they 
generally  congregate  in  small,  loose  colonies,  often  mixing 

184 


with  Avocets.  Birds  choose  nest  sites  on  bare  to  moderately 
vegetated  flat  terrain;  on  the  flat  or  irregular  surfaces  of  low 
rises  on  dry  land;  at  the  water's  edge;  or,  less  frequendy, 
built  up  in  shallow  water  (Bent  1927,  Palmer  1967,  Ham- 
ilton 1975).  When  Stilts  nest  in  vegetated  areas,  they  tend 
to  select  sites  on  the  edge  of  the  vegetation  with  good 
visibility  of  their  surroundings  (Hamilton  1975).  In  the 
Bay  Area,  Stilts  most  often  nest  on  unvegetated  or  sparsely 
vegetated  dikes  and  levees  of  salt  ponds,  and  occasionally 
in  openings  in  salt  marsh  (Gill  1972,  1977;  Hamilton 
1975;  Rigney  ek  Rigney  1981).  At  San  Francisco  Bay  salt 
evaporators,  Stilts  concentrate  in  die  interior  of  pond 
complexes  away  from  the  bayshore.  Most  nests  there  are 
on  discontinuous  levees,  insular  levee  fragments,  or  small 
dirt  mound  islands;  few  nests  are  on  continuous  or  well- 
traveled  dikes.  Hamilton  (1975)  noted  that  Stilt  nests 
tended  to  be  located  on  the  leeward  side  of  saltpond  dikes 
and  on  the  side  toward  favored  feeding  areas;  birds  may 
also  select  nest  sites  with  reference  to  the  direction  of 
human  approach.  Nests  located  on  the  centers  of  dikes 
usually  are  constructed  downwind  of  small  natural  objects, 
which  may  serve  as  windbreaks. 


Stilts  and  Avocets 


SPECIES  ACCOUNTS 


Stilts  and  Avocets 


Depending  on  the  availability  of  materials  and  the  nest 
location,  Stilt  nests  vary  from  shallow  scrapes  in  bare  earth 
with  hardly  a  vestige  of  nest  material  to  elaborate  raised 
platforms  (Dawson  1923,  Bent  1927,  Palmer  1967,  Ham- 
ilton 1975).  Nest  materials  include  pebbles,  shells,  plant 
stems,  twigs,  large  feathers  or  dried  bird  carcasses,  dry  mud 
chips,  bones,  cow  dung,  and  grasses.  Sometimes  Stilts  add 
substantial  amounts  of  material  to  nests  to  avoid  rising 
waters.  Normally,  birds  continue  to  occasionally  add  small 
amounts  of  nest  material  throughout  incubation  (Hamil- 
ton 1975).  After  the  newly  hatched  precocial  young  obtain 
mobility,  they  are  led  to  shallow-water  feeding  areas,  pref- 
erably with  low  vegetative  escape  cover. 

The  extremely  long  legs  of  Black-necked  Stilts  are  per- 
fecdy  suited  for  wading  well  out  into  shallow  water.  Stilts 
are  primarily  visual  foragers  that  obtain  most  of  their  prey 
from  an  immobile  stance  or  while  slowly  walking  (Hamil- 
ton 1975).  Their  main  mode  of  prey  capture  is  by  pecking 
at  the  mud  or  from  or  near  the  water's  surface  without 
immersing  the  head.  Stilts  also  capture  terrestrial  insects  by 
pecking  at  the  ground  or  vegetation.  Less  frequendy,  they 
plunge  their  heads  or  even  necks  or  upper  breast  into  water 
in  pursuit  of  items,  but  apparendy  their  bills  do  not  reach 
bottom.  Stilts  also  snatch  flying  insects  from  the  air  with 
their  bills  after  running  or  fluttering  toward  them.  Only 
very  rarely  do  they  forage  by  back-and-forth  scythelike 
motions  of  the  bill  as  Avocets  commonly  do  (see  account). 
On  San  Francisco  Bay,  Stilts  often  feed  in  marshes  after 
their  chicks  hatch.  Unlike  Avocets,  they  use  grass-bordered 
ephemeral  pools,  and  in  the  rare  instances  when  they  feed 
on  tidal  mudflats,  they  do  so  close  to  shore.  Hamilton 
(1975)  compared  the  foraging  niches  between  the  sexes 
and  between  Stilts  and  Avocets.  Male  Stilts,  with  their 
longer  legs,  tend  to  feed  in  deeper  water  than  do  females. 
Although  male  Stilts  can  feed  in  deeper  water  than  do 
Avocets,  both  species  concentrate  their  foraging  in  "ankle- 
deep"  water.  On  the  other  hand,  female  Stilts  do  tend  to 
feed  in  shallower  water  than  do  Avocets.  The  niches  are 
further  separated  by  Avocets  feeding  more  commonly  by 
plunging  below  the  surface  than  do  Stilts;  by  feeding  at 
greater  depths;  and  by  Avocets  using  a  number  of  tactile 
foraging  methods  (see  account). 

The  Black-necked  Stilt  diet  is  about  98.9%  animal 
matter  and  only  1.1%  vegetable  matter  in  the  form  of  a  few 
seeds  of  aquatic  or  marsh  plants  (Wetmore  1925,  n  =  80). 
The  animal  foods  are  primarily  aquatic  forms  of  true  bugs 
(water  boatmen,  water  striders,  waterbugs,  and  backswim- 
mers)  and  beedes,  along  with  lesser  amounts  of  flies  (types 
with  aquatic  larvae),  snails,  caddisflies,  small  fish,  dragon- 
fly and  mayfly  nymphs,  crustaceans,  miscellaneous  insects, 
and,  rarely,  small  frogs.  Brine  shrimp  and  brine  flies  are 
important  food  in  south  San  Francisco  Bay  salt  ponds 
(Hamilton  1975),  as  they  may  also  be  at  alkali  lakes  in  the 
interior. 


Marin  Breeding  Distribution 

There  is  no  evidence  that  Stilts  occurred  in  Marin  County 
through  the  breeding  season  prior  to  the  adas  period. 
During  the  adas  years,  they  bred  at  a  few  scattered  diked 
wedands  along  the  San  Pablo  and  San  Francisco  bay- 
shores,  with  the  stronghold  of  the  population  in  the  Rush 
Creek/Bahia  Drive  ponds  area  of  Novate  Probably  fewer 
than  50  pairs  have  nested  recendy  in  Marin  each  year,  even 
under  the  most  favorable  conditions.  Stilts  were  first  dis- 
covered nesting  in  Marin  County  in  1978  at  the  Spinnaker 
wedands,  San  Rafael  (FL  7/2/78  — ARa);  a  high  count  of 
five  nests  was  recorded  there  in  1983  (NE-FL  May  ck  Jun 
1983  -HoP).  In  1980  at  least  32  pairs  nested  at  the  Bahia 
Drive  ponds  near  the  Petaluma  River  mouth,  Novato 
(NE-FL  6/7-26/80  — DS),  and  7  pairs  attempted  nesting 
at  McGinnis  Park,  San  Rafael,  in  an  ephemeral  wedand 
created  by  a  broken  dike  (DD  5/10  ck  6/3/80  -DS). 
Nesting  failed  at  the  latter  site  because  it  had  dried  up  by 
late  June.  Since  1985,  Stilts  have  bred  each  year  at  the  Las 
Gallinas  sewage  ponds  (ABN:DAH  et  al.)  just  north  of 
McGinnis  Park.  Stilts  also  occasionally  have  bred  at  the 
Shorebird  Marsh  by  the  Village  Shopping  Center,  Corte 
Madera  (DD  3/17/87  -JGE,  FL  8/3/89  -LES). 

Historical  Trends/  Population  Threats 

Stephens  and  Pringle  (1933)  considered  the  Black-necked 
Stilt  a  rare  winter  visitant  in  Marin  County  based  on  a 
record  in  Grinnell  and  Wythe  (1927).  The  latter  authors 
reported  that  Stilts  at  that  time  occurred  in  limited  num- 
bers in  the  immediate  vicinity  of  San  Francisco  Bay  in 
summer  and  fall,  and  that  stragglers  were  present  only 
rarely  in  winter.  Sibley  (1952)  considered  the  species  an 
uncommon  summer  resident  and  a  rare  winter  visitant  to 
the  south  San  Francisco  Bay  region.  The  Black-necked  Stilt 
increased  steadily  in  saltpond  habitat  in  south  San  Fran- 
cisco Bay  in  the  1950s  and  1960s,  and  the  species  is  now 
considered  a  common  breeder  and  a  regular  winter  visitor 
there  (Gill  1972,  1977).  Breeding  probably  did  not  begin 
in  the  North  Bay  until  after  the  mid-1960s  (RE.  Gill,  Jr., 
fide  GWP),  and  the  number  of  breeders  there  still  appears 
to  be  increasing  (ABN).  An  increase  in  the  estimated 
number  of  Stilts  breeding  in  south  San  Francisco  Bay, 
from  400  to  500  pairs  in  1971  (Gill  1977)  to  600  to  650 
pairs  in  1981,  is  attributed  to  more  extensive  observer 
coverage  in  the  more  recent  survey  (Rigney  ck  Rigney 
1981).  In  the  Monterey  Bay  area,  the  wintering  population 
has  increased  at  least  since  1959  (Roberson  1985).  The 
coastal  breeding  population  is  still  increasing,  as  indicated 
by  the  recent  breeding  records  in  Marin,  the  first  breeding 
records  for  Sonoma  County  and  coastal  San  Mateo 
County  in  1977  (AB  31:1184),  and  the  extension  of  the 
breeding  range  nordi  to  near  Humboldt  Bay  in  1985  (AB 
39:958). 


185 


Stilts  and  Avocets 


MARIN  COUNTY  BRHHDING  BIRD  ATIAS 


Stilts  and  Avocets 


It  is  not  clear  what  is  fueling  the  increase  of  coastal  Stilt 
populations.  Although  evaporation  ponds  support  the 
hulk  of  the  Bay  Area  breeding  population,  these  ponds 
have  been  in  operation  and  available  to  shorebirds  starting 
in  the  1860s,  suggesting  that  odier  factors  are  responsible 
for  recent  increases.  Perhaps  the  coastal  population  is 
being  augmented  by  recruitment  of  young  from  productive 
interior  populations,  or  by  adults  fleeing  from  drought- 
diminished  interior  wetlands.  Although  the  increase  of  die 
coastal  Stilt  population  is  encouraging,  it  should  be 
remembered  that  populations  in  the  interior,  particularly 
in  die  Central  Valley,  have  been  reduced  drastically  in 
historical  times  by  the  draining  of  wedands  (G&.M  1944, 
Cogswell  1977).  These  losses  have  been  at  least  partially 


offset  by  irrigation  (especially  rice  fields),  agricultural  drain- 
age ponds,  and  sewage  ponds.  On  the  other  hand,  concen- 
trations of  pesticides,  heavy  metals,  and  other 
contaminants  in  agricultural  and  urban  waters  may  ulti- 
mately have  severe  adverse  effects  on  shorebirds.  Selenium 
from  agricultural  drainage  waters  that  concentrated  in  die 
food  chain  was  the  most  likely  cause  of  complete  reproduc- 
tive failures  of  Stilts  and  Avocets  at  Kesterson  Reservoir, 
Merced  County,  in  1984  and  1985  (Williams  et  al.  1989). 
On  the  whole,  Stilt  populations  were  relatively  stable  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989, 
despite  an  increase  in  numbers  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


An  adult  Black  Oystercatcher  solemnly  surveys  its  rocky  realm.    Photograph  by  Ian  Tait. 


Stilts  and  Avocets 


SPECIES  ACCOUNTS 


Stilts  and  Avocets 


AMERICAN  AVOCET    Recurvirostra  americana 


Occurs  year  round,  though  almost  exclusively  as  a  winter  resident  from  late  Aug  through  late  Apr.  A  rare  breeder 
(postadas)  only  since  1984- 


Ecological  Requirements 

Although  the  hues  of  their  burnt  orange  heads  and  necks 
and  pastel  blue  legs  bear  little  resemblance  to  the  attire  of 
Black-necked  Stilts,  Avocets  inhabit  a  similar  variety  of 
shallow  freshwater,  saline,  brackish,  and  alkaline  wedands. 
Despite  the  tendency  for  Avocets  to  be  more  partial  to 
saline  and  alkaline  (versus  freshwater)  habitats  than  are 
Stilts  (Hamilton  1975),  prey  availability  may  be  the  factor 
most  direcdy  affecting  distribution  of  these  shorebirds  (see 
Stilt  account).  Avocets  avoid  grass-bordered  ephemeral 
freshwater  ponds,  where  Stilts  often  feed  and  breed,  and 
because  of  their  affinity  for  barren  habitat,  Avocets  feed  less 
in  salt  marshes  (but  do  so  on  exposed  mud)  than  do  Stilts. 
Avocets  generally  breed  in  loose  colonies,  often  with  Stilts, 
in  proximity  to  suitable  foraging  areas  (Gibson  1971, 
Hamilton  1975).  Along  the  coast,  Avocets  breed  primarily 
around  diked  brackish  ponds,  especially  salt  evaporators, 
and  at  sewage  ponds.  Although  both  Avocets  and  Stilts 
feed  in  these  ponds,  only  Avocets  also  feed  extensively  on 
bay  mudflats.  There  they  feed  mosdy  on  the  water's  edge 
far  from  shore  or  in  supersaturated  mud  or  in  shallow 
saltwater  puddles  left  on  the  flats  (Hamilton  1975,  D. 
Shuford  pers.  obs.). 

The  type  and  location  of  territories  that  Avocets  defend 
change  with  the  stage  of  the  nesting  cycle  (Gibson  1971). 
Prior  to  egg  laying,  pairs  defend  a  feeding  area.  During 
incubation,  pairs  defend  the  nest  site  and  either  a  contigu- 
ous or  distant  feeding  area.  Birds  whose  nests  are  close  to 
the  primary  feeding  area  may  also  defend  a  more  distant 
secondary  feeding  area,  whereas  birds  with  separate  feed- 
ing areas  and  nest  sites  defend  only  one  feeding  area.  After 
the  chicks  hatch,  the  territory  becomes  chick  centered  and 
mobile. 

Other  than  a  tendency  to  distribute  dieir  nests  more 
irregularly  than  Stilts  do  (Hamilton  1975),  Avocets  build 
their  ground  nests  of  similar  materials  and  in  nearly 
identical  locations  to  those  of  Stilts  (see  account  and 
references).  Gibson  (1971)  noted  that  Avocets  choose  nest 
materials  available  in  the  immediate  vicinity  of  the  nest. 
Avocet  nests  are  distinguished  from  those  of  Black-necked 
Stilts  by  the  larger  size  of  Avocet  eggs. 

Like  Stilts,  Avocets  also  feed  extensively  by  pecking  at  or 
just  below  the  water's  surface  (and  at  mud),  but  Avocets 
plunge  their  heads  or  necks  below  the  water  much  more 
frequendy  than  do  Stilts  (Hamilton  1975).  Avocets  snatch 
flying  insects  from  the  air  widi  their  bills  after  running  or 


fluttering  in  pursuit  of  their  prey.  They  also  run  up  hastily 
and  strike  at  mats  of  brine  flies  on  the  mud  with  lateral 
sweeping  motions  of  their  bills  (Wetmore  1925).  Another 
rarely  used  method  of  visual  feeding  is  for  birds  to  rapidly 
open  and  close  their  bills  while  simultaneously  moving 
them  erratically  along  the  water's  surface  (Hamilton  1975). 
Unlike  Stilts,  Avocets  make  extensive  use  of  tactile  meth- 
ods of  foraging.  In  shallow  pools  over  mudflats,  Avocets 
fdter  mud  by  rapidly  opening  and  closing  their  bills  slightly 
while  at  the  same  time  moving  them  apparendy  at  random 
over  the  mud.  Birds  also  scrape  mudflats  by  placing  the 
recurved  lower  tip  of  die  bill  on  the  mud  direcdy  in  front 
of  them  and  then  moving  it  forward  and  backward  by 
stretching  the  neck.  Avocets  are  perhaps  best  known  for 
their  scythelike,  side-to-side  feeding  movements  in  mud  or 
water.  Leaning  down,  birds  progress  forward  a  step  at  a 
time,  placing  the  slighdy  opened,  recurved  tip  of  the  bill 
flat  on  the  substrate  to  one  side  and  rapidly  moving  it  to 
the  other  side.  They  pause  to  raise  the  head  and  swallow 
and  then  repeat  the  process  on  the  other  side  with  the  next 
step;  infrequendy,  birds  make  multiple  side-to-side  move- 
ments (the  first  is  longest)  before  pausing  to  swallow. 
Mosdy  outside  the  breeding  season,  birds  sometimes  con- 
gregate in  large  groups  to  forage  in  this  manner,  swaying 
back  and  forth  as  they  progress  forward  in  unison,  appar- 
endy herding  prey  in  front  of  them.  From  a  swimming  or 
breast-wading  position,  Avocets  will  tip  up  like  dabbling 
ducks  and  make  similar  sideswipes  of  their  bills  on  the 
mud  below  the  surface  while  maintaining  their  position 
with  backward-kicking  legs.  See  the  Black-necked  Stilt 
account  (above)  for  other  differences  in  the  foraging  niche 
of  these  two  species.  Hamilton  (1975)  compared  foraging 
between  male  and  female  Avocets  at  an  inland  site  where 
they  only  used  pecking  and  plunging.  Males  there  had  a 
much  greater  tendency  to  plunge-feed  than  females  did, 
perhaps  because  of  their  longer  but  less  curved  bills. 

Overall,  the  Avocet  diet  is  about  65.1%  animal  matter 
(aquatic  and  shoreline  forms)  and  34-9%  vegetable  matter 
(Wetmore  1925,  n  =  67),  die  latter  a  very  high  percentage 
for  a  shorebird.  Vegetable  matter  is  primarily  the  seeds  but 
also  die  leaves  and  stems  of  aquatic  and  marsh  plants. 
Animal  fare  is  primarily  flies,  beetles,  crustaceans,  true 
bugs,  miscellaneous  insects,  and,  rarely,  snails,  small  fish, 
and  salamanders.  In  fall  and  winter  at  south  San  Francisco 
Bay  salt  ponds,  Avocets  feed  on  brine  flies,  brine  shrimp, 

187 


Stilts  and  Avocets 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Stilts  and  Avocets 


water  boatman  beetles,  polychaete  worms,  plant  stems,  and 
a  few  small  mollusks  (Anderson  1970).  Martin  et  al. 
(1951)  reported  little  variation  in  the  proportion  of  animal 
and  vegetable  matter  in  the  diet  between  spring  and  fall. 

Marin  Breeding  Distribution 

There  was  no  evidence  of  Avocets  breeding  in  Marin 
County  during,  or  prior  to,  the  adas  period.  Subsequendy, 
the  progress  of  a  pair  nesting  on  a  tiny  island  at  Spinnaker 
Lagoon,  San  Rafael,  was  followed  during  the  breeding 
season  of  1983  (NE-FL  5/18-6/12/83  -HoP).  Avocets 
also  attempted  to  nest  at  the  Las  Gallinas  sewage  ponds  in 
1987  but  were  unsuccessful  (ABN:DAH,  CLF). 

Historical  Trends/Population  Threats 

Both  coastal  wintering  and  breeding  populations  of  Avo- 
cets have  increased  historically.  Formerly,  the  American 
Avocet  was  considered  an  irregularly  common  fall  and 
winter  visitor  to  San  Francisco  Bay  (GckW  1927),  where 
nesting  was  first  recorded  in  1926  (Gill  1977).  Although 
Avocets  began  to  use  Bay  Area  salt  ponds  by  at  least  1 899 
(Grinnell  et  al.  1918),  not  until  the  early  1940s  did  their 
population  begin  to  expand  there  to  include  large  numbers 
of  wintering  and  breeding  birds  (Storer  1951;  Gill  1972, 
1977).  By  1952,  the  Avocet  was  considered  a  common 
resident  (more  numerous  in  winter)  of  the  south  San 
Francisco  Bay  region  (Sibley  1952).  A  decrease  in  the 
estimated  number  of  Avocets  breeding  in  soudi  San  Fran- 


cisco Bay,  from  1800  pairs  in  1971  (Gill  1977)  to  650  pairs 
in  1981,  apparendy  represents  different  calculation  meth- 
ods rather  than  an  actual  population  decline  (Rigney  ck 
Rigney  1981).  Winter  numbers  have  also  increased  in 
Humboldt  Bay  since  1958,  especially  from  1961  to  1968 
(Gerstenberg  1972),  and  at  Bolinas  Lagoon,  particularly 
since  1974  (Shuford  et  al.  1989).  First  breeding  records  for 
Sonoma  County  in  1981  (AB  35:974)  and  Marin  County 
in  1984  (above)  document  continued  range  expansion  of 
breeding  Avocets  in  the  San  Francisco  Bay  Area.  See 
Black-necked  Stilt  account  for  comments  on  the  increase 
of  coastal  breeding  populations,  which  also  apply  to  Avo- 
cets. Avocet  populations  in  California's  interior  decreased 
early  in  this  century  because  of  extensive  loss  of  marsh- 
lands (G6kM  1944).  This  habitat  loss  has  been  offset  at 
least  partially  by  the  addition  of  irrigation  ponds,  agricul- 
tural drainage  ponds,  and  sewage  ponds.  On  the  other 
hand,  these  waters  may  be  very  harmful  to  shorebirds 
because  they  concentrate  pesticides,  heavy  metals,  and 
other  contaminants.  Selenium  from  agricultural  drainage 
waters  that  concentrated  in  the  food  chain  was  the  most 
likely  cause  of  complete  reproductive  failures  of  Avocets 
and  Stilts  at  Kesterson  Reservoir,  Merced  County,  in  1984 
and  1985  (Williams  et  al.  1989).  For  California  as  a  whole, 
numbers  of  Avocets  appeared  to  decrease  slighdy  on  Breed- 
ing Bird  Surveys  from  1968  to  1989  (USFWS  unpubl. 
analyses). 


Sandpipers 


SPECIES  ACCOUNTS 


Sandpipers 


Sandpipers 

Family  Scolopacidae 


SPOTTED  SANDPIPER  Actitis  macularia 


Occurs  year  round,  though  primarily  as  a  winter  resident  and  transient  from  Jul  through  May.  Only  two  (nonadas)  breed- 
ing records. 


Ecological  Requirements 

Wasting  no  time  in  taking  on  the  airs  of  their  elders,  fluffy 
newborn  Spotted  Sandpipers  teeter  and  bob  as  they  test 
their  spindly  legs  on  the  shifting  sands  and  gravels  of  their 
breeding  haunts.  In  California,  Spotted  Sandpipers  nest 
from  sea  level  to  1 1 ,000  feet— widely  in  higher  and  moister 
mountains  and  less  extensively  in  coastal  lowlands.  Breed- 
ing habitats  in  the  state  include  slow-moving  streams  and 
rivers,  freshwater  lakes,  tarns,  saline  and  alkaline  lakes, 
and,  rarely,  coastal  lagoons  (G6kM  1944,  D.  Shuford  pers. 
obs.).  Because  Spotted  Sandpipers  have  bred  only  twice  in 
Marin  County  (see  below),  there  is  little  to  say  about 
habitat  preferences  here. 

Throughout  the  range,  nest  sites  are  usually  on  open  or 
semiopen  shoreline  beaches  or  on  offshore  islands  or 
gravel  or  sandbars.  Nests  are  usually  concealed  in  grassy  or 
herbaceous  cover  and  sometimes  are  placed  next  to  or 
under  logs,  driftwood  branches,  rocks,  bushes,  or  trees 
(Dawson  1923,  Tyler  1929,  Grinnell  et  al.  1930,  Miller  6k 
Miller  1948).  Where  the  vegetation  is  low  and  open,  these 
sandpipers  often  nest  well  back  from  the  shoreline,  but 
otherwise  they  often  nest  just  above  the  wave-cast  debris 
line.  One  nest  in  the  mountains  of  California  was  on  the 
floor  of  an  open  yellow  pine  woodland  over  1 50  feet  back 
from  and  about  50  feet  above  a  beachless  lakeshore  (Grin- 
nell et  al.  1930).  On  one  island  on  a  lake  in  Minnesota,  a 
number  of  nests  were  from  65  to  165  feet  back  from  the 
shoreline  under  a  dense  canopy  of  bushes  and  trees  (Oring 
6k  Knudson  1972).  Nests  are  saucer-shaped  depressions  in 
sand,  gravel,  or  turf  that  are  thinly  to  well  lined  with 
grasses,  pine  needles,  leaves,  twigs,  bits  of  wood,  or  feath- 
ers (Dawson  1923,  Tyler  1929,  Grinnell  et  al.  1930).  A 
frequent  mating  strategy  of  Spotted  Sandpipers  is  serial 
polyandry— females  nest  successively  with  up  to  four  males, 
leave  the  care  of  the  precocial  young  to  each  male,  and  help 
incubate  only  the  last  clutch  of  eggs  (Hays  1972,  Oring  6k 
Knudson  1972,  Oring  et  al.  1983).  Sometimes  females  are 
monogamous,  and,  rarely,  they  pair  with  two  males  at  the 
same  time  (Oring  6k  Maxson  1978). 


No  detailed  work  apparendy  has  been  done  on  the  diet 
of  Spotted  Sandpipers,  but  birds  are  known  to  prey  on 
larval  and  adult  forms  of  a  variety  of  land  and  aquatic 
insects,  assorted  invertebrates,  and,  occasionally,  on  fish 
(Tyler  1929,  Palmer  1967,  Kuenzel  6k  Wiegert  1973). 
Spotteds  forage  on  aquatic  shorelines  and  also  in  adjacent 
open  upland  grass  and  sedge  covered  beaches  and  mead- 
ows. While  walking  along,  they  capture  prey  by  rapid 
downward  pecks;  by  forward  horizontal  thrusts  of  the  bill 
from  a  slow,  crouched  approach;  or  by  snapping  insects 
from  the  air.  Also,  they  wade  in  the  water  and  jump  into 
deeper  water  to  seize  floating  prey  (Palmer  1967).  Spotted 
Sandpipers  sometimes  immerse  insects  several  times  in 
water  before  swallowing  them  (Tyler  1929). 

Marin  Breeding  Distribution 

Bracketing  the  adas  period,  there  were  two  breeding 
records  for  Spotted  Sandpipers  in  Marin  County:  an  adult 
with  three  downy  young  at  the  "Canal  Street  Pond,"  San 
Rafael,  on  9  July  1971  (WMP,  ABu);  and  an  adult  with 
young  at  Rush  Creek  marsh  off  Binford  Rd.,  Novato,  on 
21  June  1985  (GWP,  BHe).  No  breeding  confirmations  or 
strongly  suggestive  breeding  evidence  was  recorded  during 
the  adas  period.  The  loosely  overlapping  spring  and  fall 
migration  periods  of  Spotted  Sandpipers  and  the  presence 
of  occasional  oversummering  individuals  here,  patterns 
typical  of  many  shorebirds,  make  it  difficult  to  determine 
breeding  status  unless  direct  evidence  of  nesting  is 
observed. 

Historical  Trends/Population  Threats 

Formerly,  Spotted  Sandpipers  were  not  known  to  breed  in 
Marin  County  (G6kW  1927,  SckP  1933,  G6kM  1944).  It 
seems  best  to  attribute  the  recent  breeding  records  to 
increased  observer  coverage  detecting  irregular  breeding 
rather  than  to  a  range  expansion.  Spotted  Sandpiper  num- 
bers appear  to  have  changed  little  in  California  in  historical 
times  (G6kM  1944).  Hydraulic  mining  on  rivers  may  have 

189 


Sandpipers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Sandpipers 


scoured  out  some  nesting  habitat,  but  then  again,  to  the 
species  advantage,  it  must  have  deposited  much  silt  and 
gravel  on  beaches  and  bars.  Increasing  recreational  use  of 
rivers  and  lakes  must  displace  some  breeding  sandpipers 


but  does  not  appear  to  have  had  a  marked  effect  on  the 
population.  Numbers  of  Spotted  Sandpipers  were  rela- 
tively stable  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989  (USFWS  unpubl.  analyses). 


The  prim  and  proper  appearance  of  a  Western  Gull  on  its  nest  belies  its  otherwise  piratical,  aggressive,  and  resourceful 
tendencies  when  in  pursuit  of  food,  any  food.    Photograph  by  Ian  Tait. 


190 


Gulls 


SPECIES  ACCOUNTS 


Gulls 


Gull: 


Family  Laridae 


WESTERN  GULL   Lams  occidentalis 


A  year-round  resident;  gulls  occupy  Faral- 

r^^-^    \           JC\~. 

lon  Island  (and  probably  Marin)  breed- 

J5k^X±B**<? 

ing  colonies  almost  year  round,  except 

X^\JsrTAL^ 

\^\^%^vX^\  \  j-V\l-A^\ J^\^-^ 

{-  - 

the  short  period  from  mid-Sep  until  late 
Oct  or  early  Nov. 

^Ck^c^c^c^^^^C 

A  common,  very  local  breeder;  overall 

v\> 

^s^^ 

breeding  population  very  small. 
Recorded  in  14  (6.3%)  of  221  blocks 

jk^s\ ',  i^^^^^-^V^A  "vlV**'\     >f^\    \*^\     \^" 

(see  Methods). 

t-<r-CT*^' — 

O    Possible        =        0   (0%) 

l^^^^v^V^A^^CAt^- 

\\>srx^ 

€    Probable       =         1    (7%) 

p^?° 

•    Confirmed  =      13  (93%) 

"^^r\>-^ 

FSAR  =  4        OPI  =  56         CI  =  2.93 

Ecological  Requirements 

What  better  avian  symbol  of  seaside  existence  dian  the 
graceful,  versatile,  yet  rapacious  Western  Gull.  Our  only 
breeding  gull  inhabits  a  wide  variety  of  habitats  ranging 
from  the  open  sea,  to  coastal  bays,  estuaries,  lagoons,  tidal 
reefs,  and  beaches— it  exploits  more  of  the  coastal  marine 
environment  than  any  other  local  breeding  seabird  (Ainley 
&  Boekelheide  1990,  Chap.  3).  At  sea,  Western  Gulls  are 
confined  largely  to  waters  over  the  continental  shelf  and 
are  rare  more  than  1 5  miles  seaward  of  the  edge  of  the  shelf 
break  (Briggs  et  al.  1987).  Foraging  areas  for  Farallon 
Island  breeders  vary  yearly  with  ocean  conditions  (Ainley 
&  Boekelheide  1990,  Chap.  3).  In  years  of  high  food 
availability  in  the  ocean,  birds  forage  mosdy  offshore  near 
the  Farallon  colony.  In  years  of  reduced  food  availability, 
birds  forage  more  in  inshore  waters,  and  they  may  fly  60 
miles  or  more  to  feed  at  garbage  dumps.  Western  Gulls  are 
very  rare  inland  except  within  a  mile  or  two  of  the  coast- 
line, where  they  bathe  at  freshwater  ponds  or  lakes  or 
forage  at  dumps. 

Western  Gulls  nest  in  large  colonies,  scattered  aggrega- 
tions, or,  occasionally,  isolated  pairs  on  islands,  offshore 
rocks,  inaccessible  mainland  cliffs,  and  human  structures, 
such  as  bridges  and  pilings.  At  the  Farallon  Islands,  they 


exploit  a  greater  range  of  nesting  habitat  than  any  other 
surface-nesting  seabirds  (i.e.,  cormorants  and  murres)  and 
are  the  most  willing  to  nest  near  people  (Ainley  &. 
Boekelheide  1990,  Chap.  7).  Western  Gulls  generally 
favor  moderate  slopes  with  rocky  cover  but  also  nest  on 
open  island  terraces,  steep  hillsides,  rocky  slopes,  ledges  of 
cliff  faces,  and  exposed  summits  of  rocks  (Bent  1921; 
Dawson  1923;  Schreiber  1970;  Harper  1971;  Coulter 
1973;  Ainley  6k  Boekelheide  1990,  Chap.  7).  Nests  are 
usually  situated  in  depressions  on  the  ground  out  in  the 
open  on  bare  soil,  grass,  or  low  matted  vegetation;  near 
sparse  low  bushes;  nesded  in  natural  hollows  among 
rocks;  in  niches  in  bare  rock;  or  on  human  structures. 
Western  Gulls  construct  small  to  bulky  nest  cups  of 
grasses,  weeds,  seaweed,  or  other  natural  debris,  including 
carcasses  of  dead  birds  or  small  mammals.  In  addition, 
they  may  incorporate  into  or  "decorate"  the  nest  with 
plastic  or  other  refuse  from  our  throwaway  society.  Some- 
times nests  are  just  a  scrape  in  soil  and  accumulated  guano 
with  a  few  feathers  or  pebbles  scattered  about  (Harper 
1971).  The  young  are  semi precocial— wandering  from  the 
nest  after  a  few  days— and  are  fed  by  regurgitation. 

191 


Gulls 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Gulls 


Western  Gulls  are  consummate  generalists,  opportunis- 
tic foragers  capable  of  searching  large  areas  for  mobile  prey. 
Although  well  known  for  their  scavenging  habits,  Farallon 
breeders  apparently  exploit  primarily  live  marine  prey, 
principally  fish,  from  the  ocean's  surface  (Ainley  6k  Boekel- 
heide  1990,  Chap.  3).  They  apparently  forage  mostly  early 
and  late  in  the  day  and  little  at  midday.  Western  Gulls 
usually  feed  in  conspecific  flocks,  especially  during  warm- 
water  years  when  food  presumably  is  less  available.  They 
also  commonly  forage  in  mixed-species  flocks  (usually  with 
Brandt's  Cormorants),  where  they  can  play  a  catalyst  role, 
attracting  other  birds  to  the  site.  Western  Gulls  are  accom- 
plished kleptoparasites,  stealing  prey  from  odier  successful 
birds  of  any  species  in  a  variety  of  settings  (see  below).  On 
their  own,  they  apparendy  follow  schools  of  fish,  hovering 
and  screaming,  and  feed  at  the  surface  by  dipping,  seizing, 
or  making  shallow  plunges,  usually  barely  immersing 
themselves.  In  addition,  they  scavenge  on  beaches  and 
mudflats;  pick  prey  from  tide  pools;  follow  boats  or  wait  at 
wharfs  and  seaside  restaurants  for  cast-off  fish  offal,  hand- 
outs, or  garbage;  pick  through  refuse  at  garbage  dumps; 
and  eat  the  eggs  and  young  of  other  seabirds  or  their  own 
species  (Bent  1921,  Pierotti  1981).  Along  the  shoreline,  it 
is  not  uncommon  to  watch  a  Western  Gull  sauntering 
along  with  a  starfish  protruding  from  its  overstuffed  maw. 
At  seabird  colonies,  one  can  see  a  single  gull  with  the  feet 
of  a  seabird  chick,  about  to  be  swallowed  whole,  pointing 
skyward  from  its  open  beak;  several  gulls  tearing  apart  a 
chick  or  a  small  seabird,  such  as  a  Cassin  s  Auklet,  in  a 
merciless  tug  of  war  is  a  frequent  occurrence  as  well. 
Western  Gulls  also  carry  clams,  mussels,  or  sea  urchins 
aloft  to  drop  them  on  hard  ground  or  rocks  to  break  them 
open.  They  also  detach  morsels  of  carrion  by  seizing  the 
body  in  die  bill,  dragging  it  away,  and  shaking  their  heads 
until  a  piece  breaks  off. 

Although  Western  Gulls  consume  a  great  diversity  of 
food  items  and  will  capitalize  on  irregularly  abundant  food 
sources,  certain  marine  organisms  predominate  in  the  diet 
at  the  Farallon  Islands,  where  chicks  are  fed  about  60%- 
80%  fish,  15%-20%  garbage,  5%-7%  marine  inverte- 
brates, and  l%-2%  birds  (Ainley  6k  Boekelheide  1990, 
Chap.  3).  In  warm-water  years,  the  diet  diversifies,  and 
adults  eat  (and  feed  to  young)  more  garbage.  Hence,  in 
those  years,  they  exploit  the  same  resources  as  roosting, 
nonbreeding  gulls  normally  do.  Juvenile  rockfish  are  the 
dominant  fish  prey,  though  cusk-eels,  Pacific  hake  (as  offal 
from  fishing  boats),  and  midshipmen  are  also  important. 
Since  many  of  the  fish  in  the  gulls'  diet  occur  in  waters 
deeper  than  they  can  exploit,  they  may  obtain  them  from 
scavenging  fish  that  cormorants  regurgitate  at  sea,  by 
exploiting  fish  driven  to  the  surface  by  cormorants  or  other 
predators  (Ainley  6k  Boekelheide  1990,  Chap.  3),  or  by 
stealing  fish  from  cormorants  or  other  seabirds  at  dieir  nest 
sites  (Bent  1921,   LB.   Spear  pers.  comm.).  The  main 

192 


invertebrate  foods  at  the  Farallones  are  barnacles  and 
euphausiids,  along  with  lesser  quantities  of  mysid  shrimp, 
miscellaneous  decapods,  squid,  limpets,  mussels,  and  a 
few  terrestrial  invertebrates  (primarily  beedes). 

Western  Gulls  sometimes  feed  on  sea  lion  placentae 
and  fecal  matter  (Schreiber  1970)  and  on  other  birds,  such 
as  Rock  Doves,  or  small  mammals  (Annett  6k  Pierotti 
1989).  Western  Gulls  at  Santa  Barbara  Island  in  the 
Channel  Islands  feed  their  chicks  mosdy  anchovies,  other 
schooling  fish,  and  squid,  and  a  few  intertidal  invertebrates 
(Hunt  6k  Hunt  1976).  During  the  period  of  extremely 
warm  ocean  waters  in  the  winter  and  early  spring  of  the 
1982-83  El  Nino,  Western  Gulls  at  the  Channel  Islands 
were  apparendy  feeding  primarily,  or  perhaps  solely,  on 
pelagic  red  crabs  (Stewart  et  al.  1984),  as  they  also  were 
then  at  the  Farallon  Islands  (PRBO  unpubl.  data).  Early  in 
the  nesting  season,  Western  Gulls  at  Alcatraz  Island  in 
San  Francisco  Bay  feed  predominately  on  garbage  (mosdy 
chicken).  They  switch  mosdy  to  fish  to  feed  their  young  at 
die  time  they  hatch,  not  when  fish  are  first  available  (Annett 
6k  Pierotti  1989).  Adult  males  feed  on  larger  food  items 
and  apparendy  travel  longer  distances  to  forage  than  do 
females  (Pierotti  1981).  Only  males  pirate  food  from  neigh- 
boring gulls  trying  to  feed  their  young,  and  they  do  so  more 
in  years  of  poor  oceanic  productivity.  Preying  on  the  eggs 
and  young  of  other  seabirds  and  neighboring  gulls  also 
increases  in  years  of  poor  ocean  food  supplies  (Ainley  6k 
Boekelheide  1990,  Chap.  8;  PRBO  unpubl.  data). 

Marin  Breeding  Distribution 

During  the  adas  period,  Western  Gulls  were  breeding  at 
13  sites  along  the  outer  coast  of  Marin  County  (Sowls  et 
al.  1980;  Table  14,  Figure  14).  At  that  time,  they  were  also 
nesting  at  at  least  four  sites  in  San  Francisco  or  San  Pablo 
bays,  but  bay  waters  were  incompletely  surveyed  (Sowls  et 
al.  1980;  Marin  adas  map).  Representative  breeding  loca- 
tions during  the  adas  period  were  the  rocks  near  the  mouth 
of  Bear  Valley  (FL  7/3/80  -DS);  Point  Reyes  Lighthouse 
(FL  6/21/81  -DS,  RSt);  Bird  Rock  off  Tomales  Point  (FL 
6/15/82  — DS);  both  West  and  East  Marin  islands  off  San 
Rafael  (NE  5/22/82  — HPr);  and  a  channel  marker  in 
Richardson  Bay  between  Sausalito  and  Belvedere  (NE 
5/22/82  -HPr). 

In  1989,  Carter  et  al.  (1992)  found  Western  Gulls 
nesting  at  16  sites  on  the  outer  coast  of  Marin  County, 
including  all  13  sites  where  they  had  been  nesting  in  1979 
and  3  new  sites  (Table  14,  Figure  14).  Their  baywide 
surveys  in  1990  revealed  about  230  Western  Gulls  nesting 
at  12  sites  in  the  Marin  County  portions  of  San  Francisco 
and  San  Pablo  bays:  Yellow  Bluff  (2),  Sausalito  Point  Area 
(4),  Peninsula  Point  and  Cone  Rock  (6),  Angel  Island  (6), 
Bluff  Point  to  Paradise  Cay  (4),  Point  San  Quentin  (6), 
Marin  Islands  (64),  The  Sisters  and  Point  San  Pedro  (96), 
Rat  Rock  (2),  Southwest  San  Pablo  Bay  Duck  Blinds  (16), 


Gulls 


SPECIES  ACCOUNTS 


Gulls 


Marin  County- West  San  Pablo  Bay  Ship  Channel  (14), 
and  Richmond-San  Rafael  Bridge  (10).  Boat  counts  tallied 
45  gull  nests  on  West  Marin  Island  in  1990  and  48  in 
1991  (H.M.  Pratt  pers.  comm.)  and  on-site  counts  in  the 
same  years  revealed  50  and  47  nests,  respectively  (R.L 
Hothem/USFWS  pers.  comm.). 

Historical  Trends/Population  Threats 

Ainley  and  Whitt's  (1973)  preliminary  surveys  of  selected 
sites  along  the  Marin  coast  probably  underestimated  the 
county's  Western  Gull  population  at  186  breeding  birds. 
Sowls  et  al.  (1980)  estimated  426  Western  Gulls  were 
nesting  on  the  outer  coast  of  Marin  County  in  1979  to 
1980,  and  Carter  et  al.  (1992)  estimated  590  were  nesting 
there  in  1989.  Carter  et  al.'s  (1992)  surveys  of  seabirds 
inside  the  San  Francisco  Bay  estuary  provided  the  first 
estimates  of  die  number  of  Western  Gulls  breeding  in  that 
region  of  Marin  County  (see  above);  prior  information  was 
fragmentary  (Sowls  et  al.  1 980). 

In  historic  times,  numbers  of  Western  Gulls  in  Califor- 
nia have  changed  most  dramatically  at  the  Farallon  Islands. 
In  the  mid-1 800s,  the  population  was  about  20,000,  close 
to  today's  size,  but  earlier  had  probably  been  smaller  before 
the  reduction  of  pinniped  populations  provided  additional 
gull  nesting  habitat  (Ainley  6k  Boekelheide  1990,  Chap. 
7).  The  Farallon  gull  population  was  reduced  by  distur- 
bance from  humans  and  domestic  animals  and  reached  a 
low  ebb  around  the  turn  of  the  century  (Ainley  6k  Lewis 
1974).  The  greatest  impact  on  the  gull  population  was 
caused  by  commercial  egg  collectors  gathering  Common 
Murre  eggs  from  1848  to  the  early  1900s.  Fearing  compe- 


tition from  the  gulls  for  murre  eggs,  collectors  stepped  on 
gull  eggs  and  young.  It  is  unknown  if  the  disturbance 
caused  many  gulls  to  abandon  breeding  on  the  Farallones 
and,  if  so,  if  diis  affected  nearby  mainland  breeding  popu- 
lations of  gulls  by  increasing  competition  for  nest  sites. 
The  Farallon  population  rebounded  from  a  low  of  at  most 
6000  gulls  to  reach  a  plateau  by  1959  and  from  then  until 
the  present  has  ranged  from  22,000  to  25,500  breeding 
birds  (Ainley  6k  Lewis  1974;  Ainley  6k  Boekelheide  1990, 
Chap.  7).  The  1979  PRBO  estimate  of  32,000  breeding 
gulls  reported  by  Sowls  et  al.  (1980)  was  subsequendy 
revised  to  25,500  by  Ainley  and  Boekelheide  (1990). 

Sowls  et  al.  (1980)  compared  their  data  with  earlier 
surveys  along  the  California  coast  and  suggested  that 
Western  Gulls  had  been  increasing  since  at  least  about 
1970.  Like  many  species  of  gulls,  Westerns  may  have 
increased  and  reached  all-time-high  population  levels  by 
taking  advantage  of  garbage  and  fish  offal  produced  by  an 
expanding  human  population,  thus  enhancing  the  gulls' 
winter  survival  (Ainley  6k  Lewis  1974,  Sowls  et  al.  1980, 
Spear  et  al.  1987).  The  recent  closing  of  many  San  Fran- 
cisco Bay  Area  dumps  may  reverse  this  trend.  Estimates  of 
the  number  of  gulls  breeding  on  the  outer  coast  of  central 
and  nordiern  California  range  from  about  39,202  birds  at 
147  colonies  in  1979  to  1980  (Sowls  etal.  1980)  to  30,534 
birds  at  205  colonies  in  1989  (Carter  et  al.  1992).  The 
estimate  of  3270  Western  Gulls  nesting  in  the  San  Fran- 
cisco Bay  estuary  in  1990  is  10%  of  the  total  of  33,804 
birds  nesting  in  die  entire  region  in  1989  to  1990;  the 
estimate  of  die  Farallon  population  at  22,278  birds  is  66% 
of  the  regional  total. 


193 


Ale  ids 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Ale  ids 


Auks,  Murres,  and  Puffins 


Family  Alcidae 


COMMON  MURRE    Uria  aalge 


A  year-round  resident;  numbers  on 

ocean  waters  swell  from  Oct  through 

A^^P^?^^-^   s         ^o^. 

Mar.  Murres  occupy  Farallon  Island 

~^^v-^5^ 

(and  probably  Marin)  breeding  colonies 

^C\  J<\\  ^\^\  3r""\  %t^\    \^\    \^\    V-^s 

irregularly  starting  in  late  Oct  (rarely  start- 

^^^^^j^j^j^^^c^P^Ca 

ing  mid-Dec)  and  regularly  from  late  Dec 

through  departure  from  Jul  to  mid-Aug. 

Yv^^^ 

Fewer  murres  nest,  and  some  desert  colo- 

X}^<\^>£}^& 

nies,  in  extremely  poor  food  years. 

\  \-ef^\  i^\<^<£-V''^A  \l\^\     j*r\    Jk^\     \-"^\      >-7 

A  very  abundant,  very  local  breeder; 

1       /\i^\         \^\"~   X  Jr*K        \  ^-*c^w    I  \    ^\          \    ^\         V -*T      ! 

overall  breeding  population  very  small. 

jfi^fjcIV^ 

Recorded  in  3  (1.4%)  of  221  blocks 
(see  Methods). 

O    Possible                  0  (0%) 

ii^,                            ^"^<r^/'^"^i<^^C^\-^Vv>^ 

©    Probable       =        0  (0%) 

•    Confirmed  =        3  (100%) 

FSAR  =  7        OPI  =  21          CI  =  3.00 

Ecological  Requirements 

These  penguin  look-alikes  are  our  most  numerous  breed- 
ing seabird.  At  sea,  Common  Murres  primarily  inhabit 
inshore  and  offshore  ocean  waters  out  to  the  edge  of  the 
continental  shelf.  Most  birds  concentrate  over  the  inner 
shelf,  usually  in  waters  from  about  200  to  500  feet  deep 
(Wahl  1975,  Briggs  et  al.  1987).  During  nesting,  over  75% 
of  the  Murres  at  sea  off  California  are  within  25  miles  of  a 
colony,  though  they  may  range  to  45  miles  or  more  during 
warm-water  years.  Areas  of  concentration  in  over-shelf 
waters  vary  both  seasonally  and  annually,  with  changes  in 
food  supply  related  to  water  temperatures  (Ainley  6k 
Boekelheide  1990,  Chap.  3).  During  early  spring,  Farallon 
Island  breeders  frequent  deep  waters  along  the  continental 
shelf  near  the  islands.  Some  birds  range  north  along  the 
continental  slope  almost  40  miles  to  the  Cordell  Bank, 
though  most  feed  much  closer.  During  May  and  June  in 
cold-water  years,  they  contract  closer  to  the  islands  (and 
mainland  colonies);  in  warm-water  years,  they  spread  out, 
especially  over  the  shelf  toward  the  mainland.  By  June  in 
cold-water  years,  they  occupy  waters  of  a  variety  of  temper- 
atures and  salinities  but  prefer  turbid  waters  near  colonies 
(Briggs  et  al.  1988).  Perhaps  Murres  are  better  able  to 
approach  and  prey  upon  relatively  mobile  fish  when  water 
clarity  is  low,  or  perhaps  the  turbid  waters  have  the  highest 

194 


abundance  offish  prey  (Briggs  et  al.  1988).  In  July  in  many 
years,  they  begin  to  exploit  nearshore  waters  along  the 
Marin  and  San  Francisco  shorelines  (Ainley  6k  Boekel- 
heide 1990,  Chap.  3).  This  shift  occurs  earlier  in  warm- 
water  years.  Inshore  movement  in  July  and  August  is 
evident  by  the  distribution  of  dependent  young  and  their 
parents— mosdy  inside  the  90-foot  depth  contour  (Ainley 
6k  Boekelheide  1990,  Chap.  8).  Inshore,  Murres  feed 
where  the  surface  estuarine  outflow  of  San  Francisco  Bay 
is  underlain  by  cold,  salty  water,  probably  upwelled  along 
the  outer  continental  shelf  (Briggs  et  al.  1988).  By  Septem- 
ber, Murres,  including  fathers  with  chicks,  have  spread  out 
south  along  the  coast  60  miles  or  more  to  Monterey  and 
beyond  (Ainley  6k  Boekelheide  1990,  Chap.  3).  Little  is 
known  of  the  seasonal  habitat  shifts  of  birds  breeding  at 
mainland  colonies  on  Point  Reyes. 

Murres  are  highly  gregarious,  nesting  shoulder  to  shoul- 
der on  islands,  offshore  rocks,  and  inaccessible  mainland 
cliffs.  The  densely  packed  colonies  usually  range  in  size 
from  groups  of  tens  to  thousands  of  pairs.  Murres  select 
nesting  terrain  varying  from  terraces,  gradual  slopes,  and 
shoreline  promontories  to  the  narrow  ledges  and  shelves 
of  cliffs,  steep  slopes,  grottoes,  and  sea  caves  (Bent  1919; 
Ainley  6k  Boekelheide  1990,  Chap.  8).  The  majority  of 


Alcids 


SPECIES  ACCOUNTS 


Alcids 


Murres  in  California  nest  on  gentle  slopes  and  flat  areas  at 
the  base  of  slopes  or  on  rounded  hilltops  (Takekawa  et  al. 
1990).  Murres  lay  a  single  egg  on  bare  rock  or  soil, 
occasionally  placing  a  few  small  stones  around  the  egg. 
They  almost  always  nest  facing  a  vertical  face,  which  they 
lean  against  while  incubating  (Ainley  &  Boekelheide 
1990,  Chap.  8).  Lacking  true  nests,  Murres  lay  pyriform 
(pear-shaped)  eggs  that  roll  in  a  circle,  an  adaptation  that 
keeps  eggs  from  easily  plummeting  off  precipices  to  smash 
on  rocks  or  fall  into  the  sea.  Unlike  other  alcids  at  the 
Farallon  Islands,  the  young  depart  from  the  nesting  ledge 
when  they  attain  only  20%- 25%  of  adult  weight  at  about 
22  to  25  days  of  age.  Depending  on  the  terrain  near  the 
nest  site,  chicks  waddle  to  the  shoreline  or  jump  off  cliffs 
to  the  sea  below  (W.J.  Sydeman  pers.  comm.).  Most 
departure  occurs  in  the  evening  or  just  after  nightfall  on 
calm  days  (Ainley  &  Boekelheide  1990,  Chap.  8).  Unable 
to  fly,  chicks  swim  with  one  parent  (the  male)  to  feeding 
areas  some  distance  from  the  breeding  colony.  The  male 
accompanies  and  feeds  the  chick  until  it  is  fully  grown  and 
capable  of  flight. 

Like  other  alcids,  Murres  pursue  their  prey  underwater, 
propelled  by  partly  folded  wings.  They  apparendy  forage 
mosdy  early  and  late  in  the  day  and  little  during  midday. 
Murres  most  often  feed  in  large  single-species  flocks  or 
occasionally  in  mixed  flocks,  especially  with  Brandt's  Cor- 
morants and  Western  Gulls  (Ainley  ck  Boekelheide  1 990, 
Chap.  3).  They  are  very  efficient  divers  and  can  descend  to 
depths  of  almost  600  feet,  or  perhaps  even  deeper  (Piatt  6k 
Nettleship  1985).  Early  in  the  nesting  season,  prior  to  the 
period  of  intense  coastal  upwelling,  adult  Murres  foraging 
on  the  outer  continental  shelf  near  the  Farallones  feed  on 
euphausiids  (Briggs  et  al.  1988;  Ainley  6k  Boekelheide 
1990,  Chap.  3).  Chicks  are  not  fed  euphausiids,  presum- 
ably because  they  provide  insufficient  nutrition  relative  to 
the  high  cost  to  adults  of  delivering  them  one  by  one  to 
young.  Generally  Murres  feed  their  young  food  items  of 
high  caloric  value  that  can  be  easily  carried  lengthwise  in 
the  bill— these  are  usually  midwater  schooling  organisms 
(fish  and  squid)  about  1.5  to  6  inches  long.  Farallon 
breeders  feed  their  chicks  predominantly  juvenile  rockfish, 
anchovies,  nightsmelt,  and  market  squid,  though  the  diet 
varies  both  seasonally  and  annually  (Ainley  6k  Boekelheide 
1990,  Chap.  3,  n  =  20,427).  In  cold-water  years,  rockfish 
account  for  85%  and  anchovies  for  7%  of  the  early-season 
diet,  but  the  diet  diversifies  later  as  Murres  move  to  inshore 
feeding  areas.  In  warm-water  years,  prey  diversity  is  greater, 
and  the  percentage  of  rockfish  in  the  diet  declines  (from 
20%  to  13%  of  the  diet)  from  early  to  late  season,  while 
the  percentage  of  anchovies  increases  (from  40%  to  70%). 
The  greater  seasonal  change  in  diet  in  warm-water  years 
reflects  the  early  movement  of  Murres  inshore.  Croll 
(1990)  also  documented  seasonal  and  annual  shifts  in  the 
Murre  diet  in  Monterey  Bay.   It  is  likely  that  seasonal 


movements  and  diet  of  Murres  breeding  on  the  mainland 
at  Point  Reyes  may  differ  from  that  of  Farallon  breeders,  as 
suggested  by  dietary  differences  between  offshore  and 
inshore  colonies  of  Rhinoceros  Auklets  in  British  Colum- 
bia and  Washington  (Vermeer  6k  Westrheim  1984,  Wil- 
son 6k  Manuwal  1986).  See  Ainley  6k  Boekelheide  (1990, 
Chap.  3),  for  possible  size  differences  in  prey  selected  by 
Murres,  Pigeon  Guillemots,  and  Tufted  Puffins  at  the 
Farallon  Islands.  Elsewhere  Murres  eat  mosdy  fish  of  a 
variety  of  species  and  euphausiids;  they  eat  minor  amounts 
of  amphipods,  isopods,  decapods,  cephalopods,  and  poly- 
chaete  worms  (Johnsgard  1987). 

Marin  Breeding  Distribution 

During  the  adas  period,  Common  Murres  were  breeding 
at  three  large  colonies  along  the  Marin  County  coast:  Point 
Reyes  Lighthouse,  Point  Resistance,  and  Double  Point 
Rocks  (Sowls  et  al.  1980;  Table  14,  Figure  14).  In  1989, 
these  three  colonies  were  still  active,  as  was  a  small  one 
established  at  Millers  Point  Rocks  at  least  by  1982  (Carter 
etal.  1992). 

Historical  Trends/  Population  Threats 

Preliminary  surveys  in  1969  to  1972  estimated  9440  Com- 
mon Murres  were  breeding  at  the  three  sites  where  the 
bulk  of  the  Marin  County  population  has  subsequendy 
bred  (Ainley  6k  Whitt  1973);  these  estimates  were  prob- 
ably low  because  the  counts  were  not  all  taken  from  boats, 
as  recent  counts  have  been.  Sowls  et  al.  (1980)  estimated 
that  a  total  of  about  37,000  Murres  were  breeding  at  three 
Marin  County  colonies  in  1979  to  1980.  Takekawa  et  al. 
(1990)  documented  declines  from  1980-1982  to  1986  in 
numbers  of  breeding  Murres  in  central  California,  includ- 
ing Marin  County;  total  numbers  in  Marin  fell  to  about 
26,900  birds.  Numbers  dropped  at  Point  Reyes  Lighthouse 
by  53.5%  (from  44,250  in  1982  to  20,590  in  1986),  at 
Point  Resistance  by  59.8%  (from  7540  in  1980  to  3030  in 
1986),  and  at  Double  Point  Rocks  by  77.9%  (from  14,870 
in  1980  to  3280  in  1986).  The  declines  had  multiple 
causes  (see  below).  In  1989,  Carter  et  al.  (1992)  estimated 
that  23,495  Murres  were  breeding  at  Marin  County  colo- 
nies. A  pattern  of  declines  of  this  magnitude  in  a  local  area 
is  best  interpreted  in  a  regional  and  historical  context. 

The  history  of  the  Farallon  Murre  colony  is  the  best 
known  of  any  in  California.  From  a  peak  of  400,000 
Murres  in  the  1850s,  the  Farallon  population  declined 
precipitously  to  about  60,000  birds  at  the  end  of  commer- 
cial egg  collecting  just  after  1900  (Ainley  6k  Lewis  1974). 
By  1959,  continued  human  disturbance  and  chronic  oil 
pollution  had  further  depressed  numbers  to  a  low  of  6000 
to  7000  birds.  With  protection  and  diminished  oil  pollu- 
tion, the  colony  rebounded  to  20,500  birds  in  1972 
(Ainley  6k  Lewis  1974),  peaked  at  102,110  birds  in  1982 
(Takekawa  et  al.  1990),  and  dropped  to  68,168  by  1989 


195 


Alcids 


MARIN  COUNTY  BRFFDING  BIRD  ATIAS 


Alcids 


(Carter  et  al.  1992).  Despite  such  fluctuations,  apparently 
numbers  of  breeding  Murres  in  general  have  increased 
along  the  entire  California  coast  throughout  much  of  this 
century  (Osborne  &  Reynolds  1971,  Osborne  1972, 
Sowls  et  al.  1980,  Briggs  et  al.  1987). 

The  entire  population  of  Common  Murres  in  Califor- 
nia breeds  along  the  state's  central  and  northern  coast. 
Sowls  et  al.  (1980)  estimated  diat  363,154  Murres  bred  at 
19  sites  in  that  region  in  1979  and  1980;  they  did  not 
include  an  estimate  for  the  North  Farallon  Islands  which 
then  held  about  51 ,540  birds  (Carter  et  al.  1992).  The  state 
population  peaked  at  about  520,000  in  1982  (Briggs  et  al. 
1987).  Between  1980-1982  and  1986,  the  central  Califor- 
nia breeding  population  declined  overall  by  52.6%  (from 
229,080  to  108,530  birds),  while  the  northern  California 
population  remained  relatively  unchanged  (Takekawa  et  al. 
1990).  The  decline  in  the  central  coast  population  was 
caused  by  a  high  rate  of  incidental  take  of  Murres  during 
an  intensive  nearshore  gill-net  fishery,  compounded  by 
mortality  from  two  major  oil  spills  and  a  severe  El  Nino 
event  in  1982-83.  Declines  at  individual  colonies  ranged 
from  46%- 100%  and  were  most  severe  at  colonies  located 
nearest  to  areas  of  highest  gill-net-fishing  mortality. 
Declines  along  the  Marin  County  coast,  as  detailed  above, 
were  among  the  most  severe.  From  1979  to  1987,  gill-net 


fishing  in  central  California  waters  killed  roughly  70,000- 
75,000  Murres.  Takekawa  et  al.  (1990)  estimated  that 
gill-net  mortality  accounted  for  roughly  40%-45%  of  the 
120,550  Murres  lost  from  the  central  California  popula- 
tion during  this  period.  An  estimated  4500  Common 
Murres  were  killed  or  debilitated  in  the  Gulf  of  the  Faral- 
lones  in  die  November  1 984  Puerto  Rican  oil  spill  (PRBO 
1985)  and  about  7500  along  die  central  California  coast  in 
die  February  1986  Apex  Houston  oil  spill  (Page  et  al.  1990); 
a  minimum  (probably  much  higher)  of  1 100  Murres  met 
a  similar  fate  in  die  1971  San  Francisco  oil  spill  (Smail  et 
al.  1972).  Carter  et  al.  (1992)  estimated  351,336  Murres 
were  breeding  at  23  sites  in  California  in  1989;  this 
number  is  only  3%  fewer  dian  die  population  estimate  for 
1979  to  1980,  and  die  proportions  of  the  population 
breeding  in  northern  and  central  California  were  similar 
in  bodi  periods. 

Murres  at  the  Farallon  Islands  have  also  experienced 
eggshell  diinning  from  pesticide  residues  (Gress  et  al. 
1971),  but  no  adverse  effects  on  reproductive  success  have 
been  detected  (Ainley  <Sl  Boekelheide  1990,  Chap.  8).  It  is 
clear,  diough,  diat  a  species  widi  such  a  history  of  popula- 
tion declines  attributable  to  human  causes  should  continue 
to  be  carefully  monitored. 


Subdued  Kissing  sounds  issue  from  the  carmine  mouths  of  Pigeon  Guillemots  scattered  widely  on  rocky  coastal  sea  cliffs. 

Photograph  b>  Ian  Tail. 


196 


Alcids 


SPECIES  ACCOUNTS 


Alcids 


PIGEON  GUILLEMOT   Cepphus  columba 


Occurs  year  round,  though  primarily  as  a 
summer  resident  from  mid-Mar  through 
Aug  (winter  lows  reached  by  mid-Oct). 

A  common,  very  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  10  (4.5%)  of  221  blocks. 

O  Possible  =  2  (20%) 
C  Probable  =  1  (10%) 
•    Confirmed  =         7   (70%) 

FSAR  =  4        OPI  =  40         CI  =  2.50 


Ecological  Requirements 

Our  dapper  "Sea  Pigeons"  inhabit  nearshore  ocean  waters, 
over  rocky  substrate,  usually  within  sight  of  land;  some- 
times they  range  up  to  three  to  (rarely)  nine  miles  from 
mainland  or  island  shores  where  they  nest  (Briggs  et  al. 
1987;  Ainley  6k  Boekelheide  1990,  Chap.  3).  Guillemots 
nest  solitarily  or  in  small,  loose  colonies  when  suitable  nest 
sites  are  clustered.  They  typically  lay  their  eggs  in  shallow 
natural  rock  cavities  in  talus  slopes,  crevices  in  solid  rocks 
of  cliffs  or  crests  of  ridges,  in  sea  caves,  or  among  boulders 
on  beaches  (Bent  1919;  Dawson  1923;  Sowls  et  al.  1980; 
Ainley  &  Boekelheide  1990,  Chap.  9).  Nest  sites  range 
from  the  rocky  shores  at  the  water's  edge  up  to  the  summit 
of  precipitous  cliffs.  Guillemots  also  sometimes  nest  in 
burrows  dug  into  clay  or  loose  conglomerate  rock,  aban- 
doned rabbit  burrows,  and  artificial  structures,  such  as 
rock  walls,  bridges,  suitable  wharf  timbers,  drainpipes, 
tires  hung  from  pilings,  or  artificial  nest  boxes  (Bent  1919; 
Sowls  et  al.  1980;  Johnsgard  1987;  Ainley  &  Boekelheide 
1990,  Chap.  9).  The  principal  nest  site  requirement  seems 
to  be  "a  roof  over  their  head"  (Ainley  &  Boekelheide  1 990, 
Chap.  9).  Most  cavities  are  slighdy  deeper  than  die  length 
of  an  adult,  thus  allowing  chicks  refuge  from  predatory 
gulls.  Even  in  deep  cavities,  suitable  for  Tufted  Puffins  or 
Rhinoceros  Auklets  (see  below),  Guillemots  lay  eggs  and 
incubate  near  the  entrance.  Sometimes  eggs  laid  under 
projecting  ledges,  boulders,  or  in  spaces  between  piles  of 
rocks  can  be  seen  from  above  (Bent  1919).  In  water-worn 
sea  caves,  Guillemots  lay  their  eggs  in  various  nooks  and 
crannies  about  the  walls  or  roof,  in  cavities  under  loose 
rock  in  the  talus  of  crumbling  walls,  in  open  situations  on 


flat  rocks  or  shelfs,  or  even  on  the  sandy  floor  of  the  cave, 
if  beyond  reach  of  daylight  and  water  (Bent  1919,  Dawson 
1923). 

Guillemots  do  not  construct  a  true  nest.  Frequendy  the 
eggs  repose  upon  a  collection  of  small  granite  chips, 
pebbles,  shell  fragments,  bones,  or  other  natural  or  human 
debris,  or  sometimes  on  bare  rock,  gravel,  or  soil.  It  is 
unclear  whether  Guillemots  just  select  hollows  with  accu- 
mulated debris  or  actually  gather  nest  material,  but  at  most 
sites  they  likely  just  scrape  together  whatever  material  is 
available  within  easy  reach  (Bent  1919).  Availability  of  nest 
sites  may  limit  Guillemot  populations  at  some  sites  (Ainley 
6k  Boekelheide  1990,  Chap.  9),  but  not  at  others  (Kuletz 
1983).  At  the  Farallon  Islands,  some  pairs  may  control 
more  than  one  nest  site  within  a  few  yards  of  the  site  being 
used  and  may  perhaps  alternate  irregularly  among  them 
(Ainley  ck  Boekelheide  1990,  Chap.  9). 

Pigeon  Guillemots  use  wing-propelled  dives  to  search 
for  prey,  primarily  on  or  over  rocky  substrate  of  the 
subtidal  zone  (Follett  ck  Ainley  1976;  Ainley  6k  Boekel- 
heide 1990,  Chap.  3).  Guillemots  are  deep  divers  and 
probably  descend  to  330  feet  or  more  (Ainley  6k  Boekel- 
heide 1990,  Chap.  3).  Once  they  reach  the  bottom,  they 
"hover"  by  paddling  their  feet  as  they  probe  nooks  and 
crannies  for  prey  (Johnsgard  1987).  Birds  apparendy  for- 
age mosdy  early  and  late  in  the  day  (Ainley  6k  Boekelheide 
1990,  Chap.  3).  In  years  of  superabundant  prey  at  the 
Farallones,  small  groups  of  Guillemots  participate  in  multi- 
species  foraging  flocks  preying  on  midwater-schooling 
rockfish,  but  otherwise  they  feed  alone  at  submerged  reefs 

197 


Alcids 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Alcids 


and  hunt  for  solitary  prey  that  hide  in  the  rocks.  In  years 
of  poor  prey  availability  in  rocky  habitat,  Guillemots  appar- 
endy  feed  more  on  sandy  bottoms,  diough  probably  near 
rocks. 

Farallon  breeders  feed  dieir  chicks  primarily  juvenile 
rockfish  and  sculpins,  along  with  small  numbers  of  a 
variety  of  other  fish,  octopuses,  and  mysid  shrimp  (Ainley 
6k  Boekelheide  1990,  Chap.  3,  n  =  2586).  Adults  bring 
food  items  one  at  a  time,  and  prey  are  held  crosswise  in  the 
bill,  grasped  by  the  head  widi  the  tail  dangling  out  of  one 
side  (Jonnsgard  1987).  During  cold-water  years  at  the 
Farallones,  rockfish  are  the  principal  prey,  whereas  in 
warm-water  years,  sculpins  and  other  bottom-dwelling  fish 
are  more  prevalent  and  dietary  diversity  is  higher  (Ainley 
6k  Boekelheide  1990,  Chap.  3).  Dietary  overlap  is  high 
between  Guillemots  and  Pelagic  Cormorants,  especially  in 
years  of  rockfish  abundance.  In  all  years,  the  Guillemot 
diet  diversifies  toward  die  end  of  die  chick-rearing  period, 
when  rockfish  decrease  and  other  species  increase  in 
importance.  In  warm-water  years,  die  proportion  of  rock- 
fish in  the  diet  decreases  from  about  50%  to  9%  during 
the  course  of  the  nestling  period,  and  in  other  years  it 
decreases  from  about  80%  to  50%  during  that  period.  In 
Alaska,  individual  Guillemots  may  display  foraging  site 
and  prey  preferences  that  are  generally  maintained  widiin 
a  season  and  between  years;  differences  in  diet  between 
individuals  appear  to  be  correlated  with  laying  date,  habitat 
use,  and  possibly  an  acquired  search  image  (Kuletz  1983). 
At  the  Farallones,  individual  Guillemots  would  more  likely 
specialize  in  different  prey  in  warm-water  years,  when 
overall  dietary  diversity  is  greater,  than  in  cold-water  years, 
when  most  individuals  concentrate  on  rockfish  (Ainley  6k 
Boekelheide  1990,  Chap.  3).  Apparendy  adults  feed  to  a 
greater  extent  on  invertebrates,  such  as  crustaceans,  mol- 
lusks,  and  marine  worms,  than  is  indicated  by  the  food  fed 
to  chicks  (Lewis  6k  Briggs  1985). 

Marin  Breeding  Distribution 

During  the  adas  period,  Pigeon  Guillemots  nested  at 
scattered  sites  along  the  outer  coast  of  Marin  County 
endowed  with  rocky  bluffs  and  sea  stacks  (Table  14,  Figure 


14).  Representative  breeding  locations  were  Double 
Point/Allamere  Falls  (ON/FY  7/5/80  -DS,  ITi)  and  the 
mouth  of  Cold  Stream,  just  N  of  Slide  Ranch  (ON 
7/26/82  -DS). 

Historical  Trends/ Population  Threats 

In  surveys  of  only  selected  portions  of  the  Marin  County 
coast,  Ainley  and  Whitt  (1973)  estimated  that  82  Pigeon 
Guillemots  were  breeding  at  four  sites.  In  1979,  Sowls  et 
al.  (1980)  estimated  that  366  Guillemots  were  nesting 
along  1 5  stretches  of  the  Marin  coasdine;  this  estimate  is 
low  because  they  only  noted  the  presence  of  Guillemots, 
without  reporting  numbers,  at  four  sites.  In  complete 
surveys,  Carter  et  al.  (1992)  estimated  that  1108  Guille- 
mots were  breeding  along  14  stretches  of  the  Marin  coast. 
The  most  notable  increase  from  1979  to  1989  was  from 
120  to  616  birds  at  the  Point  Reyes  headlands.  Estimates 
for  the  entire  Guillemot  population  breeding  on  the  cen- 
tral and  northern  California  coast  ranged  from  13,814  in 
1 979  to  1 980  (Sowls  et  al.  1 980)  to  1 2,252  in  1 989  (Carter 
etal.  1992). 

Pigeon  Guillemots  declined  on  the  Farallon  Islands 
early  in  die  1900s  because  of  oil  pollution  and  disturbance 
from  humans  and  domestic  livestock  (Ainley  6k  Lewis 
1974;  Ainley  6k  Boekelheide  1990,  Chap.  9).  Numbers 
have  since  increased,  and  the  population  estimate  for  most 
of  the  1970s  and  early  1980s  of  2000  to  2200  birds  may 
be  an  all-time  high  because  of  the  current  availability  of 
nest  burrows  formerly  occupied  by  Tufted  Puffins  during 
their  population  peak  on  the  islands  early  in  this  century. 
The  population  of  Guillemots  breeding  at  Southeast  Faral- 
lon Island  dropped  to  less  than  100  birds  during  the 
1982-83  El  Nino  event,  but  subsequendy  increased  to 
1867  birds  in  1989  (Ainley  6k  Boekelheide  1990,  Chap. 
9;  Carter  et  al.  1992). 

Oil  pollution  and  disturbance  continue  to  pose  threats 
to  Guillemot  populations  (Sowls  et  al.  1980).  In  the  1980s, 
many  were  also  killed  in  gill  nets  along  with  Murres  (H.R. 
Carter  pers.  comm.). 


198 


Aicids 


SPECIES  ACCOUNTS 


Aicids 


RHINOCEROS  AUKLET    Cerorhinca  monocerata 


Occurs  year  round,  though  primarily  as  a 
winter  resident  from  mid-Oct  to  mid- 
Apr;  occupies  Farallon  Island  (and  per- 
haps Marin)  breeding  colonies  mosdy 
from  Apr  through  Aug  (extremes  Feb- 
Sep). 

\    \   \^\      -^^S^i   >r<3v        V-^^v\^-A^\^^A\ --^V'X   ^-1 

An  uncommon,  very  local  breeder; 
overall  breeding  population  very  small. 
Recorded  in  1  (0.4%)  of  221  blocks. 

O    Possible        =         1    (100%) 
€    Probable       =        0  (0%) 
•    Confirmed   =         0   (0%) 

FSAR  =  2         OPI  =  2          CI  =  1 .00 

Ecological  Requirements 

Despite  a  horny  protuberance  on  its  bill  suggesting  a 
superficial  likeness  to  a  rhinoceros  and  a  surname  claiming 
affinity  to  the  auklets,  this  species  is  in  fact  a  puffin. 
Nevertheless,  by  habit  and  fondness  we  are  perhaps  for- 
ever doomed  to  use  the  nickname  "Rhino."  Off  California, 
these  puffins  inhabit  inshore  and  offshore  ocean  waters 
over  the  continental  shelf,  but  they  are  most  numerous  in 
deeper  waters  over  the  continental  slope  (Briggs  et  al. 
1987).  During  the  breeding  season,  most  birds  in  Califor- 
nia are  found  within  about  30  to  35  miles  of  nesting 
colonies  (Briggs  et  al.  1987;  Ainley  &.  Boekelheide  1990, 
Chap.  3).  Birds  disperse  farther  from  colonies  during 
warm-water  years,  when  food  is  scarcer  (Ainley  &  Boekel- 
heide 1990,  Chap.  3).  In  Marin  County,  Rhinoceros 
Auklets  are  seen  in  season  on  the  water  below  die  cliffs  at 
the  Point  Reyes  headlands  and  near  Bird  Rock— sites  where 
they  apparendy  breed— but  the  foraging  range  of  diese  birds 
is  unknown. 

The  generally  small,  loose  breeding  colonies  on  Cali- 
fornia s  islands  and  steep  mainland  slopes  (Sowls  et  al. 
1980,  Carter  et  al.  1992)  contrast  with  the  dense  colonies 
of  thousands  of  birds  prevalent  from  Washington  north  to 
Alaska  (Bent  1919,  Sowls  et  al.  1978).  Rhinoceros  Auklets 
initially  recolonizing  the  Farallon  Islands  were  nesting  in 
deep  natural  cavities  or  clefts  in  rocks,  in  caves,  or  in 
artificial  nest  boxes  (Sowls  et  al.  1 980;  Sander  1 986;  Ainley 
&.  Boekelheide  1990,  Chap.  11).  As  die  population  has 
continued  to  increase,  some  birds  are  now  digging  earthen 
nesting  burrows  under  boulders  in  deep  soil  areas  (W.J. 


Sydeman  pers.  comm.).  Rhinos  also  dig  earthen  burrows 
at  Afio  Nuevo  Island,  San  Mateo  County,  and  Casde 
Rock,  Del  Norte  County  (H.R.  Carter  pers.  comm.).  Nest 
cavities  on  the  Farallones  are  usually  deeper  than  the 
average  person's  reach  (Ainley  ck  Boekelheide  1990, 
Chap.  11).  In  one  Farallon  cave,  nests  were  found  up  to 
about  65  feet  back  from  the  opening  (Sander  1986).  Six  of 
eleven  nests  inside  the  cave  were  located  in  one-  to  two- 
foot-deep  rock  crevices,  while  five  were  exposed  on  the 
surface  of  the  cave  floor;  seven  nests  were  lined  with  grass, 
and  the  remainder  had  no  nesting  material.  Throughout 
most  of  the  range,  Rhinos  visit  nest  sites  only  in  the  dark 
of  night,  but  to  a  limited  extent  in  California  and  Oregon, 
diey  move  about  dieir  burrow  entrances  during  daylight 
(Sowls  et  al.  1 980;  Ainley  ck  Boekelheide  1990,  Chap.  1 1). 
At  the  Farallones,  their  activities  are  largely  crepuscular 
and  nocturnal  (Sander  1986).  Nocturnal  visitation  may  be 
an  adaptation  to  reduce  predation,  to  avoid  kleptoparasi- 
tism  by  gulls  while  feeding  chicks,  or,  perhaps  more  likely, 
to  reduce  interference  by  Tufted  Puffins,  with  which  Rhi- 
nos apparendy  compete  for  limited  nest  sites  (Ainley  &. 
Boekelheide  1990,  Chap.  11). 

To  the  north  in  the  heart  of  the  breeding  range,  Rhinos 
nest  primarily  in  earthen  burrows  on  both  forested  and 
unforested  islands  (Bent  1919,  Richardson  1961,  Sowls  et 
al.  1980,  Wilson  &  Manuwal  1986).  They  select  nest  sites 
there  on  sea-facing  slopes,  cliffs,  or  level  areas  adjacent  to 
edges  of  islands  in  terrain  varying  from  forests  with  open 
understories  to  dense  shrubbery,  grassy  slopes,  or  bare 

199 


Alcids 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Alcids 


earth.  With  their  feet  and  bills,  Rhinos  excavate  or  reno- 
vate burrows  from  about  4  to  25  feet  deep;  average  burrow 
lengths  at  different  locations  vary  from  6-8  to  10-15  feet 
(Richardson  1961).  Soil  conditions,  slope,  and  vegetation 
are  important  determinants  of  "Auklet"  occupation  and 
apparendy  burrow  length.  Rhinos  prefer  rather  firm  sandy 
soil  held  together  by  roots  at  die  surface  and  avoid  soil  that 
is  too  loose  and  sandy  or  too  hard  and  rocky.  Rhinos 
usually  dig  roughly  horizontal  burrows  into  steep  slopes  or 
into  the  base  of  small  banks  in  flatter  areas.  Burrows 
sometimes  have  one  or  more  spurs  or  blind  alleys,  and  the 
last  few  feet  of  the  main  passage  tend  to  slope  down,  often 
dropping  off  an  inch  or  two,  to  terminate  in  an  enlarged 
dome-shaped  nest  chamber.  Rhinos  lay  their  single  egg  in 
a  nest  that  varies  from  a  depression  in  the  dirt  (with  or 
without  a  little  dried  or  green  grass)  to  a  shallow  saucer- 
shaped  nest  of  grass,  leaves,  twigs,  moss,  ferns,  feathers,  or 
other  available  material  (Bent  1919,  Richardson  1961). 
Dry  grass  often  is  added  to  the  nest  or  is  found  in  the 
burrow  during  the  nesding  stage.  In  all  areas,  Rhinos 
prefer  nest  sites  with  some  slope  or  altitude  close  at  hand, 
presumably  to  aid  in  both  takeoffs  and  landings  (Richard- 
son 1961,  Wilson  &  Manuwal  1986).  In  general,  Rhinos 
favor  somewhat  more  gende  slopes  and  tolerate  taller 
vegetation  at  nest  sites  than  do  Tufted  Puffins  (Vermeer 
1979).  In  some  areas,  Rhinos  make  runways  through 
dense  vegetation  from  open  takeoff  and  landing  spots  to 
the  mouths  of  their  burrows  (Richardson  1961).  Burrows 
may  be  used  year  after  year,  often  by  die  same  pairs.  Chicks 
fledge  at  about  50%-70%  of  adult  weight  (Vermeer  6k 
Cullen  1982)  and  are  barely  able  to  fly  from  their  burrows 
down  to  the  water  (Richardson  1961). 

Rhinos'  wing-propelled  dives  apparendy  carry  them  to 
intermediate  depths— 65  to  260  feet— in  their  pursuit  of 
prey  (Ainley  &  Boekelheide  1990,  Chap.  3).  They  appar- 
endy feed  mosdy  early  and  late  in  the  day,  alone  or 
occasionally  in  small  flocks.  The  diet  fed  to  chicks  at  the 
Farallon  Islands  in  1986  (a  warm-water  year)  was  74% 
juvenile  rockfish,  22%  Pacific  saury,  and  4%  black  cod  (n  = 
27,  Sander  1986;  Ainley  6k  Boekelheide  1990,  Chap.  3). 
Ongoing  diet  studies  at  the  Farallones  from  1987  to  1989 
indicate  that  rockfish,  anchovies,  sablefish,  and  salmon  are 
in  fact  the  main  prey  items  and  that  the  diet  varies  consid- 
erably with  season  and  year  (PRBO  unpubl.  data).  Through- 
out the  range,  the  diet  fed  to  chicks  is  almost  exclusively 
small  fish  (1 .5  to  9.4  inches  long)— particularly  sandlance, 
anchovies,  smelt,  herring,  rockfish,  capelin,  and  Pacific 
saury— and  sometimes  small  amounts  of  squid  and  octopus 
(Vermeer  1980,  Hatch  1984,  Vermeer  6k  Westrheim 
1984,  Wilson  6k  Manuwal  1986).  Adults  often  carry  many 
fish  at  a  time  crosswise  in  their  bills  to  their  chicks 
(Vermeer  6k  Cullen  1982);  later  in  the  season  they  deliver 
one  fish  at  a  time  (S.D.  Emslie  and  W.J.  Sydeman  pers. 
comm.).  The  chick  diet  varies  between  nearby  offshore  and 


inshore  colonies,  latitudinally,  and  both  annually  and 
seasonally,  apparently  as  affected  by  changes  in  the  distri- 
bution and  abundance  of  prey.  At  least  in  winter,  adults 
also  eat  euphausiids  (Ainley  6k  Sanger  1979)  and  greater 
quantities  of  nonfish  prey.  In  Monterey  Bay,  the  winter 
diet  can  be  as  much  as  70%  market  squid  (Baltz  6k 
Morejohn  1977,  n  =  26). 

Marin  Breeding  Distribution 

Since  at  least  1977,  up  to  1 1  Rhinoceros  Auklets  at  a  time 
have  been  observed  on  the  water  below  the  Point  Reyes 
headlands  in  May  and  June  (ABN).  These  birds  have  been 
observed  "billing"  and  in  "passing  flights,"  which  suggest 
local  breeding.  Three  of  these  "Auklets"  were  seen  off  Bird 
Rock,  Tomales  Point,  on  5  June  1989  (Carter  et  al.  1992). 
Representative  records  during  the  adas  period  included 
one  to  three  birds  just  off  the  seabird  nesting  cliffs  by  the 
Point  Reyes  Lighthouse  (6/1 1  -24/80  -DS,  JGE;  6/21/81 
-DS,  RSt)  and  four  birds  off  Chimney  Rock  (6/20- 
7/16/77  —PRBO,  JMR).  The  apparent  establishment  of 
breeding  at  Point  Reyes  is  part  of  a  much  wider  increase 
and  range  expansion  of  the  breeding  population  described 
below. 

Historical  Trends/ Population  Threats 

Rhinoceros  Auklets  were  absent  from  the  Farallon  Islands 
from  the  1860s  (when  perhaps  eliminated  by  overzealous 
collectors)  until  die  early  1970s  (Ainley  6k  Lewis  1974; 
Ainley  6k  Boekelheide  1990,  Chap.  3).  Perhaps  aided  by 
die  elimination  of  burrow-competing  rabbits,  by  1989  the 
Farallon  population  numbered  516  birds  (Carter  ct  al. 
1992).  Coincident  widi  this  recolonization,  the  population 
was  increasing  within  the  portion  of  the  historic  range 
from  British  Columbia  to  California  and  the  breeding 
range  expanded  south  to  Point  Arguello,  Santa  Barbara 
County  (Scott  et  al.  1974,  Sowls  et  al.  1980,  Briggs  et  al. 
1987,  ABN),  and  recendy  to  the  San  Miguel  Island  area  of 
the  Channel  Islands  (Carter  et  al.  1992).  From  surveys  in 
1979  to  1980,  Sowls  et  al.  (1980)  estimated  362  Rhinoc- 
eros Auklets  were  breeding  at  six  sites  along  the  central  and 
northern  California  coast.  Continued  rapid  expansion  of 
the  population  in  that  region  is  documented  by  estimates 
of  1750  breeding  birds  at  29  colonies  in  1989  (Carter  et 
al.  1992).  The  reasons  for  this  range  expansion  and  popu- 
lation increase  appear  to  be  unknown.  Despite  this 
upswing  in  the  breeding  population,  the  Rhinoceros  Auk- 
let is  still  considered  a  Bird  Species  of  Special  Concern  in 
California  (Remsen  1978,  CDFG  1991b). 

Like  other  alcids,  Rhinos  are  susceptible  to  oil  pollution 
and  human  disturbance  at  nesting  sites.  About  1600 
Rhinoceros  Auklets  were  killed  or  debilitated  along  the 
central  California  coast  in  die  Apex  Houston  oil  spill  in 
February  1986  (Page  et  al.  1990). 


200 


Alcids 


SPECIES  ACCOUNTS 


Alcids 


TUFTED  PUFFIN    Fratercula  cirrhata 


-m^ 

Occurs  year  round,  though  primarily  as  a 

?^5^\     ^            yC\> 

winter  resident  from  Oct  through  Apr. 

'xAji^v' 

Puffins  occupy  Farallon  Island  (and  per- 

<r\X^h 

-\j^\& 

haps  Marin)  nesting  sites  from  mid-Mar 
(rarely  starting  early  Apr)  through  Aug  or 

%\\\jC\)^ 

early  Sep. 

V^ 

y$$<Kr^^^ 

An  uncommon,  very  local  breeder; 

overall  breeding  population  very  small. 

^T^V^^^f^S\%>^ 

Recorded  in  1  (0.4%)  of  221  blocks.- 

"^i^Or^v^^^^V^^^ '" 

O    Possible        =        0   (0%) 

2^s\/^cV\\^A^v-A^\3^^r y^\yc\\x — v 

C    Probable       =         1    (100%) 

•    Confirmed  =        0   (0%) 

FSAR  =  2         OPI  =  2          CI  =  2.00 

Ecological  Requirements 

At  sea,  the  oudandish  headgear  of  the  solemn  "Sea  Parrot" 
enlivens  the  deep  waters  over  the  continental  slope  (Briggs 
et  al.  1987;  Ainley  6k  Boekelheide  1990,  Chap.  3).  Near 
the  Farallon  Island  breeding  colony,  Tufted  Puffins  most 
frequendy  forage  in  waters  deeper  than  260  feet  between 
30  miles  south  of  the  island  to  the  Cordell  Bank  about  35 
miles  to  the  north  (Ainley  6k  Boekelheide  1990,  Chap.  3). 
In  warm-water  years,  breeders  disperse  farther  from  the 
island  to  feed.  The  foraging  haunts  of  Point  Reyes  breeders 
are  unknown  but  probably  are  similar  to  those  of  Farallon 
birds  and  probably  involve  longer  commutes  to  and  from 
nest  sites. 

Tufted  Puffins  breed  on  treeless  islands,  large  offshore 
rocks  and  sea  stacks,  and  steep  mainland  cliffs.  In  Califor- 
nia, Tufted  Puffins  nest  in  small,  loose  colonies  of  up  to 
100  birds  (Sowls  et  al.  1980),  unlike  the  dense  colonies  of 
thousands  of  birds  in  Alaska  (Sowls  et  al.  1978).  Because 
the  soil  is  generally  shallow  at  the  Farallones,  Puffins  diere 
do  not  dig  earthen  nest  burrows,  as  they  do  extensively 
elsewhere,  but  instead  lay  their  single  eggs  in  natural 
cavities  or  clefts  in  rock  of  steep  terrain  high  on  the  island; 
some  nest  in  artificial  cavities  of  tile  pipe  and  rock  (Ainley 
6k  Boekelheide  1990,  Chap.  11).  Puffins  probably  breed 
in  rock  cavities  at  Point  Reyes  and  other  sites  on  the 
California  coast,  though  at  Castle  Rock,  Del  Norte 
County,  some  birds  dig  burrows  in  hard  soil  (H.R.  Carter 
pers.  comm.).  Lack  of  adequate  nesting  habitat  may  limit 
Tufted  Puffins  in  California.  Recently  at  the  Farallones, 
nesting  cavities  are  usually  deeper  than  an  average  person's 
reach  (Ainley  6k  Boekelheide  1990,  Chap.  11),  but  for- 


merly, perhaps  when  nest  sites  were  more  limiting,  many 
sitting  birds  and  eggs  were  visible  from  outside  (Dawson 
1923).  Some  nesting  sites  then  were  "nothing  more  than 
the  innermost  recesses  of  niches  and  caves  occupied  by 
Murres."  Throughout  much  of  their  breeding  range,  Tuf- 
ted Puffins  prefer  grassy  slopes,  rocky  slopes,  boulder 
rubble,  and  cliff  faces  and  edges  as  nesting  habitat.  There 
they  nest  mosdy  in  earthen  burrows  dug  with  feet  and  bills 
three  or  four  feet  into  soil  or  conglomerate  rock;  less 
frequendy  they  use  rock  cavities  (Bent  1919,  Dawson 
1923,  Vermeer  1979,  Johnsgard  1987).  They  prefer  cliff 
tops  and  steep  slopes  clothed  with  low-growing  or  sparse 
vegetation  (Vermeer  1979,  Johnsgard  1987).  Rarely,  they 
drive  tunnels  dirough  matted  vegetation  and  deposit  their 
eggs  in  die  shade  on  the  surface  of  the  ground  (Dawson 
1923).  Generally,  Tufted  Puffins  favor  steeper,  more  open 
terrain  for  nesting  than  do  Rhinoceros  Auklets;  small 
numbers  of  Tufted  Puffins  nest  on  flat  islands  and  run  to 
take  off  on  beaches  below  the  vegetation  (Vermeer  1979). 
Tufted  Puffins  may  or  may  not  line  their  nests  scantily  with 
leaves,  grass,  seaweed,  or  feathers  (Bent  1919,  Dawson 
1923,  Johnsgard  1987). 

Tufted  Puffins  are  deep  divers,  probably  exceeding  330 
feet  in  depth  in  their  wing-propelled  pursuit  of  prey  (Ainley 
6k  Boekelheide  1990,  Chap.  11).  They  apparendy  feed 
mostly  early  and  late  in  the  day,  alone  or  occasionally  in 
small  flocks.  Puffins  hold  many  fish  at  a  time  crosswise  in 
dieir  bills,  often  in  an  alternating  left-  and  right-handed 
manner,  for  delivery  to  young  (Johnsgard  1987).  At  the 
Farallon  Islands,  the  chick  diet  is  mostly  anchovies,  rock- 


201 


Alcids 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Alcids 


fish,  and  squid  (Ainley  &  Boekelheide  1990,  Chap.  3,  n  = 
728).  Limited  data  suggest  that  rockfish  predominate  in 
cold-water  years,  when  abundant  in  the  diet  of  other 
Farallon  breeding  seabirds,  and  squid  replace  fish  in  warm- 
water  years.  The  diet  appears  to  diversify  as  the  nesding 
period  progresses,  largely  as  a  function  of  decreasing  use  of 
anchovies  (which  move  inshore),  increasing  use  of  squid 
and  unidentified  fish  (probably  Pacific  saury,  which  dwell 
in  slope  and  pelagic  waters),  and  stable  use  of  rockfish.  At 
the  Farallon  Islands,  adult  Puffins,  like  Murres,  may  also 
feed  on  euphausiids,  but  they  do  not  feed  them  to  chicks 
as  they  do  to  a  limited  degree  at  other  locations  (Hatch 
1984).  Elsewhere,  Tufted  Puffins  feed  mosdy  on  a  variety 
of  fish— especially  sandlance,  rockfish,  cod,  prowfish,  cape- 
lin,  smelt,  and  herring— as  well  as  euphausiids  and  poly- 
chaete  worms  (Vermeer  1979,  Hatch  1984,  Johnsgard 
1987).  The  diet,  of  course,  varies  annually,  seasonally,  and 
with  location. 

Marin  Breeding  Distribution 

Since  1976,  Tufted  Puffins  have  been  seen  almost  annually 
in  the  vicinity  of  the  Point  Reyes  headlands  from  mid-April 
through  July  (ABN).  These  birds  have  been  observed  in 
passing  flights,  gathering  algae,  and  carrying  food  up  to 
cliffs,  but  solid  confirmation  of  breeding  is  lacking  because 
the  inaccessibility  of  the  cliffs  has  impeded  efforts  to  find 
nests.  Representative  records  for  the  adas  period  include 
up  to  seven  birds  on  the  water,  diving  to  gather  algae,  and 
flying  up  to  nearby  cliffs  at  Chimney  Rock  from  1 2  June  to 
16  July  1977;  and  up  to  six  birds  on  the  water  and  in 
passing  flights  at  die  Point  Reyes  Lighthouse  from  29  May 
to  30  June  1980  (many  observers  -ABN). 


Historical  Trends/ Population  Threats 

Formerly,  small  numbers  of  Tufted  Puffins  came  to  the 
cliffs  at  Point  Reyes  during  die  nesting  season  (GckW 
1927),  and  two  pairs  were  "apparendy  nesting"  on  Bird 
Rock,  Tomales  Point,  on  18  May  1930  (S6kP  1933).  A 
paucity  of  records  until  the  mid-1 970s  (see  above)  may  have 
indicated  a  decline  and  subsequent  recovery,  or  perhaps 
just  an  upswing  in  sightings  after  a  period  of  limited 
observer  coverage  drew  to  a  close. 

Numbers  of  Tufted  Puffins  breeding  at  the  Farallones 
declined  from  about  2000  birds  in  1911  to  26  in  1959 
(Ainley  6k  Lewis  1974).  Subsequendy  the  population  has 
grown  slighdy  and  stabilized  in  the  1980s  at  about  80  to 
100  birds,  except  for  the  short-lived  decline  to  less  than  10 
birds  during  the  1982-83  El  Nino  event  (Ainley  6k 
Boekelheide  1990,  Chap.  11;  PRBO  unpubl.  data).  Ainley 
and  Lewis  (1974)  speculated  that  the  initial  decline  was 
caused  by  oil  pollution  and  that  Puffins  had  not  made  a 
full  recovery  because  humans  overexploited  die  Pacific 
sardine  stock  during  the  mid-1 940s  (see  Double-crested 
Cormorant  account).  Tufted  Puffins  have  also  contracted 
their  range  and  numbers  more  widely  and  no  longer  breed 
south  of  the  Farallones  (Sowls  et  al.  1980,  Garrett  6k  Dunn 
1981)  except  at  Prince  Island  in  the  Channel  Islands 
(Carter  et  al.  1992).  From  surveys  of  the  central  and 
northern  California  coast,  Sowls  et  al.  (1980)  estimated 
that  250  Puffins  were  breeding  at  1  3  sites,  and  Carter  et  al. 
(1992)  estimated  266  birds  at  12  sites.  The  Tufted  Puffin 
still  faces  threats  from  oil  pollution  and  human  distur- 
bance (Sowls  et  al.  1980),  and  it  remains  a  Bird  Species  of 
Special  Concern  in  California  (Remsen  1978,  CDFG 
1991b). 


202 


Pigeons  and  Doves 


SPECIES  ACCOUNTS 


Pigeons  and  Doves 


Pigeons  and  Doves 

Family  Columbidae 


ROCK  DOVE   Columbalivia 


A  year-round  resident. 

A  fairly  common,  somewhat  local 
breeder;  overall  breeding  population 

^A°  \^V  V^\  ®  %^\o  \>\  o  X^v     Vf  \*- 

\  °t-A  _ 

small. 

/TO*. 

Recorded  in  90  (40.7%)  of  221  blocks. 

O    Possible        =      52  (58%) 
€    Probable       =       13  (14%) 

--t- 

•    Confirmed  =       25   (28%) 
FSAR  =  3        OPI  =  270       CI  =  1.70 

x^iV^A^Ar^^ 

^2o 

3v  \<\      \^\°  A 

^*-Ko\^ 

Ecological  Requirements 

Flocks  of  pigeons  feeding  tamely  at  city  dwellers'  feet  are 
sometimes  the  only  "wildlife"  they  get  to  know.  North 
American  Rock  Doves  are  the  feral  descendants  of  domes- 
tic pigeons  brought  to  this  continent  by  European  settlers. 
Today,  most  of  our  pigeon  populations  still  depend  direct- 
ly or  indirecdy  on  humans  for  their  survival,  but  some 
birds  do  exist  in  a  semiwild  state.  Breeding  Rock  Doves 
require  elevated,  enclosed  sites  for  nesting  and  roosting, 
foraging  grounds  that  are  bare  or  covered  only  with  short 
or  scattered  vegetation,  and  water  for  drinking  (Goodwin 
1983,  Cramp  1985).  They  avoid  tall,  dense  vegetation  of 
any  kind,  even  grassland.  Rock  Doves  are  quite  gregarious 
and  commonly  form  flocks  of  varying  size  for  virtually  all 
activities  away  from  their  nesting  territories.  In  the  Old 
World,  truly  wild  Rock  Doves  seek  nest  sites  and  shelter 
in  cliffs  (particularly  on  the  coast)  and  feed  in  nearby 
treeless  terrain.  Today's  feral  birds  are  attached  mosdy  to 
human  settlements,  where  they  nest  in  artificial  structures 
and  feed  in  open  urban  settings  or  in  agricultural  land. 
Most  Rock  Doves  in  Marin  County  inhabit  urban  centers 
or  agricultural  ranchland,  though  small  numbers  frequent 
coastal  cliffs. 


Although  Rock  Doves  sometimes  nest  in  solitary  pairs, 
most  breed  in  loose  colonies.  In  large  colonies,  nests  may 
be  as  close  as  1.5  to  3.0  feet  (Cramp  1985).  They  prefer  to 
nest  under  cover  in  semidarkness  (Goodwin  1983,  Cramp 
1985).  Wild  (Old  World)  birds  or  semiwild  feral  birds 
usually  nest  in  caves  on  sheltered  ledges  or  in  niches;  or  in 
holes,  niches,  or  deep  crevices  in  coastal  or  inland  cliffs; 
less  frequently  they  may  nest  in  clefts  in  other  rocks  or  in 
ruined  buildings.  Their  nests  are  often  far  back  in  caves  or 
deep  in  potholes  or  wells;  birds  will  nest  on  a  cave  floor  if 
suitable  ledges  are  already  occupied.  Feral  birds,  however, 
have  mosdy  forsaken  nesting  in  the  wild  for  equivalent 
sites  in  or  on  farm  buildings,  church  towers  or  steeples, 
large  institutional  buildings,  large  gabled  houses,  bridges, 
freeway  underpasses,  above-ground  parking  lots,  and  the 
like.  Most  nest  sites  are  fairly  high  above  ground.  Although 
city-dwelling  birds  are  tolerant  of  close  human  approach 
on  the  ground,  they  prefer  abandoned  buildings  or  in- 
accessible parts  of  structures  for  nesting.  Rock  Doves  also 
nest  in  holes  or  hollows  in  trees,  forks  or  depressions  on 
large  branches,  or  recesses  in  palm  trees.  Their  nests  are 
loosely  constructed  cups  of  roots,  stems,  and  leaves,  small 

203 


Pigeons  and  Doves 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Pigeons  and  Doves 


pieces  of  driftwood,  seaweed,  and  feathers;  there  is  no  tnie 
lining  (Cramp  1985).  Most  pairs  use  two  nest  sites  alter- 
nately, though  normally  not  the  same  site  for  successive 
broods.  The  majority  of  pairs  also  use  the  same  or  adjacent 
nest  sites  over  several  years. 

Rock  Doves  form  mainly  communal,  nocturnal  roosts, 
though  they  sometimes  roost  singly  or  convene  in  die  day 
during  gloomy  or  stormy  weather  (Cramp  1985).  Gregari- 
ousness  at  roosts  is  less  pronounced  among  breeding 
birds,  though  off-duty  males  use  communal  roosts  during 
incubation.  The  birds  prefer  roosts  with  cover  all  around, 
similar  to  nest  sites.  Although  they  prefer  ledges  that  have 
broad  overhangs  and  protection  from  the  wind,  they  will 
use  ledges  more  exposed  to  weather  or  artificial  lighting. 
Roosts  and  breeding  colony  sites  may  be  the  same,  or  diey 
may  be  separate;  there  also  may  be  several  alternative  roost 
sites.  The  roost  site  chosen  may  be  die  closest  to  the  place 
where  the  birds  last  fed,  or  possibly  the  choice  may  be 
dictated  by  weather.  Roosts  are  often  used  by  birds  from 
different  feeding  flocks  and  perhaps  function  in  part  as 
foraging  information  centers.  However,  flocks  in  some 
areas  are  discrete  units  attached  to  specific  nesting,  roost- 
ing, and  feeding  areas,  while  elsewhere  they  are  chance 
aggregations. 

Rock  Doves  use  exposed  vantage  points  for  long  periods 
while  surveying  areas,  waiting  for  feeding  opportunities 
(Cramp  1985).  Birds  inhabiting  agricultural  or  undevel- 
oped lands  often  feed  near  their  nest  sites.  Birds  from 
settled  areas  may  feed  exclusively  in  urban  centers,  or  they 
may  nest  and  roost  there  and  fly  to  nearby  fields  to  forage 
(Goodwin  1983,  Cramp  1985).  Rock  Doves  commonly 
forage  up  to  one-third  mile  from  nest  sites,  but  sometimes 
as  far  as  4  to  5  miles  (Cramp  1985).  Upon  arriving  at  fields 
to  feed,  feral  birds  normally  circle,  gain  height,  and  circle 
again  before  landing  in  open  areas  with  good  visibility. 
Foraging  birds  walk  or  run  about,  pecking  at  the  ground. 
Although  most  birds  forage  on  bare  or  sparsely  vegetated 
ground,  feral  (but  not  wild)  birds  will  forage,  rarely,  for 
vegetable  fare  on  the  ground  in  woodlands  or  up  in  trees, 
bushes,  or  vines  (Goodwin  1983,  Cramp  1985).  Flocks 
frequendy  forage  all  at  once,  widi  some  birds  flying  from 
the  rear  to  the  front;  there  is  a  dominance  hierarchy  in  feral 
flocks,  with  central  birds  obtaining  more  food  (Cramp 
1985).  In  the  country,  Rock  Doves  feed  around  ranch- 
yards,  in  arable  land,  and  on  land  grazed  by  domestic 
livestock.  In  urban  areas,  they  feed  on  paved  squares, 
sidewalks,  roads,  vacant  lots,  parking  lots,  parks,  and 
gardens.  This  species  is  adapted  chiefly  to  a  seed  diet  of 
cereal  grains,  legumes,  weeds,  and  grasses  (Goodwin  1983, 
Cramp  1985).  In  agricultural  areas,  cereal  grains  predomi- 
nate in  the  diet  over  weed  or  grass  seeds.  Rock  Doves 
occasionally  eat  acorns  (usually  broken  or  damaged),  green 
leaves,  buds,  tender  roots,  flowers,  berries,  galls,  and 
seaweed.  In  addition,  they  eat  small  amounts  of  inverte- 

204 


brate  foods  or  small  snails  and  mollusks,  ticks  and  other 
arachnids,  earthworms,  slugs,  moth  larvae,  and  various 
insects.  City-dwelling  birds,  on  the  other  hand,  subsist 
mosdy  on  a  wide  variety  of  artificial  foods  offered  to  them 
by  humans  or  obtained  by  scavenging.  Of  these,  bread  is  a 
staple.  Other  foods  include  grains,  peanuts,  popcorn, 
cheese,  cooked  meat,  fat,  bacon  rind,  fish,  apple,  banana, 
potato,  chocolate,  and  ice  cream!  Overall  there  is  consid- 
erable variation  in  diet  with  season  and  locality.  Rock 
Doves  also  collect  small  stones  and  grit  to  aid  in  digestion, 
and  eat  mortar,  presumably  for  the  calcium  content. 

Adults  feed  the  young  by  regurgitation  (Goodwin  1983, 
Cramp  1985).  The  diet  of  wild  nesdings  is  similar  to  that 
of  adults,  but  it  includes  a  higher,  though  still  minor, 
proportion  of  animal  matter.  "Crop  (pigeon's)  milk"  is 
very  important  and  is  the  sole  food  initially.  At  about  four 
to  five  days  of  age,  the  young  are  fed  morsels  of  soft  food 
and  small  seeds.  The  importance  of  these  and  other  solid 
foods  in  the  diet  increases  until  just  before  fledging,  when 
the  young  consume  only  traces  of  crop  milk.  When  their 
young  are  small,  foraging  adults  take  small  seeds  in  prefer- 
ence to  larger  ones  (Goodwin  1983).  Although  adults 
usually  drink  from  the  edge  or  in  the  shallows  of  water, 
they  sometimes  alight  on  the  surface  to  drink  or  hover 
above  it;  young  are  brought  water  in  die  crop  (Goodwin 
1983,  Cramp  1985). 

Marin  Breeding  Distribution 

Marin  County's  breeding  Rock  Doves  were  concentrated 
in  the  lowlands  of  the  eastern  urban  corridor  along  High- 
way 101 .  They  were  scattered  throughout  the  farm  country 
of  central  and  northern  Marin  but  were  relatively  rare  in 
ranchlands  on  the  Point  Reyes  peninsula.  Some  of  the 
birds  in  farming  country  were  not  truly  feral,  as  some 
ranchers  had  built  special  lofts  (dovecotes)  for  the  birds 
and  probably  fed  them.  Representative  nesting  locations 
were  ranch  at  E  end  of  Clark  Road,  E  of  Tomales  Bay  (NE 
5/13/82  — DS);  abandoned  building  near  quarry  on  N 
side  of  Marshall-Petaluma  Rd.  near  Soulajoule  Reservoir 
(NE  6/23/82  — DS);  and  nest  in  depression  in  decrepit 
straw  mattress  in  abandoned  ranch  house,  Hicks  Valley 
(NY  5/16/82  -DS,  W&ST).  Birds  frequented  the  sea 
cliffs  north  of  Slide  Ranch  (south  of  Stinson  Beach)  in  the 
nesting  season,  but  because  access  is  difficult,  observers 
did  not  confirm  breeding  there. 

Historical  Trends/  Population  Threats 

It  seems  likely  that  Rock  Doves  evolved  in  arid  or  semiarid 
and  nearly  treeless  regions  of  Eurasia  (Goodwin  1983), 
though  the  original  distribution  is  obscure  because  of  the 
long  history  of  human  domestication  of  the  species  for 
food,  homing  pigeons,  and  breeding  of  fancy  varieties 
(Cramp  1985);  these  were  apparendy  the  very  first  domes- 
tic birds.   Many  have  become  feral,  especially  in  urban 


Pigeons  and  Doves 


SPECIES  ACCOUNTS 


Pigeons  and  Doves 


areas,  and  these  populations  are  still  augmented  by  escaped 
birds.  In  the  Old  World,  Rock  Doves  spread  widely  into 
many  areas  in  response  to  the  creation  of  suitable  feeding 
grounds  from  agricultural  and  tree-cutting  activities  (Good- 
win 1983).  Domestic  Rock  Doves  were  brought  to  the  New 
World,  to  Nova  Scotia,  as  early  as  1 606,  and  later  to  other 
colonies  along  the  eastern  seaboard  (Schorger  1952). 
Though  they  are  now  widespread  (AOU  1983),  the  expan- 
sion of  feral  pigeons  in  North  America  appears  to  have 
been  little  documented. 

Mailliard  (1900)  and  Stephens  and  Pringle  (1933),  for 
Marin  County,  and  Grinnell  and  Wythe  (1927),  for  the 
San  Francisco  Bay  Area,  did  not  list  the  Rock  Dove  at  all 
in  their  avifaunal  summaries.  It  seems  likely  that  Rock 
Doves  occurred  in  these  areas  at  the  time  but  went  un- 
reported because  of  their  domestic  origins.  Little  additional 


attention  has  been  paid  to  these  feral  homesteaders.  Grin- 
nell and  Miller  (1944)  gave  only  a  skeletal  account  for  this 
introduced  species  in  California.  They  reported  it  "estab- 
lished in  a  free-living  state  about  many  cities."  They  did  not 
mention  its  status  in  agricultural  areas,  its  history  of  expan- 
sion, or  the  limits  of  its  distribution  at  that  time.  A 
thorough  search  of  historical  archives  would  likely  reveal 
the  introduction  of  domestic  pigeons  to  California  at  the 
time  of  Spanish  missionaries  or  by  enthusiasts  during  the 
Gold  Rush.  Rock  Doves  are  now  established  throughout 
most  settled  and  agricultural  areas  of  California  (McCaskie 
et  al.  1979,  Garrett  <Sl  Dunn  1981).  Breeding  Bird  Surveys 
indicated  that  Rock  Dove  populations  were  still  increasing 
in  the  Central  Valley  from  1 968  to  1 979  (Robbins  et  al. 
1986)  and  in  California  as  a  whole  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


BAND-TAILED  PIGEON    Columba  fasciata 


A  year-round  resident;  numbers  can 

-W                \                          A^V, 

swell  gready  in  winter  (mosdy  Sep-Mar) 

y3r^Op;\0v 

but  are  quite  variable  then  from  year  to 

K^^X^^^K^,' 

year. 

Y-- — \  0 ^V\    -jt<<\    J*r\   ^V^A    y<^   \ 

A  fairly  common,  fairly  widespread 

breeder;  overall  breeding  population  of 

^^<\3><v\v 

<\^K\\^k^\^\\A. 

moderate  size. 

V\v5« 

Recorded  in  117  (52.9%)  of  221 

\\\°\ 

blocks. 

A  o  \>\  •■vca  P'V-'A  o  V-^A-'P  \^\J>-)*^\  '-QA 

„ 

V>\e  V>t-Q.\>>t« \>)f  o  \>T opa.e  l^<\ — 

— "T 

Ao\>a<\^Aov4«  \>Ao  v-"A  «  \>^\-vy 

O    Possible        =      83  (71%) 

'Oo 

v  O    ?    r-\ 

©    Probable      =      29  (25%) 

*j?&5P?*      ^~<_®>^oAj^p.\^^oAA<A  •V%A 

\<:d> 

•    Confirmed  =         5   (4%) 

^5 \^\o\^^^^?^\  o V-Ao^ 

I   U- 

^^^of^^k^W 

• 

FSAR  =  3        OPI  =  351         CI  =  1.33 

Ecological  Requirements 

This  gregarious  wild  pigeon  lives  in  Marin  County  s  coni- 
fer, mixed  conifer,  and  broadleaved  evergreen  forests  d^at 
provide  ample  mast,  berry,  and  small  fruit  crops.  Appar- 
endy  the  best  Band-tailed  Pigeon  habitat  is  forest  land  well 
interspersed  with  various  age  classes  of  trees  and  with 
openings;  oaks  are  of  particular  importance  in  California 
(Jeffrey  et  al.  1977).  The  birds  usually  nest  as  isolated  pairs, 
frequendy  near  permanent  streams.  Rarely  (diough  appar- 
endy  not  in  California),  they  breed  in  small,  loose  colonies; 
as  many  as  1 7  nests  have  been  found  in  a  single  tree  (Bent 
1932,  Neff  1947).  Band-tails  have  nested  in  some  part  of 


their  breeding  range  in  every  month  of  the  year,  but 
breeding  may  (Gutierrez  et  al.  1975)  or  may  not  (Michael 
1928)  be  a  response  to  abundant  mast  or  berry  crops. 

Band-tailed  Pigeons  nest  in  a  variety  of  trees  or  large 
bushes,  and  their  nest  heights  range  from  6  to  180  feet 
(most  15-40  ft.)  above  ground  (Grinnell  et  al.  1918,  Neff 
1947,  Glover  1953b,  MacGregor  &  Smith  1955,  Peeters 
1962,  Jeffrey  et  al.  1977).  A  sample  of  33  nests  in  the 
Carmel  area  of  Monterey  County  ranged  from  1 2  to  95  feet 
(av.  36  ft.)  above  ground  (MacGregor  &.  Smith  1955). 
Rarely,  these  pigeons  place  nests  on  the  top  of  a  stump,  on 


205 


Pigeons  and  Doves 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Pigeons  and  Doves 


the  ground,  or  in  blowholes  and  on  ledges  in  sandstone 
rimrock  (Neff  1947);  apparendy  no  such  records  pertain  to 
California.  Most  nests  in  coastal  California  are  in  conifers, 
oaks,  alders,  and  occasionally  in  tall  bushes,  such  as  blue 
blossom  (Ceanolhus  thyrsi florus),  or  introduced  trees  near 
human  habitation.  Nests  are  usually  placed  in  a  fork, 
against  a  trunk,  at  variable  distances  out  on  a  horizontal 
limb,  or,  infrequently,  in  dense  branches.  Tree  nests  are 
flimsy  platforms  constructed  of  dead  coarse  twigs  of  oaks, 
conifers,  or  other  plant  stems  and  forest  litter  (rarely,  they 
are  lined  with  pine  needles);  a  ground  nest  was  made  of 
leaves  and  moss.  Nest  trees  are  frequendy  on  a  slope  or 
adjacent  to  a  small  precipice  and  near  a  clearing,  leaving 
room  for  incubating  birds  to  exit  the  nest  with  a  momen- 
tum-gaining dive  (Neff  1947,  Peeters  1962). 

Band-tails  feed  singly  or  in  flocks  (even  in  the  breeding 
season)  and  procure  most  of  their  food  by  plucking  and 
gleaning  from  trees  and  shrubs  and  by  gleaning  from  the 
ground.  Birds  searching  in  forest  duff  flip  aside  leaves  and 
debris  with  horizontal  movements  of  the  bill  (Smith  1968). 
Feeding  flocks  advance  through  the  trees  or  across  open 
ground  by  the  progressive  movement  of  individuals  flying 
from  the  back  of  the  flock  to  the  front  (Peeters  1962). 
Band-tails  perform  acrobatics  while  feeding  in  trees:  they 
hang  vertically  by  their  feet  from  branches,  half  spreading 
their  wings  and  tails  to  stabilize  themselves  as  they  reach 
for  fruits  and  buds,  then  dropping  to  lower  branches  (Bent 
1932,  Peeters  1962). 

Band-tailed  Pigeons  are  almost  exclusively  vegetarians, 
specializing  on  mast,  small  wild  and  cultivated  fruits  and 
berries,  grains,  and  other  seeds;  the  few  insects  consumed 
appear  to  be  taken  incidentally.  Band-tails  tend  to  concen- 
trate on  abundant  food  sources  to  the  exclusion  of  other 
available  items,  and  their  diet  varies  considerably  with 
season  and  locality  (Neff  1947,  Smith  1968,  Jeffrey  et  al. 
1977,  Grenfell  et  al.  1980).  In  California,  acorns  (espe- 
cially of  live  oaks),  consumed  whole,  are  the  staple  of  their 
diet  from  fall  through  spring,  when  they  are  supplemented 
by  wild  fruits,  such  as  madrone  and  toyon,  and  cultivated 
grains.  Band-tails  tend  to  select  the  smaller  of  available 
acorns,  particularly  with  respect  to  width  and  weight  (Fry 
1977).  In  spring,  terminal  buds,  tender  young  leaves,  and 
blossoms  of  oaks,  madrone,  and  manzanita  take  on 
increasing  importance.  In  summer  and  fall,  fruits  and 
berries  become  prominent  dietary  items.  Important  ones 
in  California  include  elderberry,  blackberry,  raspberry, 
wild  cherry  and  grape,  dogwood,  coffeeberry,  salmonberry, 
thimbleberry,  huckleberry,  salal,  chokecherry,  and  cascara. 
Cultivated  grains,  such  as  wheat,  oats,  and  barley,  are  taken 
when  sown  in  late  winter  and  early  spring,  but  particularly 
in  summer  and  fall,  when  gleaned  from  stubble  fields  after 
harvest.  Orchards  supply  buds,  blossoms,  and  green  fruit 
in  spring  and  ripe  fruits  from  spring  through  fall;  plum, 
prune,  apricot,  peach,  cherry,  and  almond  orchards  and 


vineyards  are  die  favorites  in  California.  Crop  damage 
caused  by  the  pigeons  is  most  severe  in  spring  and  early 
summer,  when  wild  staples  are  scarce;  locally,  cultivated 
grains  then  may  be  die  predominant  item  in  the  diet 
(Smith  1968,  Grenfell  et  al.  1980).  Band-tails  will  also 
readily  "clean  out"  grain  from  bird  feeders.  Infrequently, 
they  eat  seeds  of  alders,  pines,  grasses,  forbs,  and  galls. 

For  the  first  few  days  of  life,  adults  feed  the  young 
exclusively  "pigeon's  milk,"  a  fatty,  yellow  curdlike  sub- 
stance produced  in  glands  of  the  adult's  crop.  Regurgita- 
tions from  the  parents'  crops  contain  progressively  more 
berries  and  seeds  until  the  food  of  the  young  is  nearly 
identical  to  diat  of  adults  (Neff  1947,  MacGregor  &  Smith 
1955,  Jeffrey  et  al.  1977).  Band-tails  collect  grit  to  help 
grind  food  and  perhaps  for  its  mineral  content,  and  they 
need  fresh  water  daily  (Smith  1 968).  They  frequendy  ingest 
mineral  salts  from  upland  deposits,  estuarine  borders,  and 
the  water  of  mineral  springs.  It  has  been  suggested  that  the 
minerals  may  aid  in  digestion  of  mast  (Smith  1 968)  or  that 
they  are  a  supply  of  calcium  necessary  for  egg  formation 
and  crop  gland  function  (March  ck  Sadlier  1972). 

Marin  Breeding  Distribution 

The  only  previously  published  nesting  record  from  Marin 
County  was  of  a  nest  found  at  Lagunitas  on  30  July  1912 
(Mailliard  1912).  During  the  adas  period,  the  distribution 
of  nesting  Band-tails  in  Marin  closely  approximated  the 
distribution  of  conifer  and  dense  mixed  evergreen  forest. 
A  representative  nesting  location  was  Upland  Ave.,  Mill 
Valley  (NE  summer  1980  or  1981  -KY). 

Historical  Trends/Population  Threats 

Unrestricted  sport  and  market  hunting  in  the  past,  particu- 
larly early  in  this  century,  led  to  a  decline  in  the  species  and 
an  outcry  for  legal  protection  (Chambers  1912,  Grinnell 
1913,  Grinnell  et  al.  1918).  In  the  winter  of  1911-12, 
diere  was  intense  shooting  at  Band-tailed  Pigeon  concen- 
trations in  southern  California.  One  hunter  alone  shipped 
2000  birds  to  San  Francisco  and  Los  Angeles  hotels,  and 
a  single  trainload  of  some  100  "enthusiasts"  shot  an 
estimated  3000+  birds  per  day  (Chambers  191 2).  A  closed 
season  was  in  effect  in  California  from  1913  to  1932,  and 
die  fortunes  of  the  pigeons  rose  accordingly  (G&.M  1944, 
Neff  1947,  Smith  1968,  Jeffrey  et  al.  1977).  Numbers  of 
Band-tailed  Pigeons  detected  on  Breeding  Bird  Surveys  in 
California  were  relatively  stable  from  1968  to  1989  but 
decreased  from  1980  to  1989  (USFWS  unpubl.  analyses). 
Clear-cutting  has  destroyed  vast  expanses  of  suitable 
breeding  habitat:  this  species  nests  only  in  forests  at  least 
20  years  old  (Glover  1953b).  Although  favored  berry-  and 
fruit-producing  trees  and  shrubs  are  abundant  in  the  early 
stages  of  forest  regeneration  after  logging  or  fire,  these  are 
often  eliminated  by  herbicide  spraying  that  targets  broad- 
leaved  species  and  favors  conifers  (Grenfell  et  al.  1980). 


206 


Pigeons  and  Doves 


SPECIES  ACCOUNTS 


Pigeons  and  Doves 


MOURNING  DOVE   Zenaida  macroura 


A  year-round  resident;  numbers 

nA^vpj^^T0 >^\ ® jv^to V A  «  \3A©x>-Y©  \££v,  y 

depressed  somewhat  (at  least  on  Pt. 

Reyes)  from  Oct  through  mid-Mar. 
A  common,  nearly  ubiquitous  breeder; 

^V^V  °i^\  •  3r^\  °  A^v D ;  WVo  Y>A©  V>V©  \5!M. 

overall  breeding  population  very  large. 

\<CvwN  A.  •  J^X  •  .V'x  •  V-^V  ©  Y-<^X      V<TA -•€►  V^CoX^---^ 
VS2k2tw ®A<r\ ®V^T\ '°J^\ ,» jp^^^v o \>r\  o  J 

Recorded  in  212  (95.9%)  of  221 

blocks. 

V5©ve^*3c^®Jv^®A^^°V^\    Y>-\©YJ>n. 

XV^H  3A^VA  ®  Jv<\  ®  V3A  o  Y^\  o  \^\  ©  \J>vr©  \ 

Yy°  ^*<\^s \>\ © wv^v>\o y>-\  o \ /Voi\>h-s. 

O    Possible        =       71    (33%) 
C    Probable       =     101    (48%) 

^W\^^^ 

•    Confirmed  =       40   (19%) 

L^WoJkVf  o  \>\  ©  Y-^v0  ^^A^^S^A©  WA  •x- 

•H^ka**^ — ^-5  J^x •  Jv<\ o  Y'^©  A^Ao  V>^\  •  \J<: 

v  •  7  ^ 

J%*A  >2^        ^"<--0^\  cJr<\  °  Jf-^TX  °3r<\  •  A%L\ 

IT                 ^^^^^A^V^ 

V</& 

FSAR  =  4        OPI  =  848        CI  =  1.85 

!>*                    xl/  ^-4<^<g5 

Ecological  Requirements 

These  fast-flying,  graceful  doves  are  edge  adapted.  They 
forage  in  open  country— grassland,  pastureland,  weed 
fields,  croplands,  roadside  edges  and  ditches,  and  subur- 
ban yards  and  parks— and  seek  shelter  and  nesting  sites  in 
forest  and  woodland  edges  and  woodlots.  Although  they 
may  nest  on  the  open  edges  of  almost  any  of  Marin's 
wooded  habitats,  they  are  most  frequendy  found  in  oak 
woodlands,  suburban  plantings,  riparian  woodlands,  and 
planted  woodlots  or  windbreaks  (particularly  eucalyptus). 

Mourning  Doves  build  loose  nest  platforms  of  twigs, 
roodets,  and  grass  stems.  They  usually  place  them  on  a 
horizontal  branch  or  in  crotches  of  limbs.  Nests  range  up 
to  40  feet  high  in  trees,  but  most  are  about  10  feet  above 
the  ground.  Birds  also  construct  nests  on  the  ground,  in 
low  bushes,  in  piles  of  bark,  on  shelves  on  cut  banks,  in 
used  nests  of  other  birds,  and  on  wooden  ledges  of  human 
structures  (Bent  1932,  Cowan  1952).  Pairs  usually  nest 
solitarily.  Nests  may  be  grouped  in  close  proximity  in 
limited  favored  nesting  areas  in  open  country— for  example, 
in  isolated  woodlots  or  windbreaks  in  expansive  grass- 
lands. 

Mourning  Doves  feed  almost  entirely  by  pecking  from 
the  ground  and  only  very  rarely  feed  in  trees.  During 
breeding,  foraging  birds  occur  singly  or  in  small  flocks. 
The  diet  is  almost  exclusively  grains  (Browning  1962).  A 
few  insects  are  taken  only  incidentally,  and  small  amounts 
of  snail  shells  and  bone  fragments  perhaps  satisfy  a  physio- 
logical need  of  nesting  birds  for  calcium.  These  latter  items 
might  also  be  a  source  of  grit  or  may  be  mistaken  for  seeds 


(Grenfell  et  al.  1980).  Year  round  in  California,  seeds  of 
162  species  of  plants  make  up  99.9%  of  the  diet— 22  are 
principal  food  items  that  account  for  10%  of  the  total  food 
in  any  month  or  region  (Browning  1962,  n=1016). 
Mourning  Doves  obtain  about  two-thirds  of  their  seeds 
from  annual  weeds  and  the  remainder  from  cultivated 
grains.  The  diet  varies  somewhat  with  season  and  locality 
(Browning  1959,  1962).  In  the  inner  Coast  Range  of  San 
Luis  Obispo  County,  Mourning  Doves  use  55  species  of 
plants,  of  which  10  are  principal  food  items  (n  =  183). 
Early  maturing  annuals,  such  as  buckthorn  weed,  red 
maids,  miners  lettuce,  and  California  poppy,  constitute 
about  70%  of  the  April  and  May  diet  and  together  with 
Napa  thisde  and  prostrate  pigweed  provide  over  75%  of 
the  June  and  July  diet.  Turkey  mullein  is  the  most  import- 
ant item  in  late  summer  and  early  fall.  Cultivated  wheat 
and  barley  and,  secondarily,  milo  are  most  important  from 
late  fall  through  winter,  when  they  are  taken  as  waste  grain 
from  fields  after  harvest.  Other  important  annuals  in  the 
area  are  sunflower,  hydra  stickleaf,  popcorn  flowers,  vine- 
gar weed,  vetch,  filaree,  phacelia,  valley  spurge,  bur  clover, 
and  lambs  quarters.  Mourning  Doves  also  take  advantage 
of  birdseed  spread  on  die  ground  or  at  feeders. 

As  with  other  members  of  the  pigeon  and  dove  family, 
Mourning  Doves  initially  feed  their  nestlings  mostly 
"dove's  (pigeon's)  milk."  At  the  age  of  1  to  3  days,  the 
young  are  fed  75%-90%  dove's  milk,  but  by  4  to  12  days, 
only  25%.  Then  regurgitated  seeds  form  a  progressively 
larger  fraction  of  their  diet  (Browning  1959). 

207 


Pigeons  and  Doves 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Pigeons  and  Doves 


Marin  Breeding  Distribution 

The  Mourning  Dove  was  one  of  Marin  County  s  most 
widespread  breeding  birds.  It  reached  its  greatest  abun- 
dance in  lowland  valleys  of  ranch  and  crop  lands  through- 
out the  county  and  in  suburban  areas  along  die  Highway 
101  corridor  in  eastern  Marin.  Representative  nesting 
locales  were  the  long  eucalyptus  grove  SE  of  Abbott's 
Lagoon  (NE  6/20/82  — DS);  S  side  of  Nicasio  Reservoir 
(NE  on  shelf  on  road  cut  7/6/82  -DS);  Mt.  Burdell, 
Novate  (NB-NE-NY  4/9-5/1/81  -DS);  and  Dominican 
College,  San  Rafael  (NB  3/28/79  -DS).  At  the  Abbott's 
Lagoon  eucalyptus  grove,  six  nests  were  found  in  less  than 
a  half-hour's  search  of  a  stretch  of  100  to  200  yards  (four 
were  1.5-4  ft.  above  the  ground  in  stick  and  bark  litter). 


Historical  Trends/  Population  Threats 

In  the  early  part  of  this  century,  there  was  limited  evidence 
of  local  population  declines  in  California  (Grinnell  et  al. 
1918).  Mourning  Doves  appear  to  have  increased  greatly 
since  that  time,  aided  by  human  activities,  such  as  cultiva- 
tion, grazing,  and  ditch  and  roadside  clearing,  that  have 
enhanced  their  food  supply  and  created  more  of  the  dis- 
turbed areas  they  prefer  for  foraging  (Grenfell  et  al.  1980). 
Although  some  of  their  habitat  is  currendy  being  lost  to 
increased  herbicide  use,  clean  farming,  and  urbanization, 
Mourning  Doves  adapt  by  exploiting  recendy  cleared  for- 
ests and  new  residential  developments.  Nevertheless, 
Mourning  Dove  numbers  decreased  on  Breeding  Bird 
Survey  routes  in  California  from  1968  to  1989  (USFWS 
unpubl.  analyses). 


>*A^*toO    I 


Band-tailed  Pigeons  perform  acrobatics  that  enable  them  to  gobble  up 
berries  from  dangling  clusters.    Drawing  fry  Keith  Hansen,  1 989. 


208 


Roadrunners 


SPECIES  ACCOUNTS 


Roadr 


Roadrunners 

Family  Cuculidae 


GREATER  ROADRUNNER   Geococcyx  califomianus 


Formerly  a  year-round  resident;  extirpated  by  at  least  the  1960s. 


Ecological  Requirements 

This  legendary  ground-dwelling  cuckoo  inhabits  arid  open 
land  with  scattered  brush  and  thickets,  which  in  coastal 
northern  California  consists  primarily  of  the  interface 
between  broken  chaparral  and  oak  savannah  woodlands  or 
grasslands.  Historically,  fires  have  probably  done  much  to 
maintain  this  habitat  mix.  Roadrunners  build  bulky  nest 
platforms  of  loosely  interlaced  sticks  and  twigs,  lined  (or 
not)  with  finer  miscellany  such  as  manure  flakes,  bark 
strips,  grass  tufts,  leaves,  roots,  feathers,  or  snakeskin 
(Bryant  1916,  Dawson  1923,  Bent  1940).  They  usually 
place  their  nests  about  3  to  10  feet  above  the  ground  in 
clumps  or  thickets  of  thorny  shrubs  (or  cactus  in  other 
regions).  Rarely,  they  locate  them  up  to  20  feet  above  the 
ground  in  a  tree,  direcdy  on  die  ground,  in  a  cranny  of  a 
cliff,  or  on  an  artificial  structure  (Bryant  1916,  Dawson 
1923,  Bent  1940).  The  birds  situate  their  nests  to  receive 
full  sun  in  the  early  morning  hours,  when  adults  are  off 
hunting  lizards,  and  partial  shade  in  the  heat  of  the  day 
(Ohmart  1973). 

Roadrunners  usually  forage  on  the  ground  by  slowly 
stalking  their  prey,  then  making  a  short  dash  to  finalize  the 
capture.  They  also  chase  down  mobile  prey,  jump  up  and 
snatch  insects  from  the  air,  or  glean  insects  from  bushes, 
from  the  ground,  or  by  climbing  into  shrubs  (Bryant  1916, 
Bent  1940).  In  southern  California,  the  diet  of  adults  is 
90%  animal  matter  (by  volume)  and  10%  fruit  and  seeds 
(Bryant  1916,  n  =  64).  In  the  summer  months,  Roadrun- 
ners eat  an  even  greater  percentage  of  animal  fare,  consist- 
ing largely  of  insects,  especially  grasshoppers,  crickets,  and 
beedes,  with  lesser  numbers  of  caterpillars,  true  bugs,  flies, 
ants,  bees,  wasps,  and  scorpions.  Vertebrates,  including 
lizards,  small  birds,  and  small  mammals,  make  up  only 
about  10%  (by  volume)  of  the  total  diet  (Bryant  1916); 
birds  are  probably  taken  to  a  greater  degree  in  winter  when 
cold-blooded  prey  are  inactive  (Zimmerman  1970).  Snakes 
also  are  eaten  (Bent  1940,  Ohmart  1973).  Even  though  the 
young  are  initially  fed  insects,  by  die  time  they  are  five  to 
six  days  old  they  are  fed  mosdy  lizards.  Through  most  of 


the  nesding  period,  young  are  also  fed  a  clear  viscous  liquid 
by  regurgitation  (Ohmart  1973).  Eggs  hatch  asynchro- 
nously, and  adults  and  young  are  occasionally  cannibalistic 
on  the  smallest  young  in  their  nests.  Females  also  lay  larger 
clutches  when  prey  are  more  available,  for  example  during 
the  rainy  season  in  Arizona.  These  observations  suggest 
that  Roadrunners  are  adapted  to  a  limited  or  irregular  food 
supply  (Ohmart  1973). 

Marin  Breeding  Distribution/ 
Historical  Trends/Population  Threats 

Roadrunners  formerly  lived  in  Marin  County  in  small 
numbers  (Mailliard  1900,  S&T  1933)  and  undoubtedly 
bred  here,  though  there  is  no  documentation.  The  last 
reported  sightings  were  at  Homestead,  Locust  Station,  Mill 
Valley,  on  22  April  1939  (Gull  21,  No.  5);  at  San  Rafael 
Hill  on  24  February  1941  (Gull  23,  No.  3);  and  on  Mount 
Tamalpais  sometime  in  the  1950s  (JW). 

Grinnell  and  Miller  (1944)  noted  declines  or  local 
extirpation  from  areas  throughout  California  that  had  been 
thickly  settled  or  heavily  hunted.  Roadrunners  were  widely 
persecuted  at  one  time  because  (based  on  limited  evidence) 
they  were  thought  to  prey  heavily  on  the  eggs  and  young  of 
quail  (Bryant  1916).  Grinnell  and  Wythe  (1927)  noted  a 
trend  of  increasing  rarity  of  this  species  in  the  San  Fran- 
cisco Bay  Area  that  has  continued  to  this  day,  with  Road- 
runners now  persisting  in  small  numbers  only  in  the 
hinterlands  of  the  region.  This  decline  has  followed  the 
intense  development,  habitat  alteration,  and  disturbance 
attending  a  rapidly  expanding  human  population.  Verner 
et  al.  (1980)  speculated  that  numbers  in  the  Sierra  foothills 
may  have  declined  as  chaparral-type  habitats  grew  increas- 
ingly dense  after  decades  of  fire  suppression  activities. 
Numbers  of  Roadrunners  were  relatively  stable  on  Breed- 
ing Bird  Surveys  in  California  from  1968  to  1989  but 
decreased  from  1980  to  1989  (USFWS  unpubl.  analyses); 
this  likely  reflects  trends  largely  in  soudiern  California, 
where  the  species  is  most  numerous. 


209 


Barn  Ou'ls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Barn  Owls 


Barn  Owls 

Family  Tytonidae 


BARN  OWL   Tytoalba 


A  year-round  resident. 

J~^\\ 3rt^\^>^x 

>^           \ 

An  uncommon,  local  breeder;  overall 

^C\0F^ 

Xi^"-  " 

breeding  population  very  small. 

Recorded  in  34  (15.4%)  of  221  blocks. 

^*\*><r\    V 

?P\vk 

O    Possible        =       19   (56%) 
€    Probable       =         5   (15%) 

Vy^rs 

Vt:^°A^\Jk£^5* 

?\**^r\~~*  /v^x" 

•    Confirmed  =       10  (29%) 

T^r 

vCA^T^V' 

—  i- 

FSAR  =  2        OPI  =  68         CI  =  1.74 

r/\J^ry 

kL-^y       \^-^\       \  ^4^ 

'*3rC^rr\^>~'v- 

VY^^ 

V^Vx^r 

r^a 

J  >^2z> 

~\^?y 

Ecological  Requirements 

The  whitish,  ghosdike  silhouette  and  eerie  screeching  calls 
of  this  monkey-faced  owl  of  subtropical  and  tropical  origins 
enlivens  the  darkness  in  a  number  of  Marin  County  s 
open  habitats.  Barn  Owls  hunt  in  open  ranchlands,  grass- 
lands, broken  woodland  and  brushland,  weedy  fields,  and 
marshes.  They  nest  nearby  in  a  wide  variety  of  artificial  and 
natural  sites  in  wild,  rural,  or  urban  settings.  Pairs  usually 
nest  solitarily,  but  nest  sites  are  often  limiting  (Bloom 
1979)  and  birds  sometimes  nest  in  loose  colonies  at 
particularly  attractive  sites  (Smith  et  al.  1974).  Nest  sites 
provide  a  roof  and  usually  at  least  a  modicum  of,  if  not 
pitch,  darkness.  Natural  nest  sites  include  clefts,  holes, 
grottoes,  and  caves  of  rock  cliffs,  quarries,  or  mines; 
natural  cavities  or  ground  squirrel  holes  in  earthen  banks, 
roadcuts,  or  gullies;  deserted  badger  burrows;  and  hollows 
of  trees  (Bent  1938,  Johnsgard  1988,  Voous  1988).  In 
some  areas  where  the  earthen  substrate  is  soft,  Barn  Owls 
perform  much  excavation  themselves,  using  their  feet 
(Johnsgard  1988).  Though  tree  nests  are  becoming  less 
numerous,  Barn  Owls  still  nest  in  cavities  of  sycamores 
and  live  oaks  in  California  (Bloom  1 979).  Entrances  to  tree 
cavides  in  California  range  from  5  to  16  feet  above  the 
ground,  and  the  height  of  actual  nest  sites  varies  from 

210 


ground  level  to  about  40  feet.  Unlike  some  large  owls, 
Barns  do  not  use  abandoned  nests  of  diurnal  raptors,  but 
on  rare  occasions  they  use  deserted  crow  nests  in  Califor- 
nia (Bent  1938,  Voous  1988).  Holes  in  cliffs  and  banks 
may  have  been  the  original  nest  sites,  as  the  pale  Barn  Owl 
plumage  blends  well  with  sandstone  cliffs  and  caves 
(Voous  1988).  Also,  the  Barn  Owl's  elliptical  egg  seems 
better  adapted  to  the  flat  bottoms  of  cave  niches  (where  the 
round  eggs,  typically  laid  by  other  owls,  would  be  in 
constant  danger  of  rolling  off)  than  to  enclosed  tree  hol- 
lows. 

In  today's  civilized  surroundings,  most  Barn  Owls  nest 
in  lofts,  attics,  and  dark  recesses  of  human  structures,  such 
as  barns  and  farmhouses,  church  steeples,  derelict  build- 
ings and  sheds,  large  industrial  plants,  old  deep  wells, 
mine  shafts,  water  pipes,  windmills,  discarded  agricultural 
machinery,  and  haystacks  both  inside  and  outside  of  barns 
(Bent  1938,  Bloom  1979,  Johnsgard  1988,  Voous  1988). 
Rarely,  they  will  nest  in  an  exposed,  unprotected  situation, 
such  as  the  flat  roof  of  an  occupied  dwelling.  Barn  Owls 
also  readily  nest  in  large  wooden  nest  boxes,  preferably 
placed  inside  barns,  cabins,  and  lofts.  Nests  inside  build- 
ings are  usually  close  to  a  ready  exit. 


Barn  Owls 


SPECIES  ACCOUNTS 


Barn  Owls 


Females  lay  their  eggs  in  a  crude  shallow  cup  formed 
among  dried  pellets  and  heaps  of  broken  bones  or  skull 
fragments,  right  on  top  of  the  hay  in  haylofts,  or  on  wood 
chips  or  other  natural  debris  in  tree  cavities  (Bent  1938, 
Johnsgard  1988,  Voous  1988).  Favorable  nest  sites  may  be 
used  for  many  successive  years  by  the  same  or  different 
pairs.  Birds  laying  second  clutches  may  deposit  them  in  the 
same  site  as  the  first  clutch,  or  they  may  choose  a  new  site. 
Day  roosts  may  be  at  nest  sites,  similar  cavities  or  struc- 
tures, or  in  the  thick  foliage  of  trees  (including  palms). 

Barn  Owls  are  highly  nocturnal.  They  hide  by  day  and 
typically  become  active  and  start  hunting  well  after  sunset 
and  retire  before  dawn  (Voous  1988).  Observations  of 
daytime  hunting  are  rare  and  probably  reflect  unusual 
circumstances,  such  as  a  previous  night  of  poor  hunting 
because  of  inclement  weather.  Barn  Owls  are  very  versatile 
rodent  hunters.  With  their  acute  hearing,  they  can  strike 
and  capture  sound-producing  prey  in  complete  darkness 
(Johnsgard  1988,  Voous  1988).  Light,  graceful,  searching 
flights  carry  them  over  open  country,  where  they  bank, 
hover,  and  drop  to  the  ground  erratically  (Bent  1938, 
Voous  1988).  Barn  Owls  pursue  prey  on  foot  more  than 
most  owls  do.  To  a  limited  degree,  they  also  hunt  from 
roadside  poles  (Voous  1988),  drop  from  perches  into 
bushes  below  to  capture  roosting  sparrows,  and  catch  bats 
flying  out  of  caves  (Smith  et  al.  1 974).  Barn  Owls  that  bred 
at  Casde  Rock,  Del  Norte  County,  and  fed  extensively  on 
Leach's  Storm-Petrels  (Bonnot  1928)  must  also  have 
caught  them  on  the  wing.  Foraging  owls  range  about  0.6 
to  1.9  miles  from  nest  and  roost  sites  (Johnsgard  1988, 
Voous  1988). 

Barn  Owls  are  restricted,  rather  than  generalist,  feeders 
like  Great  Horned  Owls  and  prey  primarily  on  small 
terrestrial  rodents  of  field  and  marsh  (Voous  1988).  When 
alternative  food  items  are  available,  shrews  rather  than 
birds  (at  least  in  Europe)  are  usually  the  main  prey.  This 
differs  from  Long-eared  and  Short-eared  owls  and  most 
other  rodent-hunting  species,  whose  secondary  prey  is 
birds.  The  North  American  diet  varies  by  prey  numbers 
from  1 00%  down  to  70%  mammals— mosdy  meadow  voles 
and  deer  mice— with  birds  and  large  insects  making  up 
most  of  the  balance  (Voous  1988).  Mammal  prey  range 
from  a  wide  variety  of  small  terrestrial  rodents  to  pocket 
gophers,  ground  squirrels,  moles,  muskrats,  jackrabbits, 
and  skunks  (Bent  1938).  Bird  prey  in  North  America  are 
mostly  small  songbirds  but  include  rails,  shorebirds, 
Coots,  and  Green-backed  Herons,  documenting  that  these 
owls  do  hunt  over  wet  grasslands  and  marsh.  Other 
vertebrate  prey  here  include  nocturnal  lizards,  turtles, 
frogs,  toads,  and  fish.  As  might  be  expected,  the  diet  varies 
geographically,  seasonally,  and  year  to  year,  depending  on 
prey  availability  (Marti  1974,  Voous  1988). 


In  California,  61%  of  prey  numbers  are  small  voles, 
37%  white-footed  mice,  0.2%  shrews,  and  0.5%  birds 
(Voous  1988),  but  another  analysis  showed  95%  mam- 
mals, 3%  birds,  2%  insects,  and  less  than  0.1%  reptiles 
and  amphibians  (Jaksic  et  al.  1982,  n  =  8236).  Mean 
weight  of  small  mammal  prey  in  California  is  2.4  ounces 
(Jaksic  et  al.  1982,  n  =  7827).  The  diet  of  Barn  Owls  in  the 
San  Francisco  Bay  Area  (including  Marin  County)  is  99% 
small  mammals  (96%  rodents).  Meadow  voles,  pocket 
gophers,  and  deer  mice  account  for  85%  of  the  total,  with 
the  balance  made  up  of  various  small  mice,  shrews,  small 
rabbits,  woodrats,  moles,  small  birds,  and  a  few  Jerusalem 
crickets  (Smith  ck  Hopkins  1937,  n  =  338). 

Barn  Owls  generally  eat  considerably  smaller  prey  by 
weight  than  coexisting  Great  Horned  Owls  (Marti  1974, 
Knight  &  Jackman  1984)  and  somewhat  larger  prey  than 
coexisting  Long-eared  Owls  (Marti  1974).  For  example,  in 
Colorado,  mean  prey  weight  is  1 .6  ounces  for  Barn  Owls, 
6.2  ounces  for  Great  Horned  Owls,  and  1.1  ounces  for 
Long-eared  Owls  (Marti  1974).  In  some  areas,  Barns  and 
Great  Horns  may  capture  prey  of  similar  average  weight, 
and  they  may  overlap  nearly  completely  in  their  food 
niches  (Knight  &  Jackman  1984).  Nonetheless,  foraging 
separation  occurs  between  the  species  (Rudolph  1978, 
Knight  6k  Jackman  1984).  Barn  Owls  are  more  nocturnal 
than  Great  Horns  and  can  occupy  more  extensively  open 
areas  because  they  forage  mosdy  on  the  wing  rather  than 
from  perches.  On  the  other  hand,  because  of  their  greater 
size  and  strength,  Great  Horns  generally  capture  a  wider 
range  of  prey.  Litde  is  known  of  the  dietary  differences 
between  male  and  female  Barn  Owls,  but  in  Italy  the  food 
taken  by  females  was  more  varied  in  species  and  size  than 
that  caught  by  males  (Voous  1988). 

Barn  Owls  are  prolific  breeders,  and  providing  food  for 
the  young  can  be  a  prodigious  accomplishment.  They  vary 
their  clutch  size  with  food  availability  and  sometimes  lay 
two  or  more  clutches  in  a  year  (Voous  1988).  Females 
begin  incubation  with  the  first  egg,  and  consequendy  the 
difference  in  size  between  siblings  is  as  large  as  or  larger 
than  for  other  owl  species  (Voous  1988).  Females  may 
begin  laying  the  second  clutch  before  the  youngest  owlets 
of  the  first  brood  have  fledged  (Johnsgard  1988).  Males 
feed  their  mates,  and  in  good  years  they  stockpile  food  at 
the  nest,  sometimes  even  before  the  eggs  are  laid  (Smith  et 
al.  1974,  Voous  1988).  When  the  eldest  nesdings  are 
about  three  to  four  weeks  old,  the  female  resumes  hunting, 
presumably  because  the  dark,  concealed  nest  site  allows 
her  to  leave  the  young  unprotected  for  periods  of  time 
(Voous  1988).  During  periods  of  food  shortage,  parents 
and  larger  young  will  eat  smaller  nesdings  that  behave 
abnormally  or  are  already  dead. 

211 


Barn  Ou>!s 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Barn  Owls 


Marin  Breeding  Distribution 

During  the  atlas  period,  Barn  Owls  bred  at  scattered  sites 
throughout  the  lowlands  of  Marin  County  in  bodi  rural 
and  urban-suburban  settings.  Representative  breeding 
locations  were  Lower  Pierce  Ranch,  Tomales  Point  (NY 
spring  1981  fide  JGE);  ranch  north  of  the  NW  corner  of 
Nicasio  Reservoir  (NY  7/24/82  -DS);  Willow  Ridge  Sta- 
bles, Point  Reyes  Station  (NY  6/4/81  -JGE);  Olema  (NY 
4/28/77  -RMS);  and  Rancho  Baulinas,  N  of  Bolinas 
Lagoon  (NE-NY  spring/summer  1977  &  1978  -JKip). 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  thought  that  Barn  Owls  had 
increased  historically  in  California  because  of  the  increase 
in  suitable  nesting  sites  and  the  "reduction  in  numbers  of 
owl-persecuting  falconids."  Numbers  might  also  have  been 
augmented  by  the  clearing  of  land  and  the  proliferation  of 
rodents  in  agricultural  areas.  Times  have  changed,  and, 
though  still  relatively  abundant  in  parts  of  California,  the 
species  has  declined  steadily  in  recent  years  because  of 


habitat  loss  from  suburban  and  industrial  developments 
(Bloom  1979).  Barn  Owls  are  now  also  virtually  nonexist- 
ent in  certain  intensively  cultivated  agricultural  areas  of  the 
Central  Valley.  Breeding  Bird  Surveys  indicated  that  Barn 
Owl  numbers  were  relatively  stable  in  California  from 
1968  to  1989  but  decreased  from  1980  to  1989  (USFWS 
unpubl.  analyses).  These  surveys  are  geared  toward  diurnal 
species,  limiting  their  usefulness  for  detecting  trends  in 
highly  nocturnal  species  like  the  Barn  Owl.  The  species 
was  on  the  Audubon  Society's  Blue  List  from  1972  to  1981 
and  on  their  list  of  Species  of  Special  Concern  since  1982 
(Tate  1981,  1986;  Tate  &  Tate  1982). 

Traffic  accidents  are  at  present  among  the  most  serious 
human-induced  mortality  factors,  as  is  readily  evident  from 
the  carcass-littered  roadsides  of  major  highways,  such  as 
Interstate  5  in  the  Central  Valley,  that  pass  through  prime 
Barn  Owl  country.  Cases  of  poisoning  by  mercury,  thal- 
lium, and  organic  biocides  and  thinning  of  eggshells  have 
been  recorded,  but  the  extent  of  the  threats  posed  to  Barn 
Owls  are  unknown  (Voous  1988,  Marti  &.  Marks  1989). 


212 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


Typical  Owls 

Family  Strigidae 


WESTERN  SCREECH-OWL  Otus  kennicottii 


A  year-round  resident. 

.r'OVV'Vx. 

^>><^^      \ 

A  fairly  common,  local  breeder;  overall 

\^r\        \^\  0^>-^*T;V^V~/~^T' 

breeding  population  very  small. 

C-W^V^V' 

Recorded  in  42  (19.0%)  of  221  blocks. 

\^5 

O    Possible        =       17   (40%) 
€    Probable       =       22   (52%) 
•    Confirmed  =         3   (7%) 

—  -r' 

FSAR  =  3        OPI  =  126        CI  =  1.67 

3r^\V\^c^\3Av~v 

h^a> 

x?ci 

Ecological  Requirements 

The  bouncing-ball-like  call  of  this  tiny  ear-tufted  owl  wafts 
softly  through  the  night  air  in  Marin  County's  oak  wood- 
lands and  open  broadleaved  evergreen  hardwood  forests 
where  there  is  little  understory.  Screech-Owls  are  absent 
from  Marin's  coastal  riparian  thickets,  but  further  study  is 
needed  to  determine  if  in  the  county's  interior  they  occupy 
the  limited  amounts  of  riparian  woodland,  an  important 
breeding  habitat  elsewhere  in  California's  lowlands 
(GckM  1944).  Screech-Owls  typically  nest  in  natural  cavi- 
ties of  trees  or  stubs  (elsewhere  also  saguaro  cactus);  old 
holes  of  large  woodpeckers,  such  as  Northern  Flickers;  and 
sometimes  nest  boxes  (Dawson  1923,  Bent  1938,  Johns- 
gard  1988,  Voous  1988),  even  those  meant  for  Wood 
Ducks  (S.  Simmons  pers.  comm.).  Birds  have  also  used  a 
bark-filled  crotch  of  a  eucalyptus  tree,  an  old  woodrat's 
nest,  Black-billed  Magpie  nests,  and  even  cliff  cavities 
(Dawson  1923,  Bent  1938).  Screech-Owls  sometimes  nest 
in  secluded  recesses  of  buildings.  Nests  range  from  about 
4  to  60  feet  above  the  ground,  but  most  are  at  moderate 
heights  (Dawson  1923,  Bent  1938,  Marti  &  Marks  1989). 
Nest  heights  probably  reflect  the  availability  of  suitable 
cavities  and  woodpecker  holes  rather  than  any  preference 


by  the  owls  for  particular  heights.  The  owls  do  not  make 
an  actual  nest  but  instead  lay  their  eggs  on  the  rotten  wood 
chips,  dead  leaves,  feathers,  castings,  or  other  debris  accu- 
mulated at  the  bottom  of  the  cavity  (Dawson  1923,  Bent 
1938). 

Screech-Owls  are  strictly  nocturnal  in  their  activities  and 
retreat  by  day  to  roost  in  thick  foliage,  close  against  the 
camouflaging  bark  of  trees,  in  tree  hollows,  in  old  build- 
ings, or  other  secluded  spots  (Bent  1938,  Johnsgard  1988, 
Voous  1988).  Little  has  been  observed  of  foraging  behav- 
ior. The  most  frequendy  used  hunting  technique  seems  to 
be  for  an  owl  to  swoop  down  from  a  perch  on  a  twig 
projecting  slighdy  from  the  foliage  or  beneath  the  canopy 
of  a  tree  to  capture  prey  on  bare  or  grassy  ground  (Voous 
1988).  Many  aspects  of  Screech-Owl  biology  are  poorly 
known,  but,  like  the  Eastern  Screech-Owl,  males  of  the 
Western  Screech-Owl  probably  bring  food  to  incubating 
and  brooding  females  and  sometimes  build  up  a  store  of 
food,  such  as  voles,  at  die  nest.  The  diet  of  Western 
Screech-Owls  consists  of  varying  amounts  of  insects  and 
other  arthropods,  small  birds,  small  mammals,  crayfish, 
fish,  and  occasionally  lizards,  snakes,  frogs,  and  salaman- 

213 


Typical  Owls 


MARIN  COUNTY  BRFHDING  BIRD  ATLAS 


Typical  Owls 


ders  (Bent  1938,  Johnsgard  1988,  Voous  1988).  Prey 
remains  from  nests  in  die  San  Joaquin  Valley  are  mostly 
small  mammals  and  birds,  along  wilh  some  fish  and 
crayfish  (S.  Simmons  pers.  comm.).  Reported  invertebrate 
prey  items  include  grasshoppers,  crickets,  locusts,  Jerusa- 
lem crickets,  mole  crickets,  walking  sticks,  praying  man- 
tids,  roaches,  sowbugs,  waterbugs,  large  moths, 
caterpillars,  cutworms,  beedes,  ants,  scorpions,  spiders, 
harvestmen,  and  centipedes.  Among  the  vertebrate  prey 
not  already  mentioned  are  voles,  pocket  gophers,  pocket 
mice,  deer  mice,  harvest  mice,  grasshopper  mice,  woodrats, 
kangaroo  rats,  shrews,  and  many  small  and  medium-sized 
birds  up  to  the  size  of  Northern  Flickers,  Steller's  Jays,  and 
American  Robins.  Screech-Owls  have  also  attacked  and 
sometimes  partially  eaten  Golden  Pheasants,  Ring-necked 
Pheasants,  Bantam  hens,  and  domestic  ducks.  Litde  is 
known  of  geographic  or  seasonal  changes  in  diet,  but  birds 
to  the  south  probably  consume  more  insects  and  other 
cold-blooded  prey,  and  birds  in  all  regions  probably  eat 
less  of  these  items  in  winter. 

Marin  Breeding  Distribution 

During  the  adas  period,  we  found  Screech-Owls  breeding 
primarily  in  the  eastern  and  north-central,  oak-dominated 
portions  of  Marin  County.  They  were  lacking  from  die 


grassland-dominated  areas  on  outer  Point  Reyes  and 
around  Tomales  and  from  most  of  the  moist  dense  coastal 
forests,  particularly  where  there  was  a  thick  understory. 
Representative  breeding  records  were  San  Anselmo  (NE  in 
attic  5/4/79);  Mill  Valley  (NY/FL  6/2/79);  and  Fairfax 
(FL  7/22/79).  All  these  confirmed  records  were  obtained 
years  after  the  fact  from  California  Center  for  Wildlife 
records  (S.  Hershon  in  litt.),  hence  the  locations  plotted  on 
the  atlas  map  are  only  approximate  and  observer  names  are 
lost  to  posterity. 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  felt  the  species  may  have 
increased  in  California  in  historical  times  from  the  "open- 
ing up"  of  heavy  forests.  On  the  other  hand,  many  logged 
areas  regrow  with  dense  brushy  understories  that  are 
unsuitable,  while  the  clearing  of  areas  of  hardwoods  for 
firewood,  agriculture,  or  development  must  have  had  det- 
rimental effects  on  the  species.  Further  urban-suburban 
development  is  likely  to  displace  some  of  these  owls, 
though  providing  nest  boxes  might  mitigate  the  loss  of 
some  habitat.  Pesticide  residues  have  caused  slight  eggshell 
thinning  in  wild  Screech-Owls,  but  these  pollutants  appar- 
endy  have  not  impaired  reproductive  success  (Marti  6k. 
Marks  1989). 


214 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


GREAT  HORNED  OWL   Bubo  virginianus 


A  year-round  resident. 

A  fairly  common,  widespread  breeder; 
overall  breeding  population  fairly  large. 

Recorded  in  149  (67.4%)  of  221 
blocks. 


O  Possible 
©  Probable 
W    Confirmed 


68  (46%) 
54  (36%) 
27  (18%) 


FSAR  =  3        OPI  =  447        CI  =  1.72 


Ecological  Requirements 

This  solemn,  ferocious  master  of  the  night  inhabits  the 
edges  of  all  Marin  County's  major  woodland  and  forest 
habitats,  as  well  as  planted  woodlots  and  windbreaks, 
where  they  border  on  open  tracts  of  grassland,  meadow, 
and  field.  Older  stands  of  trees  provide  more  potential  nest 
sites  and  also  offer  more  subcanopy  flying  room  because 
they  have  few  low  branches  (Johnsgard  1988).  Elsewhere, 
Great  Horned  Owls  also  occupy  extensive  treeless  areas 
with  cliffs  or  rock  outcrops  for  nesting  and  perches  from 
which  to  hunt  and  regions  ranging  from  boreal  to  tropical 
forests  and  deserts.  Habitat  preferences  for  a  species  that 
lives  over  such  a  broad  latitudinal  range  are  hard  to  define. 
The  main  requisites  seem  to  be  sheltered  nesting  and 
roosting  sites,  relatively  open  foraging  grounds  that  supply 
a  good  mammal  population,  and  suitable  elevated  hunting 
perches. 

Great  Horned  Owls  usually  lay  their  eggs  in  an  aban- 
doned nest  of  a  diurnal  raptor  (especially  Red-tailed 
Hawks)  in  trees  or  sometimes  cliffs;  various  species  of 
raptor  may  alternate  in  their  use  of  a  given  nest  (Bent  1938, 
Johnsgard  1988,  Voous  1988).  Crow,  raven,  magpie, 
heron,  or  squirrel  nests  will  also  do  as  platforms  for  Great 
Horned  Owl  eggs.  Other  suitable  nesting  sites  are  ledges 
or  caves  in  rocky  cliffs,  fissures  of  rocks,  niches  in  cut- 
banks,  rooms  in  Native  American  cliff  dwellings,  hollows 
in  tree  trunks  and  snags,  depressions  in  the  tops  of  old  or 
dead  trees,  crotches  in  trees  lacking  debris  or  nest  materi- 
als, a  box  in  a  tree  filled  with  leaves,  and  occasionally  lofts 
of  barns.  Rarely,  these  owls  have  nested  on  the  ground 
next  to  a  boulder  or  the  base  of  a  large  tree,  under  a  stump, 


in  a  hollow  log,  in  long  grass  near  a  windmill,  under 
bushes  in  the  desert,  and  in  an  old  Canada  Goose  nest  on 
a  tussock  of  grass  in  a  pond. 

Great  Horned  Owls  are  mainly  nocturnal  but  frequendy 
hunt  at  dawn  and  dusk  and  occasionally  during  the  day. 
They  usually  swoop  down  silendy  on  their  prey  from  an 
elevated  perch  in  a  direct,  low,  rapid  flight  (Marti  1974, 
Rudolph  1978).  Typical  perches  include  tall  trees,  tele- 
phone poles  and  wires,  rock  outcrops,  and  fence  posts. 
Sometimes  Great  Horns  hunt  in  harrierlike  flights  or  catch 
bats  in  the  air  as  they  emerge  from  caves  (Marti  1974). 
These  owls  also  make  night  raids  on  the  nests  of  other 
owls,  hawks,  and  crows,  and  snatch  crows  from  their  night 
roosts  (Voous  1988). 

Great  Horned  Owls  are  generalized  and  opportunistic 
predators  and  feed  on  a  wider  range  of  prey  than  is  known 
for  any  odier  owl  or  bird  of  prey  in  North  or  South 
America  (Voous  1 988).  A  complete  listing  of  all  the  prey 
eaten  is  not  necessary,  but  about  77.6%  of  prey  numbers 
in  North  America  are  mammals,  6.1%  birds,  1.6%  other 
vertebrates,  and  the  balance  insects,  spiders,  scorpions, 
crabs,  and  other  invertebrates  (Voous  1988).  Great  Horns 
will  also  feed  on  carrion  or  trapped  fur-bearing  mammals, 
particularly  in  winter.  Their  largest  prey  are  mammals  like 
muskrats,  porcupines,  skunks,  and  foxes,  and  birds  the 
size  of  grouse,  pheasants,  domestic  poultry,  ducks,  geese, 
swans,  herons,  and  gulls.  Great  Horns  prey  on  a  variety  of 
diurnal  raptors  at  least  as  large  as  Red-tailed  Hawks  and  on 
just  about  any  species  of  owl  they  encounter.  In  semiarid 
regions  of  California,  die  percentages  of  important  prey  (by 

215 


Typical  Owls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Owls 


numbers)  are  76.6%  mammals,  15%  insects  (especially 
Jerusalem  crickets),  42%  birds,  1 .6%  reptiles,  1 .8%  arach- 
nids, and  0.8%  amphibians  (Jaksic  &  Marti  1984,  n  = 
2235  prey  items).  The  most  abundant  prey  in  California 
are  voles,  woodrats,  pocket  gophers,  and  cottontails;  their 
contribution  to  the  diet  by  biomass  is  almost  in  the  reverse 
order.  In  essence,  they  prey  on  almost  all  the  available 
small  mammals  in  a  region,  mostly  those  above  0.7  ounce 
in  weight;  diurnal,  fossorial,  and  arboreal  forms  are  mosdy 
absent  in  the  diet.  In  areas  of  overlap,  Great  Horns  eat 
considerably  larger  prey  on  average  than  do  Barn  and 
Long-eared  owls  (Marti  1974).  See  Barn  Owl  account  for 
information  on  food  niche  separation.  In  the  Sierra  foot- 
hills, Great  Horns  subsist  mainly  on  small  to  medium- 
sized  mammals  (Fitch  1947).  Cottontail  rabbits  and 
woodrats  represent  79%  of  the  diet  there  by  weight;  other 
important  items  are  kangaroo  rats,  pocket  gophers,  gopher 
snakes,  and  ground  squirrels  (Fitch  1947,  n  =  654).  Vari- 
ous mice,  opossums,  skunks,  bats,  small  landbirds,  quail, 
Screech-Owls,  American  Kestrels,  Coots,  snakes,  lizards, 
toads,  Jerusalem  crickets,  and  beedes  were  also  taken.  As 
might  be  expected,  there  is  regional  variation  in  diet 
reflecting  prey  availability  and  both  seasonal  and  long-term 
variation  in  the  diet  reflecting  fluctuations  in  prey  popula- 
tions (e.g.,  Errington  et  al.  1940,  Rush  et  al.  1972,  Marti 
1974,  Jaksic  &  Marti  1984;  see  also  Voous  1988).  Al- 
though females  are  considerably  larger  than  males,  there 
are  no  data  on  average  or  absolute  prey  sizes  between  the 
sexes  (Voous  1988).  The  male  hunts  for  die  incubating 
and  brooding  female  and  for  the  nesdings  (Voous  1988). 
He  usually  provides  an  abundance  of  prey,  which  he 
deposits,  and  which  may  accumulate,  at  the  nest.  The  size 


of  food  items  brought  to  young  increases  with  nesding  age 
(Johnsgard  1988). 

Marin  Breeding  Distribution 

During  die  adas  period,  the  Great  Horned  Owl  was  the 
most  widespread  breeding  owl  in  Marin  County  and 
perhaps  the  most  widespread  of  our  larger  breeding  birds. 
The  adas  map  shows  many  small  gaps  in  the  distribution, 
particularly  away  from  roads.  This  apparendy  was  mosdy 
an  artifact  of  our  limited  coverage  of  nocturnally  active 
species.  Complete  coverage  of  owls  would  probably  have 
revealed  Great  Horned  Owls  in  almost  every  adas  block. 
Representative  breeding  locations  were  the  Fish  Docks, 
Point  Reyes  (FL  6/20/80  -DS);  Morning  Sun  Ave.,  Mill 
Valley  (NE-NY  3/5-5/15/81  -MC);  and  Tiburon  (DD 
5/27/82  -BiL). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  reported  that  Great  Horned 
Owls  had  become  scarce  locally  in  California  but  were 
holding  up  remarkably  well,  even  in  areas  closely  setded  by 
people  and  despite  much  hunting  of  "vermin."  This  assess- 
ment is  still  valid  today  for  this  remarkably  adaptable 
species.  Numbers  of  Great  Horned  Owls  were  relatively 
stable  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989  (USFWS  unpubl.  analyses).  Many  owls  are  still 
shot,  trapped,  killed  along  highways  by  vehicles,  and  elec- 
trocuted by  overhead  powerlines  (Voous  1988).  Great 
Horned  Owls  have  been  poisoned  by  biocides,  but  this  has 
not  been  as  widespread  or  as  well  documented  as  for 
certain  diurnal  birds  of  prey. 


216 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


NORTHERN  PYGMY-OWL  Glaucidium  gnoma 


A  year-round  resident. 

\                yCs 

A  rare,  very  local  breeder;  overall  breed- 

\^\?;iA>iTl/W 

ing  population  very  small. 

Recorded  in  2  (0.9%)  of  221  blocks. 

^W^^^ 

O    Possible        =         2   (100%) 

\<^>^Xp\\^ 

©    Probable       =         0   (0%) 

\  \  \  ^--a^^   *-b><rC*%  \ 

<yV"\^V^^\    \<-^\     \^\     \^\ 

•    Confirmed  =         0  (0%) 

ij^Kv^Z^i Jk\Jt\ 

%Scp° 

FSAR=1         OPI  =  2            CI  =  1.00 

J  >j^=> 

Ecological  Requirements 

Though  in  large  part  a  creature  of  daylight,  this  midget  of 
owldom  still  possesses  the  true  spirit  of  that  enigmatic  clan, 
as  one  only  rarely  stumbles  upon  little  gnoma,  and  then, 
likely  as  not,  one  beset  by  a  mobbing,  scolding  throng  of 
chickadees  and  nuthatches  that  advertises  its  presence  far 
and  wide.  Because  of  the  seeming  rarity  of  Pygmy-Owls  in 
Marin  County,  it  is  hard  to  determine  habitat  preferences 
here.  Most  encounters  in  Marin  are  of  calling  birds  on  the 
edges  of  Douglas  fir  forest  or  mixed  evergreen  forest 
dominated  by  Douglas  firs  or  oaks.  In  California  as  a 
whole,  Pgymy-Owls  prefer  open  or  broken  forests  or  wood- 
lands of  conifers  and  oaks  at  low  to  mid-elevations  (Skin- 
ner 1938,  G&M  1944,  Gaines  1988).  Although  the 
surrounding  forest  type  may  sometimes  be  moist  and 
dense,  the  owls  are  strongly  attracted  throughout  their 
range  to  forest  edges  along  meadows,  clearings,  or  other 
openings  (Skinner  1938,  Johnsgard  1988,  Voous  1988). 
Meadows  harbor  a  choice  supply  of  small  mammal  prey, 
and  forest  edges  are  renowned  for  attracting  a  diversity  and 
abundance  of  avian  prey  as  well.  Pygmy-Owls  tend  also  to 
nest  in  forests  or  woodland  edges  close  to  these  important 
open  foraging  grounds  (Skinner  1938). 

Pygmies  lay  their  eggs  in  the  bottom  of  abandoned 
woodpecker  holes  or  natural  cavities  of  trees  or  stumps  in 
the  scanty,  naturally  accumulated  debris  of  wood  chips, 
pine  needles,  twigs,  feathers,  and  leaves,  or  the  cast-off 
bones  or  beetle  wings  left  from  the  previous  year's  dining 
(Skinner  1938).  Pygmies  sometimes  nest  in  the  same  hole 
for  several  successive  years.  Known  nest  heights  range 
from  5  to  75  feet  above  the  ground  (Skinner  1938),  but 


also  probably  as  high  as  suitable  cavities  exist.  Johnsgard 
(1988)  reported  an  average  nest  height  of  19  nests  at  20.7 
feet  and  a  seeming  preference  for  broadleaved  trees  over 
conifers  for  nest  sites.  It  seems  likely,  however,  that  nest 
heights  are  largely  determined  by  the  availability  of  wood- 
pecker holes  and  natural  cavities.  The  same  goes  for  the 
types  of  trees  in  which  these  cavities  exist,  though  broad- 
leaved  trees  may  be  more  prevalent  on  forest  edges  where 
Pygmies  tend  to  nest. 

Northern  Pygmy-Owls  are  active  and  hunt  during  day- 
light hours,  especially  near  dawn  and  dusk,  though  they  are 
not  averse  to  snoozing  at  times  during  the  day  (Skinner 
1938,  Johnsgard  1988,  Voous  1988).  Foraging  owls  often 
perch  on  top  of  low  to  moderate-sized  trees  and  snags  in 
semiopen  places.  They  travel  from  perch  to  perch  shrike- 
like, dropping  and  buzzing  along  just  above  the  ground, 
then  rising  sharply  to  the  next  perch.  Pygmies  are  deter- 
mined, no-nonsense  predators  that  rely  on  speed  and 
surprise,  though  their  flight  is  more  "noisy"  than  many 
other  owls  (Skinner  1938).  They  pounce  from  perches 
onto  prey  on  the  ground,  seize  birds  from  perches  in  trees 
while  flying,  and  pull  adult  and  young  woodpeckers  out  of 
their  nest  holes.  They  also  sometimes  hunt  mice  in  open 
barns  and  cabins.  These  plucky  owls  often  attack  relatively 
large  prey.  Sometimes  they  pounce  on  a  rather  large  mam- 
mal that  drags  its  captor  along  with  it  for  a  considerable 
distance  before  succumbing  to  the  onslaught.  One  owl 
carried  off  an  Olive-sided  Flycatcher  shot  by  a  collector!  As 
a  rule,  they  grasp  avian  victims  by  the  neck.  The  male  does 
all  the  hunting  and  brings  in  the  food  to  a  perch  near  the 

217 


Typical  Owls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Chuls 


nest,  from  which  he  calls  his  mate.  The  male  typically 
decapitates  and  partly  skins  food  before  turning  it  over  to 
die  female.  The  female  comes  out  to  accept  his  offering  and 
either  remains  to  eat  it  or  retires  to  the  nest  hole.  Upon  the 
hatching  of  the  eggs,  the  male  continues  to  bring  food,  first 
delivering  small  items  to  die  young,  and  then  larger  items 
when  the  nesdings  are  more  vigorous.  There  are  sugges- 
tions in  the  literature  of  prey  caching  by  this  owl  (Skinner 
1 938,  Voous  1 988),  though  this  needs  further  documenta- 
tion. 

The  diet  of  Northern  Pygmy-Owls  consists  primarily  of 
small  mammals,  small  birds,  insects,  and  other  inverte- 
brates, along  with  smaller  amounts  of  cold-blooded  verte- 
brates (Skinner  1938,  Earhart  6k  Johnson  1970,  Snyder  6k 
Wiley  1976,  Johnsgard  1988,  Voous  1988).  Insects  and 
other  invertebrates  account  for  61%  of  the  prey  items  in 
the  diet,  mammals  23%,  birds  1 3%,  and  reptiles  and 
amphibians  3%  (Snyder  6k  Wiley  1976,  n  =  163).  Mam- 
mals and  birds  undoubtedly  are  most  important  in  terms 
of  biomass.  Earhart  and  Johnson  (1970)  reported  that  in  a 
sample  of  70  stomachs,  81%  contained  vertebrates  and 
about  one-third  contained  insects.  Mammals  are  repre- 
sented by  various  species  of  voles,  deer  mice,  house  mice, 
pocket  gophers,  chipmunks,  and  shrews.  A  wide  variety  of 
small  birds  (mosdy  passerines)  are  taken,  including  sizes 
up  to  American  Robins,  Steller's  Jays,  and  sapsuckers. 
Pygmies  occasionally  take  quail  and  chipmunks  more  dian 
twice  the  size/weight  of  the  owls.  Amphibians  and  reptiles 
in  the  diet  include  toads,  frogs,  various  lizards,  and  small 
snakes.  Insect  prey  are  grasshoppers,  cicadas,  beedes,  crick- 
ets, Jerusalem  crickets,  katydids,  dragonflies,  butterflies, 
and  large  hawk  moths.  Geographical  differences  in  the  diet 
likely  occur,  with  mammals  probably  taken  more  in  the 
north  and  reptiles  and  insects  more  to  the  south.  Reptiles 
are  taken  only  in  the  spring  and  summer  when  available 


(Earhart  6k  Johnson  1970).  On  an  annual  bisis-,  the  larger 
females  feed  more  on  mammals  (52%  vs.  37%)  and  less 
on  birds  (21%  vs.  34%)  than  do  males.  The  smaller  males 
presumably  are  more  agile  and  better  able  to  capture 
elusive  avian  prey  than  are  females. 

Marin  Breeding  Distribution 

During  the  adas  period,  Pygmy-Owls  were  recorded  in 
Marin  County  in  the  breeding  season  on  only  single  dates 
at  three  localities:  on  17  May  1980  at  the  east  end  of  Big 
Rock  Ridge  (PckMSh);  on  9  May  1981  on  Mt.  Burdell, 
Novato  (ScC);  and  on  23  March  1982  on  Mt.  Vision, 
Inverness  Ridge  (RS).  Although  they  undoubtedly  would 
have  been  found  in  more  areas  if  more  nighttime  work  had 
been  done,  the  species  is  quite  scarce  during  the  breeding 
season  in  the  county.  In  contrast,  Pygmy-Owls  are  relatively 
numerous  in  bordering  Sonoma  County,  whereas  North- 
ern Saw-whet  Owls  are  uncommon  there— the  converse  of 
the  situation  in  Marin  County.  This  difference  defies  easy 
explanation  as  broad  areas  of  roughly  similar  habitat  occur 
in  both  counties. 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  did  not  report  on  any  trends 
in  populations  of  diis  species  in  California.  Johnsgard 
(1988)  felt  Pygmy-Owls  generally  were  not  seriously 
affected  by  human  activities  and,  if  anything,  partial  clear- 
ing of  forests  may  improve  hunting  conditions  for  the 
species.  This  may  be  true,  but  conversely  it  seems  that 
large-scale  development,  snag  removal,  or  clear-cutting  of 
forests  may  have  detrimental  effects  on  Pygmy-Owl  popu- 
lations. Pygmy-Owl  numbers  were  relatively  stable  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


218 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


BURROWING  OWL   Speotyto  cunicularia 


Occurs  year  round,  though  almost  exclu- 

\           pCV_ 

sively  as  a  winter  resident  from  mid-Sep 

jOk^K^^^PXy^-^. 

through  Mar. 

^f\%(\J\\J>^ 

~-  - 

A  very  rare,  very  local  breeder;  overall 
breeding  population  very  small. 

\C\p?<^C\j>^ 

Recorded  in  1  (0.4%)  of  221  blocks. 

\5*^>S^r\l^ 

O    Possible        =         0   (0%) 

\Xk^\^^^^> 

d    Probable       =         1    (100%) 

^V   '-^V^ \^A     \^\     \^\ 

^V^Ky ,r- 

•    Confirmed  =         0   (0%) 

1    \^^ 

"\^C^^>^C\^ 

FSAR  =1         OPI  =  1            CI  =  2.00 

Ecological  Requirements 

A  fleeting  glimpse  of  an  owl  silhouette  at  dusk  is  one  thing, 
but  leisurely  views  of  the  antics  of  a  family  of  long-legged 
"Billy  Owls"  (Dawson  1923)  preening,  sunning,  bowing, 
and  bobbing  in  front  of  their  burrow  in  broad  daylight  is 
another— one  long  to  be  remembered  by  die  person  new  to 
the  world  of  birds.  These  diminutive,  ground-dwelling 
owls  inhabit  relatively  dry,  flat,  very  open  grasslands  and 
disturbed  areas  with  very  short  vegetation.  Habitat  prefer- 
ences in  Marin  County  are  difficult  to  explain.  Only  one 
pair  apparendy  bred  here  during  the  adas  period  (see 
below).  Elsewhere  in  northern  California,  Burrowing 
Owls  occupy  grasslands,  pasturelands,  edges  of  agricultural 
fields,  abandoned  fields  and  lots,  and  disturbed  sites  with 
sparse  low-growing  vegetation.  Though  receding  before  die 
tide  of  civilization,  Burrowing  Owls  can  tolerate  a  certain 
amount  of  noise  and  dismrbance  if  certain  other  require- 
ments are  met,  as  evidenced  by  birds  breeding  at  large 
airports,  golf  courses,  and  in  small  pockets  of  habitat  in 
rapidly  developing  areas.  The  main  requirements  are  ade- 
quate nest  sites,  productive  open  foraging  grounds,  and 
perching  sites,  such  as  raised  rodent  mounds,  dikes  or 
levees,  fences,  or  utility  poles  and  lines  (Coulombe  1971, 
Voous  1988,Johnsgard  1988). 

As  dieir  name  implies,  diese  owls  usually  nest  inside  die 
earthen  burrows  of  mammals,  or  even  tortoises  and  other 
animals  (Voous  1988).  Sometimes  they  select  as  nest  sites 
burrows  beneadi  rock  faces,  natural  rock  cavities  (Rich 
1986),  drainpipes  (Collins  1979),  or,  in  Soudi  America, 
Inca  ruins  or  derelict,  abandoned  houses  (Voous  1988).  In 
lowland  nordiern  California,  diey  rely  mostly  on  the  exca- 


vations of  Beechy  ground  squirrels  (Citellus  beecheyi), 
which  they  enlarge  and  improve  (Thomsen  1971).  The 
major  factor  controlling  Burrowing  Owl  numbers  appears 
to  be  the  availability  of  suitable  burrows  (Coulombe  1971), 
diough  sometimes  birds  dig  their  own  burrows  from 
scratch  using  their  feet  and,  to  a  limited  extent,  dieir  beaks 
(Thomsen  1971,  Martin  1973,  Voous  1988).  The  impor- 
tance of  burrows  to  diis  owl's  ecology  is  further  empha- 
sized by  use  of  diem  as  social  centers,  sites  for  food  storage, 
refuges  from  predators,  and  as  a  stable,  tempered  environ- 
ment during  periods  of  extremely  hot  or  cold  weather 
(Coulombe  1971,  Thomsen  1971).  At  die  Salton  Sea, 
temperatures  at  die  entrances  did  not  differ  from  those  in 
die  depdis  of  the  burrows.  Humidities,  diough,  were  much 
higher  inside  burrows,  which  would  reduce  the  water  loss 
of  owls  diere  (Coulombe  1971).  Tunnels  usually  slope 
down  about  15°  from  the  entrance  and  always  have  a  sharp 
turn  widiin  about  diree  feet  of  the  surface  (Coulombe 
1971).  Burrowing  Owls  also  readily  accept  artificial  bur- 
rows of  wood  or  pipe,  as  long  as  die  tunnel  has  one  turn 
diat  maintains  the  nest  chamber  in  complete  darkness 
(Collins  &  Landry  1977,  Collins  1979).  Unlike  most 
owls,  Burrowing  Owls  transport  nest  materials  and  line 
die  nest  and  die  burrow  entrance  liberally  with  dried 
mammal  dung,  dried  grasses,  human  litter,  and  divots 
from  golf  courses  (Thomsen  1971,  Martin  1973,  Evans 
1982,  Johnsgard  1988,  Voous  1988).  Nest  materials  may 
function  to  provide  insulation  or  to  camouflage  the  owl's 
scent  or  that  of  its  prey  from  mammalian  predators  (Martin 
1973).  The  owls  later  remove  nest  materials  from  burrows, 

219 


Typical  Owls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Owls 


apparently  during  the  early  nestling  phase  (Thomsen 
1971).  Young  Burrowing  Owls  make  hissing  and  rasping 
sounds,  which,  as  apparent  vocal  mimicry  of  rattlesnakes, 
may  discourage  prowling  carnivores  (Voous  1988);  it 
should  be  noted  that  tree  cavity- nesting  Saw-whet  Owl  and 
Screech-Owl  young  also  make  similar-sounding  begging 
calls  (Thomsen  1971).  When  the  young  owlets  (about  two 
weeks  old)  first  come  to  the  mouth  of  the  burrow,  they  (and 
their  families)  use  nearby  auxiliary  burrows  and  usually  use 
two  or  three  different  burrows  in  succession  before  they 
fledge  (Evans  1982).  Burrows  invariably  swarm  with  fleas 
(Collins  1979). 

Burrowing  Owls  limit  defense  of  their  territories  to  the 
immediate  vicinity  of  their  burrows,  and  hence  adjacent 
pairs  often  share  mutual  foraging  areas  (Coulombe  1971). 
In  most  parts  of  their  range,  Burrowing  Owls  are  highly 
crepuscular,  feeding  mosdy  in  the  dim  light  near  dawn  and 
dusk  (Coulombe  1971,  Thomsen  1971,  Collins  1979, 
Johnsgard  1988,  Voous  1988).  They  also  feed  actively 
during  daylight  hours  and  at  night;  in  some  areas  noctur- 
nal foraging  appears  to  increase  in  winter.  Regional  or 
seasonal  differences  in  the  timing  of  daily  foraging  activities 
may  reflect  those  of  their  most  frequent  prey  items  or 
changes  in  environmental  temperatures.  Based  on  prey 
numbers,  the  Burrowing  Owl  diet  is  dominated  by  arthro- 
pods, mosdy  insects,  but  apparendy  small  mammals  are 
the  most  important  prey  in  terms  of  biomass  (Snyder  &. 
Wiley  1976,  Jaksic  6k  Marti  1981 ,  Johnsgard  1988,  Voous 
1988).  The  North  American  diet  by  prey  numbers  is 
90.9%  invertebrates  (mosdy  insects),  6.9%  mammals, 
2.0%  reptiles  and  amphibians,  and  0.3%  birds  (Snyder  6k 
Wiley  1976,  n  =  3564).  The  California  diet  by  prey  num- 
bers is  70.6%  insects,  23.6%  mammals,  3.5%  birds,  2.2% 
amphibians,  0.1%  isopods,  with  trace  amounts  of  reptiles, 
scorpions,  and  centipedes  (Jaksic  6k  Marti  1981,  n  = 
3794).  Beetles  account  for  49.2%  and  orthopterans 
(mosdy  Jerusalem  crickets)  for  50.3%  of  the  invertebrate 
prey  in  California.  Vertebrate  prey  here  are  dominated  by 
voles  (69.5%  of  total),  followed  by  birds  (12.1%),  amphib- 
ians (7-4%),  jackrabbits  and  cottontails  (6.4%),  pocket 
gophers  (2.4%),  house  mice  (1.0%),  Norway  rats  (1.0%), 
bats  (0.2%),  and  reptiles  (trace).  The  diet  of  birds  at  the 
Oakland  Airport,  Alameda  County,  consists  mosdy  of 
insects  such  as  Jerusalem  crickets  and  beedes  and  verte- 
brates such  as  meadow  voles,  young  jackrabbits,  pocket 
gophers,  small  to  medium-sized  birds,  and  toads;  appar- 
endy a  high  percentage  of  vegetation  in  the  pellets  is 
consumed  direcdy  by  the  owls  (Thomsen  1971).  Near  the 
Salton  Sea  in  southern  California,  these  owls  feed  primar- 
ily on  arthropods  and  insects  (earwigs,  crayfish,  crickets, 
and  beedes)  but  also  eat  a  few  small  mammals,  birds,  frogs, 
toads,  snakes,  and  some  carrion  (Coulombe  1971).  There 
is  additional  regional  variation  in  the  diet  throughout  the 
range  and  increasing  use  of  mammals  in  winter  and  insects 


in  summer  (Johnsgard  1988,  Voous  1988).  The  mean 
weight  of  small  mammal  prey  in  California  is  1 .9  ounces 
(Jaksic  6k  Marti  1981).  Males  provide  food  to  incubating 
females,  and  they  may  temporarily  cache  food  almost 
anywhere  in  their  territory,  usually  within  100  feet  of  their 
burrows  (Johnsgard  1988).  A  cache  in  southern  California 
contained  six  freshly  decapitated  Mourning  Doves,  each  of 
which  represented  80%- 84%  of  the  body  weight  of  a 
Burrowing  Owl.  Males  bring  most  of  the  food  to  the 
young,  and  females  help  distribute  it  (Thomsen  1971); 
females  begin  to  forage  when  the  young  are  three  to  four 
weeks  old  (Martin  1973).  Unlike  most  North  American 
owls,  male  Burrowing  Owls  are  slighdy  larger  and  heavier 
than  females,  but  no  difference  has  been  found  in  average 
prey  size  between  males  and  females  (Voous  1988). 

Because  of  their  crepuscular  and  sometimes  diurnal 
habits,  Burrowing  Owls  probably  locate  most  prey  by  sight 
(Voous  1988).  Hearing  must  also  play  a  role,  though  they 
have  a  relatively  poor  ability  to  locate  prey  in  the  dark 
compared  with  many  North  American  owls.  Burrowing 
Owls  capture  prey  in  their  talons  after  short  flights  or  glides 
to  the  ground  from  elevated  perches;  by  flycatching  sorties 
from  perches;  by  direct  aerial  chases;  by  hovering  (heights 
of  about  25-50  ft.)  or  flying  low  over  fields,  then  pouncing 
on  prey  on  the  ground;  and  by  walking  or  running  down 
prey  on  the  ground  (Coulombe  1971,  Thomsen  1971, 
Martin  1973,  Johnsgard  1988,  Voous  1988).  At  Oakland, 
Alameda  County,  males  performed  98%  of  hovering 
attempts  (Thomsen  1971),  perhaps  because  this  is  a  spring 
and  summer  foraging  method  when  males  do  most  of  the 
hunting.  Birds  probably  also  take  insects  that  live  in  their 
burrows  (Coulombe  1971). 

Marin  Breeding  Distribution 

The  only  evidence  that  Burrowing  Owls  bred  in  Marin 
County  during  the  adas  period  was  the  repeated  observa- 
tion of  a  pair  in  the  Terra  Linda  area  of  San  Rafael  all 
spring  (through  May)  in  1976  and  1977  QSt).  The  near- 
absence  of  ground  squirrels  in  West  Marin  may  limit 
Burrowing  Owl  populations  there,  but  where  ground 
squirrels  are  more  numerous  in  East  Marin,  other  factors, 
perhaps  extensive  urbanization,  must  hinder  them. 

Historical  Trends/ Population  Threats 

Both  Mailliard  (1900)  and  Stephens  and  Pringle  (1933) 
considered  the  Burrowing  Owl  a  year-round  resident  in 
restricted  areas  of  Marin  County.  Given  the  current  status 
documented  by  die  adas  work,  Burrowing  Owls  appear  to 
have  declined  historically  in  Marin  County. 

Grinnell  and  Miller  (1944)  reported  that  Burrowing 
Owls  were  becoming  scarce  in  setded  parts  of  California. 
This  owl  is  currendy  on  the  state's  list  of  Bird  Species  of 
Special  Concern  (Remsen  1978,  CDFG  1991b).  Data  on 
recent  trends  in  the  population  are  conflicting.  As  of  this 


220 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


writing,  numbers  of  breeding  Burrowing  Owls  continue  to 
decline  in  the  San  Francisco  Bay  Area  because  of  ongoing 
urban  development  (L.  Feeney  pers.  comm.).  Numbers 
also  declined  on  Christmas  Bird  Counts  throughout  Cali- 
fornia from  1954  to  1986  (James  6k  Ethier  1989)  but  were 
relatively  stable  on  Breeding  Bird  Surveys  in  the  state  from 
1968  to  1989  (USFWS  unpubl.  analyses).  Widespread 
grid-based  surveys  are  currently  being  conducted  to  better 
determine  the  status  of  the  breeding  population  in  lowland 
California  (D.F.  DeSante  pers.  comm.).  The  U.S.  Fish  and 
Wildlife  Service  has  variously  categorized  the  Burrowing 
Owl  as  "rare"  in  1966,  dropped  that  classification  in  1968, 
and  assigned  it  a  status  of  "undetermined"  in  1973  (Johns- 


gard  1988).  The  species  was  on  the  Audubon  Society's 
Blue  List  from  1972  to  1981  and  has  been  on  their  list  of 
Species  of  Special  Concern  since  1982,  with  the  central 
and  northern  California  population  considered  low  or 
declining  (Tate  1981,  1986;  Tate  ck  Tate  1982).  This 
decline  has  been  blamed  mainly  on  rodent  control  pro- 
grams that  reduced  nesting  sites  for  the  owls;  on  direct  loss 
of  nesting  and  foraging  habitat  to  urban,  industrial,  and 
agricultural  development;  and  perhaps  to  pesticides  that 
have  reduced  food  supplies  and  direcdy  poisoned  owls 
(Zarn  1974,  Evans  1982,  Johnsgard  1988,  Marti  ck  Marks 
1989).  Shooting  has  been  an  important  source  of  mortality 
locally  and  in  former  times  (G6kM  1944,  Evans  1982). 


i^4.i+h  l-ldnso-n 


With  a  woodrat  clutched  tightly  in  its  talons,  an  adult  Spotted  Owl  gazes  down  on  a  dark- 
eyed,  fuzzy  youngster  absorbing  its  new  world.    Drawing  by  Keith  Hansen,  1 989. 


221 


Typical  Ou/ls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Owls 


SPOTTED  OWL    Strix  occidentalis 


A  year-round  resident. 

j*^*  \Y^r^ 

r^5^-^    K 

An  uncommon,  very  local  breeder; 

yA^vOp 

overall  breeding  population  very  small. 

\^\^%^f\^\  \  La 

OrA0r\>^" 

Recorded  in  16  (7.2%)  of  221  blocks. 

cjtA^XAjPvp 

<^CV>V^ 

O    Possible        =        6   (38%) 

\~\~ 

\V^J^  V-Ajo\ 

C    Probable      =        4  (25%) 
•    Confirmed  =        6  (38%) 

^i^&\^\\.'L^^J>^ 

-A^I^VaVV  •' 

—  -r' 

FSAR  =  2        OPI  =  32         CI  =  2.00 

i  i 

v  OVA      -\J-*A     -\>"\      V>fA 

Vo 

Ecological  Requirements 

This  recluse  of  the  shadowy  depths  of  ancient  forests  has 
in  recent  years  been  thrust  into  the  national  spodight.  The 
Spotted  Owl  symbolizes  both  the  plight  of  vanishing  old- 
growth  ecosystems— supporting  a  fragile  web  of  species 
coadapted  over  thousands  of  years  of  evolution— and  the 
difficulty  of  overcoming  political  obstacles  even  when  a 
species'  existence  hangs  in  the  balance.  Mounting  concern 
over  the  owl's  predicament,  and  the  ensuing  controversy 
surrounding  the  difficulties  of  meeting  both  the  owl's  and 
perceived  human  needs,  spawned  extensive  research  aimed 
at  developing  management  strategies  to  ensure  long-term 
survival  of  viable  owl  populations  in  remaining  habitat 
(e.g.,  Forsman  et  al.  1984;  Gutierrez  6k  Carey  1985; 
Dawson  et  al.  1987;  Simberloff  1987;  USFWS  1987a, 
1989c;  USFS  1988;  Thomas  et  al.  1990). 

Spotted  Owls  have  long  been  known  to  breed  in  a 
variety  of  moist  primeval  conifer  forests.  In  Marin  County, 
at  the  southern  limit  of  the  range  of  the  Nordiern  Spotted 
Owl  (S.  o.  caurina),  they  breed  mosdy  in  forests  dominated 
by  coast  redwoods,  Douglas  firs,  and  bishop  pines  and  in 
forests  where  any  of  these  conifers  mix  together  or  blend 
extensively  with  mixed  evergreen  hardwoods.  These  habi- 
tats are  typical  of  those  used  in  much  of  the  species'  range. 
Spotted  Owls  also  breed  to  a  limited  extent  in  Marin's 
mixed  evergreen  hardwood  forests,  such  as  those  at  Toma- 
les  Bay  State  Park  dominated  by  coast  live  oaks.  Elsewhere 
in  the  state,  some  populations  of  the  California  Spotted 
Owl  (S.  o.  occidentalis)  also  breed  in  riparian  habitats 
dominated  by  oaks  and  other  hardwoods  in  canyons  of  the 

222 


western  Sierra  Nevada  (Neals  et  al.  in  Thomas  et  al.  1990) 
and  in  southern  California  (Gould  1977). 

Recent  research  has  demonstrated  that  superior  Spotted 
Owl  habitat  is  most  commonly  found  in  old-growth  forests 
or  mixed  stands  of  old-growth  and  mature  trees,  usually 
1 50  to  200  years  old  (Thomas  et  al.  1 990).  Throughout 
their  range  and  in  all  seasons,  Spotted  Owls  consistendy 
concentrate  their  foraging  and  roosting  in  old-growth  or 
mixed-age  stands  of  mature  and  old-growth  trees.  They 
select  nest  sites  primarily  in  old-growth  trees,  whether  in 
old-growth  stands  or  in  remnant  old-growth  patches.  The 
appropriate  structural  characteristics  that  suit  the  owls  can 
sometimes  be  found  in  younger  forests,  particularly  when 
they  include  remnants  of  earlier  stands  affected  by  fire, 
windstorms,  or  inefficient  or  selective  logging.  Neverthe- 
less, with  few  exceptions,  nest  and  major  roost  sites  are 
located  where  elements  of  the  earlier  stands  remain.  That 
a  particular  suite  of  structural  elements,  radier  than  age  of 
the  forest,  is  important  to  the  owls  is  demonstrated  by 
habitat  use  in  coastal  redwood  forests  of  northwestern 
California.  There  exceptional  conditions  lacking  in  most 
of  the  owls'  range  produce  stands  50  to  80  years  old  that 
support  relatively  high  numbers  of  owls.  The  combination 
of  relatively  high  rainfall,  a  long  growing  season,  the  fast 
growth  and  stump  sprouting  abilities  of  redwoods,  and  the 
early  intrusion  of  other  conifers  and  hardwoods  in  the 
understory  produce  a  structurally  precocious  forest  with  an 
abundant  prey  base.  Aldiough  Spotted  Owls  in  California 
depend  on  old  growth  at  higher  elevation  sites  dominated 
by  Douglas  fir  or  Douglas  fir-true  fir  forests,  this  does  not 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


appear  to  be  the  case  in  the  state's  coastal  redwood  belt 
(G.I.  Gould,  Jr.,  in  litt.). 

The  structural  characteristics  of  superior  forest  habitat 
for  the  owls  are  moderate  to  high  canopy  closure  (60%- 
80%);  a  multilayered,  multispecies  canopy  dominated  by 
large  (30  in.  diameter  at  breast  height)  overstory  conifer 
trees  and  an  understory  of  shade-tolerant  conifers  or  hard- 
woods; a  high  incidence  of  large  tall  trees  with  large 
cavities,  broken  tops,  dwarf  mistletoe  infections,  or  plat- 
forms of  branches  capable  of  accumulating  organic  matter 
suitable  for  use  as  a  nest;  numerous  large  standing  dead 
trees;  a  forest  floor  with  heavy  accumulations  of  logs,  dead 
limbs,  and  other  woody  debris  to  support  abundant  prey 
populations;  and  a  canopy  open  enough  to  allow  the  owls 
to  fly  within  and  beneath  it  (Thomas  et  al.  1990).  In 
California,  90%  of  the  Spotted  Owls  surveyed  by  Gould 
(1977)  inhabited  forests  with  at  least  40%  canopy  closure, 
and  most  favored  northern  exposures;  89%  of  their  terri- 
tories were  on  the  lower  slopes  of  canyons,  and  90%  were 
within  330  feet  of  a  water  course. 

One  reason  Spotted  Owls  may  prefer  older  forests  is 
because  the  layered  structure  of  the  canopy  provides  a 
range  of  roosting  environments  and  hence  the  most  pro- 
tection under  a  variety  of  weather  conditions  (Forsman  et 
al.  1984).  In  Oregon,  these  owls  roost  in  the  day,  primarily 
on  limbs  in  trees  or  large  woody  shrubs,  but  also  on  limbs 
or  logs  on  the  forest  floor.  Owls  diere  use  large  trees  in  the 
forest  overstory  for  roosting  during  cool  or  wet  weather  and 
smaller  trees  or  shrubs  in  the  forest  understory  during 
warm  weather.  Despite  the  use  of  roosts  low  in  the  under- 
story during  warm  weather,  the  majority  of  roost  sites  in 
spring  and  summer  at  one  Oregon  study  area  had  south- 
ern exposures.  During  rainy  or  snowy  weather,  these  owls 
tend  to  roost  against  the  trunk  or  under  the  shelter  of  an 
overhead  projection  of  the  tree.  In  California,  Spotted 
Owls  tend  to  use  the  same  roost  trees  repeatedly  through- 
out the  summer  but  shift  roost  sites  frequendy  during 
winter  (Barrows  1981).  Spotted  Owls  there  tend  to  select 
roosts  in  cooler  microclimates  in  the  lower  portion  of  the 
canopy  in  summer,  apparendy  to  reduce  heat  stress  (Bar- 
rows 6k  Barrows  1978,  Barrows  1981).  Summer  roosts  in 
California  tend  to  have  dense  canopies  above  and  to  be  on 
north-facing  slopes  and  in  ravines;  winter  roosts  are  more 
variable  and  do  not  share  these  characteristics. 

Like  most  owls,  Spotted  Owls  do  not  build  nests. 
Instead  they  lay  their  eggs  in  natural  cavities  or  on  elevated 
natural  platforms  (Bent  1938,  Forsman  et  al.  1984,  Johns- 
gard  1988,  Voous  1988,  Thomas  et  al.  1990).  Nests 
typically  are  inaccessible  and  have  well  shaded,  cool  micro- 
climates. Suitable  cavities  include  those  at  the  top  of 
brokenoff  trees,  ones  lower  in  the  tnink  of  live  or  dead 
conifers  or  hardwoods,  potholes  or  cavities  of  rocky  cliffs, 
shelves  of  larger  caves,  and  washouts  in  clay  banks.  Some 
nest  sites  in  cliffs  are  on  the  remains  of  abandoned  Com- 


mon Raven  or  Golden  Eagle  nests.  Cliff  nests  are  reported 
mosdy  from  southern  California  and  the  Southwest,  where 
tree  cavity  nests  also  seem  frequent  (Bent  1938).  Truly 
exceptional  nests  were  one  on  bare  ground  at  the  base  of 
a  large  rock  (Bent  1938)  and  another  on  a  pigeon  coop 
(Johnsgard  1988). 

The  platform  nests  the  owls  use  in  trees  may  simply  be 
naturally  accumulated  debris.  More  often  these  are  old 
nests  of  raptors  (Red-tailed  Hawk,  Northern  Goshawk,  or 
Cooper's  Hawk)  or  arboreal  mammals  (squirrels  or  wood- 
rats),  often  built  among  the  dense  clusters  of  deformed 
limbs  ("witches-brooms")  of  old  trees  infected  with  dwarf 
misdetoe  (Forsman  et  al.  1984).  Platform  nests  tend  to  be 
next  to  or  close  to  the  trunk.  Within  the  range  of  the 
Northern  Spotted  Owl  in  Washington,  Oregon,  and 
northern  California,  there  is  geographical  variation  in  the 
predominance  of  platform  versus  tree  cavity  nests,  presum- 
ably reflecting  regional  availability  of  these  types  of  sites 
(Forsman  et  al.  1984,  Thomas  et  al.  1990).  Spotted  Owls 
in  Marin  County  select  both  tree  cavity  and  platform  nests, 
but  it  is  not  established  if  one  type  is  used  here  more  often 
than  the  other.  In  Oregon,  Forsman  et  al.  (1984)  reported 
that  the  height  of  tree  cavity  nests  averaged  99  feet  (range 
38-181  ft.,  n  =  30)  and  platform  nests  averaged  72  feet 
above  the  ground  (range  33-123  ft.,  n  =  17).  Nests  there 
tend  to  be  located  on  the  lower  slopes  of  hillsides  and 
widiin  about  800  feet  of  water  (Forsman  et  al.  1984),  a 
pattern  similar  to  diat  noted  above  for  territories  in  Cali- 
fornia (Gould  1977),  which  also  seems  to  hold  for  Marin 
County.  It  is  unclear  if  the  owls  select  nest  sites  close  to 
water  for  use  in  drinking  or  bathing  or  whether  other 
factors  they  select  for  coincidentally  tend  to  occur  near 
water.  Johnsgard  (1988)  reported  an  average  nest  height  of 
31  feet  for  a  small  sample  (n  =  13)  of  sites,  including  cliff 
ledges  or  cavities,  tree  platforms,  tree  cavities,  and  one 
artificial  structure. 

Regardless  of  site,  females  scrape  out  a  depression  for 
the  eggs,  which  may  sit  on  bare  soil;  on  debris  such  as 
rotted  wood,  conifer  needles,  pine  cones,  and  small  twigs 
left  naturally  or  by  the  previous  occupants;  on  bones, 
pellets,  or  feathers  accumulated  by  the  owls  themselves;  or 
on  a  mixture  of  the  above  (Bent  1938,  Forsman  et  al. 
1984).  On  rare  occasions,  females  apparendy  will  add  a 
few  sprays  of  green  conifer  needles  to  the  nest  (Forsman  et 
al.  1984). 

Spotted  Owls  dine  on  a  wide  variety  of  prey,  but  overall 
small  arboreal  or  semiarboreal  nocturnal  mammals  pre- 
dominate in  the  diet,  whether  measured  by  numbers  or 
biomass  consumed  (Thomas  et  al.  1990,  n=  15,100+). 
Throughout  the  range,  diet  studies  often  reveal  that  70%- 
90%  of  prey  biomass  is  contributed  by  just  two  or  three 
dominant  species,  such  as  northern  flying  squirrels,  dusky- 
footed  or  bushy-tailed  woodrats,  and  various  hares  or 
rabbits.  Pocket  gophers,  red  tree  voles,  and  deer  mice  may 


223 


Typical  Ou/ls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Owls 


be  regionally  important.  Broad  geographic  differences  in 
owl  diets  are  manifest  by  a  predominance  of  flying  squir- 
rels in  moist  conifer  forests  at  relatively  high  latitudes  or 
elevations  and  woodrats  in  drier  conifer  forests,  mixed 
evergreen  forests,  or  oak  woodlands  at  relatively  low  lati- 
tudes or  elevations.  In  California,  woodrats,  flying  squir- 
rels, deer  mice,  and  red  tree  voles  or  other  voles  are  die 
main  prey  items  by  numbers.  After  mammals,  birds  (in- 
cluding small  owls)  are  the  next  most  important  group  of 
prey.  Birds  contributed  as  much  as  10%- 18%  of  die 
number  of  prey  items  at  5  of  1 4  study  sites  in  California. 
Various  reptiles,  amphibians,  insects,  arthropods,  and 
other  invertebrates  are  of  minor  importance  to  the  diet; 
insects  may  be  consumed  in  numbers  in  some  areas  but 
always  represent  only  a  small  fraction  of  total  prey  biomass 
(Forsman  et  al.  1984,  Thomas  et  al.  1990).  In  Marin 
County,  88%  of  16  pellets  found  near  Palomarin  con- 
tained dusky-footed  woodrats,  69%  white-footed  mice, 
31%  Band-tailed  Pigeons,  and  6%  Steller's  Jays;  other 
observations  indicate  that  brush  rabbits  and  Sonoma  chip- 
munks also  serve  as  prey  here  (Beebe  &  Schonewald 
1977). 

Seasonal  shifts  in  the  diet  in  Oregon  relate  to  changes 
in  seasonal  abundance  or  vulnerability  of  prey  (Forsman  et 
al.  1984).  Various  mammals  are  preyed  on  more  during 
periods  of  juvenile  dispersal  or  while  juveniles  of  larger 
species  are  still  of  manageable  size;  insects  are  taken  pri- 
marily in  summer  and  early  fall.  Dietary  composition  at 
particular  sites  also  appears  to  vary  among  years.  Compar- 
ing both  percent  composition  and  mean  prey  weights, 
Forsman  et  al.  (1984)  found  no  difference  in  the  diet  of 
males  and  females  at  two  sites  in  Oregon.  Several  studies 
(Barrows  1985,  1987;  citations  in  Thomas  et  al.  1990) 
have  shown  a  positive  association  between  prey  size  and 
owl  reproductive  success  (and  breeding  status),  but  it  is 
unclear  whether  this  reflects  differential  capture  by  the  owls 
or  merely  differential  transport  of  large  prey  to  nests 
(Thomas  et  al.  1990). 

Spotted  Owls  are  primarily  nocturnal  predators  that 
leave  their  roosts  to  hunt  soon  after  sunset  and  return 
shortly  before  dawn  (Forsman  et  al.  1984).  They  forage 
primarily  in  old-growth  or  mature  timber,  from  the  ground 
to  the  upper  canopy.  Beyond  roosting,  diurnal  activity  is 
usually  restricted  to  occasional  short  flights  to  capture  prey 
below  the  roost  tree,  to  retrieve  cached  prey,  to  change 
roost  trees,  or  to  drink  or  bathe  in  nearby  streams.  Laymon 
(1991)  found  some  pairs  of  owls  in  the  Sierra  Nevada 
hunting  regularly  in  the  daytime  when  feeding  large  depen- 
dent young  that  had  already  left  the  nest.  He  speculated 
that  diurnal  foraging  may  be  a  compensatory  response  of 
adults  that  are  unable  to  meet  the  demands  of  feeding 
young  owls  solely  by  nocturnal  foraging  when  food  is 
limited.  Just  prior  to  and  during  incubation  and  when  the 


young  are  small,  the  male  supplies  all  the  food  for  the 
female,  young,  and  himself.  When  young  are  two  to  three 
weeks  old,  females  begin  to  forage  for  progressively  longer 
periods  and  farther  away  from  the  nest  each  night  (Fors- 
man et  al.  1984).  The  male  initially  brings  food  to  the 
female  (on  or  near  the  nest)  and  transfers  the  decapitated 
prey  to  her,  beak  to  beak;  later  he  will  leave  the  food  at  the 
nest  if  the  female  is  away.  The  female  always  feeds  the 
young. 

Whether  capturing  prey  in  trees  or  on  the  ground, 
Spotted  Owls  usually  dive  on  their  victims  from  an  elevated 
perch  (Forsman  et  al.  1984).  After  unsuccessful  first 
attempts  at  catching  squirrels  in  trees,  the  owls  often  hop 
or  fly  from  limb  to  limb  in  pursuit  of  the  fleeing  animals. 
Insects  are  captured  either  on  the  ground  or  on  limbs  of 
trees  (rather  than  in  the  air),  usually  by  pouncing  on  them 
with  the  feet  or  by  landing  and  picking  them  up  with  the 
beak.  It  seems  likely  that  most  birds  or  bats  are  taken  when 
active,  leaving  or  entering  roost  sites,  rather  than  when 
concealed  and  asleep  (S.A.  Laymon  pers.  comm.).  Spotted 
Owls  hold  vertebrate  prey  in  the  feet  and  kill  them  by 
crushing,  tearing,  or  breaking  the  base  of  the  cranium  or 
neck  (Forsman  et  al.  1 984).  They  sometimes  eat  small  prey 
whole,  but  usually  they  at  least  partially  dismember  ani- 
mals larger  than  deer  mice  and  consume  the  heads  first. 
Year  round,  Spotted  Owls  regularly  cache  decapitated  and 
partially  eaten  remains  of  excess  prey  and  later  retrieve 
them.  They  securely  wedge  the  remains  for  storage  on  top 
of  limbs  in  trees  or  on  the  ground  beside  logs,  trees,  or 
large  rocks. 

Marin  Breeding  Distribution 

During  the  adas  years,  Spotted  Owls  were  found  breeding 
primarily  on  Inverness  Ridge,  Bolinas  Ridge,  canyons  of 
the  Mount  Tamalpais  watershed,  and  nearby  ridges  north 
to  the  vicinity  of  San  Geronimo  and  Tocaloma.  This 
distribution  mirrors  that  of  Marin's  old-growth  and  mature 
conifer  and  associated  mixed  evergreen  forests.  Represen- 
tative breeding  locations  were  Palomarin,  PRNS  (NE-NY 
4/12-6/5/77  -GBe,  SJ,  BSo);  near  Phoenix  Lake  (ON- 
NY  3/14-4/18/76  -RMS);  and  Bolinas  Ridge  along  Boli- 
nas Lagoon  (NY  6/2/81  -ARo,  DS). 

As  part  of  a  study  of  Spotted  Owl  vocalizations,  Seth 
Bunnell  in  1989  surveyed  all  of  Inverness  Ridge  and 
limited  parts  of  the  remainder  of  West  Marin  for  these 
owls.  He  located  19  pairs  and  knew  of  five  other  sites 
where  they  had  been  reported  previously.  He  estimates  that 
more  complete  surveys  of  all  potential  habitat  in  Marin 
would  reveal  at  least  30  pairs  of  Spotted  Owls  (S.  Bunnell 
pers.  comm.).  This  compares  with  another  recent  estimate 
of  25  pairs  in  the  county  (USFWS  1987a). 


224 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


Historical  Trends/  Population  Threats 

Early  in  this  century,  the  true  status  of  this  owl  was  cloaked 
in  mystery.  Mailliard  (1900)  did  not  include  the  Spotted 
Owl  among  the  owls  listed  in  his  avifaunal  summary  of 
Marin  County's  landbirds.  Reporting  on  the  San  Fran- 
cisco Bay  region,  Grinnell  and  Wythe  (1927)  considered 
the  Spotted  Owl  "very  rare,"  with  only  three  records  for  the 
area,  all  from  Marin  County.  Stephens  and  Pringle  (1933) 
added  four  additional  Marin  County  records,  all  from  near 
Phoenix  Lake,  1931  to  1933.  With  the  accumulation  of 
additional  knowledge,  Grinnell  and  Miller  (1944)  con- 
cluded that  numbers  of  this  owl  in  California  were  "no- 
where large  ...  at  best  to  be  rated  as  only  fairly  common." 
They  further  surmised  that  "no  change  in  range  or  num- 
bers [were]  apparent  from  data  in  hand."  Surely  many  of 
these  owls  had  already  been  displaced  at  that  time  by  the 
lumbering  activities  that  now  threaten  the  species'  exis- 
tence. Population  decline  has  undoubtedly  been  greater  in 
recent  decades  because  most  timber  cutting  in  California 
has  occurred  since  the  end  of  World  War  II  in  1945 
(Thomas  et  al.  1990).  From  1973  to  1977,  Gould  (1977) 
conducted  the  first  statewide  survey  of  Spotted  Owls  in 
California.  He  found  evidence  of  122  pairs  of  Northern 
Spotted  Owls  and  195  pairs  of  California  Spotted  Owls, 
largely  within  the  range  previously  described  by  Grinnell 
and  Miller  (1944).  Gould  was  unable  to  estimate  the  total 
size  of  the  California  population,  but,  applying  conserva- 
tive assumptions  to  data  from  resurveys  of  historical  sites, 
he  concluded  that  the  state's  population  had  declined  a 
minimum  of  28%  over  prior  levels. 

Based  solely  on  inventories  during  the  period  1985  to 
1989,  Thomas  et  al.  (1990)  documented  a  minimum  of 
2022  pairs  of  Northern  Spotted  Owls  in  Washington 
(360),  Oregon  (1129),  and  northern  California  (533). 
They  suspected  the  true  number  was  somewhere  between 
3000  to  4000  pairs.  From  1973  to  January  1991,  1392 
Northern  Spotted  Owl  territories  and  1439  California 
Spotted  Owl  territories  (1142  Sierra  Nevada,  297  s.  Calif.) 
have  been  located  in  California  (G.I.  Gould,  Jr.,  in  litt.). 
These  figures  do  not  represent  breeding  pairs,  as  they  have 
not  yet  been  adjusted  for  habitat  loss  at  some  sites,  lack  of 
surveys  in  about  20%  of  the  range,  intermittent  occupation 
of  some  sites,  sites  maintaining  only  single  owls,  and 
territories  with  pairs  that  rarely  breed.  Because  data  are 
lacking  on  the  size  of  the  historic  population,  the  true 
extent  of  the  decline  of  the  Northern  Spotted  Owl  is 
unknown.  Nevertheless,  population  reduction  has  been 
severe.  Outspoken  concern  for  the  viability  of  the  popula- 
tion ultimately  led  to  protection  in  1990  when  the  subspe- 
cies was  finally  listed  as  federally  Threatened.  The 
California  Spotted  Owl  remains  a  Candidate  (Category  2) 


for  federal  listing  as  Threatened  or  Endangered  (USFWS 
1991)  and  a  Bird  Species  of  Special  Concern  in  California 
(Remsen  1978,  CDFG  1991b).  Neither  subspecies  is  in 
immediate  danger  of  extinction  in  California,  but  there  is 
major  concern  at  the  lack  of  a  regulatory  mechanism  to 
ensure  that  continued  habitat  loss  will  not  fragment  the 
population  into  small  isolated  groups  (G.I.  Gould,  Jr.,  in 
litt.).  The  population  decline  is  attributed  to  habitat  reduc- 
tion from  clearing  for  agriculture,  urban  development, 
natural  events  such  as  fire  and  windstorms,  and  most 
importandy  from  logging  (Thomas  et  al.  1990).  By  some 
estimates  (perhaps  conservative),  forest  habitat  of  this  owl 
has  been  reduced  by  60%  since  1800  (mosdy  since  1900) 
and  continues  to  be  lost  at  a  rate  of  l%-2%  per  year. 
Beyond  habitat  loss,  forest  fragmentation  can  lead  to  edge 
effects,  such  as  increased  blowdowns  of  large  trees  during 
storms;  higher  predation  rates  on  Spotted  Owls  by  Great 
Horned  Owls;  competition  with  Barred  Owls  now  rapidly 
expanding  into  the  Spotted  Owl  range;  and  potential  loss 
of  habitat  or  microhabitats  that  lessen  the  effects  of 
weather,  provide  habitat  for  prey  species,  or  serve  as  refugia 
during  catastrophic  events.  Also,  fragmentation  can 
increase  the  risks  of  local  extirpation  because  of  the  greater 
likelihood  that  small  populations  will  exhibit  or  be  affected 
by  loss  of  genetic  variability,  deleterious  demographic  pat- 
terns (such  as  skewed  sex  or  age  ratios  or  poor  reproductive 
success),  environmental  variation,  or  the  inability  of  dis- 
persing individuals  to  find  and  recolonize  suitable  habitat. 
Although  most  Spotted  Owls  here  reside  in  protected 
parklands,  isolation  of  the  Marin  County  population, 
among  others,  is  of  concern  for  the  above  reasons  (USFWS 
1989c). 

The  Interagency  Scientific  Committee  to  Address  the 
Conservation  of  the  Northern  Spotted  Owl  has  proposed 
a  management  strategy  based  on  a  network  of  Habitat 
Conservation  Areas  throughout  the  subspecies'  range 
(Thomas  et  al.  1990).  Where  possible,  these  areas  should 
support  20  pairs  of  owls  and  should  be  separated  from 
other  areas  by  a  maximum  distance  of  12  miles,  features 
designed  to  minimize  the  effects  of  habitat  fragmentation. 
Although  the  Forest  Service  has  endorsed  this  strategy,  it 
has  yet  to  complete  its  own  recovery  plan.  In  the  meantime, 
political  forces  are  proposing  plans  more  favorable  to  the 
timber  industry  and  also  attempting  to  weaken  the  Endan- 
gered Species  Act  (Liverman  1 990).  The  outcome  of  this 
struggle  is  a  true  test  of  our  society's  ability  to  adequately 
cope  with  the  stark  and  obvious  realities  that  natural 
resources  are  limited  and  that  we  are  not  alone  on  this 
planet. 


225 


Typical  Owls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Owls 


LONG-EARED  OWL  Asio  otus 


U^\\'-'P^\^ 

>>s^^      \                 ^Oa_ 

Occurs  irregularly  year  round,  though  pri- 
marily as  an  irregular  winter  resident 
from  late  Sep  through  March. 
A  very  rare,  very  local  breeder;  overall 

\*\\^  \XjO 

f^V>^r^c3^^Vv^cA 

breeding  population  very  small. 

Recorded  in  2  (0.9%)  of  221  blocks. 

\\   l 

^-^\V A^  •  \**^  \  ^^\^^V^^V^'\    ^---V^^V  ----dr^^v^kV^^X^^^^-v 

O    Possible        =        0   (0%) 

^S^S^ 

©    Probable       =         1    (50%) 

^\\^c^)^                                                   •-=" 

•    Confirmed  =         1    (50%) 

FSAR  =  1          OPI  =  2          CI  =  2.50 

Ecological  Requirements 

Regardless  of  its  uncanny  ability  to  conceal  itself  during  the 
day,  this  sleek  medium-sized  owl  is  one  of  the  most  elusive 
and  puzzling  of  this  mysterious  clan.  In  some  regions,  it  is 
numerous  and  breeds  with  regularity  (Marks  1986);  else- 
where, birds  are  nomadic,  breeding  when  and  where  prey 
populations  permit.  Hence  owl  populations  fluctuate 
markedly  from  year  to  year  at  some  sites,  and  at  others 
birds  breed  only  irregularly  (Voous  1988).  Marin  County 
appears  to  fall  into  the  latter  category.  Long-eared  Owls 
often  hunt  in  open  country  of  grasslands,  meadows,  and 
fields,  where  they  seek  small  mammal  prey,  particularly 
microtine  rodents.  Apparendy  they  also  forage  in  open 
conifer  stands  or  along  their  edges  (Bull  et  al.  1989). 
Studies  in  Europe  have  linked  fluctuations  of  Long-eared 
Owl  population  densities  and  clutch  sizes  to  annual  varia- 
tions in  microtine  prey  populations  (Johnsgard  1988, 
Voous  1988).  Such  a  link  has  not  yet  been  documented  in 
North  America  (Marks  1986),  but,  given  dietary  prefer- 
ences here  (see  below),  it  undoubtedly  will  be  widi  further 
work.  Although  no  studies  were  conducted  on  their  mam- 
mal prey,  confirmed  and  apparent  breeding  of  Long-eared 
Owls  (and  Short-eared  Owls)  in  Marin  County  during  the 
adas  period  coincided  with  a  population  peak  of  voles 
(Microtus).  These  mice  were  so  abundant  that  year  that 
observers  often  found  them  scurrying  underfoot  in  the 
daytime  Q.G.  Evens  pers.  comm.).  At  the  lone  site  where 
Long-eareds  were  confirmed  breeding  in  Marin  County 
during  the  adas  period,  the  owls  nested  in  a  nonnative  pine 
plantation  surrounded  by  grassland  and  scattered  stands 
of  open  coastal  scrub.  They  were  also  seen  displaying  at  the 

226 


edge  of  a  coast  live  oak  and  California  bay-dominated 
mixed  evergreen  forest  bordering  on  open  coastal  scrub 
mixed  with  grassland.  Hence,  the  main  nesting  require- 
ments of  Long-eared  Owls  are  open  or  semiopen  short- 
grass  or  sparsely  vegetated  foraging  areas,  an  abundance  of 
small  mammal  prey,  and  suitable  nesting  and  day-roost 
sites  on  the  edges  of  adjacent  dense  forests,  thickets,  or 
planted  woodlots  (Getz  1961,  Marks  1986,  Johnsgard 
1988,  Voous  1988).  These  owls  do  not  select  specific  plant 
communities  for  breeding  in  California  (GckM  1944). 
Nesting  birds  range  from  coastal  lowlands  to  interior 
deserts  and  seem  to  favor  riparian  groves,  planted  wood- 
lots,  and  belts  of  live  oaks  paralleling  stream  courses, 
perhaps  because  these  habitats  tend  to  occur  in  the  fertile 
bottomlands  most  often  used  for  foraging.  Long-eareds 
probable  also  nest  in  conifer  forests  in  California,  as  they 
do  in  Oregon  (Bull  et  al.  1 989).  Dense  cover  is  important 
to  inhibit  nest  predation  (Marks  1986,  Bull  et  al.  1989) 
and  predation  of  adults  by  Great  Horned  Owls  (Voous 
1988). 

Long-eared  Owls  usually  lay  their  eggs  in  vacant  stick 
nests  of  crows,  magpies,  ravens,  Buteo  or  Accipiter  hawks, 
other  birds,  or  squirrels  in  trees  or  large  bushes  (Bent 
1938,  Stophlet  1959,  Craig  &.  Trost  1979,  Marks  6k 
Yensen  1980,  Marks  1986,  Johnsgard  1988,  Voous  1988). 
In  Oregon's  conifer  forests,  they  prefer  to  nest  in  dwarf 
misdetoe  brooms  (Bull  et  al.  1989).  Rarely,  they  nest  in 
shallow  cavities  in  trees  or  stumps,  in  natural  cavities  in 
cliffs,  in  semiopen  nest  boxes  or  baskets  constructed  for 
other  birds,  or  on  the  ground  in  sheltering  vegetation 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


(references  above).  There  is  limited  evidence  that  Long' 
eareds  occasionally  modify  nests  by  adding  sticks  or  small 
amounts  of  nest  lining  (Bent  1938,  Craig  <&.  Trost  1979, 
Voous  1988,  Bull  et  al.  1989).  Maximum  nest  height  is 
about  61  feet,  and  average  nest  heights  in  various  studies 
range  from  7  to  32  feet  (Stophlet  1959,  Craig  <St  Trost 
1979,  Marks  &  Yensen  1980,  Peck  &.  James  1983,  Marks 
1986,  Johnsgard  1988,  Bull  et  al.  1989)  and  probably  vary 
locally  with  the  stature  of  the  vegetation  and  available  stick 
nests  or  other  nest  sites.  In  Idaho,  Long-eareds  prefer 
partially  canopied  Black-billed  Magpie  nests  over  open 
magpie  or  crow  nests,  presumably  because  the  former 
provide  additional  concealment  (Marks  1986).  Corvid 
nests  used  by  the  owls  there  tended  to  be  wider  and  slighdy 
higher  above  ground  than  unused  corvid  nests;  wider  nests 
provide  ample  room  for  eggs  and  young  and  probably 
better  concealment  from  ground-based  predators.  Nests 
there  are  usually  near  midheight  in  trees,  and  in  clumps  of 
trees  rather  than  in  isolated  trees  or  rows  of  trees.  Nesting 
on  the  edge  of  clumps  may  reflect  the  availability  of  corvid 
nests  (Marks  1986)  and/or  selection  for  proximity  to  open 
foraging  areas.  In  Oregon's  conifer  forests,  Long-eareds 
appear  to  nest  in  the  smallest,  most  inconspicuous  plat- 
forms that  can  accommodate  them  (Bull  et  al.  1 989).  There 
the  average  distance  of  nests  from  openings  (2.5  acres  in 
size)  is  344  feet.  Probably  because  birds  do  not  defend 
foraging  territories  (Voous  1988),  Long-eared  Owls  some- 
times nest  in  loose  "colonies"  of  three  to  ten  pairs;  nests 
are  as  close  as  52  feet  in  Idaho  (Marks  1985).  Some  owls 
return  to  reuse  the  previous  year's  nest  site,  particularly  if 
they  were  successful  the  year  before  (Marks  1 986). 

Long-eared  Owls  are  primarily  nocturnal,  but  occasion- 
ally they  hunt  in  daylight  at  far-northern  latitudes,  or  when 
they  are  forced  to  by  exceptionally  short  food  supplies  at 
the  end  of  winter  (Voous  1988).  The  owls  typically  start 
hunting  25  to  30  minutes  after  sunset  and  retire  30  to  45 
minutes  before  sunrise,  with  peak  activity  in  the  few  hours 
after  activity  starts  and  before  it  diminishes.  These  owls 
have  very  acute  hearing  and  a  highly  perfected  ability  to 
locate  prey  by  sound.  Widi  their  light  bodies  and  long 
wings,  Long-eared  Owls  hunt  from  buoyant,  moddike 
flight  resembling  a  nocturnal  harrier.  This  enables  them  to 
hunt  and  hover  efficiendy  low  or  high,  and  to  capture  prey 
in  the  short  vegetation  of  open  fields,  farmlands,  grass- 
lands, marshes,  and  deserts  (Marti  1976,  Voous  1988).  In 
winter,  they  sometimes  hover  over  bushes  to  try  to  force 
out  communally  roosting  landbirds  (Voous  1988). 

Long-eared  Owls  have  a  restricted  diet.  They  specialize 
in  capturing  voles  and  mice,  and,  unlike  some  species, 
most  Long-eareds  leave  the  area  to  breed  or  winter  else- 
where in  times  of  food  shortage  (Voous  1988).  Aldiough 
the  diet  varies  between  locations  and  habitats,  it  typically 
consists  of  relatively  few  species  of  small  mammals  and 
varies  little  over  time.  Mammals  (of  45  species)  account  for 


98.2%  of  23,888  prey  items  in  North  America  and  voles 
and  deer  mice  make  up  82.2%  of  the  total;  mammals  as 
large  as  young  rabbits  are  taken  (Marti  1976).  Voles 
account  for  53.7%  of  total  prey  here  and,  as  the  dominant 
species,  range  from  29.8%  to  94-4%  of  total  prey  items  in 
local  studies.  Deer  mice,  pocket  mice,  pocket  gophers,  and 
kangaroo  rats  have  also  been  the  dominant  prey  in  some 
studies  here  (Marti  1976,  Craig  &  Trost  1979,  Marks 
1984,  Barrows  1989,  Bull  et  al.  1989).  The  preponderance 
of  voles  in  the  North  American  diet  may  be  in  part  an 
artifact  of  limited  data  on  the  diet  in  deserts  or  conifer 
forests  (Marks  1984,  Bull  et  al.  1989).  In  the  Great  Basin 
Desert  of  Idaho,  Long-eared  Owls  feed  on  a  greater  diver- 
sity of  small  mammals  than  in  other  North  American 
studies  and  predominandy  on  three  genera  of  mammals 
rather  than  on  one  or  two,  as  is  the  case  in  studies 
elsewhere  (Marks  1984).  In  the  deserts  of  soudiern  Cali- 
fornia, the  diet  of  Long-eared  Owls  in  winter  is  about  54% 
pocket  mice  and  32%  kangaroo  rats  (Barrows  1989,  n  = 
956).  In  Oregon's  conifer  forests,  the  diet  of  breeding 
Long-eareds  is  predominandy  pocket  gophers,  with  voles  a 
distant  second  (Bull  et  al.  1989,  n  =  1123).  Small  to 
medium-sized  birds  represent  1.7%  of  North  American 
prey  items  (35  species,  Marti  1976),  including  birds  as 
large  as  quail,  Ruffed  Grouse,  and  Mourning  Doves  (Bent 
1938).  Bats,  reptiles,  amphibians,  fish,  crayfish,  and 
insects  are  very  rarely  taken  (Marti  1976,  Marks  1984).  In 
Europe,  birds  may  be  important  prey  for  Long-eared  Owls 
in  winter,  with  a  higher  proportion  of  birds  taken  in  poor 
vole  years  (Voous  1988).  Prey  size  of  mammals  rather  than 
prey  type  may  be  the  most  important  factor  in  prey  selec- 
tion (Marks  1984).  In  North  America,  most  prey  weigh 
less  than  3.5  ounces  (Marti  1976,  Marks  1984),  and 
average  prey  weight  is  1 .3  ounces  (range  0.04-28  oz.,  Marti 
1976,  n  =  23,888).  In  Colorado,  average  prey  weight  is  1.1 
ounces  for  Long-eared  Owls,  compared  with  1 .6  ounces  for 
Barn  Owls,  and  6.2  ounces  for  Great  Horned  Owls  (Marti 
1974).  An  increase  in  pocket  mice  in  the  postfledging  diet 
in  Idaho  may  reflect  a  corresponding  increase  in  numbers 
of  diese  mice  in  the  environment  from  spring  to  summer, 
or,  alternatively,  young  owls  may  have  begun  to  capture 
prey  at  that  time  and  either  have  a  preference  for  smaller 
prey  or  have  more  difficulty  catching  other  species  of  mice 
(Marks  1984).  Insects,  though  rare  in  the  diet,  are  more 
frequendy  taken  in  the  postfledging  period,  suggesting  they 
are  captured  by  young  owls.  Although  females  are  slighdy 
larger  and  heavier  dian  males  and  have  much  stronger  and 
heavier  talons,  there  is  as  yet  no  evidence  of  differential  use 
of  prey  or  hunting  niches  between  the  sexes  (Earhart  & 
Johnson  1970,  Voous  1988). 

Although  die  female  may  occasionally  hunt  early  in  the 
incubation  period  (Johnsgard  1988),  the  male  does  most 
of  the  hunting  for  the  female  and  the  young  (Voous  1988). 
The  eggs  hatch  asynchronously  over  an  extended  period— 

227 


Typical  Owls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Owls 


up  to  1 1  or  1 2  days  in  a  nest  with  six  owlets  (Johnsgard 
1988).  As  an  adaptation  to  predation,  the  young  leave  the 
nest  after  about  three  weeks  of  age  to  climb  about  the 
branches,  roosting  solitarily  in  dense  foliage  until  attaining 
flight  and  leaving  the  nest  area  at  about  five  weeks  (Marks 
1986).  Hence,  where  pairs  nest  close  together,  broods  can 
mix  and  perhaps  are  sometimes  fed  by  adults  other  than 
their  parents  (Marks  1985).  On  rare  occasions,  second 
clutches  are  reported  (Voous  1988). 

Marin  Breeding  Distribution 

During  the  adas  period,  Long-eared  Owls  were  confirmed 
breeding  by  the  observation  on  12  May  1979  of  three 
adults  and  a  full-sized  juvenile  (with  some  down  still  in  its 
plumage)  at  a  pine  plantation  along  the  Estero  Trail  at  the 
head  of  Home  Bay,  PRNS  (JLo  et  al.).  In  addition,  a 
territorial  bird  was  at  Palomarin,  PRNS,  from  9  May  to  1 3 
July  1979  (PRBO).  Because  of  their  almost  stricdy  nocturnal 
habits,  their  propensity  for  irregular  breeding,  and  the  fact 
that  winter  visitant  Long-eareds  still  gather  at  communal 
roosts  at  a  time  when  local  breeding  birds  are  already 
incubating  in  March  or  early  April  (Voous  1988),  it  can  be 
difficult  to  confirm  breeding  of  this  species.  We  likely 
would  have  confirmed  breeding  for  this  species  in  more 
blocks  if  we  had  concentrated  our  efforts  at  the  first  sign  of 
the  population  explosion  of  voles  on  the  Point  Reyes 
peninsula  in  1979,  or  soon  after  stumbling  upon  the  one 


nest  that  year.  Subsequendy,  a  nest  with  five  eggs  was 
found  at  the  pine  plantation  at  Home  Bay  on  3  May  1983 
(CCu  fide  JE).  The  only  known  prior  breeding  record  for 
Marin  County  was  of  a  nest  with  eggs  observed  in  an  oak 
near  Novato  on  6  and  20  April  1904  (Ray  1904). 

Historical  Trends/ Population  Threats 

Although  they  considered  the  species  "common"  or  even 
"abundant"  locally,  Grinnell  and  Miller  (1944)  noted  a 
reduction  in  Long-eared  Owl  numbers  in  California, 
apparendy  mosdy  because  of  the  clearing  of  bottomlands 
for  farming.  Numbers  have  continued  to  decline,  and  the 
species  is  currendy  on  the  state's  list  of  Bird  Species  of 
Special  Concern  (Remsen  1978,  CDFG  1991b).  This  owl 
was  also  on  the  Audubon  Society's  Blue  List  in  1980  (Tate 
1981).  In  addition  to  the  destruction  of  riparian  habitat, 
causes  of  the  decline  in  California  may  be  collisions  with 
traffic,  shooting  and  harassment  at  nest  sites  (Remsen 
1978),  and  land  use  changes  that  have  caused  reductions 
of  the  small  mammal  prey  base.  Long-eared  Owls  have 
been  lethaHy  contaminated  by  heavy  metals,  insecticides, 
fungicides,  rodenticides,  and  PCBs,  but  the  overall  effect  on 
their  populations  has  been  less  severe  than  in  other  species 
of  owls  and  diurnal  birds  of  prey,  probabiy  because,  unlike 
buteo  hawks,  Long-eared  Owls  do  not  eat  carrion  (Voous 
1988). 


228 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


SHORT-EARED  OWL  Asioflammeus 


Almost  exclusively  an  irregular  winter  res- 

iP^r^-^      ^               ^ 

ident  from  mid-Sep  through  Mar;  excep- 

-4. ^^\'  \  jgS*^? 

tional  in  summer. 

Vfl 

yc\^r\\\ 

A  very  rare,  very  local  breeder;  overall 
breeding  population  very  small. 

^^^r^r\^^^^^<^C^\ 

Recorded  in  1  (0.4%)  of  221  blocks. 

-^vs^vV^^V    \^\    \^<\     \^*\     \  ^--V'x  ^c^\ 

O    Possible        =         0   (0%) 

}k'T>^^ 

©    Probable      =        0  (0%) 

^ar-'V'v '' 

•    Confirmed  =         1    (100%) 

j^Wh$^^^PC\^^ 

FSAR  =1          OPI  =  1           CI  =  3.00 

Ecological  Requirements 

This  arch  nomad  wanders  and  migrates  only  to  settle 
where  it  finds  high  vole  populations,  gathering  sometimes 
by  the  hundreds  and  staying  to  nest  only  as  long  as  the 
food  abundance  lasts  (Clark  1975,  Voous  1988).  Although 
Short-eared  Owls  are  resident  in  some  suitable  marsh- 
lands, these  habitats  are  increasingly  rare;  thus  the  species 
is  an  unpredictable  migrant  in  most  of  its  range.  These 
owls  occur  irregularly  in  Marin  County,  and  since  they  are 
known  to  have  bred  here  only  once  (see  below),  it  is 
difficult  to  describe  local  breeding  habitat  preferences. 
Though  the  exact  site  of  the  Marin  breeding  record  is 
unknown,  it  was  generally  in  an  area  where  dunes,  coastal 
swales,  and  grasslands  intermingle  on  Point  Reyes.  In 
California,  these  owls  breed  in  fresh,  brackish,  and  salt 
marshes;  in  lowland  meadows  and  moist  grasslands;  in 
irrigated  fields;  and  in  fallow  or  stubble  fields  (G&M 
1944,  D.  Shuford  pers.  obs.).  The  main  requirements  for 
breeding  are  low  nesting  and  resting  cover  and  open 
foraging  grounds  supporting  an  abundance  of  small  mam- 
mals, particularly  voles  (Clark  1975,  Johnsgard  1988, 
Voous  1988). 

Short-eared  Owls  defend  breeding  territories  that  vary 
inversely  in  size  with  prey  abundance  and  sometimes  nest 
close  enough  together  to  suggest  the  existence  of  nesting 
"colonies"  (Clark  1975,  Voous  1988).  They  typically  lay 
their  eggs  in  depressions  on  the  ground,  and,  unlike  most 
owls,  they  construct  their  own  nests  (Townsend  1938, 
Clark  1975,  Johnsgard  1988,  Voous  1938).  Birds  usually 
make  a  scrape  in  the  substrate  in  open  country  and  line  it 
sparsely  with  grass  stems,  weed  or  stubble  stalks,  thin 


twigs,  or  other  vegetation,  sometimes  gathered  at  some 
distance  from  the  nest.  On  occasion,  nest  sites  may  be 
mere  scrapes  in  the  ground  or  only  the  flattened  or  dead 
vegetation  of  the  spot  chosen.  Nests  may  be  entirely 
exposed  to  the  light  but  more  often  are  shielded  by  clumps 
of  grasses,  weeds,  grains,  or  low-growing  marsh  vegetation. 
Short-eareds  tend  to  pick  drier  sites  for  their  nests  than 
Northern  Harriers  do  (Clark  1975).  Very  rarely,  nests  have 
been  found  in  a  patch  of  low  bushes,  on  the  top  of  a 
broken  tree  stump  in  a  clearing,  in  old  crows'  nests,  on  a 
ledge,  and  apparendy  in  burrows  or  cavities  in  the  ground 
(Townsend  1938,  Clark  1975,  Voous  1988).  Exception- 
ally, birds  will  nest  in  the  exact  site  in  successive  years 
(Townsend  1938).  As  an  adaptation  of  ground  nesting  to 
avoid  predation,  the  young,  after  hatching  asynchronously, 
leave  the  nest  at  the  early  age  of  12  to  16  days,  scattering 
around  in  the  safety  of  "runs"  they  make  in  the  vegetation 
(Clark  1975,  Johnsgard  1988,  Voous  1988).  Chicks  may 
disperse  up  to  nearly  200  yards  in  four  days. 

Short-eared  Owls  are  primarily  crepuscular  and  second- 
arily nocturnal  hunters,  diough  they  also  forage  more  in 
the  day  than  do  most  medium-sized  owls  (Clark  1975, 
Johnsgard  1988,  Voous  1988).  These  owls  apparendy 
forage  in  the  daytime  mostly  when  they  are  unable  to 
obtain  enough  preferred  foods  in  the  night,  for  example 
when  feeding  growing  young;  birds  breeding  at  extreme 
northern  latitudes  must  of  necessity  forage  during  daylight 
hours.  Short-eared  Owls  seem  somewhat  less  dependent 
on  hearing  for  hunting  than  are  Long-eared  Owls,  though 
dieir  hearing  is   more  acute  than  that  of  their  diurnal 


229 


Typical  Owls 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Typical  Ou/ls 


ecological  counterparts,  Northern  I  larriers  (Voous  1 988). 
The  flight  of  Short-eared  Owls  seems  even  lighter,  more 
huoyant  and  mothlike  than  that  of  Long-eared  Owls.  Short- 
eareds  take  most  prey  by  surprise  as  they  quarter  low 
(mostly  1  -6.5  ft.,  rarely  over  10  ft.)  over  fields  and  marshes 
in  slow  tilting  flight,  alternately  flapping  and  gliding  on  stiff 
wings  (Townsend  1938,  Johnston  1956b,  Clark  1975, 
Johnsgard  1988,  Voous  1988).  In  such  coursing  flights, 
the  owls  usually  head  into  the  wind  and  often  hover 
momentarily  before  pouncing  (Clark  1975).  If  they  over- 
shoot their  prey,  they  frequently  turn  180°  and  pounce, 
seemingly  headfirst,  heading  downwind.  With  no  wind, 
the  owls  seem  to  prefer  to  hunt  into  or  away  from  the  light 
rather  dian  at  right  angles  to  the  light.  Short-eared  Owls 
also  hunt  from  extended  ternlike  hovering  flight  (about 
6-100  ft.  in  height),  maintaining  themselves  in  one  place 
by  varying  amounts  of  wing  flapping.  When  hovering,  the 
birds  descend  rapidly  by  raising  the  wings  in  a  deep 
dihedral.  This  may  be  followed  quickly  by  pouncing,  or  by 
checking  the  flight  at  a  lower  height  before  pouncing  or 
flying  elsewhere  to  hunt.  Clark  (1975)  felt  hovering  was 
not  a  response  to  wind,  but  radier  is  used  when  prey  is 
scarce.  Occasionally  diese  owls  land  on  fence  posts,  tree 
stubs,  grass  tufts,  or  the  ground  and  wait  for  their  prey  to 
appear  before  launching  an  attack.  This  technique  is  fre- 
quendy  used  when  weadier  conditions  are  unfavorable.  In 
interspecific  encounters  widi  harriers,  buteo  hawks,  and 
falcons,  Short-eared  Owls  may  rob  them  of  dieir  prey,  or 
vice  versa  (Voous  1 988). 

Short-eared  Owls  specialize  in  catching  voles,  lemmings, 
and  mice,  though  diey  adapt  to  a  variety  of  odier  prey  when 
local  conditions  dictate.  The  year-round  diet  (data  mosdy 
from  winter)  in  North  America  is  94-8%  mammals,  5.1% 
birds,  and  0.1%  insects,  frogs,  and  lizards  (Clark  1975,  n  = 
9640).  Voles  (Microtus)  account  for  60.6%  of  die  mammal 
prey,  but  pocket  gophers,  deer  mice,  pocket  mice,  brown 
lemmings,  Norway  rats,  and  numerous  small  terrestrial 
species  are  also  taken.  Clark  (1975)  thought  that  Short- 
eared  Owls  did  not  really  prefer  voles  but  instead  opportu- 
nistically took  whatever  prey  species  were  most  available  in 
open  habitat.  Colvin  and  Spaulding  (1983),  on  the  other 
hand,  felt  that  the  owls  preferred  the  larger  voles  over 
smaller  deer  mice  for  energetic  reasons  and  concentrated 
their  hunting  times  during  major  periods  of  vole  activity. 
In  North  America,  at  least  60  species  of  bird  prey  have 
been  recorded,  especially  open-country  and  marsh  species, 
such  as  Red-winged  Blackbirds,  Western  Meadowlarks, 
Horned  Larks,  various  sparrows,  shorebirds,  and  rails. 
Many  birds  are  probably  captured  at  night  (Clark  1975)  or 
at  least  when  there  is  little  light.  Birds  are  taken  much  more 
extensively  during  migration  or  in  winter  (e.g.,  Page  6k 
Whitacre  1975)  and  in  coastal  or  island  situations  (Clark 
1975).  The  owls  sometimes  prey  on  birds  at  seabird 
colonies  (Townsend  1938,  Voous  1988).  Insect  remains 


found  in  pellets  of  young  in  poor  vole  years  are  probably 
captured  by  the  young  while  walking  around.  It  is  doubtful 
diat  parents  would  bodier  carrying  insects  to  them  (Clark 
1975).  Average  prey  weight  of  Short-eared  Owls  is  about 
1.2  ounces  versus  1.05-1.1  ounces  for  Long-eared  Owls 
(Voous  1988). 

The  male  hunts  for  the  female  while  she  is  involved  in 
egg  laying,  brooding,  and  caring  for  the  young  (Clark 
1975,  Voous  1988).  The  female  flies  out  to  retrieve  food 
from  die  male.  Consumption  of  die  prey  is  begun  with  the 
head.  The  female  initially  tears  off  pieces  to  feed  to  the 
begging  owlets.  The  female  usually  begins  foraging  again 
when  die  chicks  first  scatter  from  the  nest,  well  before 
fledging;  in  good  vole  years,  when  the  male  is  apparendy 
able  to  provide  enough  food  for  both  the  female  and 
young,  she  remains  close  to  the  nest  throughout  nesting. 
When  food  is  plentiful,  surplus  prey  is  often  cached  at  the 
rim  of  the  nest.  Clutch  size  varies  with  die  food  supply,  but 
birds  only  rarely  lay  second  clutches  and  raise  second 
broods,  even  in  years  of  vole  abundance. 

Marin  Breeding  Distribution 

During  the  adas  period,  Short-eared  Owls  were  confirmed 
breeding  by  the  observation  of  up  to  seven  owls,  including 
diree  recendy  fledged  young  (with  traces  of  white  down  in 
dieir  plumage),  near  the  north  entrance  to  Point  Reyes 
Beach,  PRNS,  from  24  to  26  June  1979  (S6kMK  et  al.). 
This  is  the  only  known  breeding  record  for  Marin  County 
and  it  coincided  widi  the  1978-79  vole  (Microtus  californi- 
cus)  outbreak  on  Point  Reyes  which  also  appeared  to 
induce  breeding  efforts  of  Long-eared  Owls  nearby. 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  commented  on  a  decline  in 
winter  numbers  from  shooting  by  duck  hunters  but  made 
no  mention  of  a  change  in  status  of  breeding  birds. 
Nevertheless,  the  elimination  of  60%-95%  of  the  former 
marshlands  around  San  Francisco  Bay  (Nichols  6k  Wright 
1971,  Josselyn  1983)  and  habitat  loss  elsewhere  undoubt- 
edly have  gready  reduced  both  summer  and  winter  num- 
bers. The  Short-eared  Owl  has  been  on  the  Audubon 
Society's  Blue  List  from  1976  to  1986  (Tate  1981,  1986; 
Tate  6k  Tate  1982).  It  is  also  currendy  on  California's  list 
of  Bird  Species  of  Special  Concern  (Remsen  1978,  CDFG 
1991b).  Numbers  of  Short-eared  Owls  were  relatively  sta- 
ble on  Breeding  Bird  Surveys  in  California  from  1968  to 
1989  (USFWS  unpubl.  analyses).  Grazing  may  be  another 
factor  responsible  for  the  decline  of  the  species  in  the  state. 
Where  Short-eared  Owls  nest  in  extensive  farmlands,  nests 
and  young  often  are  destroyed  by  mechanized  farm  equip- 
ment (Voous  1988).  Pesticide  residues  have  been  found  in 
tissues  and  eggs  of  Short-eared  Owls,  but  the  effects  of 
diese  contaminants  on  owl  populations  are  unknown 
(Marti  6k  Marks  1989). 


230 


Typical  Owls 


SPECIES  ACCOUNTS 


Typical  Owls 


NORTHERN  SAW- WHET  OWL  Aegolius  acadicus 


-'vgt^. 

A  year-round  resident;  numbers  appar- 
endy  swell  somewhat  from  Sep  through 

J\\^\^k> 

J^>s^^      \                JC\, 

Mar. 
An  uncommon,  local  breeder;  overall 

r\vh 

'\L^V\13c^\°^ArOr^\JV-Avir^^\ 

breeding  population  very  small. 

X^s^^^i^^c^kA 

Recorded  in  32  (14.5%)  of  221  blocks. 

r-^' 

\±^(^^\^\^^\  ^Jr^V     \^\      \^\      \-^\ 

O    Possible        =      21    (66%) 

€    Probable      =        9  (28%) 

A^Va 

•    Confirmed  =          2   (6%) 
FSAR  =  2        OPI  =  64         CI  =  1.41 

3r               \^w^&-Va^ 

^s5^^ 

■   1                                                 ^-^#\  J^<$^>^r\  ° 

.>fe=>                            ~X^_/    ^^~<j 

Pv^V^AO 

Ecological  Requirements 

An  observer  imitating  the  repetitive,  penetrating  whistled 
calls  of  a  Saw-whet  Owl  in  the  heart  of  its  territory  is  likely 
as  not  to  be  aggressively  dive-bombed  as  the  occupant 
challenges  the  intruder.  Saw-whet  Owls  inhabit  Marin 
County's  Douglas  fir,  bishop  pine,  coast  redwood,  and 
mixed  evergreen  forests  and  woodlands,  as  well  as  her 
alder  riparian  thickets.  These  habitats  are  all  relatively 
moist  and  have  diverse  ground  cover  with  variably  open  or 
fairly  dense  understories  of  shrubs  and  ferns.  Mixed  ever- 
green forests  used  by  these  owls  vary  from  a  mixture  of 
dominant  trees  to  pure  bay  laurel  stands.  Throughout  their 
range,  these  owls  are  usually  found  in  conifer-dominated 
zones,  but  often  where  there  is  a  broadleaved  component 
to  the  forest  (Johnsgard  1988,  Voous  1988). 

Saw-whet  Owls  most  frequently  nest  in  deserted  wood- 
pecker cavities  and  also  in  namral  tree  cavities  and  nest 
boxes,  including  the  spacious  ones  designed  for  Wood 
Ducks  (Bent  1938,  Johnsgard  1988,  Voous  1988).  Nest 
trees  may  be  either  broadleaved  or  coniferous  species; 
cavities  may  be  in  snags  or  dead  stubs  of  live  trees.  The 
woodpecker  cavities  used  are  those  of  the  larger  species- 
Northern  Flickers,  Pileated  Woodpeckers,  and  Hairy 
Woodpeckers— with  entrances  at  least  2.8  inches  in  diam- 
eter (Johnsgard  1988).  Nest  heights  probably  reflect  what 
is  available,  principally  from  the  dominant  large  woodpeck- 
ers in  a  given  area;  an  extreme  nest  height  was  63  feet 
above  the  ground  (Bent  1 938).  In  Ontario,  the  height  of 
13  nests  ranged  from  8  to  44  feet  above  the  ground,  with 
most  from  12  to  20  feet  (Peck  6k  James  1983).  Like  most 
owls,  Saw-whets  do  not  build  nests;  instead  they  lay  their 


eggs  on  the  bottoms  of  the  cavities  on  wood  chips,  other 
naturally  accumulated  debris,  or  the  nest  materials  of 
previous  rodent  occupants,  mixed  with  feathers  of  the  owls 
(Bent  1938,  Johnsgard  1988,  Voous  1988). 

Saw-whet  Owls  are  considered  stricdy  nocturnal  in  their 
activity  patterns.  By  day  they  roost  in  thick  patches  of 
forests  in  dense  layers  of  foliage  (or  stranded  debris)  in  tree 
canopies  or  under  cover  of  vines  in  bushes  (Bent  1938, 
Johnsgard  1988,  Voous  1988).  They  generally  prefer  roost 
sites  between  6  and  12  feet,  though  rarely  as  low  as  6 
inches,  off  the  ground.  Saw-whets  forage  at  irregular  inter- 
vals through  the  night,  apparently  largely  within  forests  or 
woodlands  or  at  their  edges  (Randle  6k  Austing  1952, 
Forbes  6k  Warner  1974,  Johnsgard  1988,  Voous  1988). 
Their  highly  developed  hearing  suggests  diat  they  can 
capture  prey  in  total  or  near-total  darkness  (Johnsgard 
1988).  Saw-whets  have  bodies  radier  light  in  weight  relative 
to  the  surface  area  of  their  wings,  which  provides  for  good 
maneuverability  and  allows  them  to  hunt  in  somewhat 
shrub-dominated  cover.  There  are  few  observations  of 
actual  foraging  behavior,  but  apparendy  birds  hunt  mosdy 
from  relatively  low  perches  and  swoop  down  to  the  ground 
or,  less  frequendy,  into  the  foliage  of  trees  to  catch  their 
prey. 

The  Saw-whet  Owl  diet  is  about  96.8%  mammals,  1 .6% 
birds,  1.4%  insects,  and  0.2%  frogs  (Snyder  6k  Wiley 
1976,  n  =  435).  The  mammal  prey  consists  mosdy  of  small 
terrestrial  species,  particularly  woodland-inhabiting  deer 
mice,  voles,  and  shrews,  but  also  other  mice,  small  rats, 
young  squirrels,   flying  squirrels,   chipmunks,   and  bats 

231 


Typical  Owls 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Typical  Owls 


(Bent  1 938,  Johnsgard  1 988,  Voous  1 988).  The  owls  seem 
to  take  birds  to  a  greater  degree  when  their  numbers 
increase  during  migration  (Graber  1962,  Catling  1971)- 
Nesting  Saw-whets  at  Silver  Valley  Lakes,  San  Mateo 
County,  relied  mostly  on  deer  mice  and  stored  extra  mice 
in  the  nest  (Santee  ck  Granfield  1939).  The  diet  varies 
between  habitats  and  regions  (Johnsgard  1988,  Voous 
1988).  Mean  prey  weight  is  about  0.7  to  0.8  ounce  (Voous 
1988).  Female  Saw-whets  are  heavier  than  males,  but 
differences  between  the  sexes  in  average  prey  size  or  feeding 
habits  have  yet  to  be  demonstrated.  Since  only  the  female 
incubates  the  eggs  (Johnsgard  1988),  the  male  must  pro- 
vide her  with  food  at  least  during  this  period. 

Marin  Breeding  Distribution 

During  the  adas  period,  Saw-whet  Owls  were  found  in  the 
breeding  season  (Feb-Jul)  mosdy  in  various  habitats  on  the 
moist  conifer-  and  mixed  evergreen-dominated  coastal 
ridges,  particularly  Inverness  Ridge,  where  it  was  the  most 
common  owl  (large  or  small)  in  moderately  dense  and 
dense  forests.  Saw-whets  were  also  found  calling  locally  in 
dense  mixed  evergreen  forests  in  the  interior  of  the  county. 
If  more  nocturnal  field  work  had  been  undertaken,  we 
undoubtedly  would  have  recorded  Saw-whets  in  more 
blocks,  particularly  on  the  conifer-dominated  ridges  of  the 


Mount  Tamalpais  and  Lagunitas  Creek  watersheds.  Saw- 
whets  were  most  vocal  in  February  and  March  at  a  time 
when  local  numbers  are  swelled  by  wintering  birds;  but 
territorial  calling  is  apparendy  restricted  to  breeding  birds, 
there  being  no  evidence  that  these  owls  call  in  regions 
where  they  occur  only  as  winter  residents  (Johnsgard  1988, 
Voous  1988).  Saw-whets  can  be  heard  calling  in  almost 
every  month  of  the  year;  a  bird  at  a  breeding  site  at 
Palomarin  frequendy  called  during  the  middle  of  the  day 
(D.F.  DeSante  pers.  comm.),  though  this  is  apparendy 
unusual  (J.  Winter  pers.  comm.). 

The  only  confirmed  breeding  records  for  Marin  County 
were  established  during  the  adas  period.  A  pair  success- 
fully fledged  seven  young  from  a  nest  box  on  the  edge  of 
an  evergreen  hardwood  forest  at  Palomarin,  PRNS  (ON-FL 
spring/summer  1 979  — PRBO),  and  another  pair  occupied 
a  nest  hole  on  the  edge  of  an  alder  riparian  thicket  at 
Laguna  Ranch,  PRNS  (ON  5/2-24/79  -JGE  et  al.). 

Historical  Trends/ Population  Threats 

No  good  information  is  available  on  any  changes  in  status 
(G&M  1944,  Johnsgard  1988,  Voous  1988),  but  logging 
in  California  has  likely  reduced  numbers  of  this  forest-  and 
woodland-inhabiting  owl. 


232 


Poorwills 


SPECIES  ACCOUNTS 


Poorwills 


Poorwills 

Family  Caprimulgidae 


COMMON  POORWILL   Phalaenoptilus  nuttallii 


A  year-round  resident;  numbers  appar- 

\                     vfv 

endy  swell  in  summer. 

{\M^%^X^^ 

A  fairly  common,  very  local  breeder; 

JV**\  ^A^\  ~^<i\ 

^-V'X     'Jf^A     .3c"\    -^""A     3^^\ 

overall  breeding  population  very  small. 
Recorded  in  2  (0.9%)  of  221  blocks. 

W\\yflfCA 

j^\\  ^\%  y<^\  y<r\  y^\  j\ 

O    Possible        =         2   (100%) 

\\  L^vv^Y 

V^XA'^&o^V^V^cv 

€    Probable      =        0  (0%) 

\     \     Ar^^\    V~^^ 

^^V/a^Vv 

•    Confirmed   =         0   (0%) 

^y -r- 

iwil 

vTX_ 

FSAR=3         OPI  =  6          CI  =  1.00 

^fTA^' 

Nf^\        \->Slt-0^^\ "'"fOf'X V 

^^^ 

__pzx> 

Ecological  Requirements 

The  burning  ember-like  eyeshine  and  mellow  self-descrip- 
tive whistled  calls  of  breeding  Poorwills  are  trademarks  of 
relatively  open  chaparral  in  the  Coast  Range,  including 
Marin  County.  Poorwills  also  nest  on  gravel  streambeds, 
in  proximity  to  Lesser  Nighthawks  (Unglish  1929),  and 
likely  use  clearings  in  open  dry  pine  forests,  recently 
burned  forests,  and  clearcuts.  They  lay  their  eggs  on  the 
ground  on  bare  soil,  gravel,  sparse  leaf  and  bark  litter, 
moss,  or  flat  rocks.  They  often  locate  their  nests  at  the  base 
of  a  bush,  grass  clump,  or  rock  overhang,  diough  they 
sometimes  place  them  in  the  open  (Aldrich  1935,  Bent 
1940,  Swisher  1978).  Undisturbed  nesdings  make  short- 
distance  movements  (<10  ft.)  from  the  nest  site,  presum- 
ably for  thermoregulation  (avoiding  wet  areas  or  direct 
sunlight)  or  concealment  from  aerial  predators  (Swenson 
ck  Hendricks  1983).  Long-distance  movement  by  young 
birds  may  be  an  antipredator  adaptation  triggered  by  dis- 
turbance. 

Poorwills  are  primarily  crepuscular  and  nocturnal  feed- 
ers. They  forage  from  die  ground  or  from  low  perches- 
rocks  or  fence  posts— in  openings  such  as  clearings  or  roads 
and  capture  prey  by  short,  fluttery,  mothlike  flycatching 
flights,  returning  to  the  ground  with  their  victims.  Appar- 


endy  Poorwills  capture  some  food  on  the  ground  (Bent 
1940).  Their  diet  is  exclusively  insects,  primarily  small 
night-flying  types  such  as  moths,  beedes,  chinch  bugs, 
grasshoppers,  and  locusts. 

Marin  Breeding  Distribution 

During  the  adas  period,  Poorwills  were  found  in  the 
breeding  season  in  only  two  areas— on  Mount  Burdell, 
Novato,  and  on  Carson  Ridge.  On  Mount  Burdell,  a 
single  bird  was  calling  from  a  small  patch  of  broken 
chaparral  on  9  May  1981  (ScC).  On  Carson  Ridge,  up  to 
six  birds  were  calling  in  an  extensive  area  of  open  serpen- 
tine chaparral  on  21  May  1977  QGE  et  al.).  Though 
certainly  not  widespread  in  Marin,  Poorwills  would  un- 
doubtedly have  been  recorded  in  more  locations  if  we  had 
conducted  more  nighttime  work  in  their  rugged,  relatively 
inaccessible  breeding  habitat.  The  only  confirmed  breed- 
ing record  for  Marin  is  of  a  nest  found  on  22  July  1908 
"among  some  fragments  of  serpentine  rock  from  which  we 
had  burnt  die  low,  scrubby  manzanita  brush  the  previous 
winter"  (Mailliard  1909a);  die  site  was  above  San  Geron- 
imo,  likely  on  or  close  to  Carson  Ridge.  Recent  controlled 

233 


Poonuills 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Swifts 


burns  in  chaparral  on  Marin  Municipal  Water  District 
lands  in  the  Mount  Tamalpais  area  should  favor  this 
species. 

Historical  Trends/ Population  Threats 

Historical  trends  are  unclear,  though  it  is  likely  that  fire 
suppression  has  reduced  Poorwill  habitat;  conversely,  log- 


ging, especially  clear-cutting,  has  increased  it.  Horn  and 
Marshall  (1975)  felt  that  clear-cutting  had  increased  the 
species'  range  in  Oregon.  In  California,  Poorwill  numbers 
were  relatively  stable  on  Breeding  Bird  Surveys  from  1968 
to  1989  but  decreased  from  1 980  to  1 989  (USFWS  unpubl. 
analyses). 


Swifts 

Family  Apodidae 


VAUX'S  SWIFT    Chaetura  vauxi 


A  summer  resident  from  mid-Apr 

^^-^    \             JC\^ 

through  mid-Oct;  numbers  swell  notice- 

j0v> Vjr 

ably  during  fall  migration  in  Sep  and 

Ajx  JL. 

(- 

Oct. 

A  rare,  very  local  breeder;  overall  breed- 

V^c^ 

Or^PvA^r^SH^Vv^PC 

ing  population  very  small. 
Recorded  in  12  (5.4%)  of  221  blocks. 

O    Possible        =      12  (100%) 

\(<*r      C    *° 

€    Probable       =         0   (0%) 

i  \jkvx  \\r\  JrV \^\\^\o  Xdv 

•    Confirmed  =        0   (0%) 

Vs\i'  XX\      \^\     \^\o\^f^)\Z^%^\^ 

^^p7z^"^         ^-<^_^\^--\      X<^\  0.\>^\    \ 

^^5^^ 

FSAR=1         OPI  =  12          CI  =  1.00 

■<^LV>K 

Ecological  Requirements 

On  the  coast,  these  airborne  apparitions  prefer  redwood 
and  Douglas  fir  forests,  especially  old-growth  or  fire-swept 
stands  that  provide  decaying  trees  for  nesting.  Evidence 
from  Oregon  suggests  that  Vaux's  Swifts  may  need  old- 
growth  forests  to  satisfy  their  nest  site  requirements  (Bull 
6k  Cooper  1991). 

Unlike  closely  related  Chimney  Swifts,  Vauxes  usually 
nest  in  natural  settings  and  build  their  nests  inside  hol- 
lowed-out  trees  or  stumps  that  are  either  heavily  decayed  or 
dead.  In  northeastern  Oregon,  21  nests  were  found  in  20 
large-diameter  old-growth  grand  fir  fAbies  grandis)  trees  (1 7 

234 


live,  3  dead);  two  nests  were  in  one  tree  in  separate 
chambers  (Bull  <St  Cooper  1991).  All  nest  trees  were 
hollowed-out  by  a  fungus  that  decays  the  heartwood; 
entrance  was  made  via  holes  excavated  by  Pileated  Wood- 
peckers, as  broken-topped  trees,  that  sometimes  provide 
swifts  access  to  potential  nest  chambers,  are  scarce  in  most 
forests.  Vaux's  Swifts  also  nest  in  chimneys,  water  tanks, 
and  even  metal  boilers  on  occasion  (Taylor  1905,  Bent 
1940,  Baldwin  6k  Hunter  1963,  Baldwin  6k  Zaczkowski 
1963).  Tree  nests  are  usually  well  below  the  top  of  the  stub 
and  sometimes  are  very  close  to  the  bottom  of  the  cavity  or 


Swifts 


SPECIES  ACCOUNTS 


Su/ifts 


even  below  ground  level  if  a  stump  has  been  undermined 
by  fire  (Dawson  1923,  Bent  1940,  Bull  ck  Cooper  1991). 
In  Oregon,  19  nests  averaged  6.7  feet  below  the  entrance 
hole  used  for  access  (some  had  two  holes)  and  5.2  feet  from 
the  bottom  of  the  chamber;  2  nests  were  1.3  and  8.2  feet 
above  the  entrance  hole  (Bull  6k  Cooper  1991).  Entrance 
holes  averaged  39.4  feet  above  ground  (range  26.2-60.0 
ft.). 

Vaux's  Swifts  construct  compact  and  shallow  nests  that 
are  narrow  and  saucer  shaped.  They  use  small  pieces  of 
twigs  or  conifer  needles  that  they  stick  together  and  attach 
to  the  wall  of  the  nest  chamber  with  their  gluey  saliva.  They 
sometimes  line  their  nests  with  conifer  needles.  Birds 
apparendy  situate  their  nests  inside  chimneys  or  trees  in 
locations  providing  protection  from  rain  (Bent  1940). 

Vaux's  Swifts  forage  on  the  wing  in  open  airways  at 
variable  heights.  Their  aerial  domain  appears  to  be  the 
insect-productive  air  space  over  moist  forested  habitat, 
canyon  bottoms,  stream  courses,  and  lakes.  Birds  propel 
themselves  with  a  number  of  very  rapid  strokes,  then  sail 
or  circle  with  their  long,  narrow  wings  curved  backward 
and  downward.  The  diet  is  poorly  known  as  the  only 
evidence  appears  to  be  from  examining  the  gullets  of 
young,  in  one  nest,  which  contained  mosdy  leafhoppers 
(Bent  1940).  Presumably  the  diet  is  exclusively  aerial 
insects  of  the  general  types  taken  by  the  Chimney  Swift. 

Marin  Breeding  Distribution 

During  die  adas  years,  Vaux's  Swifts  appeared  to  nest  in 
Marin  County  only  in  small  numbers.  Most  of  the  breed- 
ing season  sightings  then  were  from  the  vicinity  of  red- 
wood or  Douglas  fir  forest  on  the  southern  part  of  Bolinas 


Ridge.  This  species  was  seen  most  frequendy  near  Kent 
Lake,  where  it  probably  nested  upslope  on  Bolinas  Ridge 
in  an  area  replete  with  dead  snags  and  stubs  of  redwood 
and  fir  that  were  charred  by  a  1945  fire.  To  the  best  of  my 
knowledge,  nesting  of  this  species  has  never  been  con- 
firmed in  Marin,  but  breeding  has  been  surmised  from  its 
nesting  season  occurrence  here  (Allen  1880,  Mailliard 
1900,  SckP  1933,  GckM  1944,  this  study).  Representative 
locations  of  breeding  season  sightings  during  the  adas  were 
ridge  on  S  side  of  Lucas  Valley  Rd.  (5/30/82  -BiL); 
Carson  Ridge  and  vicinity  of  Kent  Lake  (4  on  6/5/82 
— DS,  ITi);  and  Garden  Club  Canyon  along  Bolinas 
Lagoon  (2  on  7/4/82  -DS). 

Historical  Trends/  Population  Threats 

Given  that  Vaux's  Swifts  nest  inside  large-diameter, 
decayed  trees  which  tend  to  occur  in  old-growth  stands,  it 
is  likely  that  numbers  of  breeding  swifts  have  declined 
historically  in  Marin  County  (as  well  as  in  much  of  their 
range)  because  of  extensive  logging  in  the  last  century.  The 
effect  of  fire  suppression  on  availability  of  swift  nest  sites  is 
unclear.  Fire  may  damage  trees  that  soon  decay  to  leave 
hollow  interiors.  On  the  other  hand,  fire  may  kill  many 
smaller  trees  that  otherwise  would  have  made  good  nest 
sites  at  maturity.  Whether  swifts  will  nest  in  forests  opened 
by  logging  or  fire,  as  long  as  suitable  nests  trees  are  left 
standing,  or  whether  they  require  other  characteristics  of 
old-growth  forests  for  nesting  needs  further  study.  Num- 
bers of  Vaux's  Swifts  were  relatively  stable  on  Breeding 
Bird  Surveys  in  California  from  1968  to  1989  (USFWS 
unpubl.  analyses). 


235 


Swifts 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Swifts 


WHITE-THROATED  SWIFT    Aeronautes  saxatalis 


A  year-round  resident. 

t^\     '■  \  ^^"\^  \  -**^7:><~~^ 

\                     jr^v 

An  uncommon,  local  breeder;  overall 

breeding  population  very  small. 

\yPk\^V^\^^\^t^' 

Recorded  in  42  (19.0%)  of  221  blocks. 

(j^^^0c\^Pk^A 

O    Possible        =      34  (81%) 

\^-^>^\\z>^^ 

-V\  AAV  \^\  V^\o  V-iCo  \ 

€    Probable       -        4   (10%) 
•    Confirmed  =        4  (10%) 

\    \   auf^x''--"^*^ 

\'  Jr\  j>^\j  \^2\  o  v-"\     y>^a  !•? 

^<^^\°\^\o )^K  -kAo vfcr^ 

\^i\  •  V^rr^  Y^vo \^^a\-^  Y3*t>- 
^J^^^^X^A     Hot 

^O 

FSAR  =  2        OPI  =  84         CI  =  1.29 

Ecological  Requirements 

These  masters  of  the  air  course  over  almost  all  terrains  and 
habitats  within  foraging  range  of  their  breeding  haunts.  In 
California,  they  breed  solitarily  or  in  small  colonies  from 
near  sea  level  probably  up  to  8000  or  9000  feet  (Gaines 
1988).  Some  traditional  colony  sites  have  a  history  of  use 
of  over  50  years  (Dobkin  et  al.  1986),  but  many  of  diese 
have  probably  been  occupied  by  breeding  swifts  for  much 
longer.  White-throated  Swifts  usually  nest  in  vertical  or 
horizontal  cracks  or  crevices  in  steep  cliffs  (Bent  1940). 
The  main  nest  site  requirements  are  narrow  recessed 
nooks  and  crannies  inaccessible  to  terrestrial  predators. 
Proximity  to  good  foraging  areas  is  probably  also  important 
(Dobkin  et  al.  1986).  Throughout  much  of  their  range  they 
nest  in  granite  cliffs,  but  also  in  a  variety  of  other  rock 
types.  Granite  occurs  in  Marin  County  only  on  the  Point 
Reyes  peninsula  and  is  perhaps  serviceable  to  White- 
throated  Swifts  only  at  the  Point  Reyes  headlands;  most 
White-throateds  in  Marin  nest  in  other  substrates.  Else- 
where, these  swifts  also  nest  in  caves,  in  dug-out  Rough- 
winged  Swallow  holes  (Bent  1940),  and  in  recesses  of 
buildings  and  wharves  (Bailey  1907,  Collins  6k  Johnson 
1982).  Nests  take  the  shape  of  the  crack  in  which  they  are 
built  and  are  made  of  feathers,  plant  down,  weed  stems1, 
grasses,  and  bark,  all  glued  together  by  the  birds'  saliva 
(Bent  1940). 

White-throateds  are  considered  die  fastest  of  North 
American  swifts  (Bent  1940).  They  forage  over  a  wide 
variety  of  habitats  at  variable  heights.  Their  flight  is  more 
or  less  direct,  but  birds  feeding  hundreds  of  feet  from  the 
ground  may  dart  and  swoop  erratically  or  alternately  flap 

236 


and  soar.  Grinnell  and  Miller  (1944)  suggested  that  "pos- 
sibly the  daily  cruising  radius  of  these  birds  is  greater  than 
any  other  species,  even  the  California  Condor,"  though  no 
data  are  available  on  how  far  diat  might  be.  Excluding  the 
isolated  Point  Reyes  sightings,  all  others  made  during  the 
Marin  adas  project  were  within  five  to  seven  miles  of 
known  breeding  sites,  in  the  southern  and  eastern  part  of 
the  county.  The  White-throated  Swift's  diet  is  exclusively 
aerial  insects,  especially  flies,  beedes,  bees,  wasps,  ants,  and 
true  bugs  (Bent  1940). 

Marin  Breeding  Distribution 

Except  for  a  nest  site  at  a  bayshore  quarry,  all  confirmed 
and  probable  Marin  County  breeding  records  pertained  to 
sea  cliffs.  Representative  breeding  locations  were  cliffs  at 
Double  Point  (ON  Apr-Jun  1977  — SGA)  and  a  quarry  at 
Larkspur  Landing  (ON/DD  5/30/82  -SSm).  Three 
observations  of  aerial  copulations  near  Palomarin  (6/5/80 
PRBO)  were  not  recorded  as  confirmations  because  of  the 
uncertainty  of  the  actual  blocks  in  which  the  birds  were 
nesting;  these  may  have  been  Double  Point  rather  than 
Palomarin  breeders. 

Historical  Trends/Population  Threats 

The  White-throated  Swift:  was  unrecorded  in  Marin 
County  by  Mailliard  (1900),  whose  ornithological  explora- 
tion here  focused  mostly  on  the  vicinity  of  San  Geronimo. 
Stephens  and  Pringle  (1933)  considered  it  "very  rare"  in 
Marin  County,  and  Grinnell  and  Wythe  (1927)  thought  it 
was  established  in  the  San  Francisco  Bay  Area  only  in  the 


Swifts 


SPECIES  ACCOUNTS 


Hummingbirds 


vicinity  of  Mount  Diablo,  Contra  Costa  County.  Although 
our  atlas  data  for  Marin  and  casual  coastal  observations  for 
the  rest  of  the  Bay  Area  (ABN)  suggest  White-throated 
Swifts  are  now  more  numerous,  this  most  likely  reflects 
increased  observer  coverage,  resulting  in  the  identification 
of  more  nesting  sites  of  this  local  breeder.  On  the  other 


hand,  the  nesting  substrate  of  White'throated  Swifts  may 
inadvertently  have  been  augmented  by  excavation  of  quar- 
ries and  construction  of  buildings— sites  that  these  birds 
increasingly  use  for  nesting  elsewhere.  From  1968  to  1989, 
numbers  of  these  swifts  were  relatively  stable  on  Breeding 
Bird  Surveys  in  California  (USFWS  unpubl.  analyses). 


Hummingbirds 

Family  Trochilidae 


ANNA'S  HUMMINGBIRD   Calypte  anna 


-1  itjl 

A  year-round  resident. 

Att&i 

A  fairly  common,  very  widespread 

breeder;  overall  breeding  population 
fairly  large. 

Recorded  in  163  (73.8%)  of  221 

Mm«gsM 

blocks. 

\QJ\r^^9o^Z\t> X^\iS>  V-"\  «\/ao  V^a  ©  J 

\^~ 

nJ^-oVv  o  x>\    \>"Y  ©  \^\ ©  \^\  •  \Z^\ 

x\- 

5k?,v^<C>^^ 

O    Possible        =       55   (34%) 

SA  JHW\  ^C<^\rJ^k  °3r^®J^A®  J^\*  \><Zx  " 

€    Probable       =       76   (47%) 
•    Confirmed  =       32   (20%) 

/^\  0 iV-^V'  Jv-rC  Jv^>«A^\0  \><©  i^CPJ7^ 

<^\\^V^\  •  3r<\  ®Jr^\  o  J^dro  V^Y»  WTi A^£v 

•7  VMCV#J\P\  <iV\  '^\  *^>T©  L^sY©  V>^\ fe  Y~s 

t  S>*d3e»^ — $o>-'\  •  v<a ©  \^\o  &^\*>  w-Y»  \Z< 

FSAR  =  3        OPI  =  489        CI  =  1.86 

^®. 

>T                                          V^°J\^^3<^^3r^^cr3P,^l 

"M                                          ^®J^?i\  ®3c^S£Ar^\  ®  >-^\  •  J? 

[ji.                    ^^^*^^^ 

Ecological  Requirements 

In  December,  daredevil  display  dives  punctuated  by 
ground  squirrel-like  squeaks  are  signs  that  our  only  resi- 
dent hummingbird,  unique  perhaps  among  our  breeding 
landbirds,  is  initiating  nesting  activities  while  day  length  is 
yet  decreasing.  For  breeding,  Anna's  hummers  frequent 
oak  woodlands,  chaparral,  broadleaved  evergreen  forests, 
riparian  woodlands,  coastal  scrub,  eucalyptus  groves,  and 
suburban  plantings  and  gardens  of  Marin's  hills  and 
lowlands.  Where  they  overlap  widi  Allen's  Hummingbirds 
near  the  coast,  Annas  generally  avoid  dense,  moist  habi- 
tats. Instead  they  prefer  more  open,  sunny  habitats  with 
less  understory,  and  they  range  into  more  upland  situa- 
tions. In  the  drier  interior  of  the  Coast  Range  (away  from 
Marin),  Annas  are  somewhat  intermediate  in  habitat  pref- 


erence between  Costas,  which  occupy  very  xeric  and  open 
habitats,  and  Black-chinned  Hummingbirds,  which  fre- 
quent more  mesic  situations,  particularly  in  or  adjacent  to 
riparian  woodlands.  The  habitat  preferences  of  Anna's 
Hummingbirds  overlap  those  of  Black-chins  to  a  much 
greater  degree  than  diose  of  Costas  (Stiles  1973). 

Male  Annas  defend  territories  in  broken  vegetation  of 
scattered  trees  or  brush  or  of  forest  edges  that  provide  a 
commanding  view  of  dieir  surroundings  (Pitelka  1951a). 
The  core  area  of  the  territory  often  consists  of  a  patch  of 
low  shrubs  of  relatively  uniform  height,  with  taller  bushes 
or  trees  all  around,  from  each  of  which  die  male  can  scan 
most  or  all  of  the  area  (Stiles  1973).  To  maintain  a  vigorous 
and  consistent  territorial   defense,   breeding  males   also 

237 


Hummingbirds 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hummingbirds 


require  rich,  dependable,  and  easily  exploitable  nectar 
sources.  Preferably,  floral  sources  are  on  the  territory,  but 
they  may  also  be  a  considerable  distance  away;  males  may 
go  about  55  to  765  yards  or,  rarely,  as  much  as  0.6  miles 
for  nectar  sources.  In  coastal  sage  scnib  and  chaparral  of 
southern  California,  the  timing  of  establishment  of  breed- 
ing territories  has  evolved  to  coincide  with  the  seasonal 
blooming  of  the  chaparral  currant  (Ribes  malvaceum), 
which  begins  after  the  first  heavy  winter  rains.  Males' 
territories  are  often  centered  around  patches  of  chaparral 
currant,  particularly  the  later  blooming  R.  speciosum  (gen- 
erally occurring  on  sheltered  exposures  in  canyon  bottoms 
and  on  northern  and  eastern  exposures),  though  manza- 
nita,  eucalyptus,  or  profusely  blooming  ornamentals  may 
be  important,  as  local  conditions  dictate.  Anywhere  in 
their  range,  certain  dominant  flowering  plants  exert  a 
profound  influence  on  the  local  distribution  of  Anna's 
Hummingbird  breeding  territories. 

Females  nest  mosdy  in  shaded  woodlands,  especially  of 
live  oak  and  eucalyptus  in  this  region,  or  in  gardens.  They 
apparendy  first  locate  a  reliable  nectar  source,  then  situate 
the  nest  site  nearby.  Since  incubating  and  brooding 
females  do  not  conserve  energy  by  entering  nocturnal 
torpor,  they  must  have  a  handy  nectar  source  available  at 
dawn  and  dusk,  when  insects  are  least  available  (Stiles 
1973).  Females  defend  the  nest  site  and  flower  clumps,  but 
once  incubation  begins,  little  time  or  energy  is  available  for 
defending  anything  but  the  nest  itself.  Females  also  have 
one  or  more  prominent  perches  in  their  regular  rounds 
from  which  to  launch  insect-catching  sallies. 

Anna's  Hummingbirds  usually  build  their  nests  in  trees 
or  bushes  on  a  large  solid  surface  (Aldrich  1945,  Legg  6k 
Pitelka  1 956).  Nest  heights  range  from  1 .5  to  30  feet  above 
the  ground  in  southern  California  (Chambers  1903),  from 
5  to  30  feet  (most  11-15  ft.)  in  Santa  Barbara  (Pitelka 
1951b),  and  from  10  to  50  feet  (av.  28  ft.)  in  Santa  Cruz 
(Legg  6k  Pitelka  1956).  Birds  also  select  nest  sites  in 
orchards,  in  hanging  vines  on  cliffs,  and  in  artificial  situa- 
tions, such  as  insulated  electrical  wires  hanging  from 
service  poles,  light  fixtures,  hanging  baskets,  and  coils  of 
wire  in  outbuildings  (Dawson  1923,  Woods  1940).  The 
nests  of  Anna's  Hummingbirds  are  smaller  and  shallower 
than  those  of  Aliens,  and  they  build  them  of  plant  down, 
shredded  plant  fibers,  mosses,  and  plant  stems  bound  with 
cobwebs.  They  line  them  with  plant  down  or  feathers  and 
adorn  them  on  the  outside  with  lichens  and  plant  seeds 
(Dawson  1923,  Woods  1940,  Legg  ck  Pitelka  1956). 
Females  may  move  early-season  nests  several  times  before 
they  lay  eggs  (Legg  ck  Pitelka  1956),  and  they  may  lay  eggs 
when  only  a  minimum  of  the  cup  is  built,  construction 
continuing  during  incubation  (Dawson  1923,  Woods 
1940,  Stiles  1973). 


From  hovering  flight  or  perches,  Annas  secure  carbohy- 
drate food  by  probing  tubular  flowers  for  nectar  or  (less 
often  during  breeding)  feeders  for  sugar  solutions.  Infre- 
quently, they  sip  at  sapsucker  drillings  and  the  juices  of 
fruits  pecked  at  by  other  birds  (Woods  1940,  Foster  6k 
Tate  1966).  Although  they  use  a  wide  variety  of  native 
flowering  plants,  important  ones  in  the  breeding  season  in 
California  are  currant  (Ribes),  monkey  flower  (Diplacus), 
sage  (Salvia),  Penstemon,  manzanita,  and  paint  brush 
(Castilleja).  Annas  use  numerous  cultivated  varieties,  and 
probably  the  most  important  naturalized  species  are  tree 
tobacco  (Nicotiana)  and  eucalyptus  (Woods  1940,  Stiles 
1973).  Insects  are  also  a  staple  that  birds  procure  by 
gleaning  and  probing  trunks,  limbs,  and  leaves  in  hovering 
flight;  by  flycatching  from  exposed  perches;  and  by  extract- 
ing entangled  individuals  from  spider  webs.  From  hover- 
ing flight,  Annas  also  startle  stationary  insects  into  flight, 
then  snap  them  up  (Mobbs  1979).  Gnats,  small  flies,  ants, 
wasps,  bees,  true  bugs,  and  spiders  are  the  main  prey 
(Woods  1940).  Females  spend  much  more  time  foraging 
for  insects  in  the  breeding  season  than  do  males,  perhaps 
partly  because  males  defend  the  best  nectar  sources  and 
also  because  females  have  greater  protein  demands  for  egg 
laying  and  feeding  the  young  (Stiles  1973).  The  female 
feeds  the  young  by  regurgitation.  Females  also  apparendy 
need  additional  minerals  in  the  breeding  season,  which 
they  procure  from  mortar,  plaster,  or  sand  (Woods  1940). 

Marin  Breeding  Distribution 

Although  they  bred  widely  in  Marin  County  during  the 
adas  period,  Anna's  Hummingbirds  were  more  evenly 
distributed  and  more  numerous  in  the  eastern  part  of  the 
county,  where  open  woodlands  are  more  prevalent.  They 
were  widespread  and  numerous  in  residential  areas  along 
the  Highway  101  corridor.  Representative  nesting  localities 
were  Muddy  Hollow,  PRNS  (NE  4/22/78  -JGE,  DS  et  al.); 
Palomarin,  PRNS  (NY  3/1/78  -GBe);  the  ridge  NE  of 
Santa  Margarita  Valley-Los  Gallinas  area  (NE  4/23/82 
-BiL);  E  end  Big  Rock  Ridge  (NE  4/30/83  -BiL);  and 
Cascade  Canyon,  Fairfax  (NE-NY  4/1 1  -5/1 2/77  -DS). 

Historical  Trends/ Population  Threats 

California  is  one  of  the  few  areas  on  Earth  that  have 
undergone  such  an  extensive  and  successful  series  of  plant 
introduction  and  naturalizations.  These  changes  have  dras- 
tically altered  the  spatial  and  temporal  array  of  flowers, 
causing  far-reaching  effects  on  the  distribution,  numbers, 
and  movements,  both  local  and  long-distance,  of  hum- 
mingbirds (Stiles  1973).  The  establishment  of  exotic  flow- 
ering species  has  enhanced  the  suitability  of  many  breeding 
territories.  It  has  also  augmented  the  food  supply  and, 
hence,  survival  of  migrants  and  particularly  the  survival  of 
birds  from  late  summer  to  early  winter,  when  native 
flowers  reach  a  low  ebb  in  dry  lowland  areas.  For  these 


238 


Hummingbirds 


SPECIES  ACCOUNTS 


Hummingbirds 


reasons,  Anna's  Hummingbirds  have  increased  gready  in 
California  in  historical  times  (Woods  1940,  G&.M  1944, 
Stiles  1973).  In  the  1960s  to  early  1970s,  Annas  continued 
to  expand  considerably  in  range  and  abundance  north- 
ward  on  the  Pacific  Coast  (records  to  Alaska),  particularly 
in  California  and  Oregon,  as  diey  did  throughout  much  of 
the  Southwest  and  adjacent  Mexico  (Zimmerman  1973). 
Most  expansion  has  been  noted  in  suburban  areas,  again 
where  ornamental  and  garden  plants  and  a  proliferation  of 


hummingbird  feeders  provide  extensive  nectar  sources. 
The  widespread  expansion  of  the  species  may  be  the  result 
of  the  birds'  success  in  human-altered  habitats  in  the  core 
of  the  California  range,  ensuring  a  large  population  for 
continuing  emigration  and  recruitment  elsewhere.  From 
1968  to  1989,  numbers  of  Anna's  Hummingbirds  were 
relatively  stable  on  Breeding  Bird  Surveys  in  California 
(USFWS  unpubl.  analyses). 


"'arj.se.n    W 


Allen's  Hummingbirds  bring  enviable  intensity  and  brilliance  to  coastal  climes. 
Drawing  fry  Keith  Hansen,  1 989. 


239 


Hummingbirds 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hummingbirds 


ALLEN'S  HUMMINGBIRD   Selasphorus  sasin 


A  summer  resident  from  late  Jan 

X~rit%Vw?$>v^             \                      w~V- 

through  Jul,  sparingly  through  Aug. 

A  common,  nearly  ubiquitous  breeder; 

overall  population  very  large. 

<^\  $  Vox  ®  >--^r\  °  Jv^\  o  \^r\-  ■'V-^\  ©  V-'A  ovV-"A  °^A 

Recorded  in  198  (89.6%)  of  221 

XXwOt3^  ©  >^\  ©  V"\  o  \>\  »  v>Afl§  v>\  ©  ixT  ©  J 
\  ^-r^  ^><\  o  Y>A  ©  J^\  ©  Xf-'A  ©T^A  ©  v-'V o  -v^a 

blocks. 

VA»V\0  V-^\  ©A^A  ©  V^v  c  V^^\  ©  V-^\  o  V-^\  o  j 

\^^JWC®JV5i\c3^\    V-'A©  V^AQ  V>A  •  V^A 
n^Hvt^A  ©  V-"A  "WaoV/\o  \>ao\>a«j 
Y-V*  3k\v®  V-'IX  ©  .A^chS-v-'A  o  v^A  o  X^\ ©A^vcr-^^ 

O    Possible        =      62  (31%) 

\  YV\©nY AAA  •  V^A  «  i&?3u«  v^-QA^^^Jt-^A  •  V^aT    ) 

YU-A.©  v^A  •  V-"A *  A-'-Aa©  v-^V*  V---A©  YA-A  ©  W??3*> 

C    Probable       =     101    (51%) 

^,- 

•    Confirmed  =      35   (18%) 

1  0;3K\  °  \^\~<i  AAT\      V^V®  V-^A  O  \A-A  ©  V-*'A-f>^--' 

L>Ak  rA>A  •■  A>A  •  Wao  \3d^  \J>A"©\AkA  © AArA 

i©\J*>7YcL\r\  ©A-'.x  •A>\  P>si\  ©  Av<5\  •  V'x  *>• ATIV 

>wopn  •  v<\ •  v^a© \^y^K^\6 V"A  ©  v^a • 
"IcrijU-Ttk^ 1°  v-^\  •Y-<\  ©  V^Ao?a2-Aa«  aaA;  ©  v<: 

o  7  ~> 

FSAR  =  4        OPI  =  792        CI  =  1.86 

^V@> 

"•Jr                               A-<A  •  v>^®^V^A:^>^'v©v-N^-><^i 

T 

-T7                                    v©  V^iC«A>^?  \x\o  Wa  ©  ^ 

Pi              ^ 

i                                           ^^^V-^S-'^^v*  V-^A  ©  y>A 

Ecological  Requirements 

With  buzzing  wings  and  feverish  activity,  Allen's  Hum- 
mingbirds are  harbingers  of  spring,  arriving  on  the  breed- 
ing grounds  in  late  January  and  early  February  while  winter 
rains  still  replenish  the  land.  In  Marin,  females  nest  in 
riparian,  mixed  evergreen,  Douglas  fir,  redwood,  and 
bishop  pine  forests,  as  well  as  in  moist  north-facing  coastal 
scrub,  eucalyptus,  and  cypress  groves,  and  to  a  limited 
extent  oak  woodland.  In  most  habitats,  they  place  their 
nests  in  dense  understory  vegetation,  but  this  need  not  be 
the  case  in  eucalyptus  and  cypress  groves  or  in  the  rare 
instance  when  birds  nest  in  oak  woodland  or  in  human 
structures.  Nest  sites  are  frequendy  near  running  water, 
where  thickets  and  dense  tangles  abound.  Males  defend 
territories,  separate  from  the  females  nest  sites,  that  are 
usually  on  the  edge  of  the  above  habitats  and  adjoining 
scrub  (especially  coastal  scrub).  In  narrow  linear  habitats 
such  as  riparian  thickets  or  eucalyptus  groves,  males  may 
establish  territories  above  the  females'  nesting  sites.  Males 
rarely  frequent  the  interior  of  dense  shaded  habitat,  as  they 
need  a  commanding  view  of  their  surroundings  (Aldrich 
1945,  Legg  ck  Pitelka  1956). 

Nest  heights  usually  range  from  0.5  to  50  feet  (rarely,  to 
90  ft.)  above  the  ground  (Bent  1940,  Aldrich  1945)  and 
generally  are  lower  dian  those  of  Annas  in  areas  of  overlap. 
In  Santa  Cruz,  Allen's  Hummingbird  nests  ranged  from 
1.5  to  40  feet  (av.  18  ft.)  above  ground,  whereas  those  of 
Annas  were  from  10  to  50  feet  (av.  28  ft.)  (Legg  &.  Pitelka 
1956).  Female  Aliens  may  nest  in  close  proximity  to  each 
other,  suggesting  that  where  habitat  is  limiting,  such  as  in 
cypress  and  eucalyptus  groves,  loose  colonies  may  exist 

240 


(Bryant  1925,  Aldrich  1945).  Unlike  Annas,  which  build 
on  top  of  a  solid  support,  Aliens  usually  build  with  part  of 
the  supporting  stnjcture  incorporated  in  the  sides  of  the 
nest.  These  structures  include  limbs  and  twigs  less  than 
one  inch  in  diameter  as  well  as  vine  runners,  fern  stems 
and  fronds,  and  the  like  (Aldrich  1945;  see  for  further 
details  on  nest  site  selection  and  attachment).  In  Marin, 
Allen's  Hummingbirds  use  many  species  of  trees,  espe- 
cially eucalyptus  and  cypress,  for  nest  support.  In  under- 
story thickets,  they  prefer  blackberry  brambles  and  sword 
ferns.  Females  here  also  select  artificial  sites  inside  build- 
ings—in rope  or  wire  slings,  on  iron  hooks,  and  under 
rafters  (Mailliard  1913,  PRBO  nest  records).  They  build 
tiny  deep  nest  cups,  using  mosdy  moss  on  the  outside  and 
willow  down  and  pappus  from  composite  seeds  in  the 
lining.  Other  important  nest  materials  are  lichens  (on  the 
outside),  feathers,  shredded  leaves,  grass  fibers,  and  hair. 
The  females  bind  them  all  together  and  attach  them  to  the 
supporting  structure  with  spider  webs  (Aldrich  1945).  As 
in  the  case  of  Annas,  the  female  Aliens  also  sometimes  lays 
eggs  on  a  mere  platform  that  is  completed  later  and 
typically  adds  nest  material  throughout  nesting  (Aldrich 
1945). 

Little  has  been  written  on  the  foraging  and  food  prefer- 
ence of  this  species,  but  diey  appear  to  be  quite  similar  to 
those  of  the  Anna's  Hummingbird  (see  account).  When 
numbers  of  Aliens  first  appear  in  Marin  in  February,  they 
use  Ribes  flowers  extensively.  The  timing  of  migratory 
movements  may  have  evolved  to  coincide  with  the  bloom- 
ing of  these  shrubs. 


Hummingbirds 


SPECIES  ACCOUNTS 


Kingfishers 


Marin  Breeding  Distribution 

During  the  atlas  period,  the  Allen's  Hummingbird  was 
one  of  the  most  common  and  widespread  of  all  of  Marin 
County's  breeding  species,  but  it  was  in  the  zone  of 
persistent  summer  fogs  near  the  immediate  coast  that  this 
species  was  most  numerous  and  evenly  distributed. 
Although  some  birds  bred  on  moist  ridges,  most  were 
concentrated  in  thickets  of  the  lowlands  and  canyon  bot- 
toms. In  the  interior  of  Marin,  most  breeding  activity 
centered  around  riparian  thickets  and  eucalyptus  groves; 
most  forests  in  this  region  generally  lack  dense  understory 
cover.  Representative  breeding  locations  were  cypress 
grove  at  Mendoza  Ranch,  Point  Reyes  (NE  5/30/80  — DS); 
near  stream  at  Bear  Valley,  PRNS  (NE  3/22/81  -DS); 
cypress  by  streamside  at  Tennessee  Valley  (NE-NY  3/28- 


4/25/77  — GMcM);  and  a  live  oak  in  open  oak  woodland 
on  Big  Rock  Ridge  near  Marinwood  (NE  3/24/79  — DS). 

Historical  Trends/ Population  Threats 

It  seems  likely  that  the  planting  of  early-blooming  exotics 
and  an  increase  in  hummingbird  feeders  has  benefited  the 
species,  especially  early  in  the  nesting  season,  when  contin- 
uing winter  rains  curtail  available  food  and  foraging  time. 
Allen's  Hummingbirds  have  undoubtedly  extended  their 
range  locally  into  areas  where  suitable  nesting  habitat 
formerly  was  limited  but  where  eucalyptus  and  cypress 
have  since  been  planted  in  grassland.  Numbers  of  Allen's 
Hummingbirds  were  relatively  stable  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989  (USFWS  unpubl. 
analyses). 


Kingfishers 

Family  Alcedinidae 


BELTED  KINGFISHER   Ce^le  alcyon 


A  year-round  resident. 

iSr 

t\^>-\ 

An  uncommon,  somewhat  local 

joV^V 

iJ\\  j^\\ <?^-^^  ^r*J~^-Ar-~J\. Jt><\^ 

breeder;  overall  breeding  population  very 

V o b<^\      \^\      i^\     i  Y^nf      V-^A      \^\ 

s  AJ^rV  °3r\*  Jer^v  Y^C  Wv  X^K 

><VoJ 

small. 
Recorded  in  73  (33.0%)  of  221  blocks. 

O    Possible        =      46   (63%) 
€    Probable       =         5   (7%) 

/jJr"\       v^^v*C  Xs-^y      \^*^\~0  \^\       Y, 

x?o» 

•    Confirmed  =       22   (30%) 
FSAR  =  2        OPI  =  146        CI  =  1.67 

"iT                   ^-o^v*5<^ 

^S^\°3r\3 

j£z>                               ~xJv 

^^^^r\ 

Ecological  Requirements 

These  dashing  crested  piscivores  raise  their  rattling  hue 
and  cry  along  streams,  freshwater  ponds,  and  shallow 
estuarine  margins  that  provide  favorable  food  supplies. 
Kingfishers  usually  excavate  nest  burrows,  using  their  bills 
and  feet,  in  well-drained  eartdien  banks  widi  vertical  or 
slightly  overhanging  faces  that  are  bare  or  sparsely  vege- 
tated (Bent  1940,  White  1953,  Cornwell   1963).  Often 


these  are  naturally  created  by  water  erosion,  but  road  cuts, 
gravel  excavations,  ditch  banks,  and  other  human  modifi- 
cations afford  nest  sites  as  well.  Kingfishers  may  excavate 
burrows  at  any  height  but  usually  do  so  at  least  five  feet 
from  the  bottom  and  not  more  than  two  feet  from  the  top 
of  die  bank,  to  limit  access  by  mammalian  predators.  They 
dig  burrows  that  vary  in  length  from  about  three  to  seven 


241 


Kingfishers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Kingfishers 


feet,  shorter  ones  generally  in  harder  substrates,  and  dig 
them  on  a  horizontal  plane  unless  they  encounter  obstacles 
(White  1953).  The  nest  chamber  is  usually  spherical  or 
ovoid  and  somewhat  flattened  on  the  bottom,  with  the  nest 
below  the  level  of  the  tunnel.  Females  lay  eggs  either  on 
bare  earth  or  on  the  debris  of  regurgitated  food  pellets. 
When  there  is  a  limited  supply  of  nest  sites,  Kingfishers 
occasionally  nest  in  the  open  tops  or  decayed  sides  of 
stumps  or  trees  and  in  earth  adhering  to  roots  of  large 
upturned  trees;  they  even  nest  in  sawdust  piles,  though 
generally  unsuccessfully  (White  1953).  A  dead  or  dying 
tree  or  other  suitable  perch  generally  overlooks  each  nest 
site.  Although  most  nests  are  over  or  near  water,  they  may 
be  up  to  a  mile  from  a  water  source  (Cornwell  1963). 

Kingfishers  feed  either  from  perches  or  from  hovering 
flight  20  to  50  feet  in  the  air.  They  dive  headlong,  nearly 
vertically  or  at  an  angle,  into  relatively  shallow  and  calm 
water,  securing  prey  with  their  large  bills.  Kingfishers  dive 
mosdy  in  water  less  than  two  feet  deep,  and  even  in  deeper 
water  they  probably  do  not  catch  prey  below  this  depth 
(White  1953).  They  often  subdue  or  stun  prey  before 
swallowing  by  whacking  them  against  a  perch.  Foraging 
flights  take  the  birds  0.5  to  5  miles  from  the  nest  site;  most 


trips  are  within  a  1-mile  distance,  though  daily  flights  of  2 
miles  are  not  uncommon  (Cornwell  1963).  Although  the 
diet  is  often  up  to  90%- 100%  fish  (Salyer  6k  Laglar  1946, 
White  1953),  at  some  sites  crayfish  occasionally  predomi- 
nate (White  1953,  Eipper  1956).  Other  minor  food  items 
are  large  insects,  other  invertebrates,  salamanders,  frogs, 
lizards,  young  birds,  mice,  shrews,  and  even  berries  (Bent 
1940,  Salyer  6k  Laglar  1946,  White  1953).  Small  adult  and 
larval  insects  found  in  Kingfisher  pellets  undoubtedly  are 
from  the  ruptured  stomachs  of  their  fish  prey  (White 
1953).  Adults  feed  the  young  relatively  large  fish,  such  that 
one  to  three  will  fill  the  stomach  of  a  single  nesding. 

Marin  Breeding  Distribution 

Breeding  Kingfishers  were  patchily  distributed  in  Marin 
County  during  the  adas  period  because  of  limitations  of 
suitable  feeding  and  nesting  sites.  Breeders  concentrated 
along  the  west  side  of  Tomales  Bay,  where  steep  banks  are 
almost  continuous  from  Inverness  north  to  Tomales  Point. 
Representative  nesting  sites  were  Abbott's  Lagoon  (FL 
6/14/82  — DS);  near  Sacramento  Landing,  Tomales  Bay 
(FL  6/18/82  -DS);  Salmon  Creek  along  the  Marshall- 


J*4~ 


y  0 


' 


;  v 


BE 

Fish  obscures  face  as  this  Belted  Kingfisher  brakes  to  enter  its  burrow  and  feed  its  growing  young.    Photograph  b}  Ian  Tail. 


242 


Kingfishers 


SPECIES  ACCOUNTS 


Woodpeckers 


Petaluma  Rd.  (FY  6/21/82  -DS);  and  Stafford  Lake, 
Novate  (ON  5/1/82  -ScC). 

Historical  Trends/Population  Threats 

Numbers  were  formerly  reduced  (G&M  1944)  by  shoot- 
ing resulting  from  fishermen's  disfavor.  After  it  was  real- 
ized that  Kingfishers  help  control  some  fish  species 
destructive  to  trout's  eggs  and  young,  human  persecution 
of  Kingfishers  decreased  and  the  birds'  populations 
increased.  Fishermen's  needs  have  also  been  met  by  cover- 
ing rearing  ponds  with  wire  mesh.  Although  the  creation 


of  reservoirs  may  have  increased  habitat  in  areas  such  as 
Marin  County,  where  natural  lakes  and  permanent 
streams  are  few,  elsewhere  damming  of  year-round  streams 
and  riprapping  for  bank  protection  have  probably  more 
than  counterbalanced  these  positive  effects.  Human  deple- 
tion of  fish  resources  upon  which  Kingfishers  depend 
likely  has  also  been  to  the  species'  detriment.  Numbers  of 
Kingfishers  were  relatively  stable  on  Breeding  Bird  Surveys 
in  California  from  1968  to  1989  but  decreased  from  1980 
to  1989  (USFWS  unpubl.  analyses). 


Woodpeckers 

Family  Picidae 


ACORN  WOODPECKER    Melanerpes  formicivorus 


A  year-round  resident. 

if%>- 

A  fairly  common,  somewhat  local 

A-^^O^A 

breeder;  overall  breeding  population 

A%t 

A  JV"A  -A^A'OA'  •\QA^^®3^\°3r\L^ 
"\   Ar\   Ar\  °A^A    A-""A  •  A-"A  o  V-r  \ 

small. 

Recorded  in  86  (38.9%)  of  221  blocks. 

r\  J<\  J<^\  3r^-3r^°3PA^A^A 

\ A-^\  -^yr\   A^V    V^xoA^A    A^\  •  J 
vKA  -J<\  Ar\    A-^A    A^\    A-"\  •  V-^A 

O    Possible        =      40   (47%) 

«JiAk  \  ^A^\  ^Vv\  ^V\  ^V\  j^\«Jl 

A^A    A-^A  •  jtr^A  *Ai>A  •  v<2\-'0  \^AA»  \A--A  ^L\ 
<^Ak  tfV^*iV^*At^*^Sr»>^®A-^ 

H  \  ^->7V  I    V>"^       V^\  *A^\  <T^--"A  •  «^c1\»  \J-^\  Q  \" 

— --r" 

€    Probable       =       14   (16%) 
•    Confirmed  =       32   (37%) 

FSAR=3        OPI  =  258       CI  =  1.91 

J><V   vV\     VA  ° \^o\>5nA^«' VA     \>\oS^ 
><X~>^        ^-_V"A  GJ^\   ■  ■JpzX*>%<\ °Ar«^\  </  /A 

i^^                                             \~^j            ^~^*^*iSQ<^**\ 

Ecological  Requirements 

As  their  name  suggests,  Acorn  Woodpeckers  are  intimately 
dependent  on  the  fruits  of  oak  trees,  mostly  of  die  genus 
Quercus.  They  are  permanent  territorial  residents  in  almost 
all  California  forests  and  woodlands  with  a  reasonable 
density  and  diversity  of  oaks.  In  Marin  County,  their 
habitat  includes  oak  woodlands  and  savannah;  relatively 
open  Douglas  fir,  redwood,  mixed  evergreen,  and  riparian 
forests;  and  residential  areas  where  oaks  have  been  pre- 
served or  planted. 


Acorn  Woodpeckers  nest  exclusively  in  cavities  diey 
excavate  in  living  trees  or  dead  snags,  including  pines, 
oaks,  sycamores,  and  palm  trees;  they  may  also  use  utility 
poles.  Holes  are  often  reused  for  nesting  and  are  also  used 
for  nocturnal  roosting  outside  the  breeding  season. 

Nesting,  as  well  as  all  other  phases  of  Acorn  Wood- 
pecker home  life,  is  performed  in  groups,  and  up  to  12 
individuals  may  participate  in  incubation  and  feeding  of 
nestlings  (Ritter  1938,  MacRoberts  &  MacRoberts  1976, 

243 


Woodpeckers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Woodpeckers 


Koenig  ck  Mumme  1987).  Only  one  nest  at  a  time  is 
attended  by  a  group.  Within  a  group,  up  to  three  females 
may  jointly  lay  eggs,  and  up  to  at  least  four  males  may 
compete  for  matings  with  the  breeding  females.  These 
cobreeding  sets  of  birds  are  almost  always  close  relatives, 
usually  siblings  or  else  a  parent  and  its  offspring  of  the 
same  sex.  There  is  considerable  competition  among  joint- 
nesting  females  within  a  group,  and  a  female  that  lays  her 
eggs  first  frequendy  has  them  removed  from  the  nest  and 
subsequendy  eaten  by  her  cobreeding  female  relatives. 
Additional  group  members  consist  of  offspring  of  both 
sexes  that  may  remain  in  their  natal  group  as  nonbreeding 
"helpers"  for  one  to  five  years  prior  to  dispersal  (Koenig  6k 
Mumme  1987).  Breeding  takes  place  in  die  spring  and 
early  summer  (Apr  to  mid-Jul,  with  die  peak  of  egg  laying 
near  the  end  of  Apr),  although  in  bumper  acorn  years  it 
may  also  occur  in  the  fall  (Aug-Nov).  The  latest  docu- 
mented first-egg  date  is  23  September,  at  Hastings  Reserva- 
tion in  Monterey  County  (Koenig  6k  Mumme  1987). 

Acorn  Woodpeckers  are  critically  dependent  on  mast. 
The  birds  store  acorns  or  other  mast,  harvested  direcdy 
from  the  trees  in  fall,  one  by  one  in  individual  holes  drilled 
in  communally  defended  storage  trees  or  "granaries." 
Though  granaries  typically  contain  about  1000  to  4000 
storage  holes,  they  may  host  up  to  20,000  or  more!  These 
storage  facilities  are  usually  in  snags,  dead  limbs,  thick 
bark,  or  structures  such  as  the  wooden  eaves  or  roofs  of 
houses.  They  may  be  in  pines,  oaks,  sycamores,  redwoods, 
Douglas  firs,  incense  cedars,  cottonwoods,  fence  posts, 
utility  poles,  palm  trees  (Ritter  1938),  or,  exceptionally,  in 
large  pine  cones  (Jenl  1979).  The  birds  usually  store 
acorns,  but  also,  to  a  lesser  degree,  cultivated  nuts  (Ritter 
1929),  pine  seeds  (MacRoberts  ck  MacRoberts  1976, 
Stacey  6k  Jansma  1977),  and  such  bizarre  items  as  stones 
(Ritter  1938)  and  Douglas  fir  cones  (W.D.  Koenig  pers. 
obs.).  These  latter  items  are  probably  secured  by  young 
birds  that,  in  their  zeal  to  store  food,  fail  to  discriminate 
between  suitably  shaped  edible  and  nonedible  items. 

Stored  acorns  are  eaten  diroughout  the  winter  mondis 
and  are  critical  to  successful  spring  reproduction  in  at  least 
some  areas.  Insect  predators  of  acorns,  especially  weevil 
larvae,  may  also  be  eaten  if  encountered,  but  the  myth  that 
acorns  are  stored  as  "nurseries"  for  these  insects  is  untrue 
(see  MacRoberts  1974).  Acorn  Woodpeckers  also  eat 
diverse  other  foods  that  they  capture  with  a  variety  of 
techniques  (MacRoberts  1970).  Flycatching  is  common  at 
all  seasons  during  good  weather.  Sapsucking  occurs  regu- 
larly in  late  summer  (Jul  and  Aug)  and  late  winter  (Jan- 
Mar).  Oak  catkins  are  eaten  in  late  winter  and  early  spring, 
and  bark  gleaning  occurs  regularly.  Finally,  birds  have  even 
been  recorded  hovering  and  picking  at  wild  oat  seeds 
(MacRoberts  ck  MacRoberts  1976).  Major  food  items 
include  acorns,  sap,  catkins,  ants,  beedes,  bees,  wasps,  true 
bugs,  and  earwigs.  Observers  at  Hastings  Reservation  occa- 


sionally have  even  seen  Acorn  Woodpeckers  eating  lizards 
(genus  Sceloporus).  Exceptionally,  diese  birds  prey  on  the 
eggs  or  young  of  other  species  of  birds  (Shuford  1985). 
They  particularly  prize  crane  flies  as  food  for  their  nesdings 
but  also  feed  die  young  a  wide  variety  of  insects,  as  well  as 
acorn  fragments  (Beal  1911,  MacRoberts  ck  MacRoberts 
1976,  Koenig  6k  Mumme  1987). 

Marin  Breeding  Distribution 

During  die  adas  period,  Acorn  Woodpeckers  were  wide- 
spread breeders  in  Marin  County's  forested  regions  and, 
as  elsewhere  in  their  range,  were  limited  to  extensive  stands 
of  oaks.  Most  coastal  birds  were  dependent  on  coast  live 
oaks,  but  valley  oaks  became  increasingly  important  in  the 
northeastern  corner  of  the  county  near  Novate  Acorn 
Woodpeckers  were  absent  from  the  largely  treeless  tracts  of 
land  on  outer  Point  Reyes  and  east  of  Tomales  Bay,  and 
they  occurred  only  to  a  limited  extent  along  the  shore  of 
San  Francisco  and  San  Pablo  bays.  Representative  breed- 
ing localities  were  Mt.  Burdell,  Novato  (ON  5/?/82  — 
ScC);  Pioneer  Park,  Novato  (ON  5/?/82  -ScC);  and 
Olompali,  Novato  (ON  4/V79  —ScC).  Of  interest  is  a 
small  population  of  birds  with  golden,  rather  than  red, 
crowns  that  was  resident  in  die  San  Geronimo  area  up 
until  at  least  1980  (W.D.  Koenig  pers.  obs.). 

Historical  Trends/  Population  Threats 

Locally,  birds  are  threatened  by  the  loss  of  oaks  to  develop- 
ment, but  often  they  are  able  to  adapt  well  to  exotic 
conditions  as  long  as  mast  trees  remain.  Perhaps  a  more 
important  long-term  threat  is  the  possible  future  loss  of 
large  stands  of  oaks  because  of  a  lack  of  recruitment  of 
young  oaks;  the  causes  of  this  include  grazing  pressures  of 
cattle  and  deer  on  seedlings  and  damage  to  acorns  from 
insects  and  rodents  (Griffin  1977).  Although  logging  prac- 
tices tend  to  open  up  dense  forests  and  favor  hardwood 
trees  such  as  oaks,  these  species  are  generally  slow  growing 
and  are  often  removed  by  forest  managers  to  favor  econom- 
ically important  conifers. 

The  only  major  hole  competitor  of  the  Acorn  Wood- 
pecker is  the  introduced  European  Starling  which  can,  at 
least  occasionally,  render  breeding  difficult  for  groups  of 
woodpeckers  by  usurping  their  favored  holes.  However, 
the  only  study  of  competition  between  these  species  per- 
formed to  date  reported  that  reproductive  success  and 
group  size  of  Acorn  Woodpeckers  were  not  affected  by 
Starlings  (Troetschler  1976).  It  remains  to  be  seen  whether 
this  conclusion  will  hold  at  other  study  sites,  or  if  Starlings 
continue  to  expand  in  California.  Numbers  of  Acorn 
Woodpeckers  on  Breeding  Bird  Surveys  in  California  were 
relatively  stable  from  1968  to  1989  but  increased  from 
1980  to  1989  (USFWS  unpubl.  analyses). 

WALTER  D.  KOENIG 


244 


Woodpeckers 


SPECIES  ACCOUNTS 


Woodpeckers 


RED-BREASTED  SAPSUCKER   Sphyrapicus  ruber 


Occurs  year  round,  though  primarily  as  a 

\                  J«Oa_ 

winter  resident  from  late  Sep  through 

y\^\js^ 

C^t\^ 

mid-Mar. 

S^CX^k 

\\  %<^\\^\\^\ \ 

V^-  - 

A  rare,  very  local  breeder;  overall  breed- 
ing population  very  small. 

-^^AfAp^V^C^ 

Recorded  in  5  (2.3%)  of  221  blocks. 

P^kv 

O    Possible        =         3   (60%) 

,\^Vo JSe*?\'  \^<Jjf^ \^\ 

^VA^r^y -r- 

€    Probable       =        0  (0%) 
•    Confirmed  =         2   (40%) 

\ — -^3''\VV*'A  A^V J$r' 

^^5^°- 

FSAR=1         OPI  =  5           CI  =  1.80 

i 

^>^> 

Ecological  Requirements 

In  California,  the  nasal  breeding  calls  of  Red-breasted 
Sapsuckers  emanate  primarily  from  moist  conifer  forests  or 
woodlands,  as  well  as  bordering  riparian  zones  dominated 
by  aspens  or  alders  (Shuford  1986).  In  Marin  County, 
Red-breasted  Sapsuckers  breed  in  mixed  evergreen  wood- 
lands or  riparian  groves  of  alders  and  willows  adjacent  to 
Douglas  fir  forests.  They  drill  their  nest  holes  from  4  to  70 
feet  above  the  ground;  in  the  Sierra  Nevada,  average  nest 
height  of  49  nests  was  42  feet  (Raphael  6k  White  1984). 
Birds  use  dead  trees,  limbs,  stubs,  or  live  trees  for  nesting; 
occasionally  they  occupy  previously  used  holes  (Lawrence 
1967).  Although  they  appear  to  prefer  deciduous  trees  over 
conifers  (Bent  1939,  Howell  1952,  Crockett  ck  Hadow 
1975),  in  the  Sierra  Nevada,  Red-breasted  Sapsuckers  may 
select  predominandy  conifer  snags  (Raphael  ck  White 
1984).  Sapsuckers  find  live  aspens  with  tough  outer  shells 
of  sapwood  and  centers  decaying  from  "infection"  by  shelf 
fungi  (Fomes)  especially  attractive;  such  sites  provide  better 
protection  than  dead  trees  do  from  the  ravages  of  predators 
like  raccoons  (Bent  1939,  Kilham  1971).  Nest  hole  orien- 
tation appears  to  favor  light  and  warmth,  with  a  tendency 
for  southern  or  eastern  exposures,  lower  height  in  open 
surroundings,  and  location  on  the  edges  of  clearings  (Law- 
rence 1967,  Inouye  1976). 

Unlike  most  woodpeckers,  these  birds  rarely,  if  ever,  dig 
deep  into  decaying  trees  for  wood-boring  insects  and  lar- 
vae. Instead  they  primarily  glean  active  exposed  insects 
from  trunks  and  limbs  and,  secondarily,  flycatch  against 
clusters  of  leaves  or  needles.  They  also  make  flycatching 
sorties  into  the  air  from  perches,  fly  to  the  ground  after 


visible  insects,  and  search  for  ants  on  the  ground  in  the 
manner  of  flickers  (Bent  1939,  Howell  1952,  Kilham 
1977,  Raphael  ck  White  1984).  They  use  conifers  exten- 
sively for  insect  foraging.  Although  they  pick  many  wild 
fruits  from  trees  and  bushes  (and  hang  chickadeelike  on 
branch  tips  to  pluck  off  aspen  buds),  most  vegetable  matter 
that  sapsuckers  consume  comes  from  the  characteristic 
small  square  holes  that  they  drill  in  trees,  most  frequendy 
in  series  of  horizontal  and  vertical  rows  (Tate  1973). 
Sapsuckers  show  a  strong  preference  for  drilling  these 
holes  in  young  trees  in  dense  stands,  in  trees  marked  by 
previous  sapsucker  working,  and  in  those  already  weak- 
ened or  wounded  in  some  manner  (Kilham  1964,  Law- 
rence 1967).  In  California,  they  drill  them  preferentially  in 
native  members  of  the  willow  and  birch  families,  though 
they  also  use  conifers  to  a  lesser  extent  (Bent  1 939,  GckM 
1944).  They  also  use  orchard  trees  extensively.  The  birds 
drink  sap  from  the  holes  and  also  eat  the  soft  inner  bark, 
or  cambium,  of  the  trees.  Although  some  authors  feel  that 
sapsuckers  take  many  insects  that  are  attracted  to  the 
oozing  sap  (Tate  1973),  others  feel  this  practice  is  infre- 
quent (Kilham  1977). 

Adults  feed  the  young  primarily  insects  (Howell  1952) 
and  also  some  sap  (Kilham  1977),  though  perhaps  inciden- 
tally (Lawrence  1 967).  The  size  of  insects  they  feed  to  young 
increases  with  the  nesdings'  age  (Lawrence  1967).  The 


Some  information  on  aspects  of  natural  history  were  obtained 
from  studies  of  the  Yellow-bellied  Sapsucker  (S.  varius),  formerly 
considered  conspecific  with  the  Red-breasted  Sapsucker,  whose 
habits  do  not  appear  to  differ  materially  from  its  congener. 

245 


Woodpeckers 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Woodpeckers 


September-to-March  diet  of  the  Red-breasted  Sapsucker 
(exclusive  of  sap)  is  69%  animal  and  31%  vegetable  (Beal 
1911,  n  =  34);  in  montane  California,  the  birds'  summer 
diet  is  96%  animal  and  4%  vegetable  (Otvos  &.  Stark 
1985,  n  =  19);  in  the  Sierra  Nevada,  its  June-to-July  diet  is 
88%  animal  and  1 2%  vegetable  (Dahlsten  et  al.  1985,  n  = 
8).  Animal  fare  is  mosdy  made  up  of  ants  and  scale  insects 
along  with  smaller  amounts  of  beedes,  bees,  wasps,  aphids, 
termites,  and  miscellaneous  insects.  Vegetable  fare  consists 
of  fruits  and  berries,  cambium,  and  seeds;  bark  use  peaks 
in  spring  (Tate  1973). 

Marin  Breeding  Distribution 

Red-breasted  Sapsuckers  were  unknown  as  breeders  in 
Marin  County  before  the  adas  project  began  (Mailliard 
1900,  S6kP  1933,  GckM  1944).  We  found  them  to  be  very 
local  breeders  in  the  Olema  Valley  and  vicinity.  Represen- 
tative breeding  locales  were  Bear  Valley  Headquarters, 
PRNS  (NY  6/22/80  -DS)  and  Five  Brooks,  PRNS  (FL 
10/18/82  —EH,  MAS).  The  young  at  the  former  site  were 


apparently  destroyed  by  Acorn  Woodpeckers  (Shuford 
1985).  See  Shuford  (1986)  for  additional  possible  and 
probable  breeding  records  for  Marin  County. 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  mapped  the  breeding  distribu- 
tion in  coastal  California  as  extending  south  as  far  as 
central  Mendocino  County.  Shuford  (1986)  reviewed 
recent  records  and  concluded  that  Red-breasted  Sapsuck- 
ers breed  continuously  south  to  northern  Sonoma  County, 
with  a  small  disjunct  population  in  Marin  County.  A 
search  of  historical  sources  revealed  that  there  had  been 
very  little  ornithological  investigation  of  any  kind  in  the 
area  of  apparent  range  extension  until  recent  years.  This 
strongly  suggested  that  sapsuckers  previously  had  been 
overlooked  in  this  region,  rather  dian  that  they  had 
expanded  their  breeding  range.  Current  adas  work  in 
Sonoma  County  is  likely  to  add  further  details  to  the 
known  breeding  range. 


NUTTALL'S  WOODPECKER   Picoides  nuttalli 


A  year-round  resident. 

vv^>5rv\  ^V\  aVa\ 0Avaap  A^tf*  K\o  \>-\c>  A 
\  A-cSX   w^\    A-^\  °\^\  Q\^\  o^c^\  o\^*C< &\^\ 

V5  X>=fA  AA^A  oVA  *  \7\o  l/TowcM 

A  fairly  common,  somewhat  local 

breeder;  overall  breeding  population 
small. 

Recorded  in  72  (32.6%)  of  221  blocks. 

O    Possible        =       51    (71%) 

\  A 

vXA  Ar    \  Ar"f\    A-^A    A^"\  °  V-^\  ®A 

^fCv-T  V\  Jk\^<\  ®V<\  a^ca ftA-"\o-^ 

\  Ar^J3?<\    A^V*>A<i.jO  VATo  V^A    '  A-^A   *  r 
#r\  -A-^A_jA<^A'  ••'jA'A  o  Xs^\  *  A^"A  o  \^\  *  \^j 
Q\  J<\+^c\  'A\^A    \A\    j^OA^Vo^^T  • 
^A"\  At     \  Ar'lAA>"'i\    A<T\     A--'\,Q-A>A '--_\ 
'A.i — \  AV^\  *AV^\'--O^A  &  A-^\     A-^A  *  A^-A 

' 

€)    Probable       =       14  (19%) 
•    Confirmed   =         7    (10%) 

Air    \   Ay^\    A-^\   A"^\J  \-^\     A-^\  o  \*<\~\  A' 

FSAR  =  3        OPI  =  216        CI  =  1.39 

^p& 

Ecological  Requirements 

The  dry  rattling  calls  of  Nuttall's  Woodpeckers  resound 
from  open,  primarily  deciduous  oak  woodlands,  and  bor- 
dering riparian  groves,  which  may  be  especially  attractive 
for  nesting.  In  Monterey's  Carmel  Valley,  Nuttalls  usually 
center  their  home  ranges  around  drainages  (Miller  6k  Bock 
1972).  In  the  interior  of  Marin  County,  they  apparendy 
also  sometimes  nest  in  open  eucalyptus  and  cypress  groves, 

246 


far  from  oak  woodlands,  but  then  usually  near  streamside 
vegetation.  Elsewhere  in  California  in  ecological  zones 
supporting  oaks,  Nuttall's  Woodpeckers  may  also  breed  in 
open  riparian  forests  devoid  of  oaks  or  where  gray  pines 
(Pinus  sabiniana)  mix  with  oaks.  Nevertheless,  throughout 
its  range  as  a  whole,  perhaps  the  most  consistent  element 
of  Nuttall's  Woodpecker  foraging  habitat  is  a  dominance 


Woodpeckers 


SPECIES  ACCOUNTS 


Woodpeckers 


of  oak  trees  (Block  1991).  Openness  also  seems  to  be  a  key 
character  of  Nuttall's  Woodpecker  habitat.  In  the  breeding 
season  these  woodpeckers  generally  avoid  Marin's  coastal 
riparian  habitat  which  tends  to  be  dense  and  is  never 
bordered  by  true  oak  woodland. 

Although  Nuttalls  drill  many  of  their  nest  cavities  in 
oaks  (Block  1991),  they  appear  to  prefer  soft-wooded  spe- 
cies of  trees  when  available,  perhaps  because  their  foraging 
style  leaves  them  ill-equipped  for  deep  digging  in  hard 
wood  (Miller  6k  Bock  1972).  Nest  holes  range  from  3  to 
45  feet  (av.  1 7  ft.,  n  =  54)  above  the  ground  and  are  usually 
in  dead  limbs  or  trunks. 

Nuttall's  Woodpeckers  are  much  more  versatile  and 
acrobatic  foragers  than  either  Downy  or  Hairy  woodpeck- 
ers (Miller  6k  Bock  1972).  Nuttalls  forage  for  insects 
principally  on  the  surface  and  shallow  subsurface  of  trees 
mosdy  by  light  pecking  and  tapping,  bark  scaling,  probing, 
gleaning,  and  foliage  and  twig  scanning  (Miller  6k  Bock 
1972,  Jenkins  1979,  Block  1991).  To  a  limited  degree,  they 
drill  and  excavate  extensively  in  classic  woodpecker  fash- 
ion, sapsuck,  flycatch,  and  pick  seeds  from  pinecones.  At 
times,  birds  climb  through  foliage  clusters,  fluttering  and 
balancing  with  their  wings  and  hanging  upside  down  to 
procure  fruits  (Miller  6k  Bock  1972).  Nuttalls  generally 
glean  more  but  peck  and  probe  less  during  breeding  than 
in  the  nonbreeding  season  (Block  1991).  The  proportional 
reliance  on  various  foraging  techniques  also  varies  between 
habitats,  as  does  use  of  foraging  substrates.  Across  various 
habitats,  Nuttall's  Woodpeckers  perform  about  90%  (n  = 
907)  of  their  foraging  maneuvers  on  branches  or  trunks; 
about  53%  involve  twigs  and  small  branches  (Block  1991). 
About  75%  of  foraging  attempts  are  directed  at  live  stems 
of  trees  and  only  about  2%  at  fruits,  cones,  and  leaves.  On 
average,  trees  used  for  foraging  are  larger  indiameter  and 
taller  than  those  generally  available;  die  size  characteristics 
(height,  trunk  diameter,  and  canopy  size)  of  trees  used  for 
foraging  differs  among  study  sites  and  between  seasons 
and  years.  Nuttall's  Woodpeckers  tend  to  forage  mosdy 
about  two-thirds  up  the  height  of  the  tree  and  40%- 70% 
of  the  distance  from  the  center  to  the  edge  of  the  canopy, 
which  corresponds  to  the  location  of  small  and  medium- 
sized  branches,  the  two  most  frequendy  used  foraging 
substrates  (Block  1991). 

Although  closely  tied  to  oaks  at  all  seasons,  Nuttall's 
Woodpeckers  vary  their  preference  for  foraging  trees  both 
among  sites  and  between  seasons,  as  indicated  by  selection 
of  tree  species  out  of  proportion  to  their  availability  (Miller 
6k  Bock  1972,  Block  1991).  In  the  Carmel  Valley  during 
the  breeding  season— when  deciduous  oaks  are  newly 
leafed  out— birds  forage  almost  exclusively  in  oaks,  primar- 
ily on  and  around  branchlets  and  leaves  (Miller  6k  Bock 
1972).  At  other  times,  birds  there  shift  much  of  their 
foraging  to  live  oaks,  particularly  during  winter  and  early 
spring  when  other  trees  are  bare.  Block  (1991)  confirmed 


the  tendency  of  Nuttalls  to  concentrate  foraging  in  the 
breeding  season  on  white  (deciduous)  oaks,  but  at  some 
sites  found  that  birds  increased  foraging  in  trees  such  as 
gray  pines,  rather  than  live  oaks,  during  the  nonbreeding 
season. 

In  one  study  in  the  Carmel  Valley,  Jenkins  (1979) 
detected  sexual  differences  in  foraging  behavior  during  the 
postbreeding  season  (Jun-Oct).  There  females  fed  primar- 
ily by  gleaning.  They  foraged  more  frequendy  on  smaller 
branches,  twigs,  and  foliage,  and  used  more  obliquely 
oriented  positions  than  did  males.  Males  fed  primarily  by 
surface  tapping  and  also  fed  lower  in  trees  than  did 
females.  In  contrast,  Block  (1991),  working  at  two  sites  in 
the  Sierra  Nevada  and  one  in  the  Tehachapi  Mountains, 
found  little  variation  between  the  sexes  in  either  foraging 
behavior  or  foraging  habitat  during  breeding  (Apr-Jun) 
and  nonbreeding  (Nov-Feb)  seasons.  Males  and  females 
at  his  study  sites  used  similar  foraging  maneuvers,  sub- 
strates, and  macrohabitats.  The  size  of  trees  used  by  males 
and  females  differed  slighdy,  and  males  tended  to  forage 
relatively  higher  in  trees  than  did  females  (contra  Jenkins 
1979).  These  slight  differences  may  have  allowed  the  sexes 
to  partition  limited  resources  or  may  reflect  dominance  by 
one  sex  over  the  odier  (Block  1991). 

The  diet  in  California  is  79%  animal  matter,  primarily 
beedes,  true  bugs,  caterpillars,  and  ants  and  other  hyme- 
nopterans  (Beal  1911,  n  =  53).  Consumption  of  animal 
matter  varies  from  about  87%  of  the  diet  in  winter,  to  80% 
in  spring  and  summer,  to  65%  in  fall  (Martin  et  al.  1951, 
n  =  52).  Vegetable  fare  includes  wild  fruits  and  seeds,  such 
as  elderberry,  blackberry,  raspberry,  poison  oak,  and 
acorns,  along  with  cambrium  and  flower  buds  (Beal  1910, 
1911).  Sap  is  taken  as  the  opportunity  arises  (Miller  6k 
Bock  1972). 

Marin  Breeding  Distribution 

During  the  adas  period,  breeding  Nuttall's  Woodpeckers 
were  concentrated  in  the  northern  interior  of  Marin 
County,  especially  around  Novate  They  were  extremely 
rare  on  the  immediate  coast  during  the  nesting  season  but 
occurred  there  with  greater  regularity  during  postbreeding 
dispersal,  starting  in  mid-  to  late  June  (see  adas  map).  At 
that  time,  some  birds  shift  to  coastal  eucalyptus  and  cypress 
groves  and  riparian  woodlands.  Representative  nesting 
locations  were  Mt.  Burdell,  Novato  (ON  5/7/82  — ScC); 
Stafford  Lake,  Novato  (ON  4/V82  -ScC);  and  Novato 
area  (NY  5/6/77  —RMS).  An  old  nesting  record  for  Ross 
(see  below)  and  a  pair  entering  a  nest  hole  at  Bear  Valley 
Headquarters,  PRNS,  on  1 1  May  1985  (DS)  indicate  occa- 
sional nesting  in  southern  and  coastal  Marin  County. 

Historical  Trends/ Population  Threats 

In  his  annotated  list  of  Marin  County's  landbirds, 
Mailliard  (1900)  considered  die  Nuttall's  Woodpecker  an 

247 


Woodpeckers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Woodpeckers 


"exceedingly  rare  visitant  in  major  portion  of  county,  but 
more  numerous  near  northern  boundary."  Stephens  and 
Pringle  (1933)  listed  it  as  "uncommon"  here,  and  a  record 
of  a  pair  feeding  young  at  Ross  on  16  June  1929  (Gull  1 1 , 
No.  7)  was  considered  noteworthy.  These  reports  occurred 


before  much  exploration  of  the  Novato  area,  where  we 
found  the  species  numerous  during  the  adas  period.  From 
1968  to  1989,  numbers  of  Nuttall's  Woodpeckers  were 
relatively  stable  on  Breeding  Bird  Surveys  in  California 
(USFWS  unpubl.  analyses). 


DOWNY  WOODPECKER    Picoides  pubescens 


A  year-round  resident. 

A — C*^ 

An  uncommon,  widespread  breeder; 

vVJ^ 

overall  breeding  population  small. 
Recorded  in  145  (65.6%)  of  221 

YssrS  XxV\  °3<<a  °  A^v  •  j^v.  \<c\o  V^C  \^\ 
\c5oNa-^ --jJ*r\   jxr\°b^\    V^\    \^\    \^\ 

blocks. 

O    Possible        =      81    (56%) 
©    Probable       =       25   (17%) 

U-^v  Jen®  v^0^^^^^^^^^^  jA\ °v 

-•r- 

•    Confirmed  =       39   (27%) 
FSAR=2        OPI  =  290       CI  =  1.71 

^ 

Ecological  Requirements 

This  petite  lively  woodpecker  inhabits  Marin  County's 
riparian  tracts  and  moist  mixed  evergreen  forests,  espe- 
cially those  dominated  by  California  bay  trees.  Downies 
also  occasionally  forage  in  adjacent  shrubby  habitats  and 
tall  weed  fields.  They  overlap  to  a  limited  degree  widi  die 
larger  Hairy  Woodpecker  in  broadleaved  forests,  but  for 
the  most  part  they  avoid  the  conifer  forests  preferred  by 
that  species.  Downies  also  overlap  to  a  small  degree  with 
Nuttall's  Woodpeckers  in  riparian  groves  or  at  the  ecotone 
between  broadleaved  evergreen  forests  and  oak  woodlands, 
but  the  latter  species  prefers  more  open  woodlands.  Down- 
ies usually  drill  their  nest  holes  in  the  soft  wood  of  dead 
trees,  dead  branches  of  live  trees,  and  stumps,  and  occa- 
sionally in  live  trees;  most  nest  cavities  are  close  to  the  tops 
of  brokenoff  stubs  of  dead  trees  (Bent  1939,  Lawrence 
1967,  Conner  et  al.  1975).  Nest  heights  range  from  3  to 
50  feet  or  more  above  the  ground  (Bent  1939).  Downies 
excavate  their  nest  cavities  in  shorter,  smaller-diameter 
trees  and  at  lower  heights  than  do  Hairies  (Conner  et  al. 
1975;  see  Hairy  Woodpecker  account).  Eleven  Downy 
Woodpecker  nests  in  Ontario  ranged  from  12  to  45  feet 
and  averaged  29  feet  above  the  ground  (Lawrence  1967), 
whereas  19  nests  in  Virginia  ranged  from  4  to  38  feet  and 

248 


averaged  16  feet  above  the  ground  (Conner  et  al.  1975).  In 
some  areas,  nest  holes  appear  to  be  oriented  with  respect 
to  light  and  warmth  and  tend  to  have  southern  or  eastern 
exposures  and  occur  at  lower  heights  in  open  surround- 
ings (Lawrence  1967);  elsewhere,  a  northeasterly  orienta- 
tion may  provide  shelter  from  wind  and  rain  (Conner 
1975,  1977).  The  slope  of  die  trunk  appears  to  be  the  most 
important  factor  in  nest  orientation  (Conner  1975,  1977); 
nest  holes  facing  slightly  downward  prevent  rain  from 
entering  the  cavity  and  aid  in  defense  of  the  hole  from 
predators. 

Downies  forage  primarily  by  drilling  and  scaling  but 
also  by  gleaning,  probing,  and  occasionally  by  hovering 
and  flycatching.  They  direct  most  foraging  attempts  at  bark 
but  do  some  gleaning  from  leaves  and  flower  clusters. 
Though  Downies  forage  more  frequendy  in  the  lower 
zones  of  the  canopy,  they  can  feed  from  the  tops  of  trees  to 
the  ground  (Willson  1970,  Williams  1975).  Downies  also 
exploit  insects  in  galls  on  tall  weed  stalks  (Confer  6k  Paicos 
1985);  birds  involved  seem  always  to  be  males  (Grubb  6k 
Woodrey  1990).  Compared  with  the  closely  related  but 
larger  Hairy  Woodpecker,  Downies  forage  more  on  the 
smaller  branches  and  twigs  of  trees;  they  probe  and  glean 


Woodpeckers 


SPECIES  ACCOUNTS 


Woodpeckers 


Downy  Woodpeckers  often  select  nest  holes  on 
where  gravity  can  hinder  tree<limbing 

to  a  greater  extent;  they  do  not  drill  as  often  or  penetrate 
to  as  great  a  depth;  and  they  feed  on  different  tree  species 
(Koplin  1969,  Kisiel  1972,  Conner  1981).  See  Nuttall's 
Woodpecker  for  comparison  to  that  species. 

It  is  well  documented  that  the  sexes  of  Downy  Wood- 
peckers exploit  different  foraging  niches.  Males  drill  more 
on  small  branches  and  twigs  than  do  females,  which  tend 
to  forage  more  on  larger  branches  and  trunks  (Jackson 
1970;  Kilham  1970;  Willson  1970;  Kisiel  1972;  Williams 
1975,  1980).  Experimental  studies  suggest  that  males  may 
choose  the  more  productive  portions  of  the  forest  and 
exclude  females  from  these  sites  (Grubb  ck  Woodrey 
1990).  On  the  whole,  there  is  no  consistent  relationship 
between  the  vertical  foraging  distribution  on  trees  of  males 
versus  females,  as  has  been  found  in  individual  studies 
(Grubb  &.  Woodrey  1990).  Because  of  the  above  substrate 
preferences,  males  generally  tend  to  forage  more  by  dril- 
ling, females  more  on  the  surface  by  probing  and  gleaning 
(Jackson  1970,  Kisiel  1972,  Williams  1980).  In  winter, 
males  feed  more  on  dead  substrates  and  on  a  wider  array 
of  tree  species  than  do  females  (Williams  1980).  In  general, 
Downies  forage  more  on  live  than  on  dead  trees  (Jackson 
1970,  Kisiel  1972,  Williams  1975),  though  their  use  of 


the  downward-oriented  side  of  leaning  trees, 
predators.    Photograph  b)i  Ian  Tait. 

dead  trees  increases  in  winter  when  it  can  be  roughly 
equivalent  to  their  use  of  live  trees  (Jackson  1970).  Since 
surface  foraging  techniques  are  more  important  on  live 
trees  and  subsurface  techniques  on  dead  trees,  Downies 
increase  their  drilling  and  decrease  surface  probing  and 
gleaning  in  winter  (Jackson  1970,  Conner  1981).  Travis 
(1977)  also  noted  that  in  winter,  Downies  forage  more  on 
furrowed  wood  and  larger  trees  and  less  on  branches;  see 
Conner  (1981)  for  additional  differences  in  seasonal  forag- 
ing methods.  Between-habitat  foraging  differences  have 
also  been  noted  (Williams  1975). 

The  annual  diet  of  the  Downy  Woodpecker  in  Califor- 
nia is  77%  animal  and  23%  vegetable  (Beal  1910,  n  =  80), 
which  is  remarkably  similar  to  the  species'  continentwide 
diet  of  76%  animal  and  24%  vegetable  (Beal  1911,  n  = 
723).  In  the  mountains  of  California  (season  unspecified), 
the  diet  of  males  (n  =  12)  is  95%  animal  and  that  of 
females  (n  =  1 7)  99%  (Otvos  ck  Stark  1985;  see  for  further 
slight  sexual  differences  in  diet).  In  the  East,  reliance  on 
animal  matter  varies  from  86%  in  summer  to  71%  in  fall 
and  winter  (Martin  et  al.  1951,  n  =  828).  In  Illinois  in 
winter,  females  consume  more  homopterans  and  spiders 
than  do  males,  presumably  because  they  probe  more  in 

249 


Woodpeckers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Woodpeckers 


bark  crevices  and  select  rough-barked  trees  to  forage  in 
more  than  males  do  (Williams  1980).  Males  take  more 
ants  than  do  females,  apparently  because  they  peck  into 
smaller  limbs  and  are  more  adept  at  removing  them  witJi 
their  larger  tongues.  The  bulk  of  the  species'  animal  food 
is  insects,  especially  beedes  (particularly  wood-boring  lar- 
vae), ants,  caterpillars,  and  true  bugs  (scale  and  plant  lice); 
other  insects,  spiders,  millipedes,  pseudoscorpions, 
sowbugs,  and  snails  are  taken  infrequendy.  Although 
wood-boring  beede  larvae  are  important  to  both  Downy 
and  Hairy  woodpeckers,  Downies  eat  only  about  half  the 
amount  that  Hairics  do,  substantiating  the  fact  that  Down- 
ies peck  into  wood  much  less  frequently  (Beal  1911).  The 
size  of  insects  fed  to  young  increases  with  nesding  age 
(Lawrence  1967).  The  vegetable  component  of  die  diet  is 
largely  various  fruits,  mast,  and  seeds,  though  grain,  galls, 
flower  petals  and  buds,  and  cambium  are  eaten  to  a  limited 
extent.  Sap  is  also  eaten  occasionally  (Foster  6k  Tate  1966). 


Marin  Breeding  Distribution 

Although  Downy  Woodpeckers  were  distributed  widely 
diroughout  the  forested  regions  of  Marin  County  during 
die  atlas  period,  they  occurred  primarily  in  the  lowlands 
and  along  moist  drainages.  Representative  nesting  loca- 
tions were  Chileno  Valley  (FY  5/30/82  -DS);  along 
Miller  Creek,  E  end  Big  Rock  Ridge  (FY  6/6/82  -BiL); 
near  Alpine  Lake  (NY  6/5/82  — DS);  and  Panoramic 
Hwy.,  W  of  Pantoll  (FY  6/2/81  -DS). 

Historical  Trends/Population  Threats 

Few  prior  data  exist,  but  numbers  of  Downy  Woodpeckers 
decreased  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989  (USFWS  unpubl.  analyses). 


HAIRY  WOODPECKER   Picoides  villosus 

A  year-round  resident. 

An  uncommon,  somewhat  local 

breeder;  overall  breeding  population 

^~~<\    vx^C-'x  ^\\  >-VaV  Jv    \    \/YoV/a    VX,  j 

small. 

Recorded  in  82  (37.1%)  of  221  blocks. 

x^^N^^vA^vA^J^^V^rjXv 

O    Possible        =       54   (66%) 

V^^VCvn- V^\  A^b3^^^\^A^\^V^C 

€    Probable      =       10  (12%) 

T- 

•    Confirmed  =       18  (22%) 
FSAR  =  2        OPI  =  164       CI  =  1.56 

^3^^--^>iv^Y\^c^V 

AO\>A 

5^€ 

^S^ 

VD 

.     l^>              -^<—%^ 

<sWr- 

Ecological  Requirements 

Although  near  look-alikes  except  for  subtle  differences  in 
size  and  plumage,  Hairy  and  Downy  woodpeckers  are 
nonetheless  quite  distinct  ecologically.  The  Hairy  Wood- 
pecker occupies  Marin  County's  conifer,  mixed  conifer, 
and  moist  evergreen  hardwood  forests  and  coastal  riparian 
thickets.  In  the  latter  two  forest  types,  it  overlaps  to  a 
limited  degree  with  the  Downy  Woodpecker.  Hairies  exca- 
vate their  nest  cavities  in  live  trees,  dead  trees,  or  dead  parts 
of  live  trees.  Some  authors  have  reported  that  Hairies 

250 


prefer  live  trees  for  nesting  (Kilham  1965,  Lawrence  1967), 
but  they  use  dead  trees  or  dead  portions  of  live  trees  more 
commonly  in  the  Sierra  Nevada  (Raphael  ck  White  1984). 
Nest  holes  range  from  3  to  1 00  feet  above  the  ground  (Bent 
1939)  and  on  the  average  are  in  firmer  wood,  in  larger 
trees,  and  higher  above  the  ground  than  those  of  Downies 
(Conner  et  al.  1975).  The  heights  of  1 1  Hairy  Woodpecker 
nests  in  Ontario  ranged  from  1 5  to  45  feet  and  averaged 
35  feet  (Lawrence  1967);  those  of  10  nests  in  Virginia 


Woodpeckers 


SPECIES  ACCOUNTS 


Woodpeckers 


ranged  from  8  to  65  feet  and  averaged  29  feet  (Conner  et 
al.  1975);  and  those  of  19  nests  in  the  Sierra  Nevada 
averaged  16  feet  (Raphael  6k  White  1984).  In  some  areas, 
nest  holes  appear  to  be  oriented  with  respect  to  light  and 
warmth,  with  most  having  a  southern  or  eastern  exposure 
and  those  in  open  surroundings  occurring  at  lower  heights 
(Lawrence  1967).  Conner  (1975,  1977)  reported  that  the 
slope  of  the  trunk  appears  to  be  the  most  important  factor 
in  nest  orientation.  Nest  holes  facing  slighdy  downward 
prevent  rain  from  entering  the  nest  cavity,  though  locally  a 
northeasterly  orientation  may  also  provide  shelter  from 
prevailing  winds  and  rain.  The  downward  orientation  also 
aids  in  defense  of  the  nest  hole  from  predators.  Lawrence 
(1967)  reported  that  Hairy  Woodpecker  nest  holes  are 
often  excavated  near  some  sort  of  protrusion  that  provides 
camouflage  and  protection  from  weather. 

Birds  forage  mosdy  by  rapid  drilling,  pecking,  probing, 
scaling,  gleaning,  and  excavating  on  live  and  dead  trees, 
stumps,  downed  logs,  and  occasionally  on  the  ground;  they 
sometimes   hover  and   flycatch  (Kilham   1965,   Stallcup 

1968,  Kisiel  1972,  Conner  1981,  Raphael  &  White  1984, 
Lundquist  6k  Manuwal  1990).  Hairies  sometimes  take 
advantage  of  insects  uncovered  by  Pileated  Woodpeckers' 
prying  off  thick  bark  or  digging  deep  holes  (Maxson  6k 
Maxson  1981).  In  Virginia  in  winter,  Hairies  rely  more  on 
scaling  and  excavating  and  less  on  pecking  (Conner  1981 ; 
see  for  additional  seasonal  differences).  In  die  Washington 
Cascades,  Hairies  increase  pecking,  decrease  probing,  and 
eliminate  gleaning  from  spring  to  winter  (Lundquist  6k 
Manuwal  1990).  Compared  with  Downies,  they  tend  to 
drill  more  often  and  deeper  and  to  forage  more  on  larger 
branches  and  trunks  and  on  different  tree  species  (Koplin 

1969,  Kisiel  1972,  Conner  1981). 

Hairy  Woodpeckers  expand  their  foraging  niche  by  the 
males  and  females  working  different  species  of  trees,  or  by 
each  sex  using  different  proportions  of  various  foraging 
techniques,  substrates,  or  heights.  Females  tend  to  special- 
ize in  surface  foraging  methods  on  larger  branches  and 
limbs,  whereas  the  males  excavate  deeper  in  dead  trees  and 
spend  more  time  on  smaller  branches  (Kilham  1965, 
Kisiel  1972).  Morrison  and  With  (1990)  described  the 
seasonal  changes  in  the  foraging  niche  of  male  and  female 
Hairy  Woodpeckers  (relative  to  White-headeds)  in  the 
mixed  conifer  zone  of  the  Sierra  Nevada.  In  summer, 
males  and  females  forage  both  in  trees  of  similar  height 
and  at  similar  heights  in  these  trees.  Although  both  sexes 
forage  at  greater  heights  and  in  taller  trees  in  winter,  males 
exceed  females  in  both  categories  then  but  still  forage  at  die 
same  relative  height  in  trees  as  do  females.  Both  sexes 
choose  similar-diameter  trees  at  both  seasons.  Males  and 
females  both  concentrate  their  foraging  on  trunks  at  both 
seasons,  but  both  sexes  increase  use  of  limbs  during 
winter;  they  seldom  use  twigs  in  either  season.  Bodi  sexes 
divide  foraging  activities  relatively  evenly  between  dead  and 


live  substrates  in  summer  and  winter.  On  the  other  hand, 
males  make  relatively  even  use  of  available  tree  species  for 
foraging  during  both  seasons,  whereas  females  concentrate 
foraging  on  white  fir  and  ponderosa  pine  in  summer  and 
incense  cedar  and  black  oak  in  winter.  Males  and  females 
concentrate  their  foraging  during  the  first  five  hours  after 
sunrise  in  summer  and  the  five  to  nine  hours  after  sunrise 
in  winter.  Lundquist  and  Manuwal  (1990)  reported  sea- 
sonal changes  in  Hairy  Woodpecker  foraging  in  the  Wash- 
ington Cascades  but  did  not  distinguish  between  the 
patterns  of  males  and  females. 

The  Hairy  Woodpecker  annual  diet  is  about  78%  ani- 
mal and  22%  vegetable  (Beal  1 91 1 ,  n  =  382).  It  varies  litde 
seasonally,  with  animal  matter  comprising  74%-76%  in 
winter  and  fall  and  80%-82%  in  spring  and  summer 
(Martin  et  al.  1951,  n  =  405).  In  the  mountains  of  Califor- 
nia (season  unspecified),  the  diet  is  about  92%-93% 
animal  matter  (Otvos  6k  Stark  1985,  n  =  69).  The  main 
animal  foods  are  wood-boring  beede  larvae,  ants,  caterpil- 
lars, weevils,  true  bugs,  and  scale  insects,  along  with  other 
insects,  spiders,  and  millipedes.  Although  their  diets  are 
generally  quite  similar  to  Downies',  Hairies  consume 
about  twice  as  many  wood-boring  beede  larvae,  attesting  to 
dieir  more  frequent  and  deeper  drilling  (Beal  191 1).  Com- 
pared with  female  Hairies,  the  males  consume  more  wood- 
boring  beetle  larvae,  bark  beetles  that  inhabit  thicker  bark, 
and  carpenter  ants,  again  because  die  larger-billed  males 
drill  deeper;  females  consume  more  scale  insects  found 
under  the  loose,  scaly  bark  of  incense  cedar  (Otvos  6k  Stark 
1985,  Morrison  6k  Widi  1990).  The  size  of  insects  fed  to 
young  increases  with  the  age  of  nesdings  (Lawrence  1967). 
Vegetable  foods  include  fruits,  seeds,  grain,  mast,  cam- 
bium, and  sap.  In  the  nonbreeding  season,  mast  and  pine 
seeds  may  be  important  foods  (Beal  191 1 ,  Stallcup  1968). 

Marin  Breeding  Distribution 

During  the  adas  period,  the  breeding  distribution  of  the 
Hairy  Woodpecker  in  Marin  County  was  much  more 
restricted  than  that  of  the  Downy  Woodpecker.  Hairies 
were  confined  largely  to  Inverness  Ridge,  Bolinas  Ridge, 
and  the  Mount  Tamalpais  watersheds.  Breeding  birds 
away  from  these  areas  were  usually  found  in  patchily 
distributed  conifer  or  moist  evergreen  hardwood  forests  in 
canyons  or  on  north-facing  slopes.  Representative  nesting 
locations  were  Inverness  (ON  5/2/80  — DS);  Bear  Valley, 
PRNS  (NY  5/26/76  -RMS);  Alpine  Lake  (FY  6/5/82 
-DS);  and  Bon  Tempe  Lake  (FY  5/1 2/76  -RMS). 

Historical  Trends/ Population  Threats 

Few  prior  data  exist,  but  numbers  of  Hairy  Woodpeckers 
were  relatively  stable  on  Breeding  Bird  Surveys  in  Califor- 
nia from  1968  to  1989,  despite  a  decrease  from  1980  to 
1989  (USFWS  unpubl.  analyses). 


251 


Woodpeckers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Woodpeckers 


NORTHERN  FLICKER   Colaptes  auratus 


-i.-rtft 

A  year-round  resident;  numbers  swell 

yCK^A?? 

substantially  from  Sep  through  Mar. 

An  uncommon,  widespread  breeder; 

x°2^ 

overall  breeding  population  small. 

^X\°Jk 

C3^\°V\^MPcv\o^^ 

Recorded  in  143  (64-7%)  of  221 

blocks. 

O    Possible        =      85  (59%) 

©    Probable       =      44  (31%) 

^& 

•    Confirmed  =      14  (10%) 
FSAR  =  2        OPI  =  286       CI  =  1.50 

•>*                      w  ^- <*^g 

Ecological  Requirements 

Once  highly  prized  for  ornamentation  by  Native  Ameri- 
cans, the  intermittendy  flashing,  fiery  orange-red  flight 
feathers  of  Red-shafted  Flickers  still  draw  our  admiration 
as  birds  course  overhead  in  undulating  flight.  The  Red- 
shafted  subspecies  of  Northern  Flicker,  like  its  eastern 
counterpart,  the  Yellow-shafted  Flicker,  is  wedded  to  grass- 
land edges  of  forests  or  to  woodlands  or  openings  within 
them.  Flickers  nest  in  all  of  Marin's  forests,  woodlands,  or 
planted  groves  as  long  as  open  ground  for  foraging  is 
available  either  within  the  habitat,  in  nearby  meadows,  or 
in  grasslands.  Flickers  excavate  most  of  their  nest  holes  in 
dead  trees,  dead  limbs  of  live  trees,  or  stubs,  but  they 
sometimes  select  sides  of  houses,  posts,  and  earthen  banks. 
They  rarely  use  live  trunks  or  limbs  of  trees,  as  Flickers 
prefer  very  soft  wood  for  excavating  (Raphael  ck  White 
1984).  Nests  range  from  ground  level  to  100  feet,  though 
most  are  from  8  to  30  feet  above  the  ground  (Bent  1939). 
The  height  of  68  nests  in  the  Sierra  Nevada  averaged  25 
feet;  some  were  enlarged  nest  cavities  of  other  species  of 
woodpeckers  (Raphael  &  White  1 984). 

Of  our  woodpeckers,  Flickers  are  least  dependent  on 
foraging  on  or  beneath  die  bark  of  trees.  They  obtain  much 
of  their  food  by  pecking  and  probing  in  the  ground  widi 
their  beaks,  scratching  the  surface  of  the  ground,  and 
picking  fruits  from  trees  and  bushes;  they  sometimes  hang 
almost  upside  down  from  swaying  branches  to  procure 
elderberries.  Birds  also  pick  items  from  the  surface  of  the 
ground,  dig  (peck  and  tear)  into  rotten  stumps  or  logs, 
glean  insects  from  trees  and  bushes,  and,  rarely,  flycatch 
(Bent  1939).  In  ponderosa  pine  forest  in  Arizona,  North- 

252 


ern  Flickers  show  annual  variation  in  their  use  of  foraging 
techniques  and  other  resource-use  behaviors  (Szaro  et  al. 
1990).  The  diet  of  the  Red-shafted  Flicker  in  California  is 
about  54%  animal  food  and  46%  vegetable  matter  (Beal 
1910,  n  =  118),  compared  with  61%  and  39%,  respec- 
tively, for  the  Yellow-shafted  form  of  the  East  (Beal  1911, 
n  =  684).  The  animal  food  is  overwhelmingly  dominated 
by  ants,  particularly  ground-dwelling  forms,  though  bee- 
tles, crickets,  grasshoppers,  caterpillars,  miscellaneous 
insects,  spiders,  sowbugs,  snails,  and  myriopods  contrib- 
ute minor  amounts.  Animal  food  may  vary  from  99%  of 
the  summer  diet  (n  =  35)  to  only  33%  in  the  fall  (n  =  48), 
when  fruits  predominate  (Martin  et  al.  1951).  Vegetable 
food  consists  primarily  of  small  wild  fruits,  such  as  elder- 
berries and  gooseberries,  cultivated  fruits,  acorns  and  other 
mast,  poison  oak  seeds,  grains,  and,  infrequendy,  cam- 
bium and  weed  seeds.  Flicker  young  are  fed  by  regurgita- 
tion (Lawrence  1967). 

Marin  Breeding  Distribution 

Although  Flickers  bred  widely  in  Marin  County  during  the 
adas  period,  diey  were  concentrated  more  toward  the  coast 
dian  the  interior.  The  coastal  area  is  more  heavily  forested 
and  has  generally  thicker  and  moister  soil  in  openings, 
which  presumably  aids  ground  foraging.  Representative 
nesting  locations  were  Laguna  Ranch,  PRNS  (ON  7/20/79 
— JGE),  and  beside  a  small  pond  near  Soulajoule  Reservoir 
(FY  6/17/82 -DS). 


Woodpeckers 


SPECIES  ACCOUNTS 


Woodpeckers 


Historical  Trends/Population  Threats 

Although  data  are  lacking,  it  seems  likely  that  Flickers  have 
increased  as  breeding  birds  in  historic  times  as  a  result  of 
the  opening  up  of  dense  coastal  forests  by  clearing  for 
human  needs.  Although  placed  on  the  Audubon  Society's 


Blue  List  for  1971  (Tate  1981),  based  on  recommenda- 
tions from  southern  California  and  the  central  Rockies, 
numbers  of  Flickers  were  relatively  stable  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989  and  increased 
from  1980  to  1989  (USFWS  unpubl.  analyses). 


PILEATED  WOODPECKER   Dryocopus  pileatus 


A  year-round  resident. 

^^-^    \          ,rX^_ 

An  uncommon,  very  local  breeder; 

fj<^s3^ 

overall  breeding  population  very  small. 

\\%r^t%\  \^K^<\\r\t^C 

Recorded  in  28  (12.7%)  of  221  blocks. 

^S^O^^c^c^c^^C^ 

O    Possible        =       18   (64%) 

\dj~5 

•>&<A^^^ 

€    Probable      =        7   (25%) 

Vu 

V       Jr^^O^vX      \^*\l£^\&  \^\      jf^\      'Jr-i 

•    Confirmed  =         3   (11%) 

^^^^^^Jk^^^0<\^ 

\" 

-T^St— — -  "r" 

FSAR  =  2        OPI  =  56         CI  =  1.46 

\  jr~"s 

W^?°* 

Ecological  Requirements 

This  primeval-looking  woodpecker  inhabits  Marin 
County's  Douglas  fir  and  redwood  forests,  moist  mixed 
evergreen  forests  dominated  by  Douglas  fir,  and,  to  a 
limited  degree,  mixed  bishop  pine-hardwood  forests.  Pile- 
ateds  are  adapted  to  mesic  forests  with  large-diameter  trees, 
characteristic  of  ancient  stands,  but  may  not  be  dependent 
on  old-growth  forest  since  they  use  isolated  patches  of 
decay  in  highly  productive  conifer  forests  less  than  75  years 
old  (Harris  1982).  Pileateds  select  structural  features  of  nest 
trees  and  forest  patches  around  their  nests  that  are  inde- 
pendent of  the  productivity  or  age  of  the  stand.  In  Califor- 
nia, stands  of  trees  around  nest  sites  are  characterized  by  a 
high  density  of  large  trees  and  dead  material,  particularly 
clusters  of  dead  trees  (Harris  1982).  Pileateds  in  California 
need  about  four  1-acre  patches  of  dense,  naturally  occur- 
ring tree  mortality  per  247  acres  of  forest.  Although  they 
use  stumps  and  logs  for  foraging,  the  densities  and  volume 
of  these  are  variable  around  nesting  sites  and  are  therefore 
not  good  indicators  of  the  suitability  of  a  stand  for  nest 
location.  Although  Pileateds  do  not  use  the  venerable 
remnant  trees  from  older  forests  for  nesting,  such  trees 
may  be  a  crucial  habitat  feature  since  carpenter  ant  galler- 


ies, a  prime  food  source,  are  usually  found  in  large  diame- 
ter logs,  stumps,  standing  dead  trees,  and  live  trees  with 
basal  wounds  (Harris  1982).  Although  Pileateds  often 
select  nest  trees  close  to  water  (Harris  1982),  or  sometimes 
standing  in  it  (Carriger  &  Wells  1919),  this  appears  to  be 
an  artifact  of  the  moist  forests  they  inhabit  rather  than  a 
factor  the  birds  consider  when  choosing  a  nest  site  (R.D. 
Harris  pers.  comm.). 

In  California,  Pileateds  excavate  nest  cavities  most  fre- 
quendy  in  conifers  such  as  white  fir,  ponderosa  pine, 
Douglas  fir,  red  fir,  coast  redwood,  and  giant  sequoia,  as 
well  as  in  broadleaved  trees  such  as  quaking  aspen,  black 
oak,  madrone,  black  cottonwood,  big-leaf  maple,  elm,  and 
white  alder  (Harris  1982).  In  this  state,  diey  choose  trees 
with  an  average  diameter  (at  breast  height)  of  26  inches 
(range  20-36  in.,  n  =  24)  for  nesting,  even  when  larger 
snags  are  available;  this  compares  widi  an  average  of  30 
inches  (range  15-47  in.,  n  =  58)  in  Montana  (McClelland 
1979),  30  inches  (range  23-39  in.,  n  =  13)  in  Oregon  (Bull 
6k  Meslow  1977),  and  22  inches  (range  13-36  in.,  n  =  18) 
in  Virginia  (Conner  et  al.  1975).  In  the  respective  studies, 
nest  hole  heights  averaged  59  feet  above  the  ground  in 

253 


Woodpeckers 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Woodpeckers 


California,  50  feet  (range  18-98  ft.)  in  Montana,  43  feet 
(range  23-62  ft.)  in  Oregon,  and  67  feet  (range  24-120  ft.) 
in  Virginia.  Nest  holes  may  rarely  be  as  low  as  about  2  feet 
off  the  ground  (Bent  1939).  Of  the  California  nest  trees, 
those  of  the  pine  family  were  all  snags,  usually  with  broken 
tops  (Harris  1982).  Nests  in  trees  with  intact  tops  were 
located  just  above  midbole,  whereas  those  in  trees  with 
broken  tops  were  near  the  top,  where  decay  would  be  most 
likely.  Of  the  remaining  nest  trees,  five  of  ten  hardwoods 
were  alive,  two  giant  sequoias  were  alive,  and  one  of  two 
redwoods  was  alive.  Of  the  eight  nest  cavities  in  live  trees, 
one  was  in  a  live  portion  of  a  redwood,  while  the  others 
were  in  dead  portions  of  the  live  trees.  All  of  the  California 
nests  were  in  trunks  (radier  than  limbs),  had  clear  flight 
paths  to  the  entrance,  and  were  not  consistendy  oriented 
with  any  specific  compass  directions.  They  tended  to  be 
located  on  the  underside  of  the  incline  of  a  nest  tree,  as 
noted  also  in  Virginia  (Conner  1975),  presumably  because 
this  affords  protection  from  rain  and  predators.  The 
entrance  holes  of  Pileateds  are  larger  relative  to  the  bird's 
body  size  than  holes  of  odier  California  woodpeckers  and 
are  distincdy  oblong  from  top  to  bottom,  instead  of  round. 
Since  the  nest  cavity  is  usually  excavated  through  advanced 
decayed  heartwood,  the  chamber  shape  follows  that  of  the 
decayed  portion  of  the  wood;  the  sound  sapwood  around 
the  cavity  apparendy  provides  protection  from  predators. 
Like  other  woodpeckers,  in  most  cases  Pileateds  keep  the 
bottom  of  the  nest  cavity  practically  bare,  with  only  a  few 
chips  of  wood  left  from  excavation.  One  wonders  if  these 
woodpeckers  bring  in  the  sand  or  the  few  pebbles  that  on 
rare  occasions  are  found  on  die  floor  of  the  nest  chamber 
(Hoyt  1957).  Pileateds  often  use  nest  trees  in  successive 
years  in  die  East  (Hoyt  1957),  but  not  in  California  (R.D. 
Harris  pers.  comm.);  only  very  rarely  do  they  use  a  previous 
year's  nest  cavity  again  (McClelland  1979).  Pileateds  have 
been  known  to  re-lay  in  the  same  cavity  after  the  first  set  of 
eggs  is  taken  (Carriger  6k  Wells  1919,  Bent  1939).  In 
addition  to  nesting,  snags  are  also  important  for  roosting 
cavities  (Bull  6k  Meslow  1977). 

Pileateds  put  their  massive  bills  to  good  use  by  drilling 
gaping  holes  deep  into  the  rotting  timber  of  large  snags, 
logs,  and  stumps  or  by  scaling  off  large  pieces  of  bark  with 
glancing  blows  in  search  of  sequestered  prey.  The  home- 
spun name  "stump-breaker"  apdy  fits  birds  working  on 
downed  logs,  as  they  strike  alternate  blows  from  side  to 
side  in  the  manner  of  lumberjacks,  sending  wood  chips 
several  inches  long  flying  in  every  direction.  Birds  also  peck 
and  probe  on  the  wood's  surface,  tear  up  anthills  on  the 
ground,  or  swing  by  their  feet,  head  down,  like  giant 
pendulums  as  they  grasp  branches  and  gobble  berries.  The 
annual  diet  is  about  73%  animal,  primarily  carpenter  ants 
and  wood-boring  beede  larvae,  and  27%  vegetable,  princi- 
pally wild  fruit,  along  with  a  few  seeds,  mast,  and  a  little 
cambium  (Beal  1 91 1 ,  n  =  80).  The  diet  varies  with  season, 

254 


as  do  the  methods  of  procurement.  Animal  matter  in  the 
diet  varies  from  94%  in  spring  (n  =  1  5)  to  51%  in  fall  (n  = 
30)  (Martin  et  al.  1951).  During  spring  and  summer, 
surface  foraging  methods  predominate  (Hoyt  1957,  Con- 
ner 1981),  and  a  wider  variety  of  insects  is  eaten  (Hoyt 
1957).  At  least  in  areas  with  harsh  winters,  breeding  birds 
forage  more  on  fallen  logs,  low  stumps,  and  the  lower 
portions  of  snags  and  live  trees,  presumably  because  of 
insect  sources  newly  available  on  these  substrates  after 
snowmelt  (Hoyt  1957,  McClelland  1979).  Later  in  the  fall, 
wild  fruits  and  mast  take  on  increased  importance.  In  the 
winter,  birds  eat  chiefly  insects,  especially  carpenter  ants 
(the  main  prey  throughout  their  range),  secured  predomi- 
nandy  by  excavating  deep  into  the  heart  of  trees,  stumps, 
logs,  power  poles,  and  even  decaying  buildings  (Bent 
1939,  Hoyt  1957,  Conner  1981).  Although  decayed  wood 
is  a  preferred  foraging  substrate,  Pileateds  also  feed  on  live 
trees,  particularly  when  infested  with  insects  (Bull  6k 
Meslow  1977).  In  Oregon,  prime  feeding  areas  are  dense 
mixed-species  forests  widi  high  snag  densities  and  more 
than  10%  of  the  ground  covered  with  logs  (Bull  6k  Meslow 
1977);  logs  without  limbs  and  bark  are  preferred,  as  are 
natural  stumps  over  cut  stumps.  Pileateds  forage  in  selec- 
tively logged  areas,  as  long  as  substantial  numbers  of  snags 
and  logs  are  available  (McClelland  1979),  but  rarely  on 
logs  and  stumps  in  cut-over  areas  less  than  40  years 
old— probably  because  dense  shrub  and  sapling  cover  limit 
access  to  them  (Mannan  1984). 

Marin  Breeding  Distribution 

In  Marin  County,  Pileated  Woodpeckers  were  restricted 
during  die  adas  period  to  the  conifer  forests  of  Inverness 
Ridge,  Bolinas  Ridge,  and  the  Mount  Tamalpais  water- 
sheds. A  representative  nesting  record  was  Lake  Lagunitas 
(NE-FL  4/10-5/28/79  -RDH). 

Historical  Trends/Population  Threats 

Unrecorded  in  Marin  County  by  Mailliard  (1900),  the 
Pileated  Woodpecker's  range  on  the  California  coast  was 
thought  to  extend  "casually"  south  to  Marin  County  at  the 
time  of  Grinnell  and  Miller's  (1944)  comprehensive  avifau- 
nal  summary.  Knowledge  of  its  status  in  Marin  County 
then  was  apparendy  based  solely  on  sightings  by  C.  Hart 
Merriam  at  Larkspur  and  along  San  Geronimo  Creek  in 
die  vicinity  of  Lagunitas  "on  various  occasions  between 
1911  and  1918"  (G6kW  1927).  Grinnell  and  Miller 
(1944)  noted  declines  of  the  species  in  California  following 
the  expansion  of  lumbering  operations. 

Although  the  Pileated  Woodpecker's  range  in  Marin 
County  today  is  probably  similar  to  what  it  was  early  in  this 
century,  numbers  may  have  increased  since  the  era  of 
intensive  logging  here.  Harris  (1982)  noted  that  mainte- 
nance of  Pileated  populations  was  not  incompatible  with 
some  logging.  He  felt  that  young-growth  high-productivity 


Woodpeckers 


SPECIES  ACCOUNTS 


Tyrant  Flycatchers 


sites  now  probably  supported  these  woodpeckers  because 
the  harvest  methods  and  management  strategies  in  vogue 
60  to  80  years  ago  left  standing  many  large  trees  of  low 
commercial  value.  He  cautioned  that  today's  intensive 
management  practices  may  threaten  to  extirpate  Pileateds 
from  major  portions  of  their  California  range,  especially  in 


low-productivity  sites  where  old-growth  forest  is  the  only 
suitable  habitat.  Despite  these  concerns,  Pileated  Wood- 
pecker numbers  on  Breeding  Bird  Surveys  in  California 
increased  in  the  period  1 968  to  1 979  (Robbins  et  al.  1 986), 
increased  slightly  from  1968  to  1989,  and  were  relatively 
stable  from  1980  to  1989  (USFWS  unpubl.  analyses). 


Tyrant  Flycatchers 

Family  Tyrannidae 


OLIVE-SIDED  FLYCATCHER   Contopus  borealis 


A  summer  resident  from  mid-Apr 

A^\^P\ 

^V^-_       \                   JCba~ 

through  late  Sep. 

f  \^\®2<r 

A  fairly  common,  fairly  widespread 

J>c\  y<r\    \**x\^\    \^\\^\    J\ 

breeder;  overall  breeding  population 
small. 

<r\   J>c\  -A"XA    ji^\  *  \^\  *>  \^\    \^\ 

Recorded  in  96  (43.4%)  of  221  blocks. 

V-c"^- 

\Jr\>A^\(lr\  3r"\  Jv^v cJv^\    \ 

Vu 

O    Possible        =       16   (17%) 

v ° 3r<7>%r9?<\   \^\  x^\ -© v-^a    v-^\    v^\    ^ 

€    Probable       =       72   (75%) 

-r- 

•    Confirmed  =         8   (8%) 

<V^>?\  ®>V<\  ®3r<\ «  ><^»  >^T©  \-^\VPr< 

■7  wv  iJ^rx  ®V«\  °><\©A^rv o  L<lC»  v--a  ».  x — S 

L-*<V  Jk-V\     VM'i^ov^A^fcv^ouA    ^ 

v><^r^ ^~S><\  *Jc^\  c  3r<\ C$V<\*V^V "  V< 

FSAR  =  3        OPI  =  288        CI  =  1 .92 

5^ 

r^T                                  V^^V^TP^V^l^V^A^Y^^ 

IT                 ^^W^M^w 

^                       x^/   ^~^\^ 

Ecological  Requirements 

The  loud  whisded  calls  of  this  sturdy  flycatcher  announce 
its  presence  in  Marin  County's  open  conifer  and  mixed 
conifer  forests  and  near  the  coast  in  planted  groves  of 
eucalyptus  and  Monterey  cypress.  In  addition  to  openings 
for  foraging  sallies,  Olive-sideds  apparendy  need  some 
degree  of  coolness  or  moisture,  as  they  do  not  use  eucalyp- 
tus groves  in  the  dry  interior.  These  flycatchers  construct 
their  nests  from  5  to  72  feet  above  the  ground.  In  the  West 
(more  than  in  the  East),  their  nests  are  often  higher  dian 
50  feet,  rivaling  their  lofty  foraging  perches  (Bent  1942). 
Olive-sideds  prefer  conifers  as  nesting  trees,  diough  they 
occasionally  select  broadleaved  trees  such  as  alders  or  oaks 
and,  locally,  eucalyptus.  They  usually  place  their  nests  well 
out  on  horizontal  or  drooping  limbs,  on  cone  clusters,  or, 
rarely,  in  a  crotch  against  a  trunk.  The  nest  itself  is  a 


shallow  cup  constructed  of  dead  twigs,  coarse  weed  stems, 
dry  grass,  lichens,  moss,  roodets,  and  dead  pine  needles 
and  is  lined  widi  lichens  and  fine  roodets,  grass,  pine 
needles,  or  hair. 

Olive-sideds  are  born  lookouts,  having  the  highest  for- 
aging beat  of  any  of  our  flycatchers.  They  normally  perch 
on  the  uppermost  branches,  spires,  or  dead  limbs  of  the 
tallest  trees  in  the  vicinity,  ones  that  give  a  wide,  open  view 
of  the  airways.  They  forage  solely  by  flycatching  sallies  of 
variable  distance,  mixed  widi  tumbling  aerial  acrobatics 
when  in  hot  pursuit  of  elusive  prey,  and  the  birds  then 
return  to  the  same  or  alternate  perches.  In  the  Colorado 
Rockies,  Olive-sided  Flycatchers  forage  primarily  from 
dead  perches  and  make  longer  sallies  (mosdy  <50  ft.)  than 
do  Western   Wood-Pewees   (mosdy   <25   ft.)   (Eckhardt 

255 


Tyrant  Flycatchers 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Tyrant  Flycatchers 


1979).  Both  species  there  prefer  horizontal  (lights  and, 
secondarily,  downward  (over  upward)  flights,  unlike 
Pewees  in  California  (see  account). 

The  Olive-sided  Flycatcher  diet  is  almost  exclusively 
animal  food,  of  which  83%  consists  of  bees  and  wasps, 
indicating  a  very  high  degree  of  specialization  (Beal  1912, 
n  =  69).  Among  other  items  they  regularly  eat  are  beedes, 
moths,  true  bugs,  dragonflies,  grasshoppers,  and  a  few 
other  miscellaneous  insects.  Interestingly,  they  are  not 
known  to  eat  caterpillars,  spiders,  and  millipedes  (regularly 
eaten  by  most  flycatchers);  thus  Olive-sideds  apparently  eat 
only  airborne  flying  insects. 

Marin  Breeding  Distribution 

During  the  adas  period,  the  distribution  of  this  species  in 
Marin  County  closely  paralleled  that  of  native  conifer 
forests.  An  exception  was  where  Olive-sideds  occupied 
some  groves  of  eucalyptus  or  cypress  trees  in  the  fog  belt 
(e.g.,  near  Tomales)  far  from  conifer  forests  or,  for  that 
matter,  from  any  stands  of  tall  native  trees.  Representative 
breeding  locations  were  eucalyptus-cypress  grove  in 
Bolinas  (FL  7/25/82  -DS)  and  near  Phoenix  Lake  (NB 
5/21/77  -DS). 


Historical  Trends/Population  Threats 

For  the  south  San  Francisco  Bay  region,  Sibley  (1952) 
noted  that  Olive-sided  Flycatchers  had  "rather  recendy 
invaded  die  lowland  portions  of  the  area,  possibly  follow- 
ing the  extensive  planting  of  conifers  and  eucalyptus."  The 
birds  appear  to  have  expanded  their  range  locally  in  Marin 
County,  as  well,  by  occupying  planted  eucalyptus  and 
cypress  as  noted  above.  In  the  period  1968  to  1979, 
numbers  of  Olive-sided  Flycatchers  on  Breeding  Bird  Sur- 
veys declined  sharply  in  western  North  America  but  held 
their  own  in  areas  of  the  species'  greatest  abundance  in 
California  (Robbins  et  al.  1986).  Survey  numbers  in  Cali- 
fornia declined  from  1968  to  1989  but  were  relatively 
stable  from  1980  to  1989  (USFWS  unpubl.  analyses).  A 
similar  decline  in  Survey  numbers  in  USFWS  Region  1 
(including  California)  led  to  placing  the  Olive-sided  Fly- 
catcher on  the  USFWS  list  of  Migratory  Nongame  Birds  of 
Management  Concern  (USFWS  1987b).  In  addition,  Mar- 
shall (1988)  documented  the  disappearance  of  this  fly- 
catcher from  undisturbed  climax  forests  of  the  southern 
Sierra  and  suggested  the  decline  was  caused  by  destruction 
of  forests  on  the  Central  American  wintering  grounds. 


WESTERN  WOOD-PEWEE   Conwpus  sordidulus 


-l'-iW»-^ 

A  summer  resident  from  mid-Apr 

,-r~T\X-\V\^x><>t          k               .a^x 

through  early  Oct. 

A  fairly  common,  widespread  breeder; 

^^y^^^^^^K^b^' 

overall  breeding  population  of  moderate 

size. 

V5~   \&Cx -JtfCX  ®Y-'\  •  i^\  ©  \^\  •  x^\  ©  \^\ 

Recorded  in  136  (61.5%)  of  221 
blocks. 

\  \  A^A  *vi-><AJ •  jk^A""©7  \s^\  ©  \^\  ©  \-^\  O  V-^\  ©  X^i 

O    Possible        =      23  (17%) 
€    Probable      =      90  (66%) 

1     .'3fr\  ©  X^XX>  X^\  ©  V^VO  \Z^\  •  V^T  C  X^-X    '.    ^> 

-;  \  V-tv*.  \r^\  o  v-c\  ©A^\  ctAj^X  ©  \^t\b  \^\  ©  V~ 

•    Confirmed  =      23  (17%) 

>*>V  Jr%\  ©  Vv\®3^A-#  V^TtKA^-lf  ©V^A      UA 

'  "=~J^3i^^ X?  X^l\  ©  \X\  ©  X^\  ©  $C^\4b  Y^a  '■•  X 

rQo» 

FSAR  =  3        OPI  =  408        CI  =  2.00 

J>;W                                                                              ^\I°/           ^^:~^^-vS!V\ 

Ecological  Requirements 

Emphatic  breeding  calls  of  the  Western  Wood-Pewee  leap 
out  from  the  hardwood  stands  of  Marin  County's  mixed 
evergreen  forests,  and  also  from  her  riparian,  mixed  coni- 
fer, and  conifer  forests.   Pewees  usually  frequent  either 

256 


relatively  open  stands  or  habitat  edges  in  these  forests.  Nest 
heights  range  from  2  to  75  feet  above  the  ground  (mosdy 
15-30  ft.)  in  either  live  or  dead  trees  (Bent  1942).  Pewees 
usually  build  their  nests  in  the  open,  on  top  of  a  limb  or 


Tyrant  Flycatchers 


SPECIES  ACCOUNTS 


Tyrant  Flycatchers 


at  the  fork  of  a  horizontal  branch,  though  occasionally  in 
an  upright  crotch.  Their  nests  are  shallow  cups  made  of 
plant  fibers,  grasses,  coarse  weed  straws,  plant  down, 
spider  webs,  shredded  bark,  lichens,  and,  rarely,  green 
leaves  (Bent  1942,  Goodpasture  1953).  Pewees  artfully 
camouflage  their  nests  by  shape  and  color  to  give  them  the 
appearance  of  a  bump  or  stub  of  the  supporting  limb,  and 
they  vigorously  defend  them  against  intruders. 

In  central  coastal  California,  Western  Wood-Pewees 
patrol  their  foraging  beats  mainly  from  perches  such  as 
treetops,  outer  tree  canopies,  and  telephone  wires  (Verbeek 
1975a).  Although  they  prefer  bare  branches  at  middle  to 
high  elevations  in  the  outer  parts  of  trees,  Pewees  also 
perch  on  fences,  downed  trees,  saplings,  weed  stalks,  and 
occasionally  inside  tree  canopies.  Pewees  there  forage  pre- 
dominandy  by  hawking  insects  in  the  open  air,  generally 
away  from  vegetation  and  the  ground,  and  more  often  in 
descending  than  in  ascending  or  horizontal  flight.  They 
occasionally  hawk  inside  the  canopy,  over  grass,  and  under 
trees  and,  rarely,  glean  from  branches  and  foliage  in  their 
hawking  flight.  Where  they  overlap  with  Pacific-slope  Fly- 
catchers and  Black  Phoebes,  die  height  range  of  Pewees' 
foraging  perches  (1  -1 1 5  ft.)  is  greater  than  that  of  the  other 
two  species,  but  the  median  height  (18  ft.)  is  significandy 
different  only  from  that  of  die  Black  Phoebe.  In  distance, 
Pewees'  foraging  flights  range  from  1  to  1 1 5  feet  (median 
1 2  ft.)  and  are  significandy  greater  than  those  of  Pacific- 
slope  Flycatchers  and  Black  Phoebes.  In  Colorado,  Beaver 
and  Baldwin  (1975)  found  Pewees  feeding  mosdy  at  mid- 
foliage  portions  of  trees  and  in  the  air  space  immediately 
below;  there  and  in  California,  they  forage  mosdy  at  about 
10  to  40  feet  above  ground  (Verbeek  1975a,  Beaver  6k 


Baldwin  1975).  Pewees  generally  forage  from  lower 
perches  and  make  shorter  sallies  after  prey  than  do  Olive- 
sided  Flycatchers  (see  account). 

The  Pewee's  diet  (Apr-Sep)  is  almost  exclusively  animal 
matter,  consisting  primarily  of  insects.  The  main  items  are 
flies,  wasps,  bees,  ants,  beedes,  moths,  butterflies,  and 
caterpillars;  minor  items  are  true  bugs,  dragonflies,  lace- 
winged  flies,  mayflies,  termites,  caddisflies,  leafhoppers, 
and  spiders  (Beal  1912,  n  =  174;  Beaver  6k  Baldwin  1975, 
n  =  69).  In  Colorado,  lepidopterans  accounted  for  only 
13%  of  the  diet  by  numbers,  but  44%  by  dry  weight 
(Beaver  6k  Baldwin  1975). 

Marin  Breeding  Distribution 

Pewees  bred  widely  in  Marin  County  during  the  adas 
period,  and  their  distribution  matched  well  that  of  forested 
areas  here.  Within  the  limits  of  this  distribution,  the 
species  appeared  to  have  no  obvious  geographical  trend  or 
center  of  abundance.  More  careful  study  might  reveal  that 
Pewees  are  most  numerous  in  the  central  portions  of  the 
county,  which  provide  more  forests  of  moderately  open 
character  and  likewise  more  edge  situations.  Representative 
breeding  locations  were  Chileno  Valley  (NY  7/2/82  — 
DS);  Laguna  Ranch  Canyon,  PRNS  (NE  6/?/80  -JGE); 
Cascade  Canyon,  Fairfax  (NE  5/1 1/81  — DS);  and  Hick's 
Valley  (NE  5/15/82 -ScC). 

Historical  Trends/ Population  Threats 

Few  prior  data  exist,  but  Pewee  numbers  declined  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


257 


Tyrant  Flycatchers 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Tyrant  Flycatchers 


PACIFIC-SLOPE  FLYCATCHER   Empidonax  difficilis 


A  summer  resident  from  late  Mar 

^^■«~           \                yc~\j 

through  early  Oct. 

/\3nC\^\ 

\s*^\         \^ —  \   ©I"- ""^^"^ — ^\^D    Y^-\  ©  \^^\   \ 

A  common,  very  widespread  breeder; 

V     v^!\  ©  \-<*\~'6  v     \  ci  Y^a  ©  v-^\  o  \s\iS 

overall  breeding  population  large. 

^Vv-iV 

\^\  O  V>A  O  W>V«' V-^A  ®  K\OVA;  ©  J\ 

Recorded  in  163  (73.8%)  of  221 

k   \^^©>^'©3^^,5:?^iAV^©jk><\©^ 

V-^A      V-"A®  V^A©  U-"A©  t^e\/\d  V^\ 

blocks. 

<"     V^A  ©  ;V^\  ©  v^v  •  V^\  •  A^C  ©  \^\  ©  J 

\^<\~^ 

^  VrH  ©Jv^^x  •  \^\  ©  V^\  ©  V^A  ©  \^\  ©  j^a 

>^J^?^c3r>\#3r-fC   J^\  ©A^A  ©VvC  Jl^. 

O    Possible        =       20   (12%) 

« o  w^?a?<C©  V^VcY^Xj**  v^a  3t^\   jr^\  *r^ 

C    Probable       =     102   (63%) 

DV:>A  »A-^\  GJt5^©^^©><A*>^T©->-^A,1«»<\ 

-••s- 

•    Confirmed  =      41    (25%) 

■■  jP"\  ©  \-"\"«  V^A-.©^-'5^©  i5r\  •  ><A  ©  V^\-;y 

-"f"\k  rt\^\  *VV\  ©.Ar^X  •  ><^©  A^V  ®.Y<£\  ©3<-<A— . 

-i  vWytV^A  *Vv\  ©^^\©3^T\  ©J^V^A^rx  Ha\ 

V^?  rv 

FSAR  =  4        OPI  =  652       CI  =  2.13 

tv^j^p* ^~~<T©  V^A  © W-'A  •-■^*A  ©'V<TA  •  \*£\ 
rX />^                 ^"<©  A^A©  \i-iA ''•■i<iA'''©^V^\^vi. 

v^ 

-  Y^                           \><C •  v-~&-^  W^^V^A'J©^5^- 

Ecological  Requirements 

The  warm  olive  and  yellowish  hues  of  our  only  breeding 
Empidonax  flycatcher  blend  well  with  its  Marin  County 
nesting  haunts— moist,  relatively  dense,  and  shaded  forests 
of  broadleaved  evergreen,  mixed  broadleaved-conifer,  coni- 
fer, and  riparian  trees.  Within  these  habitats,  Pacific-slope 
Flycatchers  are  most  numerous  in  canyon  bottoms  near 
permanent  or  ephemeral  streams.  They  place  their  nests  in 
a  wide  variety  of  relatively  open  settings  with  the  main 
requirements  being  support  from  below  and  behind  and, 
often,  shelter  from  above.  Natural  sites  selected  include 
forks  of  trees,  cavities  in  trees  or  cutbanks,  narrow  shelves 
of  banks  or  mossy  cliffsides,  behind  loose  flaps  of  bark, 
among  the  roots  of  upturned  trees,  the  tops  of  low  stumps, 
and  abandoned  Black  Phoebe  nests.  Birds  also  nest  com- 
monly on  human  supporting  structures  both  inside  and 
outside  buildings,  on  road  cuts,  on  bridges,  in  flowerpots 
or  fern  baskets,  and  over  porch  lights.  Nest  heights  range 
from  ground  level  to  30  feet  (av.  about  1 1  ft.)  (Bent  1942, 
Davis  et  al.  1963).  Exceptionally,  these  flycatchers  will 
construct  a  nest  on  flat  ground  (Reynolds  1942).  They 
often  use  nest  sites  for  successive  broods  in  a  single  year 
and  also  in  subsequent  years;  at  least  in  the  latter  case  the 
same  individuals  are  sometimes  involved  (Sakai  1988). 
Since  nest  cups  are  usually  placed  against  verdcal  surfaces, 
they  are  often  triangular  in  shape  or  broadly  oval,  with  the 
long  side  flattened  (Davis  et  al.  1963).  Pacific-slope  Fly- 
catchers often  construct  nests  primarily  of  green  mosses 
when  available,  but  they  also  use  bark  strips,  leaves, 
grasses,  twigs,  spider  webs,  and  artificial  materials  found 

258 


near  buildings  (Bent  1942,  Davis  et  al.  1963).  They  usually 
line  their  nest  cups  with  fine  dried  grasses,  alone  or  with 
lichens  and/or  bark. 

In  riparian  woodland  on  the  central  California  coast, 
foraging  Pacific-slope  Flycatchers  perch  primarily  within 
the  middle  and  lower  interior  of  trees,  an  area  largely 
avoided  by  our  other  locally  breeding  flycatchers  (Verbeek 
1975a).  To  a  limited  extent,  they  also  perch  toward  the 
outside  and  upper  parts  of  trees,  in  understory  trees  and 
shrubs,  on  downed  branches,  and  on  buildings.  Perch 
heights  range  from  slightly  less  than  1  foot  to  about  55  feet 
(median  1 7  ft.).  Although  the  range  of  their  perch  heights 
there  is  intermediate  between  those  of  Western  Wood- 
Pewees  and  Black  Phoebes,  the  median  height  is  signifi- 
candy  different  only  from  that  of  the  Black  Phoebe  (it  is 
higher).  Pacific-slope  Flycatchers  there  hawk  insects  from 
the  air  about  60%  of  the  time;  they  make  relatively  short, 
quick  darts,  with  ascending  flights  predominating;  and 
they  use  hawking  about  equally  in  open  air  space  and 
within  the  foliage  and  branchwork  of  trees.  For  the  other 
40%  of  their  foraging,  they  make  direct  sallies  or  hovering 
flight  to  glean  from  the  foliage  and  branchwork  of  trees 
and,  to  a  limited  extent,  from  the  ground  or  buildings.  The 
distances  of  their  foraging  flights  range  from  about  1  to  26 
feet  (median  6  ft.)— significandy  shorter  than  those  of 
Western  Wood-Pewees  but  not  of  Black  Phoebes. 

In  Douglas  fir-tanbark  oak  habitat  in  northwestern 
California,  Pacific-slope  Flycatchers  change  their  foraging 
behaviors  during  the  course  of  the  breeding  season.  Gen- 
erally, they  capture  their  prey  there  during  various  stages  of 


Tyrant  Flycatchers 


SPECIES  ACCOUNTS 


Tyrant  Flycatchers 


Necks  extend  and  heads  bob  instantly  as  young  Pacific-slope  Flycatchers  beg  at  the  first 

sensation  of  an  insect-bearing  adult  alighting  on  their  mossy  nest  rim. 

Drawing  b)i  Keith  Hansen,  1 990. 


the  breeding  cycle,  72%-85%  by  hover-gleaning,  12%- 
27%  by  flycatching,  and  l%-4%  by  gleaning  (Sakai  6k 
Noon  1990).  They  hover-glean  more  than  expected  during 
preincubation  and  incubation  but  flycatch  more  than 
expected  during  periods  with  young  in  the  nest.  On  the 
whole,  these  birds  take  their  prey  mosdy  from  foliage; 
secondarily  from  the  air,  twigs,  and  small  branches;  and, 
rarely,  from  large  branches  and  trunks.  The  proportion  of 
prey  captures  from  various  substrates  also  varies  among 
periods  of  the  breeding  cycle.  A  shift  by  foraging  birds 
from  extensive  initial  use  of  Douglas  fir  to  heavy  use  of 
hardwoods  later  on  is  associated  with  decreasing  reliance 
on  overstory  vegetation  and  increasing  reliance  on  under- 
story  vegetation  as  the  season  progresses.  Corresponding 


to  the  change  in  plant  species  use  was  a  shift  from  favoring 
horizontal  prey  attack  flights  early  on  to  increased  use  of 
vertical  attack  flights  later  in  the  season.  Regardless  of  the 
direction  of  flights,  die  birds  appeared  to  favor  the  shortest 
distance  to  capture  prey  during  all  breeding  stages.  The 
flycatchers  did  not  change  foraging  position  seasonally  but 
remained  at  moderate  heights  and  intermediate  distances 
from  the  canopy  edge  throughout.  Sympatric  Hammond's 
Flycatchers  there  select  taller  trees  and  forage  higher  in  the 
subcanopy  than  do  Pacific-slope  Flycatchers.  Nevertheless, 
both  species  shift  their  seasonal  use  of  substrate  and 
foraging  techniques  in  a  corresponding  manner,  suggest- 
ing these  changes  in  foraging  behavior  reflect  changes  in 
prey  availability. 

259 


Tyrant  Flycatchers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Tyrant  Flycatchers 


In  Washington,  Pacific-slope  Flycatchers  spend  over 
60%  of  their  time  foraging  either  within  the  tree  canopy  or 
in  the  air  space  below  it;  secondary  foraging  zones  are 
brush,  open  air,  the  herb  layer,  and  on  the  ground  (Frakes 
&.  Johnson  1982).  Foraging  there  is  about  equally  split 
between  hawking  and  gleaning,  via  hawking  and  hovering 
flight;  foraging  heights  range  from  the  ground  to  about  79 
feet  Between  Douglas  fir  and  cottonwood-willow  riparian 
habitats  there,  the  flycatchers'  foraging  strategy  differs  in 
the  relative  amount  of  time  spent  foraging  in  various 
substrates,  the  proportion  of  gleaning  directed  at  different 
substrates,  height  of  foraging  perches,  and  die  directions 
and  lengths  of  foraging  flights. 

Also  in  Washington,  the  foraging  ecology  of  Pacific- 
slope  and  Willow  flycatchers  is  more  alike  where  they 
overlap  in  riparian  habitat  than  where  they  occupy  differ- 
ent habitats  (Frakes  ck  Johnson  1982).  In  riparian,  they 
show  little  difference  in  frequency  of  hawking  versus  glean- 
ing, in  perch  height,  in  flight  length,  in  flight  direction,  or 
in  frequency  of  return  to  the  same  perch.  However,  Pacific- 
slope  Flycatchers  feed  more  in  the  tree  canopy,  in  the  air 
space  under  the  canopy,  and  in  brush  and  less  in  the  herb 
layer  and  in  the  open  air  than  do  Willows.  They  glean 
more  from  trunks  and  less  from  grass  and  herbs  than  do 
Willows.  Willow  Flycatchers  also  perch  frequendy  in  wil- 
lows, grass,  and  herbs,  which  are  rarely  if  ever  used  by 
Pacific-slope  Flycatchers. 


The  Pacific-slope  Flycatcher's  diet  is  about  99.3%  ani- 
mal matter,  the  rest  consisting  of  a  few  seeds  and  skins  of 
fruit  (Beal  1912,  n  =  157).  The  main  components  of  the 
diet  are  bees,  wasps,  ants,  flies,  true  bugs,  moths,  caterpil- 
lars, and  beedes;  a  few  other  insects  and  spiders  are  also 
taken. 

Marin  Breeding  Distribution 

Pacific-slope  Flycatchers  were  widespread  breeders  in 
Marin  County  during  the  adas  period,  reflecting  the  exten- 
sive distribution  of  moist  forests  in  this  coastal  county. 
They  were  most  numerous  and  widespread  toward  the 
coast,  where  moist  forests  cover  large  continuous  areas, 
and  less  numerous  and  more  local  toward  the  interior, 
where  such  forests  are  found  only  in  narrow  canyons  or  on 
north-facing  slopes.  Representative  breeding  locales  were 
Inverness  (NY/NE  7/10/82  -DNe);  Skywalker  Ranch, 
Lucas  Valley  Rd.  (NY  7/1 7/82  -DS,  HBa);  Cataract  Trail, 
Mt.  Tamalpais  (NE  5/8/82  -BiL);  and  Gloria  Dr.,  San 
Rafael  (NE  6/4/78  -ITi). 

Historical  Trends/  Population  Threats 

Few  prior  data  exist,  but  numbers  were  relatively  stable  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


*3**i8E* 


260 


Tyrant  Flycatchers 


SPECIES  ACCOUNTS 


Tyrant  Flycatchers 


BLACK  PHOEBE   Sayornis  nigricans 


A  year-round  resident. 

A  fairly  common,  very  widespread 
breeder;  overall  breeding  population 
fairly  large. 

Recorded  in  167  (75.6%)  of  221 
blocks. 


O  Possible 
©  Probable 
•    Confirmed 


40  (24%) 
30  (18%) 
97  (58%) 


FSAR  =3        OPI  =  501         CI  =  2.34 


Ecological  Requirements 

In  Marin  County,  as  elsewhere,  our  nattily  dressed  Black 
Phoebes  inhabit  the  edges  of  open  country  and  maintain 
an  intimate  association  with  water.  Individual  Black  Phoe- 
bes scout  for  insect  prey  from  a  series  of  well-spaced 
foraging  perches  on  the  margins  of  grasslands,  weed  fields, 
lawns,  meadows,  marshes,  and  woodland  clearings.  Breed- 
ing birds  are  usually  found  near  streams  and  ponds,  but 
cattle  troughs,  small  seeps,  or  well-watered  lawns  will 
suffice  as  long  there  is  a  sufficient  supply  of  insects  and 
foraging  perches,  mud  for  nest  building,  and  suitable  nest 
sites.  In  presettlement  times,  Black  Phoebes  nested  on  the 
vertical  surfaces  of  cliffs,  boulders,  steep  banks,  caverns, 
and,  rarely,  on  dead  trunks  or  limbs  of  trees.  Today  they 
select  nest  sites  mostly  on  human  structures,  such  as 
buildings,  duck  blinds,  wells,  and  especially  bridges  and 
stream  culverts  (Woods  1942,  Ohlendorf  1976).  Nest 
heights  can  range  from  1 5  feet  below  the  ground  (in  wells) 
to  35  feet  above  the  ground  or  water  (Woods  1942, 
Ohlendorf  1976).  In  Texas,  the  average  height  of  Black 
Phoebe  nests  was  10  feet  (range  1-35  ft.,  n=  36),  not 
significantly  different  from  that  of  Say's  Phoebes 
(Ohlendorf  1976)  (but  see  Say's  Phoebe  account  for  other 
nest  site  differences).  Black  Phoebes  plaster  their  nests, 
which  are  half-cup  shaped,  on  vertical  or  nearly  vertical 
surfaces  that  have  an  overhang  above  for  protection.  They 
construct  their  nest  bowls  of  small  pellets  of  mud  mixed 
with  lots  of  dry  grass,  weed  fibers,  or  hair  and  line  them 
with  weed  fiber,  fine  roots,  bark,  grass  hairs,  or  wool 
(Woods  1942).  Nests  must  be  within  carrying  distance  of 


a  mud  source,  found  in  Texas  to  be  less  than  50  feet 
(Ohlendorf  1976).  Black  Phoebes  may  reuse  their  nests  for 
successive  broods  in  the  same  year  and  also  in  subsequent 
years. 

Black  Phoebes  forage  from  low  perches  such  as  fences, 
the  outer  lower  tree  canopy,  fallen  dead  trees  in  meadows, 
weed  stalks,  rocks,  buildings,  and  overhead  wires  (Ober- 
lander  1939,  Verbeek  1975a,  Ohlendorf  1976).  They  tend 
to  retire  to  shaded  perches  in  die  heat  of  the  day  (Verbeek 
1975b).  In  coastal  California,  Verbeek  (1975a)  recorded 
perch  heights  of  breeding  birds  ranging  from  about  2.5  to 
33  feet  (median  4  ft.).  About  77%  of  prey  capture  attempts 
by  breeding  birds  are  by  hawking,  primarily  in  the  open  air 
or  over  grass.  The  rest  are  by  gleaning  from  the  ground, 
grass,  buildings,  or  tree  foliage,  using  darting  and  hovering 
flights.  Unlike  most  flycatchers,  Black  Phoebes  even  perch 
on  the  ground  to  catch  their  prey.  When  open  water  is 
available,  they  may  direct  the  preponderance  of  their  flights 
at  insects  on  or  near  the  water  (Oberlander  1939).  When 
insects  are  scarce  or  less  active  (in  winter,  on  rainy  days,  or 
on  cold  mornings),  birds  hover  and  glean  more  from  grass 
and  from  building  walls.  Their  foraging  sallies  tend  to  be 
relatively  short  (median  7  ft.,  range  1-49  ft.),  with  no  flight 
direction  predominant,  and  after  prey  capture,  birds  usu- 
ally return  to  a  different  perch  (Verbeek  1975a).  However, 
Oberlander  (1939)  noted  that  toward  dusk,  Black  Phoebes 
directed  more  foraging  attempts  upward,  presumably 
because  under  these  lighting  conditions  they  could  see 

261 


Tyrant  Flycatchers 


insects  more  easily  against  the  pale  sky.  See  Western 
Wood-Pewee  and  Pacific-slope  Flycatcher  accounts  for 
comparison  of  foraging  niches. 

The  Black  Phoebe  diet  is  about  99%  animal  matter,  with 
die  remainder  consisting  of  a  few  seeds,  fruit  pulp,  and 
"rubbish"  (Beal  1912,  n  =  344;  Ohlendorf  1976,  n  =  14). 
The  main  food  items  are  bees,  wasps,  ants,  flies,  beedes, 
true  bugs,  moths,  and  caterpillars;  minor  items  are  grass- 
hoppers, crickets,  dragonflies,  damselflies,  termites,  butter- 
flies, and  spiders.  Insect  hard  parts  are  expelled  as  pellets 
(Oberlander  1939).  Black  Phoebes  also  occasionally  dip 
their  heads  in  water  nearly  to  dieir  eyes  to  catch  minnows 
(Oberlander  1939)!  In  a  portion  of  Texas,  where  Black 
and  Say's  phoebes  coexist,  the  major  food  types  in  their 
diet  overlapped  by  77%  based  on  orders,  but  only  by  43% 
based  on  families  (Ohlendorf  1976).  By  volume,  dragon- 
flies,  damselflies,  other  water-associated  insects,  and  ter- 
mites were  important  for  Black  Phoebes,  whereas 
grasshoppers,  flies,  and  bees  were  most  important  for  Say's 
Phoebes. 


MARIN  COUNTY  BREEDING  BIRD  ATIAS  Tyrant  Flycatchers 

Marin  Breeding  Distribution 

During  the  atlas  period,  Black  Phoebes  bred  throughout 


most  of  Marin  County  but  were  patchily  distributed  here, 
as  elsewhere,  in  response  to  the  limitation  of  water  sources 
and  suitable  nesting  sites.  Representative  nesting  locations 
were  Olema  Marsh  at  Whitehouse  Pool  (NE  4/22-5/3/81 
-DS);  Chileno  Valley  (NY  7/2/82  -DS);  and  San  Jose 
Creek  at  Commercial  Blvd.,  Novato  (NY  5/7/78  -DS). 

Historical  Trends/ Population  Threats 

Black  Phoebes  have  probably  increased  historically  in 
Marin  County  from  construction  of  reservoirs,  ranch 
ponds,  and  catde  troughs,  which  have  increased  the  avail- 
ability of  water  in  the  breeding  season,  augmenting  both 
insect  supplies  and  mud  for  nest  building.  Additionally, 
human  structures  have  gready  increased  suitable  nest  sites. 
Numbers  of  Black  Phoebes  increased  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989  but  were  rela- 
tively stable  from  1980  to  1989  (USFWS  unpubl.  analyses). 


SAY'S  PHOEBE    Sayornis  saya 


Almost  exclusively  a  winter  resident  from 

^V>^^       \                     yr~ 

early  Sep  through  Mar;  exceptional  in 

T^r^^^Or 

summer. 

\^2^T\ 

\^K\^\ 

A  very  rare,  very  local  breeder;  overall 
breeding  population  very  small. 
Recorded  in  1  (0.4%)  of  221  blocks. 

P^^V^Pc^^^O^ 

O    Possible        =        0   (0%) 

€    Probable      =        0  (0%) 

^\\\^v^rj>^<\^ 

-^xy^K^^r '' 

•    Confirmed  =         1    (100%) 

'TV                                                ^-J^f\^ 

^^^^^^?°' 

FSAR  =1         OPI  =  1            CI  =  3.00 

Ecological  Requirements 

Although  Say's  Phoebes  are  cheery  and  widespread  mem- 
bers of  Marin  County's  wintering  avifauna,  only  one 
known  pair  has  graced  us  with  its  presence  in  the  breeding 
season.  Hence,  little  can  be  said  of  its  breeding  habitat 
requirements  in  the  county,  except  that  the  one  nesting  site 
adjoined  arid  grassland  and  open  oak  savannah— typical 


habitat  of  die  nearest  breeding  populations,  in  the  interior 
Coast  Range  east  of  San  Francisco  Bay. 

Unlike  the  vertical  surfaces  preferred  by  Black  Phoebes, 
Says  choose  horizontal  surfaces  or  shelves  with  protection 
from  above  on  which  to  build  their  nests.  Despite  this 
difference— and    the   Black   Phoebe's   affinity   for   nearby 


262 


Tyrant  Flycatchers 


SPECIES  ACCOUNTS 


Tyrant  Flycatchers 


water— both  species  place  their  nests  in  very  similar  situa- 
tions that  provide  shade  from  midday  heat.  Natural  nest 
sites  for  Say's  Phoebes  are  crevices  or  shelves  on  cliffs  or 
boulders,  inside  caves,  in  earthen  banks,  and  in  natural 
cavities  of  trees.  They  also  use  old  or  appropriated  nests  of 
Cliff  and  Barn  swallows,  Black  Phoebes,  burrows  of  Bank 
Swallows,  and,  rarely,  American  Robin  nests  in  bushes 
(Bent  1942,  Ohlendorf  1976).  Today,  however,  most  birds 
have  adapted  to  building  their  nests  on  human  structures, 
especially  those  that  are  abandoned  or  receive  little  use. 
Typical  artificial  sites  include  ranch  buildings,  outhouses, 
bridges,  wells,  mine  shafts,  and  old  mailboxes.  Nest 
heights  may  range  from  15  feet  below  the  surface  of  the 
ground  (in  a  well)  to  perhaps  hundreds  of  feet  high  on  cliffs 
(Bent  1942).  The  height  of  1 1 2  nests  in  Texas  ranged  from 
4  to  40  feet  and  averaged  9  feet;  this  was  not  significandy 
different  from  the  height  of  Black  Phoebe  nests  there 
(Ohlendorf  1 976).  Say's  Phoebes  make  their  nest  cups  of 
weed  stems,  dry  grasses,  other  plant  fibers,  mosses,  wool, 
spider  webs,  rags  and  the  like  near  human  habitation,  and 
occasionally  mud.  They  line  them  with  wool  or  hair  (Bent 
1942).  They  may  reuse  nests  for  successive  broods  in  one 
year  and  in  subsequent  years  (Ohlendorf  1976). 

Say's  Phoebes  forage  from  relatively  low  perches  such  as 
rocks,  bushes,  fences,  and  the  corners  of  buildings.  After 
sallying  from  a  perch,  they  catch  their  prey  in  midair  by 


hawking  or  by  dropping  to  the  ground  direcdy  or  from 
hovering  flight.  The  diet  is  99.8%- 100.0%  animal  matter, 
consisting  primarily  of  insects;  rarely,  it  includes  a  few 
seeds  or  fruits  (Beal  1912,  n  =  111;  Ohlendorf  1976,  n  = 
23).  The  main  food  items  are  bees,  wasps,  grasshoppers, 
crickets,  flies,  beedes,  moths,  caterpillars,  and  true  bugs; 
minor  items  are  dragonflies,  cicadas,  nerve-winged  insects, 
spiders,  millipedes,  and  sowbugs.  See  Black  Phoebe 
account  for  a  discussion  of  differences  in  diet. 

Marin  Breeding  Distribution 

During  the  adas  period,  there  was  one  nesting  record  of 
the  Say's  Phoebe,  a  nest  found  under  the  eave  of  a  building 
at  the  base  of  Mount  Burdell,  Novato,  in  June  1976  (ScC). 
This  is  the  only  known  breeding  record  for  Marin  County 
and  also  the  farthest  north  and  most  coastward  breeding 
record  for  coastal  northern  California  (McCaskie  et  al. 
1979,  ABN). 

Historical  Trends/ Population  Threats 

Little  prior  information  exists,  but  numbers  of  Say's  Phoe- 
bes were  relatively  stable  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1989,  despite  a  decrease  from 
1980  to  1989  (USFWS  unpubl.  analyses). 


263 


Tyrant  Flycatchers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Tyrant  Flycatchers 


ASH-THROATED  FLYCATCHER   Myiarchus  cinerascens 


A  summer  resident  from  mid-Apr 

^v^^v^ 

through  mid-Sep,  sparingly  to  late  Oct 

l\r\5^ 

A  common,  widespread  breeder;  over- 

3rA^%^\5Sfc?A?^- 

all  breeding  population  large. 

\^V©X- 

Recorded  in  150  (67.9%)  of  221 

blocks. 

Y*^\%Vxfc\^'A>©_^^ 

\Vj--" 

V^»V^^n\  ®Vv\  ®  A>"V •  A^A  o  V^A©  V>"l 

■x5<V\  VrV\  ®Jv^°A^\ « 3t^V »  V^A» J 

O    Possible        =       16   (11%) 

r\  >* A-A  •Jv^A    _£&>3C*  A^V©.  ,\^A-«- i>*A  ©  V°^A 

J^A  ;-^r<^JKiA'*'Jir->A  ©  A^A  ©A^\  •  V^A  ©  V^y 
S>\  ^K\  J<*\  zJ^A  ®Jv<A  *A-^A®  Jr^A  ®  A><Y  " 

€    Probable      =      80  (53%) 
•    Confirmed  =      54  (36%) 

<\&?T7\  ®^r\  Jtt*  Jv-^®  >-"T»  A^A'l^CL 
-7  VXvV  LV^A  J>r\  *^^A  ^2l\  ®  L<rT»  V^a  \  \ — s 

-fSY^rQ,     \    \  Avi-  Vv*vf«  VA  0  vA  <• 

FSAR  =  4        OPI  =  600        CI  =  2.25 

i^r?r7>^      ^^-^  j^A  ©  V^QA^*A©-\^r\  ©  Wrv 

^ 

"M                              ^-WX^^^3<^JvA\®^ 

liU                   ^^cy^^-^^Vj 

Ecological  Requirements 

The  plucky  Ash-throated  Flycatcher  dwells  in  Marin 
County's  relatively  open  broadleaved  evergreen  forests,  oak 
savannah  woodlands,  riparian  forests,  mixed  conifer- 
broadleaved  evergreen  forests,  and  chaparral-edge  habitats. 
Ash-throateds  nest  in  natural  tree  cavities,  woodpecker 
holes  (sometimes  usurped  from  the  intended  occupants), 
cavities  behind  the  loose  bark  of  trees,  and,  rarely,  in  old 
nests  of  other  birds.  They  also  readily  adapt  to  bird  boxes, 
hollow  vertical  or  angled  pipes,  old  tin  cans  or  pots,  old 
mailboxes,  and  the  like.  Nest  cavities  range  from  about  2.5 
to  20  feet  above  the  ground.  The  birds  fill  the  bottom  of 
these  cavities  with  weed  stems,  roodets,  grass,  or  bits  of 
dried  cow  or  horse  manure;  they  build  the  rest  (most)  of 
the  nest  from  the  hair  and  fur  of  animals  and,  rarely,  snake 
and  lizard  skins  (Bent  1942).  The  bulk  of  the  nest  varies 
considerably  according  to  the  size  of  the  cavity. 

Foraging  at  low  to  moderate  heights,  Ash-throated  Fly- 
catchers capture  their  prey  by  flycatching  and  fly  gleaning 
(Block  1990).  In  foothill  oak  woodlands  in  California, 
these  flycatchers  direct  prey  capture  attempts  at  leaves, 
twigs  and  small  branches,  air,  ground,  and,  rarely,  larger 
branches  and  trunks.  Ash-throateds  vary  their  foraging 
activities  and  substrates  geographically  (Block  1990,  Petit 
et  al.  1 990).  In  California,  the  height  of  trees  selected  for 
foraging  and  foraging  height  of  birds  varied  geographically, 
whereas  the  crown  radius  and  diameter  of  trees  selected  for 
foraging  and  the  crown  position  and  relative  height  of 
foraging  birds  did  not. 

264 


The  diet  (Apr-Dec)  is  about  92.3%  animal  and  7.7% 
seeds  and  fruits  (Beal  1912,  n  =  91).  The  main  articles  of 
food  are  bees,  wasps,  true  bugs,  caterpillars  and  moths, 
flies,  beedes,  grasshoppers,  and  crickets;  minor  items  are 
snakeflies,  dragonflies,  and  spiders. 

Marin  Breeding  Distribution 

Aldiough  Ash-throated  Flycatchers  were  widespread  breed- 
ers in  Marin  County  during  the  adas  years,  they  largely 
avoided  die  very  open  grasslands  and  dense  moist  forests 
along  the  immediate  coast.  Hence  they  were  most  numer- 
ous in  the  central  and  northeastern  interior  of  the  county 
(e.g.,  Big  Rock  Ridge),  where  moderately  open  broadleaved 
evergreen  forests  predominate.  Representative  breeding 
stations  were  Marshall-Petaluma  Rd.  about  V2  mi.  E  of 
Marshall  (NY/FY  6/11/82  -DS);  Phoenix  Lake  (NY/FY 
6/8/79  — ITi);  vicinity  of  Rock  Springs,  Mt.  Tamalpais 
(NY/FY  6/13/78  -ITi);  and  China  Camp  SP  (ON 
6/19/82 -BiL). 

Historical  Trends/Population  Threats 

Little  prior  information  exists.  Numbers  of  Ash-throated 
Flycatchers  increased  on  Breeding  Bird  Surveys  in  Califor- 
nia from  1968  to  1989,  despite  relative  stability  from  1980 
to  1989  (USFWS  unpubl.  analyses). 


Tyrant  Flycatchers 


SPECIES  ACCOUNTS 


Tyrant  Flycatchers 


CASSIN'S  KINGBIRD   Tyrannus  vociferans 


Accidental  breeder  with  only  one  record. 


Ecological  Requirements 

Little  can  be  said  of  Cassin's  Kingbirds'  habitat  require- 
ments in  Marin  County  since  only  one  pair  has  strayed  to 
nest  here.  These  pioneers  set  up  domestic  duties  on  the 
outer  coast  near  Palomarin,  in  a  ranchyard  treed  with 
planted  Monterey  cypress  and  eucalyptus  and  surrounded 
by  grassland,  weed  fields,  and  patchy  coastal  scrub.  Struc- 
turally, this  site  must  have  struck  a  responsive  chord  in  the 
vociferans  psyche,  but  the  climate  of  Marin's  fog-shrouded 
coasdine  bears  little  resemblance  to  that  of  the  dry  inner 
Coast  Range  valleys  of  southern  California  where  the 
species  reaches  its  apex  of  abundance  as  a  breeder  in  the 
state  (GckM  1944).  In  the  latter  region,  Cassins  primarily 
inhabit  grassland  edges  of  broken  oak  woodlands  and 
cottonwood-sycamore  riparian  groves  (Dawson  1923, 
Pough  1957,  GckM  1944). 

In  California,  where  Cassin's  and  Western  kingbirds 
often  nest  side  by  side  (Dawson  1923),  the  differences  in 
habitat  choice  between  the  two  species  are  particularly 
subde.  Garrett  and  Dunn  (1981)  stated  that  Cassins  prefer 
habitat  that  is  "less  open"  than  Westerns'.  Elsewhere, 
habitat  separation  between  the  two  is  more  apparent,  but 
they  nonetheless  overlap  strongly  in  some  areas.  In  the 
Southwest,  Cassins  prefer  the  denser  habitats  of  pine-oak- 
juniper  (on  canyon  sides),  riparian,  and  oaks,  while  West- 
erns prefer  more  open  desert  shrub,  dry  creek  washes,  and 
farmland  habitats  (Hespenheide  1964,  Smith  1966, 
Ohlendorf  1974,  Blancher  ck  Robertson  1984).  A  tend- 
ency of  Cassins  to  occur  at  higher  elevations  appears  to 
reflect  the  availability  of  preferred  habitat.  In  the  South- 
west, overlap  of  the  two  species  is  strong  in  open  riparian 
and  slight  in  dry  creek  washes,  desert  shrub,  and  planted 
trees. 

Cassin's  Kingbirds  usually  build  their  nests  near  die 
ends  of  horizontal  branches  of  trees  from  about  8  to  80  feet 
above  the  ground  (Bent  1942;  references  below).  Nest 
heights  vary  with  the  height  of  available  trees;  mean  nest 
heights  among  various  habitats  in  the  Southwest  range 
from  15  to  53  feet  (Ohlendorf  1974,  Goldberg  1979, 
Blancher  ck  Robertson  1 984).  Cassins  tend  to  nest  in  the 
upper  third  of  the  canopy  (Hespenheide  1964,  Ohlendorf 
1974,  Blancher  ck  Robertson  1984);  in  Arizona,  relative 
height  (nest  height/tree  height)  ranges  only  between  0.73 
and  0.78  (Blancher  ck  Robertson  1984).  Also  in  Arizona, 
Goldberg  (1979)  reported  an  average  nest  height  of  53  feet 
(n  =  34)  in  riparian  habitat.  Cassin's  and  Western  king- 
birds exhibit  only  minor  differences  in  nest  height  prefer- 


ences within  the  same  habitats  (Hespenheide  1964, 
Blancher  ck  Robertson  1984).  Cassins  also  occasionally 
nest  in  human  structures— on  utility  poles,  log  fences,  and 
farm  gates  (Bent  1942)— but  not  nearly  as  often  as  West- 
erns do  (Ohlendorf  1974).  Both  species  vigorously  defend 
their  nests  against  intruders.  Cassins  build  bulky  nest  cups 
of  twigs,  roodets,  weed  stalks,  bark,  and  other  plant  fibers 
mixed  with  string,  rags,  or  dry  leaves  (Bent  1942).  They 
line  them  with  fine  roodets,  fine  grasses,  and  perhaps  a  few 
feathers.  Bent  (1942)  reported  that  Cassin's  Kingbird  nests 
"average  somewhat  larger  and  rather  more  firmly  built" 
than  those  of  Westerns,  but  Dawson  (1923)  and  Blancher 
and  Robertson  (1985)  noted  great  similarity  between  nests 
of  these  species. 

Both  species  of  kingbirds  forage  primarily  by  sallying  off 
perches  to  catch  flying  insects  and,  secondarily,  by  flying 
down  to  pick  insects  off  the  ground  (Blancher  ck  Robert- 
son 1984).  Rarely,  they  glean  from  vegetation,  though 
Westerns  do  so  more  than  Cassins  do  (Goldberg  1979). 
In  general,  intraspecific  differences  in  foraging  behavior 
between  habitats  are  greater  than  any  interspecific  differ- 
ence in  behavior  in  the  same  habitat.  In  riparian  forest  and 
open  riparian  habitats,  Cassin's  Kingbird  average  sally 
distances— respectively,  66  feet  (n  =  379)  and  52  feet  (n  = 
226)— are  significandy  different,  as  are  their  average  perch 
heights  of  39  feet  (n  =  382)  and  25  feet  (n  =  225).  In  open 
riparian  habitat,  Cassins  perch  significandy  lower  than 
Westerns  do,  but  the  two  species  both  pursue  prey  at 
heights  from  the  ground  up  to  about  164  feet  and  at  similar 
average  heights  in  this  habitat.  Average  pursuit  heights  by 
Cassins  of  49  feet  (n  =  390)  and  36  feet  (n  =  229)  in 
riparian  forest  and  open  riparian  habitat,  respectively,  are 
significantly  different.  Goldberg  (1 979)  noted  interspecific 
differences  in  the  tendency  to  return  to  the  same  perch 
after  foraging  and  in  the  takeoff  angle  from  the  perch,  but 
this  did  not  result  in  differences  in  the  height  at  which  prey 
were  taken. 

In  Texas,  the  respective  diets  of  Cassin's  and  Western 
kingbirds  are  94.6%  (n  =  79)  and  97.5%  (n  =  48)  insectiv- 
orous (Ohlendorf  1974).  The  main  prey  items  by  volume 
are  grasshoppers,  beedes,  wasps,  bees,  true  bugs,  cicadas, 
butterflies,  and  moths;  minor  items  are  fleshy  fruits,  seeds, 
spiders,  and  flies.  Beal  (1912)  reported  that  Cassins  eat 
more  vegetable  food  (as  fruit)  in  North  America  than  do 
any  other  tyrant  flycatchers;  but  virtually  all  fruit  is  eaten  in 
fall  and  winter.  Both  Ohlendorf  (1974)  and  Blancher  and 

265 


Tyrant  l-lycalchers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Tyrant  Flycatchers 


Robertson  (1984)  reported  complete,  or  nearly  complete, 
dietary  overlap  (at  the  level  of  insect  order)  between  the  two 
kingbird  species.  As  with  foraging  behavior,  diere  are 
greater  intraspecific  differences  in  diet  between  habitats 
dian  interspecific  differences  in  the  same  habitat.  In  con- 
trast to  these  similarities,  males  of  both  species  take  a 
greater  proportion  of  hymenoptera  than  do  their  conspe- 
cific  females  (Goldberg  1979).  Adults  of  both  kingbird 
species  feed  grasshoppers  of  the  same  size  to  their  young 
(Blancher  &.  Robertson  1984);  as  Westerns'  young  grow, 
diey  are  fed  progressively  larger  grasshopper  prey  (data  are 
unavailable  for  Cassins).  Based  on  the  great  similarity  in 
the  ecology  of  these  two  kingbirds  where  they  co-occur, 
Blancher  and  Robertson  (1984)  argued  that  it  is  unlikely 
that  their  habitat  separation  reduces  their  competition  for 
food,  as  has  previously  been  implied. 

Marin  Breeding  Distribution 

The  sole  Marin  County  breeding  record  of  Cassin's  King- 
bird occurred  prior  to  the  adas  period.  From  20  May  to  14 
July  1972,  a  pair  was  observed  nesting  at  a  ranch  along 


Mesa  Road,  Bolinas,  about  one  mile  SE  of  Point  Reyes 
Bird  Observatory's  Palomarin  field  station  {fide  RS,  PRBO). 
The  nest  was  situated  about  40  feet  up  in  a  planted 
Monterey  cypress.  This  extralimital  breeding  record  is  the 
northernmost  for  California.  The  species  reaches  the 
northern  limit  of  its  range  in  California  in  the  interior  of 
Alameda  County,  east  of  San  Francisco  Bay  (McCaskie  et 
al.  1979,  ABN). 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  noted  an  apparent  decline  of 
the  California  population  in  the  50  to  80  years  previous  to 
1944.  From  1968  to  1979,  the  Cassin's  Kingbird  popula- 
tion increased  in  the  "California  Foothills"  (Robbins  et  al. 
1986),  which  includes  coastal  counties  south  of  San  Fran- 
cisco Bay.  From  1968  to  1989,  though,  it  was  relatively 
stable  in  California  as  a  whole  (USFWS  unpubl.  analyses). 


WESTERN  KINGBIRD    Tyrannus  verticalis 


A  summer  resident  from  early  Apr 

X^vVJoV^vir^^        N                wTx, 

through  Aug,  sparingly  to  mid-Sep. 

r^^V^°Jv<\  JV^°V*\  'j^v »Jv>A ^\>\o\ 

A  fairly  common,  somewhat  local 
breeder;  overall  breeding  population 
small. 

Recorded  in  74  (33.5%)  of  221  blocks. 

O    Possible        =      25  (34%) 

\\j^^'z2^^^ 

€    Probable      =      17  (23%) 

v^A^vS-VaSVy^V^ 

. ■  T- 

•    Confirmed  =       32   (42%) 

Psv  >V\   Va  yrp^i^\x\^ 

hP^ 

FSAR  =  3        OPI  =  222       CI  =  2.09 

Ecological  Requirements 

In  Marin  County,  these  pugnacious  tyrannids  primarily 
inhabit  the  grassland  edges  of  oak  savannah,  broken  oak 
woodlands,  open  riparian,  and  planted  windbreaks  and 
woodlots  (particularly  eucalyptus).  Although  trees  provide 
nest  sites  and  foraging  perches,  Western  Kingbirds  avoid 
large  blocks  of  woodland  in  favor  of  small  isolated  stands 
encircled  by  relatively  dry,  insect-rich  grasslands.  A  trunk 


or  two  will  suffice,  and  even  these  need  not  be  present  as 
long  as  tall  bushes  or  artificial  structures  provide  a  few 
requisite  foraging  perches  and  a  nest  support. 

Nests  are  usually  placed  in  tall  trees,  if  available,  but 
bushes,  tops  of  dead  stumps,  and,  rarely,  rocky  cliffs  or  old 
nests  of  birds  (such  as  robins  or  orioles)  will  do  (Bent 
1942).  Artificial  nest  sites,  such  as  utility  poles,  fence  posts, 


266 


Tyrant  Flycatchers 


SPECIES  ACCOUNTS 


Tyrant  Flycatchers 


and  parts  of  buildings,  are  also  readily  used.  Western 
Kingbirds  most  frequently  build  tree  nests  on  horizontal 
branches,  but  sometimes  they  place  them  against  trunks, 
in  crotches,  or  on  dead  branches.  Nest  heights  range  from 
about  5  to  100  feet  above  the  ground  (Bent  1942,  refer- 
ences below,  D.  Shuford  pers.  obs.).  Average  nest  heights 
from  a  variety  of  habitats  in  the  West  range  from  1 2  to  50 
feet  (Ohlendorf  1 974,  Goldberg  1 979,  MacKenzie  &  Sealy 
1981,  Blancher  &.  Robertson  1984).  Western  Kingbirds 
tend  to  locate  their  nests  in  the  middle  to  upper  portions 
of  the  tree  canopy;  mean  relative  nest  heights  (nest 
height/tree  height)  in  a  variety  of  habitats  range  from  0.64 
to  0.80  (Hespenheide  1964,  MacKenzie  ck  Sealy  1981, 
Blancher  ck  Robertson  1984).  See  Cassin's  Kingbird 
account  for  comparison  of  nest  location  with  that  species, 
and  MacKenzie  and  Sealy  (1981)  for  comparison  with 
Eastern  Kingbird.  Westerns  build  compact  nest  cups  of 
twigs,  weed  stems,  plant  fibers,  and  roodets  mixed  with 
wool,  plant  down,  string,  hair,  paper,  and  feathers  (Bent 
1942).  The  lining  consists  of  animal  hair,  wool,  cotton,  or 
plant  down. 

Like  Cassins,  Western  Kingbirds  forage  primarily  by 
sallying  off  perches  to  catch  flying  insects  and  secondarily 
by  flying  down  to  pick  insects  off  die  ground  (Blancher  <Sl 
Robertson  1984).  Rarely,  Westerns  glean  from  vegetation, 
but  more  so  than  Cassins  do  (Goldberg  1979).  In  Arizona, 
Western  Kingbirds'  perch  heights,  sally  distances,  and 
heights  of  prey  pursued  were  all  significandy  different 
between  open  riparian  and  desert  habitats.  Their  perch 
heights  averaged  30  feet  (n  =  363)  and  15  feet  (n  =  791), 
respectively  (Blancher  &  Robertson  1984).  Their  sally 
distances  averaged  50  feet  (n  =  368)  and  42  feet  (n  =  808), 
and  the  heights  of  prey  pursued  averaged  40  feet  (n  =  380) 
and  18  feet  (n  =  846)  in  open  riparian  and  desert  habitats. 


For  comparison  of  Westerns'  and  Cassins'  foraging  niches 
and  for  dietary  information,  see  the  Cassin's  Kingbird 
account;  see  Beal  (1912)  and  Dick  and  Rising  (1965)  for 
further  information  on  diet. 

Marin  Breeding  Distribution 

Although  Western  Kingbirds  bred  on  the  Marin  County 
coast  along  the  shores  of  Tomales  Bay  during  the  adas 
period,  they  primarily  occupied  lowland  ranchlands,  oak 
savannah,  and  oak  woodland  districts  of  the  northern 
interior.  The  absence  of  breeding  kingbirds  on  the  grass- 
land'swathed,  fog-drenched  Point  Reyes  peninsula  may 
have  reflected  the  low  availability  in  this  moist  environ- 
ment of  large  insects,  such  as  grasshoppers,  needed  to 
supply  the  demands  of  voracious  young.  Suitable  nest  sites 
are  surely  available  there,  around  ranchyards  and  wind- 
breaks. Representative  nesting  locations  were  about  1  mi. 
N  of  Millerton  Point,  Tomales  Bay  (NE  6/27/82  -DS); 
Soulajoule  Reservoir  (NE  5/21/82  -DS);  Hicks  Valley 
(ON  5/?/82  -ScC);  and  Mt.  Burdell,  Novate  (NE 
4/29/81  -DS). 

Historical  Trends/ Population  Threats 

Historically,  numbers  of  breeding  Western  Kingbirds  have 
no  doubt  increased  in  Marin  County,  at  least  locally  in 
pastoral  areas.  The  reason  for  this  trend  is  the  large 
increase  in  available  nesting  sites  for  the  species  from  tree 
plantings  (especially  eucalyptus)  in  open  country  and  from 
construction  of  artificial  structures.  On  the  whole,  num- 
bers of  Western  Kingbirds  were  relatively  stable  on  Breed- 
ing Bird  Surveys  in  California  from  1968  to  1989,  though 
they  increased  from  1980  to  1989  (USFWS  unpubl.  analy- 
ses). 


267 


fairies 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Larks 


Larks 

Family  Alaudidae 


HORNED  LARK    Eremophila  alpestris 


A  year-round  resident. 

A  common,  fairly  widespread  breeder; 
overall  breeding  population  fairly  large. 

Recorded  in  123  (55.6%)  of  221 
blocks. 

O  Possible  =  23  (19%) 
C  Probable  =  66  (54%) 
•    Confirmed  =       34   (28%) 

FSAR  -  4       OPI  =  492        CI  =  2.09 


Ecological  Requirements 

These  aerial  songsters  inhabit  Marin  County's  short- 
cropped  grasslands  of  the  fladands  or  low  rolling  hills, 
sparsely  vegetated  sand  dunes,  barren  disturbed  fields,  and 
summer-fallow  stubble  fields.  The  salient  features  of 
Horned  Larks'  breeding  habitats  are  relative  dryness  and 
very  sparse  grass  or  weed  cover.  Pickwell  (1931)  found  that, 
in  a  single  season,  growth  and  increase  in  vegetation 
during  the  first  nesting  effort  caused  abandonment  of  the 
initial  site  and  selection  of  a  more  open  site  for  the  second 
nesL  This  emphasizes  the  importance  to  Horned  Larks  of 
very  open  ground  for  nesting. 

Horned  Larks  usually  build  their  nests  flush  to  the 
ground  in  shallow  cavities  that  females  dig  out  widi  their 
bills  and  feet;  less  frequently  they  place  diem  in  natural 
depressions.  A  nest  generally  has  a  protective  feature,  such 
as  a  small  rock  or  tuft  of  overhanging  grass,  on  the  side  of 
the  prevailing  winds.  On  the  opposite  side  there  is  a 
"pavement"  covering  the  excavated  dirt  made  of  flattened 
pellets  of  dried  mud,  corncobs,  cornstalks,  or  cow  dung. 
This  presumably  serves  as  camouflage.  The  birds  build 
their  nest  cups  primarily  of  dried  grasses  and  weed  stems 
and  line  them  with  fine  grasses,  plant  down,  soft  plant 
fibers,  seed  heads,  wool,  fur,  rags,  paper,  string,  or  feathers 

268 


(Pickwell  1931,  DuBois  1935,  Verbeek  1967,  Beason  &. 
Franks  1974). 

Foraging  Horned  Larks  walk  and  run,  but  never  hop, 
between  stops  to  pick  items  from  the  ground  or  low 
vegetation.  The  diet  of  the  coastal  and  San  Joaquin  Valley 
breeding  subspecies  (E.  a.  actia)  was  found  by  McAtee 
(1905)  to  differ  "remarkably"  from  those  subspecies  out- 
side of  California  in  the  high  percentage  of  vegetable 
matter  consumed.  Vegetable  food  composes  91%  of  the 
diet  for  California  birds  (n  =  267)  compared  with  less  than 
80%  for  those  in  the  rest  of  the  country.  Of  the  vegetable 
food,  51%  is  weed  seed  and  the  rest  is  grain,  both  wild  and 
cultivated  varieties.  Animal  food  comprises  about  9%  of 
the  diet  overall,  with  a  peak  of  28%  in  June,  and  consists 
of  beedes,  true  bugs,  ants,  grasshoppers,  caterpillars,  other 
insects,  and  spiders  (McAtee  1905,  Beal  1910);  adults,  of 
course,  feed  the  insects  to  their  young. 

Marin  Breeding  Distribution 

During  the  adas  period,  Horned  Larks  were  concentrated 
in  Marin  County's  low,  rolling  ranchlands  of  the  central 
and  northern  sectors  and  along  the  western  fringe  of  the 
Point  Reyes  peninsula.  They  avoided  steep  grassy  hills 


Larks 


SPECIES  ACCOUNTS 


Swallc 


throughout  their  range  here.  Representative  breeding  local- 
ities were  ranch  on  S  side  of  Walker  Creek  about  1.5  mi. 
E  of  Hwy.  1  (FY  6/12/82  -DS);  E  side  of  Tomales  Bay 
near  Millerton  Point  (FY  5/13/82  -DS);  Mt.  Burdell, 
Novato  (NY  4/29/81  — ITi);  Redwood  Dump,  Novato  (NE 
5/17/78  -DS);  Big  Rock  Ridge  (FL  5/9/81  -DS). 

Historical  Trends/Population  Threats 

Few  prior  data  exist,  but  numbers  of  Horned  Larks  were 
relatively  stable  on  Breeding  Bird  Surveys  in  California 
from  1968  to  1989,  despite  a  decline  from  1980  to  1989 
(USFWS   unpubl.    analyses).    Historically,   the   intensive 


changes  to  grasslands  brought  about  by  crop  agriculture 
and  grazing  in  California  must  have  had  a  profound  effect 
upon  Horned  Larks.  Grazing  likely  has  improved  the 
Horned  Lark's  lot  by  keeping  vegetation  short  and  sparse. 
Crop  agriculture  likely  has  eliminated  much  habitat  for 
breeding  birds,  but  fallow  fields  may  support  larger  winter 
populations  than  formerly.  The  California  Horned  Lark 
(E.  a.  actia)  is  currendy  a  Candidate  (Category  2)  for 
federal  listing  as  Threatened  or  Endangered  (USFWS 
1991),  though  the  Marin  population,  at  least,  appears 
healthy. 


Swallows 

Family  Hirundinidae 


PURPLE  MARTIN    Progne  subis 

A  summer  resident  from  early/mid-Mar 

Xj5po?^^-^  s         j(\ 

through  mid-Sep. 

An  uncommon,  very  local  breeder; 

^A^^x3rA3r^xXA  \^\\jr\t^' 

overall  breeding  population  very  small. 
Recorded  in  24  (10.8%)  of  221  blocks. 

^^^T^\^^<^^\^^^?\^^\ 

V<rN/V^^  Vi^y     \^\\^\\^\^\^\^)^^\ 

O    Possible        =       16   (67%) 

x\\~^K%-*\^\ 

€    Probable       =         5   (21%) 

xjJ^^'i^^^-iA^^)^^^9^^^^^^  y<c\  \^y 

•    Confirmed  =         3   (13%) 

-s" 

FSAR=2       OPI  =  48          CI  =  1.46 

VO> 

i^^                                  \L~  /        ^~^*~^*£S<**^\ 

Ecological  Requirements 

The  largest  of  our  swallows  is  also  by  far  the  most  enig- 
matic. Of  the  two  known  colony  sites  in  Marin  County, 
one  is  in  a  large  dead  snag  in  a  clearing  in  the  Douglas  fir 
forest  atop  Inverness  Ridge.  The  other  is  on  the  eastern 
slope  of  Bolinas  Ridge,  above  Kent  Lake,  where  a  fire  in 
1945  devastated  the  Douglas  fir-coast  redwood  forest  and 
left  numerous  large  snags.  The  Marin  County  sites  seem 


typical  of  those  in  forested  regions  elsewhere  in  California 
and  the  West,  where  most  Martins  breed  in  natural  clear- 
ings or  those  left  by  forest  fires  or  lumbering  activities 
(GckM  1944,  Richmond  1953,  Finlay  1975,  Jackman  6k 
Scott  1975).  Forests  or  trees  per  se  are  not  required  as  long 
as  suitable  nest  sites  and  foraging  areas  are  present.  Breed- 
ing sites  are  often  near  the  insect-productive  waters  of 


269 


Swallows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Swallows 


ponds,  lakes,  reservoirs,  and  rivers  (Richmond  1953,  Jack- 
son &  Tate  1974,  Jackman  &.  Scott  1975,  D.  Shuford 
pers.  obs.).  However,  these  foraging  habitats  may  be  at 
some  distance  from  the  nest,  since  Purple  Martins  have  a 
long  daily  cruising  radius. 

Martins,  like  many  swallows,  are  cavity  nesters.  For- 
merly most  Martins  nested  in  natural  situations,  but  popu- 
lations east  of  the  Rockies  now  nest  mosdy  in  artificial 
sites,  particularly  in  Martin  "apartment  houses"  (as  many 
as  200  boxes)  and  in  gourds  hung  from  poles.  Most 
western  birds  nest  in  natural  sites,  and  they  rarely  use  nest 
boxes,  among  artificial  sites  (GckM  1944,  Richmond 
1953,  Phillips  et  al.  1964).  Most  natural  nest  sites  are  tree 
or  stump  cavities,  usually  abandoned  holes  of  our  larger 
woodpeckers.  Other  natural  sites  include  cavities  or  crev- 
ices in  cliffs,  in  lava  tubes,  or  under  boulders  (Sprunt 
1942,  ABN).  Artificial  sites  include  cracks  and  crevices  of 
buildings,  undersides  of  bridges,  and  streedights  (Sprunt 
1942,  GckM  1944,  Roberson  1985).  Pristine  surround- 
ings are  not  the  issue,  as  indicated  by  a  Sacramento  colony 
that  habitually  occupies  the  air  vents  on  the  underside  of  a 
freeway  overpass  above  a  transit  bus  parking  lot.  Nests 
have  been  recorded  from  3  to  1 30  feet  above  ground  or 
water  (Sprunt  1942).  In  the  East,  Martins  showed  no 
preference  for  the  various  height  intervals  of  nest  boxes 
placed  between  7  and  26  feet  (Jacks°n  &.  Tate  1974). 
Hence,  Sprunt's  (1942)  report  that  most  nests  in  houses 
are  from  15  to  20  feet  probably  reflects  the  preference  of 
the  "landlords"  rather  than  the  tenants.  My  few  observa- 
tions of  Martins'  tree  nest  sites  in  California  suggest  that 
most  are  situated  high  in  large  dead  snags.  These  large- 
diameter  boles  are  likely  to  be  most  attractive  to  large 
woodpeckers  and  to  have  decayed  first  near  their  tops  (see 
woodpecker  accounts). 

Martins  construct  nests  sporadically  for  about  a  month 
prior  to  egg  laying.  Initially  they  add  such  materials  as  dead 
leaves,  sticks,  and  paper  but  then  lay  down  a  relatively  solid 
mat  of  sticks  and  mud  to  about  the  level  of  the  entry  hole. 
The  mat  slopes  back  to  the  rear  and  has  a  small,  shallow 
cup  for  the  eggs  (Johnston  ck  Hardy  1962).  Other  nesting 
materials  might  include  grass,  feathers,  rags,  pieces  of 
rubber,  string,  or  bark.  Occasionally  when  the  nest  is  open 
to  the  elements,  the  birds  build  a  rim  of  mud  in  front  of 
the  nest  (Sprunt  1942,  Allen  6k  Nice  1952).  After  complet- 
ing the  structure  of  the  nest,  the  adults  add  green  leaves 
and  replace  them  as  they  dry  out.  The  green  leaves  may 
possibly  serve  to  supply  moisture  to  the  eggs  during  incu- 
bation (Taverner  1933),  to  cool  the  nest  cavity  by  evapora- 
tion (Sprunt  1 942),  or  to  supply  fumigant  that  acts  against 
ectoparasites  developing  in  the  detritus  of  the  nest  (John- 
ston &.  Hardy  1962). 

Martins  forage  almost  exclusively  on  the  wing.  They  fly 
with  a  rapid  flapping  of  wings,  alternating  with  periods  of 
sailing  in  straight  lines  or  long,  sweeping  arcs.  They  appar- 

270 


endy  feed  occasionally  on  the  ground  for  terrestrial  insects 
(Sprunt  1942)  or  catch  insects  from  the  tops  of  weeds  as 
diey  dart  past  (Beal  1918).  Martins  forage  at  heights  from 
a  few  feet  to  greater  than  500  feet,  but  most  frequendy 
between  about  200  and  300  feet  (J°bnston  ck  Hardy 
1 962)— generally  higher  than  our  other  swallows.  In  Marin 
County,  Martins  apparently  forage  mainly  above  the 
higher  ridges  over  terrestrial  habitats.  Birds  also  come 
down  to  feed  in  die  lowlands,  especially  over  ponds  and 
coastal  estuaries  (in  particular  Bolinas  Lagoon).  Birds  for- 
age either  singly  or  in  groups,  especially  early  in  the  spring, 
when  insect  food  is  localized  (Johnston  6k  Hardy  1962). 
The  diet  (Feb-Sep)  is  entirely  animal,  consisting  primarily 
of  insects  (Beal  1918,  n  =  205).  The  main  prey  are  bees, 
wasps,  ants,  flies,  dragonflies,  true  bugs,  beedes,  and 
moths;  minor  items  are  grasshoppers,  butterflies,  mayflies, 
spiders,  and  sowbugs.  In  Alberta,  the  main  prey  fed  to 
nestlings  are  dragonflies,  flower  flies,  butterflies,  and 
midges  (Walsh  1978).  The  diet  there  varies  with  time  of 
day,  season,  and  weather.  The  size  of  prey  fed  to  young 
increases  as  the  young  develop  (Finlay  1971,  Walsh  1978). 
Martins  regurgitate  pellets  consisting  of  the  hard  parts  of 
insects  (Richmond  1953).  They  may  need  calcium,  per- 
haps for  egg  formation,  which  they  obtain  from  crushed 
bivalve  shells,  eggshells,  grit,  lime,  or  bones  (Richmond 
1953). 

Marin  Breeding  Distribution 

During  the  adas  years,  Purple  Martins  were  recorded  in 
Marin  County  in  the  breeding  season  mosdy  around  the 
southern  portions  of  Inverness  and  Bolinas  ridges.  Many 
of  these  records  could  have  pertained  to  birds  foraging  at 
some  distance  from  the  two  known  localized  colonies 
described  above  and  below.  Confirmed  nesting  records 
were  Inverness  Ridge  above  Five  Brooks  (FY  6/?/77  — 
RMS;  NB  5/31/80  -JGE);  Kent  Lake  (NY  5/31/77  - 
RMS;  FY  7/23/81  -GFMc);  and  Alpine  Lake  (FY  6/?/82 
— ITi).  The  latter  record  may  have  involved  birds  that  had 
moved  from  the  vicinity  of  Kent  Lake.  In  Marin  County, 
breeding  Martins  were  locally  fairly  numerous  in  the  Kent 
Lake  area  and  nearby  on  Bolinas  and  Carson  ridges  (e.g., 
1 5  seen  in  this  general  area  on  6/5/82  — DS,  ITi).  Most  of 
these  birds  probably  nested  on  the  slopes  of  Bolinas  Ridge 
above  Kent  Lake,  but  the  steep  terrain  and  difficult  access 
have  so  far  limited  observer  attempts  to  explore  this  area 
thoroughly.  Since  at  least  the  late  1980s,  Purple  Martins 
have  been  seen  regularly  in  die  breeding  season  around  the 
Seadrift  spit  at  Bolinas  Lagoon,  suggesting  that  they  may 
now  nest  there  (K.  Hansen  pers.  comm.).  Elsewhere  in 
Marin,  breeding  Martins  were  very  infrequendy  encoun- 
tered. The  patchy  distribution  of  breeding  Purple  Martins 
in  Marin  County  and  elsewhere  in  California  and  the 
West  is  puzzling.  Although  nest  sites  may  limit  their 
occurrence  locally,  the  woodpecker  holes  upon  which  Mar- 


Swallows 


SPECIES  ACCOUNTS 


Swallows 


tins  depend  are  widespread.  It  may  be  that  the  combina- 
tion of  few  nest  sites  and  few  suitable  foraging  areas  limit 
them.  In  the  arid  West,  conditions  that  favor  adequate  prey 
for  these  large  aerial  insectivores  are  probably  much  more 
localized  than  they  are  in  the  humid  East— but  still  perhaps 
more  widespread  than  the  distribution  of  breeding  Martins 
in  the  West  suggests. 

Historical  Trends/Population  Threats 

Both  early  historical  and  recent  accounts  indicate  that 
Purple  Martins  have  always  been  very  local  breeders  in 
Marin  County  and  central  California.  Mailliard  (1900) 
considered  the  Purple  Martin  "sparingly  summer  resident" 
in  Marin  County.  Grinnell  and  Wythe  (1927)  reported 
only  three  sites  in  the  San  Francisco  Bay  Area  where 
Purple  Martins  were  "known  to  have  remained  through 
the  nesting  season."  Two  of  these  sites  were  in  Marin 
County,  at  Olema  and  Nicasio.  Stephens  and  Pringle 
(1933)  considered  the  Martin  an  uncommon  migrant  or 
transient  in  Marin  County;  they  made  no  mention  of  it 
breeding  in  the  county.  For  California  in  general,  Grinnell 
and  Miller  (1944)  noted  that,  although  Purple  Martins  are 
considered  "fairly  common  .  .  .  many  suitable  localities  lack 
this  swallow."  In  addition,  they  noted  Martins  spreading 
to  some  districts  built  up  by  people  "in  recent  years"  and 
that  their  numbers  were  probably  increasing. 

Because  of  declining  populations,  the  Purple  Martin  is 
currendy  considered  by  the  California  Department  of  Fish 
and  Game  as  a  Bird  Species  of  Special  Concern  (Remsen 
1978,  CDFG  1991b).  Additionally,  the  Purple  Martin  has 
been  on  the  Audubon  Society  Blue  List  from  1975  to  1981 
and  on  their  list  of  Species  of  Special  Concern  from  1982 
to  1986  (Tate  1986).  In  California,  though,  Martins  have 
declined  substantially  only  in  the  southern  region  of  the 
state  (Remsen  1978,  Garrett  &  Dunn  1981).  Most 
reported  declines  in  northern  California  (including  Marin 
County)  have  involved  only  local  areas  and  have  been 
based  largely  on  anecdotal  evidence.  Tate  (1981)  quoted 
one  northern  California  observer  who  claimed  that  "the 
species  no  longer  nests  in  forests  in  central  California. 
This  statement  is  far  off  the  mark,  as  documented  by  the 
Marin  County  data  and  by  incidental  observations  else- 


where in  northern  California  (ABN).  Martin  numbers  on 
Breeding  Bird  Surveys  were  relatively  stable  from  1968  to 
1989  (Robbins  et  al.  1986,  USFWS  unpubl.  analyses). 
However,  Breeding  Bird  Survey  techniques  may  not  be 
adequate  to  determine  trends,  in  California  or  elsewhere, 
of  species  like  the  Martin  that  occur  in  low  relative  abun- 
dance and  are  patchily  distributed.  In  California,  it  would 
be  more  effective  to  identify  a  large  number  of  Martin 
colonies  and  monitor  them  on  a  regular  basis. 

Although  North  American  Martin  populations  have 
been  stable  or  increasing  in  recent  years  (Robbins  et  al. 
1986),  competition  with  European  Starlings  and  House 
Sparrows  has  been  widely  reported  as  the  cause  of  Purple 
Martin  declines  continentwide.  Very  few  studies  have 
addressed  the  problem  specifically  (Brown  1981).  Jackson 
and  Tate  (1974)  generally  found  an  inverse  correlation 
between  the  rates  of  Martin  and  of  House  Sparrow  occu- 
pancy of  apartment  houses  and  gourds.  They  also  con- 
cluded that  House  Sparrows  were  more  serious 
competitors  with  Martins  than  were  Starlings.  They 
drought  that  House  Sparrows  repel  Martins  at  small  colo- 
nies and  usurp  their  nests  and  destroy  eggs  at  larger  ones, 
and  that  Starlings  are  not  serious  nest  site  competitors  but 
more  a  threat  as  predators  on  nesdings  and  eggs.  Brown 
(1981),  on  the  other  hand,  concluded  that  Starlings  were 
the  main  threat  to  Martins  and  documented  declines  of 
Martins  and  increases  in  Starlings  at  unmanaged  colonies. 
Both  the  House  Sparrow  and  Starling  likely  have  less  effect 
on  the  more  remote  and  patchily  distributed  Martin  colo- 
nies in  the  West.  More  specific  studies  are  needed  to 
document  the  effects  of  these  alien  species  on  Martins  and 
other  native  birds. 

Prolonged  periods  of  rain  during  the  nesding  phase  may 
prove  fatal  to  both  young  and  adult  Purple  Martins  and 
may  produce  dramatic  changes  in  local  populations  (Rob- 
bins et  al.  1986).  This  should  be  taken  into  account  in  any 
monitoring  scheme.  Although  logging  may  open  up  some 
habitat  to  this  species,  it  may  also  eliminate  potential  nest 
sites  by  snag  removal,  especially  following  forest  fires,  in 
areas  that  otherwise  might  be  colonized  by  Martins. 


271 


Swallo 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


Swallc 


TREE  SWALLOW    Tachycineta  bicolor 


Occurs  almost  year  round,  though  pri- 

marily as  a  summer  resident  from  mid- 

Feb  through  late  Sep. 

"As^S-w^^ 

An  uncommon,  widespread  breeder; 

r\#i\1V^#V^^ 

overall  breeding  population  small. 

Y\NT  \  \JrJ>c\  °Jk\  O  \^r\     XJ^\      \^<\-    -X  J*\c>  X  Z^\ 

Recorded  in  132  (59.7%)  of  221 

^^vS^^A^ 

blocks. 

O    Possible        =      68  (52%) 
€    Probable       =      18  (14%) 

•    Confirmed  =      46  (35%) 

^a 

FSAR  =  2       OPI  =  264        CI  =  1.83 

Ecological  Requirements 

The  dazzling  metallic  blue  backs  of  breeding  Tree  Swallows 
inspire  awe  as  the  birds  dip  low  over  their  favored  foraging 
haunts  of  ponds,  open  streams,  wet  meadows,  marshes, 
and  irrigated  fields.  Of  Marin  County's  swallows,  Trees  are 
the  most  closely  wedded  to  moist  habitats  for  feeding  and 
nesting.  Tree  Swallows  nest  solitarily  or  only  loosely  colo- 
nially.  When  suitable  nest  sites  are  abundant,  these  birds 
choose  not  to  nest  close  together;  when  nest  sites  are  in 
close  proximity,  there  is  spatial  and  temporal  spacing  of 
nests  enforced  by  territorial  defense  (Muldal  et  al.  1985). 
Tree  Swallows  are  cavity  nesters  whose  natural  nest  sites 
are  decaying  pockets  in  trees,  such  as  hollow  limbs,  dead 
trunks,  or  old  woodpecker  holes.  These  are  usually  found 
at  the  heads  of  lakes,  borders  of  freshwater  marshes,  and 
along  river  valleys,  where  whole  stands  of  dead  trees  occur 
(Kuerzi  1941).  The  birds  strongly  prefer  isolated  nest  sites 
or  those  in  open  stands;  they  avoid  sites  shaded  by  vegeta- 
tion (Austin  &.  Low  1932).  Tree  Swallows  also  readily 
adapt  to  nest  boxes  or  cavities  in  the  eaves  of  buildings. 
Suitable  nest  sites  can  be  such  a  limiting  factor  that  the 
erection  of  nest  boxes  may  cause  colonization  far  from 
moist  habitats  where  ecological  conditions  are  poor  (Kuerzi 
1941).  Nest  height  ranges  from  about  2  to  50  feet  (av. 
about  15  ft.)  (Tyler  1942,  Airola  1980,  D.  Shuford  pers. 
obs.).  The  nest  foundation  is  an  accumulation  of  dry  grass, 
straw,  pine  needles,  or  roodets  at  the  bottom  of  the  nest 
cavity  (Austin  6k  Low  1932,  Kuerzi  1941,  Tyler  1942).  A 
hollow  for  the  eggs,  either  to  one  side  or  in  the  center,  is 
lined  thickly  with  feathers.  The  quills  are  buried  in  the 

272 


foundation  or  point  away  from  the  central  hollow  (Austin 
6k  Low  1932),  and  die  feathers  cover  the  eggs  when  left 
unattended  (Stocek  1970).  Older  birds  add  most  feathers 
to  the  nest  before  egg  laying.  Younger  breeders  tend  to  add 
fewer  feathers,  mostly  as  incubation  progresses,  and  some- 
times construct  an  incomplete  foundation  or  lay  eggs  on 
the  bare  floor  of  a  nest  box  (Kuerzi  1941).  Reuse  of  nests 
by  the  same  individuals  in  successive  years  has  been  low  in 
some  studies  (Low  1933,  1934)  and  high  in  others  (Chap- 
man 1935,  1939). 

Tree  Swallows  normally  forage  for  aerial  insects  within 
50  to  100  feet  of  the  ground  and  often  much  lower,  for 
instance  while  skimming  close  to  the  surface  of  ponds. 
Their  flight  is  rapid  and  includes  much  swooping  and 
darting,  but  infrequent  soaring.  They  will  also  alight  on  the 
ground  or  on  bushes  to  procure  insects  and  vegetable 
matter,  especially  when  aerial  insects  are  unavailable  (Tyler 
1942,  Erskine  1984).  The  diet  overall  consists  of  about 
80.5%  animal  food  and  19.5%  vegetable  (Beal  1918,  n  = 
343).  The  animal  food  is  primarily  insects,  along  with  a  few 
spiders;  the  main  items  are  flies,  beedes,  bees,  wasps,  ants, 
and  true  bugs;  minor  items  are  moths,  caterpillars,  grass- 
hoppers, dragonflies,  and  mayflies.  The  diet  differs  from 
diat  of  other  swallows  of  this  latitude  in  the  appreciable 
quantity  of  vegetable  food,  in  the  form  of  fruits  and  seeds, 
consumed  throughout  the  year.  In  the  East,  vegetable  fare 
ranges  from  1%  in  spring,  to  21%  in  summer,  to  30%  in 
fall  and  winter  (Martin  et  al.  1951,  n  =  362).  Kuerzi  (1941) 
reported  that  the  normal  foraging  radius  at  a  Connecticut 


Swallows 


SPECIES  ACCOUNTS 


Su/allc 


colony  is  about  a  mile  and  sometimes  up  to  three  miles. 
Tree  Swallows  sometimes  depart  en  masse  from  colonies 
on  overcast  days.  On  cold  and  cloudy  days,  they  probably 
travel  to  lakes  and  ponds  where  the  air  over  the  water  is 
warmer  and  more  insect-productive  (Chapman  1955). 
Birds  forage  much  farther  afield  in  rainy  than  in  fair 
weather.  During  a  period  of  inclement  weather,  a  banded 
female  was  found  five  miles  from  her  nest  site  at  a  Marin 
County  colony  (Stewart  1972).  At  such  times,  adults  also 
resort  to  feeding  on  fruits  for  lack  of  insects  (Chapman 
1955).  Although  adults  can  subsist  on  vegetable  fare,  they 
do  not  feed  it  to  their  young.  During  periods  of  cold  and 
rain  there  can  be  high  nest  failure  (Stewart  1972),  but, 
presumably  by  switching  to  fruit,  adult  Tree  Swallows 
survive  better  under  these  conditions  than  do  other  species 
of  swallows. 

Marin  Breeding  Distribution 

During  the  adas  period,  Tree  Swallows  were  widespread, 
but  patchily  distributed  breeders  in  Marin  County.  They 
were   concentrated   somewhat   along   the   coast  where 


marshes  and  permanent  streams  are  more  prevalent.  Many 
confirmed  records  for  the  interior  of  the  county  were  near 
major  roads  that  invariably  paralleled  streams.  Representa- 
tive breeding  records  were  Muddy  Hollow  at  Lynantour 
Estero  (FY  6/29/81  -DS);  Palomarin  (NB-NE  4/16- 
5/15/77  -SJ);  Slide  Ranch,  S  of  Stinson  Beach  (ON 
5/24/81  — DS);  and  Maggetti  Ranch,  Marshall-Petaluma 
Rd.  (ON  5/27/82  -DS). 

Historical  Trends/ Population  Threats 

Mailliard  (1900)  considered  the  Tree  Swallow  a  summer 
resident  that  was  "abundant"  in  Marin  County's  "white 
oak"  regions.  I  suspect  this  was  a  typographic  error  as  he 
also  reported  the  Violet-green  Swallow  as  "sparingly  sum- 
mer resident."  Currendy,  the  relative  abundance  of  these 
species  is  roughly  the  reverse  of  that  reported  by  Mailliard. 
Also,  the  Violet-green,  not  the  Tree  Swallow,  is  the  swallow 
of  the  "white  oaks."  Tree  Swallows  were  relatively  stable  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989, 
despite  an  apparent  slight  decline  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


VIOLET-GREEN  SWALLOW   Tachycineta  thalassina 


Occurs  almost  year  round,  though  pri- 

Jr~* 

marily  as  a  summer  resident  from  mid- 

y\(\if 

jPc<5Py~>^  n     _^^*3^-^ 

Feb  through  mid-Oct;  numbers  swell 

substantially  during  peak  of  fall  migra- 

tion (late  Sep  to  mid-Oct). 

A  common,  very  widespread  breeder; 

><A  \^\      A-^\  °  jP\  •  Vr-^\  o  \^\  ©  \^\  ti'-Y--'\ 

kOXx-C  \^\    A<T\  •  jt^"v  o  \^\  •  >-^\  o  \>^\  o  J 

V<\S&fr-Q  X^\  °  V"\  o  \^\  ©  V-^A  ©  \>^\  •  V^\ 

overall  breeding  population  large. 

Recorded  in  177  (80.1%)  of  221 

blocks. 

\  PV^A  •  \-^\  *J^\fr£^\0  V^AO  \>v»Av^\ vOv 

v^\  %jr\  *A<\  •3?i\  •  3^#»>>viDJv^v •Vwv-^ 

O    Possible        =      94   (53%) 

©    Probable       =      24  (14%) 

ivOr^T?^        ^<L°  A^"\  ©" V-'a  ©-¥>*\  o><\  •  Vvca 

^?& 

•    Confirmed  =       59   (33%) 

rff               ^^^^^a>^^ 

J^                                         X°/      ^~^kcA^ 

FSAR  =  4       OPI  =  708        CI  =  1.80 

Ecological  Requirements 

This  stunning  beauty  is  our  only  truly  widespread  wood- 
land- and  forest-inhabiting  swallow.  The  Violet-green  Swal- 
low, unlike  the  Tree,  generally  has  no  strong  attachment  to 
water,  though  it  may  prefer  to  nest  near  it  in  arid  areas  with 
an  otherwise  low  prey  base.  In  Marin  County,  it  nests  on 
the  edges  of,  or  in  clearings  in,  all  the  major  forest  and 
woodland  types,  as  well  as  in  urban-suburban  areas.  Vio- 


let-greens here  especially  favor  open  oak  woodlands  for 
nesting.  Locally,  they  select  mosdy  old  woodpecker  holes 
or  natural  cavities  in  trees  for  nest  sites,  although  birds  will 
readily  use  nest  boxes  and  crevices  in  buildings,  such  as 
those  found  under  Spanish-style  roof  tiles.  In  some  regions 
they  nest  more  frequendy  in  cracks  or  cavities  in  cliffs,  in 
boulder  piles,   in  tufa  towers,  and,  rarely,   in  old  Cliff 

273 


Swallc 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Swallows 


Swallow  nests  or  Bank  Swallow  burrows  (Bent  1942, 
Gaines  1988).  Nest  heights  may  range  from  ground  level, 
as  in  boulder  crevices,  presumably  up  to  a  hundred  feet  or 
more  in  cliffs.  Violet-greens  make  nests  primarily  of  fine 
grass  stems,  twigs,  and  roodets,  and  they  line  the  cups 
thickly  with  feathers  (Bent  1942,  Edson  1943,  Combellack 
1954). 

Violet-green  Swallows  forage  at  varying  altitudes.  They 
sweep  low  over  ponds,  fields,  and  marshes  but  often  sail 
hundreds  of  feet  above  the  ground,  alternately  flapping  and 
gliding  with  their  downcurved  wings.  They  also  land  on 
the  ground  and  hop  about,  presumably  in  search  of  insects 
(Erskine  1984).  In  contrast  to  Tree  Swallows,  Violet-greens 
are  not  inclined  to  forage  only  over  moist  habitats  but  will 
search  for  their  aerial  prey  over  virtually  any  terrain.  The 
diet  (Mar-Sep)  is  100%  insectivorous,  with  the  most 
important  items  being  true  bugs,  flies,  wasps  and  bees, 
beedes,  and  ants;  minor  items  are  moths,  caterpillars,  and 
mayflies  (Beal  1918,  n  =  110).  Seasonal  variation  in  the 
insect  diet  has  been  noted. 


Marin  Breeding  Distribution 

Violet-green  Swallows  bred  widely  in  Marin  County  dur- 
ing the  atlas  period  and  appeared  to  be  most  numerous  in 
the  open  oak  woodlands  in  the  Nova  to  area.  They  were 
sparse  or  lacking  as  breeders  in  some  of  the  grassland  areas 
in  the  northwestern  part  of  the  county,  presumably 
because  of  a  paucity  of  suitable  nesting  locations.  Represen- 
tative breeding  stations  were  Hick's  Valley  Rd.,  Novato 
(ON  4/?/82  -ScC);  Mt.  Burdell,  Novato  (NY/FY  4/2/81 
— ITi);  near  Pine  Mountain/Carson  Ridge  area  (ON 
6/5/82  — DS,  ITi);  and  Cascade  Canyon,  Fairfax  (ON 
5/11/81  -DS). 

Historical  Trends/  Population  Threats 

See  comments  under  Tree  Swallow.  Numbers  of  Violet- 
green  Swallows  were  relatively  stable  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989,  despite  an 
apparent  slight  increase  from  1980  to  1989  (USFWS 
unpubl.  analyses). 


Barn  and  Cliff  swallows  bustling  about  their  domestic  duties  enliven  ranchyards  throughout  most  of  Marin  Count}. 

Drawing  by  Keith  Hansen,  1 990. 


274 


Swallows 


SPECIES  ACCOUNTS 


Swallows 


NORTHERN  ROUGH- WINGED  SWALLOW    Stelgidopteryx  serripennis 


A  summer  resident  from  early  Mar 

through  late  Sep. 

An  uncommon,  fairly  widespread 

x\^<vo><\  Jv^a  jr^K*\i  \  i v2-a   v^a   W^y 

breeder;  overall  breeding  population 

\***\  ©  K^\     V^\  °  v^a    A^x      w^A     V-^a     \^\ 

small. 

VS&^^CA  3r^°A^#Jr^*A>^C^\     A><\  °^ 

Recorded  in  104  (47.0%)  of  221 

\\2-^YS^r\   A^A  •  a-Ha  o  \>\  o  V-"a    V-^t\     \ 

blocks. 

Vv*  3^r^V^®  Ji^bA^-^A  o  y^a    V^YlA^ir^-- 

\  \V^T\^  t-AeJp\   JE^WV^^J^^-Jl^A     V"" 

.. 

O    Possible        =      58  (56%) 
€    Probable      =      16  (15%) 

•    Confirmed  =      30  (29%) 

1pSfe3Jp^--^S><A0A><\    V-A   A-^V-  V-"A 

^a 

FSAR  =  2        OPI  =  208        CI  =  1.73 

\^q^Wk 

^                        \jz/      ^-^k: 

jY^Ty^ 

Ecological  Requirements 

Rough-winged  Swallows,  with  their  earth-tone  plumages 
and  guttural  voices,  usually  breed  around  Marin  County's 
streams,  ponds,  estuarine  margins,  and  ocean  bluffs  that 
afford  suitable  nest  sites.  Water  is  not  a  strict  requirement, 
though,  as  these  birds  are  equally  at  home  far  from  water 
where  banks  in  gullies,  road  cuts,  or  similar  settings  serve 
their  nesting  needs.  Although  Grinnell  and  Miller  (1944) 
recognized  the  breadth  of  moisture  conditions  over  which 
Rough-wings  are  found,  they  emphasized  their  tolerance 
for  and  apparent  choice  of  arid  environments.  To  my 
mind,  moisture  conditions  are  of  minor  importance  as 
long  as  suitable  nest  sites  and  very  open  terrain  for  foraging 
are  available.  Nest  site  preference  appears  to  limit  Rough- 
wing  numbers,  which  in  turn  may  allow  their  languid 
foraging  style,  effective  in  catching  certain  types  of  insects 
that  occur  over  a  range  of  moisture  conditions  but  in  no 
great  abundance. 

Rough-winged  Swallows  nest  in  isolated  pairs  or  in 
small  loose  colonies,  and  their  earthen  hues  blend  well 
with  their  typical  nest  holes  in  vertical  sand,  dirt,  or  gravel 
banks.  It  appears  that  Rough-wings,  unlike  Bank  Swal- 
lows, rarely  if  ever  dig  nest  holes  from  scratch,  although 
there  is  some  controversy  over  this  point  (Lunk  1962).  The 
holes  Rough-wings  occupy  in  earthen  banks  are  usually 
made  by  kingfishers,  rodents,  and  Bank  Swallows. 
Although  their  predisposition  not  to,  or  inability  to,  dig 
burrows  limits  their  numbers  locally,  Rough-winged  Swal- 
lows  generally   are   much   more  widespread   than   Bank 


Swallows,  which  are  restricted  by  their  need  for  soft  soil  in 
which  to  dig  burrows  (Garrison  et  al.  1987).  Rough-wings 
also  nest  in  natural  cracks  and  crevices  in  rock  faces,  cliffs, 
and  caves,  but  only  very  rarely  in  trees.  They  also  readily 
use  artificial  sites,  such  as  crevices  in  buildings,  ledges  and 
crannies  under  bridges  and  culverts,  air  vents  under  free- 
way overpasses,  drainpipes,  gutters,  and  artificial  nest  tubes 
(Dingle  1942,  Lunk  1962,  D.  Shuford  pers.  obs.).  Nest 
holes  may  be  1  to  50  feet  above  the  ground  or  water,  and 
burrow  length  may  range  from  nine  inches  to  six  feet 
(Dingle  1942).  The  nest  foundation  is  an  "indiscriminate 
pile"  of  material,  but  d^e  nest  cup  itself  is  well  shaped  and 
lined  with  softer  materials.  The  main  nest  materials  are 
twigs,  weed  stems,  roodets,  grass,  leaves,  bark  shreds,  plant 
fibers,  flower  parts,  or  dung.  The  lining  is  usually  of  fine 
grasses  with  a  few  green  leaves  or  petals  sometimes  added 
as  a  final  touch.  In  contrast  to  Bank  Swallows,  Rough- 
wings  do  not  line  their  nests  with  feathers  (Lunk  1962). 

Rough-winged  Swallows  generally  forage  in  rather  slow, 
deliberate,  often  straight  flight  very  low  to  the  ground  over 
ponds,  streams,  estuaries,  fields,  gullies,  and  dry  arroyos; 
birds  will  occasionally  land  on  the  ground  to  procure  food 
(Wolinski  1980,  Sealy  1982).  The  diet  (Apr-Sep)  is  virtu- 
ally all  animal  matter,  primarily  insects  (Beal  1918,  n  = 
1 36).  The  main  food  items  are  flies,  wasps,  bees,  true  bugs, 
beetles,  and  ants;  minor  items  are  moths,  caterpillars, 
dragonflies,  mayflies,  grasshoppers,  spiders,  and  snails. 

275 


Swallows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Swallc 


Marin  Breeding  Distribution 

Breeding  Rough-winged  Swallows  were  patchily  distrib- 
uted throughout  Marin  County  during  the  adas  years. 
They  generally  occupied  lowland  valleys,  usually  near 
water,  and  their  presence  reflected  that  of  available  nesting 
sites.  Representative  nesting  locations  were  Abbott's 
Lagoon  (ON  4/V82  -JGE);  low  hills  NE  of  Schooner  Bay, 
Point  Reyes  (ON  4/20/82  -DS);  near  Tomales  (NY 
6/2/77   —RMS);   base  of  Antonio   Mountain,   Chileno 


Valley  (FY  6/4/82  — DS,  ScC);  and  pipes  in  seawall  at 
Tiburon  Fisheries  Lab  (ON  several  years  during  adas 
period  — BiL). 

Historical  Trends/ Population  Threats 

Little  historical  data  exist.  Numbers  increased  on  Breeding 
Bird  Surveys  in  California  from  1968  to  1979  (Robbins  et 
al.  1986)  but  were  relatively  stable  when  analyses  were 
extended  from  1968  to  1989  (USFWS  unpubl.). 


CLIFF  SWALLOW    Hirundo  pyrrhonota 


A  summer  resident  from  early/mid-Mar 
to  early  Sep. 

A  very  common,  nearly  ubiquitous 
breeder;  overall  breeding  population 
extremely  large. 

Recorded  in  202  (91.4%)  of  221 
blocks. 

O    Possible        =      67   (33%) 
©    Probable       =        5  (2%) 
•    Confirmed  =     130  (64%) 

FSAR=5       OPI  =  1010      CI  =  2.31 


Ecological  Requirements 

This  swallow's  name  harkens  back  to  days  of  former  glory 
when  most  Cliff  Swallow  colonies  looked  out  with  com- 
manding views  over  the  untrammeled  open  spaces  of  the 
American  West.  Today,  most  Cliff  Swallows  have  forsaken 
their  ancestral  haunts  for  the  company  of  others  of  their 
kind  that  have  taken  up  domestic  duties  in  more  "civilized" 
surroundings.  The  main  requisites  of  nesting  Cliff  Swal- 
lows are  vertical  walls  for  nest  attachment,  a  nearby  source 
of  mud  for  nest  building,  and  open  foraging  areas  (Emlen 
1954).  Vertical  walls  limit  access  of  predators,  and  an 
overhang  usually  shields  the  nest  from  being  dissolved  by 
rains.  Cliff  Swallows  are  highly  gregarious,  and  it  is  not 
uncommon  to  find  hundreds  or  even  thousands  of  nests 
at  one  site.  Natural  nest  sites  include  cliffs,  caves,  sand- 
banks, and,  very  rarely,  the  undersides  of  large  tree 
branches  (Gross  1942).  In  addition,  Cliffs  sometimes  take 
over  and  usually  modify  occupied  or  abandoned  nests  of 

276 


Bank  or  Barn  swallows,  Black  Phoebes,  and  American 
Robins  (Mayhew  1958).  Today  most  Cliff  Swallows  nest 
on  human  structures.  Perhaps  the  most  common  sites  are 
under  the  eaves  of  buildings,  especially  barns;  nests  are 
usually  on  the  outsides  of  barns  but  sometimes  are  inside, 
particularly  in  the  East.  In  California,  Cliff  Swallows  also 
nest  abundantly  under  bridges  and  freeway  overpasses,  in 
stream  or  irrigation  ditch  culverts,  and  on  dam  faces. 
Unlike  Barn  Swallows,  they  will  not  enter  buildings 
through  tiny  openings  but  must  have  a  large  entrance  of  at 
least  about  eight  feet  on  a  side  (Samuel  1971). 

There  is  no  well-defined  upper  limit  to  the  height  of 
nests,  as  Cliff  Swallows  sometimes  place  them  hundreds 
of  feet  above  die  ground  on  cliffs.  At  the  lower  end, 
though,  they  must  have  at  least  a  three-foot  clearance  over 
water  or  an  eight-foot  clearance  over  land  (Emlen  1954).  A 
typical  mud  nest  is  gourd  or  retort  shaped;  the  globular 


Swallc 


SPECIES  ACCOUNTS 


Swallows 


nest  chamber  extends  forward  into  a  short  tubular  en- 
trance tunnel  with  the  mouth  directed  downward  (Emlen 
1954).  Since  nests  are  often  crammed  together  or  built  on 
top  of  each  other,  the  shape  varies.  Birds  may  reuse  or 
repair  last  year's  nests,  but  these  are  usually  not  the  same 
individuals  that  used  the  nests  the  previous  year  (Mayhew 
1958).  Gathering  mud  is  a  highly  social  activity  that  a 
group  participates  in  together.  To  collect  mud  with  their 
beaks,  birds  land  at  a  favorable  site  and  hold  their  wings 
partly  or  fully  extended  above  their  backs  and  fluttering 
slighdy  (Emlen  1954).  They  usually  collect  mud  close  to 
the  colony,  but  birds  may  go  up  to  a  half  mile  or  a  mile  to 
bring  it  back  (Storer  1927,  Emlen  1954).  Nest  building 
proceeds  intermittendy  as  successive  layers  of  mud  are 
allowed  to  dry  before  adding  the  next  (Buss  1942,  Emlen 
1954).  The  lining  of  straw,  grass,  and  leaves  is  often 
deposited,  and  eggs  laid,  before  completion  of  the  nest 
(Buss  1942);  nest  construction  or  repair  may  continue 
throughout  the  season.  In  the  same  areas  as  nesting  Barn 
Swallows,  Cliffs  choose  mud  with  a  higher  sand  and  lower 
silt  content  (Kilgore  6k  Knudsen  1977),  presumably 
because  this  mixture,  though  not  as  strong  as  less  sandy 
ones,  is  more  easily  worked  in  construction  of  the  Cliff 
Swallow's  more  complex  nests. 

This  species  often  forages  relatively  low  over  meadows, 
fields,  and  open  water,  but  in  the  warmth  of  the  day,  birds 
will  soar  at  heights  of  500  to  1500  feet  over  various  habitats 
(Emlen  1952).  Cliffs  usually  forage  more  than  100  feet 
high,  consistendy  higher  than  Barn  Swallows  often  forag- 
ing over  the  same  area  (Samuel  1971).  Cliff  Swallows 
mosdy  forage  within  a  quarter  mile  of  their  colonies,  but 
birds  may  go  as  far  afield  as  four  miles,  especially  during 
the  warmer  parts  of  the  day  (Emlen  1952).  Their  social 
tendencies  extend  to  the  feeding  grounds,  where  most 
birds  at  any  moment  are  loosely  aggregated  in  a  single 
foraging  unit.  The  diet  (Mar-Sep)  is  99.4%  animal  food, 
primarily  insects,  along  with  a  few  spiders  (Beal  1918,  n  = 
375).  The  main  food  items  are  beedes,  true  bugs,  bees, 
wasps,  ants,  and  flies;  minor  items  are  moths,  caterpillars, 
grasshoppers,  dragonflies,  mayflies,  lace-winged  flies,  spi- 
ders, and  snails.  Vegetable  food  consists  of  a  few  berries. 

Marin  Breeding  Distribution 

The  Cliff  Swallow  was  one  of  the  most  common  and 
ubiquitous  breeding  birds  in  Marin  County  during  the 
adas  period.  Most  of  its  breeding  sites  were  in  the  open 


lowland  valleys  or  rolling  hills,  where  the  vast  majority  of 
colonies  were  on  human  structures;  scattered  colonies 
occurred  on  ocean  bluffs  and  a  few  small  inland  cliffs. 
Representative  nesting  locations  were  ocean  cliff  at  Drake's 
Beach  (NB  4/2/81  -DS);  Red  Barn,  Bear  Valley  Head- 
quarters, PRNS  (ON  7/18/80  -DS);  Kleiser  Ranch, 
Walker  Creek  (ON  5/23/82  -DS);  and  Stafford  Lake, 
Novato  (ON  5/?/82  -ScC). 

Historical  Trends/ Population  Threats 

With  the  spread  of  European  settlers  across  the  continent, 
Cliff  Swallows  were  able  to  expand  dramatically  as  suitable 
nesting  sites  increased  and  much  of  the  land  was  opened 
up  (Gross  1942).  California  was  no  exception  (GckM 
1944).  In  the  arid  West,  irrigation  and  watering  of  lawns 
and  gardens  has  also  increased  the  availability  of  mud 
during  the  dry  season,  which  coincides  with  most  of  the 
breeding  season  in  California.  In  recent  times,  such 
advances  have  been  offset  to  a  limited  degree  by  nest 
parasitism  and  ejection  of  the  swallows'  young  and  eggs  by 
House  Sparrows;  by  dense  urban  development,  eliminat- 
ing feeding  areas;  by  the  painting  of  barns,  which  reduces 
adhesion  of  the  nests;  and  by  destruction  of  nests  by 
people  concerned  with  the  "unsighdy  and  unsanitary" 
droppings  under  colonies.  Concern  over  the  cost  of  paint- 
ing and  maintenance  of  the  Red  Barn  at  the  Point  Reyes 
National  Seashore  Headquarters  at  Bear  Valley  prompted 
destruction  of  the  nests  there  in  1981  and  1982.  A  com- 
promise struck  between  the  Park  Service  and  local 
Audubon  groups  provided  for  fencing  off  some  nest  sites 
and  allowing  others  to  remain.  Elsewhere,  management  for 
Cliff  Swallows  has  been  very  effective  in  increasing  local 
populations  (Buss  1942,  Gross  1942).  Like  other  swallows, 
Cliff  Swallow  nesdings  and  adults  may  suffer  high  mortal- 
ity when  extended  periods  of  cold  or  rainy  weather  depress 
their  prey  base  of  aerial  insects  (Gross  1942,  Stewart  1972). 
Numbers  of  Cliff  Swallows  on  Breeding  Bird  Surveys  in 
California  increased  from  1968  to  1979  (Robbins  et  al. 
1986)  but  were  relatively  stable  when  analyses  were 
extended  from  1968  to  1989  (USFWS  unpubl.).  These 
increases  are  almost  certainly  linked  to  ongoing  develop- 
ment in  the  state  that  provides  additional  nest  sites  and 
also  perhaps  to  continued  expansion  of  the  agricultural 
industry  and  its  irrigation  systems,  which  provide  mud  for 
nest  building. 


277 


Swallc 


MARIN  COUNTY  BREEDING  BIRD  AT\AS 


Swallows 


BARN  SWALLOW    Hirundo  rustica 


A  summer  resident  from  early  Mar 
through  mid-Oct. 

A  common,  nearly  ubiquitous  breeder; 
overall  breeding  population  very  large. 

Recorded  in  203  (91.8%)  of  221 
blocks. 

O    Possible        =      52  (26%) 
€    Probable       =       11    (5%) 
•    Confirmed  =     140  (69%) 

FSAR  =  4       OPI  =  812        CI  =  2.43 

t 

\  *\<a  *X>\  °\^1\ 

^V-*3r^4A  °3P%P  Jr-<\ 
ir^\o  v^\  o\M  o  X^\ 

Ecological  Requirements 

The  graceful,  fork-tailed  profile  of  this  sleek  swallow  is  a 
familiar  image  of  Marin  County's  open  lowland  ranch- 
lands,  where  the  bird  nests  most  commonly  around  barn- 
yards. Barn  Swallows  occur  widely  throughout  unforested 
regions,  even  where  developed,  as  long  as  there  are  suitable 
nest  sites,  nest  material,  and  extensive  insect-productive 
airways  low  to  the  ground.  The  latter  occur  over  grasslands, 
marshlands,  ponds,  estuaries,  meadows,  weed  fields,  and 
beaches.  Under  natural  conditions,  Barn  Swallows  attach 
their  nests  to  the  ceilings  or  walls  of  shallow  caves;  to  the 
inner  walls  of  great  hollow  trees;  or  place  them  in  niches, 
crevices,  or  fissures  in  rocky  cliffs;  on  shelves  or  ledges  of 
projecting  rock  with  an  overhang  above;  and  in  holes  or 
natural  cavities  of  cutbanks  (Bent  1942,  Speich  et  al. 
1986).  The  most  commonly  reported  natural  nest  sites  are 
sea  caves  and  ocean  bluffs  and,  inland,  cliffs  and  banks  of 
rivers  and  lakes.  Water  does  not  appear  to  be  a  requisite; 
rather  wave  action  or  erosion  often  have  produced  suitable 
sites  for  nest  attachment.  In  caves,  Barn  Swallows  place 
nests  on  the  walls,  on  small  irregularities  or  niches,  or  on 
the  ceiling  on  vertical  faces,  at  cracks,  or  where  pieces  of 
rocks  have  fallen  (Speich  et  al.  1986).  Today  their  nests  in 
the  wilds  are  rare.  They  now  nest  mosdy  under  the  eaves 
of  (or  inside)  barns  and  other  buildings  or  under  culverts, 
bridges,  wharves,  and  boathouses.  The  tops  of  nests 
located  in  caves  and  culverts  are  usually  within  a  couple  of 
inches  of  the  overhang  of  the  ceiling  (Grzybowski  1 979, 
Speich  et  al.  1986).  Unlike  Cliff  Swallows,  Barns  need 
only  a  small  opening  to  enter  an  enclosed  nest  site,  such 
as  a  building  (Samuel  1971).  In  addition  to  their  greater 

278 


availability,  advantages  of  human  structures  as  nest  sites 
may  be  reduced  risks  of  predation,  substrates  superior  for 
long-term  attachment  of  nests,  more  favorable  thermal 
environments,  and  access  to  otherwise  unexploited  local- 
ized food  sources  (Speich  et  al.  1986).  Barn  Swallows  are 
only  loosely  (passively)  colonial  with  1  to  perhaps  30  or, 
exceptionally,  up  to  50  nests  at  a  single  site  (Bent  1942). 
Barn  Swallows  are  territorial  and,  unlike  Cliff  Swallows, 
maintain  a  minimum  distance  between  nests.  In  New 
York,  Snapp  (1976)  found  that  Barn  Swallow  nests  in 
buildings  were  rarely  less  than  about  10  feet  apart,  but  in 
Oklahoma,  Grzybowski  (1979)  found  that  60%  of  the 
active  nests  in  culvert  colonies  were  closer  together  than 
that.  These  differences  perhaps  reflect  the  availability  of 
suitable  nest  attachment  sites. 

A  nearby  source  of  mud  is  usually  a  requisite  for  nest 
building.  The  most  common  type  of  nest  is  an  adherent 
mud  nest  in  the  shape  of  a  half  cone  attached  to  a  vertical 
surface  under  an  overhang.  As  in  Cliff  Swallow  nest  sites, 
the  vertical  surface  limits  access  of  predators,  and  the 
overhang  protects  the  mud  nest  from  the  dissolving  effects 
of  rain.  Barn  Swallows'  mud  gathering,  unlike  Cliff 
Swallows',  is  an  individual  activity,  not  a  social  one.  Birds 
fly  to  the  ground  and  stand  around  with  their  wings  held 
at  their  sides  (unlike  Cliffs)  and  gather  mud  on  or  inside 
their  bills  (Samuel  1971).  "In  building  their  nests  the  barn 
swallows  show  themselves  expert  masons,  but  unlike  the 
cliff  swallows  and  like  the  ancient  Egyptians  they  cannot 
make  bricks  without  straw"  (Bent  1942).  Indeed,  Barn 
Swallows  incorporate  straw,  grass,  and  horse  hair  into  the 


Swalloifs 


SPECIES  ACCOUNTS 


Swall 


OUIS 


mud  walls,  apparently  to  aid  in  holding  the  mud  together; 
this  likely  explains  why  their  nests  are  more  durable  than 
those  of  Cliff  Swallows  (Kilgore  ck  Knudsen  1977).  See  the 
Cliff  Swallow  account  for  differences  in  types  of  mud  used. 
Barn  Swallows  typically  line  their  nests  with  feathers  and 
may  add  some  of  this  lining  even  after  eggs  are  laid  (Samuel 
1971).  Nests  placed  on  flat  supporting  structures  are  more 
circular  and  shallower  than  the  cone-shaped  nests  attached 
to  walls,  and  those  in  corners  or  crevices  are  built  to  fit  the 
constraints  of  the  space.  Nests  in  narrow  crannies  or  holes 
with  supporting  sides  and  floors  may  lack  a  mud  founda- 
tion and  may  be  made  entirely  of  grasses,  straw,  feathers, 
or  other  available  materials;  some  nests  in  sea  caves  are 
made  and  lined  with  seaweed  (Bent  1942).  Barn  Swallows 
also  nest  in  incomplete  or  abandoned  Cliff  Swallow  or 
Black  Phoebe  nests.  They  may  add  to  or  rebuild  nests  from 
previous  years  or  prior  nests  of  the  same  season  (Davis 
1937,  Bent  1942,  Samuel  1971),  with  a  high  frequency  of 
reuse  by  the  original  occupants  (Shields  1 984). 

While  foraging,  Barn  Swallows  fly  with  rapid  directed 
flight,  with  their  wing  tips  sweeping  back  almost  parallel  to 
the  body  as  they  course  low  to  the  ground  (cf.  Cliff  Swallow 
account).  In  addition  to  generally  foraging  at  lower  heights 
than  Cliffs,  Barns  also  tend  to  forage  nearer  their  nest  sites 
(within  three-quarters  of  a  mile  of  nest  sites)  (Samuel 
1971).  Barn  Swallows  may  prefer  to  feed  along  edge 
habitats,  such  as  woodland/field  borders  (Samuel  1971), 
where  wind  speeds  are  reduced  and  insects  are  more 
abundant  than  in  adjacent  fields  (Grzybowski  1979),  but 
they  do  forage  extensively  in  very  open  terrain  (D.  Shuford 
pers.  obs.).  Birds  also  occasionally  alight  on  the  ground  to 
catch  food  (Bent  1942).  More  often,  especially  on  cool, 
foggy  mornings  when  aerial  insects  are  not  about  in  num- 
bers, they  follow  grazing  animals  or  walking  people  as  they 
disturb  insects  from  damp  grass  (D.  Shuford  pers.  obs.). 
The  species'  North  American  diet  (Mar-Oct)  consists  of 


99.8%  animal  matter,  primarily  insects,  along  with  a  few 
spiders;  the  little  vegetable  food  eaten  is  mosdy  seeds  (Beal 
1918,  n  =  467).  Barn  Swallows'  main  food  items  are  flies, 
true  bugs,  beedes,  ants,  bees,  and  wasps;  moths,  butter- 
flies, caterpillars,  grasshoppers,  crickets,  dragonflies,  may- 
flies, spiders,  and  snails  are  of  minor  importance.  Adult 
birds  feed  their  young  mosdy  food  items  smaller  than  0.4 
inch  (Turner  1982).  They  tend  to  feed  on  larger  items  in 
that  size  range  if  available  and  feed  larger  items  to  their 
broods  than  they  take  themselves. 

Marin  Breeding  Distribution 

Like  the  Cliff  Swallow,  the  Barn  Swallow  was  one  of  Marin 
County's  most  ubiquitous  breeders  during  the  adas  period, 
and  the  two  species  had  almost  identical  distributions. 
Most  individuals  of  both  species  bred  in  the  county's  open 
lowland  valleys  or  rolling  hills  and  built  nests  in  or  on 
human  structures.  Small  numbers  of  Barn  Swallows  still 
nest  at  scattered  sites  in  ocean  bluff  sea  caves,  as  detailed 
below.  Representative  nesting  locations  were  six  nests  in 
sea  caves  along  ocean  bluffs  just  S  of  Estero  Americano 
(NE/NY  7/12/82  -DS);  Wildcat  Beach,  PRNS  (NE  in 
large  crack  on  inside  ceiling  of  sea  cave  4/3/81  — DS);  and 
Chileno  Valley  (NB  5/5/82  -DS). 

Historical  Trends/  Population  Threats 

Like  Cliff  Swallows  (see  account),  Barn  Swallows  have 
undoubtedly  increased  in  historical  times  in  California 
because  of  human  activities.  From  1968  to  1989,  Barn 
Swallow  numbers  decreased  on  Breeding  Bird  Surveys  in 
California  (USFWS  unpubl.  analyses).  Possible  explana- 
tions of  this  recent  trend  are  that  fewer  suitable  nest  sites 
exist  on  modern-day  structures  than  on  old  barns  and 
houses,  and  also  diat  fewer  low  foraging  areas  exist  in 
densely  developed  areas. 


279 


]ays  and  Crows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


]ays  and  Crows 


Jays  and  Crows 

Family  Corvidae 


STELLER'S  JAY    Cyanocitta  stelleri 


A  year-round  resident. 

P^vo^^       N               yav. 

A  fairly  common,  widespread  breeder; 

^<\3^v 

•'v     \  ^A\      \  A-\"^\^\AO A^\  *>A^\   \ 

overall  breeding  population  fairly  large. 

3r^\^3<r^o3^X  •V-A^\^CoVAr^'- 

Recorded  in  154  (69.7%)  of  221 

j[  \A 

"\  °A-<\  oJ'rx  •<V^\     v>"V o  v-"A    V-^a 

blocks. 

\a< 

O    Possible        =      81    (53%) 

o  >T\V  V^\    A^v>'A^\  o  V-^\  o  N^-a  oA-^r?*--^ 
rA,\Osi  U-A    A<r\    JiS^>-  V^v\  ■oA^A-*~*->A  o  V>"'^^> 

C    Probable       =      40  (26%) 

\ °>r<r^3?<\ ®JV^T®>;>aV£>  A^A® V^^A-^V O r-^ 

Jp^A  •%^A^A>A<?\'*,Jir>A  OVAO  A-^A  O  V>A  •  V^-/ 

£A   A^CA  •J-?eC\  •  A^A  ®  V^tQ  \>\o  iXo  \>^V  •» 

•    Confirmed   =       33   (21%) 

^V^A °A<\ mJ^C\9^>^\o A-^ao  \>A^o- v-AAVv 

^Y,Or<A  cA^^A^A^Jv-<A  •  K\0  Yv^V  •  V^-V— 

_.-J**" 

>%a\5a<\"£a^5a-;^^ 

■3\  \wcfT\  ?An\  B--An\  °A--MnDJ^\  ®A<A  *A-<\— . 

FSAR  =  3        OPI  =  462        CI  =  1.69 

<^YJrQ     \^#Ar^-PA-^v^V^Te  VA»V>\o^ 

1  "><^r$^ ^2A^^*3r^eA^^«2v^*\^\0  V< 

A   ? 

^5^  ^^53r^M^^ 

^o 

17              ^^^^^ra 

Ecological  Requirements 

These  crested  firebrands  inhabit  Marin  County's  conifer, 
mixed  conifer,  broadleaved  evergreen,  and  coastal  riparian 
forests  and  bordering  eucalyptus  groves.  All  these  habitats 
are  generally  moist  and  have  relatively  tall,  closed,  shaded 
canopies.  As  a  rule,  though,  where  forests  are  extensive, 
Steller's  Jays  are  more  numerous  near  breaks  in  the  forest 
than  deep  within  it  (Goodwin  1986).  Numerous  openings, 
edges,  and  developed  areas  for  foraging,  and  denser  stands 
for  nesting  and  shelter,  presumably  provide  the  optimal 
mix  for  breeding  birds.  Stellers  overlap  somewhat  with 
Scrub  Jays  on  the  brushy  edges  of  these  habitats,  especially 
along  hardwood  and  riparian  forests.  The  Scrub  Jay  is 
usually  the  dominant  species  when  the  two  come  into 
contact— except  immediately  around  Steller's  Jay  nests 
(Brown  1963,  1964).  Steller's  Jays  do  not  defend  territories 
in  the  classic  sense  (Brown  1963,  1964).  Instead  they 
defend  exclusive  areas  around  their  nests  beyond  which 
dominance  over  other  Steller's  Jays  can  be  viewed  as 
decreasing  in  a  series  of  concentric  circles  as  distance  from 
the  nest  area  increases.  Steller's  Jays  build  their  nests  in 
both  conifers  and  broadleaved  trees  from  2  to  100  feet  or 
more  (most  8-25  ft.)  above  the  ground.  They  usually  place 
them   on   horizontal   branches  close  to   the  trunk,   less 

280 


commonly  well  out  on  limbs,  in  holes  or  troughlike  cavities 
in  trees  or  stubs,  or  on  shelves  inside  sheds  (Bent  1946). 
The  nest  itself  has  a  bulky  foundation  of  large  sticks 
reinforced  with  mud  and  dead  leaves  and  a  deeply  hol- 
lowed interior  of  coarse  roodets,  grasses,  and  pine  needles. 
Like  most  jays,  Stellers  are  generalist  foragers.  They 
forage  singly  or  in  pairs,  but  many  feed  together  at  centrally 
located  sources  of  food,  such  as  at  picnic  areas  and  camp- 
grounds. In  Tilden  Regional  Park,  Alameda  and  Contra 
Costa  counties,  about  two-thirds  of  foraging  occurs  on  the 
ground  and  the  rest  in  trees;  ground  foraging  occurs  both 
beneath  the  canopy  and  in  openings  such  as  forest  clear- 
ings or  borders  (Brown  1 964).  Steller's  Jays  obtain  most  of 
their  food  on  the  ground  by  hopping  about,  picking  from 
the  surface,  and,  secondarily,  by  inserting  their  bills  in 
loose  materials  like  leaf  litter  or  soil,  tossing  them  aside 
with  sideways  flips  of  the  bill.  In  trees,  they  hop  or  fly  short 
distances  to  procure  acorns  and  fruits,  forage  on  trunks, 
peel  loose  bark  from  branches,  inspect  old  squirrel  nests, 
and  glean  caterpillars  and  other  insects  from  the  foliage  or 
branchwork.  They  break  open  hard  objects  such  as  acorns, 
bay  laurel  nuts,  and  sunflower  seeds.  Holding  such  an  item 
in  one  or  both  feet,  the  bird  raises  its  whole  body  and 


]ays  and  Crows 


SPECIES  ACCOUNTS 


]ays  and  Crows 


brings  it  down  strongly,  with  its  bill  slightly  open  and  the 
lower  mandible  making  the  initial  puncturing  blow. 
Acorns  and  seeds  are  stored  throughout  the  year,  primarily 
in  the  ground  and  in  each  jay  s  own  dominance  area 
(Brown  1963,  1964).  A  bird  digs  a  hole  with  sideways  flips 
of  the  bill,  inserts  the  object,  and  covers  it  over  with  litter. 
By  storing  acorns,  Steller's  Jays,  like  Scrubs,  are  active 
agents  of  oak  dispersal,  particularly  in  the  uphill  direction 
(Grinnell  1936).  Steller's  Jays  are  known  to  steal  the  food 
caches  of  Clark's  Nutcrackers  and  Gray  Jays  and  are 
suspected  of  robbing  the  stores  of  Acorn  Woodpeckers 
(Burnell  &l  Tomback  1985).  The  incubating  female  is  fed 
on  and  off  the  nest  by  the  male  (Goodwin  1986).  The 
California  diet  is  about  72%  vegetable  and  28%  animal 
overall,  though  the  latter  fare  increases  considerably  in  the 
breeding  season  (Beal  1910,  n  =  93).  Acorns  provide  the 
bulk  of  the  vegetable  food,  though  other  fruits,  nuts, 
grains,  seeds,  and  galls  are  also  eaten.  Insects,  especially 
bees,  wasps,  beedes,  grasshoppers,  crickets,  caterpillars, 
and  moths,  predominate  in  the  animal  portion  of  the  diet. 
Steller's  Jays  also  eat  other  birds'  eggs,  nesding  birds,  small 
mammals,  frogs,  and  spiders  (Beal  1910).  In  setded  areas, 
they  also  consume  a  wide  variety  of  human  foods,  which 
may  be  very  important  in  the  diet  locally,  particularly  at 
picnic  sites  and  at  bird  feeding  trays. 


rolling  hills  dominated  by  grassland,  near  Tomales  and  on 
the  outer  Point  Reyes  peninsula,  and  in  the  low-lying  diked 
former  marshlands  around  Novate  Most  numerous  on 
the  conifer-dominated  coastal  ridges,  Steller's  Jays  were 
much  more  localized  in  the  county's  interior  and  along  its 
northern  edge,  where  the  birds  occurred  mosdy  in  deep 
shaded  canyons  and  on  north-facing  slopes.  Representative 
nesting  locations  were  Inverness  (NB  4/18/82  — DS); 
Laguna  Ranch,  PRNS  (FY  8/21/79  -JGE);  and  north  slope 
of  Mt.  Burdell,  Novate  (FL  6/2/78  -RMS). 

Historical  Trends/ Population  Threats 

Steller's  Jays  have  held  their  own  in  California  despite 
organized  persecution  by  hunters  in  earlier  times  (Erickson 
1937,  Hooper  1938,  G&lM  1944).  Any  minor  population 
decreases  in  Marin  County  and  elsewhere  in  California 
that  may  have  occurred  from  extensive  logging  or  clearing 
for  development  have  probably  been  offset  by  the  effects  of 
increased  openings  and  edges  for  foraging  and  supplemen- 
tal food  sources  from  humans.  While  increasing  elsewhere 
in  the  West  from  1965  to  1979  (Robbins  et  al.  1986), 
Steller's  Jay  numbers  remained  relatively  stable  on  Breed- 
ing Bird  Surveys  in  California  from  1968  to  1989  (USFWS 
unpubl.  analyses). 


Marin  Breeding  Distribution 

During  the  adas  period,  Steller's  Jays  bred  throughout 
Marin  County  wherever  extensive  shaded  forests  occurred. 
Hence  they  were  absent  from  broad  areas  only  in  the  low 


281 


)ays  and  Crows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


jays  and  Crows 


SCRUB  JAY   Aphelocoma  coerulescens 


1 

A  year-round  resident. 

A^P^^kS^^      ^            .X^w 

A  common,  nearly  ubiquitous  breeder; 

so  V-A*  s>-A  P.V^'A*"^-^                ^^CijM    >n 

overall  breeding  population  very  large. 

V^V  •  -V-A*  A-A  °  A-A  •  V-"\  o  V'A  •  V'A  •  A^v  \ 

Recorded  in  214  (96.8%)  of  221 

^"T  •  V<i\  o  V^"\  o  Y>A  o  wAo- V--A  ©  \AA  •  ,Y^A  *A 
WAA 1*  ><\  °V\  •  Wve  v*A-Q  ViCA^Jr^A  ®  V'^  \ 

blocks. 

V^OA^A  °  V^\  •  \^*\  •3k^\  P  X^&V^X  •3r*<\  P-4 

\  V<i\V\  o  V-^fo  Y>A  o  V--A;  •>-?A  •  >^\  °jc<r\ 

V->\«VW>\0  w-"\  o  \>A •  v^vo  v^A  •  v>A  o  Y>A  •  J 

r-^^v^.V'A  •  Y^A  •  wcCo  Y>A  o  Y>\  •  Y-'A  •  J 

O    Possible        =       81    (38%) 

VV»  A<\N?  \^\e  A-APA^A°  3r-Ao  \-^A  •>r;l\o~^>^ 

VAX  •  YV^OaiKA  •  V-^VcY^A-O  V-^A  •  A^A  *V-"\   *J 

€    Probable               35   (16%) 

\   Pl^A  »-^><A»'Yx<iC©  \2Ao  \^\o  \>A  •  Y^A  •  V-7 
Vpv/a  o  \^\  *  V^A  ©A^-A  o  V-<?A  O  V>\,J»  Y-"A  *»A 

•    Confirmed   =       98   (46%) 

\PAp  Y^A*>  Y^A*Y->vG)A'A  •  V<\*  jkA  .•  V**"^? — ' 

"    * 

loAtAo  V>A<  ^«>4o\Z\0K\*V^-V 

L-r-A  %V-A©  >>V •A-A  •  A^drOjv-^v  *  A<\  »A<v~ , 

FSAR  =  4        OPI  =  856        CI  =  2.08 

^-AV-1VA«!Y— A°\AA©  VA«  \>Ao/l>A*  Y-"A  •  V< 

*•  /  n. 

P^A^J^ ^~<C° \^\*  wA©A^*A ® ><A *Jv%^ 
-AxkV^^            ^^<«  \>A©  V^oj^^Vivv, 

\£& 

•  Y-^                       N^iC •  Wrti^*v^\viji>\i 

-t-r                                X>  \  Ay\Xj  a>A©  Y^a  •  ? 

J>u                 xj?  ^^^«\^ 

Ecological  Requirements 

The  inimitable  Scrub  Jay  is  the  more  open  habitat-loving 
of  our  two  jays  in  Marin  County  and  is  dominant  where  it 
overlaps  with  the  Steller's  Jay  (Brown  1963,  1964).  Scrub 
Jays  inhabit  Marin's  open  oak  woodlands;  drier,  more 
open  phases  of  her  broadleaved  evergreen  hardwood  for- 
ests; brushy  edges  of  conifer  forests;  riparian  thickets; 
chaparral;  coastal  scrub;  eucalyptus  patches  with  a  scrubby 
understory;  and,  in  the  county's  more  urban  areas,  planted 
trees  and  shrubbery.  The  birds  seem  "especially  abundant 
locally  where  woodland  areas  adjoin  chaparral-covered 
[and  coastal  scrub-covered]  slopes  and  ridges"  (Pitelka 
1951c);  Verbeek  (1970)  noted  that  they  hold  territories  in 
edge  situations.  Suitable  habitats  seem  to  have  in  common 
a  mix  (close  at  hand)  of  broken  woodland  and  brush  for 
nesting  and  cover  and  open  ground  areas  for  foraging. 

Scrub  Jays  place  their  nests  in  a  variety  of  trees,  shrubs, 
and  vines,  but  they  choose  oaks  frequendy,  presumably 
because  of  their  abundance  in  lowland  California  (where 
the  species  has  been  most  thoroughly  studied).  J.  W. 
Mailliard  (1912)  found  69  of  83  Marin  County  nests  in 
oaks;  Atwood  (1980)  reported  that  121  of  172  nests  in 
coast  live  oak  woodland  on  Santa  Cruz  Island  were  in 
oaks;  and  Ritter  (1983)  reported  that  84%  of  the  nests  in 
valley  oak  woodland  of  die  Central  Valley  were  eidier  in 
California  wild  grape  vine  tangles,  blue  elderberry,  interior 
live  oak,  or  coffeeberry  (all  19  nests  in  suburban  habitats 
were  placed  in  evergreen  shrubs  and  trees).  Nest  heights 
range  from  2  to  59  feet  above  die  ground  but  vary,  of 
course,  with  the  structure  of  available  habitat.  Verbeek 

282 


(1973)  reported  an  average  nest  height  of  five  feet  (range 
2-8  ft.,  n  =  25)  in  Monterey  County;  Ritter  (1983) 
reported  an  average  height  of  1 1  feet  (range  3-50  ft.,  n  = 
119)  in  the  Central  Valley;  and  Atwood  (1980)  reported 
an  average  height  of  14  feet  (range  3-59  ft.,  n  =  171)  on 
Santa  Cruz  Island.  However,  Atwood  (1980)  indicated 
average  nest  height  on  Santa  Cruz  Island  varied  from  4  feet 
(n  =  5)  in  Baccharis  thickets,  to  10  feet  (n  =  45)  in  south- 
slope  chaparral,  and  1 7  feet  (n  =  36)  in  north-facing  chap- 
arral associated  with  live  oak  woodland.  Atwood  (1980) 
found  nests  on  Santa  Cruz  Island  were  generally  in  dense 
brush  and  trees,  where  numerous  twigs  and  small 
branches  provided  suitable  support  and  concealment; 
most  nests  were  placed  in  terminal  branches.  In  plants 
lacking  an  abundance  of  small  stiff  divergent  twigs,  nests 
were  usually  supported  by  major  branches  or  by  the  trunk. 
All  nests  were  remarkably  well  concealed  and  normally 
visible  only  from  below.  Ritter  (1983)  found  greater  varia- 
tion among  nest  sites  in  the  Central  Valley:  there  nests 
were  situated  in  terminal  branches,  forks  of  branches, 
forks  of  tree  trunks,  on  lateral  branches,  and  in  vines. 
Ritter  (1983)  found  that  Central  Valley  Scrub  Jays  built 
false  nests  prior  to  building  complete,  functional  nests; 
Atwood  (1980)  found  that  Santa  Cruz  Island  Scrub  Jays 
did  not.  A  typical  functional  nest  is  an  open  bulky  struc- 
ture composed  of  coarse  sticks,  occasionally  mixed  widr 


Information  for  this  account  is  drawn  only  from  studies  of 
western  races,  since  the  behavior  of  the  Florida  Scrub  Jay  is  quite 
different  (Woolfenden  6k  Fitzpatrick  1984). 


)ays  and  Crows 


SPECIES  ACCOUNTS 


]ays  and  Crows 


moss  and  dry  grass,  and  lined  with  finer  twigs,  roodets, 
and  sometimes  grass  or  horsehair  (Bent  1946,  Atwood 
1980).  Exceptionally,  Scrub  Jays  in  California  will  breed  in 
fall  (Stanback  1991). 

Scrub  Jays  forage  in  much  the  same  ways  as  Steller's  Jays 
do  (see  account),  but  they  spend  more  time  lower  in  trees 
and  the  scrub  canopy,  and  more  time  in  open  areas.  Scrubs 
use  "anvil"  sites  to  break  open  nuts.  They  store  acorns  in 
the  ground  with  a  thrust  into  loose  soil  or  by  hammering 
them  in  with  their  beaks  and  then  covering  them  with  dirt 
clods,  rocks,  or  leaves  (Michener  6k  Michener  1945);  they 
also  wedge  them  into  cracks  or  crevices  in  trees,  stumps, 
and  logs  (Beal  1910).  In  their  habit  of  ground  storage  of 
acorns,  Scrub  Jays  are  active  agents  of  oak  dispersal, 
particularly  in  the  uphill  direction  (Grinnell  1936).  Scrub 
Jays  also  remove  the  hairs  from  caterpillars  by  rubbing 
them  in  sand  (Verbeek  1970).  Where  Scrub  Jays  overlap 
with  Yellow-billed  Magpies  in  Monterey  County,  Verbeek 
(1970)  found  that  Scrub  Jays  were  more  generalists  than 
were  the  Magpies.  Scrub  Jays  there  have  a  wider  variety  of 
feeding  styles,  a  wider  habitat  range,  and  feed  on  a  greater 
diversity  of  prey,  including  more  vertebrates  and  plant 
material.  Magpies  tend  to  concentrate  on  pockets  of  abun- 
dant prey  of  a  few  species,  whereas  Scrub  Jays  search 
randomly  for  food.  Overall,  the  Scrub  Jay  diet  is  about 
27%  animal  and  73%  vegetable  matter;  there  is  consider- 
able seasonal  variation,  with  animal  food  comprising  up  to 
70%  of  the  diet  in  April  and  as  little  as  5%  in  January  (Beal 
1910,  n  =  326).  The  animal  matter  includes  insects  (espe- 
cially beedes,  bees,  wasps,  ants,  grasshoppers  and  crickets, 
and  moths  and  caterpillars),  spiders,  eggs  and  nesdings  of 
wild  birds,  eggs  and  chicks  of  domestic  fowl,  mice  and 
shrews,  lizards,  snakes,  and  frogs.  The  vegetable  food  is 
primarily  acorns  and,  to  a  lesser  extent,  wild  and  cultivated 
fruits,  berries,  and  grain.  Although  Scrub  Jays  in  Monterey 
County  feed  their  young  a  wide  variety  of  food,  including 


most  of  the  items  listed  above,  invertebrates  are  of  over- 
whelming importance  to  the  nesding  diet  there  (Verbeek 
1970);  the  young  are  also  fed  some  seeds  and  fruits, 
including  acorns.  Although  there  is  great  similarity 
between  the  families  of  invertebrates  diat  Scrub  Jays  and 
Yellow-billed  Magpies  feed  their  nesdings,  there  is  little 
overlap  in  the  families  most  important  to  each  species. 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Scrub  Jay  was  one  of  the  most 
widespread  breeders  in  Marin  County.  Its  presence  in  the 
open  grassland-dominated  hills  in  the  northwest  sector  of 
the  county  attested  to  its  ability  to  subsist  in  small  patches 
of  scrub  and  trees  in  ravines.  Scrub  Jays  were  absent  only 
from  die  extreme  outer  tip  of  Point  Reyes,  where  these 
bare-minimum  requisites  were  lacking.  Representative 
nesting  localities  were  Bear  Valley  Headquarters,  PRNS 
(NB  5/11/81  -JGE);  Tennessee  Valley  (FL/FY  5/21/82 
-HPr);  near  Sleepy  Hollow  (NY  5/6/76  -RMS);  E 
approach  to  Loma  Alta  (NB  5/2/82  — BiL);  Terra  Linda 
(FY  5/30/82  -BiL);  and  Kentfield  (NB  4/3/82  -BiL). 

Historical  Trends/ Population  Threats 

Scrub  Jays  have  probably  increased  since  die  settlement  of 
California  as  they  colonized  tree  plantings  in  open  valleys 
(G&M  1944),  despite  organized  persecution  by  hunters  in 
earlier  times  (Erickson  1937,  Hooper  1938).  At  least  as 
recendy  as  1968  to  1979,  Scrub  Jay  populations  increased 
significantly  in  parts  of  California  diat  include  the  coastal 
region  from  die  Monterey  area  northward  (Robbins  et  al. 
1986).  Additional  data  suggest  that  numbers  increased 
slighdy  on  Breeding  Bird  Surveys  in  California  as  a  whole 
from  1968  to  1989,  but  were  stable  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


283 


Jays  and  Crouds 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Jays  and  Crows 


AMERICAN  CROW    Corvus  brachyrhynchos 


A  year-round  resident. 

xT^pJvtAo^sp^              \                      vr~v 

A  fairly  common,  very  widespread 

breeder;  overall  breeding  population 

\><V',  3£^o  Y-^o  Y^bY'    \  o  V^Toj^oVW' 

fairly  large. 

><*"a  o  \^\  o  v--^a  o  V--^\  oi  \^\  o  \^\  o  V-^a  o  x^r    \ 

Recorded  in  169  (76.5%)  of  221 

blocks. 

WA^X  \>^\     3A\  °  A^X  •  iAa  »  YAA  o  V-^x  O-v^x 

s^\  3-r\P3r<r\*J\<r\®  3Avo  v-A  •  JA"\»  jAA  •  J 

V<«Av><?*  Q  Jr^X  O  Y>"A  o  .V-^X       \->"A       V>\       V^l 

\  x^^xbo, m'  X  o  w^x  c  \&^TiO  V/vo  X^^'a^Y^a  •  X^^  i 

O    Possible        =     118   (70%) 

\A£\ "   3A\  o~?^\p\>r\  0\>TOlM.-P>y\  o  \5>T<  •* 

C    Probable       =       23   (14%) 

YAw  V-'x  °  >-^\'<>-j?^vo  jAa'  o  Y>a  o  Y^-a  o  Y-^J5V— 

-■•s- 

•    Confirmed   =       28   (17%) 

i    /jJrx  °  3Ax"°  '><rvP  jA^Vj  A^Tx  o  V-A  o  Y>^-\--HA 

\>^%V>ao.Y>^\«>3AAo  V^dro  \^  oV^c lAv_ 

w\  tcJtv  i  YJ>a     v/\  o.\>a  i¥L>a  o  wtT^  Y^x  «.\ — s 

!^*<\fO  VJfX       X^"\       ^0\>TM^8C\/\0\X\I^ 

>  "A>AiiA — LVA°jA\oiA\  S^\-oV>\#jJ< 

IX^J^^^    ^~^^^  A-Ao  VAo  .i^\o  -Y-<r\  ®A*£^ 

<§A^         ^VA^^5^a%oa2^ 

^& 

FSAR  =  3        OPI  =  507        CI  =  1.47 

-17                      ^AVAt»5a^^aao\Aa  ^ 

Ecological  Requirements 

These  jet-black,  gregarious  corvids  reside  in  Marin 
County's  lowland  valley  grazing  and  agricultural  lands, 
though  they  also  frequent  open  disturbed  areas,  grassy 
playfields,  and,  to  a  limited  extent,  estuarine  margins. 
Crows  generally  forage  in  open  areas  but  retreat  to  forest 
and  woodland  edges,  woodlots,  planted  windbreaks,  or 
residential  trees  for  nesting  and  roosting;  orchards  are 
common  nesting  grounds  elsewhere  in  California.  Ameri- 
can Crows  nest  in  pairs  or  loose  colonies  in  a  wide  variety 
of  trees,  shrubs,  and  bushes  (Emlen  1942,  G&M  1944, 
Goodwin  1986).  Although  nests  are  usually  well  spaced 
(e.g.,  Emlen  1942),  three  occupied  nests  have  been  found 
in  one  small  tree  (Goodwin  1986).  In  the  Central  Valley, 
Emlen  (1942)  noted  that  early  nests,  built  before  leaves  in 
trees  were  fully  opened,  were  somewhat  more  centrally 
located  in  an  orchard  than  later  nests.  Nest  heights  range 
from  the  ground  (rarely)  to  100  feet  high  (Bent  1946). 
Although  most  nests  are  generally  about  20  to  60  feet 
above  ground,  in  some  areas  most  are  under  20  feet.  In  a 
Central  Valley  orchard  widi  trees  about  20  to  30  feet  in 
height,  Emlen  (1942)  found  that  80%  of  1 1 1  occupied 
nests  were  from  16  to  24  feet  above  ground  (range  6.5-29 
ft.)  and  that  they  were  placed  about  three-fourths  of  the  way 
up  the  nest  tree.  Unusual  nest  sites  are  on  the  ground  near 
a  lake  or  marsh  edge,  in  the  hollow  of  an  old  stub,  on  top 
of  a  chimney,  and  on  the  crossarms  of  a  telephone  pole 
(Bent  1946).  Crows  build  deep,  wide  nest  cups,  which  they 
frequendy  place  in  the  fork  or  crotch  of  a  tree.  Emlen 
(1942)  noted  that  about  one-third  of  orchard  nests  were  in 
basal  crotches  or  on  branches  greater  than  two  inches  in 

284 


diameter;  most  nests  constructed  after  leaves  had  opened 
were  peripheral  in  the  tree,  often  in  small  terminal 
branches.  The  basal  nest  platform  and  frame  are  built  of 
stout  sticks  that  may  be  mixed,  in  varying  degrees,  with  fine 
twigs,  grasses,  rope  strands,  rags,  cornhusks,  roots,  moss, 
weed  stems,  and  bark  strips  (Emlen  1942,  Bent  1946). 
Later  in  the  season,  the  nest  foundation  may  be  composed 
entirely  of  fine  twigs  and  grasses  (Emlen  1942).  In  most 
early  nests  in  the  Central  Valley,  mud  is  used  to  form  a 
hard,  firm  floor;  later  nests  generally  contain  little  or  no 
mud,  perhaps  because  it  is  unavailable  locally  at  that  time 
(Emlen  1942).  Crows  usually  line  their  nests  with  fine  bark 
fibers,  hair,  wool,  fur,  or  moss  (Emlen  1942,  Bent  1946). 
Rarely,  they  build  false  nests  before  completing  functional 
nests  (Goodwin  1986).  In  very  rare  instances,  they  will  lay 
eggs  in  a  nest  before  its  completion  and  then  continue 
construction  for  a  few  days  (Emlen  1942).  Old  nests  or 
nest  platforms  of  previous  seasons  occasionally  form  the 
foundations  for  "new"  nests,  and  sometimes  birds  use  the 
same  nest  for  renesting  after  destruction  of  the  first  eggs 
(Emlen  1942).  Crows  form  large  community  roosts  at 
night  within  nesting  colonies,  and  occupied  nests  may  be 
situated  within  die  confines  of  the  roosting  area;  by  late 
May,  the  roosting  flock  may  more  than  double,  with  the 
addition  of  neighboring  birds  from  outside  the  nesting 
colony  (Emlen  1942). 

Crows  are  generalist  foragers  that  feed  singly  or  in  flocks 
of  varying  size,  even  in  the  breeding  season.  They  forage 
mosdy  on  the  ground  by  picking  from  the  surface,  by 
probing  in  soft  soil,  or  by  turning  over  sticks,  clods  of 


]ays  and  Crows 


SPECIES  ACCOUNTS 


jays  and  Crows 


earth,  or  dung.  They  also  alight  in  trees  or  bushes  to 
procure  both  vegetable  and  animal  matter.  In  some  areas, 
American  Crows  forage  on  the  shore  and  drop  shellfish  to 
break  them  (Goodwin  1986),  but  on  the  whole  they  are 
much  less  shore  feeders  than  are  Fish  or  Northwestern 
crows.  Tame  birds  regularly  hide  food,  but  it  is  uncertain 
to  what  extent  this  occurs  in  the  wild. 

The  Crow  is  omnivorous.  Animal  food  comprises  about 
28%  of  its  diet  overall  (up  to  52%  in  May);  vegetable  food 
averages  72%  but  rises  to  89%  in  the  colder  months  when 
animal  prey  is  less  available  (Kalmbach  1918,  n  =  1340). 
Undigestible  items  are  regurgitated  as  pellets.  The  most 
important  animal  foods  are  insects  (mainly  beedes,  grass- 
hoppers, caterpillars,  and  true  bugs),  spiders,  crustaceans, 
mollusks,  fish,  reptiles,  amphibians,  wild  birds  and  their 
eggs.  poultry  and  their  eggs,  small  mammals,  and  carrion. 
The  vegetable  food  consists  primarily  of  corn,  other  grains, 
wild  fruits,  nuts,  seeds,  and  cultivated  fruits  and  nuts.  In 
some  instances,  Crows  can  do  serious  economic  harm  to 
crops,  but  this  is  offset  to  some  degree  by  their  depreda- 
tions  on  insect  pests.  They  readily  take  scraps  of  human 
foods,  and  in  some  areas  Crows  habitually  scavenge  at 
refuse  dumps  and  around  slaughterhouses  (Goodwin 
1986).  Crows  are  very  wary  and  will  desert  a  major  food 
source  when  only  a  few  of  their  kind  have  been  killed  with 
poisoned  samples  of  the  food  in  question. 


Marin  Breeding  Distribution 

American  Crows  bred  widely  in  the  lowlands  of  Marin 
County  during  the  adas  period,  but  they  just  barely  pene- 
trated the  fringes  of  the  Point  Reyes  peninsula  and  Marin 
Headlands;  over  most  of  this  area  they  were  replaced  by 
Common  Ravens.  A  lack  of  breeding  confirmations  in  the 
grassland-dominated  ranchlands  northeast  of  Tomales  Bay 
suggested  that  summer  fogs  may  have  also  reduced  the 
appeal  of  this  coastal  region  to  Crows.  Representative 
breeding  locations  were  Home  Bay,  PRNS  (FL  6/17/81 
-DS);  Bolinas  (NB  3/21/81  -DS);  San  Marin  High 
School,  Novato  (NE-FL  May-Jun  1982  -ScC);  north  of 
Ml  Burdell,  Novato  (FL  6/2/78  -RMS);  and  Tiburon 
Fisheries  Lab  (NE  5/17/82  -BiL). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  thought  Crow  numbers  had 
remained  fairly  constant  in  California,  as  losses  from 
"crow  shoots"  and  bombings  of  winter  roosts  were  bal- 
anced by  gains  from  augmentation  of  their  habitat  in 
agricultural  areas.  The  vast  expansion  of  agriculture  in 
California  to  the  present  day  has  likely  added  tremen- 
dously to  the  natural  food  supply  of  Crows,  and  we 
probably  now  see  a  far  larger  population  compared  with 
prehistorical  times.  Crow  numbers  were  increasing  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


285 


]ays  and  Crows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


]ays  and  Crows 


COMMON  RAVEN    Corvus  corax 


-'      Sl<-<~ 

A  year-round  resident. 

An  uncommon,  very  widespread 

Jo 

breeder;  overall  breeding  population  of 

moderate  size. 

>'"a  o  A^\°J^\  °jk^\oi\^-Vo  \^\     V-"A     V>^\ 

-""18 WA °A<\ 0Jr\ ° Vvq A^A o Ar-"\    IV-'v    J\ 
i<c-oAC*AiX\  o  V>^\  ©  \^\o\3i-\-o  \^\    \^K   \^ — \ 

Recorded  in  170  (76.9%)  of  221 

\  i?^  X>^\  •  Jk-"\  °Jv^\  o  U-^r  o a£>A  o  \>\    \^\ 

blocks. 

^\*S><\.0  >^\03r^\O  \/\'0\>X  •  l/To  V-^A       J 

V^qO^^  PJ^C\  °3r\  0V^®Jv-^A°A^\     ax"a 

Va  •  ^iV-P  V<A  °  J^te^A^^C     A^\  O  \>^\Cl\^\^~^. 
\    \J«<r\  •Ok  LlA  *  V- — A  O  UcQvVQ  V--"A-OApx^-©- Vi>r\  C  V^^      ) 

O    Possible        =     130  (76%) 

€    Probable       =      22   (13%) 

\K\-,° 3«-^\ o  ><\-,o. x^vQ \^X*>  '  v-"\ o  \>>\    \^<\t 

1  •/Afr'IX      >>A'"0  V-^-P  Jr-"wA>0  \x"A  •  V"-"a  O  ix^-V-P^-' 

-•s- 

•    Confirmed  =       18   (11%) 

l>Ak%Vx\  oA>Yo  A>xC  o  \Zrff*  V>Af  VisA     \A<< 

AVlV<^>;\<lr  \  '^-^xa^LxA  »><j\oy\  *u"\- 

X-^V°WhA°V^\     3r^^ Ax^T?^^-^^^^  O  V>\     <■; 

^\£>"^                 ^\OAx^\oV^r\     A--^oA_>^v^> 

v?£> 

FSAR  =  2        OPI  =  340       CI  =  1.34 

-ir/                 ^fi-ic^^S^c^A> 

4                          ^-<«  \>>S''^co  v>-Tr  o  \^f 

i>^=                                        "U/          ^"^^X0^ 

Ecological  Requirements 

The  largest  of  passerine  birds,  these  masters  of  the  air  soar 
or  dive  in  convoluted  aerial  acrobatics  over  almost  any 
terrain  and  further  command  attention  by  their  hoarse, 
resonant,  croaking  calls.  In  Marin  County,  Ravens  reside 
primarily  in  open  or  semiopen  country  of  low  rolling 
grasslands,  beaches,  and  estuarine  margins.  These  habitats 
are  especially  attractive  if  they  adjoin  bluffs  or  ridges,  since 
Ravens  show  a  propensity  for  soaring  on  updrafts,  like 
raptors  (and  unlike  crows).  They  forage  in  open  country  at 
any  elevation;  they  nest  solitarily  on  seaside  or  inland  cliffs, 
in  trees  on  woodland  or  forest  edges,  or  in  planted  wind- 
breaks or  woodlots.  Planted  cypresses  and  pines  provide 
important  nest  sites  in  Marin's  coastal  grasslands.  Cliff 
nests  can  range  up  to  200  feet  above  the  ground  and  are 
placed  on  ledges  or  inside  cavities  or  crevices;  they  are 
usually  protected  from  above  by  an  overhang  and  below  by 
a  steep  vertical  face  (Bent  1946,  Hooper  1977).  Tree  nests 
can  vary  from  a  few  feet  up  to  100  feet  or  more.  They  are 
usually  in  the  tallest  trees  in  the  vicinity,  are  placed  in  a 
crotch,  and  are  well  concealed  in  the  foliage  (Bent  1946). 
Human  structures  such  as  oil  derricks,  windmills,  the 
insides  of  abandoned  houses  and  barns,  high-tension 
poles,  and  railroad  bridges  will  also  suffice  as  nesting 
platforms.  Of  87  nests  in  the  Great  Basin  of  eastern 
Oregon,  64  were  on  rimrocks,  20  in  human  structures, 
and  3  were  in  trees  (Stiehl  1985).  Nests  there  on  rimrock 
ledges  usually  filled  the  space  available,  whereas  those  in 
buildings  and  trees  were  generally  larger  than  ledge  nests. 
Ravens  use  the  same  nests  in  successive  years,  but  most 
pairs  have  two  or  more  sites  that  they  use  alternately  in 


different  years  (Goodwin  1986).  Ravens  will  also  use  old 
nests  of  raptors,  such  as  Golden  Eagles  and  Great  Horned 
Owls  (initially  built  by  other  raptors),  and  vice  versa  (Stiehl 
1985). 

Ravens  build  large,  bulky  nests.  They  construct  the 
outer  parts  of  branches,  coarse  sticks,  twigs,  mammal 
bones,  or  wire  and  reinforce  them  with  lumps  of  earth  and 
clumps  of  grass  or  moss;  they  use  thinner  sticks  for  the  nest 
rim  (Bent  1946,  Stiehl  1985,  Goodwin  1986).  The  central 
part  of  the  nest  is  of  thin  sticks,  twigs,  clumps  of  earth, 
wool,  hair,  and  similar  material;  the  deep  inner  cup  is  lined 
with  finer  strands  of  wool,  hair,  fur,  shredded  bark,  grass, 
and  fine  stems  (Stiehl  1985,  Goodwin  1986).  Females  sink 
the  eggs  deliberately  in  the  nest  lining  before  incubation 
and  half  bury  the  young  in  the  soft  lining  in  cold  weather. 

Like  most  corvids,  Ravens  are  generalist  feeders. 
Although  they  actually  procure  most  of  their  food  on  the 
ground,  they  spend  considerable  time  soaring  in  search  of 
their  meals.  Ravens  forage  mosdy  while  walking  or,  less 
often,  hopping  on  die  ground.  They  pick  their  food  from 
the  surface,  probe  in  soft  earth,  turn  over  objects,  pick 
through  refuse  at  dumps,  drop  shellfish  on  hard  surfaces 
to  break  them  open,  pounce  on  unsuspecting  prey,  attack 
sick  or  injured  individuals  of  species  normally  left  alone, 
and  even  force  vultures  to  disgorge  (Bent  1946,  Goodwin 
1986).  Although  Ravens  are  omnivorous,  they  tend  to  be 
more  carnivorous  than  crows  (Bent  1946,  Harlow  et  al. 
1975,  Goodwin  1986).  Mammals  usually  supply  the  staple 
of  the  diet,  with  most  large  and  medium-sized  ones  taken 
as  carrion  while  the  smaller  ones  are  preyed  upon  live; 


286 


]ays  and  Crows 


SPECIES  ACCOUNTS 


jays  and  Crows 


afterbirth  of  large  mammals  is  also  eaten.  Other  important 
animal  foods  are  birds  and  their  eggs,  insects,  reptiles, 
amphibians,  marine  invertebrates,  and  garbage.  Ravens' 
stomach  contents  suggest  that  when  these  birds  visit  rot- 
ting carcasses,  they  sometimes  feed  chiefly  or  entirely  on 
blow  fly  maggots  and  beedes  in  and  around  them  (Good- 
win 1986).  Ravens  often  are  bold  scavengers  about  human 
dwellings  and  encampments,  and  large  numbers  some- 
times gather  at  garbage  dumps,  slaughterhouses,  or  other 
sources  of  abundant  food.  Vegetable  foods  include  culti- 
vated grains  and  wild  fruits  and  berries;  much  vegetable 
matter  may  be  ingested  incidentally  or  comes  from  the 
stomachs  of  prey.  Indigestible  items  are  cast  as  pellets. 
Ravens  habitually  store  surplus  food.  They  preferentially 
store  fat,  even  over  foods  they  prefer  to  eat,  except  that 
breeding  birds  most  eagerly  store  insects  or  other  foods 
suitable  for  their  young  (Goodwin  1986).  While  feeding 
small  nesdings,  Ravens  at  first  feed  them  small  items;  they 
kill  and  crush  even  small  insects  for  the  young,  remove  all 
hard  parts  and  bits  of  bone  from  prey,  and  supply  the 
young  with  soaked  food  by  drinking  water  before  feeding 
them.  Adults  bring  the  young  water  alone  on  hot  days. 
During  the  nesting  season,  adult  males  feed  females  on  or 
off  the  nest.  In  eastern  Oregon,  Stiehl  (1985)  noted  a 
late-season  (Jul)  shift  of  the  diet  from  carrion,  small  mam- 
mals, and  eggs  to  insects,  principally  grasshoppers;  pre- 
sumably this  reflected  seasonal  availability. 


Marin  Breeding  Distribution 

Common  Ravens  bred  widely  in  Marin  County  during  the 
adas  period.  They  were  most  numerous  around  the  wind- 
swept bluffs  and  shorelines  of  the  immediate  coast,  espe- 
cially on  the  Point  Reyes  peninsula,  and  were  sparse  or 
absent  in  the  lowlands  bordering  the  San  Francisco  and 
San  Pablo  bayshores.  Representative  nesting  localities  were 
Upper  Pierce  Ranch,  Tomales  Point  (NY  5/18/82  -DS); 
Abbott's  Lagoon  (NE  4/15/81  -DS);  and  Drake's  Beach 
sea  cliff  (NE  or  NY  6/3/81  -DS). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  noted  historical  declines  or 
local  extirpation  of  Raven  populations  in  settled  areas  of 
California.  DeSante  and  Ainley  (1980)  also  implicate 
human  disturbance  as  the  cause  of  extirpation  of  breeding 
Ravens  on  the  Farallon  Islands.  Recendy  these  negative 
effects  must  have  been  offset  to  a  certain  degree  by  aug- 
mented food  supplies  from  domestic  livestock  and  by  the 
proliferation  of  road  kills  with  our  expanding  mobile 
population.  From  1968  to  1989,  Raven  numbers  increased 
on  Breeding  Bird  Surveys  in  California,  though  the  trend 
was  less  pronounced  since  1980  (USFWS  unpubl.  analy- 
ses). At  least  from  1 968  to  1 979,  the  increase  was  concen- 
trated in  the  foothills  in  areas  including  coastal  counties 
from  Monterey  south  and  parts  of  those  to  the  north 
(Robbins  et  al.  1986). 


^-—7    \W— is, 


287 


Titmice 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Titmice 


Titmice 

Family  Paridae 


CHESTNUT-BACKED  CHICKADEE    Varus  rufescens 


A  year-round  resident. 

A  common,  nearly  ubiquitous  breeder; 
overall  breeding  population  very  large. 

Recorded  in  195  (88.2%)  of  221 
blocks. 


O  Possible 
C  Probable 
W    Confirmed 


62  (32%) 

31   (16%) 

102  (52%) 


FSAR  =  4        OPI  =  780         CI  =  2.20 


Ecological  Requirements 

The  cheery  calls  o{  our  only  breeding  chickadee  ring  out 
from  virtually  all  of  Marin  County's  moist,  well-shaded 
forests.  The  Chestnut-backed  Chickadee's  main  nesting 
haunts  here  are  redwood,  Douglas  fir,  bishop  pine,  mixed 
conifer,  broadleaved  evergreen,  and  willow  and  alder  ripar- 
ian forests.  They  also  reside  in  extensive  groves  of  planted 
pine,  cypress,  and  eucalyptus  and,  sparingly,  in  the  edges 
of  oak  woodlands. 

Like  most  chickadees,  Chestnut-backs  nest  in  cavities  in 
stumps,  tree  stubs,  or  decayed  trees.  The  cavities  may  be 
natural,  excavated  in  decayed  wood  by  the  birds  them- 
selves, or  old  woodpecker  holes.  Nest  boxes,  holes  in 
buildings,  old  pipes  (Bent  1946),  or  old  Cliff  Swallow 
nests  (Dixon  1954)  are  used  less  frequendy.  Nest  holes 
range  from  1.5  to  80  feet  above  the  ground,  and  the  nest 
cavity  is  lined  with  soft  materials  such  as  mosses,  fur,  hair, 
small  feathers,  and  rope  fiber  (Bent  1946). 

Chestnut-backs  forage  mosdy  by  gleaning  from  foliage 
and  small  twigs  as  they  spiral  through  the  canopy  and 
subcanopy  of  the  forest.  They  also  glean  from  flowers, 
buds,  fruits,  and  cones,  less  commonly  from  large 
branches  and  trunks,  and,  rarely,  from  the  ground.  While 
gleaning,  they  frequendy  hang  upside  down  or  sideways 
from  twigs  or  from  the  corrugations  of  bark  on  large  limbs. 

288 


Less  frequendy,  they  hover  or  flycatch  in  a  "clumsy"  man- 
ner (Dixon  1954,  Root  1964,  Smith  1967,  Sturman  1968, 
Hertz  et  al.  1976).  Compared  to  Plain  Titmice,  Chestnut- 
backs  forage  faster,  hang  beneath  perches  more  often, 
hammer  items  held  under  their  feet  at  "anvil"  sites  less 
often,  and  apparendy  eat  smaller  food  items  (Root  1964). 
Chestnut-backs  also  spend  more  time  in  mixed  evergreen 
than  live  oak  woodland,  forage  more  in  the  foliage  zone  of 
the  canopy  than  on  large  branches  and  limbs  of  the 
subcanopy,  and  go  to  the  ground  less  frequendy  than 
Titmice  do. 

In  a  San  Mateo  County  mixed  deciduous-live  oak 
woodland,  Chestnut-backs  forage  at  virtually  the  exact 
same  levels,  0  to  39  feet  (mosdy  10-30  ft.),  as  both  the 
Plain  Titmouse  and  the  Bushtit  (Hertz  et  al.  1976). 
Resources  there  are  partitioned  by  the  type  of  substrate 
used  within  that  zone:  the  Chestnut-backed  Chickadee  is  a 
composite  foliage  and  bark  forager,  intermediate  between 
the  foliage  specialist  Bushtit  and  the  bark  specialist  Plain 
Titmouse.  Chestnut-backs  there  forage  on  foliage  about 
60%  of  the  time  and  stems  about  40%.  Although  they  only 
forage  in  shrubbery  7%  of  the  time,  they  are  intermediate 
in  their  use  of  that  substrate  compared  with  Bushtits  (20%) 
and  Titmice  (2.5%).  Also  in  San  Mateo  County,  Wagner 


Titmice 


SPECIES  ACCOUNTS 


Titmice 


(1981)  found  Chestnut-backs  using  evergreen  (vs.  decidu- 
ous) oaks  more  than  Titmice  but  less  than  Bushtits.  Chest- 
nut-backs there  show  some  seasonal  and  annual  variation 
in  the  size  of  foraging  perches  they  use. 

In  a  live  oak-mixed  evergreen  woodland  in  Contra 
Costa  County,  Root  (1964)  also  found  that  Chestnut-backs 
rely  more  heavily  on  foliage  and  related  substrates,  Titmice 
predominandy  on  woody  substrates;  Titmice  there  concen- 
trate on  live  oaks  and  chickadees  on  a  wide  variety  of  trees. 
However,  in  a  live  oak-bay  laurel-eucalyptus  woodland  in 
Berkeley,  Alameda  County,  Dixon  (1954)  reported  the 
opposite  trend— Chestnut-backs  forage  mosdy  in  live  oaks 
and  Titmice  in  a  variety  of  trees.  Although  Chestnut-backs 
there  forage  on  foliage  and  stems  in  roughly  equal  propor- 
tions, Titmice  forage  in  foliage  overwhelmingly  (87%). 

In  mixed  conifer  habitat  in  the  Sierra,  Chestnut-backs 
vary  foraging  techniques  (and  tree  species  use)  seasonally 
(Brennan  6k  Morrison  1990).  Foliage  use  and  gleaning 
peak  there  in  spring  and  summer  and  decrease  as  twig  use 
increases  in  late  fall/early  winter.  In  the  Washington 
Cascades,  these  chickadees  probe  more  in  winter  than 
spring  and  shift  relative  use  of  tree  species  in  winter 
(Lundquist  6k  Manuwal  1990). 

In  an  area  of  overlap  with  Blackopped  Chickadees  in 
Vancouver,  B.C.,  and  Washington  state,  Chestnut-backs 
forage  in  slighdy  different  manners  on  different  substrates 
and  at  greater  heights— from  0  to  140  feet  (peak  45-50  ft.) 
versus  0  to  70  feet  (mosdy  0-5  ft.)— than  do  Blackops 
(Smith  1967,  Sturman  1968).  In  contrast  to  Black-caps, 
breeding  Chestnut-backs  are  restricted  mosdy  to  conifer- 
dominated  habitat  and  are  stereotypically  adapted  to  coni- 
fer foraging  (Sturman  1968)— that  is,  they  change  their 
foraging  strategy  little  when  moving  from  conifers  to  hard- 
woods. Compared  with  Black-caps,  Chestnut-backed 
Chickadees  forage  more  often  near  the  ends  of  branches; 
forage  more  often  in  the  foliage  of  the  canopy  than  in  the 
branchwork  of  the  subcanopy;  choose  perches  on  twigs 
more  often  than  on  large  branches  and  trunks;  forage  more 
often  on  foliage,  buds,  and  cones  than  on  bark  surfaces; 
and  forage  more  on  the  upper  surfaces  of  branches  and 
twigs,  from  an  upright  stance.  Black-caps  forage  more  from 
a  hanging  than  an  upright  stance,  primarily  because  they 
increase  the  proportion  of  foraging  by  hanging  when 
feeding  in  hardwoods  while  Chestnut-backs  do  not.  As  a 
rule,  Chestnut-backs  forage  at  greater  heights  (relative  to 
tree  height)  than  do  Black-caps,  even  though  Chestnut- 
backs  forage  at  relatively  lower  heights  in  hardwoods  than 
conifers  and  vice  versa  for  Blackops.  Overall,  Chestnut- 
backs  are  less  diverse  in  their  foraging  style  than  Black- 
caps, but  both  forage  in  a  greater  variety  of  places  in 
hardwoods  than  in  conifers.  Among  seasonal  differences, 
Chestnut-backs  there  forage  more  often  on  newly  opened 
buds  and  cones  early  in  the  season,  and  they  hang  upside 
down  more  in  winter. 


The  Chestnut-backed  Chickadee  diet  in  California  is 
about  65%  animal  matter  and  35%  vegetable  matter  (Beal 
1907).  The  main  animal  foods  are  true  bugs,  caterpillars, 
wasps,  spiders,  and  beedes;  this  part  of  the  diet  naturally 
increases  in  the  spring  and  summer.  The  vegetable  foods 
are  chiefly  fruits  and  seeds,  the  latter  primarily  coniferous. 

Marin  Breeding  Distribution 

During  the  adas  period,  Chestnut-backed  Chickadees  bred 
throughout  Marin  County  but  were  most  numerous  and 
widespread  on  coastal  ridges  where  denser,  moister  forests 
prevail.  In  the  northern  and  interior  sections  of  the  county, 
Chestnut-backs  were  restricted  to  the  moist  drainages  of 
narrow  canyons,  north-facing  slopes,  and  the  larger 
planted  groves  of  eucalyptus,  pine,  or  cypress.  Representa- 
tive breeding  locations  were  eucalyptus  grove  at  Upper 
Pierce  Ranch,  Tomales  Point,  (NY/FY  5/18/82  -DS); 
Palomarin,  PRNS  (NE-NY  4/23-5/15/82  -PRBO);  and 
Mt.  Burdell,  Novato  (NY  5/?/82  -ScC). 

Historical  Trends/  Population  Threats 

Historically,  tree  plantings  appear  to  have  caused  a  local 
expansion  of  the  breeding  range  of  Chestnut-backed 
Chickadees  in  Marin  County.  This  is  most  notable  in  the 
grassy  ranchlands  near  Tomales  that  before  European 
settlement  apparendy  were  essentially  treeless  except  for 
low  willows  along  streams.  Chestnut-backs  have  also 
expanded  their  breeding  range  considerably  in  central 
coastal  California  since  at  least  1938  (GckM  1944;  Dixon 
1954,  1960),  and  chickadee  populations  in  this  region 
continue  to  increase  (Brennan  &  Morrison  1991).  Dixon 
postulated  that  following  the  growth  of  the  human  popula- 
tion, coastal  Chestnut-backs  were  able  to  expand  in  range, 
via  planted  groves  of  shade  and  orchard  trees,  across  areas 
formerly  dominated  by  grassland  and  oak  savannah. 
Chestnut-backs  have  also  expanded  their  range  south 
along  the  coast  to  Santa  Barbara  County  (Garrett  6k  Dunn 
1981)  and  into  and  south  along  the  Sieira  Nevada  (Crase 
1976,  ABN);  at  least  in  the  Sierra,  chickadee  numbers  have 
since  stabilized  (Brennan  6k  Morrison  1991).  Expansion 
into  the  Sierra  Nevada  may  have  been  in  response  to  an 
increase  of  Douglas  fir— an  important  chickadee  foraging 
tree— after  extensive  clear-cutting  there  around  the  turn  of 
the  century  (Brennan  6k  Morrison  1991).  Perhaps  Chest- 
nut-backed Chickadee  populations  have  also  increased  in 
Marin  County  for  the  same  reasons  following  the  extensive 
logging  here  in  the  nineteenth  and  early  twentieth  centu- 
ries. In  contrast  to  these  earlier  and  continued  local 
increases,  on  the  whole  Chestnut-backed  Chickadee  num- 
bers appeared  to  decrease  slighdy  on  Breeding  Bird  Sur- 
veys in  California  from  1968  to  1989,  though  they  were 
relatively  stable  from  1980  to  1989  (USFWS  unpubl.  anal- 
yses). 


289 


Titmice 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Titmice 


PLAIN  TITMOUSE    Parus  inornatus 


A  year-round  resident. 

r—jT?     V^X" 

A  common,  widespread  breeder;  over- 

f\^s3^ 

all  breeding  population  fairly  large. 

'x  J<\  QJ*r\  ©>  W"\  ©  \^\  •  \^\  •  V-^s 
\   Jv^\  °  vn«\>AD  v?<\*  V-^Y©  v>^ro  J 

Recorded  in  129  (58.4%)  of  221 
blocks. 

O    Possible        =      37   (29%) 

\  \- 

C    Probable       =       34   (26%) 
•    Confirmed  =       58   (45%) 

^o 

FSAR  =  4        OPI  =  516       CI  =  2.16 

Ecological  Requirements 

Though  drab  in  color,  this  crested  parid  is  the  voice  and 
soul  of  the  oaks.  Titmice  breed  in  Marin  County's  oak 
woodlands,  oak  savannah,  open  broadleaved  evergreen 
forests,  and  open  riparian  woodlands.  The  broadleaved 
evergreen  forests  they  inhabit  are  generally  spacious,  oak- 
dominated  ones  on  south-facing  slopes.  Characteristic  of 
these  habitats  are  a  predominance  of  hardwood  trees  with 
moderate  to  large  boles  and  relatively  open  branchwork. 
Plain  Titmice  select  nest  sites  from  about  3  to  32  feet  above 
the  ground  in  natural  (rotted-out)  tree  cavities,  in  hollows 
they  excavate  or  partially  excavate  in  decayed  wood  of  trees, 
in  old  woodpecker  holes,  or  in  nest  boxes  (Bent  1946, 
Dixon  1954).  More  unusual  nest  sites  are  holes  in  earthen 
cliff  banks,  old  Cliff  Swallow  nests,  and  human  structures. 
Nest  cavities  are  lined  with  soft  materials  such  as  fur,  moss, 
hairs,  fine  grasses,  weed  stems  and  fibers,  and  a  few 
feathers  (Bent  1946,  Dixon  1949). 

In  general,  Plain  Titmice  forage  much  like  chickadees 
do,  but  at  a  slower  pace.  They  glean  from  bark  and  foliage, 
hang  from  twigs  and  trunks,  or  occasionally  hover  or 
flycatch.  The  Plain  Titmouse  is  a  bark  specialist  compared 
with  the  more  generalist  Chestnut-backed  Chickadee  and 
the  foliage  specialist  Bushtit,  but  the  three  species  generally 
forage  at  the  same  heights  (Hertz  et  al.  1976).  Compared 
with  Chestnut-backed  Chickadees,  in  oak  woodlands  Tit- 
mice generally  spend  more  time  in  the  subcanopy  than  the 
canopy  and  spend  much  more  time  gleaning  from  twigs, 
branches,  limbs,  and  trunks  than  from  foliage.  They  also 
go  to  the  ground  (or  to  low  plants  such  as  thisdes)  more 
frequently  to  gather  fruits  and  nuts,  use  their  larger  bills 

290 


more  for  hammering  and  splitting  open  nuts  and  chipping 
off  bark,  do  less  hanging  beneath  perches,  and  apparendy 
eat  larger  food  items  than  Chestnut-backed  Chickadees  do 
(Root  1964,  Hertz  et  al.  1976).  Dixon  (1954)  observed  that 
in  live  oak  woodlands,  Plain  Titmice  forage  predominandy 
by  gleaning  from  foliage  and  bark-glean  infrequendy.  Tit- 
mice also  come  to  feeders  more  readily  than  Chestnut- 
backed  Chickadees  do  (B.  Lenarz  pers.  comm.).  See  the 
Chestnut-backed  Chickadee  and  Bushtit  accounts  for  fur- 
ther details  of  niche  separation  among  these  species.  In 
California's  foothill  oak  woodlands,  Titmice  show  sea- 
sonal, annual,  and  geographic  variation  in  many  aspects  of 
their  foraging  ecology  (Wagner  1981,  Block  1990). 

The  California  diet  of  Titmice  (from  areas  encompass- 
ing orchards,  which  are  not  the  main  haunts  of  the  species) 
is  "43  percent  of  animal  to  57  of  vegetable"  (Beal  1907). 
The  animal  food  is  primarily  true  bugs,  caterpillars,  bee- 
ties,  wasps,  ants,  spiders,  and  other  insects.  Vegetable  food 
consists  of  cultivated  fruits  and  grains,  wild  fruits,  seeds 
and  nuts,  leaf  galls,  oak  and  willow  catkins,  and  leaf  buds 
(Beal  1907,  Dixon  1949). 

Marin  Breeding  Distribution 

During  the  adas  period,  Plain  Titmice  bred  primarily  in  the 
drier  interior  sections  of  the  eastern  part  of  Marin  County, 
where  open,  oak-dominated  broadleaved  evergreen  forests 
and  oak  woodlands  predominate.  The  hills  dotted  with 
valley  oaks  around  Novato  are  the  mecca  for  Titmice  in 
Marin.  Titmice  are  rare  and  local  on  the  Point  Reyes 
peninsula  and  elsewhere  on  the  immediate  coast,  where 


Titmice 


SPECIES  ACCOUNTS 


Titmice 


open  oaks  or  open  riparian  woods  are  difficult  to  find  amid 
the  dense  moist  coastal  forests.  Representative  nesting 
locations  were  Antonio  Creek,  near  Point  Reyes-Petaluma 
Rd.  (NY/FY  5/12/77  -DS);  near  Stafford  Lake,  Novato 
(FY  5/6/79  -KH);  E  side  Loma  Alta  (FY  5/30/82  -BiL); 
China  Camp  SP  (ON  4/17/82  -BiL);  and  Peacock  Gap, 
San  Rafael  (FY  4/27/76  -RMS). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  noted  retractions  of  the  Plain 
Titmouse's  range  locally  in  California  where  oaks  were 


cleared  for  agriculture  and  expansion  of  their  range  where 
trees  had  been  planted  in  previously  unoccupied  areas. 
Titmice  numbers  appeared  to  decrease  slighdy  on  Breed- 
ing Bird  Surveys  in  California  from  1968  to  1989  and 
significandy  from  1980  to  1989  (USFWS  unpubl.  analyses). 
In  the  future,  oak  woodland -dependent  species  such  as 
this  bird  may  experience  extensive  habitat  loss,  since  seed- 
ling oaks  are  rare  in  these  woodlands  today  (see  Plant 
Community  section).  Removal  of  oak  stands  for  firewood 
and  to  clear  land  for  development  is  also  a  problem  in  the 
Sierran  foothills  (E.C.  Beedy  pers.  coram.). 


Beak  crammed  with  insects,  a  Chestnut-backed  Chickadee  pauses  before  descending  into  its  cavity 
to  feed  the  clamoring  young.  Photograph  b^  Ian  Tait. 


291 


Bushtils 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Bushtils 


Bushtits 

Family  Aegithalidae 


BUSHTIT    Psaltriparus  minimus 


A  year-round  resident. 

J      ^\  '•     JH^     \ 

o>5>s^              \                       vr^cv 

A  fairly  common,  nearly  ubiquitous 

a   J^\* j&\ '•% -\  o  VV\o V^oW/ 

breeder;  overall  breeding  population 
large. 

/» 

•  -V"\  0.V^\  •  Vt^v*  V^Co  v-"a  eAJ^v  •  ^X 

Recorded  in  207  (93.7%)  of  221 

-"X  •  A^\  CA^V«  A^V-°  \<5rV»--Y>^C«  \^\ 

blocks. 

Sr\  mJ^\  ojP^\  oM  o y^\o  \^\o\J>\ 

\-^\°!>< 

\AXtx  *J>r\  •  Jr^A  o  4^\  o  \>^\  o  V>\  •  Y^"A 

V\V 

O    Possible        =       80   (39%) 

iX  *V^\  O^LX  ^IV^  •  \^V  •A-;<A  *Jr^\  «  A^lX  " 

©    Probable       =       23   (11%) 

•\^\  •  Jr^X  •  jJ^X  9^&^\  •  Jk^AO  >^A43  X^C  ^*J\ 

_.<■- 

€    Confirmed  =     104   (50%) 

Q'AirCrx  o  V^vt5  Jr-^^^O-V^V*  V-r'TA  o  V^A  •  \>^-V- J*^ 

^1*K\  ©_V<\  •Jrr\  ®  ><2ro  V^y  ©  V^a  o  ><\__ 

-7  \  S?y  9  V^°A<\  •-V-^v &^2rx  •  j^cC*  \^x  *u — v 

V«      /      .-N 

FSAR  =  3        OPI  =  621        CI  =  2.12 

^V£i 

•Jr                                  N^-iA  •  v^T^A^^^  V^X^AP^^j 

IT               ^^^^^$k&^ 

j^>                  xri/   ^~ <*\^v 

Ecological  Requirements 

These  "bird  children  that  never  grew  up"  (Dawson  1923) 
frequent  the  mixed  vegetation  along  sunny  edges  of  all  of 
Marin  County's  major  forest,  woodland,  and  scrub  habi- 
tats, including  planted  woodlots,  such  as  eucalyptus.  Coni- 
fers themselves  are  little  used,  but  Bushtits  inhabit  conifer 
forest  edges  and  clearings  with  borders  of  live  oaks,  Ceano- 
thus,  coyote  bush,  and  the  like.  The  broadleaved  evergreen 
vegetation  of  coastal  scrub,  chaparral,  and  oak  woodland  is 
most  to  dieir  liking,  though  generally  not  in  homogeneous 
stands:  Bushtits  seem  to  prefer  a  mixture  of  trees  and 
shrubs,  with  somewhat  open  airways. 

Unlike  our  other  songbirds  (except  orioles),  Bushtits 
build  pensile  nests.  They  hang  them  from  4  to  50  feet,  but 
mosdy  less  than  15  feet,  above  the  ground  in  various  trees 
or  shrubs,  both  native  and  introduced  (Bent  1946);  live 
oak  and  Ceanothus  are  favorites  on  the  coast  Bushtits 
generally  conceal  their  striking  nests  in  lichen-festooned 
dense  foliage,  but  occasionally  they  build  them  in  plain 
view.  One  wonders  at  the  fate  of  an  obvious  nest.  A  nest 
is  a  long  (about  7-10  in.),  intricately  woven,  domed-over, 
pendant  bag  with  a  small  entrance  hole  on  one  side  near 
the  top.  The  nest  materials  Bushtits  use  most  frequendy  in 
the  San  Francisco  Bay  Area  are  mosses,  lichens,  oak  leaves, 

292 


grasses,  and  the  staminate  flowers  of  coast  live  oak  (Addi- 
cott  1938).  In  addition  they  use  other  flowers,  fruits,  plant 
down,  conifer  needles,  bark  fibers,  insect  cocoons,  feath- 
ers, and  bits  of  paper  and  string.  They  bind  all  these 
together  with  copious  amounts  of  spider  web. 

Where  they  overlap  with  Chestnut-backed  Chickadees 
and  Plain  Titmice  in  oak  woodland  on  the  central  Califor- 
nia coast,  Bushtits  forage  at  similar  heights  (see  accounts) 
but  have  the  broadest  niche  of  the  three  species  (Hertz  et 
al.  1976).  Bushtits  there  forage  in  a  greater  variety  of  trees 
and  bushes  and  spend  more  time  in  bushes  and  vines 
(20%)  than  do  die  other  two  species.  The  10%  of  foraging 
time  Bushtits  spend  on  honeysuckle  vines  indicates  a 
strong  preference  for  the  vines,  as  they  were  the  least 
abundant  of  the  shrubby  plants  surveyed.  Bushtits  are 
foliage  specialists,  primarily  of  the  canopy  and  subcanopy. 
They  spend  90%  of  their  time  gleaning  from  foliage,  the 
remainder  from  stems;  nonfoliage  foraging  is  directed  at 
green  twigs  and  petioles  rather  than  woody  surfaces. 

Where  Bushtits  overlap  with  Plain  Titmice  in  foothill 
oak-pine  woodland  in  the  central  Sierra  Nevada,  both 
species  vary  monddy  in  their  intraspecific  use  of  foraging 
sites  (plant  species)  and  substrates,  and  yearly  in  their  use 


Bushtits 


SPECIES  ACCOUNTS 


Bushtits 


of  foraging  substrates  (Hejl  ck  Verner  1990).  Despite 
overall  tendencies  of  Bushtits  to  forage  more  often  on 
buckbrush  and  Titmice  on  blue  oak,  both  bird  species 
show  parallel  use  of  various  plants  across  the  breeding 
season.  Both  species  use  live  oak  and  buckbrush  more, 
and  blue  oak  less,  in  March;  increase  their  use  of  blue  oak 
in  March;  and  increase  their  use  of  gray  pine  and  other 
species  in  May.  Bushtits  and  Titmice  show  different  pat- 
terns of  foraging  substrate  use  across  the  breeding  season. 
Paralleling  phenological  changes  of  plants,  Bushtits  forage 
mosdy  from  buckbrush  flowers  in  March,  and  from  leaves 
and  twigs  of  buckbrush  and  blue  oak  leaves  in  April  and 
May.  Substrate  use  by  Titmice  varies  in  a  similar  pattern, 
though  they  rely  more  on  blue  oak  leaves  in  April  and  May. 
These  within-season  shifts  in  foraging  behavior  probably 
reflect  changing  prey  availability  with  different  stages  of 
plant  phenology. 

Bushtits  inhabiting  mixed  oak  woodland  on  the  central 
California  coast  forage  more  in  evergreen  and  less  in 
deciduous  oaks,  more  from  smaller  perches,  and  more  in 
bushes  than  either  Plain  Titmice  or  Chestnut-backed 
Chickadees  do  (Wagner  1981).  A  lack  of  seasonal  or  yearly 
differences  in  foraging  behavior  of  Bushtits  there  may 
reflect  limited  sampling  of  these  behaviors  rather  than  a 
lack  of  variability  of  foraging  patterns  over  time. 

The  Bushtit's  diet  in  California  is  about  81%  animal 
and  19%  vegetable  (Beal  1907,  n  =  353),  with  the  latter 
increasing  slighdy  in  importance  in  autumn  and  winter 
(Beal  1907,  Martin  et  al.  1951).  Animal  fare  consists 
mainly  of  true  bugs,  beedes,  butterflies  and  moths  (mosdy 
caterpillars),  and  spiders  (Beal  1907);  other  insect  taxa  and 


pseudoscorpions  are  of  minor  importance.  The  vegetable 
matter  includes  fruit  pulp,  granules  of  poison  oak,  leaf 
galls,  and  seeds. 

Marin  Breeding  Distribution 

During  the  adas  period,  Bushtits  bred  widely  throughout 
Marin  County.  They  did  not  exhibit  any  marked  dis- 
tributional patterns  of  abundance,  except  that  they  seemed 
to  be  somewhat  less  numerous  in  areas  dominated  by  the 
coastal  prairie  on  Point  Reyes  peninsula  and  around 
Tomales  and  by  dense  forest  on  Inverness  and  Bolinas 
ridges.  Representative  nesting  areas  were  Inverness  (NB 
3/26/82  -DS);  Chileno  Valley  (NE  5/5/82  -DS);  Mt. 
Burdell,  Novato  (NB  4/21/81  -ITi);  near  Rock  Springs, 
Ml  Tamalpais  (NB  3/28/81  -DS);  and  Phoenix  Lake 
(NB  4/19/80 -ITi). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  felt  that  Bushtits  had  increased 
locally  in  "open  valleys  and  plains"  in  parts  of  California, 
as  habitat  was  enhanced  by  the  planting  of  trees  and 
shrubbery.  It  also  seems  likely  that  their  numbers  have 
increased  in  areas  where  clearing  has  opened  up  formerly 
dense  forests,  creating  edge  situations  to  the  species'  liking. 
Clearing  of  open  oak  woodlands,  though,  has  probably 
been  to  their  detriment.  Breeding  Bird  Surveys  revealed  a 
fairly  stable  population  in  California  from  1968  to  1989, 
though  numbers  decreased  from  1980  to  1989  (Robbins 
et  al.  1986,  USFWS  unpubl.  analyses). 


293 


Nuthatches 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Nuthatches 


Nuthatches 

Family  Sittidae 


RED-BREASTED  NUTHATCH   Sitta  canadensis 


Occurs  year  round,  though  primarily  as  a 

^v^-^         ^ 

fall  transient  and  winter  resident  from 

j    \^\   j&r^ 

■ 

Sep  through  Mar,  when  numbers  vary 

^K\n\ 

V\>V^\^A^\l^C ~ 

gready  from  year  to  year. 
An  uncommon,  local  breeder;  overall 

\    ^V^\     \r^\     \^\ 

ft^CV>V^ 

breeding  population  very  small. 

V\^ 

Recorded  in  39  (17.6%)  of  221  blocks. 

^.. 

O    Possible        =       20   (51%) 
€    Probable               16   (41%) 

rvp\ 

•    Confirmed  =         3   (8%) 

\OVXA       V>A»&^l'Ol/ 

XL?/       ^^~^ci. 

Wv^ 

FSAR  =  2        OPI  =  78         CI  =  1.56 

Ecological  Requirements 

High-pitched,  nasal,  ank-ank  calls  betray  the  presence  of 
breeding  Red-breasted  Nuthatches  in  Marin  County's 
dense  Douglas  fir  stands  and  may  also  resound  from 
redwoods  and  planted  pines  and  cypress.  They  are  gener- 
ally "replaced"  in  bishop  pines  by  Pygmy  Nuthatches. 
Red-breasted  Nuthatches  nest  in  cavities  they  excavate  in 
the  rotted  interiors  of  live  trees,  tree  stubs,  or  dead  trees, 
or  in  old  woodpecker  holes  or  nest  boxes.  They  use  nest 
cavities  in  conifers  or  hardwoods  at  heights  ranging  from 
2  to  120  feet  above  the  ground  (Tyler  1948a).  In  Yosemite, 
Michael  (1934)  found  nest  holes  from  5  to  40  feet  and 
estimated  average  height  was  probably  1 5  feet.  In  Sierra 
County,  Airola  (1980)  reported  nest  holes  averaging  30 
feet  in  height  (range  5-86  ft.).  The  nest  cavity  bottom  may 
be  just  a  deep  layer  of  fine  sawdust  (Gunderson  1939),  but 
more  commonly  it  is  lined  with  soft  vegetable  matter  such 
as  fine  grasses,  roots,  or  shredded  bark  (Tyler  1948a).  A 
curious  habit  of  this  nuthatch,  the  function  of  which  is 
unknown,  is  to  liberally  smear  the  entire  circumference  of 
its  nest  hole  with  pitch.  Perhaps  this  serves  to  repel 
predators  such  as  squirrels,  as  apparently  do  the  chemical 
secretions  spread  at  their  nest  entrances  by  White-breasted 
Nuthatches  (see  account). 

294 


Red-breasted  Nuthatches  tend  to  forage  at  intermediate 
heights  and  on  different  substrates  compared  with  the 
Pygmy  and  White-breasted  nuthatches  (see  accounts). 
Although  they  will  forage  throughout  the  crown  (Stallcup 
1968),  Red-breasteds  generally  forage  at  medium  heights 
relative  to  insect  gleaners,  and  higher  than  most  bark 
gleaners  in  mixed  conifer  forests  in  the  Sierra  Nevada 
(Airola  &  Barrett  1985,  Morrison  etal.  1987).  They  forage 
on  a  wide  variety  of  substrates,  including  small  branches, 
trunks,  foliage,  twigs,  and  medium  branches.  In  general, 
Red-breasteds  spend  more  time  on  the  inner  branches  of 
the  tree  crown  than  in  the  outer  canopy  or  on  trunks, 
diough  they  make  more  use  of  limbs  and  trunks  and  less 
of  twigs  in  winter  (Stallcup  1968,  Morrison  et  al.  1985).  In 
contrast,  Pygmy  Nuthatches  tend  to  forage  higher  in  coni- 
fers on  peripheral  foliage  and  branches,  while  White- 
breasted  Nudiatches  tend  to  forage  lower  down  on  the 
trunk  and  on  larger  branches.  In  Sierran  mixed  conifer 
forests,  Red-breasteds  change  their  relative  use  of  various 
tree  species  for  foraging  between  summer  and  winter 
(Airola  ck  Barrett  1985,  Morrison  et  al.  1987).  There  they 
forage  over  80%  of  the  time  on  live  trees,  but  overall  about 
35%  of  the  time  on  dead  substrates  of  live  or  dead  trees 
(Morrison  et  al,  1987). 


Nuthatches 


SPECIES  ACCOUNTS 


Nuthatches 


Red-breasted  Nuthatches  forage  primarily  by  gleaning, 
secondarily  by  probing  and  pecking,  and  to  a  limited  extent 
by  digging,  flycatching,  and  hovering.  They  do  flycatch 
frequendy  at  the  edges  of  clearings  when  suitable  insect 
prey  are  abundant  (D.  Shuford  pers.  obs.).  Like  other 
nuthatches,  Red-breasteds  are  experts  at  clinging  to  bark 
and  hitching  up  or  down  trunks  and  along,  under,  or 
around  limbs  and  branches  in  any  plane.  They  chip  or 
flake  off  pieces  of  bark,  particularly  in  winter.  In  addition 
to  tree  foraging,  they  also  fly  to  the  ground  or  low  vegeta- 
tion for  seeds  or  insects.  In  the  Washington  Cascades, 
Red-breasteds  reduce  gleaning  and  increase  probing  and 
pecking  from  spring  to  winter  (Lundquist  &  Manuwal 
1990).  These  nuthatches  do  not  show  substantial  geo- 
graphic variation  in  prey  capture  methods  (Petit  et  al. 
1990). 

Red-breasteds  pick  some  seeds  and  fruits  from  exposed 
sites.  They  also  pry  open  cone  scales  and  insert  their  bills 
to  procure  the  seeds,  which  they  frequently  wedge  in  a 
crack  or  crevice  to  work  upon.  These  nudiatches  also 
occasionally  suck  sap  from  "the  bleeding  stumps  of  trees" 
(Tyler  1948a).  They  dine  on  insects  (especially  beedes, 
hymenoptera,  true  bugs,  aphids,  and  caterpillars),  spiders, 
conifer  seeds,  wild  fruits,  and  buds  (Tyler  1948a,  Martin 
et  al.  1951,  Otvos  &.  Stark  1985).  In  a  study  in  Oregon, 
Red-breasteds  ate  negligible  amounts  of  plant  material 
except  in  winter,  when  seeds  (mosdy  of  sedge)  accounted 
for  12%- 17%  of  the  menu  (Anderson  1976).  An  increase 
in  bark  beedes  and  the  inclusion  of  stink  bugs  and  ladybird 
beedes  in  the  winter  diet  there  further  suggests  that  Red- 
breasteds  forage  more  on  large  proximal  branches  and 
trunks  at  that  season. 

Marin  Breeding  Distribution 

The  distribution  of  breeding  Red-breasted  Nuthatches  in 
Marin  County  during  the  adas  period  generally  reflected 
the  distribution  of  large  stands  of  Douglas  fir  and  coast 
redwood  on  Mount  Tamalpais,  Bolinas  Ridge,  and  the 
southern  part  of  Inverness  Ridge.  Representative  breeding 


locales  included  Benstein  Trail,  Mt.  Tamalpais  (ON 
5/1 9/76 -DS)  and  Bolinas  Ridge  N  of  Fairfax-Bolinas  Rd. 
(NB  5/24/76  -DS).  Although  Red-breasted  Nuthatches  in 
California  nest  mosdy  above  2500  feet  in  elevation  (GckM 
1944),  they  nest  close  to  sea  level  in  Bolinas. 

Historical  Trends/ Population  Threats 

Early  accounts  considered  the  Red-breasted  Nuthatch  a  fall 
and  winter  visitant  to  this  area  (Mailliard  1900,  S&.P  1933, 
GckW  1927).  It  was  first  reported  in  Marin  County  in 
summer  in  June  and  July  1 936  (Orr  1 937),  although  it  had 
probably  been  breeding  here  for  a  long  time  and  had  gone 
undetected  until  its  breeding  haunts  were  more  thoroughly 
explored. 

Population  levels  of  Red-breasted  Nuthatches  are 
known  to  fluctuate  dramatically  in  winter,  when  numbers 
of  birds  invade  lowland  areas  on  roughly  a  two-  to  three- 
year  cycle  as  a  result  of  poor  conifer  seed  crops  over  large 
areas  (Widrlechner  &  Dragula  1984).  Grinnell  and  Miller 
(1944)  also  commented  on  "the  vagrant  tendency  of  the 
species,  even  as  attempted  or  completed  nesting."  A  graph 
of  data  from  Breeding  Bird  Surveys  in  California  from 
1968  to  1979  (Robbins  et  al.  1986)  also  shows  marked 
year-to-year  variation  in  population  levels,  suggestive  of 
long-term  cycles.  This  might  just  as  easily  be  explained  by 
differential  survival  in  winter  between  irruptive  and  non- 
irruptive  years,  rather  than  by  irregular  changes  in  breed- 
ing distribution.  To  my  knowledge,  a  tendency  for 
irruptive  or  irregular  breeding  is  not  substantiated  by 
extralimital  (confirmed)  breeding  records,  or  even  by 
strong  circumstantial  evidence  of  shifting  breeding  popula- 
tions. On  the  whole,  numbers  on  Breeding  Bird  Surveys 
in  California  were  relatively  stable  from  1968  to  1989, 
despite  an  increase  from  1980  to  1989  (USFWS  unpubl. 
analyses). 

Logging  practices  that  reduce  conifer  diversity  or  create 
monocultures  are  also  likely  to  reduce  numbers  of  this  and 
other  species  that  inhabit  mixed  conifer  forests  (Morrison 
etal.  1987). 


295 


Nuthatches 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Nuthatches 


WHITE-BREASTED  NUTHATCH   Sitta  carolinensis 


A  year-round  resident. 

^»><x.                             \                                                A^V 

A  fairly  common,  local  breeder;  overall 

~i^^\^  Y^gg^vv 

breeding  population  small. 

PrV^W^W^- 

Recorded  in  59  (26.7%)  of  221  blocks. 

O    Possible        =       28   (47%) 

V^ 

-o^rv  \^\    V-Vx  ^V\  S-Vx  •3r\  °M 
^^vJ^£T   \  -^V^\  ^X^T\    \^^\     \^\     \^*\o  \ 

©    Probable       =       18   (31%) 

\TVi 

r-''\^^:\'3r^^^ 

•    Confirmed  =       13   (22%) 

-f 

FSAR  =  3        OPI  =  177        CI  =  1.75 

Lp^wVnV^V'w 

4^fT^>^^      ^~<C^V^\\3r^v^Vi\?A<A 

\?o 

Ecological  Requirements 

In  Marin  County,  as  elsewhere,  White-breasted  Nut- 
hatches are  habitual  "bark  combers."  They  breed  here 
primarily  in  open  oak  woodlands  and  oak  savannah  and 
only  occasionally  in  mixed  stands  of  Douglas  firs  and 
hardwoods.  In  California  oak  woodlands,  they  prefer 
deciduous  oaks  over  live  oaks  for  foraging  (Wagner  1981, 
Block  1990).  Overall,  their  main  requirements  seem  to  be 
trees  with  extensive  rough  bark  surfaces  and  open  branch- 
work  for  foraging  (G&M  1944)  and  cavities  for  nesting. 

In  accordance  with  the  nuthatch  psyche,  White-breast- 
eds  nest  exclusively  in  cavities.  They  may  use  natural 
cavities,  excavate  their  own,  or  modify  preexisting  ones; 
they  may  use  cavities  bored  out  by  individuals  of  other 
species  (usually  woodpeckers)  or  by  conspecifics  or  "make 
do"  with  nest  boxes;  excavation  entirely  by  White-breasteds 
is  rare  (Tyler  1948b,  Bent  1948,  McEllin  1979a).  Cavities 
are  reused  in  successive  years  (Butts  1931,  McEllin  1979a). 
Nest  cavities  can  be  in  a  variety  of  deciduous  or  coniferous 
trees,  and  nest  heights  can  range  from  1  to  61  feet  above 
the  ground  (Bent  1948,  Tyler  1948b).  In  Colorado, 
McEllin  (1979a)  found  seven  nests,  all  in  live  ponderosa 
pines  and  ranging  from  1 2  to  56  feet  in  height  (av.  35  ft.). 
All  were  in  trunks,  all  but  one  had  a  large  limb 
immediately  below  the  entrance,  and  they  tended  to  face 
east  or  south,  away  from  the  prevailing  wind  and  rain  from 
the  west  or  north.  In  Minnesota,  the  height  of  five  nests  in 
deciduous  trees  ranged  from  1 3  to  39  feet  and  averaged  20 
feet  (Ritchison  1981).  Airola  (1980)  reported  nest  hole 
heights  in  Sierra  County,  California,  averaging  19  feet  and 
ranging  from  4  to  61  feet. 

296 


The  nest  cavity  is  lined  with  fur,  hair,  shreds  of  bark, 
twigs,  grasses,  roodets,  dried  earth,  lumps  of  mud,  a  few 
feathers,  or  even  coyote  scat  or  pellets  ejected  by  birds  of 
prey  (Bent  1 948,  Tyler  1 948b).  White-breasted  Nuthatches 
are  known  to  perch  at  the  nest  tree,  swinging  the  whole 
body  in  an  ark,  and  sweep  insects  and  other  objects  held 
in  the  bill  back  and  forth  over  the  bark.  Sweeping  is 
concentrated  inside  and  outside  the  nest  entrance  and  at 
nearby  protuberances  and  branch  and  trunk  junctions. 
Since  these  nuthatches  usually  nest  in  relatively  large 
natural  cavities,  for  which  they  compete  with  tree  squirrels, 
Kilham  (1968)  theorized  that  this  bill  sweeping  makes  use 
of  the  chemical  defense  secretions  of  insects  to  repel 
squirrels  from  approaching  or  entering  their  nest  cavities. 

As  if  to  defy  gravity,  White-breasted  Nuthatches  use 
their  sharp  curved  nails  to  cling  to  bark  as  they  hitch  up 
or,  usually,  down  trunks  or  along,  under,  or  around  limbs 
and  branches.  Compared  with  our  other  nuthatches, 
White-breasteds  forage  mosdy  on  extensive  open  bark 
surfaces  (see  Pygmy  and  Red-breasted  nuthatch  accounts). 
They  concentrate  their  efforts  mosdy  from  the  lower  half 
of  the  tree  crown  downward  and  on  the  trunk  and  the 
inner  portions  of  large  limbs  and  branches  (Stallcup  1968, 
Bock  1969,  McEllin  1979b,  Wagner  1981,  Grubb  1982). 
They  tend  to  forage  relatively  little  on  smaller  branches  (but 
see  Block  1990),  dead  trees,  stumps,  logs,  rocks,  or  the 
ground.  White-breasted  Nuthatches  glean  from  the  bark 
surface,  peer  and  poke,  probe  fissures,  scale  and  chip  off 
small  flakes  of  bark,  and,  rarely,  flycatch.  They  take  seeds 
from  fallen  cones  on  the  ground  (not  from  intact  cones  on 


Nuthatches 


SPECIES  ACCOUNTS 


Nuthatches 


trees)  or  from  crevices  in  bark  where  previously  cached  by 
themselves  or  other  species.  Birds  frequendy  wedge  food 
items  in  crannies  of  horizontal  branches  and  break  them 
up  or  crush  them  with  blows  of  the  bill  (Stallcup  1968). 
Males  feed  females  at  the  nest  (Ritchison  1981).  In  Colo- 
rado's ponderosa  pine  forests,  McEllin  (1979b)  found  that 
the  sexes  differed  in  their  foraging  niches.  Female  White- 
breasted  Nuthatches  foraged  higher  than  males  and  more 
on  limbs  than  trunks.  During  the  breeding  season,  the 
sexes  used  significandy  different  foraging  methods— males 
tended  to  scale  more,  females  to  peer  and  poke  more.  In 
winter  in  the  deciduous  forest  in  Ohio,  Grubb  (1982) 
found  no  difference  between  the  foraging  niches  of  the 
sexes.  McEllin  (1979b)  noted  that  White-breasteds  were 
specialists  in  the  foraging  substrates  selected  but  generalists 
in  the  feeding  behavior  and  food  items  taken.  This  sug- 
gested to  him  that  they  were  preying  on  evenly  distributed 
food  items,  in  contrast  with  Pygmy  Nuthatches  (see 
account).  Anderson  (1976)  also  noted  that  White-breast- 
eds were  opportune  feeders  because  they  shift  their  diet 
more  between  habitats  than  do  Red-breasted  Nuthatches. 

Broad-based  comparisons  indicate  that  neither  of  these 
nuthatches  show  substantial  geographic  variation  in  prey 
capture  methods,  and  that  White-breasteds  have  a  rela- 
tively narrow  foraging  niche  (Petit  et  al.  1990).  On  the 
other  hand,  White-breasted  Nuthatches  breeding  in  oak 
woodlands  in  California  exhibit  considerable  geographic 
variation  in  their  selection  of  size  characteristics  of  trees 
and  substrates  for  foraging,  and  foraging  locations  within 
the  canopy  (Block  1990).  In  ponderosa  pine  forests  in 
Arizona,  they  show  annual  variation  in  foraging  tech- 
niques and  other  resource-use  measures  (Szaro  et  al.  1990). 

In  the  breeding  season,  White-breasted  Nuthatches  eat 
primarily  animal  foods,  but  they  switch  more  to  seeds  and 
nuts  in  the  colder  months  (Tyler  1948b,  Martin  et  al. 
1951).  The  main  animal  items  are  beedes,  spiders,  caterpil- 


lars, true  bugs,  ants  and  other  hymenoptera,  along  with 
some  flies,  grasshoppers,  moths,  and  millipedes.  Overall 
in  North  America,  plant  foods  make  up  68%  of  the  winter 
diet  (Martin  et  al.  1951,  n  =  45)  whereas  in  Oregon  they 
amount  to  1 7%  (sedge  seeds)  of  the  diet  in  oak  habitat,  and 
8%  (seeds  and  grass)  in  ponderosa  pine  forest  (Anderson 
1976).  In  Oregon,  White-breasteds  eat  larger  items  in 
pines  than  in  oaks  (Anderson  1976). 

Marin  Breeding  Distribution 

The  distribution  of  White-breasted  Nuthatches  in  Marin 
County  during  the  adas  period  reflected  the  distribution  of 
open  oak  woodland  to  the  northeast  around  Novato, 
where  the  birds  were  most  widespread  and  numerous,  and 
that  of  open  stands  of  mixed  evergreen  forests  on  Mount 
Tamalpais.  Representative  breeding  localities  were  Mt. 
Burdell,  Novato  (NY/FY  4/21/81  — ITi)  and  Olompali, 
Novato  (ON  6/?/82  -ScC). 

Historical  Trends/Population  Threats 

Early  accounts  stated  or  implied  that  the  White-breasted 
Nuthatch  was  "rare"  and  occurred  primarily  as  a  winter 
visitant  in  Marin  County,  and  a  breeding  record  at  Wood- 
acre  was  deemed  noteworthy  (Mailliard  1900,  G&.W 
1927,  SckP  1933,  G&M  1944).  Today  the  species  is  a 
fairly  widespread  and  numerous  breeder  in  Marin  County, 
but  it  is  probable  that  the  actual  status  has  not  changed 
much  over  the  years.  Mailliard  (1900)  stated  that  the 
species  was  "probably  resident  near  Sonoma  County  line, 
but  observers  appear  to  have  spent  little  if  any  time  in  that 
region  until  the  period  of  the  Marin  adas  project.  On  the 
whole,  White-breasted  Nuthatch  numbers  increased  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989, 
though  they  were  relatively  stable  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


297 


Nuthatches 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Nuthatches 


PYGMY  NUTHATCH   Sitta  pygmaea 


-i  .jrtr^^ 

A  year-round  resident. 

^r^p^Ap?^^^     \               rv 

A  fairly  common,  local  breeder;  overall 
breeding  population  very  small. 

S^\\  jfr\\  ^\\  ^-V"\  *>(r\  y<^\  y<\  jy 

£^L~  " 

Recorded  in  40  (18.1%)  of  221  blocks. 

^^^^\^^^\^v^0\^^ 

O    Possible        =       15   (38%) 

\^*y>&\\^ 

©    Probable       =       11    (28%) 

V-V\  •  \vvTuVf   V^T^^rC--V''  \  '^r\yi 

•    Confirmed  =      14  (35%) 

\  \.X'^*J£><&3k<^-'V'a    w^A    V"A 

Wa°V-"\« j<^\''  v^\    V-^-v-.  v-"V  W 

\      V>^^t    °" 

\fbV>T»jv-^»A^\^'V^\    a^v*  kv 

■\v^V^lj^" 

"T 

FSAR  =  3        OPI  =  120       CI  =  1.98 

L^^A^VVv^AcYvAoVir^X/^  \ 

*<n\       ~\^\ 

1  V^^TV  l  J«^\*J*^\*\^\  ^%^\<>jy<F 

^V/T\jp 

>W  J*VT    V^A • j?^^\^\^6^%^ 

"4*ki3ei^ — ^JkXx'jP^o  V-^a  »m^ 

\o  V-^\\  V, 

^£^§ 

\2& 

^TV 

)j^>                               XL°/ 

Ecological  Requirements 

The  Morse  code-like  calls  of  the  Pygmy  Nuthatch  are  a 
characteristic  sound  of  Marin  County's  bishop  pine  for- 
ests. Pygmy  Nuthatches  breed  here  secondarily  in  Douglas 
fir  and  redwood  forests  and  to  a  limited  degree  in  groves 
of  planted  pines  (particularly  Monterey  pine)  and 
cypresses.  They  typically  use  conifer  stands  with  relatively 
open  canopies,  branchwork,  and  foliage.  Since  they  gener- 
ally avoid  densely  foliaged,  closed-canopied  conifer  forests, 
they  occur  much  more  locally  here  in  Douglas  fir  and 
redwood  forests  than  in  bishop  pine. 

Pygmy  Nuthatches  are  notoriously  gregarious,  feeding  in 
flocks  when  not  nesting  and  congregating  in  large  commu- 
nal roosts  at  night  throughout  the  nonbreeding  season 
(Norris  1958,  Sydeman  <Sl  Guntert  1983).  Although  most 
birds  split  off  into  pairs  to  breed,  about  20%-30%  of  die 
nests  are  occupied  by  threesomes  (Norris  1958,  Sydeman 
et  al.  1988,  Sydeman  1989).  The  additional  helpers  at 
these  nests  are  males,  usually  yearlings,  and  often  the 
offspring  or  siblings  of  the  birds  they  aid.  The  second  male 
is  intimately  involved  in  the  nesting  effort  and  may  help  in 
nest  construction,  feeding  the  female  during  incubation 
and  brooding,  cleaning  the  nest,  and  feeding  nesdings  and 
fledglings;  he  also  roosts  in  the  nest  cavity  with  the  other 
birds. 

Like  our  other  nuthatches,  Pygmies  are  exclusively  cavity 
nesters.  They  may  use  natural  cavities,  excavate  their  own 
cavities,  or  modify  preexisting  ones  made  by  other  species 
(usually  woodpeckers)  or  by  conspecifics  (Bent  1948,  Nor- 
ris 1958,  McEllin  1979a);  exceptionally,  a  nest  may  be 

298 


"under  loose  bark  on  a  dead  tree"  (Bent  1948).  Cavities  are 
usually  located  in  the  trunks  of  snags,  in  lightning  strikes 
or  dead  branches  of  live  trees,  or,  occasionally,  in  the  partly 
dead  and  rotten  heartwood  of  a  living  tree  (Bent  1948, 
Norris  1958,  McEllin  1979a,  Hay  ck  Guntert  1983).  Nest 
trees  generally  are  in  the  stand  of  pines  where  the  birds 
forage.  Occasionally,  nest  cavities  are  in  an  adjacent  stand 
of  a  different  conifer  where  Pygmies  do  not  forage,  in 
isolated  trees  in  brushland  as  far  as  100  feet  from  mature 
conifer  stands,  or  in  stubs  standing  in  water  (Norris  1958). 
Although  Pygmies  most  often  choose  pines  for  their  nest 
cavities,  they  occasionally  locate  them  in  broadleaved  oaks 
(W.J.  Sydeman  pers.  comm.).  Norris  (1958)  reported  nest 
heights  of  coastal  birds  ranging  from  6  to  60  feet  (median 
25  ft.,  n  =  74),  and  those  of  interior  montane  birds  ranging 
from  3  to  100  feet  (median  22  ft.,  n  =  52).  Airola  (1980) 
reported  nest-hole  heights  in  Sierra  County  averaging  16 
feet  (range  7-30  ft.).  In  Colorado,  McEllin  (1979a) 
reported  heights  of  26  nests  ranging  from  12  to  57  feet 
(av.  35  ft.).  All  of  these  nests  had  limbs  near  the  cavity  (23 
below  the  entrance,  3  to  the  side)  that  birds  used  for 
perching  or  alighting  before  entering  the  nest.  The  nest 
openings  faced  south  or  east,  away  from  the  prevailing 
winds  and  rain  from  die  west  and  north.  In  Arizona,  Hay 
and  Guntert  (1983)  reported  the  height  often  nests  aver- 
aging 18  feet.  Compared  with  roost  cavities  used  in  any 
season,  nesting  cavities  there  were  lower  in  shorter  trees. 
Nest  cavities  and  winter  roost  cavities  had  smaller 
entrances  and  were  predominandy  in  trunks  compared 


Nuthatches 


SPECIES  ACCOUNTS 


Nuthatches 


with  summer  and  fall/spring  roost  cavities,  which  were 
situated  about  equally  in  trunks  or  branches.  Placement  of 
nest  cavities  lower  in  shorter  and  smaller-diameter  trees 
may  represent  a  response  to  wind.  Generally  the  nest 
cavities  are  positioned  to  obtain  a  moderate  angle  of 
insolation,  face  east  to  receive  morning  sunlight,  and  are 
protected  from  prevailing  westerly  winds. 

Pygmy  Nuthatches  line  their  nest  cavities  with  materials 
with  good  insulative  qualities.  The  materials  they  use  most 
frequendy  are  feathers,  bark  shreds  or  fibers,  moss,  fur, 
hair,  and  wool  (Norris  1958).  Snakeskin,  plant  down, 
cotton  or  cottony  substances,  string,  grass  blades,  bits  of 
cloth,  lichen,  cocoon  fibers,  papery  material  from  yellow- 
jacket  nests,  and  miscellaneous  soft  materials  are  used  less 
often;  decayed  wood  or  wood  chips  are  used  to  an 
unknown  degree.  Pygmies  may  add  materials  to  die  lining 
well  into  the  egg-laying  period,  and  perhaps  throughout  it. 
They  may  use  nest  cavities  in  successive  years  (Norris 
1958,  McEllin  1979a,  W.J.  Sydeman  pers.  comm.). 

Pygmy  Nuthatches  are  more  likely  to  be  heard  than  seen 
as  they  forage  in  boisterous  groups  of  5  to  15  birds,  mosdy 
in  the  upper  half  of  live  pines  in  peripheral  branches  and 
foliage,  including  needle  clusters,  cones,  and  young  shoots 
(Norris  1958,  Stallcup  1968,  Bock  1969,  Manolis  1977, 
McEllin  1 979b).  To  a  lesser  extent,  and  more  frequendy 
outside  the  breeding  season,  they  forage  on  larger  inner 
branches  and  the  trunk  (Stallcup  1968,  Manolis  1977). 
Minor  foraging  substrates  include  dead  branches,  trees, 
stumps,  and  logs;  branches  and  foliage  of  live  broadleaved 
trees  or  shrubs  are  used  more  often  during  the  breeding 
season  (Stallcup  1968).  The  range  of  foraging  heights 
increases  during  the  nonbreeding  season  (Manolis  1977, 
McEllin  1979b).  Ground  foraging  varies  seasonally 
(Manolis  1977,  Stallcup  1968),  apparently  depending 
upon  the  availability  of  seeds  in  opened  cones  that  have 
fallen  singly  or  on  limbs  or  boughs;  seeds  are  also  obtained 
from  cones  in  the  tree  crown.  In  ponderosa  pine  forest  in 
Arizona,  Pygmies  exhibit  annual  variation  in  foraging  tech- 
niques and  other  resource-use  measures  (Szaro  et  al.  1990). 

Pygmy  Nuthatches  forage  mosdy  by  probing  the  basal 
portions  of  pine  needle  clusters,  pine  cones,  twigs,  and 
small  branches  (Norris  1958,  McEllin  1979b).  To  a  lesser 
extent,  they  forage  by  peering  and  poking,  probing  fissures 
in  bark,  scaling  or  flaking  off  bark,  and  by  hovering  or 
flycatching.  Like  other  nuthatches,  they  are  adept  at  hitch- 
ing along  branches  and  limbs  in  any  plane  while  searching 
for  prey.  They  cache  seeds  in  crevices  or  under  flakes  of 
bark  on  the  trunk  or  branches  of  trees.  To  open  the  seeds, 
Pygmies  wedge  them  in  a  crack  or  crevice  on  a  horizontal 
branch  and  hammer  them  vigorously.  Rarely,  insects 
caught  by  flycatching  are  also  cached  under  bark  (Sealy 
1984).  Since  food  caching  is  energetically  cosdy,  it  is  most 


appropriate  when  a  food  resource  is  available  periodically 
and/or  unpredictably  and  is  stimulated  when  food  is  in 
excess  and  can  be  stored  for  times  of  need. 

Over  much  of  their  range,  though  not  in  Marin  County, 
Pygmy  Nuthatches  overlap  broadly  in  habitat  use  (but  not 
foraging  strategies)  with  White-breasted  Nuthatches  (Stall- 
cup 1968,  Bock  1969,  McEllin  1979b;  see  White-breasted 
account).  White-breasteds  complement  their  specialization 
in  foraging  substrates  by  generalizing  in  their  feeding 
behavior  and  in  the  food  items  they  take  (McEllin  1979b). 
Pygmies,  on  the  other  hand,  are  generalists  regarding 
foraging  substrates  but  specialists  in  feeding  behavior  and 
food  items  taken,  though  they  specialize  less  in  the  non- 
breeding  season.  These  patterns  suggest  that  White-breast- 
eds forage  for  evenly  distributed  food  items,  whereas 
Pygmies  forage  for  patchy  ones.  Anderson  (1976)  also 
noted  that  Pygmies  selected  food  from  only  a  few  taxa  in 
the  breeding  season  although  many  forms  were  available. 
See  Bock  (1969)  and  Manolis  (1977)  for  comparison  of 
foraging  strategy  widi  Mountain  Chickadee. 

Based  on  31  stomachs,  Beal  (1907)  reported  that  the 
diet  of  Pygmy  Nuthatches  in  California  was  83%  animal 
matter  and  17%  conifer  seeds.  Norris  (1958)  felt  Beal's 
samples  were  probably  taken  mosdy  in  late  spring  or  early 
summer,  thus  overestimating  the  animal  proportion  of  the 
diet.  Norris  (1958)  examined  73  stomachs  taken  through- 
out the  year  in  Marin  County  and  found  that  pine  seeds 
made  up  65%  of  the  diet  overall.  May  was  the  only  month 
in  which  animal  food  exceeded  70%,  and  the  April-to-july 
diet  (weighted  by  month)  averaged  about  57%  animal 
matter.  In  Marin  County,  from  October  to  at  least  January, 
the  monthly  diet  ranged  from  86%  to  99%  pine  seeds. 
However,  a  late-December  sample  (n  =  8)  from  Howell 
Mountain,  Napa  County,  averaged  61%  animal  matter.  In 
Oregon,  the  winter  diet  in  ponderosa  pine  was  96% 
animal  matter  and  4%  seeds;  the  use  of  bark-dwelling 
insects  increased  there  in  winter  (Anderson  1976).  On  the 
whole,  Pygmies'  main  animal  prey  are  wasps,  ants,  true 
bugs,  spitdebugs,  beedes,  caterpillars,  crickets,  and  spiders. 
Norris  (1958)  noted  a  much  greater  reliance  on  beedes  and 
less  reliance  on  hymenoptera  than  did  Beal  (1907).  Adults 
foraging  for  young  rarely  travel  more  than  400  feet  (av.  1 70 
ft.)  from  the  nest,  with  the  average  distance  traveled  varying 
inversely  with  the  density  of  the  forest  (Norris  1958). 
Adults  initially  feed  young  nesdings  tiny  insects  and  spi- 
ders, but  later,  as  they  grow,  adults  feed  them  larger  items. 
After  removing  the  hard  integument,  adults  sometimes 
feed  pine  seeds  to  well-developed  nesdings.  When  young 
first  fledge,  they  tend  to  remain  high  in  pines,  and  adults 
forage  largely  then  in  the  topmost  branches  and  foliage.  As 
the  young  mature,  they  often  descend  to  the  lower  strata 
and  are  prone  to  visit  open  cones  on  fallen  pines.  Vegeta- 
ble food  is  nearly  as  important  to  juveniles  as  it  is  to  adults. 


299 


Nuthatches 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Nuthatches 


Marin  Breeding  Distribution 

The  distribution  of  Pygmy  Nuthatches  in  Marin  County 
during  the  adas  period  reflected  the  distribution  of  open 
conifer  stands  on  Inverness  Ridge  (the  species'  strong- 
hold), Bolinas  Ridge,  and  Mount  Tamalpais.  The  distribu- 
tion of  Pygmy  Nuthatches  was  similar  to  that  of 
Red-breasteds,  except  the  latter  were  absent  in  die  bishop 
pines  on  the  north  end  of  Inverness  Ridge,  whereas  the 
former  were  less  widely  distributed  east  of  Bolinas  Ridge 
in  the  Lucas  Valley  area,  where  dense  conifer  stands  in 
narrow  canyons  are  more  prevalent.  Representative  nesting 


locations  of  Pygmy  Nuthatches  were  near  Tomales  Bay  SP 
(NY/FY  6/1 4/82  — DS;  diis  cavity  was  shared  with  a  pair 
of  Starlings!);  Tomales  Bay  SP  (NB  4/1 3/77  -RMS);  and 
Vedanta  Trail,  Olema  Valley  (ON  4/24/82  -JGE). 

Historical  Trends/Population  Threats 

Few  prior  data  exist.  Pygmy  Nuthatch  numbers  appeared 
to  increase  slightly  on  Breeding  Bird  Surveys  in  California 
from  1968  to  1989  but  were  relatively  stable  from  1980  to 
1989  (USFWS  unpubl.  analyses). 


Its  sturdy  long  toes  and  stiff  tail  feathers  enable  the  Brown  Creeper  to  cling  effortlessly  to  its  coarse-grained  domain. 

Photograph  fry  Ian  Tatt. 


300 


Creepers 


SPECIES  ACCOUNTS 


Creepers 


Creepers 

Family  Certhiidae 


BROWN  CREEPER    Certhia  americana 


A  year-round  resident. 

r^r~2e^          ^                   .JCS 

A  common,  widespread  breeder;  over- 

ly^K^: 

\^fPt>>Vr^ol>\ 

all  breeding  population  fairly  large. 

Recorded  in  128  (57.9%)  of  221 

blocks. 

^>\*%<' 

O    Possible        =      42   (33%) 

\\\ 

r^S^PC^^^^ 

C    Probable              42  (33%) 

\  o  xX^-vr^srAT  © V'TotP'a*  Y^a    V^\  ' \^\  o ^ 

•    Confirmed  =       44   (34%) 

V"A  •  Ji^X  *>Jr^\  9rs^\' ©  Jr^-V«  JV>A  -i^V-Qj\ 

"v.- 'A-^\ •  y?~\ .♦jk>v» a^a •  v^a   >^v ° v^^s — 

-•-r* 

■JJrx  °-V^^"*  J^>-®A-^v#  \^i\  ©  \-^A  ©  vx^-v-i  J-' 

-;  \  V7Y  I  .V^A  ©Jr^\  ©-V"A  0\^\  ©  i^<l\.  ©  >^\  Q.  \ — S 

FSAR  =  4       OPI  =  512        CI  =  2.02 

Jr^^VJr^X     Y^cJp\»\^^yO^^^\*\^\   h 

■  "4^2*^ — ^SL>^»  V<\  ©  \^\  t>3^\*  \^\  ■  V< 

v?& 

"■J>r                          \^\  •  V^r^j^^%\^^°'->^» 

<r            x-^#^^?Vov!V\^as 

j3s=                                        \L*/         ^^^^^Vx^ 

Ecological  Requirements 

These  bark  brethren  inhabit  Marin  County's  moist,  well- 
shaded,  closed-canopied  forests  that  provide  moderate  to 
large  trunks  and  limbs  for  foraging.  Breeding  Creepers  are 
particularly  at  home  here  in  redwood,  Douglas  fir,  bishop 
pine,  mixed  conifer  hardwoods,  and  broadleaved  ever- 
green forests;  in  the  broadleaved  evergreen  realm,  Califor- 
nia bay  laurels  are  important.  To  a  limited  extent,  Creepers 
also  frequent  groves  of  planted  cypresses  and  pines,  and 
sometimes  even  eucalyptus.  Creepers  almost  invariably 
place  their  nests  in  the  cavities  created  by  the  bark  separat- 
ing from  trees.  Rarely,  they  locate  them  in  knotholes, 
deserted  woodpecker  holes,  on  the  tips  of  decaying  stubs, 
or  behind  the  shutters  of  a  cabin  (Tyler  1948c,  Bent  1948). 
They  situate  nests  in  a  variety  of  coniferous  and  deciduous 
trees  but  prefer  dead  or  dying  individuals  or  loose-barked 
species.  Nests  heights  range  from  1  to  60  feet,  but  most  are 
less  than  20  feet  above  the  ground  (Bent  1948,  Davis  1978, 
Airola  1980).  Airola  (1980)  reported  that  nest  sites  in  the 
Sierra  Nevada  average  7  feet  (range  1-21  ft.),  whereas 
Davis  (1978)  reported  that  nest  heights  in  Michigan  aver- 
age 10  feet  (range  5-23  ft.,  n  =  20).  In  Michigan,  openings 
in  the  canopy  permit  light  penetration  to  each  nest  site. 
The  nest  conforms  to  the  shape  of  the  cavity  and   is 


attached  to  the  rough  bark  (not  the  tree)  with  spider  web 
cases  and  insect  cocoons.  The  base,  made  of  twigs  and 
pieces  of  bark,  is  a  hammock-  or  crescent-shaped  structure 
that  extends  up  on  the  sides  in  long  narrow  points  or 
"horns"  several  inches  above  a  centrally  located  nest  cup. 
The  cup  is  made  of  fine  bark  and  wood  fibers  with  lesser 
amounts  of  moss,  feathers,  or  plant  down. 

Foraging  Creepers  procure  most  of  their  food  by  glean- 
ing from  die  surface  and  by  probing  or  pecking  crevices, 
cracks,  and  fissures  of  the  bark  with  their  fine,  slighdy 
decurved  beaks  (Airola  &  Barrett  1985,  Franzreb  1985, 
Morrison  et  al.  1987,  Lundquist  &  Manuwal  1990).  They 
very  rarely  hover-glean  or  hawk  insects.  Creepers  use  three 
basic  patterns  to  scour  bark  surfaces  while  foraging 
(Franzreb  1985).  They  climb/hitch  straight  up  trunks, 
carefully  detouring  around  branches.  They  may  also  work 
up  the  trunk,  then  climb  out  branches  clinging  to  the 
undersurface  upside  down.  They  then  fly  to  the  top  of  the 
branch,  work  their  way  back  along  the  top  of  it  to  the  trunk, 
and  repeat  the  process  as  they  advance  up  the  tree.  In 
addition,  they  may  spiral  around  the  trunk  and  branches 
as  they  move  upward.  Regardless  of  the  method  of  upward 
movement,  all  birds  generally  work  to  within  about  3  to  10 

301 


Creepers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Creepers 


feet  of  the  treetop.  Then  they  fly  to  the  base  of  a  trunk  of 
another  tree,  generally  to  within  a  few  feet  of  the  ground, 
and  begin  again  their  search  for  prey.  Creepers  tend  to 
change  trees  when  they  reach  a  height  where  branch 
density  increases  to  such  a  degree  that  maneuverability  is 
impaired. 

Birds  prefer  large  trees  for  feeding  because  they  have 
more  foraging  surface  and  tend  to  have  bark  with  deeper 
and  more  numerous  crevices  for  harboring  prey.  Foraging 
Creepers  generally  select  more  for  tree  height  than  for  tree 
species  (Airola  6k  Barrett  1985,  Franzreb  1985,  Lundquist 
6k  Manuwal  1990).  See  Morrison  et  al.  (1985,  1987)  for 
seasonal  changes  in  preferences  for  foraging  on  various 
conifers  in  the  Sierra  Nevada.  Creepers  forage  almost 
exclusively  on  trunks  and  branches  and  only  rarely  on  logs 
or  the  ground  (Airola  6k  Barrett  1985;  Franzreb  1985; 
Morrison  et  al.  1985,  1987).  Breeding  birds  choose  trunks 
as  their  foraging  substrate  about  70%-90%  of  the  time 
(Franzreb  1985;  Morrison  et  al.  1985,  1987;  Lundquist  6k 
Manuwal  1990).  In  the  Sierra  Nevada,  birds  increase 
trunk  use  from  about  80%  in  summer  to  over  95%  in 
winter  (Morrison  et  al.  1985).  In  the  Washington  Cas- 
cades, by  contrast,  Creepers  reduce  trunk  foraging  from 
about  90%  in  spring  to  70%  in  winter  (Lundquist  6k 
Manuwal  1990).  Airola  and  Barrett  (1985)  considered  the 
Brown  Creeper  a  medium-height  forager  in  comparison  to 
other  insect-gleaning  (mosdy  on  foliage)  birds  in  the  Sierra 
Nevada.  Working  in  the  same  forest,  however,  Morrison 
et  al.  (1987)  found  that  Creepers  foraged  significandy 
lower  than  other  bark  gleaners.  These  differences  probably 
reflect  the  wide  range  of  heights  at  which  Creepers  forage, 
rather  than  a  preference  by  the  birds  to  forage  low  in  trees. 
As  noted  above,  Creepers  forage  where  there  are  large, 
exposed  bark  surfaces,  and  by  nature  these  tend  to  be 
distributed  more  on  the  lower  trunks  but  can  also  occur  at 
considerable  heights  in  large  trees.  Creepers  vary  little 
seasonally  or  geographically  in  their  prey  capture  methods 
(Lundquist  6k  Manuwal  1 990,  Petit  et  al.  1 990),  or  in  their 
choice  of  spatial  (horizontal  or  vertical)  aspects  of  foraging 
locations  (Lundquist  6k  Manuwal  1990).  Creepers  forage 
predominandy  on  live  trees  (Airola  6k  Barrett  1985,  Mor- 
rison et  al.   1987).   In  Arizona,  Franzreb  (1985)  found 


Creepers  feeding  on  snags  slightly  more  than  would  be 
predicted  by  their  availability  in  the  forest  (Franzreb  1985). 
In  Washington,  Creepers  use  live  and  dead  trees  in  pro- 
portion to  their  availability,  regardless  of  season  or  forest 
age  (Lundquist  6k  Manuwal  1990). 

What  little  is  known  of  the  Creeper  diet  indicates  it  is 
largely  beedes,  wasps,  ants,  tme  bugs,  moths,  caterpillars, 
spiders,  pseudoscorpions,  flies,  and  a  few  seeds  (Beal 
1907,  Martin  et  al.  1951,  Davis  1978,  Dahlsten  et  al. 
1985,  Otvos  6k  Stark  1985).  Spiders  may  be  an  important 
Creeper  food.  In  the  Washington  Cascades,  spiders  were 
found  in  all  (n  =  6)  Creeper  digestive  tracts  examined 
(Mariani  6k  Manuwal  1990).  Creeper  abundance  there 
was  correlated  positively  with  large  Douglas  fir  trees 
(known  for  deeply  furrowed  bark)  and  the  abundance  of 
medium-size  spiders.  Spiders  (all  sizes)  and  soft-bodied 
arthropods  were  positively  associated  with  bark  furrow 
depth,  which  in  turn  was  highly  correlated  with  tree  diame- 
ter. 

Marin  Breeding  Distribution 

The  distribution  of  breeding  Creepers  in  Marin  County 
during  the  adas  period  mirrored  that  of  closed-canopied 
forests  here.  Creepers  were  most  numerous  and  wide- 
spread in  the  forests  in  the  fog  zone  of  the  immediate 
coastal  ridges.  In  the  northern  interior,  they  were  patchily 
distributed  in  narrow  canyons  or  on  north-facing  slopes. 
Representative  breeding  locations  were  Upper  Pierce 
Ranch  cypress  grove,  Tomales  Point  (FY/NY  6/15/82 
-DS);  Mt.  Burdell,  Novate  (NY/FY  5/25/81  -ScC,  DS); 
and  Cascade  Canyon,  Fairfax  (NY/FY  5/11/81  -DS). 

Historical  Trends/Population  Threats 

Grinnell  and  Miller  (1944)  suspected  that  removal  of 
old-growth  forests  had  reduced  the  California  population, 
particularly  in  the  interior  mountains.  This  likely  also 
occurred  at  one  point  in  the  coastal  region.  Creeper  popu- 
lations did  decrease  in  the  Sierra-Trinity  mountains  of 
California  during  the  period  1 968  to  1 979  (Robbins  et  al. 
1 986)  but  showed  no  trend  for  California  as  a  whole  from 
1968  to  1989  (USFWS  unpubl.  analyses). 


302 


Wrens 


SPECIES  ACCOUNTS 


Wrens 


Wrens 

Family  Troglodytidae 


ROCK  WREN    Salpinxes  obsoletus 


_(      0*^1 

A  year-round  resident. 

/luAn 

^>s^^    \ 

An  uncommon,  very  local  breeder; 
overall  breeding  population  very  small. 

^^Vv 

." 

Recorded  in  15  (6.8%)  of  221  blocks. 
O    Possible        =       11    (73%) 

v-^^3^ 

0^C\ ~->%^\  \^\ 

©    Probable       =         4   (27%) 

V? 

^-V^a^- 

•    Confirmed  =         0   (0%) 

--V\^-W\S- 

JpV 

^5<^ 

-<■ 

FSAR  =  2         OPI  =  30         CI  =1.27 

js^fv^f\\^ 

^^ 

\3A  o*- 

^?0 

JL 

=s*u^oY 

Ecological  Requirements 

This  spritely  bouncy  wren  usually  breeds  in  relatively 
barren  rocky  substrates,  though  in  some  regions,  arroyos 
of  hard  sun-baked  earth  provide  alternative  habitat. 
Migrants  and  wintering  birds  may  pause  at  small  rock 
tumbles,  cutbanks,  or  even  at  woodpiles  or  among  the 
roots  of  upturned  trees.  Breeding  birds,  however,  generally 
need  a  fair  extent  of  broken  or  fractured  rock  or  burrowed 
earth  with  numerous  crannies  and  crevices  for  foraging 
and  nesting  sites.  Rock  Wrens  flourish  over  a  wide  range 
of  altitude,  humidity,  and  temperature,  factors  that  appear 
to  have  little  overall  influence  on  habitat  selection  in  this 
species  (G&M  1944).  The  broad  tolerances  of  Rock 
Wrens  are  not  matched  by  their  cousins,  Canyon  Wrens. 
Where  they  overlap  (not  in  Marin),  these  species  are 
separated  by  slope  and  microclimate  preferences.  In  Ari- 
zona, Tramontano  (1 964)  found  that  where  the  two  species 
breed  sympatrically,  Rock  Wrens  inhabit  slopes  of  loose 
rock  and  scattered  boulders  whereas  Canyon  Wrens  fre- 
quent precipitous  outcroppings,  cliffs,  and  canyon  walls. 
Rock  Wrens  there  choose  nest  sites  on  rocky  slopes  of  any 
orientation  except  north  facing,  whereas  Canyon  Wrens 
choose  nest  sites  invariably  along  north-,  northwest-,  or 


west-facing  cliffs.  In  essence,  Rock  Wrens  prefer  more 
open,  sunny  exposures,  Canyon  Wrens  cooler  shaded 
ones. 

Marin  County  is  rather  meagerly  endowed  with  rocky 
cliffs  or  boulder  piles  and  entirely  wanting  in  inland  talus 
slopes  and  lava  flows.  The  few  Rock  Wrens  that  breed  here 
inhabit  coastal  sea  cliffs  of  Monterey  shale  and  conglomer- 
ate and  the  odd  quarry  or  serpentine  outcrop.  Although 
our  sea  cliffs  are  of  wide  extent,  they  provide  few  gende  or 
moderate  slopes  and  are  poorly  outfitted  with  boulders, 
nooks,  and  crannies. 

Rock  Wrens  usually  place  their  nests  inside  cavities  and 
small  crevices  among  or  under  rocks,  or  in  natural  or 
rodent-excavated  holes  in  earthen  cutbanks.  Less  com- 
monly, they  build  them  in  human  structures,  such  as 
adobe  walls  of  buildings  or  old  stone  reservoirs;  in  some 
areas,  they  even  use  fallen  tree  trunks  (Dawson  1923,  Bent 
1948).  The  nest  entrance  is  almost  invariably  paved  with  a 
runway  of  small  flat  stones,  rock  flakes,  or  pebbles  (or, 
infrequently,  similar  human  debris).  The  same  materials 
underlie  or  are  incorporated  into  the  nest  itself.  The 
function  of  the  paving  is  unknown,  but  it  may  aid  in 

303 


Wrens 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wrens 


preventing  dampness  inside  the  nest  (Bent  1948).  Alterna- 
tively, perhaps  the  rattling  of  the  stones  by  a  potential 
predator  attracts  the  attention  of  the  sitting  bird  and  serves 
as  a  burglar  alarm  of  sorts  (Dawson  1923)!  Rock  Wrens 
sometimes  use  nest  sites  for  successive  broods 
(Tramontano  1964).  The  nest  is  a  shallow  saucer  made  of 
twigs,  grasses,  straw,  weed  stems,  and  roodets.  It  is  some- 
times scantily  lined  with  fine  grasses,  bark  strips,  roodets, 
horsehair,  sheep's  wool,  or  perhaps  a  few  feathers. 

While  foraging,  Rock  Wrens  run  with  ease  over  open 
or  broken  rocky  terrain,  gleaning  from  the  surface  or 
probing  cracks  and  crevices.  They  seldom  hop  or  creep 
while  foraging  as  Canyon  Wrens  commonly  do 
(Tramontano  1964).  Rock  Wrens  also  occasionally  fly- 
catch  for  insects,  especially  when  breeding,  and  sometimes 
take  aquatic  insects  from  small  pools  of  water.  Rock  Wrens 
spend  nearly  90%  of  their  foraging  time  in  open  or 
relatively  uncovered  situations.  In  contrast,  Canyon  Wrens 
spend  70%  of  their  time  foraging  in  relatively  covered  or 
secluded  microclimates,  for  which  their  relatively  longer, 
more  slender  bills  and  shorter  tarsi  are  better  suited.  Rock 
Wrens  commonly  forage  over  rocky  hillsides,  open  slopes, 
dry  washes,  and  riverbeds,  but  only  rarely  along  crevices  of 
cliffs  or  steep  canyon  walls.  They  spend  about  70%  of  their 
foraging  time  during  breeding  on  south-,  southeast-,  or 
east-facing  slopes.  Breeding  Canyon  Wrens,  on  the  other 
hand,  are  adapted  to  forage  along  steep  but  relatively  cool 
exposed  slopes.  They  spend  about  60%-85%  of  their  time 
foraging  on  cliffs  or  canyon  walls  and  about  90%-95%  of 
their  time  on  north-,  northwest-,  or  west-facing  slopes. 
During  breeding,  males  of  both  species  feed  the  females  at 
the  nest. 


The  Rock  Wren  diet  consists  of  a  variety  of  primarily 
ground-dwelling  insects  in  the  0.1-  to  0.5-inch  size  range 
plus  small  amounts  of  seeds  and  other  plant  material 
(Tramontano  1964).  The  main  animal  fare  is  beedes, 
leafhoppers,  ants,  ant  lions,  moths  and  their  larvae,  true 
bugs,  grasshoppers,  and  spiders. 

Marin  Breeding  Distribution 

Although  recorded  at  scattered  sites,  Rock  Wrens  were  not 
confirmed  breeding  in  Marin  County  during  the  adas 
period.  The  only  known  confirmed  breeding  record  for 
Marin  is  of  a  nest  with  young  discovered  at  Tiburon  on  29 
April  1933  (SckP  1933).  Areas  in  Marin  County  where 
Rock  Wrens  were  seen  consistendy  in  the  breeding  season 
were  die  Point  Reyes  headlands  near  the  lighthouse  (T 
4/30-7/1/81  -DS);  the  Double  Point  cliffs  (T  Mar-Jun 
1978  &  1979  — SGA);  and  a  quarry  near  Larkspur  Land- 
ing (T  spring  1982  — SSm). 

Historical  Trends/  Population  Threats 

Historically,  breeding  Rock  Wrens  have  always  occurred  in 
limited  numbers  in  Marin  County,  with  most  residing 
along  ocean  cliffs  (Mailliard  1900,  SckP  1933).  The  exca- 
vation of  quarries  in  Marin  may  have  slightly  increased  the 
number  of  breeding  stations  here.  Rock  Wrens  have 
declined  historically  as  breeders  on  the  nearby  Farallon 
Islands,  though  this  appears  to  be  a  local  phenomenon, 
perhaps  attributable  to  predation  by  a  'rebounding  West- 
ern Gull  population  (DeSante  ck  Ainley  1980).  An 
increase  of  Rock  Wrens  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1979  (Robbins  et  al.  1986)  was 
not  evident  for  the  period  1968  to  1989  (USFWS  unpubl. 
analyses). 


304 


Wrens 


SPECIES  ACCOUNTS 


Wrens 


BEWICK'S  WREN    Thryomanes  beiuickii 


A  year-round  resident. 

y\©A^A,  j^^KlZk-^                         ^A\jt>Ai_^ 

A  common,  nearly  ubiquitous  breeder; 
overall  breeding  population  very  large. 

^^v-a^a^a A^c3eRWnY«,A2^3^A°3A^  - 

Recorded  in  205  (92.8%)  of  221 

blocks. 

VS©^^c\  ©  3r<\  •  Ji^X  ®3t^\  ,*  A^Mfl*  A^A©  A><\  *-4 

\  ^^\  ^>^\  •  a^a  ©Jv^a  *\^\  oT>^\  •  v>-a  ®Sv^\ 

^^©:><^©A-^§A>\®A-'v©  V^A©  A-"A  ©\^\  ©A 
V<«x><a\  ®3ri\  ^A^X  ©  a^a  ©  A-^x  •  A^\  •  ir^M. 

O    Possible        =        9   (4%) 

VA^©  A<y^  V"A  ©  A^^S^A  ©  A^"\  ©  V-"A  AV^A©^?^ 
\  VV^\©v\  iA\  ©  A-^\  *  -£&£&•  V^-©  A>^"©"A-AA  ©  A^"-    ; 

C    Probable       =     131    (64%) 

VAA  ©  A%^-CA?<_\  ©  \^\*\^\&  v--^\  ©  A^A  "^Jk^^A  *r^ 

VAff*  V-'A  •Af'A •  v^A  ©  W-A^A^A*  A^A  •  ^r(  " 

©    Confirmed  =      65  (32%) 

\  r»V^A  *  A^A  ©  APA  ©AA^a    A-^A*  A^A-fiA^A  "©^A 

VpiepYe  A^Ty*- A^A^PA^A •  A^A  •  A^V©  ViT^? — 

-  'T 

T  «'3PA  ©  A^^A^v©A-^©  A=c\  •  A^A  •  A^V-Jtr-^ 

l^A\©iV^r\  •  A-<A °J^A ©  >"ffiv®  A-""A  © A-$\  •  AaJA— 
-a  ^y?A/®  Y^-A  ©  V-'A  ©A>A  #^--a  ©  L*rtv»  v^A  ©.  \ — s 

FSAR  =  4       OPI  =  820        CI  =  2.20 

Z*<\(    vJiTi  ©  v^\  °  v-^jB  v^A3**^^  «  v--A  ©  WA  • 

^-^jk^BSa — i©A^^\©A>^A  ©  V-^A  ©a^v-^A^A  •  V< 
^^•A?^    ^^<©  A^A  ©V>\  »  A>-*A  ©  A<r\  •  A%^ 
<XvJ^                   ^~"<T  •  V-'A©  V^^^AA^A  ©A-^A  »CL 

^ 

"■Jr                          n^^o\>^v»V^^aJ^©a>^, 

--V-T                                       VfAAiV  ©AP^a? a7i\  ©  A^A  ©3? 

ju          ^Hr^&%p 

Ecological  Requirements 

The  boisterous  song  and  petulant  scolding  calls  of  the 
Bewick's  Wren  are  heard  much  more  frequently  than  the 
bird  is  seen  as  it  scurries  through  the  underbrush  of  a  wide 
variety  of  Marin  County  habitats.  The  Bewick's  Wren 
generally  occupies  an  intermediate  position  on  the  local 
habitat  scale  between  the  Winter  Wren,  which  favors  thick 
tangly  growth  under  dense  forests  close  to  permanent 
creeks,  and  the  House  Wren,  which  dwells  here  in  open 
woodlands  with  little  or  no  understory.  The  strongholds  of 
the  Bewick's  Wren  in  this  region  are  the  coastal  scrub-  and 
chaparral-covered  hillsides.  It  also  breeds  commonly  in 
riparian  thickets;  along  the  brushy  margins  of  oak  wood- 
lands, mixed  evergreen  forests,  and  conifer  forests;  and  in 
hedgerows  and  suburban  plantings,  including  eucalyptus. 
Although  Bewick's  Wrens  frequently  use  a  mixture  of  trees 
and  shrubs  in  these  habitats,  all  they  need  is  a  moderately 
dense  brush  layer  with  some  openings,  as  evidenced  by 
their  abundance  in  pure  stands  of  coastal  scrub  and  chap- 
arral. In  fact,  they  avoid  a  dense  overstory,  because  light 
penetration  to  the  shrub  layer  and  ground  is  essential.  In 
Oregon,  territories  of  Bewick's  and  House  wrens  may 
overlap,  although  the  species  have  distincdy  different  habi- 
tat preferences  (Kroodsma  1973).  There  (as  in  Marin) 
Bewick's  Wrens  prefer  a  fairly  dense  understory,  whereas 
House  Wrens  prefer  an  open  one,  and  the  two  species 
coexist  in  heterogeneous  habitat  where  patches  suitable  to 
each  intermingle.  In  parts  of  coastal  California,  House 
Wrens  sometimes  defend  territories  that  exclude  Bewick's 
Wrens  (Root  1969a).  This  is  probably  an  infrequent  occur- 


rence, since  habitat  preferences  alone  usually  separate 
these  birds,  except  at  edges  of  oak  woodlands  and  some 
riparian  woodlands. 

Bewick's  Wrens  locate  their  nests  from  ground  level  to 
about  25  feet,  though  most  are  below  6  feet  (Bent  1948). 
They  are  almost  exclusively  cavity  nesters,  but  the  variety  of 
sites  they  use  is  somewhat  astonishing  (Bent  1948).  Com- 
mon nest  sites  are  natural  cavities  in  trees  or  stumps,  holes 
in  the  ground  or  in  low-cut  banks,  old  woodpecker  holes, 
the  centers  of  dense  clumps  of  brush,  and  spaces  under  the 
upturned  roots  of  fallen  trees.  Less  frequendy  used,  and 
presumably  less  available,  are  sites  under  the  peeled  bark 
of  a  tree,  in  rock  piles  or  cliff  cavities,  in  bird  boxes,  at  the 
mouths  of  Rough-winged  Swallow  burrows,  or  in  old  nests 
of  birds  such  as  orioles  and  mockingbirds.  Bewick's 
Wrens  also  commonly  use  "artificial"  sites  in  inhabited 
areas.  These  include  deserted  automobiles,  cow  skulls  in 
pastures,  tin  cans,  discarded  cardboard  cartons  on  the 
ground,  the  pockets  of  jackets  hung  on  a  wall,  and  inside 
the  walls  of  a  trailer  (to  name  but  a  few).  The  nest  itself  is 
generally  a  bulky  open  cup  conforming  to  the  size  of  the 
cavity.  Occasionally,  if  placed  in  a  situation  without  a 
complete  obstruction  on  all  sides,  nests  are  domed  or 
arched  over  at  the  top,  with  a  side  entrance  (E.V.  Miller 
1941).  Nest  materials  include  sticks  and  twigs,  straw, 
coarse  feathers,  fine  bark,  weed  stems,  rootlets,  moss,  dead 
leaves,  string,  and  other  debris.  The  wrens  mat  these 
together  with  spider  webs  and  cocoons  and  line  the  nests 
with  fur,  soft  feathers,  hair,  wool,  or  cotton  (E.V.  Miller 
1941,  Bent  1948). 

305 


Wrens 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wrens 


In  various  habitats  in  the  Berkeley  area,  Bewick's  Wrens 
forage  from  the  ground  to  the  tops  of  lofty  trees,  though 
mostly  at  the  lower  levels  (E.V.  Miller  1941).  They  gather 
most  food  there  by  gleaning  and  probing  while  hopping 
and  flitting  among  the  dense  branches,  limbs,  and  foliage 
of  weeds,  bnish,  and  trees.  They  sometimes  venture  more 
into  the  open,  clinging  to  tree  trunks  or  die  underside  of 
branches.  These  wrens  will  also  drop  to  the  ground  to  pick 
from  the  surface  or  overturn  leaves  with  their  bill,  but  they 
do  not  scratch  the  litter  or  soil  with  their  feet.  On  occasion, 
Bewick's  Wrens  will  fly  direcdy  to,  or  flutter  underneath, 
a  branch  to  pick  insects  from  it  while  airborne.  In  the  early 
spring,  the  sexes  seem  to  split  the  foraging  niche  in  mixed 
habitat:  males  feed  up  in  the  trees,  whereas  females  work 
within  a  foot  or  two  of  the  ground  (E.V.  Miller  1941). 

In  oak  woodlands  in  Arizona,  Bewick's  Wrens  forage  in 
the  lower  strata,  mosdy  by  probing  and  gleaning  from 
branches,  twigs,  trunks,  and  leaves  on  the  ground;  rarely, 
they  hawk  or  hover  (Miles  1990).  Over  two  years  of  study, 
probing  represented  77%-82%  of  foraging  attempts  in 
May  and  June  and  35%-46%  in  July;  gleaning  varied  from 
1 7%  to  1 8%  and  from  54%  to  64%  of  foraging  attempts 
in  the  corresponding  periods.  Gleaning  not  only  increased 
in  July,  but  also  shifted  gready  then  to  the  ground,  presum- 
ably in  response  to  the  flush  of  annual  plant  growth  (and 
insects)  following  summer  rains.  Bewick's  Wrens  there 
also  varied  their  monthly  and  annual  use  of  many  other 
foraging  substrates.  Wagner  (1981)  found  seasonal  differ- 


ences in  substrate  use  and  foraging  height  of  Bewick's 
Wrens  in  one  year  of  a  two-year  study  in  mixed  oak 
woodland  on  the  central  California  coast. 

The  diet  of  the  Bewick's  Wren  in  California  is  about 
97%  animal  matter  and  3%  vegetable,  the  latter  including 
a  few  seeds,  galls,  and  "rubbish"  (Beal  1907,  n  =  146).  The 
animal  food  is  primarily  true  bugs,  beedes,  ants,  wasps, 
caterpillars,  moths,  grasshoppers,  other  insects,  and  spi- 
ders. 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Bewick's  Wren  bred  through- 
out most  of  Marin  County.  It  was  absent  from  only  a  few 
adas  blocks  in  grassland  areas  devoid  of  extensive  brushy 
draws.  Representative  breeding  locations  were  Limantour 
Spit  (NY  4/27/80  -JGE);  Kleiser  Ranch,  Walker  Creek 
(NY  above  a  headlight  of  a  defunct  Ford  Falcon  5/23/82 
-DS);  Hick's  Valley  (NY  5/16/82  -DS  et  al.);  Woodacre 
(FY  5/31/82  -BiL);  and  the  ridge  and  valley  W  of  Loma 
Alta  (FL  6/4/82  -BiL). 

Historical  Trends/Population  Threats 

Few  historical  data  exist.  Bewick's  Wren  numbers  were 
relatively  stable  on  Breeding  Bird  Surveys  in  California 
from  1968  to  1989  but  declined  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


306 


Wrens 


SPECIES  ACCOUNTS 


Wrens 


HOUSE  WREN    Troglodytes  aedon 


"'v^>. 

\ 

Primarily  a  summer  resident  from  late 
Mar  through  Oct;  irregular  through  late 

j^3r;^CSp\>v^r 

fall  and  early  winter. 

7T??a»a^Y>W 

An  uncommon,  very  local  breeder; 

v^-V\*i. 

overall  breeding  population  very  small. 
Recorded  in  29  (13.1%)  of  221  blocks. 

^t^S-^Vv^ 

i^»\ 

^YV\^\%V\°3ir\ ^-4 

O    Possible        =         5   (17%) 

\jV^f^ 

><^-^><^A 

vA-^A^\AV;:vA^\AVv</ 

C    Probable       =       12    (41%) 

Ca^\    A^Ac* A-AA -V-aCa ' 
^AtA%3rA^WO^V^ 

_-r' 

•    Confirmed  =       12   (41%) 

"0*<\/   X, 

lV\S\ 

\^\^ Jr^^J^vlAr^v*>r^ 

\?o 

FSAR  =  2         OPI  =  58         CI  =  2.24 

b^1^ 

Ecological  Requirements 

Those  who  know  House  Wrens  well  in  Marin  County 
might  consider  their  name  an  alias,  as  diey  are  infrequendy 
seen  here  around  human  habitation.  Most  of  our  nesting 
birds  frequent  openonopied  deciduous  oak  woodlands, 
with  little  or  no  understory,  or  relatively  open  interior 
riparian  woodlands.  Rarely,  diey  set  up  domestic  dudes 
here  in  open,  mixed  evergreen  forests  or  eucalyptus  groves. 
Although  House  Wren  territories  do  sometimes  abut  or 
overlap  those  of  Bewick's  Wrens,  the  latter  generally 
choose  woodlands  or  brushy  habitats  with  denser  tangles 
(see  account). 

House  Wrens  are  cavity  nesters,  and  their  choice  of  sites 
is  as  varied  and  eccentric  as  that  of  Bewick's  Wrens  (see 
account).  Since  House  Wrens  are  less  of  a  dooryard  bird 
in  our  area,  and  in  the  West  in  general,  they  nest  here 
mosdy  in  natural  cavities,  crevices,  or  old  woodpecker 
holes  in  trees,  stumps,  or  fallen  logs.  They  also  occupy  nest 
boxes  and  an  array  of  artificial  sites.  In  Marin  County,  a 
House  Wren  once  nested  near  San  Geronimo  "in  the  end 
of  the  exhaust  pipe  of  a  temporarily  idle  stationary  steam 
engine  attached  to  a  large  pump"  (Mailliard  1936).  Nest 
heights  can  range  from  ground  level  to  about  164  feet 
(Bent  1948).  An  average  nest  height  of  14  feet  (range 
2.5-42  ft.,  n  =  21)  in  the  Sierra  Nevada  (Airola  1980)  is 
probably  representative  of  the  species'  predilections.  Nests 
are  large  bulky  structures  made  mainly  of  small  twigs  or 
sticks  dtat  generally  fill  the  entire  cavity  except  for  the 
nesting  chamber.  In  the  rare  case  in  which  an  enclosed 
cavity  is  not  selected,  the  nest  may  be  a  conical  or  pyramid- 
shaped  pile  of  sticks,  nearly  closed  at  the  top,  with  a  tiny 


entrance  to  admit  the  owner.  The  nest  lining  is  usually  of 
feathers,  grass,  hair,  or  roodets.  A  wide  variety  of  other  nest 
materials  may  be  used,  including  human  artifacts  and 
snakeskin.  Males  are  in  the  habit  of  building  additional 
"fake"  or  "dummy"  nests  either  before  or  after  the  female 
has  begun  incubation  (Kendeigh  1941a,  Bent  1948,  Gross 
1948).  Although  House  Wrens  have  frequendy  been 
reported  destroying  the  nests,  eggs,  and  young  of  other 
birds,  this  trait  has  apparendy  not  been  found  in  the 
western  race  (Bent  1948). 

House  Wrens  forage  by  gleaning  and  probing  cracks 
and  crevices  as  they  scurry  about  on  the  ground,  on  the 
trunks  and  limbs  of  trees,  or  in  vine  tangles,  brush,  or 
downed  branches.  On  occasion,  they  also  hawk  aerial 
insects  (Gross  1948).  The  diet  in  California  is  97.5% 
animal  matter  and  2.5%  vegetable,  though  die  latter  is 
mainly  "rubbish"  and  probably  swallowed  accidentally 
(Beal  1907,  n  =  36).  The  main  animal  foods  are  true  bugs, 
caterpillars,  beedes,  grasshoppers,  ants  and  other  hyme- 
noptera,  other  insects,  and  spiders. 

Marin  Breeding  Distribution 

During  the  adas  period,  Marin  County's  breeding  House 
Wrens  were  concentrated  in  the  northeastern  hills  around 
Novato,  especially  on  Mount  Burdell.  This  area  supports 
the  county's  most  extensive  deciduous  oak  woodlands.  The 
few  House  Wrens  found  in  soudiern  Marin  were  in  open 
mixed  evergreen  forest  or  eucalyptus  groves.  Representative 
breeding  localities  included  Mt.  Burdell,  Novato  (NB-FY 
4/24-5/9/81    -ITi);    near   Stafford   Lake,   Novato   (ON 

307 


Wrens 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


Wrens 


5/6/79  -KH;  FY  spring  1982  -ScC);  and  Nicasio  (ON 
5/9/81  -EV). 

Historical  Trends/ Population  Threats 

Mailliard  (1900)  considered  the  House  Wren  a  "common 
summer  resident  [and]  not  very  abundant"  in  Marin 
County,  whereas  Stephens  and  Pringle  (1933)  considered 
it  a  "fairly  common"  summer  resident  here.  It  currendy  fits 
these  rough  verbal  descriptions  of  abundance  only  in  the 
Novato  area,  which  suggests  (but  does  not  document)  a 


decline  here  since  the  earlier  part  of  this  century.  On  the 
other  hand,  data  from  the  Even  Cheaper  Thrills  Spring 
Bird  Count  suggest  that  House  Wrens  were  increasing  in 
northeastern  Marin  from  1978  to  1987  (Appendix  A). 
House  Wren  populations  declined  on  Breeding  Bird  Sur- 
veys in  the  California  Foothills,  including  coastal  counties 
south  of  Monterey  and  parts  of  those  to  the  north,  from 
1968  to  1979  (Robbins  et  al.  1986)  but  were  relatively 
stable  in  California  as  a  whole  from  1968  to  1989  (USFWS 
unpubl.  analyses). 


TKe  Marsh  Wren's  energy  abounds  as  both  a  chatterbox  and  a  prolific  nest  builder.    Photograph  by  Ian  Tait. 


308 


Wrens 


SPECIES  ACCOUNTS 


Wrens 


WINTER  WREN    Troglodytes  troglodytes 


A  year-round  resident;  numbers  swell 

{\^S^kf{ 

£-  - 

somewhat  from  midAug  to  early  Apr. 

A  common,  local  breeder;  overall 
breeding  population  small. 

Recorded  in  56  (25.3%)  of  221  blocks. 

V^\»^x^ 

*     V-"\     \^\     Y-"\>     V-^A*  V-"A      V-^A 

O    Possible        =         7   (13%) 

o  X^-^-Oje-cX     V^avHo'  V^A    \^\ 
k-""A  ^<>^A-b-lV^A''--'>^A  ©V<\    Jr\    Jc 

.  jJr\     V^v©  Y-^v  J^w  Wf\  ©  v<a 

\Sr\  " 

„- 

€    Probable       =      35   (62%) 
•    Confirmed  =       14   (25%) 

^As  rt\^\  ©• v^A  ©  j£<\  ©  V-^5r©  v^A'      V< 
\  V^V  I  V^A  ©  jP\  ••  V^\  «>%^rA  *>  1*<LV 

l5w 

-^•V^A 

x?0> 

FSAR  =  4        OPI  =  224        CI  =  2.12 

u? 

X^1'                                                      \ f 

"*^^^Y 

Ecological  Requirements 

This  stubby  dark  fidgety  wren  blends  well  with  its  breeding 
season  surroundings  in  Marin  County's  dense,  well- 
shaded,  moist  forests  of  conifers,  mixed  conifers  and 
hardwoods,  or  broadleaved  evergreen  trees— forests  that 
host  a  tangled  understory  of  huckleberry,  sword  ferns,  and 
mossy  downed  logs.  Winter  Wrens  usually  occupy  can- 
yons with  permanent  streams,  where  their  loud  bubbling 
song  bursts  forth  over  the  sound  of  rushing  water.  Most 
Winter  Wrens  in  Europe  are  polygynous  breeders,  but 
most  in  North  America  are  monogamous  (Home  &  Bader 
1990).  Favorite  nesting  sites  are  in  cubbyholes  and  cran- 
nies in  the  upturned  roots  of  fallen  logs,  among  the  roots 
of  trees  overhanging  gully  banks,  fire  holes  in  half-burned 
stumps,  in  or  under  rotted  stumps  or  downed  logs,  and  in 
attached  moss  or  crevices  on  rock  faces  or  cliffs  (Bent 
1948).  Less  commonly,  Winter  Wrens  will  nest  between 
the  logs  of  an  unoccupied  log  hut,  in  an  old  woodpecker 
hole,  in  the  center  of  a  baby  fir,  in  the  low  drooping 
branches  of  a  conifer,  or  in  a  clump  of  shoots  growing  from 
the  trunk  of  an  alder.  Although  nests  in  some  areas  have 
been  found  100  feet  above  die  ground,  most  nests  in 
forested  habitats  range  from  the  ground  to  about  12  feet. 
The  nest  proper  is  a  globular,  more  or  less  bulky  affair  that 
fits  the  shape  of  the  cavity  and  has  a  tiny  side  entrance.  The 
outer  part  of  the  nest  is  mostly  mosses  with  a  base  of  (or 
reinforced  with)  grass,  weed  stems,  fine  twigs,  and  roodets; 
the  lining  consists  of  fur,  feathers,  delicate  roots,  or  fine 
filamentous  lichens. 


Winter  Wrens  forage  by  gleaning  and  probing  low  in 
the  undergrowth,  on  the  ground,  and  along  stream  edges 
(where  they  also  occasionally  dip  their  heads  under  water 
in  pursuit  of  aquatic  insects).  In  coastal  Oregon,  adults 
forage  on  virtually  any  substrate  within  about  10  feet  of  the 
ground,  including  shrubs,  logs,  and  slash  and  litter  on  the 
ground  itself  (Home  &  Bader  1990).  In  the  East,  Winter 
Wrens  consume  almost  100%  animal  matter;  the  main 
prey  there  are  beedes,  true  bugs,  spiders,  caterpillars,  and 
ants  and  other  small  hymenoptera  (Bent  1948).  Among 
the  four  taxa  most  commonly  fed  to  nesdings  in  Oregon, 
spiders  and  adult  beetles  appear  (based  on  fecal  samples) 
to  be  preferred  over  lepidoptera  (butterfly  and  moth)  larvae 
and  adult  flies  (Home  &.  Bader  1 990).  Adults  wrens  there 
select  a  higher  number  of  larger  prey  than  are  randomly 
available  and  on  average  bring  in  larger  arthropods  to  the 
young  wrens  as  they  mature.  A  proportional  increase  in 
beedes,  and  decrease  in  lepidoptera  larvae,  in  the  diet  of 
maturing  young,  may  reflect  greater  selectivity  of  adults  (for 
caterpillars)  early  on  when  food  demands  and  feeding  rates 
are  low,  or  the  difficulty  that  small  young  have  in  digesting 
insects  encased  in  hard  chitinous  shells. 

Marin  Breeding  Distribution 

The  distribution  of  breeding  Winter  Wrens  in  Marin 
County  during  the  adas  period  closely  paralleled  the  distri- 
bution of  moist  forests  on  the  immediate  coast.  Strong- 
holds were  Inverness  Ridge,  southern  Bolinas  Ridge,  and 
additional  moist  lower  canyons  of  the  Mount  Tamalpais 

309 


Wrer 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Wrens 


watersheds.  A  few  small  isolated  populations  occupied 
north-facing  slopes  and  canyons  of  Big  Rock  Ridge,  more 
toward  the  interior  of  the  county.  Representative  breeding 
records  were  Upper  Pierce  Ranch,  Tomales  Point  (FY 
5/18/82  -DS);  '/2  mi.  S  of  Inverness  (NB  4/19/77  - 
RMS);  and  Lake  Ranch  Gate,  Inverness  Ridge  (FY/FL 
5/1/16  -JGE). 


Historical  Trends/Population  Threats 

Little  prior  data  exist.  Numbers  of  Winter  Wrens  on 
Breeding  Bird  Surveys  in  California  increased  from  1968 
to  1979  (Robbins  et  al.  1986);  this  was  balanced  by  a 
decrease  in  numbers  from  1980  to  1989,  leaving  no 
upward  or  downward  trend  for  the  entire  period  1968  to 
1989  (USFWS  unpubl.  analyses). 


MARSH  WREN    Cistothorus  palustris 


A  year-round  resident. 

A  common,  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  34  (15.4%)  of  221  blocks. 


O  Possible 
©  Probable 
•    Confirmed 


4  (12%) 
17  (50%) 
13  (38%) 


FSAR  =  4       OPI  =  1 36        CI  =  2.26 


Ecological  Requirements 

The  effervescent  song  of  this  high-spirited  wren  enhances 
Marin  County's  freshwater  and  brackish  marshes  and 
coastal  swales.  The  basic  requisites  for  breeding  birds  seem 
to  be  standing  water  or  saturated  soil  and  tall,  dense  marsh 
vegetation  for  concealment  and  placement  of  nests.  In 
Marin  County,  Marsh  Wrens  almost  always  breed  in  fairly 
extensive  tall  stands  of  cattails  and  California  tules.  They 
are  more  choosy  here  about  nesting  in  die  low-growing 
marsh  vegetation  of  coastal  swales.  Although  Marsh 
Wrens  use  rush-dominated  (]uncus)  swales,  that  is  not 
always  the  rule.  Marsh  Wrens  typically  avoid  breeding  in 
swales  dominated  by  the  low-growing  bulrush  (Scirpus 
microcarpus)—a  habitat  used  by  Common  Yellowthroats, 
which  generally  have  more  stringent  habitat  preferences 
than  Marsh  Wrens. 

Because  Marsh  Wrens  are  polygamous,  males  build 
multiple  nests.  They  use  these  to  attract  females,  which 
may  choose  one  of  them  or  initiate  a  new  one,  completed 
mosdy  by  the  male  (Verner  1963,  1964,  1965).  Verner  and 
Engelson  (1970)  reported  that  the  number  of  nests  each 

310 


male  built  ranged  from  10  to  50  and  averaged  about  25. 
Nests  are  domed  ellipsoids  with  the  single,  round,  wren- 
sized  opening  placed  in  the  upper  half  (Welter  1935,  Bent 
1948,  Verner  1965).  Birds  construct  the  outer  shell  of  the 
nest  by  interlacing  pliable,  water-soaked  cattail  leaves, 
rushes,  and  stems  and  leaves  of  sedges  and  grasses  and 
stuffing  the  latticework  with  cattail  or  other  plant  down. 
Display  or  dummy  nests  are  devoid  of  a  lining.  To  brood 
nests,  the  female  adds  a  lining  consisting  of  grass  and  sedge 
leaves  and  an  insulating  layer  of  cattail  down,  feathers, 
small  roodets,  and  shredded  plant  material.  Marsh  Wrens 
prefer  to  anchor  their  nests  to  cattails,  in  stands  of  moder- 
ate density,  and  less  frequendy  use  bulrushes,  sedges,  tall 
marsh  grasses,  and,  rarely,  small  bushes  or  trees.  They 
generally  (but  not  always)  nest  in  emergent  vegetation;  a 
preference  for  cattails  may  switch  to  bulrushes  when  water 
levels  drop  as  the  season  progresses  (Verner  6k  Engelson 
1970).  Nest  heights  can  range  from  6  inches  in  low  marsh 
vegetation  to  15  feet  in  trees.  A  large  sample  (n  =  629)  of 
breeding  and  nonbreeding  nests  at  various  cattail-bulrush 


Wrens 


SPECIES  ACCOUNTS 


Wrens 


marshes  in  Washington  ranged  in  height  from  12  to  77 
inches  and  averaged  35.6  inches  above  the  marsh  floor 
(Verner  1965).  Nest  height  varies  in  direct  relation  to  the 
seasonal  change  in  height  of  supporting  cover  caused  by 
plant  growth;  early  nests  may  be  in  the  remains  of  the 
previous  season's  growth.  Dummy  nests,  besides  their  use 
in  courtship,  also  serve  as  nighttime  roosts  and  secondary 
shelters  for  fledged  young  (Bent  1948,  Verner  1965,  Ver- 
ner ck  Engelson  1970). 

Marsh  Wrens  obtain  most  of  their  sustenance  by  glean- 
ing from  marsh  vegetation,  from  bordering  brushy  wil- 
lows, from  the  floor  of  the  marsh,  and  near  or  from  the 
surface  of  the  water.  They  infrequendy  hawk  flying  insects. 
In  Washington's  cattail-bulrush  marshes,  Marsh  Wrens 
prefer  bulrushes  for  foraging.  Presumably  bulrushes  pro- 
mote higher  productivity,  because  they  are  more  thor- 
oughly broken  down  in  winter  than  are  cattails,  thus 
allowing  more  light  to  penetrate  to  the  water's  surface 
(Verner  1964).  The  California  diet  is  98%  animal  matter 
along  with  a  few  seeds  of  marsh  plants  (Beal  1907,  n  =  53). 
The  main  animal  items  are  true  bugs,  caterpillars,  beedes, 
ants,  wasps,  flies  (especially  crane  flies  and  mosquitoes), 
grasshoppers,  dragonflies,  other  insects,  spiders,  and 
snails.  Marsh  Wrens  have  long  been  known  to  occasion- 
ally prey  on  the  eggs  of  other  marsh-nesting  birds  (Bent 
1948);  this  may  affect  habitat  choice  of  other  species  in  an 
area  where  the  wrens  are  particularly  abundant. 


Marin  Breeding  Distribution 

The  patchy  distribution  of  Marin  County's  breeding 
Marsh  Wrens  during  the  adas  period  reflected  that  of  their 
nesting  marshes.  Most  breeding  birds  were  found  in  the 
lowlands,  especially  on  the  Point  Reyes  peninsula  and  in 
marshes  bordering  San  Pablo  Bay  near  Novate  Represen- 
tative nesting  locations  were  Drake's  Beach  visitor's  center, 
Point  Reyes  (FL  5/27/80  -DS);  Olema  Marsh  (NE-NY 
Apr  1984-1988  -JGE);  and  Pine  Gulch  Creek,  Bolinas 
Lagoon  (NE/NY  4/24/77  -DS). 

Historical  Trends/Population  Threats 

Since  these  wee  Cistothores  are  wedded  to  luxuriant  marsh 
vegetation,  they  have  undoubtedly  declined  dramatically 
with  the  clearing  and  draining  of  marshes  for  agriculture 
and  development,  especially  around  San  Francisco  Bay. 
Historically,  there  has  been  an  estimated  loss  of  60%-95% 
of  former  tidal  marsh  habitat  around  San  Francisco  Bay 
(Nichols  ck  Wright  1971,  Josselyn  1983).  The  loss  of 
freshwater  marshland,  with  which  the  Marsh  Wren  is 
closely  associated,  has  probably  been  even  greater,  as  this 
plant  community  occupies  the  upland  bayshore  areas  most 
prone  to  development.  Numbers  of  Marsh  Wrens  were 
relatively  stable  on  Breeding  Bird  Surveys  in  California 
from  1968  to  1989  (USFWS  unpubl.  analyses),  a  period 
after  the  greatest  loss  of  wedands. 


311 


Dippers 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Dippe 


Dippers 

Family  Cinclidae 


AMERICAN  DIPPER   Cinclus  mexicanus 


Formerly  a  year-round  resident;  now  occurs  as  an  irregular  winter  resident,  mosdy  from  Oct  through  Mar. 


Ecological  Requirements 

The  celebrated  water-ouzel  truly  embodies  the  spirit  of  swift 
and  turbulent  mountain  streams.  Although  Dippers  live 
on  a  variety  of  fast-flowing  streams,  creeks,  and  rivers,  their 
favorites  (at  least  in  Colorado)  are  those  with  a  rubble- 
strewn  bottom  (rocks  1  -8  in.  in  size)  and  many  emergent 
rocks  harboring  an  adequate  and  easily  obtainable  food 
supply  (Price  6k  Bock  1983).  In  the  breeding  season, 
adequate  nest  sites  are  also  a  limiting  factor.  Dippers 
characteristically  choose  nest  sites  that  are  over,  or  nearly 
over,  the  edge  of  a  stream;  are  sheltered  from  weather;  and 
are  inaccessible  to  predators  (Hann  1950,  Price  &  Bock 
1983).  Very  rarely,  they  select  sites  set  back  as  much  as  28 
feet  from  the  water  (Sullivan  1966).  Dippers  build  their 
nests  on  narrow  ledges  or  niches  in  vertical  rock  walls 
(often  among  mosses  and  ferns),  under  the  roots  of  stand- 
ing or  fallen  trees  at  streamside,  under  overhanging  banks, 
on  midstream  rocks,  on  support  beams  of  bridges  or  other 
buildings,  or,  rarely,  in  a  cavity  in  the  sloping  top  of  a 
stream-edge  stump  (Bent  1948,  Hann  1950,  Bakus  1959, 
Price  6k  Bock  1983).  They  also  use  artificial  nest  boxes  on 
vertical  faces  over  water  (Hawthorne  1979). 

Although  nests  may  conform  to  the  size  of  the  available 
space  and  may  occasionally  be  open  at  the  top,  most 
consist  of  a  spherical  or  domelike  outer  shell  made  chiefly 
of  mosses  interwoven  with  a  few  grass  stalks  and  roots;  an 
inner  cup-shaped  lining  of  dry,  coarse  grasses;  and  a  neady 
arched  opening  at  the  bottom  (Bent  1948,  Hann  1950, 
Bakus  1959).  Dippers  may  place  their  nests  behind  or  near 
waterfalls,  and  if  they  situate  them  within  the  spray  zone, 
the  mosses  of  the  nest  stay  green  throughout  the  nesting 
season.  Although  generally  solitary,  monogamous  breed- 
ers, Dippers  are  on  occasion  polygynous,  with  males  mated 
simultaneously  to  two  females  with  separate  nests  (Price  6k 
Bock  1973,  1983;  Marti  6k  Everett  1978). 

To  procure  food,  Dippers  become  one  with  their  ele- 
ment. Although  noted  for  their  mastery  of  rapids  and 
underwater  dives,  Dippers  actually  obtain  most  food  where 
it  is  more  readily  available— from  the  slow-flowing  water  of 
pools,  backwaters,  stream  edges,  and  lake  margins  (Thut 
1970).  In  search  of  prey,  ouzels  run,  walk,  or  hop  (in  rough 
or  steep  terrain)  along  rocky  stream  margins  and  wade  into 
the  water,  clinging  to  slippery  rocks  with  the  aid  of  stout 

312 


legs  and  sharp  claws.  Often  a  bird  will  stand  on  submerged 
rocks  and,  facing  the  current,  hold  its  head  under  the  water 
to  glean  prey  from  rock  surfaces,  probe  among  and  under 
small  stones,  or  catch  items  carried  downstream  by  the 
current.  Dippers  also  skim  food  from  the  surface  as  they 
traverse  open  water,  paddling  with  their  nonwebbed  feet 
and  flapping  their  wings.  They  will  also  frequendy  fly  low 
in  the  air  (less  than  10ft.  above  streams)  to  snatch  airborne 
insects  (Bent  1948,  Hann  1950,  Bakus  1959,  Goodge 
1959).  These  aquatic  passerines  show  their  true  chutzpah 
by  diving,  usually  against  the  current,  from  the  air,  from 
perches  or  emergent  rocks,  or  from  the  water's  surface. 
Once  they  make  subsurface  contact,  they  seemingly  walk 
on  the  bottom,  though  rarely  without  lots  of  aid  from 
flapping  wings  (Goodge  1 959).  The  diet  is  predominandy 
aquatic  insect  larvae— particularly  midges,  caddisflies, 
stoneflies,  mayflies,  and  mosquitoes— as  well  as  adults  of 
aquatic  insects  such  as  waterbugs  and  beedes,  aerial 
insects,  segmented  worms,  snails,  and  fish  fry  and  eggs 
(Burcham  1904,  Bent  1948,  Bakus  1959,  Thut  1970). 

Marin  Breeding  Distribution/ Historical 
Trends/ Population  Threats 

Dippers  were  not  found  nesting  in  Marin  County  during 
the  adas  period.  In  fact,  die  only  historical  breeding  evi- 
dence is  the  report  of  Mailliard  (1 900)  that  "a  pair  formerly 
bred  near  the  headwaters  of  Lagunitas  Creek.  None  seen 
for  some  years."  Historically,  the  American  Dipper  may 
always  have  been  a  rare  and  irregular  breeder  in  Marin 
County  because  of  the  marginal  suitability  of  local  streams. 
The  construction  of  a  system  of  four  dams  and  reservoirs 
in  the  Lagunitas  Creek  watershed  from  1873  to  1953 
probably  sealed  the  fate  of  nesting  Dippers  in  Marin 
County,  though  a  sighting  of  a  Dipper  at  Samuel  P.  Taylor 
State  Park  on  24  June  1966  (Gull  48:61)  leaves  hope  for 
dieir  occasional  nesting.  At  present,  American  Dippers 
occur  in  Marin  County  only  as  rare  and  irregular  winter 
residents  on  coastal  streams  of  the  Point  Reyes  and  Mount 
Tamalpais  watersheds  (Shuford  1982,  ABN).  On  the 
whole,  Dipper  numbers  were  relatively  stable  on  Breeding 
Bird  Surveys  in  California  from  1968  to  1989,  though  they 
increased  from  1 980  to  1 989  (USFWS  unpubl.  analyses). 


Kinglets  and  Gnatcatchers 


SPECIES  ACCOUNTS 


Kinglets  and  Gnatcatchers 


Kinglets  and  Gnatcatchers 

Family  Muscicapidae 


Subfamily  Sylviinae 


GOLDEN-CROWNED  KINGLET   Regulus  satrapa 


A  year-round  resident;  numbers  swell 
from  mid-Oct  through  Mar. 

An  uncommon,  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  42  (19.0%)  of  221  blocks. 

O  Possible  =  11  (26%) 
€  Probable  =  25  (60%) 
•    Confirmed  =        6  (14%) 

FSAR  =  2        OPI  =  84         CI  =  1.88 


Ecological  Requirements 

These  diminutive  Old  World  warblers  are  among  the  most 
difficult  of  small  landbirds  to  see  in  the  nesting  season 
when  they  stay  well  concealed  in  closed-  or  open-canopy 
conifer  forests  dominated  by  trees  with  high  needle  density 
(Beedy  1981,  Franzreb  1984).  In  Marin  County,  they 
breed  almost  exclusively  in  cool,  shaded  Douglas  fir  and 
redwood  forests,  but  not  in  bishop  pine  forests. 

Nest  heights  have  been  recorded  from  4  to  64  feet  above 
the  ground,  but  because  nests  are  generally  well  concealed 
in  the  upper  canopy,  extreme  heights  may  be  greater  (Bent 
1949,  Galati  &  Galati  1985).  In  Minnesota,  Galati  and 
Galati  (1985)  found  19  nests  that  averaged  50  feet  in  height 
(range  27-64  ft.).  In  second-growth  habitat  in  New  Hamp- 
shire, Durfee  (in  Bent  1949)  found  9  nests  ranging  from  8 
to  46  feet  in  height,  but  except  for  the  highest  the  rest 
averaged  only  14  feet.  Rathbun  (in  Bent  1949)  reported  a 
similar  range  of  9  to  45  feet  for  an  unspecified  number  of 
nests  near  Seattle.  Golden-crowned  Kinglets  generally 
attach  their  nests  to  the  radiating  twigs  of  conifer  boughs 
at  varying  distances  from,  but  usually  near,  the  trunk.  They 
conceal  them  so  well  that  they  are  not  visible  to  humans 
from  above  or  at  nest  level  and  are  only  partly  visible  from 


below.  Dense  overhanging  foliage  protects  the  nests  from 
rain,  sun,  and  wind.  Protection  from  the  wind  is  further 
ensured  by  placement  of  the  nest  on  the  leeward  side  of  the 
tree  (Galati  ck  Galati  1985). 

The  nest  is  a  deep  globular  or  oblong  cup,  constricted 
or  arched  over  slighdy  at  the  top.  It  is  made  chiefly  of 
mosses  bound  by  spider  webs,  parts  of  insect  cocoons,  and 
soft  plant  fibers.  Kinglets  interweave  additional  materials 
or  ornamentation  of  lichens,  dead  leaves  and  grasses,  and 
conifer  needles  into  the  mossy  matrix.  They  line  the  cup 
with  fine  strips  of  bark,  lichens,  animal  hair,  feathers,  fine 
roodets,  and  other  soft  vegetable  fibers  (Bent  1949,  Galati 
6k  Galati  1985). 

The  Golden-crowned  Kinglet's  elusiveness  is  more  a 
function  o(  the  time  it  spends  in  dense  foliage  than  its 
height  above  the  observer.  These  kinglets  forage  through- 
out tall  conifers  but  concentrate  at  middle  elevations;  they 
infrequendy  use  pines,  oaks,  and  snags  (Franzreb  1984, 
Airola  &.  Barrett  1985,  Morrison  et  al.  1985).  They 
expend  most  foraging  effort  at  the  tips  of  boughs  in  foliage, 
on  small  twigs  and  branches,  and  only  rarely  on  trunks, 
cones,  logs,  or  the  ground.  These  kinglets  capture  prey 

313 


Kinglets  and  Gnatcatchers 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Kinglets  and  Gnatcatchers 


primarily  by  gleaning,  secondarily  by  hovering,  and  infre- 
quently by  lunging,  hawking,  pecking  or  probing.  The  diet 
is  prcdominandy  adults,  larvae,  and  eggs  of  arthropods, 
including  wasps,  ants,  true  bugs,  flies,  beetles,  moths, 
butterflies,  caterpillars,  spiders,  and  pseudoscorpions  (Beal 
1907,  n  =  9;  Bent  1949;  Dahlsten  et  al.  1985);  surpris- 
ingly, vegetable  matter  made  up  27.5%  of  the  diet  of  a 
small  sample  of  breeding  birds  (n  =  9)  in  the  Sierra  Nevada 
(Dahlsten  et  al.  1985). 

Marin  Breeding  Distribution 

During  the  adas  period,  Golden-crowned  Kinglets  bred 
here  primarily  in  the  Douglas  fir  forests  on  Inverness  Ridge 
and  in  die  fir  and  redwood  forests  of  the  Bolinas  Ridge, 
Mount  Tamalpais,  and  Lagunitas  Creek  watersheds.  An 
isolated  population  inhabited  redwoods  on  the  north  slope 


of  Big  Rock  Ridge  in  Novate  Representative  nesting  sites 
were  Balboa  Road,  Inverness  Ridge  (NB  4/20/79  -DS); 
Glen  Trail,  PRNS  (FL/FY  7/25/82  -DS);  and  Inverness 
Ridge  above  Five  Brooks  (NE  or  NY  early  1980s  — ITi). 

Historical  Trends/Population  Threats 

Early  Marin  County  ornithologists  were  not  aware  that 
Golden-crowned  Kinglets  bred  in  the  area  (Mailliard  1900, 
S&.P  1933),  but  the  truth  was  uncovered  by  the  time  of 
Grinnell  and  Miller's  (1944)  classic  work  on  California's 
avifauna.  Marin  s  breeding  population  probably  took  a 
plunge  at  the  time  of  extensive  logging  here  early  in  this 
century  but  subsequendy  recovered  with  the  regeneration 
of  dense  forests.  Numbers  of  Golden-crowned  Kinglets 
were  fairly  stable  on  Breeding  Bird  Surveys  in  California 
from  1968  to  1989  (USFWS  unpubl.  analyses). 


BLUE-GRAY  GNATCATCHER   Polioptila  caerulea 


A  summer  resident  from  late  Mar 

^r">-^       K              .XoS 

through  mid-Oct;  irregular  in  late  fall 

~l^^\^\-  ^^; 

^C^PV^^-^v^^ 

and  winter. 

a   V^\  \^\  V  \  .  \^\o \^K  W-y 

J<r\  J*c\  y^\    \^\   A-"\#3r\  XP\ 

A  fairly  common,  very  local  breeder; 

w^\VA 

\  ^\\  ^\\  jftc^K  ^V^\  J\^\  ®A^^    \ 

overall  breeding  population  very  small. 

i^\    \^\  Jr\    )>h\    X^\  ®  Jv^\  o-\f^\ 
\  _Ar\  J^CX  J>rV    3r^\   Jr\  ®V\    ^ 

Recorded  in  16  (7.2%)  of  221  blocks. 

■^C^rX     V^A     \^l\     X^\     V"\  •  V^A     J 

O    Possible        =         5   (31%) 

«^\  ■'^i^iv^AiA\  j<^\  *y<<\  y<^\  j^? 

.„ 

©    Probable       =         7   (44%) 

V>— —  '**' 

•    Confirmed  =        4  (25%) 

^^a 

FSAR  =  3        OPI  =  48         CI  =  1.94 

Ecological  Requirements 

The  somber  hues  of  these  lithe  insectivores  blend  in  well 
with  their  Marin  County  nesting  haunts  of  deciduous  and 
live  oak  woodlands  interfacing  with  chaparral  or  brushy 
openings.  Gnatcatchers  here  are  particularly  attracted  to 
slopes  with  open  stands  of  small  valley  oaks  with  adjacent 
patches  of  coast  live  oaks  and  openings  with  low  brush.  In 
Monterey  County,  Blue-gray  Gnatcatchers  prefer  extensive 
stands  of  oaks  varying  from  live  oak  woodland,  mixed  live 
oak-deciduous  oak  woodland,  dense  oak  scrub,  and  open 
stands  of  mature  deciduous  oaks  (Root  1 967).  Blue-grays 
there  also  nest  in  stands  of  large  (about  9  ft.  tall)  arbores- 
cent chaparral  resembling  oak  scrub  but  are  absent  in 

314 


extensive  stands  of  low  chaparral,  except  where  it  adjoins 
oak  woodlands.  Rarely,  they  use  open  stands  of  streamside 
willows  adjacent  to  chaparral  and  oak  woodland.  The  fact 
that  Gnatcatchers  occupy  some  habitats  with  different 
physiognomy  among  those  available  while  shunning  oth- 
ers with  similar  structure  to  those  occupied,  suggests  that, 
in  addition  to  habitat  structure,  nest  sites  and  particularly 
food  abundance  must  also  be  important  in  habitat  selec- 
tion. 

In-depth  ecological  study  has  revealed  that  Gnatcatchers 
shift  their  habitat  use,  reflected  in  their  almost  continual 
realignment  of  territorial   boundaries,    in    response   to 


Kinglets  and  Gnatcatchers 


SPECIES  ACCOUNTS 


Kinglets  and  Gnatcatchers 


changes  in  the  seasonal  distribution  and  abundance  of 
their  arthropod  prey  (Root  1967,  1969b).  When  birds  first 
arrive  in  Monterey  County  in  March  and  April,  they 
concentrate  their  foraging  efforts  in  the  evergreen  foliage  of 
live  oaks  and  chaparral.  By  late  April,  when  deciduous  oak 
foliage  is  well  developed,  they  shift  most  foraging  to  these 
woodlands  and  center  it  there  through  July.  Fledglings  are 
led  to  stands  of  dense  evergreen  foliage,  partly  for  protec- 
tion from  predators,  and  later  they  wander  to  nonbreeding 
habitats,  such  as  adjacent  riparian  groves.  By  August, 
adults  and  juveniles  leave  deciduous  oak  woodlands  for 
adjacent  live  oak  woodlands  and  chaparral. 

Gnatcatchers  build  deep  cup-shaped  nests,  which  they 
anchor  to  twigs  and  branches  that  they  sometimes  incorpo- 
rate in  the  structure  (Bent  1949;  Root  1967,  1969b).  They 
make  the  nest  body  from  dried  grasses  and  plant  fibers, 
welded  together  with  spider  silk.  Birds  ornament  the  nest 
exterior  with  crustose  lichens  and  an  occasional  grass  seed 
hull,  oak  leaf,  or  feather,  and  they  line  the  inside  with  plant 
down  and  feathers.  Gnatcatchers  place  most  nests  in 
vertical  forks  (against  a  trunk  or  limb  or  at  the  splitting  of 
large  branches)  or  saddle  them  between  upright  branches 
or  twigs  on  a  horizontal  branch;  rarely,  they  build  them  in 
dense  tangles  of  twigs.  The  same  birds  may  use  individual 
nest  sites  in  different  nest  attempts  in  the  same  or  subse- 
quent years  (Root  1967).  Nests  may  or  may  not  be 
screened  by  foliage.  Concealment  is  based  more  on  cam- 
ouflage: Gnatcatchers'  nests  might  easily  be  mistaken  for 
weathered  stubs  or  an  accumulation  of  debris.  The  outer 
adornment  of  lichens  is  the  standard  camouflage,  but  in 
burned-over  areas,  pieces  of  scorched  bark  may  serve  the 
same  purpose  (Chamberlin  1901).  Gnatcatchers  build 
their  nests  in  a  variety  of  trees  and  bushes.  In  California, 
they  situate  most  nests  in  oaks  or  chaparral  shrubs  but  also 
in  pines,  alders,  and  even  eucalyptus  (Bent  1949).  In  the 
Monterey  area,  90%  of  their  nests  are  in  deciduous  oaks, 
reflecting  the  foraging  beat  at  that  season.  The  height  of  66 
nests  diere  varied  from  about  3  to  34  feet  above  the  ground 
with  about  79%  between  7  and  23  feet  high  (Root  1967). 
The  few  chaparral  nests  were  near  the  top  of  die  shrub, 
while  oak  nests  were  at  least  3  feet  below  the  top  of  the  tree 
and  usually  at  least  a  third  of  the  way  up  the  tree.  Through- 
out California,  nest  heights  range  from  3  to  45  feet;  one 
was  30  feet  up  in  a  pine  but  on  a  branch  hanging  over  a 
gully  and  60  feet  above  the  ground.  Extreme  nest  heights 
in  the  East  can  reach  70  to  80  feet  (Bent  1949). 

Gnatcatchers  forage  throughout  the  height  of  the  vegeta- 
tion but  concentrate  in  the  foliage  zone;  in  chaparral  they 
tend  to  use  the  subcanopy  more.  Foraging  birds  perch 
mosdy  on  twigs  and  small  branches,  but  occasionally  they 
also  perch  on  the  upper  surface  of  limbs  and,  rarely,  on 
upright  trunks  and  limbs,  grass  culms,  or  tree  leaves  (Root 
1967).  Gnatcatchers  are  rapid,  energetic  foragers.  They 
typically  hop   rhythmically   from   perch   to   perch,   stop 


briefly,  and  cock  their  heads  quickly  from  side  to  side  to 
survey  their  surroundings  for  potential  "victims."  They 
capture  prey  by  gleaning  (direcdy  or  by  leaning  over  with 
wings  aflutter),  lunging,  hovering,  and  by  acrobatic  hawk- 
ing in  which  birds  rarely  return  to  the  same  perch.  Gnat- 
catchers also  tumble,  with  wings  checking  their  descent,  in 
pursuit  of  insects  that  have  dropped  from  the  foliage. 
Rarely,  they  hang  beneath  perches  like  chickadees  and 
titmice.  When  the  sun  is  low,  Gnatcatchers  forage  with 
other  species  in  sunlit  banks  of  foliage  bordering  openings. 
Seasonal  shifts  in  foraging  preferences  are  evident, 
although  most  attempts  occur  on  foliage  (Root  1967).  Early 
in  the  season,  before  deciduous  foliage  is  well  developed, 
attempts  on  twigs  and  branches  predominate.  Adults  with 
young  increase  foraging  on  herbaceous  plants  and  the 
ground.  They  make  such  attempts  from  perches  low  in 
trees  or  from  downed  limbs.  Adults  make  aerial  surveys  up 
to  15  feet  from  such  perches,  hovering  to  inspect  tall  grass 
spikes  for  grasshoppers  and  other  large  insects  not  nor- 
mally included  in  the  adult  diet.  Gnatcatchers  subdue  large 
prey  by  beating  them  against  branches.  In  July  and  August, 
when  adults  are  feeding  fledglings,  they  often  forage  while 
frequendy  opening  and  closing  the  tail  rapidly.  This  action 
displays  the  white  outer  retrices  with  a  flashing  effect  that 
presumably  functions  to  flush  insects  from  the  foliage. 
Adults  with  young  also  do  more  hawking  and  hovering 
than  adults  without  young.  In  June  and  July,  there  is  a 
slight  increase  in  the  frequency  of  hawking  irrespective  of 
parental  obligations,  reflecting  the  characteristics  of  avail- 
able prey.  The  March  to  August  diet  of  California  birds  is 
exclusively  small  (0.1-1.2  in.)  arthropods  of  70  families 
(Root  1967,  n  =  58).  The  main  groups,  which  may  change 
seasonally,  are  true  bugs,  beedes,  wasps  and  bees,  moths 
and  butterflies,  cicadas  and  allies,  flies,  and  spiders. 

Marin  Breeding  Distribution 

During  the  adas  period,  Blue-gray  Gnatcatchers  bred  in 
Marin  County  only  on  relatively  dry  ridges  in  the  interior. 
They  were  most  widely  distributed  on  the  eastern  flanks  of 
Mount  Burdell  and  Big  Rock  Ridge  and  more  locally  on 
Blue  Ridge  near  White's  Hill  and  on  Mount  Tamalpais. 
Representative  breeding  stations  were  Mt.  Burdell,  Novato 
(NY  5/30/82  -ScC);  Olompali,  Novato  (NY  5/20/82 
— ScC);  Big  Rock  Ridge  near  Blackstone  Canyon  (NY 
5/25/77  — BBi,  DS);  and  along  the  Yolanda  Trail  near 
Phoenix  Lake  (FL/FY  6/20/83  -MB). 

Historical  Trends/Population  Threats 

Blue-gray  Gnatcatchers  increased  on  Breeding  Bird  Sur- 
veys in  die  California  foothill  region,  including  coastal 
counties  from  Monterey  south  and  parts  of  those  to  the 
north,  from  1968  to  1979  (Robbins  et  al.  1986).  For 
California  as  a  whole,  they  increased  from  1968  to  1989, 
though  they  stabilized  from  1980  to  1989  (USFWS  unpubl. 


315 


Kinglets  and  Gnatcatchers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Thrushes 


analyses).  Counts  on  the  Even  Cheaper  Thrills  Spring 
Bird  Count  near  Novato  were  relatively  stable  from  1978 
to  1987  except  for  high  counts  in  1985  and  1987  that  were 
well  above  the  average  for  previous  years  (Appendix  A). 


Clearing  of  woodlands  would  tend  to  depress  Gnatcatcher 
populations,  whereas  fires  might  open  up  habitat  to  their 
liking. 


Thrushes 

Family  Muscicapidae 
Subfamily  Turdinae 


WESTERN  BLUEBIRD   Sialia  mexicana 


A  year-round  resident. 

A  fairly  common,  very  widespread 
breeder;  overall  breeding  population 
fairly  large. 

Recorded  in  170  (76.9%)  of  221 
blocks. 


O    Possible 
O    Probable 

9    Confirmed 


74  (44%) 
28  (16%) 
68  (40%) 


FSAR=3        OPI  =  510       CI  =  1.96 


Ecological  Requirements 

The  azure  and  rusty  hues  of  Western  Bluebirds  add  a 
tasteful  tint  to  the  borders  of  a  wide  variety  of  Marin 
County's  habitats.  Breeding  birds  require  grasslands  or 
very  open  brushlands,  with  suitable  perch  sites  for  foraging 
and  nearby  trees  for  shelter  and  nest  sites.  Our  oak 
savannah  or  oak  woodland  edges  are  best  outfitted  widi 
these  requisites,  although  the  edges  of  virtually  all  of 
Marin's  forested  habitats,  planted  windbreaks,  or  residen- 
rial  plantings  will  do— as  long  as  they  adjoin  meadows, 
grasslands,  weedy  fields,  or  open  scrub  fields.  Clearings  in 
forests  or  very  open  woodlands  may  also  suit  this  blue- 
bird's needs.  Western  Bluebirds  require  more  foraging 
perches  and  prefer  somewhat  denser  ground  cover  than  do 
Mountain  Bluebirds  (Pinkowski  1979);  where  they  overlap 
(not  in  Marin),  these  two  bluebird  species  are  interspecific- 
ally  territorial  (Pinkowski  1979,  Herlugson  1982). 

316 


Western  Bluebird  nests  are  simple  and  "carelessly"  built 
affairs— made  of  dry  grasses,  a  few  feathers  and  other  soft 
materials— placed  from  about  3  to  45  feet  high  in  old 
woodpecker  holes,  natural  tree  cavities,  bird  boxes,  cavities 
of  buildings,  or  old  Cliff  Swallow  nests  (Bent  1949,  D. 
Shuford  pers.  obs.). 

The  fundamental  foraging  strategy  of  Western  (as  well 
as  Mountain  and  Eastern)  Bluebirds  is  to  search  for 
ground-dwelling  prey  from  a  perch  (Pinkowski  1979). 
Perch-foraging  bluebirds  prefer  open,  well-lighted  areas 
containing  low,  sparse  vegetation  and  little  understory;  tall 
vegetation  would  interfere  in  hunting  for  ground-dwelling 
prey.  Birds  usually  sit  motionless  on  a  perch  of  low  to 
moderate  height  that  commands  a  wide  view  and  carefully 
watch  for  prey.  Typical  perches  are  the  upper  and  outer 
(preferably  dead)  branches  of  trees,  isolated  bushes,  large 
rocks,  coarse  weed  stalks,  and  a  variety  of  artificial  sites, 


Thrushes 


SPECIES  ACCOUNTS 


Thrushes 


including  fences  and  fence  posts,  utility  poles  and  wires, 
buildings,  highway  signs,  stakes,  picnic  tables,  refuse  cans, 
nesting  boxes,  and  ground  debris;  bluebirds  sometimes 
also  perch  horizontally  on  tree  trunks.  When  they  detect 
food  from  their  vantage  points,  bluebirds  drop,  swoop,  or 
flutter  to  the  ground  to  seize  prey  in  their  bill.  Small  items 
are  usually  eaten  on  the  ground,  whereas  larger  ones  are 
carried  to  a  perch  for  "preparation"  before  consumption. 
Birds  switch  positions  on  the  same  perch  or  move  to  a  new 
one  when  they  have  difficulty  locating  prey.  Western  Blue- 
birds also  frequendy  make  short,  butterflylike  flights  from 
perches  to  hawk  insects  and  may  forage  exclusively  by  this 
tactic  when  aerial  prey  are  abundant.  Less  frequendy, 
Western  Bluebirds  descend  toward  the  ground  and  glean 
prey  from  low  herbaceous  foliage  while  remaining  airborne 
or  hover  over  it  to  catch  flying  insects  they  have  disturbed. 
They  sometimes  also  land  to  glean  prey  from  the  foliage 
and  branches  of  trees  and  shrubs  or  from  tree  trunks.  In 
addition,  bluebirds  hop  along  the  ground  feeding  on  items 
they  encounter,  particularly  when  seeking  small  prey  or 
when  foraging  in  areas  containing  few  perches  (Pinkowski 
1979).  When  searching  for  prey  on  the  ground,  they  do 
not  work  areas  with  much  leaf  litter  and  do  not  flip  aside 
debris  with  the  bill  like  other  thrushes.  Also  when  perches 
are  few,  they  may  hover  with  their  wings  flapping  and  tails 
spread  or  with  the  aid  of  strong  breezes  or  updrafts, 
dropping  to  the  ground  quickly  when  prey  is  sighted. 
When  feeding  nesdings,  adults  increase  their  use  of  energy- 
cosdy  foraging  behaviors,  such  as  hovering  and  hawking, 
and  they  feed  the  young  larger  (heavier)  prey  items  (on 
average)  than  they  eat  themselves  (Herlugson  1982). 
Because  they  are  more  dependent  on  perches,  Western 
Bluebirds  generally  flycatch  more  and  hover  and  flight- 
glean  less  than  Mountain  Bluebirds  (Pinkowski  1979). 
However,  bluebirds  are  opportunistic  foragers,  and  there  is 
more  variation  in  foraging  tactics  of  a  given  species 
between  habitats  than  between  different  species  in  the 
same  habitat.  Block  (1990)  documented  geographic  varia- 
tion of  Western  Bluebird's  foraging  techniques  and  loca- 
tions in  California  oak  woodlands,  while  Szaro  et  al. 
(1990)  similarly  demonstrated  annual  variation  in  foraging 
techniques  and  other  measures  of  resource  use  in  pon- 
derosa  pine  forests  in  Arizona. 

The  Western  Bluebird  diet  year  round  is  about  80% 
animal  matter  (Beal  1915,  n  =  217).  In  California,  animal 
matter  ranges  from  94%-100%  of  the  diet  in  spring  and 
summer  to  74%-79%  in  fall  and  winter  (Martin  et  al. 
1951,  n  =  215).  Dominant  prey  are  grasshoppers  and 
crickets,  beetles,  butterflies  and  moths,  and  caterpillars; 
secondarily,  true  bugs,  ants  and  wasps,  spiders,  and  cica- 
das; minor  items  are  flies,  earwigs,  isopods,  centipedes, 
myriopods,  angleworms,  snails,  and  sowbugs  (Beal  1915, 
Herlugson  1982).  In  Washington,  Herlugson  (1982) 
noted  that  the  adult  diet  in  the  prenesding  phase  is  domi- 


nated by  beedes  and  lepidopterans.  These  items  decrease 
in  importance  during  the  nesding  phase,  when  ants, 
wasps,  and  true  bugs  increase  in  importance.  Nesding 
diets  of  Western  Bluebirds  are  dominated  by  grasshop- 
pers, crickets,  and  beedes  (Beal  1915,  Herlugson  1982). 
Where  Western  and  Mountain  bluebirds  overlap  in 
Washington,  the  adult  diets  of  the  two  species  are  similar 
in  the  prenesding  phase,  but  overall  they  differ  in  the 
proportions  of  various  food  items  consumed  (Herlugson 
1982);  foods  delivered  to  nesdings  do  not  differ  between 
species.  Western  Bluebirds  obtain  their  vegetable  fare  of 
dry  and  succulent  fruits  and  berries  and,  rarely,  hard  seeds, 
by  picking  them  while  they  perch  in  vegetation  (Pinkowski 
1979).  Important  items  are  wild  fruits  such  as  elderberries 
and  misdetoe,  seeds  of  poison  oak  and  various  weeds,  as 
well  as  cultivated  fruits  and  berries  (Beal  1915).  These 
bluebirds  most  frequendy  consume  vegetable  items  early 
on  cool  mornings,  before  temperatures  rise  and  insects 
become  active  (Pinkowski  1 979). 

Marin  Breeding  Distribution 

During  the  adas  period,  Western  Bluebirds  bred  through- 
out most  of  Marin  County.  They  were  sparse  or  absent  on 
outer  Point  Reyes  and  absent  from  much  of  the  corridor 
along  Highway  101  and  from  steep  ridges  densely  clothed 
with  forests  or  chaparral.  Although  much  of  eastern  Marin 
is  urbanized,  there  are  still  large  open  spaces  with  seem- 
ingly suitable  habitat  where  breeding  Western  Bluebirds 
are  lacking  (B.  Lenarz  pers.  comm.).  Representative  nesting 
locations  were  eucalyptus  grove  outer  Tomales  Point  (FY 
6/1 5/82  — DS);  cypress  grove  at  Fish  Docks,  Point  Reyes 
(NY  5/20/81  — DS);  planted  pine  grove  Marconi 
Ranch/Synanon  (FY/FL  6/27/82  -DS);  Mt.  Burdell, 
Novate  (NB  4/21/81  -ITi);  and  Carson  Ridge  (NY 
6/5/82  -DS,  ITi). 

Historical  Trends/  Population  Threats 

Aldiough  Mailliard  (1900)  considered  the  Western  Blue- 
bird an  "abundant  resident"  in  Marin  County,  Stephens 
and  Pringle  (1933)  considered  it  "common"  but  "present 
in  winter  only"  here.  The  similar  abundance  categories  but 
different  seasonal  status  ascribed  by  these  audiors  is  puz- 
zling. Grinnell  and  Wythe  (1927)  and  Grinnell  and  Miller 
(1944)  reported  the  species  as  breeding  in  the  San  Fran- 
cisco Bay  Area  but  listed  no  records  from  Marin  County. 
Given  the  current  status,  it  seems  likely  that  Western 
Bluebirds  were  breeding  regularly  in  Marin  County 
throughout  this  period.  Historically,  Western  Bluebirds 
likely  have  increased  locally  as  breeders  in  the  grasslands 
in  the  northwest  corner  of  the  county.  This  area  was 
formerly  devoid  of  large  trees;  consequendy,  planted  wind- 
breaks have  created  suitable  nest  sites  and  foraging 
perches,  die  latter  further  augmented  by  human  structures 
such  as  fences  and  utility  lines. 

317 


Thrushes 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Thrushes 


The  Western  Bluebird  was  on  the  Audubon  Society's 
Blue  List  in  1972  and  from  1978  to  1981,  on  its  list  of 
Special  Concern  in  1982,  and  on  its  list  of  Local  Concern 
in  1986  (Tate  1981,  1986;  Tate  6k  Tate  1982).  There  is 
speculation  that  pesticide  use,  snag  and  decaying  tree 
removal,  changing  agricultural  practices,  and  competition 
for  nest  sites  with  European  Starlings  and  House  Sparrows 
have  all  had  adverse  effects  on  Western  Bluebird  popula- 
tions (Elizroth  1983).  Starlings  are  perhaps  most  often 
implicated  in  postulated  declines  of  Western  Bluebirds 
(e.g.,  Herlugson  1978).  Aldiough  it  is  true  that  Starlings 
will   aggressively  displace   other   hole-nesting   birds   and 


reduce  their  breeding  populations,  particularly  if  nest  holes 
are  in  short  supply  (Weitzel  1988),  it  is  not  clear  if  this 
pressure  has  actually  caused  widespread  declines  of  blue- 
birds in  California.  Western  Bluebird  populations  in  Cali- 
fornia appear  to  have  declined  only  slighdy  from  1 968  to 
1 989  while  Starlings  have  been  declining  or  stable  (USFWS 
unpubl.  analyses).  On  the  other  hand,  the  effects  of  Star- 
lings may  have  been  offset  by  human  activities  that  open 
up  forested  habitats,  making  them  more  to  this  bluebird's 
liking,  or  by  those  that  provide  additional  nest  sites  or 
perches  in  formerly  open  terrain. 


SWAINSON'S  THRUSH   Catharus  ustulatus 


A  summer  resident  from  late  Apr 

A^a!a?\^>^         \                'tf-v 

through  early  Oct. 

A  very  common,  widespread  breeder; 

^^vTojkA  V^ej^ryT  V--a  Wa  V- 

V-Z-  - 

overall  breeding  population  large. 

V^Y©A-'\ ''Jt^X    A^A  oiV^A      X^\     V-TV     V 
/l?\^«P\«Mo\/t:fl\/\     \^\     Y--A 

\     N^-^A    ^.    ^^  "       ^"^  "      ^^            ^^            ^^            ^^ 

Recorded  in  137  (62.0%)  of  221 
blocks. 

vWf ftj^A  «>  A^x    AA-A     Wa    V-a 

•^  A^AA  c  \^\  •  Va\  O  V^A  O  V--A      V 
f^\^^iAA€A^\    3£&&\Z^%-*i&=^X-'~ 

*lV<A  CA^\  •AtrC\  9  A^A  «  ><A  •«  V-'A  - 

-^An*A>A  •  'A^\  *>3r^A  •  \Adr©  \A^Y 
icWyt  A^A  •3r->A  ©AA^AC^^rA©  L< 
,Pv7  JkVT  •  V<\  ®  A^V®  \A-^*=A>^f< 

iiprxcV^^A 

-•s- 

O    Possible        =       17   (12%) 
C    Probable       =      95   (69%) 
•    Confirmed  =      25   (18%) 

» A^KSSr^— A«>-^A  ©  \>A  ©  Y^A  e$r 
^L^zrj^y^^          ~<v*  A-^A  •  v-'A  ©-  Y^A 
-^\'9>-^                 ^^<  »  YA-A  ©  Y>^\ °  A 

v?^ 

FSAR  =5        OPI  =  685       CI  =  2.06 

Ecological  Requirements 

The  haunting,  upward-spiraling  song  of  the  Swainson's 
Thrush  issues  forth  from  Marin  County's  dense  riparian 
groves,  mixed  evergreen  forests  on  the  lower  slopes  of 
stream  drainages,  locally  from  patches  of  north-facing 
coastal  scrub,  and  from  the  moist  intergradations  of  all 
these  with  other  forested  habitats.  The  unifying  character- 
istic of  these  varied  breeding  haunts  is  the  presence  of  a 
dense  moist  understory  or  shrub  layer  (c{.  Wilson's  War- 
bler). However,  Swainson's  Thrushes  inexplicably  do  not 
breed  in  the  dense  understory  of  Douglas  fir  and  bishop 
pine  forests  except  along  stream  courses.  In  Marin  County, 
the  closely  related  Hermit  Thrush  breeds  on  shady  forested 
slopes  with  an  open  understory  (see  account). 

Swainson's  Thrushes  fashion  attractive,  well-made  nest 
cups  from  dead  leaves,  mosses,  twigs,  fern  stalks,  and  strips 

318 


of  inner  bark,  all  mixed  with  mud.  They  line  the  nest  cup 
with  dry  grasses,  fine  rootlets,  fine  plant  fibers,  and  skele- 
ton leaves.  Swainson's  Thrushes  place  their  nests  in  the 
crotches  of  slender  willows,  in  low-hanging  dense  branches 
of  bushes,  on  top  of  fallen  masses  of  dead  bracken  ferns, 
or,  rarely,  near  the  extremity  of  a  limb  of  a  tree  (Bent  1949). 
Nest  height  varies  from  6  inches  to  40  or,  rarely,  perhaps 
60  feet  (most  are  4-5  ft.). 

Little  has  been  published  on  die  western  forms  of  the 
Swainson's  Thrush,  but  studies  elsewhere  shed  light  on 
their  foraging  habits.  Like  other  members  of  this  genus,  the 
Swainson's  Thrush  is  primarily  a  ground  forager.  The 
birds  uncover  savory  morsels  by  flipping  aside  the  debris 
of  the  forest  floor  with  their  bills,  after  which  they  progress 
to  the  next  seemingly  suitable  spot  by  means  of  long 


Thrushes 


SPECIES  ACCOUNTS 


Thrushes 


springing  hops  (Dilger  1956).  Swainson's  Thrushes  glean, 
lunge,  and  flycatch  more  in  the  foliage  of  trees  and  bushes 
than  do  Hermit  Thrushes.  The  foraging  beat  is  generally 
low  to  the  ground.  They  also  obtain  fruits  by  plucking 
while  perched  in  trees  or  bushes  or  by  retrieving  them  from 
the  forest  floor.  The  spring  to  fall  diet  of  adults  in  Califor- 
nia is  about  52%  animal  and  48%  vegetable  matter  (Beal 
1907,  n  =  1 57).  For  North  America  as  a  whole,  the  animal 
portion  of  the  diet  decreases  from  92%  in  spring  (n  =  1 74) 
to  36%  in  fall  (n  =  129)  (Martin  et  al.  1951).  Animal  food 
consists  primarily  of  beedes,  caterpillars,  and  ants,  with 
smaller  amounts  of  wasps,  true  bugs,  flies,  grasshoppers, 
other  insects,  spiders,  and,  rarely,  salamanders  (Beal 
1907).  Vegetarian  fare  includes  elderberries,  blackberries, 
raspberries,  twinberries,  coffeeberries,  poison  oak  berries, 
and  assorted  cultivated  fruits.  As  would  be  expected,  the 
food  fed  to  nestlings  is  overwhelmingly  arthropods 
(92.6%),  chiefly  caterpillars,  beedes,  true  bugs,  ants  and 
wasps,  and  arachnids  (principally  daddy-long-legs). 

Marin  Breeding  Distribution 

The  breeding  distribution  of  the  Swainson's  Thrush  in 
Marin  County  during  the  adas  period  closely  paralleled 
that  of  the  persistent  penetration  inland  of  the  coastal 
summer  fogs,  which  are  requisite  for  die  broad-scale  devel- 


opment here  of  dense  moist  undergrowth.  Most  breeding 
birds  occurred  here  within  a  few  hundred  feet  of  sea  level, 
in  conjunction  with  die  distribution  of  moist  dense  shrub- 
bery. Representative  nesting  locations  were  moist  coastal 
scrub  at  mouth  of  Estero  San  Antonio  (FY  6/24/82  —  DS); 
Vedanta  Trail,  Olema  Valley  (FY  6/15/81  -DS);  and 
Marshall-Petaluma  Rd.,  W  of  Gambonini  Ranch  (FY 
6/23/82  — DS).  The  lack  of  breeding  Swainson's 
Thrushes,  at  least  locally,  along  permanent  streams  in  the 
northeastern  corner  of  the  county  may  be  due  to  the 
overgrazing  of  understory  vegetation  or  the  effects  of  high 
cowbird  populations,  or  it  may  just  reflect  subdeties  of 
habitat  choice  unseen  by  the  human  (but  not  the  Catharus) 
eye. 

Historical  Trends/ Population  Threats 

For  unknown  reasons,  Swainson's  Thrushes  have  de- 
clined dramatically  since  the  1920s  on  the  west  slope  of  the 
Sierra  Nevada  (Gaines  1988).  On  the  whole,  Swainson's 
Thrush  populations  appeared  to  decline  slighdy  on  Breed- 
ing Bird  Surveys  in  California  from  1968  to  1989  but  were 
relatively  stable  from  1980  to  1989  (USFWS  unpubl.  analy- 
ses). 


319 


Thrushes 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Thrushes 


HERMIT  THRUSH   Catharus  guttatus 


A  year-round  resident;  numbers  swell 

^>s^^    \           jrv 

gready  from  late  Sep  through  mid-Apr. 

f\^K%>\ 

A  fairly  common,  local  breeder;  overall 

a  y<i\  ^ij\  A'  \  'j\^\  j^<^\  At^-v  -  - 

breeding  population  very  small. 

^\\Jk 

*\  y<^\  j^s\  'jsp^A  3r^\  j^c\  y<^^\ 

Recorded  in  48  (21.7%)  of  221  blocks. 

\^\  \^\  \^\*> \^\  \^\  \^\  \-^\ 

O    Possible        =       11    (23%) 

V*\ 

■x-i  NA^\      \-^\     \^\      v^\  •  .v-'n      V-^a    ^ 
>c\v.  V-"A    \^%A&^\  o  A"A    V"\  -j^rx^?*^ 

€    Probable      =      30  (63%) 

•    Confirmed  =        7   (15%) 

^V^\\^\    \^K^\^Ko\^&j^Kr--\^^-J\ 

^\  ■  X^\     \^x ■"■  A^V»  v<\  ®  \AA  o  V^V    V^"V 

— * 

3  x  MA/ 1  \^-A    WA    A--A  #^-A     V*<t\.  c  V-A  \  i 

FSAR  =  3        OPI  =  144       CI  =  1.92 

>W  Pc\  V^o>^A>^^v-^^Jv<\  Jva\ 

'^^^y^        <L  A-^^v-AftA-^A *A<\   A^cO 
'<x/>^                ^~~<  *>  v>A«v>v\  *>A'A0A^\^ 

r^?o* 

3f           ^%^^A 

1       hi^^                                                                                                                               \~-^/                                               ^^0<^     \ 

Ecological  Requirements 

Hermit  Thrushes  are  common  and  widespread  in  Marin 
County  in  the  winter,  but  wintering  birds  are  replaced  in 
the  breeding  season  by  a  race  (C.  g.  slevini)  of  more 
restricted  distribution  here  (G&.M  1944;  AOU  1957, 
1983).  The  transcendent,  flutelike  song  of  Marin's  breed- 
ing birds  rises  from  cool,  shady  redwood  and  Douglas  fir 
forests  with  a  sparse  understory  and,  locally,  from  bishop 
pine  forests  of  similar  structure.  The  local  requisites  of 
breeding  for  Hermit  Thrushes  seem  to  be  a  conifer  over- 
story,  scattered  saplings  or  bushes  for  nest  sites  and  cover, 
and  open  ground  with  a  well-developed  leaf  litter  layer  for 
foraging.  Suitable  forests  occur  here  primarily  on  the 
midlevel  to  upper  slopes  of  shaded  canyons  and  north- 
facing  drainages.  Although  coolness  and  moistness  charac- 
terize the  Marin  County  breeding  haunts,  these  seem  not 
to  be  of  ultimate  importance.  The  race  (C.  g.  polionota)  that 
breeds  in  the  Great  Basin  of  California  occurs  in  arid, 
low-stature  mountain  mahogany  (Cercocarpus  ledifolius) 
woodlands  (G&M  1944;  AOU  1957,  1983),  also  with  an 
open  understory  and  an  adequate  leaf  litter  layer.  In  Marin 
County,  the  closely  related  Swainson's  Thrush  breeds 
more  widely,  primarily  in  lowland  riparian  and  broad- 
leaved  evergreen  forests  widi  a  moist  dense  understory  (see 
account). 

Hermit  Thrushes  build  compact,  deeply  cup-shaped 
nests  fashioned  from  twigs,  small  branches  of  bushes, 
shredded  bark,  dead  leaves,  mosses,  and  roodets  (Bent 
1949).  They  line  them  with  fine  shredded  bark,  fine 
roodets,  dried  grasses,  and  decomposed  leaves.  Hermits 

320 


generally  construct  dieir  nests  in  branches  near  the  trunks 
of  saplings  or  bushes,  but  may  also  place  them  in  support- 
ing branches  and  twigs  of  small  intertwining  trees  or, 
rarely,  well  out  on  the  limbs  of  tall  conifers.  Nest  height 
varies  from  about  1.5  to  30  feet  above  ground  (most  3-5 
ft.). 

As  is  the  case  with  the  Swainson's  Thrush,  the  details 
of  the  foraging  habits  of  western  forms  of  the  Hermit 
Thrush  have  not  been  well  studied.  In  the  East,  the  general 
foraging  methods  employed  by  the  Hermit  Thrush  are 
similar  to  those  of  the  Swainson's  Thrush  (see  account), 
but  the  Hermit  is  considered  more  a  ground  forager  and 
less  a  flycatcher  (Dilger  1 956).  In  one  study,  though,  in  an 
area  of  dense  cover,  Hermits  spent  only  about  one-fourth 
of  their  foraging  time  on  the  ground  and  far  more  in  the 
foliage  of  saplings  and  the  midstory  of  trees  (Paszkowski 
1984). 

For  the  continent  as  a  whole,  the  animal  portion  of  the 
Hermit  Thrush  diet  decreases  progressively  from  93%  in 
spring  (n  =  171)  to  40%  in  winter  (n  =  180)  (Martin  et  al. 
1951).  The  June  to  July  diet  of  birds  breeding  in  the  Sierra 
Nevada  is  98.7%  animal  and  1.3%  vegetable  (Dahlsten  et 
al.  1985,  n  =  12),  whereas  that  of  birds  wintering  in  low- 
land California  is  56%  animal  and  44%  vegetable  (Beal 
1907,  n  =  68).  Principal  animal  foods  are  ants,  true  bugs, 
flies,  beedes,  scorpionflies,  and  caterpillars;  incidental 
items  are  snails  and  salamanders  (Beal  1907,  Dahlsten  et 
al.  1985).  The  main  vegetable  items  in  the  diet  are  fruits 
and  seeds.   Important  ones  are  misdetoe,  seeds  of  the 


Thrushes 


SPECIES  ACCOUNTS 


Thrushes 


pepper  tree,  poison  oak  seeds,  toyon,  manzanita,  pyracan- 
tha,  and  cotoneaster  berries,  and  raspberries  and  other 
cultivated  fruits  (Beal  1907,  GckM  1944). 

Marin  Breeding  Distribution 

During  the  adas  period,  Hermit  Thrushes  bred  in  Marin 
County  primarily  at  the  southern  end  of  Inverness  Ridge, 
in  the  Mount  Tamalpais  and  Lagunitas  Creek  watersheds, 
and  on  intervening  ridges  north  to  Big  Rock  Ridge. 
Although  the  central  and  northern  sections  of  Inverness 
Ridge  harbor  suitable  conifers,  the  dense  understory  shrub 
layer  (dominated  by  huckleberry)  precludes  breeding  by 
Hermit  Thrushes  except  locally,  where  suitable  openings 
in  the  shrub  cover  occur.  Representative  nesting  locations 


were  W  end  of  Big  Rock  Ridge  (NY  6/21/82  -ScC);  W 
end  of  Lucas  Valley  Rd.  (FY  7/1 1/82  -DS);  N  side  of  the 
ridge  N  of  San  Geronimo  and  Forest  Knolls  (NY  5/29/82 
— DS);  and  Bolinas  Ridge  below  lower  end  of  Kent  Lake 
(FY  6/16/82 -BiL). 

Historical  Trends/ Population  Threats 

Few  historical  data  are  available.  On  the  whole,  numbers 
of  Hermit  Thrushes  were  fairly  stable  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989,  though  they 
appeared  to  increase  slighdy  from  1980  to  1989  (USFWS 
unpubl.  analyses). 


The  haunting  countersinging  of  Swainson's  Thrushes  rising  from  forest  depths  on  a  still,  foggy  evening  is  tKe  pure 
essence  of  summer  on  the  Marin  County  coast.    Drawing  by  Keith  Hansen,  1991. 


321 


Tli  rushes 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Thrushes 


AMERICAN  ROBIN    Turdus  migratorius 


A  year-round  resident,  though  numbers 

swell  irregularly  from  Oct  through  Feb  or 
Mar. 

■^r\  *>^r\'0Jc^A  °JrA\  «Dcr<V~V^r\^Or>A  «A"\  \     ^ 

v  V^^J^oV^ol^Ae  V  „\  «\>A    J^\     >-V-<  -  - 
^A  ©  \Ay*  >A^  ©  a^a  ®  \>a  •  Y>ao  Jv\    Jr-"\©^A\ 

A  common,  nearly  ubiquitous  breeder; 

V^A  O  ,V>A  ®  A<T\  O  A-^\  0:UA  C  V"\  •  X^\  O  V<_   \ 

^T  o  V<r\  ©  v^\  o  \^\  o  W^v*  \^\  •  V^A  ©  a-^a  °^A 

overall  breeding  population  very  large. 

A    si><A    N>-^\  ©  A-""\  •  A^\  ®  \P\  ©  Y^"A  °  V^\  ©"-V- —    \ 

Recorded  in  197  (89.1%)  of  221 

V<>JXiA  ■*>  Af^iX  ®A^\®  V^A  Oi/AtpA  c  V<V 

blocks. 

\S.>--^A^rC\ ®Jv>\    A-^«V^°A'^»A--'A  *X^ 

W©  A<vvf  V<\  cJ^fe^A^\  *>3<^\©  A^x  Ayr^Tx^*^ 
\  Na^aVA  r  \  °  a--a  o  xsS&s  Yz^-f),&^-'~js?z\  «a<1    ; 

Via o  \-?^^  a?<a ®  V^v©Y^\js(  v^a   a^a  ♦a^'x  #/"^ 

O    Possible        =      32  (16%) 

V^\-P  A^X  ®  A-'-X  >JKV*>?A'  •  A-^A  •  \^\-*J^Z"\ 

T  ®/AiA\  O  AJ>A"©  \>^\*>\^\4  wrC©  A^"A  •A><A  -**x 
KqWV«  A^A'JV^A  *\^C#^^A  •  Jt^iV'A^A  ^A\ 

-•s-- 

€    Probable       =       78   (40%) 

•    Confirmed  -      87   (44%) 

^^VTXafea A^V^'A^A*  V^^'EV^V*  A^A  •A^ 

V*      7      7~\ 

^->^'^>^           ~~~"C©  V-"A  ©  W^A  ©-i^A  °A-<A  •VfwA 

^c> 

FSAR  =  4        OPI  =  788        CI  =  2.28 

kn                         ^-^S^\*^<^f^7^\*j^\»3 

rjj.               ^W^^^S*^ 

Ecological  Requirements 

The  American  Robin  is  one  of  the  best  known  North 
American  birds  and  for  good  reason,  since  it  is  at  home 
both  in  suburban  neighborhoods  and  in  the  forested 
wilds.  Another  of  our  edge  species,  Robins  use  the  borders 
of  all  of  Marin  County's  forested  habitats  along  moist 
grassy  openings.  They  also  favor  human  plantings  around 
ranchyards,  suburban  yards,  parks,  and  playing  fields. 
Although  Robins  will  occasionally  nest  well  inside  forests 
or  woodlands,  they  must  be  in  fairly  close  proximity  to 
openings  for  foraging,  and  consequently  most  of  them  nest 
on  edges  or  along  clearings.  Their  basic  requirements  seem 
to  be  adequate  nest  sites  and  protective  cover  in  trees, 
bushes,  or  human  structures;  moist  open  areas  with  sparse 
vegetation  and  soft  soil  for  ground  foraging;  and  mud  for 
nest  building. 

Robins  are  remarkably  adaptable  in  their  choice  of  nest 
sites,  though  a  variety  of  coniferous,  broadleaved  ever- 
green, or  deciduous  trees  and  bushes  are  their  mainstays. 
Other  natural  sites  include  crevices  in  cliffs,  ledges  of 
rocks,  among  upturned  roots  of  trees,  in  natural  cavities  or 
woodpecker  holes  in  trees  or  stumps,  or  on  top  of  old 
oriole,  wren,  or  hornet  nests.  Robins  will  even  nest  on  the 
ground,  particularly  where  substantial  vegetation  is  lack- 
ing; one  bird  laid  its  eggs  on  leaves  near  a  house  with  no 
sign  of  a  nest.  Additionally,  they  will  nest  in  a  variety  of 
artificial  sites  even  when  trees  are  at  hand.  These  include 
beams  inside  and  outside  buildings,  window  ledges,  eaves, 
gutters,  bird  boxes,  fire  escapes,  fence  rails,  statues,  chan- 
deliers, and  even  movable  sites,  such  as  fence  gates  or  train 

322 


signals.  Although  Robins  seem  to  build  many  nests  with- 
out regard  to  concealment,  they  usually  partly  conceal  and 
elevate  them  beyond  reach  of  predators.  Most  nests  in 
conifers  seem  to  have  an  overhanging  branch  to  protect 
them  from  sun  and  rain  (E.C.  Beedy  pers.  comm.).  Nest 
heights  range  from  ground  level  to  80  feet,  but  most  are 
about  5  to  20  feet  above  ground  in  trees  and  bushes 
(Howell  1942,  Bent  1949,  Tyler  1949,  Young  1955, 
Klimstra  &.  Stieglitz  1957,  Knupp  et  al.  1977,  Yahner 
1983).  Of  244  nests  in  New  York  (ranging  up  to  65  ft), 
half  were  from  2  to  10  feet  and  only  five  were  over  40  feet 
(Howell  1942).  Average  nest  heights  in  Iowa  and  Illinois 
are  11  feet  (range  5-45  ft.)  and  15  feet  (range  3-35  ft.), 
respectively  (Klimstra  &.  Stieglitz  1957);  in  Maine,  17  feet 
(Knupp  et  al.  1977,  n  =  60);  and  in  Wisconsin,  7  feet 
(range  2-30  ft.;  Young  1955,  n=  202).  Tree  nests  are 
usually  supported  by  branches  next  to  the  trunk,  but  they 
may  be  placed  well  out  on  horizontal  limbs  and,  rarely,  in 
upright  forks.  In  colder  climates,  Robins  most  frequently 
choose  evergreens  for  first  nests  and  deciduous  trees  for 
second  nests.  Sometimes  they  will  use  one  nest  to  raise 
more  than  one  brood  in  a  season,  and  in  successive  years 
they  may  build  nests  over  the  foundation  of  the  previous 
year's  nest. 

Robins  generally  build  bulky,  rough,  usually  bowl- 
shaped  nests,  though  shape  is  governed  to  a  large  extent  by 
the  site  chosen.  They  usually  construct  the  outer  wall  of 
long,  coarse  dead  grass  stems,  twigs,  weed  stems,  paper, 
string,  feadiers,  or  roodets;  rarely,  they  also  incorporate 


Thrushes 


SPECIES  ACCOUNTS 


Thrushes 


items  such  as  snakeskin,  dead  leaves,  cloth,  lace,  or  other 
human  artifacts  (Howell  1942,  Bent  1949,  Tyler  1949). 
The  birds  plaster  the  inside  of  their  nests  with  mud,  which 
they  may  go  up  to  a  quarter  of  a  mile  to  procure  (Howell 
1942).  They  will  even  make  their  own  mud  by  entering 
water  to  wet  their  feathers  and  then  shake  it  off  to  moisten 
dust;  one  bird  was  observed  to  fill  its  bill  with  dry  earth 
and  then  dip  it  into  a  bird  bath.  Generally  they  will  stop 
building  for  a  day  or  two  after  adding  the  mud  layer  to  let 
it  dry.  Robins  sometimes  substitute  manure  for  mud; 
rarely,  they  omit  the  mud  layer,  particularly  in  drought 
conditions.  Unusual  nests  have  been  composed  solely  of 
feathers,  shredded  paper,  or  just  cotton  and  mud.  The  nest 
lining  is  composed  mostly  of  dried  grass  blades,  perhaps 
with  a  few  grass  stems  or  twigs.  Other  lining  substrates  are 
seaweed,  cloth,  string,  cotton,  paper,  or  horsehair. 

Most  people  associate  foraging  Robins  with  their  stop- 
and-go  antics  on  lawns.  Birds  run  or  hop  for  short  dis- 
tances, pause  in  an  upright  stance  and  cock  their  heads 
from  side  to  side,  then  secure  their  prey,  once  located,  by 
probing,  pecking,  or  gleaning.  Almost  everyone  has  seen 
the  ensuing  tug-of-war  when  an  earthworm  is  rudely 
stretched  from  its  protective  burrow.  Robins  use  visual 
rather  than  auditory  or  tactile  cues  when  stalking  earth- 
worms (Heppner  1965).  Robins  specialize  on  earthworms 
when  moisture  brings  them  to  the  surface  or  at  dawn  and 
dusk  when  worms  are  foraging  near  the  surface.  They  also 
pick  up  prey  tossed  up  on  wave-washed  shorelines  or 
plunge  their  bills  into  shallow  water  to  secure  more  mobile 
prey.  Although  primarily  ground  foragers,  Robins  also 
glean  or  hawk  large  insects  from  the  foliage  or  adjoining 
air  space  of  trees  and  bushes,  and  they  gobble  up  berries 
while  perched  or  from  hovering  flight  (Paszkowski  1982) 

Robins  have  a  varied  omnivorous  diet  that  can  be 
weighted  to  over  99%  animal  life  in  midsummer  in  the 
Sierra  Nevada  (Dahlsten  et  al.  1985,  n  =  14).  Continent- 
wide,  animal  foods  range  from  79%  of  the  diet  in  spring 
to  19%-40%  from  summer  to  winter  (Martin  et  al.  1951, 
n  =  1423).  Prominent  animal  items  in  the  diet  of  western 
birds  are  caterpillars,  beedes,  earthworms,  flies,  grasshop- 
pers and  crickets,  butterflies  and  moths,  ants,  centipedes, 
spiders,  snails,  and  occasionally  small  fish  (Bent  1949, 
Dahlsten  et  al.  1985).  Common  California  fruits,  which 
predominate  in  the  diet  later  in  the  season,  are  berries  of 
madrone,  toyon,  elderberry,  coffeeberry,  misdetoe,  and 
blackberry;  berries  of  ornamentals,  such  as  pyrocantha, 
cotoneaster,  eugenia,  and  camphor;  and  cultivated  fruit 
where  available  (Bent  1949).  Adults  apparendy  feed  die 
young  by  regurgitation  for  the  first  few  days  (Howell  1 942). 


Marin  Breeding  Distribution 

During  the  adas  period,  the  American  Robin  was  one  of 
the  most  widespread  breeding  birds  in  Marin  County 
because  of  its  ability  to  exploit  a  variety  of  habitats  from 
forest  edges  of  the  hinterlands  to  urban-suburban  settings. 
Representative  breeding  localities  were  Bear  Valley  Trail, 
PRNS  (NY  7/3/80  -DS);  Walker  Creek,  near  Hwy.  1  (NB 
5/1/82  -DS);  Miwok  Park,  Novate  (NY  5/?/82  -ScC); 
and  Mt.  Burdell,  Novato  (NB  4/1 1/81  -DS). 

Historical  Trends/  Population  Threats 

The  American  Robin  was  not  always  a  widespread,  numer- 
ous breeder  here.  Mailliard  (1900),  Storer  (1926),  and 
Stephens  and  Pringle  (1933)  all  considered  Robins  to  be 
only  winter  visitants  in  Marin  County.  However,  Grinnell 
and  Wythe  (1927),  in  their  authoritative  book  on  the 
avifauna  of  the  San  Francisco  Bay  region,  stated  that  prior 
to  1915  Robins  reached  the  southern  limit  of  their  coastal 
breeding  range  in  Sonoma  and  Marin  counties.  They  list 
San  Geronimo  and  Inverness  as  stations  of  record  for 
permanent  resident  Robins  before  1915.  Starting  in  1915, 
American  Robins  were  first  reported  nesting  in  San  Fran- 
cisco. Further  breeding  reports  quickly  surfaced  elsewhere 
in  the  Bay  Area  and  the  Sacramento  Valley,  areas  formerly 
devoid  of  breeding  Robins  (Storer  1926).  These  Robins 
were  colonizing  lowland  areas  rendered  suitable  by  human 
irrigation  and  setdement,  and  they  continued  to  do  so 
(G&.M  1944,  Sibley  1952).  The  planting  of  lawns  and 
irrigation  of  orchards  provided  moist  foraging  habitat  in 
the  normally  bone-dry  summers  of  much  of  lowland  Cali- 
fornia; tree  plantings  augmented  nesting  sites.  Although 
Robins  were  breeding  in  the  moist,  fog-drenched  coastal 
ridges  of  Marin  County  prior  to  their  colonization  of  much 
of  the  Bay  Area,  they  surely  also  expanded  in  the  setded 
areas  of  Marin.  Areas  of  Marin  where  Robins  undoubtedly 
expanded  gready  are  the  urban-suburban  corridor  along 
Highway  101  and  die  nordiern  and  eastern  ranchlands.  In 
the  former  region,  expansion  probably  followed  tree  and 
grass  plantings  in  some  areas  and  tree  clearing  in  others. 
In  the  ranchlands,  Robins  probably  spread  with  watering 
in  ranchyards  and  gardens  and  with  the  establishment  of 
trees  and  buildings  in  formerly  wide  open  terrain. 
Whether  die  expansion  of  concrete  and  asphalt  will  out- 
strip that  of  lawns  and  exotic  tree  plantings  and  cause  a 
reversal  of  the  trend  in  Robin  populations  remains  to  be 
seen.  Perhaps  it  already  has,  as  Robin  numbers  decreased 
on  Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


323 


Wrentits 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wrentits 


Wrentits 

Family  Muscicapidae 
Subfamily  Timaliinae 


WRENTIT   Chamaea  fasciata 


~^-&?r^ 

A  year-round  resident. 

/f^P\pV^>s^^           \                       J(V 

A  common,  very  widespread  breeder; 

i^^X^^                                                                      , 

overall  breeding  population  very  large. 

^ToY^v* VA»i>\e\/\o  \>-A     V^A  o \^\ ©O,  - 

Recorded  in  182  (82.4%)  of  221 

v*i\  ©  r\^\  ©  V"\  ©  V^A  ©A^^T©  \^\     x^\     V-r    \ 
^C ®V-1A®  V^©>^\©W^v    \^\     VA    A^v®^ 

blocks. 

\<r^^X)PJr<A©3^^*A^^©>^^><^©"V>A-    \^k\ 

xxtoOAA^x®  \^A©  V^"A©  V^C®  \^"<\C^n^\     vxa  °J 

X   s<>>\   >><r\  ©  Ar^X  ©  Jv-^x  ©  \?^\  ©  V^TX  ©  A-"\    \V^\ 

V^\©xXx;>s, «  XT---A  ©.•V>A  ©  V-^V©  V^A  ©  V-^x  ©  V-^\      J 
V<«Nj£><i\  ®  Jr^X  ©  3r-"A  °  .V-"\  ©  A^X  ©  A^X      V^A 

O    Possible        =       15   (8%) 

\  \^<^^VA  tiA ©  v^x ©\8^« A^^^A^v^-j^fx © A^T  ) 

C    Probable       =     131    (72%) 

vca © >?^-vr9K^\ © v^rcY^C-2' v^x © jv<r\ ®^\  °r^ 

Vt£x*>  V^x « J2£"A »  A>A  •  \>^Y  ©A-^-Y®  A-^A  •  A^T ;  "" 

•    Confirmed  =       36   (20%) 

\1*><A  ©Jit^X  *JiT\  f>^\  ©  Jv<?A"®JV>'V  -  Ar^X  "-^pX 

\P\-«®  jr-^x  ©  3r<rx  ••^\^©Jv>a  •  J^x  ©  j^v-©  Jt-^T"^v> — ' 

-  "^ 

T  oP'A©v>v* \>^©JV^v©\^iC® j^\»j^\--'f>^r 

U-^\S®?A<1\  •  A^X  ©Jr^X  •  A^dr®  V^X"  ©A-<S\  •3i^w\_~_ 

FSAR  =  4        OPI  =  728        CI  =  2.12 

J-*<V©  Vl\  ®  V^X  ®  Ar^A-*  A^^tKV^K  ©  >^\  •  Ar-^A  °  Z- 

>^*^^      ^<®>^C  ®  3i^\  ®i^\  ®3t<A  ®A%& 

^a 

■\£^                                          \^^©\!-"r^  V-^^X^V®  V-5*^ 

^j^cv^^^y 

Jj^                           v^/    ^"^k«A> 

Ecological  Requirements 

The  Wrentit  is  the  sole  representative  of  the  Old  World 
Babbler  or  Timalinae  subfamily  in  North  America.  Its 
entire  distribution  is  limited  to  the  West  Coast  and  is 
bounded  to  the  north  by  die  Columbia  River,  to  the  south 
by  the  deserts  of  Baja  California,  and  to  the  east  by  the  west 
slope  of  the  Sierra  Nevada  (AOU  1983).  In  Marin  County, 
it  occurs  in  a  variety  of  habitats  with  a  dense  continuous 
shrub  layer  and  gaps  no  greater  than  a  few  meters  across 
which  Wrentits  must  fly.  The  preferred  haunts  here  are 
mature  chaparral  and  coastal  scrub.  Wrentits  also  breed 
widely  in  Marin  in  suitable  scrub  in  riparian  thickets, 
along  the  brushy  borders  of  most  other  forested  habitats, 
in  successional  scrub  fields,  and  in  suburban  yards.  They 
do  inhabit  conifer  forests  here  to  a  degree  but  generally 
around  sunny  openings;  they  avoid  dense  huckleberry 
thickets  under  shaded  Douglas  fir  forests. 

Since  1979,  the  Wrentit  has  been  one  of  three  key 
species  that  have  been  the  object  of  intensive  research  in 
Point  Reyes  Bird  Observatory's  study  of  the  coastal  scrub 
bird  community  at  Palomarin.  The  average  height  above 
ground  of  236  nests  at  Palomarin  was  25.9  inches  (range 
6.7-53.9  in.,  G.R.  Geupel  unpubl.  data).  Wrentits  there 

324 


built  88%  of  their  nests  in  either  coastal  sage  or  coyote 
brush,  and  the  remainder  in  blackberry,  poison  oak, 
bracken  fern,  sticky  monkeyflower,  coffeeberry,  Douglas 
fir,  lizard  tail,  and  even  rushes  (PRBO  unpubl.  data). 
Elsewhere  they  use  a  wide  variety  of  shrubs  and,  rarely, 
trees  (Erickson  1938,  Bent  1948).  In  coastal  scrub  at 
Berkeley,  Erickson  (1938)  found  44  nests,  of  which  31 
were  in  coyote  brush.  The  height  of  25  nests  she  measured 
ranged  from  1 2  to  42  inches,  but  most  were  from  18  to  24 
inches  above  ground.  She  also  reported  three  unusual 
nests  found  by  others  from  1 2  to  1 5  feet  up  in  live  oaks  or 
alders.  Taking  a  week  or  longer,  the  male  and  female 
construct  a  tight,  open-cupped  nest  that  they  normally 
conceal  in  the  crotch  of  a  dense  shrub  or,  less  frequendy, 
in  twigs  of  die  leafy  crown  (Erickson  1938,  G.R.  Geupel 
unpubl.  data).  At  Palomarin,  Wrentits  fashion  the  nest 
foundation  from  shreds  of  bark  pulled  off  living  coastal 
sage  and  coyote  brush  (G.R.  Geupel  unpubl.  data), 
although  they  may  use  bark  from  a  variety  of  other  shrubs 
(Erickson  1938).  They  glue  the  bark  strips  together  with 
balls  of  carefully  collected  cobwebs.  Wrentits  line  the 
inside  of  the  nest  cup  with  fine  shreds  of  bark  or  grasses 


Wrentits 


SPECIES  ACCOUNTS 


Wrentits 


and  usually  festoon  the  outside  with  small  bits  of  lichens 
(Erickson  1938,  G.R.  Geupel  pers.  obs.).  Near  civilization, 
Wrentit  nests  sometimes  contain  string,  tissue  paper,  and 
cigarette  butts  (G.R.  Geupel  pers.  obs.).  The  importance  of 
quality  materials  is  indicated  by  the  fact  that  if  a  nest  fails 
or  the  pair  decides  to  double  brood,  the  first  nest  is  usually 
dismanded  and  the  materials  are  recycled  in  the  next  nest 
attempt  (PRBO  unpubl.  data).  It  is  not  uncommon  for  a 
pair  to  complete  a  nest  and  then  decide  to  move  it  to  a  new 
location  before  the  first  egg  is  laid.  Wrentits  normally 
conceal  their  nests  well  from  above  to  avoid  predation  by 
Scrub  Jays.  Concealment  from  below  does  not  seem  to  be 
as  important,  probably  because  Wrentits  actively  feign 
injury  around  their  nest  to  distract  snakes  approaching 
from  the  ground  (Geupel  1981).  Despite  a  longer  nesting 
cycle  (33  days),  Wrentits  at  Palomarin  have  higher  nesting 
success  than  other  species  nesting  in  the  same  habitat 
(Geupel  6k  DeSante  1983). 

Wrentits  actively  glean  larvae,  insects,  and  spiders  from 
the  bark  and,  less  frequendy,  from  the  green  leaves  or 
fruiting  stems  of  the  shrubbery  (Erickson  1938,  G.R. 
Geupel  pers.  obs.).  Most  items  are  within  "peck  range," 
but  if  the  prey  is  high  in  the  shrub,  the  Wrentit  will  quickly 
fly  to  it  and  just  as  quickly  leap  down.  Sometimes  individu- 
als fly  up  and  hang  inverted  while  hunting  among  the 
leaves  of  live  oaks,  as  a  Bushtit  or  Plain  Titmouse  might 
do.  Wrentits  also  hover  briefly  at  sticky  monkeyflowers 
and,  rarely,  will  flycatch  for  butterflies  or  the  like.  Individu- 
als attacking  centipedes  sometimes  use  both  feet  to  subdue 
prey  (Erickson  1938).  Wrentits  also  consume  great  quanti- 
ties of  small  fruits.  If  the  fruit  is  small,  it  is  swallowed 
whole;  otherwise  it  is  grasped  with  one  foot,  and  small 
pieces  are  pulled  off  with  the  bill  (Erickson  1 938).  Wrentits 
also  eat  grain  and  seeds  when  invertebrates  and  fruit 
become  scarce  in  the  winter.  At  Palomarin,  traps  baited 
with  "chicken  scratch"  are  normally  successful  only  in 
winter  and  then  only  when  placed  in  the  tops  of  bushes 
(G.R.  Geupel  pers.  obs.).  Rarely  do  Wrentits  forage  on  the 
ground. 

The  year-round  diet  of  Wrentits  in  California  is  about 
52%  animal  and  48%  vegetable  matter  (Beal  1907,  n  = 
165).  Animal  matter  in  the  diet  here  ranges  from  a  high  of 
94%  in  spring  (n  =  13)  to  a  low  of  36%  in  fall  (n  =  62) 
(Martin  et  al.  1951).  The  main  animal  foods  are  ants  and 
wasps,  beetles,  caterpillars,  moth  cocoons,  true  bugs,  and 
scale  insects,  along  with  various  other  insects  and  spiders 
(Beal  1907).  In  contrast  to  Bushtits,  Wrentits  consume  a 
large  proportion  of  ants  and  wasps  and  a  small  proportion 
of  true  bugs;  the  former  items,  at  least,  reflect  the  low 


foraging  beat  of  Wrentits.  At  Palomarin,  small  green  geo- 
metrid  (inchworm  moth)  larvae  are  the  preferred  forage 
brought  back  to  nesdings  (G.R  Geupel  pers.  obs.).  This  is 
in  accord  with  Beal's  (1 907)  report  of  the  stomach  contents 
of  one  brood  that  was  largely  caterpillars  and  secondarily 
spiders,  true  bugs,  and  beedes;  all  but  the  latter  are  very 
soft  in  nature.  The  vegetable  fare  is  fruit  such  as  elderber- 
ries, snowberries,  coffeeberries,  twinberries,  blackberries, 
and  poison  oak  seeds;  the  latter  are  especially  important 
from  August  to  February,  when  they  make  up  one-quarter 
of  the  diet.  A  few  weed  seeds,  leaf  galls,  and  rubbish  make 
up  the  remainder. 

Marin  Breeding  Distribution 

During  the  adas  period,  Wrentits  bred  widely  throughout 
most  of  Marin  County.  They  were  most  numerous  along 
the  immediate  coast  where  coastal  scrub  and  other  brush 
is  prevalent  and  on  selected  drier  interior  hills  and  ridges, 
such  as  Mount  Tamalpais  and  Carson  Ridge,  where  chap- 
arral is  extensive.  They  were  lacking  in  Marin  only  from 
the  outer  tip  of  Point  Reyes,  from  sections  of  the  grassland- 
dominated  hills  around  Tomales,  and  from  certain  open, 
oak-studded  hills  or  bayshore  fladands  near  Novato  that 
generally  lack  suitable  brush.  Representative  nesting  loca- 
tions were  Palomarin,  PRNS  (NE-NY  late  Mar-late  Jul 
1979-1982  -PRBO);  Limantour  Spit,  Point  Reyes  (NB 
4/24/80  -DS);  Ledum  Swamp,  Point  Reyes  (FY/FL 
6/13/82  -DS);  and  China  Camp  SP  (FY  6/19/82  -BiL). 

Historical  Trends/ Population  Threats 

Grinnell  and  Miller  (1944)  did  not  mention  any  historical 
changes  in  Wrentit  populations  in  California.  Presumably 
diis  was  because  any  changes  were  slight  or  because  the 
positive  and  negative  effects  of  human  activities  had  been 
counterbalancing.  Clearing  of  coastal  scrub  or  chaparral 
for  housing  has  been  offset  to  a  degree  by  the  planting  of 
suburban  gardens,  which  Wrentits  have  invaded.  Fire, 
agriculture,  and  other  development  are  probably  the  main 
forces  reducing  Wrentit  habitat.  On  the  other  hand,  chap- 
arral is  fire  adapted,  and  Wrentits  normally  reinvade  the 
new  vigorous  growth  within  a  few  years.  Extensive  clearing 
of  forests  that  are  replaced  by  dense  brushfields  must  have 
gready  benefited  Wrentits  in  some  areas.  Analyses  of 
Breeding  Bird  Survey  data  for  1968  to  1979  indicated 
Wrentits  were  increasing  in  California  (Robbins  et  al. 
1986),  but  not  when  extended  to  include  data  through 
1989  (USFWS  unpubl.). 

GEOFFREY  R.  GEUPEL 


325 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wrentits  are  very  solicitous  parents.    Photograph  by  Ian  Tait. 


326 


Mockingbirds  and  Thrashers 


SPECIES  ACCOUNTS 


Mockingbirds  and  Thrashers 


Mockingbirds  and  Thrashers 

Family  Mimidae 


NORTHERN  MOCKINGBIRD  Mimus  polyglottos 


A  year-round  resident. 

/5~#% 

A  fairly  common,  somewhat  local 
breeder;  overall  breeding  population 
small. 

Recorded  in  67  (30.3%)  of  221  blocks. 
O    Possible        =       10   (15%) 

\^l\    \^\    Jv-'x  •  \^"a  •  J> 
--Y^A  ^V^a  ^-V\.  ^v^A  ^Vk\— 

-<- 

€    Probable       =       34   (51%) 
•    Confirmed  =      23  (34%) 

FSAR=3        OPI  =  201         CI  =  2.19 

j^> 

^O 

Ecological  Requirements 

In  California,  the  Northern  Mockingbird  originally  inhab- 
ited desert  wash  scrub,  broken  chaparral,  or  open  wood- 
land edges  in  the  southern  part  of  the  state  (Grinnell  191 1, 
Unitt  1984).  With  the  expansion  of  human  setdement,  the 
Mockingbird  has  become  predominandy  a  bird  of  residen- 
tial and  agricultural  landscapes.  In  Marin  County,  these 
classy  and  highly  visible  vocal  mimics  largely  dwell  in 
urban  and  suburban  yards  or  parks  and,  more  sparingly, 
rural  ranchyards.  Important  features  of  these  habitats  are  a 
sparse  cover  of  large  bushes  and  densely  foliaged  trees  for 
shelter  and  nesting,  intervening  open-ground  foraging 
areas,  and  a  supply  of  berry-  and  fruit-bearing  trees.  Mock- 
ingbirds are  most  numerous  in  residential  areas  widi  open 
lawns  and  scattered  plantings.  In  1981,  Mockingbirds 
were  breeding  locally  in  a  natural  habitat  of  scattered 
stunted  oaks  and  grassland  at  die  end  of  San  Andreas 
Road  at  the  base  of  Mount  Burdell,  Novato  (D.  Shuford 
pers.  obs.),  but  this  area  may  soon  be  swallowed  up  by 
suburban  sprawl. 

Mockingbirds  construct  their  bulky  cup  nests  primarily 
of  small  twigs  and  line  them  with  grass  and  roodets.  They 
may  also  incorporate  various  items— such  as  string,  paper, 
foil,  and  trash— into  the  wall  of  the  nest.  Nest  placement 


varies  from  about  1  to  40  feet  above  the  ground  (Bent 
1948).  In  northern  California,  most  nests  are  3  to  15  feet 
up  in  vines,  thickets,  small  trees,  or  even  on  fence  posts  or 
stumps  (Harrison  1978).  In  Louisiana,  average  nest  height 
of  one  sample  of  108  nests  was  6  feet  (Joern  &  Jackson 
1 983),  and  of  another  of  1 51  nests  was  8  feet  (range  1 .5-29 
ft.,  Taylor  1965);  in  the  latter  study,  nest  height  increased 
as  the  season  progressed. 

The  Mockingbird  diet  is  varied  and,  continentwide,  the 
proportion  of  animal  food  ranges  from  a  high  of  73%  in 
spring  (n  =  84)  to  a  low  of  33%  in  fall  (n  =  65)  (Martin  et 
al.  1951).  The  diet  of  the  Mockingbird  in  southern  Cali- 
fornia from  late  July  to  late  August  is  about  23%  animal 
matter  and  77%  vegetable  (Beal  1907,  n  =  33).  The  vege- 
table matter  is  predominantly  fruit  and  minor  amounts  of 
seeds.  In  Marin,  wild  blackberries,  elderberries,  and  poi- 
son oak  seeds  would  be  included,  as  well  as  the  berries  of 
pyrocantha,  cotoneaster,  Crataegus,  and  other  fruits  from 
ornamental  and  residential  plantings.  Mockingbirds 
spend  much  of  their  time  feeding  on  the  ground,  and  thus 
grasshoppers  and  ants  constitute  about  90%  of  the  animal 
matter  in  the  diet  (Beal  1 907).  They  eat  smaller  amounts 
of  beedes,  caterpillars,  other  insects,  and  spiders,  and, 

327 


Mockingbirds  and  Thrashers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Mockingbirds  and  Thrashers 


rarely,  small  lizards  and  snakes.  Besides  plucking  berries 
from  trees  and  bushes,  Mockingbirds  also  glean  some 
insects  from  the  foliage.  Home  range  sizes  increase  during 
the  course  of  nesting  (Biedenweg  1983),  and  abundant 
food  sources  such  as  feeding  trays  will  attract  many  birds 
within  a  quarter-mile  radius  (Michener  1951).  For  their 
first  six  days,  nesdings  are  fed  almost  all  animal  matter, 
predominandy  small  insects  and  spiders.  After  this  they 
are  fed  more  fruit,  which,  by  10  to  20  days  after  hatching, 
comprises  30%-35%  of  the  nesding  diet  (Breitwiech  et  al. 
1984).  The  switch  occurs  about  the  time  the  young  are  first 
able  to  regulate  their  own  body  temperatures.  At  this  time, 
nesdings  are  fed  greater  proportions  of  fruit  later  in  the 
day.  This  may  be  because  fruit  provides  water,  which  is  in 
greater  demand  during  the  heat  of  the  day,  or  because  the 
carbohydrates  of  fruit  are  needed  later  for  energy  demands 
in  the  cool  hours  of  night  (Breitwiech  et  al.  1984).  Perhaps 
this  also  reflects  daily  changes  in  insect  activity  and  hence 
availability  (see  Loggerhead  Shrike  account).  The  young  are 
also  fed  small  amounts  of  limestone  bits  or  snail  shells. 

Marin  Breeding  Distribution 

Mockingbirds  now  breed  commonly  in  Marin  County 
only  in  die  urban-suburban  environment  along  die  High- 
way 101  corridor  in  the  eastern  portion  of  the  county. 
During  the  adas  period,  a  small  population  appeared  to  be 
established  in  the  rural  Tomales  area,  as  were  marginal 
populations  on  the  immediate  coast  in  the  Point  Reyes 
Station  (S  5/21-7/15/82  — DS)  and  Stinson  Beach  (sing- 
ing bird  4/14/82  — HS)  areas.  Subsequendy,  there  has 
been  confirmed  evidence  of  coastal  breeding  in  Point  Reyes 
Station  (FY/FS  "early  summer"  1987  -RS)  and  at  the 
RCA  station  near  Bolinas  (FY/FL  "summers"  of  1986  and 
1987  — DDeS).  Other  representative  nesting  locations 
included  the  base  of  Mt.  Burdell,  Novato  (UN  5/19/81 
-DS;  NY  5/.V82  -ScC);  Novato  (NY  5/25/78  -RMS); 
and  Kentfield  (NB  4/6/82  -BiL). 


Historical  Trends/Population  Threats 

Mockingbirds  of  both  die  western  and  eastern  subspecies 
have  been  expanding  their  breeding  ranges  northward  for 
many  years.  In  California,  die  Mockingbird's  breeding 
range  has  increased  gready  in  this  century  in  concert  with 
the  expansion  of  the  human  population  in  urban,  subur- 
ban, and  rural  agricultural  areas,  in  the  latter  especially 
where  orchards  predominate  (Arnold  1935,  1980).  In 
1911,  the  Mockingbird  was  spreading  rapidly  in  the  low- 
lands of  southern  California  and  the  San  Joaquin  Valley 
(Grinnell  1911).  In  1927,  it  was  considered  "a  sparse 
winter  visitant  to  the  San  Francisco  Bay  region"  (G<SlW 
1927),  but  at  that  time  breeding  had  not  yet  been  docu- 
mented along  the  northern  California  coast.  Nesting  was 
established  in  the  San  Francisco  Bay  Area  in  1928  and 
1929,  and  Mockingbirds  continued  to  expand  their  breed- 
ing range  throughout  die  San  Joaquin  and  Sacramento 
valleys  (Arnold  1935,  1980;  Sibley  1952).  Although  first 
recorded  in  Marin  County  at  least  by  1900  (Mailliard 
1900),  Mockingbirds  were  not  seen  with  regularity  here 
until  about  1960,  and  then  mosdy  in  the  fall  and  winter 
(ABN).  Although  the  history  of  initial  breeding  in  Marin 
County  is  unknown,  it  must  have  followed  soon  after  their 
first  influx,  in  the  early  1960s.  A  breeding  season  record 
of  a  Mockingbird  in  Tiburon  from  1  to  15  June  1958  was 
considered  worthy  of  publication  in  the  Condor  (Stern 
1959),  but  by  the  time  of  the  adas  work  from  1976  to  1982, 
Mockingbirds  were  breeding  widely  in  eastern  Marin 
County.  Although  Breeding  Bird  Surveys  indicate  that  the 
Mockingbird  population  in  California  has  been  relatively 
stable  from  1968  to  1989  (Robbins  et  al.  1986,  USFWS 
unpubl.  analyses),  it  is  still  expanding,  at  least  locally,  along 
the  immediate  coast  north  of  the  San  Francisco  Bay  region 
(e.g.,  AB  34:929).  It  seems  likely  that  the  Mockingbird  will 
continue  to  consolidate  and  expand  its  range  in  California 
in  association  with  the  burgeoning  human  population, 
though  to  a  much  more  modest  extent  than  in  past 
decades. 

JOHN  R  ARNOLD 


328 


Mockingbirds  and  Thrashers 


SPECIES  ACCOUNTS 


Mockingbirds  and  Thrashers 


CALIFORNIA  THRASHER    Toxostoma  redivivum 


-vg^W 

F^A^fr-.               ^ 

A  year-round  resident. 
An  uncommon,  very  local  breeder; 

J^L\    J<K 

t^_  " 

overall  breeding  population  very  small. 
Recorded  in  15  (6.8%)  of  221  blocks. 

C-VA>r^f3r\T 

V^rCV^ 

O    Possible        =        6  (40%) 

YV 

>c    Jt^^X  *-j^^^  \  o_\^x> 

\^\  \ — \*> jt — ' 

— \      V-'A*  V-"A 
v^-V\  ^rx'LV' 
*£r  Ar-<V-  A^x©^ 

©    Probable       =        9  (60%) 
•    Confirmed  =        0   (0%) 

v^\  \^\^-*&*?^\  x  A^ 

\  3r\^V\° 

\V>^C     " 

-^\-  ■  \^\    v^v^'Ai---^ 

0"  Jr-^V  O V-^\     jf^ 

Jv^x^^r 

—  -r" 

FSAR=2        OPI  =  30         CI  =  1.60 

2^<vMLVV^v^\V 

^V^\  ^2^=CA  *lAf<^ 

Vo 

Ecological  Requirements 

These  voluble  thrashers  reside  in  Marin  County  only  in 
tall  dense  chaparral  on  interior  ridges  shielded  from  the 
influence  of  persistent  summer  coastal  fogs.  Suitable  chap- 
arral is  open  next  to  the  ground,  while  close  overhead  there 
is  a  strongly  interlacing  branchwork  and  an  evergreen  leafy 
canopy  (Grinnell  1917).  Tall  protective  brushy  cover  for 
concealment  and  nest  sites,  and  loose,  generally  dry  soil  for 
foraging  are  the  California  Thrasher's  main  habitat 
requirements.  Marin's  breeding  Thrashers  do  not  inhabit 
coastal  scrub  along  the  immediate  coast  or  suburban  yards 
with  appropriate  shrubbery,  as  they  do  south  of  San 
Francisco,  or  thick  riparian  brush,  as  they  do  to  a  limited 
extent  throughout  much  of  their  range. 

California  Thrashers  build  rough  nest  bowls  of  coarse 
interlaced  sticks  and  finer  twigs,  and  line  them  with  dried 
grasses,  rootlets,  and  bark  strips  (Dawson  1923,  Woods 
1948).  They  conceal  their  nests  from  about  2  to  12  feet 
above  ground  in  the  dense  branchwork  of  bushes,  scrubby 
trees,  or  hedges;  nests  are  rarely  found  in  live  oaks  or  far 
from  continuous  brush  cover  (Grinnell  1917,  Engels 
1940,  Woods  1948). 

California  Thrashers  forage  primarily  on  the  ground  in 
the  litter  and  soil  under  chaparral  cover,  from  which  they 
rarely  stray  far.  They  do  not  employ  their  feet  in  scratching 
as  do  many  ground  foraging  birds  of  brushy  habitats. 
Instead,  birds  run  swiftly  or  hop  to  suitable  feeding 
grounds,  where  they  use  their  long  decurved  bills  to 
unearth  prey,  mosdy  by  subsurface  digging.  With  its  legs 
well  braced,  the  bird  strikes  its  bill  into  the  ground  with 


rapid  strokes  of  its  head  and  neck,  and  hooks  the  dirt  back 
and  out  widi  a  powerful  pull  of  its  neck.  Frequendy,  its 
mandibles  are  slighdy  open  when  it  digs,  but  usually  not 
when  dirt  or  litter  is  swept  away  with  side-to-side  motions 
of  die  bill  (Engels  1940).  Thrashers  obtain  fruit  and  berries 
from  bushes  or  from  the  ground  and  presumably  also 
secure  some  insect  prey  from  the  foliage  (Grinnell  1917). 
California  Thrashers  are  omnivorous,  and  their  year- 
round  diet  in  California  is  about  59%  vegetable  and  41% 
animal  matter  (Beal  1907,  n  =  82).  Limited  data  (n  =  7) 
suggest  that  animal  matter  comprises  about  97%  of  the 
spring  diet,  but  otherwise  it  constitutes  only  34%-45%  of 
die  diet  from  summer  through  winter  (n  =  25-39/season) 
(Martin  et  al.  1951).  Vegetable  fare  consists  of  wild  and 
cultivated  fruits  and  berries,  including  those  of  elderberry, 
coffeeberry,  manzanita,  poison  oak,  other  Rhus  bushes, 
raspberry,  sumac,  buckthorn,  and  grape  (Beal  1907,  Mar- 
tin et  al.  1951).  Mast,  weed  seeds,  leaf  galls,  rubbish,  and 
grains  are  of  secondary  importance.  The  animal  fare  con- 
sists of  beedes,  ants,  wasps,  bees,  caterpillars,  cocoons, 
moths,  true  bugs,  flies,  grasshoppers,  Jerusalem  crickets, 
spiders,  centipedes,  and  millipedes  (Beal  1907). 

Marin  Breeding  Distribution 

During  the  adas  period,  we  found  that  California  Thrash- 
ers had  a  restricted  breeding  distribution  in  Marin  County. 
They  bred  here  primarily  on  the  top  of  Mount  Tamalpais 
and  on  Carson  and  Big  Rock  ridges.  Small  populations 
inhabited  isolated  patches  of  chaparral  in  the  hills  near 

329 


Mockingbirds  and  Thrashers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Shrikes 


Soulajoule  Reservoir  in  north-central  Marin.  Thrashers 
have  yet  to  be  confirmed  as  breeders  in  Marin  County,  but 
because  they  are  nonmigratory,  permanent  residents,  there 
can  be  no  doubt  that  they  nest  here  regularly.  Representa- 
tive nesting  locations  based  on  presumed  evidence  of 
breeding  were  Dolcini  Ranch  near  Soulajoule  Reservoir 
(PO— seen  6/16/82  — DS);  headwaters  of  San  Jose  Creek 
on  Big  Rock  Ridge  (PR-S  3/26-5/9/79  -DS);  Carson 
Ridge  (PR-S  2/26-6/14/80-82  -DS);  near  East  Peak  Mt. 


Tamalpais  (PR  5/14-6/11/82  -DSi);  and  Blithedale 
Ridge  (PR  4/20  &.  5/8/82  -DSi). 

Historical  Trends/Population  Threats 

There  is  little  prior  information,  but  Breeding  Bird  Survey 
data  indicate  that  numbers  of  California  Thrashers  were 
declining  in  California  from  1968  to  1989  (USFWS 
unpubl.  analyses). 


Shrikes 

Family  Laniidae 


LOGGERHEAD  SHRIKE   Lanius  ludovicianus 


A  year-round  resident;  numbers  swell 
slightly  from  Sep  through  Mar. 

An  uncommon,  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  40  (18.1%)  of  221  blocks. 


O    Possible        = 

23  (58%) 

©    Probable       = 

5  (13%) 

W    Confirmed  = 

12  (30%) 

FSAR  =  2        OPI  = 

80         CI  =  1.72 

Ecological  Requirements 

These  poised  and  efficient  mandibular  hunters  inhabit 
Marin  County's  open  lowland  valleys  of  grasslands,  fields, 
and  broken  woodlands.  Like  that  of  many  grassland  breed- 
ers here,  the  Shrike's  preference  for  valley  bottoms  (over 
steeper  hillsides)  presumably  reflects  greater  prey  availabil- 
ity there.  Shrikes  do  reside  on  relatively  level  ridgetops 
elsewhere  in  the  Bay  Area  (S.L.  Granholm  pers.  comm.). 
Shrikes  center  their  activities  in  breeding  territories  around 
one  to  a  few  "headquarters"  that  provide  adequate  nest 
sites,  nocturnal  roosts,  and  lookout  posts  for  scanning 
broad,  open  vistas  where  suitable  prey  abound  (Miller 
1931a,  1950).  In  Marin's  ranching  lands,  foraging  perches 

330 


such  as  fence  posts  and  powerlines  are  common,  but 
suitable  nest  sites  may  be  limiting  locally.  Blackberry,  rose, 
and  willow  thickets  and  eucalyptus  groves  provide  nest 
sites  in  diese  areas. 

Loggerhead  Shrikes  build  nests  of  twigs,  weed  stalks, 
and  grasses  (Miller  1931a,  1950;  Graberetal.  1973;  Porter 
et  al.  1975;  Kridelbaugh  1983).  They  often  place  nests  on 
the  remains  of  old  nests  of  Shrikes  or  other  birds;  occasion- 
ally they  dispense  with  the  base  of  sticks  (Miller  1931a, 
1950).  The  nest  lining  forms  a  thick  warm  felt  whose 
margins  frequendy  project  an  inch  over  the  stick  founda- 
tion. Lining  materials  are  principally  cottonlike  substances 


S/iri/ces 


SPECIES  ACCOUNTS 


Shrikes 


such  as  plant  down  and  wool,  along  with  hair,  feathers, 
roodets,  strips  of  bark,  willow  catkins,  and  string.  One  nest 
lining  in  Marin  County  of  black-and-white  skunk  fur 
blended  smartly  with  the  Shrike's  attire  (D.  Shuford  pers. 
obs.).  Shrikes  conceal  most  nests  at  medium  heights  in 
dense  bushes  or  small,  thickly  foliaged  trees  of  various 
species  (references  above).  Site  selection  is  apparendy 
based  on  the  degree  of  protective  cover  rather  than  on  a 
particular  plant  species;  if  several  choices  are  readily  avail- 
able, trees  with  thorns  seem  to  be  used  first  (Porter  et  al. 
1975).  Atypically,  Shrikes  have  nested  in  loose  tangled 
bailing  wire,  between  the  upright  boards  of  a  support  for 
telephone  wires,  in  a  brush  pile,  against  a  bank  covered 
with  creeping  vines,  or  in  the  heart  of  a  tumbleweed  (Miller 
1931a,  1950).  Actual  nest  support  in  an  arborescent  set- 
ting is  usually  provided  by  crotches  of  large  limbs  or  tangles 
of  fine  dense  twigs  (Miller  1931a,  1950),  usually  well 
within  the  periphery  of  the  tree  or  shrub  (Porter  et  al. 
1975).  Although  nest  height  in  western  birds  varies  from 
1 .5  to  30  feet  above  ground,  it  is  rarely  less  dian  3  or  more 
than  25  feet  (Miller  1931a,  1950;  Bent  1950);  an  excep- 
tional nest  in  the  East  was  at  a  height  of  50  feet  (Ford 
1936).  Reports  of  average  overall  nest  height  range  from  7 
to  10  feet,  but  vary  from  2.5  feet  in  subsets  of  brush  nests 
to  1 7  feet  in  second  nests  (vs.  9  ft.  in  first  nests)  (Porter  et 
al.  1975,  Kridelbaugh  1983). 

With  their  large  heads  and  powerful  hooked  beaks, 
Shrikes  are  admirably  suited  for  a  predatory  existence.  In 
the  early  morning  and  afternoon/early  evening  hours, 
breeding  Loggerheads  actively  seek  prey  by  scanning  from 
low  perches  and  quickly  moving  to  the  next  perch  (Miller 
1931a,  1950).  At  midday,  most  birds  forage  in  a  passive 
manner  from  high  perches,  from  which  they  infrequendy 
sally  forth  after  particularly  inviting  prey.  Although  attack 
rates  in  warm  months  are  highest  in  early  morning,  attack 
rates  in  the  winter  are  low  in  the  morning  and  reach 
highest  levels  by  midafternoon,  reflecting  the  activity  peri- 
ods of  cold-blooded  prey  (Craig  1978).  Shrikes  usually 
make  short-distance  flights  between  low  perches  by  drop- 
ping down  to  a  low,  even  flight,  then  abrupdy  rising  at  the 
next  stop  (Miller  1931a,  1950).  Longer  flights  from  high 
perches  usually  involve  undulating  finchlike  flights.  Morri- 
son (1980)  noted  that  Shrikes  used  higher  hunting  perches 
during  breeding,  perhaps  because  this  allowed  them  better 
views  over  taller  annual  vegetation  at  that  season.  He  found 
that  90%  of  attacks  and  captures  were  within  about  30  feet 
of  a  perch  during  the  prebreeding  period  and  within  46 
feet  during  breeding.  He  also  noted  that  hunting  perches 
during  breeding  were  less  than  50  feet  from  the  nest,  but 
Craig  (in  Morrison  1980)  found  Shrikes  usually  hunting 
from  perches  over  1 30  feet  from  nests.  Shrikes  make  nearly 
vertical  or  diagonal  plunges,  either  with  set  wings  or  rapid 
wing  motion,  in  pursuit  of  prey  on  or  close  to  the  ground. 
They  frequendy  hover  at  the  end  of  an  approach  flight,  and 


they  are  adept  at  pursuing  fleeing  prey  because  of  the 
maneuverability  afforded  them  by  their  short  rounded 
wings  and  long  tails.  Shrikes  also  hop  actively  on  the 
ground  or  on  the  tops  of  bushes  to  scare  up  prey,  and  they 
flycatch  from  perches  in  the  manner  of  clumsy  kingbirds. 
Overall,  ground  attacks  are  more  common,  but  air  attacks 
increase  during  breeding,  reflecting  the  greater  availability 
then  of  flying  prey  (Morrison  1980).  Although  Shrikes 
usually  take  larger  flying  prey,  such  as  butterflies,  on  or 
near  the  ground  (Morrison  1980),  they  sometimes  relent- 
lessly chase  and  tire  small  birds  (Graber  et  al.  1973).  They 
characteristically  seize  prey  with  their  strong  beaks;  for 
predatory  birds,  their  feet  are  weakly  developed.  Logger- 
heads occasionally  shift  prey  from  their  beaks  to  their  feet 
in  flight  (Esterly  1917)  and,  rarely,  catch  larger  prey  with 
their  feet  (Caldwell  1967).  Shrikes  dispatch  smaller  prey 
with  rapid  biting  motions  of  the  bill,  while  for  larger  prey 
they  aim  at  the  vertebrae  just  below  the  base  of  the  skull 
(Miller  1931a,  1950;  Smith  1973).  Shrikes  are  notorious 
for  carrying  larger  prey  (1.6  in.,  Craig  1978)  to  perches, 
where  they  impale  them  on  a  pointed  projection  or  wedge 
them  in  a  crotch  to  facilitate  tearing  them  apart.  Impaling 
stations  are  often  within  a  few  feet  of  the  ground  and 
seldom  higher  than  15  feet  (Miller  1931a,  1950).  Thorns, 
branch  tips,  and  barbed  wire  fences  are  typical  impaling 
spots.  After  satiation  birds  will  cache  their  food  there, 
returning  later  that  day  or  on  subsequent  days  to  feed. 
Most  authors  consider  the  prime  function  of  impaling  and 
wedging  to  be  facilitation  of  prey  manipulation,  since 
Shrikes'  feet  are  of  limited  use  in  holding  large  prey  (e.g., 
Miller  1931a,  1950;  Wemmer  1969;  Smith  1972;  Craig 
1978).  Food  storage  is  considered  secondary,  though, 
rarely,  it  may  be  of  aid  during  prey  shortage,  especially  in 
arid  climates  where  impaled  animals  will  dry  without 
spoiling  (Watson  1910).  Alternatively,  prey  storage  by 
males  may  reduce  the  energy  demands  of  hunting  on 
females,  whose  dme  might  be  more  profitably  devoted  to 
incubating  or  brooding  (Appelgate  1977).  In  support  of 
this  theory  are  observations  of  a  female  Shrike  during 
breaks  from  incubation  eating  food  cached  on  fences  by 
her  mate;  of  the  female  feeding  the  young  mosdy  food 
cached  by  the  male;  and,  in  the  evening,  of  the  male 
presenting  the  brooding,  female  with  food  partly  from  his 
caches.  Smidi  (1972,  1973)  noted  that  prey  was  usually 
impaled  within  50  feet  of  capture  and  often  considerably 
closer.  The  distance  might  be  expected  to  vary  with  the 
availability  of  suitable  impaling  posts. 

Although  Loggerhead  Shrikes  have  "an  indiscriminate 
taste  for  all  sorts  of  animal  matter,"  the  diet  is  primarily 
insectivorous  (Miller  1931a,  1950).  On  a  yearly  basis, 
vertebrate  food  amounts  to  only  1 2%  of  the  diet  of  the 
western  races.  Although  Shrikes  take  prey  ranging  from 
insects  0.2  inches  in  length  to  mice  or  snakes  weighing  0.9 
ounce,  most  prey  are  in  the  0.6-  to  0.9-inch  range  (Craig 


331 


Shrikes 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Shrikes 


1978,  Morrison  1980).  Shrikes  apparently  prefer  prey  that 
is  easy  to  catch  over  large  prey  (Slack  1975).  In  California 
studies,  Craig  (1978)  and  Morrison  (1980)  found  that 
average  prey  size  did  not  vary  seasonally  and  Shrikes  did 
not  capture  larger  prey  as  a  means  of  meeting  food  de- 
mands during  breeding.  Western  birds  apparendy  depend 
more  on  insects  than  do  eastern  birds.  Shrikes  most 
frequendy  take  grasshoppers,  crickets,  Jerusalem  crickets, 
locusts,  beedes,  larval  and  adult  lepidopterans,  bees,  centi- 
pedes, millipedes,  and  spiders  (Miller  1931a,  1950).  They 
also  consume  lesser  quantities  of  flies,  dragonflies,  may- 
flies, damselflies,  termites,  true  bugs,  and  cicadas,  and, 
rarely,  gastropods  or  crustaceans.  Vertebrate  prey  include 
small  mammals  such  as  harvest,  white-footed  and  house 
mice,  voles,  kangaroo  rats,  and  shrews;  birds  such  as 
sparrows,  finches,  and  warblers;  a  variety  of  snakes  and 
lizards,  and,  rarely,  tree  frogs  and  minnows.  Like  most 
rapacious  birds,  Shrikes  regurgitate  pellets  of  undigested 
hard  parts  of  prey,  and  the  males  feed  the  incubating  and 
brooding  females  (Miller  1931a,  1950).  Shrikes  sometimes 
cannibalize  young  that  die  after  winds  blow  them  out  of 
nests  (Kridelbaugh  1983).  Most  of  die  vegetable  matter 
Shrikes  consume  arrives  fortuitously  in  die  stomachs  of 
larger  prey,  but  2%-3%  of  the  diet  appears  to  consist  of 
seeds,  debris,  and  other  vegetable  matter  taken  voluntarily 
(Miller  1931a,  1950). 

Marin  Breeding  Distribution 

During  the  adas  period,  most  Shrikes  in  Marin  County 
bred  locally  in  agricultural  lands  in  the  Tomales  and 
Chileno  Valley  area  and  in  fields  and  reclaimed  salt 
marshes  along  the  San  Pablo  Bay  shoreline.  Representative 
nesting  localities  were  2.5  mi.  N  of  Tomales  near  junction 
of  Hwy.  1  and  Stemple  Creek  (NE  4/14-28/78  -SJ,  DS); 
base  of  Antonio  Mountain,  Chileno  Valley  (FY/FL 
6/4/82  -DS,  ScC);  and  Hicks  Valley  (NE-NY  4/22- 
5/16/82  — DS).  The  absence  of  Shrikes  as  widespread 


breeders  in  the  ranchlands  of  the  remainder  of  Marin 
County  is  puzzling.  Miller  (1931a)  stated  that  they  were 
lacking  in  many  areas  widi  fog  or  summer  rain,  which  may 
partly  explain  their  absence  as  breeders  on  fog-enshrouded 
Point  Reyes.  However,  they  are  relatively  widespread  near 
Tomales,  where  summer  fogs  are  frequent,  but  absent 
from  many  areas  inland  where  fog  is  infrequent.  Since 
perch  and  nest  sites  must  be  available  over  broad  areas,  a 
lack  of  an  abundant  food  supply  may  be  the  main  limiting 
factor. 

Historical  Trends/ Population  Threats 

Loggerhead  Shrikes  have  declined  continentwide  since  at 
least  the  mid-1950s,  most  dramatically  in  the  East  (Morri- 
son 1981a).  The  species  has  been  on  the  Audubon  Society 
Blue  List  every  year  since  its  inception  in  1972  (Tate  1981 , 
1986;  Tate  ck  Tate  1982).  The  species  is  currendy  a 
Candidate  (Category  2)  for  federal  listing  as  Threatened  or 
Endangered  by  the  U.S.  Fish  and  Wildlife  Service  (USFWS 
1991)  and  is  on  their  list  of  Migratory  Nongame  Birds  of 
Management  Concern  (USFWS  1987b).  Western  popula- 
tions generally  have  not  declined  dramatically,  though  the 
insular  San  Clemente  Loggerhead  Shrike  (L.  I.  mearnsi)  is 
listed  as  federally  Endangered  (USFWS  1989a).  Christmas 
Bird  Count  data  from  1955-56  to  1978-79  indicate  the 
Pacific  Coast  population  is  stable  or  slighdy  declining 
(Morrison  1981a).  From  1968  to  1979,  Shrikes  declined 
on  Breeding  Bird  Surveys  in  the  West  as  a  whole,  but  not 
in  California  (Robbins  et  al.  1986).  Further  analysis  of  data 
from  these  surveys  indicates  that  Shrike  numbers  were 
fairly  stable  in  California  from  1968  to  1989,  despite  a 
decline  from  1980  to  1989  (USFWS  unpubl.).  Habitat  loss 
and  pesticide  contamination  have  been  suggested  as  pos- 
sible causes  of  the  overall  decline  (Anderson  ck  Duzan 
1978,  Robbins  et  al.  1986,  USFWS  1987b).  This  species 
bears  close  watching  in  Marin  and  throughout  its  range. 


332 


Starlings 


SPECIES  ACCOUNTS 


Starlings 


Starlings 

Family  Sturnidae 


EUROPEAN  STARLING   Stumus  vulgaris 


A  year-round  resident. 

A  common,  nearly  ubiquitous  breeder; 
overall  breeding  population  very  large. 

Recorded  in  194  (87.8%)  of  221 
blocks. 


O  Possible 
O  Probable 
W    Confirmed 


41   (21%) 

15  (8%) 

138  (71%) 


FSAR  =  4       OPI  =  776       CI  =  2.50 


Ecological  Requirements 

Although  these  aggressive  invaders  have  called  Marin 
County  home  for  only  about  40  years,  they  are  now  one  of 
our  most  numerous  and  ubiquitous  breeding  birds  in 
open  surroundings.  Essentially  an  edge  species,  Starlings 
feed  in  open  habitats  and  seek  shelter  in  open  stands  of 
almost  any  nearby  woodland,  forest,  residential  tree  plant- 
ing, or  human  structure  that  provides  suitable  nest  sites 
and  cover.  Since  Starlings  breed  colonially,  good  breeding 
habitat  includes  clumps  of  trees  or  buildings  widi  a  num- 
ber of  nest  cavities  and  adjoining  short-grassland  feeding 
areas,  where  the  birds  can  forage  in  loose  flocks  (Feare 
1984).  In  Marin  County  as  elsewhere,  the  prime  foraging 
areas  are  grazed  pasturelands,  but  lawns,  playing  fields, 
mowed  hayfields,  tilled  farmland,  salt  marshes,  and  land- 
fills are  widely  used  alternative  foraging  sites.  All  foraging 
habitats  are  very  open,  providing  Starlings  with  great 
mobility  and  good  visibility. 

Starlings  show  great  adaptability  in  their  choice  of  nest 
sites.  Although  they  prefer  natural  cavities  in  trees  and  old 
or  new  holes  of  larger  woodpeckers  such  as  Northern 
Flickers,  they  also  use  a  wide  array  of  other  sites  (Bent 
1950,  Kessel  1957).  Frequent  domiciles  are  convenient 
cavities  in  or  on  barns,  outbuildings,  or  deserted  houses  or 


schools;  old  drainpipes;  church  steeples  and  belfries;  and 
crevices  in  cliffs  and  road  cuts.  Also  used,  perhaps  less 
frequendy,  are  mailboxes,  holes  in  haystacks,  old  burrows 
of  kingfishers  and  Bank  Swallows,  old  dome  nests  of 
magpies,  or  the  side  of  an  Osprey  nest.  Other  unusual  sites 
are  old  rabbit  holes,  cracks  in  the  ground,  holes  in  rock 
piles,  tins  or  boxes  in  rubbish  heaps,  the  branches  of  trees, 
dense  clumps  of  bushes,  or  ivy  on  the  walls  of  buildings. 
In  suburban  areas  of  lowland  California,  Starlings  also 
nest  in  cavities  among  the  dead  fronds  in  the  skirts  of 
Washington  fan  palms  (Washingtonia  filifera)  (Troetschler 
1976,  D.  Shuford  pers.  obs.). 

Bent  (1950)  reported  that  nest  heights  range  from  about 
2  to  60  feet,  though  most  are  from  10  to  20  feet  high.  In 
oak  savannah  in  Santa  Clara  County,  Troetschler  (1976) 
reported  that  Starlings  use  suitable  natural  cavities  at 
almost  any  height.  Nest  heights  there  averaged  26  feet 
(range  5-59  ft.).  In  the  Sacramento  Valley,  Planck  (1967) 
found  that  Starlings  showed  no  preference  as  to  the  height, 
substrate,  or  the  immediate  terrain  or  other  features  of  the 
habitat  of  nest  boxes.  They  did  show  a  preference  for  nest 
sites  close  to  primary  foraging  areas  and  staging  points 
along  their  flight  lines  to  roosts.  In  one  European  study, 

333 


Starlings 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


Starlings 


Verheyan  (1980)  noted  a  preference  for  high  cavities  facing 
east  or  southeast.  Feare  (1984)  emphasized  the  insulative 
qualities  of  the  nest  cavity.  In  oak  savannah,  Troetschler 
(1976)  reported  that  later  in  the  season,  as  the  weather 
warms,  nest  hole  use  decreased  in  dry  areas,  but  more 
holes,  including  marginal  older  ones  with  large  worn 
entrances,  were  used  in  moist  areas  that  still  could  supply 
adequate  nesding  food.  In  the  cool  early  spring  only  the 
better-insulated  holes  are  adequate  for  nesding  protection. 
Although  Starlings  often  reuse  nest  holes  in  the  same  or 
successive  years,  individuals  frequendy  switch  nest  holes 
and  mates  between  successive  broods  in  the  same  year  and 
between  years  (Verheyan  1980). 

Like  many  colonial  and  polygynous  birds,  male  Star- 
lings build  rough  nests  as  enticement  to  females  to  become 
their  mate  (Feare  1984).  Along  with  incipient  nest  mate- 
rial, the  male  adds  to  the  nest  cavity  petals  of  flowers  or 
fresh  green  leaves,  which  he  changes  regularly.  Once  a  pair 
bond  is  formed,  the  female  usually  takes  the  initiative  and 
completes  the  nest  and  its  lining,  often  first  removing 
material  placed  by  the  male.  The  nest  is  a  bulky  structure 
of  dry  vegetation,  mainly  dry  grasses  and  perhaps  fine 
twigs,  weed  stems,  dry  leaves,  roodets,  vines,  or  pine 
needles  (Bent  1950,  Kessel  1957,  Feare  1984).  The  size  of 
the  nest  reflects  that  of  the  cavity  (Bent  1950),  and  the  nest 
cup  is  always  situated  in  that  part  of  the  nest  cavity  most 
remote  from  the  entrance  (Feare  1984).  Starlings  usually, 
though  not  always,  line  the  nest  cup  with  softer  material  of 
fine  dry  grasses  and  feathers,  and  also  with  artificial  mate- 
rials such  as  cloth,  string,  paper,  cellophane,  cotton  wool, 
or  even  cigarette  butts.  When  birds  depart  from  the  nest, 
they  partially  cover  the  eggs  with  leaves  or  other  pieces  of 
material. 

Starlings  are  highly  gregarious  birds  diat  breed  colo- 
nially  and  synchronously.  They  appear  to  learn  from  each 
other  the  whereabouts  and  abundance  of  food  and  are 
more  efficient  in  exploiting  it  by  feeding  in  flocks 
(Tinbergen  ck  Drent  1980,  Feare  1984).  Flocking  behavior 
helps  birds  to  discover  and  exploit  localized  transient 
patches  of  food  and  to  feed  at  faster  rates  (up  to  a  point) 
because  of  the  lessened  need  of  individuals  to  be  vigilant 
toward  predators. 

During  winter,  Starlings  forage  in  large  inter-  or  intra- 
specific  flocks,  but  during  the  breeding  season  they  more 
often  feed  singly,  in  pairs,  or  in  small  flocks  (Williamson 
ck  Gray  1975,  Feare  1984).  Males  defend  a  small  area 
around  the  nest  site  and  during  egg  laying  defend  their 
mates  to  prevent  them  from  mating  widi  other  males  (Feare 
1984).  Consequendy,  at  that  time  males  and  females  travel 
as  pairs  to  feeding  areas  (Dunnet  1955,  Feare  1984).  From 
colonies,  birds  fly  to  common  feeding  grounds  that  are 
usually  within  a  few  hundred  yards  of  nest  sites,  though 
they  may  range  up  to  a  third-  or  half-mile  away  (Dunnet 
1955,  Feare  1984). 

334 


Starlings  feed  primarily  in  grasslands,  where  they  take 
invertebrates  (and,  to  a  lesser  extent,  seeds)  from  the 
foliage,  from  the  surface  of  the  ground,  and  from  the  upper 
inch  or  so  of  the  soil  (Bent  1950,  Dunnet  1955,  William- 
son ck  Gray  1975,  Brownsmith  1977,  Tinbergen  ck  Drent 
1980,  Tinbergen  1981,  Feare  1984).  They  probe  into  the 
soil  with  wide  open  or  closed  bills;  they  sometimes  bore  in 
with  a  closed  bill,  forcibly  open  it,  and  peer  into  the  hole 
so  formed  for  food.  Starlings  also  glean  insects  from  trees, 
flycatch  from  perches,  and  catch  aerial  insects  in  extended, 
graceful,  swallowlike  flights.  They  appear  to  flycatch  more 
commonly  in  the  autumn  than  other  seasons  (Dunnet 
1955). 

Starlings  obtain  fruit  while  perched  in  trees  and  bushes 
or  from  the  ground  along  with  grains;  they  may  eat  germi- 
nating grains  in  the  soil  or  remove  them  by  probing. 
Starlings  sometimes  feed  in  close  association  with  live- 
stock, whose  disturbance  of  insects  may  benefit  the  birds; 
they  also  search  for  external  parasites  on  the  animals' 
backs. 

Starlings  are  omnivorous,  and  their  diet  varies  consider- 
ably both  seasonally  and  geographically  (Feare  1984).  Dur- 
ing the  breeding  season,  they  eat  mosdy  invertebrates  and, 
rarely,  vertebrates  such  as  newts,  frogs,  and  lizards.  Despite 
the  variety  in  their  diet,  Starlings  concentrate  on  only  a  few 
prey  species  while  breeding.  In  most  areas,  these  are  larvae 
of  beedes,  moths,  or  butterflies  that  live  on  or  just  under 
the  soil  surface. 

The  diet  in  Texas  (Russell  1971),  which  by  geography 
and  climate  is  likely  to  be  similar  to  that  in  California, 
shows  a  much  higher  percentage  of  insects  than  found  in 
the  East  (Kalmbach  ck  Gabrielson  1921,  Lindsay  1939). 
Year  round,  the  diet  in  Texas  is  73%  animal  food  and  27% 
vegetable;  animal  food  there  increases  to  85%  in  summer 
(Russell  1971,  n  =  200).  In  the  East,  animal  food  com- 
prises 93%  of  the  diet  in  spring  (n  =  249)  and  reaches  a 
low  of  32%  in  winter  (n  =  644)  (Martin  et  al.  1951).  The 
main  insect  prey  of  western  birds  are  adult  and  larval 
beedes,  moths,  butterflies,  grasshoppers,  and  crickets,  with 
smaller  quantities  of  ants,  true  bugs,  flies,  cicadas  (and 
related  species),  along  with  a  few  spiders,  isopods,  and 
gastropods  (Russell  1971,  Moore  1986).  The  vegetable 
component  consists  principally  of  fruits  and  a  few  seeds, 
mosdy  in  fall  and  winter  (Russell  1971);  in  the  West, 
wintering  birds  often  feed  on  large  quantities  of  grain  from 
feedlots,  corn  silage,  and  garbage  (Killpack  ck  Crittenden 
1952).  Nesdings  are  fed  primarily  animal  food,  but  their 
diets  can  vary  with  time  of  day,  weather,  nesding  age 
(depending  on  prey  availability  and  developmental  require- 
ments), and  brood  size;  dietary  diversity  is  greater  for 
younger  birds  and,  overall,  for  larger  broods  (Feare  1984, 
Moore  1986). 

Foraging  adults  tend  to  select  for  large  items  for  their 
young  and  eat  small  ones  themselves  (Tinbergen  1981). 


Starlings 


SPECIES  ACCOUNTS 


Starli 


mgs 


Very  small  young  generally  receive  soft-bodied  insects, 
smaller  caterpillars,  and  more  spiders  than  older  young. 
Caterpillars  are  quite  important  to  fledged  young,  which 
spend  much  more  time  in  trees  than  do  adults  (Feare 
1984).  Once  their  requirements  for  invertebrate  foods 
relax,  the  fledglings'  arboreal  tendencies  predispose  them 
to  switch  to  summer-ripening  fruits.  Although  Starlings 
feed  mosdy  in  grasslands  throughout  the  year,  in  winter 
they  more  readily  use  alternative  sites  and  switch  to  plant 
foods,  even  when  there  is  no  apparent  limitation  on 
feeding  on  animal  matter  in  grasslands.  Perhaps  it  takes 
them  less  time  to  feed  on  grains  than  on  invertebrates, 
allowing  them  more  time  for  maintenance  activities.  With 
their  seasonal  shift  in  diet,  in  winter  Starlings  tend  to  feed 
more  in  urban  areas,  in  gardens,  at  bird  feeders,  on 
household  wastes,  at  dumps,  dockyards,  around  ware- 
houses, and  on  grain  around  farmyards  and  in  cattle 
troughs.  They  readily  enter  buildings  in  pursuit  of  food. 
Males  predominate  at  catde  troughs,  but  females  may  have 
to  feed  elsewhere  to  obtain  a  higher  proportion  of  protein 
to  maintain  reserves  for  early  breeding  and  to  lay  large 
clutches. 

Marin  Breeding  Distribution 

During  the  adas  period,  the  European  Starling  was  one  of 
the  most  widespread  of  Marin  County's  breeding  birds.  It 
was  most  numerous  in  the  productive  foraging  grounds  of 
lowland  valleys  and  gendy  sloping  hills  of  the  ranchlands 
of  Point  Reyes  and  much  of  north  and  central  Marin. 
Representative  nesting  localities  were  Upper  Pierce  Ranch, 
Tomales  Point  (FY/NY  6/1/82  -DS);  Chileno  Valley  (FY 
5/5/82  — DS);  Bolinas  Ridge  above  the  lower  end  of  Kent 
Lake  (FY  5/21/82  -BiL);  and  Kentfield  (NB  5/7/82 
-BiL). 

Historical  Trends/  Population  Threats 

Although  a  number  of  attempts  were  made  to  release 
Starlings  in  the  East  in  the  mid-  to  late  1880s,  the  100  birds 
"liberated"  in  New  York's  Central  Park  in  1890  and  1891 
were  the  core  nucleus  that  spawned  the  hordes  that  have 
since  spread  far  and  wide  over  the  entire  continent  (Bent 
1950).  Colonization  was  rapid  and  most  pervasive  to  the 
south  and  west,  in  line  with  the  species'  traditional  north- 
east to  southwest  movements  in  Europe.  New  areas  ini- 
tially were  settied  in  the  fall  and  winter,  primarily  by 
dispersing  juveniles,  followed  roughly  five  years  later  by  the 
establishment  of  breeding  populations  (Bent  1950).  Star- 
lings first  reached  northeastern  California  in  1942  (Jewett 
1942)  and  were  reported  breeding  there  by  1949  (Ball  &. 
Koe  fide  DeHaven  1973).  They  were  first  reported  on  the 
coast  of  northern  California  on  Point  Reyes  in  1949 
(Gullion  1949),  and  hundreds  were  seen  there  by  1954 
(Gull  36:17,  37:3,  38:2);  over  2000  were  seen  in  Novato 
on  12  February  1956  (Gull  38:1 1).  Although  first  reported 


nesting  on  the  southern  California  coast  in  1958  (Howard 
1959),  Starlings  were  not  reported  nesting  on  the  northern 
coast  (in  San  Francisco)  until  1964  (Tenaya  ck  Tenaya 
1966).  Given  the  pattern  of  establishment  elsewhere,  Star- 
lings likely  nested  in  these  areas  earlier  and  went  un- 
reported. Starling  populations  on  Christmas  Bird  Counts 
in  northern  California  increased  slowly  at  first,  then 
expanded  rapidly  (DeHaven  1973).  Numbers  began  to 
swell  quickly  in  the  mid-1950s.  They  exploded  beginning 
in  1961,  with  an  increase  of  about  1600%  in  the  next  ten 
years  despite  extensive  control  efforts  at  feedlots  and  other 
areas  in  1964  and  1967  (DeHaven  1973).  Starlings 
increased  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1979,  while  for  the  West  as  a  whole  they  increased 
sharply  from  1968  to  1973,  with  signs  of  stabilization 
thereafter  (Robbins  et  al.  1986).  Extension  of  data  analysis 
indicates  that  Starling  numbers  generally  decreased  as 
breeding  birds  in  California  from  1968  to  1989,  despite  a 
relatively  stable  trend  from  1980  to  1989  (USFWS 
unpubl.). 

The  rapid  range  expansion  and  numerical  increase  of 
Starlings  has  caused  alarm  because  of  their  aggressive 
usurpation  of  nesting  holes  of  woodpeckers,  swallows, 
bluebirds,  Wood  Ducks,  and  other  cavity  nesters,  and 
because  of  the  potential  effect  of  competition  for  food 
between  Starlings  and  species  that  overlap  with  them  in 
diet  requirements  (Bent  1950).  Although  Starlings  have 
undoubtedly  had  a  negative  effect  on  California's  native 
birds,  the  extent  of  that  effect  is  unknown.  It  is  clear, 
though,  that  Starlings  do  aggressively  displace  other  hole- 
nesting  birds,  particularly  if  nest  sites  are  in  short  supply 
(Weitzel  1988).  From  1968  to  1974,  during  the  rapid 
increase  of  the  Starling's  population  in  California,  Troet- 
schler  (1976)  studied  the  interactions  of  Acorn  Woodpeck- 
ers and  Starlings  in  Santa  Clara  County.  Her  data  suggest 
diat  Starlings  did  not  affect  the  reproductive  success  or 
group  size  of  Acorn  Woodpeckers  there.  She  suggested, 
though,  that  long-term  success  of  the  Acorn  Woodpeckers 
might  be  compromised  by  the  extra  energy  they  had  to 
spend  on  hole  defense  and  drilling  new  holes,  energy  that 
might  be  expended  more  profitably  on  adequate  acorn 
storage  and  defense.  Even  if  Acorn  Woodpeckers  are 
flexible  enough  to  adapt  to  Starling  competition,  other 
species  may  not  be.  The  Purple  Martin  may  be  a  case  in 
point  (see  account).  Although  Starling  impacts  on  native 
birds  seem  not  to  be  as  drastic  as  some  doomsayers 
predicted,  the  long-term  interactions  of  this  alien  with  our 
native  fauna  should  be  carefully  monitored. 

The  Starling's  effect  on  human  interests  have  been  well 
documented,  and  expensive  control  efforts  have  been 
undertaken  (Howard  1959,  Palmer  1973,  Wright  et  al. 
1980,  Feare  1984).  Damage  to  agriculture  has  been 
reported  since  c.  200  B.C.  and  continues  to  be  the  main 
complaint  (Feare  1984).  Starlings  do  considerable  harm  by 

335 


Starlings 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Starlings 


consuming  soft  fruit  crops,  winter-sown  cereal  grain  crops 
as  they  germinate,  and  livestock  feed  (which  they  also  foul), 
especially  of  cattle.  In  California,  locally  reared  juveniles 
inflict  most  damage  to  spring  and  summer  fruit  crops 
(Palmer  1973).  On  the  other  hand,  adults  and  subadults 
(mainly  migrants)  cause  most  of  the  damage  to  livestock 
and  poultry  feed  in  fall  and  winter  (Palmer  1973).  Addi- 
tional complaints  lodged  against  Starlings  include  their 
roosts   causing  unsightly  contamination   of  buildings, 


breaking  of  tree  limbs,  and  killing  of  trees  from  the 
accumulation  of  droppings;  possible  transmission  of  ani- 
mal and  human  disease;  and  noise.  Extensive  control 
efforts  have  had  only  limited  and  temporary  local  success 
(Wright  et  al.  1980,  Feare  1984).  With  their  flexible  nest 
site  requirements,  mating  system,  and  foraging  strategies 
(Feare  1984),  Starlings  are  the  rats  of  the  bird  world  and 
are  here  to  stay. 


Why  are  Loggerhead  Shrike  populations  declining  sharply  in  the  East,  and  u/ill  California  populations  be  so  affected? 

Photograph  fcry  Ian  Tait. 


336 


Vireos 


SPECIES  ACCOUNTS 


Vii 


Vireos 

Family  Vireonidae 


SOLITARY  VIREO    Vireo  solitarius 


A  summer  resident  from  late  Mar 

^\P~>^      \                     yr~\ 

through  mid-Oct. 

f\^\jj^ 

An  uncommon,  very  local  breeder; 

J\\_\ 

J<\>\~ 

overall  breeding  population  very  small. 
Recorded  in  8  (3.6%)  of  221  blocks. 

0KjpKjP^x^ky^ 

v^^ 

O    Possible        =         4   (50%) 

V\\ 

">^Tv  X\  \r^^f^\° ]Jc^ 

t^-V— \^K\^ 

©    Probable       =         1    (12%) 

A^y\  ."^C^~^A<^\ x\r^     J^\ 

.. 

•    Confirmed  =        3  (38%) 

§Vo 

FSAR  =  2         OPI  =  16         CI  =  1.88 

x^=>                                   \L_^ 

Ecological  Requirements 

The  attentive  listener  hears  the  call-pause-and-response 
song  of  this  "greenlet"  only  locally  in  Marin  County  during 
the  breeding  season.  It  issues  forth  from  relatively  dry, 
open  mixed  evergreen  forests  dominated  either  by  broad- 
leaved  hardwoods  or  Douglas  fir  mixed  widi  a  hardwood 
component.  In  comparison  with  Hutton's  Vireos,  which 
prefer  moister,  denser  hardwood  woodlands,  Solitaries 
select  those  with  a  more  open  canopy.  Although  some 
birds  nest  near  water,  it  is  not  essential  on  their  nesting 
territories;  instead,  streamsides  may  provide  the  only  hard- 
wood elements  in  some  forest  areas  dominated  by  conifers. 
For  nesting  areas,  Solitary  Vireos  prefer  shaded  glades 
along  woodland  openings,  meadow  edges,  and  trailsides. 
Solitary  Vireos  build  semipensile  basket  nests  that  are 
somewhat  bulkier  and  looser  than  those  of  most  other 
vireos  (Dawson  1923).  They  weave  them  of  vegetable 
fibers,  grasses,  dead  leaves,  and  bark  strips.  They  lash  these 
materials  to  limb  forks  by  vegetable  fibers  and  a  little  spider 
silk,  and  ornament  them  extensively  with  spider  cases, 
flower  petals,  catkin  bits,  lichens,  paper,  and  the  like 
(Dawson  1923,  Bent  1950).  Solitaries  line  their  nests  with 
dry  grass  stems,  grass  heads  (with  seeds  removed),  small 
leaf  stems,  and  horsehair.  Western  birds  place  their  nests 
toward  the  end  of  horizontal  or  drooping  branches  of  small 


hardwoods,  conifers,  or  understory  bushes.  Nest  height 
varies  from  about  4  to  40  feet,  but  most  nests  are  almost 
or  quite  widiin  reach  from  the  ground  (Bent  1950). 

In  the  mixed  conifer  zone  of  the  Sierra  Nevada,  Solitary 
Vireos  forage  at  medium  heights  mosdy  by  slow  pause-and- 
search  gleaning  from  foliage,  twigs,  and,  to  a  lesser  degree, 
branches  (Airola  &  Barrett  1985).  They  also  hover,  fly- 
catch,  and  occasionally  lunge  for  prey.  These  vireos  show 
substantial  geographic  variation  in  their  use  of  various  prey 
capture  methods  (Petit  et  al.  1990),  but  Szaro  et  al.  (1990) 
found  no  annual  variation  in  use  of  foraging  techniques 
and  only  moderate  annual  variation  in  other  measures  of 
resources  use  in  ponderosa  pine  forests  in  Arizona.  The 
diet  of  California  birds  (Apr-Nov)  is  over  98%  animal, 
consisting  of  true  bugs,  caterpillars  and  moths,  wasps  and 
ants,  and  beedes,  along  with  a  few  miscellaneous  insects 
and  spiders  (Beal  1907,  n  =  46;  Dahlsten  et  al.  1985,  n  = 
6).  Solitaries  also  eat  a  few  leaf  galls  and  poison  oak  seeds 
(Beal  1907). 

Marin  Breeding  Distribution 

During  the  adas  period,  Solitary  Vireos  bred  locally  in 
Marin  County,  primarily  in  the  Mount  Tamalpais  and 
Lagunitas  Creek  watersheds.  They  resided  at  elevations 

337 


Vireos 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Vireos 


and  exposures  where  the  open  quality  of  the  conifers  and 
associated  hardwoods  results  from  a  lack  of  significant 
moisture  from  summer  fog.  Representative  nesting  locali- 
ties were  Phoenix  Lake  (NY  6/8/79  —  ITi);  Rock  Springs, 
Mt.  Tamalpais  (FL/FY  7/8/78  -BGM  et  al.);  and  Cascade 
Canyon,  Fairfax  (FL/FY  6/19/80  -DS). 

Historical  Trends/  Population  Threats 

Solitary  Vireos  have  been  sighted  in  the  breeding  season 
in  the  Ross/Phoenix  Lake  area  regularly  since  at  least  1931 


(Gull  1  3,  No.  7);  nesting  was  confirmed  at  Ross  on  1 3  June 
1937  (NY;  Gull  19,  No.  7).  From  1968  to  1979,  Solitary 
Vireos  increased  on  Breeding  Bird  Surveys  in  the  Califor- 
nia Foothills,  which  include  the  coastal  counties  from 
Monterey  south  and  part  of  those  to  the  north  (Robbins  et 
al.  1986);  from  1968  to  1989  they  increased  in  California 
as  a  whole  (USFWS  unpubl.  analyses). 


HUTTON'S  V1REO    Vireo  huttoni 


-!._.£ 

A  year-round  resident. 

/\©-Y> 

A^wPa^s.            \                    vr^v. 

A  fairly  common,  very  widespread 

<^\cyv 

iwwv_^A^ 

breeder;  overall  breeding  population 

\r\  J<\\  Jr^X  ®V"A  °  \^\  •  JV-^A  ©  \^\  *3A  - 

fairly  large. 

A    A-'x  ®3r<\  ®Jr>\©:W-^C©  \^\m  \-^Ko  \^\ 

Recorded  in  184  (83.2%)  of  221 

blocks. 

^\    >^r\  ®  Jr<\  ®V\  •  W^A  ©  \^\  •  \>^\  &\^\ 

\\°-><C\ J?*\9Jk^X  «\^v  •  Jr^v *>Jt^A«  \^V  ®  J 

x^^A**^, ®>¥iT\  cA^®3^^*A^^®3t^\  ©  Y^l 

O    Possible        =       33   (18%) 

V\^«\<A  c^?>r\  ^x^x  o  v^cjv^v®  V^\     \>^c  •- 

C    Probable      =    121    (66%) 

\  I^Vo\  fA<\  *tV<\  f'^^A  ®Jv<A  •*>  i^vO-V-^x "-On 

__  _- 

•    Confirmed  =       30   (16%) 

T  M^\  °J<^^y^\fy?*\Q  A<r\©  \>a»  >^v#  J7^ 

^AV©i<v<\  ©  v>A  «  >>r\  ©  \3<^»  X^Vfc  xz*<\  £\5r\ 

"iy^7  xv^\>*r*  \  ta<\  f^A  ®v£\  ®a<\  «u~v 

FSAR  =  3       OPI  =  552        CI  =  1.90 

>&& 

>r                              N^^®J\^^?®J^^x*'3^^^A^>> 

">  /                                ^-Jf^^^D^S^zy^x  ©  \~-^\  © A 

LL                        ^^^^<2^1V^ 

{t^~                                                v-^-<                     "-^-^lo\^- 

Ecological  Requirements 

The  Hutton's  Vireo  has  apdy  been  called  "the  spirit  of  the 
live  oak  tree"  (Van  Fleet  1919).  Lichen-draped  coast  live 
oaks  are  the  principal  component  of  the  broadleaved 
evergreen  forests  where  this  vireo  dwells  locally.  It  prefers 
evergreen  forests  of  moderate  to  dense  crown  closure 
dominated  by  live  oaks  over  dense  north-facing  bay  laurel 
stands  or  open  oak  woodlands.  In  the  breeding  season, 
this  vireo  also  frequents  Douglas  fir  and  bishop  pine 
(where  diey  mix  with  hardwoods),  willow  riparian  groves, 
the  edges  of  tall  chaparral,  and,  sparingly,  planted  eucalyp- 
tus, cypress,  and  pine  groves. 

Hutton's  Vireos  construct  round,  deeply  cupped  nests 
primarily  of  strands  of  the  gray-green  hanging  lichen 
(Ramalina  reticulata),  where  available,  which  they  lash 
together  with  cobwebs  (Van  Fleet  1919,  Bent  1950).  They 
may  use  other  nest  materials,  such  as  plant  down,  hair,  and 

338 


bark,  and  they  usually  line  the  nest  with  fine  grasses  and 
perhaps  some  hair  or  feathers.  They  attach  their  nests  in 
trees  and  bushes  from  about  4  to  75  feet  above  the  ground, 
but  mosdy  at  moderate  heights.  Coast  live  oak  is  the 
preferred,  though  not  exclusive,  nesting  tree  in  this  region. 
Nests  are  usually  ensconced  in  twigs,  forks,  or  foliage  near 
the  ends  of  branches,  and  they  are  camouflaged  by  natu- 
rally growing  lichens  of  the  type  from  which  the  nest  is 
made. 

Hutton's  Vireos  forage  primarily  by  gleaning,  hovering, 
and,  to  a  limited  degree,  flycatching  in  the  foliage  and 
subcanopy  of  the  forest  and  occasionally  in  the  herb  layer 
below  it  (Root  1967).  Within  these  zones,  they  secure  most 
prey  on  foliage  and  flowers;  secondarily  on  twigs,  lichens, 
and  fruits;  and  lasdy  on  herbs.  Foraging  birds  make  long 
pauses  to  inspect  the  foliage  for  prey  before  moving  rapidly 
to  another  spot.  While  extracting  prey  from  dense  terminal 


ViT 


SPECIES  ACCOUNTS 


Vireos 


sprigs  of  foliage  they  often  hang  upside  down,  chickadee- 
like, for  a  moment.  The  diet  is  over  98%  animal  matter 
along  with  a  few  seeds  and  galls  (Beal  1907,  n  =  54; 
Chapin  1925,  n  =  70;  Root  1967).  The  animal  menu 
consists  primarily  of  true  bugs,  caterpillars,  moths,  butter- 
flies, beetles,  bees,  wasps,  and  ants,  as  well  as  a  few 
miscellaneous  insects  and  spiders. 

Marin  Breeding  Distribution 

During  the  adas  period,  Hutton's  Vireos  bred  widely  in 
Marin  County's  extensive  mixed  evergreen  forests.  They 
were  absent  or  scarce  only  on  the  outer  tip  of  Point  Reyes 
and  in  the  low  rolling  grasslands  around  Tomales.  Repre- 


sentative breeding  stations  were  Bolema  Trail,  Olema 
Valley  (NY  5/?/77  -JGE);  near  Stafford  Lake,  Novato  (NB 
5/6/79  -KH);  Mt.  Burdell,  Novato  (NB  5/17/81  -HoP, 
DS;  NY  5/?/82  -ScC);  China  Camp  SP  (FL  6/19/82 
— BiL);  and  Camino  Alto,  between  Corte  Madera  and  Mill 
Valley  (FL  6/1 2/82  -BiL). 

Historical  Trends/  Population  Threats 

Hutton's  Vireo  numbers  increased  on  Breeding  Bird  Sur- 
veys in  California  from  1968  to  1979  (Robbins  et  al. 
1986),  but  further  analysis  indicated  a  fairly  stable  popula- 
tion in  the  periods  1968  to  1989  and  1980  to  1989 
(USFWS  unpubl.). 


A  male  Warbling  Vireo  singing  on  the  nest  attests  to  its  ebullient  nature.    Photograph  by  Ian  Tail. 


339 


Vireos 


MARIN  COUNTY  BRHHDING  BIRD  ATLAS 


Vireos 


WARBLING  VIREO    Vireo  gilvus 


A  summer  resident  from  late  Mar 

*—#;  v^X 

^^-^^^t^ 

through  early  Oct. 

YV'awP 

An  abundant,  very  widespread 

•JV''^  ®  Jr^\<>  W^©'\^--^©  \^--T*A  ^--Y^         \ 

breeder;  overall  breeding  population 
extremely  large. 

$°WS#WwW^ 

Recorded  in  164  (74.2%)  of  221 

V^ 

blocks. 

_  .-■- 

O    Possible        =       19   (12%) 
©    Probable      =     112  (68%) 
•    Confirmed  =       33   (20%) 

:iwx?A'©\^V.^v*^^ 

•OV  ^TfcA  *  Y*>\*Jli-'^iJ*  V^\©"^^TT©  V-^  ©  V-V\  K^- 

5?& 

FSAR  =  6       OPI  =  984        CI  =  2.08 

Ecological  Requirements 

What  this  vireo  lacks  in  distinctiveness  of  plumage  it 
makes  up  for  with  one  of  the  brightest,  most  persistent  and 
ubiquitous  songs  in  all  of  Marin  County.  Males  are  so 
loquacious  that  they  sing  even  while  incubating  eggs  on  the 
nest!  Locally,  the  Warbling  Vireo's  breeding  stronghold  is 
the  complex  of  moist,  shady,  broadleaved  evergreen  forests 
dominated  by  coast  live  oak  and  California  bay  laurel;  it 
also  includes  willow  and  alder  riparian  groves.  Although 
exhibiting  a  predilection  for  moderately  tall  evergreen  or 
deciduous  broadleaved  trees,  Warbling  Vireos  also  inhabit 
Douglas  fir,  bishop  pine,  and,  sparingly,  redwood,  partic- 
ularly where  they  mix  with  hardwoods.  These  birds'  forest 
haunts  are  generally  denser  than  those  of  Solitary  and 
Hutton's  vireos,  though  they  overlap  extensively  with 
Huttons,  particularly  in  live  oaks,  and  narrowly  with  Soli- 
taries in  mesic  drainages. 

Like  our  other  vireos,  Warblings  tend  a  hanging,  cup- 
shaped  nest  that  is  lashed  to  a  fork  of  a  branch  or  twig  well 
out  from  the  trunk.  They  build  the  body  of  the  nest  from 
grasses,  plant  down,  bark  strips,  leaves,  bits  of  string  and 
lichen,  and  vegetable  fibers  (Rust  1920,  Dawson  1923, 
Bent  1950).  They  often  ornament  the  outside  with  lichens 
and  catkins,  and  they  line  the  inside  widi  fine  grasses,  bark 
from  weed  stalks,  horsehair,  and,  rarely,  plant  down.  Nests 
of  western  birds  range  from  about  4  to  40  feet,  but  mosdy 
15  to  25  feet,  above  ground.  Warbling  Vireos  orient  their 
nests  to  overhanging  foliage  that  provides  shade  from  the 
afternoon  sun,  rather  than  to  a  thermally  favorable  side  of 
a  tree  indicated  by  a  certain  compass  direction  (Walsberg 
1981). 

340 


Relative  to  our  other  two  vireos,  Warblings  are  more 
active  foragers.  In  coastal  oak  woodlands  and  in  the  mixed 
conifer  zone  of  the  Sierra  Nevada,  Warbling  Vireos  forage 
at  moderate  heights  by  gleaning,  hovering,  and  hawking 
from  twigs,  foliage,  branches,  and,  rarely,  herbs  (Root 
1 967,  Airola  &.  Barrett  1 985).  They  feed  more  in  the  outer 
foliage  zone  than  do  Hutton's  Vireos  (Root  1967).  On  the 
whole,  Warbling  Vireos  show  considerable  geographic 
variation  in  foraging  behavior  (Petit  et  al.  1990).  The  diet 
of  California  birds  (Apr-Oct)  is  over  97%  arthropods 
consisting  of  caterpillars,  moths,  butterflies,  true  bugs, 
beedes,  leafhoppers  and  allies,  along  with  spiders  and 
miscellaneous  insects  (Beal  1907,  n  =  110;  Dahlsten  et  al. 
1985,  n  =  6).  Plant  material  consists  of  a  few  elderberry, 
poison  oak,  dogwood,  and  snowberry  seeds,  and  galls, 
mosdy  taken  in  late  summer  and  fall  (Beal  1907,  Martin 
etal.  1951). 

Marin  Breeding  Distribution 

During  the  adas  period,  Warbling  Vireos  were  slighdy  less 
widespread  in  Marin  County  in  the  breeding  season  than 
were  Hutton's  Vireos,  though  Warblings  were  much  more 
numerous  overall.  Warbling  Vireos  were  absent  as  breed- 
ers from  some  areas  with  scrubby  oaks  on  the  Point  Reyes 
peninsula  and  east  of  Tomales  Bay  and  from  drier  oak 
woodlands  near  Novato,  both  of  which  were  suitable  to 
Hutton's  Vireos.  In  the  drier  interior  portions  of  Marin 
County,  Warbling  Vireos  were  restricted  primarily  to 
moist  narrow  canyons  and  north-facing  slopes.  Represen- 
tative nesting  localities  were  Laguna  Ranch,  PRNS  (NE 


Vireos 


SPECIES  ACCOUNTS 


Vireos 


5/21/80  — JGE);  Millerton  Gulch,  east  side  of  Tomales 
Bay  (NB  5/27/82  -DS);  O'Hare  Park,  Novate  (NE 
5/19/82  -ScC);  northeast  side  of  Big  Rock  Ridge  (NE 
5/16/82  — BiL);  Bolinas  Ridge  above  lower  end  of  Kent 
Lake  (FL  6/16/82  —BiL);  and  Cascade  Canyon,  Fairfax 
(NE  5/7-18/77 -DS). 

Historical  Trends/Population  Threats 

The  Warbling  Vireo  was  on  the  Audubon  Society's  Blue 
List  from  1978  to  1980  and  on  dieir  list  of  Local  Concern 
in  1982  (Tate  1981,  Tate  6k  Tate  1982).  In  California, 
Warbling  Vireos  have  declined  historically  as  breeders  on 
the  southern  coast  (Gairett  6k  Dunn  1981),  in  the  Central 
Valley  (Gaines  1974),  and  at  least  locally  in  the  Sierra 
Nevada  (Rothstein  et  al.  1980,  Verner  6k  Ritter  1983, 
Gaines  1988).  They  generally  appear  to  be  holding  their 
own  in  coastal  northern  California.  Breeding  Bird  Surveys 
indicate  that  on  the  whole  Warbling  Vireos  were  increas- 


ing in  California  from  1968  to  1989  (USFWS  unpubl. 
analyses).  Based  on  long-term  banding  data  from  PRBO's 
Palomarin  field  station,  DeSante  and  Geupel  (1987)  docu- 
mented a  total  reproductive  failure  of  Warbling  Vireos  in 
1986  in  central  coastal  California.  A  large  number  of  other 
species  failed  to  reproduce  partially  or  totally  as  well. 
Although  it  may  be  highly  coincidental,  the  timing  of  these 
reproductive  failures  coincided  remarkably  well  with  the 
passage  of  a  radioactive  "cloud"  from  the  Chernobyl 
nuclear  power  plant  accident  and  associated  rainfall.  How- 
ever, the  number  of  adults  remained  at  normal  levels  at 
Palomarin  that  year,  as  they  did  on  Marin's  Even  Cheaper 
Thrills  Spring  Bird  count  in  both  1986  and  1987  (Appen- 
dix A).  Whether  radiation  was  responsible  for  the  repro- 
ductive failures  requires  further  field  and  laboratory 
investigation.  Nevertheless  the  population  trends  of  War- 
bling Vireos  and  other  species  with  reduced  reproductive 
success  should  be  monitored  closely. 


A  female  Yellow  Warbler  will  soon  be  dwarfed  by  the  Brown-headed  Cowbird  youngster  she  instinctively  feeds. 

Photograph  by  Ian  Tait. 


341 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Wood-Warblers 


Wood-Warblers 

Family  Emberizidae 
Subfamily  Parulinae 


ORANGE-CROWNED  WARBLER   Vermivora  celata 


Occurs  year  round,  though  primarily  as  a 

summer  resident  from  late  Feb/early 

/oV 

Mar  through  Sep. 

~^A 

(^^^ 

A  very  common,  nearly  ubiquitous 

i*v^3£V^^ 

breeder;  overall  breeding  population 

^^£©15^^ 

extremely  large. 

-^■C^A^S^^ 

Recorded  in  191  (86.4%)  of  221 

VV;  ®^vV-?  V<\  ®Jv-^bA^\©  A^V  •  V^«iV^Ti^>^ 

blocks. 

Y\A cJv<^^3?<A ®Jv-iJv°>^A-«  v^\ •  A-^\  oA>-\  •  r^ 

\  \JpiA  ©^r^-JtA^^^Ar-ix  ©  V-A ©  A^"A  ©  V"v©  A-^ 
\  rAr<C\  ©  A-^A  •  AF"A  •Ap^a  ©  V-jA*  \>A*> \—-A v® LX 

O    Possible        =      14  (7%) 

NKv©  i^\  ©  i^rV\>-'\\»  \^\'4>  \^Km  v>-A:  •  V^<N-^— 

V  /Mr\' ©  A^A^V^A^Vi  \>A©  \>^C>  J? — 

V^,*iV>\  •A^v •3ka  ®A^d^»  v^Y«\-«v «> A^v 

-  ~° 

©    Probable       =     113   (59%) 

boj!'H^©AP\©A^®A^^©^^ — "> 

•    Confirmed  =      64   (34%) 

U.'^SSj?^ — -^0^^*Ar^®A-^©2V^*A^\  *.A<<< 
^rJ^Z^^     ^^\*  A-"\  ©  v-'a  »A^*\  ©'i-<\  ©  A*cv^ 

5?^ 

FSAR  =  5        OPI  =  955       CI  =  2.26 

i^*                            \j°/     ^""""^-k^S- 

Ecological  Requirements 

Arriving  in  numbers  on  the  breeding  grounds  in  early 
March  before  our  other  parulids,  the  Orange-crowned 
Warbler's  trilling  song  rises  from  riparian  thickets,  oak 
woodland,  coastal  scrub,  chaparral,  and  openings  in  Doug- 
las fir  and  bishop  pine  forests  where  there  is  sufficient 
ground  cover.  Coastal  scrub  breeders  prefer  moist,  dense 
drainages,  especially  adjoining  willows  and  alders,  or  other 
forest  edges.  Chaparral  breeders  are  fond  of  oak  woodland 
borders,  and  postbreeding  movements  greatly  swell  diis 
species'  ranks  in  extensive  stands  of  pure  chaparral.  A 
moderately  closed  canopy  or  understory  and  dense  ground 
cover  for  concealing  nests  seem  to  be  breeding  requisites. 
The  Orange-crowned  Warblers  that  breed  extensively 
on  the  California  coast  (V.  c.  lutescens)  may  build  their 
nests  up  to  6  feet  high  in  bushes  or  trees,  but  they  generally 
place  most  of  them  in  depressions  on  the  ground  under 
concealing  vegetation.  In  contrast,  the  race  that  breeds  on 
the  Channel  Islands  and  patchily  on  the  southern  Califor- 
nia mainland  (V.  c.  sordida)  builds  most  nests  up  to  1 5  feet 
high  in  bushes  and  small  trees,  with  ground  nests  the 
exception  (Bent  1953).  Ground  nests  may  be  on  level 
terrain  or  in  earthen  crevices  of  trailside  banks,  road  cuts, 

342 


or  under  uprooted  trees.  A  profusion  of  annual  growth, 
dried  weeds  and  ferns  from  the  previous  season,  or  under- 
story bushes  usually  shield  ground  nests  from  above.  Nests 
in  vines,  clumps  of  ferns,  bushes,  or  trees  are  usually  well 
screened  by  leaf  debris,  lichen  sprays,  or  thick  leaf  clusters. 
Orange-crowns  construct  neat  but  rather  bulky  nest  cups 
from  dried  grasses,  leaves,  bark  strips,  and  vegetable  fibers. 
They  line  them  with  fine  grasses  and  hair;  an  occasional 
nest  in  an  earthen  hollow  will  lack  a  lining  (D.  Shuford 
pers.  obs.). 

Orange-crowned  Warblers  forage  primarily  by  gleaning 
from  the  surface  of  foliage  and,  to  a  limited  extent,  from 
the  bark  of  twigs  and  branches;  they  hover  and  flycatch 
only  sparingly  (Root  1967).  Although  wedded  to  the  earth 
for  nesting,  foraging  birds  spend  most  of  their  time  in  the 
canopy  and  small  amounts  in  the  subcanopy  or  herb 
layers.  They  move  rapidly  through  the  trees  and  tall 
bushes,  probing  their  bills  into  leaf  clusters,  and  they 
characteristically  lean,  stretch,  or  hang  momentarily  from 
perches  to  peck  at  nearby  foliage.  The  diet  of  California 
birds  is  about  91%  animal  matter,  consisting  primarily  of 
true  bugs,  beedes,  caterpillars,  wasps,  ants,  and  spiders 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


(Beal  1907,  n  =  65).  The  consumption  of  these  items  and 
a  minimal  amount  of  flies  suggests  that  Orange-crowns  are 
most  successful  at  capturing  sluggish  game  (Beal  1907, 
Root  1967).  Vegetable  fare  includes  fruit,  leaf  galls,  and 
seeds,  presumably  taken  mosdy  in  the  fall  and  winter. 

Marin  Breeding  Distribution 

During  the  adas  period,  Orange-crowned  Warblers  bred 
widely  in  Marin  County.  They  were  scarce  or  absent  only 
on  the  outer  tip  of  Point  Reyes  and  in  the  low  rolling 
grassland-dominated  hills  near  Tomales.  Representative 
breeding  localities  were  near  Palomarin  (NE  5/6/77  — SJ; 
garter  snake  coiled  up  in  nest!);  O'Hare  Park,  Novato  (FL 
6/15/81  -ScC);  Lucas  Valley  Rd.  (FY  6/8/82  -BiL); 
Woodacre  (FY  5/31/82  -BiL);  Deer  Park  School,  Fairfax 
(NY  5/10/76  -RMS);  and  China  Camp  SP  (NB  4/1 7/82 
-BiL). 


Historical  Trends/  Population  Threats 

Orange-crowned  Warblers  have  probably  not  changed 
markedly  in  abundance  in  Marin  County  in  historical 
times.  Development  has  undoubtedly  destroyed  some  hab- 
itat, as  has  grazing  by  eliminating  or  degrading  the  under- 
story  of  riparian  groves.  On  the  other  hand,  clearing  of 
forests  may  have  encouraged  the  growth  of  brush  or 
ground  cover  suitable  for  nesting  needs.  Numbers  of  this 
warbler  were  relatively  stable  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1989  (USFWS  unpubl.  analyses). 


NORTHERN  PARULA    Parula  americana 


"JPt^x- 

^>t-^      N             ^C 

An  irregular  spring  transient,  summer 
resident,  and  fall  transient  from  mid-May 
to  mid-Oct. 

r-Vv-Tv 

^VjPr55r\&H^V 

J*r\i£c 

A  very  rare,  very  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  1  (0.4%)  of  221  blocks. 

v$ 

C^^^P^W0C^d 

LAA^p?N 

O    Possible        =        0   (0%) 
C    Probable       =        0  (0%) 

^cS<\\<¥S^S?^f^ 

•    Confirmed  =         1    (100%) 

v^^<^^^k\^^^^ 

FSAR  =1          OPI  =  1           CI  =  3.00 

^^^^^?(y 

Ecological  Requirements 

In  the  East,  this  dainty  warbler  breeds  in  a  wide  variety  of 
habitats  from  boreal  spruce  forests  to  sweet  gum-oak 
swamps  (Bent  1953,  Morse  1967).  In  northern  spruce  it  is 
primarily  a  species  of  the  forest  edge,  while  in  soudiern 
lowland  hardwood  forests  it  is  primarily  a  bird  of  the 
unbroken  forest  canopy.  In  mixed  forests  in  Minnesota, 
Parulas  locate  their  nests  in  forest  to  forest-edge  habitat 
with  variable  numbers  of  large  deciduous  and  coniferous 
trees  and  a  relatively  open  canopy  (Collins  1 981 ).  Foraging 
studies  suggest  that  Northern  Parulas  are  primarily  adapted 


to  deciduous  forests  and  diat  competition  with  kinglets  and 
"spruce-woods  warblers"  restricts  them  to  the  edge  of 
conifers  (Morse  1967).  The  few  nesting  birds  found  in 
California  have  been  in  habitats  that  fall  within  the  range 
described  for  the  East.  In  Monterey  County,  one  nest  was 
situated  in  a  radier  open  stand  of  mature  Monterey  pines 
interspersed  widi  a  few  live  oaks  near  a  pasture  (Williams 
et  al.  1958).  The  understory  consisted  of  low,  dense  ever- 
green and  deciduous  shrubs.  A  second  nearby  nest  was  in 
a  somewhat  denser  stand  of  diese  pines  with  a  radier 

343 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wood-Warblers 


sparse  understory  of  small,  scattered  live  oaks  and  a  few 
shrubs.  In  San  Mateo  County,  Parulas  nested  in  a  coastal 
riparian  forest  in  a  narrow  canyon  with  an  open  Douglas 
fir-mixed  evergreen  forest  on  the  slopes  above  (P.J.  Metro- 
pulos  pers.  comm.).  Parulas  have  nested  in  Marin  County 
on  the  edge  of  Douglas  fir  forests  interspersed  with  mixed 
evergreen  forest  and  in  proximity  to  riparian  habitat 

Nesting  distribution  in  the  East  generally  coincides  wid\ 
the  distribution  of  plentiful  nest  sites  and  materials.  In  the 
Northeast,  most  birds  build  their  nests  in  and  of  "old 
man's  beard"  lichen  (Usnea  sp.),  whereas  in  die  Soudieast 
they  build  them  primarily  in  a  flowering  plant,  "Spanish 
moss"  (Tillandsia  usneoides).  Both  of  these  grow  epiphyti- 
cally on  the  trees  of  humid  forests.  Although  distribution 
and  abundance  over  broad  areas  may  mirror  that  of  the 
preferred  nesting  substrates  (Bent  1953),  Morse  (1967) 
found  no  direct  relationship  between  this  warbler  and 
lichen  densities  at  a  Maine  study  site.  This  suggests  other 
factors  are  also  important.  The  few  California  nests  have 
been  built  from  the  lichen  (Ramalina  reticulaia)  that  hangs 
profusely  from  the  limbs  of  trees  in  coastal  conifer,  mixed 
evergreen,  and  riparian  forests.  This  lichen  resembles  the 
typical  eastern  nesting  substrates  in  superficial  appearance 
and  drooping  manner  of  growth  and  also  has  been  used 
for  nesting  to  a  limited  degree  in  the  Mississippi  Valley 
(Williams  et  al.  1958).  In  areas  of  Usnea  abundance, 
Parulas  usually  suspend  and  conceal  their  semipensile, 
oriolelike  nests  inside  a  festoon  of  free-hanging  lichen, 
which  sometimes  trails  a  foot  or  more  below  the  nest 
(Wilde  1897,  Graber  &  Graber  1951,  Bent  1953). 

Parulas  weave  or  felt  their  generally  compact  nests 
almost  exclusively  from  the  lichen  strands  to  which  they 
are  attached  or  from  those  brought  from  outside.  The 
festoon  generally  provides  a  cylindrical  curtain  above  and 
around  the  nest.  The  birds  come  and  go  through  one  (or 
occasionally  two  or  more)  side  entrances  through  the 
lichen,  situated  at  or  slighdy  above  the  level  of  the  nest  cup 
rim.  They  may  incorporate  a  few  pine  needles  or  fine  grass 
stems  into  the  nest,  probably  for  support  or  attachment 
purposes.  Rarely,  the  nest  is  open  from  above  and  sus- 
pended from  twigs,  branches,  foliage,  or  between  a  trunk 
and  a  lichen  tuft.  In  the  Southeast,  Parulas  most  often 
conceal  the  nest  near  the  branch  from  which  long  fila- 
ments of  "Spanish  moss"  hang.  They  may  make  these 
nests  from  the  flower  or  fine  decaying  inner  fiber  of 
"Spanish  moss"  or  from  thisdedown.  Rarely,  where  Usnea 
and  Tillandsia  are  scarce,  Parulas  build  nests  in  hanging 
clusters  of  twigs,  ivy  vines,  and  in  bunches  of  leaves  or 
other  rubbish  deposited  by  freshets  on  branches  over 
streams  (Bent  1953).  In  such  situations  they  construct 
nests  from  fine  dry  grasses,  fine  bark  shreds,  box  elder 
blossoms,  spider  webs,  plant  down,  and  leaves.  Through- 
out the  range,  Parulas  line  their  nests  scantily  with  fine 
materials,  including  shreds  of  lichen,  grasses,  pine  needles, 

344 


horsehair,  down  from  the  stems  of  swamp  ferns,  "Spanish 
moss"  fiber,  roodets,  twigs,  and  strips  of  weed  stems; 
rarely,  they  line  them  elaborately  with  plant  down.  Parulas 
build  nests  in  dead  or  live  conifers,  deciduous  trees,  or 
bushes,  and  they  situate  them  against  the  trunk  to  well  out 
on  outstretched  or  drooping  branches.  Nests  have  been 
reported  from  5  inches  to  over  100  feet  above  the  ground, 
but  they  range  from  1  to  20  feet  (av.  5  ft.)  in  New  Jersey 
(Wilde  1897,  n  =  33)  and  26  to  40  feet  in  Quebec  (Mous- 
ley  in  Bent  1953).  Two  nests  in  Monterey  County  were  1 5 
and  30  feet  up  in  the  dead  branches  of  Monterey  pines 
(Williams  et  al.  1958).  Nest  height  and  simation  is  perhaps 
most  dependent  on  the  distribution  and  abundance  of  the 
lichen  and  "Spanish  moss"  nesting  substrate. 

In  conifers,  Parulas  forage  at  the  forest  edge  at  medium 
heights  (range  5-60  ft.,  av.  33  ft.,  Morse  1967).  In  the 
absence  of  competition  on  coastal  Maine  islands,  Parulas 
exhibit  plasticity  by  expanding  their  range  of  foraging 
heights  and  using  a  greater  diversity  of  foraging  stations.  In 
southern  deciduous  forests,  they  forage  uniformly  through- 
out the  breadth  of  the  forest  but  primarily  in  the  canopy 
above  49  feet.  In  general,  males  tend  to  forage  at  greater 
heights  than  do  females  (Morse  1971).  The  need  to  satisfy 
the  increasing  energy  demands  of  young  approaching 
fledging  appears  to  explain  the  expansion  at  that  time  of 
conifer-foraging  adults  to  nearby  deciduous  growth  and  of 
deciduous  foragers  to  the  understory  (Morse  1967). 
Despite  the  above  differences,  Parulas  in  both  habitats 
forage  on  similar  substrates  by  similar  methods.  They  feed 
primarily  on  the  extreme  tips  of  foliage,  secondarily  on 
small  live  twigs,  and  to  a  limited  extent  on  dead  twigs, 
branches,  and  epiphitic  growth.  They  capture  most  prey  by 
gleaning,  with  limited  use  of  flycatching,  hovering,  hover- 
walking,  stretching,  and  hanging.  Their  habit  of  clinging 
to  the  underside  of  foliage  while  foraging  spawned  the 
name  panda,  reflecting  the  warbler's  likeness  to  its  larger 
parid  cousins,  titmice  and  chickadees,  which  characteristi- 
cally forage  in  this  manner.  Parulas  also  forage,  rarely,  on 
the  ground  or  by  clinging  to  tree  trunks  (Bent  1953). 
Compared  to  other  treetop  warblers,  Parulas  are  overall 
more  sedate  and  deliberate  in  their  movements  as  they 
hop,  creep,  or  flit  from  twig  to  twig. 

The  diet  appears  to  be  almost  exclusively  insectivorous. 
The  only  quantitative  work  (from  Puerto  Rico)  indicates 
Pandas  eat  about  97.7%  animal  matter  and  2.3%  vegetable 
matter,  in  the  form  of  seeds  of  small  berries  (Bent  1953). 
The  principal  animal  fare  is  beedes,  spiders,  true  bugs, 
flies,  planthoppers,  caterpillars,  moths,  and  a  few  ants  and 
other  small  hymenopterans. 

Marin  Breeding  Distribution 

The  only  Marin  County  adas  breeding  record,  and  the 
second  for  California,  involved  at  least  three  Parulas  at  Five 
Brooks  Pond  in  the  Olema  Valley  in  1977.  A  singing  male 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


was  first  discovered  there  on  2  June  (JM).  The  male  was 
rediscovered  on  4  June,  and  on  5  June  two  males  and  a 
female  were  present  (SJ  et  al.).  On  the  latter  date,  careful 
observations  of  the  female  carrying  nesting  material 
revealed  a  nest  about  25  to  30  feet  up  in  a  lichen-draped 
(Ramalina  reticulata)  blue  blossom  (Ceanothus  thrysiflorus) 
tree  (SJ).  The  ceanothus  was  at  the  base  of  a  Douglas 
fir-dominated  slope,  where  it  graded  into  a  patch  of  red 
alders,  just  west  of  the  pond.  The  following  observations 
document  further  incidents  at  the  nest  site:  10  June- 
female  still  carrying  nest  material;  1 2  June— 2  males,  female 
not  incubating;  17  June— male  singing,  female  incubating; 
27  June— male  and  female  feeding  young  and  female 
remaining  on  nest  after  feeding  (brooding  recendy  hatched 
young?);  5  July— two  fledglings  seen  (ITa);  6  July— male 
scolding  Steller's  Jay;  7  July— male  and  female  present;  16 
July— male  last  seen  (EYM). 

A  second  confirmed  Marin  County  breeding  record  was 
of  a  male  and  female  feeding  a  fledgling  one-half  mile  north 
of  Inverness  Park  from  9  to  16  June  1984;  the  juvenile  was 
still  present  on  26  June  (MFe,  SEF  et  al.).  A  male  and  a 
female  were  feeding  a  juvenile  in  the  vicinity  on  28  and  29 
July  1984  (RHa),  suggesting  that  a  second  pair  had  also 
bred;  an  adult  male  was  present  through  9  August.  In 
1985,  observations  suggestive  of  breeding  were  recorded  at 
Bear  Valley  Headquarters,  PRNS,  and  at  Five  Brooks  Pond. 
At  Bear  Valley,  a  pair  was  seen  from  1  to  4  June,  with  the 
male  at  least  to  28  June  (RMS  et  al.),  while  at  Five  Brooks 
a  pair  was  recorded  on  19  June,  with  the  female  present  to 
the  29th  (RS,  SEF).  In  1991 ,  Parulas  again  nested  near  Five 
Brooks;  a  pair  was  seen  from  16  June  to  10  July  and  the 
female  was  carrying  food  (RS,  DaS).  Also  that  year,  a 
singing  male  was  present  north  of  Bear  Valley  Headquar- 
ters, PRNS,  from  26  May  until  early  July  (DaS  et  al.).  The 


number  of  breeding  season  sightings  of  Parulas  at  Five 
Brooks  and  Bear  Valley  probably  reflects  greater  coverage 
of  these  sites  rather  than  any  particular  affinity  of  the 
warblers,  as  such  habitat  is  widespread  on  Point  Reyes. 

Other  than  the  Monterey  and  Marin  records,  the  only 
other  confirmed  breeding  record  of  Northern  Parulas  in 
California  is  from  Gazos  Creek,  San  Mateo  County,  in 
1991.  Two  singing  males  and  a  female  were  first  found 
there  on  1  June;  nest  building  was  underway  on  2  June; 
and  adults  were  observed  from  15  to  30  June  repeatedly 
carrying  food  to  (and  removing  fecal  sacs  from)  a  site  where 
a  nest  was  apparendy  hidden  (BS,  PJM  et  al.). 

Historical  Trends/ Population  Threats 

Since  the  discovery  of  the  first  California  nest,  increased 
field  work  has  revealed  that  Northern  Parulas  occur  on  the 
northern  California  coast  annually  as  vagrants,  in  small 
numbers  in  May  and  June  and  irregularly  from  September 
to  early  October  (ABN).  Most  of  these  birds  apparendy 
perish  or  continue  on  their  off-course,  long-distance  jour- 
neys. Since  a  few  have  remained  to  breed,  all  sightings  in 
suitable  potential  nesting  habitat  should  be  followed  up  to 
determine  their  nesting  status.  Whether  Northern  Parulas 
will  establish  a  regular  breeding  population  in  California 
bears  watching.  If  they  do  so,  it  will  likely  be  on  the 
immediate  northern  California  coast,  where  vagrants  "con- 
centrate" and  where  moist,  Ramalina-draped  forests  occur. 
At  least  in  the  period  1965  to  1979  the  Northern  Parula 
"showed  a  strong  and  continuing  population  increase"  in 
the  East  (Robbins  et  al.  1 986).  Increases  such  as  this  would 
be  likely  to  provide  extra  "pioneers"  to  potential  breeding 
habitat  in  California. 


345 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wood-Warblers 


YELLOW  WARBLER   Dendroica  petechia 


-'ygtc^^ 

A  summer  resident  from  early  Apr 
through  mid-Oct;  numbers  swell  substan- 

y\^V^Yv^ 

^>s^^^    \          yc^^ 

tially  during  peak  of  fall  migration  (Aug 

to  early  Oct). 

^L\     J<K 

'V--^v^^V\  'iX^A^A^N  3r^A  \^\ 

A  fairly  common,  very  local  breeder; 

\  ^\\  ^V\^3^\^3?<a^A^\^j*>^\^^J 

overall  breeding  population  very  small. 

V-c^- 

Recorded  in  22  (10.0%)  of  221  blocks. 

V? 

O    Possible        =         7   (32%) 

^5^?$^^ 

K\°° 

€    Probable       =       12   (54%) 

■sf^y —  '' 

•    Confirmed  =         3   (14%) 

tw^rv3rA5VAXo3r^^ 

^\\\ — \ 

r1*3NL-^jv&^_Jy'   >^\o\-^a    U3^    L-^fT  \ 

^v^Z^^          ~e^-~J^\®Jk<\;^^\  J^Z 

^Sc?^ 

FSAR=3         OPI  =  66        CI  =  1.82 

i\                                           ^^^\^^^*^r\ 

3r^\®><\ 

_>fS^>                                                      \L_  /             ^■to""*<S 

^©v^\"o 

Ecological  Requirements 

In  Marin  County,  we  hear  the  uplifting  song  of  the  Yellow 
Warbler  rising  from  willow  and  alder  riparian  thickets— 
usually  ones  in  relatively  early  stages  of  succession.  Yellow 
Warblers  seem  to  prefer  willows  here,  perhaps  because 
alder  groves  frequendy  lack  a  dense  brushy  understory, 
apparendy  an  important  feature  noted  in  other  studies 
(e.g.,  Morse  1973).  In  fact,  in  the  Sierra  Nevada  they 
sometimes  nest  far  from  water  in  dry  montane  chaparral 
with  scattered  trees  (Beedy  &  Granholm  1985,  Gaines 
1988).  Although  birds  sometimes  nest  in  predominandy 
brushy  areas,  they  generally  require  taller  trees  for  foraging 
(Kendeigh  1941b). 

Yellow  Warblers  usually  build  their  nests  in  bushes  and 
saplings  from  about  1  to  15  feet  above  ground  (most  3-8 
ft.),  or  infrequendy  from  40  to  60  feet  in  tall  trees  (Bent 
1953).  They  weave  their  well-formed  nest  cups  around  the 
branches  of  an  upright  fork  or  crotch,  or  in  taller  trees  they 
sometimes  attach  them  on  lateral  branches  against  the 
trunk.  Nests  are  generally  deeper  than  wide,  and  in  narrow 
crotches  may  be  cone-shaped  (Schrantz  1943,  Bent  1953). 
Yellow  Warblers  construct  their  nests  of  plant  fibers, 
grasses,  plant  down,  and  bark  shreds,  and  they  line  them 
with  plant  down,  fine  grasses,  hair,  and  occasionally  feath- 
ers; rarely,  they  make  a  nest  entirely  of  wool  or  chicken 
feathers!  The  Yellow  Warbler  is  one  of  the  species  most 
frequendy  parasitized  by  Brown-headed  Cowbirds  (Fried- 
mann  1929,  1963).  The  warblers  usually  respond  by 
deserting  the  nest  or  by  covering  the  cowbird  eggs  with  a 

346 


second  nest  built  atop  the  first;  in  some  cases  Yellow 
Warblers  have  constructed  six  layers  over  successively  laid 
cowbird  eggs  (Bent  1953)! 

Yellow  Warblers  forage  primarily  by  gleaning,  and  sec- 
ondarily by  hawking  and  hovering,  from  foliage  and  small 
branches  (Morse  1973,  Busby  6k  Sealy  1979,  Hutto  1981). 
The  relative  importance  of  hawking  versus  hovering  varied 
among  these  studies,  and  in  general  the  species  shows 
much  geographic  variation  in  prey  capture  methods  (Petit 
et  al.  1990).  Busby  and  Sealy  (1979)  studied  sexual  differ- 
ences in  Yellow  Warblers'  foraging  in  Manitoba.  They 
found  that  females  hovered  more  and  foraged  at  lower 
heights,  in  smaller  trees  and  more  in  bushes,  and  more  in 
the  lower  and  inner  parts  of  trees.  Females  also  moved 
shorter  distances  while  foraging  and  foraged  less  in  willows 
than  did  males.  Morse  (1973)  also  noted  females  foraging 
at  lower  heights;  while  in  several  instances  he  found 
females  hovering  more  than  males,  this  was  not  always  the 
case.  These  foraging  differences  appear  to  reflect  the  differ- 
ential roles  of  the  sexes  in  nesting  activities,  rather  than 
partitioning  of  the  food  resource,  since  both  sexes  eat 
similar  prey  species  and  sizes  (Busby  6k  Sealy  1979).  The 
fact  that  males  forage  higher,  in  the  outer  canopy,  in  more 
open  willows,  and  over  longer  distances,  is  apparendy  a 
function  of  the  time  they  spend  in  display  and  territorial 
establishment  and  maintenance  while  moving  about  in 
conspicuous  positions  in  the  canopy.  It  would  seem  more 
advantageous  from  an  energetic  viewpoint  for  them  to 
forage  in  display  areas  rather  than  fly  elsewhere  to  forage 
and  then  return  to  greater  heights  to  defend  territories. 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


Since  females  are  tied  more  to  nesting  duties,  it  appears 
beneficial  for  them  to  feed  lower  and  more  inconspicu- 
ously in  the  inner  parts  of  denser  trees  and  bushes. 
Females  foraging  over  shorter  distances  and  hovering  more 
apparendy  are  maximizing  food  intake  while  minimizing 
the  time  off  the  nest  by  feeding  with  rapid  and  varied 
movements.  Generally,  these  foraging  differences  were  the 
greatest  during  the  early  breeding  season  and  decreased  as 
the  season  progressed.  After  die  cessation  of  nesting  activi- 
ties, both  sexes  foraged  higher,  a  fact  also  noted  for  the 
species  as  a  whole  by  Hutto  (1981). 

Overall,  Yellow  Warblers  tend  to  feed  relatively  high  in 
riparian  habitat  (Busby  6k  Sealy  1979,  Hutto  1981).  In 
Wyoming  riparian,  Yellow  Warblers  forage  at  a  greater 
absolute  height  than  Wilson's  Warblers,  Common  Yel- 
lowthroats,  and  MacGillivray's  Warblers  (Hutto  1981). 
Although  absolute  foraging  height  varies  gready  among 
habitats  and  seasons  in  the  West,  the  height  these  four 
species  forage  relative  to  each  other  remains  constant;  all 
four  species  forage  a  bit  higher  in  August  after  the  cessation 
of  nesting  activities.  Of  this  group,  Yellow  and  Wilson's 
warblers  are  relatively  high  foragers,  and  the  other  two 
species  are  relatively  low  foragers.  Between  Yellow  and 
Wilson's  warblers,  absolute  foraging  height  was  the  only 
significant  difference  in  foraging  strategy;  relative  foraging 
height,  vegetation  density,  position  in  the  canopy,  foraging 
substrate,  and  feeding  techniques  were  similar  for  both 
species;  there  was  a  slight  tendency  for  Yellow  Warblers  to 
feed  more  in  the  outer,  more  open  foliage  and  to  hawk  less 
for  insects.  See  Morse  (1973)  for  comparison  of  Yellow 
Warbler  and  American  Redstart  foraging.  In  areas  of 
brush,  Yellow  Warblers  may  move  up  to  0.3  of  a  mile  off 
their  territories  to  forage  in  taller  trees  (Kendeigh  1941b). 

The  summer  diet  of  California  birds  consists  of  over 
97%  animal  matter,  including  ants,  bees,  wasps,  caterpil- 
lars, beedes,  true  bugs,  flies,  spiders,  and  miscellaneous 
insects;  vegetarian  fare  includes  fruit  pulp  and  an  occa- 
sional seed  (Beal  1907,  n  =  98).  In  general,  Yellow  War- 
blers are  diverse  and  unspecialized  arthropod  feeders  diat 
take  prey  in  proportion  to  their  availability  (Busby  6k  Sealy 
1979);  see  Busby  ck  Sealy  (1979)  and  Frydendall  (1967) 
for  dietary  information  elsewhere  in  the  West. 

Marin  Breeding  Distribution 

During  the  adas  period,  Yellow  Warblers  were  patchily 
distributed  as  breeders  in  Marin  County.  They  were  most 
prevalent  in  the  Olema  Valley  and  near  Limantour  Estero. 
Representative  breeding  localities  were  Olema  Marsh  (NB 
5/10/80  -JGE);  Pine  Gulch  Creek,  Bolinas  Lagoon 
(NE/NY  5/21/77  -GBe  et  al.);  and  Lagunitas  Creek, 
Tocaloma  (NB  5/6/85  -JGE). 


Historical  Trends/  Population  Threats 

Mailliard  (1900)  and  Stephens  and  Pringle  (1933),  respec- 
tively, considered  the  Yellow  Warbler  to  be  a  "common" 
and  "fairly  common"  summer  resident  in  Marin  County; 
it  is  unclear,  however,  to  what,  if  any,  degree  these  assess- 
ments were  colored  by  status  in  the  fall  migration  when,  at 
least  currendy,  the  Yellow  Warbler  is  the  most  numerous 
warbler  in  Marin  County  (D.  Shuford  pers.  obs.).  A 
comparison  of  the  historical  status  of  the  Yellow  Warbler 
with  that  of  the  Orange-crowned  and  Wilson's  warblers 
provides  additional  insight  on  the  relative  abundance  of 
these  species  in  former  times.  Mailliard  (1900)  considered 
both  the  Orange-crowned  and  Wilson's  warblers  "abun- 
dant" summer  residents.  Stephens  and  Pringle  (1933) 
considered  the  Orange-crowned  Warbler  "common  and 
abundant"  and  the  Wilson's  Warbler  "fairly  common" 
summer  residents.  These  impressions  suggest  that,  for- 
merly, the  Yellow  Warbler  was  a  somewhat  less  numerous 
breeding  bird  than  Orange-crowned  and  Wilson's  war- 
blers, though  not  gready  so.  Currendy,  Yellow  Warblers 
are  much  less  widely  distributed  (adas  maps)  and  much 
less  numerous  (Appendixes  A  and  B)  than  either  of  these 
two  other  species.  This  suggests,  but  does  not  confirm,  a 
historical  decline  of  Yellow  Warblers  in  Marin  County. 
Grinnell  and  Wythe  (1927)  considered  the  Yellow  War- 
bler a  "common"  summer  resident  in  the  Bay  Area,  and 
Grinnell  and  Miller  (1944)  considered  it  "common"  or 
"even  abundant  locally"  in  this  role  for  California  as  a 
whole.  Although  neither  of  the  latter  two  authors  indicated 
any  historical  change  in  the  Yellow  Warbler  population  up 
to  that  time,  the  species  undoubtedly  must  have  declined 
considerably  by  then,  from  the  extensive  destruction  of 
riparian  habitat  that  had  already  precipitated  a  major 
decline  of  California's  riparian-obligate  Yellow-billed 
Cuckoo  (G6kM  1 944);  the  latter  decline  has  continued  to 
this  day  (Gaines  ck  Laymon  1984,  Laymon  6k  Halterman 
1987).  Declines  in  Yellow  Warblers  in  the  Central  Valley 
and  elsewhere  in  the  state  led  to  the  inclusion  of  the  species 
on  Fish  and  Game's  list  of  Bird  Species  of  Special  Concern 
in  California  (Remsen  1978,  CDFG  1991b;  see  also  Garrett 
ck  Dunn  1981).  These  declines  were  apparendy  caused  by 
the  clearing  of  riparian  habitat,  for  development  and  agri- 
culture, and  by  the  effects  of  cowbird  parasitism.  In  addi- 
tion, in  Marin  County  and  elsewhere  in  California,  catde 
grazing  has  drastically  altered  much  riparian  habitat,  mak- 
ing it  unsuitable  for  Yellow  Warblers  and  other  species.  It 
is  encouraging  that,  given  the  chance,  Yellow  Warblers  can 
make  rapid  recovery  once  grazing  impacts  are  lessened  by 
reductions  in  catde  numbers  or  by  fencing  off  sensitive 
areas  (Taylor  6k  Litdefield  1986).  The  Yellow  Warbler  was 
on  the  Audubon  Society's  Blue  List  for  10  of  the  first  11 
years  since  its  inception  in  1972  (Tate  1981,  Tate  6k  Tate 
1982),  with  particular  concern  for  both  northern  and 
southern  California  breeding  populations.  It  currendy  is 

347 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wood-Warblers 


on  the  Audubon  Society's  list  of  Species  of  Special  Con- 
cern (Tate  1986).  Yellow  Warblers  declined  on  Breeding 
Bird  Surveys  from  1965  to  1979  in  the  "Far  Western 
States"  but  not  in  California  and  the  West  as  a  whole 
(Robbins  et  al.  1986);  through  1989  the  California  popu- 
lation remained  stable  (USFWS  unpubl.  analyses).  These 
conclusions  should  be  viewed  cautiously,  as  riparian  habi- 
tats in  many  areas  are  patchily  distributed  and  therefore  are 
difficult  to  census  with  broad-scale  techniques.  Addition- 


ally, stable  trends  where  the  species  is  most  numerous  may 
mask  local  declines  where  the  species  is  less  numerous. 
Conservationists  have  begun  restoring  riparian  habitat  to 
help  stop,  and  perhaps  reverse,  the  decline  of  the  Yellow- 
billed  Cuckoo  in  California  (Laymon  6k  Halterman  1987). 
This  work  should  be  extended  where  it  can  help  other 
riparian  species  whose  populations  have  also  been 
reduced,  though  less  critically. 


YELLOW-RUMPED  WARBLER   Dendroica  coronata 


Occurs  year  round,  though  primarily  as  a 
winter  resident  from  late  Sep  through 
Apr. 

A  fairly  common,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  19  (8.6%)  of  221  blocks. 

O  Possible  =  6  (32%) 
€  Probable  =  11  (58%) 
•    Confirmed  =         2   (11%) 


FSAR  =  3        OPI  =  57 


CI  =  1.79 


Ecological  Requirements 

A  mainstay  of  mixed  species  foraging  flocks  in  winter  in  a 
variety  of  relatively  open  habitats,  the  Audubon's  form  of 
the  Yellow-rumped  Warbler  also  breeds  sparingly  in  rela- 
tively open  stands  of  Marin  County's  mixed  evergreen 
forests  dominated  by  Douglas  fir  and  in  pure  Douglas  fir 
forests.  Audubons  here  favor  meadow  or  grassland  edges 
and  generally  avoid  the  dense  interiors  of  these  forests. 
They  also  have  bred  in  planted  Monterey  pine,  both  in 
Marin  County  (Kelly  1 942)  and  elsewhere  in  the  Bay  Area 
(Seibert  1942),  but  this  is  apparendy  of  irregular  occur- 
rence. Audubons  locate  their  nests  from  about  4  to  80  feet, 
but  mosdy  from  about  12  to  30  feet  above  die  ground 
(Dawson  1923,  Bent  1953).  They  often  place  them  well  out 
on  limbs  but  sometimes  against  the  trunk  or  at  the  tips  of 
branches;  rarely,  they  situate  a  nest  behind  a  loose  piece  of 
bark  or  in  a  hollow  or  cavity  in  a  tree.  Audubons  prefer 
conifers  for  nest  supports  in  California,  but  occasionally 
they  use  deciduous  trees.  Their  nests  are  deep,  cup-shaped 
structures  composed  of  twigs,  fine  grasses,  pine  needles, 

348 


weed  stems  or  tops,  fine  shredded  bark,  or  even  string, 
flower  pedicels,  catkins,  and  other  plant  fibers,  any  of 
which  may  be  mixed  with  feathers.  The  nest  cup  is  heavily 
lined  with  feathers  (which  often  curve  upward  and  inward 
to  partially  conceal  the  eggs),  along  with  horse,  catde,  or 
deer  hair  or  other  fine  fibers. 

Yellow-rumps,  or  "Butter-butts"  as  they  are  often  fondly 
called,  are  active  and  conspicuous  as  they  go  about  making 
their  livelihood.  They  generally  forage  at  mid-  to  high 
elevations  in  the  canopy,  with  a  preference  for  open,  less 
dense  foliage,  but  they  may  feed  at  almost  any  level  and  on 
the  ground.  In  a  Sierran  mixed  conifer  forest,  Airola  and 
Barrett  (1985)  found  that  Yellow-rumps  forage  by  gleaning 
about  75%  of  the  time,  by  hovering  and  hawking  about 
20%,  and  for  the  rest  by  lunging;  they  perform  aerial 
maneuvers  more  than  any  other  species  in  the  insect-glean- 
ing guild  of  that  forest  except  the  Western  Tanager.  Audu- 
bons diere  direct  foraging  attempts  mosdy  at  foliage  and 
secondarily  at  twigs,   air,   trunks,   and   branches.   In  an 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


Arizona  mixed  conifer  forest,  Franzreb  (1983b)  reported 
that  Yellow-rumps  spend  about  87%  of  their  time  gleaning 
and  the  rest  hovering  and  hawking.  The  males  there  tend 
to  forage  in  both  taller  trees  and  at  greater  heights  than 
females,  likely  because  males  forage  closer  to  song  posts 
and  females  closer  to  nest  sites,  thereby  reducing  energy 
expenditures  and  maximizing  fitness  of  the  respective 
sexes.  Where  Yellow-rumps  breed  in  Minnesota,  males 
also  forage  higher  than  females  (Hanowski  &.  Niemi 
1990).  Species  of  trees  they  prefer  for  foraging  vary  among 
habitats  (Franzreb  1983b,  Airola  ck  Barrett  1985)  and 
between  the  sexes  (Franzreb  1983b).  Yellow-rumps  in 
logged  forests  appear  to  select  smaller  trees,  and  forage  at 
lower  heights,  than  birds  in  unlogged  areas.  Also,  in  logged 
areas,  they  apparendy  are  more  generalized  in  tree  species 
use,  tree  height  preferences,  and  foraging  heights  (Franzreb 
1983a).  Yellow-rumped  Warblers  wintering  in  various  oak 
woodlands  in  California  do  not  vary  geographically  in  the 
foraging  activities  they  use  to  capture  prey;  they  do  vary 
among  habitats  in  use  of  foraging  substrate,  foraging 
perches,  position  in  tree,  and  species  and  tree  height  use 
(Block  1990).  Despite  such  variation,  on  the  whole  Yellow- 
rumps  show  litde  geographic  variation  in  use  of  foraging 
techniques  and  substrates  (Petit  et  al.  1990). 

The  diet  of  Yellow-rumped  Warblers  in  California  from 
July  through  May  is  about  85%  animal  matter  and  15% 
vegetable  (Beal  1907,  n  =  383).  In  the  West  as  a  whole,  the 
fall  and  winter  diet  ranges  from  72%  to  76%  animal  matter 
(Martin  etal.  1951,  n  =  210).  A  small  sample  for  the  West 
(n  =  20)  suggests  1 00%  reliance  on  animal  matter  in 
spring  and  summer  (Martin  et  al.  1951),  but  the  contents 
of  three  stomachs  from  the  Sierra  Nevada  suggest  a  sum- 
mertime diet  of  81%  animal  and  19%  vegetable  matter 
(Dahlsten  et  al.  1985).  The  most  important  animal  items 
in  the  diet  are  wasps  and  ants,  true  bugs,  flies,  hemipter- 
ans,  caterpillars,  and  beedes  (Beal  1907);  spiders  and 
pseudoscorpions  are  also  taken  (Dahlsten  et  al.   1985, 


Otvos  6k  Stark  1 985).  Vegetable  foods  are  primarily  weed 
seeds  and  small  wild  fruits,  particularly  poison  oak  (mosdy 
the  waxy  outer  coating),  elderberry,  grape,  wax  myrtle,  and 
peppertree  (Beal  1907,  Martin  et  al.  1951). 

Marin  Breeding  Distribution 

During  the  adas  period,  Yellow-rumped  Warblers  bred  in 
Marin  County  on  Mount  Tamalpais,  Bolinas  Ridge,  and 
other  nearby  ridges  of  the  Lagunitas  Creek  watershed,  as 
well  as  on  Inverness  Ridge.  This  distribution  was  similar 
to  that  of  the  Black-throated  Gray  and  Hermit  warblers, 
except  for  the  extension  of  the  Yellow-rump's  range  on  the 
southern  part  of  Inverness  Ridge.  Representative  breeding 
records  were  the  first  meadow  NW  of  Rock  Springs,  Mt. 
Tamalpais  (FY/FL  7/10/81  -DS)  and  the  junction  of  the 
Cataract  and  Helen  Mark  trails  above  the  SW  corner  of 
Alpine  Lake  (FY/FL  8/1/81  -DS).  Apparendy  the  only 
other  confirmed  Marin  County  breeding  record  prior  to 
the  adas  period  is  of  a  pair  feeding  young  on  the  grounds 
of  the  College  of  Marin,  Kentfield,  on  14  June  1942  (Kelly 
1942).  Other  historical  reports  for  June  and  July  are  from 
Rock  Springs,  Mount  Tamalpais  (Orr  1937)  and  from 
Ross  (Kelly  1944).  Audubons  breed  here  mosdy  above 
about  700  feet  elevation,  but  the  Kentfield  and  Ross 
records  were  presumably  close  to  sea  level. 

Historical  Trends/Population  Threats 

Audubon's  Warblers  were  first  suspected  of  breeding  in 
Marin  County  on  Mount  Tamalpais  in  1936  (Orr  1937). 
This  discovery  very  likely  was  a  result  of  more  thorough 
coverage  of  a  poorly  explored  or  unexplored  area,  rather 
than  a  range  extension. 

For  California  as  a  whole,  Yellow-rumped  Warblers 
were  generally  increasing  on  Breeding  Bird  Surveys  from 
1968  to  1989,  despite  relative  stability  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


349 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wood-Warblers 


BLACK-THROATED  GRAY  WARBLER   Dend 


roica  nigrescens 


A  summer  resident  from  late  Mar/early 

^>s^^^         \                         JO*^ 

Apr  through  late  Oct 

iOv^vOr 

A  common,  very  local  breeder;  overall 

VyX 

3r\3rv3rA  \^\\S<r\jc\&'~ 

breeding  population  very  small. 

Recorded  in  23  (10.4%)  of  221  blocks. 

^C^y^<\^\^^0<^^?K^ 

V-c*^ 

*v  \c\J^\\  JV"\  y<r\  ^<r\^\^\   J\ 

O    Possible        =        3  (13%) 

\\\ 

r^T^j^r^^vl^w 

C    Probable       =       14  (61%) 

cf^A^-^5-^^ 

•    Confirmed  =        6  (26%) 

wd^#^\$^ 

-r- 

FSAR  =  4         OPI  =  92        CI  =  2.13 

*4jprOt^# — \_  3^\     V-^A      V^\  ®?1^V<>  V-""\   'i 

^^ 

i^^                                          \__  /           ^^*"^vXV^\ 

Ecological  Requirements 

Breeding  haunts  of  Marin  County's  Black-throated  Grays 
are  the  relatively  dry,  open  mixed  evergreen  forests  usually 
dominated  by  Douglas  fir  but  generously  mixed  with  coast 
live,  canyon  live,  or  tanbark  oaks  or  other  broadleaved 
evergreen  trees,  saplings,  or  shrubs.  Especially  favored 
areas  are  those  where  more  continuous  Douglas  fir  cover 
mixes  with  oaks  and  saplings  along  meadow  edges  or 
where  the  firs  grade  into  mixed  or  serpentine  chaparral. 
Chaparral  may  even  dominate  as  long  as  there  are  a  few 
relatively  tall  firs  for  song  posts.  Black-throated  Grays  also 
breed  here  sparingly  in  relatively  moist  but  open  mixed 
woodlands  of  black  oak,  madrone,  and  live  oaks.  Black- 
throated  Grays  overlap  here  to  a  limited  degree  with 
Hermit  Warblers,  where  the  above-mentioned  habitats 
grade  into  the  denser  Douglas  fir  preferred  by  the  latter 
species  (see  account).  In  mixed  Douglas  fir-oak  forest  in 
Oregon,  Black-throated  Grays  use  habitat  with  a  relatively 
heavy  deciduous  tree  cover,  primarily  of  small  oaks  in  high 
density  (Morrison  1982).  In  Oregon,  at  least,  they  show  a 
general  though  not  significant  tendency  to  avoid  conifers; 
their  habitat  there  also  has  a  relatively  high  vegetative  cover 
in  lower  layers  up  to  about  30  feet. 

Black-throated  Grays  place  their  nests  from  1.5  to  50 
feet  above  the  ground  in  deciduous,  broadleaved  ever- 
green, or  coniferous  growth.  They  secure  them  in  conceal- 
ing foliage  in  vertical  crotches  low  in  dense  bushes  or 
relatively  open  saplings,  or  higher  on  horizontal  branches 
of  conifers  (Dawson  1923,  Bent  1953).  Black-throated 
Grays  build  deeply  cupped  nests  of  dead  and  often  frayed 

350 


grasses,  weed  stalks  or  bark,  flower  stems,  and  perhaps 
other  fine  plant  fibers,  a  few  leaves,  moss,  catkins,  string, 
or  thread.  They  may  bind  their  nests  firmly  with  spider 
webs  and  decorate  them  with  numerous  bits  of  spider 
cocoons.  Birds  line  nests  with  fine  grasses,  feathers,  and 
fur  or  hair  from  deer,  rabbit,  cow,  or  horse. 

Black-throated  Grays  generally  forage  at  moderate 
heights  in  forest  and  woodland  habitat.  They  search  for 
prey  with  rather  methodical,  deliberate  movements,  at 
times  leaning  way  over  to  peer  under  leaves  or  reaching  up 
to  twigs  overhead  in  search  of  insects.  They  forage  more 
than  80%  (often  90%- 100%)  of  the  time  by  gleaning,  and, 
infrequently,  by  hovering  and  flycatching  (Morrison  1982, 
Miles  1990).  In  Arizona  oak  woodlands,  most  gleaning  is 
from  leaves  and  secondarily  from  small  branches  and 
twigs,  though  the  proportion  of  prey  capture  attempts 
directed  at  these  substrates  varies  seasonally  and  annually 
(Miles  1990).  Morrison  (1982)  found  consistent  differ- 
ences in  foraging  substrates  and  heights  between  sexes  in 
Black-throated  Grays  and  between  that  species  and  Hermit 
Warblers  in  a  mixed  Douglas  fir-oak  habitat  in  Oregon. 
Black-throated  Gray  males  forage  at  greater  heights  than 
females  in  both  firs  and  oaks,  and  in  taller  firs  (but  not 
oaks)  than  do  females.  Males  forage  mosdy  in  relatively  tall 
Douglas  firs  that  are  scattered  throughout  their  otherwise 
oak-dominated  territories.  Females  concentrate  their  forag- 
ing activities  in  oaks  and  on  longer  limbs  than  do  males, 
but  both  sexes  forage  toward  the  tips  of  branches.  On  the 
whole,  the  sexual  differences  found  in  foraging  presumably 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


resulted  from  males  concentrating  their  efforts  near  where 
they  sang  from  tall  Douglas  firs,  and  females  focusing  their 
activities  nearer  the  nest  site. 

Where  they  overlap,  Black-throated  Grays  tend  to  forage 
lower  than  Hermit  Warblers.  The  former  species'  relatively 
short  blunt  wings  may  enhance  foraging  in  the  lower 
denser  vegetation  of  oaks.  Hermit  Warblers'  relatively 
longer,  more  pointed  wings  may  promote  ease  of  move- 
ment within  and  between  the  trees  and  less  dense  foliage 
of  their  preferred  conifer  forests.  Female  Black-throated 
Grays  tend  to  use  longer  branches  than  do  female  Hermits, 
but  males  of  the  two  species  use  branches  of  similar  length 
(Morrison  1982).  Both  sexes  of  both  species  use  similar 
foraging  tactics  in  the  same  relative  proportions.  Little  is 
known  of  the  Black-throated  Gray  diet,  but  it  appears  to  be 
mainly,  if  not  entirely,  insects  (Bent  1953,  Dahlsten  et  al. 
1985);  oak  worms  and  other  green  caterpillars  appear  to  be 
favorites  (Bent  1953). 

Marin  Breeding  Distribution 

During  the  adas  period,  Black-throated  Gray  Warblers 
restricted  themselves  as  breeders  to  the  drier  Douglas  fir- 
and  oak-dominated  ridges  and  slopes  from  Mount  Tamal- 
pais  north  to  Lucas  Valley.  The  appropriate  habitats  are 
sheltered  from  persistent  summer  fogs,  either  by  being 
high  enough  on  Mount  Tamalpais  to  be  above  the  usual 
level  of  the  summer  inversion  layer  of  warmer  air  or  by 
being  east  or  north  of  the  first  major  coastal  ridges  that 
block  the  penetration  of  summer  fog.  Black-throated  Grays 


did  not  occur  in  the  extensive  moist,  dense  Douglas  fir 
habitat  on  Inverness  Ridge.  Representative  breeding 
locales  were  Lucas  Valley  Rd.,  about  %  mi.  E  of  "Bull  Tail 
Valley"  (FY/FL  7/26/82  -DS);  Cascade  Canyon,  Fairfax 
(FY/FL  6/19/80  -DS);  Lake  Lagunitas  (NY  about  15  ft. 
up  in  big-leaf  maple  6/5/82  — DnB);  Benstein  Trail,  Mt. 
Tamalpais  (NB  15-20  ft.  up  in  coast  live  oak  5/4/77 
— DS);  Simmons  Trail,  Mt.  Tamalpais  (FY/FL  adult  BTG 
feeding  fledgling  Brown-headed  Cowbird  7/6/81  — DS); 
and  south  end  of  Potrero  Meadow,  Mt.  Tamalpais  (NY  12 
ft.  up  in  16-ft.  sapling  tanbark  oak  7/6/81  — DS). 

Historical  Trends/ Population  Threats 

Black-throated  Gray  Warblers  were  first  widely  suspected 
of  breeding  in  Marin  County  based  on  the  publication  of 
observations  from  the  breeding  season  of  1936  on  Mount 
Tamalpais  (Orr  1937).  Adults  of  this  species,  though,  had 
already  been  seen  feeding  young  near  Phoenix  Lake  on  21 
and  28  June  1931  (Gull  13,  No.  7).  These  observations 
and  others  elsewhere  in  the  Bay  Area  from  the  1930s 
onward  (Seibert  1942,  Sibley  1952;  cf.  Grinnell  ck  Wythe 
1927)  appear  to  be  the  result  of  more  thorough  coverage  of 
a  region  where  die  species  is  patchily  distributed,  rather 
than  of  a  change  in  breeding  status  or  range. 

Black-throated  Gray  Warblers  appeared  to  increase 
slighdy  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989  but  were  relatively  stable  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


351 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wood-Warblers 


HERMIT  WARBLER   Dendroica  occidentalis 


-I,  .jrt>w 

Occurs  year  round,  though  primarily  as  a 
spring  (mid-Apr  to  mid-May)  and  fall 
(late  Jul  to  mid-Oct)  transient 

An  uncommon,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  11  (5.0%)  of  221  blocks. 

vS 

O    Possible        =        4  (36%) 
C    Probable       =         5   (45%) 
•    Confirmed  =         2   (18%) 

FSAR  =  2        OPI  =  22         CI  =  1.82 

1^                ^w^^^^3^V>^ 

Ecological  Requirements 

The  Hermit  Warbler  adds  a  touch  of  the  high  mountains 
to  Marin  County's  moderately  dense  Douglas  fir  forests, 
where  it  resides  in  relatively  pure  stands  and  also  in  mixed 
stands  with  coast  redwoods  and  moderate  numbers  of  live 
oak  or  other  broadleaved  trees.  Hermits  here  do  not 
inhabit  dense,  very  moist  pure  stands  of  Douglas  fir  or 
redwood.  Elsewhere,  Hermits  are  found  in  moderately 
dense  conifer  stands,  especially  of  Douglas  fir,  true  firs 
(Abies),  and  large  pines  (G6kM  1944,  Morrison  1982, 
Chappell  6k  Ringer  1983,  Airola  6k  Barrett  1985).  In 
Washington,  Hermits  occupy  second-growth  as  well  as 
mature  and  old-growth  forests  with  a  mean  canopy  cover 
of  70%  (Chappell  6k  Ringer  1 983).  Deciduous  trees  are 
frequendy  codominant  there  in  the  understory  or  are  a 
minor  component  of  the  canopy,  especially  in  young 
stands;  variable  shrub  cover  seems  to  have  little  effect  on 
habitat  choice,  as  Hermits  concentrate  their  activities  in  the 
canopy.  Hermits  tend  to  occupy  denser  and  more  conifer- 
dominated  forests  than  Black-throated  Grays,  but  the  two 
species  do  overlap  at  the  ecotone  between  their  respective 
habitats.  Where  they  co-occur  with  Black-throated  Grays  in 
Oregon,  Hermits  prefer  habitat  with  relatively  heavy  total 
conifer  cover  and  relatively  low  deciduous  cover  (Morrison 
1982).  Hermit  habitat  there  also  has  relatively  little  vegeta- 
tive cover  up  to  about  30  feet  above  the  ground  and 
relatively  greater  cover  above  about  60  feet. 

Hermit  Warbler  nests  have  been  found  as  low  as  2.5  feet 
up  in  a  sapling,  but  most  are  saddled  on  a  good-sized 
horizontal  or  upturned  limb  of  a  conifer  well  out  from  the 
trunk  and  about  20  to  45  feet  above  the  ground  (Bent 

352 


1953);  exceptionally,  nests  have  been  found  on  the  ground 
at  the  base  of  a  bush  (Munson  6k  Adams  1984)  and  as 
high  as  125  feet  above  the  ground  (Bent  1953).  The  nest 
is  a  compact  cup  composed  mainly  of  herbaceous  plant 
fibers  and  weed  stalks,  fine  dead  twigs,  pine  needles, 
lichens,  dry  moss,  and  plant  down.  All  of  these  materials 
may  be  wadded  together,  rather  than  woven,  and  securely 
bound  with  cobwebs  and  other  woolly  substances  (Barlow 
1899,  Bent  1953).  The  lining  is  made  of  fine  grasses,  the 
soft  inner  bark  of  conifers,  and  horse  or  wild  animals'  hair. 

Breeding  Hermit  Warblers  generally  avoid  deciduous 
growth  and  concentrate  over  90%  of  their  foraging  activi- 
ties in  conifers  (Morrison  1982,  Airola  6k  Barrett  1985). 
Foraging  birds  glean  80%-95%  of  the  time,  and  hover, 
flycatch,  and  lunge  only  to  a  limited  degree.  In  a  Douglas 
fir-oak  forest  in  Oregon,  Hermits  concentrate  foraging 
activities  near  the  center  of  limbs  in  contrast  to  Black- 
throated  Grays,  which  focus  toward  the  tips  (Morrison 
1982).  In  a  Sierran  mixed  conifer  forest,  Hermits  forage 
about  60%  of  the  time  on  foliage  and  secondarily  on  twigs 
and  branches  (Airola  6k  Barrett  1985).  Hermits  in  both 
habitats  forage  mosdy  at  mid-  to  high  elevations  (roughly 
15-80  ft.)  though  they  do  range  from  near  the  ground  to 
over  100  feet.  Males  forage  considerably  higher  in  conifers 
and  use  slighdy  longer  limbs  than  do  females  (Morrison 
1982).  See  the  Black-throated  Gray  account  for  further 
habitat  and  foraging  comparisons. 

The  diet  of  the  Hermit  Warbler  is  poorly  known,  but  a 
small  sample  (n  =  6)  from  the  Sierra  Nevada  indicates  the 
summer  diet  is   about  92%   animal   and   8%  vegetable 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


(Dahlsten  et  al.  1985).  The  Hermit  is  apparently  unique 
among  western  warblers  in  its  consumption  of  pine  seeds 
(Martin  et  al.  1951).  Animal  foods  include  true  bugs, 
beedes,  homopterans,  bees  and  wasps,  other  flying  insects, 
caterpillars,  and  small  spiders  (Martin  et  al.  1951,  Bent 
1953,  Dahlsten  et  al.  1985). 

Marin  Breeding  Distribution 

During  the  adas  period,  Hermit  Warblers  bred  locally  in 
Marin  County  from  Mount  Tamalpais  north  to  the  ridges 
of  the  Lagunitas  Creek  watershed.  This  distribution  was 
very  similar  to  that  of  Black-throated  Grays  except  that 
Hermits  were  more  restricted  to  deeper  canyons  and  more 
easterly  or  northerly  exposures.  Representative  breeding 


locations  included  the  Cataract  Trail,  Mt.  Tamalpais 
(FY/FL  7/10/81  -DS)  and  the  Dipsea  Trail  near  Laurel 
Dell,  Mt.  Tamalpais  (FL  7/3/82  -BiL). 

Historical  Trends/ Population  Threats 

Grinnell  and  Wythe  (1927)  and  Stephens  and  Pringle 
(1933),  respectively,  considered  the  Hermit  Warbler  pri- 
marily a  transient  in  the  Bay  Area  and  in  Marin  County. 
Subsequent  confirmation  of  breeding  in  the  Santa  Cruz 
Mountains  (GckM  1944,  Sibley  1952)  and  during  the 
Marin  adas  period  appear  to  be  a  result  of  more  thorough 
observer  coverage  rather  than  of  a  true  range  extension. 

From  1968  to  1989,  Hermit  Warblers  appeared  to 
increase  slighdy  on  Breeding  Bird  Surveys  in  California 
(USFWS  unpubl.  analyses). 


MACGILLIVRAY'S  WARBLER   Oporomis  tolmiei 


A  summer  resident  from  late  Apr 

r3^--^    K          JC^ 

through  early  Oct. 

y\>^%^ 

An  uncommon,  very  local  breeder; 

\\^(%\\^ 

r-  " 

overall  breeding  population  very  small. 
Recorded  in  8  (3.6%)  of  221  blocks. 

^C^C^c^C^r^^C 

V^-^ 

O^sr^V^^ 

O    Possible        =         1    (12%) 

\v 

©    Probable       =         7   (88%) 

^^T^^?^^ 

•    Confirmed  =         0  (0%) 

^^Ky^^^^^^^^ 

"\!>r^v- —  <' 

V%S~\ 

FSAR  =  2         OPI  =  16        CI  =  1.88 

i*2z>                                          \\_  /          ^^^ 

Ecological  Requirements 

In  Marin  County,  this  inveterate  skulker  breeds  sparingly 
in  the  moist  dense  shrubbery  of  riparian  thickets,  especially 
where  they  adjoin  the  moist  phase  of  coastal  scrub.  Ripar- 
ian forest  or  woodland  is  not  true  MacGillivrays'  habitat: 
these  birds  avoid  deciduous  trees  for  foraging  and  are 
drawn  to  shrubbery  (Morrison  1981b).  Their  occupation 
of  fog-shrouded  lowland  scrub  in  the  vicinity  of  streams 
and  their  avoidance  of  dry  foothill  chaparral  suggest  that 
MacGillivrays  have  an  affinity  for  moisture  here.  However, 
these  warblers  do  breed  in  montane  chaparral  in  Cali- 
fornia's higher  mountains  (e.g.,  Beedy  6k  Granholm 
1985). 


MacGillivray's  Warblers  construct  bulky  loose  nest 
cups,  which  they  place  in  the  upright  forks  of  bushes  or 
saplings  or  around  the  ascending  stems  of  rank  herbage 
(Dawson  1923).  Nest  height  varies  from  a  few  inches  off 
the  ground  to  about  five  feet,  with  most  under  three  feet 
(Dawson  1923,  Bent  1953).  MacGillivrays  construct  their 
nests  from  coarse  grasses,  weed  stalks,  roodets,  and  bark 
shreds  and  line  them  with  fine  grasses,  small  roodets,  and 
horsehair.  Four  species  of  breeding  warblers  overlap  in 
riparian  habitat  in  Wyoming  but  are  separated  by  absolute 
foraging  height  (Hutto  1981).  The  MacGillivray's  Warbler 
and  the  Common  Yellowthroat  forage  at  low  levels,  almost 


353 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Wood-Warblers 


exclusively  by  gleaning,  while  the  Wilson's  and  Yellow 
warblers  forage  higher,  by  a  combination  of  gleaning  and 
sallying.  MacGillivrays  forage  somewhat  higher  than  Com- 
mon Yellowthroats  but  mostly  below  three  feet  and  only 
occasionally  to  about  ten  feet  (Hutto  1981,  Morrison 
1984).  MacGillivray's  Warblers  and  Common  Yellow- 
throats  show  significant  differences  in  absolute  and  relative 
foraging  height,  foraging  position,  and  foraging  substrate. 
MacGillivrays  glean  about  70%  from  bark,  20%  from 
foliage,  and  10%  from  the  ground,  whereas  Yellowthroats 
feed  from  these  substrates  in  nearly  equal  proportions. 
MacGillivrays  also  tend  to  forage  more  in  the  inner  parts 
of  the  vegetation  than  do  Yellowthroats.  Yet  these  two 
species  forage  by  the  same  method  and  in  vegetation  of 
similar  density. 

The  June  to  July  diet  of  MacGillivray's  Warblers  in 
California  is  exclusively  insects,  including  true  bugs, 
homopterans,  beetles,  flies,  bees,  wasps,  and  ants 
(Dahlsten  et  al.  1985,  n  =  15). 

Marin  Breeding  Distribution 

During  the  atlas  period,  MacGillivray's  Warblers  were  very 
patchily  distributed  as  breeding  birds  in  moist  drainages 
along  Marin  County's  outer  coast.  The  only  confirmed 
breeding  records  for  the  county  (pre-  and  post-atlas)  were 


near  San  Geronimo  (NE  5/7/08  -Mailliard  1909b);  at 
Palomarin  (FY/FL  6/29/69  -RMS);  and  Mt.  Wittenberg, 
Inverness  Ridge  (FY  6/26/89  — JGE).  Other  representative 
breeding  areas  based  on  presumptive  evidence  during  the 
atlas  period  were  Laguna  Ranch,  PRNS  (S/T  4/22- 
6/14/78  —JGE  et  al.)  and  Volunteer  Canyon,  Bolinas 
Lagoon  (S  through  June  1980  — ARo). 

Historical  Trends/ Population  Threats 

Mailliard  (1900)  considered  the  MacGillivray's  Warbler 
"sparingly  summer  resident,"  while  Stephens  and  Pringle 
(1933)  reported  it  here  as  "uncommon"  through  the  sum- 
mer. Its  status  during  the  atlas  period  suggests  there  has 
been  little  historical  change  in  the  Marin  population.  The 
species  does  appear  to  have  declined  as  a  breeder  in 
Monterey  County  (Roberson  1985).  For  the  coast  as  a 
whole,  any  such  decline  has  probably  been  offset  gready  in 
the  north  coast  mountains  by  increases  as  the  species 
expanded  into  the  relatively  moist,  low,  second-growth 
shrubbery  that  regenerates  after  logging. 

MacGillivray's  Warblers  generally  increased  on  Breed- 
ing Bird  Surveys  in  California  from  1968  to  1989,  despite 
relative  stability  from  1980  to  1989  (USFWS  unpubl.  analy- 


354 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


COMMON  YELLOWTHROAT   Geothlypis  trichas 


A  year-round  resident. 

\ 

A  common,  local  breeder;  overall 
breeding  population  small. 
Recorded  in  38  (17.2%)  of  221  blocks. 

O    Possible        =         7   (18%) 

Y-'v 

vr3it\S 

C    Probable       =      23  (61%) 

A*  V"\ 

y^Q 

•    Confirmed  =         8   (21%) 
FSAR  =  4        OPI  =  152       CI  =  2.03 

i 

^^c* 

Ecological  Requirements 

These  perky  masked  warblers  inhabit  Marin  County's 
freshwater  marshes,  coastal  swales,  swampy  riparian  thick- 
ets, brackish  marshes,  salt  marshes,  and  die  edges  of 
disturbed  weed  fields  and  grasslands  that  border  on  these 
soggy  habitats.  About  80%  of  Marin's  Yellowthroats  breed 
in  freshwater  marsh,  coastal  swale,  and  riparian  thickets 
and  swamps,  with  the  remainder  in  brackish  marsh,  salt 
marsh,  and  upland  habitats  (Hobson  et  al.  1986,  D. 
Shuford  pers.  obs.).  In  the  San  Francisco  Bay  region  as  a 
whole,  about  60%  breed  in  brackish  marsh,  20%  in 
riparian  woodland/swamp,  10%  in  freshwater  marsh,  5% 
in  salt  marsh,  and  5%  in  upland  vegetation  (Hobson  et  al. 
1986).  In  this  region,  Yellowthroats  frequendy  use  the 
borders  between  these  various  plant  communities.  In 
brackish  marsh,  they  rarely  occupy  pure  stands  of  alkali 
bulrush  (Scirpus  robustus);  instead  they  frequent  areas 
where  this  bulrush  mixes  with  other  marsh  and  upland 
plants.  In  salt  marsh,  Yellowthroats  center  their  activity  in 
taller  vegetation,  such  as  gumplant  and  coyote  brush  on  the 
raised  border  of  sloughs  and  levees,  though  they  often 
forage  in  pickleweed.  Territories  also  commonly  straddle 
the  interface  of  riparian  corridors  and  freshwater  marsh,  or 
the  ecotone  between  freshwater  or  tidal  marshes  and  the 
upland  vegetation  of  weed  fields  and  grassland.  Some 
Yellowthroats  here  do  inhabit  the  interiors  of  riparian 
swamps  such  as  Olema  Marsh.  Low,  dense,  rather  lush, 
tangled  vegetation  appears  to  be  the  primary  requisite. 
Although  a  source  of  free  water  promotes  this  type  of 
growth,  it  does  not  appear  to  be  absolutely  essential 
(Kendeigh  1945).  Yellowthroat  territories  usually  include 


open  water  or  damp  ground,  but  not  always,  especially  in 
drought  years  (Hobson  et  al.  1986).  In  California,  Yellow- 
diroats  sometimes  breed  up  to  300  yards  from  a  source  of 
water,  even  after  a  very  wet  winter  (Johnson  1904).  The 
dense  ground  cover  provides  concealment  for  nests,  teeter- 
ing young,  and  foraging  adults.  There  must  be  other  subde 
habitat  needs.  During  intensive  Bay  Area  surveys  of  the 
Saltmarsh  Common  Yellowthroat  (G.  t.  sinuosa),  Hobson 
et  al.  (1986)  sometimes  found  birds  absent  in  what 
appeared  (to  the  human  eye,  at  least)  to  be  suitable  breed- 
ing areas. 

Nest  sites  are  varied  and  may  be  adjacent  to,  above,  or 
well  away  from  water.  Nests  are  well  concealed,  mosdy  on 
or  near  the  ground  in  grass  tussocks,  low  herbaceous 
vegetation,  cattails,  tules,  and  bushes  generally  to  about  five 
feet  above  the  ground,  though  many  are  below  six  inches 
(Kendeigh  1945,  Gross  1953,  Stewart  1953).  Yellow- 
diroats  less  frequendy  place  their  nests  in  trees  such  as 
willows,  alders,  eucalyptus,  orchard  trees,  black  oaks  (in 
thick  branches  of  misdetoe),  and  cypress  up  to  about  23 
feet  above  the  ground  (Johnson  1904).  Unusual  nest  sites 
include  an  old  nest  of  a  Red-winged  Blackbird  3.5  feet  up 
in  an  emergent  willow  sapling,  in  grain  fields,  in  a  culti- 
vated rose  trained  against  the  side  of  a  house,  and  in  one 
of  a  pair  of  shoes  left  on  the  back  stoop  of  a  house  (Johnson 
1904).  Yellowthroats  wedge  the  cup-shaped  nest  among,  or 
lash  it  to,  concealing  vegetation.  The  nest  varies  from 
compact  to  loosely  woven  and  bulky;  sometimes  loosely 
attached  materials  extend  above  the  main  rim,  partially  or 
completely  roofing  over  the  structure  (Kendeigh   1945, 

355 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wood-Warblers 


Gross  1953,  Stewart  1953).  The  nest  may  have  three 
distinct  layers  of  material,  increasing  in  fineness  from  the 
outside  in  (Stewart  1953).  Birds  generally  construct  the 
outer  layers  from  coarse  grass,  dead  leaves,  weed  stalks, 
cattail  blades,  rush  and  sedge  stems,  strips  of  bark,  willow 
catkins,  and  dead  ferns.  They  line  the  nest  with  fine  grasses 
and  sedges,  tendrils,  delicate  bark  fibers,  hair,  and  occa- 
sionally fine  roodets  or  moss. 

Yellowthroats  gather  their  insect  prey  on  or  near  die 
ground  by  gleaning  from  low  herbaceous  vegetation, 
bushes,  and  small  trees  or  from  the  surface  of  the  mud. 
They  forage  mosdy  within  5  to  6  feet  of  the  ground  or 
water's  surface  (Kendeigh  1945,  Gross  1953).  Of  four 
warbler  species  breeding  in  riparian  habitat  in  Wyoming, 
the  Common  Yellowthroat  and  MacGillivray's  Warbler 
are  a  pair  that  forage  at  low  levels,  almost  exclusively  by 
gleaning,  while  Wilson's  and  Yellow  warblers  forage 
higher  by  a  combination  of  gleaning  and  sallying  (Hutto 
1981).  While  breeding,  Yellowthroats  there  do  90%  of 
their  foraging  below  1  foot,  and  the  remainder  below  2  feet 
in  height.  After  relief  from  nesting  duties  in  August,  while 


foraging,  they  range  about  eight  times  higher,  up  to  16  feet 
Yellowthroats  there  glean  from  bark,  foliage,  and  the 
ground  in  roughly  equal  proportions.  See  the  Mac- 
Gillivray's Warbler  account  for  a  comparison  of  foraging 
strategies. 

Year  round,  Yellowthroats  in  California  eat  99.8%  ani- 
mal matter  (n  =  1 1 4);  the  few  seeds  and  miscellaneous 
vegetable  matter  in  their  stomachs  were  probably  taken 
incidentally  (Beal  1907).  The  main  items  in  the  diet  of 
California  birds  are  ants,  wild  bees  and  wasps,  true  bugs, 
beedes,  caterpillars  and  moths,  flies,  grasshoppers,  and 
spiders.  Elsewhere,  Yellowthroats  have  also  been  noted  to 
consume  damselflies,  dragonflies,  caddisflies,  mayflies, 
and  a  few  small  mollusks  (Gross  1953). 

Marin  Breeding  Distribution 

During  the  adas  period,  Marin's  breeding  Yellowthroats 
were  concentrated  in  the  moist  coastal  and  bayshore  low- 
lands around  the  periphery  of  the  county.  The  areas  of 
their  greatest  abundance  were  on  Point  Reyes  (in  the 
Limantour   Estero   drainage,    near   the    road    between 


Table  19.    Numbers  of  breeding  pairs  of  Saltmarsh  Common  Yellowthroats  (Geothlypis  trichas  sinuosa)  in  Marin  and  other 
San  Francisco  Bay  Area  counties  in  1985.    Data  from  Hobson  et  al.  (1986). 


County 

Location 

Number  of  Breeding 

Pairs 

Marin 

Point  Reyes  peninsula 

6 

Abbott's  Lagoon 

25 

Limantour  Estero 

74 

Olema  and  Bear  Valley  marshes 

25 

Bolinas  Lagoon  and  Dogtown  marsh 

5 

Rodeo  Lagoon  and  Tennessee  Valley 

6 

Novato  Creek 

7 

Petaluma  Point 

9 

Black  John  Slough 

11 

Marin  Total 

168 

Sonoma 

81 

Napa 

63 

Solano 

31 

Contra  Costa 

0 

Alameda 

37 

Santa  Clara 

118 

San  Mateo 

57 

San  Francisco 

14 

Bay  Area  Total 

569* 

*  Foster  (1977)  found  166  pairs  in  these  counties  in  a  less  complete  survey  in  the  drought  year 
of  1977. 


356 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


Abbott's  Lagoon  and  Kehoe  Beach,  and  at  Olema  and 
Bear  Valley  marshes)  and  along  the  sloughs  and  bayshore 
marshes  from  Novato  north  along  the  Petaluma  River 
drainage  (Table  19).  Breeding  Yellowthroats  were  absent 
from  interior  sites  except  for  a  probable  breeders)  at 
Stafford  Lake,  Novato.  In  the  interior  of  the  county,  fresh- 
water marshland  is  scant  and  riparian  groves  are  generally 
sparsely  vegetated  because  of  the  drier  climate  and  inten- 
sive cattle  grazing. 

Representative  breeding  localities  were  Tomales  Point, 
north  side  of  tule  elk  fence  (FY  5/31/82  -DS);  gully  SW 
of  head  of  Barries  Bay,  Drake's  Estero  (FY  6/9/82  -DS); 
and  Olema  Marsh  (NB  4/29/81  — DS).  A  more  recent 
record  of  an  active  nest  is  of  one  found  at  Glenbrook 
drainage  behind  Limantour  Estero  (NE  5/6/85  — DS, 
BoB). 

Historical  Trends/Population  Threats 

The  extent  of  tidal  marshes  in  the  San  Francisco  Bay 
ecosystem  has  been  reduced  by  60%-95%  over  historical 
levels  (Nichols  6k  Wright  1971,  Josselyn  1983),  and  fresh- 
water marsh  probably  has  been  reduced  to  an  even  greater 
degree  because  of  its  greater  proximity  to  upland  develop- 
ment Yellowthroats  have  declined  markedly  because  of 
this  extensive  habitat  loss.  Grinnell  6k  Miller  (1944)  did 
not  report  a  decline  in  Yellowthroat  populations,  though 
one  must  have  been  well  underway  at  that  time  from  loss 
of  habitat.  Foster  (1977)  estimated  that  the  number  of 
Saltmarsh  Common  Yellowthroats  in  the  San  Francisco 
Bay  Area  had  declined  by  about  80%-95%  in  the  last  100 
years.  However,  her  data  were  collected  during  drought 
years  and  may  not  be  valid  for  comparison  with  historical 


estimates  from  the  few  sites  for  which  these  are  available. 
In  1985,  Hobson  et  al.  (1986)  conducted  more  extensive 
surveys  and  recorded  over  three  times  the  number  of 
Yellowthroats  found  in  1977.  Despite  the  increase  in 
numbers  because  of  better  wedand  conditions  and  more 
thorough  coverage,  they  found  Yellowthroats  at  only  4  of 
16  sites  where  they  were  reported  only  prior  to  1970,  and 
at  only  15  of  34  sites  where  they  were  reported  from  1970 
onward.  Although  it  will  never  be  possible  to  determine 
with  numerical  precision  the  extent  of  the  decline  of  the 
Yellowthroat  population  of  the  San  Francisco  Bay  Area,  it 
is  clear  that  this  decline  has  been  of  major  proportions. 
The  1985  figures  provide  a  solid  baseline  against  which  to 
compare  future  trends.  The  species  is  still  imperiled  with 
further  declines  from  habitat  loss,  degradation,  and  frag- 
mentation from  various  sources  ranging  from  land  devel- 
opment to  flood  control  management.  Its  population  in 
this  region  can  only  be  augmented  substantially  by  con- 
certed habitat  restoration  efforts. 

On  the  whole,  numbers  of  Yellowthroats  (all  subspe- 
cies) increased  on  Breeding  Bird  Surveys  in  California 
from  1968  to  1989,  though  perhaps  only  slighdy  from 
1980  to  1989  (USFWS  unpubl.  data).  Still  it  should  be 
noted  that  the  Common  Yellowthroat  was  on  the  Audu- 
bon Society's  Blue  List  in  1973  and  1974  (Tate  1981) 
because  of  concern  in  northern  California  (AB  27:945). 
The  Saltmarsh  Common  Yellowthroat  currendy  is  a  Can- 
didate (Category  2)  for  federal  listing  as  Threatened  or 
Endangered  (USFWS  1989b,  1991)  and  is  a  Bird  Species 
of  Special  Concern  in  California  (CDFG  1991b). 


357 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Wood-Warblers 


WILSON'S  WARBLER   Wilsonia  pusilla 


A  summer  resident  from  late  Mar 

_^>»<-               K.                      vr^w 

tluough  early  Oct. 

f9\^V  Jr\ 

A  very  common,  very  widespread 

\^-\  C  ^"Y©  V-"\  ©  V>"A       V-'A      V-"\    ^A 

breeder;  overall  breeding  population  very 

P&vk 

©A>A  ®>^\  ®  W*V     Jk^X       3r^\      U^V     ^A 

large. 

^A^JV-^X  ®A--<A7®Jir--*A^  ><£A»A^V    A-*"! 

Recorded  in  161  (72.8%)  of  221 

V-^C^-r 

i^X  ®  A^A  ©  A^A  •  VfA  ®  V-"A  •  V"A    '-V^x 

blocks. 

Y\*£ 

■^V^V^X  •  xJ>"AO  \_>rx©  \^>A  ©  V>A  c  Y^a     J 

Yxl®  ' 

-^\©^ T  X  ©>^\»ii>53J*  A^A«/X>^"®-Jk-'^\    .V^      ; 

O    Possible        =      15  (9%) 

^®Jk^^®Jkr^;*:^^Jr^®Jk'-'A   J^x-  Jx^te^ — 

_..-•- 

©    Probable       =    102  (63%) 

•    Confirmed  =      44  (27%) 

-!<\  Wy^  )>P\  ®JV'\  ®-Y-"a  •%>A  ®  Jl^J\  ®  3r-<\  *OT^V 

'io^Votfea— — a®  y^-a  •  Y-^a©  Y^a  ©jY->v  V-^  •  V< 
C^^5^     ^~<T®  v-a©  VMi-i^ ®  -><\o  Yvca^ 

^a 

FSAR=5        OPI  =  805       CI  =  2.18 

<T              ^w^m^ 

>U                             X^/     ^"^*^»- 

Ecological  Requirements 

County  breeding  haunts  of  the  perky  "Pileolated  Warbler" 
are  moist,  primarily  forested  habitats  with  a  relatively  dense 
understory,  principally  willow  and  alder  riparian,  red- 
wood, bishop  pine,  Douglas  fir,  mixed  conifer,  and  broad- 
leaved  evergreen  forests.  The  importance  of  the  understory 
is  illustrated  by  the  fact  Wilson's  Warblers  also  breed 
locally  in  coastal  scrub  (which  by  nature  has  no  overstory 
of  trees)  where  it  is  north-facing  and  dominated  by  sword 
fern  or  salal. 

The  breeding  biology  of  Wilson's  Warbler  in  California 
has  been  investigated  in  two  different  areas  of  sharply 
contrasting  topography  and  climate,  though  at  the  same 
latitude:  near  sea  level  at  Palomarin  on  the  Point  Reyes 
peninsula  (Stewart  1973)  and  at  10,000  feet  at  the  crest  of 
the  Sierra  Nevada  at  Tioga  Pass,  Mono  County  (Stewart  et 
al.  1977).  These  are  among  the  few  comparative  studies  of 
passerines  at  the  extremes  of  their  climatic  ranges,  and  they 
reveal  a  number  of  important  differences  in  the  ecology  of 
the  species  with  respect  to  breeding  areas. 

Arrival  dates  on  the  breeding  ground  and  mean  dates  of 
initiation  of  egg  laying  in  the  two  locales  differ  by  two 
months:  males  arrive  in  late  March  on  the  Point  Reyes 
peninsula  and  in  late  May  at  Tioga  Pass.  In  some  years  of 
extremely  high  snow  pack,  Sierran  birds  will  not  breed  at 
higher  altitudes  at  all.  Territory  size  of  Sierran  birds  aver- 
ages about  twice  that  of  coastal  birds,  though  vegetation 
volume  is  probably  similar  between  these  areas  because  of 
the  taller  stature  of  most  coastal  habitat.  On  the  coast, 
Wilson's  Warblers  typically  conceal  and  support  their 
nests  in  understory  vine  tangles,  small  bushes,  ferns,  or  tall 


annual  plants.  Of  111  nests  from  13  coastal  California 
counties,  74%  were  built  in  blackberry  vines,  9%  in  ferns, 
6%  in  nettle,  and  2%  in  wild  rose  (Stewart  et  al.  1977). 
Blackberries  offered  the  advantages  of  horizontal  runners 
for  nest  support,  overhanging  leaves  for  nest  concealment, 
and  a  dense  tangle  of  brambles  serving  to  deter  predators 
(Stewart  1973).  Only  4%  of  the  nests  were  on  the  ground, 
and  die  average  height  of  above-ground  nests  was  20 
inches  (Stewart  et  al.  1977).  Coastal  nests  at  Palomarin 
ranged  from  13  to  32  inches  above  die  ground  (av.  27  in., 
n  =  11).  Coastal  birds  build  bulky  nest  cups  composed  of 
leaves,  twigs,  and  small  branches  of  blackberry,  nettle,  and 
oak  and  line  them  with  animal  hair  interwoven  with  fine 
stems,  moss,  and  deteriorated  leaves  (Stewart  1973).  In 
contrast,  Sierran  birds  build  nests  with  much  smaller  nest 
cups,  situated  at  ground  level  or  sunk  slighdy  below  it  in 
depressions;  concealment  is  provided  by  location  at  the 
base  of  horizontal  willow  branches  and  by  a  thick  growth 
of  perennial  herbs  (Stewart  et  al.  1977).  The  difference  in 
nest  position  on  the  coast  versus  the  high  Sierra  appears  to 
reflect  differences  in  the  growth  form  of  vegetation  most 
suitable  for  concealing  the  nest  from  predators  in  the 
respective  habitats.  Nest  placement  at  ground  level  may 
also  provide  greater  insulation  needed  in  the  colder  sub- 
alpine  environment.  See  White-crowned  Sparrow  account 
for  discussion  of  similar  differences  in  nest  placement  with 
respect  to  altitude  or  latitude  and  of  the  tailoring  of  nest 
size  and  external  appearance  to  the  microclimate  of  the 
nest  site. 


358 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


With  a  longer  breeding  season,  18%  of  individuals  in 
the  coastal  population  successfully  raise  two  broods,  while 
Sierran  birds  never  make  more  than  a  single  nesting 
attempt  (Stewart  et  al.  1977).  Although  hatching  success  is 
similar  in  both  areas,  nesting  success  is  much  higher  in  the 
Sierra  (71%,  n  =  45)  compared  with  the  coast  (33%,  n  = 
18),  probably  because  of  differences  in  predation  rates 
between  the  habitat  types.  In  the  Sierran  population,  26% 
of  the  males  (n  =  27)  are  polygynous,  while  on  the  coast  all 
are  monogamous.  Note  that  polygyny  is  very  rare  among 
wood  warblers,  and  only  about  5%  of  all  passerine  birds 
in  North  America  are  known  to  be  regularly  polygynous 
(Verner  ck  Willson  1969).  The  Sierran  population  of 
Wilson's  Warblers,  occupying  a  transient  habitat  and 
unpredictable  climate  with  rain,  hail,  or  snow  occurring  at 
any  time,  has  evolved  this  strategy  to  maximize  reproduc- 
tion. The  coastal  population,  inhabiting  mature  forests 
with  a  well  developed  understory  and  more  predictable, 
stable  climate,  has  evolved  a  strategy  of  a  lower  but  more 
constant  reproductive  rate. 

Wilson's  Warblers  feed  actively  on  small-bodied, 
winged  insects.  They  forage  mosdy  at  low  to  moderate 
heights  in  both  understory  and  trees,  but  generally  not 
higher  than  about  5  feet  below  the  roof  of  the  canopy.  In 
coastal  broadleaved  evergreen  forest,  they  frequendy  forage 
from  about  30  to  55  feet  up  in  the  overstory  (Stewart  1 973). 
Overall  in  California,  gleaning  accounts  for  about  49%  of 
foraging  attempts,  followed  by  hovering  (46%)  and  fly- 
catching  (5%),  with  some  variation  between  habitats  (Stew- 
art et  al.  1977,  n  =  244).  In  a  variety  of  coastal  habitats, 
adults  make  97%  of  food-catching  attempts  (n  =  70)  on 
leaves  and  the  remainder  on  small  twigs.  In  riparian 
habitat  in  Wyoming,  Wilson's  Warblers  forage  more  in 
the  upper  half  and  outer  portions  of  the  canopy,  in  vegeta- 
tion of  moderate  to  open  density,  and  they  direct  foraging 
attempts  roughly  equally  toward  foliage,  bark,  and  the  air, 
and,  rarely,  toward  the  ground  (Hutto  1981).  Wilson's 
Warblers  there  forage  57%  by  gleaning,  37%  by  sallying, 
and  6%  by  hovering  (n  =  219). 

The  diet  in  California  is  about  93%  animal  matter  and 
less  than  7%  vegetable  matter  (Beal  1907,  n  =  52).  The 
main  animal  foods  are  true  bugs,  wasps  and  ants,  beedes, 
and  flies,  with  small  numbers  of  caterpillars  and  spiders; 
the  vegetable  fare  is  almost  entirely  fruit  pulp  consumed  in 
fall.  In  the  Sierra  Nevada,  vegetable  matter  accounts  for  3% 
of  the  summer  diet  (Dahlsten   et  al.    1985,   n  =  8).   In 


Wyoming,  Wilson's  Warblers  take  beedes,  mayflies,  stone- 
flies,  flies,  and  wasps  (and  somewhat  larger  prey)  in  greater 
proportion  than  their  availability.  Preferred  prey  tend  to  be 
noncryptic  and  patchily  distributed  (Raley  6k  Anderson 
1990).  Some  groups  that  rank  low  in  preference  are, 
nevertheless,  still  important  in  the  diet  because  of  their 
abundance  in  warbler  foraging  habitat;  for  example,  leaf- 
hoppers  comprise  16%  of  the  diet  and  miscellaneous 
larvae  30%.  Nonpreferred  prey  are  generally  diose  that 
exhibit  cryptic  coloration,  a  choice  of  camouflaging  sub- 
strate, or  good  escape  behavior. 

Marin  Breeding  Distribution 

During  the  adas  period,  Wilson's  Warblers  bred  through- 
out much  of  Marin  County  but  occurred  in  greatest  abun- 
dance on  Inverness  Ridge  on  the  Point  Reyes  peninsula. 
Toward  the  interior,  breeding  populations  were  smaller 
and  generally  restricted  locally  to  narrow  canyons  and 
north-facing  slopes  with  moist  dense  understory  vegeta- 
tion. Wilson's  Warblers  were  absent  as  breeders  over 
substantial  areas  only  in  fladands  along  the  San  Pablo  Bay 
shoreline,  in  oak  woodland -dominated  areas  near  Novato, 
and  in  an  area  east  of  Tomales  where  grasslands  prevail. 
These  areas  generally  lack  the  topographic  relief  that  pro- 
vides microclimates  conducive  to  the  development  of 
dense  understory  vegetation,  or  else  they  have  riparian 
habitat  without  a  suitable  understory.  Representative 
breeding  locations  were  Tomales  Bay  SP  (NE-NY  5/7- 
6/5/76  -RMS);  Inverness  Ridge  (NE-NY  5/15-6/15/76 
-RMS);  Palomarin,  PRNS  (NE-NY  4/28-6/1/76  -RMS); 
and  Big  Rock  Ridge  above  Stafford  Lake  (NY  5/?/82 
-ScC). 

Historical  Trends/ Population  Threats 

Although  no  clear  trends  are  evident,  it  seems  likely  that 
Wilson's  Warblers  have  decreased  locally  in  some  areas  of 
riparian  habitat  along  the  California  coast  because  of 
clearing  for  development  and  agriculture  and  from  degra- 
dation of  the  understory  by  catde  grazing  and  trampling. 
At  present,  Breeding  Bird  Surveys  from  1968  to  1989 
indicate  that  Wilson's  Warbler  numbers  are  relatively 
stable  in  California  (Robbins  et  al.  1986,  USFWS  unpubl. 
data). 

ROBERT  M.  STEWART 


359 


Wood-Warblers 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wood-Warblers 


YELLOW-BREASTED  CHAT   kteria  virens 


An  irregular  transient  and  summer  resi- 
dent from  late  Apr  through  mid-Sep. 

A  very  rare,  very  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  2  (0.9%)  of  221  blocks. 


o 

Possible 

0  (0%) 

€ 

Probable 

2  (100%) 

• 

Confirmed  = 

0  (0%) 

AR 

=  1          OPI  = 

2          CI  =  2.00 

Ecological  Requirements 

This  furtive  but  ebullient  songster  is  an  inhabitant  of  dense 
riparian  understory  tangles  with  small  trees,  tall  weeds, 
blackberry  thickets,  brush,  and  vines.  Dense  low  cover  in 
a  moist  setting  seems  essential. 

Chats  build  bulky  nests,  which  they  place  precariously 
from  about  1.5  to  5  feet  (rarely  to  8  ft.)  high  in  the  thick 
cover  of  small  trees  and  bushes  (Dawson  1923,  Bent 
1953).  They  construct  their  nests  of  dead  leaves,  coarse 
grasses,  weed  stems,  and  small  vines,  and  line  them  spar- 
ingly with  fine  grasses,  weed  stems,  weed  bark,  and  horse- 
hair. 

Apparendy  no  detailed  foraging  studies  of  Chats  exist, 
presumably  because  of  the  difficulty  of  observing  them. 
Birds  probably  forage  mosdy  below  10  feet  (G&M  1944) 
by  gleaning  from  foliage,  branches,  and  the  ground.  The 
diet  consists  mainly  of  animal  matter,  but  even  in  summer 
wild  fruits  may  make  up  a  substantial  portion  of  the  menu. 
The  diet  of  birds  in  spring  averages  2%  plant  food  (n  =  9), 
whereas  that  of  birds  in  summer  averages  35%  plant  food 
(n=19)  (Martin  et  al.  1951).  Regularly  occurring  food 
items  include  caterpillars,  moths,  butterflies,  grasshoppers, 
locusts,  beedes,  true  bugs,  ants,  weevils,  bees,  wasps,  may- 
flies, and  a  few  spiders  and  crustaceans  (Martin  et  al.  1951 , 
Bent  1953).  Western  birds  eat  wild  fruits  such  as  madrone, 
thimblebeny,  sumac,  dogwood,  and  nightshade  (Martin  et 
al.  1951). 

Marin  Breeding  Distribution 

During  the  adas  period,  there  were  only  two  records  of 
probable  breeding  of  Yellow-breasted  Chats  in  Marin 
County.   Single   individuals  were   heard   singing  over  a 

360 


period  of  time  at  Laguna  Ranch,  PRNS  (S  5/20-6/4/82 
— SCP)  and  along  Walker  Creek  about  1 .5  miles  upstream 
from  Hwy.  1  (S  5/1-6/12/82  -DS).  Chats  have  been 
recorded  only  casually  in  Marin  County  in  potential  breed- 
ing habitat  from  April  to  July,  and  most  have  apparendy 
been  transients  (Stephens  1936,  Kinsey  1945,  ABN).  No 
confirmed  breeding  records  for  the  county  are  known.  In 
fact,  the  adas  records  above  represent  the  reports  of  longest 
seasonal  occupation  of  a  particular  site  here.  It  seems 
logical  to  conclude  that  Marin  County's  riparian  habitat  is 
only  marginally  attractive  to  Chats. 

Historical  Trends/ Population  Threats 

Mailliard  (1900)  considered  the  Yellow-breasted  Chat  a 
"rare  spring  visitant"  to  Marin  County,  and  Stephens  and 
Pringle  (1933)  repeated  his  assessment.  Prior  to  1944, 
Kinsey  (1945)  had  encountered  Chats  only  three  times 
from  July  to  September  "during  twenty  years  of  residence 
and  extensive  field  work"  in  Marin  County.  From  23  April 
to  about  14  June  1944  at  Manor  (near  Fairfax),  he  and  his 
wife  trapped  three  males  and  saw  another  individual  of 
unknown  sex.  On  6  May  1945,  they  captured,  banded, 
and  placed  in  an  aviary  a  "pair"  of  Chats.  Despite  this  spate 
of  war-time  records,  it  is  clear  that  historically  in  Marin 
County,  Chats  were  rare  at  any  season.  Although  earlier 
observers  may  have  missed  some  breeding  Chats  in  un- 
explored regions  of  Marin  County,  it  is  clear  that  this 
species  has  long  been  scarce  here.  If  Chats  did  once  have 
local  viable  breeding  populations  in  Marin  County,  it 
Seems  unlikely  they  would  return  now  without  manage- 
ment efforts,  considering  that  much  of  our  riparian  habitat 
has  been  destroyed  or  degraded. 


Wood-Warblers 


SPECIES  ACCOUNTS 


Wood-Warblers 


Yellow-breasted  Chat  populations  have  declined  in 
recent  decades  on  the  northern  California  coast,  at  least 
from  the  Bay  Area  south  (Remsen  1978,  Roberson  1985). 
Because  of  a  more  widespread  decline,  the  Yellow-breasted 
Chat  is  on  California's  list  of  Bird  Species  of  Special 
Concern  (Remsen  1978,  CDFG  1991b).  Declines  in  Cali- 
fornia are  attributed  to  habitat  destruction  and  perhaps 
cowbird  parasitism  or  other  factors.  The  Yellow-breasted 
Chat  was  listed  on  the  National  Audubon  Society's  Blue 


List  or  on  its  list  of  Species  of  Special  Concern  from  1 976 
to  1981,  and  on  its  list  of  Local  Concern  in  1982  (Tate 
1981,  Tate  ck  Tate  1982).  From  1968  to  1989,  Breeding 
Bird  Surveys  suggested  that  Chats  might  be  increasing 
slighdy  in  California,  though  numbers  were  relatively  sta- 
ble from  1980  to  1989  (USFWS  unpubl.  analyses).  Contin- 
ued monitoring  of  Chat  populations  is  warranted, 
considering  this  history  and  the  continued  threats  to  ripar- 
ian habitat  from  our  expanding  human  population. 


Viewed  from  a  window  through  a  tangle  of  blackberry,  salal,  and  reeds, 
a  Wilson's  Warbler  stealthily  approaches  its  nest.    Photograph  by  Ian  Tait. 


361 


Tanagers 


MARIN  COUNTY  BRITDING  BIRD  ATLAS 


Tanagers 


Tanagers 

Family  Emberizidae 
Subfamily  Thraupinae 


WESTERN  TANAGER   Piranga  ludoviciana 


A  summer  resident  from  late  Apr 

^5^-^     N            ^O^. 

through  mid-Oct. 

AJV'a^ 

An  uncommon,  very  local  breeder; 

^VQr 

0K\^K^^\^<^^\^<^^ 

overall  breeding  population  very  small. 
Recorded  in  12  (5.4%)  of  221  blocks. 

Lrv 

vWV""^^^ 

O    Possible                  4   (33%) 

^^Z^\\^^^ 

€    Probable       =         5   (42%) 

*<^\  ~^<>^-i^'^^\"c\^\  3**^\  ^-v\  ^-V\  3^x 

«o 

•    Confirmed  =         3   (25%) 

^A^-'tC    V^^\    \^-^\   A^-^\    V^vC-*"  \i>"A    X^^v-O  \ 

j>4r\  ^V\'  ^V\  -A^y*As^\  ^-V\  ciA^:\"d-< 

t —  ^ 

FSAR=2        OPI  =  24         CI  =  1.92 

Cp^ 

c 

!M                      \Z7    ^^<^ 

Ecological  Requirements 

These  flashy  birds  have  been  dubbed  the  "Sunset  Tanager" 
by  their  human  admirers.  The  blazing  males  stake  out  their 
territories  in  Marin  County's  mixed  conifer  forests  where 
Douglas  fir,  or,  sparingly,  redwoods,  mix  with  coast  live, 
canyon  live,  and  tanbark  oaks.  To  a  limited  extent,  they 
also  use  mixed  woodlands  of  live  oaks,  black  oak,  and 
big-leaf  maple  along  streams.  Western  Tanagers  here  pre- 
fer relatively  open  mesic  mixed  forests  for  nesting.  They 
avoid  dense  pure  stands  of  Douglas  fir,  redwoods,  oaks  or 
bays,  and  drier,  very  open  stands  of  oaks.  Shy  (1984) 
measured  habitat  variables  of  21  Western  Tanager  territo- 
ries at  various  locations  in  die  West.  Canopy  cover  aver- 
aged 66.6%,  "ground  cover"  averaged  38.8%,  and  the 
number  of  tree  species  averaged  4-1.  This  documents  the 
relative  openness  and  mixed  character  of  Western  Tanager 
breeding  habitat. 

Western  Tanagers  customarily  settle  dieir  nests  in  the 
enveloping  foliage  of  horizontal  branches  of  conifers  (usu- 
ally near  the  dps)  or,  less  frequendy,  in  broadleaved  trees 
or  large  shrubs;  nest  heights  vary  from  about  6  to  65  feet 
above  the  ground  (Dawson  1923,  Hayward  1935,  Wiggins 

362 


ck  Wiggins  1939,  Sibley  1955,  Bent  1958,  Tatschl  1967). 
Tatschl  (1967)  reported  that  nest  trees  in  New  Mexico  are 
usually  in  "open  areas,"  though  this  could  use  additional 
confirmation.  Exceptionally,  Western  Tanagers  have 
nested  on  the  ground  under  an  overhanging  rock  ledge 
(Wiggins  &  Wiggins  1939).  Western  Tanagers  construct 
substantial  but  rather  roughly  assembled  nest  cups  of 
twigs,  weed  stems,  roodets,  long  pine  needles,  leaves,  and 
moss.  They  line  them  somewhat  heavily  with  fine  roodets, 
horse  or  cow  hair,  grasses,  lichens,  or  other  soft  material 
(Dawson  1923,  Wiggins  ck  Wiggins  1939). 

Western  Tanagers  use  a  variety  of  foraging  techniques, 
including  gleaning,  hawking  and,  to  a  lesser  extent,  hover- 
ing and  lunging.  They  not  only  take  nearby  insects  of  all 
sizes  by  gleaning,  but  they  also  search  for  large  insects  at 
greater  distances.  In  Sierran  mixed  conifer  forests,  West- 
ern Tanagers  devote  about  47%  of  their  efforts  to  gleaning 
and  about  38%  to  hawking;  they  hawk  for  insects  about 
three  times  more  than  any  other  species  in  the  insect-glean- 
ing guild  of  that  forest  (Airola  &.  Barrett  1985).  These 
birds  hawk  large  slow  insects  from  exposed  perches,  often 


Tanagers 


SPECIES  ACCOUNTS 


Tanagers 


between  bouts  of  gleaning.  They  direct  most  foraging 
activities  at  the  foliage  or  air,  and  only  a  minor  amount  at 
twigs  and  branches.  Western  Tanagers  forage  mosdy  at 
middle  to  upper  heights  of  trees,  perhaps  because  these 
layers  are  more  open,  making  hawking  maneuvers  easier. 
Western  Tanagers  search  foliage  in  a  deliberate  manner 
and  often  remain  motionless  except  for  moving  the  head 
from  side  to  side  while  scanning  die  air  for  prey  (Isler  & 
Isler  1987).  As  with  many  bird  species,  they  change  the 
height  of  flycatching  efforts  in  trees  by  moving  from  the 
treetops  downward  in  the  morning,  then  back  upward  in 
the  afternoon,  following  insect  activity  that  is  stimulated  by 
the  ascending  and  descending  sun  (Bent  1958).  Western 
Tanagers  also  feed  on  the  ground,  for  refuse  in  logging 
camps  (McAllister  &  Marshall  1945)  and  in  campgrounds 
(E.C.  Beedy  6k  S.L  Granholm  pers.  obs.). 

Between  April  and  September,  the  diet  of  Western 
Tanagers  is  about  82%  animal  and  18%  vegetable  in  the 
form  of  fruit  and  trace  amounts  of  conifer  seeds  (Beal 
1907,  n  =  46).  Their  reliance  on  vegetable  fare  probably 
increases  with  the  ripening  of  fruits  in  late  summer  and 
fall.  Their  animal  foods  are  predominandy  hymenopterans 
(mosdy  wasps  and  some  ants),  followed  by  beedes,  true 
bugs,  grasshoppers,  and  caterpillars  (Beal  1907);  termites, 
homopterans,  snails,  and  spiders  are  also  eaten  (Dahlsten 
et  al.  1985).  A  wide  variety  of  wild  and  cultivated  fruits  and 
berries  is  eaten,  generally  the  smaller  types,  as  Western 
Tanagers  prefer  to  swallow  dieir  "dessert'  whole  (Beal 
1907).  Wild  fruits  eaten  include  elderberries,  mulberries, 
raspberries,  blackberries,  and  serviceberries  (Beal  1907, 
Martin  et  al.  1951).  Migrant  Western  Tanager  "swarms" 
have  been  known  to  inflict  severe  damage  on  lowland 


cherry  crops  (Beal  1907,  Bent  1958).  These  tanagers  also 
occasionally  eat  new  buds  and  sip  the  sweet  liquid  that 
exudes  from  some  flower  blossoms. 

Marin  Breeding  Distribution 

During  the  adas  period,  breeding  Western  Tanagers  were 
restricted  primarily  to  mixed  conifer  forests  at  mid-  to  high 
elevations  on  the  slopes  of  Mount  Tamalpais  and  north- 
ward along  the  Lagunitas  Creek  watershed.  These  areas 
have  moderate  to  high  rainfall  but  are  out  of  the  zone  of 
persistent  summer  fog,  which  is  either  blocked  by  interven- 
ing ridges  or  by  an  inversion  layer  of  warmer  air  higher  on 
the  slopes  of  Mount  Tamalpais.  Tanagers  may  also  breed 
occasionally  in  mixed  oak  woodlands  on  Mount  Burdell, 
Novato,  but  this  needs  verification.  An  adult  male  was 
briefly  seen  to  feed  a  female  or  immature  Western  Tanager 
in  a  moist  oak  drainage  on  Mount  Burdell  on  26  June 
1980  (DS),  but  it  seems  best  to  consider  this  probable 
breeding  evidence  at  best.  A  representative  breeding  local- 
ity was  San  Geronimo  (FL  summer  1976  — BTr). 

Historical  Trends/  Population  Threats 

The  Western  Tanager  was  first  confirmed  breeding  in 
Marin  County  in  1945  (FY  7/7/45,  2000  ft.  at  extreme 
headwaters  Lagunitas  Creek,  1 .5  mi.  SW  of  West  Peak, 
Mt.  Tamalpais  —Miller  1946).  Previous  workers  (Mailliard 
1900,  G&W  1927,  SckP  1933,  GckM  1944)  were  not 
aware  of  Western  Tanagers  breeding  in  Marin  County,  but 
this  most  likely  reflects  limited  field  work  at  the  time. 

Western  Tanager  numbers  appeared  to  increase  slighdy 
on  Breeding  Bird  Surveys  in  California  from  1968  to  1989 
but  were  fairly  stable  from  1980  to  1989  (USFWS  unpubl. 
analyses). 


363 


Cardinal™  Grosbeaks  &  Buntings  MARIN  COUNTY  BREEDING  BIRD  ATLAS  Cardinaline  Grosbeaks  &  Buntings 

Cardinaline  Grosbeaks  and  Buntings 

Family  Emberizidae 
Subfamily  Cardinalinae 


BLACK-HEADED  GROSBEAK   Pheucticus  melanocephalus 


A  summer  resident  from  early  Apr 

through  late  Sep  or,  sparingly,  mid-OcL 

/A^Or 

A  common,  widespread  breeder;  over- 

x^x^vr v^ 

^<&^(^r^r^(^-- 

all  breeding  population  fairly  large. 

^\^<\yp^\^\%Mj\ 

Recorded  in  129  (58.4%)  of  221 

^\^^\^^k%k^\ 

blocks. 

*r\  Jv<\  *L-V\  jP\  *>jP\  *>\^\*\^\ 

vJf\9>Jr\    >^i  ©  v^  ©  A^A     V>A  ©  J 

\^~~ 

VKA ->-¥v\ °A<\    3^\°>^\    \^\*>X^\ 

O    Possible        =       18   (14%) 

\    ><vo--Cy?>c\  ©  V^toY^Xj©  X^\     \^\    \^\     z—' 

€    Probable      =      78  (60%) 
•    Confirmed  =      33  (26%) 

Ap\o j^>\€ij^\s> \£*\*£i\k>  \>A©  \>^C  P 

■<\\  ilV'x  •iV>\  ®JrC\  •  \>dr*>  V^Y©  vV\  o  VVC 

i  vkvx.  OP^°J<^c^^^^A^j^\^yf^*jr\ 

^^^$^\^^^K^k^^< 

FSAR  =  4        OPI  =  516       CI  =  2.12 

JV>T~>^       ^ J^\  ©Jv^"\  ©Jt-^A  ©  i><\  •  )^k\ 

v?0» 

i^T                                 X^^\*V^P*Ji-^^V^«vA^V- 

![                                 ^-^^*>^^S^^^®3r^\©3f' 

Ecological  Requirements 

At  dawn  on  a  spring  day,  the  vibrant  song  of  the  Black- 
headed  Grosbeak  drowns  out  that  of  almost  all  other  birds 
in  Marin  County's  willow  and  alder  riparian  thickets  and 
her  relatively  open  moist  broadleaved  evergreen  forests. 
Locally,  Black-headed  Grosbeaks  breed  sparingly  on  the 
edges  of  conifer  forests  where  they  border  on  openings  and 
mix  with  broadleaved  trees.  The  bulk  of  the  population 
occurs  near  stream  courses.  Black-headeds  are  absent  in 
dense  closed  stands  of  bay,  mixed  bay  and  live  oak,  and 
conifers.  Grinnell  and  Miller  (1944)  thought  that  perhaps 
important  factors  to  Black-headed  Grosbeaks  were  the 
local  diversity  of  plant  growth  and  extensive  "edge"  condi- 
tions, hinting  these  were  necessary  because  of  the  birds' 
varied  diet.  Comparing  the  habitat  of  three  age  classes  of 
males  in  New  Mexico,  Hill  (1988)  found  that  the  prime 
habitat  of  older  males  was  the  most  heterogenous,  had  the 
greatest  vertical  vegetation  structure,  had  many  large  trees, 
and  was  generally  open. 

Black-headed  Grosbeaks  fashion  bulky  loose  nests  that 
vary  in  shape  from  saucerlike  platforms  to  ones  resembling 
cups  (Weston  1947).  They  ordinarily  construct  them  of 
slender  twigs,  plant  stems,  and  roodets  and  line  them  with 

364 


fine  stems  and  rootlets.  Black-headeds  usually  build  their 
nests  in  deciduous  bushes  and  trees  bordering  streams,  but 
also  occasionally  in  closed  woods,  dense  brushland,  and 
parklands  away  from  water.  The  nest  plants  they  most 
commonly  use  in  California  are  willow,  coast  live  oak, 
alder,  big-leaf  maple,  blackberry,  cottonwood,  and  elder- 
berry. The  height  of  163  California  nests  ranged  from  3 
feet  to  32  feet;  average  height  was  10  feet,  and  two-thirds 
of  the  nests  were  between  4  feet  and  12  feet  above  the 
ground  (Weston  1947).  The  height  of  21  nests  in  Utah 
ranged  from  about  7  feet  to  23  feet  and  averaged  13  feet 
(Ritchison  1983).  The  nest  support  usually  consists  of  a 
crotch  or  fork  in  a  group  of  horizontal  or  vertical  secondary 
branches  at  variable  locations  within  a  tree  or  bush  (Wes- 
ton 1947). 

In  Sierran  mixed  conifer  forests,  Black-headeds  forage 
(and  sing)  mosdy  high  in  trees  (Airola  &.  Barrett  1985),  but 
in  coastal  riparian  and  mixed  evergreen  forests,  they  forage 
throughout  the  trees  and  even  occasionally  on  the  ground 
(Weston  1947,  D.  Shuford  pers.  obs.).  In  the  mixed 
conifer  forests,  foraging  Black-headed  Grosbeaks  prefer 
black  oaks  and  pines.  Birds  usually  glean  while  foraging 


Cardinaline  Grosbeaks  &  Buntings 


SPECIES  ACCOUNTS 


Cardinaline  Grosbeaks  &  Buntings 


for  insects,  but  they  also  appear  to  search  below  them  for 
large  insects  at  greater  distances  within  the  crown  (Airola 
ck  Barrett  1985).  Upon  locating  larger  flying  or  stationary 
prey  up  to  about  10  feet  away,  they  lunge  down  upon  it 
Black-headeds  use  lunging  about  four  times  more  fre- 
quendy  than  any  other  species  in  the  insect-gleaning  guild 
of  mixed  conifer  forest  birds.  These  grosbeaks  hawk  flying 
insects  on  fewer  than  10%  of  their  foraging  attempts. 
Airola  and  Barrett  (1985)  also  found  that  Black-headeds 
forage  primarily  on  foliage,  secondarily  on  twigs,  and  to 
only  a  minor  extent  on  branches  or  in  the  air.  They  will 
also  cling  head  down  from  a  slender  twig  to  procure  rolled 
up  leaves  with  caterpillars  inside  them  (Austin  1968).  After 
retiring  to  a  perch,  they  open  the  leaf  with  a  few  quick 
movements  of  the  beak,  subdue  the  caterpillar  by  biting  it 
along  its  length,  then  swallow  it  whole. 

The  California  diet  from  April  to  September  is  about 
57%  animal  and  43%  vegetable  (Beal  1910,  n  =  225). 
Reliance  on  vegetable  foods  increases  from  spring  to  fall, 
paralleling  the  availability  of  fruits  (Beal  1907,  Martin  et  al. 
1951).  The  animal  component  is  predominandy  beedes, 
scale  insects,  and  caterpillars,  with  only  minor  amounts  of 
hymenoptera  (bees  and  wasps  and  a  few  ants),  other  true 
bugs,  flies,  grasshoppers,  other  insects,  and  spiders  (Beal 
1910);  rarely,  snails  and  small  fish  are  eaten  (McAtee 
1908,  Beal  1910).  A  small  June-July  sample  (n  =  7)  from 
the  mixed  conifer  zone  of  the  Sierra  Nevada  indicates  a  diet 
of  over  98%  animal  matter  (Dahlsten  et  al.  1985).  This 
may  reflect  grosbeaks'  concentration  on  animal  food  while 
feeding  nesdings,  a  period  of  low  fruit  availability,  or 
regional  differences  in  food  availability  and  hence  diet. 
Vegetable  foods  include  a  wide  variety  of  wild  and  culti- 
vated fruits,  weed  seeds,  buds,  flowers,  catkins,  and  pine 
seeds.  Elderberry  and  blackberry  are  important  food 
plants,  and  additional  ones  in  the  Berkeley  hills  include 
wild  oats,  black  mustard,  thimbleberry,  wild  rose,  coto- 
neaster,  wild  plum,  locust,  red-stem  filaree,  poison  oak, 
coffeeberry,  cow  parsnip,  flddlenecks,  and  various  thisdes 
(Weston  1947).  Seasonal  changes  in  the  vegetable  diet 
begin  with  an  initial  focus  on  soft  succulent  matter  such  as 
leaf  buds,  flowers,  and  flower  buds,  as  well  as  early-forming 
fruits  (Weston  1947).  There  is  a  gradual  shift  to  fruits  as 


these  mature  and  then,  with  their  disappearance,  mainly  to 
seeds  found  in  bushes  and  on  the  ground.  Nesdings  are 
initially  fed  a  soft,  pale  green  mash,  but  soon  they  are 
introduced  to  soft  animal  matter  such  as  caterpillars.  Soft 
animal  foods  decline  in  importance  as  hard  insect  matter 
such  as  beedes  (and  vegetable  matter,  too)  increase  in  the 
diet  (Beal  1910,  Weston  1947). 

Marin  Breeding  Distribution 

During  the  adas  period,  Black-headed  Grosbeaks  bred 
widely  in  Marin  County.  Their  distribution  here  coincided 
with  that  of  riparian  thickets  of  the  lowland  valleys  and 
open,  broadleaved  evergreen  forests  of  the  hillsides.  Black- 
headeds  were  absent  as  breeders  in  the  grassland-domi- 
nated areas  of  outer  Point  Reyes  and  near  Tomales;  on 
some  drier  interior  ridges  (especially  near  Novato);  and 
throughout  much  of  the  sedimentary  plains  bordering  San 
Francisco  and  San  Pablo  bays.  Representative  breeding 
locations  were  Inverness  (NE  7/3/82  —LP);  O'Hare  Park, 
Novato  (FL  6/23/82  — ScC);  Cascade  Canyon,  Fairfax  (NE 
5/12/77  -DS);  and  Phoenix  Lake,  Ross  (NY  5/21/77 
-DS). 

Historical  Trends/  Population  Threats 

Historically,  Black-headed  Grosbeaks  appear  to  have  held 
their  own  in  Marin  County  and  California  in  general 
(Mailliard  1900,  S&P  1933,  GckM  1944,  Robbins  et  al. 
1986,  USFWS  unpubl.  analyses).  In  1986,  though,  based 
on  long-term  banding  data  from  PRBO's  Palomarin  field 
station,  DeSante  and  Geupel  (1987)  documented  a  total 
reproductive  failure  of  Black-headed  Grosbeaks  in  central 
coastal  California.  Partial  or  total  reproductive  failure 
occurred  in  a  large  number  of  other  species  as  well. 
Although  it  may  be  highly  coincidental,  the  timing  of  the 
reproductive  failure  coincided  remarkably  with  the  passage 
of  a  radioactive  cloud  from  the  Chernobyl  nuclear  power 
plant  accident  and  the  associated  rainfall.  This  relationship 
bears  further  investigation,  and  the  population  trends  of 
Black-headed  Grosbeaks  and  other  species  that  reproduced 
poorly  in  1 986  should  be  watched  closely. 


365 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


A  Black-headed  Grosbeak  launched  in  flightsong  and  display  energizes  the  airways.    Drawing  i>y  Keith  Hansen,  1 989. 


366 


Cardinaline  Grosbeaks  &  Buntings 


SPECIES  ACCOUNTS 


Cardinaline  Grosbeaks  &  Buntings 


LAZULI  BUNTING    Passerina  amoena 


A  summer  resident  from  late  Apr 

"VfftV-«s^ 

through  late  Sep. 

^x5x^     N               rv 

A  fairly  common,  fairly  widespread 

^XXX^X^^^ 

breeder;  overall  breeding  population  of 

X^\®XX  XA0  XA*XX°X\^  ^X  ~ 

moderate  size. 

«\  ®A"C\  9>r\  ©A-^x    J<^\  ®Jv-^A     V-r    \ 

-"X  ®X\®  X^Y©J^X«  viTA     W'a     X"X 

Recorded  in  1 1 5  (52.0%)  of  221 

V  ®XX  ^XX^XX^XXt^XX    jXC    ^ 

^X\  •XXXXx  »XX©  X^T •  XX °  XX 

blocks. 

\#>"\  QA--^©>>\'©  V^x©  V^a®  V>A     J 

\^-~ 

Oi><7tt-®JX\  °V"\®  A^A©  Y^A©  X"\       VX 

XssX^#X^»>k\cXX©X'\©XX  j, 

-XX\ X\CXX°J^^AXC«XX'®XX   X^  J 

O    Possible        =       31    (27%) 

v  X'^XyX\cXX®X^v-°Xi\  Jv^x  X"\  X 

fV"    \^\      J^X  ®  A>A  ©  V^V°-  jXa-«  V-^X       \VC    *" 

C    Probable       =      67  (58%) 

XX  XX°XX»XX®X^<>:Xv  -XX-X 

•    Confirmed  =       17   (15%) 

XX    XX^XX®3XXXX«  XX©  XXPX^ 

-XkttXx  X\  X\e>^X\'»>A  XX 

>^7j^Xr\^^^ 

FSAR=3        OPI  =  345       CI  =  1.88 

!    S^S?^ XX"\     .VX  °  jX\      ZV"V    jX\    '  J<X       /  /-v 

May  hybridize  with  Indigo  Bunting  (P. 

;  U-,                                           >r      /       ^-^"*C*AXC©\>? 

cyanea)— an  irregular  spring  transient, 

X^                                ^ — f           ^'^^x 

summer  resident,  and  fall  transient 
mosdy  from  mid-May  through  late  Sep. 

Ecological  Requirements 

Another  archetypal  edge  species,  the  Lazuli  Bunting  breeds 
on  the  brushy  borders  of  Marin  County's  mixed  evergreen 
forests,  oak  woodlands,  Douglas  fir  forests,  riparian  groves, 
chaparral,  coastal  scrub,  and  planted  cypress  groves— where 
these  communities  interface  with  grasslands,  meadows, 
and  weed  fields.  In  these  simations,  large  clumps  of  intro- 
duced diisdes  are  especially  attractive  to  Lazuli  Buntings. 
Brush  and  trees  provide  nest  sites,  cover,  and  song  posts, 
while  grassland  and  thistle  patches  provide  good  foraging 
grounds.  What  constitutes  the  proper  vegetative  mix  is 
imprecisely  known,  as  Lazulis  are  often  absent  in  seem- 
ingly suitable  edge  situations.  In  areas  of  overlap  with 
Indigos  in  Utah,  Lazulis  prefer  areas  with  higher  shrub 
density  and  lower  ground  cover  (Whitmore  1975);  Lazulis 
also  seem  to  prefer  more  xeric  sites  (Wauer  1 969). 

Lazuli  Buntings  generally  lash  their  nests  to  the  support- 
ing stalks  of  weeds,  bracken  ferns,  and  diisdes,  or  settle 
them  in  forks  of  bushes,  berry  vines,  or  low  in  trees 
(Dawson  1923,  Erickson  1968).  Nest  height  usually  varies 
from  1.5  to  4  feet,  and  exceptionally  reaches  10  feet  above 
the  ground  (Erickson  1968).  Lazulis  weave  their  coarse  nest 
baskets  out  of  dried  grass  (especially  the  leafy  portions), 
weed  stalks,  strips  of  bark,  small  twigs,  and  fibrous  roots 
(Dawson  1923,  Erickson  1968).  They  line  them  with  fine 
grasses,  horsehair,  or  plant  down. 

Lazuli  Buntings  forage  for  insects  by  gleaning  or  lunging 
in  foliage  and  branches  and  by  occasional  flycatching  or 
hovering  (Erickson  1968).  Often  diey  strip  grassheads  of 
seeds  while  diey  perch  on  the  stout  stems.  But  sometimes 
a  bird  takes  a  whole  seed  bead  in  its  bill  after  a  short 


hovering  flight,  returns  to  a  perch  holding  the  still-attached 
seed  head  in  its  foot,  and  then  picks  out  the  seeds.  The  diet 
of  western  birds  (primarily  in  California)  varies  in  animal 
content  from  about  64%  in  spring  to  53%  in  summer 
(Martin  et  al.  1951,  n  =  46).  Important  insects  are  grass- 
hoppers, caterpillars,  beedes,  true  bugs,  bees,  and  ants. 
Vegetable  fare  includes  wild  oats,  miners  lettuce,  needle- 
grass,  canarygrass,  annual  bluegrass,  and  small  amounts  of 
melicgrass,  velvet  grass,  filaree,  and  chickweed. 

Marin  Breeding  Distribution 

During  the  adas  period,  Lazuli  Buntings  bred  widely  in  the 
central  interior  of  Marin  County.  They  were  scarce  to 
absent  on  the  Point  Reyes  peninsula,  in  the  grassland- 
dominated  rolling  hills  around  Tomales,  in  the  eastern 
urban  corridor,  and  along  the  San  Pablo  and  San  Fran- 
cisco bayshores.  Representative  breeding  stations  were 
upper  Millerton  Gulch,  E  of  Tomales  Bay  (NB  5/27/82 
-DS);  old  Cerini  Ranch  near  Marshall  (NY  6/29/82  - 
DS);  Nicasio  Reservoir  dam  (FL  6/15/82  — ScC);  Bolinas 
Ridge  above  Olema  (NB  5/29/82  -DT);  and  Skywalker 
Ranch,  Big  Rock  Ridge  (NY/NE  7/8/82  -ITi,  DS). 

Historical  Trends/ Population  Threats 

Because  of  their  fondness  for  open  edge  habitat,  Lazuli 
Buntings  were  already  expanding  their  local  distribution  in 
Humboldt  County  at  the  turn  of  the  century  by  invading 
areas  opened  up  by  logging  (Fisher  1902).  Because  of  the 
continuation  and  expansion  of  logging  practices,  Lazulis 
have  most  likely  increased  in  die  coastal  mountains  in 

367 


Cardinal™  Grosbeak  &  Buntings  MARIN  COUNTY  BREEDING  BIRD  ATLAS  Cardinaline  Grosbeaks  &  Buntings 


recent  decades.  The  detrimental  effects  of  overgrazing  on 
grassland  seed  sources  may  have  been  offset  by  the  spread 
and  encouragement  of  introduced  diistles.  Lazuli  Bunting 
populations  were  relatively  stable  on  Breeding  Bird  Sur- 
veys in  California  from  1968  to  1989  (USFWS  unpubl. 
analyses).  In  Marin  County,  diey  appeared  to  increase  on 
the  Even  Cheaper  Thrills  Spring  Bird  Count  from  1978 
to  1987  (Appendix  A). 

Remarks:  Hybridization  with  Indigo  Buntings 

Lazuli  and  Indigo  buntings  were  formerly  isolated  from 
contact  with  each  odier  by  die  Great  Plains.  As  the  popu- 
lation of  European  setders  expanded  in  that  area,  the 
planting  of  trees  and  shrubs  in  shelterbelts,  control  of  fires, 
the  demise  of  the  buffalo,  and  an  amelioration  of  climate 
all  caused  an  increase  in  suitable  bunting  habitat.  Indigos 
and  Lazulis  invaded  this  area  from  the  east  and  west, 
respectively,  and  in  the  1950s  occupied  a  zone  of  overlap 
and  hybridization  as  great  as  400  miles  wide  (Sibley  6k 
Short  1959).  The  spread  of  Indigos  westward  has  been 
more  dramatic  than  diat  of  Lazulis  eastward  and  may  have 
been  fueled  by  a  large  increase  in  Indigos'  population 
because  of  the  opening  of  the  eastern  deciduous  forest  by 
agriculture,  logging,  and  burning  (Wells  1958).  The  west- 
ern spread  of  Indigos  has  continued  at  the  expense  of 
Lazulis  (Emlen  et  al.  1975). 

Although  the  expansion  and  contact  of  these  species 
were  first  noted  early  in  the  century,  the  first  reports  of 
hybrids  and  of  breeding  Indigo  types  in  the  far  West 
occurred  in  the  1940s  and  1950s  (Sibley  6k  Short  1959). 
The  first  confirmed  breeding  record  in  California  of  an 
apparent  male  Indigo  with  a  female  Lazuli  was  docu- 
mented in  1956  (NE  6/10/56  Soledad  Canyon,  Los  Ange- 
les Co.   -Bleitz    1958).    Sibley   and   Short  (1959)   have 


cautioned  that  all  recent  records  of  cyanea  west  of  the  Great 
Plains  are  likely  to  be  hybrids  and  that  sight  records  are  not 
satisfactory  as  die  basis  for  records  of  "pure"  Indigos, 
because  hybrid  characters  may  not  be  apparent  in  the  field. 
This  would  make  it  extremely  difficult  to  document  the 
breeding  of  a  pure  pair  of  Indigos,  which  would  be  neces- 
sary before  adding  dial  species  to  the  breeding  avifauna  of 
die  state.  On  the  other  hand,  the  small  percentage  of 
hybrids  in  the  zone  of  overlap  in  recent  studies  (Emlen  et 
al.  1975)  suggests  that  most  apparent  Indigos  reaching 
California  are  of  "pure"  stock. 

In  Marin  County,  an  apparent  "pure"  Indigo  was  seen 
on  territory  at  Olema  Marsh  from  6  June  to  15  July  1976 
(AB  30:1001)  and  was  sighted  there  again  for  short  periods 
in  1977  and  1979  (ABN).  An  obvious  hybrid  male  (dark 
blue  with  prominent  white  wingbars  and  white  belly)  was 
seen  at  the  same  site  on  22  June  1979  with  Lazulis  (AB 
33:895),  suggesting  that  a  successful  hybrid  breeding  had 
occurred  there  in  a  previous  year.  In  1984,  a  male  "Indigo" 
was  first  observed  near  the  town  of  Olema  on  7  July,  and 
on  12  July  a  nest  with  two  young  was  found,  attended  by 
a  female  Lazuli  widi  which  die  "Indigo"  was  mated  (RMS). 
The  male  was  seen  with  food  in  his  bill  in  the  vicinity  of 
the  nest  and  accompanying  the  female  on  foraging  trips  in 
nearby  fields.  Although  "Indigos"  are  recorded  annually  in 
May  and  June  as  rare  transients  in  coastal  northern  Cali- 
fornia (ABN),  the  above  records  and  single  ones  from 
Mendocino  (AB  33:895)  and  San  Mateo  (AB  40:1253) 
counties  are  die  only  indications  of  breeding  between  these 
species  in  this  region. 

The  breeding  biology  of  Lazuli  and  Indigo  buntings  is 
very  similar,  and  the  reader  is  referred  to  the  accounts  of 
Indigos  by  Taber  and  Johnston  (1968)  and  Ellison  (1985). 


368 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


Emberizine  Sparrows 

Family  Emberizidae 
Subfamily  Emberizinae 


RUFOUS-SIDED  TOWHEE   Pipilo  erythrophthalmus 


A  year-round  resident. 

^O^A~t^^<^           \                 vr^;^ 

A  common,  nearly  ubiquitous  breeder; 

j\  o. 

overall  breeding  population  very  large. 

ouAoVA  ©  x^A  ©  v-o,  •  Y>A"  ©A^A  ©A^x.®^^ 

Recorded  in  195  (88.2%)  of  221 

iKo  \A^A  ©  >^®J\^A  •  >-^®>Ar\€,Jv^A  CA^«\ 

C  ©  V<r\  ©  VA"\  ®Ar<A  ©  W^V«  Ar-^A  °3r\  ®  Ur^'Y  V-\ 

blocks. 

^A  i  t>  V^A  ®  A^A  ®  A^V©  A^A  -P  A-iCA :*  >^A  ®  A^^  \ 

"^A-A^iA  ©\^A  ©\^\*A^A  ^V^Ai^V^xCjr^A  °A 

^C^A  %V>^\  c  V>A  ©Ar\  •  \>"A  o  \^\  mJ?"\  ®JA<r  \ 

-^v  «V\  o  V^A  ©  A^x  ©  vA  ©  w^  •  \^\  ©  V"\  ©  J 

V^^S^^rsA^X  ®Ar>\  ®  A^A  ®  A^A  •3r\  ®><\ 

O    Possible        =       17   (9%) 

KV^VA  ©  V-'x  o  wA  o  V<A  ©  V^A  •  V^  VU^. 

VV»  A^Ts®  V^A  ©  \*^%&3£^\  ©  V>A  •  X>A  ft A/T>?v 

xxj®-^©^^  \®  K\oM«  A-^«<a^v&3^A  ®Ar«J> 

€    Probable       =     124   (64%) 

W\  ©  x^v  <3a<^\  ©  v--Tr»i>>Ar©  x^a  •Ar-"x  ®Ar\  •' 

\  \  JF-^»-^>^J\^«,3r\ « ><\  CA»\  *>x<r\  *>r  « 

XA-pvto  X^A  •  jS^\  ©  X>r\  ©  X^-^A  •  V<rX  ®  V'x  •  V<_  k 

•    Confirmed  =       54   (28%) 

\P\^A©  V^»>^»^^A^^®>^»A^^ 

^_- 

VUAf©  V^A  ©  V-^X  ♦  \^AA»  \^\  •  >^\  ®  J^TX  •  A-a'-"? — 

-  ■  - 

'1-3. vHXLiA— —a®  V-^\  •  A-^x  ©  x-^A  ©  sv^\®  A-^\  •Jk<- 

'.■S^^^y^       ^<©  V'x  ©A^A  ©A^-^A ®Ac^T\  •A-^ii 

<x /\^              ^^C®  V-'A © ><\ •■Ar<A ftA^Tx *£?* 

5?& 

FSAR  =  4       OPI  =  780        CI  =  2.19 

>r                                  X©\T-ArvA><L©  \>A»Y>-A  •  s 

r>  /                                    ""— *=-*  XJ^'S"""*^'  <>  \^-"\  ©  x^x 

]>U                       x5/   ^^^<^ 

Ecological  Requirements 

The  plumage  of  western  "Spotted  Towhees"  may  serve  as 
cryptic  coloration  against  their  sun-dappled  backdrop 
beneath  woody  shrubs  without  extensive  arboreal  cover. 
These  haunts  contrast  with  the  more  mesic  forested  habi- 
tats of  their  eastern  counterparts.  In  Marin  County, 
Rufous-sided  Towhees  are  conspicuous  breeders  in  coastal 
scrub,  chaparral,  brushy  riparian  thickets,  and  on  the 
shrubby  edges  or  openings  of  the  remaining  forest  or 
woodland  plant  communities.  They  also  use  suburban 
plantings  of  suitable  structure.  Rufous-sided  Towhees 
avoid  dense  shrubbery  when  it  occurs  within  the  heart  of 
Marin's  closed-canopy  conifer  or  mixed  evergreen  forests. 
Because  they  require  a  well-developed  leaf  litter  and  humus 
layer  in  which  to  forage,  they  prefer  chaparral  and  brushy 
areas  bordering  on  trees  (particularly  oaks)  that  provide 
fallen  or  windblown  leaves  (Davis  1957). 

Although  Rufous-sided  Towhees  nest  mostly  on  the 
ground,  they  place  nests  occasionally  in  bushes  or  vine 
tangles  up  to  six  feet  high  (Baumann  1959,  Davis  1960). 
They  typically  build  their  nests  in  depressions  with  the  rim 
flush  or  slighdy  above  ground  level,  invariably  in  sites 


protected  from  above  by  overhanging  bushes,  vines,  or 
clumps  of  grass.  Characteristic  nest  sites  are  grassy  and/or 
leaf-littered  areas  on  the  edges  of  thickets  or  near  isolated 
shrubs  or  trees.  Some  Rufous-sided  Towhees  place  their 
nests  on  the  ground  between  the  branches  of  fallen  oak 
limbs.  They  construct  their  cup-shaped  nests  with  a  frame- 
work of  strips  of  inner  bark,  dead  leaves,  and  coarse  grass, 
and  an  inner  lining  of  fine  dry  grass  stems  or  roodets. 
Rufous-sided  Towhees  are  inveterate  ground  foragers,  but 
diey  specialize  more  in  scratching  for  their  subsistence  than 
do  California  Towhees  (Davis  1957;  see  California 
Towhee  account).  Prime  foraging  areas  are  deep  leaf  litter 
and  humus  under  vegetative  cover.  Rufous-sided  Towhees 
rarely  forage  in  areas  not  screened  from  above  by  overhang- 
ing vegetation,  or  in  bare  or  sparsely  covered  soil.  Unlike 
California  Towhees,  Rufous-sideds  scratch  from  a  perky 
upright  posture  with  the  head  high,  knees  moderately 
flexed,  and  the  tail  in  line  with  the  back  or  more  frequendy 
cocked.  They  toss  leaf  litter  and  soil  behind  them  with  their 
long  claws,  by  vigorous  backwards  thrusts  of  both  feet 
simultaneously,  and  follow  this  with  a  short  hop  forward 

369 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


to  regain  the  original  position  and  initiate  the  next  scratch- 
ing maneuver.  Rufous-sided  Towhees  obtain  most  of  their 
food  from  the  middle  or  lower  layers  of  the  leaf  litter  and 
humus  or  in  the  upper  layers  of  the  soil  proper  where  it  is 
gleaned  or  pecked  after  uncovering.  Rufous-sideds  will  also 
scratch  for  food  above  ground  level— on  top  of  woodrat 
nests  built  in  trees  or  in  accumulations  of  leaves  or  debris 
in  crotches  or  cavities  of  oaks.  They  usually  travel  between 
scratching  in  a  series  of  short  hops.  From  spring  to  fall, 
Rufous-sideds  will  also  peck  and  glean  insects  from  the 
leaves,  branches,  and  lichens  in  bushes  and  trees  (espe- 
cially oaks).  Rarely,  birds  will  also  make  vertical  flycatching 
attempts  to  about  two  feet  off  the  ground,  and  they  will  run 
through  the  grass  pursuing  grasshoppers.  In  the  East, 
Greenlaw  (in  Smith  1978)  noted  that  males  made  flycatch- 
ing attempts  more  often  than  females.  Rufous-sided 
Towhees  also  take  fruits  and  berries  from  trees  or  bushes 
while  perched  or  from  hovering  flight.  They  also  some- 
times visit  feeders. 

Year-round,  the  diet  of  California  birds  is  about  24% 
animal  and  76%  vegetable  (Beal  1910,  n  =  139).  In  the 
Pacific  states  (mainly  California),  the  Spotted  Towhee  diet 
varies  from  49%-62%  vegetable  matter  in  spring  and 
summer  (n  =  66)  to  91%-92%  in  fall  and  winter  (n  =  84) 
(Martin  et  al.  1951).  A  small  sample  (n  =  6)  from  the  Sierra 
Nevada  indicates  the  summer  diet  there  is  about  84% 
animal  (Dahlsten  et  al.  1985).  Arthropod  fare  includes 
beedes,  true  bugs,  ants,  bees,  wasps,  caterpillars,  and 
moths,  along  with  a  few  grasshoppers,  flies,  miscellaneous 
insects,  spiders,  millipedes,  and  sowbugs.  Insect  food  fed 
to  the  young  shifts  from  mostly  larvae  early  in  the  season 
to  mosdy  grasshoppers  later  on  (Davis  1960).  Important 
vegetable  foods  are  weed  seeds,  wild  and  cultivated  fruits 
and  berries,  acorns  (already  opened),  and  grain.  In  spring, 


Rufous-sideds  feed  on  the  seeds,  seed  capsules,  and  bracts 
of  miners  lettuce,  young  valley  oak  leaves,  and  blossoms  of 
gooseberry  and  blackberry  (Davis  1957).  In  California,  the 
wild  fruits  and  berries  that  they  feed  on  most  frequendy  in 
the  late  summer  and  fall  are  elderberries,  coffeeberries, 
hollyleaf  redberries,  snowberries,  gooseberries,  poison  oak 
drupes,  blackberries,  toyon,  honeysuckle,  manzanita, 
twinberries,  and  madrone  (Beal  1910,  Davis  1957). 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Rufous-sided  Towhee  was  a 
widespread  breeder  in  Marin  County,  and  its  distribution 
overlapped  that  of  the  California  Towhee  with  only  a  few 
exceptions.  Although  California  Towhees  can  subsist  in 
the  sparse  cover  of  ranchyards  in  the  grasslands  around 
Tomales,  Rufous-sideds  cannot.  On  Tomales  Point, 
Rufous-sideds  occupied  the  dense  east-facing  brushy  gullies 
where  California  Towhees  were  absent.  Both  species  were 
lacking  on  the  grass-  and  dune-dominated  tip  of  Point 
Reyes.  Representative  breeding  stations  were  Chaparral 
Hill  near  Mt.  Burdell,  Novato  (NE  5/V79  -ScC);  ridge  N 
of  San  Geronimo  (FL  7/11/81  -DS);  Carson  Ridge  (NE 
5/28/79  -ITi);  and  Mt.  Tamalpais  (FY  4/27/81  -DS). 

Historical  Trends/Population  Threats 

In  the  past,  clearing  of  forests,  with  the  subsequent  intru- 
sion of  brush,  and  planting  of  cover  in  residential  areas 
may  have  favored  Rufous-sided  Towhees,  whereas  fire 
suppression  or  extensive  development  may  have  harmed 
them.  Rufous-sided  Towhee  numbers  generally  were  fairly 
stable  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989,  despite  increasing  from  1980  to  1989  (USFWS 
unpubl.  analyses). 


370 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


CALIFORNIA  TOWHEE   Pipilo  crissalis 


A  year-round  resident. 

.f^S^W^               K                       ^ 

A  common,  nearly  ubiquitous  breeder; 

overall  breeding  population  very  large. 

Recorded  in  201  (91.0%)  of  221 
blocks. 

Y\>-c\  AJt-VlX  • ^r\  •  A^v*  i^\  o  v>^v»  V^Y^VVA 

O    Possible        =       34   (17%) 

©    Probable       =       88   (44%) 

•    Confirmed  =      79  (39%) 

^,®A^CA^»A^A^A-^'^ 

__  ^,- 

^-tTcA  .A^*J'r^®A^*Jk<^» J^A»V^#.^^ 

FSAR  =  4       OPI  =  804        CI  =  2.22 

ffWJfQo  N^°Jv^3^^v>^\^V»  vA  •v 

\  ^k2jp5^ — ^-2><r\c3r^^cV-^®S^vo  V>^\  #\Z< 

_    7 

^^^  ^^<o^\^i^^^t 

^£i 

^7                  ^^^^^\#^ 

d 

>=>                       x^7   ^-^^} 

Ecological  Requirements 

A  common  dooryard  bird,  taken  for  granted  by  most,  the 
California  Towhee  is  one  of  the  most  characteristic  birds 
of  lowland  California.  A  die-hard  edge  species,  this  towhee 
occupies  Marin  County's  broken  chaparral  and  coastal 
scrub,  the  brushy  edges  or  clearings  of  all  the  major  forest 
and  woodland  types  (especially  oak  woodland  and  ripar- 
ian), ranchyards,  and  particularly  suburban  plantings  and 
lawns.  Its  main  requisites  are  open  ground  for  foraging 
and  brush  or  trees  for  cover  and  nesting. 

California  Towhees  construct  bulky,  well  built  nests  that 
they  conceal  in  the  dense  foliage  of  bushes,  trees,  or,  rarely, 
on  the  ground.  Although  nests  may  range  up  to  about  35 
feet  above  the  ground,  most  are  from  about  2.5  to  12  feet 
(Davis  1951,  Childs  1968).  California  Towhees  fashion 
nest  cups  from  twigs,  weed  stalks,  dry  grass,  or  inner  bark 
and  line  them  with  fine  grass,  plant  stems,  hair,  or  wool 
(Childs  1968).  Reports  of  unusual  nest  sites  include  a  cleft 
five  feet  up  on  the  face  of  a  rock  wall,  on  top  of  an  old 
mockingbird  nest,  in  an  accumulation  of  bark  in  a  eucalyp- 
tus tree,  and  in  a  berry  basket  ten  feet  inside  a  barn  (Davis 
1951,  Childs  1968). 

California  Towhees  forage  primarily  on  the  ground  in 
open  areas  near  (or  less  frequendy  under)  trees  and  brush. 
They  glean  food  items  from  the  soil  surface  or  obtain  them 
by  scratching  in  the  leaf  litter,  humus,  or  upper  layers  of 
exposed  soil.  Although  California  Towhees  will  forage 
alongside  Rufous-sided  Towhees  in  leaf  litter  under  vegeta- 
tion, they  seldom  penetrate  far  into  very  dense  brush, 
where  the  latter  species  frequendy  feeds.  In  the  open, 
California  Towhees   feed   in   bare   soil  or  in   sparse  or 


modified  grassland;  tall  continuous  grassland  is  used  only 
when  broken  by  animal  trails  or  other  interruptions.  Cali- 
fornia Towhees  usually  forage  in  pairs.  They  utilize  both 
pecking  and  two-footed  scratching  techniques  extensively, 
unlike  Rufous-sideds  that  use  primarily  scratching.  Califor- 
nia Towhees  characteristically  crouch  with  knees  deeply 
bent  and  head  and  tails  down  when  gleaning  or  scratching. 
They  scratch  less  vigorously  than  do  Rufous-sideds.  When 
foraging  or  seeking  cover,  California  Towhees  travel  on  the 
ground  by  one-  or  two-footed  hopping  or  by  running  for 
longer  distances.  In  the  summer  months,  they  also  procure 
insects  from  vegetation:  in  trees  and  bushes  they  peck  at 
leaves,  branches,  oak  catkins,  and  lichens,  while  on  die 
ground  they  glean  insects  from  grasses  and  low  annuals. 
In  the  late  summer  and  fall  they  pick  elderberries, 
coffeeberries,  poison  oak,  and  other  fruits  and  berries;  they 
forage  on  these  foods  while  perched  or,  less  frequendy, 
from  hovering  flight.  California  Towhees  also  jump  up 
and  bend  grass  seed  heads  down  to  strip  the  seeds,  and 
they  eat  blades  of  freshly  sprouted  grass  or  garden  vegeta- 
bles, small  mushrooms,  newly  grown  plant  buds  or  oak 
leaves,  and,  occasionally,  opened  acorns  on  the  ground. 
California  Towhees  frequendy  visit  bird  feeders. 

The  year-round  diet  of  birds  in  California  is  about  86% 
vegetable  and  14%  animal  matter  (Beal  1910,  n  =  399). 
Consumption  of  animal  food  reaches  a  peak  of  38%  in 
spring  (n  =  34)  and  a  low  of  4%-8%  in  fall  and  winter  (n  = 
177)  (Martin  et  al.  1951).  The  main  vegetable  foods  are 
weed  seeds,  wild  fruits  and  berries  (mentioned  above), 
cultivated  fruits  usually  found  on  the  ground,  and  grain. 

371 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


Animal  fare  includes  beetles,  ants,  bees,  wasps,  true  bugs, 
caterpillars,  grasshoppers,  and  crickets.  Nesdings  start  out 
on  a  diet  entirely  of  insects,  particularly  grasshoppers  and 
caterpillars,  but  they  graduate  to  consume  as  much  as  8% 
vegetable  matter  before  fledging. 

Marin  Breeding  Distribution 

During  the  adas  period,  California  Towhees  bred  widely 
in  Marin  County,  particularly  in  the  lowlands  and  toward 
the  drier  interior.  Broadly,  they  were  sparse  or  lacking  only 
in  the  windswept  grasslands  on  the  tip  of  Point  Reyes. 
Locally,  they  were  scarce  or  absent  on  steep  slopes,  in  thick 
forests,  and  in  extensive  grasslands.  Representative  breed' 
ing  localities  were  Point  Reyes  Station  mesa  (NB  7/1 2/81 
— JGE);  Slide  Ranch,  3  miles  S  of  Stinson  Beach  (NE 


5/24/81  -DS);  Mt.  Burdell,  Novato  (NB  4/27/81  -DS); 
ridge  on  south  side  of  Lucas  Valley  Rd.  (FY  6/18/82 
-BiL);  and  near  Phoenix  Lake  (NE  5/10/76  -RMS). 

Historical  Trends/Population  Threats 

Although  some  of  man's  activities  have  made  parts  of  the 
California  Towhee's  original  haunts  uninhabitable,  this 
has  been  more  than  compensated  for  by  expansion  of 
gardening  and  ranching  into  formerly  barren  lowland 
terrain  (G&.M  1944).  Undoubtedly  the  clearing  of  some 
forested  areas  has  also  opened  up  habitat  to  this  towhee's 
liking.  From  1968  to  1989,  California  Towhee  numbers 
were  relatively  stable  on  Breeding  Bird  Surveys  in  Califor- 
nia (USFWS  unpubl.  analyses). 


RUFOUS-CROWNED  SPARROW   Aimophila  ruficeps 


A  year-round  resident. 

/\°-\>\V  - 

\  iV\  °^k\    %r\   S\ 

An  uncommon,  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  52  (23.5%)  of  221  blocks. 

>y^\  o>^\  •jv^ 

'op^t\\y^c\ 

O    Possible        =      27   (52%) 

\d~v 

x^rC 

€    Probable       =       16   (31%) 

^^^V\3c 

\^\\  ^  A^-^^\     j^^x     V^-^a 

•    Confirmed  =        9  (17%) 

_ -r- 

FSAR  =  2        OPI  =  104        CI  =  1.65 

v*  V-^a    A><C©  Y>J\     x-JXT 

Ecological  Requirements 

This  rusty-capped  skulker  occupies  a  restricted  niche.  In 
Marin  County,  Rufous-crowned  Sparrows  generally  occur 
on  steep,  sunny,  south-  or  west-facing  slopes  with  patchy 
or  open  coastal  scrub  dominated  by  coastal  sage;  in  low, 
broken  serpentine  chaparral  or  short,  sparse  recendy 
burned  chaparral;  along  tall  chaparral  edges;  or  in  rocky 
gullies  with  a  few  scattered  shrubs.  Their  main  require- 
ments seem  to  be  low  sparse  brush  cover  for  protection 
and  grass  or  forb  ground  cover  for  foraging;  although  rock 
outcrops  are  frequently  present,  they  are  not  essential.  The 
broken  scrub  or  chaparral  that  Rufous-crowns   favor  is 

372 


found  most  widely  on  Marin's  steep  dry  slopes,  but  it  also 
occurs  extensively  on  the  flat  or  low  rolling  ridgetops  on 
Mount  Tamalpais  and  Carson  Ridge,  where  the  chaparral 
grows  low  and  open  on  harsh  serpentine  soils. 

In  coastal  California,  Rufous-crowned  Sparrows  charac- 
teristically build  their  nests  flush  with  the  ground— in 
hollows  under  clumps  of  grass  or  at  the  bases  of  bushes— in 
open  brush  or  on  grassy  slopes  in  proximity  to  scrub  or 
chaparral.  Elsewhere,  they  more  frequendy  place  their 
nests  in  low  bushes  up  to  three  feet  off  the  ground  or, 
rarely,  under  low  ledges  on  a  hillside  or  inside  a  tin  can 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


(Austin  1968).  Nest  cups  vary  from  compact  to  loosely 
woven  affairs  made  of  coarse  grass,  fine  twigs,  bark,  and 
vegetable  fibers  and  lined  with  fine  grasses  or  horsehair. 

The  diet  is  poorly  known,  but  it  appears  to  vary  with 
season  and  availability.  The  summer  diet  of  birds  in 
California  is  21%  animal  and  79%  vegetable  matter  (Mar- 
tin et  al.  1951,  n  =  25).  Reliance  on  animal  matter  gener- 
ally decreases  from  summer  to  winter  (Austin  1968). 
Arthropod  food  consists  of  grasshoppers,  ants,  bees, 
wasps,  beedes,  true  bugs,  leafhoppers,  caterpillars,  flies, 
spiders,  and  miscellaneous  insects.  The  young  are  prob- 
ably fed  just  insects.  Vegetable  matter  is  principally  small 
grass  and  forb  seeds,  fresh  grass  stems,  and  tender  plant 
shoots.  Wild  oats,  filaree,  miners  lettuce,  chickweed,  dock, 
and  pigweed  are  important  plant  foods  in  California  (Mar- 
tin et  al.  1951).  These  sparrows  apparendy  forage  by 
gleaning  and  pecking  as  they  hop  slowly  about,  over,  or 
through  the  herbaceous  layer  close  to  the  ground;  they  may 
occasionally  forage  in  taller  shrubs  or  low  oak  trees. 

Marin  Breeding  Distribution 

During  the  adas  period,  Rufous-crowned  Sparrows  were 
distributed  patchily  throughout  Marin  County,  as  is  die 
combination  of  slope  and  shrub  cover  that  suits  their 
needs.  They  avoided  lowland  valleys  and  plains,  rolling 
grassy  hills,  and  heavily  forested  areas.  Rufous-crowned 
Sparrows  were  somewhat  more  numerous  in  the  interior 
of  the  county  than  on  the  immediate  coast.  Areas  of 
particular  concentration  included  serpentine  chaparral  on 
Carson  Ridge  along  the   Pine  Mountain   fire  trail   and 


coastal  sage-dominated  slopes  of  the  Walker  Creek  can- 
yon. Representative  breeding  stations  were  Palomarin, 
PRNS  (NY  4/25/78  -SJ);  near  Soulajoule  Reservoir  (FY 
5/21/82  -ScC,  DS);  ridge  W  of  Loma  Alta  (FL  6/1 1/82 
-BiL);  and  Carson  Ridge  (NY  5/13/77  -DS,  GBe). 

Historical  Trends/ Population  Threats 

Their  habitat  preferences  for  sparse  brush  suggests  that 
Rufous-crowned  Sparrows  are  short-distance  colonizers, 
adapted  to  invade  areas  swept  by  fire  or  other  disturbances 
that  open  up  the  cover.  Conversely,  they  will  abandon  an 
area  if  the  brush  becomes  too  dense.  Consequendy, 
Rufous-crowned  Sparrow  populations  are  probably  always 
undergoing  upward  or  downward  trends  in  abundance 
over  the  short  term  in  local  areas.  Because  it  allows  chap- 
arral to  grow  in  dense  decadent  stands,  long-term  fire 
suppression  since  the  turn  of  the  century  has  likely  reduced 
numbers  of  Rufous-crowned  Sparrows  in  California. 
Development  may  occasionally  open  up  (or  destroy)  habi- 
tat, though  man's  activities  are  usually  restricted  on  the 
steep  slopes  that  Rufous-crowns  often  occupy.  From  1968 
to  1989,  numbers  of  Rufous-crowned  Sparrows  were  rela- 
tively stable  on  Breeding  Bird  Surveys  in  California 
(USFWS  unpubl.  analyses),  though  these  surveys  were 
conducted  decades  after  policies  of  fire  suppression  had 
been  in  place.  The  Southern  California  Rufous-crowned 
Sparrow  (A.  r.  canescens)  is  currendy  a  Candidate  (Cate- 
gory 2)  for  federal  listing  as  Threatened  or  Endangered 
(USFWS  1991). 


373 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Emberizine  Sparrows 


CHIPPING  SPARROW    Spizella  passerina 


A  summer  resident  from  early  Apr 

through  late  Oct. 

A  fairly  common,  somewhat  local 

^i    X^\o  X^\  c3r^A°X^A  c  \^\    X^-a    \yPK 

breeder;  overall  breeding  population 

^Va    iV\    Jv<TX  •Xr\  o  X^-"\  ©  V^\  •  V-'A     XA""\ 
ri  ^  V^vX   Jf\  oJv^x  o  X^-a    X>A©  X>a    a^-v     A 

small. 

X  ^^oA^^CX  o  Xr-^A  •  X^-^\©X>A7©  \><ArSto\^~:A     V>^a       j 

Recorded  in  93  (42.1%)  of  221  blocks. 

^vJ^^^A^^A^®^^*^^*^^  V^\    J 

VT  >^r^5-x^°3P\oJ\^^«\^^®V^\   V-"i 

O    Possible        =      17  (18%) 

YU^£2>^£^^^ 

€    Probable       =       50   (54%) 

-"A-.       Xr^\          >^\*>^V©V^A            X-^\          \^\          X^^^-T- 

-r- 

•    Confirmed  =       26   (28%) 

ff% &\^\  y^\*J^X< •  X^-dr  X^v  W\    x>A 
-,'  3JV7Y  L\r\  ®A<r\  #A^©>c2v ©  AWC  V^\  \ V 

<^o»<^Q& — I© X>A© \5Ar  \ ^-Yv>& >VT \ ^ArT\ 

FSAR=3        OPI  =  279         CI  =  2.10 

rvo 

Ecological  Requirements 

In  Marin  County,  the  dry  buzzy  trill  of  breeding  Chipping 
Sparrows  can  be  heard  on  the  edges  of  oak  woodlands, 
mixed  evergreen,  Douglas  fir,  bishop  pine,  and  redwood 
forests  and,  sparingly,  in  cypress  and  eucalyptus  groves 
where  these  habitats  border  on  gendy  sloping  grasslands 
or  meadows  of  open  character.  Trees  and  brush  provide 
cover  and  nest  sites.  Grassland  and  woodland  edge  appear 
to  be  this  species'  principal  foraging  beat.  Chipping  Spar- 
rows generally  locate  their  nests  in  trees  or  bushes  from 
about  2  to  57  feet  above  ground.  Occasionally  diey  place 
them  on  the  ground  in  grass  or  in  odd  settings— on  a 
mowing  machine  in  a  semiopen  tool  shed,  on  the  side  of 
old  straw  stacks,  in  a  moss-filled  hanging  basket  on  a  stoop 
by  a  door,  in  pepper  plants  hung  to  dry  in  a  shed,  or  six 
inches  down  at  the  bottom  of  a  Hairy  Woodpecker  winter 
roost  hole  (Walkinshaw  1944,  Stull  1968,  Reynolds  & 
Knapton  1984).  Chipping  Sparrows  usually  conceal  arbo- 
real nests  in  dense  foliage,  from  close  to  the  trunk  to  well 
out  on  horizontal  branches  (Walkinshaw  1944).  Nest 
height  seems  to  increase  through  the  summer  (Walkin- 
shaw 1944).  At  least  in  some  areas,  nests  are  oriented  on 
the  south  or  east  side  of  trees,  where  they  catch  the  early 
morning  sun  and  are  protected  from  the  prevailing  winds 
and  rain  (Reynolds  6k  Knapton  1984).  Chipping  Sparrows 
construct  compact  or  loose  nest  cups  made  of  roodets, 
dead  grass,  and  weed  stalks,  and  line  them  with  fine 
roodets,  fine  grasses,  or  hair  (Walkinshaw  1944,  Stull 
1968,  Reynolds  ck  Knapton  1984). 

Chipping  Sparrows  are  primarily  ground  foragers  that 
take  most  of  their  food  within  about  three  feet  of  the 

374 


ground  (Allaire  6k  Fisher  1975).  They  peck  or  glean  grass 
and  weed  seeds  from  the  ground  while  hopping  around  in 
low,  sparse  vegetation  or  they  pick  them  from  the  tips  of 
grass  or  weed  stems  while  reaching  out  from  perches  in 
brush  piles,  fallen  trees,  and  barbed  wire  fences.  While 
searching  for  insect  prey,  these  birds  actively  move  among 
low  perches,  from  which  they  peer  down  to  the  ground  or 
herbaceous  vegetation  and  then  fly  down  to  catch  prey  in 
their  bills.  They  also  occasionally  flycatch;  they  apparendy 
feed  on  insects  and  new  buds  in  trees  in  the  spring  (Stull 
1968).  Chipping  Sparrows  show  no  annual  variation  in 
use  of  foraging  techniques  and  the  least  variation  in  other 
measures  of  resource  use  of  nine  species  breeding  in 
ponderosa  pine  forests  in  Arizona  (Szaro  et  al.  1990). 

The  April  through  October  diet  of  birds  in  California  is 
about  45%  animal  and  55%  vegetable  food  (Beal  1910, 
n  =  96),  though  reliance  on  vegetable  matter  peaks  at  98% 
of  the  diet  in  fall  and  winter  (Beal  1907,  Martin  et  al. 
1951).  Continentwide,  animal  matter  accounts  for  59%- 
66%  of  the  diet  in  spring  and  summer  (Martin  et  al.  1951 , 
n  =  336).  Arthropod  prey  are  caterpillars,  ants,  beedes, 
grasshoppers,  true  bugs,  flies,  leafhoppers,  planthoppers, 
spiders,  wasps,  and  a  few  moth  pupae.  Vegetable  matter  is 
dominated  by  weed  seeds  with  only  small  amounts  of  grain 
and  a  trace  of  fruit.  Important  plant  foods  in  the  West  are 
filaree,  pigweed,  brisde  grass,  panic  grass,  oats,  and  chick- 
weed,  along  with  needlegrass,  bluegrass,  red  maids,  and 
miners  lettuce  (Martin  et  al.  1951). 

In  Michigan,  breeding  Chipping  Sparrows  feed  on  a 
greater  diversity  of  insects  and  seeds  in  summer  than  in 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


spring  (Evans  1964).  The  young  are  fed  mostly  on  insects, 
and  the  vegetable  matter  they  consume  is  usually  leaf  or 
stem  tissue  or,  rarely,  seeds.  Adults  feed  the  young  many 
lepidopteran  larvae  and  spiders,  which  adults  themselves 
seldom  eat.  Adults  also  feed  the  young  more  rapid-flying 
insects  and  sluggish  larvae  than  they  consume  themselves; 
both  adults  and  young  eat  ground-dwelling  insects  and  in 
the  same  proportion.  The  types  of  food  the  young  consume 
suggest  that  in  searching  for  food  for  young,  adult  Chip- 
ping Sparrows  spend  less  time  on  the  ground  and  more 
time  in  active  flight  or  in  the  higher  strata  of  vegetation. 

Marin  Breeding  Distribution 

During  the  adas  period,  Chipping  Sparrows  were  most 
numerous  and  widespread  in  central  Marin  County  where 
edge  habitats  predominate.  They  were  sparse  or  absent  in 
densely  forested  areas  on  moist  coastal  ridges,  in  grassland 


areas  on  Point  Reyes  and  near  Tomales,  and  in  a  relatively 
broad  strip  along  the  eastern  urban  corridor  and  bayshore. 
Representative  breeding  localities  were  Synanon  Ranch, 
Walker  Creek  (NY  5/15/82  -DS);  the  south  side  of 
Nicasio  Reservoir  (NB  7/6/82  — DS);  and  Rock  Springs, 
Mt.  Tamalpais  (NB  5/19/76  -DS). 

Historical  Trends/Population  Threats 

Historically,  Chipping  Sparrows  have  likely  increased  in 
California,  as  they  have  in  the  East,  as  logging  and  clearing 
of  woodlands  and  forests  have  provided  additional  edge 
and  open  habitats  (Stull  1968).  From  1968  to  1989, 
however,  for  unknown  reasons,  population  levels  of  Chip- 
ping Sparrows  decreased  on  Breeding  Bird  Surveys  in 
California  (Robbins  et  al.  1986,  USFWS  unpubl.  analyses). 


Like  other  songbirds,  young  Chiding  Sparrows  avoid  fouling  the  nest  by  depositing  fecal  sacs  which  the  parents  carry  away. 

Photograph  b^  Jan  Tait. 


375 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


BLACK-CHINNED  SPARROW   Spizella  atrogularis 


An  irregular  summer  resident  from  at 

^r1*"^-^         ^                  ff~^ 

least  early    May  through  late  Jul. 

J  V^V ■  j£r 

A  very  rare,  very  local  breeder;  overall 

r-Vv-n 

-^V\3cvAa  \^K^<\^k\^\' 

breeding  population  very  small. 
Recorded  in  5  (2.3%)  of  221  blocks. 

Or^P\f^Vi0?^V\^>^CA 

VnV 

^<X^^K\ 

O    Possible        =        0  (0%) 

/VMVT    \^\     Jl&!s£/>--  X^+r-.  \^^~'\^*\     V--^*^ 

C    Probable      =        5  (100%) 

Xr^V^^^S^r^^pr^v 

•    Confirmed  =        0   (0%) 

FSAR  =1          OPI  =  5         CI  =  2.00 

Ecological  Requirements 

Black-chinned  Sparrows  inhabit  a  wide  variety  of  primarily 
arid  brushland  habitats  in  the  western  United  States.  In 
Marin  County,  birds  irregularly  occupy  chaparral  vegeta- 
tion and,  to  a  lesser  extent,  coastal  sage  scrub.  Typical  plant 
species  in  suitable  chaparral  habitat  include  chamise,  scrub 
oak,  and  several  species  of  ceanothus  and  manzanita, 
whereas  coyote  brush  and  coastal  sage  are  prevalent  in 
suitable  coastal  scrub  habitat.  All  habitats  occupied  by 
Black-chins  have  the  following  characteristics:  (1)  shrub 
composition  is  a  mixture  of  several  species;  (2)  shrub  cover 
is  moderate  to  dense,  but  the  canopy  usually  has  openings 
exposing  either  the  soil  or  small  rock  outcrops;  (3)  the 
vegetation  is  fairly  young  and  is  not  a  decadent  stand  that 
has  not  burned  for  a  long  period;  (4)  trees,  large  shrubs, 
or  boulders  are  scattered  throughout  breeding  territories 
and  are  used  as  song  perches;  (5)  topography  is  gendy  to 
steeply  sloping  hillsides;  and  (6)  the  hillside  is  relatively  dry 
and  frequendy  south  facing. 

The  typical  nest  of  a  Black-chinned  Sparrow  is  a  cup 
composed  on  the  exterior  of  dry  grasses  and  possibly  a  few 
weed  stems.  The  interior  usually  is  lined  with  fine  grasses, 
shredded  plant  fibers,  hair,  or  a  few  feathers.  Nest  structure 
has  been  described  as  compact  (Dawson  1923)  or  "some- 
times fairly  compact  but  usually  of  rather  loose  construc- 
tion" (Newman  1 968).  The  nest  generally  is  placed  out  of 
view  in  the  interior  branchwork  of  a  large  shrub  and  from 
0.5  to  4.0  feet  above  the  ground  (Pough  1957). 

The  Black-chinned  Sparrow  is  one  of  the  least  studied 
sparrows  in  North  America,  and  little  is  known  about  its 
foraging  habitats  and  diet.  Grinnell  and  Miller  (1944) 

376 


reported  that  foraging  birds  moving  through  the  brush  fly 
near  the  ground,  through  alleyways,  and  over  bushtops. 
However,  nothing  is  known  about  the  microhabitat(s)  in 
which  Black-chins  forage  or  the  extent  of  seasonal  variation 
in  their  foraging  habits.  Presumably,  they  eat  seeds,  fruits, 
and  insects  like  most  other  sparrows,  and  the  proportion 
of  insects  in  the  diet  is  higher  in  the  breeding  season.  The 
only  direct  observations  of  their  food  items  have  been 
sightings  of  individuals  carrying  insects,  presumably  to 
nesdings  (Johnson  et  al.  1948,  Hardy  1949). 

Marin  Breeding  Distribution 

Black-chinned  Sparrows  "invade"  Marin  County  at  irregu- 
lar intervals  and  during  these  "invasions"  are  usually 
reported  for  two  to  dtree  consecutive  years  as  either  rare 
migrants  or  as  a  rare  breeding  species.  Records  from 
Palomarin  and  the  Carson  Ridge/Pine  Mountain  area  give 
a  good  indication  of  the  frequency  of  "invasions,"  since 
intensive  censuses  of  landbirds  in  coastal  scrub  have  been 
conducted  annually  at  Palomarin  since  1972  and  Carson 
Ridge  has  been  checked  most  years  from  1 976  until  at  least 
the  mid-1 980s.  The  dearth  of  records  from  other  sites  is 
likely  a  result  of  limited  observer  coverage. 

The  first  records  for  the  county  were  of  up  to  six  singing 
males  at  PRBO's  Palomarin  field  station  from  1 7  May  1972 
through  at  least  June  of  that  year.  Breeding  was  confirmed 
diere  by  the  presence  of  a  nest  with  young  1.2  feet  up  in  a 
coastal  sage  bush  from  4  to  10  June  1972  (RMS).  Subse- 
quendy,  birds  were  recorded  singing  at  Palomarin  from  18 
to  24  May  1973  and  on  15  May  1974,  but  apparendy  they 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


did  not  remain  to  breed.  Black-chins  next  appeared  at 
Palomarin  in  1984,  when  a  male  and/or  female  were 
present  from  1 5  May  to  at  least  4  July,  and  two  nests  were 
discovered.  One  was  found  empty  (preyed  upon  or  aban- 
doned) 23  inches  up  in  a  coastal  sage  bush  on  15  June. 
The  other  was  located  12  inches  up  in  a  sticky  monkey 
flower  bush  and  was  followed  from  nest  building  on  12 
June  until  4  July,  when  the  young  were  found  dead  and  the 
nest  abandoned.  Both  nests  were  at  the  interface  between 
mature  and  disturbed  south-facing  coastal  scrub  domi- 
nated by  coastal  sage  and  sticky  monkey  flower.  A  singing 
bird  at  Laguna  Ranch,  PRNS,  on  4  June  1972  (AP)  repre- 
sents the  only  record  for  coastal  scrub  away  from  the 
Palomarin  site. 

The  Carson  Ridge/Pine  Mountain  area  has  been 
another  focus  for  recent  Marin  records  since  Black-chins 
were  discovered  there  in  1976.  A  singing  male  was 
recorded  there  from  27  May  to  13  June  1976  and  on  13 
May  1977  (DS).  One  bird  was  there  on  6  May  1984,  and 
nesting  was  confirmed  with  the  observation  of  a  fledgling 
begging  food  from  a  female  on  23  July  1984  (DT  et  al.). 
One  to  two  birds  were  recorded  there  from  18  April  to  26 
June  1985  (DT  et  al.)  and  two  on  22  May  1986  (DAH). 

Two  birds  were  detected  aurally  on  Big  Rock  Ridge  on 
17  May  1980  (PSh  et  al.)  and  also  sometime  in  May  1981 
(PCo). 

Historical  Trends/Population  Threats 

Like  most  aspects  of  the  natural  history  of  Black-chinned 
Sparrows,  little  is  known  about  population  status.  Nearly 
all  authors  classify  Black-chins  as  rare,  erratic,  and  locally 
distributed  in  their  California  range  (e.g.,  G&.M  1944, 
Roberson  1985),  and  our  ability  to  understand  population 


trends  is  confounded  by  these  characteristics.  For  example, 
the  Black-chinned  Sparrow  was  unrecorded  in  Marin 
County  early  in  this  century  (Mailliard  1900,  SckP  1933, 
G&M  1 944),  at  a  time  of  limited  observer  coverage.  We 
now  know,  as  noted  above,  that  the  species  currendy 
occurs  only  irregularly  in  Marin,  even  in  areas  with  contin- 
uous observer  coverage.  Since  the  first  half  of  this  century, 
the  known  breeding  range  of  Black-chinned  Sparrows  has 
continually  expanded  northward  along  the  eastern  and 
western  edges  of  the  Central  Valley.  Grinnell  and  Miller 
(1944)  reported  breeding  records  as  far  north  as  Contra 
Costa  County  on  the  western  edge  and  Mariposa  County 
on  the  eastern  edge.  More  recent  records  have  confirmed 
or  strongly  suggested  breeding  at  scattered  sites  ringing  the 
northern  end  of  the  Sacramento  Valley  in  Lake,  Glenn, 
Trinity,  and  Butte  counties  (ABN).  This  increase  in  known 
range  could  be  interpreted  as  a  true  range  expansion  in  the 
last  40  years,  but  it  much  more  likely  indicates  better 
coverage  by  observers  over  a  longer  period.  On  the  other 
hand,  occupancy  of  the  northern  reaches  of  the  range 
undoubtedly  is  highly  erratic  and  might  be  restricted  to 
"invasion"  years.  Populations  of  Black-chinned  Sparrows 
decreased  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989,  despite  relative  stability  from  1980  to  1989 
(USFWS  unpubl.  analyses).  Because  of  the  erratic  nature  of 
this  species,  less  confidence  should  be  placed  in  these 
trends  than  in  those  for  most  species.  Bailey  et  al.  (1987) 
speculated  that  the  erratic  nature  of  Black-chinned  Sparrow 
populations  is  a  response  to  dry  conditions,  but  the  factors 
controlling  the  distribution  and  abundance  of  this  species 
have  not  been  investigated  and  remain  unknown. 

A.  SIDNEY  ENGLAND 


377 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


LARK  SPARROW    Chondestes  grammacus 


A  year-round  resident. 

A  common,  fairly  widespread  breeder; 
overall  breeding  population  fairly  large. 

Recorded  in  124  (56.1%)  of  221 
blocks. 


O  Possible 
O  Probable 
W    Confirmed 


20  (16%) 
42  (34%) 
62   (50%) 


FSAR  =  4       OPI  =  496        CI  =  2.34 


Ecological  Requirements 

In  Marin  County,  this  handsome  sparrow  is  at  home  in 
sparse  to  moderately  dense,  relatively  arid  grasslands.  Lark 
Sparrows  are  edge  species,  though.  They  also  need  the 
relief  of  trees,  bushes,  or  rock  outcrops  for  song  perches, 
cover,  and  sometimes  nest  sites.  Breeding  birds  are  seldom 
found  in  expansive  grasslands  without  these  features.  In 
Marin,  Lark  Sparrows  most  commonly  inhabit  grasslands 
bordering  oak  savannah,  oak  woodland,  and  mixed  ever- 
green forest. 

Lark  Sparrows  place  their  nests  in  shallow  depressions 
in  the  ground  (usually  but  not  always  shaded  by  a  grass 
clump  or  a  lone  broadleaved  plant)  or  in  small  trees  or 
bushes  generally  to  about  7  feet  or,  exceptionally,  to  25  feet 
above  the  ground  (Dawson  1923,  Baepler  1968).  They 
sometimes  locate  them  from  5  to  10  feet  high  in  crevices 
of  cliffs  of  small  rock  mesas  (Markle  1946).  Ground  nests 
are  thick-walled  but  coarsely  built  cups  of  grass  lined  widi 
fine  grasses  or  horsehair.  Elevated  nests  are  sturdy  deep 
cups  of  stout  grasses,  weed  stems,  string,  or  trash  placed 
on  a  foundation  of  twigs  and  lined  widi  fine  grasses, 
horsehair,  or  roodets. 

The  foraging  habits  of  Lark  Sparrows  have  been  little 
studied,  but  they  appear  to  feed  primarily  on  the  ground. 
They  glean  or  pounce  on  insects  on  the  earth  or  on  annual 
vegetation,  or  they  glean  or  pick  seeds  from  the  ground  or 
from  plants.  Birds  feed  singly  or  in  small  flocks  in  the 
breeding  season.  The  diet  in  spring  and  summer  is  about 
equal   parts  of  animal   and  vegetable  matter,   the  latter 


increasing  in  importance  through  fall  to  account  for  about 
98%  of  the  menu  in  winter  (Martin  et  al.  1951).  Grasshop- 
pers are  the  most  important  insect  food,  followed  by 
locusts,  beetles,  and  caterpillars  (Martin  et  al.  1951, 
Baepler  1968).  Vegetable  fare  is  almost  entirely  grass  and 
weed  seeds  and  waste  grain.  Important  seed  plants  for 
California  birds  are  red  maids,  oats,  knotweed,  wheat, 
tarweed,  turkey  mullein,  filaree,  chickweed,  and  pigweed 
(Martin  et  al.  1951). 

Marin  Breeding  Distribution 

During  the  atlas  period,  Lark  Sparrows  were  widespread 
breeders  in  central  Marin  County.  They  were  sparse  or 
absent  on  the  Point  Reyes  peninsula,  in  the  grasslands 
around  Tomales,  and  in  die  lowlands  of  the  eastern  urban 
corridor  and  bayshore.  Representative  breeding  localities 
were  Chileno  Valley  (NE  7/2/82  -DS);  Mt.  Burdell, 
Novato  (NE  5/29/78  -ScQ  NB-NE  4/21-5/9/81  -ITi); 
Carson  Ridge  (FY/FL  6/8/81  -DS);  and  Potrero  Mead- 
ows, Mt.  Tamalpais  (FY/FL  7/6/81  -DS). 

Historical  Trends/ Population  Threats 

Litde  historical  information  is  available,  but  Lark  Sparrow 
populations  were  relatively  stable  on  Breeding  Bird  Sur- 
veys in  California  from  1968  to  1989  (USFWS  unpubl. 
analyses). 


378 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


SAGE  SPARROW  Amphispiza  belli 


xv3M\ 

^^-^    \             jrv 

A  year-round  resident;  numbers  perhaps 
depressed  from  Oct  through  Mar. 

An  uncommon,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  4  (1.8%)  of  221  blocks. 

^\^CV^V$^^^cv-V^cA 

O    Possible        =        0  (0%) 

©    Probable       =         3   (75%) 

<rf'\  !'^<^i\<^'y3r\      JK""\     y<r\     Jr^X      \^7 

•    Confirmed  =         1    (25%) 

FSAR  =2          OPI  =  8         CI  =  2.25 

Ecological  Requirements 

In  Marin  County,  the  Sage  Sparrow  is  a  rare  resident  in 
stands  of  relatively  dry  chaparral  brushlands.  As  the  name 
implies,  Sage  Sparrows  inhabit  stands  of  big  sagebrush 
(Artemisia  tridentata);  this  is  the  case  for  most  interior 
races,  but  not  for  the  one  that  breeds  in  Marin  County  and 
the  rest  of  coastal  California  (A.  b.  belli,  formerly  recog- 
nized as  a  separate  species  called  Bell's  Sparrow).  This  race 
typically  occupies  relatively  homogeneous  stands  of  chap- 
arral vegetation  dominated  by  chamise  (Adenostoma  fasci- 
culatum^.  All  ages  of  chamise  chaparral  may  be  used  by 
Sage  Sparrows,  but  the  birds  occur  in  highest  numbers  in 
relatively  young,  vigorous  stands  recovering  from  recent 
fire  and  with  little  accumulated  dead  material. 

Sage  Sparrows  usually  build  a  well-concealed  cup  nest 
placed  less  than  three  feet  above  the  ground  in  a  crotch 
between  shrub  branches  (Miller  1968).  The  nest  occasion- 
ally may  be  placed  in  a  shallow  depression  on  the  ground 
beneath  a  shrub.  Typical  cup  nests  are  composed  of  small 
twigs  and  dry  stalks  of  grasses  and  weeds  and  are  lined  with 
fine  dry  plant  material,  shredded  bark,  hair,  and  occasion- 
ally feathers. 

While  foraging,  the  Sage  Sparrow  is  a  ground  dweller 
that  gleans  for  insects  and  seeds  on  the  ground,  in  leaf 
litter,  and  by  reaching  up  from  the  ground  into  the  lower 
portions  of  shrubs  (G&.M  1944,  Miller  1968,  Ryser 
1985).  It  may  scratch  the  leaf  litter  in  towhee  fashion,  but 
this  is  not  common  (Miller  1968).  Another  unusual  forag- 
ing technique  is  gleaning  insects  at  the  tops  of  chaparral 
shrubs  three  to  five  feet  above  the  ground.  In  early  spring, 
the  tips  of  chamise  branches  are  young  and  succulent  and 


may  support  relatively  dense  populations  of  herbivorous 
insects,  such  as  inchworms.  During  this  short  period, 
these  insects  may  be  the  dominant  item  in  the  Sage 
Sparrow's  diet,  and  birds  may  regularly  be  seen  foraging 
well  above  the  ground  (A.S.  England  unpubl.  data).  How- 
ever, foraging  Sage  Sparrows  are  relatively  shy  birds,  typi- 
cally observed  moving  about  quickly  on  the  ground 
beneath  or  between  shrubs  searching  for  food. 

The  Sage  Sparrow  diet  includes  seeds,  insects,  and 
succulent  vegetation.  Seeds  are  the  most  important  food 
during  winter  (Martin  et  al.  1951,  Miller  1968,  A.S. 
England  unpubl.  data).  In  spring,  the  diet  includes  seeds 
but  is  dominated  by  insects  such  as  beedes,  caterpillars, 
ants,  spiders,  and  grasshoppers  (Miller  1968,  Rotenberry 
1980,  A.S.  England  unpubl.  data).  Succulent  vegetation 
and  insects  are  important  dietary  components  during  the 
hot  months  of  summer  and  fall  when  free  water  may  not 
be  accessible  (Moldenhauer  &.  Wiens  1970).  The  mois- 
ture in  these  foods  enables  Sage  Sparrows  to  inhabit  dry 
sites  without  available  surface  water  (Moldenhauer  & 
Wiens  1970,  Weadiers  1983). 

Marin  Breeding  Distribution 

Marin  County's  breeding  Sage  Sparrows  are  restricted  to 
stands  of  chamise-dominated  chaparral,  which  occur  on 
relatively  xeric  south-facing  slopes  of  interior  ridges.  The 
ridges  that  support  chaparral  vegetation  generally  have 
thin,  dry  soils,  in  part  because  of  the  limited  penetration 
inland  of  coastal  summer  fog.  This  moisture  is  blocked 

379 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


either  by  intervening  ridges  or  by  an  inversion  layer  of 
warmer  air  that  generally  keeps  the  tops  of  higher  peaks 
such  as  Mount  Tamalpais  fog-free. 

During  the  atlas  period,  all  breeding  season  sightings 
were  from  the  Carson  Ridge/Pine  Mountain  area.  Breed- 
ing was  confirmed  there  with  the  observation  of  nest 
building  on  19  April  1980  (Kello)  and  a  nest  under 
construction  one  foot  up  in  a  bush  on  25  May  1980  (DSi). 
Formerly,  Sage  Sparrows  were  reported  from  "Nicasio" 
and  from  Mount  Tamalpais,  where  nesting  was  confirmed 
on  the  east  slope  west  of  Larkspur  by  the  observation  on  2 
June  1917  of  "several  young  just  leaving  the  nest  and 
hardly  able  to  fly"  (Squires  1917);  they  were  reported  also 
from  the  summit  of  Mount  Tamalpais  (G&.W  1927).  A 
record  of  a  Sage  Sparrow  was  reported  without  comment 
in  a  list  of  birds  sighted  on  a  14  March  1926  Audubon 
Society  trip  to  Point  Bonita  (Gull  8,  No.  4);  it  was  subse- 
quendy  cited  by  Stephens  and  Pringle  (1933)  and  Grinnell 
and  Miller  (1944),  with  the  suggestion  of  residence  or 
breeding.  This  record  is  anomalous  and  may  pertain  to  an 


early  migrant;  the  brushy  habitat  in  that  area  consists  of 
coastal  scrub,  in  which  there  is  no  evidence  of  breeding 
Sage  Sparrows  in  the  county. 

Historical  Trends/ Population  Threats 

The  trends  in  Sage  Sparrow  populations  on  the  California 
coast  are  unclear.  Long-term  fire  suppression  may  cause 
populations  to  be  reduced  or  eliminated  locally,  but  the 
species  will  return  shortly  following  either  natural  or 
human-caused  fires.  Perhaps  the  greatest  threat  to  the 
species  is  extensive  residential  development  of  chaparral 
hillsides,  particularly  in  southern  California.  Sage  Sparrow 
populations  increased  on  the  whole  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989,  but  less  so  from 
1980  to  1989  (USFWS  unpubl.  analyses).  Nevertheless,  the 
Bell  s  Sage  Sparrow  (A.  b.  belli)  is  currendy  a  Candidate 
(Category  2)  for  federal  listing  as  Threatened  or  Endan- 
gered (USFWS  1991). 

A.  SIDNEY  ENGLAND 


SAVANNAH  SPARROW    Passerculus  sandwichensis 


A  year-round  resident. 

A^^\^r^>^       \             w~v 

A  very  common,  fairly  widespread 

~t<k£^V&k^^^ 

breeder;  overall  breeding  population 

fairly  large. 

JV-\  ©iv<\  °J^\  f>X^\*>;\^\     \^K  V-^r    \z*^\ 

Recorded  in  115  (52.0%)  of  221 

blocks. 

V"\i*->C\©  j^\  •A-"\  ©  V-'V©  \^\      \^\       \S>*\        \ 

O    Possible        =       23   (20%) 
©    Probable      =      50  (44%) 

w\^  \  *>  v-^  \ <->  v^\  •'-W--A  m  \^*\---  \^\      \  x\'-     \ 

^~ 

•    Confirmed  =      42   (36%) 

©J^r\© Jv-^V  \^\*\^\':^^>\     \^\    \^X'  y — 

'^v  ®£V"\  ©  J^\  QJ^ZS.  •  \>Cfh>  Ut  Vcja   Ax 

FSAR  =  5       OPI  =  575       CI  =  2.16 

Jr^             ^^^^^^^^S^^^^ 

Q& 

"^   /                                                            ^S^rS     ^P*^)A^^©Wa©  >■ 

Ecological  Requirements 

In  Marin  County,  the  insecdike  song  of  the  Savannah 
Sparrow  can  be  heard  rising  from  ground  level  on  coastal 
hills  clothed  in  grassland  and  also  in  lowland  coastal  and 
bayshore  salt  marshes.  The  grasslands  this  species  fre- 
quents are  relatively  moist  ones  in  the  zone  of  persistent 
summer  fogs.  They  generally  have  scattered  forbs  and  a 
fairly  dense  ground  layer  of  grasses  and  accumulated  litter 
(Wiens  1969).  Moisture  is  required  only  as  it  influences 

380 


the  density  of  low  vegetation,  and  birds  will  breed  in  drier 
upland  sites  if  their  vegetation  requirements  are  met. 
Unlike  saltmarsh-breeding  Song  Sparrows,  Savannah 
Sparrows  are  found  nesting  in  the  older  and  higher  parts 
of  the  marsh  (5-10  ft.  above  mean  sea  level),  where 
pickleweed  less  than  one  foot  high  grades  into  moist 
grassland  (Marshall  1948;  Johnston  1956a,  1968a).  In 
Marin's   moist  upland   grasslands,   Savannah   Sparrows 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


overlap  broadly  with  Grasshopper  Sparrows.  Habitat  dif- 
ferences between  the  species  are  subde,  but  Savannah 
Sparrows  generally  prefer  shorter  and  less  diverse  grass- 
lands than  do  Grasshopper  Sparrows  (see  account). 

Savannah  Sparrow  nest  sites  tend  to  be  in  denser  cover 
and  to  have  much  more  litter  associated  with  them  than 
those  of  the  Grasshopper  Sparrow  (Wiens  1969,  1973). 
Savannahs  usually  conceal  their  nests  inside  grass  tussocks 
or  under  matted  grasses  or  weeds.  Nineteen  of  27  nests  in 
Wisconsin  were  either  partially  domed  over  or  were  placed 
under  overhanging  litter;  14  (75%)  of  these  opened  north 
or  east.  Although  birds  of  some  other  races  may  occasion- 
ally place  their  nests  in  small  bushes  or  cacti  up  to  four  feet 
from  the  ground  (Austin  1968),  Savannahs  on  the  central 
California  coast  (P.  s.  alaudinus)  invariably  place  them  on 
the  ground  or  raise  them  up  to  about  four  inches  on 
supporting  grass  or  pickleweed  (Johnston  1968a).  Even  in 
tidal  marshes,  birds  place  most  nests  direcdy  on  the 
ground.  Grassland  nests  are  often  sunk  in  depressions  at 
the  base  of  grass  clumps  and  are  coarsely  made  cups  of 
dried  grass  and  fine  weed  stems  lined  with  finer  grasses 
and  horsehair  (Austin  1968).  Saltmarsh  nests  are  tighdy 
formed,  relatively  deep  cups  composed  of  dead  grass  stems, 
pickleweed  stalks,  hair,  and  occasionally  eelgrass  (Zostera). 

Savannah  Sparrows  forage  primarily  on  the  ground  in 
low  grass  or  marsh  cover.  Generally  they  feed  more  around 
grass  clumps  and  less  in  open  unvegetated  areas  dian  do 
Grasshopper  Sparrows  (Wiens  1973).  In  salt  marshes, 
Savannahs  will  forage  on  marsh  mud  and  in  tangles  of  salt 
grass,  pickleweed,  and  gumplant.  They  usually  glean  seeds 
from  the  ground  or  occasionally  pick  them  from  grass 
stems.  Birds  move  by  hopping,  and  they  may  scratch  the 
ground  like  towhees  do.  Savannah  Sparrows  generally 
glean  insects  from  the  ground  or  herbaceous  vegetation, 
but,  infrequendy,  birds  will  jump  in  the  air  after  them 
(Austin  1968).  Although  the  diet  of  upland  birds  is  about 
equally  divided  between  plant  and  animal  food,  Savannah 
Sparrows  are  generally  more  insectivorous  than  other  spar- 
rows (Martin  et  al.  1951,  Austin  1968).  Animal  matter 
peaks  at  about  74%  of  the  menu  in  summer  (n  =  39)  and 
drops  to  as  little  as  8%  in  winter  (n  =  118)  (Martin  et  al. 
1951).  Animal  food  may  be  of  greater  importance  in  winter 
in  tidal  marshes,  where  it  is  more  readily  available.  Import- 
ant animal  prey  of  upland  birds  are  beedes,  caterpillars, 
grasshoppers,  ants,  true  bugs,  flies,  miscellaneous  insects, 
spiders,  and  snails.  In  salt  marshes,  intertidal  invertebrates 
such  as  small  crustaceans,  crabs,  snails,  and  other  gastro- 
pods are  important  foods.  Vegetable  matter  is  almost 
exclusively  grass  and  weed  seeds.  Seed  plants  important  to 
these  sparrows  in  California  are  knotweed,  turkey  mullein, 
pigweed,  oats,  canarygrass,  annual  bluegrass,  rabbitfoot 


grass,  ryegrass,  miners  lettuce,  chickweed,  bromegrass, 
barley,  red  maids,  sheep  sorrel,  and  tarweed  (Martin  et  al. 
1951). 

Marin  Breeding  Distribution 

During  the  adas  period,  Savannah  Sparrows  bred  widely 
in  Marin  County's  moist  coastal  upland  grasslands  in  the 
fog  zone,  where  they  overlapped  broadly  with  Grasshopper 
Sparrows.  They  were  of  local  occurrence  in  salt  marshes  on 
the  outer  coast  and  along  the  bayshore  near  Novato.  They 
were  sparse  or  absent  as  breeders  in  the  somewhat  drier 
grasslands  in  the  eastern  portion  of  the  county  and  in 
bayshore  marshes  south  of  Novato.  Representative  nesting 
locations  were  Abbott's  Lagoon  (NY  4/19/82  — KeHo, 
DS);  Hall  Ranch,  Point  Reyes  (NE  6/11/81  -ECB,  DS); 
former  Synanon  Ranch,  Walker  Creek  (NE  5/15/82  — 
DS);  end  of  Clark  Rd.,  east  side  Tomales  Bay  (NY  7/7/82 
-DS);  and  Bolinas  Ridge  above  Olema  (NY  5/11/77 
-DS). 

Historical  Trends/  Population  Threats 

Grinnell  and  Miller  (1944)  gave  no  hint  of  a  population 
decline  of  this  species,  but  the  population  breeding  in  salt 
marshes  must  have  declined  dramatically  with  the  historic 
loss  of  about  60%-95%  of  the  tidal  marshlands  of  the  San 
Francisco  Bay  system  (Nichols  6k  Wright  1971,  Josselyn 
1983).  Walton  (1978)  estimated  that,  historically,  Song 
Sparrow  populations  breeding  in  marshlands  of  the  San 
Francisco  Bay  system  had  been  reduced  by  50%- 7 5%, 
primarily  from  habitat  loss.  Saltmarsh-breeding  Savannah 
Sparrows  were  probably  reduced  to  an  even  greater  extent, 
since  they  inhabit  the  upper  reaches  of  the  marshes  more 
subject  to  being  filled,  diked,  or  developed.  The  Belding's 
Savannah  Sparrow,  breeding  in  southern  California  salt 
marshes,  remains  on  the  state  Endangered  list,  though  its 
numbers  have  increased  recendy  (CDFG  1991a). 

Upland  breeding  populations  of  Savannah  Sparrows 
have  fared  better,  and  they  are  currendy  numerous  in  moist 
grassland.  It  should  be  noted  diat  the  structure  of  our 
grasslands  has  been  drastically  altered,  from  domination 
by  native  bunch  grasses  to  domination  by  introduced 
Mediterranean  annuals  (Shuford  6k  Timossi  1989;  see 
Plant  Communities  section  this  volume).  The  moist  coastal 
grasslands  where  Savannah  Sparrows  are  numerous  today 
still  retain  much  of  the  native  flora.  Drier  inland  grass- 
lands, on  the  other  hand,  are  now  almost  entirely  com- 
posed of  introduced  annual  grasses.  Have  these  changes 
had  an  effect  on  populations  of  Savannah  Sparrows  or 
other  grassland  species?  Probably,  but  we  don't  know  to 
what  extent.  Savannah  Sparrow  populations  were  relatively 
stable  on  Breeding  Bird  Surveys  in  California  form  1968 
to  1989  (USFWS  unpubl.  analyses). 


381 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


GRASSHOPPER  SPARROW    Ammodramus  savannarum 


A  summer  resident  from  early  Apr 

x^J^C^-s-       k          jr^s 

through  late  Sep. 

5© \-*\ ''O.J^A  *>- A^\©!>--^             ■■       _;-  ^~A     \><V^j^ 

A  fairly  common,  fairly  widespread 

^A  o  \><\ ■■'  \^\  ©  \-^\  « A^A  ©  \^\    a-"A    v/a  r5'" 

Va  ®A<\  ®A<\  cJr\  •''A^A  o  A-^\  °\^\    Vr\ 

ca  .  V^m  * \^\  © Ar^\    \^\  ©Ar^\    A-^\    o^y    ^A 

- 

breeder;  overall  breeding  population 
small. 

\<\svrS  X  a  ^V^T\  ©  At-^\  •  \-^\    V-^V    ><lA ■"  '\f*\     \^^  \ 

^'V©.><X,\-'^  ©3r^^®  V"^©  Y-'-'A        \^\       V-^\ 

Recorded  in  96  (43.4%)  of  221  blocks. 
O    Possible        =       14  (15%) 

3-/^ 

C    Probable      =      66  (69%) 

Ji<^>^    ^^<^©>--^  eA^\.*^lr\  jV^ 

Q^kv^ 

•    Confirmed  =       16   (17%) 
FSAR  =  3        OPI  =  288        CI  =  2.02 

©                                        ^^IVx^-^^e  V>Te  VA  \\ 

3^>                             \jo/      ^-<^a>-a"\>i 

Ecological  Requirements 

This  phantom  grassland  waif  inhabits  Marin  County's 
moist  coastal  prairie  grasslands,  especially  where  native 
bunch  grasses  are  prevalent.  Along  the  immediate  coast, 
Grasshopper  Sparrows'  typical  habitat  has  scattered 
clumps  of  bracken  ferns  and  the  low-growing  form  of 
coyote  bush  (Baccharis  pilularis);  these  may  be  absent,  and 
they  generally  drop  out  toward  the  county's  interior.  Over- 
all, the  species  prefers  short  to  middle-height  grasslands 
(Smith  1963,  1968;  Whitmore  1981).  These  generally 
have  a  fairly  thick  but  low  cover  of  grasses  and  a  variety  of 
taller  forbs  and  usually  occur  on  dry  upland  sites  (Wiens 
1969).  "Optimum"  habitat  of  the  eastern  subspecies  (A.  s. 
pratensis)  is  about  28%  grass  cover,  73%  litter  cover,  and 
28%  bare  ground  (Whitmore  1979b). 

Grasshopper  Sparrows  overlap  broadly  in  habitat  use 
with  Savannah  Sparrows  here  in  Marin  County  and  else- 
where in  the  two  species'  range.  Compared  with  other 
grassland  breeders,  both  species  frequent  generally  inter- 
mediate conditions  along  a  gradient  of  vegetation  height, 
density,  and  litter  (Wiens  1969),  yet  studies  of  eastern 
birds  have  shown  subde  habitat  differences  between  the 
two  species.  These  distinctions  are  greatest  at  the  time 
when  birds  initially  occupy  breeding  areas,  but  habitat 
overlap  increases  seasonally  widi  vegetative  growth  (Whit- 
more 1979a).  Compared  with  Savannah  Sparrows,  Grass- 
hopper Sparrows  occupy  grasslands  with  less  grass  cover 
and  more  bare  ground  but  widi  greater  "effective  grass 
height,"  vertical  and  horizontal  diversity,  vertical  and  over- 
all grass  density,  and  forb  cover  (Wiens  1973,  Whitmore 
1979a).  The  frequent  reference  to  the  semicolonial  nature 

382 


of  the  Grasshopper  Sparrow  may  reflect  individuals  clump- 
ing in  patches  of  structurally  suitable  grassland  rather  than 
any  social  tendencies  of  the  species.  Grasshopper  Sparrows 
also  tend  to  sing  from  higher  perches  than  do  Savannahs 
(Wiens  1969,  1973). 

Although  Grasshopper  Sparrow  nests  tend  to  be  situ- 
ated in  more  open  cover  than  those  of  Savannah  Sparrows, 
they  are  usually  well  concealed  in  depressions  at  the  base 
of  grass  clumps  with  the  rim  level  at  or  slightly  above 
ground  level  (Smith  1968,  Wiens  1973,  Whitmore  1981). 
Wiens  (1969)  found  15  nests  in  Wisconsin,  all  of  which 
were  domed  over  to  some  extent,  and  most  (64%)  faced 
north  or  northeast.  Grasshopper  Sparrow  nest  sites  tend 
to  have  less  litter  and  somewhat  taller  and  more  widely 
dispersed  forbs  than  those  of  Savannah  Sparrows  (Wiens 
1969).  Nests  are  built  of  stems  and  blades  of  grass,  lined 
with  fine  grass,  roodets,  and  occasionally  horsehair  and  are 
usually  arched  or  domed  over  at  the  back,  giving  an 
ovenlike  appearance. 

Little  has  been  written  on  the  foraging  habits  of  Grass- 
hopper Sparrows  but  die  birds  apparendy  hop  and  run 
through  low  herbage  gleaning  and  picking  insects  and 
seeds  from  the  ground  or  from  low  in  the  vegetation. 
Grasshopper  Sparrows  forage  more  frequendy  in  open 
unvegetated  areas  than  do  Savannah  Sparrows  (Wiens 
1973).  Continentwide,  the  diet  of  the  Grasshopper  Spar- 
row from  February  to  October  is  about  63%  animal  and 
37%  vegetable  (Judd  in  Smith  1968,  n  =  1 70).  The  animal 
portion  of  the  diet  decreases  from  60%  in  spring  and 
summer  (n  =  1 26)  to  about  29%  in  fall  (n  =  1 7)  (Martin  et 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


al.  1951).  Animal  fare  is  primarily  grasshoppers,  beetles, 
caterpillars,  ants,  and  true  bugs,  along  with  a  few  spiders, 
snails,  and  miscellaneous  invertebrates.  The  vegetable 
menu  includes  the  seeds  of  grasses,  weeds,  and  sedges. 
Important  seed  plants  in  California  in  fall  are  knotweed, 
campion,  oats,  and  pigweed  (Martin  et  al.  1951). 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Grasshopper  Sparrow  bred 
widely  in  Marin  County's  moist  coastal  prairie  grasslands, 
primarily  within  the  zone  of  frequent  summer  fog  toward 
the  immediate  coast.  Its  distribution  overlapped  remark- 
ably well  with  that  of  the  Savannah  Sparrow,  except  in  salt 
marshes,  where  the  Grasshopper  Sparrow  was  absent.  In 
contrast  to  Marin,  for  the  south  San  Francisco  Bay  region, 
Sibley  (1952)  noted  that  most  breeding  records  were  from 
the  dry  inner  Coast  Range,  20  to  25  miles  from  the  coast. 
This  may  have  reflected  observer  coverage,  because  most 
records  of  Grasshopper  Sparrows  for  coastal  northern 
California  counties  in  the  last  two  decades  have  been  from 
the  coastal  slope  and  nearby  ridges  within  about  ten  miles 
of  the  coast  (ABN).  Besides  being  widespread  in  Marin 
County,  Grasshopper  Sparrows  are  also  relatively  numer- 
ous here.  One  observer  recorded  a  minimum  of  1 50  birds 
while  conducting  extensive  adas  surveys  in  the  low  rolling 
hills  of  northern  Point  Reyes  and  east  of  Tomales  Bay  in 
the  spring  and  summer  of  1982  (AB  36:1014).  Represen- 
tative breeding  stations  were  north  of  McClure's  Ranch, 
Point  Reyes  (FY  7/1 3/82  -DS);  old  Cerrini  Ranch  oppo- 
site Cypress  Grove,  east  shore  of  Tomales  Bay  (FY  6/29 
&.  7/20/82  -DS);  off  Marshall-Petaluma  Rd.  near  former 
Synanon  Walker  Creek  Ranch  (NE/NY  6/23/82  -DS); 
and  Bolinas  Ridge  above  Olema  (NE  5/20/78  -ITi, 
RMS). 

Historical  Trends/  Population  Threats 

Until  recendy,  the  Grasshopper  Sparrow  was  considered  a 
rather  uncommon  or  rare  breeding  species  in  California. 
Mailliard  (1900)  reported  it  as  "sparingly  summer  resi- 
dent" in  Marin  County.  Stephens  and  Pringle  (1933)  listed 
it  in  their  "rare  visitant"  category  for  Marin,  but  they 
quoted  mosdy  from  Grinnell  and  Wythe  (1927).  The  latter 
authors  considered  Grasshopper  Sparrows  "rare  .  .  . 
locally"  in  the  San  Francisco  Bay  region,  but  they  did  list 
four  localities  for  the  species  in  Marin  County,  which  up 
to  that  time  had  been  relatively  poorly  explored.  For 
California  as  a  whole,  Grinnell  and  Miller  (1944)  consid- 
ered the  Grasshopper  Sparrow  a  "sparse  and  irregularly 
distributed  resident"  and  "variable  in  occurrence  from  year 
to  year."  Even  recendy,  McCaskie  et  al.  (1979)  considered 
the  species  rare  to  very  uncommon  along  the  California 
coast 


These  reports  are  at  odds  with  what  we  found  in  the 
Marin  County  adas  project,  in  which  the  Grasshopper 
Sparrow  was  recorded  in  over  40%  of  all  the  blocks  in  the 
county,  many  of  which  do  not  have  extensive  grassland. 
This  difference  could  be  due  to  at  least  one  of  three 
reasons:  a  historical  increase  in  the  species;  year-to-year 
variability,  with  the  adas  years  corresponding  to  a  high 
point  in  the  population  cycle;  or  the  much  more  thorough 
coverage  during  the  adas  project. 

Although  formerly  considered  scarce,  Grasshopper 
Sparrow  populations  generally  increased  on  Breeding  Bird 
Surveys  in  California  from  1968  to  1989,  but  were  fairly 
stable  from  1980  to  1989  (USFWS  unpubl.  analyses); 
continentwide,  their  numbers  declined  from  1965  to  1979 
(Robbins  et  al.  1986).  The  Grasshopper  Sparrow  was  on 
the  Audubon  Society  Blue  List  from  1974  to  1986  (Tate 
1986).  Regarding  year-to-year  variability,  some  authors 
have  felt  that  Grasshopper  Sparrow  populations  fluctuate 
markedly  between  years  in  spite  of  available  and  suitable 
habitat  (Smith  1963,  1968).  Others  feel  that  Grasshopper 
Sparrows  choose  patches  of  grassland  with  a  particular 
suite  of  structural  characteristics  along  the  vegetation  con- 
tinuum, perhaps  not  readily  evident  to  the  human  eye.  In 
diis  light,  populations  appear  to  fluctuate  in  response  to 
structural  changes  in  the  grassland  community,  brought 
about  by  succession,  grazing  pressure,  variable  rainfall, 
fires,  and  other  disturbances  (Wiens  1974,  Whitmore 
1979b).  Hence,  populations  may  be  shifting  spatially  to 
take  advantage  of  the  changing  suitability  of  the  habitat, 
with  population  size  fluctuating  to  an  unknown  degree. 
Because  grasslands  are  climax  communities  over  much  of 
California,  grazing  intensity  and  year-to-year  variation  in 
the  highly  seasonal  winter  rainfall  are  the  factors  most 
likely  to  affect  the  structural  characteristics  of  grasslands 
here.  Although  fires  could  have  a  marked  effect  on  grass- 
land structure,  they  are  rare  in  the  moist  coastal  grasslands 
with  bunch  grasses,  where  Grasshopper  Sparrows  are  most 
frequent.  Influxes  of  birds  to  Marin  in  June,  in  some  years 
at  least  Q.G.  Even  &  D.  Shuford  pers.  obs.),  may  reflect 
sparrows  changing  habitat  in  midbreeding  season  in 
response  to  vegetational  changes.  For  example,  these  late- 
arriving  birds  may  represent  a  shift  after  first  nesting 
attempts  from  interior  grasslands,  by  then  parched,  to  the 
still-moist  grasslands  of  the  coastal  fog  zone  (AB  43:534). 

Although  some  variability  in  population  levels  has  been 
noticed  in  Marin  over  the  years  (D.  Shuford  pers.  obs.), 
the  species  is  seen  here  year  after  year  at  many  traditional 
roadside  sites,  for  example  near  Nicasio  Reservoir.  It  was 
not  until  the  adas  years  that  most  of  Marin's  grasslands 
were  first  explored  for  breeding  birds.  Given  the  reliability 
of  the  species  at  traditional  sites  in  prior  years,  it  seems 
unlikely  that  the  greater  extent  of  sightings  during  the  atlas 
years  was  due  to  just  a  coincidental  population  peak  at  that 
time.  It  seems  much  more  likely  that  the  thorough  coverage 

383 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


revealed  the  true  status  of  the  species  as  a  fairly  numerous 
and  widespread  breeder  in  coastal  grasslands.  The  Grass- 
hopper Sparrow  was  almost  "preadapted"  for  being  over- 


looked, since  it  is  a  relatively  inconspicuous  and  weak 
songster  that  dwells  in  a  habitat  typically  infrequendy 
checked  because  of  its  low  bird  diversity. 


9S«? 


Those  intimate  with  the  Grasshopper  Sparrow  know  that  besides  its  typical  insectlike  buzz  it  also,  infrequently,  sings 
a  quiet  but  bubbly  Winter  Wren-lilce  song.    Drawing  by  Keith  Hansen,  1 990. 


384 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


SONG  SPARROW   Melospiza  melodia 


A  year-round  resident. 

A  very  common,  nearly  ubiquitous 
breeder;  overall  breeding  population 
extremely  large. 

Recorded  in  192  (86.9%)  of  221 
blocks. 


O  Possible 
C  Probable 
•    Confirmed 


9  (5%) 

91  (47%) 

92  (48%) 


FSAR  =  5        OPI  =  960        CI  =  2.43 


Ecological  Requirements 

These  perky  sparrows  inhabit  Marin  County's  coastal 
scrub;  salt,  fresh,  and  brackish  marshes;  riparian  groves; 
dense  phases  of  dune  scrub;  and  the  moist  brushy  and 
weedy  edges  of  these  habitats.  Marshall's  (1948)  detailed 
observations  provide  insight  into  the  critical  factors  of 
these  habitats  to  Song  Sparrows.  Coastal  scrub  is  most 
suitable  where  the  growth  is  divided  into  small  clumps  of 
bushes  and  separate  tangles  of  vines;  bordered  by  small 
grasses,  ferns,  and  flowers;  and  separated  by  bare  ground 
that  is  wet.  Song  Sparrows  use  only  the  moist  phases  of 
coastal  scrub.  They  are  absent  where  the  brush  forms  a 
continuous  high  canopy  and  where  it  penetrates  wood- 
lands or  forests  as  an  understory.  In  salt  marshes,  Song 
Sparrows  concentrate  along  the  tidal  sloughs  in  the  taller 
vegetation  of  cord  grass,  pickleweed,  or  gumplant.  They 
avoid  areas  where  the  cord  grass  is  18  inches  or  less  in 
height  and  also  the  broad  belt  of  pickleweed  less  than  a  foot 
tall  in  the  highest  upland  portions  of  the  marsh.  In  both 
salt  and  brackish  marshes,  Song  Sparrows  shun  habitat 
where  the  tidal  flow  is  cut  off  by  diking  and  the  water  is 
stagnant  and  foul,  even  though  the  vegetation  has  the 
growth  form  they  usually  prefer.  In  fresh  or  brackish 
marshes,  Song  Sparrows  prefer  tall  rank  growth  of  cattails 
and  bulrushes,  particularly  along  the  edges  or  where  mixed 
with  a  variety  of  smaller  plants  and  openings.  The  under- 
story growth  of  riparian  habitat  is  important,  as  Song 
Sparrows  are  absent  where  it  is  removed  by  the  grazing  and 
trampling  of  cattle  or  other  factors.  Song  Sparrows  are  also 
absent  from  riparian  that  is  roofed  over  by  large  trees  (e.g., 
at  Muir  Woods  where  redwoods  tower  over  the  riparian), 


even  though  the  riparian  vegetation  shows  no  other 
marked  change  from  that  outside  the  higher  canopy.  Wil- 
lows themselves  limit  Song  Sparrows  when  they  grow  in  a 
continuous  dense  canopy.  Song  Sparrows  avoid  the  more 
open  or  drier  phases  of  dune  scrub  or  areas  where  the 
succulent  vegetation  between  the  lupines  has  been 
removed  by  overgrazing. 

From  these  observations,  Marshall  (1948)  concluded 
that  the  main  habitat  requirements  of  Song  Sparrows  are 
(1)  moderately  dense  vegetation  for  nest  sites,  hiding 
places,  and  concealment  during  most  foraging  (dense  vege- 
tation is  tolerated  if  it  is  somewhat  open  near  the  ground 
because  of  water  flow  or  mammal  runways);  (2)  a  source  of 
standing,  running,  or  tidal  water  or,  in  coastal  scrub  or 
dune  scrub,  constant  moisture  from  fog,  dew,  or  seepage; 
(3)  plenty  of  light  (as  evidenced  by  the  lack  of  Song 
Sparrows  in  moist  brush  under  closed  forest  canopies); 
and  (4)  exposed  ground  or  leaf  litter  for  foraging. 

Song  Sparrows  build  substantial  nest  cups  of  weed 
stems,  grasses,  dead  leaves,  bark  strips,  ferns,  and  twigs. 
They  line  them  with  fine  dry  grasses,  roodets,  and  horse- 
hair or  other  animal  hair  (Dawson  1923,  Austin  1968). 
Song  Sparrows  place  many  of  their  nests  in  depressions  in 
the  ground  under  the  concealing  vegetation  of  grasses, 
weed  stalks,  ferns,  brush  piles,  or  fallen  trees.  They  fre- 
quendy  situate  ground  nests  on  ditch  banks  or  on  low  cliff 
faces.  These  sparrows  often  build  nests  in  low  marsh 
vegetation,  bushes,  and  vine  tangles,  mosdy  below  three 
feet  in  height.  In  San  Francisco  Bay  salt  marshes,  Song 
Sparrows  place  all  their  nests  above  the  ground  in  clumps 

385 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


of  picklewecd,  cord  grass,  salt  grass,  or  gumplant  bushes  to 
avoid  flooding  by  summer  high  tides  (Johnston  1956a). 
The  saltmarsh  vegetation  there  averages  less  than  2  feet 
high,  and  nests  on  the  average  are  elevated  9.5  inches  in 
the  marsh  as  a  whole  and  1 2  inches  in  the  lower  marsh; 
nests  below  5  inches  are  flooded  by  the  tides.  In  the 
Petaluma  Marsh,  vegetation  must  be  at  least  21  inches  high 
to  provide  safety  to  nest  sites  and  nests  (Collins  &.  Resh 
1985).  Nests  there  (often  built  in  suspended  litter)  must  be 
8  inches  high  to  avoid  tidal  flooding.  In  both  upland  and 
saltmarsh  habitats,  nest  height  tends  to  increase  dirough 
the  nesting  season  in  conjunction  with  the  growth  of 
concealing  vegetation  (Nice  1937,  Johnston  1956a,  Austin 
1968).  Less  often,  high  spring  lake  levels  cause  nest  place- 
ment to  be  high  early  in  the  season,  with  a  general  decrease 
in  nest  height  as  water  levels  fall  (Austin  1968).  Infre- 
quendy,  Song  Sparrows  build  nests  in  saplings  or  trees  up 
to  28  feet  from  the  ground  (Austin  1968).  They  commonly 
build  bush  or  tree  nests  in  stranded  flood  debris  and  often 
build  them  over  water.  More  unusual  nest  sites  include 
cavities  in  trees  or  hollow  logs,  in  unoccupied  buildings 
such  as  wood  sheds,  in  nest  boxes,  in  a  roll  of  wire  on  the 
ground,  in  the  side  of  a  paper  wasp  nest  in  a  tree,  and  in 
the  previous  year's  nest  of  a  Swainson's  Thrush  (Nice 
1937,  Austin  1968). 

Song  Sparrows  forage  primarily  on  the  ground.  They 
pick  their  food  from  the  bare  ground  or  leaf  litter  under  or 
at  the  base  of  bushes,  under  twig  or  branch  piles,  along 
runways  beneath  ground  cover  and  pickleweed  mats,  and 
from  floating  marsh  plants  (Marshall  1948,  Austin  1968). 
They  also  search  the  mud,  ooze  or  shallow  water  between 
the  stems  of  marsh  plants,  along  stream,  pond,  or  marsh 
margins,  and  in  the  recesses  beneath  undercut  stream  and 
slough  banks.  In  typical  foraging  bouts,  Song  Sparrows 
progress  slowly  by  short  hops  in  a  jerky  manner  with  the 
head  up,  accompanied  by  wing  and  upward  tail  flicks  and 
punctuated  by  frequent  pecks  at  food  items  (Marshall 
1948,  Johnston  1956a).  When  pursuing  airborne  prey 
reachable  from  the  ground,  they  make  a  rapid  series  of 
hops  with  the  head  and  tail  held  low  or  run  with  die  tail 
elevated  and  wings  half  outstretched.  They  frequendy 
scratch  vigorously  with  both  feet  to  expose  invertebrate  and 
plant  food  within  and  under  the  surface  litter.  Song  Spar- 
rows occasionally  climb  tules  nuthatchlike  to  glean  insects, 
feed  on  caterpillars  high  in  willows,  seize  and  devour 
minnows,  and  flycatch  from  exposed  perches  (Marshall 
1948,  Austin  1968,  Johnston  1968b).  In  British  Colum- 
bia, Smith  (1978)  noted  that  males  flycatch  much  more 
frequendy  than  do  females.  He  suggested  diis  was  a  result 
of  greater  opportunities  afforded  the  males  who  spend 
much  of  their  time  on  high  perches  singing  or  looking  out 
for  intruders.  In  contrast,  females  seldom  use  high 
perches,  often  move  about  inside  dense  thickets,  and 
spend  much  time  incubating.  Additionally,  Song  Sparrows 

386 


feed  finchlike  on  peeled  gumplant  seeds  while  perched  on 
the  top  of  flowering  stalks,  and,  more  frequently  in  the  fall, 
they  feed  on  cord  grass  flowers  and  the  fleshy  fruits  and 
seeds  of  pickleweed  by  alighting  on  the  stems  (Marshall 
1948,  Austin  1968,  Johnston  1968b).  Foraging  for  insects 
in  grass,  brush,  and  trees  apparently  increases  in  the  spring 
and  summer  (Austin  1968). 

The  year-round  diet  of  Song  Sparrows  in  California  is 
about  21%  animal  matter  and  79%  vegetable  matter  (Beal 
1910,  n  =  321).  Animal  prey  rise  from  a  from  a  low  of  3% 
of  the  diet  in  September  to  over  71%  in  May.  Important 
animal  items  include  beedes,  caterpillars,  bees,  ants  and 
wasps,  true  bugs,  and  flies,  along  with  miscellaneous 
insects,  spiders,  and  snails.  Saltmarsh  birds  appear  to  feed 
more  heavily  on  invertebrates  (particularly  snails,  nereid 
polychaete  worms,  and  insects)  than  do  upland  birds 
(Marshall  1948),  presumably  because  these  foods  occur  in 
greater  year-round  abundance  in  the  marshes.  The  chief 
plant  food  of  the  Song  Sparrow  is  weed  seed,  whereas  fruit 
and  grain  make  only  a  minor  contribution  (Beal  1910). 
The  important  weed  seeds  used  by  Song  Sparrows  in 
California  are  rough  pigweed,  knotweed,  mayweed,  night- 
shade, chickweed,  miners  lettuce,  and  filaree  (Beal  1910). 
Most  of  these  are  apparendy  picked  from  the  ground 
(Marshall  1948).  Other  seeds  of  importance  to  the  diet  are 
those  of  tules  in  brackish  marshes,  pickleweed  seeds  from 
the  surface  of  saltmarsh  mud,  and  the  other  saltmarsh 
plants  mentioned  above  (Marshall  1948,  Johnston 
1968b). 

Marin  Breeding  Distribution 

During  the  adas  period,  Song  Sparrows  bred  widely  in 
Marin  County's  lowlands.  Their  populations  were  densest 
along  the  immediate  coasdine  where  coastal  scrub  vegeta- 
tion prevails  and  along  the  bayshore  salt  marshes.  In  the 
drier  interior  of  the  county,  Song  Sparrows  were  restricted 
to  stream  drainages  and  lake  and  pond  borders.  Represen- 
tative breeding  localities  included  Bear  Valley  Trail,  PRNS 
(NB  3/22/81  -DS);  O'Hare  Park,  Novato  (FL  5/16/82 
-ScC);  Miller  Creek  at  Hwy.  101  (FY  6/6/82  -  BiL); 
Phoenix  Lake  (NB  4/19/80  — ITi);  Corte  Madera  Creek, 
Kentfield  (FL  5/22/82  -BiL);  and  Corte  Madera  Ecologi- 
cal Reserve  (NE  3/?/82  -JGE). 

Historical  Trends/ Population  Threats 

The  Song  Sparrow  has  been  considered  a  model  of  evolu- 
tionary divergence,  because  it  has  the  greatest  number  of 
genetically  distinct  populations  of  any  bird  species  in 
North  America.  Of  the  31  subspecies  recognized,  1 3  breed 
in  California  and  9  are  endemic  to  the  state  (GckM  1944, 
AOU  1957).  Of  the  6  breeding  subspecies  found  in  coastal 
northern  California,  the  3  inhabiting  salt  and  brackish 
marshes  around  die  shores  of  San  Francisco,  San  Pablo, 
and  Suisun  bays  are  of  particular  interest  (M.  m.  pusillula, 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


M.  m.  samuelis,  and  M.  m.  maxillaris).  These  relatively 
small  but  distinct  populations  have  apparently  evolved 
because  of  the  spatial  isolation  of  segments  of  the  marshes, 
separated  by  open  water  and  ranges  of  hills;  only  narrow 
corridors  connect  saltmarsh  populations  to  upland  popu- 
lations (Marshall  1948).  Differentiation  was  encouraged 
not  only  by  the  geographic  isolation  of  the  populations, 
reinforced  by  the  species'  sedentary  nature,  but  by  different 
ecological  conditions. 

Grinnell  and  Miller  (1944)  considered  these  three  races 
"abundant."  However,  since  1850,  these  marshland  popu- 
lations have  been  fragmented  and  reduced  by  an  estimated 
50%-75%  (Walton  1978).  Among  other  things,  the  San 
Francisco  Bay  ecosystem  has  been  altered  by  increasing 
salinity;  by  increasing  domestic  and  industrial  sewage;  by 
decreasing  circulation,  tidal  action,  and  dissolved  oxygen; 
and  by  a  lowering  of  its  water  table.  Marshland  Song 
Sparrow  populations  have  declined  mainly  because  of 
habitat  loss  from  land  filling,  diking,  dredging,  and  land 
subsidence  (Walton  1978).  M.  m.  pusillula  has  been 
severely  reduced  in  south  San  Francisco  Bay  between  the 
San  Mateo  and  Dumbarton  bridges  and  especially  on  the 
east  side  of  that  bay  from  Richmond  south  to  Hayward. 
M.  m.  samuelis  also  has  been  severely  reduced,  particularly 
in  the  southern  part  of  its  range  in  Marin  and  Contra 
Costa  counties.  Reductions  of  these  populations  have 
amounted   to   extermination   along  three-   to   six-mile 


stretches  of  bayshore  that  have  been  highly  industrialized. 
Habitat  for  M.  m.  maxillaris  has  been  reduced  by  90%  and 
currendy  supports  only  about  8%  of  the  original  popula- 
tion (Marshall  et  al.  1988).  The  most  recent  estimates  of 
the  size  of  the  remaining  populations  are  2320  pairs  for 
M.  m.  pusillula,  4599  for  M.  m.  samuelis  (Walton  1978), 
and  5666  for  M.  m.  maxillaris  (Marshall  et  al.  1988). 
Although  mosquito  control  ditches  are  not  optimal  habi- 
tat, their  development  has  increased  suitable  habitat  for  M. 
m.  samuelis  in  the  Petaluma  Marsh  by  300%,  thus  adding 
an  estimated  2000  Song  Sparrow  territories  in  remaining 
marshlands  (Collins  &.  Resh  1985).  All  three  races  cur- 
rendy are  Candidates  (Category  2)  for  federal  listing  as 
Threatened  or  Endangered  (USFWS  1989b,  1991),  and  all 
are  currendy  considered  Bird  Species  of  Special  Concern 
in  California  (CDFG  1991b).  A  petition  submitted  to  list 
maxillaris  as  Endangered  at  the  state  level  (Marshall  et  al. 
1988)  was  turned  down  in  late  1989;  a  petition  for  federal 
listing  is  currendy  under  review.  Although  small  popula- 
tions of  Song  Sparrows  are  likely  to  survive  in  the  bay 
marshes,  the  continued  existence  of  the  three  distinct  races 
remains  uncertain  because  of  additional  habitat  loss  and 
the  possible  effects  of  habitat  fragmentation.  On  the  whole, 
Song  Sparrow  populations— mosdy  interior  or  upland 
forms— were  relatively  stable  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1989  (USFWS  unpubl.  analyses). 


m 


* 


The  natural  response  when  first  seeing  an  adult  White-crowned  Sparrow  feeding  an  outsized,  begging 
Brown-headed  Cowbird  fledgling  is,  "What's  wrong  with  this  picture!"    Drawing  by  Keith  Hansen,  1992. 


387 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


WHITE-CROWNED  SPARROW    Zonotrichia  leucophrys 


A  year-round  resident;  numbers  (migra- 
tory races)  swell  from  mid-Sep  through 
mid-Apr,  particularly  east  of  Point  Reyes. 

A  very  common,  somewhat  local 
breeder;  overall  breeding  population  of 
moderate  size. 

Recorded  in  85  (38.5%)  of  221  blocks. 


o 

Possible        =        7  (8%) 

c 

Probable       =       33   (39%) 

• 

Confirmed  =       45   (53%) 

AR 

=  5        OPI  =  425        CI  = 

2.45 


Ecological  Requirements 

The  Nuttall's  White-crowned  Sparrow  (Z.  I.  nuttalli)  is  a 
characteristic  resident  of  coastal  terraces  and  adjacent 
shrubby  ridges  of  Marin  County.  In  February  and  March, 
resident  White-crowns  break  out  of  winter  flocks  to  take 
possession  of  their  breeding  territories  in  coastal  scrub, 
dune  scrub,  and  brushy  forest  edges  and  woodland  clear- 
ings on  the  immediate  coast.  Denser,  mature  (vs.  open, 
disturbed)  coastal  scrub  is  preferred,  as  indicated  by  the 
predominance  of  adults  over  immature  breeders  in  that 
habitat  (D.F.  DeSante  pers.  comm.).  White-crown  territo- 
ries invariably  have  a  patchy  mixture  of  dense  shrubbery, 
bare  ground,  and  grass  in  the  right  proportions  to  permit 
ground  foraging  with  quick  escape  to  shelter  (DeWolfe 
1968).  Dense  shrubbery  provides  concealment  for  nests 
and  for  adults  moving  to  and  from  them. 

At  PRBO's  coastal  scrub  ecology  study  site  at  Palomarin, 
White-crowns  almost  always  conceal  their  nests  well  in 
bushes  or  vine  tangles,  although  "nonconformist"  nuttalli 
will,  very  rarely,  nest  on  the  ground  (D.F.  DeSante  pers. 
comm.).  On  Point  Reyes  peninsula,  these  sparrows  nest 
most  frequendy  in  coyote  brush,  poison  oak,  coastal  sage, 
and  bush  lupine.  Almost  any  dense  bush  will  do,  though, 
as  White-crowns  nest  widely  in  ornamentals  in  suburban 
areas  and  occasionally  use  nonwoody  plants  as  well  (Grin- 
nell  &.  Linsdale  1936,  Kern  1984).  Nest  heights  average 
3.5  feet  (range  1.5-11  ft.)  at  Berkeley,  Alameda  County 
(Blanchard  1941,  n  =  31);  1.8  feet  (range  1-4  ft.)  at  Point 
Lobos,  Monterey  County  (Grinnell  6k  Linsdale  1936,  n  = 
16);  1.3  feet  near  Lompoc,  Santa  Barbara  County  (Kern 
1984,  n  =  54);  and  1.5  feet  (range  0-4-8  ft.)  at  Palomarin 

388 


(D.F.  DeSante  pers.  comm.,  n  =  226).  Although  Nuttall's 
White-crowned  Sparrows  rarely  nest  on  the  ground 
(Blanchard  1941),  other  races  often  do  so,  generally  with 
increasing  frequency  with  increasing  altitude  or  latitude 
(DeWolfe  1968,  Kern  1984).  Atypical  nuttalli  nest  sites 
include  35  feet  up  in  a  cypress,  in  the  outer  drooping 
branches  of  an  acacia  tree,  and  in  an  ivy  vine  on  a  building 
(Blanchard  1941).  In  Berkeley,  White-crowns  build  most 
nests  only  a  few  inches  inside  the  tips  of  dense  new  growth 
in  a  mass  of  low  shrubbery,  and  no  more  than  arm's  length 
from  one  edge  of  a  clump.  They  locate  a  few  in  small 
isolated  trees,  but  always  within  a  yard  or  so  of  more 
extensive  shrubbery.  Nests  are  deep,  cup-shaped  affairs  of 
weed  stems,  grasses,  fine  twigs,  dead  ferns,  bark  strips, 
roodets,  dead  leaves,  and  sometimes  paper,  rags,  or  other 
debris  (Dawson  1923,  DeWolfe  1968,  Kern  1984).  They 
are  lined  with  fine  grasses,  weed  stems,  leaves,  flower 
heads,  rhizomes,  mammal  hair,  feathers,  or  perhaps  bits  of 
waxed  paper.  Although  the  nests  of  the  various  races  are 
similar  in  structure,  they  differ  considerably  in  size  and 
external  appearance,  and  apparendy  are  tailored  to  the 
microclimate  at  the  nest  site  (Kern  1984).  Above-ground 
nests  generally  have  much  thicker  walls  and  floors,  pre- 
sumably because  they  are  subjected  to  greater  convecfive 
cooling  and  lack  die  additional  insulation  of  vegetation  and 
soil  around  ground  nests. 

White-crowns  are  principally  ground  foraging  grani- 
vores.  The  main  fare  of  these  sparrows  year  round  in 
coastal  California  is  dried  seeds  of  such  plants  as  red 
maids,  filaree,  knotweed,  chickweed,  and  various  grasses 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


(De Wolfe  1968).  Fresh  vegetable  matter  such  as  flower 
blossoms,  immature  leaf  and  fruit  buds,  leaves,  and  leafy 
vegetables  are  also  important  items  on  the  White-crown 
menu.  After  the  dry  summer  and  early  fall  of  the  coastal 
climate,  White-crowns  readily  shift  from  seeds  to  newly 
sprouted  grass  shoots  upon  the  commencement  of  winter 
rains  (Grinnell  6k  Linsdale  1936,  D.F.  DeSante  pers. 
comm.).  They  less  frequendy  consume  fruit  pulp,  willow 
pollen,  and  sap  (De Wolfe  1968).  They  pick  most  food 
from  the  ground  or  low  herbaceous  vegetation  and,  spar- 
ingly, from  bushes  or  trees.  Insects  form  only  a  minor  part 
of  the  adult  diet,  even  in  the  breeding  season,  and  appar- 
endy  are  absent  in  nuttalli  stomachs  from  September  to 
February.  The  insects  White-crowns  eat  most  frequendy 
are  ants,  wasps,  caterpillars,  beedes,  and  weevils.  They  pick 
or  glean  them  from  the  grass  or  ground  or  catch  them  as 
they  rise  to  escape.  White-crowns  also  occasionally  flycatch 
for  or  jump  into  the  air  after  insects.  Adults,  of  course,  feed 
nesdings  mosdy  insects. 

Marin  Breeding  Distribution 

During  the  adas  period,  Marin's  White-crowned  Sparrows 
bred  only  in  a  narrow  strip  about  three  miles  wide  along 
the  immediate  coast.  This  region  corresponds  to  the  zone 
of  intense,  persistent  summer  fog  and  includes  most  of  the 
county's  extensive  tracts  of  coastal  scrub  vegetation.  Breed- 
ing White-crowns  occurred  slighdy  farther  inland  in  the 
low  hills  east  of  Tomales  Bay  than  they  did  where  the 
steeper  Inverness  and  Bolinas  ridges  provided  more  of  a 
barrier  to  the  inland  penetration  of  coastal  fog.  A  tiny  part 
of  the  breeding  population,  however,  has  "spilled  over" 
Inverness  Ridge  into  the  Olema  Valley  between  Dogtown 
and  Five  Brooks.  Representative  breeding  localities  were 
Tomales  Point  (NB  4/13/82  -DS);  Drake's  Beach,  PRNS 
(FY/FL  cowbird  8/15/81  -DS);  Fish  Docks,  Point  Reyes 


(NY  4/25/77  -DS);  Limantour  Spit  (NY  5/1/80  -JGE); 
Palomarin,  PRNS  (NE-NY  multiple  nests  each  year  1976- 
1982  -PRBO);  and  Five  Brooks  (FY/FL  6/6/78  -RMS). 

Historical  Trends/Population  Threats 

Litde  prior  data  exist.  White-crowned  Sparrow  populations 
decreased  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989  but  were  relatively  stable  from  1980  to  1989 
(USFWS  unpubl.  analyses). 

Remarks 

The  White-crowned  Sparrow  is  one  of  the  best  studied 
species  of  songbirds  in  the  world.  Research  on  Point  Reyes 
has  investigated  reproductive  physiology  and  phenology 
(Mewaldt  et  al.  1968,  Mewaldt  6k  King  1977),  effect  of  age 
on  breeding  success  (Ralph  ck  Pearson  1971),  home  range 
and  site  fidelity  (Baker  6k  Mewaldt  1979),  and  longevity 
(Baker  et  al.  1981),  to  name  but  a  few.  Particularly  fascinat- 
ing are  the  localized  song  dialects  of  the  resident  White- 
crowns  in  coastal  California  (Blanchard  1941).  From  work 
on  Point  Reyes,  Milligan  and  Verner  (1971)  showed  that 
sonograms  from  Marin  White-crowns  differ  from  those  of 
birds  resident  in  Berkeley  and  at  Sunset  Beach  in  Santa 
Cruz  County.  Using  song  dialects,  Baptista  (1975)  com- 
pared the  White-crowns  of  Marin  County  with  those  of 
San  Francisco,  and  with  the  fragmented  populations  just 
east  of  San  Francisco  Bay.  His  findings  suggest  that  the 
Golden  Gate  channel  is  an  effective  water  barrier  to  dis- 
persal and  thus  to  the  exchange  of  genes  between  Marin 
populations  and  those  of  the  rest  of  the  San  Francisco  Bay 
Area.  More  recendy,  Baker  and  Thompson  (1985)  have 
described  the  geographical  limits  of  six  populations  on  the 
basis  of  their  dialects,  all  on  the  Point  Reyes  peninsula 
between  Bolinas  and  Tomales  Point.  Although  they  all 
sound  delightfully  alike  to  most  of  us,  these  White-crowns 
have  much  to  tell  those  who  pause  to  learn  their  language. 


389 


Emberizine  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Emberizine  Sparrows 


DARK-EYED  JUNCO   Junco  hyemalis 


A  year-round  resident. 

A~\^P\ 

®>>^^           \                        Vfi^a 

A  very  common,  nearly  ubiquitous 

3r<r\  •ir-^A  ®  A^A  •  \>\  •V>\  ®  V^a  ©rS 

breeder;  overall  breeding  population 
extremely  large. 

\H  oA- 

^v®!>< 

"A  ®Y<A  *JrA  •  V^\  •>>A  •  A^A  o  V-r\ 

-V«\  *A<\  #>^^«>^\  ®  J^\  ®  A^v  »A 

-"x  ®JV^\  •  aAa#  Y^y©  V-iA •\J>\m  \^\ 

A-^A  •  Jv^\®A->A  •\A\  »  v^A  •V---'A  •A--->\. 
\  AA\  *jV^\  ®  V^A»  V--A©  A^\«  v-^\  ©  J 

Recorded  in  188  (85.1%)  of  221 
blocks. 

V\  i 

^K\ <r  V-'x  *>  A-^^kAA^X  ©  i^A  ©  V-^A  JLA-^xi-^^. 

O    Possible        =       25   (13%) 

x  ®  A^^-O^c^A    A^A^Y^^V ®  \^A«  V^A  O A>'A  •  r^ 
A-^A  •  \^\  •A>"\  9^s^\*  A<2v*  A-^oAA'A '-•LA 

'  iM  Orv 5Vo\  •^<\*>^V c3if2A%\^*>AV. 

-<- 

€    Probable       =      58  (31%) 
•    Confirmed  =     105   (56%) 

.A*vv  JV^CA     V«\cJv-^-»Ar^\T>^^*3<^\#Ar;iA    i 

^?& 

FSAR  =  5        OPI  =  940        CI  =  2.43 

Ecological  Requirements 

The  handsomely  dressed  Oregon  form  of  the  Dark-eyed 
Junco  breeds  widely  in  Marin  County,  around  the  open- 
ings and  edges  of  moist,  shaded  mixed  evergreen,  Douglas 
fir,  bishop  pine,  and  coast  redwood  forests  and,  to  a  lesser 
extent,  Monterey  pine  and  eucalyptus  plantings.  Although 
Juncos  will  breed  in  almost  any  shaded  forest  with  some 
ground  cover  that  remains  green  through  the  summer,  they 
are  particularly  attracted  to  meadow/forest  edges  and  moist 
places  in  general  (Miller  1941,  White  1973).  Relatively 
open  ground  is  important  for  foraging,  sufficient  ground 
cover  or  logs  are  necessary  for  concealing  nests,  while 
bushes  and  trees  provide  shelter  and  limited  foraging 
substrate. 

Juncos  place  most  nests  in  cup-shaped  depressions  in 
the  ground  that  are  usually  hidden  under  a  low  canopy  of 
large  forbs,  ferns,  grasses,  vine  tangles,  bushes,  seedlings, 
downed  limbs  or  logs,  overhanging  rocks,  or  boards  or 
sheet  metal;  rarely,  they  place  nests  inside  tin  cans  (Phelps 
1968,  White  1973,  D.  Shuford  pers.  obs.).  Juncos  some- 
times locate  their  nests  off  the  ground  in  crevices  of  road 
cuts,  rock  ledges,  walls  of  shallow  caves,  and  appropriate 
recesses  in  the  eaves  and  rafters  of  buildings.  Relatively 
often,  particularly  in  coastal  California,  they  build  nests  up 
to  20  feet  high  in  trees,  either  in  dense  foliage  or  in  the 
open  well  out  on  large  limbs  or,  rarely,  in  deserted  wood- 
pecker holes.  Nests  are  sturdy,  usually  tightly  woven  cups 
of  grasses,  weed  stems,  leaves,  other  coarse  herbage,  bark, 
conifer  needles,  and  perhaps  moss  (Phelps  1968,  White 
1973).  They  are  lined  with  finer  grasses,  herbage,  animal 
hair,  or  porcupine  quills.  Some  Juncos  make  a  great  effort 

390 


to  integrate  the  living  stems,  roots,  and  leaves  of  surround- 
ing plants  into  the  nest  cup  (White  1973).  Although 
Juncos  often  renest  close  to  the  same  site,  they  do  not  use 
the  actual  nest  site  or  materials  of  the  first  nest;  rarely,  they 
will  use  the  same  depression  in  successive  years. 

Breeding  birds  usually  feed  singly  or  in  pairs,  although 
mated  territorial  males  in  meadow  habitat  often  feed 
together  in  small  groups,  particularly  during  incubation 
(White  1973).  Oregon  Juncos  feed  mosdy  on  the  surface 
of  the  ground  by  pecking  and  picking  up  objects,  but  only 
infrequently  by  scratching  in  the  litter  to  expose  food  items. 
On  the  ground,  Juncos  feed  mainly  among  the  plants  but 
occasionally  peck  at  insects  or  seeds  on  plants.  Juncos  also 
glean  insects  from  the  foliage  and  branches  of  trees  and 
bushes  and,  rarely,  flycatch  for  airborne  insects  by  making 
short  sallies  or  hops  from  the  ground,  large  rocks,  or  trees; 
rarely,  they  procure  seeds  from  cone-laden  trees  (Hagar 
1960,  Phelps  1968,  White  1973).  In  the  Sierra  Nevada, 
White  (1973)  investigated  the  foraging  habits  of  Oregon 
Juncos  breeding  along  meadow  edges  and  in  adjacent 
forests.  She  found  that  meadow-nesting  birds  foraged  over 
96%  of  the  time  on  the  ground;  this  time  was  about  evenly 
distributed  on  litter,  on  vegetation,  and  under  shrubs  (and, 
infrequently,  under  trees).  The  remainder  of  the  time  was 
spent  mosdy  gleaning  in  trees  and  bushes.  Meadow  birds 
increased  foraging  under  trees  and  shrubs  in  August  and 
September  because  of  increased  seed  numbers  there.  In 
contrast,  forest-nesting  birds  forage  about  78%  of  the  time 
on  the  ground,  about  half  of  this  in  the  open  (not  under  a 
canopy)  and  feeding  upon  needle  litter.  The  remainder  of 


Emberizine  Sparrows 


SPECIES  ACCOUNTS 


Emberizine  Sparrows 


ground  foraging  was  more  evenly  distributed  under  trees, 
shrubs,  and  in  other  open  substrate.  Overall,  forest-dwell- 
ing birds  spent  about  20%  of  their  time  gleaning  in  trees. 
Time  spent  gleaning  in  trees  decreased  as  the  summer 
progressed,  reaching  a  low  of  5%  in  August.  Juncos  breed- 
ing in  ponderosa  pine  forests  in  Arizona  exhibit  annual 
variation  in  their  use  of  foraging  techniques  and  in  other 
resource-use  measures  (Szaro  et  al.  1990). 

Year-round,  the  diet  is  about  50%-80%  vegetable  mat- 
ter, but  in  the  summer  it  varies  from  about  60%  to  95% 
animal  matter  (Beal  1910,  Martin  et  al.  1951,  Gashwiler 
&l  Ward  1968,  White  1973,  Smith  6k  Anderson  1982, 
Dahlsten  et  al.  1985).  In  the  Sierra  Nevada,  White  (1973) 
noted  that  die  volume  of  seeds  in  the  diet  increased  steadily 
from  4%  in  June  to  52%  in  September;  Gashwiler  and 
Ward  (1968)  noted  a  similar  trend.  Animal  foods  con- 
sumed included  beedes,  ants,  caterpillars,  leafhoppers  and 
other  homopterans,  true  bugs,  and  lesser  numbers  of 
grasshoppers,  spiders,  wasps,  flies,  and  miscellaneous 
insects  (references  above).  Plant  matter  is  almost  exclu- 
sively seeds  of  weeds,  grasses,  conifers  (particularly  Doug- 
las fir),  and  berry-producing  bushes.  Seeds  eaten  may  be 
dormant,  germinating,  or  still  attached  to  freshly  sprouted 
seedlings.  Important  plant  foods  to  Juncos  in  California  in 
summer  are  chickweed,  red  maids,  miners  lettuce,  and 
Cryptantha  (Martin  et  al.  1951). 


in  some  extensive  grassland  areas  around  Tomales.  They 
were  most  numerous  in  the  conifer  and  associated  mixed 
evergreen  forests  in  the  coastal  fog  zone  and  were  some- 
what more  restricted  inland  to  shaded,  north-facing  slopes 
and  narrow  canyons.  Representative  breeding  localities 
were  eucalyptus  grove  SE  of  Abbott's  Lagoon  (FY/FL 
6/20/82  -DS);  Mt.  Burdell,  Novate  (NE  4/14/81  -DS); 
Big  Rock  Ridge,  Novate  (FL  6/1 5/82  -ScC);  China  Camp 
SP  (FL/FY  6/19/82  -BiL);  and  Ross  (NE-NY  4/9-18/76 
-PLW). 

Historical  Trends/ Population  Threats 

Breeding  Juncos  have  increased  locally  in  residential  plant- 
ings in  the  Bay  Area  since  at  least  1917  (Allen  1933,  1943; 
Miller  1941:294).  Like  many  widespread  numerous  spe- 
cies, Juncos  are  adaptable,  and  their  populations  have 
probably  fluctuated  within  reasonable  bounds  even  with 
large-scale  habitat  changes  brought  on  by  humans. 
Aldiough  populations  can  increase  in  some  early  succes- 
sional  stages  after  logging  (Hagar  1960),  they  decline  where 
living  trees  are  few  and  brush  stands  are  dense  (White 
1973).  Dark-eyed  Junco  populations  appeared  to  decrease 
slighdy  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989,  despite  relative  stability  from  1980  to  1989 
(USFWS  unpubl.  analyses). 


Marin  Breeding  Distribution 

During  the  atlas  period,  Oregon  Juncos  bred  widely 
throughout  Marin  County.  They  were  sparse  or  absent 
only  on  the  outer  reaches  of  the  Point  Reyes  peninsula  and 


391 


Neu/  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATEAS         New  World  Blackbirds  &  Orioles 

New  World  Blackbirds  and  Orioles 

Family  Emberizidae 
Subfamily  Icterinae 


RED- WINGED  BLACKBIRD   Agelaius  phoeniceus 


A  year-round  resident. 

A  very  common,  very  widespread 

breeder;  overall  breeding  population 

^?^^ 

very  large. 

V^'OA^i  •Ji^\  •Jr>\  •'A^X  °A^\  *>4o  wi  \ 

Recorded  in  172  (77.8%)  of  221 

blocks. 

\  ><*<\ ^y^\  X^aJP\*yP\»y^\°j^\*^^^. 

vA  »3<\«  \/\  #4^     \/T!oV^i     >-^\®A-^\°J 

O    Possible        =       30   (17%) 

\1>A  ©  \^\      \^\+~x-^vq  X^x'*  \^\  ©  Y^v     W2>>*j 

©    Probable       =      44  (26%) 
•    Confirmed  =       98   (57%) 

\ooSr\   \^^<)^^^\^\S)Zr\    Y>a    i>A-v 

V^TvA\^\  ?iV\  *J<*\  *y<^K~  J>c\  *Jt<£\  c 'VvV- - v 

J--^a7»!^c\ © V"A   jr^vo v^T=^^f«' >^\ o V^A •v- 

FSAR  =  5      OPI  =  860       CI  =  2.40 

Px^5^^^^^^ 

^?o> 

:n                 ^Vs^^^&A^f^ 

gU                 "^^^^ 

Ecological  Requirements 

The  marsh-side  stroller  on  a  spring  morning  would  have 
to  be  lost  in  the  depths  of  inner  contemplation  not  to 
notice  the  male  Red-winged  Blackbird,  both  feet  firmly 
planted  on  the  swaying  vertical  stalk  of  a  cattail  or  tule, 
epaulets  puffed  and  ablaze,  and  throat  aquiver  with  a 
full-tilt  gurgle.  Breeding  Red-winged  Blackbirds  inhabit 
Marin  County's  fresh  and  brackish  marshes,  coastal 
swales,  brush  and  weed  fields  adjoining  marshy  aquatic 
habitats,  roadside  ditches,  and  irrigated  meadows,  fields, 
and  croplands.  They  apparendy  prefer  edge  habitat  on  the 
periphery  of  fields  or  wedands  (Albers  1978),  though  they 
do  sometimes  nest  in  the  center  of  dense  cattail  stands. 
Where  Red-wings  overlap  with  Yellow-headed  Blackbirds 
(not  in  Marin),  Red-wings  are  excluded  from  the  outer 
marsh  that  borders  open  water  and  therefore  are  concen- 
trated in  the  denser  vegetation  on  the  periphery  of  the 
marsh  close  to  shore  (Willson  1966).  Hordes  of  Tricolored 
Blackbirds  can  also  displace  Red-wings  to  upland  sites  and 
marsh  edges  (E.C.  Beedy  pers.  comm.). 

392 


Red-winged  Blackbirds  weave  neat  but  rather  bulky  nest 
cups  from  the  leaves  of  marsh  plants  (worked  while  wet), 
grasses,  or  weed  bark.  They  fill  the  interstices  with  rotten 
wood,  marsh-grass  roots,  fibrous  peat,  or  mud,  and  they 
line  the  nests  with  fine  dry  grasses  or  slender  rushes 
(Dawson  1923,  Bent  1958).  Rarely,  Red-wings  will  build 
deep  pensile  nests  reminiscent  of  those  of  orioles,  will  use 
and  reline  year-old  Northern  Oriole  nests,  or  will  place 
their  nests  in  holes  in  trees  or  in  bird  boxes  (Bent  1958, 
Orians  1980).  Red-wings  usually  lash  their  nests  to  the 
upright  stalks  of  emergent  vegetation,  or  they  place  them 
in  weeds,  bushes,  or  trees,  either  over  water  or  in  upland 
sites  sometimes  far  from  water.  They  prefer  nesting  areas 
with  erect  residual  vegetation  and  sturdy  tall  dense  vegeta- 
tion (Albers  1978).  Nest  placement  can  range  from  the 
ground,  supported  by  surrounding  vegetation,  up  to  30 
feet  in  trees,  but  most  nests  are  situated  from  about  1  to  8 
feet  high.  Nest  height,  of  course,  varies  with  habitat. 
Late-season  nests  tend  to  be  higher  because  of  the  seasonal 
growth  of  vegetation  (Allen  1914,  Bent  1958).  However,  in 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


one  upland  area,  there  was  a  seasonal  shift  from  tree,  bush, 
or  raspberry  vine  nests  to  lower  nesting  sites,  as  low 
herbaceous  growth  became  suitable  for  support  and  cover 
(Holcomb  &  Twiest  1968).  Red-wings  will  also  switch 
their  preference  for  certain  plants  or  nest  sites  seasonally, 
relative  to  their  availability  or  proximity  to  changing  water 
levels  (Case  &  Hewitt  1963,  Albers  1978). 

In  the  breeding  season,  Red-winged  Blackbirds  feed 
singly,  in  small  groups,  or  sometimes  in  large  flocks.  They 
have  a  polygynous  breeding  system,  and  both  males  and 
females  feed  extensively  off  as  well  as  on  their  territories 
(Orians  1961,  1980).  Red-wings  nesting  in  aquatic  habitats 
forage  primarily  in  marshes  at  midday,  during  the  peak  of 
aquatic  insect  emergence,  and  also  in  upland  sites,  during 
early  morning  and  late  afternoon  (Orians  ck  Horn  1969, 
Orians  1980).  Wilson  (1978)  noted  that  where  Red-wings 
were  nesting  in  a  marsh  adjoining  a  grassy  field  the  males 
fed  much  more  frequendy  in  the  field  than  did  females. 
This  may  have  reduced  competition  for  food  by  allowing 
the  females  to  gather  food  for  nesdings  in  the  more 
productive  marsh  that  tended  to  harbor  large  prey  items. 
Although  Red-wings  frequendy  forage  by  gleaning  insects 
from  the  vertical  stalks  of  emergent  vegetation,  they  are  also 
adept  at  foraging  in  hay,  alfalfa,  or  weed  fields,  and  in 
upland  bushes  and  trees.  Compared  with  Yellow-headed 
or  Brewer's  blackbirds,  Red-wings  forage  more  extensively 
in  bushes  and  trees  (Orians  1980).  There  female  Red- 
wings work  inside  the  branchwork,  rather  than  from  below 
or  on  top  of  the  canopy  as  the  male  Red-wings  and  other 
species  of  blackbirds  do.  Although  most  arboreal  foraging 
consists  of  vireolike  gleaning,  Red-wings  occasionally  hover 
to  grab  insects  from  leaves  and  sometimes  to  pick  samara 
seeds  or  extract  pine  cone  seeds  (Bent  1 958).  In  calm  warm 
weather,  Red-wings  (particularly  the  males)  catch  insects  on 
the  wing  (Orians  1961).  In  open  fields  and  on  marsh 
edges,  Red-wings  uncover  prey  by  flipping  over  sticks, 
rocks,  cow  patties,  and  other  floating  or  stationary  debris 
with  gaping  movements  of  their  bills  (Orians  1961,  1980). 
Gaping  is  also  used  in  cattails,  grasslands,  and  tree  foliage, 
the  bill  being  inserted  into  vegetation  and  then  opened  to 
expose  any  insects  and  seeds  within.  Ground-foraging 
birds  intersperse  bouts  of  scratching  (particularly  for  seeds) 
with  digging  fairly  deep  holes  with  their  bills.  However, 
while  foraging  for  nesdings,  they  move  more  rapidly,  never 
pursue  mobile  prey,  and  do  not  dig  or  flip  over  objects. 
Bendell  and  Weatherhead  (1982)  reported  that  Red-wings 
selectively  prey  on  cryptically  colored,  slow-moving  foliage 
insects  rather  than  on  more  mobile  forms. 

The  diet  of  Red-winged  Blackbirds  year  round  in  Cali- 
fornia is  roughly  10%- 30%  animal  matter  and  70%-90% 
vegetable  fare  (Beal  1910,  Soriano  1931,  Crase  &. 
DeHaven  1978).  Because  these  studies  have  focused  on 
potential  crop  damage  in  the  state's  agricultural  valleys, 
where  very  large  concentrations  of  blackbirds  winter,  they 


may  not  reflect  the  true  range  of  dietary  preference.  There 
is  considerable  variation  in  the  diet,  both  on  a  broad 
geographic  scale  and  between  aquatic-  and  upland-feeding 
birds  (Orians  1980).  In  Manitoba,  for  example,  Bird  and 
Smith  (1964)  found  that  breeding  birds  from  marshes 
were  eating  100%  insects,  whereas  those  in  agricultural 
areas  were  eating  only  70%  insects.  In  the  breeding  season, 
California  birds  may  eat  as  much  as  91%  animal  matter 
(Beal  1910).  Adults  feed  nestlings  almost  exclusively 
insects  (Beal  1910,  Orians  1980)  but  also,  rarely,  small 
quantities  of  grain  (Bendell  &.  Weatherhead  1982). 
Important  animal  foods  in  California  include  beedes, 
caterpillars,  and  grasshoppers,  along  with  lesser  numbers 
of  dipterans,  true  bugs,  ants,  wasps,  moths,  miscellaneous 
insects,  and  spiders.  If  dietary  work  had  concentrated 
around  aquatic  systems,  damselflies,  dragonflies,  mayflies, 
and  caddisflies  would  probably  have  been  more  important 
(Orians  1980).  In  Quebec,  Bendell  and  Weatherhead 
(1982)  noted  seasonal  changes  in  the  insect  diet  fed  to 
young.  The  early-nesting  birds  concentrated  on  lepidop- 
teran  larvae,  whereas  later  ones  fed  on  slow-moving  adult 
grasshoppers.  Wilson  (1978)  noted  that  nesdings  were  fed 
a  much  greater  proportion  of  nymphs  and  larvae,  relative 
to  their  availability,  than  adult  insects.  This  may  have 
reflected  dieir  ease  of  capture  or  the  fact  they  are  assimi- 
lated fast,  promoting  nesding  growth.  Young  were  also  fed 
a  high  proportion  of  larger  food  items  relative  to  their 
availability.  Important  vegetable  foods  in  California  are 
cereal  grains,  including  rice,  oats,  wheat,  barley,  corn,  and 
sorghum,  and  wild  seeds  such  as  watergrass  (strong  prefer- 
ence), smartweed,  pigweed,  filaree,  and  Johnson  grass. 
Crase  and  DeHaven  (1978)  noted  historical  changes  in  the 
diet  that  reflected  changes  in  the  importance  of  various 
grain  crops  in  California's  Central  Valley.  In  areas  of 
sympatry,  breeding  Red-winged  Blackbirds  overlap  exten- 
sively in  their  diet  with  Yellow-headed  and  Brewer's  black- 
birds, but  they  feed  their  young  more  diverse  prey  than 
Yellow-headeds  do.  Foraging  differences  between  these 
species  are  expressed  largely  through  temporal  and  habitat 
patch  use  differences  (Orians  1980;  see  other  accounts). 
Sexual  foraging  differences  indicate  that  males  eat  more 
rice,  cultivated  grain,  and  plant  matter  and  less  wild  seed 
than  do  females  (Crase  &.  DeHaven  1978— see  also  for 
additional  information  on  dietary  differences  between  the 
various  species  of  blackbirds). 

Marin  Breeding  Distribution 

During  the  atlas  period,  Red-winged  Blackbirds  bred 
widely  in  the  lowlands  of  Marin  County.  The  few  gaps  in 
the  distribution  primarily  reflected  their  absence  from 
steep  or  heavily  forested  terrain.  Representative  breeding 
locales  were  Tomales  Point  (NB  4/13/82  — DS);  Olema 
Marsh  (NE  4/30/81  -DS);  E  end  of  Chileno  Valley  (NE 

393 


New  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATEAS         New  World  Blackbirds  &  Orioles 


6/4/82  -DS);  Hicks  Valley  (NB  4/22/82  -DS);  Stafford 
Lake,  Novato  (NE-FL  5/? -6/1 5/82  -ScC);  and  Mt. 
Burdell,  Novato  (NE  4/21/81  -ITi). 

Historical  Trends/  Population  Threats 

Because  Red-wings  are  such  common  breeders  in  Califor- 
nia, it  is  tempting  to  diink  that  their  status  has  changed 
litde  historically.  However,  the  elimination  of  over  90%  of 
die  marshland  around  San  Francisco  Bay  and  die  draining 


of  marshes  in  interior  valleys  has  undoubtedly  caused  large 
local  declines  in  breeding  numbers.  Irrigation,  the  planting 
of  grain  crops,  and  die  establishment  of  catde  feed  lots 
have  offset  diese  declines  to  an  unknown  degree  by  increas- 
ing alternative  habitats  or  enhancing  winter  survival.  Red- 
wing populations  increased  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1979  (Robbins  et  al.  1986),  but 
the  trend  was  stable  when  analysis  extended  from  1968  to 
1989  (USFWS  unpubl.  analyses). 


TRICOLORED  BLACKBIRD  Agelaius  tricolor 


Occurs  year  round,  diough  primarily  as 

a  winter  resident  from  Sep  dirough  Mar. 

A  fairly  common,  very  local  breeder; 

^\^Jk^ J^^J^^Sr\*j^K^ 

overall  breeding  population  very  small. 

Recorded  in  15  (6.8%)  of  221  blocks. 

\§^^V>\>A^V^V 

\d^>^f^!vS\>\3r^\X^\^VA' 

O    Possible                 8  (53%) 

V^^^VCv^^CVc 

\      \^\  --iX^^X^?*^ 

©    Probable      =        0  (0%) 

\  Wt^^x  j^^^^-^A^              3k^\ 

/iXYVV., 

•    Confirmed  =         7    (47%) 

\  -J4f^\   \^^\   \^\  \^\^\f\^'^ 

v^cwc^^r'' 

FSAR=3       OPI  =  45        CI  =  1.93 

\ 

i>*° 

Ecological  Requirements 

Roving  bands  of  Tricolored  Blackbirds  nest  colonially  in 
the  vicinity  of  fresh  water,  especially  in  marshy  areas  in 
emergent  cattails  and  rules.  As  freshwater  marsh  habitats 
have  declined,  an  increasing  proportion  of  Tricolor  nesting 
colonies  have  been  found  in  vegetation  such  as  black- 
berries, willows  and  odier  riparian  fringes,  thistles,  netdes, 
mustard,  mulefat,  and  planted  grains  (Orians  1961, 
DeHaven  et  al.  1975a,  Hosea  1986,  Beedy  et  al.  1991). 
Although  Tricolored  Blackbirds  may  overlap  in  nesting 
habitat  with  marsh-nesting  Red-winged  or  Yellow-headed 
blackbirds,  on  average  they  nest  in  denser  vegetation  and 
will  sometimes  successfully  displace  these  icterids— by  sheer 
numbers  rather  dian  by  aggression  (Payne  1969).  Suitable 
nesting  sites  for  Tricolors  must  be  surrounded  by  expanses 
of  open  feeding  grounds  (Orians  1961).  Wide-ranging 
flocks  of  Tricolors  forage  at  freshwater  marshes,  pastures, 
pond  margins,  agricultural  fields,  feed  lots,  riparian 
fringes,  ditch  banks,  roadsides,  weed  and  brush  piles,  and, 

394 


occasionally,  scrub  habitats  (Orians  1961,  Beedy  & 
Hayworth  in  press).  Hence  die  factors  necessary  for  Tricol- 
ored Blackbirds  to  nest  successfully  are  (1)  proximity 
(widiin  four  miles  or  less)  to  a  large  productive  source  area 
of  insect  food;  (2)  protection  from  potential  predators  at 
the  nest  site,  provided  by  emergent  or  other  vegetation 
surrounded  by  a  moat  of  water  or  by  naturally  armored 
plants  such  as  blackberries,  diisdes,  or  netdes;  (3)  a  dense 
sturdy  nesting  substrate;  (4)  proximity  to  fresh  water  of 
limited  or  greater  extent  (E.C.  Beedy,  R.  DeHaven,  6k  J. 
Skorupa  pers.  obs.). 

Tricolored  Blackbirds  usually  bind  dieir  nests  to  upright 
plant  stems  from  a  few  inches  to  a  few  feet  above  water  or 
ground  (Harrison  1978),  but  diey  occasionally  build  them 
on  the  ground  (Neff  1937).  Their  deep  cup  nests  are 
constructed  with  outer  layers  of  long  leaves  (such  as  cattail 
diatch)  woven  tightly  around  supporting  stems,  whereas 
die  inner  layers  are  coiled  stems  of  grasses  and  soft  plant 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


down  (Harrison  1978).  A  little  mud  is  sometimes  added  to 
the  inside  of  the  nest  (Payne  1969).  Tricolor  nests  are  more 
loosely  built  than  Red-wing  nests,  and  their  lining  is  of 
green  rather  than  dried  grass  (Orians  1961,  Payne  1969). 
In  the  Central  Valley,  the  nests  of  different  breeding 
colonies  vary,  but  most  pairs  within  the  same  colony  make 
use  of  similar  locally  abundant  plant  material  (Beedy  6k 
Hayworth  in  press). 

The  Tricolored  Blackbird's  nomadic,  colonial  social 
organization  is  one  of  the  most  unusual  ecological  adapta- 
tions  among  California's  avifauna.  This  gregarious,  gypsy- 
like lifestyle  evolves  most  frequendy  in  semiarid  regions  of 
great  climatic  fluctuation  (Orians  1961).  Climatic  instabil- 
ity in  lowland  California  is  due  to  the  great  annual  varia- 
tion in  winter  rainfall  and  the  extent  of  flooding.  The 
Tricolored  Blackbird  is  the  most  intensely  colonial  of  all 
North  American  passerine  birds  (Orians  1980).  Under 
favorable  conditions,  colonies  can  host  staggering  num- 
bers of  breeding  birds.  As  many  as  20,000  to  30,000  nests 
have  been  recorded  in  an  area  of  ten  acres  or  less  (Neff 
1937,  DeHaven  et  al.  1975a).  One  expansive  colony  was 
estimated  to  contain  200,000  nests  (Neff  1937)!  The 
difficulty  of  estimating  the  number  of  breeding  individuals 
in  a  tightly  packed  colony  of  this  polygynous  species  is 
compounded  by  the  fact  that  many  birds  diat  initially 
attempt  to  settle  may  not  breed  (Orians  1 961 ,  Payne  1 969), 
and  birds  may  switch  nesting  sites  within  a  colony  (E.C. 
Beedy  pers.  obs.).  The  colonial  nesting  of  Tricolors  evolved 
as  a  strategy  to  maximize  exploitation  of  a  locally  abundant 
food  supply  and  perhaps  secondarily  to  avoid  predation 
(Orians  1961,  Payne  1969).  The  evolutionary  pressure  for 
predator  avoidance  has  probably  increased  gready  with  the 
loss  and  fragmentation  of  our  once  vast  marshlands. 

Since  the  territories  of  males  average  only  a  yard  or  two 
in  radius  (Orians  1961,  1980)  and  part  of  the  available 
nesting  habitat  generally  is  left  unoccupied,  territorial 
behavior  does  not  limit  colony  size  (Orians  1961).  Instead, 
the  size  of  colonies  appears  to  be  related  to  the  availability 
of  food  (Orians  1961,  Payne  1969).  Colony  sizes  are 
generally  much  larger  in  the  heart  of  the  species'  range  in 
the  Central  Valley,  where  marshlands  and  rice  culture  are 
extensive  (Neff  1937,  DeHaven  et  al.  1975a).  Colonies 
tend  to  be  much  smaller  in  the  Coast  Range,  and  those  in 
Marin  County  are  no  exception.  From  year  to  year 
throughout  the  range,  colony  size  is  unpredictable,  many 
sites  are  not  occupied,  and  centers  of  breeding  abundance 
shift  substantially  (Orians  1961,  Payne  1969,  DeHaven  et 
al.  1975a,  Beedy  et  al.  1991).  Banding  studies  provide 
additional  evidence  of  nomadic  behavior,  indicating  that 
nesting  birds  are  unlikely  to  breed  at  sites  where  they  were 
hatched  or  where  they  have  nested  in  previous  years 
(DeHaven  et  al.  1975b).  Evidendy  Tricolors  can  move 
from  one  colony  to  another  and  renest  less  than  ten  days 
after  deserting  an  unsuccessful  nest  (Payne  1969). 


Nomadism  and  a  short  nesting  cycle  enable  Tricolors  to 
exploit  unoccupied  habitats  when  high-quality  food 
resources  become  temporarily  abundant  (Orians  1961, 
Payne  1969).  Although  the  initiation  of  nesting  often 
coincides  with  rainfall  or  the  flooding  of  fields  for  planting 
rice  (Payne  1969),  nesting  appears  to  be  triggered  by  an 
abundance  of  food  (Orians  1961,  Payne  1969).  Evidence 
suggests  that  during  the  first  few  days  of  colony  establish- 
ment, an  assessment  is  made  of  the  food  supply  available 
in  the  surrounding  environment  by  means  of  mass  feeding 
flights.  These  feeding  flights  form  the  most  conspicuous 
activity  around  colonies  at  this  time.  Male  Tricolors  do  not 
establish  territories  until  the  morning  of  the  day  breeding 
begins;  nest  building  by  females  takes  only  four  days;  and 
nesting  is  usually  highly  synchronous,  as  all  nests  within  a 
colony  are  typically  constructed  within  the  period  of  one 
week  (Orians  1961).  Tricolors  react  quickly  to  any  changes 
in  the  surrounding  environment  affecting  food  availability, 
and  food  sources  are  apparendy  communicated  to  others 
by  the  direction  from  which  incoming  birds  approach  the 
colony.  To  support  large  numbers  of  young,  Tricolor 
adults  may  travel  up  to  four  miles  from  colonies  and 
exploit  30  square  miles  of  land  (Orians  1961);  feeding 
areas  also  may  be  shared  by  birds  nesting  in  different 
colonies  (Payne  1969).  Because  of  the  great  energy  expendi- 
ture needed  for  food  gathering,  the  Tricolor  colonial  sys- 
tem demands  more  favorable  environmental  conditions 
than  the  Red-winged  Blackbird  system  (Orians  1961). 
These  more  exacting  requirements  may  explain  the  pecu- 
liarly spotty  breeding  distribution  of  Tricolors.  In  addition, 
the  Tricolored  Blackbird  is  one  of  very  few  California  birds 
that  breed  in  both  spring  and,  very  rarely,  fall,  although 
nesting  success  of  autumnal  breeding  is  very  low  (Orians 
1960,  1961;  Payne  1969;  DeHaven  et  al.  1975a). 

Tricolors  forage  in  large  flocks  and  occasionally  mingle 
with  other  blackbirds.  Although  they  often  fly  long  dis- 
tances to  seek  food,  Tricolors  typically  exploit  locally  abun- 
dant and  changing  food  supplies  and  minimize  the 
distance  of  their  foraging  flights  (Crase  6k  DeHaven  1977). 
They  glean  insects  and  seeds  from  dry  ground,  flooded 
fields,  mudflats,  floating  algae  mats,  and  low  vegetation; 
occasionally  they  hawk  insects  in  midair  (Beedy  6k  Hay- 
worth  in  press).  Flocks  feeding  in  grasslands  progress 
smoothly  over  the  ground  as  birds  from  the  rear  fly  over 
the  rest  of  the  flock  to  the  front  (Orians  1961).  In  one 
instance,  birds  from  a  Marin  colony  repeatedly  fed  by 
probing  into  eucalyptus  flowers,  oriole  style  (D.  Shuford 
pers.  comm.).  In  breeding  season  foraging  studies  in  the 
San  Joaquin  Valley,  animal  matter  made  up  91%  of  the 
food  volume  of  nesdings  and  fledglings  (n  =  95),  56%  of 
that  of  adult  females  (n  =  107),  and  28%  of  that  of  adult 
males  (n  =  27)  (Skorupa  et  al.  1980).  The  animal  taxa  most 
often  consumed  were  beedes  (63%),  lepidopterans  (35%), 
and  flies  (1 4%).  Plant  foods  eaten  most  often  included  oats 


395 


Neu/  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATLAS         New  World  Blackbirds  &  Orioles 


(27%),  chickweed  (1 5%),  and  filaree  (9%).  Important  plant 
foods  in  the  Sacramento  Valley  are  rice,  watergrass,  sor- 
ghum, and  oats  (Crase  &  DcHaven  1978).  Payne  (1969) 
reported  diat  at  one  upland  colony  two  species  of  range- 
land  grasshopper  accounted  for  47%  of  nestling  food. 
Tricolors  appear  to  be  particularly  well  adapted  to  take 
advantage  of  irregular  locust  plagues  (Orians  1961,  Payne 
1969).  In  fall  and  winter,  Tricolors  forage  in  large  nomadic 
flocks  and  eat  about  90%  weed  seeds  and  waste  grain  from 
agricultural  fields  (Crase  6k  DeHaven  1978,  n  =  142). 

Colonial  breeding  and  declining  wedands  make  Tricol- 
ors vulnerable  to  disturbance,  and  mass  desertion  of  breed- 
ing colonies  have  been  reported.  DeHaven  et  al.  (1975a) 
reported  that  10%-50%  of  colonies  are  partially  or  com- 
pletely abandoned  each  year.  These  desertions  have  been 
attributed  to  various  factors,  including  bird,  mammal,  or 
snake  predation  (Heermann  1853,  Mailliard  1914,  Ever- 
mann  1919,  Neff  1937,  Lack  &  Emlen  1939);  excessive 
wind  and  rain  (Neff  1937,  Payne  1969);  flooding  of 
marshes;  large  European  Starling  roosts'  usurping  nesting 
areas  (Payne  1969);  decreased  food  supplies  (Orians  1961, 
Payne  1969);  poisoning  (McCabe  1932,  Hosea  1986);  and 
human  disturbance  (Beedy  6k  Hayworth  in  press).  Recent 
studies  in  the  Central  Valley  suggest  diat  contamination  by 
trace  elements  (such  as  selenium)  are  also  potential  causes 
of  Tricolored  Blackbird  nesting  failures  (Grau  et  al.  1987, 
Beedy  6k  Hayworth  in  press).  Although  nesting  failure  can 
occur  throughout  the  breeding  season,  it  is  more  prevalent 
early  and  late  in  the  year,  suggesting  a  relationship  to 
insufficient  food  supplies  for  the  breeding  birds  and  their 
young  (Orians  1960,  1961;  DeHaven  et  al.  1975a). 

Marin  Breeding  Distribution 

Tricolored  Blackbirds  apparently  breed  every  year  in 
Marin  County  in  small  numbers,  but,  true  to  their 
nomadic  tendencies,  they  usually  do  not  breed  at  the  same 
sites  here  in  consecutive  years.  Most  breeding  colonies 
have  been  established  in  the  moister  ranchlands  towards 
the  coast  in  the  general  vicinity  of  Tomales  and  on  the 
Point  Reyes  peninsula.  Representative  breeding  locations 
during  the  adas  period  included:  rule  marsh  at  pond  at 
Drake's  Beach  visitor's  center,  PRNS  (NB-FL  6/8-7/1 5/80 
— JM,  LCB,  DS);  blackberry  and  thimbleberry  thicket  in 
coastal  swale  at  Brazil  Ranch,  SE  of  Dillon  Beach  (NB/DD 
4/28/82  — DS);  and  by  a  pond  near  the  junction  of  the 
Marshall-Petaluma  Rd.  and  Wilson  Hill  Rd.  (NB  5/2/77 
—RMS).  Post-adas,  Tricolored  Blackbirds  nested  in  a  fresh- 
water marsh  at  Cypress  Grove  near  Marshall  on  Tomales 
Bay  (NB-NE-NY  5/19-6/21/88  and  5/20-6/14/89  -JPK 
et  al.).  In  1 989,  about  85%  of  that  colony  was  abandoned 
between  30  May  and  2  June. 


Historical  Trends/ Population  Threats 

It  seems  safe  to  assume  that,  historically,  Tricolored  Black- 
birds have  always  been  relatively  uncommon  breeders  in 
Marin  County.  Mailliard  (1900)  and  Stephens  and  Pringle 
(1933)  considered  Tricolors  migrants  or  transients  in 
Marin  County.  Grinnell  and  Wythe  (1927)  reported  that 
they  were  irregular  residents  or  vagrants  in  a  few  parts  of 
the  San  Francisco  Bay  region  and  were  "nesting,"  among 
other  places,  on  Point  Reyes.  Their  account  may  refer  to 
Booth's  (1926)  observation  of  a  colony  building  nests  in  a 
dense  growth  of  raspberry  bushes  "a  short  distance  north 
of  Point  Reyes,  Marin  County,"  sometime  between  17  and 
20  April  1926.  Neff  (1937)  also  reported  a  breeding  colony 
at  White's  Gulch,  Tomales  Point,  on  14  May  1933. 
Although  the  historical  record  is  sketchy,  it  seems  likely 
that  the  status  of  such  nomads  in  peripheral  parts  of  the 
range,  such  as  Marin  County,  would  be  tied  to  the  fortunes 
of  the  species  in  the  heart  of  its  range. 

Grinnell  and  Miller  (1944)  considered  Tricolors  locally 
"common  to  abundant"  throughout  their  California  range. 
They  also  noted  population  declines  in  southern  Califor- 
nia and  increases  in  the  Sacramento  Valley  "as  a  result  of 
human  management  of  water  supplies."  This  latter  sugges- 
tion of  increase  is  apparendy  traceable  to  Neff  (1937)  who 
had  conducted  the  only  major  survey  of  the  species  up  to 
that  time.  He  felt  the  species  had  reached  a  low  ebb  after 
massive  draining  and  reclamation  of  marshes  in  the  late 
1800s  and  early  1900s,  only  to  later  rebound  with  the 
establishment  of  rice  culture  and  extensive  irrigation.  He 
felt  that  by  the  1930s  Tricolors  might  have  been  more 
abundant  than  in  earlier  times  because  of  the  recent 
benefits  of  irrigation  that  included  an  increased  food  sup- 
ply, a  regaining  of  lost  marshland,  and  an  extension  of 
suitable  habitat  into  formerly  arid  areas.  Surveys  conducted 
from  1969  to  1972  indicated  that  the  breeding  range  and 
major  nesting  areas  were  unchanged  from  conditions 
described  by  Neff  (1937)  and  other  historical  workers. 
Despite  a  fourfold  increase  in  the  previous  30  years  in  the 
acreage  under  rice  cultivation,  however,  the  valley  popula- 
tion had  declined  by  perhaps  more  than  50%  (DeHaven 
et  al.  1975a).  If  rice  culture  and  irrigation  had  been 
beneficial,  it  must  have  been  more  than  offset  by  other 
deleterious  factors,  such  as  draining  of  natural  marshlands 
and  applications  of  pesticides  and  herbicides  in  agricul- 
tural areas. 

A  recent  survey  of  the  Tricolored  Blackbird's  historical 
and  current  status  revealed  that  its  population  declined  by 
more  than  72%  from  the  1970s  to  the  1980s  and  overall 
by  about  89%  from  the  1930s  to  1989  (Beedy  et  al.  1991). 
Losses  of  colonies  in  the  Sacramento  and  San  Joaquin 
valleys,  the  heart  of  the  species'  historical  range,  account 
for  much  of  the  overall  population  decline.  Because  of  this 
dramatic  decline,  the  Tricolored  Blackbird  is  now  a  Can- 
didate (Category  2)  for  federal  listing  as  Threatened  or 


396 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


Endangered  (USFWS  1991)  and  is  a  Bird  Species  of  Special 
Concern  in  California  (CDFG  1991a).  Tricolored  Black- 
birds may  continue  to  decline  in  die  future  as  continued 
loss  of  wedands  and  other  nesting  habitat  forces  them  into 
confined  areas,  where  they  are  vulnerable  to  predation, 
contamination,  and  other  mortality  factors.  Because  the 


species  relies  on  patchy  superabundant  food,  the  quality, 
not  just  the  extent,  of  remaining  habitat  is  of  paramount 
importance. 

EDWARD  C.  BEEDY 


WESTERN  MEADOWLARK  Stumella  neglecta 


A  year-round  resident;  numbers  swell  on 
Pt.  Reyes  from  late  Sep  through  Apr. 

A  common,  widespread  breeder;  over- 
all breeding  population  fairly  large. 

Recorded  in  135  (61.1%)  of  221 
blocks. 


O  Possible 
C  Probable 
w    Confirmed 


26  (19%) 
83  (62%) 
26  (19%) 


FSAR  =  4       OPI  =  540       CI  =  2.00 


Ecological  Requirements 

The  rich,  powerful  flutelike  song  of  the  Western  Meadow- 
lark  penetrates  the  daydreams  of  the  motorist  rolling  down 
the  back  roads  of  Marin  County's  grassy  hill  country.  Since 
the  county's  agricultural  base  is  primarily  ranching,  Mead- 
owlarks  breed  here  mosdy  in  pasturelands  and  to  a  limited 
extent  in  cultivated  fields  or  weed  fields.  They  prefer 
lowland  valleys  and  gendy  rolling  hills  covered  with  rela- 
tively tall,  dense  grass.  The  alluvial  soil  there  presumably 
is  more  easily  probed  for  food  by  their  long  bills,  and  dense 
grass  provides  protective  nest  sites.  Soil  texture  appears  to 
be  most  important,  as  steep  ridges  with  compact  soil,  even 
when  luxuriantly  clothed  with  grasses,  are  generally 
avoided  for  breeding.  Throughout  California,  pasturelands 
are  Western  Meadowlarks'  preferred  nesting  habitat  (Bry- 
ant 1914a).  Observations  elsewhere  in  California  indicate 
that  birds  will  also  nest  where  grasses  and  forbs  mix  with 
low  open  brush.  Like  many  other  icterids,  Western  Mead- 
owlarks are  polygynous  breeders  (Lanyon  1957). 

Meadowlarks  choose  shallow  depressions  in  the  ground 
in  thick  tufts  of  grass  or  at  the  base  of  bushes  for  their  nest 
sites.  They  typically  build  dome-shaped  nests  with  arched- 


over  canopies  constructed  of  grasses  or  the  fibers  of  bark 
or  plant  stems,  which  they  may  weave  into  the  surrounding 
grass  (Bryant  1914a,  Bent  1958).  Meadowlarks  usually 
reach  die  round  entrance  hole  on  the  side  of  the  nest  via  a 
one-  to  five-foot  runway  through  the  grass.  Nests  are 
variable,  however,  and  they  range  from  open  nests  without 
runways  to  completely  roofed  nests  with  elaborate  entrance 
tunnels  (Lanyon  1957).  Meadowlarks  make  their  nests 
proper  of  dried  grasses  and  line  them  with  finer  specimens 
of  the  same  material.  In  Wisconsin,  Lanyon  (1957)  found 
that  nests  tended  to  be  oriented  toward  the  north  or  east, 
in  concert  with  the  depression  of  vegetation  in  those 
directions  by  the  prevailing  winds. 

The  diet  of  Western  Meadowlarks  in  California  year 
round  is  about  63%  animal  and  37%  vegetable  (Bryant 
1914a,  n  =  1920).  In  die  breeding  season,  food  of  animal 
origin  accounts  for  over  95%  of  the  diet,  whereas  vegetable 
food,  mosdy  grain,  approaches  that  level  of  importance 
from  December  to  February.  Adults  feed  nesdings  almost 
exclusively  insects  and  only  an  occasional  weed  seed. 
Important  items  of  the  animal  menu  are  beedes,  grasshop- 

397 


Ne^  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATLAS         hlew  World  Blackbirds  &  Orioles 


pers,  crickets,  caterpillars,  ants,  bees  and  wasps,  tme  bugs, 
flies,  and  spiders,  along  with  a  few  miscellaneous  insects, 
sowbugs,  and  snails.  Meadowlarks  also  eat  carrion  when 
hard  pressed  (Hubbard  ck  I  Iubbard  1969).  Vegetable  fare 
consists  principally  of  grain,  largely  wild  oats  (Avena  fatua); 
Meadowlarks  consume  lesser  amounts  of  other  weed  seeds 
(particularly  in  Sep  and  Oct)  and  occasional  grape  seeds. 
Other  important  grains  in  California  are  barley  and  wheat. 
Important  weed  seeds  are  filaree,  tarweed,  mustard,  tum- 
bleweed,  Napa  thisde,  pigweed,  amaranth,  canarygrass, 
Johnson  grass,  foxtail,  sunflower,  bur  clover,  turkey  mul- 
lein, and  nightshade. 

Western  Meadowlarks  forage  almost  exclusively  on  the 
ground.  They  pick  grains  and  seeds  from  the  ground,  not 
from  seed  heads,  and  probe  the  ground  near  the  base  of 
sprouts  to  obtain  the  grain  kernel,  which  may  be  eaten  or 
just  crushed  for  the  "milk."  Meadowlarks  glean  some 
insects  from  the  surface  of  the  ground  and  grass  and  from 
underneath  flippedover  dirt  clods  or  manure.  They  pro- 
cure others  by  probing  in  the  soil  (Bryant  1914a).  When 
probing  the  earth,  Meadowlarks  first  set  aside  previously 
obtained  food  on  the  ground  (Orians  ck  Horn  1969).  They 
then  thrust  their  bills  in  and  open  them  against  the 
resistance  of  the  soil  (Beecher  1951). 


Marin  Breeding  Distribution 

During  the  atlas  period,  Western  Meadowlarks  bred 
widely  in  Marin  County.  They  avoided  the  steeper,  drier 
grassy  ridges  and  they  inexplicably  shunned  much  of  the 
grassland  habitat  on  Point  Reyes  for  breeding,  although 
diey  were  numerous  there  in  winter.  Representative  breed- 
ing stations  were  near  Tomales  (FY  6/8/78  —RMS);  Mt. 
Burdell,  Novato  (NE  5/1/19  — ScC);  and  the  grassy  upland 
border  of  Rush  Creek  marsh,  Novato  (NY  5/19/81  -DS). 

Historical  Trends/ Population  Threats 

Historically,  Western  Meadowlarks  may  have  increased  as 
breeders  locally  along  the  San  Pablo  bayshore  where  diked 
marshlands  have  been  converted  to  grain  fields.  Con- 
versely, they  may  have  decreased  in  lowland  valleys  in 
eastern  Marin  that  have  been  transformed  by  massive 
development.  Western  Meadowlark  populations  decreased 
on  Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(Robbins  et  al.  1986,  USFWS  unpubl.  analyses). 


BREWER'S  BLACKBIRD    Euphagus  cyanocephalus 


A  year-round  resident. 

A  common,  nearly  ubiquitous 

breeder;  overall  breeding  population 

-V-IN  •  T#fV|0  Jr^\  °  A^\  ©tr^V^T^Tii  X>^\  ©~\^W\ 

very  large. 

?^^^^\3^k^k^^ 

Recorded  in  193  (87.3%)  of  221 

blocks. 

\  >rivi    >)-'i\  •  Jr^\  *J?~\  •  \Z^\  O  Y->"A  •  \Z^\i\^\ 

^•3^J^V?A<A  •V'V*  V-'V •  .V"A»  \^V»  \ 

\^y^^*^f^0Jy^°j^\  J^\°j^X  Wl 

O    Possible        =      38  (20%) 

\  ><I^^^\*V^#J£^^  Y^^«A^^ 

vrw\-PJ^\    3e^v  #-\>^vP  \^x»  \Z^\o  \z>\9  \J<^_ 

C    Probable      =      22  (11%) 
•    Confirmed  =    133  (69%) 

l  °'^k\9\^\^y^SS>J>^\9  V^\     \^\    \>^\-¥J' 

\^\S¥^\  cJ\^^cJr^\«\>dr"  V-^V"  Wa«  V-^v 

Y^WVi  %£^\°J>C\  *bV^V *%^\   \fQV  A^V *U~\^ 

FSAR  =  4      OPI  =  772       CI  =  2.49 

"$& 

\i[            ^^^^k^\&^ 

J3^                         Xjj/     ^"^s^Ti: 

Ecological  Requirements 

This  long-legged  blackbird  is  a  creature  of  the  wide  open 
spaces.  Brewers  forage  in  almost  any  conceivable  open 
habitat,  wet  or  arid,  though  they  prefer  the  edges  of 
streams,  lakes,  and  marshes.  Foraging  areas  must  have 


bare  or  sparsely  vegetated  ground  and  very  open  or  non- 
existent canopies.  In  the  rural  areas  of  Marin  County, 
Brewers  forage  in  grasslands,  oak  savannah,  meadows, 
streams,  lakes,  or  marsh  edges,  irrigated  croplands,  plowed 


398 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


fields,  beaches  (both  above  and  at  the  high-tide  debris  line), 
weedy  fields,  feed  lots,  horse  corrals,  highway  shoulders, 
campgrounds,  picnic  areas,  and  trailhead  parking  lots.  In 
more  developed  regions,  they  inhabit  lawns,  playing  fields, 
golf  courses,  abandoned  lots,  sidewalks,  gutters,  shopping 
center  and  fast-food  parking  lots,  or  anywhere  else  they  are 
likely  to  get  human  handouts  or  inadvertent  crumbs. 
Besides  open  foraging  areas,  breeding  birds  need  adequate 
nesting  sites  with  relatively  high  perches— such  as  trees, 
cliffs,  or  telephone  wires— adjoining  them  (Horn  1968). 
Brewers  usually  nest  in  small,  isolated  colonies,  but  single 
nests  sometimes  do  occur  (Horn  1970).  Brewers  are 
polygynous,  but  unlike  Red-winged,  Yellow-headed,  and 
Tricolored  blackbirds,  they  do  not  defend  traditional  terri- 
tories (Williams  1952).  Multiple  nests  of  a  polygynous 
male  may  be  widely  spaced  among  nests  of  other  males  in 
the  colony.  Aggressive  defense  behavior  centers  around  the 
nest,  which  the  female  guards  more  carefully  than  the  male, 
and  around  the  perches  where  males  stand  guard  during 
nest  building  and  incubation.  Although  males  will  defend 
nests  to  a  degree,  they  devote  most  of  their  energy  to  the 
protection  of  females  from  the  advances  of  other  males. 
Coloniality  in  this  species  has  apparendy  evolved  as  an 
adaptation  to  the  exploitation  of  food  resources  that  are 
intensely  clumped  in  space  and  time  (Horn  1968).  For  this 
reason,  nesting  colonies  are  often  localized  even  where 
potential  nesting  sites  may  occur  over  broad  areas.  In  other 
instances,  colonies  are  found  in  isolated  stands  of  suitable 
breeding  habitat. 

Although  Brewer's  Blackbirds  sometimes  conceal  their 
nests  on  dry  or  damp  ground  in  low  dense  vegetation,  they 
most  frequendy  build  them  in  bushes  or  trees.  Tree  nests 
are  usually  at  moderate  heights,  though,  exceptionally,  they 
may  be  over  150  feet  from  the  ground  (Williams  1958). 
Nest  placement  among  Brewer's  Blackbirds  varies  consid- 
erably, both  geographically  and  between  habitats  (e.g., 
Walkinshaw  6k  Zimmerman  1961).  In  Monterey  County, 
the  average  height  of  nests  in  Monterey  pine  trees  was  25 
feet  (range  7.5-42  ft.,  Williams  1958,  n  =  72).  Brewer's 
Blackbirds  usually  locate  tree  nests  in  dense  foliage  on 
horizontal  limbs  or  towards  the  tips  of  branches  of  a  wide 
variety  of  native  and  ornamental  species  (Williams  1958). 
Rarely,  they  place  nests  in  trees  in  cavities  at  the  tops  of 
broken-off  stubs  or  in  enlarged  abandoned  woodpecker 
holes  (Williams  1958,  Ritter  6k  Purcell  1983).  On  occa- 
sion, they  even  choose  nest  sites  in  crevices  and  on  ledges 
of  cliffs  (Furrer  1975).  Besides  typical  dry-land  sites,  nests 
may  also  be  placed  over  water  in  bushes,  downed  brush 
clumps,  or  even  on  wharf  pilings  (Williams  1958).  A 
variety  of  odier  artificial  sites  have  also  been  used,  includ- 
ing support  beams,  wooden  ledges,  fence  posts,  telephone 
poles,  haystacks,  and  a  road  grader;  such  sites  seem  to  be 
used  chiefly  early  in  the  season  when  they  offer  better 
concealment  than  some  natural  sites  (Buder  1981).  Brew- 


ers appear  to  favor  bushes  affording  better  concealment, 
and  they  usually  build  their  nests  in  the  densest  parts  of 
bushes  (Furrer  1975).  Nest  sites  in  bushes  over  water, 
though,  may  apparendy  trade  concealment  for  lessened 
accessibility  to  land  predators.  In  dry  uplands,  Brewers 
usually  place  ground  nests  near  or  under  small  bushes, 
whereas  on  moist  or  even  wet  ground  they  usually  build 
them  on  small  hummocks  and  conceal  them  in  fresh  lush 
vegetation.  Although  these  blackbirds  often  use  several 
nest  types  simultaneously,  there  is  generally  a  predomi- 
nance of  one  type  in  a  colony.  In  sagebrush  habitat  in 
Washington,  Furrer  (1975)  found  two-thirds  of  a  colony's 
nests  in  bushes  in  dry  uplands  and  the  remainder  almost 
equally  split  between  ground  sites  and  bushes  over  water. 
He  also  noted  seasonal  and  yearly  differences  in  propor- 
tions of  the  various  nest  types.  As  the  season  progressed, 
the  number  of  bush  nests  declined  whereas  those  in  moist 
ground  sites  increased,  presumably  because  of  the  growth 
and  hence  availability  of  concealing  herbaceous  vegetation. 
Upland  ground  nests  were  of  rare  occurrence  late  in  a  dry 
year  but  not  in  a  wet  year,  apparendy  because  of  the 
persistence  of  dense  vegetation  in  the  latter  case.  These 
patterns  illustrate  the  behavioral  flexibility  of  Brewer's 
Blackbirds  in  nest  site  selection  in  a  heterogeneous  and 
unpredictable  environment. 

Nests  are  sturdy  structures  of  interlaced  twigs,  weed 
stems,  grasses,  or  pine  needles  that  may  or  may  not  be 
mixed  with  manure  and  mud  that  hardens  to  form  a  firm 
plasterlike  cup;  the  nest  lining  is  made  of  coiled  roodets  or 
hair  (Williams  1958,  Hansen  6k  Carter  1963). 

Of  the  many  foraging  habitats  mentioned  above,  Brew- 
ers prefer  the  rich  edges  of  lakes  and  streams  that  are 
devoid  of  emergent  vegetation  (Orians  1980).  When  these 
aquatic  habitats  are  available,  they  forage  there  primarily 
during  midday  at  the  peak  of  aquatic  insect  emergence; 
they  forage  in  dry  upland  sites  in  the  early  morning  and 
late  afternoon  (Horn  1968,  Orians  6k  Horn  1969).  Brew- 
ers are  principally  ground  foragers.  They  walk  with  short 
forward  jerks  of  the  head,  picking  insects  from  the  ground 
or  from  low  grasses  or  sedges.  They  also  forage  on  relatively 
flat  emergent  vegetation  or  walk  or  hop  with  the  aid  of 
wings  in  belly-deep  water  (Williams  1958).  Compared  to 
Red-winged  and  Yellow-headed  blackbirds,  Brewers  move 
at  a  more  rapid  and  steady  rate  and  seldom  dig  in  the  turf 
for  hidden  prey,  scratch,  or  use  their  bills  in  gaping 
movements  to  flip  over  sticks,  rocks,  or  dried  dung  in 
search  of  food  (Orians  1980).  When  foraging  in  open 
brushy  areas,  Brewers  either  walk  under  bushes  and  leap 
up  to  secure  prey  from  the  branches  or  walk  on  top  of  the 
shrub  canopy,  picking  visible  insects  (Orians  6k  Horn 
1969,  Orians  1980).  To  a  limited  extent,  Brewers  also 
glean  insects  from  the  foliage  of  their  nest  trees,  flycatch 
from  exposed  elevated  perches  or  in  short  flights  from  the 
ground,  or  hover  over  the  water,  snapping  food  from  the 


399 


New  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATLAS         New  World  Blackbirds  &  Orioles 


surface  (Williams  1 958).  Most  foraging  takes  place  in  areas 
adjacent  to  the  colony,  but  these  blackbirds  occasionally 
make  feeding  flights  up  to  a  mile  or  more  from  the  colony 
(Walkinshaw  ck  Zimmerman  1961,  Morn  1968).  When  a 
number  of  foraging  areas  are  available  near  a  colony,  birds 
usually  concentrate  in  one  area  at  a  given  time,  presumably 
the  most  productive  one;  individuals  follow  other  success- 
ful birds  to  prime  feeding  areas  (Horn  1968).  Where 
Brewers  occur  together  with  Red-winged  and  Yellow- 
headed  blackbirds,  dietary  overlap  is  high.  However,  there 
are  temporal  differences  and  considerable  separation  in  the 
habitat  patches  used  for  foraging,  with  Brewers  being  the 
most  terrestrial  of  the  diree  species  (Orians  6k  Horn  1969, 
Orians  1980). 

Brewer's  Blackbirds  are  relatively  omnivorous,  and  their 
diet  varies  considerably  geographically  according  to  habitat 
and  food  availability.  The  diet  year  round  in  California  is 
about  32%  animal  matter  and  68%  vegetable  fare;  nest- 
lings are  fed  about  89%  animal  and  11%  vegetable  food, 
the  latter  increasing  with  nesding  age  (Beal  in  Williams 
1958,  n  =  312).  For  the  West  as  a  whole,  animal  matter 
ranges  from  82%  of  the  diet  in  summer  (n  =  453)  to  22% 
in  winter  (n  =  150)  (Martin  et  al.  1951).  Important  animal 
foods  include  caterpillars,  flies,  grasshoppers,  beetles, 
damselflies  and  dragonflies,  ants,  and  spiders;  items  of 
minor  importance  are  miscellaneous  insects,  centipedes, 
sowbugs,  and  snails  (Soriano  1931,  Beal  1948,  Horn 
1968,  Orians  6k  Horn  1969,  Crase  6k  DeHaven  1978). 


Vegetable  food  in  California  consists  of  wild  oats, 
watergrass,  cereal  grains  (especially  rice  and  wheat),  and 
wild  forb  seeds  such  as  amaranth,  fiddleneck,  chickweed, 
sorghum,  filaree,  knotwecd,  and  currant  (Soriano  1931, 
Crase  6k  DeHaven  1978).  In  urban-suburban  settings, 
Brewer's  Blackbirds  readily  and  widely  exploit  crumbs  and 
castoffs  from  the  human  larder. 

Marin  Breeding  Distribution 

During  the  adas  period,  the  Brewer's  Blackbird  was  one  of 
the  most  widespread  breeders  in  Marin  County.  It  concen- 
trated here  in  the  lowland  valleys  and  was  sparse  or  absent 
in  steep,  hilly,  or  heavily  forested  terrain.  Representative 
breeding  locales  were  near  Abbott's  Lagoon  (NE  5/1 1/82 
-DS);  the  edge  of  Tomales  Bay  SP  (NE  4/29/82  -DS); 
Chileno  Valley  (NB  5/5/82  -DS);  and  Marshall-Petaluma 
Rd.  (NE  5/12/82  -DS). 

Historical  Trends/ Population  Threats 

Historically,  Brewer's  Blackbirds  have  apparently 
increased  considerably  in  California  as  a  result  of  clearing 
of  brush  and  trees,  cultivation  of  crops,  irrigation,  and 
livestock  husbandry  (G6kM  1944,  Williams  1958).  They 
probably  also  increased  in  the  past  in  urban-suburban 
areas  because  of  the  amenities  inadvertendy  provided.  On 
the  other  hand,  populations  of  this  blackbird  decreased  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


400 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


BROWN-HEADED  COWBIRD   Molothrus  ater 


Occurs  year  round,  though  primarily  as 

a  summer  resident  from  mid-Mar 

through  Sep. 

NfOpH-^VM  ®3r<^\o\>A  O  V^-V     V^C     W\CT3  ""  " 

A  fairly  common,  very  widespread 

Asvjw^C^Ya^^^ 

breeder;  overall  breeding  population 

fairly  large. 

XA^-^^^lX^Jir^xO  WfCcY^^V     \>A  ©  \--\C*  J 

X  !•  V-'A  •  >^\  ©  Jr=^\  ©"\»^\       V^'O  V>A    -\/\  >*_\ 
\rV>*J^\  ®JV^T\ '■^Jp^V*3r-^A ^  Jv-^x  •  >^v©  vvH — 

, 

Recorded  in  173  (78.3%)  of  221 
blocks. 

O    Possible        =      60   (35%) 
€    Probable      =      92  (53%) 

-m  'v'?  Y©  v^  \    j<  \  o-v^\  ^v^\     u<\\  ©  W\  •  \ — s 
^sV©A-!fc\  ©  V\©  V^V©  v^vM^Hcr  v-"\     i^A® 
©  *=ijkT3yj^ — -^  >-^\  ©  \^\  o  V-^\  ©fiJ-^v^o  V-^\  ©  V< 

_>*=•                                 XL*/        ^^*<©\2- 

^& 

•    Confirmed  =       21    (12%) 
FSAR  =  3       OPI  =  519       CI  =  1.77 

Ecological  Requirements 

As  with  many  facets  of  the  Brown-headed  Cowbird's 
biology,  its  use  of  various  habitats  is  shaped  by  its  parasitic 
mode  of  reproduction.  Because  breeding  Cowbirds  are  not 
tied  to  a  particular  nest  where  they  must  deliver  parental 
care,  they  are  free  to  carry  out  different  daily  activities  in 
widely  disjunct  areas  (Rothstein  et  al.  1986).  In  the  morn- 
ing, Cowbirds  are  dispersed  throughout  a  wide  variety  of 
habitats  where  potential  hosts  are  common.  The  greatest 
morning  abundance  occurs  in  riparian  vegetation  (Roth- 
stein et  al.  1980),  but  Cowbirds  are  likely  to  spend  the 
morning  in  almost  any  habitat,  including  freshwater 
marshes,  grasslands  with  occasional  trees  or  shrubs,  or 
even  suburban  and  urban  areas  such  as  the  San  Francisco 
Bay  region.  While  they  are  rare  in  unbroken  stands  of 
chaparral  and  dense  forests,  they  commonly  use  forest 
edges  or  open  woodland.  Female  Cowbirds  spend  their 
morning  time  in  these  habitats  searching  for  host  nests, 
while  males  try  to  court  females  and  compete  with  one 
another  for  social  dominance  (Rothstein  et  al.  1984). 
Relatively  little  feeding  is  done  during  the  morning. 
Females  and  some  males  occupy  the  same  morning  home 
range  throughout  the  breeding  season  and  even  in  succes- 
sive seasons  (Dufty  1982).  Many  males,  however,  seem  to 
wander  over  large  areas.  These  may  be  mosdy  subordinate 
yearling  males  prospecting  for  potential  breeding  sites. 

Most  individuals  leave  their  morning  breeding  ranges 
between  10  a.m.  and  1  p.m.  and  commute  up  to  4  miles 
or  more  to  feeding  sites,  where  they  forage  in  flocks  of  25 
or  more  through  the  rest  of  the  day  (Rothstein  et  al.  1984). 
Most  feeding  sites  consist  of  artificial  habitat,  such  as  horse 


corrals,  feed  lots,  bird  feeders,  lawns,  and  campgrounds. 
As  their  name  implies,  Cowbirds  have  a  strong  preference 
for  foraging  near  livestock  (Friedmann  1929),  which,  as 
foraging  associates,  provide  Cowbirds  with  several  sources 
of  food— insects  attracted  by  livestock  and  their  manure, 
insects  flushed  by  livestock  feeding  in  short  grass,  and 
grain  and  hay  at  corrals  and  feedlots.  Cowbirds  sometimes 
perch  on  cows  or  horses  and,  on  occasion,  feed  on  insects 
and  possibly  ticks  in  the  fur  of  these  associates.  They  also 
feed  on  table  scraps  at  campgrounds.  Most  feeding  occurs 
on  the  ground,  but  Cowbirds  will  readily  visit  bird  feeders 
well  above  the  ground.  They  usually  catch  insects  while 
walking  on  the  ground,  often  after  dashing  after  these  prey. 
Cowbirds  rarely  glean  insects  from  foliage,  but  they  occa- 
sionally flycatch.  Grasshoppers  seem  especially  prevalent 
in  their  diet,  although  the  long  list  of  arthropods  con- 
sumed (Friedmann  1 929)  suggests  that  Cowbirds  will  eat 
anything  they  can  catch.  Plant  matter  in  their  diet  consists 
mosdy  of  the  seeds  of  grasses  and  other  plants.  Fruit  is 
eaten  rarely.  In  the  winter,  the  diet  is  mosdy  plant  matter, 
and  there  is  a  shift  to  animal  matter  during  breeding.  This 
shift  is  much  more  pronounced  in  females,  for  whom  the 
animal  proportion  may  gready  exceed  50%  (Ankney  6k 
Scott  1980).  The  dietary  shift  is  related  to  the  female's 
increased  need  for  protein  while  laying  eggs.  Females  also 
seem  to  make  special  efforts  to  consume  calcium-rich  food 
items,  such  as  snails,  probably  to  secure  material  for 
eggshells.  In  the  few  observations  available,  females  ate  the 
eggs  they  took  from  host  nests,  and  this  may  also  be  an 
important  source  of  protein  and  calcium. 


401 


New  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATIAS         New  World  Blackbirds  &  Orioles 


The  Cowbird's  commuting  behavior  means  that  it  is 
abundant  at  some  sites,  such  as  horse  corrals,  in  the 
afternoon,  yet  totally  absent  from  the  same  site  in  the 
morning.  The  total  daily  home  range  of  many  Cowbirds, 
including  breeding  and  feeding  sites  used,  is  enormous 
and  ranges  up  to  990  acres  or  more,  compared  with  the 
2.4  to  7.4  acres  used  by  most  birds  of  their  size  (1  -1 .8  oz.) 
(Rothstein  et  al.  1984).  Even  the  morning  ranges  alone  can 
average  nearly  1 70  acres  and  can  extend  for  more  than  0.6 
to  1.2  miles.  In  areas  with  little  artificial  foraging  habitat,  a 
single  site,  such  as  a  horse  corral,  can  provide  food  for  the 
hundreds  of  Cowbirds  breeding  over  a  surrounding  area 
of  more  than  90  square  miles.  But  Cowbirds  are  not 
limited  to  using  the  commuting  pattern  (Rothstein  et  al. 
1986).  In  areas  where  there  are  many  feeding  sites  (e.g., 
backyard  feeders),  Cowbirds  may  feed  and  breed  in  the 
same  locality.  In  such  cases,  one  rarely  sees  large  afternoon 
flocks.  In  short,  breeding  Cowbirds  are  remarkably  oppor- 
tunistic in  their  use  of  space  (Rothstein  et  al.  1986,  1987) 
and  have  an  extraordinary  ability  to  find  feeding  sites.  In 
the  nonbreeding  season,  they  tend  to  occur  in  large  flocks, 
often  with  other  blackbirds  and  Starlings.  These  flocks  are 
usually  located  near  the  same  type  of  feeding  sites  that 
Cowbirds  prefer  during  the  breeding  season. 

The  enormous  literature  on  the  Cowbird's  use  of  hosts 
has  been  summarized  by  Herbert  Friedmann  and  his 
associates  (Friedmann  1929,  1963;  Friedmann  et  al.  1977; 
Friedmann  ck  Kiff  1985).  Throughout  its  North  American 
range,  the  Cowbird  has  been  known  to  parasitize  220 
species  and  to  have  its  chicks  reared  successfully  by  144  of 
these.  Generalizations  regarding  host  use  are  often  difficult 
to  make  because  there  is  considerable  geographic  variation 
in  this  parameter.  For  example,  Cowbirds  heavily  parasi- 
tize Red-winged  Blackbirds  on  the  Great  Plains  but  rarely 
in  California.  Perhaps  the  strongest  generalization  is  that 
Cowbirds  may  parasitize  any  passerine  in  their  breeding 
range,  except  the  larger  corvids.  Intensively  parasitized 
species  range  in  size  from  Empidonax  flycatchers  to  mead- 
owlarks.  Although  cavity  nesters  are  occasionally  parasi- 
tized, most  hosts  are  open  cup-nesting  species  of  tyrant 
flycatchers,  thrushes,  vireos,  wood  warblers,  orioles  and 
blackbirds,  tanagers,  sparrows,  and  finches.  There  are  even 
occasional  bizarre  cases  of  Cowbird  eggs  being  found  in 
the  nests  of  certain  ducks  and  hawks,  species  that  could 
never  rear  a  Cowbird.  This  extremely  generalized  host  use 
extends  even  to  the  individual  level:  the  best  evidence  to 
date,  based  on  biochemical  data,  shows  that  a  single  female 
will  parasitize  several  species  during  a  season  (Fleischer 
1985).  Host  use  has  been  studied  much  more  extensively 
in  the  Midwest  and  the  East  than  in  California.  In  Califor- 
nia, the  best  data  on  recorded  host  species  and  the  percent- 
age of  nests  parasitized  within  certain  samples  of  nests  or 
family  groups  come  from  the  Sierra  Nevada  (Friedmann  et 
al.  1977,  Gaines  1977,  Rothstein  et  al.  1980,  Verner  &. 

402 


Ritter  1983,  Airola  1986).  In  suburban  Santa  Barbara, 
Hooded  Orioles  are  parasitized  much  more  heavily  than 
any  other  species  (S.I.  Rothstein  pers.  obs.).  As  for  coastal 
northern  California,  frequent  hosts  include  Pacific-slope 
Flycatcher,  Warbling  Vireo,  Common  Yellowthroat, 
Wilson's  Warbler,  Song  Sparrow,  and  White-crowned 
Sparrow  (Friedmann  1963,  RM.  Stewart  &.  D.  Shuford 
pers.  obs.). 

Cowbird  parasitism  is  usually  detrimental  to  the  host's 
own  reproductive  output.  The  adult  females  remove  one 
host  egg  for  each  one  to  two  eggs  they  lay  (Friedmann 
1963).  The  Cowbird  nestling  is  usually  larger  than  its  host 
nestmates  and  therefore  outcompetes  them,  both  as  a 
result  of  its  larger  size  and  of  its  relatively  short  (11-12  day) 
incubation  period.  Small  hosts  with  long  incubation  peri- 
ods, such  as  Empidonax  flycatchers  and  some  vireos,  rarely 
fledge  any  of  their  own  young  if  parasitized.  Larger  hosts 
such  as  the  Hooded  Oriole,  Brewer's  Blackbird,  and  Song 
Sparrow— or  small  ones  with  short  incubation  periods  such 
as  the  Yellow  Warbler— often  succeed  in  raising  some  of 
their  own  young.  Because  the  great  majority  of  passerines 
feed  their  young  the  same  diet  of  small,  usually  soft-bodied 
insects,  dietary  quality  is  seldom  a  critical  variable  in 
Cowbird-host  dynamics.  However,  diet  is  a  major  factor  for 
Cowbirds  among  those  few  host  passerines  that  use  fruit 
or  seeds  to  feed  their  young,  most  notably  the  cardueline 
finches.  Cowbird  nesdings  usually  starve  to  death  in  the 
nests  of  species  such  as  the  House  Finch. 

Cowbird  parasitism  is  a  potent  evolutionary  pressure  on 
most  host  species,  and  some  such  as  the  American  Robin 
and  Northern  Oriole  have  evolved  rejection  of  Cowbird 
eggs.  Nearly  all  individuals  of  these  "rejecter"  species  (or  at 
least  the  females)  eject  Cowbird  eggs  from  their  nests 
(Rothstein  1975,  1977).  But  most  species  are  "accepters" 
and  show  nearly  1 00%  tolerance  of  Cowbird  eggs,  even  if 
these  are  highly  divergent  in  size  and  coloration  from  their 
own  eggs.  A  few  species,  such  as  the  Yellow  Warbler,  are 
somewhat  intermediate  and  only  reject  Cowbird  eggs  laid 
early  in  their  nesting  cycle  (in  this  warbler's  case,  by 
burying  the  Cowbird  egg  under  nesting  material,  Clark  &. 
Robertson  1981).  Another  possible  defense  against  parasit- 
ism is  to  drive  away  Cowbirds  before  they  can  lay  in  a  nest. 
Some  hosts  seem  to  recognize  Cowbirds  and  are  particu- 
larly aggressive  toward  them  (Robertson  ck  Norman 
1977).  It  is  unclear  whether  such  aggression  is  effective  for 
small  hosts  because  it  may  draw  attention  to  host  nests, 
thereby  increasing  the  risk  of  parasitism  (Smith  et  al. 
1984).  In  California,  host  aggression  seems  especially 
strong  in  the  Western  Wood-Pewee,  American  Robin, 
Northern  Oriole,  and  Red-winged  Blackbird  (S.I.  Roth- 
stein pers.  obs.). 

Female  Cowbirds  lay  eggs  on  60%-80%  of  the  days 
during  their  two-  to  three-month  breeding  season  for  a  total 
of  35  or  more  eggs.  This  number  of  eggs  laid  far  surpasses 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


that  for  any  other  species  of  wild  bird  (Scott  &.  Ankney 
1983),  except  possibly  one  of  the  other  four  species  of 
parasitic  Cowbirds.  The  high  laying  rate  has  been  found 
in  all  three  subspecies  of  the  Cowbird  and  in  a  wide  variety 
of  habitats  ranging  from  lowland  agricultural  areas  to  the 
High  Sierra  (Rothstein  et  al.  1986).  The  huge  egg  mass 
each  female  lays  may  impose  slight  physiological  costs 
(Keys  et  al.  1986,  Fleischer  et  al.  1987)  but  is  achieved 
without  depletion  of  major  body  reserves  of  calcium,  pro- 
tein, and  other  resources  (Ankney  &.  Scott  1980).  Their 
great  reproductive  effort  may  explain  why  females  have 
higher  mortality  rates  than  males  (Darley  1971),  which  in 
turn  explains  why  males  are  one  and  a  half  to  three  times 
more  numerous  than  females.  Males  may  seem  to  be  even 
more  than  three  times  as  abundant  as  females,  because  the 
latter  are  very  secretive  in  the  morning. 

Cowbird  parasitism  has  the  potential  to  limit  or  even 
extirpate  host  populations.  Declines  in  a  number  of  Cali- 
fornia songbirds,  especially  the  Bell's  Vireo  and  Willow 
Flycatcher,  are  correlated  with  increases  in  Cowbird  abun- 
dance (Gaines  1974).  Other  species  affected  in  the  state 
include  the  Yellow  Warbler,  Yellow-breasted  Chat,  Blue 
Grosbeak,  Warbling  Vireo,  and,  particularly  in  southern 
California,  Wilson's  Warbler.  Current  efforts  to  save  Cali- 
fornia's endangered  Least  Bell's  Vireo  include  extensive 
control  programs  to  remove  large  numbers  of  Cowbirds 
from  the  host's  few  remaining  breeding  sites.  It  is  impor- 
tant to  note,  though,  that  all  the  California  species  that 
now  seem  endangered  by  Cowbird  parasitism  were 
reduced  to  small  populations  by  humans'  massive  habitat 
destruction  during  this  century.  Loss  of  habitat,  rather  than 
Cowbird  parasitism,  may  be  the  main  culprit  in  the  decline 
of  species  such  as  the  Bell's  Vireo.  On  the  other  hand,  the 
Cowbird  may  be  delivering  the  coup  de  grace  to  these 
species;  other  riparian  nesters,  ones  less  susceptible  to 
Cowbird  parasitism,  are  not  threatened  with  extirpation 
(the  exception  is  the  Yellow-billed  Cuckoo).  Cowbird  con- 
trol should  be  viewed  as  a  stopgap  measure  to  be  employed 
until  the  more  difficult  goal  of  habitat  restoration  is 
achieved.  In  any  event,  it  may  prove  to  be  surprisingly 
difficult  to  control  Cowbird  numbers  in  some  areas  (Roth- 
stein et  al.  1987).  Furthermore,  the  longest-running  Cow- 
bird control  program  has  produced  mixed  results.  The 
tens  of  thousands  of  Cowbirds  that  have  been  killed  on  the 
Michigan  breeding  grounds  of  the  endangered  Kirtland's 
Warbler  since  1972  may  have  kept  the  warbler  from 
extinction,  but  its  population  has  shown  no  increase  (Kelly 
&.  DeCapita  1982).  See  Laymon  (1987)  for  further  discus- 
sion of  Cowbird  management  options  in  California. 

Marin  Breeding  Distribution 

Cowbirds  are  now  widespread  breeders  in  Marin  County. 
During  the  atlas  period,  the  greatest  concentrations 
occurred  in  the  lowland  valleys  and  gende  rolling  hills  of 


ranchlands  on  the  Point  Reyes  peninsula  and  to  the  east 
in  the  central  and  northern  sections  of  the  county.  Repre- 
sentative breeding  stations  were  Fish  Docks,  Poirit  Reyes 
(FL/FY  by  White-crowned  Sparrow  5/29/81  -DS); 
Drake's  Beach,  Point  Reyes  (FL/FY  by  White-crowned 
Sparrow  6/30/80  -DS);  Bolinas  (FL/FY  by  Song  Sparrow 
8/9/82  -DS);  and  Simmons  Trail,  Mt.  Tamalpais  (FL/FY 
by  Black-throated  Gray  Warbler  7/6/81  -DS). 

HistoricalTrends/  Population  Threats 

As  is  true  for  all  of  North  America  (Mayfield  1965), 
Cowbirds  in  California  have  increased  in  abundance  and 
distribution  more  than  any  other  native  bird  species  (Roth- 
stein et  al.  1980).  Before  this  century,  Cowbirds  in  Califor- 
nia were  apparendy  limited  to  the  Colorado  River,  where 
the  Dwarf  Cowbird  (M.  a.  obscurus)  occurred,  and  parts  of 
the  Great  Basin  (Modoc  Plateau,  Mono  Lake  area,  and 
possibly  the  Owens  Valley),  where  the  Sage  Brush  Cow- 
bird (M.  a.  artemisiae)  occurred.  The  latter  population  has 
undergone  a  small  increase  on  the  east  side  of  the  Sierra- 
Cascade  axis,  while  the  former  has  colonized  virtually  all 
of  California  west  of  the  Sierra-Cascade  crest.  While  gen- 
erally absent  from  the  crest  itself,  Cowbirds  appear  to 
disperse  across  it  resulting  in  so  much  interbreeding 
between  the  two  subspecies  that  these  are  now  less  distinct 
than  earlier  in  the  century  (Fleischer  &  Rothstein  1988, 
Fleischer  et  al.  1991). 

The  first  breeding  records  for  Los  Angeles  and  Ventura 
counties,  respectively,  are  from  1905  and  1904  (Willett 
1912),  and  Cowbirds  were  common  in  the  Los  Angeles 
basin  by  the  1930s  (Willett  1933).  Cowbirds  increased  in 
the  Central  Valley  by  1927,  if  not  earlier  (GckM  1944).  In 
coastal  northern  California,  breeding  was  first  docu- 
mented near  Irvington,  Alameda  County,  in  1922,  and 
there  were  a  number  of  additional  records  in  the  next  few 
years  (GckW  1927,  Sibley  1952).  Although  not  reported 
in  Stephens  and  Pringle's  (1933)  summary  of  the  county's 
avifauna,  Cowbirds  were  first  recorded  in  Marin  on  15 
October  1930  on  the  Tennessee  Cove  Road,  and  Cowbird 
eggs  were  found  in  an  American  Goldfinch  nest  at  Point 
Reyes  Station  sometime  prior  to  1936  (Gull  18,  No.  6). 
Another  early  Cowbird  record  for  Marin  was  of  a  sighting 
at  Inverness  on  13  May  1934  (Stephens  1936).  Grinnell 
and  Miller  (1944)  reported  a  phenomenal  increase  in  the 
population  in  the  San  Francisco  Bay  region  (and  else- 
where), and  Pray  (1950)  reported  continued  expansion  of 
breeding  numbers  there.  Laymon  (1987)  reported  that 
after  the  first  records  in  an  area  diere  is  generally  a  10-year 
lag  until  the  first  major  influx  is  noted  and  20  years  until 
population  saturation  is  reached.  Rothstein  et  al.  (1980) 
documented  the  expansion  of  Cowbird  populations  in  the 
Sierra  Nevada  since  1930  and  indicated  that  increases  were 
probably  still  occurring.  This  contention  was  supported  by 
continued  population  increases  on  Breeding  Bird  Surveys 

403 


New  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATIAS         New  World  Blackbirds  &  Orioles 


in  California  from  1968  to  1979  (Robbins  ct  al.  1986), 
though  numbers  were  relatively  stable  when  analysis 
extended  to  the  period  1968  to  1989  (USFWS  unpubl.). 
Cowbirds  may  still  find  opportunities  to  increase  in  coastal 
California,  especially  in  the  more  remote  forested  regions, 
as  human  developments  begin  to  encroach  on  wild  lands. 
See  Laymon  (1987)  for  further  details  of  historical  changes 
in  California. 

Much  and  possibly  all  of  this  phenomenal  increase  was 
caused  by  habitat  alterations  by  humans.  Just  about  every 
environmental  change  inflicted  on  California,  other  than 
the  paving  over  of  downtown  urban  areas,  has  made  the 
environment  more  favorable  for  Cowbirds.  Such  changes 
include  die  irrigation  of  arid  regions,  the  dispersal  of 
free-ranging  livestock,  and  the  establishment  of  horse  cor- 
rals in  wilderness  areas.  While  die  widespread  destruction 
of  riparian  vegetation  has  taken  away  some  prime  breeding 
habitat  for  Cowbirds,  the  equally  widespread  planting  of 
trees  in  fruit  orchards  and  around  houses,  as  in  the  Central 
Valley  and  perhaps  some  coastal  valleys,  has  created  new 
habitat  in  areas  that  previously  could  support  few  Cow- 
birds. 

Remarks 

Besides  its  range  extension  and  interactions  with  host 
species,  other  facets  of  the  Cowbird's  biology  have 
prompted  numerous  studies.  Studies  of  the  development 


and  use  of  the  male's  song  have  shown  that  Cowbirds  have 
a  complex  society  (West  et  al.  1981).  Studies  of  another 
male  vocalization,  the  flight  whisde,  have  demonstrated  a 
well-defined  system  of  local  dialects  (Rothstein  6k  Fleischer 
1987).  Despite  the  lack  of  parental  care,  Cowbirds  in 
California  are  monogamous,  and  the  females  seem  to  be 
more  faidiful  to  their  mates  than  is  the  case  in  most 
nonparasitic  songbirds  (Yokel  1986,  Yokel  6k  Rothstein 
1991).  Cowbirds  have  a  strange  behavior  in  which  they 
suddenly  run  up  to  other  birds  and  then  freeze  in  a 
head-bowed  posture  (Selander  6k  LaRue  1961,  Rothstein 
1980).  If  the  other  bird  is  of  another  species,  it  often  then 
preens  the  Cowbird.  Even  birds  such  as  Red-winged  Black- 
birds, though  not  known  to  preen  members  of  their  own 
species,  will  preen  Cowbirds.  Although  Cowbirds  some- 
times give  this  display  to  other  Cowbirds,  it  almost  never 
results  in  preening  then.  This  display  is  most  easily  seen 
in  wintering  flocks  while  Cowbirds  are  perched  in  trees  or 
bushes. 

While  the  Cowbird  will  not  win  any  popularity  contests, 
its  spectacular  range  expansion,  its  adaptations  for  parasit- 
ism, and  its  highly  social  nature  have  made  it  one  of  the 
most  frequendy  studied  North  American  birds.  Surely  it  is 
one  of  the  most  interesting  birds  in  any  region  in  which  it 
occurs. 

STEPHEN  I.  ROTHSTEIN 


404 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


HOODED  ORIOLE    Icterus  cucullatus 


^<\3rV 

A  summer  resident  from  late  Mar 
through  early  Sep. 

A  fairly  common,  very  local  breeder; 
overall  breeding  population  very  small. 

Recorded  in  15  (6.8%)  of  221  blocks. 

^\^ 

^V^VrX  \^\  \^t\  \r\ JV^\  3r^\5-W~ 

O    Possible        =        0   (0%) 

€    Probable       =         2   (13%) 
•    Confirmed  =       13  (87%) 

^?0> 

FSAR  =  3           OPI  =  45      CI  =  2.87 

Ecological  Requirements 

Though  near  opposites  in  vocal  ability  and  intensity  of 
plumage,  the  Hooded  Oriole  and  Northern  Mockingbird 
share  a  common  thread  of  history— a  spectacular  north- 
ward expansion  in  California  following  the  planting  of 
ornamental,  shade,  and  fruit  trees  in  settled  areas.  For- 
merly, Hooded  Orioles  bred  in  parts  of  southern  Califor- 
nia in  broadleaved  woodlands— of  native  fan  palms, 
willows,  cottonwoods,  and  especially  sycamores— along 
watercourses,  canyons,  and  dry  arroyos  (G&.M  1944). 
These  orioles  still  nest  in  native  fan  palms  in  southern 
California  deserts,  but  coastal  breeders  now  seldom  breed 
in  the  sycamore  groves  they  originally  favored  diere  (Pleas- 
ants 1979,  Unitt  1984).  Instead,  coastal  birds  have  colo- 
nized residential  areas  and  parks  in  urban  and  suburban 
centers  and,  to  a  lesser  extent,  orchards  and  trees  about 
rural  dwellings.  In  these  developed  areas,  fan  palms  are  the 
overwhelming  choice  of  these  orioles  for  nest  sites  and  nest 
materials.  Hooded  Orioles  began  to  colonize  central  and 
northern  California  in  the  1930s,  again  establishing  them- 
selves primarily  in  urban  and  suburban  areas  well  supplied 
with  planted  fan  palms  (GckM  1944). 

In  Marin  County,  studies  from  1976  to  1991  confirmed 
the  marked  dependence  here  of  Hooded  Orioles  on  Wash- 
ington fan  palms  for  nest  sites  and,  particularly,  nest 
materials  (H.  Peake  unpubl.  data).  The  distribution  and 
density  of  Hooded  Orioles  in  Marin  is  closely  tied  to  the 
availability  of  suitable  fan  palms  in  residential  yards  and 
gardens,  parks,  and  along  roadways.  In  fact,  nearly  all 
Hooded  Oriole  nest  sites  here  can  be  referred  to  by  street 
address.  The  orioles  prefer  nest  palms  that  have  nearby, 


but  not  touching,  trees  that  serve  as  approach  and  depar- 
ture routes.  Palms  are  rarely  used  as  nest  sites  if  they  stand 
in  isolation  from  other  trees  or  if  they  touch  other  trees, 
wires,  or  buildings  that  might  provide  access  for  terrestrial 
predators.  The  male  stands  sentry  in  nearby  trees  to  guard 
the  nest  tree  during  the  month-long  incubation  and  nest- 
ling period.  After  the  female  has  begun  nest  building,  the 
male  rarely  lands  on  the  nest  palm  until  joining  in  the 
feeding  of  newly  hatched  young.  Other  ornamental  (and 
sometimes  native)  trees  and  bushes  provide  cover  for 
adults  and  fledged  young,  substrate  for  insect  foraging, 
nectar-producing  flowers,  and  fruit.  Sugar-water  feeders 
furnish  an  additional  energy  source,  and  bird  baths  are 
attractions  for  bathing  rather  than  drinking. 

Based  on  several  hundred  nests  found  in  Marin  County 
from  1977  to  1991,  the  preferred  nest  tree  here  is  the 
California  fan  palm  (Washingtonia  filifera).  This  native 
palm  of  the  state's  southern  deserts  harbors  an  abundance 
of  blond  filaments  that  fray  from  the  edges  of  leaf  seg- 
ments. The  use  of  these  filaments  as  the  basic  ingredient 
for  nest  building  explains  much  of  the  Hooded  Oriole's 
local  nesting  patterns.  Females  that  nest  in  palms  without 
fibers,  or  in  other  types  of  trees,  will  carry  back  to  their 
chosen  nest  trees  filaments  from  other  suitable  palms  up 
to  several  hundred  yards  away.  The  second  choice  for  nest 
trees  here  is  the  Mexican  fan  palm  (Washingtonia  robusta), 
but  only  some  individuals  of  this  palm  sparingly  produce 
filaments.  The  third  choice  for  nest  sites  in  Marin  is  the 
Canary  (Island)  date  palm  (Phoenix  canariensis),  a  feather 
rather  than  a  fan  palm,  which  lacks  leaf  filaments.  Fourth 

405 


Netv  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATLAS         New  World  Blackbirds  &  Orioles 


choice  is  the  fortune  or  windmill  palm  (Trachycarpus 
excelsa),  a  fan  palm  from  China,  which  also  lacks  leaf 
filaments  but  has  a  coarse,  hairlike  covering  on  its  seem- 
ingly inverted  trunk  (smaller  at  the  base  and  wider  at  the 
top).  The  season's  first  nests  are  often  on  the  east  side  of 
the  selected  palm,  the  second  nest  on  the  west  side; 
successive  nests  sometimes  are  built  on  adjoining  leaves. 
In  only  one  known  instance  (in  San  Francisco)  did  orioles 
reuse  a  nest  that  earlier  in  the  season  had  produced  young 
(H.  Peake  pers.  obs.). 

Females  here  appear  to  always  start  the  season  by 
nesting  in  palms,  but  sometimes  they  later  switch  to  other 
infrequendy  used  nest  trees.  In  Marin  County,  less  than 
20  nests  were  found  in  nonpalm  trees  including  blue  gum 
eucalyptus  (Eucalyptus  globulus),  American  elm  (Ulmus 
americana),  monkey  puzzle  tree  (Araucaria  imbricata),  west- 
ern catalpa  (Catalpa  speciosa),  green  dracena  (Coryline 
australis),  and  cypress.  Conceivably,  competition  for  avail- 
able California  fan  palms  might  lead  to  the  orioles'  select- 
ing alternative  trees,  but  breeches  of  security  seem  to  be  the 
most  frequent  reason,  especially  during  nest  construction. 
Females  in  San  Rafael  that  built  three  or  four  nests  in  one 
season  apparendy  did  so  because  perceived  threats  (includ- 
ing this  observer)  made  them  reject  their  original  nest  site 
and  sometimes  select  nest  trees  other  than  California  fan 
palms.  The  height  of  the  several  hundred  nests  observed 
in  Marin  County  ranged  from  6  feet  in  a  young  fdifera  to 
90  feet  in  a  mature  robusta,  though  most  were  built  35  to 
40  feet  up  in  mature  fdifera. 

No  matter  what  the  tree  species  selected  as  a  nest  site, 
virtually  all  Marin  nests  were  made  solely  from  the  blond 
leaf  filaments  of  Washington  fan  palms.  Of  a  dozen  or  so 
nests  examined  closely,  coarser  fibers  were  used  for  the 
outside  of  the  nest  and  finer  filaments  for  the  lining.  The 
one  exception  to  the  exclusive  use  here  of  palm  leaf 
filaments  for  nest  construction  was  a  female  that  built  two 
nests  in  a  fortune  palm  using  the  hairy  fibers  from  its 
trunk.  In  fan  palms,  the  new  growth  of  leaves  emanates 
vertically  from  the  bud  at  the  top  of  the  trunk  like  a  slow 
motion  fountain  from  the  top  of  an  upright  pipe.  The  palm 
fronds  bend  out  and  curve  down  more  each  year  until  they 
dry,  turn  tan,  and  clasp  against  the  palm  trunk,  forming  a 
skirt  of  dead  leaves.  Females  typically  select  nest  sites  in  the 
lower  half  of  tree  crowns,  where  the  broad  green  palm 
leaves  have  assumed  a  somewhat  horizontal,  umbrella-like 
arc  diat  protects  the  nests  from  sun,  rain,  and  overhead 
predators.  Fan  palm  leaves  are  pleated  and  split  from  the 
tip  to  the  midpoint  into  50  to  70  narrow  pointed  leaf 
segments  with  filaments  fraying  from  the  edges.  The  female 
typically  builds  the  nest  on  the  underside  of  the  unsplit 
part  of  a  green  palm  leaf.  The  lower  browning  leaves  are 
rarely  used,  though  females  occasionally  place  their  nests 
under  the  dried  leaves  of  the  palm  skirt.  In  San  Rafael,  one 
brood  was  lost  when  the  female  chose  for  the  first  nest  a 

406 


leaf  that  was  turning  brown.  A  June  heat  wave  appeared  to 
hasten  die  leafs  drying,  causing  it  to  clasp  down  tight 
against  the  trunk  three  or  four  days  before  the  young  would 
have  left  the  nest  under  more  favorable  circumstances. 
Female  orioles  at  Dominican  College  in  San  Rafael  tend  to 
build  nests  in  palm  skirts  more  frequendy  than  do  females 
at  other  sites  in  Marin,  perhaps  because  the  leaf  crowns 
there  are  more  open  and  provide  less  protection  than  those 
elsewhere.  Marin's  "100-year  freeze"  of  December  1990 
and  January  1991  killed  the  palm  leaves  in  the  lower  half 
of  most  palm  tree  crowns,  the  area  where  the  orioles  prefer 
to  nest.  Consequendy,  in  the  1991  nesting  season,  most 
orioles  used  for  nest  sites  the  second  choice,  dried  leaf 
skirts  hanging  down  against  Washingtonia  fdifera  trunks 
(H.  Peake  pers.  obs.). 

In  typical  nest  construction  in  Washington  fan  palms, 
the  female  flies  up  under  the  selected  green  leaf  and  clings 
like  a  fly  on  a  ceiling.  She  pokes  holes  up  through  the  leaf, 
using  her  sharp  slender  beak  both  as  punch  and  awl, 
twisting  her  head  left  and  right  to  enlarge  these  holes. 
Flying  to  another  palm  leaf  on  her  tree,  or  often  to  another 
fdifera,  she  plucks  a  blond  filament.  Returning  to  her  nest 
leaf,  she  pokes  and  pushes  the  filament  up  through  a  hole, 
then  flying  to  the  upper  side  of  the  leaf,  pulls  some  length 
of  the  filament  up,  dien  pokes  the  end  down  through 
anodier  hole,  literally  sewing  the  nest  anchors  to  the  leaf. 
Upon  completion,  the  anchoring  threads  suspend  the 
elongate,  semipensile  nest  hammocklike,  snug  to  the 
underside  of  the  leaf.  Arrival  and  departure  is  made 
through  two,  or  occasionally  only  one,  open  sides  of  the 
nest  close  to  the  palm  leaf.  Females  building  in  Canary 
date  palms  stitch  less  and  wrap  more  of  the  filaments 
around  the  stems  of  the  leaf  segments  to  secure  the  nest. 
Females  nesting  in  other  trees  that  lack  the  strong  petioles 
(stems)  of  the  Washingtonia  palms  stitch  two  or  more 
leaves  together  with  filaments  to  provide  the  protective 
"awning"  for  the  nest.  Such  is  the  case  with  nests  in 
fortune  palm,  blue  dracena,  American  elm,  common 
catalpa,  and  young  blue  gum  eucalyptus. 

Throughout  most  of  California,  Hooded  Orioles  now 
select  fan  palms  overwhelmingly  as  their  nest  tree  of  first 
choice,  though  formerly  other  tree  species  must  also  have 
been  important  when  the  birds  nested  extensively  in 
broadleaved  woodlands.  Other  trees  these  orioles  have 
used  as  nest  sites  in  California,  in  addition  to  those 
mentioned  above,  include  pepper,  walnut,  live  oak,  banana 
plant,  tree  yucca,  cottonwood,  fig,  sycamore,  maple,  mes- 
quite,  olive,  ash,  acacia,  umbrella  tree,  and  avocado;  excep- 
tional nests  were  one  in  ornamental  vines  on  a  porch  and 
another  suspended  from  a  single  fiber  strand  wedged  in  a 
crack  under  the  eaves  of  a  house  (Illingsworth  1901 ,  Bailey 
1910,  G&M  1944,  H.W.  Grinnell  1944,  Huey  1944, 
Bent  1958,  Unitt  1984,  S.  Fitton  in  lift.).  Hurd  (in  Bent 
1958)  noted,  contrary  to  observations  in  Marin  County, 


New  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


blew  World  Blackbirds  &  Orioles 


that  Hooded  Orioles  in  Riverside  selected  mosdy  eucalyp- 
tus trees  for  first  nest  attempts  and  palm  trees  for  second 
nest  attempts.  In  the  Arcata/Eureka  area  along  the  moist 
coast  of  Humboldt  County,  where  Washington  fan  palms 
are  few  and  less  well  developed  than  at  most  interior  sites 
where  Hooded  Orioles  breed,  the  orioles  nest  almost 
exclusively  in  date  palms,  usually  on  the  leeward  side  (S. 
Fitton  pers.  comm.).  The  growth  form  of  date  palms  in 
Humboldt  County  is  such  that  often  fronds  touch  each 
other,  providing  protected  areas  where  nests  are  built. 

No  matter  what  nest  tree  they  select  in  California,  these 
orioles  almost  exclusively  prefer  palm  leaf  filaments,  pri- 
marily from  Washington  fan  palms,  for  nest  material.  The 
Arcata/Eureka  area  again  is  an  exception.  Females  there 
frequendy  use  (singly  or  in  combination)  both  Washington 
fan  palm  filaments  and  fibers  hammered  loose  from  the 
fronds  of  date  palms;  one  nest  there  was  made  entirely 
from  grass  (S.  Fitton  in  litt.).  Other  nest  materials  Hooded 
Orioles  have  used  infrequendy  in  California  are  the  white 
hairs  of  "old  man"  cactus  (Cepha locerus  senilis),  dodder  (an 
orange-colored  parasitic  vine)  (H.W.  Grinnell  1944,  Bent 
1958),  and,  as  mentioned  above,  the  hairy  fibers  from  the 
trunks  of  fortune  palms;  other  coarse  fibers,  such  as  those 
of  yucca,  used  elsewhere  in  the  species'  range,  are  probably 
also  used  here  on  occasion.  California  nests  are  usually 
either  lined  with  finer  palm  fibers  or  are  left  unlined; 
occasionally  they  are  scantily  lined  with  felted  vegetable 
down  or  a  few  feathers  (Dawson  1923).  On  one  rare 
occasion,  a  female  in  San  Rafael  landed  on  the  ground  to 
procure  some  tissue  paper,  presumably  for  nest  material 
(H.  Peake  pers.  obs.). 

Nest  sites  and  nest  materials  in  California  vary  consid- 
erably from  those  in  Arizona  and  Texas.  In  these  latter 
states,  palm  (or  palmetto)  trees  are  used  for  nest  sites  and 
materials  less  frequently  than  in  California,  and  nesting  is 
usually  concentrated  in  deciduous  woodlands  along  low- 
land stream  courses  (Bent  1958,  Phillips  et  al.  1964, 
Oberholser  1974).  In  Texas,  Hooded  Orioles  frequendy 
build  their  nests  in  and  of  Spanish  moss  (Tillandsia);  nests 
may  be  placed  in  living  trusses  of  this  plant  or  in  the  lower 
limbs  and  drooping  outer  branches  of  undergrowth  where 
pieces  of  Spanish  moss  are  brought  for  nest  construction. 
Nests  there  are  also  built  in  bushes  using  a  black  hairlike 
moss  or  in  yuccas  using  the  tough  fibers  from  the  trunk, 
also  used  in  Arizona.  In  Arizona,  nests  are  often  placed  in 
deciduous  trees  (frequendy  secured  in  clumps  of  misde- 
toe),  and  wiry  grasses  are  favorite  nest  materials  (Bent 
1958);  one  nest  in  the  desert  was  built  entirely  of  horsehair 
(Huey  1944).  The  lining  of  nests  seems  to  be  more  com- 
monly practiced  in  Arizona  and  Texas;  lining  materials 
include  dry  moss,  grasses,  wool,  horsehair,  yucca  fibers, 
Spanish  moss,  plant  down,  and  sometimes  a  few  feathers. 


Where  studied  in  San  Rafael,  Hooded  Orioles  forage 
mosdy  from  5  to  40  feet  above  the  ground,  methodically 
gleaning  insects  and  caterpillars  from  the  foliage  and 
branchwork  of  trees  and  bushes.  Rarely,  they  flycatch  from 
a  perch  and  at  dusk  pursue  insects  attracted  to  porch  lights, 
catching  their  prey  in  flight  (H.  Peake  pers.  obs.).  Although 
consumption  of  grasshoppers  (Bent  1958)  suggests  they 
forage  on  the  ground,  this  behavior  has  never  been 
observed  in  Marin  County  (H.  Peake  pers.  obs.),  though 
elsewhere  it  apparendy  occurs  rarely  (Bent  1958).  The  diet 
is  poorly  documented,  though  a  variety  of  insects,  caterpil- 
lars, and  probably  spiders  are  consumed  (Bent  1958). 
Hooded  Orioles  probe  or  puncture  tubular  flowers  for 
nectar  and  drink  sugar  water  from  hummingbird  type 
feeders  regularly;  they  also  consume  fruit,  especially  figs 
and  loquats,  in  season.  These  foods  appear  to  be  eaten  by 
the  young  only  after  leaving  the  nest.  In  San  Rafael  on  10 
November  1990,  a  female  Hooded  Oriole  hungrily  ate 
seeds  while  resting  on  her  belly  at  a  backyard  feeder  (H. 
Peake  pers.  obs.).  This  atypical  feeding  behavior  was  prob- 
ably a  reaction  to  food  stress  at  a  time  when  most  of  these 
orioles  are  wintering  in  Mexico. 

Marin  Breeding  Distribution 

During  the  adas  period,  Hooded  Orioles  were  found 
breeding  only  in  the  urban  corridor  along  Highway  101 
from  Novato  south  to  the  Corte  Madera/Larkspur  area. 
This  distribution  matched  that  of  extensive  plantings  of 
palm  trees  in  the  county's  least  fog-shrouded  suburban  and 
urban  areas.  Representative  nesting  locations  during  the 
adas  period  included  Warren  Court,  San  Rafael  (NY/FY 
5/7/82  -HoP);  Greenwood  Ave.,  San  Rafael  (NY/FY 
8/3/82  -HoP);  and  Lamont  Ave.,  Novato  (NE  5/6/79 
-DS  et  al.). 

In  Marin  County,  Hooded  Orioles  concentrate  in  east 
and  west  Corte  Madera  and  in  central  and  northern  San 
Rafael.  In  one  week  in  May  1983,  a  search  of  much  of 
central  and  southern  Marin  located  50  active  nests— 10  in 
Corte  Madera  and  40  in  San  Rafael  (H.  Peake  unpubl. 
data).  Distribution  was  determined  by  the  availability  of 
preferred  palm  nesting  sites— 42  nests  were  in  Wash- 
ingtonia  filifera,  5  in  W.  robusta  (a.k.a.  gracilis),  and  3  in  the 
Canary  (Island)  date  palm.  Only  a  handful  of  Washington 
fan  palms  were  scattered  south  of  Corte  Madera.  To  the 
north,  when  palms  were  clustered,  nests  were  separated  by 
100  feet  or  more,  except  in  one  instance  in  which  single 
nests  were  in  two  palms  30  feet  apart.  Areas  of  greatest 
oriole  density  were  old  (central)  San  Rafael  and  around 
Dominican  College,  where  22  active  nests  were  located  in 
an  area  of  about  two  square  miles;  and  Terra  Linda  with 
1 3  active  nests  and  Santa  Venetia  with  5  active  nests,  the 
two  areas  totalling  about  one  square  mile.  Potential  nesting 
sites  with  fan  palms  in  Marinwood,  Hamilton  Field,  Bel 
Marin  Keys,  and  Novato  were  not  included  in  the  survey. 

407 


Net*/  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATLAS         Neu,  World  Blackbirds  &  Orioles 


Hooded  Orioles  have  nested  in  two  areas  with  fan  palms 
in  Novato,  one  west  of  Highway  101  south  of  Dclong 
Avenue  and  a  second  east  of  Highway  101  and  south  of 
Atherton  Avenue  (D.  Shuford  pers.  comm.);  there  are  few 
fan  palms  elsewhere  in  Novato,  though  it  has  a  suitable 
climate.  Veteran  Marin  nurserymen  suggested  that  the 
limited  distribution  of  palms  in  Novato  was  perhaps  due 
to  its  development  mosdy  in  the  post- World  War  II  era, 
when  landscape  budgets  were  reduced  and  people  were 
discouraged  from  planting  palms  on  small  lots  because  of 
the  difficulty  of  the  necessary  tree  care.  Fan  palms,  espe- 
cially W.  filifera,  are  generally  unsuccessful  in  moist  and 
foggy  coastal  climates  because  of  dieir  susceptibility  to 
crown  rot  (Maino  6k  Howard  1955).  This  probably 
explains  the  scarcity  of  filifera  in  Mill  Valley,  Sausalito,  and 
the  outer  coast  and,  hence,  the  lack  of  nesting  Hooded 
Orioles  in  these  areas  as  well. 

Historical  Trends/Population  Threats 

During  this  century,  the  Hooded  Oriole  has  spread  spec- 
tacularly northward  as  a  breeder  in  both  Arizona  (Phillips 
et  al.  1964)  and  California  (G6kM  1944,  Sibley  1952, 
ABN).  In  California's  San  Joaquin  Valley,  notable  sight- 
ings were  in  Fresno,  Fresno  County,  in  1915  and  in 
Modesto,  Stanislaus  County,  in  1937  (GckM  1944).  In 
the  1920s,  Hooded  Orioles  reached  the  main  limit  of  their 
breeding  range  on  the  California  coast  at  Santa  Barbara 
(Dawson  1923).  These  orioles  were  initially  reported  in  the 
San  Francisco  Bay  Area  in  Alameda,  Contra  Costa,  and 
Santa  Clara  counties  in  1930;  first  nesting  records  were 
from  Santa  Cruz  in  1932  and  San  Leandro,  Alameda 
County  in  1939  (GckM  1944,  Sibley  1952).  There  were 
no  records  for  Marin  County  as  of  1933  (S6kP  1933),  but 
breeding  was  first  reported  here  at  Larkspur  on  22  May 
1941  with  the  observation  of  a  nest  with  young  (Gull 
23:21).  Hooded  Orioles  continued  to  increase  around  the 
Bay  Area  with  first  reports  for  San  Francisco  in  1939 


(Sibley  1952)  and  Napa  and  Solano  counties  in  1948  (AFN 
2:187).  Reports  in  Audubon  field  Notes  and  American  Birds 
documented  widespread  increases  of  the  oriole  population 
in  the  1950s  and  1960s  along  the  coast  and  in  the  San 
Joaquin  and  Sacramento  valleys.  These  orioles  made  a 
notable  northward  expansion  on  the  coast  by  colonizing 
Humboldt  County  and  breeding  in  Ferndale  in  1972 
(Yocum  ck  Harris  1975,  AB  26:903).  Nesting  was 
attempted  in  Areata,  Humboldt  County,  in  1981  (AB 
35:977)  and  by  1985  a  search  of  the  Arcata/Eureka  area 
revealed  40+  birds  (AB  39:961).  Expansion  also  continued 
northward  in  the  Central  Valley,  highlighted  by  the  discov- 
ery of  24  birds  in  the  Anderson/Redding  area  of  Shasta 
County  from  26  to  31  May  1985  (AB  39:348).  Such 
expansions  are  now  of  limited  extent,  as  indicated  by 
relatively  stable  numbers  of  Hooded  Orioles  on  Breeding 
Bird  Surveys  in  California  from  1968  to  1989  (USFWS 
unpubl.  analyses).  In  the  coming  years,  Hooded  Orioles 
will  likely  continue  to  expand  locally  as  palm  plantings 
increase  in  suburban  and  urban  areas,  and  they  will  likely 
consolidate  their  holdings  at  the  edge  of  their  range  as  well. 
It  is  unlikely  that  they  will  expand  much  farther  to  the 
north,  though,  as  they  have  now  reached  the  limit  of 
extensive  palm  plantings. 

On  a  local  scale,  at  least,  numbers  of  Hooded  Orioles 
breeding  in  Marin  County  declined  steadily  over  the 
course  of  the  five-year  drought  from  1986-87  to  1990-91. 
Presumably  because  of  the  combination  of  the  heavy  freeze 
in  the  winter  of  1990-91  and  the  fifth  year  of  a  drought, 
Hooded  Oriole  numbers  in  San  Rafael  in  1991  reached 
there  lowest  point  since  studies  began  there  in  1976,  and 
apparendy  no  young  were  produced  (H.  Peake  unpubl. 
data).  It  will  be  interesting  to  see  if  nesting  numbers 
rebound  when  wetter  climatic  conditions  return. 

HOLLY  PEAKE 


408 


Neu>  World  Blackbirds  &  Orioles 


SPECIES  ACCOUNTS 


New  World  Blackbirds  &  Orioles 


NORTHERN  ORIOLE   Icterus  galbula 


-^^ 

A  summer  resident  from  late  Mar 

through  early  Sep. 
A  common,  widespread  breeder;  over- 

all breeding  population  fairly  large. 

Y^-^J^a  A^r^x    3^\ * X--"A     V^A     \^\     V^-n 

Recorded  in  129  (58.4%)  of  221 
blocks. 

f 

O    Possible        =       25   (19%) 
€    Probable       =      32   (25%) 
•    Confirmed  =       72   (56%) 

'■^j^z>^       ~<s_  v-^a   '\*^\ ..■\>*\   -\-<\ •  jv¥C\ 

^2o 

FSAR  =  4        OPI  =  516       CI  =  2.36 

Ecological  Requirements 

These  brighdy  colored  "blackbirds"  are  inhabitants  of 
Marin  County's  native  oak  savannah,  oak  woodland,  and 
willow  riparian  habitats  in  valleys  or  gendy  rolling  terrain, 
especially  where  trees  are  well  spaced  or  in  isolated  clumps. 
They  now  also  nest  commonly  in  planted  eucalyptus 
groves;  along  the  fog-bound  coast,  they  are  found  breeding 
almost  exclusively,  though  sparingly,  in  this  habitat.  In 
suburban  areas  and  ranchyards  away  from  the  fog  belt, 
they  sometimes  nest  in  other  introduced  plantings  widi 
tree  spacing  similar  to  their  other  natural  habitats.  Marin 
and  California's  nesting  birds  are  of  the  western,  Bullock's 
form  of  the  Northern  Oriole. 

Nests  are  situated  in  a  variety  of  tree  species,  bodi  native 
and  introduced  but  locally  are  most  frequendy  found  in 
deciduous  oaks  (especially  the  valley  oak),  eucalyptus,  and 
willows.  Although  often  found  in  riparian  areas,  nests  may 
be  built  far  from  available  surface  water.  Concentrations  of 
nesting  birds  along  stream  courses  and  valleys  may  reflect 
the  appropriate  spacing  of  nest  trees  and  proximity  to 
upslope  foraging  areas. 

While  Northern  Orioles  have  been  known  to  build 
their  nests  as  low  as  5  feet  and  as  high  as  80  feet  or  more 
above  the  ground,  they  usually  place  them  between  1 5  and 
50  feet  high.  The  long  pendulous  nests  are  most  often 
attached  to  small  hanging  branches  on  the  outside  of  the 
canopy  or  alongside  vertical  or  horizontal  branches  near 
the  top  of  the  canopy  of  the  tree.  Mean  nest  height  of 
Northern  Orioles  at  20  sites  on  the  Great  Plains  and  in 
Canada  ranged  from  1 2  to  36  feet  (mean  of  means  =  26 


ft.,  Schaefer  1976,  n  =  516).  These  orioles  show  geo- 
graphic variation  in  nest  placement  unrelated  to  taxonomic 
differences  in  populations.  Nest  placement  is  most  easily 
explained  by  geographic  differences  in  vegetation.  Region- 
ally, though,  where  squirrel  predation  is  a  problem,  some 
nests  may  be  placed  high  in  trees,  and  in  some  localities 
they  may  be  placed  on  the  leeward  side  of  trees  to  reduce 
nest  damage  or  loss  from  strong  winds. 

Northern  Orioles  also  show  geographic  variation  in  the 
insulative  qualities  of  nests  correlated  with  local  tempera- 
tures: nests  are  better  insulated  from  heat  in  hotter  climates 
(Schaefer  1980).  The  female  weaves  the  nest  of  a  variety  of 
materials,  commonly  including  grasses,  fibers  stripped 
from  the  stems  of  a  variety  of  plants  (often  nettles),  and 
Ramalina  lichens.  Northern  Orioles  will  build  their  nests 
almost  entirely  of  horsehair  if  it  is  available,  and  they  are 
attracted  by  artificial  fibers  of  all  kinds,  building  nests  of 
fishing  line,  string,  yarn  (often  in  bright  colors),  or  even 
plastic  Easter  grass,  when  available. 

Nests  can  occur  in  clusters,  with  20  nests  recorded 
within  a  2.5-acre  area  of  oak  savannah  and  up  to  5  nests 
in  a  single  tree.  Pairs  do  not  always  nest  so  densely  in 
savannah  habitat,  and  when  they  settle  areas  at  lower 
densities,  they  seem  to  defend  larger  territories  (Miller 
1931b).  In  areas  with  a  dense  canopy  and/or  understory 
vegetation,  their  nests  are  predictably  more  dispersed, 
often  widi  no  other  pairs  or  only  one  other  pair  in  the 
vicinity.  Birds  may  cluster  their  nests  even  when  there  is 
no  apparent  limitation  on  the  availability  of  suitable  nest 

409 


New  World  Blackbirds  &  Orioles         MARIN  COUNTY  BREEDING  BIRD  ATIAS         New  World  Blackbirds  &  Orioles 


sites  (Williams  1982,  1988).  At  some  sites  where  only  a 
few  trees  are  available,  though,  nest-site  limitation  may 
force  colonial  nesting  as  suggested  by  Pleasants  (1979). 

Northern  Orioles  defend  only  the  immediate  vicinity  of 
their  nest,  and,  although  they  are  rarely  seen  foraging  in 
groups,  a  number  of  pairs  may  overlap  in  foraging  areas 
away  from  their  nests.  Radiotelemetry  studies  in  the  Car- 
mel  Valley,  Monterey  County,  indicate  that  solitary  nesting 
females  tend  to  forage  alone  and  near  their  nests,  whereas 
females  with  near  neighbors  may  forage  up  to  985  yards 
away  from  their  nests  at  group  foraging  sites  (Williams 
1988,  1990).  Although  Northern  Orioles  glean  insects 
extensively  from  the  foliage  and  flowers  of  trees,  they  also 
spend  considerable  amounts  of  time  foraging  in  shrubs 
and  grassland.  They  use  a  technique  common  to  many 
species  in  the  subfamily  Icterinae,  that  of  "gaping."  This 
technique  entails  poking  the  bill  into  vegetation  or  the 
body  of  an  invertebrate  and  then  opening  the  bill  to  allow 
extraction  of  hidden  prey  from  the  crevices  of  plant  tissues 
or  removal  of  soft  tissue  from  an  inedible  shell  (such  as  the 
urticating  hairs  on  the  body  of  a  tent  caterpillar).  They  will 
also  remove  the  stinger  from  a  honey  bee  before  consum- 
ing it. 

Northern  Orioles'  diet  in  California  from  April  to 
August  is  about  79%  animal  matter  and  21%  vegetable  fare 
(Beal  1910,  n=162).  For  the  West  as  a  whole,  their 
consumption  of  animal  food  peaks  at  92%-98%  in  spring 
and  fall  (n  =  87)  and  reaches  a  low  of  81%  in  summer  (n= 
213)  (Martin  et  al.  1951).  Principal  food  items  include 
caterpillars  and  lepidoptera  pupae— 63%  of  the  diet  in 
April  but  only  8%  in  July  (Beal  1910);  beedes,  including 
the  cotton  boll  weevil  (Howell  1906)— 35%  of  diet  (Beal 
1910);  bees  and  ants— 15%  (Beal  1910);  many  species  of 
orthopterans,  including  grasshoppers  (Bryant  1914b), 
camel  crickets  and  species  in  the  genus  Timema;  hemipter- 
ans,  such  as  scale  insects,  stink  bugs,  leafhoppers,  and 


treehoppers;  earwigs  (only  available  since  the  1920s);  as 
well  as  some  spiders  and,  rarely,  lizards  or  mollusks. 
Vegetable  fare  includes  fruits  (mainly  in  the  summer 
months,  especially  July),  sap,  and  nectar  (Emerson  1904). 

Marin  Breeding  Distribution 

During  the  atlas  period,  Northern  Orioles  were  wide- 
spread breeders  in  most  of  Marin  County,  but  they  nested 
at  only  a  few  scattered  sites  on  the  Point  Reyes  peninsula. 
Aldiough  there  was  a  general  trend  of  increasing  abun- 
dance from  the  coast  toward  die  drier  interior,  Northern 
Orioles  were  numerous  breeders  in  eucalyptus  groves  even 
along  the  shores  of  Tomales  Bay.  Representative  breeding 
localities  were  Bear  Valley  Headquarters,  PRNS  (FY  6/1/81 
— DS);  Bolinas  Community  Gardens  (FY  6/4/76  — DS); 
Chileno  Valley  (NB  5/5/82  -DS);  Magetti  Ranch,  Point 
Reyes-Petaluma  Rd.  (NY  5/27/82  -DS);  Mt  Burdell, 
Novato  (NE  4/21/81  — ITi);  and  San  Antonio  Creek,  just 
W  of  Hwy.  101  (NE  5/17/80  -DS). 

Historical  Trends/ Population  Threats 

The  planting  of  eucalyptus  groves  appears  to  have  gready 
increased  the  breeding  distribution  of  Northern  Orioles  in 
Marin  County  in  historical  times,  especially  in  the  low 
rolling  hills  and  valleys  of  the  grassland-dominated 
ranchlands  to  the  east  and  north  of  Tomales  Bay.  Besides 
providing  suitable  nesting  sites  and  cover  in  areas  formerly 
largely  devoid  of  trees,  eucalyptus  also  furnish  these  orioles 
with  a  rich  source  of  nectar  from  their  profusely  blooming 
flowers.  Populations  of  Northern  Orioles  were  relatively 
stable  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989  (USFWS  unpubl.  analyses). 

PAMELA  L  WILLIAMS 


410 


Cardueline  Finches 


SPECIES  ACCOUNTS 


Cardueline  Finches 


Cardueline  Finches 

Family  Fringillidae 
Subfamily  Carduelinae 


PURPLE  FINCH    Carpodacus  purpureas 


A  year-round  resident;  winter  numbers 

a^X^C^^^     N          j>(*^ 

variable— may  swell  (usually)  or  decrease 

-L<\    -s^rv    \*\    A^^c^r^^^T^TcJv^iA °at\ \     r 

from  late  Sep  through  Mar. 

^C   \J\ o  V-^Y     V-"A  c  A-^A©  \ '  ~  \    :  \^A  ®A->\    VV/ 

a    i>A^*N  \   ^^\  o  \  ^-*A  c  \ \  ci  A  ^-^T  o  \  ^""\  #  \^^A       \^*      \ 

A  common,  very  widespread  breeder; 

x-'T     YAAA  ©  V-^\  ©  \^A  ©  V/A'f  V-'A  O  _V^A  O  'vV'A.    ©^.A 
C^  ^A  \  *  V^A  ©  V^A  ©  V^A7©  V^A-O  ViA      V^A       \-^    \ 

overall  breeding  population  large. 

\  \><\t\^X  c  V--A  ©  Jv>A  ©  V>A  © A^A  ®><A  v>r\ 

Recorded  in  177  (80.1%)  of  221 

N^ve^x^x*  V^A©A-<A®  V'v©  V^A  CJ^\  ®Ar^T\    ^J 

blocks. 

r\VV^\^Ae  V^c\-^©\^A®3rAC\  cA<v\  .A-_ 

V^Vci  A^-*a\_©  v-'A  ©  V^fcAA^A  ©  j^^  ©  V^\  QyC\ c^*^ 
XA?^''\»^  X^  >^J&^^                            /TV 

\  \  x^-A  ©a>2aw\^<)V©  V-'A  ©  W^A  •AtAV\    ArV*A</  .» 

O    Possible        =       18   (10%) 

XlfeV^A  ©  V^A  •\>A\  •0>^-A*  V-^-Y*  Jr^V  A-*Al\  Ts*^ 

XPa  ©  v-'a  ©  A<r\  *j?A«jrA  *Jv<\  *a<\  *^Va  "-^ — 

-  -r' 

€    Probable       =     127   (72%) 

To  a£>A©  v-"y®  jv^x^A^a*  A<£r\  ®A<a  qJkt?\->< 

|  ![?>^S^^ ^-<©  \>A©  w^y *  A^A  •3r<A  ®A%£ 

^^ 

•    Confirmed  =       32   (18%) 

b-r                                  X? \5-X©A>^ Y^A©  VAe> 

FSAR  =  4       OPI  =  708       CI  =  2.08 

Ecological  Requirements 

The  wild  watery  trill  of  the  Purple  Finch  rolls  forth  from 
Marin  County's  conifer,  mixed  conifer,  broadleaved  ever- 
green, and  riparian  forests  and  dense  eucalyptus  groves. 
Less  dependent  on  ground  foraging  than  the  other  Car- 
podacus finches,  Purples  occupy  denser  moister  forests 
than  their  congeners.  They  also  inhabit  open  woodlands 
and,  frequendy,  forest  edges,  though  not  as  dependent  on 
these  features  as  are  Cassin's  Finches  (which  breed  in 
distant  higher,  cooler,  and  drier  mountains).  Also  in  com- 
parison with  Purples,  House  Finches  are  strongly  edge- 
dependent.  House  Finches  frequent  relatively  arid  open 
habitats,  where  they  forage  in  grasslands  and  weed  fields 
and  seek  shelter  or  nest  sites  in  adjoining  trees,  brush,  or 
human  edifices.  Purple  Finches  generally  respond  indi- 
recdy  to  moisture  through  its  effects  on  vegetation  struc- 
ture, but  metabolic  studies  have  shown  that  at  high 
temperatures  they  need  a  huge  percentage  of  moist  food  or 
an  easily  available  supply  of  drinking  water  for  use  in  their 
efficient  cooling  systems  (Salt  1952). 


In  California,  Purple  Finches  build  their  nests  from 
about  5  to  50  feet  above  the  ground  in  coniferous,  broad- 
leaved  evergreen,  and  deciduous  trees,  generally  on  a 
horizontal  or  ascending  branch  well  out  from  the  trunk 
(Dawson  1923,  Bent  1968a).  Nests  are  well-built  cups 
made  of  twigs  and  roodets  and  lined  with  moss,  Ramalina 
lichens,  fine  grasses,  string,  horsehair,  wool,  or  other  soft 
materials. 

Based  on  a  small  sample  (n  =  7)  of  birds  from  the  Sierra 
Nevada,  the  summer  diet  is  about  42%  vegetable  and  58% 
animal  in  origin,  the  latter  consisting  of  beedes,  aphids, 
caterpillars,  hymenopterans,  and  spiders  (Dahlsten  et  al. 
1985).  In  the  spring  and  summer,  Purple  Finches  rely 
heavily  on  blooming  trees  and  bushes,  from  which  they 
pick  the  flowers,  trim  off  the  petals,  and  eat  the  ovaries, 
stamens,  and  pistils  (Salt  1952,  Bent  1968a).  They  also  eat 
large  quantities  of  buds,  berries,  fruits,  willow  catkins,  and 
seeds.  They  glean  insects  from  the  foliage  or  branches  of 
bushes  and  trees  and  pick  vegetable  fare  largely  from  the 

411 


Cardueline  Finches 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Cardueline  Finches 


branch-  and  twig-work  while  perched.  Purple  Pinches 
revert  to  an  almost  exclusively  vegetarian  menu  in  the 
winter. 

Marin  Breeding  Distribution 

During  the  adas  period,  Purple  Finches  were  widespread 
breeders  in  Marin  County  but  were  most  evenly  distrib- 
uted where  moister  denser  forests  prevail,  toward  the 
immediate  coast.  In  the  interior  of  the  county,  they  were 
restricted  largely  to  forests  and  woodlands  in  the  vicinity  of 
permanent  streams,  in  narrow  shaded  canyons,  and  on 
north-facing  slopes.   Areas   of  marginal  occurrence  or 


absence  were  the  grassland-dominated  terrain  of  outer 
Point  Reyes,  around  Tomales,  and  bordering  the  bayshore 
near  Novato.  Representative  breeding  stations  were 
Tomales  Bay  SP  (NB  4/29/82  -DS);  Pike  County  Gulch, 
Bolinas  Lagoon  (NB  6/15/80  — DS);  and  near  Barnabe 
Mountain  (NB  mid-May  1982  -BTr). 

Historical  Trends/ Population  Threats 

Prior  data  are  limited,  but  Purple  Finches  were  relatively 
stable  on  Breeding  Bird  Surveys  in  California  from  1968 
to  1989  (USFWS  unpubl.  analyses). 


HOUSE  FINCH    Carpodacus  mexicanus 


A  year-round  resident. 

foV/i  •  \r^A  tiv^\  ©">--^             _i^~x©  >-*a\ rs~>-s. 
-ci-A •-vM^o  V^-A  •  A^'wr>-'A^~r'^r©  A^A  •  A^xix     ^ 

A  common,  nearly  ubiquitous  breeder; 
overall  breeding  population  very  large. 

^A©  \^\€>  X>^\  •  A^A  ©A^A  ©  Y>A;©  Y>A  •  Ar\  ©D-\ 

Recorded  in  207  (93.7%)  of  221 

V-at «  lA-A  •  A^A  ©Ar^A  ©A--^\  ©  A-^A  #Ar\  ©A-^-  \ 

blocks. 

WAAlf A-^©A^^©A^^®A^^®A-^*A-'iA •Jv^l  \ 

V^lVVs^T  ©V>A  •  A'^'AaC  •  A^A(^Ar\  •A>"A  ©A 

X^^A   ^>^»>^#Ac^©A^^®Ar<\#3r\  mJk^\ 

v-^\©A><>x©  V^a  ©A^\  #\^A  ©v^a  ©A-^\  ©Ar^lN  •^ 
^K^^^A^^©V^©>^©V^®A^®A':;1a  i-U 

O    Possible        =       21    (10%) 

W^>  xAv*  V\  ©  A-"A2fhA^\  ®Ar<\,A-:^A*ArA\\A?>^ 
VYv^Afc-A A^  A  •Ar^c^^^Af^^Ac^'^A<r\  •>•  ,_? 
Vaa  •  v^ArAKii  A-''a©>->a-«  a-^aoaai\  •Ar\  */~^ 

©    Probable       =       58   (28%) 

\  Pi>Av»-^><^A<^'©'>^A  •  V^A  °A(<A  •A<A»>Ay .„ 
Vt£A*  \k\o  j^a©  a*a  ©  \a-t©.  A>A  ©jA"A  •  aa^Tv 

•    Confirmed  =     128   (62%) 

Y^A-A©  >^©A^^©A^^®A^^*Jv^.»A^'"*Pv 

__- 

\Pa  .©Jv^A  ©  AA^*A<Xy«A-<a  •A-"\  •  AAAA  ■•A-"*' j>- — 
T©.'AP"\  ©  >-"v*  A^y°A-^A-®  A=c\  °A^\  ®Ar^A  -t< 

~  ° 

U£^©>Y^A  ©AA^ ©A^A  ®  v^dr    V--A  ©A-<s\  ©AAv\~> 
H\Wyivn   Jr\e'K\itA    Aviv •  A-AT\ *AA«V 

FSAR  =  4        OPI  =  828       CI  =  2.52 

(Wo  vV\  o  v'A     A-^V©  V'^fr>V^T*V'\  ®ArAAv  *A 

ru^w-dvAa— I    V^\oA5A;o  V^A  ®Kv^V-®AA\  ©A^A 
V*\+\^                 ^C  o  V-A  •  V-A     J^A^ArAAv'C^ 

3& 

\*y^                         \->A     V>^A^^«A-^>*A--\i 

t-^7                            X*  V--V ©AP*^?  A^\  •  A-"a  •  3? 

^L          ^vir^^p 

Ecological  Requirements 

One  of  our  most  familiar  birds  and  another  classic  edge 
species,  the  House  Finch  occupies  the  open  or  brushy 
borders  of  all  of  Marin  County's  major  forest,  woodland, 
or  brushland  plant  communities  but  is  nowhere  more 
common  than  about  human  dwellings.  With  the  spread  of 
civilization,  House  Finches  have  adapted  remarkably  to 
ranch-  and  farmyards,  as  well  as  urban  and  suburban 
settings.  They  do  not  frequent  forests,  woodlands,  or 
scrublands  that  offer  a  continuous  canopy  but  prefer  the 
edges  that  adjoin  sparse  grasslands  or  weed  fields  or  where 
the  latter  habitats  are  interspersed  with  scattered  shrubs  or 
clumps  of  trees.  Primarily  ground  foragers  in  open  habi- 
tats, House  Finches  also  need  tall  perches,  such  as  trees, 
buildings,  or  transmission  lines,  to  fly  up  to  for  safety's 

412 


sake.  They  are  hesitant  to  venture  far  into  grasslands  or 
weed  lots  without  high  perches  close  at  hand.  A  nearby 
source  of  fresh  water  is  also  an  important  requisite  (Salt 
1952). 

Nest  sites  are  extremely  varied  and  range  from  the 
ground  up  to  about  50  feet  (Dawson  1923,  Salt  1952, 
Evenden  1957,  Thompson  1960,  Woods  1968);  they  are 
almost  always  eidier  covered  or  shaded  by  vegetation  or 
some  other  structure  (Salt  1952).  Around  homes,  barns, 
and  outbuildings,  any  support  or  odd  cubbyhole  will  serve 
as  a  nest  site.  House  Finches  frequendy  use  supports  under 
eaves,  on  drainpipes,  on  beams,  or  amid  ivy  clinging  to 
walls.  They  also  commonly  build  their  nests  in  the  dense 
foliage  or  in  the  open  interiors  of  native,  cultivated,  or 


Cardueline  Finches 


SPECIES  ACCOUNTS 


Cardueline  Finches 


ornamental  trees  and  hedges.  Sometimes  they  place  them 
in  thisde  patches  or  on  the  ground  under  weeds.  When  a 
lack  of  nest  supports  on  human  structures  forces  birds  to 
resort  to  bushes  or  shrubbery,  they  usually  choose  one  as 
close  to  the  building  as  possible.  House  Finches  will,  of 
course,  nest  far  from  buildings.  Other  nest  sites  include 
cavities  in  walls,  trees,  and  cliffs,  tin  cans  hanging  on 
fenceposts,  mailboxes,  old  hats,  stovepipes,  haystacks,  and 
old  woodpecker  cavities.  House  Finches  also  occupy  old 
bird  nests  and  usually  reline  them.  In  California,  aban- 
doned nests  of  "Bullock's"  and  Hooded  orioles,  Barn  and 
Cliff  swallows,  and  Black  Phoebes  are  the  prime  candidates 
for  House  Finch  use.  House  Finches  are  not  strongly 
territorial.  Male  defense,  centering  around  the  female  as 
well  as  a  space  around  the  nest,  wanes  during  incubation 
(Thompson  1960).  Consequendy,  House  Finches  some- 
times place  their  nests  within  a  few  feet  or  even  inches  of 
each  other  (Thompson  1960,  Woods  1968).  They  may 
reuse  nests  for  successive  broods  in  a  season  and  often 
reuse  nest  sites  in  successive  years.  "Choice  of  nest  materi- 
als is  as  catholic  as  that  of  nest  sites,"  and  includes  almost 
anything  soft;  often  nest  cups  are  constructed  of  a  single 
material  (Dawson  1923).  Nest  materials  include  such  items 
as  straw,  grass,  weed  stems,  flower  heads,  string,  wool,  soft 
paper,  cotton,  plant  down,  bark  strips,  moss,  lichens, 
leaves,  roodets,  hair,  frayed  cigarette  filters,  and,  rarely, 
feathers.  The  nest  lining  is  of  finer  materials  of  these  sorts. 

In  the  breeding  season,  males  feed  in  flocks  along  with 
some  nonincubating  females;  flocking,  of  course,  increases 
at  other  seasons  (Thompson  1960).  House  Finches  are 
much  more  dependent  on  ground  foraging  for  seeds  than 
are  the  other  Carpodacus  finches.  They  also  pick  seeds  or 
flowering  heads  from  plants  while  hanging  onto  stems  or 
branches  and  eat  fruits  attached  to  trees  or,  less  frequendy, 
when  they  have  fallen  to  the  ground  (Salt  1952,  Woods 
1968).  Additionally,  in  the  spring  they  eat  leaf  and  blos- 
som buds  from  bushes  and  trees  and  sip  sap  oozing  from 
cut  branches  of  pruned  trees.  House  Finches  also  readily 
obtain  seeds  from  feeding  trays.  They  probably  glean  a  few 
insects  from  foliage,  branches,  and  fruit,  but  some  authors 
suspect  they  take  them  incidentally  with  vegetable  matter 
(Thompson  1960). 

The  diet  of  House  Finches  in  California  is  about  97.6% 
vegetable  matter  and  2.4%  animal  matter  (Beal  1907,  n  = 
1 206).  Animal  food  is  principally  plant  lice,  small  caterpil- 
lars, and  a  few  beedes.  House  Finches  will  also  eat  fat, 
especially  suet  The  vegetable  portion  of  the  diet  consists  of 
weed  seeds  (86.2%  of  the  annual  total),  fruit  (10.5%),  and 
miscellaneous  vegetable  matter  (0.9%).  The  proportion  of 
weed  seeds  in  the  diet  decreases  and  that  of  fruit  increases 
over  the  course  of  summer.  The  most  important  weed 
seeds  in  California  are  Napa  thisde,  black  mustard,  wild 


radish,  filaree,  knotweed,  amaranth,  and  turkey  mullein. 
The  fruits  that  House  Finches  eat  are  largely  the  large 
soft-bodied  cultivated  types,  such  as  apples,  apricots,  avoca- 
dos, raspberries,  cherries,  figs,  grapes,  peaches,  pears, 
plums,  and  strawberries  (Woods  1968,  Palmer  1973);  they 
prefer  these  over  small  berries  eaten  by  mockingbirds  and 
waxwings.  House  Finches  are  almost  exclusively  vegetarian 
in  fall  and  winter.  Agriculturists  consider  the  House  Finch 
one  of  the  most  destructive  bird  "pests"  in  California,  and 
they  spend  considerable  money  for  control  efforts  (Palmer 
1973).  Other  vegetable  matter  eaten  includes  very  small 
quantities  of  flower  parts,  grain,  and  leaf  galls  (Beal  1907). 
Salt  is  also  eaten  (Woods  1968).  House  Finches  are  a 
notable  exception  to  the  rule  that  most  fringillid  finches  eat 
a  considerable  quantity  of  insects  in  the  breeding  season 
and  initially  feed  their  young  almost  exclusively  insects 
(Beal  1907,  Woods  1968).  Adult  House  Finches  feed  their 
young,  by  regurgitation,  the  same  vegetarian  diet  they 
themselves  eat.  Males  also  feed  incubating  females  (at  least 
in  the  early  stages)  by  regurgitation  when  females  fly  up 
from  the  nest  or,  less  frequendy,  on  the  nest  (Thompson 
1960). 

Marin  Breeding  Distribution 

During  the  adas  period,  the  House  Finch  was  one  of  the 
most  widespread  breeders  in  Marin  County  and  had  no 
large  gaps  in  its  distribution  here.  Because  of  their  adapta- 
tions to  more  arid,  open,  and  human-influenced  habitats 
than  those  preferred  by  Purple  Finches  (Salt  1952),  House 
Finches  were  more  common  in  the  low  rolling  hills  and 
lowland  valleys  of  Marin's  interior  ranching  country  and 
in  the  urbanized  corridor  along  Highway  101.  Representa- 
tive breeding  locales  were  Abbott's  Lagoon  (NE  6/20/82 
-DS);  the  Fish  Docks,  Point  Reyes  (NB  5/1 3/80  -DS); 
Chileno  Valley  (NE  5/6/82  -DS);  and  Bolinas  Ridge 
above  Olema  (NB  4/28/77  -DS). 

Historical  Trends/  Population  Threats 

With  the  coming  of  civilization,  the  House  Finch  occupied 
new  habitats  and  increased  the  density  of  its  populations 
within  its  original  range  (Woods  1968).  Although  Grinnell 
and  Miller  (1944)  did  not  comment  on  population  trends 
in  California,  the  species  undoubtedly  had  increased  dra- 
matically in  the  state  up  to  that  time,  and  continued  to  do 
so  along  with  the  vast  expansion  of  agricultural  and  subur- 
ban habitats.  More  recendy,  House  Finch  populations 
decreased  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989  (USFWS  unpubl.  analyses),  despite  stability 
from  1980  to  1989.  Still,  California  has  far  and  away  the 
highest  densities  of  House  Finches  of  any  state  or  province 
on  the  continent  (Robbins  et  al.  1986). 


413 


Cardueline  Finches 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Cardueline  Finches 


RED  CROSSBILL    Loxia  curvirostra 


Occurs  year  round,  but  numbers  quite 
variable  seasonally  and  yearly— may  be 
present  or  absent  in  any  month;  usually 
most  numerous  from  Sep  through  Apr. 

A  very  rare,  very  local  breeder;  overall 
breeding  population  very  small. 

Recorded  in  12  (5.4%)  of  221  blocks. 

^T^\  -^\^-*£^r\  XJ^C^X      JK^\     ^-\^\      \^\      \^7 

O    Possible        =       12   (100%) 

<rV\iiV\   Jv^oJrA  o\>d^V^Y    WT' TK 

€    Probable      =        0  (0%) 

•    Confirmed  =         0  (0%) 

FSAR=1          OPI  =  12         CI  =  1.00 

Ecological  Requirements 

Renowned  for  its  fantastic  bill  and  erratic  seasonal  wander- 
ings, the  Red  Crossbill  is  one  of  our  most  enigmatic 
breeding  birds.  Crossbills  are  apparendy  indifferent  to 
temperature,  humidity,  or  altitude  (Griscom  1937)  within 
the  conditions  that  give  rise  to  cone-bearing  trees,  their 
lifeblood.  Crossbills  prefer  to  breed  in  mature  forests  with 
tall  well-spaced  trees— the  stage  at  which  these  forests  yield 
the  most  cones  (Newton  1973).  At  all  seasons,  Crossbills 
are  closely  wedded  to  the  conifer  forests  to  satisfy  their 
seed-dependent  diet,  and  their  movements,  lacking  in 
predictable  seasonal  periodicity,  appear  to  be  largely  reliant 
on  the  fortunes  of  the  cone  crops,  which  are  by  nature 
irregular.  The  birds  depart  rapidly  from  areas  depleted  of 
seeds,  no  matter  what  the  season  or  reason,  and  they  will 
travel  long  distances  in  almost  any  direction  in  search  of 
cone-heavy  conifers.  Length  of  occupancy  of  a  particular 
area  depends  on  the  number  of  types  of  conifers  and  the 
synchrony  and  abundance  of  cone  crops  in  the  habitat 
(Benkman  1987a). 

Crossbill  movements  and  breeding  attempts  are  predi- 
cated on  maximizing  seed  intake  rates,  given  the  vagaries 
of  spatially  and  temporally  fluctuating  cone  crops  (Benk- 
man 1987a).  This  necessitates  a  religious  attention  to 
changes  in  this  highly  unpredictable  food  source,  as  conifer 
crops  at  a  site  can  vary  several  orders  of  magnitude  between 
years  with  intervals  of  2  to  10  years  between  good  cone 
crops.  Likewise,  cone  crops  fail  over  large  regions  every  2 
to  4  years,  forcing  irruptive  movements  of  Crossbills  from 
their  "normal"  range.  The  rate  of  food  intake  (profitability) 
derived  from  a  particular  conifer  depends  on  cone  struc- 

414 


ture,  timing  of  cone  opening  and  seed  release,  and  seed 
mass.  Profitability  generally  peaks  as  cones  first  open, 
when  there  are  high  numbers  of  seeds  per  cone  that  are 
readily  accessible,  and  declines  as  seeds  are  shed  from 
cones.  The  timing  of  cone  ripening  varies  from  year  to 
year— cool  moist  conditions  may  delay  cone  opening  and 
unseasonal  warm  weather  can  cause  seeds  to  be  shed 
rapidly  (Benkman  1987a,  1990).  Although  seeds  of  all 
conifers  form  in  late  summer,  cones  do  not  mature  and 
open  until  3  to  22  months  later,  depending  on  the  species 
of  conifer  (Newton  1973).  Consequently,  to  maximize 
profitability,  Crossbills  shift  their  use  of  various  conifers  to 
match  the  seasonal  patterns  of  cone  opening  among  coni- 
fer species,  though  they  often  hedge  their  bets  by  foraging 
on  more  than  one  conifer  species  at  a  time.  Furthermore, 
as  cone  crops  are  depleted  Crossbills  must  emigrate  to  take 
advantage  of  the  great  geographic  variation  in  cone  crop 
abundance,  cone  opening  pattern,  and  seed  mass. 

The  timing  of  breeding  is  equally  unpredictable,  since 
Crossbills  will  nest  in  any  month  of  the  year  (Bailey  et  al. 
1953,  Bent  1968b).  They  have  even  been  known  to  have 
three  distinct  breeding  periods  in  six  months  at  the  same 
location  (Griscom  1937)!  In  general,  Crossbills  breed  most 
commonly  in  late  summer  and  early  autumn  (Aug-Oct) 
and  in  late  winter  and  early  spring  (Jan-Apr),  when  snow- 
rimmed  nests  are  not  uncommon  (Griscom  1937,  Bailey 
et  al.  1953,  Bent  1968b,  Newton  1973,  Benkman  1990). 
In  a  given  region,  though,  birds  rarely  breed  in  the  same 
month  in  consecutive  years.  Year-to-year  variability  in 
breeding  is  also  great  at  any  particular  location  within  a 


Cardueline  Finches 


SPECIES  ACCOUNTS 


Cardueline  Finches 


region.  Birds  may  nest  for  several  successive  years  and  then 
vanish,  or  they  may  arrive  one  year,  breed,  and  then  not  be 
seen  again  for  many  years.  Generally,  Crossbills  are  rarely 
numerous  in  the  same  area  two  years  in  succession.  Not 
only  does  the  time  of  breeding  vary  from  year  to  year  in  the 
same  forest  type,  but  some  birds  may  breed  in  different 
types  of  conifer  forest  in  successive  years  (Newton  1973). 
In  the  mountains  of  Colorado,  Crossbills  are  known  to 
progressively  shift  breeding  upslope  into  different  conifer 
zones  from  early  winter  to  summer  (Bailey  et  al.  1953). 
Crossbills  may  also  abruptly  cease  breeding  and  emigrate 
if  seed  intake  rates  decline  from  natural  perturbations, 
such  as  weather-induced  seed  shedding  or  insect  outbreaks 
that  decimate  developing  seed  crops  (Benkman  1 990). 

Although  it  ha$  long  been  known  that  Crossbills  need 
an  abundant  cone  crop  to  nest,  it  is  just  now  being 
appreciated  that  they  initiate  (or  terminate)  breeding  in 
response  to  both  the  levels  and  rates  of  change  of  seed 
intake  (Benkman  1990).  Seed  intake  must  be  sufficient  for 
egg  formation  and,  particularly,  the  more  energy-demand- 
ing nesding  phase  of  reproduction.  Birds  that  start  nesting 
at  high  seed  levels  will  abandon  if  intake  rates  decline, 
indicating  that  energy  intake  will  be  insufficient  at  the 
nesding  stage.  Conversely,  birds  will  start  nesting  at  seed 
intake  rates  just  necessary  for  egg  formation  if  these  rates 
are  increasing,  suggesting  that  energy  intake  will  later  be 
adequate  to  meet  nesding  demands. 

In  Marin  County,  the  main  cone-producing  trees  attrac- 
tive to  Crossbills  are  Douglas  fir  and  bishop  pine.  Cross- 
bills here  frequent  these  and  also  coast  redwoods,  planted 
Monterey  pines  and  cypress,  and  occasionally  alder  thick- 
ets. Exacdy  what  the  Crossbills'  preferences  are  in  the 
"breeding  season"  in  Marin  County  are  not  well  known, 
because  no  nests  have  been  found  here. 

Elsewhere,  Crossbills  typically  build  their  nests  at 
heights  from  about  10  to  90  feet  (most  under  40  ft.,  Bent 
1968b).  In  Colorado,  16  nests  in  yellow  pines  averaged  31 
feet  (range  15-48  ft.)  above  ground  (Bailey  et  al.  1953). 
There  nests  were  located  in  fairly  open  conifer  groves  or  in 
semi-isolated  groves  of  trees  rather  than  in  densely  tim- 
bered areas.  A  nest  tree  is  often  close  to  a  dead  or  dying 
pine  that  the  male  uses  for  singing,  preening,  and  a 
cautionary  stopping  place  before  entering  or  leaving  the 
nest  area;  territories  are  maintained  only  during  nest  site 
selection.  Crossbills  usually  saddle  their  nests  on  horizon- 
tal branches  close  to  or,  more  commonly,  well  out  from  the 
trunk  and  often  conceal  them  in  thick  tufts  of  cones  and 
needles,  clusters  of  branchlets,  or  cups  of  lichen;  only 
rarely  can  nests  be  seen  from  below  (Bailey  et  al.  1953, 
Bent  1968b).  Crossbills  tend  to  place  their  nests  on  the 
south  side  of  trees  where  they  receive  the  warmth  of  the  sun 
and  are  sheltered  from  north  winds  (Bailey  et  al.  1953, 
Newton  1973).  Crossbill  nests  are  bulky,  comparatively 
deep  cups  of  conifer  twigs,  roodets,  bark  strips,  decayed 


wood,  weed  stalks,  dried  grass,  moss,  lichens,  and  perhaps 
a  few  pine  needles,  stiff  feathers,  or  picnic  litter  (Bailey  et 
al.  1953,  Bent  1968b).  They  are  thickly  (warmly)  lined  with 
finer  materials  such  as  hair,  fur,  fine  roodets  or  grass, 
lichens,  moss,  shredded  bark,  and  a  few  feathers  (Lawrence 
1949,  Bent  1968b).  Crossbills  tend  to  build  bulkier  and 
more  thickly  lined  nests  in  winter  than  in  summer  (New- 
ton 1973).  In  one  case  in  Colorado,  birds  reused  the  same 
nest  for  a  second  breeding  attempt  (Bailey  et  al.  1953). 

While  breeding,  Crossbills  generally  tend  to  forage  in 
loose  knit  flocks— composed  of  males  feeding  incubating 
females,  pairs  feeding  nesdings,  and  birds  with  fledglings 
in  tow— that  constandy  fluctuate  in  size  as  birds  move  to 
and  from  nests  (Bailey  et  al.  1953).  On  some  days,  no 
foraging  flocks  form  and  then  birds  work  in  isolated  pairs 
or  family  groups.  Crossbills  derive  the  bulk  of  their  suste- 
nance from  the  seeds  of  conifers,  obtained  by  first  prying 
open  the  cone  scales  with  their  crossed  mandibular  tools 
and  then  extracting  the  seeds  with  their  tongues.  Crossbills 
are  adept  at  climbing  around  conifer  branches  using  both 
their  bills  and  feet  in  parrot-fashion  (Bent  1968b,  Newton 
1973).  While  reaching  for  nearby  cones,  they  may  hang  by 
both  feet,  chickadee-like,  or  just  by  the  bill  or  only  one  foot. 
Cones  may  be  worked  in  situ,  or  they  may  be  cut  off  and 
carried  in  the  bill  or  claws  to  a  perch,  where  the  bird  holds 
die  cone  against  a  branch  with  its  feet  and  extracts  the 
seeds  in  a  leisurely  fashion.  Crossbills  insert  their  partly 
opened  bills  between,  and  parallel  to  the  long  axis  of,  cone 
scales  and  separate  the  scales  primarily  by  sideways  move- 
ments of  the  mandibles  (Torduff  1954,  Newton  1973, 
Benkman  1 987b).  Regardless  of  the  sex  of  Crossbills,  the 
direction  in  which  the  tips  of  the  mandibles  cross  is 
roughly  evenly  divided  in  the  population,  as  the  lower 
mandible  curves  upward  and  slightly  either  left  or  right. 
Consequently,  birds  are  either  "right-  or  left-handed"  in 
their  attempts  to  open  pine  cones  (Torduff  1954).  Feeding 
on  the  cone  with  the  long  axis  of  its  head  at  right  angles  to 
the  axis  of  the  cone,  the  bird  orients  the  tip  of  the  lower 
mandible  on  the  side  toward  the  distal  end  of  the  cone. 
After  an  initial  gap  is  created  by  a  biting  motion  of  the 
upper  mandible,  the  jaws  are  spread  sideways.  The  lower 
jaw  is  abducted  laterally  in  the  direction  that  its  tip  points, 
pressing  and  pivoting  against  the  distal  scale  while  the  side 
of  the  upper  mandible  pushes  die  basal  scale  open  (Benk- 
man 1987b).  If  need  be,  the  upper  mandible  may  be  driven 
further  between  the  scale  gap  and  the  rest  of  the  process 
repeated  until  the  gap  between  scales  widens  and  deepens, 
enabling  the  bird  to  reach  the  seed.  Then  the  Crossbill 
protrudes  its  long,  agile  tongue  using  the  spoon-shaped  tip 
to  scoop  the  seed  back  to  the  bill  to  be  husked. 

Although  conifer  seeds  are  their  mainstay,  Crossbills 
will  also  eat  the  tender  buds  or  soft  green  cones  of  conifers; 
the  seeds  and  buds  of  deciduous  trees  such  as  birches, 
alders,  box  elders,  elms,  willows,  and  poplars;  and  the  seed 


415 


Cardueline  Finches 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


Cardueline  Finches 


heads  of  ragweed,  hemp,  dandelions,  and  other  weeds. 
Crossbills  will  eat  diese  items  in  place  or,  like  seeds  and 
nuts  occasionally  procured  from  the  ground,  will  cat  diem 
after  flying  to  a  perch.  It  appears  that  a  Crossbill  scoops 
seeds  from  seed  heads  with  its  saliva-covered  tongue,  which 
is  then  used  to  manipulate  the  seed  into  position  and  crack 
it  between  the  cutting  edges  of  the  bill  (Sutton  1976). 
Crossbills  may  also  hold  large  seeds  with  their  feet,  bite  the 
end  with  the  tips  of  the  mandible,  insert  the  mandibles  in 
the  crack,  pry  the  shell  open  with  lateral  movements,  and 
again  extract  the  contents  with  the  tongue  (Torduff  1954). 
They  also  forage  for  fresh,  dried,  and  frozen  fruits  (Law- 
rence 1949),  but  stomach  contents  indicate  that  just  the 
seeds  are  eaten  after  extraction  from  the  pulp  (Sutton 
1976).  Anything  more  than  a  passing  reliance  on  alterna- 
tive foods  is  usually  necessitated  by  cone  crop  failures 
forcing  irruptive  movements  beyond  the  range  of  conifer 
forests  (Newton  1973).  Then  fruits  as  large  as  apples  may 
be  split  open  for  their  seeds.  Although  Crossbills  are 
almost  exclusively  vegetarians  from  fall  through  spring  (n= 
225),  dieir  summer  diet  includes  about  18%  animal  matter 
(n  =  30)  (Martin  et  al.  1951).  Benkman  (1990)  remarked 
that  in  the  East  insect  larvae  may  make  up  a  major  portion 
of  the  diet  in  late  June  and  July.  The  main  animal  food 
items  are  spiders,  caterpillars,  plant  lice,  aphids,  beedes, 
ants,  and  larvae  of  other  insects  (Martin  et  al.  1951,  Bent 
1968b).  Crossbills  awkwardly  glean  some  insects  from 
foliage  or  cones  or  pry  them  from  crevices  or  from  beneath 
bark  with  their  bills  or  tongues.  They  may  also  use  their 
tongues  to  procure  insects  after  using  their  bills  in  scissor- 
like  fashion  to  cut  open  curled  leaves  or  after  inserting  their 
open  bills  into  leaf  galls  until  the  mandibles  are  practically 
closed  and  crossed,  and  a  slight  twist  of  the  head  splits 
open  the  gall.  It  is  also  well  established  that  Red  Crossbills 
have  a  fondness  for  salt  or  salty  substances.  They  may 
obtain  these  from  natural  mineral  deposits,  from  salt 
spread  to  melt  snow,  from  poured-out  soapy  dishwater, 
and  even  from  snow  discolored  by  dog  urine  (Aldrich 
1939,  Bent  1968b);  they  sometimes  secure  scrapings  from 
bleached  deer  bones  (Bailey  et  al.  1953).  Like  many  seed- 
eating  finches,  the  female  is  fed  on  the  nest  by  the  male, 
and  the  young  are  fed  by  regurgitation.  The  initial  pabulum 
proferred  to  nesdings  is  a  watery  or  dark  viscid  substance, 
suggesting  a  composition  of  animal  matter,  and  later  a 
thicker  substance  of  sodden  pine  seeds  transferred  in  soft 
balls  (Lawrence  1949,  Bailey  et  al.  1953,  Snyder  1954). 


Marin  Breeding  Distribution 

The  unpredictable,  "unseasonal"  breeding  habits  of  Cross- 
bills present  formidable  challenges  to  adas  work.  Although 
confirming  breeding  on  a  case-by-case  basis  is  apparendy 
no  more  difficult  than  for  other  finches,  it  is  nigh  impossi- 
ble if  observers  are  looking  for  evidence  in  a  season  during 
which  Crossbills  may  not  nest  in  the  years  of  the  adas 
project.  For  this  reason,  the  Marin  County  adas  map  of 
Crossbills  is  probably  incomplete,  since  most  of  our  data 
collection  was  done  from  April  through  July.  Conversely, 
other  studies  suggest  we  may  have  recorded  birds  that  had 
no  intention  of  breeding  here  at  the  time.  Johnston  and 
Norris  (1956)  observed  up  to  40  birds  in  bishop  pine 
forest  on  Inverness  Ridge  from  1 5  March  to  1 1  June  1954, 
but  of  the  total  of  9  birds  they  collected  on  31  May  and  1 1 
June,  none  were  in  breeding  condition.  As  a  consequence, 
our  distribution  map  of  Crossbills  is  not  really  comparable 
to  that  of  a  regular  nesting  species  with  a  well-defined, 
spring  to  summer  breeding  season.  The  adas  records  do  all 
occur  in  areas  of  Marin  with  extensive  conifers,  and  the 
long-term  breeding  range  of  the  Red  Crossbill  here  is 
probably  equivalent  to  the  combined  breeding  distribution 
of  the  Red-breasted  and  Pygmy  nuthatches,  two  obligate 
conifer  breeders.  The  only  indications  of  Crossbill  breed- 
ing in  Marin  County  predate  the  adas  period.  A  female  was 
observed  "gathering  grass"  on  Inverness  Ridge  on  23  April 
1960  (GMi)  and  another  female  "carrying  nest  material"  at 
Tomales  Bay  State  Park  on  29  April  1973  (PRBO). 

Historical  Trends/Population  Threats 

Population  trends  of  an  obligate  nomad  such  as  the  Red 
Crossbill  are  extremely  difficult  to  document  and  may  just 
as  easily  be  affected  by  very  distant  conditions  as  by  local 
ones.  It  is  unclear  what  effect  extensive  logging  of 
California's  conifer  forests  has  had  on  Red  Crossbills.  It  is 
worth  noting  that  die  subspecies  from  northeastern  North 
America  (L.  c.  neogaea)  may  have  been  brought  to  the  brink 
of  extinction  near  the  turn  of  this  century  by  extensive 
lumbering  activities  (Dickerman  1987).  Nevertheless,  Red 
Crossbill  populations  increased  on  Breeding  Bird  Surveys 
in  California  from  1968  to  1989,  despite  relatively  stable 
numbers  from  1980  to  1989  (USFWS  unpubl.  analyses). 


416 


Cardueline  Finches 


SPECIES  ACCOUNTS 


Cardueline  Finches 


PINE  SISKIN    Carduelis  pinus 


A  year-round  resident;  numbers  variable 

^I^V>^w        N              JT^ 

in  winter— may  increase  (usually)  or 

decrease  from  Sep  through  Mar. 

A  common,  widespread  breeder;  over- 

^\°VaCo3r<\ 3rC  V^Co3rC  JV^\°JV\  C^A 

\       U/*\  \  m  V— "n,  O  V^\       V-^Y  O  V-?A       V^'V      >^~A      _>^^     1 

all  breeding  population  large. 

\    VM^i^ACVA      3r^\©  \^\  O.V>\0  3i^\     >c^  \ 

Recorded  in  151  (68.3%)  of  221 

blocks. 

^^><n»V>-X    V^AoVfcC   C^x^V^x    V<a  .X^. 

O    Possible        =       73   (48%) 

-r' 

C    Probable       =      48  (32%) 

•    Confirmed  =       30  (20%) 

'■^^^^     ^~<C°  >^\  ®  Jv^x  «-3v<!r\  C)3r^A  °A&> 

\\^f                                             VO  \^-A  ifV^-C*  V^A  O  V^\      J? 

5& 

FSAR  =  4        OPI  =  604         CI  =  1.72 

jjL          ^^f^^^p 

Ecological  Requirements 

These  plain-looking  but  exuberant  "goldfinches"  are 
closely  linked,  but  not  tied,  to  Marin  County's  conifer 
forests.  Siskins  breed  here  in  extensive  bishop  pine,  Doug- 
las fir,  and  coast  redwood  forests  and  also  in  extensive  or 
small  isolated  stands  of  planted  Monterey  cypress,  Monte- 
rey pine,  and  eucalyptus.  Although  Siskins  feed  here  in 
alder  and  willow  thickets  during  the  winter  and  in  the 
breeding  season,  they  apparently  do  not  nest  in  these 
habitats.  Siskins  nest  most  commonly  in  open  forests  or 
woodlands  and  along  openings  of  (or  borders  with)  grass- 
lands, weed  fields,  and  thistle  patches. 

Siskins  may  breed  solitarily  or  semicolonially  in  the 
same  tree,  and  they  typically  conceal  their  nests  well  out  on 
densely  foliaged  horizontal  limbs  (Palmer  1968).  Nest 
heights  range  from  about  3  to  50  feet  but  mosdy  from  10 
to  20  feet.  Although  Siskins  place  most  nests  in  conifers, 
in  the  western  states,  birds  also  occasionally  use  box  elders, 
maples,  oaks,  cottonwoods,  and  lilacs.  On  the  California 
coast,  Siskins  nest  primarily  in  native  conifers  but  also  in 
planted  conifers,  particularly  Monterey  cypress,  and  euca- 
lyptus (Carriger  &  Pemberton  1907,  Palmer  1968).  Their 
nests  are  shallow  compact  cups  made  of  twigs,  rootlets, 
grass,  weed  stems  or  bark,  leaves,  and  tree  moss  or  lichens. 
They  are  lined  with  fine  roodets,  hair,  fur,  plant  down,  or, 
rarely,  feathers  (Carriger  &  Pemberton  1907,  Dawson 
1923,  Palmer  1968). 

Siskins  maintain  their  gregarious  proclivities  in  the 
breeding  season,  when  they  continue  foraging  in  flocks— 
albeit  smaller  ones— up  to  about  six  birds.  Flocks  or  single 
birds  feed  in  trees,  bushes,  weeds,  thistles,  and  on  the 


ground.  Siskin  flocks  typically  forage  from  the  top  of  a  tree 
downward,  but  they  also  move  up  through  trees  or  hori- 
zontally from  one  tree  to  another  (Rodgers  1937).  Like 
crossbills  or  chickadees,  they  often  hang  upside  down  from 
cone  or  catkin  clusters.  Siskins  frequendy  cling  to  thisde 
heads,  pull  out  the  cottony  seed  tufts,  and  dexterously  and 
rather  rapidly  work  dieir  bills  along  to  the  seed,  which  they 
then  remove,  throwing  the  fluff  to  the  breeze  (Palmer 
1968).  They  are  less  well  adapted  for  ground  foraging  and 
walk  with  very  short  steps  and  occasional  hops.  Like  other 
seed  eaters,  they  need  a  reliable  source  of  water.  Siskins 
glean  insects  from  foliage  or  even  the  walls  of  houses.  They 
also  obtain  insects  by  shelling  galls  from  the  underside  of 
oak  leaves  and  by  breaking  off  twig  ends  to  get  at  the  larvae 
of  twig-boring  insects.  Males  initially  feed  incubating  and 
brooding  females  by  regurgitation.  The  females  in  turn 
feed  the  young  up  to  the  seventh  or  eighth  day  in  a  like 
manner;  insects  are  important  to  the  developing  young 
(Palmer  1968). 

Although  Siskins  are  primarily  seed  eaters,  their  diet  is 
composed  of  up  to  81%  animal  matter  in  summer  (n  = 
19),  but  only  10%  in  winter  (n  =  142)  (Martin  et  al.  1951). 
Siskins  consume  copious  amounts  of  seeds  from  conifers, 
alders,  willows,  eucalyptus,  thistles,  dandelions,  and  other 
weeds  (Palmer  1968).  They  take  the  seeds  in  place  or  after 
they  have  fallen  to  the  ground.  Siskins  also  eat  flower  and 
leaf  buds,  blossoms,  leaves  of  garden  seedlings,  the  sweet 
liquid  inside  eucalyptus  flowers,  and  (rarely)  the  sap  from 
sapsucker  drillings.  About  one-sixth  of  the  Siskin's  yearly 
diet  is  insects  (McAtee  in  Palmer  1968).  Important  ones 

417 


Cardueline  Finches 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Cardueline  Finches 


are  caterpillars,  plant  lice,  scale  insects,  true  bugs,  fly  larvae, 
and  grasshoppers;  spiders  are  also  eaten  and  suet  is  an 
occasional  supplement.  Siskins  are  also  fond  of  salt  and 
clay  from  mineral  deposits,  ashes,  gravel  and  sand  mixed 
with  chloride,  and  newly  set  cement. 

Marin  Breeding  Distribution 

During  the  adas  period,  Pine  Siskins  bred  widely  in  the 
moister,  most  coast-influenced  areas  of  Marin  County  that 
are  dominated  by  conifer,  mixed  conifer,  and  broadleaved 
evergreen  forests.  Representative  breeding  localities  were 
Fish  Docks,  Point  Reyes  (NE  5/13  ck  29/80  -DS);  Aban- 
doned Ranch,  Point  Reyes  (NB  5/1 3/80  -DS);  vicinity  of 
Tomales  Bay  SP  (NB  4/29/82  -DS);  and  Bolinas  (NB 
4/14/77  -DS). 


Historical  Trends/Population  Threats 

Historically,  Pine  Siskins  have  expanded  their  range  locally 
on  outer  Point  Reyes  and  around  Tomales,  where  cypress 
and  eucalyptus  groves  have  been  planted  for  windbreaks  in 
extensive  areas  of  grassland.  While  grassland  birds  gener- 
ally may  have  suffered  from  overgrazing,  Siskins  have 
probably  benefitted  from  die  introduction  and  spread  of 
otherwise  noxious  drisdes.  Whether  clearing  of  forests  has 
affected  them  is  unclear.  Siskin  populations  decreased  on 
Breeding  Bird  Surveys  in  California  from  1968  to  1989 
(USFWS  unpubl.  analyses). 


LESSER  GOLDFINCH   Carduelis  psaltria 


A  year-round  resident. 

A  common,  widespread  breeder;  over- 
all breeding  population  large. 

Recorded  in  145  (65.6%)  of  221 
blocks. 


O  Possible 
€  Probable 
9    Confirmed 


60  (41%) 
54  (37%) 
31   (21%) 


FSAR  =  4        OPI  =  580         CI  =  1.80 


Ecological  Requirements 

Small  frisky  bands  of  "Green-backed"  Goldfinches  inhabit 
die  edges  of  Marin  County's  relatively  dry  oak  savannah 
and  oak  woodland,  chaparral  (including  Sargent  cypress 
woodland/brushland),  riparian  woodland,  and,  more 
sparingly,  die  edges  of  broadleaved  evergreen,  conifer,  and 
eucalyptus  forests.  These  goldfinches  prefer  warm  soudv 
and  west-facing  slopes,  and  diey  forage  extensively  in 
grasslands  and  weed  fields  of  pastures,  roadsides,  and  hill 
slopes  adjoining  the  cover  where  they  nest  and  seek  protec- 
tion. They  also  forage  extensively  in  trees  and  bushes. 
American  Goldfinches  overlap  to  a  limited  degree  with 
Lessers  along  the  edges  of  interior  riparian  stretches,  but 
they  generally  breed  in  moister  coastal  situations.  Law- 
rence's Goldfinches,  on  the  other  hand,  generally  frequent 

418 


the  warmest  and  driest  habitats  of  our  three  species  of 
goldfinches  and  are  of  irregular  occurrence  in  Marin 
County.  Where  Lawrences  overlap  extensively  with  Less- 
ers, diey  exhibit  subde  differences  in  habitat  use,  nest  sites, 
and  food  preferences  (see  below  and  Lawrence's  Goldfinch 
account).  In  southern  California,  at  least,  breeding  Law- 
rences primarily  occupy  oak  woodland  edges,  whereas 
Lessers  use  both  oak  woodland  and  chaparral  extensively 
(Coudee  1968a). 

The  large  winter  flocks  of  all  three  species  of  goldfinch 
disintegrate  at  the  time  of  pair  formation.  But  unlike  many 
passerines,  goldfinches  do  not  establish  territories  until 
after  they  choose  nest  sites  (Coudee  1968a).  Lesser  Gold- 
finches maintain  small  territories  centered  around  the  nest 


Cardueline  Finches 


SPECIES  ACCOUNTS 


Cardueline  Finches 


tree,  and  birds  tend  to  nest  semicolonially,  leaving  many 
areas  of  apparendy  suitable  babitat  unoccupied  (Coudee 
1968a).  Lessers  place  tbeir  nests  in  a  wide  variety  of  trees 
and  busbes,  especially  oaks.  They  tend  to  locate  them  in 
dense  foliage  or  lichen  clumps  and,  more  often  than  not, 
toward  the  tips  of  drooping  or  horizontal  branches  (Lins- 
dale  1957,  1968a;  Coudee  1968a).  Nests  are  small  com- 
pact cups  made  of  a  wide  variety  of  materials,  including 
dried  grass,  plant  fibers,  fine  tree  or  weed  bark,  lichens, 
plant  down,  wool,  thread,  cotton,  leaves,  catkins,  and 
cocoons.  Nests  have  a  thin  lining  of  fine  plant  fibers  or 
down,  hair,  or  feathers.  Nest  heights  range  from  about  2 
to  30  feet,  and  although  nest  sites  are  similar  to  those  of 
Lawrences,  those  of  Lessers  average  lower  in  height  (Lins- 
dale  1957,  Coudee  1968a). 

Like  their  congeners,  Lesser  Goldfinches  forage  in  small 
flocks  of  about  four  to  six  birds  in  the  breeding  season  and 
travel  about  one-quarter  to  one-half  mile  from  their  nest 
sites  (Coudee  1968a).  Although  they  feed  on  die  flowers, 
buds,  catkins,  and  new  leaves  of  trees  such  as  oaks  and 
willows,  much  of  their  food  is  seeds  and  dried  fruits 
gathered  from  low  bushes  and  tall  herbaceous  plants 
(Linsdale  1957,  1968a).  The  importance  of  a  good  seed 
crop  is  indicated  by  the  abundance  of  Lessers  observed  in 
a  profusion  of  herbs  and  annuals  following  a  fire  (Linsdale 
1957).  These  goldfinches  generally  take  vegetable  matter 
while  perched  in  the  seed-  or  fruit-bearing  plant  or  in  one 
nearby  from  which  they  can  reach  the  food.  Herbaceous 
plants  often  bend  under  the  goldfinches'  weight,  and  the 
birds  reach  up  or  down  or  hang  upside  down  to  obtain 
their  meals,  picking  off  the  seeds  and  fruits  and  man- 
dibulating  them  to  remove  hulls  or  pappus.  They  swallow 
small  seeds  and  dried  fruits  whole  but  pick  at  die  pulp  of 
fleshy  fruits,  such  as  those  of  coffeeberry  and  madrone, 
probably  just  for  the  juice.  Birds  sometimes  forage  on  the 
ground  for  fallen  seeds  or  on  low,  nearly  horizontal  stems. 
Lessers  also  glean  a  few  insects  from  foliage.  In  California, 
the  year-round  diet  is  abut  98.3%  vegetable  matter  and 
1.7%  animal  matter  (Beal  1910,  n  =  476).  Although 
almost  exclusively  granivorous  at  other  seasons,  in  summer 
Lesser  Goldfinches  eat  enough  insects  to  account  for  9% 
of  the  diet  (Martin  et  al.  1951,  n  =  459).  Animal  foods  are 
mosdy  plant  lice  (woolly  aphids),  caterpillars,  and  a  few 
miscellaneous  insects  (Beal  1910,  Martin  et  al.  1951).  The 
main  vegetable  fare  is  weed  seeds,  which  account  for  96% 
of  the  yearly  diet;  grain,  fruit,  and  miscellaneous  vegetable 
material  are  of  minor  importance.  Throughout  California, 
the  most  important  food  item  is  Napa  or  bur  thisde,  with 
groundsel,  pigweed,  tarweed,  and  turkey  mullein  also 
taken  in  considerable  quantities  (Beal  1910).  Studies  at 
Hastings  Reservation,  Monterey  County,  revealed  that 
Lessers  fed  on  55  species  of  plants,  of  which  Napa  thisde, 
chamise,  common  fiddleneck,  and  vinegarweed  were  the 
most  prominent  (Linsdale   1957,   1968a).   In  that  area, 


Lawrences  fed  on  only  20  species  of  plants,  about  70%  of 
them  plants  also  eaten  by  Lessers.  Linsdale  (1957)  noted 
that  in  mixed  flocks  these  two  species  persistendy  and 
exclusively  fed  on  one  single  kind  of  seed.  The  lower 
number  of  plant  species  in  the  Lawrence's  Goldfinch  diet 
may  have  been  due  to  their  lower  population  size  (Linsdale 
1957)  or  to  bill  size  and  shape  differences  and  differing 
foraging  strategies  (Coudee  1 968b).  Lessers  have  bills  that 
are  considerably  longer  and  more  pointed  than  Lawrences 
and  therefore  may  be  able  to  handle  larger  seeds  and 
extract  seeds  more  easily,  enabling  them  to  use  a  greater 
variety  of  plants  (Coudee  1 968b).  Laboratory  experiments 
indicate  that  Lawrences  feed  in  longer  bouts  than  do 
Lessers  and  may  spend  more  time  searching  out  rich  food 
sources  where  they  can  remain  and  feed  for  several  min- 
utes. In  contrast,  Lessers  may  feed  for  shorter  periods  on 
isolated  stalks,  enabling  them  to  exploit  a  greater  variety  of 
plants  in  a  broader  range  of  sites,  as  well  as  in  areas  where 
Lawrences  have  already  fed  (Coudee  1968b).  Like  other 
cardueline  finches,  Lessers  need  a  reliable  source  of  water 
to  help  soften  the  dry,  hard  seeds  and  fruits  they  eat;  they 
also  show  a  fondness  for  salt  and  grit  (Linsdale  1957). 
During  incubation  and  the  first  four  days  after  the  young 
hatch,  males  feed  females  on  the  nest  by  regurgitation.  The 
young  apparendy  are  fed  entirely  regurgitated  seeds,  ini- 
tially from  the  female  via  the  male. 

Marin  Breeding  Distribution 

During  the  adas  period,  Lesser  Goldfinches  bred  widely  in 
the  eastern  and  north-central  sections  of  Marin  County 
and  reached  their  greatest  abundance  in  the  oak  wood- 
lands and  oak  savannah  around  Novate  The  contrast 
between  this  distribution  and  die  American  Goldfinch's 
indicates  that,  in  general,  Lessers  are  adapted  to  a  drier 
climate  and  more  open  vegetation.  Representative  breeding 
locations  were  Three  Peaks  (DD  6/1 7/82  — DS);  Chileno 
Valley  (NB  5/5/82  -DS);  Mt.  Burdell,  Novato  (NE 
5/1 7/80  — DS);  Sargent  cypress  grove,  Carson  Ridge  (NE 
6/5/82  — DS);  and  Cataract  Trail,  N  of  Rock  Springs,  Mt. 
Tamalpais  (FL/FY  8/1/81  -DS). 

Historical  Trends/  Population  Threats 

Although  population  trends  of  this  species  are  difficult  to 
detect  because  of  marked  year-to-year  variability  (Robbins 
et  al.  1986),  numbers  were  relatively  stable  on  Breeding 
Bird  Surveys  in  California  from  1968  to  1989  (USFWS 
unpubl.  analyses).  On  Spring  Bird  Counts  around  Novato 
from  1978  to  1987,  highest  numbers  of  Lesser  Gold- 
finches were  recorded  in  the  drought  year  of  1987,  and 
second  highest  numbers  in  1 984  (Appendix  A).  These  two 
dry  years  were  also  the  only  ones  when  Lawrence's  Gold- 
finches were  recorded  on  these  counts  (see  account). 


419 


Cardueline  Finches 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Cardueline  Finches 


LAWRENCE'S  GOLDFINCH   Carduelis  lawrencei 


An  irregular  summer  resident  from  early 

^x~y?~^       ^ 

Apr  through  late  Oct 

Ml- 

A  very  rare,  very  local  breeder;  overall 
breeding  population  very  small. 
Recorded  in  4  (1.8%)  of  221  blocks. 

v^ 

^VCaOtxJt 

O    Possible                 2   (50%) 

Vu 

cj>Qw£3c 

'^^TvJ^WV^C^ 

C    Probable       =         1    (25%) 

3^5?^ 

•    Confirmed  =         1    (25%) 
FSAR  =1          OPI  =  4          CI  =  1 .75 

t 

1 1 

Ecological  Requirements 

"Larry's"  Goldfinch  is  the  archgypsy.  Even  in  the  heart  of 
its  breeding  haunts  in  the  dry  interior  Coast  Range  of 
southern  California,  birds  may  be  abundant  at  a  locality 
one  year  and  sparse  or  absent  the  next.  Its  distribution  is 
"notably  discontinuous"  and  movements  are  "erratic" 
(G&.M  1944).  The  species'  irregular  movements  are  appar- 
endy  tied  to  fluctuations  in  the  kinds  and  amounts  of  the 
seed  crops  upon  which  it  depends  (Linsdale  1957). 
Although  they  range  more  widely  in  the  offseason,  particu- 
larly into  chaparral,  breeding  Lawrence's  Goldfinches  con- 
fine themselves  largely  to  the  grassy  and  weedy  edges  of  oak 
savannah  and  oak  woodland  (Linsdale  1957,  Coudee 
1968a).  Rather  than  a  particular  habitat,  the  determining 
factors  appear  to  be  the  structure  of  the  edge  habitat  of 
open  woodland  or  brushland  that  borders  on  grasslands, 
as  well  as  the  suitability  of  seed  crops;  these  goldfinches 
have  also  bred  in  cypress  groves  and  in  native  conifers 
(Linsdale  1957).  Lawrence's  Goldfinches  are  so  irregular 
in  Marin  County  that  it  is  hard  to  discuss  habitat  prefer- 
ences here.  They  have  occurred  on  only  two  of  ten  Even 
Cheaper  Thrills  Spring  Bird  Counts  that  center  around 
Novato  (Appendix  A),  an  area  of  Marin  that  most  resem- 
bles the  dry  interior  Coast  Range.  Most  breeding  season 
occurrences  in  Marin  County  have  been  along  the  edges 
of  oak  savannah  and  oak  woodland  or  in  open  broadleaved 
evergreen  forest  bordering  or  intermixed  with  grassland. 
Birds  have  nested  here  in  planted  cypress,  though,  and  on 
the  edge  of  Douglas  fir  forest  near  the  coast.  Regardless,  on 

420 


a  scale  of  preference  for  climatic  moistness,  Lawrences 
generally  fall  at  the  driest  end,  with  Lessers  intermediate, 
and  Americans  on  the  moist  end. 

For  nesting,  oaks  are  generally  the  bungalows  of  choice, 
but  a  variety  of  trees  and  bushes  are  also  used.  At  Hasting's 
Reservation,  Monterey  County,  Lawrences  prefer  small 
lichen-festooned  blue  oaks  as  nest  sites  (Linsdale  1957). 
Birds  choose  nest  sites  there  on  the  higher  parts  of  the 
hills,  about  one-half  mile  from  the  best  food-producing 
areas  on  flats  along  a  creek  and  on  open  ground  on  a 
hilltop  (Linsdale  1957).  In  a  southern  California  canyon, 
where  foliose  lichens  are  absent,  they  often  use  sycamores 
and  misdetoe  clumps  early  on,  but  as  the  season  progresses 
they  use  oaks  more  and  more  commonly  (Coudee  1968a). 
Lawrence's  Goldfinches  usually  build  their  nests  in  dense 
vegetation  or  lichen  clumps  toward  the  tips  of  branches. 
Nest  height  ranges  from  3  to  40  feet  and  averages  about  1 5 
to  25  feet— higher  than  that  of  sympatric  Lessers  (Linsdale 
1957,  Coudee  1968a).  Lawrences  occasionally  nest  in  the 
same  tree  with  Lessers,  but  generally  both  species  have 
small,  mutually  exclusive  territories  around  the  nest  tree; 
Lessers  are  dominant  over  Lawrence's  Goldfinches 
(Coudee  1968a).  Lawrences  also  tend  to  nest  semicoloni- 
ally.  As  many  as  ten  nests  have  been  observed  in  two 
adjoining  trees  in  an  isolated  stand  of  cypress  (Linsdale 
1957,  1968b).  Nests  "are  exquisite  creations,  highly  varied 
in  construction  and  sometimes  quite  picturesque"  (Daw- 
son 1923).  The  small  compact  cups  are  made  of  weed 
stems  and  leaves,  lichens,  flower  stalks,  grass,  flower  bios- 


Cardueline  Finches 


SPECIES  ACCOUNTS 


Cardueline  Finches 


soms,  leaves,  and  buds.  They  are  thinly  lined  with  fine 
plant  fibers,  fine  bark  strips,  hair,  feathers,  or  cotton 
(Linsdale  1957,  Coudee  1968a). 

Breeding  Lawrence's  Goldfinches  search  in  small  single- 
or  mixed-species  flocks  (with  Lessers  and  House  Finches) 
for  patches  of  low,  seed-bearing  herbaceous  plants  and 
shrubs  (Linsdale  1957,  1968b).  They  apparendy  are 
entirely  granivorous  (Martin  et  al.  1951).  Both  Lawrences 
and  Lessers  feed  on  these  seeds,  at  least  superficially,  in  an 
identical  manner  (see  Lesser  account).  Although  Law- 
rences concentrate  on  chamise  seeds  in  chaparral  in  win- 
ter, in  the  breeding  season  they  are  primarily  found  around 
oak  woodlands  and  at  Hastings  Reservation  are  highly 
dependent  on  patches  of  fiddleneck  (Linsdale  1957, 
Coudee  1968a).  At  Hastings,  they  feed  on  at  least  20  kinds 
of  plants,  especially  natives  (Linsdale  1957,  1968b).  Other 
important  plants  there  besides  fiddleneck  are  red  maids, 
red-stem  filaree,  annual  bluegrass,  common  peppergrass, 
and  shepherd's  purse.  In  addition,  Lawrences  feed  to  a 
limited  degree  on  berries  (pecking  at  the  pulp)  and  greens 
in  gardens;  exceptionally,  they  eat  Mourning  Dove  eggs 
and  jumping  galls  in  (and  on  the  ground  below)  infested 
valley  oaks  (Linsdale  1957,  1968b).  See  the  Lesser  Gold- 
finch account  for  a  comparison  of  the  foraging  niche.  Like 
the  other  goldfinches,  Lawrences  need  a  source  of  fresh 
water  to  aid  in  digesting  seeds,  and  they  have  a  fondness 
for  salt  and  grit  Males  feed  females  at  the  nest  by  regurgi- 
tation during  incubation  and  the  first  few  days  of  the 
nestling  phase,  and  the  young  are  fed  a  diet  of  regurgitated 
seeds,  initially  from  the  female  via  the  male  (Linsdale  1957, 
Coudee  1968a). 


Marin  Breeding  Distribution 

Lawrence's  Goldfinches  were  observed  in  only  four  blocks 
during  the  adas  period:  two  in  the  Mount  Tamalpais 
watershed  and  two  near  Novato.  The  only  adas  breeding 
confirmation  was  of  a  nest  under  construction,  observed  at 
Elliott  Nature  Preserve  in  Fairfax  on  21  May  1977  (BSp  et 
al.).  Surprisingly,  but  probably  because  of  the  preadas 
distribution  of  observer  coverage,  all  other  Marin  breeding 
records  are  from  coastal  sites:  Tennessee  Cove  (NY 
6/15/24  Gull  6,  No.  7;  S&P  1933);  in  the  Abandoned 
Ranch  and  RCA  cypress  groves,  Point  Reyes  ("nesting" 
early  June  1972  — DDeS);  and  in  Douglas  fir  at  Bear  Valley 
Headquarters,  PRNS  (NB  6/3/72  -M&LG). 

Historical  Trends/  Population  Threats 

Mailliard  (1900)  reported  that  the  Lawrence's  Goldfinch 
was  "abundant  in  some  years  and  "rare"  in  others  in 
Marin  County.  Stephens  and  Pringle  (1933)  considered  it 
uncommon  here.  Lawrence's  Goldfinches  were  recorded 
on  only  two  of  ten  Even  Cheaper  Thrills  Spring  Bird 
Counts  from  1978  to  1987  (in  the  dry  years  of  1984  and 
1987),  and  on  one  of  three  South  Marin  Spring  Bird 
Counts  (in  the  drought  year  of  1 977)  (Appendix  A).  These 
years  also  corresponded  to  the  highest  totals  of  Lesser 
Goldfinches  on  both  these  counts.  The  marked  year-to-year 
variability  in  Lawrence's  Goldfinch  populations  makes  it 
difficult  to  detect  population  trends  even  over  broad  areas 
(Robbins  et  al.  1986).  Nevertheless,  their  numbers  were 
fairly  stable  on  Breeding  Bird  Surveys  in  California  from 
1968  to  1989  (USFWS  unpubl.  analyses). 


421 


Cardueline  Finches 


MARIN  COUNTY  BREEDING  BIRD  ATI  AS 


Cardueline  Finches 


AMERICAN  GOLDFINCH   Carduelis  tristis 


A  year-round  resident,  though  numbers 

Aa&yfoSpSfc^         \                 k~v 

much  depleted  on  Point  Reyes  peninsula 

from  Nov  through  late  Mar. 

A  common,  very  widespread  breeder; 
overall  breeding  population  large. 

Recorded  in  173  (78.3%)  of  221 

V?« ^J^X  VV^Tv  ®3r\    ir^\  o  V-^v e  \^\     V-^' 

blocks. 

O    Possible        =      48  (28%) 
C    Probable       =       70   (40%) 

•    Confirmed  =      55  (32%) 

v?0 

FSAR  =  4        OPI  =  692        CI  =  2.04 

Ecological  Requirements 

Although  the  California  form  of  this  cheery  finch  has  been 
called  the  "Willow  Goldfinch,"  it  is  by  no  means  restricted 
to  the  vicinity  of  willows.  Like  our  other  goldfinches,  it  is 
edge  adapted  and  in  the  breeding  season  frequents  the 
open  brushy  and  weedy  borders  of  riparian  thickets,  fresh- 
water marshes,  open  coastal  scrub,  dune  scrub,  planted 
cypress  and  eucalyptus  groves,  weed  fields,  and  brushy 
roadside  margins.  Compared  with  Lesser  and  Lawrence's 
goldfinches,  Americans  occupy  relatively  moist  habitats  in 
proximity  to  permanent  water  or  in  areas  of  high  humidity 
within  the  influence  of  coastal  summer  fog.  Presumably 
these  moist  conditions  nourish  the  plants  upon  which  this 
goldfinch  depends  for  seeds.  The  other  two  species  of 
goldfinches  will  also  nest  near  water  but  generally  adjacent 
to  arid  surroundings.  Unlike  their  Eastern  relations,  which 
begin  breeding  in  July,  American  Goldfinches  in  Califor- 
nia initiate  nests  in  late  April  or  May,  probably  because  of 
the  earlier  maturation  of  seed-bearing  plants  in  our  winter- 
wet  Mediterranean  climate. 

American  Goldfinches  place  their  nests  in  a  wide  variety 
of  bushes,  saplings,  trees,  stout  herbaceous  plants,  and 
even  ferns.  In  some  areas,  at  least,  they  increase  their  use 
of  forbs  as  nest  sites  as  the  season  advances  (Stokes  1950). 
Americans  cradle  most  of  their  nests  in  upright  forks,  with 
several  points  of  attachment.  They  also  place  some 
between  two  parallel  uprights  with  no  support  beneath, 
and  some  in  tufts  of  small  upright  twigs  growing  from 
horizontal  branches  (Nickell  1951).  They  saddle  others 
over  and   around   horizontal   branches   or  wedge  them 

422 


between  horizontal  forks  where  they  resemble  the  semi- 
pensile  nests  of  vireos.  Nests  sites  are  generally  in  open 
sunny  situations  and,  diough  seldom  well  concealed,  usu- 
ally have  some  protection  from  the  leafy  canopy  or  shrub 
cover  (Stokes  1950).  Nest  heights  range  from  1  to  60  feet, 
but  nests  over  30  feet  high  are  rare  (Walkinshaw  1938; 
Batts  1948;  Stokes  1950;  Nickell  1951;  Berger  1957, 
1968;  Austin  1968;  Holcomb  1969;  Middleton  1979). 
Nest  heights,  of  course,  vary  with  habitat.  Nests  in  shrubs, 
thisdes,  and  forbs  are  by  far  the  most  numerous,  and 
average  heights  from  various  studies  range  from  about  4  to 
6  feet  above  the  ground;  average  heights  in  trees  are 
roughly  between  1 2  and  20  feet.  Nest  territories  often  have 
a  taller  tree  used  for  song  and  territorial  defense.  Because 
birds  defend  limited  territories  around  the  nest  tree  and 
forage  in  flocks  in  nondefended  areas,  nesting  may  be 
semicolonial  with  concentrations  around  favorable  nest 
sites  and  food  supplies. 

In  upright  forks,  American  Goldfinches  usually  fill  the 
crotches  beneath  their  nests  with  supporting  materials 
such  as  thisde  or  cattail  down  or  dry  willow  catkins.  They 
construct  the  outer  basketwork  of  the  nest  mosdy  of  the 
thin  outer  bark  of  shrubs,  bark  or  fiber  strips  of  weed 
stalks,  or  grasses,  and  perhaps  a  few  twigs  or  roodets. 
These  are  held  in  place  by  small  amounts  of  fine  fibers, 
spider  silk,  cocoons,  caterpillar  webs,  and  dried  froth  of 
spittlebugs,  apparendy  aided  by  some  moistening  secretion 
of  the  bird  (Nickell  1951).  The  compact  nest  cups  are  so 
thickly  lined  they  may  hold  water.  The  matted  lining  is 


Cardueline  Finches 


SPECIES  ACCOUNTS 


Cardueline  Finches 


made  mostly  of  thistle  down  or  other  plant  down  or 
pappus,  and  sometimes  small  amounts  of  willow  or  cotton- 
wood  catkins,  fine  grasses,  feathers,  or  moss.  Within  the 
lining  there  is  a  supportive  layer  of  hairlike  fibers  consist- 
ing of  finely  shredded  shrub  bark  or,  more  rarely,  roots  or 
animal  hair.  Although  they  collect  most  nest  materials  near 
the  nest  site,  females  will  go  up  to  one-half  mile  or  more, 
if  necessary,  to  the  nearest  source  of  thisde  down  (Drum 
1939).  Females  will  also  salvage  nest  materials  from  other 
birds  such  as  Northern  Orioles  or  Yellow  Warblers,  from 
old  nests  after  failure  of  initial  attempts,  or  even  from  active 
neighboring  goldfinch  nests  (Nickell  1951). 

American  Goldfinches  eat  principally  seeds  of  wild 
plants  and  have  a  particular  fondness  for  thistles  (Beal 
1910).  They  generally  pluck  seeds  while  perched  in  the 
seed-bearing  plant  or  from  a  nearby  support,  and,  like  the 
other  goldfinches,  they  may  stretch  in  acrobatic  contor- 
tions to  reach  pensile  or  swaying  seed  heads.  In  California, 
the  annual  diet  is  about  95%  vegetable  and  5%  animal,  the 
latter  consisting  of  a  few  caterpillars,  plant  lice,  and  larval 
flies  taken  from  spring  to  fall  (Beal  1910,  n  =  84).  Con- 
tinentwide,  animal  foods  account  for  4%  or  less  of  the  diet 
from  summer  through  winter  (n  =  82),  but  up  to  49%  in 
spring  (n  =  41)  (Martin  et  al.  1951).  The  birds  glean 
insects  from  foliage  or  branches  or  obtain  them  by  opening 
oak  galls  or  infected  seeds  (Austin  1968).  The  principal 
seed  plants  identified  in  California  are  bur  thisde,  filaree, 
sunflower,  and  groundsel  (Beal  1910).  American  Gold- 
finches also  eat  flower  and  leaf  buds,  young  leaves,  and, 
rarely,  fruit  or  berries.  They  may  obtain  these  in  the 
treetops,  particularly  in  late  winter  and  spring  (G&M 
1944). 

Observers  have  variously  identified  diis  species'  foraging 
range  from  the  nest  site  as  invariably  less  dian  200  to  350 


yards  and  mosdy  100  yards  or  less  (Nickell  1951);  at  times 
within  one-quarter  but  up  to  one-half  mile  (Coudee  1 967); 
and  up  to  a  mile  or  more  (Drum  1939).  Like  other 
goldfinches,  Americans  need  a  source  of  fresh  water  to  aid 
in  seed  digestion  (Beal  1910).  The  males  feed  the  females 
on  the  nest  by  regurgitation  during  incubation  and  up  to 
about  the  fifth  to  eighdi  day  of  the  nesding  phase  (Drum 
1939).  The  young  are  fed  primarily  regurgitated  seeds  that 
are  provided  initially  by  the  female  via  the  male. 

Marin  Breeding  Distribution 

During  the  atlas  period,  American  Goldfinches  bred 
widely  in  Marin  County.  They  were  most  numerous  along 
the  moist  immediate  coast  and  occurred  sparingly  around 
permanent  water  in  the  lowland  valleys  of  the  drier  north- 
eastern and  north-central  portions  of  the  county.  Represen- 
tative breeding  localities  were  eucalyptus  grove  at  Abbott's 
Lagoon  (NB  6/20/82  — DS);  cypress  grove  at  Abandoned 
Ranch,  Point  Reyes  (NE  5/29/80  -DS);  Brazil  Beach  near 
Lawson's  Landing,  Tomales  Bay  (NE  6/3/82  — DS);  and 
Old  Cerini  Ranch,  E  of  Hwy.  1  at  Cypress  Grove,  Tomales 
Bay  (NE  7/20/82  -DS). 

Historical  Trends/Population  Threats 

Populations  of  American  Goldfinches  generally  decreased 
on  Breeding  Bird  Surveys  in  California  from  1968  to 
1989,  despite  relative  stability  of  numbers  from  1980  to 
1989  (USFWS  unpubl.  analyses).  On  one  hand,  grazing 
has  stimulated  the  growth  of  seed-bearing  thisdes,  but  on 
the  other  hand,  it  has  degraded  nesting  and  foraging 
habitat  of  riparian  edges  by  trampling. 


423 


Old  World  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Old  World  Sparrows 


Old  World  Sparrows 

Family  Passeridae 


HOUSE  SPARROW    Passer  domesticus 


A  year-round  resident. 

A  common,  widespread  breeder;  over- 

all breeding  population  fairly  large. 

Recorded  in  144  (65.2%)  of  221 

Vi\oA^\    3r\  #Jr\  o')V^\o><\o  3r\°  3X1  \ 

blocks. 

\n^a^c  °  jk^\  •  V"v»  y^\p  j^ap  j^\»j^x*^a 

\\<^^^^ov>\»\>\  )zy\*\>\Q)^\*\^i\ 

^x^S^k^k}^t\y^^Y^ 

O    Possible        =      33  (23%) 

Vt€C»  V^'^^'A^A  °  \^V*Jr^A-^3r^\  •  3XlA 

€    Probable       =       14   (10%) 
•    Confirmed   =      97   (67%) 

\p\^Po^5^ 

_-r- 

T  Q-MXa  •  v-^\-d  JsXa  •_V^Y*  VX\     V^\  »  jX<Y*X 

W^^Jr-A^^e^ 

FSAR  =  4       OPI  =  576       CI  =  2.44 

0^/  k>^r   v-\   x-v  v-^v=^^ir>v^\»v,r\* 

^\£>^                xA^^.X<A>^v£xs 

^?o> 

Ecological  Requirements 

As  its  name  implies,  the  House  Sparrow  has  an  intimate 
relationship  with  humans  that  spans  more  than  10,000 
years  since  the  development  of  cereal  grain  monoculture 
and  the  attendant  long-term  storage  and  use  of  diese 
staples  as  an  overwinter  food  supply  for  people  and  live- 
stock (Johnston  &  Klitz  1977).  As  this  relationship  solidi- 
fied in  the  Fertile  Crescent  of  die  Near  East,  the  House 
Sparrow  expanded  its  range  widely  in  the  Old  World 
following  the  spread  of  agriculture.  It  has  since  been 
introduced  broadly  on  other  continents  and  is  now  almost 
certainly  the  most  widespread  landbird  on  Earth  (Sum- 
mers-Smith 1963).  House  Sparrows  inhabit  a  wide  variety 
of  agricultural  and  urban-suburban  environments,  but 
particularly  places  where  occupied  buildings  and  associ- 
ated trees  are  close  together  and  interspersed  widi  patches 
of  open  ground  (Summers-Smith  1963).  Such  situations 
generally  afford  a  regular  source  of  food  supplied  by 
humans,  supplemented  to  a  limited  degree  by  natural 
sources.  These  conditions  are  best  met  in  cities  and  towns 
and  in  highly  populous  arable  lands,  particularly  where 
chickens,  pigs,  and  other  livestock  are  kept.  Because  of 
their  sedentary  habits,  House  Sparrows  reach  their  highest 
densities  only  where  buildings  and  open  farming  areas 

424 


occur  side  by  side:  food,  nest  sites,  and  roost  sites  must  be 
in  close  proximity.  House  Sparrow  populations  are  usually 
not  as  dense  in  less  populated  farm  districts,  even  when 
there  is  considerable  cereal  grain  production,  presumably 
because  high  year-round  food  supplies  and  other  requisites 
are  not  as  easily  met  there.  Although  concentrated  by 
association  with  humans  and  buildings,  House  Sparrows 
form  distinct  breeding  colonies,  so  some  suitable  breeding 
places  are  not  occupied.  Their  colonial  habits  appear  to  be 
an  adaptation  to  nesting  in  close  proximity  to  concentrated 
food  supplies. 

In  Marin  County,  die  incessant,  unmusical  chattering 
and  aggressive  antics  of  House  Sparrows  are  characteristic 
of  urban  parks,  sidewalks  and  gutters,  shopping  mall  and 
fast-food  parking  lots,  suburban  backyards  (especially  those 
with  bird  feeders),  and  the  ranchyards  and  barnyards  of  the 
pastoral  cattle  and  sheep  country— that  is,  virtually  every- 
where they  can  obtain  intentional  or  unintentional  hand- 
outs of  food  and  protected  nest  sites. 

House  Sparrows  build  dieir  bulky  loose  nests  in  a 
variety  of  situations  (Weaver  1939,  Bent  1958,  Summers- 
Smith  1963).  In  most  areas,  the  majority  of  nest  sites  are 
in  and  about  buildings,  in  crevices  and  crannies  such  as 


Old  World  Sparrows 


SPECIES  ACCOUNTS 


Old  World  Sparrows 


under  eaves,  on  rafters,  beneath  adobe  tiles,  in  rain  spouts, 
and  in  bird  boxes.  House  Sparrows  will  also  nest  in  ivy  and 
other  vines  on  buildings  and  in  the  dense  branchwork  of 
trees.  They  use  a  variety  of  deciduous  and  coniferous  trees, 
but  palms  are  a  particular  favorite  in  California.  To  a  lesser 
degree,  House  Sparrows  also  use  natural  cavities  in  trees, 
old  woodpecker  holes,  Cliff  Swallow  nests,  the  lower 
portions  of  hawk  nests,  Bank  Swallow  holes,  caves,  and 
holes  in  cliffs,  earthen  banks,  or  stone  walls.  As  a  rule, 
House  Sparrows  prefer  hole  and  cavity  nests  and  normally 
use  open  tree  sites  only  when  other  sites  are  unavailable. 
They  appear  to  use  tree  sites  more  commonly  in  warmer 
parts  of  the  species'  range.  Nests  in  trees  are  globular  in 
shape,  are  domed  over,  and  have  a  side  entrance  or,  less 
frequendy,  a  top  or  bottom  one  (McGillivray  1 981).  House 
Sparrows  will  use  open-cup  nests  of  other  species  of  birds 
as  foundations  that  they  dome  over.  One  enterprising  pair 
of  sparrows  used  a  hornet  nest,  pulling  out  a  large  part  of 
the  comb  and  substituting  their  usual  nest  materials  for  it 
(Bent  1958).  Birds  construct  the  outer  layer  of  die  nest  with 
coarse  hay,  dried  weeds,  or  straw  and  line  it  with  softer 
materials,  especially  feathers,  as  well  as  string,  leaves, 
cotton,  cloth,  paper,  hair,  frayed  rope,  plastic,  or  other 
debris.  Females  lay  eggs  before  the  final  lining  is  added 
(Weaver  1939).  Cavity  nests  vary  in  size  according  to  the 
space  available,  which  is  filled  up  with  nest  material;  cavity 
nests  may  not  be  domed  over  and  may  consist  of  just  the 
lining  materials.  House  Sparrows  nest  colonially  and 
defend  small  territories  just  around  the  nest  site.  Neverthe- 
less, a  few  compound  nests  have  been  found— one  was  a 
large  ball  of  hay  with  three  small  openings  leading  to 
separate  nest  chambers.  Nest  heights  range  from  a  few 
inches  off  the  ground  (most  above  8  to  10  ft.)  to  50  feet. 
House  Sparrows  select  larger  and  denser  trees  for  "open" 
nests,  which  they  typically  build  next  to  the  main  trunk 
(McGillivray  1981).  In  colder  climes,  they  tend  to  position 
tree  nests  more  centrally  in  tree  rows,  lower  in  trees,  and 
with  south-facing  entrances,  all  for  protection  from  strong 
north  winds  early  in  the  season;  later  in  the  season  they 
tend  to  build  nests  with  north-facing  entrances  to  take 
advantage  of  the  cooling  effects  of  wind  (McGillivray 
1981).  Nest  sites  are  frequendy  occupied  by  different 
individuals  in  successive  nesting  attempts  in  the  same 
season  (Weaver  1939,  1943;  Sappington  1977). 

The  House  Sparrow's  diet  consists  primarily  of  seeds, 
especially  grains,  but  it  varies  locally  and  regionally  (e.g., 
Kalmbach  1940,  Southern  1945,  Summers-Smith  1963, 
Griin  1975,  Wiens  &.  Dyer  1977).  Kalmbach's  (1940) 
exhaustive  study  revealed  that  the  diet  in  the  U.S.,  overall 
by  volume,  is  about  97%  vegetable  matter  and  3%  animal 
matter.  About  78%  of  the  vegetable  fare  is  cereal  grains, 
such  as  cracked  corn,  oats,  wheat,  grain  sorghums,  barley, 
buckwheat,  and  rice.  Grass  and  weed  seeds  comprise  about 
17%  of  the  diet,  and  important  plants  include  ragweed, 


crabgrass,  smartweed  or  knotgrass,  pigweed,  and  ama- 
ranth. The  remainder  of  the  vegetable  menu  includes  mast 
and  wild  fruit,  cultivated  fruits  and  vegetables,  and  miscel- 
laneous vegetable  matter.  Consumption  of  animal  matter 
in  the  U.S.  varies  from  none  in  winter  to  12%  at  the  peak 
of  breeding  in  May.  However,  these  figures  mask  the  fact 
that  House  Sparrows  will  sometimes  exploit  abnormal 
abundance  of  insects.  The  main  animal  items  in  their  diet 
are  weevils  and  various  other  beedes,  grasshoppers  and 
crickets,  caterpillars  and  moths,  hymenopterans,  and  flies, 
along  with  miscellaneous  insects,  spiders,  millipedes, 
earthworms,  snails,  and  garbage.  Near  the  sea,  House 
Sparrows  also  take  mollusks  and  crustaceans  (Summers- 
Smith  1963). 

Sappington  (1977)  found  that,  in  addition  to  the  par- 
ents, nest  helpers  also  fed  young  at  a  majority  of  nests  in 
Mississippi.  The  nestling  diet  decreases  from  nearly  all 
animal  matter  (about  85%- 100%)  in  the  first  few  days  of 
life  (when  fed  partly  by  regurgitation)  to  about  20%-30% 
at  fledgling,  with  a  corresponding  increase  in  vegetable 
food  (Kalmbach  1940,  Summers-Smith  1963).  The  con- 
sumption of  soft-bodied  insects  decreases  with  age, 
whereas  that  of  hard  chitinous  insects  increases  until 
vegetable  foods  become  predominant;  a  higher  frequency 
of  spider  consumption  at  early  ages  may  be  due  to  their 
easier  digestibility  (Kalmbach  1940)  or  perhaps  to  their 
greater  energy  or  nutritive  value  (Wieloch  1975).  In  addi- 
tion to  other  seasonal  and  age-  or  sex-related  dietary  differ- 
ences, Pinowska  (1975)  found  that  females  engaged  in  egg 
laying  ate  more  insects  (protein)  and  weed  seeds  (mineral 
salts  and  vitamins);  increased  consumption  of  grit  may  aid 
in  digestion  of  hard  insects  or  satisfy  the  changing  require- 
ments of  females  for  mineral  salts.  The  general  consump- 
tion of  eggshells,  mortar,  and  salt  may  serve  similar 
purposes  (Summers-Smith  1963). 

House  Sparrows  forage  mosdy  on  or  close  to  the 
ground.  They  pick  up  waste  grain  after  harvest,  grain 
spread  on  the  ground  as  livestock  feed,  semidigested  grain 
from  the  droppings  of  livestock,  seed  from  bird  feeders, 
and  food  dropped  or  offered  direcdy  by  humans  (Barrows 
1889,  Bent  1958,  Summers-Smith  1963).  They  also 
scratch  up  planted  or  sprouted  seeds,  clip  off  or  pull  up 
tender  new  shoots,  cut  out  the  embryo  fruit  of  flower  buds, 
clip  vegetable  leaves,  eat  undeveloped  vegetable  seeds,  and 
peck  fruits  on  the  vine  or  in  trees.  House  Sparrows  will 
alight  on  stalks  to  pluck  grain  from  the  fruiting  heads  or  to 
shake  the  kernels  down  to  the  ground  to  be  picked  up  later; 
occasionally,  they  will  hover  next  to  a  seed  head  to  obtain 
the  seeds.  Grass  and  weed  seeds  are  obtained  by  stripping 
the  head.  Animal  food  is  also  obtained  in  a  variety  of  ways. 
Birds  will  methodically  search  for  slow-moving  insects, 
which  they  glean  from  the  ground,  bushes,  tree  trunks,  and 
the  undersides  of  tree  foliage.  They  also  take  flies  and  other 
insects  from  under  eaves  where  caught  in  cobwebs  or  from 

425 


Old  World  Sparrows 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Old  World  Sparrows 


the  grills  of  parked  cars,  and  they  catch  moths  attracted  to 
lights.  House  Sparrows  catch  active  insects  using  clumsy 
flycatching  maneuvers  from  perches  or  the  ground,  by 
pouncing  down  from  low  flight,  or  by  darting  up  from  the 
ground  to  bushes.  They  also  hover  kestrellike,  tails 
depressed  and  fanned  and  legs  dangling,  to  obtain  insects 
from  buildings  or  foliage.  Rarely,  House  Sparrows  also 
flush  prey  from  trees  by  grasping  a  twig  in  their  feet  and 
vigorously  flapping  their  wings  (Guillory  &.  Deshotek 
1981).  Sometimes  House  Sparrows  follow  American  Rob- 
ins and  European  Starlings  foraging  on  lawns  for  worms 
and  gnibs,  to  rob  diem  of  their  catch  (Bent  1958). 

Nesting  House  Sparrows  generally  range  only  up  to 
about  200  to  500  yards,  or  rarely  a  mile,  from  nest  sites 
when  foraging  (Summers-Smith  1963,  Wieloch  1975).  In 
the  summer,  flocks  of  primarily  immature  birds  form. 
Large  numbers  of  birds  roost  communally  at  night  in  tall, 
densely  foliaged  trees  in  the  countryside  or  in  cities  near 
nesting  locations,  and  they  commute  out  to  feed  in  grain- 
fields  during  the  day  (Summers-Smith  1963,  North  1973, 
Dyer  etal.  1977).  These  flocks  generally  commute  less  than 
two  miles,  or  rarely  up  to  three  to  four  miles,  from  roost 
sites  to  foraging  areas.  While  foraging  in  grainfields  they 
only  venture  about  five  yards  from  cover  (Summers-Smith 
1963). 

Marin  Breeding  Distribution 

During  the  adas  period,  House  Sparrows  bred  widely  in 
Marin  County,  but  their  distribution  was  most  continuous 
in  the  urban-suburban  corridor  along  Highway  101  in 
eastern  Marin.  In  the  remainder  of  the  county,  they  were 
more  patchily  distributed  in  association  widi  die  human 
population  in  small  towns  and  around  ranches  on  coastal 
bluffs,  inland  valleys,  and  low,  rolling  hills.  They  avoided 
areas  that  lacked  human  occupation,  which  generally  coin- 
cided with  steep  and  densely  vegetated  ridges.  On  Point 
Reyes,  for  example,  House  Sparrows  concentrated  on  the 
outer  peninsula  around  dairy  ranches  and  in  or  near  the 
Olema  Valley,  from  the  small  communities  of  Inverness  to 
Bolinas,  but  they  shunned  most  of  Inverness  Ridge.  Rep- 
resentative breeding  records  included  Maggetti  Ranch,  E 
side  Tomales  Bay  (NB  5/27/82  -DS);  Chileno  Valley 
(NB  6/4/82  -DS);  Hicks  Valley  (FL  6/?/82  -ScC);  and 
Novate  (NB  5/27/78  -RMS). 

Historical  Trends/ Population  Threats 

The  introduction  of  House  Sparrows  and  their  rapid 
spread  in  North  America  is  fairly  well  documented  (Bar- 
rows 1889,  Bent  1958,  Robbins  1973).  House  Sparrows 
were  introduced  on  this  continent  because  European 
immigrants  longed  for  the  familiar  birds  of  their  homeland 
and  because  they  believed  the  sparrows  would  be  useful  in 
controlling  insect  pests.  House  Sparrows  were  first  liber- 
ated in  New  York  City  from  1851  to  1 853.  In  the  following 

426 


decades,  scores  of  other  introductions  were  made  in  the 
East  (varying  from  5  to  over  1000  birds  each),  primarily  of 
stock  from  Great  Britain  and,  to  a  lesser  extent,  Germany. 
The  spread  of  the  House  Sparrow  population  was  also 
aided  gready  by  transplants  to  other  areas  of  birds  already 
established  in  the  United  States.  Up  until  1886,  the  only 
known  successful  introductions  west  of  the  100th  merid- 
ian were  at  San  Francisco  (1871  or  1872,  origin 
unknown),  at  Stockton,  California  (1883,  from  San  Fran- 
cisco), and  at  Salt  Lake  City  (1873  or  1874,  from  Europe). 
Initially,  introductions  and  transplants  took  on  the  propor- 
tions of  a  "craze,"  with  hordes  of  enthusiastic  "benefactors" 
urging  introductions  in  increased  numbers  and  aiding  and 
abetting  birds  already  established,  to  the  point  of  legal 
protection.  From  1855  to  1870,  there  was  only  weak 
resistance  to  the  introductions  by  a  few  enlightened  natu- 
ralists and  by  citizens  who  had  previous  experience  control- 
ling the  sparrows  in  Europe.  A  gradual  turn  in  the  tide  of 
opinion  against  the  sparrows  became  marked  by  1880, 
especially  among  agriculturalists.  Even  with  increasing 
opposition,  sparrow  enthusiasts  were  still  providing  "nest- 
ing boxes  by  the  thousands"  and  "food  by  the  barrel" 
(Barrows  1889).  Control  efforts  had  little  effect  except  to 
lessen  numbers  locally.  After  the  initial  rash  of  introduc- 
tions, which  lasted  about  35  years,  little  was  recorded  of 
further  releases.  The  spread  of  House  Sparrows  continued 
at  a  rapid  pace,  with  birds  moving  out  from  cities  and 
towns  to  the  agricultural  areas.  In  addition  to  dissemina- 
tion by  purposeful  release,  House  Sparrows  expanded  their 
range  by  following  highways,  where  they  could  pick  up 
grain  dropped  by  passing  vehicles  or  semidigested  grain 
from  the  droppings  of  horses,  and  by  unintentional  long- 
distance dispersal  via  grain  or  cattle  cars.  The  latter  method 
was  particularly  effective  in  the  West.  By  1900,  House 
Sparrows  had  extended  their  range  across  the  Great  Plains 
to  the  base  of  the  Rockies,  but  they  had  spread  only  slighdy 
from  the  western  colonies  (Bent  1958,  Robbins  1973).  By 
1910,  House  Sparrows  occupied  nearly  all  of  the  United 
States  except  central  Nevada,  southern  California,  and  the 
northern  Rockies.  By  1915  they  were  present,  at  least 
locally,  even  in  these  areas.  All  of  the  U.S.  and  a  large  part 
of  southern  Canada  were  colonized  by  1 969,  with  expan- 
sion and  consolidation  still  occurring  on  the  edge  of  the 
range.  Some  observers  felt  diat  the  House  Sparrow  popu- 
lation had  reached  a  peak  in  the  East  by  1890  and  declined 
thereafter  coincident  with  the  shift  from  horse  to  automo- 
bile transportation.  They  speculated  that  the  decline  was 
due  either  to  a  decrease  in  grain  supplies  and  grain  spilling 
from  nosebags  and  found  in  horse  dung  or  to  a  natural 
decline  typical  of  many  rapidly  spreading  species  that 
overshoot  their  limits. 

Although  birds  arriving  in  San  Francisco  in  1871  or 
1872  apparendy  came  from  transplants  from  the  East,  it 
has  been  suggested   that  the   species   repeatedly  entered 


Old  World  Sparrows 


SPECIES  ACCOUNTS 


Old  World  Sparrows 


California  unintentionally  via  railroad  lines  (G&.M  1944). 
By  1 886,  House  Sparrows  had  appeared  generally  through- 
out the  San  Francisco  Bay  region  and  at  Eureka,  Stockton, 
and  Hollister.  By  1915,  the  species  occupied  virtually  all 
sections  of  the  state,  at  least  sparingly.  Although  not 
reported  in  Marin  County  at  the  turn  of  the  century 
(Mailliard  1900),  House  Sparrows  were  considered  "very 
common"  here  by  1933  (S&.P  1933).  A  decrease  in  the 
California  population  was  noted  locally  in  the  two  decades 
prior  to  1944  (G&M  1944),  perhaps  for  the  same  reasons 
suggested  for  the  eastern  population.  House  Sparrow  pop- 
ulations were  relatively  stable  on  Breeding  Bird  Surveys  in 
California  from  1968  to  1989  (USFWS  unpubl.  analyses). 
The  House  Sparrow's  great  success  as  a  colonizer  can  be 
attributed  to  its  preadaptation  to  a  niche  not  previously 
occupied  by  other  native  birds,  its  great  tolerance  for 
extremes  in  environmental  conditions,  its  varied  feeding 
methods,  its  choice  of  a  variety  of  nest  sites,  its  ability  to 
quickly  exploit  new  food  sources,  and  its  tolerance  of 
human  disturbance  (Summers-Smith  1963).  Food  supply 
seems  to  be  the  main  factor  in  controlling  House  Sparrow 
numbers  at  present.  Changes  in  die  dirust  of  human 
endeavors  will  continue  to  affect  House  Sparrows,  with 
various  factors  such  as  increased  human  populations  aug- 
menting numbers  and  others,  such  as  increasing  mechani- 
zation of  harvest  methods,  depressing  them. 

Remarks 

The  House  Sparrow  has  been  accused,  to  varying  degrees, 
of  a  multitude  of  transgressions  to  human  interests,  includ- 
ing economic  damage  to  grain  and  other  agricultural  crops, 


fouling  water,  spreading  parasites  and  disease  in  poultry 
and  livestock,  clogging  drain  pipes  with  their  nests,  and 
marring  statues,  buildings,  or  trees  with  their  "filth"  (Bar- 
rows 1889,  Kalmbach  1940,  Southern  1945,  Bent  1958). 
Perhaps  their  greatest "  fault"  is  their  aggressive  interactions 
with  native  birds.  House  Sparrows  frequendy  defend  and 
use  nest  sites  before  other  species  arrive  and  actively 
displace  other  species  to  the  point  of  destroying  or  throw- 
ing out  their  eggs  and  young.  The  species  most  affected  are 
the  cavity  nesters  such  as  swallows,  bluebirds,  and  wrens, 
though  attacks  also  extend  to  open  nesters  such  as  Ameri- 
can Robins  and  House  Finches.  Efforts  at  House  Sparrow 
control  have  proven  effective  on  only  a  local  scale,  but 
considering  all  of  the  problems  humans  have  caused  native 
birds,  the  least  that  can  be  done  is  to  protect  them  from 
the  offenses  of  introduced  birds  when  possible.  In  the  case 
of  the  House  Sparrow,  this  can  be  most  effective  by 
eliminating  the  food  supply  that  attracts  them  and,  second- 
arily, by  removing  their  nest  materials  before  they  are  well 
established. 

Although  the  introduction  of  the  House  Sparrow  has 
had  an  overwhelmingly  negative  effect,  on  a  positive  note 
it  has  allowed  the  study  of  rapid  evolution  of  geographic 
variation  in  body  size  and  dimensions,  plumage,  the  onset 
and  duration  of  the  breeding  season,  clutch  size,  and 
various  physiological  characteristics  (see  Murphy  1978). 


427 


SPECIES  OF  UNCLEAR  BREEDING 
STATUS  OR  POTENTIAL  BREEDERS 


The  following  accounts  describe  what  we  know  of 
species  with  equivocal  historical  or  recent  breeding 
evidence  in  Marin  County,  or  of  species  that  have  bred 
elsewhere  around  San  Francisco  Bay  and  potentially  could 
breed  in  Marin  County.  Some  of  these  species  may  for- 
merly have  bred  in  Marin  County  at  a  time  of  very  limited 
observer  coverage  and  may  have  gone  undetected  before 
extirpation. 


EARED  GREBE 

Podiceps  nigricollis 

Eared  Grebes  have  bred  irregularly  in  the  San  Francisco 
Bay  Area  (in  Alameda,  Santa  Clara,  and  Sonoma  counties) 
since  1983  (AB  37:1022,  ABN,  B.  Burridge  pers.  comm.). 
Potential  breeding  habitat  of  shallow-water  marshlands 
could  be  created  for  the  species  in  Marin  County's  historic 
bayside  marshlands,  much  of  which  is  now  diked  off  from 
the  bay;  the  paucity  of  Bay  Area  breeding  records  suggests 
such  habitat  might  be  used  only  under  unusual  circum- 
stances though.  Eared  Grebes  now  occur  in  Marin  almost 
exclusively  as  winter  residents  (or  migrants)  from  October 
through  May  (Shuford  et  al.  1989). 


FORK-TAILED  STORM-PETREL 

Oceanodroma  furcata 

The  nearest  known  breeding  colony  of  Fork-tailed  Storm- 
Petrels  is  in  northern  Humboldt  County  (Sowls  et  al. 
1980,  Carter  et  al.  1992).  Intriguing  was  the  capture  of  an 
adult  Fork-tailed  Storm-Petrel  with  a  bare  brood  patch  on 
27-28  May  1990  at  the  Farallon  Islands  (Carter  et  al. 
1992,  PRBO  unpubl).  Although  it  is  possible  that  a  few  of 
these  petrels  may  nest  on  the  Farallones,  it  is  more  likely 
the  captured  bird  was  on  an  extended  foraging  trip  from  a 
distant  colony.  Even  though  this  petrel  may  never  breed  in 
Marin  County,  it  does  appear  that  some  breeding  birds  at 
least  rarely  visit  our  offshore  or  pelagic  waters.  The  Fork- 
tailed  Storm-Petrel  is  currendy  a  Bird  Species  of  Special 
Concern  in  California  (Remsen  1978,  CDFG  1991b). 

LEACH'S  STORM-PETREL 

Oceanodroma  leucorhoa 

Leach's  Storm-Petrels  breed  nearby  on  the  Farallon  Islands 
and  at  Gull  Rock,  Sonoma  County  (Carter  et  al.  1992), 
suggesting  that  they  could  possibly  nest  in  Marin  County, 
perhaps  at  Bird  Rock,  where  Ashy  Storm-Petrels  breed. 


WESTERN  GREBE 

Aechmorphorus  occidentalis 

CLARK'S  GREBE 

A.  clarkii 

"Western"  Grebes  (when  the  above  two  species  were 
considered  one)  formerly  bred  on  Lake  Merced  in  the  city 
and  county  of  San  Francisco  (G&W  1927,  G&M  1944). 
Western  and  Clark's  grebes  occur  in  Marin  County  year 
round,  though  primarily  as  winter  residents  from  Septem- 
ber through  May  (Shuford  et  al.  1989).  Despite  summer 
occurrence  here  on  salt  water,  it  seems  only  remotely 
possible  they  will  ever  colonize  some  of  Marin  County's 
marsh-bordered  lakes,  all  of  which  are  probably  too  small 
to  provide  adequate  nesting  habitat. 


LITTLE  BLUE  HERON 

Egretta  caerulea 

Up  to  two  adult  Little  Blue  Herons  were  seen  in  or  near 
the  West  Marin  Island  heron  and  egret  rookery  off  San 
Rafael  in  the  breeding  seasons  of  1965,  1968,  1969,  1970, 
and  1971  (Unitt  1977).  Observers  suspected  Little  Blues 
were  breeding  there  or  hybridizing  with  Snowy  Egrets,  but 
neither  was  ever  confirmed.  A  specimen  at  the  California 
Academy  of  Sciences  from  the  West  Marin  Island  colony 
thought  possibly  to  be  a  young  Little  Blue  Heron  is  of 
uncertain  identity  (J.  Morlan  pers.  comm.).  Subsequendy, 
diey  have  probably  been  breeding  or  hybridizing  with 
Snowy  Egrets  in  south  San  Francisco  Bay  since  at  least 
1981  (Morlan  ck  Erickson  1988,  AB  42:1336),  but  breed- 
ing was  not  confirmed  there  until  1 988  (P.  Woodin  pers. 
comm.). 

429 


Short  Accounts 

CATTLE  EGRET 

Bubulcus  ibis 

The  Cattle  Egret  has  spread  rapidly  in  California  since  its 
arrival  in  the  state  in  1964  (McCaslcie  1965).  Nesting  was 
first  observed  in  southern  California  in  1970  (AFN  24:716) 
and  in  northern  California  in  1978  (AB  32:1204).  Among 
other  sites,  the  species  now  breeds  in  small  numbers  in 
Santa  Clara  County  in  south  San  Francisco  Bay  (AB 
39:345),  the  closest  colony  to  Marin  County.  Cattle  Egrets 
occur  in  Marin  County  primarily  as  late  fall  and  winter 
dispersants  from  mid-October  to  mid-January;  breeding 
season  records  are  few  for  the  county  (Shuford  et  al.  1989). 
The  observation  of  one  Catde  Egret  at  the  Audubon 
Canyon  Ranch  heron  and  egret  rookery  on  16  April  1974 
(MSd)  is  the  only  evidence  of  nest  site  prospecting  by  this 
species  in  the  county.  The  Cattle  Egret  may  still  possibly 
become  established  here,  especially  if  the  California  breed- 
ing population  continues  to  expand. 


FULVOUS  WHISTLING-DUCK 

Dendrocygna  bicolor 

Whisding-Ducks  formerly  bred  (probably  sporadically) 
near  Mountain  View,  Santa  Clara  County  in  south  San 
Francisco  Bay  (GckM  1944).  Grinnell  and  Miller  (1944) 
considered  records  in  Marin  County  prior  to  1895 
(Mailliard  1904)  to  represent  the  occurrence  of  vagrants  or 
migrants,  though  the  true  seasonal  status  was  probably 
poorly  known  because  of  limited  observer  coverage.  Num- 
bers of'  breeding  Fulvous  Whisding-Ducks  have  since 
declined  drastically  in  California,  leading  to  their  being 
listed  in  the  state  as  a  Bird  Species  of  Special  Concern 
(Remsen  1978,  CDFG  1991b).  The  population  in  the 
Southwest  (including  California)  is  also  a  Candidate  (Cate- 
gory 2)  for  federal  listing  as  Threatened  or  Endangered 
(USFWS  1991).  It  is  unlikely  that  they  will  return  to  breed 
in  the  Bay  Area  in  the  foreseeable  future. 


WATERFOWL 

Several  other  species  of  ducks— Green-winged  Teal  (Anas 
crecca),  American  Wigeon  (Anas  americana),  Canvasback 
(Aythya  valisineria),  Redhead  (Aythya  americana),  and 
Lesser  Scaup  (Aythya  affinis)— have  bred  sporadically  or 
accidentally  around  San  Francisco  Bay,  though  as  a  group 
they  occur  there  (and  in  Marin  County)  primarily  as  winter 
residents  from  September  or  October  through  March  or 
April  (GckM  1944,  ABN).  All  these  species  have  been  seen 
in  Marin  County  for  short  or  extended  periods  (though 
irregularly)  in  summer  (Shuford  et  al.  1989,  ABN)  and 
potentially  could  breed  here. 

430 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


SKort  Accounts 


CALIFORNIA  CONDOR 

Gymnogyps  californianus 

Although  California  Condors  formerly  occurred  as  far 
north  as  southern  British  Columbia,  breeding  was  con- 
firmed only  as  far  north  as  Monterey  and  San  Benito 
counties,  California  (Koford  1953).  Wilbur  (1973b)  spec- 
ulated that  they  may  once  have  bred  as  far  north  as  the 
Pacific  Northwest  but  went  undetected  before  the  species 
began  its  rapid  decline  toward  extinction.  Apparendy  the 
only  solid  Marin  County  record  of  Condors  is  of  at  least  a 
dozen  birds  from  the  mountains  near  Fairfax  in  July  of 
1847,  though  a  specimen  from  the  "mountains  north  of 
San  Francisco"  perhaps  was  collected  in  Marin  (Koford 
1953).  The  locality  designated  as  "San  Rafael"  where  eggs 
were  collected  prior  to  1869  (GckM  1944)  refers  to  a  site 
in  Monterey  (not  Marin)  County  (Koford  1953).  It  is 
possible  that  California  Condors  once  bred  in  Marin 
before  any  ornidiological  exploration  of  the  county. 

Because  this  federal  and  state  Endangered  species  was 
teetering  on  the  brink  of  extinction,  a  controversial  captive 
breeding  program  was  initiated  in  1980,  and  by  1987  the 
last  remaining  Condors  were  all  in  confinement.  As  of 
September  1991,  there  were  52  condors  in  captivity— 27 
brought  in  from  the  wild  as  adults,  chicks,  or  eggs,  and  25 
raised  from  eggs  laid  in  captivity  (R.  Mesta  pers.  comm.). 
Given  the  burgeoning  development  and  increase  in 
human  numbers  in  the  country's  most  populous  state,  it 
seems  unlikely  we  will  ever  see  free-flying  Condors  on  a 
regular  basis  in  the  Bay  Area,  even  if  the  captive  rearing 
program  is  highly  successful  by  today's  standards.  Two 
young  captive-reared  California  Condors  were  released  in 
January  1992  in  die  Sespe  Condor  Sanctuary,  Ventura 
County  (R.  Mesta  pers.  comm.).  Only  time  will  tell  if  these 
birds  embodying  the  soul  and  spirit  of  wild  California  will 
rise  again  or  fall  to  the  onslaught  of  so-called  progress. 


BALD  EAGLE 

Haliaeetus  leucocephalus 

Although  there  are  no  known  nesting  records  for  Marin 
County  (GckW  1927,  SekP  1933,  GckM  1944,  Detrich 
1986),  the  county  is  clearly  within  the  historic  breeding 
range.  Bald  Eagle  bones  have  been  identified  in  shell 
middens  of  aboriginal  people  along  the  shore  of  San 
Francisco  Bay  at  Alameda  County  (Howard  1929),  indicat- 
ing the  species  was  present  in  the  Bay  Area  in  prehistoric 
times.  In  historic  times,  Bald  Eagles  were  "formerly  com- 
mon and  widely  distributed"  along  the  entire  length  of 
California,  but  by  the  1940s  they  were  nearly  extirpated  as 
breeders  (GckM  1944).  Detrich  (1986)  suspected  that  the 
near  absence  of  breeding  records  of  Bald  Eagles  in  the  San 
Francisco  Bay  Area  was  a  gap  in  the  record  radier  than  in 
the  original  range  of  the  species.  The  closest  known  coastal 


Short  Accounts 


UNDOCUMENTED  &  POTENTIAL  BREEDERS 


Snort  Accounts 


nesting  records  are  from  near  Guerneville,  Sonoma 
County,  in  1904  (Detrich  1986)  and  near  La  Honda,  San 
Mateo  County,  about  1915  (GckW  1927).  The  least  popu- 
lated western  sectors  of  Marin  County,  where  conifer-clad 
ridges  overlook  a  series  of  near-pristine  estuaries,  would 
seemingly  have  provided  suitable  nesting  habitat.  In  the 
mid-1 880s,  Point  Reyes  and  other  parts  of  Marin  County 
supported  "the  greatest  dairy  operations  in  the  state" 
(Mason  1970),  in  an  era  when  predators,  especially  eagles, 
were  routinely  subjected  to  severe  persecution  by  ranchers 
and  stockmen  (Detrich  1986).  A  newspaper  report  of  a 
"bald  head  eagle"  shot  at  Camp  Taylor  on  1 7  August  1 868 
(Marin  Journal,  22  Aug  1868),  suggests  that  a  resident 
population  may  have  been  extirpated.  The  species  is  cur- 
rendy  a  rare  and  irregular  winter  visitant  to  Marin  County, 
mosdy  from  October  through  March. 

The  Bald  Eagle  is  currendy  listed  as  state  and  federally 
Endangered  in  California.  A  proposal  to  introduce  32 
Bald  Eagles  into  the  Point  Reyes  National  Seashore  over 
three  years  in  the  early  1990s  in  hopes  of  establishing  a 
breeding  population  has  met  with  resistance  from  some 
local  biologists  and  conservationists.  They  question  the 
wisdom  of  introducing  a  species— currendy  expanding  on 
its  own— into  an  area  with  no  known  historic  breeding 
population  because  of  the  potential  detrimental  effects  on 
already  naturally  established  Ospreys,  heron  and  egret 
colonies,  or  other  potential  prey  of  the  eagles.  Once  data 
are  in  on  population  size  and  reproductive  success  from 
the  1991  breeding  season,  the  U.S.  Fish  and  Wildlife 
Service  will  give  consideration  to  downlisting  die  Bald 
Eagle  from  Endangered  to  Threatened  in  parts  of  its  range 
(P.  Detrich  pers.  comm.).  Although  our  national  symbol 
can  use  all  die  help  it  can  get,  introductions  or  reintroduc- 
tions  should  be  done  only  after  careful  studies  have  evalu- 
ated any  possible  effects  that  might  upset  the  finely  tuned 
balance  of  the  ecosytem  in  question. 


PRAIRIE  FALCON 

Falco  mexicanus 

A  sighting  of  a  Prairie  Falcon  flying  south  from  Sonoma 
County  to  Marin  County  over  Estero  Americano  about  1 .5 
miles  east  of  its  mouth  on  1  July  1982  (DS)  is  the  only 
known  breeding  season  record  for  the  county.  This  bird 
likely  represented  a  postbreeding  dispersant  or  a  non- 
breeder.  An  open  country-inhabiting  raptor  such  as  a 
Prairie  Falcon  would  most  likely  have  been  seen  at  least 
with  some  regularity  during  the  years  of  intensive  adas 
work  if  in  fact  the  species  was  breeding  here.  Prairie 
Falcons  typically  occur  in  Marin  as  rare  winter  residents 
(or  migrants),  mosdy  from  mid-August  through  Febniary 
(ABN).  Prairie  Falcons  do  breed  in  drier  portions  of  the 
interior  Coast  Range  in  some  San  Francisco  Bay  Area 
counties  (Garrett  6k  Mitchell  1973,  ABN).  The  habitat  in 


Marin  County  most  similar  to  breeding  habitat  elsewhere 
in  the  Bay  Area  is  found  around  Nova  to,  but  it  appears  to 
lack  suitable  breeding  cliffs.  The  Prairie  Falcon  is  a  Bird 
Species  of  Special  Concern  in  California  (Remsen  1978, 
CDFG  1991b). 


WILD  TURKEY 

Meleagris  gallopavo 

Wild  Turkeys  are  not  native  to  California,  but  they  have 
been  released  and  now  wild,  free-ranging  resident  popula- 
tions inhabit  large  areas  of  the  state  (GckM  1944,  Harper 
6k  Smith  1973,  Graves  1975,  Mallette  6k  Slosson  1987). 
Although  Wild  Turkeys  raised  in  Marin  County  were  sold 
in  San  Francisco  in  1883  (Schorger  1966),  there  appears 
to  have  been  no  effort  to  establish  a  wild  population  here 
until  recendy.  In  February  1988,  California  Department  of 
Fish  and  Game  personnel  released  17  Wild  Turkeys  on 
the  ridges  south  of  Big  Rock  Ranch  off  Lucas  Valley  Road. 
These  were  wild-trapped  Rio  Grande  Turkeys  (M.  g.  inter- 
media) taken  from  populations  established  in  Napa 
County,  originally  captured  in  the  native  range  of  the 
subspecies  (F.  Botti  pers.  comm.).  If  these  birds  enjoy  the 
success  of  other  populations  now  established  in  much  of 
the  Coast  Range,  they  will  probably  be  widely  distributed 
in  oak  woodlands  and  oak  savannah  in  northeastern 
Marin  within  a  few  years.  The  evidence  to  date  suggests 
diat  the  Marin  birds  are  doing  well.  The  population  is 
expanding  and  sightings  span  from  at  least  Alameda  del 
Prado,  Ignacio,  on  the  north,  south  to  the  Loma  Alta  and 
Sleepy  Hollow  areas  near  Sir  Francis  Drake  Boulevard  (F. 
Botti  6k  B.  Beard  pers.  comm.).  From  1988  to  1991 ,  many 
adults  widi  broods  have  been  seen  (e.g.,  two  adults  with  1 2 
large  young  crossing  Lucas  Valley  Rd.  on  flats  E  of  Big 
Rock  Ranch  7/17/91  -DS  et  al.). 

WILSON'S  PHALAROPE 

Phalaropus  tricolor 

In  California,  this  species  breeds  in  the  short  vegetation  of 
freshwater  marshes  and  wet  meadows,  primarily  east  of  the 
Cascade-Sierra  axis,  though  formerly  it  bred  irregularly  (or 
at  least  in  smaller  numbers)  in  the  central  San  Joaquin 
Valley  (GckM  1944).  Extralimital  confirmed  breeding 
records  have  been  reported  for  the  coast  from  Lake  Talawa, 
Del  Norte  County  (FL  7/10-8/5/77  -RSW)  and  from  the 
Cader  Lane  Ponds  in  Petaluma,  Sonoma  County  (FL 
6/26/82  — RLe  et  al.);  a  few  additional  records  suggestive 
of  coastal  breeding  have  been  reported  as  well  (ABN).  In 
Marin  County,  Wilson's  Phalaropes  were  seen  in  one  of 
the  marshy  diked  Bahia  Ponds  in  Novato  on  17  May,  7 
June,  and  26  June  1980  (GiT,  DS).  Although  the  timing 
of  these  records  and  the  proximity  to  the  Cader  Lane 
Ponds  (3-4  mi.)  is  tantalizing,  the  overlap,  or  near  overlap, 

431 


Short  Accounts 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Short  Accounts 


in  the  timing  of  spring  and  fall  migration  on  the  coast 
(Shuford  et  al.  1989)  clouds  interpretation  of  this  and 
odier  potential  coastal  breeding  records.  Direct  confirma- 
tion of  breeding  of  tliis  species  is  the  only  way  to  add  it  to 
the  main  list  of  breeding  species  for  a  coastal  California 
county. 


HEERMANN'S  GULL 

Larus  heermanni 

From  1979  to  1981,  Heermann's  Gulls  attempted  to  breed 
on  Alcatraz  Island,  San  Francisco,  about  775  miles  north 
of  the  nearest  Mexican  breeding  colony  at  San  Benitos 
Islands  (Howell  et  al.  1 983).  This  tnily  exceptional  breed- 
ing record  is  not  likely  to  be  repeated,  especially  since  the 
Alcatraz  birds  were  unsuccessful  in  their  attempts.  But  if 
successful,  it  is  remotely  possible  that  Heermann's  Gulls 
might  select  a  breeding  site  on  one  of  Marin  County  s 
islands  in  San  Francisco  Bay.  Heermann's  Gulls  occur  in 
Marin  County  primarily  as  fall  and  early  winter  disper- 
sants,  mosdy  from  June  through  November  (Shuford  et  al. 
1989). 


CALIFORNIA  GULL 

Larus  californicus 

California  Gulls  began  to  breed  in  salt  pond  habitat  in 
south  San  Francisco  Bay  near  Alviso,  Santa  Clara  County, 
in  1980  and  near  Newark,  Alameda  County,  in  1984  and 
are  continuing  to  expand,  at  least  in  the  former  county 
(PWo  for  S.F.  Bay  Bird  Obs.).  This  is  the  only  known 
breeding  area  on  die  Pacific  Coast;  they  nest  primarily  in 
the  Great  Basin  Desert  and  the  northern  Great  Plains.  As 
with  the  three  species  of  terns  (see  below),  the  California 
Gull  nucleus  in  the  Soudi  Bay  might  possibly  provide 
colonizers  for  Marin  County  if  suitable  habitat  were  avail- 
able here  in  diked  wedands  along  the  shorelines  of  San 
Pablo  and  San  Francisco  bays.  California  Gulls  currendy 
occur  in  Marin  County  year  round,  though  mostly  as  fall 
dispersants  and  winter  visitants  from  September  (numbers 
drop  by  mid-Jan)  through  May  (Shuford  et  al.  1989).  This 
gull  is  a  Bird  Species  of  Special  Concern  in  California 
(Remsen  1978,  CDFG  1991b). 


TERNS 

Caspian  (Sterna  caspia)  and  Forster's  (S.  jorsleri)  terns  and 
the  state  and  federally  Endangered  Least  Tern  (S.  antil- 
larum)  all  breed  at  scattered  sites  around  San  Francisco  Bay 
in  disturbed  or  human  created  habitats.  It  seems  very  likely 
that  one  or  more  of  these  species  might  breed  in  Marin 

432 


County  if  suitable  nesting  sites  were  provided  in  diked 
ponds  or  marshes  along  die  shorelines  of  San  Francisco 
and  San  Pablo  bays. 


MARBLED  MURRELET 

Brachyramphus  marmoratus 

The  Marbled  Murrelet  is  a  year-round  resident  along  the 
northern  California  coast  diat  nests  in  old-growth  forests 
up  to  25  miles  inland  and  forages  in  nearshore  ocean 
waters,  mosdy  within  a  mile  or  so  of  land  (Carter  6k 
Erickson  1988).  Although  birds  have  been  seen  off  the 
outer  coast  of  Marin  County  in  the  breeding  season 
(1  Apr-1  Sep,  Carter  6k  Erickson  1988),  a  lack  of 
nearshore  records  from  2  May  to  30  June  and  a  total  lack 
of  inland  records  suggests  that  Marbled  Murrelets  do  not 
breed  regularly  in  Marin  County  despite  the  availability  of 
seemingly  suitable  nesting  habitat  on  conifer-clad  coastal 
ridges.  Local  July  and  August  records  probably  pertain  to 
postbreeding  dispersants  from  elsewhere;  the  species 
occurs  in  nearshore  waters  off  Marin  County  mosdy  from 
August  to  March  (ABN).  Marbled  Murrelets  may  once  have 
bred  in  Marin  County  before  the  era  of  intense  observer 
coverage  and  before  logging  eliminated  extensive  nesting 
habitat  along  the  coast.  The  California  population  has 
probably  declined  mainly  because  of  the  destruction  of 
old-growth  forests  (Carter  6k  Erickson  1988).  Recent 
reviews  of  the  species'  status  have  prompted  government 
agencies  to  list  this  murrelet  as  state  Endangered  in  Cali- 
fornia and  federally  Threatened. 


YELLOW-BILLED  CUCKOO 

Coccyzus  americanus 

Mailliard  (1900)  listed  the  status  of  the  Yellow-billed 
Cuckoo  in  Marin  County  as  "Doubtful.  Some  reported  as 
having  been  seen  at  Olema  in  1898,  but  no  specimens 
taken."  Stephens  and  Pringle  (1933)  reported  a  record  of 
an  injured  bird  captured  at  "Point  Reyes"  on  19  July  1919. 
Marin  County  is  within  the  overall  historic  breeding  range 
of  Yellow-billed  Cuckoos  in  California— they  formerly 
ranged  north  on  the  coast  to  the  vicinity  of  Sebastapol, 
Sonoma  County  (G6kM  1944).  Populations  of  this  ripar- 
ian obligate  declined  drastically  in  the  state  in  later  years 
because  of  habitat  loss,  and  the  species  is  now  listed  as  state 
Endangered  (G6kM  1944,  Gaines  6k  Laymon  1984, 
Laymon  6k  Halterman  1987).  It  is  plausible  that  cuckoos 
may  once  have  bred  here,  perhaps  at  Olema  Marsh  cur- 
rendy the  county's  largest  riparian  forest,  but  went  unde- 
tected before  extirpation.  In  recent  years,  Yellow-billed 
Cuckoos  have  occurred  irregularly  in  June  and  July  as  very 
rare  vagrants  on  Marin's  outer  coast  away  from  suitable 
breeding  habitat. 


Short  Accounts 


UNDOCUMENTED  &  POTENTIAL  BREEDERS 


Short  Accounts 


CHIMNEY  SWIFT 

Chaetura  pelagica 

A  record  of  a  Chimney  Swift  at  Bolinas  Lagoon  on  19  July 
1975  (AB  29:1027)  suggests  the  possibility  of  breeding  in 
Marin  County.  The  species  has  bred  along  the  southern 
California  coast  (Garrett  6k  Dunn  1981)  and  to  the  north 
in  Mendocino  County  (AB  29:1027,  McCaskie  et  al. 
1979). 


BLACK-CHINNED  HUMMINGBIRD 

Archilochus  alexandri 

A  female  hummingbird,  identified  as  a  Black-chinned,  was 
observed  at  Ross,  Marin  County,  from  the  time  of  nest 
building  on  13  May  1941  until  three  days  after  the  fledging 
of  her  young  on  26  June  (Stephens  1941).  Grinnell  and 
Miller  (1944)  cast  doubt  on  the  authenticity  of  this  record. 
On  the  other  hand,  the  extended  period  of  observation  by 
a  number  of  bird  students  (including  two  of  the  region's 
most  prominent— Laura  A.  Stephens  6k  Junea  Kelly),  cou- 
pled with  their  knowledge  of  the  rarity  of  the  species  at  any 
season  in  Marin  County  (S6kP  1933),  suggests  that  it  may 
have  been  a  correct  identification  and  valid  breeding 
record.  It  seems  best  to  leave  the  question  open  until 
another  record  is  documented,  although  other  species 
characteristic  of  the  dry  interior  Coast  Range,  such  as  Say's 
Phoebe  and  Cassin's  Kingbird,  occasionally  have  nested  in 
the  more  humid  clime  of  Marin  County.  Black-chinned 
Hummingbirds  currently  occur  very  rarely/irregularly  in 
Marin  from  mid-July  to  mid-September  (ABN). 


WILLOW  FLYCATCHER 

Empidonax  traillii 

Although  never  known  to  breed  in  Marin  County 
(Mailliard  1900,  S6kP  1933),  Willow  Flycatchers  formerly 
bred  as  close  as  the  south  San  Francisco  Bay  region  (G6kM 
1944).  The  Willow  Flycatcher  is  now  listed  by  the  Califor- 
nia Department  of  Fish  and  Game  Commission  as  state 
Endangered,  and  the  U.S  Forest  Service  considers  it  a 
sensitive  species  in  California  (USFS  1984).  A  singing  bird 
about  one  mile  northeast  of  Wildcat  Camp,  Point  Reyes 
National  Seashore,  on  5  July  1980  (DS,  ITi)  represents  the 
only  known  midsummer  record  for  Marin  County,  though 
this  individual  may  have  been  a  late  migrant.  On  the  other 
hand,  this  bird  may  have  been  prospecting  for  a  breeding 
site,  although  there  are  only  sporadic  recent  nesting 
records  for  lowland  northern  California  (McCaskie  et  al. 
1979,  Roberson  1985,  Harris  et  al.  1987).  Willow  Fly- 
catchers occur  in  Marin  mosdy  from  mid-August  to  early 
October  and  irregularly  from  mid-May  to  early  July  (ABN). 


BANK  SWALLOW 

Riparia  riparia 

The  former  status  of  this  species  in  Marin  County  is 
puzzling.  Mailliard  (1900)  reported  the  Bank  Swallow  was 
"an  abundant  summer  resident  in  favorable  localities." 
Stephens  and  Pringle  (1933)  list  the  Bank  Swallow  under 
their  category  of  birds  "present  through  the  summer  only," 
but  then  list  only  four  spring  records  (22  Mar-1 2  Apr)  and 
one  early  fall  record  for  25  July.  Intimations  of  breeding  at 
Nicasio  (G6kW  1927,  Laymon  et  al.  1987)  apparendy 
pertain  solely  to  a  record  from  that  locality  on  19  March 
1876  by  C.  A.  Allen  that  was  reported  by  Belding  (1890) 
with  no  details  of  numbers  of  birds  or  nesting  status.  No 
Marin  County  sites  are  listed  by  Grinnell  and  Miller 
(1 944)  among  their  "definitely  known"  locations  of  nesting 
in  California.  The  Bank  Swallow  is  currendy  listed  as 
Threatened  in  the  state.  This  swallow  now  occurs  in  Marin 
irregularly  in  spring  from  late  March  though  late  May  and 
in  fall  from  mid-August  to  late  September  (ABN). 

CEDAR  WAXWING 

Bombycilla  cedrorum 

In  California,  Cedar  Waxwings  breed  with  regularity  only 
on  the  north  coast  in  Del  Norte  County  and  south  to  the 
vicinity  of  Eureka,  Humboldt  County  (G6kM  1944,  ABN). 
Extralimital  breeding  records  exist  for  the  interior  of  north- 
ern California  and  for  the  coast  down  to  southern  Califor- 
nia (Garrett  6k  Dunn  1981).  Birds  breed  or  oversummer 
irregularly  in  central  California  (e.g.,  AB  41:1485).  Cedar 
Waxwings  occur  annually  in  Marin  County  in  variable 
numbers  as  winter  residents/visitants,  mosdy  from  late 
August  through  early  June.  The  lack  of  records  between 
late  June  and  early  August  suggests  that  a  record  of  an  adult 
feeding  immatures  at  Inverness  on  31  August  1959  (GMi) 
represented  birds  that  had  migrated  or  dispersed  some 
distance  before  arriving  in  Marin  County.  Birds  in  juvenile 
plumage  are  frequendy  seen  as  migrants. 

AMERICAN  REDSTART 

Setophaga  ruticilla 

The  American  Redstart  was  first  confirmed  breeding  on 
the  northern  California  coast  in  1972  (Binford  6k  Stallcup 
1972),  and  additional  observations  of  confirmed  or  prob- 
able breeding  suggest  it  is  an  irregular  breeder  on  the 
coastal  slope  of  Humboldt  and  Del  Norte  counties  (ABN). 
The  species  typically  occurs  along  the  California  coast  as  a 
rare  but  regular  vagrant  in  spring  and  fall.  In  Marin 
County,  it  occurs  mainly  as  a  rare  vagrant  in  spring  from 
early  June  to  early  July  and  in  fall  from  mid-August  to  early 
November  (ABN).  Two  intriguing  records  suggest  that 
redstarts  may  occasionally  breed  in  Marin  County.  A  bird 

433 


Short  Accounts 


MARIN  COUNTY  BREEDING  BIRD  AT1AS 


Short  Accounts 


identified  as  a  hatching-year  male  was  banded  at  PRBO's 
Palomarin  field  station  on  7  July  1982  (RJRy),  suggesting 
it  may  have  been  raised  from  a  nest  somewhere  in  Marin. 
A  first-year  male  was  singing  one-half  mile  north  of  Inver- 
ness Park  27  May-11  June  1984  (AckWG),  but  good 
observer  coverage  revealed  no  signs  of  breeding. 


BOBOLINK 

Dolichonyx  oryzivorus 

Bobolinks  have  long  been  suspected  of  breeding  in  Cali- 
fornia in  the  Surprise  Valley,  Modoc  County,  in  the 
extreme  northeastern  corner  of  the  state,  but  breeding 
confirmation  has  not  yet  been  obtained  (Dawson  1923, 
Mailliard  1924a,  G6kM  1944,  Morlan  6k  Erickson  1988). 
This  area  is  relatively  close  to  a  regular  breeding  colony  at 
Malheur  National  Wildlife  Refuge  in  eastern  Oregon 
(Wittenberger  1978).  Along  the  California  coast,  Bobo- 
links occur  as  rare  or  irregular  vagrants  in  spring  from 
mid-May  to  mid-July  and  in  fall  in  September  and  October 
(McCaskie  et  al.  1979).  The  possibility  of  extralimital 
nesting  in  Marin  County  was  suggested  by  the  presence  of 
up  to  two  males  and  one  female  Bobolink  at  the  RCA 
station  on  Point  Reyes  from  5  to  19  June  1983  (AB 
37:1025).  Singing,  displaying,  and  copulation  were 
observed,  but  mowing  of  the  field  they  were  occupying 
eliminated  the  possibility  of  a  nesting  attempt.  It  remains 
a  mystery  whether  these  birds  were  fulfilling  hormonal 
urges  on  migration  or  were  actually  attempting  to  nest.  Del 
Norte  County  records— of  adults  feeding  young  on  the 
coast  near  Fort  Dick  in  July  1977  (undocumented,  fide 
R.A.  Erickson)  and  one  to  three  singing  males  at  Klamath 
from  5  to  19  June  1982  (AB  36:1014,  R-A.  Erickson  pers. 
comm.)— add  further  intrigue  to  the  possibility  of  occa- 
sional extralimital  nesting  on  the  coast. 


YELLOW-HEADED  BLACKBIRD 

Xanthocephalus  xanthocephalus 

Yellow-headed  Blackbirds  were  formerly  rare  breeders  in 
die  San  Francisco  Bay  Area  with  nesting  records  for 
Sonoma,  Contra  Costa,  Alameda,  and  Santa  Clara  coun- 
ties (G6kW  1927,  G6kM  1944).  Rccendy,  breeding  was 
suspected  at  Skaggs  Island,  Sonoma  County  (T  25  adult 
males  5/28/86  — DRu  et  al.),  and  breeding  was  confirmed 
at  the  town  of  American  Canyon,  Napa  County  (T,  NB, 
FY  5/24-6/29/91  — ESa  et  al.).  Apparent  migrants/va- 
grants, such  as  a  male  seen  at  a  pond  near  the  mouth  of 
Novato  Creek  along  the  San  Pablo  Bay  shoreline  on  16 
April  1988  (DS  et  al.),  potentially  might  provide  colonizers 
that  would  breed  in  Marin  if  conditions  were  right  at  the 
time  of  their  arrival.  Yellow-headed  Blackbirds  currendy 
occur  in  Marin  irregularly  in  spring  in  April  (one  June 
record)  and  in  fall  from  mid-September  to  early  October 
(ABN). 


GREAT-TAILED  GRACKLE 

Quiscalus  mexicanus 

Expansion  of  the  breeding  range  of  Great-tailed  Grackles 
in  southern  California  (Garrett  6k  Dunn  1981,  AB 
40:1257,  AB  42:1341)  probably  explains  the  small  but 
growing  number  of  records  of  this  species  in  northern 
California.  A  male  Great-tailed  Grackle  found  in  San 
Francisco  in  1978  was  joined  by  a  female  in  1979  and  they 
have  attempted  to  nest  since  1980,  but  without  success 
(Morlan  6k  Erickson  1988).  A  record  of  a  Great-tailed 
Grackle  at  the  Marin  Headlands  from  15  to  17  June  1988 
(AB  42:1338)  suggests  the  possibility  that  the  species  may 
some  day  attempt  to  breed  in  Marin  County  as  well. 


434 


APPENDIXES 


APPENDIX  A. 
Data  from  three  Spring  Bird  Counts  conducted  in  Marin  County  from  1977  to  1987. 


Since  1977,  three  Spring  Bird  Counts  have  been  con- 
ducted in  Marin  County:  Even  Cheaper  Thrills— partly 
in  Sonoma  County,  Marin  County  (southern),  and  Point 
Reyes  Peninsula.  These  counts  were  patterned  after  Christ- 
mas Bird  Counts  published  in  American  Birds  and  use  the 
same  1 5-mile  diameter  count  circles.  In  addition  to  record- 
ing numbers  of  individuals,  observers  on  count  day  assign 
each  species  they  encounter  one  of  three  general  breeding 
categories— Possible,  Probable,  and  Confirmed  (or  non- 
breeder)— used  in  the  Marin  County  Breeding  Bird  Adas 
Project  (see  Table  5).  On  the  Spring  Counts  the  category  S 
(singing  male  present)  is  considered  as  probable  breeding 
if  the  bird  in  question  is  in  a  habitat  where  it  normally 
breeds,  despite  the  lack  of  evidence  of  longterm  occupancy 
of  a  site.  Data  for  all  these  counts  are  presented  below  in 
tabular  form.  Bold-faced  names  or  numbers  indicate  spe- 
cies that  are  very  rare  in  this  area  year  round  or  for  the 
season  in  question,  or  represent  high  counts.  Descriptions 
of  rare  bird  sightings  are  on  file  with  the  author.  Standard 
data  on  weather  and  observer  coverage  are  listed  for  each 
count;  a  participant  list  summarizes  names  of  all  counters 
for  all  years  of  each  count. 

When  comparing  counts,  please  bear  in  mind  that 
count  dates  range  from  early  May  until  early  June.  On  early 
season  counts,  there  are  more  migrant  species  and  more 
individuals  of  species  that  occur  here  both  as  breeders  and 
migrants.  On  later  season  counts,  there  should  be  more 
individuals  of  breeding  species  since  both  adults  and  fully 
independent  young  are  counted.  This  increase  in  popula- 
tion size  from  recruitment  of  young  may  be  offset  by  a 
seasonal  decline  in  song  by  which  many  individuals  of 
passerine  species  are  tallied. 

MARIN  COUNTY  (SOUTHERN),  CALIFORNIA. 

37°55'N  122°34'W,  center  1.5  mi  n.w.  of  Mill  Valley, 
elevation  0  to  2600  ft;  count  circle  and  habitat  coverage  as 
described  1976  for  the  CBC  of  the  same  name  (AB 
30:592).  Coverage  1977,  1982,  and  1983. 

1)  21  May  1977,  0430  to  1900.  Partly  cloudy,  locally 
foggy  in  a.m.,  patchy  overcast  in  p.m.  Temp.  48-63°  F. 
Wind  Werly  3-15  m.p.h.  Although  numbers  of  individu- 
als and  species  were  compiled  immediately,  the  data  on 
party-miles,  party-hours,  and  observers  were  not  tallied 


until  1984  and  consequendy  data  were  not  complete. 
Observers  were  not  recorded  for  1  of  1 2  areas  and  party- 
hours  and  party-miles  were  not  available  for  3  areas.  The 
latter  were  estimated  by  taking  an  average  for  the  1 2  areas 
from  which  data  were  available  and  applying  it  to  the  3 
questionable  areas.  About  60  observers  in  about  16  par- 
ties. Total  party-hours,  about  185  (169  on  foot,  16  by  car), 
total  party-miles  about  248  (144  on  foot,  104  by  car). 

2)  5  June  1982,  0430  to  1915.  Fog  in  a.m.  coastally  and 
on  higher  ridges,  clearing  to  sunny  with  few  clouds.  Temp 
39-71  °  F.  Wind  NWerly  0-10  m.p.h.  Sixty-four  observers 
in  23  parties.  Total  party-hours,  224.5  (201.5  on  foot,  23 
by  car)  plus  8  night  hours.  Total  party-miles,  385.5  (159.5 
on  foot,  226  by  car). 

3)  4  June  1983,  0500  to  1800.  Clear,  sunny  all  day. 
Temp  45-78°  F.  Wind  NWerly  0-5  m.p.h.  Forty-six 
observers  in  26  parties,  plus  one  feeder  watcher.  Total 
party-hours,  207  (188  on  foot,  19  by  car)  plus  1  feeder  hour 
and  4  night  hours.  Total  party-miles,  306  (145  on  foot,  161 
by  car). 

Participants:  Peter  6k  Julia  Allen,  Jane  Anderson,  Betty 
Beade,  Dennis  Beall,  Max  Beckwith,  Gordon  Beebe,  Betty 
Bossi,  Herb  Brandt,  Kate  Brennan,  Pat  Briggs,  Courtney 
Buechert,  Jean  Burnett,  Betty  Burridge,  Jean  Canepa,  Scott 
Carey,  Janice  Chism,  Carolyn  6k  Frank  Christian,  Harold 
Conner,  Rosamond  Day,  Larry  Desmond,  John  Dillon, 
Mary  During,  Doug  Ellis,  Jules  6k  Meryl  Evens,  Mary  Farr, 
Carter  Faust,  Ann  Gilbert,  Tony  Grady,  Helen  6k  Paul 
Green,  Ann  Gross,  Kem  Hainebach,  Rita  Halbeisen, 
Nancy  Hanson,  Roger  Harris,  Sheila  Hershon,  Laura 
Hines,  Bob  Hogan,  David  6k  Richard  Holway,  Alan  Hop- 
kins, Ken  Howard,  George  Hugenberg,  Stuart  Johnston, 
Kadileen  Jones,  Doug  Judell,  Anne  Knobloch,  Bill  6k 
Paget  Lenarz,  Donna  Lion,  Susan  Martin,  Emmy  Hill, 
Marie  Mans,  Gloria  Markowitz,  Grace  (co-compiler  1982) 
6k  Mort  McMichael,  Bonnie  6k  Woody  Nackley,  Michael 
Nelligan,  Julie  Numainville,  Cynthia  Oglove,  Dana  6k 
Todd  Olson,  Lynda  Orman,  Kate  Partridge,  Charlotte  6k 
Chriss  Poulsen,  Lina  Jane  Prairie,  Helen  Pratt,  Barbara 
Prince,  Alton  Raible,  Faith  Rendell,  Inez  Riney,  Mary 
Lousie  Rosegay,  Ane  Roverta,  Barbara  Salzman,  Don  6k 
Phyllis  Samson,  Marisela  de  Santa  Anna,  Phil  (compiler 

435 


Appendix  A 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Appendix  A 


1977)  6k  Margaret  Schaeffer,  Carol  6k  Stuart  Schneider, 
Bob  ck  Ruth  Scott,  Betty  Short,  Dave  Shuford  (co-compiler 
1982),  Dianne  Sierra  (compiler  1983),  Ann  Spencer,  Barry 
Spitz,  Jean  Starkweather,  Lynne  Stenzel,  Bob  Stewart,  Don 
Stiver,  Nick  Story,  Jim  6k  Marta  Sullivan,  Gil  Thomson, 
Carol  6k  Noel  Thoney,  Irene  Timossi,  Dorothy  Tobkin, 
Carol  6k  Michael  Trent,  Pat  Triggs,  Phil  Unitt,  Keiko 
Yamane,  Bob  6k  Carol  Yutzy,  Jim  Weigand,  Janet  Wessel, 
Jack  Whetstone,  Diane  Williams,  Summer  Wilson,  David 
Wimpfheimer,  Jon  Winter,  Keiko  Yamane,  Jon  Zablackis, 
Dianne  Ziola,  and  various  unidentified  observers  in  1977. 

POINT  REYES  PENINSULA,  CALIFORNIA. 

38°08'N  122°53'W,  center  USC&GS  triangulation  point 
in  Tomales  Bay  State  Park;  elevation  0  to  1470  ft;  count 
circle  and  habitat  coverage  as  described  1971  for  CBC  of 
the  same  name  (AB  25:501).  Coverage  1982  only. 

1)  23  May  1982,  0600  to  1700.  Partly  cloudy  all  day. 
Temp.  44-94°  F.  Wind  SEerly  1  m.p.h.  Thirty  observers 
in  14  parties.  Total  party-hours,  104  (78.25  on  foot,  25.75 
by  car),  zero  night  hours.  Total  party-miles,  178  (60  on 
foot,  1 18  by  car).  (In  count  area  count  week  but  not  seen 
count  day:  Yellow-breasted  Chat). 

Participants:  Ted  Beedy,  Betty  Burridge,  Scott  Carey, 
Karen  Cartier,  Chris  D'Orgieux,  Dave  DeSante,  Jules 
Evens,  Ben  6k  Char  Glading,  Steve  Granholm,  Paul 
Green,  Ruth  Hawksley,  Gregg  Martinsen,  Nancy  Norvell, 
Paul  O'Brien,  Sabrina  Patterson,  Lina  Jane  Prairie,  Cindy 
Reittinger,  Elsie  Richey,  Susan  Sanders,  Dave  Shuford 
(co-compiler),  Bob  Stewart,  Sylvia  Sykora,  Dorothy  Tob- 
kin, Kent  Van  Vuren,  Bob  (co-compiler)  6k  Carol  Yutzy, 
Sally  Walters,  Bette  Wentzel,  Janet  Wessel. 

EVEN  CHEAPER  THRILLS,  CALIFORNIA. 

38°08'N  122°37'W,  center  the  spring  1.4  mi  n.  of  jet.  San 
Marin  Dr.  and  Novato  Blvd.,  Novato;  elevation  0  to  1887 
ft;  count  circle  and  habitat  coverage  as  described  1978  for 
the  Arroyo  Cheap  Thrills,  California  CBC  (AB  32:852). 
Coverage:  10  consecutive  years  from  1978  to  1987. 

1)  7  May  1978,  0500  to  1830.  Clear,  sunny  all  day. 
Temp.  49-84°  F.  Wind  Werly,  0-5  m.p.h.  Twenty-nine 
observers  in  1 1  parties.  Total  party-hours,  119  (88  on  foot, 
31  by  car).  Total  party-miles,  303.5  (51.5  on  foot,  252  by 
car). 

2)  6  May  1979,  0445  to  1845.  Scattered  clouds  and 
occasional  showers  in  a.m.,  overcast  with  gende  rain  (0.1 
in.)  in  p.m.  Temp.  46-64°  F.  Wind  Serly,  1-12  m.p.h. 
Twenty-nine  observers  in  15  parties.  Total  party-hours, 
153  (106.5  on  foot,  44.5  by  car,  2  by  boat)  plus  1  night 
hour.  Total  party-miles,  433  (75  on  foot,  357  by  car,  1  by 
boat). 


3)  17  May  1980,  0200  to  1900.  Clear,  sunny  all  day. 
Temp  45-83°  F.  Wind  W-SEerly,  0-8  m.p.h.  Thirty-one 
observers  in  14  parties.  Total  party-hours,  121  (91.5  on 
foot,  24. 5  by  car,  6  by  boat)  plus  6  night  hours.  Total 
party-miles,  416.5  (66  on  foot,  342.5  by  car,  8  by  boat). 

4)  9  May  1981,  0100  to  1830.  Clear  with  haze  on  the 
horizon.  Temp.  56-73°  F.  Wind  NWerly  5-10  m.p.h. 
Twenty-nine  observers  in  12  parties.  Total  party-hours, 
124.5  (100.75  on  foot,  18.75  by  car,  5  by  boat)  plus  11 
night  hours.  Total  party-miles,  360  (75  on  foot,  275  by  car, 
10  by  boat).  (In  count  area  count  week  but  not  seen  count 
day:  Cattle  Egret,  Black-chinned  Sparrow). 

5)  16  May  1982,  0300  to  1830.  Local  fog  in  a.m., 
clear/sunny  for  the  rest  of  the  day.  Temp.  44-77°  F.  Wind 
NWerly  0-10  m.p.h.  Twenty-six  observers  in  12  parlies. 
Total  party-hours,  118  (96.5  on  foot,  1 2.5  by  car,  9  by  boat) 
plus  5.75  night  hours.  Total  party-miles,  280  (56  on  foot, 
214  by  car,  10  by  boat). 

6)  22  May  1983,  0400  to  1800.  Sunny,  with  few 
scattered  high  cumulus  clouds.  Temp.  49-75°  F.  Wind 
NWerly  0-10  m.p.h.  Twenty-one  observers  in  12  parties. 
Total  party-hours,  1 1 2.5  (76  on  foot,  30.5  by  car,  6  by  boat) 
plus  3  night  hours.  Total  party-miles  467.5  (68  on  foot, 
391.5  by  car,  8  by  boat)  plus  2  night  miles. 

7)  3  June  1984,  0430  to  1800.  Mosdy  clear.  Temp. 
45-79°  F.  Wind  Werly,  5-20  m.p.h.  Twenty-five  observ- 
ers in  12  parties.  Total  party-hours,  108  (80.25  on  foot, 
21.75  by  car,  6  by  boat)  plus  1.25  night  hours.  Total 
party-miles,  324.5  (49.5  on  foot,  269  by  car,  6  by  boat)  plus 
3.5  night  miles.  (In  count  area  count  week  but  not  seen 
count  day:  Cedar  Waxwing). 

8)  2  June  1985,  0430  to  1800.  Overcast  with  drizzle  in 
early  a.m.  clearing  to  sunny.  Temp  52-74°  F.  Wind 
NWerly  0-10  m.p.h.  Twenty-five  observers  in  13  parties. 
Total  party-hours,  107.25  (84.5  on  foot,  15.25  by  car,  7.5 
by  boat),  plus  9.25  night  miles  (0.25  on  foot,  6  by  car,  3 
by  boat)  and  3.5  night  hours  (1  on  foot,  0.5  by  car,  2  by 
boat).  Total  party-miles  286.5  (50  on  foot,  226.5  by  car,  10 
by  boat). 

9)  31  May  1986,  0430  to  1800.  Patchy  morning  fog, 
otherwise  sunny  with  scattered  clouds.  Temp.  55-70°  F. 
Litde  wind.  Twenty-two  observers  in  1 1  parties.  Total 
party-hours  88.5  (54-75  on  foot,  27.75  by  car,  and  4  by 
boat)  plus  3.75  night  hours.  Total  party-miles  188  (45  on 
foot,  1 37  by  car,  and  6  by  boat)  plus  1 1  night  hours. 

10)  31  May  1987,  0530  to  1800.  Cloudy  overcast  in 
a.m.,  breaking  to  clear,  sunny.  Temp.  52-76°  F.  Wind 
NWerly  10-15+  m.p.h.  Twenty-two  observers  in  12  par- 
ties. Total  party-hours  101.75  (87  on  foot,  14-25  by  car, 
and  0.5  by  bike)  plus  0.5  night  hours.  Total  party-miles 
236  (66  by  foot,  168  by  car,  and  2  by  bike)  plus  1  night 


436 


Appendix  A 


APPENDIXES 


Appendix  A 


Participants  (*  denotes  counter  for  5  or  more  years):  Julia 
Allen,  Jane  Anderson,  Terry  Babineaux,  Bob  Baez,  Bryant 
Bainbridge,  Dennis  Beall*,  Max  Beckwith,  Gordon  Beebe, 
Bob  Boekelheide,  Courtney  Buechert,  Pat  6k  Trisha  Bun- 
sen,  Betty  Burridge*,  Kurt  Campbell  (compiler  1983  6k 
1984),  Scott  Carey*,  Mary  Caswell,  Diane  Caualo,  Peter 
Colasanti*,  Pam  Conley,  Nancy  Conzett,  Chris  Coulon, 
Dick  Cunningham,  Mark  Delwiche,  Larry  Desmond,  Bev- 
erly Ehreth,  Doug  Ellis*,  Dick  ck  Linda  Erickson,  Jules 
Evens*,  Steve  Gellman,  Ed  Good,  Sarah  Griffin,  Nelson 
Hall,  Janine  Haller,  Keith  Hansen,  Deyea  Harper,  Roger 
Harris,  Tony  Harrow,  Luanna  Helfman,  Phil  Henderson, 
Bob  Hogan*,  Ken  Howard,  Steve  Howell,  George 
Hugenberg*,  Joanie  Humphrey,  Deborah  Jacques,  Debbie 
Johnston,  Stuart  Johnston,  Bill*  6k  Paget  Lenarz,  Robin 
Leong,  Marc  Liverman,  Gloria  Markowitz,  Roger  Mar- 
lowe, Gregg  Martinsen,  John  McCormick,  Joe  McGee, 
Grace  6k  Mort  McMichael,  Richard  Merriss,  Andrea 
Meyer,  Charlene  Modena,  Derek  Mooney,  Gerry  ck  Kathy 


Mugele,  Bonnie  6k  Woody  Nackley,  Adeene  6k  Mike 
Nelligan,  Dan  6k  Wini  Nelson,  Cynthia  Oglove,  Todd 
Olson,  Kate  O'Neill,  Gary  Page,  Chris  Pattillo,  Holly 
Peake,  Susan  Claire  Peaslee,  Teya  Penniman,  Nancy 
Petersen,  Meghan  Piercy,  Lina  Jane  Prairie,  Barbara  Prince, 
Nancy  Pullen,  Bertha  6k  Bob  Rains,  Ivana  Roland,  Louis 
Roth,  Ruth  Rudesill,  Marisela  de  Santa  Anna,  Phil  6k 
Margaret  Schaeffer,  Jerry  Scoville,  Dave  Shuford*  (com- 
piler all  years  except  1983  6k  1984),  Dianne  Sierra*,  Hank 
Skewis,  Sue  Smith,  Eric  Sorenson,  Chris  Spooner,  Rich 
Stallcup,  Lynne  Stenzel,  Bob  Stewart,  Chris  Swarth,  Ian 
Tait,  Dan  Taylor,  Gil  Thomson*,  Irene  Timossi*,  Doro- 
thy Tobkin,  David  Tomb,  Susan  6k  Wayne  Trivelpiece, 
Betsy  Udey,  Ed  Vine,  Dave  6k  Colleen  Ward,  Nils  War- 
nock,  Christine  Weigen,  Bette  Wentzel,  Janet  Wessel,  Jack 
Whetstone*,  Pete  White,  Greg  6k  Russ  Wilson,  David 
Wimpfheimer,  Lori  Withington,  Keiko  Yamane,  Steve 
Yaninek. 


437 


Appendix  A. 


Mann  County 
(Southern) 


Point  Reyes 
Peninsula 


Even  Cheaper  Thnlls 


2  1  May 
1977 

21  May 
1982 

4  June 
1983 

23  May 
1982 

7  May 
1978 

6  May 
1979 

17  May 
1980 

9  May 

1981 

16  May 
1982 

22  May 
1983 

3  June 
1984 

2  June 
1985 

31  May 
1986 

31   May 
1987 

Red-throated  Loon 

15 

2 

6 

14 

2 

Pacific  Loon 

48 

4 

26 

Common  Loon 

6 

19 

9 

24 

1 

1 

loon  spp. 

1 

1 

Pied-billed  Grebe 

10 

6 

6 

2 

20 

18 

13 

23 

19 

10 

22 

18 

27 

10 

Homed  Grebe 

40 

1 

1 

1 

Eared  Grebe 

6 

4 

1 

18 

15 

4 

19 

4 

1 

Western/Clark's  Grebe 

264 

457 

60 

97 

3 

7 

5 

8 

5 

2 

1 

2 

Amencan  White  Pelican 

1 

Brown  Pelican 

14 

261 

48 

10 

Double-cresced  Cormorant 

6 

45 

55 

120 

45 

26 

4 

47 

1 

9 

1 

6 

25' 

12 

Brandt's  Cormorant 

323 

129 

180 

8 

Pelagic  Cormorant 

46 

63 

52 

97 

American  Bittern 

1 

4 

1 

1 

Great  Blue  Heron 

45 

128 

36 

30 

27 

41 

68 

89 

46 

108 

60 

56 

78 

64 

Great  Egret 

124 

381 

76 

31 

13 

34 

16 

24 

29 

98 

68 

50 

51 

27 

Snowy  Egret 

261 

518 

78 

16 

47 

46 

39 

75 

80 

92 

81 

66 

75 

35 

Green-backed  Heron 

3 

1 

3 

4 

1 

1 

3 

7 

7 

5 

Black-crowned  Night-Heron 

21 

102 

31 

4 

12 

14 

33 

28 

7 

20 

9 

23 

35 

18 

(Black)  Brant 

5 

97 

Ross'  Goose 

1 

Canada  Goose 

4 

1 

1 

1 

2 

10 

3 

21 

Green-winged  Teal 

1 

1 

2 

1 

2 

1 

2 

Mallard 

320 

410 

403 

51 

114 

130 

119 

183 

295 

144 

149 

339 

244 

406 

Northern  Pintail 

2 

7 

1 

7 

7 

13 

25 

7 

17 

12 

18 

27 

23 

Blue-winged  Teal 

1 

5 

2 

6 

4 

1 

5 

Cinnamon  Teal 

6 

14 

8 

23 

63 

42 

52 

98 

62 

52 

99 

91 

81 

135 

teal  spp. 

1 

Northern  Shoveler 

6 

8 

16 

21 

20 

11 

8 

13 

2 

11 

Gadwall 

8 

2 

13 

18 

18 

20 

7 

48 

61 

62 

55 

Amencan  Wigeon 

1 

2 

3 

1 

1 

Canvasback 

7 

1 

7 

5 

2 

3 

1 

1 

1 

3 

Greater  Scaup 

292 

75 

5 

6 

17 

42 

23 

10 

92 

6 

6 

16 

5 

22 

Lesser  Scaup 

27 

2 

5 

6 

19 

6 

2 

3 

4 

3 

1 

scaup  spp. 

227 

25 

5 

75 

19 

500 

7 

10 

Harlequin  Duck 

1 

1 

Oldsquaw 

1 

Black  Scoter 

5 

20 

Surf  Scoter 

35 

108 

49 

191 

2 

4 

22 

1 

White-winged  Scotet 

1 

14 

12 

164 

Common  Goldeneye 

1 

3 

2 

2 

Bufflehead 

3 

5 

1 

1 

3 

3 

3 

2 

I 

1 

Red-breasted  Merganser 

7 

2 

24 

1 

2 

Ruddy  Duck 

26 

13 

11 

52 

52 

96 

54 

43 

113 

10 

32 

39 

26 

25 

duck  spp. 

2 

3 

Turkey  Vulture 

181 

226 

182 

124 

149 

208 

167 

187 

209 

210 

200 

154 

194 

155 

Osprey 

8 

9 

13 

9 

2 

5 

7 

1 

5 

7 

4 

2 

Black-shouldered  Kite 

5 

3 

2 

7 

9 

11 

2 

3 

7 

15 

14 

10 

Northern  Harrier 

1 

3 

13 

1 

3 

9 

11 

7 

3 

2 

7 

7 

3 

Appendix  A.  (cont'd) 


Mann  County 
(Southern) 


Point  Reyes 
Peninsula 


Even  Cheaper  Thnlls 


21  May 
1977 

21  May 

1982 

4  June 
1983 

2  3  May 
1982 

7  May 
1978 

6  May 
1979 

17  May 

1980 

9  May 

1981 

16  May 
1982 

22  May 
1983 

3  June 
1984 

2  June 
1985 

31  May 
1986 

31  May 

1987 

Sharp-shinned  Hawk 

2 

3 

2 

1 

3 

4 

1 

Cooper's  Hawk 

4 

1 

3 

4 

1 

2 

1 

2 

1 

4 

3 

Accipirer  spp. 

1 

1 

2 

2 

Red-shouldered  Hawk 

2 

9 

8 

6 

6 

9 

14 

13 

12 

9 

12 

15 

6 

8 

Red-tailed  Hawk 

59 

64 

74 

46 

57 

61 

51 

76 

61 

50 

61 

45 

25 

40 

Golden  Eagle 

1(0 

3(2a,li) 

2(l..,l.) 

2(u) 

2(h..lu) 

3fo) 

3(2„.  1 ,) 

4(2a,  20 

3(u) 

5(2a,  3u) 

5(4a.  10 

3W 

Peregnne  Falcon 

1 

Amencan  Kestrel 

15 

21 

21 

5 

19 

32 

30 

25 

20 

20 

22 

21 

10 

18 

Ring-necked  Pheasant 

1 

11 

6 

7 

6 

9 

8 

5 

2 

4 

8 

Wild  Turkey 

8 

California  Quail 

203 

275 

408 

233 

134 

258 

159 

170 

180 

122 

142 

114 

110 

113 

Black  Rail 

1 

10 

5 

14 

4 

7 

1 

5 

2 

Clapper  Rail 

1 

1 

4 

Virginia  Rail 

1 

1 

10 

2 

2 

5 

5 

2 

Sora 

1 

1 

1 

1 

3 

Common  Moorhen 

2 

1 

2 

Amencan  Coot 

7 

51 

SI 

17 

103 

80 

86 

96 

86 

68 

49 

25 

56 

44 

Black-bellied  Plover 

8 

14 

4 

13 

8 

7 

15 

4 

31 

Snowy  Plover 

2 

5 

1 

Semipalmated  Plover 

1 

1 

33 

101 

12 

1 

Killdeer 

91 

71 

90 

47 

128 

97 

84 

128 

91 

62 

136 

110 

102 

104 

Black  Oystercatcher 

1 

3 

1 

4 

Black-necked  Stilt 

2 

5 

15 

23 

59 

55 

56 

9 

81 

40 

47 

36 

Amencan  Avocet 

3 

10 

30 

13 

12 

5 

21 

65 

4 

27 

Greater  Yellowlegs 

4 

7 

11 

5 

2 

34 

4 

11 

8 

9 

11 

27 

Lesser  Yellowlegs 

1 

1 

yellowlegs  spp. 

1 

Willet 

26 

27 

27 

34 

6 

30 

5 

21 

3 

3 

1 

Wandenng  Tattler 

1 

Spotted  Sandpiper 

19 

1 

8 

17 

2 

9 

17 

14 

11 

1 

3 

3 

Whimbrel 

9 

3 

86 

36 

15 

1 

1 

4 

Long-billed  Curlew 

2 

7 

5 

6 

1 

5 

2 

2 

18 

"curlew"  spp. 

30 

15 

Marbled  Godwit 

6 

33 

20 

93 

1 

141 

5 

26 

10 

3 

5 

Ruddy  Turnstone 

4 

6 

Black  Turnstone 

3 

3 

Red  Knot 

1 

Sanderling 

13 

16 

Western  Sandpiper 

62 

3 

97 

247 

-      ' 

3 

3 

4 

1 

Least  Sandpiper 

1 

153 

19 

25 

6 

2 

Dunlin 

6 

8 

18 

4 

3 

peep  spp. 

250 

2C 

75 

23 

Short-billed  Dowitcher 

15 

12 

Long-billed  Dowitcher 

2 

32 

20 

175 

8 

10 

dowitcher  spp. 

110 

3 

68 

3 

1 

Common  Snipe 

7 

3 

1 

Wilson's  Phalarope 

2 

5 

2 

4 

3 

10 

2 

Red-necked  Phalarope 

2 

19 

20 

11 

3 

15 

12 

1 

Red  Phalarope 

3 

Bonaparte's  Gull 

1103 

40 

10 

105 

16 

17 

932 

111 

352 

93 

116 

20 

310 

7 

Appendix  A    (cont'd) 


Mann  County 
(Southern) 


Point  Reyes 
Peninsula 


Even  Cheaper  Thnlls 


21   May 
1077 

21  May 
1982 

4  June 

1983 

21  May 
1982 

7  May 
1978 

6  May 
1979 

17  May 
1980 

9  May 
1981 

16  May 
1982 

22  May 
1983 

3  June 
1984 

2  June 
1985 

31  May 
1986 

31  May 
1987 

Heermann's  Gull 

2 

Ring-billed  Gull 

51 

43 

48 

28 

8 

50 

7 

182 

10 

15 

17 

4 

55 

5 

California  i  lull 

13 

2 

2 

148 

322 

14 

262 

550 

2 

19 

1 

1 

19 

5 

Western  Gull 

850 

831 

2235 

992 

308 

78 

22 

93 

50 

234 

94 

1 

63 

14 

Glaucous-winged  Gull 

3 

8 

6 

38 

5 

17 

1 

11 

3 

2 

2 

2 

3 

3 

gull  >pp 

54 

96 

11 

123 

75 

1 

101 

40 

44 

41 

16 

21 

Caspian  Tern 

101 

9C 

74 

34 

35 

40 

31 

6 

10 

45 

15 

38 

30 

37 

Elegant  Tern 

25 

6 

Forster's  Tern 

158 

81 

87 

76 

23 

30 

11 

8 

22 

12 

3 

13 

25 

5 

Black  Tern 

4 

Common  Murre 

213 

92 

32 

49 

Pigeon  Guillemot 

15 

27 

2 

15 

Rock  Dove 

32 

356 

169 

29 

164 

161 

168 

294 

179 

179 

190 

92 

98 

157 

Band-tailed  Pigeon 

199 

294 

169 

69 

34 

82 

41 

72 

109 

37 

44 

52 

84 

2 

Mourning  Dove 

251 

467 

315 

146 

175 

126 

156 

196 

215 

135 

142 

237 

109 

171 

Bam  Owl 

3 

8 

1 

1 

4 

1 

1 

3 

2 

1 

1 

1 

Western  Screech-Owl 

2 

3 

3 

5 

4 

6 

8 

5 

4 

1 

1 

Great  Horned  Owl 

7 

12 

6 

2 

8 

11 

11 

17 

14 

6 

9 

7 

3 

3 

Northern  Pygmy-Owl 

1 

1 

1 

Sported  Owl 

2 

1 

1 

1 

Northern  Saw-whet  Owl 

1 

1 

Common  Poorwill 

4 

1 

Vaux's  Swift 

5 

2 

13 

6 

White-throated  Swift 

52 

38 

37 

2 

10 

1 

1 

swift  spp. 

14 

5 

Anna's  Hummingbird 

135 

153 

105 

25 

24 

40 

48 

43 

66 

65 

18 

42 

40 

81 

Rufous  Hummingbird 

1 

1 

5 

3 

1 

Allen's  Hummingbird 

219 

173 

188 

76 

34 

49 

42 

41 

33 

38 

23 

22 

9 

24 

Selasphorous  spp. 

30 

9 

5 

5 

8 

19 

17 

18 

4 

hummingbird  spp. 

23 

9 

4 

4 

2 

3 

Belted  Kingfisher 

4 

2 

5 

12 

4 

2 

2 

3 

2 

2 

5 

2 

5 

3 

Lewis'  Woodpecker 

7 

Acorn  Wtxxlpecker 

62 

73 

71 

27 

19 

73 

48 

28 

33 

29 

34 

34 

14 

31 

Red-naped  or  Yellow- 
bellied  Sapsucker 

1 

Red-breasted  Sapsucker 

1 

Nuttall's  Woodpecker 

2 

5 

3 

4 

24 

24 

47 

52 

26 

53 

75 

91 

47 

59 

Downy  Woodpecker 

31 

30 

34 

20 

6 

11 

12 

17 

9 

9 

14 

17 

13 

9 

Hairy  Woodpecker 

6 

15 

17 

6 

2 

2 

5 

1 

2 

5 

2 

Northern  (Red-shafted) 
Flicker 

46 

48 

37 

14 

4 

5 

4 

8 

9 

3 

8 

7 

6 

6 

Pileated  Woodpecker 

6 

7 

11 

1 

1 

Olive-sided  Flycatcher 

53 

76 

76 

6 

8 

18 

9 

11 

8 

2 

12 

9 

18 

7 

Western  Wood-Pewee 

38 

19 

60 

46 

25 

29 

28 

39 

43 

61 

54 

75 

65 

35 

Willow  Flycatcher 

1 

Pacific-slope  Flycatcher 

184 

206 

217 

65 

66 

95 

58 

74 

92 

108 

66 

119 

113 

124 

Emptdonax  spp. 
(non-Pacific-slope) 

2 

2 

Black  Phoebe 

18 

26 

25 

42 

35 

49 

51 

61 

44 

51 

60 

48 

36 

69 

Ash-throated  Flycatcher 

72 

88 

75 

24 

56 

67 

88 

151 

118 

124 

69 

119 

79 

130 

Western  Kingbird 

2 

16 

77 

44 

67 

52 

30 

50 

58 

6C 

46 

65 

Appendix  A.  (cont'd) 


Mann  County 
(Southern) 


Point  Reyes 
Peninsula 


Even  Cheaper  Thnlls 


21   May 
1977 

21   May 
1982 

4  June 
1983 

23  May 
1982 

7  May 
1978 

6  May 
1979 

17  May 
1980 

9  May 
1981 

16  May 
1982 

22  May 
1983 

3  June 
1984 

2  June 
1985 

31  May 
1986 

31  May 
1987 

Homed  Lark 

13 

4 

10 

40 

18 

122 

39 

26 

57 

62 

25 

39 

22 

24 

Purple  Martin 

9 

24 

4 

3 

1 

Tree  Swallow 

44 

41 

72 

76 

64 

111 

83 

54 

48 

31 

49 

64 

77 

42 

Violet-green  Swallow 

103 

230 

263 

54 

95 

334 

213 

380 

230 

275 

169 

140 

156 

239 

N.  Rough-winged  Swallow 

17 

18 

10 

36 

3 

58 

14 

14 

9 

41 

18 

31 

28 

11 

Bank  Swallow 

1 

Cliff  Swallow 

384 

1149 

666 

495 

1035 

2366 

1103 

1962 

1794 

2099 

1385 

1763 

2343 

1531 

Bam  Swallow 

120 

573 

325 

403 

568 

1022 

634 

537 

355 

454 

472 

463 

418 

544 

Steller's  Jay 

175 

192 

154 

24 

43 

47 

34 

63 

46 

48 

59 

56 

45 

61 

Scrub  Jay 

469 

457 

370 

174 

155 

146 

173 

204 

165 

129 

178 

170 

89 

193 

American  Crow 

81 

224 

127 

123 

245 

222 

252 

357 

226 

344 

297 

315 

175 

218 

Common  Raven 

24 

36 

38 

125 

38 

37 

22 

54 

31 

31 

15 

17 

24 

18 

Chestnut-backed  Chickadee 

298 

401 

347 

80 

44 

75 

139 

67 

58 

87 

88 

138 

148 

167 

Plain  Titmouse 

166 

72 

89 

17 

74 

122 

176 

99 

84 

78 

110 

105 

109 

216 

Bushtit 

597 

336 

417 

78 

108 

171 

217 

182 

88 

223 

205 

294 

238 

228 

Red-breasted  Nuthatch 

10 

21 

8 

2 

3 

White-breasted  Nuthatch 

1 

3 

6 

22 

31 

20 

20 

18 

21 

32 

25 

17 

21 

Pygmy  Nuthatch 

224 

9 

13 

7 

Btown  Creeper 

46 

81 

55 

7 

1 

9 

6 

7 

18 

16 

16 

16 

15 

17 

Rock  Wren 

4 

3 

1 

5 

2 

2 

Bewick's  Wren 

140 

286 

148 

81 

55 

73 

78 

117 

157 

65 

61 

89 

42 

102 

House  Wren 

2 

5 

3 

9 

6 

23 

18 

27 

17 

41 

17 

29 

Winter  Wren 

6 

36 

52 

8 

1 

3 

2 

2 

5 

3 

Marsh  Wren 

10 

12 

11 

82 

78 

52 

36 

104 

62 

128 

163 

122 

148 

96 

Golden-crowned  Kinglet 

20 

35 

41      . 

4 

1 

1 

1 

Ruby-crowned  Kinglet 

2 

8 

1 

Blue-gray  Gnatcatcher 

4 

9 

11 

3 

15 

20 

20 

19 

3 

40 

13 

98 

Western  Bluebird 

17 

16 

17 

53 

69 

76 

73 

98 

75 

63 

68 

71 

88 

110 

Swainson's  Thrush 

74 

102 

102 

136 

6 

8 

9 

31 

8 

12 

21 

24 

36 

24 

Hermit  Thrush 

7 

37 

55 

1 

5 

3 

7 

3 

2 

1 

Catrmrus  thrush  spp. 

4 

American  Robin 

259 

272 

319 

55 

48 

106 

77 

65 

65 

61 

40 

57 

73 

44 

Varied  Thrush 

1 

1 

1 

Wrentit 

373 

385 

265 

171 

17 

30 

41 

59 

74 

34 

30 

37 

23 

65 

Northern  Mockingbird 

125 

119 

101 

2 

61 

57 

99 

70 

41 

81 

90 

59 

53 

59 

California  Thrasher 

12 

6 

3 

1 

2 

3 

4 

10 

2 

3 

1 

2 

1 

Water  Pipit 

2 

1 

Cedar  Waxwing 

361 

65 

29 

56 

190 

87 

65 

98 

2 

Loggerhead  Shrike 

2 

1 

1 

15 

14 

15 

12 

11 

9 

9 

14 

1 

7 

European  Starling 

675 

417 

794 

436 

380 

1117 

524 

490 

603 

922 

392 

730 

393 

492 

Solitary  Vireo 

10 

10 

10 

4 

5 

2 

4 

1 

1 

2 

2 

3 

Yellow-throated  Vireo 

1 

Hutton's  Vireo 

92 

63 

58 

21 

33 

52 

72 

53 

59 

65 

21 

60 

36 

58 

Warbling  Vireo 

359 

372 

488 

108 

124 

183 

132 

206 

196 

197 

90 

204 

141 

150 

Orange-crowned  Warbler 

414 

338 

444 

88 

135 

148 

132 

155 

177 

218 

92 

213 

180 

143 

Nashville  Warbler 

1 

1 

2 

2 

Yellow  Warbler 

7 

1 

4 

19 

19 

2 

28 

14 

6 

4 

3 

10 

3 

10 

Yellow-rumped  (Audubon's) 

4 

29 

18 

10 

1 

2 

Black-throated  Gray 

20 

27 

34 

6 

1 

3 

1 

1 

3 

1 

Townsend's  Warbler 

7 

13 

5 

29 

8 

10 

Appendix  A.  (cont'd) 


Mann  County 
(Southern) 


Point  Reyes 
Peninsula 


Even  Cheaper  Thnlls 


21  May 
1977 

21  May 
1982 

4  June 
1983 

23  May 
1982 

7  May 
1978 

6  May 
1979 

17  May 
1980 

9  May 
1981 

16  May 
1982 

22  May 
1983 

3  June 
1984 

2  June 
1985 

31  May 
1986 

31  May 
1987 

Hermit  Warbler 

3 

3 

4 

5 

1 

3 

MacGiUivray's  Warbler 

1 

3 

3 

1 

Common  Yellowthroat 

27 

14 

16 

22 

5 

4 

6 

8 

27 

3 

15 

12 

12 

12 

Wilson's  Warbler 

72 

110 

83 

135 

95 

76 

75 

63 

70 

33 

34 

47 

36 

50 

Yellow-breasted  Chat 

1 

1 

Western  Tanager 

16 

2 

2 

1 

14 

4 

1 

4 

2 

3 

1 

Black-headed  Grosbeak 

106 

72 

76 

47 

67 

97 

65 

83 

46 

36 

40 

54 

56 

30 

Rose-breasted  Grosbeak 

1 

Lazuli  Bunnng 

73 

4 

2 

16 

11 

21 

8 

4 

28 

30 

27 

39 

10 

42 

Indigo  Bunting 

1 

Rufous-sided  Towhee 

308 

336 

313 

65 

88 

119 

145 

120 

143 

124 

70 

98 

153 

121 

California  Towhee 

241 

374 

243 

105 

122 

112 

142 

108 

103 

133 

125 

119 

169 

126 

Rufous-crowned  Sparrow 

25 

17 

5 

1 

2 

5 

1 

3 

2 

2 

1 

5 

Chipping  Sparrow 

28 

36 

18 

8 

22 

36 

19 

22 

22 

30 

21 

25 

35 

12 

Black-chinned  Sparrow 

6 

2 

Lark  Sparrow 

24 

15 

22 

36 

44 

75 

69 

110 

92 

65 

70 

57 

28 

97 

Sage  Sparrow 

6 

3 

3 

1 

Savannah  Sparrow 

11 

27 

43 

246 

9 

11 

20 

9 

31 

22 

37 

11 

37 

18 

Grasshopper  Sparrow 

4 

1 

3 

9 

2 

1 

5 

2 

3 

5 

3 

16 

9 

9 

Fox  Sparrow 

1 

Song  Sparrow 

252 

469 

364 

388 

217 

480 

231 

282 

260 

319 

186 

312 

277 

210 

White-throated  Sparrow 

1 

Golden-crowned  Sparrow 

1 

10 

4 

White-crowned  Sparrow 

119 

169 

94 

335 

3 

5 

5 

2 

Dark-eyed  (Oregon)  Junco 

204 

266 

290 

49 

65 

148 

201 

180 

150 

187 

98 

168 

189 

187 

Red-winged  Blackbird 

556 

687 

594 

646 

1250 

2217 

1628 

1951 

1049 

989 

1070 

1867 

1801 

1395 

Tricolored  Blackbird 

209 

1 

40 

1 

3 

17 

Western  Meadowlark 

92 

93 

57 

94 

167 

202 

200 

186 

171 

137 

115 

156 

98 

146 

Brewer's  Blackbird 

275 

435 

370 

453 

715 

1652 

651 

469 

830 

791 

687 

1104 

650 

973 

Brown-headed  Cowbird 

50 

44 

22 

58 

59 

25 

32 

50 

20 

32 

21 

57 

22 

29 

blackbird  spp. 

20 

50 

Hooded  Oriole 

10 

12 

17 

1 

5 

1 

1 

1 

1 

2 

2 

4 

Northern  (Bullock's)  Onole 

7 

30 

28 

22 

85 

108 

117 

89 

89 

103 

87 

104 

59 

119 

Northern  (Baltimore) 

1 

Purple  Finch 

98 

179 

120 

76 

29 

16 

25 

51 

37 

52 

25 

61 

78 

92 

House  Finch 

927 

1120 

967 

340 

972 

1517 

732 

1211 

652 

1035 

564 

1069 

482 

666 

Red  Crossbill 

29 

5 

Pine  Siskin 

162 

472 

233 

176 

26 

45 

23 

25 

11 

92 

60 

54 

36 

37 

Lesser  Goldfinch 

182 

147 

74 

22 

74 

107 

125 

191 

129 

122 

153 

110 

123 

286 

Lawrence's  Goldfinch 

4 

11 

25 

American  Goldfinch 

602 

246 

272 

262 

84 

83 

68 

73 

37 

134 

80 

47 

59 

84 

House  Sparrow 

207 

250 

183 

111 

321 

571 

219 

299 

427 

312 

324 

431 

120 

209 

Total  Species 

158 

152 

154 

153 

156 

56 

148 

153 

146 

135 

131 

134 

134 

141 

Total  Individuals 

1 7,482 

19,455 

16,869 

10,884 

11,710 

18.233 

13,444 

15,390 

12,645 

1 3,299 

10,823 

14,119 

12,426 

12,625 

Total  Confirmed  Breeders 

64 

69 

68 

30 

47 

40 

49 

45 

45 

46 

48 

57 

51 

46 

o 

00 

ON 

' — 1 

o 

<-J 

r^ 

on 

• — 1 

6 

p 

* 

& 

c 

a 

o 

U 

c 

■p 

efl 

s 

C 

-a 

u 

'.; 

3 

-a 

c 

0 

'J 

VI 

V 

3 

2 

c 

c: 

R 

3 

CO 

U 

-n 

_2 

u 

T-) 

cu 

c 

be 

Efl 

c 

~n 

<u 

V 

-n 

M 

u 

fi 

V 

CO 

1) 

C 

u 

o 

£ 

c 

V 

5/i 

CO 

c 

c 

sis 

1) 

n 

T) 

u 

'r 

£ 

3 

la 

-0 

u 

c 

> 

efl 

0 

Efl 

o 

E 

14 

-u 

w 

£ 

P 

3 

C 

o 

U 

c 

T3 

o 

a 

-n 

u 

u 

t- 

V} 

4; 

i1 

be 

-s 

c 

Efl 

(A 

1- 

V 

c 

efl 

V 

a 

<A 

C 

a 

6* 
C 

V 

6 

-o 

Ifl 

_o 

-n 

M 

(1) 

.XI 

-o 

Si* 

0 

<u 

CQ 

l- 

u 

_^, 

oj 

oo 

E 

■<J- 

3 

z 

d 

w 

CQ 

0 

X 

S 

-a 

oj 

c 
u 

s 

a 

d> 

a 

< 

VI 

CO     * 

O       M 

v  t: 

o  i2 
e2 

o 

J 

■ 

o 

CO 

o 

sO 

2 

o 

3 

o 

o 

o 

o 

s 

o 

o 

2 

o 

o 

o 

O 

o 

•*■ 

o 

&■ 

o 

R 

o 

d 

Os 

• 

■* 

d 

°! 

d 

2 

d 

5 

s 

d 

d 

d 

d 

5 

;; 

■^ 

d 

oq 

s 

a 

d 

°! 

2 

o 

<5 

2 

o 

f! 

o 

1 

o 

o 

J 

o 

s 

O 

o 

7 

O 

' 

o 

o 

>£> 

o 

o 

o 

NO 

■ 

oo 

oo 

s 

o 

o 

2 

cl 

T 

o 

a 

3 

R 

d 

■«; 

2 

2 

£ 

O 

d 

2 

- 

• 

d 

d 

5 

S 

5 

5 

5 

5 

- 

s 

•flj1 

* 

s 

j 

5 

a 

2 

j 

c 

1 

S 

c3 

0 

0 

1 

i 

— 

C 

E 
1 

i 
i 

0 

5 

c 

CO 

"1 

8 
3 

,,0 

I 

-C 

0 

l 

(3 

5 

0 

C 
a 
in 

~ 

c 
3 
& 

V 

v0 
a. 

| 

CO 

a 

u 

3 

i 

a 
J 

5 

0 

t 

a 

I 

a 

c 

3 
0 
C 

a 

S. 

a 

0 

O 

i 

t 

i 

en 

■a 

c 
g 

0 

c 
o 

6 

1 

c2 

T3 
CO 

1 

"o 
■fi 
h 

"5 

0 

3 

E 

"E 

CQ 
CQ 

3 

c3 

"8 

T5 
C 

i 

0 
CQ 

0 

1 

c 

c 

o 

X 

c 

B 

"o 

o 
j 

c 
-o 

0 

O 

c 

E 
< 

i 

0 

t 
— 

X 

oo     M 
OS 

CO 
^O 

o 

CO 

2 

o 

o 

o 

E 

' 

o 

O 

o 

o 

7 

o 

o 

^ 

C^■ 

o 

o 

o 

-o 

o 

o 
o 

00 

7 

■ 

' 

o 

o 

O 

■ 

a 

a 

J 

o 

d 

- 

a 

S 

' 

p 

d 

5 

2 

o 
^o 

a 

2 

^d 

d 

d 

d 

3 

d 

5 

s 

a 

■ 

• 

5 

j 

d 

■ 

o 

- 

s 

• 

o 

o 

o 

O 

O 

o 

o 

o 

-r 

2 

o 

R 

o 

o 

• 

• 

o 

■ 

7 

s 

o 

O 

O 

o 

■ 

o 

o 

R 

a 

o 

' 

- 

d 

vO 

- 

d 

■<; 

3 

s 

^ 

o 

o 

s 

j 

d 

• 

1 

s 

■ 

5 

d 

O 

d 

■ 

d 

d 

% 

u 
J 

-o 

5 
§ 

3 
0 

§ 

SI 

a 

a 
•1 
z 

_o 

c2 

1 

1 
z 

| 

i 

■§ 

-s 

3 

z 

1 

s. 

u 
1 

CQ 

c 

E 

1 

CQ 

0 

X 

C 

a 

c 

;5 

C 

i 

S 

p 

c 

o 
O 

-2 
-5 

CQ 

E 
1 

E 
IS 

"c 

0 

c 

i 

2 

1 

c 
15 
cS 

c 

c 

i 
< 

c 

IB 

c 

1 

2 

e 
■§ 

o 

1 

(3 

c 

1 

3 

9 

C 

c 

8 

£ 

LL) 

1 
> 

% 

8 

> 

"c 
5 

X 

> 

1 

e 
| 

c 

a 

0 

IB 

"5 

z 

2 

j 

lo 

*C 

i 

-a 
< 

c 
0 

1 

g 

| 

-O 

$ 

o 
s 

I2 

o 

O 

o 

o 

O 

o 

3 

o 

n 

o 

o 

so 

o 

o 

o 

\D 

0 

ON 

0 

7 

0 

0 

0 

0 

O 
O 

0 

0 

s 

7 

ON 

0 

d 

d 

d 

d 

d 

5 

NO 

3 

<* 

d 

d 

\0 

00 

2 

d 

CO 

2 

d 

00 

d 

ON 

d 

d 

2 

5 

SO 

Ch 

d 

0 

2 

- 

ON 

• 

o 

o 

• 

■ 

o 

o 

o 

s 

o 

o 

o 

o 

o 

i5 

•flr 

=1 

0 

-i 

• 

■ 

' 

7 

*- 

O 

z 

ON 
O 

2 

2 

5 

O 

■ 

d 

d 

' 

■ 

i*j 

-o" 

d 

1 

d 

5 

d 

- 

d 

o 

2 

°i 

2 

5 

■ 

■ 

' 

•^ 

CO 

d 

d 

5 

d 

sD 

ON 

d 

O 

3 

12 
E 

0 

i 

o 

"5 

Q 

i 

£ 

z 

9 

I 

j 

5 

i 

E 
X 

3 
< 

1 

_5 
5 
"E 

£ 

X 

"c 
< 

PS 

8. 

j 

e 

0 

< 

I 

i 
i 

c 
S 
B 
Q 

1 
1 

X 

■o 
•x: 

-a 

1 

I 

-C 

ul 

■? 

> 

5 

1 

a. 

1 

E 
1 

j 

cE 

X 
-0 

2 
< 

~2 
Ic 

5 
-2 

E 

1 

j 

E 
X 

j 

_o 
5 

1 
& 

> 

1 
J 

it 
U 

_0 
3 

E 

| 

J3 

1 
U 

c 

c 
E 
< 

i. 

c 

0 

e 

E 

6 

0 
0 

* 

GO 

? 

M 

_ 

*■ 

ON 

r- 

ON 

^ 

^ 

vn 

0 

M 

CO 

NO 

l~J 

r- 

rsi 

- 

**- 

vn 

M 

s 

00     K 
O     « 

0 

O 

00 

JS 

a 

0 

0 

c. 

J. 

O 

0 

O 

- 

O 

»i 

O 

ri 

0 

0 

0 

0 

0 

O 

O 

0 

O 

A 

£ 

w  ^ 

■i* 

00 
00 

O 

r- 

^~ 

0 

■o 

O 

rN 

„ 

„ 

m 

— 

ON 

00 

0 

0 

— 

u-. 

- 

s0 
SO 

»ft 

r^ 

0 

CO 

" 

~" 

0 

0 

- 

O 

^* 

0 

ON 

u-i 

0 

- 

O 

""* 

0 

O 

- 

- 

fN 

^. 

— 

_^ 

__ 

* 

— 

— 

_ 

^. 

^ 

■*- 

* 

„ 

^ 

„ 

r-j 

^ 

o- 

S  £ 

O 

O 

0 

O 

0 

T(- 

O 

0 

0 

O 

— 

0 

10 

0 

O 

0 

O 

O 

* 

u 

>o 

sD 

„, 

^_ 

— 

^ 

„ 

^. 

KS 

e> 

^. 

r- 

_ 

SO 

_ 

m 

^ 

, 

0 

O 

0 

O 

0 

ON 

O 

0 

0 

" 

^ 

" 

- 

0 

0 

0 

" 

- 

„ 

e 
P 

E 
0 

X 

_ 

6 

1 
i 
i 

M 

3 

J 

c 

•6 

•2 

3 

n 

C 
J 

a. 

2 

CQ 

2 
X 

CQ 

I 
O 

I 

UJ 

i 
0 

1 

UJ 

r 

5 

c 

X 

1 

c 

i 

0 

z 

a 
j 

CO 

8 
0 

■n 

c 

c3 

1 

J 
> 
& 

6 

1 

0 

oa 

"l 

X 

i 

1 
12 

3 
0 
X 

I 

"3 
X 

r 
C£ 

E 
< 

d 
1 

<3 

J 

I 

C 

c 

1 
< 

ii 
12 

_2 

S. 

u. 
-0 

c 

I 

0 

c 

5, 

c 

0 

6 

2 

-O 

if 

c 

"5 
0 

1 

u 

"5 
O 

E 
1 

I 

C 

I 

O 

O 

E 

c 
.3 

6 

E 
h 

■: 
u- 

J 
1 

3 

y 

c 

PQ 

1 

C 

1 

3 
0 
2 

Appendix  C 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Appendix  C 


APPENDIX  C. 
A  list  of  Breeding  Bird  Censuses  conducted  in  Marin  County,  California,  1951  to  1990. 

Dates  listed  represent  the  actual  year  of  each  census.  From  1951  to  1975,  data  were  published  in  the  same  calendar 
year;  thereafter,  data  were  published  in  die  following  calendar  year.  The  name  and  size  of  some  plots  have  changed 
over  die  years— the  most  current  data  are  listed. 


1)  Bishop  Pine  Forest  (A).  Location:  3.75  mi  WNW  of 
Inverness.  Size:  10.5  ha  =  26  acres.  Coverage:  1951  &  1952 
(AFN  6:312-314),  1953  (AFN  7:351),  1972  (AB  26:986),  1973 
(AB  27:998-999),  1974  (AB  28:1039-1040),  1975  (AB 
29:1126-1127),  1977  (AB  32:90). 

2)  Bishop  Pine  Forest  (B).  Location:  1.5  mi  W  of  Inver- 
ness, 0.75  mi  NW  of  Mt.  Vision.  Size:  8.5  ha  =  21  acres. 
Coverage:  1972  (AB  26:985-986),  1973  (AB  27:999),  1974 
(AB  28:1039),  1975  (AB  29:1127). 

3)  Bishop  Pine  Forest  (C).  Location:  1.7  mi  W  of  Inver- 
ness, 1.1  mi  NW  of  Mt.  Vision.  Size:  6.2  ha  =  15.4  acres. 
Coverage:  1974  (AB  28:1038). 

4)  Disturbed  Bishop  Pine  Forest.  Location:  3  mi  NW  of 
Inverness  Park.  Size:  12.0  ha  =  29.7  acres.  Coverage:  1972 
(AB  26:984-985),  1973  (AB  27:999-1000),  1974  (AB 
28:1040),  1975  (AB  29:1127),  1977  (AB  32:90). 

5)  California  Bay-Bishop  Pine  Mixed  Forest.  Location: 
0.5  mi  S  of  Inverness.  Size:  11.7  ha  =  29  acres.  Coverage: 
1972  (AB  26:981),  1973  (AB  27:997-998),  1974  (AB  28:1037- 
1038),  1975  (AB  29:1125-1126),  1976  (AB  31:72),  1977  (AB 
32:87). 

6)  Mature  Douglas  Fir  Forest.  Location:  4  mi  NW  of 
Bolinas,  1.75  mi  N  of  PRBO  Palomarin  Field  Station. 
Size:  6.1   ha  =  15  acres.  Coverage:  1971  (AB  25:987-988), 

1972  (AB  26:984),  1973  (AB  27:1001),  1974  (AB  28:1041), 
1975  (AB  29:1128). 

7)  Logged  Douglas  Fir  Forest.  Location:  4.5  mi  S  of 
Olema,  200  yds  S  of  east  gate  to  Lake  Ranch,  PRNS.  Size:  6.1 
ha  =  15  acres.  Coverage:  1971  (AB  25:1004). 

8)  Logged  Douglas  Fir  Forest  Reseeded  with  Monterey 

Pine.  Location:  4.5  mi  S  of  Olema,  about  0.5  mi  E  of  east 
gate  to  Lake  Ranch,  PRNS.  Size:  8.2  ha  =  20.2  acres.  Cover- 
age: 1972  (AB  26:983-984),  1973  (AB  27:1000-1001),  1974 
(AB  28:1040-1041),  1975  (AB  29:1127-1128),  1976  (AB 
31:73-74),  1977  (AB  32:91). 

9)  Mixed  Evergreen  Forest.  Location:  Cataract  Gulch,  400 
ft  E  of  Ridgecrest  Blvd.  Size:  6.1  ha  =  15  acres.  Coverage: 
1966  (AFN  20:629-630),  1967  (AFN  21:629). 

10)  Oak-California  Bay-Buckeye  Mixed  Forest.  Loca- 
tion: 3.5  mi  NW  of  Bolinas,  just  inside  southern  boundary 
of  PRNS.  Size:  4  ha  =  10  acres.  Coverage:  1972  (AB  26:979), 

1973  (AB  27:995-996),  1974  (AB  28:1035),  1975  (AB 
29:1123). 

444 


1 1)  Coastal  Scrub.  Location:  4  mi  NW  of  Bolinas,  0.5  mi 
inside  southern  boundary  of  PRNS.  Size:  8.1  ha  =  20  acres. 
Coverage:  1971  (AB  25:1003-1004),  1972  (AB  26:987),  1973 
(AB  27:1004),  1974  (AB  28:1042),  1975  (AB  29:1129),  1977 
(AB  32:98),  1979  (AB  34:80-81),  1980  (AB  35:93-94),  1981 
(AB  36:94),  1982  (AB  37:95),  1983  (AB  38:129),  1984  (AB 
39:114),  1985  (AB  40:71),  1986  (PRBO  unpubl.),  1987 
(PRBO  unpubl.),  1988  (JFOs  60:56),  1989  (JFOs  61:69-70), 
1990  (JFOs  62:78-79). 

1 2)  Disturbed  Coastal  Scrub  (A).  Location:  3.5  mi  NW  of 
Bolinas,  just  inside  soudiern  boundary  of  PRNS. Size:  4.7  ha 
=  11.6  acres.  Coverage:  1972  (AB  26:987-988),  1973  (AB 
27:1004),  1974  (AB  28:1042-1043),  1975  (AB  29:1129), 
1977  (AB  32:100),  1978  (AB  33:91),  1979  (AB  34:81),  1980 
(AB  35:94),  1981  (AB  36:94),  1982  (AB  37:95),  1983  (AB 
38:129<Sd34),  1984  (AB  39:114),  1985  (AB  40:71),  1986 
(PRBO  unpubl.),  1987  (PRBO  unpubl.),  1988  (JFOs  60:54- 
55),  1989  (JFOs  61:68),  1990  (JFOs  62:79). 

13)  Disturbed  Coastal  Scrub  (B).  Location:  3.5  mi  NW 
Bolinas,  0.16  mi  inside  southern  boundary  of  PRNS.  Size:  8.1 
ha  =  20  acres.  Coverage:  1971  (AB  25:1002-1003),  1972  (AB 
26:988),  1973  (AB  27:1004-1005),  1974  (AB  28:1043),  1975 
(AB  29:1129),  1977  (AB  32:100),  1978  (AB  33:91),  1979  (AB 
34:81),  1980  (AB  35:94),  1981  (AB  36:94),  1982  (AB  37:95- 
96),  1983  (AB  38:134),  1984  (AB  39:114),  1985  (AB  40:71), 
1986  (PRBO  unpubl.),  1987  (PRBO  unpubl.),  1988  (JFOs 
60:55),  1989  (JFOs  61:69),  1990  (JFOs  62:79-80). 

14)  Burned  Disturbed  Coastal  Scrub.  Location:  5.5  mi 
NW  of  Bolinas,  2  mi  inside  southern  boundary  PRNS.  Size: 
8.1  ha  =  20  acres.  Coverage:  1983  (AB  38:129). 

15)  Coastal  Riparian  Marsh.  Location:  Olema  Marsh,  0.5 
mi  SW  of  Pt.  Reyes  Station.  Size:  17.5  ha  =  43.8  acres. 
Coverage:  1985  (AB  40:71),  1986  (ACR  Report  85-1-2),  1987 
(ACR  Report  85-1-3),  1988  (ACR  Report  85-14),  1989  (ACR 
Report  85-1-5),  1990  (JFOs  62:75-76). 

16)  Coastal  Freshwater  Marsh.  Location:  Livermore 
Marsh,  0.5  mi  NW  of  Marshall.  Size:  10.5  ha  =  26.2  acres. 
Coverage:  1985  (AB  40:71),  1986  (ACR  Report  85-1-2),  1987 
(ACR  Report  85-1-3),  1988  (JFOs  60:64),  1989  (JFOs  61:76), 
1990  (JFOs  62:74-75). 

1 7)  Coastal  Prairie.  Location:  0.5  mi  NW  of  Marshall.  Size: 
31  ha  =  77.5  acres.  Coverage:  1988  (JFOs  60:56-57),  1989 
(JFOs  61:70-71),  1990  (JFOs  62:80). 


LITERATURE  CITED 


Adams,  D.  A.  and  T.  L  Quay.  1958.  Ecology  of  the  Clapper 
Rail  in  southeastern  North  Carolina.  J.  Wildl.  Mgmt. 
22:149-156. 

Adamus,  P.  R.  1987.  Atlas  of  Breeding  Birds  in  Maine,  1978- 
1983.  Maine  Dept.  Inland  Fisheries  and  Wildl.,  Augusta. 

Addicott,  A.  B.  1938.  Behavior  of  the  bush-tit  in  the  breeding 
season.  Condor  40:49-63. 

Ainley,  D.  G.  1976.  The  occurrence  of  seabirds  in  the  coastal 
region  of  California.  W.  Birds  7:33-68. 

.   1984a.   Storm-Petrels.   In  D.   Haley,  ed.  Seabirds  of 

Eastern  North  Pacific  and  Arctic  Waters,  58-63.  Pacific 
Search,  Seattle. 

.  1984b.  Cormorants.  In  D.  Haley,  ed.  Seabirds  of  Eastern 

North  Pacific  and  Arctic  Waters,  92-101.  Pacific  Search, 
Seattle. 

.  1990.  Seasonal  and  annual  patterns  in  the  marine 

environment  near  the  Farallones.  In  D.  G.  Ainley  and  R. 
J.  Boekelheide,  eds.  Seabirds  of  the  Farallon  Islands:  Ecology, 
Dynamics,  and  Structure  of  an  Upwelling-System  Community, 
23-50.  Stanford  Univ.  Press,  Stanford. 

Ainley,  D.  G.,  D.  W.  Anderson,  and  P.  R.  Kelly.  1981. 
Feeding  ecology  of  marine  cormorants  in  southwestern 
North  America.  Condor  83:1 20-1 31 . 

Ainley,  D.  G.  and  R.  J.  Boekelheide,  eds.  1990.  Seabirds  of  the 
Farallon  Islands:  Ecology,  Dynamics,  and  Structure  of  an 
Upwelling-System  Community.  Stanford  Univ.  Press,  Stan- 
ford. 

Ainley,  D.  G.  and  T.  J.  Lewis.  1974.  The  history  of  Farallon 
Island  marine  bird  populations,  1854-1972.  Condor  76: 
432-446. 

Ainley,  D.  G.,  S.  Morrell,  and  T.  J.  Lewis.  1974.  Patterns  in 
the  life  histories  of  storm  petrels  on  the  Farallon  Islands. 
Living  Bird  13:295-312. 

Ainley,  D.  G.  and  T.  Osborne.  1972.  A  Marin  County, 
California,  breeding  site  for  Ashy  Petrels.  Calif.  Birds  3:71 . 

Ainley,  D.  G.  and  G.  A.  Sanger.  1979.  Trophic  relationships 
of  seabirds  in  the  northeastern  Pacific  Ocean  and  Bering 
Sea.  In  J.  Bartonek  and  D.  N.  Nettleship,  eds.  Conserva- 
tion of  marine  birds  of  northern  North  America.  U.S.  Fish 
Wildl.  Serv.  Wildl.  Res.  Rept.  11. 

Ainley,  D.  G.  and  M.  C.  Whitt.  1973.  Numbers  of  marine 
birds  breeding  in  northern  California.  W.  Birds  4:65-70. 

Airola,  D.  A.,  ed.  1980.  California  Wildlife  Habitat  Relation- 
ships Program.  Northeast  Interior  Zone.  Vol.  3:  Birds. 
Almanor  Ranger  District,  Lassen  Nad.  Forest,  P.O.  Box 
767,  Chester,  CA  96020. 

Airola,  D.  A.  1986.  Brown-headed  Cowbird  parasitism  and 
habitat  disturbance  in  the  Sierra  Nevada.  J.  Wildl.  Mgmt. 
50:571-575. 


Airola,  D.  A.  and  R.  H.  Barrett.  1985.  Foraging  and  habitat 

relationships  of  insect-gleaning  birds  in  a  Sierra  Nevada 

mixed-conifer  forest.  Condor  87:205-216. 
Albers,  P.  H.  1978.  Habitat  selection  by  breeding  Red-winged 

Blackbirds.  Wilson  Bull.  90:619-634. 
Aldrich,  E.  C.  1935.  Nesting  of  the  Dusky  Poor-will.  Condor 

37:49-55. 
.   1939.  Notes  on  the  salt-feeding  habits  of  the  Red 

Crossbill.  Condor  41 :1 72-1 73. 
-.  1945.  Nesting  of  the  Allen  Hummingbird.  Condor 


47:137-148. 
Allaire,  P.  N.  and  C.  D.  Fisher.  1975.  Feeding  ecology  of 

three  resident  sympatric  sparrows  in  eastern  Texas.  Auk 

92:260-269. 
Allen,  A.  A.  1914-  The  Red-winged  Blackbird:  A  study  in  the 

ecology  of  a  cattail  marsh.  Proc.  Linn.  Soc.  N.Y.  24-25: 

43-128. 
Allen,  A.  S.  1933.  Arrival  and  departure  of  avian  visitants  in 

the  San  Francisco  Bay  region.  Condor  35:225-227. 
.   1943.  Additional  notes  on  the  birds  of  a  Berkeley 

hillside.  Condor  45:149-157. 
Allen,  C.  A.   1880.   Habits   of  Vaux's   Swift.   Bull.  Nutt. 

Omithol.  Club  5:55-56. 
.  1881.  Collecting  on  the  Pacific  Coast.  Ornithologist 

and  Oologist  6:18-19. 
Allen,  R.  W.  and  M.  M.  Nice.  1952.  A  study  of  the  breeding 

biology  of  the  Purple  Martin  (Progne  subis).  Am.  Midi.  Nat. 

47:606-665. 
American  Ornithologists'  Union.  1957.  ChecJc-Iist  of  North 

American  Birds.  5th  ed.  Lord  Baltimore,  Baltimore. 
.  1983.  ChecJc-list  of  North  American  Birds.  6th  ed.  Allen 

Press,  Lawrence,  Kans. 
Ames,  P.  L  and  G.  S.  Mersereau.  1964.  Some  factors  in  the 

decline  of  the  Osprey  in  Connecticut.  Auk  81:173-185. 
Anderson,  D.  W.  and  J.  J.  Hickey.  1972.  Eggshell  changes  in 

certain  North  American  birds.  In  K.  H.  Voous,  ed.  Proc. 

XVth  Int.   Ornithol.   Congress,   514-540.   E.  G.   Brill, 

Leider,  Netherlands. 
Anderson,  S.  H.  1976.  Comparative  food  habits  of  Oregon 

nuthatches.  Northwest  Sci.  50:213-221. 

Anderson,  W.  1970.  A  preliminary  study  of  the  relationship 

of  saltponds  and  wildlife— south  San  Francisco  Bay.  Calif. 

Fish  Game  56:240-252. 
Anderson,  W.  L  and  R.  E.  Duzan.  1978.  DDE  residues  and 

eggshell  diinning  in  Loggerhead  Shrikes.  Wilson  Bull. 

90:215-220. 
Andrle,  R.  F.  and  J.  R.  Carroll,  eds.   1988.  The  Atlas  of 

Breeding  Birds  in  New  York  State.  Cornell  Univ.  Press, 

Ithaca. 


445 


MARIN  COUNTY  BREEDING  BIRD  ATEAS 


Ankncy,  C.  D.  and  A.  D.  Afton.  1988.  Bioenergerics  of 
breeding  Northern  Shovelers:  Diet,  nutrient  reserves, 
clutch  size,  and  incubation.  Condor  90:459-472. 

Ankney,  C.  D.  and  D.  M.  Scott.  1980.  Changes  in  nutrient 
reserves  and  diet  of  breeding  Brown-headed  Cowbirds. 
Auk  97:684-696. 

Annett,  C.  and  R.  Pierotti.  1989.  Chick  hatching  as  a  trigger 
for  dietary  switching  in  the  Western  Gull.  Colonial  Water- 
birds  12:4-11. 

Appelgate,  R.  D.  1977.  Possible  ecological  role  of  food  caches 
of  Loggerhead  Shrikes.  Auk  94:391. 

Arnold,  J.  R.  1935.  The  changing  distribution  of  the  Western 
Mockingbird  in  California.  Condor  37:193-199. 

.  1980.  Distribution  of  the  Mockingbird  in  California. 

W.  Birds  11:97-102. 

Asay,  C.  E.  1987.  Habitat  and  productivity  of  Cooper's 
Hawks  nesting  in  California.  Calif.  Fish  Game  73:80-87. 

Atwater,  B.  F.,  S.  G.  Conrad,  J.  N.  Dowden,  C.  W.  Hedel, 
R.  L  MacDonald,  and  W.  Savage.  1979.  History,  land- 
forms,  and  vegetation  of  the  estuary's  tidal  marshes.  In  T. 
J.  Conomos,  ed.  San  Francisco  Bay:  The  Urbanized  Estuary, 
347-386.  Pacific  Div.,  Am.  Assoc.  Adv.  Sci.,  San  Fran- 
cisco. 

Atwood,  J.  L  1980.  Breeding  biology  of  the  Santa  Cruz  Island 
Scrub  Jay.  In  D.  M.  Power,  ed.  The  California  Islands: 
Proceedings  of  a  Muhidisciplinary  Symposium,  675-678. 
Santa  Barbara  Nat.  Hist.  Mus.,  Santa  Barbara. 

Austin,  O.  L,  Jr.,  ed.  1968.  A.  C.  Bent  et  al.'s  Life  histories 
of  North  American  cardinals,  grosbeaks,  buntings,  tow- 
nees, finches,  sparrows,  and  allies.  U.S.  Nad.  Mus.  Bull. 
237  (Parts  1-3). 

Austin,  O.  L,  Jr.  and  S.  H.  Low.  1932.  Notes  on  the  breeding 
of  the  Tree  Swallow.  Bird-Banding  3:39-44. 

Azevedo,  J.  and  D.  L  Morgan.  1974-  Fog  precipitation  in 
coastal  California  forests.  Ecology  55:1135-1141. 

B 

Baepler,  D.  H.  1968.  Lark  Sparrow.  In  O.  L  Austin,  Jr.,  ed. 
A.  C.  Bent  et  al.'s  Life  histories  of  North  American 
cardinals,  grosbeaks,  buntings,  towhees,  finches,  sparrows, 
and  allies.  U.S.  Nad.  Mus.  Bull.  237  (Part  2):  886-902. 

Bailey,  A.  M.,  R  J.  Niedrach,  and  A.  L  Baily.  1953.  The  Red 
Crossbills  of  Colorado.  Denver  Mus.  Nat.  Hist.  Mus. 
Pictorial  9. 

Bailey,  F.  M.  1907.  White-throated  Swifts  at  Capistrano. 
Condor  9:169-172. 

.  1910.  The  palm-leaf  oriole.  Auk  27:33-35. 

.  1928.  Birds  of  New  Mexico.  New  Mexico  Dept.  Game 

and  Fish. 

Bailey,  S.  F.,  R  A.  Erickson,  and  K.  F.  Campbell.  1987.  The 
spring  migration:  Middle  Pacific  coast  region.  Am.  Birds 
41:486. 

Baker,  M.  C.  and  L  R  Mewaldt.  1979.  The  use  of  space  by 
White-crowned  Sparrows:  Juvenile  and  adult  ranging  pat- 
terns and  home  range  versus  body  size  comparisons  in  an 
avian  granivore  community.  Behav.  Ecol.  Sociobiol.  6: 
45-52. 


Baker,  M.  C,  L  R.  Mewaldt,  and  R.  M.  Stewart.  1981. 

Demography  of  White-crowned  Sparrows  (Zonotrichia  leu- 

cophrys  nuttalli).  Ecology  62:636-644. 
Baker,  M.  C.  and  D.  B.  Thompson.  1985.  Song  dialects  of 

White-crowned   Sparrows:    Historical   processes   inferred 

from  patterns  of  geographic  variation.  Condor  87:127- 

141. 
Bakun,  A.  1973.  Coastal  upwelling  indices,  west  coast  of 

North  America,  1946-71.  U.S.  Dept.  Commerce,  NOAA 

Tech.  Rept.  NMFS  SSRF-671. 
Bakus,  G.  J.  1959.  Observations  on  the  life  history  of  the 

Dipper  in  Montana.  Auk  76:190-207. 
Baldwin,  P.  H.  and  W.  F.  Hunter.  1963.  Nesting  and  nest 

visitors  of  the  Vaux's  Swift.  Auk  80:81-85. 
Baldwin,  P.  H.  and  N.  K.  Zaczkowski.  1963.  Breeding  biology 

of  the  Vaux's  Swift.  Condor  65:400-406. 
Balgooyen,  T.  G.  1976.  Behavior  and  ecology  of  the  Ameri- 
can Kestrel  (Falco  sparverius  L)  in  the  Sierra  Nevada  of 

California.  Univ.  Calif.  Publ.  Zool.  103. 
.  1990.  Orientation  of  American  Kestrel  nest  cavities: 

Revisited.  J.  Raptor  Res.  24:27-28. 
Baltz,  D.  M.  and  G.  V.  Morejohn.  1977.  Food  habits  and 

niche  overlap  of  sea  birds  wintering  on  Monterey  Bay, 

California.  Auk  94:526-543. 
Baptista,  L  F.  1975.  Song  dialects  and  demes  in  sedentary 

populations  of  the  White-crowned  Sparrow  (Zonotrichia 

leucophrys  nuttalli).  Univ.  Calif.  Publ.  Zool.  105:1-52. 
Barbour,  M.  G.,  T.  M.  Dejong,  and  A.  F.  Johnson.  1976. 

Synecology  of  beach  vegetation  along  the  Pacific  coast  of 

the  United   States  of  America:  A  first  approximation. 

J.  Biogeogr.  3:55-69. 
Barlow,  C.  1897.  Some  notes  on  the  nesting  habits  of  the 

White-tailed  Kite.  Auk  14:14-21. 
.  1899.  Nesting  of  the  Hermit  Warbler  in  the  Sierra 

Nevada  Mountains,  California.  Auk  16:156-161. 
Barrows,  C.  W.  1981.  Roost  selection  by  Spotted  Owls:  An 

adaptation  to  heat  stress.  Condor  83:302-309. 
.  1985.  Breeding  success  relative  to  fluctuations  in  diet 

for  Spotted  Owls  in  California.  In  R  J.  Gutierrez  and  A.  B. 

Carey,  eds.  Ecology  and  management  of  the  Spotted  Owl 

in  the  Pacific  Northwest.  U.S.  For.  Serv.  Gen.  Tech.  RepL 

PNW-185. 
.  1987.  Diet  shifts  in  breeding  and  non-breeding  Spotted 

Owls.  J.  Raptor  Res.  21:95-97. 
-.  1989.  Diets  of  five  species  of  desert  owls.  W.  Birds 


20:1-10. 
Barrows,  C.  W.  and  K.  Barrows.  1978.  Roost  characteristics 

and  behavioral  thermoregulation   in  the  Spotted  Owl. 

W.  Birds  9:1-8. 
Barrows,  W.  B.  1889.  The  English  Sparrow  (Passer  domesti- 

cus)  in  North  America.   U.S.  DepL  Agri.,  Div.  Econ. 

Ornirhol.  and  Mamm.  Bull.  1. 
Bartholomew,  G.  A.,  Jr.  1942.  The  fishing  activities  of  Dou- 
ble-crested Cormorants  on  San  Francisco  Bay.  Condor 

44:13-21. 
Batts,  H.  L,  Jr.  1948.  Some  observations  on  the  nesting 

activities  of  the  eastern  goldfinch.  Jack-Pine  Warbler  26: 

51-58. 


446 


LITERATURE  CITED 


Baumann,  S.  A.  1 959.  The  breeding  cycle  of  the  Rufous-sided 
Towhee,  Pipilo  erythrophthalmus  (Linnaeus)  in  central  Cali- 
fornia. Wasmann  J.  Biol.  17:161-220. 

Beal,  F.  E.  L  1907.  Birds  of  California  in  relation  to  the  fruit 
industry  (Part  I).  U.S.  DepL  Agri.  Biol.  Surv.  Bull.  30. 

.  1910.  Birds  of  California  in  relation  to  the  fruit  industry 

(Part  II).  U.S.  Dept.  Agri.  Biol.  Surv.  Bull.  34. 

.  1911.  Food  of  the  woodpeckers  of  the  United  States. 

U.S.  Dept.  Agri.  Biol.  Surv.  Bull.  37. 

.  1912.  Food  of  our  more  important  flycatchers.  U.S. 


Dept  Agri.  Biol.  Surv.  Bull.  44. 
— .  1915.  Food  of  the  robins  and  bluebirds  of  the  United 

States.  U.S.  DepL  Agri.  Bull.  171. 
— .  1918.  Food  habits  of  the  swallows,  a  family  of  valuable 


native  birds.  U.S.  Dept.  Agri.  Bull.  619. 
-.  1948.  Some  common  birds  useful  to  the  farmer.  U.S. 


Dept.  Inter.  Conserv.  Bull.  18. 

Beason,  R.  C.  and  E.  C.  Franks.  1974.  Breeding  behavior  of 
the  Horned  Lark.  Auk  91:65-74. 

Beaver,  D.  L  and  P.  L  Baldwin.  1975.  Ecological  overlap  and 
the  problem  of  competition  and  sympatry  in  the  Western 
and  Hammond's  flycatchers.  Condor  77:1-13. 

Beebe,  G.  D.  and  J.  Schonewald.  1977.  Spotted  Owls  near 
Palomarin.  Point  Reyes  Bird  Obs.  Newsl.  43:6-7. 

Beecher,  W.  J.  1951.  Adaptations  for  food-getting  in  the 
American  blackbirds.  Auk  68:41 1-440. 

Beedy,  E.  C  1981.  Bird  communities  and  forest  structure  in 
the  Sierra  Nevada  of  California.  Condor  83:97-105. 

Beedy,  E.  C  and  S.  L  Granholm.  1985.  Discovering  Sierra 
Birds:  Western  Slope.  Yosemite  and  Sequoia  Natural  His- 
tory associations. 

Beedy,  E.  C.  and  A.  Hayworth.  In  press.  Tricolored  Blackbird 
nesting  failures  in  the  Central  Valley  of  California:  Gen- 
eral trends  or  isolated  phenomena?  In  D.  Williams,  ed. 
Proc.  of  the  Symp.  on  Endangered  Species  of  the  San 
Joaquin  Valley,  Bakersfield,  California,  December  1987. 

Beedy,  E.  C,  S.  D.  Sanders,  and  D.  A.  Bloom.  1991. 
Breeding  status,  distribution,  and  habitat  associations  of 
the  Tricolored  Blackbird  (Agelaius  tricolor),  1850-1989. 
Jones  6k  Stokes  Associates  Inc.  (JSA  88-187),  Sacramento. 
Prepared  for  U.S.  Fish  6k  Wildl.  Serv.,  Sacramento. 

Belding,  L.  1890.  Land  birds  of  the  Pacific  district.  Occas. 
Papers  II.  Calif.  Acad.  Sci.,  San  Francisco. 

Bellrose,  F.  C.  1980.  Ducks,  Geese,  and  Swans  of  North 
America.  2nd  ed.  Stackpole,  Harrisburg,  Penn. 

Bellrose,  F.  C,  K.  L  Johnson,  and  T.  U.  Meyers.  1964. 
Relative  value  of  natural  cavities  and  nesting  houses  for 
Wood  Ducks.  J.  Wildl.  Mgmt.  28:661-676. 

Bendell,  B.  E.  and  P.  J.  Weatherhead.  1982.  Prey  characteris- 
tics of  upland-breeding  Red-winged  Blackbirds,  Agelaius 
phoeniceus.  Can.  Field-Nat.  96:265-271. 

Benkman,  C.  W.  1987a.  Food  profitability  and  the  foraging 
ecology  of  crossbills.  Ecol.  Monogr.  57:251-267. 

.  1987b.  Crossbill  foraging  behavior,  bill  structure,  and 

patterns  of  food  profitability.  Wilson  Bull.  99:351-368. 

.  1990.  Intake  rates  and  the  timing  of  crossbill  reproduc- 
tion. Auk  107:376-386. 


Bent,  A.  C  1919.  Life  histories  of  North  American  diving 

birds.  U.S.  Nad.  Mus.  Bull.  107. 
.  1921 .  Life  histories  of  North  American  gulls  and  terns. 

U.S.  Nad.  Mus.  Bull.  113. 

1922.  Life  histories  of  North  American  petrels  and 


pelicans  and  their  allies.  U.S.  Nad.  Mus.  Bull.  121. 
— .   1923.   Life  histories  of  North  American  wild  fowl 

(Part  I).  U.S.  Nad.  Mus.  Bull.  126. 
— .  1926.  Life  histories  of  North  American  marsh  birds. 

U.S.  Nad.  Mus.  Bull.  135. 
— .  1927.  Life  histories  of  North  American  shore  birds 


(Part  1).  U.S.  Nad.  Mus.  Bull.  142. 

— .  1929.  Life  histories  of  North  American  shore  birds 
(Part  2).  U.S.  Nad.  Mus.  Bull.  146. 

1932.  Life  histories  of  North  American  gallinaceous 


birds.  U.S.  Nad.  Mus.  Bull.  162. 
— .  1937.  Life  histories  of  North  American  birds  of  prey 

(Part  1).  U.S.  Nad.  Mus.  Bull.  167. 
— .  1938.  Life  histories  of  North  American  birds  of  prey 

(Part  2).  U.S.  Nad.  Mus.  Bull.  170. 
— .  1939.  Life  histories  of  North  American  woodpeckers. 

U.S.  Nad.  Mus.  Bull.  174. 
-.  1940.  Life  histories  of  North  American  cuckoos,  goat- 


suckers, hummingbirds,  and  their  allies.  U.S.  Nad.  Mus. 

Bull.  176. 
.   1942.  Life  histories  of  North  American  flycatchers, 

larks,  swallows,  and  their  allies.  U.S.  Nad.  Mus.  Bull.  179. 
.  1946.  Life  histories  of  North  American  jays,  crows,  and 

titmice.  U.S.  Nad.  Mus.  Bull.  191. 
.  1948.  Life  histories  of  North  American  nuthatches, 

wrens,  thrashers,  and  their  allies.  U.S.  Nad.  Mus.  Bull. 

195. 
.  1949.  Life  histories  of  North  American  thrushes,  king- 
lets, and  their  allies.  U.S.  Nad.  Mus.  Bull.  196. 
.    1950.    Life   histories   of  North  American  wagtails, 


shrikes,  vireos,  and  their  allies.  U.S.  Nad.  Mus.  Bull.  197. 
— .  1953.  Life  histories  of  North  American  wood  warblers. 

U.S.  Nad.  Mus.  Bull.  203. 
— .   1958.  Life  histories  of  North  American  blackbirds, 

orioles,  tanagers,  and  allies.  U.S.  Nad.  Mus.  Bull.  211. 
-.  1968a.  Eastern  and  California  Purple  finches.  In  O.  L 


Austin,  Jr.,  ed.  A.  C.  Bent  et  al.'s  Life  histories  of  North 
American  cardinals,  grosbeaks,  buntings,  towhees, 
finches,  sparrows,  and  allies.  U.S.  Nad.  Mus.  Bull.  237 
(Part  1):  264-280. 

.  1968b.  Red  Crossbill  (various  races).  In  O.  L  Austin, 

Jr.,  ed.  A.  C.  Bent  et  al.'s  Life  histories  of  North  American 
cardinals,  grosbeaks,  buntings,  towhees,  finches,  sparrows, 
and  allies.  U.S.  Nad.  Mus.  Bull.  237  (Part  1):  497-526. 

Berger,  A.  J.  1951.  Nesting  density  of  Virginia  and  Sora  rails 
in  Michigan.  Condor  53:202. 

.   1957.  Population  density  of  Alder  Flycatchers  and 

Common  Goldfinches  in  Crataegus  habitats  of  soudieast- 
ern  Michigan.  Wilson  Bull.  69:317-322. 

.    1968.  Clutch  size,  incubation   period,  and  nesding 

period  of  die  American  Goldfinch.  Wilson  Bull.  85:494- 
498. 


447 


MARIN  COUNTY  BREEDING  BIRD  ATIAS 


Biedenweg,  D.  W.  1983.  Time  and  energy  budgets  of  the 
Mockingbird  (Mimus  polyglottos)  during  the  breeding  sea- 
son. Auk  100:149-160. 

Binford,  L  C.  and  R.  W.  Stallcup.  1972.  American  Redstart 
breeding  in  California.  Calif.  Birds  3:87-90. 

Bird,  R.  D.  and  L  B.  Smith.  1964.  The  food  habits  of  the 
Red-winged  Blackbird,  Agelaius  phoeniceus,  in  Manitoba. 
Can.  Field-Nat.  78:179-186. 

Blanchard,  B.  D.  1941.  The  White-crowned  Sparrows  (Zon- 
otrichia  leucophrys)  of  the  Pacific  seaboard:  Environment 
and  annual  cycle.  Univ.  Calif.  Publ.  Zool.  46:1-178. 

Blancher,  P.  J.  and  R.  J.  Robertson.  1984.  Resource  use  by 
sympatric  kingbirds.  Condor  86:305-313. 

.  1985.  Predation  in  relation  to  spacing  of  kingbird  nests. 

Auk  102:654-658. 

Bleitz,  D.  1958.  Indigo  Bunting  breeding  in  Los  Angeles 
County,  California.  Condor  60:408. 

Block,  W.  M.  1990.  Geographic  variation  in  foraging  ecolo- 
gies of  breeding  and  nonbreeding  birds  in  oak  woodlands. 
In  M.  L  Morrison,  C.  J.  Ralph,  J.  Verner,  and  J.  R.  Jehl, 
Jr.,  eds.  Avian  foraging:  Theory,  methodology,  and  appli- 
cations, 264-269.  Studies  Avian  Biol.  13. 

.  1991.  Foraging  ecology  of  Nuttall's  Woodpecker.  Auk 

108:303-317. 

Bloom,  P.  H.  1979.  Ecological  studies  of  die  Barn  Owl  in 
California.  In  P.  P.  Schaeffer  and  S.  M.  Ehlers,  eds.  Proc. 
Nad.  Audubon  Society's  Symp.  on  Owls  of  the  West: 
Their  ecology  and  conservation,  36-39.  Western  Educa- 
tion Center,  Tiburon,  Calif. 

Bock,  C.  E.  1969.  Intra- vs.  interspecific  aggression  in  Pygmy 
Nuthatch  flocks.  Ecology  50:903-905. 

Bolander,  L.  Ph.  and  C.  A.  Bryant.  1930.  Some  notes  on 
Point  Reyes  birds.  Condor  32:70-72. 

Bolin,  R.  L  and  D.  P.  Abbott.  1963.  Studies  on  the  marine 
climate  and  phytoplankton  of  the  central  coastal  area  of 
California,  1954-1960.  Calif.  C.O.F.I.  Rept.  9:23-45. 

Bond,  R.  M.  1940.  Food  habits  of  the  White-tailed  Kite. 
Condor  42:168. 

.  1942.  White-tailed  Kites  feeding  on  house  mice.  Con- 
dor 44:231. 

Bonnot,  P.  1928.  An  oudaw  Barn  Owl.  Condor  30:320. 

Booth,  E.  J.  1926.  Observations  in  the  San  Francisco  Bay 
region.  Condor  28:271. 

Breitwiech,  R.,  P.  G.  Merritt,  and  G.  H.  Whitesides.  1984. 
Why  do  Northern  Mockingbirds  feed  fruit  to  their  nest- 
lings? Condor  86:281-287. 

Brennan,  L  A.  and  M.  L  Morrison.  1990.  Influence  of 
sample  size  on  interpretations  of  foraging  patterns  by 
Chestnut-backed  Chickadees.  In  M.  L  Morrison,  C.  J. 
Ralph,  J.  Verner,  and  J.  R.  Jehl,  Jr.,  eds.  Avain  foraging: 
Theory,  methodology,  and  applications,  187-192.  Studies 
Avian  Biol.  13. 

.  1991.  Long-term  trends  of  chickadee  populations  in 

western  North  America.  Condor  93:130-137. 

Briggs,  K.  T.,  D.  G.  Ainley,  L  B.  Spear,  P.  B.  Adams,  and 
S.  E.  Smith.  1988.  Distribution  and  diet  of  Cassin's  Auk- 
let  and  Common  Murre  in  relation  to  central  California 
upwellings.  In  H.  Ouellet,  ed.  Acta  XIX  Congressus  Inter- 


national Ornidtologici,  Vol  I,  982-990.  Ottawa,  Can- 
ada, 22-29  June  1986.  Nad.  Mus.  Nat.  Sci.,  Univ.  Ottawa 

Press. 
Briggs,  K.  T.,  W.  B.  Tyler,  D.  B.  Lewis,  and  D.  R  Carlson. 

1987.  Bird  communities  at  sea  off  California:  1975  to 

1983.  Studies  Avian  Biol.  11. 
Brown,  C.  R.  1981.  The  impact  of  Starlings  on  Purple  Martin 

populations  in  unmanaged  colonies.  Am.  Birds  35:266- 

268. 
Brown,  J.  L  1963.  Aggressiveness,  dominance  and  social 

organization  in  the  Steller  Jay.  Condor  65:460-484. 
.   1964-  The  integration  of  agnostic  behavior  in  the 

Steller's  Jay,  Cyanocitta  stelleri  (Gmelin).  Univ.  Calif.  Publ. 

Zool.  60:223-328. 
Brown,  L  and  D.  Amadon.  1968.  Eagles,  Hawks,  and  Falcons 

of  the  World.  Vol  2.  McGraw-Hill,  New  York. 
Brown,  W.  H.  1973.  Winter  population  trends  in  the  Marsh, 

Cooper's  and  Sharp-shinned  hawks.  Am.  Birds  27:6-7. 
.   1976.  Winter  population  trends  in  the  Black  and 

Turkey  vultures.  Am.  Birds  30:909-912. 
Browning,  B.  M.  1959.  An  ecological  study  of  the  food  habits 

of  the  Mourning  Dove.  Calif.  Fish  Game  45:313-331. 
.  1962.  Food  habits  of  the  Mourning  Dove  in  California. 

Calif.  Fish  Game  48:91 -11 5. 
.  1977.  Appendix  B.  Foods  of  the  California  Quail.  In 

A.  S.  Leopold.   The  California  Quail,  229-249.  Univ. 

California  Press,  Berkeley. 
Brownsmith,  C.  B.  1977.  Foraging  rates  of  Starlings  in  two 

habitats.  Condor  79:386-387. 
Bryant,  H.  C.  1914a.  A  determination  of  the  economic  status 

of  the  Western  Meadowlark  in  California.  Univ.  Calif. 

Publ.  Zool.  11:377-510. 
.  1914b.  Birds  as  destroyers  of  grasshoppers  in  Califor- 
nia. Auk  31:168-177. 
.  1916.  Habits  and  food  of  the  Roadrunner  in  California. 


Univ.  Calif.  Publ.  Zool.  17:21-50. 
.  1925.  Nesting  of  the  Allen  Hummingbird  in  Golden 

Gate  Park.  Condor  27:98-100. 
Bull,  E.  L  and  H.  D.  Cooper.  1991.  Vaux's  Swift  nests  in 

hollow  trees.  W.  Birds  22:85-91. 
Bull,  E.  L  and  E.  C.  Meslow.  1977.  Habitat  requirements  of 

the  Pileated  Woodpecker  in  northeastern  Oregon.  J.  For. 

75:335-337. 
Bull,  E.  L,  A.  L  Wright,  and  M.  G.  Henjum.  1989.  Nesting 

and  diet  of  Long-eared  Owls  in  conifer  forests,  Oregon. 

Condor  91:908-912. 
Bunni,  M.  K.  1959.  The  Killdeer,  Charadrius  v.  vociferus  L, 

in  the  breeding  season:  Ecology,  behavior,  and  the  devel- 
opment of  homoiothermism.  Ph.D.  thesis,  Univ.  Mich., 

Ann  Arbor. 
Burcham,  J.  S.  1904.  Notes  on  the  habits  of  the  Water  Ouzel 

fCindus  mexicanus).  Condor  6:50. 
Burnell,  K.  L  and  D.  F.  Tomback.  1985.  Steller's  Jays  steal 

Gray  Jay  caches:  Field  and  laboratory  observations.  Auk 

102:417-419. 


448 


LITERATURE  CITED 


Busby,  D.  G.  and  S.  G.  Sealy.  1979.  Feeding  ecology  of  a 
population  of  nesting  Yellow  Warblers.  Can.  J.  Zool. 
57:1670-1681. 

Buss,  I.  C  1942.  A  managed  Cliff  Swallow  colony  in  south- 
ern Wisconsin.  Wilson  Bull.  54:153-161. 

Buder,  R.  W.  1981.  Nesting  of  Brewer's  Blackbirds  on 
man-made  structures  and  natural  sites  in  British  Colum- 
bia. Can.  Field-Nat.  95:476-477. 

Butts,  W.  K.  1931.  A  study  of  the  chickadee  and  White- 
breasted  Nuthatch  by  means  of  marked  individuals.  Part 
III.  The  White-breasted  Nuthatch  (Sitta  carolinensis  cookei). 
Bird-Banding  2:59-76. 

Byrd,  G.  V.  and  C.  F.  Zeillemaker.  1981.  Ecology  of  nesting 
Hawaiian  Common  Gallinules  at  Hanalei,  Hawaii. 
W.  Birds  12:105-116. 


Cade,  T.  J.,  J.  H.  Enderson,  C.  G.  Thelander,  and  C.  M. 
White,  eds.  1988.  Commentary— The  role  of  organochlo- 
rine  pesticides  in  Peregrine  Falcon  population  changes.  In 
Cade  et.  al.,  eds.  Peregrine  Falcon  Populations:  Their  Man- 
agement and  Recovery,  463-468.  The  Peregrine  Fund, 
Boise,  Idaho. 

Cadman,  M.  D.,  P.  F.  J.  Eagles,  and  F.  M.  Helleiner.  1987. 
Atlas  of  the  Breeding  Birds  of  Ontario.  Federation  of  Ontario 
Naturalists  and  the  Long  Point  Bird  Obs.  Univ.  Waterloo 
Press,  Waterloo. 

Caldwell,  L  D.  1967.  Attack  behavior  of  a  Loggerhead 
Shrike.  Wilson  Bull.  79:116-117. 

California  Department  Fish  and  Game.  1991a.  1990  annual 
report  on  the  status  of  California's  state  listed  Threatened 
and  Endangered  plants  and  animals.  Sacramento. 

.  1991b  (January).  Bird  and  mammal  Species  of  Special 

Concern.  Sacramento. 

California  Department  Water  Resources.  1978.  Wind  in 
California.  Bulletin  185. 

.  1980.  California  rainfall  summary  monthly  total  precip- 
itation, 1849-1979.  Sacramento. 

Carnie,  S.  K.  1954.  Food  habits  of  nesting  Golden  Eagles  in 
the  Coast  Ranges  of  California.  Condor  56:3-12. 

Carriger,  H.  W.  and  J.  R.  Pemberton.  1907.  Nesting  of  the 
Pine  Siskin  in  California.  Condor  9:18-19. 

Carriger,  H.  W.  and  G.  Wells.  1919.  Nesting  of  the  northern 
Pileated  Woodpecker.  Condor  21:153-156. 

Carter,  H.  R.  and  R.  A.  Erickson.  1988.  Population  status 
and  conservation  problems  of  die  Marbled  Murrelet  in 
California,  1897-1987.  Final  Rept.  to  Calif.  Dept.  Fish 
Game,  contract  FG7569(FY  1987-88),  Sacramento. 

Carter,  H.  R.  and  K.  A.  Hobson.  1988.  Creching  behavior  of 
Brandt's  Cormorant  chicks.  Condor  90:395-400. 

Carter,  H.  R.,  K.  A.  Hobson,  and  S.  G.  Sealy.  1984.  Colony- 
site  selection  by  Pelagic  Cormorants  (Phalacrocorax  pela- 
gicus)  in  Barkley  Sound,  British  Columbia.  Colonial 
Waterbirds  7:25-34. 

Carter,  H.  R.,  D.  L  Jaques,  G.  J.  McChesney,  C.  S.  Strong, 
M.  W.  Parker,  and  J.  C.  Takekawa.  1990.  Breeding  popu- 
lations of  seabirds  on  the  northern  and  central  California 


coasts  in  1989  and  1990.  Draft  Final  Rept.  U.S.  Fish 
Wildl.  Serv.,  Dixon,  Calif. 

Carter,  H.  R.,  G.  J.  McChesney,  D.  L.  Jaques,  C.  S.  Strong, 
M.  W.  Parker,  J.  E.  Takekawa,  D.  L  Jory,  and  D.  L 
Whitworth.  1992.  Breeding  populations  of  seabirds  in 
California,  1989-1991.  Unpubl.  Rept.,  U.S.  Fish  Wildl. 
Serv.,  Northern  Prairie  Wildl.  Res.  Ctr,  Dixon,  Calif. 

Case,  N.  A.  and  O.  H.  Hewitt.  1963.  Nesting  and  productiv- 
ity of  the  Red-winged  Blackbird  in  relation  to  habitat 
Living  Bird  2:7-20. 

Cading,  P.  M.  1971.  Spring  migration  of  Saw-whet  Owls  at 
Toronto,  Ontario.  Bird-Banding  42:1 10-114. 

Chamberlin,  C  1901.  Some  architectural  traits  of  the  West- 
ern Gnatcatcher.  Condor  3:33-36. 

Chambers,  W.  L  1903.  Early  nesting  of  Calypte  anna  in  the 
vicinity  of  Santa  Monica,  California.  Condor  5:133. 

.  1912.  Who  will  save  the  Band-tailed  Pigeon?  Condor 

14:108. 

Chan,  G.  L.  1979.  Reconnaissance  survey  of  the  Double 
Point  Area  of  Special  Biological  Significance.  Draft  #2. 
Rept.  to  Calif.  Dept.  Fish  Game  and  State  Water 
Resources  Control  Board. 

Chapin,  E.  A.  1925.  Food  habits  of  the  vireos:  A  family  of 
insectivorous  birds.  U.S.  Dept.  Agri.  Bull.  1355:1-44- 

Chapman,  L.  B.  1935,  1939,  1955.  Studies  of  a  Tree  Swallow 
colony.  Bird-Banding  6:45-57;  10:61-72;  26:45-70. 

Chappell,  C.  B.  and  B.  J.  Ringer.  1983.  Status  of  the  Hermit 
Warbler  in  Washington.  W.  Birds  14:185-196. 

Childs,  H.  E.,  Jr.  1968.  Brown  Towhee  (various  races).  In 
O.  L  Austin,  Jr.,  ed.  A.  C.  Bent  et  al.'s  Life  histories  of 
North  American  cardinals,  grosbeaks,  buntings,  towhees, 
finches,  sparrows,  and  allies.  U.S.  Nad.  Mus.  Bull.  237 
(Part  2):  603-619. 

Church,  R.  L  1966.  Water  exchanges  in  California  vole 
(Microtus  calif omicus) .  Physio.  Zool.  39:326-340. 

Clark,  K.  L  and  R.  J.  Robertson.  1981.  Cowbird  parasitism 
and  evolution  of  anti-parasitic  strategies  in  the  Yellow 
Warbler.  Wilson  Bull.  93:249-258. 

Clark,  R.  J.  1975.  A  field  study  of  the  Short-eared  Owl,  Asio 
flammeus  (Pontoppidan),  in  North  America.  Wildl. 
Monogr.  47. 

Cogswell,  H.  L  1977.  Waterbirds  of  California.  Univ.  Califor- 
nia Press,  Berkeley. 

Collins,  C.  T.  1979.  The  ecology  and  conservation  of  Bur- 
rowing Owls.  In  P.  P.  Schaeffer  and  S.  M.  Ehler,  eds.  Proc. 
Nad.  Audubon  Society's  Symp.  on  Owls  of  the  West: 
Their  ecology  and  conservation,  6-17.  Western  Education 
Center,  Tiburon,  Calif. 

Collins,  C.  T.  and  E.  V.  Johnson.  1982.  Further  records  of 
White-throated  Swifts  utilizing  manmade  structures. 
W.  Birds  13:25-28. 

Collins,  C.  T.  and  R.  E.  Landry.  1977.  Artificial  nest  burrows 
for  Burrowing  Owls.  N.  Am.  Bird  Bander  2:151-154- 

Collins,  J.  N.  and  V.  H.  Resh.  1985.  Utilization  of  natural 
and  man-made  habitats  by  die  salt  marsh  Song  Sparrow, 
Melospiza  melodia  samuelis  (Baird).  Calif.  Fish  Game  71: 
40-52. 


449 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Collins,  S.  C.  1981.  A  comparison  of  nest-site  and  perch-site 
vegetation  structure  for  seven  species  of  warblers.  Wilson 
Bull.  93:542-547. 

Colvin,  B.  A.  and  S.  R.  Spaulding.  1983.  Winter  foraging 
behavior  of  Short-eared  Owls  (Asio  flammeus)  in  Ohio. 
Am.  Midi.  Nat.  110:124-128. 

Combellack,  C.  R  B.  1954-  A  nesting  of  Violet-green  Swal- 
lows. Auk  71:435-442. 

Confer,  J.  L  and  P.  Paicos.  1985.  Downy  Woodpecker 
predation  at  goldenrod  galls.  J.  Field  Ornithol.  56:56-64. 

Connelly,  D.  P.  and  D.  L  Chesemore.  1980.  Food  habits  of 
Pintails,  Anas  acuta,  wintering  on  seasonally  flooded  wet- 
lands in  the  northern  San  Joaquin  Valley,  California. 
Calif.  Fish  Game  66:233-237. 

Connelly,  J.,  Jr.  1978.  Trends  in  Blue-winged  and  Cinnamon 
teal  populations  in  eastern  Washington.  Murrelet  59:2-6. 

Connelly,  J.  W.  and  I.  J.  Ball.  1984.  Comparisons  of  aspects 
of  breeding  Blue-winged  and  Cinnamon  teal  in  eastern 
Washington.  Wilson  Bull.  96:626-633. 

Conner,  R.  N.  1975.  Orientation  of  entrances  to  woodpecker 
nest  cavities.  Auk  92:371-374. 

.  1977.  The  effect  of  tree  hardness  on  woodpecker  nest 

entrance  orientation.  Auk  94:369-370. 

1981.  Seasonal  changes  in  woodpecker  foraging  pat- 


terns. Auk  98:562-570. 
Conner,  R.  N.,  R  G.  Hooper,  H.  S.  Crawford,  and  H.  S. 

Mosby.   1975.  Woodpecker  nesting  habitat  in  cut  and 

uncut  woodlands  in  Virginia.  J.  Wildl.  Mgmt.  39:144- 

150. 
Cornwell,  G.  W.  1963.  Observations  on  the  breeding  biology 

and  behavior  of  a  nesting  population  of  Belted  Kingfishers. 

Condor  65:426-431. 
Coulombe,  H.  N.  1971.  Behavior  and  population  ecology  of 

the  Burrowing  Owl,  Speotyto  cunicularia,  in  the  Imperial 

Valley  of  California.  Condor  73:162-176. 
Coulter,  M.  C.  1973.  Breeding  biology  of  the  Western  Gull, 

Larus  occidentalis.  M.S.  thesis,  Oxford  Univ. 
Coulter,  M.  C  and  R.  W.  Risebrough.  1973.  Shell-thinning 

in  eggs  of  the  Ashy  Petrel  (Oceanodroma  homochroa)  from 

the  Farallon  Islands.  Condor  75:254-255. 
Coudee,  E.  L  1967.  Agonistic  behavior  in  the  American 

Goldfinch.  Wilson  Bull.  79:89-109. 
.  1968a.  Comparative  breeding  behavior  of  Lesser  and 

Lawrence's  goldfinches.  Condor  70:228-242. 
.  1968b.  Maintenance  behavior  of  Lesser  and  Lawrence's 


goldfinches.  Condor  70:378-384. 

Cowan,  J.  B.  1952.  Life  history  and  productivity  of  a  popula- 
tion of  Mourning  Doves  in  California.  Calif.  Fish  Game 
38:505-521. 

Craig,  R  B.  1978.  An  analysis  of  the  predatory  behavior  of 
the  Loggerhead  Shrike.  Auk  95:221-234. 

Craig,  T.  H.  and  C.  H.  Trost.  1979.  The  biology  and  nesting 
density  of  breeding  American  Kestrels  and  Long-eared 
Owls  on  the  Big  Lost  River,  southeastern  Idaho.  Wilson 
Bull.  91:50-61. 

Cramp,  S.,  ed.  1985.  Handbook  of  the  Birds  of  Europe,  the 
Middle  East,  and  North  Africa:  The  Birds  of  tke  Western 


Palearctic.  Vol.  IV:  Terns  to  Woodpeckers.  Oxford  Univ. 
Press,  New  York. 

Crase,  F.  T.  1976.  Occurrence  of  the  Chestnut-backed  Chick- 
adee in  the  Sierra  Nevada  Mountains,  California.  Am. 
Birds  30:673-675. 

Crase,  F.  T.  and  R.  W.  DeHaven.  1977.  Food  of  nesding 
Tricolored  Blackbirds.  Condor  79:265-269. 

.  1978.  Food  selection  by  five  sympatric  California  black- 
bird species.  Calif.  Fish  Game  64:255-267. 

Crockett,  A.  B.  and  H.  H.  Hadow.  1975.  Nest  site  selection 
by  Williamson  and  Red-naped  sapsuckers.  Condor 
77:365-368. 

Croll,  D.  A.  1990.  Physical  and  biological  determinants  of  the 
abundance,  distribution,  and  diet  of  the  Common  Murre 
in  Monterey  Bay,  California.  In  S.  G.  Sealy,  ed.  Auks  at 
sea,  139-148.  Studies  Avian  Biol.  14. 

Cunningham,  J.  D.  1955.  Notes  on  food  habits  of  the 
White-tailed  Kite  in  southern  California.  Condor  57:371. 

Custer,  T.  W.,  G.  L  Hensler,  and  T.  E.  Kaiser.  1983.  Clutch 
size,  reproductive  success,  and  organochlorine  contami- 
nants in  Adantic  coast  Black-crowned  Night-Herons.  Auk 
100:699-710. 

D 

Dahlsten,  D.  L,  M.  L  Morrison,  D.  L  Rowney,  and  M.  Wil- 
son. 1985.  Bird  diets  and  prey  availability  in  the  western 
Sierra  Nevada,  California.  Calif.  Fish  Game  71:172-178. 

Dale,  F.  H.  1936.  Eagle  "control"  in  northern  California. 
Condor  38:208-210. 

Darley,  J.  A.  1971.  Sex  ratio  and  mortality  in  the  Brown- 
headed  Cowbird.  Auk  88:560-566. 

Davis,  C.  M.  1978.  A  nesting  study  of  the  Brown  Creeper. 
Living  Bird  17:237-263. 

Davis,  E.  M.  1937.  Observations  on  nesting  Barn  Swallows. 
Bird-Banding  8:66-73. 

Davis,  J.  1951.  Distribution  and  variation  of  the  Brown 
Towhee.  Univ.  Calif.  Publ.  Zool.  52:1-120. 

.  1957.  Comparative  foraging  behavior  of  the  Spotted 

and  Brown  towhees.  Auk  74:129-166. 

.  1960.  Nesting  behavior  of  the  Rufous-sided  Towhee  in 

coastal  California.  Condor  62:434-456. 

Davis,  J.,  G.  R.  Fisler,  and  B.  S.  Davis.  1963.  The  breeding 
biology  of  the  Western  Flycatcher.  Condor  65:337-382. 

Davis,  W.  B.  1933.  The  span  of  the  nesting  season  of  birds 
in  Butte  County,  California,  in  relation  to  their  food. 
Condor  35:151-154. 

Dawson,  W.  L  1923.  The  Birds  of  California.  South  Moulton, 
San  Diego. 

Dawson,  W.  R.,  J.  D.  Ligon,  J.  R.  Murphy,  J.  P.  Myers,  E. 
Simberloff,  and  J.  Verner.  1987.  Report  of  the  Scientific 
Advisory  Panel  on  the  Spotted  Owl.  Condor  89:205-229. 

DeHaven,  R.  W.  1973.  Winter  population  trends  of  the 
Starling  in  California.  Am.  Birds  27:836-837. 

DeHaven,  R  W.,  F.  T.  Crase,  and  P.  P.  Woronecki.  1975a. 
Breeding  status  of  the  Tricolored  Blackbird  1969-1972. 
Calif.  Fish  Game  61:166-180. 


450 


LITERATURE  CITED 


.  1975b.  Movements  of  Tricolored  Blackbirds  banded  in 

the  Central  Valley  of  California  1965-1972.  Bird-Banding 
46:220-229. 

Demaree,  S.  R.  1975.  Observations  on  roof-nesting  Killdeers. 
Condor  77:487-488. 

Dement'ev,  G.  P.  and  N.  A.  Gladkov,  eds.  1951-1954.  Birds 
of  the  Soviet  Union.  6  Vols.  Sovetskaya  Nauka,  Moskow. 

DeSante,  D.  F.  and  D.  G.  Ainley.  1980.  The  avifauna  of  the 
South  Farallon  Islands,  California.  Studies  Avian  Biol.  4- 

DeSante,  D.  F.  and  L  F.  Baptista.  1989.  Factors  affecting  the 
termination  of  breeding  in  Nuttall's  White-crowned  Spar- 
rows. Wilson  Bull.  101:120-124. 

DeSante,  D.  F.  and  G.  R.  Geupel.  1987.  Landbird  productiv- 
ity in  central  coastal  California:  The  relationship  to  annual 
rainfall,  and  a  reproductive  failure  in  1986.  Condor  89: 
636-653. 

DeSante,  D.  F.  and  P.  Pyle.  1986.  Distributional  Checklist  of 
North  American  Birds.  Vol.  I:  United  States  and  Canada. 
Artemisia  Press,  Lee  Vining,  Calif. 

DeSante,  D.  F.  and  E.  Scriven.  1977.  Sexual  size  dimorphism 
in  the  Osprey— a  new  hypothesis.  Abstract,  1977  Annual 
Meeting  Northwestern  Bird  and  Mamm.  Assoc. 

Detrich,  P.  J.  1986.  The  status  and  distribution  of  the  Bald 
Eagle  in  California.  M.S.  thesis,  Calif.  State  Univ.,  Chico. 

DeWolfe,  B.  B.  1968.  Nuttall's  White-crowned  Sparrow.  In 
O.  L.  Austin,  Jr.,  ed.  A.  C  Bent  et  al.'s  Life  histories  of 
North  American  cardinals,  grosbeaks,  buntings,  towhees, 
finches,  sparrows,  and  allies.  U.S.  Nad.  Mus.  Bull.  237 
(Part  3):  1292-1324. 

Diamond,  J.  M.  1969.  Avifaunal  equilibria  and  species  turn- 
over rates  on  the  Channel  Islands  of  California.  Proc.  Nad. 
Acad.  Sci.  64:57-73. 

Dick,  J.  A.  and  J.  D.  Rising.  1965.  A  comparison  of  foods 
eaten  by  Eastern  Kingbirds  and  Western  Kingbirds  in 
Kansas.  Kans.  Ornithol.  Soc.  Bull.  16:23-24. 

Dickerman,  R.  W.  1987.  The  "old  northeastern"  subspecies 
of  Red  Crossbill.  Am.  Birds  41:189-194. 

Dilger,  W.  C  1956.  Adaptive  modifications  and  ecological 
isolating  mechanisms  in  the  thrush  genera  Catrmrus  and 
Hylocichla.  Wilson  Bull.  68:177-199. 

Dingle,  E.  v.  S.  1942.  Rough-winged  Swallow.  In  A.  C.  Bent, 
ed.  Life  histories  of  North  American  flycatchers,  larks, 
swallows,  and  their  allies.  U.S.  Nad.  Mus.  Bull.  179: 
424-433. 

Dixon,  J.  1924-  Nesting  of  the  Wood  Duck  in  California. 
Condor  26:41-66. 

Dixon,  J.  B.  1937.  The  Golden  Eagle  in  San  Diego  County, 
California.  Condor  39:49-56. 

Dixon,  J.  B.,  R.  E.  Dixon,  and  J.  E.  Dixon.  1957.  Natural 
history  of  the  White-tailed  Kite  in  San  Diego  County, 
California.  Condor  59:156-165. 

Dixon,  K.  L  1949.  Behavior  of  the  Plain  Titmouse.  Condor 
51:110-136. 

.   1954.  Some  ecological  relations  of  chickadees  and 

titmice  in  central  California.  Condor  56:1 1 3-1 24- 

.   1960.  Additional  data  on  the  establishment  of  the 

Chestnut-backed  Chickadee  at  Berkeley,  California.  Con- 
dor 62:405-408. 


Dobkin,  D.  S.,  J.  A.  Holmes,  and  B.  A.  Wilcox.  1986. 
Traditional  nest  site  use  by  White-throated  Swifts.  Condor 
88:252-253. 

Drobney,  R.  D.  1980.  Reproductive  bioenergetics  of  Wood 
Ducks.  Auk  97:480-490. 

.   1982.   Body  weight  and   composition  changes  and 

adaptations  for  breeding  in  Wood  Ducks.  Condor  84: 
300-305. 

Drobney,  R.  D.  and  L  H.  Fredrickson.  1979.  Food  selection 
by  Wood  Ducks  in  relation  to  breeding  status.  J.  Wildl. 
Mgmt.  43:109-120. 

Drum,  M.  1939.  Territorial  studies  on  the  eastern  goldfinch. 
Wilson  Bull.  51:69-77. 

DuBois,  A.  D.  1935.  Nests  of  Horned  Larks  and  longspurs 
on  a  Montana  prairie.  Condor  37:56-72. 

Dubowy,  P.  J.  1985.  Feeding  ecology  and  behavior  of  post- 
breeding  male  Northern  Shovelers  and  Blue-winged  Teal. 
Can.J.Zool.  63:1292-1297. 

Duebbert,  H.  F.  1966.  Island  nesting  of  the  Gadwall  in  North 
Dakota.  Wilson  Bull.  78:12-25. 

Dufty,  A.  M.,  Jr.  1982.  Movements  and  activities  of  radio- 
tracked  Brown-headed  Cowbirds.  Auk  99:316-327. 

Duncan,  D.  C.  1987.  Nest-site  distribution  and  overland 
brood  movements  of  Northern  Pintails  in  Alberta. 
J.  Wildl.  Mgmt.  51:716-723. 

Dunne,  P.,  D.  Sibley,  and  C.  Sutton.  1988.  Hawks  in  Flight. 
Houghton  Mifflin,  Boston. 

Dunnet,  G.  M.  1955.  The  breeding  of  the  Starling  Stumus 
vulgaris  in  relation  to  its  food  supply.  Ibis  97:619-662. 

Dwyer,  T.  J.  1974.  Social  behavior  of  breeding  Gadwalls  in 
North  Dakota.  Auk  91:375-386. 

Dwyer,  T.  J.,  G.  L  Krapu,  and  D.  M.  Janke.  1979.  Use  of 
prairie  pothole  habitat  by  breeding  Mallards.  J.  Wildl. 
Mgmt.  43:526-531. 

Dyer,  M.  I.,  J.  Pinowski,  and  B.  Pinowska.  1977.  Population 
dynamics.  In  J.  Pinowski  and  S.  C.  Kendeigh,  eds.  Graniv- 
orous  Birds  in  Ecosystems:  TheiT  Evolution,  Populations,  Ener- 
getics, Impact,  and  Control,  53-105.  Int.  Biol.  Progr.  12. 
Cambridge  Univ.  Press,  London. 

Dzubin,  A.  1969.  Comments  on  carrying  capacity  of  small 
ponds  for  ducks  and  possible  effects  on  Mallard  produc- 
tion. Saskatoon  Wedands  Seminar,  138-160.  Can.  Wildl. 
Serv.  Rept.  Ser.  6. 

Dzubin,  A.  and  J.  B.  Gollop.  1972.  Aspects  of  Mallard 
breeding  ecology  in  Canadian  parkland  and  grassland.  In 
Population  ecology  of  migratory  birds:  A  symposium,  113- 
152.  U.S.  Fish  Wildl.  Serv.  Res.  Rept.  2. 


Eadie,  J.  McA,  T.  D.  Nudds,  and  C.  D.  Ankney.  1979. 

Quantifying  interspecific  variation  in  foraging  behavior  in 

syntopic  Anas  (Anatidae).  Can.  J.  Zool.  57:412-415. 
Earhart,  C  M.  and  N.  K.  Johnson.  1970.  Size  dimorphism 

and  food  habits  of  North  American  owls.  Condor  72: 

251-264. 


451 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Eckhardt,  R  C.  1979.  The  adaptive  syndromes  of  two  guilds 
of  insectivorous  birds  in  the  Colorado  Rocky  Mountains. 
Ecol.  Monogr.  49:129-149. 

Edminster,  F.  C.  1954.  American  Game  Bird's  of  Field  and 
Forest:  TheiT  Habits,  Ecology,  and  Management.  Charles 
Scribner,  New  York. 

Edson,  J.  M.  1943.  A  study  of  the  Violet-green  Swallow.  Auk 
60:396-403. 

Ehrlich,  P.  R,  D.  S.  Dobkin,  and  D.  Wheye.  1988.  TKe 
Birder's  Handbook:  A  Field  Guide  to  the  Natural  History  of 
North  American  Birds.  Simon  6k  Schuster,  New  York. 

Ehrlich,  P.  R.  and  A.  H.  Ehrlich.  1990.  The  Population 
Explosion.  Simon  6k  Schuster,  New  York. 

Eipper,  A.  W.  1956.  Differences  in  vulnerability  of  the  prey 
of  nesting  kingfishers.  J.  Wildl.  Mgmt.  20:177-183. 

Eisenmann,  E.  1971.  Range  expansion  and  population 
increase  in  North  and  Middle  America  of  the  White-tailed 
Kite  (Elanus  leucurus).  Am.  Birds  25:529-536. 

Elizroth,  E.  K.  1983.  Breeding  biology  and  mortality  of 
Western  Bluebirds  near  Corvallis,  Oregon.  Sialia  5:83-87. 

Elliott,  H.  W.,  Ill  and  J.  D.  Wehausen.  1974.  Vegetational 
succession  on  coastal  rangeland  of  Point  Reyes  peninsula. 
Madrono  22:231-238. 

Ellison,  W.  G.  1985.  Indigo  Bunting.  In  S.  B.  Laughlin  and 
D.  P.  Kibbe,  eds.  The  Atlas  of  Breeding  Birds  of  Vermont, 
334-335.  Univ.  Press  of  New  England,  Hanover,  N.H. 

Emerson,  W.  O.  1904.  Icterus  bullocki  as  a  Honey-eater. 
Condor  6:78. 

Emlen,  J.  T.,  Jr.  1942.  Notes  on  a  nesting  colony  of  Western 
Crows.  Bird-Banding  13:143-153. 

.  1952.  Social  behavior  in  nesting  Cliff  Swallows.  Con- 
dor 54:177-199. 

.  1954-  Territory,  nest  building,  and  pair  formation  in 

the  Cliff  Swallow.  Auk  71:16-35. 

Emlen,  J.  T.,  Jr.  and  B.  Glading.  1945.  Increasing  Valley 
Quail  in  California.  Calif.  Agri.  Exp.  Sta.  Bull.  695. 

Emlen,  S.  T,  J.  D.  Rising,  and  W.  L  Thompson.  1975. 
A  behavioral  and  morphological  study  of  sympatry  in  the 
Indigo  and  Lazuli  buntings  of  the  Great  Plains.  Wilson 
Bull.  87:145-179. 

Engels,  W.  L  1940.  Structural  adaptations  in  the  thrashers 
(Mimidae:  genus  Toxostoma)  with  comments  on  interspe- 
cific relationships.  Univ.  Calif.  Publ.  Zool.  42:341-400. 

Erickson,  M.  M.  1937.  A  jay  shoot  in  California.  Condor 
39:111-115. 

.  1938.  Territory,  annual  cycle,  and  numbers  in  a  popu- 
lation of  Wren-tits  (Chamaea  fasciata).  Univ.  Calif.  Publ. 
Zool.  42:247-334. 

.  1968.  Lazuli  Bunting.  In  O.  L  Austin,  Jr.,  ed.  A.  C. 

Bent  et  al.'s  Life  histories  of  North  American  cardinals, 
grosbeaks,  buntings,  towhees,  finches,  sparrows,  and 
allies.  U.S.  Nad.  Mus.  Bull.  237  (Part  1):  111-132. 

Emngton,  P.  L  and  W.  J.  Breckenridge.  1936.  Food  habits 
of  Marsh  Hawks  in  the  glaciated  prairie  region  of  north- 
central  United  States.  Am.  Midi.  Nat.  7:831-848. 


Errington,  P.  L,  F.  Hamerstrom,  and  F.  N.  Hamerstrom,  Jr. 

1940.  The  Great  Horned  Owl  and  its  prey  in  north-central 

United  States.  Iowa  State  Coll.  Agri.  Res.  Bull.  277. 
Erskine,  A.  J.  1 984.  Swallows  foraging  on  the  ground.  Wilson 

Bull.  96:136-137. 
Esterly,  C.  O.  1917.  How  does  the  shrike  carry  its  prey? 

Condor  19:25. 
Euliss,  N.  H.,  Jr.  and  S.  W.  Harris.  1987.  Feeding  ecology  of 

Northern  Pintails  and  Green-winged  Teal  wintering  in 

California.  J.  Wildl.  Mgmt  51:724-732. 
Evans,  D.  L  1982.  Status  reports  on  twelve  raptors.  U.S.  Fish 

Wildl.  Serv.  Spec.  Sci.  Rept.  Wildl.  238. 
Evans,  F.  C.  1964.  The  food  of  Vesper,  Field,  and  Chipping 

sparrows  nesting  in  an  abandoned  field  in  southeast  Mich- 
igan. Am.  Midi.  Nat  72:57-75. 
Evenden,  F.  G.,  Jr.  1957.  Observations  on  nesting  behavior 

of  the  House  Finch.  Condor  59:112-117. 
Evens,  J.  G.  1985.  Monitoring  the  Osprey  colony  at  Kent 

Lake,  Marin  County  California:  Five  year  summary,  1981  - 

1985.  Rept.  to  Marin  Municipal  Water  District.  PRBO 
Contrib.  331 . 

.  1987.  Reproductive  success  of  Osprey  at  Kent  Lake, 

California,  1987.  Rept.  to  Marin  Municipal  Water  Dis- 
trict. PRBO  Contrib.  381. 

.  1 989.  Reproductive  success  of  Osprey  at  Kent  Lake  with 

notes  on  an  incipient  population  at  Tomales  Bay,  Califor- 
nia, 1989.  Rept.  to  Marin  Municipal  Water  District  PRBO 
Contrib.  481. 

.  1991.  Reproductive  success  of  the  Osprey  population 

in  Marin  County,  California,  1981-1990:  A  decade  of 
growth.  Rept.  to  Marin  Municipal  Water  District  PRBO 
ContTib.  504. 

.    in   press.   Growth   and   reproductive   success  of  the 

Osprey  population  in  western  Marin  County,  California, 
1981-1990.  W.  Birds. 

Evens,  J.  G  and  G.  W.  Page.  1983.  The  ecology  of  rail 
populations  at  Corte  Madera  Ecological  Reserve:  With 
recommendations  for  management.  PRBO  Contrib.  255. 

.  1984-  California  Clapper  Rail  (Rallus  longirostris  obso- 

letus).  Endangered  Species  Info.  System,  U.S.  Fish  Wildl. 
Serv. 

.  1986.  Predation  on  Black  Rails  during  high  tides  in  salt 

marshes.  Condor  88:107-109. 

Evens,  J.  G,  G.  W.  Page,  S.  A.  Laymon,  and  R.  W.  Stallcup. 
1991.  Distribution,  relative  abundance,  and  status  of  the 
California  Black  Rail  in  western  North  America.  Condor 
93:952-966. 

Evens,  J.  G,  G.  W.  Page,  L  E.  Stenzel,  R.  W.  Stallcup,  and 
R.  P.  Henderson.  1989.  Distribution  and  relative  abun- 
dance of  the  California  Black  Rail  fLaterallus  jamaicensis 
coturniculus)  in  tidal  marshes  of  the  San  Francisco  Bay 
estuary.  Rept.  to  Calif.  Dept  Fish  Game,  Sacramento. 

Evens,  J.  G,  G.  W.  Page,  L  E.  Stenzel,  and  N.  D.  Warnock. 

1986.  Distribution,  abundance,  and  habitat  of  California 
Black  Rails  in  tidal  marshes  of  Marin  and  Sonoma  coun- 
ties, California.  Point  Reyes  Bird  Obs.  Sci.  Rept 

Evermann,  B.  W.  1919.  A  colony  of  Tricolored  Blackbirds. 
Gull  1:2-3. 


452 


LITERATURE  CITED 


Faber,  R.  A.,  R.  W.  Risebrough,  and  H.  M.  Pratt.  1972. 
Organochlorines  and  mercury  in  Common  Egrets  and 
Great  Blue  Herons.  Envir.  Pollution  3:1 1 1  -122. 

Fairley,  L  1987.  Mount  Tamalpais:  A  History.  Scottwall  Asso- 
ciates, San  Francisco. 

Feare,  C.  1984.  The  Starling.  Oxford  Univ.  Press,  New  York. 

Ferguson-Lees,  J.  1 976.  Foreword.  In  J.  T.  R.  Sharrock,  comp. 
1976.  The  Atlas  of  Breeding  Birds  in  Britain  and  Ireland, 
9-11.  British  Trust  for  Ornithology,  Tring,  England. 

Ferrel,  C.  M.,  H.  Twining,  and  N.  B.  Herkenbaum.  1949. 
Food  habits  of  the  Ring-necked  Pheasant  (Phasianus  colchi- 
cus)  in  the  Sacramento  Valley,  California.  Calif.  Fish 
Game  35:51-69. 

Findholt,  S.  L  1984.  Organochlorine  residues,  eggshell  thick- 
ness, and  reproductive  success  of  Snowy  Egrets  nesting  in 
Idaho.  Condor  86:163-169. 

Finlay,  J.  C  1971.  Breeding  biology  of  Purple  Martins  at  the 
northern  limit  of  their  range.  Wilson  Bull.  83:254-269. 

.  1975.  Nesting  of  Purple  Martins  in  natural  cavities  and 

in  man-made  structures  in  Alberta.  Can.  Field-Nat.  89: 
454-455. 

Fisher,  W.  K.  1902.  The  redwood  belt  of  northwestern 
California.  I.  Faunal  peculiarities  of  the  region.  II.  Land 
birds.  Condor  4:111-114,  131-135. 

Fitch,  H.  S.  1947.  Predation  by  owls  in  the  Sierran  foothills 
of  California.  Condor  49:137-151. 

Fitch,  H.  S.,  B.  Glading,  and  V.  House.  1946.  Observations 
on  Cooper  Hawk  nesting  and  predation.  Calif.  Fish  Game 
32:144-154. 

Fitch,  H.  S.,  F.  Swenson,  and  D.  F.  Tillotson.  1946.  Behavior 
and  food  habits  of  the  Red-tailed  Hawk.  Condor  48: 
205-237. 

Heischer,  R.  C.  1985.  A  new  technique  to  identify  and  assess 
the  dispersion  of  eggs  of  individual  brood  parasites.  Behav. 
Ecol.  Sociobiol.  17:91-99. 

Heischer,  R.  C.  and  S.  I.  Rothstein.  1988.  Known  secondary 
contact  and  rapid  gene  flow  among  subspecies  and  dialects 
in  the  Brown-headed  Cowbird.  Evolution  42:1146-1158. 

Heischer,  R  C,  S.  I.  Rothstein,  and  L  S.  Miller.  1991. 
Mitochondrial  DNA  variation  indicates  gene  flow  across  a 
zone  of  known  secondary  contact  between  two  subspecies 
of  the  Brown-headed  Cowbird.  Condor  93:185-189. 

Heischer,  R.  C,  A.  P.  Smyth,  and  S.  I.  Rothstein.  1987. 
Temporal  and  age-related  variation  in  the  laying  rate  of  the 
parasitic  Brown-headed  Cowbird  in  the  eastern  Sierra 
Nevada,  California.  Can.  J.  Zool.  65:2724-2730. 

Follett,  W.  I.  and  D.  G.  Ainley.  1976.  Fishes  collected  by 
Pigeon  Guillemots,  Cepphus  columba  (Pallas),  nesting  on 
Southeast  Farallon  Island,  California.  Calif.  Fish  Game 
62:28-31. 

Forbes,  J.  A.  and  D.  W.  Warner.  1974.  Behavior  of  a 
radio-tagged  Saw-whet  Owl.  Auk  91 :783-795. 

Ford,  E.  R.  1936.  Unusual  nest  site  of  the  Loggerhead  Shrike 
(Lanius  ludovicianus  ludovicianus).  Auk  53:219. 


Forsman,  E.  D.,  E.  C.  Meslow,  and  H.  M.  Wight.  1984. 

Distribution  and  biology  of  the  Spotted  Owl  in  Oregon. 

Wildl.Monogr.  87:1-64. 
Foster,  M.  L  1 977.  A  breeding  season  study  of  the  Salt  Marsh 

Yellowthroat  (Geothlypis  trichas  sinuosa)  of  the  San  Fran- 
cisco Bay  Area,  California.  M.A.  thesis,  San  Jose  State 

Univ. 
Foster,  W.  L.  and  J.  Tate,  Jr.  1966.  Activities  and  coactions 

of  animals  at  sapsucker  trees.  Living  Bird  5:87-113. 
Frakes,  R.  A.  and  R.  E.  Johnson.  1982.  Niche  convergence 

in  Empidonax  flycatchers.  Condor  84:286-291. 
Francis,  W.  J.  1968.  Temperature  and  humidity  conditions 

in  potential  pheasant  nesting  habitat.  J.  Wildl.  Mgmt 

32:36-46. 
Franzreb,   K.   E.   1983a.  A  comparison  of  avian  foraging 

behavior  in  unlogged  and  logged  mixed-coniferous  forest 

Wilson  Bull.  95:60-76. 
.  1 983b.  Intersexual  habitat  partitioning  in  Yellow-rump- 

ed  Warblers  during  the  breeding  season.  Wilson  Bull. 

95:581-590. 
.  1984.  Foraging  habits  of  Ruby-crowned  and  Golden- 


crowned  kinglets  in  an  Arizona  montane  forest  Condor 
86:139-145. 
-.  1985.  Foraging  ecology  of  Brown  Creepers  in  a  mixed- 


coniferous  forest.  J.  Field  Ornithol.  56:9-16. 

Fredrickson,  L  H.  1970.  Breeding  biology  of  American 
Coots  in  Iowa.  Wilson  Bull.  82:445-457. 

.  1971.  Common  Gallinule  breeding  biology  and  devel- 
opment. Auk  88:914-919. 

Fredrickson,  L  H.,  J.  M.  Anderson,  F.  J.  Kozlik,  and  R.  A. 
Ryder.  1977.  American  Coot  (Fulica  americana).  In  G.  C 
Sanderson,  ed.  Management  of  migratory  shore  and  up- 
land game  birds  in  North  America,  123-147.  Int.  Assoc. 
Fish  Wildl.  Agencies  and  U.S.  Fish  Wildl.  Serv. 

Friedmann,  H.  1929.  The  Cowhirds:  A  Study  in  th«  Biology  of 
Social  Parasitism.  C.  C.  Thomas,  Springfield,  111. 

.  1963.  Host  relations  of  the  parasitic  cowbirds.  U.S. 

Nad.  Mus.  Bull.  233. 

Friedmann,  H.  and  L  F.  Kiff.  1985.  The  parasitic  cowbirds 
and  their  hosts.  Proc.  West.  Found.  Vert.  Zool.  2:227- 
304. 

Friedmann,  H.,  L  F.  Kiff,  and  S.  I.  Rothstein.  1977.  A  further 
contribution  to  knowledge  of  the  host  relations  of  the 
parasitic  cowbirds.  Smithson.  Contr.  Zool.  235. 

Fry,  D.  K.,  Jr.  1966.  Recovery  of  the  White-tailed  Kite.  Pac. 
Discovery  19:27-30. 

Fry,  M.  E.  1977.  Acorn  selection  by  Band-tailed  Pigeons. 
Calif.  Fish  Game  63:59-60. 

Frydendall,  M.  J.  1967.  Feeding  ecology  and  territorial  behav- 
ior of  the  Yellow  Warbler.  Ph.D.  thesis,  Utah  State  Univ., 
Logan. 

Furrer,  R.  K.  1975.  Breeding  success  and  nest  site  stereotypy 
in  a  population  of  Brewer's  Blackbirds  Euphagus  cyano- 
cephalus.  Oecologia  20:339-350. 


453 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Gaines,  D.  1974-  A  new  look  at  the  nesting  riparian  avifauna 

of  the  Sacramento  Valley,  California.  W.  Birds  5:61-80. 
.    1977.    Birds   of  the   Yosemite   Sierra:   A   Distributional 

Survey.  California  Syllabus,  Oakland.  * 
.  1988.  Birds  of  Yosemite  and  the  East  Slope.  Artemisia 

Press,  Lee  Vining,  Calif. 
Gaines,  D.  and  T.  Beedy.  1987  (revised).  Checklist  of  the 

birds  of  Yolo  County.  Davis  Audubon,  Davis,  Calif. 
Gaines,  D.  and  S.  A.  Laymon.  1984-  Decline,  status  and 

preservation  of  the  Yellow-billed  Cuckoo  in  California. 

W.  Birds  15:49-80. 
Galati,  B.  and  C.  B.  Galati.  1985.  Breeding  of  the  Golden- 
crowned  Kinglet  in  northern  Minnesota.  J.  Field  Ornithol. 

56:28-49. 
Garrett,  K.  and  J.  Dunn.  1981.  Birds  of  Southern  California: 

Status  and  Distribution.  Los  Angeles  Audubon,  Los  Ange- 
les. 
GarTett,  R.  L  and  D.  J.  Mitchell.  1973.  A  study  of  Prairie 

Falcon  populations  in  California.  Wildl.  Mgmt.  Branch 

Admin.  Rept.  73-2.  Calif.  Dept.  Fish  Game,  Sacramento. 
Garrison,  B.  A.,  J.  M.  Humphrey,  and  S.  A.  Laymon.  1987. 

Bank  Swallow  distribution  and  nesting  ecology  on  the 

Sacramento  River,  California.  W.  Birds  18:71-76. 
Gashwiler,  J.  S.  and  A.  L  Ward.  1968.  Oregon  Junco  foods 

in  coniferous  forests.  Murrelet  49:29-36. 
Gates,  J.   M.    1962.   Breeding  biology  of  the  Gadwall   in 

northern  Utah.  Wilson  Bull.  74:43-67. 
Gerstenberg,  R.  H.  1972.  A  study  of  shorebirds  (Charadrii) 

in  Humboldt  Bay,  California,  1968  to  1969.  M.S.  thesis, 

Humboldt  State  Univ.,  Areata. 
Getz,  L   L   1961.   Hunting  areas  of  the  Long-eared  Owl. 

Wilson  Bull.  73:79-82. 
Geupel,  G.  R  1981.  The  unique  Wrentit  of  California's 

coastal  scrub.  Point  Reyes  Bird  Obs.  Newsl.  56:9-10. 
Geupel,  G.  R  and  D.  F.  DeSante.  1983.  Abstract,  101st 

meeting  of  the  American  Ornithologists'  Union.  New 

York,  N.Y. 
Geupel,  G.  R  and  D.  F.  DeSante.  1990.  Incidence  and 

determinants  of  double  brooding  in  Wrentits.  Condor 

92:67-75. 
Gibson,  F.   1971.  The  breeding  biology  of  the  American 

Avocet  (Recurvirostra  americana)  in  central  Oregon.  Con- 
dor 73:444-454. 
Gill,  R  E.,  Jr.  1972.  South  San  Francisco  Bay  breeding  bird 

survey.  Wildl.  Mgmt.  Branch  Admin.  Rept.  72-6.  Calif. 

Dept.  Fish  Game,  Sacramento. 
.  1977.  Breeding  avifauna  of  the  south  San  Francisco  Bay 

estuary.  W.  Birds  8:1-12. 

1979.  Status  and  distribution  of  the  California  Clapper 


Rail  (Rallus  longirostris  obsoletus).  Calif.  Fish  Game  65: 
36-49. 

Gilliam,  H.  1962.  Weather  of  the  San  Francisco  Bay  Region. 
Calif.  Nat.  Hist  Guides  6.  Univ.  California  Press,  Berke- 
ley. 

Glading,  B.  1938.  Studies  on  the  nesting  cycle  of  the  Califor- 
nia Valley  Quail  in  1937.  Calif.  Fish  Game  24:318-340. 


Glahn,  J.  F.  1974-  Study  of  breeding  rails  with  recorded  calls 
in  north-central  Colorado.  Wilson  Bull.  86:206-214- 

Glover,  F.  A.  1953a.  Nesting  ecology  of  the  Pied-billed  Grebe 
in  northwestern  Iowa.  Wilson  Bull.  65:32-39. 

.    1953b.  A  nesting  study  of  the  Band-tailed  Pigeon 

(Columba  f.  fasciata)  in  northwestern  California.  Calif. 
Fish  Game  39:397-407. 

Godfrey,  W.  E.  1966.  The  Birds  of  Canada.  Nad.  Mus. 
Canada  Bull.  203.  Ottawa. 

Goldberg,  N.  H.  1979.  Behavioral  flexibility  and  foraging 
strategies  in  Cassin's  and  Western  kingbirds  (Tyrannus 
vociferans  and  T.  verticalis)  breeding  sympatrically  in  ripar- 
ian habitats  in  central  Arizona.  Ph.D.  thesis,  Univ.  111., 
Champaign. 

Goodge,  W.  R  1959.  Locomotion  and  other  behavior  of  the 
Dipper.  Condor  61:4-17. 

Goodpasture,  K.  A.  1953.  Wood  Pewee  builds  with  green 
leaves.  Wilson  Bull.  65:117-118. 

Goodwin,  D.  1983.  Pigeons  and  Doves  of  the  World.  3rd  ed. 
British  Mus.  (Nat.  Hist.).  Comstock,  Ithaca,  N.Y. 

.  1986.  Crows  of  the  World.  2nd  ed.  British  Mus.  (Nat 

Hist). 

Gould,  G.  I.,  Jr.  1977.  Distribution  of  the  Spotted  Owl  in 
California.  W.  Birds  8:131-146. 

Gould,  G.  I.,  Jr.  and  R.  M.  Jurek.  1988.  Osprey  status  review. 
Job  Final  Rept.  11-19,  W-65-R-4-  Calif.  Dept.  Fish  Game, 
Sacramento. 

Graber,  R.  R.  1962.  Food  and  oxygen  consumption  of  three 
species  of  owls  (Strigidae).  Condor  64:473-487. 

Graber,  R.  R  and  J.  W.  Graber.  1951.  Nesting  of  the  Parula 
Warbler  in  Michigan.  Wilson  Bull.  63:75-83. 

Graber,  R  R,  J.  W.  Graber,  and  E.  L  Kirk.  1973.  Illinois 
birds:  Laniidae.  111.  Nat.  Hist.  Surv.  Biol.  Notes  83. 

Granholm,  S.  L  1989.  Seasonal  wedands  in  San  Francisco 
and  San  Pablo  bays:  Current  status,  projected  losses,  and 
cumulative  losses  since  1975.  In  Endangered  habitat  A 
report  on  the  status  of  seasonal  wedands  in  San  Francisco 
Bay  and  a  recommended  plan  for  their  protection,  7-43. 
National  Audubon  Society  and  others. 

Grau,  R,  E.  Richardson,  G.  M.  Santolo.  1987.  Toxicity  of 
selenium  to  nesding  Tricolored  Blackbirds  (Agelaius  tri- 
color). Unpubl.  Rept.,  23  Oct  1987.  Dept.  Avian  Sci., 
Univ.  Calif.,  Davis. 

Graves,  W.  C  1975.  Wild  Turkey  management  in  Califor- 
nia. In  L  K.  Halls,  ed.  Proc.  3rd  Nad.  Wild  Turkey  Symp., 
1-5.  Texas  Parks  and  Wildl.  Dept.,  Austin. 

Gray,  B.  J.  1980.  Reproduction,  energetics,  and  social  struc- 
ture of  the  Ruddy  Duck.  Ph.D.  thesis,  Univ.  Calif.,  Davis. 

Grenfell,  W.  E.,  Jr.,  B.  M.  Browning,  and  W.  E.  Stienecker. 
1980.  Food  habits  of  California  upland  gamebirds.  Wildl. 
Mgmt.  Branch  Admin.  Rept.  80-1.  Calif.  DepL  Fish 
Game,  Sacramento. 

Grenfell,  W.  E.,  Jr.  and  W.  F.  Laudenslayer,  Jr.,  eds.  1983. 
The  distribution  of  California  birds.  California  Wild- 
life/Habitat Relationships  Program  Publ.  4-  Calif.  DepL 
Fish  Game,  Sacramento,  and  USDA  For.  Serv.,  San  Fran- 
cisco. 


454 


LITERATURE  CITED 


Gress,  R,  R.  W.  Risebrough,  D.  W.  Anderson,  L  F.  Kiff,  and 

J.  R.  Jehl,  Jr.  1973.  Reproductive  failures  of  Double-crested 

Cormorants  in  southern  California  and  Baja  California. 

Wilson  Bull.  85:197-208. 
Gress,  F.,  R.  W.  Risebrough,  and  F.  C.  Sibley.  1971.  Shell 

thinning  in  eggs  of  the  Common  Murre,  Uria  aalge,  from 

the  Farallon  Islands,  California.  Condor  73:368-369. 
Griese,  H.  J.,  R.  A.  Ryder,  and  C.  E.  Braun.  1980.  Spatial 

and  temporal  distribution  of  rails  in  Colorado.  Wilson 

Bull.  92:96-102. 
Griffin,  J.  R.  1977.  Oak  woodland.  In  M.  G.  Barbour  and 

J.  Major,  eds.  Terrestrial  Vegetation  of  California,  383-415. 

John  Wiley  &  Sons,  New  York. 
Grinnell,   H.  W.   1944.  The  Hooded  Oriole's  choice  of 

nesting  sites  in  the  settled  portions  of  southern  California. 

Condor  46:298. 
Grinnell,  J.  1909,  1924,  1939.  A  bibliography  of  California 

ornithology.  Pac.  Coast  Avifauna  5,  16,  &  26. 
.  1911.  Distribution  of  the  Mockingbird  in  California. 

Auk  28:293-300. 
.   1913.  The  oudook  for  conserving  the  Band-tailed 

Pigeon  as  a  game  bird  of  California.  Condor  15:25-38. 
.   1917.   The   niche   relationships  of  the  California 

Thrasher.  Auk  34:427-433. 
.  1936.  Uphill  planters.  Condor  38:80-82. 


Grinnell,  J.,  H.  C.  Bryant,  and  T.  I.  Storer.  1918.  The  Game 

Birds  of  California.  Univ.  California  Press,  Berkeley. 
Grinnell,  J.,  J.  S.  Dixon,  and  J.  M.  Linsdale.  1930.  Vertebrate 

natural  history  of  a  section  of  northern  California  through 

the  Lassen  Peak  region.  Univ.  Calif.  Publ.  Zool.  35. 
.  1937.  Fur-bearing  Mammals  of  California:  Their  Natural 

History,  Systematic  Status,  and  Relations  to  Man.  Vols.  /  &  11. 

Univ.  California  Press,  Berkeley. 
Grinnell,  J.  and  J.  M.  Linsdale.  1936.  Vertebrate  animals  of 

Point  Lobos   Reserve,   1934-35.   Carnegie  Inst.  Wash. 

Publ.  481. 
Grinnell,  J.  and  A.  H.  Miller.  1944.  The  distribution  of  the 

birds  of  California.  Pac.  Coast  Avifauna  27. 
Grinnell,  J.  andT.  I.  Storer.  1924.  Animal  Life  in  the  Yosemite. 

Univ.  California  Press,  Berkeley. 
Grinnell,  J.  and  M.  W.  Wythe.  1927.  Directory  to  the  bird-life 

of  the  San  Francisco  Bay  region.  Pac.  Coast  Avifauna  18. 
Griscom,  L  1937.  A  monographic  study  of  the  Red  Crossbill. 

Proc.  Boston  Soc.  Nat.  Hist.  41:71-210. 
Gross,  A.  O.  1942.  Northern  Cliff  Swallow.  In  A.  C.  Bent, 

ed.  Life  histories  of  North  American  flycatchers,  larks, 

swallows,  and  their  allies.  U.S.  Nad.  Mus.  Bull.  179:463- 

484. 
.  1948.  Eastern  House  Wren.  In  A.  C.  Bent,  ed.  Life 

histories  of  North  American  nuthatches,  wrens,  thrashers, 

and  their  allies.  U.S.  Nad.  Mus.  Bull.  195:113-141. 
.  1953.  Northern  and  Maryland  yellowthroats,  Horida 

Yellowthroat,  Western  Yellowthroat,  and  Salt  Marsh  Yel- 

lowthroat.   In  A.  C.   Bent,  ed.  Life  histories  of  North 

American  wood  warblers.   U.S.  Nad.   Mus.   Bull.   203: 

542-577. 


Groves,  S.  1984.  Chick  growth,  sibling  rivalry,  and  chick 

production  in  American  Black  Oystercatchers.  Auk  101: 

525-531. 
Grubb,  T.  C,  Jr.  1982.  On  sex-specific  foraging  behavior  in 

the  White-breasted  Nuthatch.  J.  Field  Ornithol.  53:305- 

314. 
Grubb,  T.  O,  Jr.  and  M.  S.  Woodrey.   1990.  Sex,  age, 

intraspecific  dominance  status,  and  the  use  of  food  by  birds 

wintering  in  temperate-deciduous   and  cold-coniferous 

woodlands:  A  review.  In  M.  L  Morrison,  C.  J.  Ralph, 

J.  Verner,  and  J.  R.  Jehl,  Jr.,  eds.  Avian  foraging:  Theory, 

methodology,  and  applications,  270-279.  Studies  Avian 

Biol.  13. 
Griin,  G.  1975.  Die  Ernahrung  der  sperlinge  Passer  domesti- 

cus  (L)  und   Passer  montanus  (L)  untes  verschiedenen 

Umweltbedingungen.  Int.  Studies  Sparrows  8:24-103. 
Grzybowski,  J.  A.  1979.  Response  of  Barn  Swallows  to  eggs, 

young,  nests  and  nest  sites.  Condor  81:236-246. 
Guillory,  H.  D.  and  J.  H.  Deshotek.  1981.  House  Sparrow 

flushing  prey  from  trees  and  shrubs.  Wilson  Bull.  93:554- 
The  Gull.   1919-present.   Golden  Gate  Audubon  Society 

(formerly  Audubon  Assoc,  of  the  Pacific)  monthly  bulletin. 

GGAS,  1250  Addison  St.,  #107B,  Berkeley,  CA  94702. 
Gullion,  G.  W.  1949.  Starlings  on  Point  Reyes  peninsula, 

Marin  County,  California.  Condor  51:273. 
.  1954.  The  reproductive  cycle  of  American  Coots  in 

California.  Auk  71:366-412. 
Gunderson,  A.   1939.  Nesting  habits  of  the  Red-breasted 

Nuthatch.  Condor  41:259-260. 
Gutierrez,  R.  J.  1980.  Comparative  ecology  of  the  Mountain 

and  California  quail  in  the  Carmel  Valley,  California. 

Living  Bird  18:71-93. 
Gutierrez,  R.  J.,  C.  E.   Braun,  and  T  P.  Zapatka.   1975. 

Reproductive  biology  of  the  Band-tailed  Pigeon  in  Colo- 
rado and  New  Mexico.  Auk  92:665-677. 
Gutierrez,  R.  J.  and  A.  B.  Carey,  eds.  1985.  Ecology  and 

management  of  the  Spotted  Owl  in  the  Pacific  Northwest. 

U.S.  For.  Serv.  Gen.  Tech.  Rept.  PNW-185. 

H 

Hagar,  D.  C.  1960.  The  interrelationships  of  logging,  birds 
and  timber  regeneration  in  the  Douglas-fir  region  of  north- 
western California.  Ecology  41:116-125. 

Hamilton,  R.  B.  1975.  Comparative  behavior  of  the  Ameri- 
can Avocet  and  die  Black-necked  Stilt  (Recurvirostridae). 
Ornithol.  Monogr.  17. 

Hancock,  J.  and  J.  Kushlan.  1984.  The  Herons  Handbook. 
Harper  6k  Row,  New  York. 

Hann,  H.  W.  1950.  Nesting  behavior  of  the  American 
Dipper  in  Colorado.  Condor  52:49-62. 

Hanowski,  J.  M.  and  G.  J.  Niemi.  1990.  Effects  of  unknown 
sex  in  analyses  of  foraging  behavior.  In  M.  L.  Morrison, 
C.  J.  Ralph,  J.  Verner,  and  J.  R.  Jehl,  Jr.,  eds.  Avian 
foraging:  Theory,  methodology,  and  applications,  280- 
283.  Studies  Avian  Biol.  1 3. 


455 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Hansen,  E.  L  and  B.  E.  Carter.  1963.  A  nesting  study  of 
Brewer's  Blackbirds  in  Klamath  County,  Oregon.  Murre- 
let  44:18-21. 

Hanson,  W.  R  1970.  Pheasant  nesting  and  concealment  in 
hayfields.  Auk  87:714-719. 

Hardy,  R.  1949.  Ground  Dove  and  Black-chinned  Sparrow 
in  southern  Nevada.  Condor  51:272-273. 

Harlow,  D.  L  and  P.  H.  Bloom.  1989.  Buteos  and  the 
Golden  Eagle.  In  National  Wildlife  Federation.  Proc. 
Western  Raptor  Mgmt.  Symp.  and  Workshop,  102-109. 
Nad.  Wildl.  Fed.  Sci.  and  Tech.  Ser.  12. 

Harlow,  R.  F.,  R.  G.  Hooper,  D.  R  Chamberlain,  and  H.  S. 
Crawford.  1975.  Some  winter  and  nesting  season  foods  of 
the  Common  Raven  in  Virginia.  Auk  92:298-306. 

Harper,  C.  A.  1971.  Breeding  biology  of  a  small  colony  of 
Western  Gulls  (Larus  occidentalis  wymani)  in  California. 
Condor  73:337-341. 

Harper,  H.  T.  and  W.  A.  Smith.  1973.  California's  turkey 
stocking  program.  In  G.  C.  Sanderson  and  H.  C.  Schultz, 
eds.  Wild  Turkey  Management:  Current  Problems  and  Pro- 
grams, 55-63.  Univ.  Missouri  Press,  Columbia. 

Harris,  J.  H.,  S.  D.  Sanders,  and  M.  A.  Rett.  1987.  Willow 
Hycatcher  surveys  in  the  Sienra  Nevada.  W.  Birds  18: 
27-36. 

Harris,  R.  D.  1982.  The  nesting  ecology  of  the  Pileated 
Woodpecker  in  California.  M.S.  thesis,  Univ.  Calif., 
Berkeley. 

Han-is,  S.  W.  and  R  J.  Wheeler.  1965.  Hybrid  of  Blue- 
winged  Teal  x  Cinnamon  Teal  in  northwestern  California. 
Condor  67:539-540. 

Harrison,  C.  1978.  A  Field  Guide  to  the  Nests,  Eggs,  and 
Nestlings  of  North  American  Birds.  Collins,  Glasgow. 

Hartwick,  E.  B.  1974.  Breeding  ecology  of  the  Black  Oyster- 
catcher  (Haematopus  bachmani  Audubon).  Syesis  7:83-92. 

.   1976.   Foraging  strategy  of  the  Black  Oystercatcher 

(Haematopus  bachmani  Audubon).  Can.  J.  Zool.  54:142- 
155. 

Hartwick,  E.  B.  and  W.  Blaylock.  1979.  Winter  ecology  of  a 
Black  Oystercatcher  population.  In  F.  A.  Pitelka,  ed.  Shore- 
birds  in  marine  environments,  207-215.  Studies  Avian 
Biol.  2. 

Harvey,  T.  E.  1980a.  A  breeding  season  survey  of  the  Califor- 
nia Clapper  Rail  (Rallus  longirostris  obsoletus)  in  south  San 
Francisco  Bay,  California.  Final  Rept.,  U.S.  Fish  Wildl. 
Serv.,  S.F.  Bay.  Nad.  Wildl.  Refuge,  Newark. 

.  1980b.  California  Clapper  Rail  survey,  1978-1979.  Job 

Final  Rept.,  Job  V-1.8.  Calif.  Dept.  Fish  Game,  Sacra- 
mento. 

.  1983.  Breeding  season  study  of  the  California  Clapper 

Rail  in  San  Francisco  Bay,  1982.  Rept.  for  U.S.  Fish  Wildl. 
Serv.,  S.  F.  Bay  Nad.  Wildl.  Refuge,  Newark. 
-.  1987.  The  California  Clapper  Rail:  Biology,  present 


status,  and  future  trends.  Manuscript  of  oral  presentation 
given  at  A.O.U.  meeting  in  San  Francisco  in  1987.  Avail- 
able from  S.F.  Bay  Nad.  Wildl.  Refuge,  Newark. 
Hatch,  D.  E.  1970.  Energy  conserving  and  heat  dissipating 
mechanisms  of  the  Turkey  Vulture.  Auk  87:111-124. 


Hatch,  S.  A.  1984.  Nesding  diet  and  feeding  rates  of  Rhinoc- 
eros Auklets  in  Alaska.  In  D.  N.  Netdeship,  G.  A.  Sanger, 
and  P.  F.  Springer,  eds.  Marine  birds:  Their  feeding 
ecology  and  commercial  fisheries  relationships,  106-115. 
Proc.  Pac.  Seabird  Group  Symp.  Seatrie,  Wash.,  6-8  Jan 
1982.  Canadian  Wildl.  Serv.  for  P.S.G 

Hawbecker,  A.  C.  1940.  The  nesting  of  the  White-tailed  Kite 
in  southern  Santa  Cruz,  County,  California.  Condor  42: 
106. 

.  1942.  A  life  history  study  of  the  White-tailed  Kite. 

Condor  44:267-276. 

Hawthorne,  V.  M.  1979.  Use  of  nest  boxes  by  Dippers  on 
Sagehen  Creek,  California.  W.  Birds  10:215-216. 

Hay,  D.  B.  and  M.  Guntert.  1983.  Seasonal  selection  of  tree 
cavities  by  Pygmy  Nuthatches  based  on  cavity  characteris- 
tics. U.S.  For.  Serv.  Gen.  Tech.  Rept.  RM-99. 

Hays,  H.  1972.  Polyandry  in  the  Spotted  Sandpiper.  Living 
Bird  11:43-57. 

Hayward,  C.  L  1935.  Observations  of  some  breeding  birds 
of  Mount  Timpanogos,  Utah.  Wilson  Bull.  47:161-162. 

Heermann,  A.  L  1853.  Catalog  of  the  oological  collection  of 
the  Academy  of  Natural  Sciences  of  Philadelphia.  Proc. 
Nad.  Acad.  Sci.  6:17. 

Hejl,  S.  J.  and  J.  Vemer.  1990.  Within-season  and  yearly 
variation  in  avian  foraging  locations.  In  M.  L  Morrison, 
C.  J.  Ralph,  J.  Verner,  and  J.  R.  Jehl,  Jr.,  eds.  Avian 
foraging:  Theory,  methodology,  and  applications,  202- 
209.  Studies  Avian  Biol.  13. 

Heady,  H.  F.  1977.  Valley  grassland.  In  M.  G.  Barbour  and 
J.  Major,  eds.  Terrestrial  Vegetation  of  California,  491-513. 
John  Wiley  &  Sons,  New  York. 

Henny,  C.  J.  1977.  Research,  management  and  status  of  the 
Osprey  in  North  America.  In  R  D.  Chancellor,  ed.  Proc. 
World  Birds  of  Prey  Conf.,  199-222.  Int.  Council  Bird 
Preserv.,  Vienna. 

.  1983.  Distribution  and  abundance  of  nesting  Ospreys 

in  the  United  States.  In  D.  M.  Bird,  N.  R  Seymour,  and 
J.  M.  Gerrard,  eds.  Biology  and  Management  of  Bald 
Eagles  and  Ospreys,  175-186.  Proc.  1st  Int.  Symp.  on 
Bald  Eagles  and  Ospreys,  Montreal,  28-29  Oct  1981. 
Harpell  Press,  Quebec. 

.  1988.  Osprey.  In  R.  S.  Palmer,  ed.  Handbook  of  North 

American  Birds.  Vol.  4:  Diurnal  Raptors  (Part  I),  73-101. 
Yale  Univ.  Press,  New  Haven. 

Henny,  C.  J.  and  D.  W.  Anderson.  1979.  Osprey  distribu- 
tion, abundance,  and  status  in  western  North  America:  III. 
The  Baja  California  and  Gulf  of  California  population. 
Bull.  S.  Calif.  Acad.  Sci.  78:89-106. 

Henny,  C.  J.  and  J.  T.  Annear.  1978.  A  White-tailed  Kite 
breeding  record  for  Oregon.  W.  Birds  9:131-133. 

Henny,  C.  J.  and  R  G.  Anthony.  1989.  Bald  Eagle  and 
Osprey.  In  National  Wildlife  Federation.  Proc.  Western 
Raptor  Mgmt.  Symp.  and  Workshop,  66-82.  Nad.  Wildl. 
Fed.  Sci.  and  Tech.  Ser.  12. 

Henny,  C.  J.,  D.  J.  Dunaway,  R.  D.  Mallette,  and  J.  R.  Koplin. 
1978.  Osprey  distribution,  abundance,  and  status  in  west- 
ern North  America:  I.  The  northern  California  popula- 
tion. Northwest  Sci.  52:261-271. 


456 


LITERATURE  CITED 


Henny,  C.  J.  and  H.  W.  Wight.  1972.  Population  ecology  and 
environmental  pollution:  Red-tailed  and  Cooper's  hawks. 
In  Population  ecology  of  migratory  birds:  A  symposium, 
229-250.  Bur.  Sport  Fish  and  Wildl.,  Wildl.  Res.  Rept.  2. 

Heppner,  F.  1965.  Sensory  mechanisms  and  environmental 
cues  used  by  the  American  Robin  in  locating  earthworms. 
Condor  67:247-256. 

Herlugson,  C.  J.  1978.  Comments  on  the  status  and  distribu- 
tion of  Western  and  Mountain  bluebirds  in  Washington. 
W.  Birds  9:21-32. 

.  1982.  Food  of  adult  and  nesding  Western  and  Moun- 
tain bluebirds.  Murrelet  63:59-65. 

Herman,  S.  G.  1971.  The  Peregrine  Falcon  decline  in  Cali- 
fornia. II.  Breeding  status  in  1970.  Am.  Birds  25:818- 
820. 

Herman,  S.  G.,  M.  N.  Kirven,  and  R.  W.  Risebrough.  1970. 
The  Peregrine  Falcon  decline  in  California.  I.  A  prelimi- 
nary review.  Aud.  Field  Notes  24:609-613. 

Hertz,  P.  E.,  J.  V.  Remsen,  Jr.,  and  S.  I.  Zones.  1976. 
Ecological  complementarity  of  three  sympatric  parids  in  a 
California  oak  woodland.  Condor  78:307-316. 

Hespenheide,  H.  A.  1964.  Competition  and  the  genus  Tyran- 
nus.  Wilson  Bull.  76:265-281. 

Hickey,  J.  J.,  ed.  1969.  Peregrine  Falcon  Populations:  Their 
Biology  and  Decline.  Univ.  Wisconsin  Press,  Madison. 

Hill,  G.  E.  1988.  Age,  plumage  brightness,  territory  quality, 
and  reproductive  success  in  the  Black-headed  Grosbeak. 
Condor  90:379-388. 

Hjersman,  H.  A.  1947.  A  history  of  the  establishment  of  the 
Ring-necked  Pheasant  in  California.  Calif.  Fish  Game 
33:3-11. 

Hobson,  K.,  P.  Perrine,  E.  B.  Roberts,  M.  L  Foster,  and 
P.  Woodin.  1986.  A  breeding  season  survey  of  Salt  Marsh 
Yellowthroats  Geothlypis  trichas  sinuosa  in  the  San  Fran- 
cisco Bay  region.  S.  F.  Bay  Bird  Obs.  Rept.  to  U.S.  Fish 
Wildl.  Serv.,  Contract  84-57. 

Hobson,  K.  A.  and  H.  R.  Carter.  1988.  Bill  deformity  in  a 
Brandt's  Cormorant  chick.  Calif.  Fish  Game  74:184-185. 

Hoffmann,  R.  1927.  Birds  of  the  Pacific  States.  Houghton 
Mifflin,  Boston. 

Holcomb,  L  C.  1969.  Breeding  biology  of  the  American 
Goldfinch  in  Ohio.  Bird-Banding  40:26-44. 

Holcomb,  L  C.  and  G.  Twiest.  1968.  Ecological  factors 
affecting  nest  building  in  Red-winged  Blackbirds.  Bird- 
Banding  39:14-22. 

Hooper,  E.  T.  1938.  Another  jay  shoot  in  California.  Condor 
40:162-164. 

Hooper,  R.  G.  1977.  Nesting  habitat  of  Common  Ravens  in 
Virginia.  Wilson  Bull.  89:233-242. 

Horak,  C.  J.  1970.  A  comparative  study  of  the  food  habits  of 
the  Sora  and  Virginia  Rail.  Wilson  Bull.  82:206-213. 

Horn,  H.  S.  1968.  The  adaptive  significance  of  colonial 
nesting  in  the  Brewer's  Blackbird  (Euphagus  cyanocepha- 
lus).  Ecology  49:682-694. 

.  1970.  Social  behavior  of  nesting  Brewer's  Blackbirds. 

Condor  72:15-23. 


Horn,  K.  M.  and  D.  B.  Marshall.  1975.  Status  of  Poor-will  in 
Oregon  and  possible  extension  due  to  clearcut  timber 
harvest  methods.  Murrelet  56  (l):4-5. 

Home,  B.  V.  and  A.  Bader.  1990.  Diet  of  nesding  Winter 
Wrens  in  relationship  to  food  availability.  Condor  92: 
413-420. 

Hosea,  R  C.  1986.  A  population  census  of  the  Tricolored 
Blackbird,  Agelaius  tricolor  (Audubon),  in  four  counties  in 
the  northern  Central  Valley  of  California.  M.A.  thesis, 
Calif.  State  Univ.,  Sacramento. 

Houston,  D.  C.  1986.  Scavenging  efficiency  of  Turkey  Vul- 
tures in  tropical  forest.  Condor  88:31 8-323. 

Howard,  H.  1929.  Avifauna  of  an  Emeryville  shellmound. 
Univ.  Calif.  Publ.  Zool.  32:301-394. 

Howard,  W.  E.  1959.  The  European  Starling  in  California. 
Calif.  Dept.  Agri.  Bull.  48:171-179. 

Howell,  A.  H.  1906.  Birds  that  eat  the  cotton  boll  weevil: 
A  progress  report.  U.S.  Dept.  Agri.  Bull.  25. 

.  1932.  Florida  Bird  Life.  Florida  Dept.  Game  and  Fresh 

Water  Fish. 

Howell,  J.,  D.  Laclergue,  S.  Paris,  W.  I.  Boarman,  A.  R. 
DeGange,  and  L  C.  Binford.  1983.  First  nests  of  Heer- 
mann's  Gull  in  the  United  States.  W.  Birds  14:39-46. 

Howell,  J.  C.  1942.  Notes  on  the  nesting  habits  of  the 
American  Robin  (Turdus  migratorius  L).  Am.  Midi.  Nat 
28:529-603. 

Howell,  T.  R.  1952.  Natural  history  and  differentiation  in  the 
Yellow-bellied  Sapsucker.  Condor  54:237-282. 

Hoyt,  S.  F.  1957.  The  ecology  of  the  Pileated  Woodpecker. 
Ecology  38:246-256. 

Hubbard,  J.  P.  and  C.  L  Hubbard.  1969.  Meadowlarks 
feeding  on  road-kills.  Wilson  Bull.  81:107-108. 

Huey,  L  M.  1944-  Nesting  habits  of  the  Hooded  Oriole. 
Condor  46:297. 

Hunt,  G.  L,  Jr.  and  M.  W.  Hunt.  1976.  Exploitation  of 
fluctuating  food  resources  by  Western  Gulls.  Auk  93:301  - 
307. 

Hunt,  G.  L,  Jr.,  R.  L  Pitman,  M.  Naughton,  K.  Winnet, 
A.  Newman,  P.  R.  Kelly,  and  K.  T.  Briggs.  1979.  Distribu- 
tion, status,  reproductive  ecology,  and  foraging  habits  of 
breeding  seabirds.  In  Summary  of  marine  mammal  and 
seabird  surveys  of  the  Southern  California  Bight  area, 
1975-1978.  U.S.  Dept.  Inter.,  Bur.  Land  Mgmt.,  Los 
Angeles. 

Hutto,  R.  L  1981 .  Seasonal  variation  in  the  foraging  behavior 
of  some  migratory  western  wood  warblers.  Auk  98:765- 
777. 

I 

Illingsworth,  J.  F.  1901.  The  Bullock's  and  Arizona  Hooded 

orioles.  Condor  3:98-100. 
Inouye,  D.  W.  1976.  Non-random  orientation  of  entrance 

holes  to  woodpecker  nests  in  aspen  trees.  Condor  78: 

101-102. 
Isler,  M.  L  and  P.  R.  Isler.  1987.  The  Tanagers:  Natural 

History,   Distribution,   and   Identification.   Smithson.   Inst. 

Press,  Washington,  D.C. 


457 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Ives,  J.  H.  1972.  Common  Egret  and  Great  Blue  Heron  nest 
study,  Indian  Island,  Humboldt  County,  California  1971- 
72.  Wildl.  Mgmt.  Branch  Admin.  Rept.  72-9.  Calif.  Dept. 
Fish  Game,  Sacramento. 

J 

Jackman,  S.  M.  and  J.  M.  Scott.  1975.  Literature  review  of 
twenty-three  selected  forest  birds  of  the  Pacific  Northwest. 
U.S.  For.  Serv.,  Portland. 

Jackson,  J.  A.  1970.  A  quantitative  study  of  the  foraging 
ecology  of  Downy  Woodpeckers.  Ecology  51 :31 8-323. 

.  1983.  Nesting  phenology,  nest  site  selection,  and  repro- 
ductive success  of  Black  and  Turkey  vultures.  In  S.  R. 
Wilbur  and  J.  A.  Jackson,  eds.  Vulture  Biology  and  Manage- 
ment, 245-269.  Univ.  California  Press,  Berkeley. 

.  1988.  Turkey  Vulture.  In  R.  S.  Palmer,  ed.  Handbook 

of  'North  American  Birds.  Vol.  4-'  Diurnal  Raptors  (Part  I). 
Yale  Univ.  Press,  New  Haven. 

Jackson,  J.  A.  and  J.  Tate,  Jr.  1974-  An  analysis  of  nest  box 
use  by  Purple  Martins,  House  Sparrows  and  Starlings  in 
eastern  North  America.  Wilson  Bull.  86:435-449. 

Jaksic,  F.  M.  and  C.  D.  Marti.  1981.  Trophic  ecology  of 
Athene  Owls  in  Mediteiranean-type  ecosystems:  A  compar- 
ative analysis.  Can.  J.  Zool.  59:2331-2340. 

.  1984-  Comparative  food  habits  of  Bubo  Owls  in  Medi- 
terranean-type ecosystems.  Condor  86:288-296. 

Jaksic,  F.  M.,  R.  L  Seib,  and  C.  M.  Herrera.  1982.  Predation 
by  Barn  Owl  (Tyto  alba)  in  Mediterranean  habitats  of 
Chile,  Spain  and  California:  A  comparative  approach. 
Am.  Midi.  Nat  107:151-162. 

James,  P.  C.  and  T.  J.  Ethier.  1989.  Trends  in  die  winter 
distribution  and  abundance  of  Burrowing  Owls  in  North 
America.  Am.  Birds  43:1225. 

Jeffery,  R.  G.  (Chairman)  et  al.  1977.  Band-tailed  Pigeon 
(Columba  fasciata).  In  G.  C.  Sanderson,  ed.  Management 
of  migratory  shore  and  upland  game  birds  in  North 
America,  210-245.  Int.  Assoc.  Fish  Game  Agencies, 
Washington,  D.C. 

Jehl,  J.  R,  Jr.  1979.  Pine  cones  as  granaries  for  Acorn 
Woodpeckers.  W.  Birds  10:219-220. 

.  1988.  Biology  of  the  Eared  Grebe  and  the  Wilson's 

Phalarope  in  the  nonbreeding  season:  A  study  of  adapta- 
tions to  saline  lakes.  Studies  Avian  Biol.  12. 

Jenkins,  J.  M.  1979.  Foraging  behavior  of  male  and  female 
Nuttall  Woodpeckers.  Auk  96:418-420. 

Jewett,  S.  G.  1942.  The  European  Starling  in  California. 
Condor  44:79. 

Joem,  W.  T.  and  J.  F.  Jackson.  1983.  Homogeneity  of 
vegetational  cover  around  the  nest  and  avoidance  of  nest 
predation  in  Mockingbirds.  Auk  100:497-499. 

Johnsgard,  P.  A.  1978.  Ducks,  Geese,  and  Swans  of  the  World. 
Univ.  Nebraska  Press,  Dncoln. 

.  1981.  The  Plovers,  Sandpipers,  and  Snipes  of  the  World. 

Univ.  Nebraska  Press,  Lincoln. 

.  1986.  Pheasants  of  trie  World.  Oxford  Univ.  Press,  New 

York. 


.  1987.  Diving  Birds  of  North  America.  Univ.  Nebraska 

Press,  Dncoln. 

.  1988.  North  American  Ovuls:  Biology  and  Natural  His- 
tory. Smithson.  Inst.  Press,  Washington,  D.C. 

Johnson,  A.  W.  1904-  Notes  on  unusual  nesting  sites  of  the 
Pacific  Yellowthroat.  Condor  6:129-131. 

Johnson,  D.  H.,  M.  D.  Bryant,  and  A.  H.  Miller.  1948. 
Vertebrate  animals  of  the  Providence  Mountains  area  of 
California.  Univ.  Calif.  Publ.  Zool.  48:221-375. 

Johnson,  N.  K.  and  C.  Cicero.  1986.  Richness  and  distribu- 
tion of  montane  avifaunas  in  the  White-Inyo  region,  Cali- 
fornia. In  C.  A.  Hall,  Jr.  and  D.  J.  Young,  eds.  Natural 
history  of  the  White-Inyo  Range,  eastern  California  and 
western  Nevada  and  high  altitude  physiology,  137-159. 
Univ.  Calif.  White  Mtn.  Res.  Sta.  Symp.  Vol.  1,  August 
23-25.  Univ.  Calif.  White  Mtn.  Res.  Sta.,  Los  Angeles. 

Johnson,  R.  and  J.  J.  Dinsmore.  1986.  Habitat  use  by  breed- 
ing Virginia  Rails  and  Soras.  J.  Wildl.  Mgmt.  50:387-392. 

Johnson,  S.  R.  and  C.  F.  Yocum.  1966.  Breeding  waterfowl 
in  the  Lake  Earl-Lake  Talawa  area,  Del  Norte  County, 
California.  Murrelet  47:1-5. 

Johnston,  D.  W.  and  R.  A.  Norris.  1956.  Observations  on 
Red  Crossbills  in  Marin  County,  California.  Condor  58: 
77. 

Johnston,  R.  F.  1956a.  Population  structure  in  salt  marsh 
Song  Sparrows.  Part  I.  Environment  and  annual  cycle.  Part 
II.  Density,  age,  structure,  and  maintenance.  Condor  58: 
24-44,  254-272. 

.  1956b.  Predation  by  Short-eared  Owls  on  a  Salicornia 

salt  marsh.  Wilson  Bull.  68:91-102. 

.  1968a.  Coastal  Savannah  Sparrow.  In  O  L  Austin,  Jr., 

ed.  A.  C.  Bent  et  al.'s  Life  histories  of  North  American 
cardinals,  grosbeaks,  buntings,  towhees,  finches,  sparrows, 
and  allies.  U.S.  Nad.  Mus.  Bull.  237  (Part  2):  712-714. 

.  1968b.  Song  Sparrow:  San  Francisco  Bay  marsh  sub- 
species. In  O.  L  Austin,  Jr.,  ed.  A.  C.  Bent  et  al.'s  Ufe 
histories  of  North  American  cardinals,  grosbeaks,  bun- 
tings, towhees,  finches,  sparrows,  and  allies.  U.S.  Nad. 
Mus.  Bull  237  (Part  3):  1547-1553. 

Johnston,  R.  F.  and  J.  W.  Hardy.  1962.  Behavior  of  the 
Purple  Martin.  Wilson  Bull.  74:243-262. 

Johnston,  R.  F.  and  W.  J.  Klitz.  1977.  Variation  and  evolu- 
tion in  a  granivorous  bird:  The  House  Sparrow.  In 
J.  Pinowski  and  S.  C.  Kendeigh,  eds.  Granivorous  Birds  in 
Ecosystems:  Their  Evolution,  Populations,  Energetics,  Impact, 
and  Control,  15-51.  Int.  Biol.  Progr.  12.  Cambridge  Univ. 
Press,  London. 

Jones,  J.  C.  1940.  Food  habits  of  the  American  Coot  with 
notes  on  distribution.  U.S. D.I.  Biol.  Serv.  Wildl.  Res. 
Bull.  2. 

Josselyn,  M.  N.  1983.  The  ecology  of  San  Francisco  Bay  tidal 
marshes:  A  community  profile.  U.S.  Fish  Wildl.  Serv., 
Div.  Biol.  Serv.,  Washington,  D.C.  FWS/OBS83/23. 

Josselyn,  M.  N.  and  J.  W.  Buchholz.  1984.  Marsh  restoration 
in  San  Francisco  Bay:  A  guide  to  design  and  planning. 
Tiburon  Center  for  Environmental  Studies,  San  Francisco 
State  Univ.  Tech  Rept.  3. 


458 


LITERATURE  CITED 


Joyner,  D.  1973a.  Effects  of  interspecific  nest  parasitism  by 
Redheads  and  Ruddy  Ducks.  J.  Wildl.  Mgmt.  40:33-38. 

.  1973b.  Interspecific  nest  parasitism  by  ducks  and  coots 

in  Utah.  Auk  90:692-693. 

.  1977a.  Behavior  of  Ruddy  Duck  broods  in  Utah.  Auk 

94:343-349. 

.   1977b.   Nest  desertion   by  Ruddy  Ducks  in   Utah. 

Bird-Banding  48:19-24. 

Jurek,  R.  M.  1976.  California  Black  Rail  survey.  Nongame 
Wildl.  Invest.  Job  Progr.  Rept.,  Proj.  No.  W-54-R-8,  Job 
I-I-l  .3.  Calif.  Dept.  Fish  Game,  Sacramento. 

K 

Kalmbach,  E.  R.  1918.  The  crow  and  its  relation  to  man.  U.S. 
Dept.  Agri.  Bull.  621. 

.  1940.  Economic  status  of  the  English  Sparrow  in  the 

United  States.  U.S.  Dept.  Agri.  Tech.  Bull.  711. 

Kalmbach,  E.  R.  and  I.  N.  Gabrielson.  1921.  Economic  value 
of  the  Starling  in  the  United  States.  U.S.  Dept.  Agri.  Bull. 
868. 

Kashiwagi,  J.  H.  1985.  Soil  survey  of  Marin  County,  Califor- 
nia. Nad.  Coop.  Soil  Surv.,  Soil  Cons.  Serv.,  U.S.  Dept. 
Agri. 

Kelly,  I.  1978.  Coast  Miwok.  In  R.  F.  Heizer,  ed.  Handbook 
of  North  American  Indians.  Vol.  8.  California.  Smithson. 
Inst,  Washington,  D.C 

Kelly,  J.  W.  1942.  Audubon  Warbler  nesting  in  Marin 
County.  Gull  24:25-26. 

.  1944.  Audubon  Warblers  at  Ross.  Gull  26:26. 

Kelly,  S.  T.  and  M.  E.  DeCapita.  1982.  Cowbird  control  and 
its  effect  on  Kiitland's  Warbler  reproductive  success.  Wil- 
son Bull.  94:363-365. 

Kendeigh,  S.  C.  1941a.  Territory  and  mating  behavior  of  the 
House  Wren.  111.  Biol.  Monogr.  18:1-120. 

.  1941b.  Birds  of  a  prairie  community.  Condor  43:165- 

174. 

.  1945.  Community  selection  by  birds  on  the  Helderberg 

Plateau  of  New  York.  Auk  62:41 8-436. 

Kennedy,  P.  L  and  D.  R.  Johnson.  1986.  Prey-size  selection 
in  nesting  male  and  female  Cooper's  Hawks.  Wilson  Bull. 
98:110-115. 

Kern,  M.  D.  1984.  Racial  differences  in  nests  of  White- 
crowned  Sparrows.  Condor  86:455-466. 

Kessel,  B.  1957.  A  study  of  the  breeding  biology  of  the 
European  Starling  (Sturnus  vulgaris  L)  in  North  America. 
Am.  Midi.  Nat  58:257-331. 

Keyes,  G.  C,  YL  C  Heischer,  and  S.  I.  Rothstein.  1986. 
Relationships  between  elevation,  reproduction,  and  the 
hematocrit  level  of  Brown-headed  Cowbirds.  Comp.  Bio- 
chem.  Physiol.  83A:765-769. 

Kibbe,  D.  P.  1986.  Determining  adequacy  of  coverage  in 
statewide  breeding  bird  adas  projects:  When  enough  is 
enough.  In  S.  M.  Sutcliffe,  R.  E.  Bonney,  Jr.,  and  J.  D. 
Lowe,  comps.  Proc.  2nd  Northeastern  Breeding  Bird  Adas 
Conference,  18-24.  April  25-27,  1986.  Lab.  ofOrnithol., 
Cornell  Univ.,  Ithaca,  N.Y. 


Kiff,  L  F.  1978.  Probable  Black  Rail  nesting  record  for 
Alameda  County,  California.  W.  Birds  9:169-170. 

.   1988.   Commentary.  Changes   in  the  status  of  the 

Peregrine  in  North  America:  An  overview.  In  T.  J.  Cade, 
J.  H.  Enderson,  C.  G.  Thelander,  and  C.  M.  White,  eds. 
Peregrine  Falcon  Populations:  Their  Management  and  Recov- 
ery, 123-139.  The  Peregrine  Fund,  Boise,  Idaho. 

Kilgore,  D.  L,  Jr.  and  K.  L  Knudsen.  1977.  Analysis  of 
materials  in  Cliff  and  Barn  Swallow  nests:  Relationship 
between  mud  selection  and  nest  architecture.  Wilson  Bull. 
89:562-571. 

Kilham,  L  1964-  The  relations  of  breeding  Yellow-bellied 
Sapsuckers  to  wounded  birches  and  other  trees.  Auk 
81:520-527. 

.   1965.  Differences  in  feeding  behavior  of  male  and 

female  Hairy  Woodpeckers.  Wilson  Bull.  77:134-145. 

.  1968.  Reproductive  behavior  of  White-breasted  Nut- 
hatches. I.  Distraction  display,  bill  sweeping  and  nest  hole 
defense.  Auk  85:477-492. 

1970.  Feeding  behavior  of  Downy  Woodpeckers.  1. 


Preference  for  paper  birches  and  sexual  differences.  Auk 
87:544-556. 

.  1971.  Reproductive  behavior  of  Yellow-bellied  Sapsuck- 
ers. I.  Preference  for  nesting  in  Fomes-infected  aspens  and 
nest  hole  interrelations  with  flying  squirrels,  raccoons,  and 
other  animals.  Wilson  Bull.  83:159-171. 

.  1977.  Nesting  behavior  of  Yellow-bellied  Sapsuckers. 

Wilson  Bull.  89:310-324. 

Killpack,  M.  L  and  D.  N.  Crittenden.  1952.  Starlings  as 
winter  residents  in  the  Uinta  Basin,  Utah.  Condor  54: 
338-344. 

Kingery,  H.  E.  and  W.  D.  Graul,  eds.  1978.  Colorado  bird 
distribution  latilong  study.  Colorado  Field  Ornithologists. 

Kinsey,  E.  C.  1945.  More  records  of  the  Chat  in  Marin 
County,  California.  Condor  47:269-270. 

Kisiel,  D.  S.  1972.  Foraging  behavior  of  D.  vtllosus  and  D. 
pubescens  in  eastern  New  York  state.  Condor  74:393-398. 

Klimkiewicz,  M.  K.  and  J.  K.  Solem.  1978.  The  breeding  bird 
adas  of  Montgomery  and  Howard  counties,  Maryland. 
Maryland  Birdlife  34:3-39. 

Klimstra,  W.  D.  and  W.  O.  Stieglitz.  1957.  Notes  on  repro- 
ductive activities  of  Robins  in  Iowa  and  Illinois.  Wilson 
Bull.  69:333-337. 

Knight,  R.  L  and  R.  E.  Jackman.  1984-  Food-niche  relation- 
ships between  Great  Horned  Owls  and  Common  Barn- 
Owls  in  eastern  Washington.  Auk  101:175-179. 

Knupp,  D.  M.,  R.  B.  Owen,  Jr.,  and  J.  B.  Dimond.  1977. 
Reproductive  biology  of  American  Robins  in  northern 
Maine.  Auk  94:80-85. 

Koenig,  W.  D.  and  R.  L  Mumme.  1987.  Population  Ecology 
of  the  Cooperatively  Breeding  Acorn  Woodpecker.  Princeton 
Univ.  Press,  Princeton. 

Koford,  C.  B.  1953.  The  California  Condor.  Nad.  Audubon 
Soc.  Res.  Rept.  4- 

Koplin,  J.  R.  1969.  The  numerical  response  of  wookpeckers 
to  insect  prey  in  a  subalpine  forest  in  Colorado.  Auk 
71:436-435. 


459 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


.  1973.  Differential  habitat  use  by  sexes  of  American 

Kestrels  wintering  in  northern  California.  Raptor  Res. 
7:39-42. 

Korschgen,  L  J.  1964-  Foods  and  nutrition  of  Missouri  and 
Midwestern  pheasants.  Trans.  N.  Am.  Wildl.  Conf.  29: 
159-181. 

Krapu,  G.  L  1974a.  Foods  of  breeding  Pintails  in  North 
Dakota.  J.  Wildl.  Mgmt.  38:408-417. 

.  1974b.  Feeding  ecology  of  Pintail  hens  during  repro- 
duction. Auk  91:278-290. 

.  1979.  Nutrition  of  female  dabbling  ducks  during  repro- 
duction. In  T  A.  Bookhout,  ed.  Waterfowl  and  wedands— 
an  integrated  review,  59-70.  Proc.  Symp.  1977  N.  Cent. 
Sect,  The  Wildl.  Soc. 

.  1981.  The  role  of  nutrient  reserves  in  Mallard  repro- 
duction. Auk  98:29-38. 

Krebs,  C.  J.  1966.  Demographic  changes  in  fluctuating  pop- 
ulations of  Microtus  californicus.  Ecol.  Monogr.  36:239- 
273. 

Kridelbaugh,  A.  1983.  Nesting  ecology  of  the  Loggerhead 
Shrike  in  central  Missouri.  Wilson  Bull.  95:303-308. 

Kroodsma,  D.  E.  1973.  Coexistence  of  Bewick's  Wrens  and 
House  Wrens  in  Oregon.  Auk  90:341-352. 

Kruckeberg,  A.  R  1984.  California  serpentines:  Flora,  vege- 
tation, geology,  soils,  and  management  problems.  Univ. 
Calif.  Publ.  Bot.  73.  Univ.  California  Press,  Berkeley. 

Kuenzel,  W.  J.  and  R.  G.  Wiegert.  1973.  Energetics  of  a 
Spotted  Sandpiper  feeding  on  brine  fly  larvae  (Parocoenia; 
Diptera;  Ephydridae)  in  a  thermal  spring  community. 
Wilson  Bull.  85:473-476. 

Kuerzi,  R.  G.  1941.  Life  history  studies  of  the  Tree  Swallow. 
Proc.  Linn.  Soc.  N.Y.  52-53:1-52. 

Kuletz,  K.  J.  1983.  Mechanisms  and  consequences  of  foraging 
behavior  in  a  population  of  breeding  Pigeon  Guillemots. 
M.S.  thesis,  Univ.  Calif.,  Irvine. 


Lack,  D.  and  J.  T.  Emlen.  1939.  Observations  on  breeding 

behavior  in  Tricolored  Red-wings.  Condor  41:225-230. 
Lack,  P.,  ed.  1986.  The  Atlas  of  Wintering  Birds  in  Britain  and 

Ireland.  British  Trust  for  Ornithology  and  Irish  Wildbird 

Conservancy.  T.  &.  A.  D.  Poyser,  Calton. 
Landers,  J.  L,  T.  T  Fendley,  and  A.  S.  Johnson.   1977. 

Feeding  ecology  of  Wood   Ducks   in  South  Carolina. 

J.  Wildl.  Mgmt.  41:118-127. 
Lanyon,  W.  E.  1957.  The  comparative  biology  of  the  mead- 

owlarks  (Stumella)  in  Wisconsin.  Publ.  Nutt.  Omithol. 

Clubl. 
Larson,  D.  1980.  Increase  in  the  White-tailed  Kite  popula- 
tions of  California  and  Texas— 1944-1978.  Am.   Birds 

34=689-690. 
Latta,  W.  C.  and  R.  F.  Sharkey.  1966.  Feeding  behavior  of 

the  American  Merganser  in  captivity.  J.  Wildl.  Mgmt. 

30:17-23. 
Laughlin,  S.  B.  and  D.  P.  Kibbe.  1985.  The  Atlas  of  Breeding 

Birds  of  Vermont.  Univ.  Press  of  New  England,  Hanover, 

N.H. 


Laughlin,  S.  B.,  D.  P.  Kibbe,  and  P.  F.  J.  Eagles.  1982. 
Adasing  the  distribution  of  the  breeding  birds  of  North 
America.  Am.  Birds  36:6-19. 

Lawrence,  L  DeK.  1949.  The  Red  Crossbill  at  Pimisi  Bay, 
Ontario.  Can.  Field-Nat.  63:147-160. 

.  1967.  A  comparative  life-history  study  of  four  species  of 

woodpeckers.  Ornithol.  Monogr.  5. 

Laymon,  S.  A.  1987-  Brown-headed  Cowbirds  in  California: 
Historical  perspectives  and  management  opportunities  in 
riparian  habitats.  W.  Birds  18:63-70. 

.  1991.  Diurnal  foraging  by  Spotted  Owls.  Wilson  Bull. 

103:138-140. 

Laymon,  S.  A.,  B.  A.  Garrison,  and  J.  M.  Humphrey.  1987. 
Historic  and  current  status  of  the  Bank  Swallow  in  Califor- 
nia, 1987.  Wildl.  Mgmt.  Div.  Admin.  Rept  88-2.  Calif. 
Dept.  Fish  Game,  Sacramento. 

Laymon,  S.  L  and  M.  D.  Halterman.  1987.  Can  the  western 
subspecies  of  the  Yellow-billed  Cuckoo  be  saved  from 
extinction?  W.  Birds  18:19-25. 

Leach,  H.  R,  C.  M.  Ferrel,  and  E.  E.  Clark.  1953.  A  study  of 
the  food  habits  of  the  Ring-necked  Pheasant  on  irrigated 
pasture  in  California.  Calif.  Fish  Game  39:517-525. 

Legg,  K.  and  F.  A.  Pitelka.  1956.  Ecologic  overlap  of  Allen 
and  Anna  hummingbirds  nesting  in  Santa  Cruz,  Califor- 
nia. Condor  58:393-405. 

Leopold,  A.  S.  1977.  TKe  California  Quail.  Univ.  California 
Press,  Berkeley. 

Leopold,  A.  S.,  M.  Erwin,  J.  Oh,  and  B.  Browning.  1976. 
Phytoestrogens:  Adverse  effects  on  reproduction  in  Califor- 
nia Quail.  Science  191:98-100. 

Lewis,  D.  B.  and  K.  T.  Briggs.  1985.  Pigeon  Guillemot.  In 
California  seabird  ecology  study:  Synthesis  of  information, 
126-138.  Center  for  Marine  Studies,  Univ.  Calif.,  Santa 
Cruz.  Rept.  for  Pac.  OCS  Region  Minerals  Mgmt.  Serv., 
U.S.  Dept.  Inter. 

Lewis,  H.  F.  1929.  TKe  Natural  History  of  the  Double-crested 
Cormorant  (Phalacrocorax  auritus  auritus  L.).  Ru-Mi-Lou 
Books,  Ottawa. 

Lidicker,  W.  Z.,  Jr.  and  F.  C.  McCollum.  1979.  Canada 
Goose  established  as  a  breeding  species  in  San  Francisco 
Bay.  W.  Birds  10:159-162. 

Lindsay,  A.  A.  1939.  Food  of  the  Starling  in  central  New  York 
state.  Wilson  Bull.  51:176-182. 

Linsdale,  J.  M.  1957.  Goldfinches  on  the  Hastings  Natural 
History  Reservation.  Am.  Midi.  Nat.  57:1-119. 

.  1968a.  Green-backed  Goldfinch.  In  O.  L  Austin,  Jr., 

ed.  A.  C.  Bent  et  al.'s  Life  histories  of  North  American 
cardinals,  grosbeaks,  buntings,  towhees,  finches,  sparrows, 
and  allies.  U.S.  Nad.  Mus.  Bull.  237  (Part  1):  474-486. 

.  1968b.  Lawrence's  Goldfinch.  In  O.  L  Austin,  Jr.,  ed. 

A.  C.  Bent  et  al.'s  Life  histories  of  North  American 
cardinals,  grosbeaks,  buntings,  towhees,  finches,  sparrows, 
and  allies.  U.S.  Nad.  Mus.  Bull.  237  (Part  1):  486-496. 

Linthicum,  J.,  ed.  1988.  Peregrine  Falcon  monitoring,  nest 
management,  hack  site,  and  cross-fostering  efforts,  1988. 
Rept.  of  Santa  Cmz  Pred.  Bird  Res.  Group,  Univ.  Calif., 
Santa  Cruz. 


460 


LITERATURE  CITED 


Littrell,  E.  E.  1986.  Shell  thickness  and  organochlorine  pesti- 
cides in  Osprey  eggs  from  Eagle  Lake,  California.  Calif. 
Fish  Game  72:182-185. 

Liverman,  M.  C.  1990.  The  (Endangered)  Endangered  Spe- 
cies Act:  Political  economy  of  the  Northern  Spotted  Owl. 
Endangered  Species  UPDATE  7(10  &  ll):l-4. 

Lord,  J.  and  D.  J.  Munns,  eds.  1970.  Atlas  of  Breeding  Birds 
of  the  West  Midlands.  Collins,  London. 

Lovell,  H.  E.  1958.  Baiting  offish  by  a  Green  Heron.  Wilson 
Bull.  70:280-281. 

Low,  J.  B.  1941.  Nesting  of  the  Ruddy  Duck  in  Iowa.  Auk 
58:506-516. 

Low,  S.  H.  1933.  Further  notes  on  the  nesting  of  the  Tree 
Swallow.  Bird-Banding  4:76-87. 

.   1934-  Nest  distribution  and  survival  ratio  of  Tree 

Swallows.  Bird-Banding  5:24-30. 

Lundquist,  R  W.  and  D.  A.  Manuwal.  1990.  Seasonal 
differences  in  foraging  habitat  of  cavity-nesting  birds  in  the 
southern  Washington  Cascades.  In  M.  L  Morrison,  C.  J. 
Ralph,  J.  Verner,  and  J.  R.  Jehl,  Jr.,  eds.  Avian  foraging: 
Theory,  methodology,  and  applications,  218-225.  Studies 
Avian  Biol.  13. 

Lunk,  W.  A.  1962.  The  Rough-winged  Swallow  Stelgidopteryx 
ruficollis  (Vieillot):  A  study  based  on  its  breeding  biology 
in  Michigan.  Publ.  Nutt.  Ornithol.  Club  4. 

M 

McAllister,  T  H.,  Jr.  and  D.  B.  Marshall.  1945.  Summer 
birds  of  the  Fremont  National  Forest,  Oregon.  Auk  62: 
177-189. 

MacArthur,  R.  H.  and  E.  O.  Wilson.  1967.  The  Theory  of 
Island  Biogeography.  Princeton  Univ.  Press,  Princeton. 

McAtee,  W.  L  1905.  The  Horned  Larks  and  their  relation  to 
agriculture.  U.S.  Dept.  Agri.  Biol.  Surv.  Bull.  23. 

.  1908.  Food  habits  of  the  grosbeaks.  U.S.  Dept.  Agri. 

Biol.  Surv.  Bull.  32. 

McAtee,  W.  L  and  F.  E.  L  Beal.  1912.  Some  common  game, 
aquatic,  and  rapacious  birds  in  relation  to  man.  U.S.  Dept. 
Agri.  Farmer's  Bull.  497. 

McCabe,  T.  T.  1932.  Wholesale  poison  for  the  Red-wings. 
Condor  34:49-50. 

McCaskie,  R.  G.  1965.  The  Cattle  Egret  reaches  the  West 
Coast  of  the  United  States.  Condor  67:89. 

McCaskie,  R  G.,  P.  DeBenedictis,  R.  A.  Erickson,  and 
J.  Morlan.  1979.  Birds  of  northern  California:  An  anno- 
tated field  list.  2nd  ed.  Golden  Gate  Audubon  Soc., 
Berkeley. 

McChesney,  G.  L  1988.  Mark-recapture  population  esti- 
mates and  diet  of  Ashy  and  Leach's  storm-petrels  on 
Southeast  Farallon  Island,  California,  1987.  B.A.  thesis, 
Univ.  Calif.,  Santa  Cruz. 

McClelland,  B.  R.  1979.  The  Pileated  Woodpecker  in  forests 
of  the  northern  Rocky  Mountains.  In  J.  G.  Dickson,  R.  N. 
Conner,  R.  R.  Heet,  J.  C.  Kroll,  and  J.  A.  Jackson,  eds.  The 
Role  of  Insectivorous  Birds  in  Forest  Ecosystems,  283-299. 
Academic  Press,  New  York. 


McCurdy,  G.  F.  1983.  The  status  of  the  Osprey  at  Kent  Lake, 
Marin  County,  California.  RepL  for  the  Marin  Municipal 
Water  District 

MacDonald,  K.  B.  1977.  Coastal  salt  marsh.  In  M.  G. 
Barbour  and  J.  Major,  eds.  Terrestrial  Vegetation  of  Califor- 
nia, 263-294-  John  Wiley  &  Sons,  New  York. 

McEllin,  S.  M.  1979a.  Nest  sites  and  population  demogra- 
phies of  White-breasted  and  Pigmy  nuthatches  in  Colo- 
rado. Condor  81:348-352. 

.  1979b.  Population  demographics,  spacing  and  foraging 

behavior  of  White-breasted  and  Pygmy  nuthatches  in  pon- 
derosa  pine  habitat.  In  J.  G.  Dickson,  R  N.  Conner,  R.  R 
Heet,  J.  C.  Kroll,  and  J.  A.  Jackson,  eds.  The  Role  of 
Insectivorous  Birds  in  Forest  Ecosystems,  301-331.  Academic 
Press,  New  York. 

McGillivray,  W.  B.  1981.  Climatic  influences  on  productivity 
in  the  House  Sparrow.  Wilson  Bull.  93:196-206. 

MacGregor,  W.  G.  and  W.  M.  Smith.  1955.  Nesting  and 
production  of  the  Band-tailed  Pigeon  in  California.  Calif. 
Fish  Game  41:315-326. 

MacKenzie,  D.  I.  and  S.  G  Sealy.  1981 .  Nest  site  selection  in 
Eastern  and  Western  kingbirds:  A  multivariate  approach. 
Condor  83:310-321. 

McLandress,  M.  R.  and  D.  G.  Raveling.  1981a.  Hyperphagia 
and  social  behavior  of  Canada  Geese  prior  to  spring 
migration.  Wilson  Bull.  93:310-324. 

.   1981b.  Changes  in  diet  and  body  composition  of 

Canada  Geese  before  spring  migration.  Auk  98:65-79. 

MacRoberts,  M.  H.  1970.  Notes  on  the  food  habits  and  food 
defense  of  the  Acorn  Woodpecker.  Condor  72:196-204. 

.  1974.  Acorns,  woodpeckers,  grubs,  and  scientists.  Pac. 

Discovery  27:9-15. 

MacRoberts,  M.  H.  and  B.  R.  MacRoberts.  1976.  Social 
organization  and  behavior  of  the  Acorn  Woodpecker  in 
central  coastal  California.  Ornithol.  Monogr.  21:1-115. 

Mailliard,  J.  1900.  Land  birds  of  Marin  County,  Cal.  Condor 
2:62-68. 

.  1904-  A  few  records  supplementary  to  GrinnelPs  check- 

-list  of  California  birds.  Condor  6:14-16. 

.   1909a.  Nest  of  the  Dusky  Poor-will  (Phalaenoptilus 

nuttallii  califomicus).  Condor  11:45-47- 

.  1909b.  Nest  of  the  Tolmie  Warbler.  Condor  1 1 :65-66. 

.  1911.  Odds  and  ends.  Condor  13:49-50. 

.  1912.  Breeding  of  the  Band-tailed  Pigeon  in  Marin 

County,  Calif.  Condor  14:194- 
-.  1913.  Some  curious  nesting  places  of  the  Allen  Hum- 


mingbird on  the  Rancho  San  Geromino.  Condor  15: 

205-207. 
— .  1914-  Notes  on  a  colony  of  Tri-colored  Red-wings. 

Condor  16:204-207. 
— .  1924a.  Some  new  records  for  northeastern  California. 

Condor  26:213-217. 
— .  1924b.  Autobiography  of  Joseph  Mailliard.  Condor 

26:10-29. 
— .  1936.  Poor  selection  of  building  sites.  Condor  38:249. 


Mailliard,  J.  W.  1912.  Concerning  nesting  sites  of  the  Cali- 
fornia Jay.  Condor  14:42. 


461 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Maino,  E.  and  F.  Howard.  1955.  Ornamental  Trees:  An 
Illustrated  Guide  to  their  Selection  and  Care.  Univ.  Califor- 
nia Press,  Berkeley. 

Major,  J.  1 977.  California  climate  in  relation  to  vegetation.  In 
M.  G.  Barbour  and  J.  Major,  eds.  Terrestrial  Vegetation  of 
California,  11-74-  John  Wiley  6k  Sons,  New  York. 

Mallette,  R.  D.  and  J.  R  Slosson.  1987.  Upland  game  of 
California.  Calif.  Dept.  Fish  Game,  Sacramento. 

Mannan,  R.  W.  1984.  Summer  area  requirements  of  Pileated 
Woodpeckers  in  western  Oregon.  Wildl.  Soc.  Bull.  12: 
265-268. 

Manolis,T.  1977.  Foraging  relationships  of  Mountain  Chick- 
adees and  Pygmy  Nuthatches.  W.  Birds  8:13-20. 

.  1978.  Status  of  the  Black  Rail  in  central  California.  W. 

Birds  9:151-158. 

.  1991.  Adasing  California's  breeding  birds— county  by 

county.  W.  Birds  22:92-94. 

March,  G.  L  and  R.  M.  F.  S.  Sadlier.  1972.  Studies  on  the 
Band-tailed  Pigeon  (Columba  fasciata)  in  British  Colum- 
bia, II.  Food  resource  and  mineral-graveling  activity.  Syesis 
5:279-284. 

Mariani,  J.  M.  and  D.  A.  Manuwal.  1990.  Factors  influencing 
Brown  Creeper  (Certhia  americana)  abundance  patterns  in 
the  southern  Washington  Cascade  Range.  In  M.  L  Mor- 
rison, C.  J.  Ralph,  J.  Verner,  J.  R.  Jehl,  Jr.,  eds.  Avian 
foraging:  Theory,  methodology,  and  applications,  53-57. 
Studies  Avian  Biol.  13. 

Markle,  J.  M.  1946.  A  nesting  site  of  the  Lark  Sparrow. 
Condor  48:245-246. 

Marks,  J.  S.  1984.  Feeding  ecology  of  breeding  Long-eared 
Owls  in  southwestern  Idaho.  Can.  J.  Zool.  62:1528-1533. 

.  1985.  Yearling  male  Long-eared  Owls  breed  near  natal 

nest.  J.  Field  Ornithol.  56:181-182. 

.  1 986.  Nest  site  characteristics  and  reproductive  success 

of  Long-eared  Owls  (Asio  otus)  in  southwestern  Idaho. 
Wilson  Bull.  98:547-560. 

Marks,  J.  S.  and  E.  Yensen.  1980.  Nest  sites  and  food  habits 
of  Long-eared  Owls  in  southwestern  Idaho.  Murrelet  61: 
86-91. 

Marshall,  J.  T.  1948.  Ecological  races  of  Song  Sparrows  in  the 
San  Francisco  Bay  region.  Part  I:  Habitat  and  abundance. 
Part  II:  Geographic  variation.  Condor  50:193-215,  233- 
256. 

.  1988.  Birds  lost  from  a  giant  sequoia  forest  during  fifty 

years.  Condor  90:359-372. 

Marshall,  M.  F.,  L  R.  Mewaldt,  M.  F.  Rippey,  R  L  C.  Leong, 
H.  L  Cogswell,  K.  Dedrick,  S.  Gregory,  H.  T.  Harvey,  R. 
F.  Johnston,  and  S.  E.  Senner.  1988.  Petition  to  list  the 
Suisun  Song  Sparrow  (Melospiza  melodia  maxilfaris^  as 
Endangered.  Submitted  to  Calif.  Fish  Game  Comm. 

Marti,  C.  D.  1974.  Feeding  ecology  of  four  sympatric  owls. 
Condor  76:45-61. 

.  1976.  A  review  of  prey  selection  by  the  Long-eared  Owl. 

Condor  78:331-336. 

Marti,  C.  D.  and  S.  W.  Everett.  1978.  Polygyny  in  Utah 
Dippers.  W.  Birds  9:174- 

Marti,  C.  D.  and  J.  S.  Marks.  1989.  Medium-sized  owls.  In 
National  Wildlife   Federation.   Proc.  Western   Raptor 


Mgmt.  Symp.  and  Workshop,  124-133.  Nad.  Wildl.  Fed. 

Tech.  and  Sci.  Ser.  1 2. 
Martin,  A.  C,  H.  S.  Zim,  and  A.  L  Nelson.  1951 .  American 

Wildlife  and    Plants:    A   Guide   to    Wildlife   Food   Habits. 

McGraw  Hill,  New  York. 
Martin,   D.  J.   1973.   Selected  aspects  of  Burrowing  Owl 

ecology  and  behavior.  Condor  75:446-456. 
Martin,  J.  W.  1989.  Harriers  and  kites.  In  National  Wildlife 

Federation.   Proc.   Western   Raptor  Mgmt.   Symp.   and 

Workshop,  83-91.  Nad.  Wildl.  Fed.  Sci.  and  Tech.  Ser. 

12. 
Mason,  J.  1970.  Point  Reyes:  The  Solemn  Land.  North  Shore 

Books,  Inverness,  Calif. 
.   1981.  The  Black  Forest   Point  Reyes  Historian  6: 

635-637,  640. 
Mason,  J.  and  H.  V.  C.  Park.  1971 .  Ear!}  Marin.  North  Shore 

Books,  Inverness. 
.    1975.   The   Making  of  Marin.   North   Shore  Books, 

Inverness. 
Maxson,  S.J.  and  G.  D.  Maxson.  1981.  Commensal  foraging 

between   Hairy   and   Pileated   woodpeckers.   J.   Field 

Ornithol.  52:62-63. 
Mayfield,  H.  1965.  The  Brown-headed  Cowbird  with  old  and 

new  hosts.  Living  Bird  4:13-28. 
Mayhew,  W.  W.  1958.  The  biology  of  the  Cliff  Swallow  in 

California.  Condor  60:6-37. 
Melbostad,  G.  W.  1969.  A  history  of  transportation,  land 

use,  and  economic  development  in  coastal  Marin  County, 

1800-1900.  MA.  thesis,  Dominican  College,  San  Rafael. 
Meserve,  P.  L   1977.  Food  habits  of  a  White-tailed  Kite 

population  in  central  Chile.  Condor  79:263-265. 
Mewaldt,  L  R.,  S.  S.   Kibby,  and  M.  L  Morton.   1968. 

Comparative  biology  of  Pacific  coastal  White-crowned 

Sparrows.  Condor  70:14-30. 
Mewaldt,  L  R.  and  J.  R.  King.  1977.  The  annual  cycle  of 

White-crowned  Sparrows  (Zonotrichia  leucophrys  nuttalli) 

in  coastal  California.  Condor  79:445-455. 
Michael,  C.  W.  1928.  Nesting  time  of  Band-tailed  Pigeons  in 

Yosemite  Valley.  Condor  30:127. 
.  1934-  Nesting  of  the  Red-breasted  Nuthatch.  Condor 

36:113. 
Michaelson,  J.  C.  1977.  North  Pacific  sea  surface  tempera- 
tures  and  California  precipitation.   M.A.   thesis,  Univ. 

Calif,  Berkeley. 
Michener,  H.  and  J.  Michener.  1945.  California  jays,  their 

storage  and  recovery  of  food,  and  observations  atone  nest 

Condor  47:206-210. 
Michener,  J.  R.  1951.  Territorial  behavior  and  age  composi- 
tion in  a  population  of  Mockingbirds  at  a  feeding  station. 

Condor  53:276-283. 
Middleton,  A.  L  A.  1979.  Influence  of  age  and  habitat  on 

reproduction  by  the  American  Goldfinch.   Ecology  60: 

418-432. 
Miles,  D.  B.  1990.  The  importance  and  consequences  of 

temporal  variation  in  avian  foraging  behavior.  In  M.  L 

Morrison,  C.  J.  Ralph,  J.  Verner,  and  J.  R.  Jehl,  Jr.,  eds. 


462 


LITERATURE  CITED 


Avian  foraging:  Theory,  methodology,  and  applications, 

210-217.  Studies  Avian  Biol.  13. 
Millar,  C.  I.  1986.  Bishop  Pine  (Pinus  muricata)  of  inland 

Marin  County  California.  Madrono  33:123-129. 
Miller,  A.  H.  1931a.  Systematic  revision  and  natural  history 

of  the  American  shrikes  (Lanius).  Univ.  Calif.  Publ.  Zool. 

38:11-242. 
.   1931b.  Notes  on  the  song  and  territorial  habits  of 

Bullock's  Oriole.  Wilson  Bull.  43:102-108. 
.  1941.  Speciation  in  the  avian  genus  )unco.  Univ.  Calif. 

Publ.  Zool.  44:173-434. 

— .  1946.  Western  Tanager  summer  resident  in  Marin 


County.  Gull  28:33. 
.  1950.  California  Shrike.  In  A.  C.  Bent,  ed.  Life  histo- 
ries of  North  American  wagtails,  shrikes,  vireos,  and  their 

allies.  U.S.  Nad.  Mus.  Bull.  197:157-179. 
.  1951.  An  analysis  of  the  distribution  of  the  birds  of 

California.  Univ.  Calif.  Publ.  Zool.  50:531-644. 
.  1968.  Sage  Sparrow.  In  O.  L.  Austin,  ed.  A.  C.  Bent  et 

al.'s  Life  histories  of  North  American  cardinals,  grosbeaks, 

buntings,  towhees,  finches,  sparrows,  and  allies.  U.S.  Nad. 

Mus.  Bull.  237  (Part  2):  1004-1021. 
Miller,  A.  H.  and  C.  E.  Bock.  1972.  Natural  history  of  the 

Nuttall  Woodpecker  at  the  Hastings  Reservation.  Condor 

74=284-294. 
Miller,  E.  V.  1941.  Behavior  of  the  Bewick  Wren.  Condor 

43:81-99. 
Miller,  J.  R.  and  J.  T  Miller.  1948.  Nesting  of  the  Spotted 

Sandpiper  at  Detroit,  Michigan.  Auk  65:558-567. 
Miller,  M.  R.  1983.  Foraging  dives  by  post-breeding  Northern 

Pintails.  Wilson  Bull.  95:294-296. 
.  1987.  Fall  and  winter  foods  of  Northern  Pintails  in  the 

Sacramento  Valley,  California.  J.  Wildl.  Mgmt.  51:405- 

414. 
Miller,  R.  F.  1942.  The  Pied-billed  Grebe,  a  breeding  bird  of 

the  Philadelphia  region.  Cassinia  32:23-34. 
Milligan,  M.  M.  and  J.  Verner.  1971.  Inter-populational  song 

dialect  discrimination   in   the  White-crowned  Sparrow. 

Condor  73:208-213. 
Mills,  G.  S.  1976.  American  Kestrel  sex  ratios  and  habitat 

separation.  Auk  93:740-748. 
Mobbs,  A.  J.  1979.  Methods  used  by  the  Trochilidae  when 

capturing  insects.  Avicul.  Mag.  85:26-30.  CWalsall,  West 

Midlands,  England.) 
Moffitt,  J.  1939a.  Notes  on  the  distribution  of  herons  in 

California.  Condor  41:81-82. 
.  1939b.  Notes  on  the  distribution  of  Whisding  Swan 

and  Canada  Goose  in  California.  Condor  41:93-97- 
.  1941 .  Notes  on  the  food  of  the  California  Clapper  Rail. 

Condor  43:270-273. 
Moldenhauer,  R   R.  and  J.  A.  Wiens.   1970.  The  water 

economy  of  the  Sage  Sparrow,  Amphispiza  belli  nevadensis. 

Condor  72:265-275. 
Monk,  J.  G.,  M.  N.  Kirven,  and  B.  J.  Walton.  1989.  Califor- 
nia Peregine  Falcon  monitoring  and  management  effort  in 

1989  with  a  discussion  of  population   trend   analysis. 

Appendix  6.  In  J.  Linthicum,  ed.  Peregrine  Falcon  moni- 


toring,  nest  management,  hacksite,   and  cross-fostering 

efforts,  1989.  Annual  activity  statement  of  the  Santa  Cruz 

Pred.  Bird  Res.  Group,  Univ.  Calif.,  Santa  Cruz. 
Moore,  J.  1986.  Dietary  variation  among  nesding  Starlings. 

Condor  88:181-189. 
Moore,  R.  T.  and  A.  Barr.  1941.  Habits  of  the  White-tailed 

Kite.  Auk  58:453-462. 
Morlan,  J.  and  R.  Erickson.  1988.  Supplement  to  the  Birds 

of  northern  California,   1988.   In  R.  G.   McCaskie,  P. 

DeBenedictis,  R.  Erickson,  and  J.  Morlan.  Birds  of  north- 
ern California:  An  annotated  field  list,  85-97.  2nd  ed. 

Golden  Gate  Audubon,  Berkeley. 
Morrell,  S.  H.,  H.  R.  Huber,  T.  J.  Lewis,  and  D.  G.  Ainley. 

1979.  Feeding  ecology  of  Black  Oystercatchers  on  South 

Farallon  Island,  California  (abstract  only).  In  F.  A.  Pitelka, 

ed.  Shorebirds  in  marine  environments,  183-186.  Studies 

Avian  Biol.  2. 
Morrison,  M.  L  1980.  Seasonal  aspects  of  the  predatory 

behavior  of  Loggerhead  Shrikes.  Condor  82:296-300. 
.  1981a.  Population  trends  of  the  Loggerhead  Shrike  in 

the  United  States.  Am.  Birds  35:754-757. 
.  1981b.  The  structure  of  western  warbler  assemblages: 

Analysis  of  foraging  behavior  and   habitat  selection  in 

Oregon.  Auk  98:578-588. 
.  1982.  The  structure  of  western  warbler  assemblages: 

Ecomorphological  analysis  of  the  Black-throated  Gray  and 

Hermit  warblers.  Auk  99:503-51 3. 
.  1 984-  Influence  of  sample  size  on  discriminant  function 

analysis  of  habitat  use  by  birds.  J.  Field  Ornithol.  55: 

330-335. 
Morrison,  M.  L,  I.  C.  Timossi,  K.  A.  With,  and  P.  N. 

Manley.  1985.  Use  of  tree  species  by  forest  birds  during 

winter  and  summer.  J.  Wildl.  Mgmt.  49:1098-1102. 
Morrison,  M.  L  and  K.  A.  With.  1987.  Intersexual  and 

interseasonal  resource  partitioning  in  Hairy  and  White- 
headed  woodpeckers.  Auk  104:225-233. 
Morrison,  M.  L,  K.  A.  With,  I.  C.  Timossi,  W.  M.  Block, 

and  K.  A.  Milne.  1987.  Foraging  behavior  of  bark-foraging 

birds  in  the  Sierra  Nevada.  Condor  89:201-204. 
Morse,   D.   H.    1967.   Competitive   relationships   between 

Parula  Warblers  and  other  species  during  the  breeding 

season.  Auk  84:490-502. 
.    1971.  The  foraging  of  warblers   isolated  on   small 

islands.  Ecology  52:216-228. 
.   1973.  The  foraging  of  small  populations  of  Yellow 

Warblers  and  American  Redstarts.  Ecology  54:346-355. 
Muldal,  A.,  H.  L  Gibbs,  and  R.  J.  Robertson.  1985.  Preferred 

nest  spacing  of  an  obligate  cavity-nesting  bird,  the  Tree 

Swallow.  Condor  87:356-363. 
Munro-Fraser,  J.  P.  1880.  History  of  Marin  Count},  California. 

Alley,  Bowen,  &  Co.  Republished  1972  by  C.  B.  Veronda, 

P.O.  Box  505,  Petaluma,  CA  94952. 
Munson,  C.  R.  and  L  W.  Adams.  1984-  A  record  of  ground 

nesting  by  the  Hermit  Warbler.  Wilson  Bull.  96:301. 
Murphy,  E.  C.  1978.  Breeding  ecology  of  House  Sparrows: 

Spatial  variation.  Condor  80:180-193. 


463 


MARIN  COUNTY  BRKEDING  BIRD  ATIAS 


N 

National  Oceanic  and  Atmospheric  Administration.  1982. 
Monthly  normals  of  temperature,  precipitation,  and  heat- 
ing and  cooling  degree  days  1951-80.  Climatography  of 
U.S.  81  (California). 

Naylor,  A.  E.  1960.  The  Wood  Duck  in  California  with 
special  reference  to  the  use  of  nest  boxes.  Calif.  Fish  Game 
46:241-269. 

Neff,  J.  A.  1937.  Nesting  distribution  of  the  Tri-colored 
Red-wing.  Condor  39:61-81. 

.  1947.  Habits,  food,  and  economic  status  of  the  Band- 
tailed  Pigeon.  N.  Am.  Fauna  58:1-76. 

Nelson,  L  and  J.  Hooper.  1976.  California  upland  game  and 
their  management.  Leaflet  2720.  Div.  Agri.  Sci.,  Univ. 
Calif.,  Davis. 

Newman,  J.  D.  1968.  Black-chinned  Sparrow.  In  O.  L 
Austin,  ed.  A.  C.  Bent  et  al.'s  Life  histories  of  North 
American  cardinals,  grosbeaks,  buntings,  towhees, 
finches,  sparrows,  and  allies.  U.S.  Nad.  Mus.  Bull.  237 
(Part  2):  1241-1248. 

Newton,  I.  1973.  Finches.  Taplinger,  New  York 

Nice,  M.  M.  1937.  Studies  in  the  life  history  of  the  Song 
Sparrow.  Trans.  Linn.  Soc.  N.Y.  4:1-246. 

Nichols,  D.  R.  and  N.  A.  Wright.  1971.  Preliminary  map  of 
the  historic  marshlands,  San  Francisco  Bay,  California. 
Open  File  Rept.  Basic  Data  Contrib.  9.  U.S.  Geol.  Surv., 
Menlo  Park. 

Nickell,  W.  P.  1951.  Studies  of  habitats,  territory,  and  nests 
of  the  eastern  goldfinch.  Auk  68:447-470. 

Nisbet,  I.  C.  T.  1988.  The  relative  importance  of  DDE  and 
dieldrin  in  the  decline  of  Peregrine  Falcon  populations.  In 
T.  J.  Cade,  J.  H.  Enderson,  C.  G.  Thelander,  and  C.  M. 
White,  eds.  Peregrine  Falcon  Populations:  Their  Management 
and  Recovery,  351-375.  The  Peregrine  Fund,  Boise,  Idaho. 

Norris,  C.  A.  1960.  The  breeding  distributions  of  thirty  bird 
species  in  1952.  Bird  Study  7:129-184. 

Norris,  R.  A.  1958.  Comparative  biosystematics  and  life 
history  of  the  nuthatches  Sitta  pygmaea  and  Sitta  pusilla. 
Univ.  Calif.  Publ.  Zool.  56:199-300. 

North,  C.  A.  1973.  Population  dynamics  of  the  House 
Sparrow  (Passer  domesticus  L.)  in  Wisconsin.  In  S.  C. 
Kendeigh  and  J.  Pinowski,  eds.  Productivity,  Population 
Dynamics,  and  Systematics  of  Granivorous  Bird's,  195-219. 
Polish  Sci.  Publ.,  Warsaw. 

Nudd,  T.  D.  1982.  Ecological  separation  of  grebes  and  coots: 
Interference  competition  or  microhabitat  selection?  Wil- 
son Bull.  94:505-514. 

o 

Oakleaf,  B.,  H.  Downing,  B.  and  M.  Raynes,  and  O  Scott, 

eds.  1979.  Working  draft  of  Wyoming  avian  adas.  Wyom. 

Game  and  Fish  Dept.,  Lander. 
Oberholser,  H.  C.  1974.  The  Bird  Life  of  Texas.  Vol.  2.  Univ. 

Texas  Press,  Austin. 
Oberlander,  G.   1939.  The  history  of  a  family  of  Black 

Phoebes.  Condor  41:133-151. 


Oberlander,  G.  T.  1956.  Summer  fog  precipitation  on  the 
San  Francisco  peninsula.  Ecology  37:851-852. 

Odum,  R.  R  1977.  Sora  (Porzana  Carolina).  In  G.  C.  Sander- 
son, ed.  Management  of  migratory  shore  and  upland  game 
birds  in  North  America,  57-65.  Int.  Assoc.  Fish  Wildl. 
Agencies  and  U.S.  Fish  Wildl.  Serv. 

Ogden,  J.  D.,  ed.  1977.  Transactions  of  the  North  American 
Osprey  Research  Conference.  USDI,  U.S.  Nad.  Park  Serv. 
Proc.  Ser.  2,  Washington,  D.C. 

Ohlendorf,  H.  M.  1974-  Competitive  relationships  among 
kingbirds  (Tyrannus)  in  Trans-Pecos,  Texas.  Wilson  Bull. 
86:357-373. 

.  1976.  Comparative  breeding  ecology  of  phoebes  in 

Trans-Pecos,  Texas.  Wilson  Bull.  88:255-271. 

Ohlendorf,  H.  M.,  T.  W.  Custer,  R.  W.  Lowe,  M.  Rigney, 
and  E.  Cromartie.  1988.  Organochlorines  and  mercury  in 
eggs  of  coastal  terns  and  herons  in  California,  USA. 
Colonial  Waterbirds  1 1 :85-94. 

Ohlendorf,  H.  M.  and  W.  J.  Heming.  1988.  Birds  and 
environmental  contaminants  in  San  Francisco  and  Ches- 
apeake bays.  Marine  Pollution  Bull.  19:487-495. 

Ohlendorf,  H.  M.,  E.  E.  Klaas,  and  T  E.  Kaiser.  1978. 
Environmental  pollutants  and  eggshell  thinning  in  the 
Black-crowned  Night-Heron.  In  Wading  birds,  63-82. 
Nad.  Aud.  Soc.  Res.  Rept.  7. 

Ohmart,  R.  D.  1973.  Observations  on  the  breeding  adapta- 
tions of  die  Roadrunner.  Condor  75:140-149. 

Olsen,  D.  W.  1977.  A  literature  review  of  pheasant  habitat 
requirements  and  improvement  methods:  Annual  perfor- 
mance report  for  Federal  Aid  Project.  Publ.  Utah  Div. 
Wildl.  Res.  77-7,  Salt  Lake  City. 

Orians,  G.  H.  1960.  Autumnal  breeding  in  the  Tricolored 
Blackbird.  Auk  77:379-398. 

.  1961.  The  ecology  of  blackbird  (Agelaius)  social  sys- 
tems. Ecol.  Monogr.  31:285-312. 

.  1980.  Some  adaptations  of  marsh-nesting  blackbirds. 

Monogr.  Pop.  Biol.  14-  Princeton  Univ.  Press,  Princeton. 

Orians,  G.  H.  and  H.  S.  Horn.  1969.  Overlap  in  foods  and 
foraging  of  four  species  of  blackbirds  in  the  Potholes  of 
central  Washington.  Ecology  50:930-938. 

Oring,  L  W.  and  M.  L  Knudson.  1972.  Monogamy  and 
polyandry  in  the  Spotted  Sandpiper.  Living  Bird  11:59- 
73. 

Oring,  L  W.,  D.  B.  Lank,  and  S.  J.  Maxson.  1983.  Popula- 
tion studies  of  the  polyandrous  Spotted  Sandpiper.  Auk 
100:272-285. 

Oring,  L  W.  and  S.  J.  Maxson.  1978.  Instances  of  simulta- 
neous polyandry  by  a  Spotted  Sandpiper,  Actitis  macularia. 
Ibis  120:349-353. 

Orr,  R.  T  1937.  Summer  records  of  birds  of  Marin  County, 
California.  Condor  39:38. 

Osborne,  T  O.  1972.  Ecology  and  avian  use  of  the  coastal 
rocks  of  Northern  California.  M.A.  thesis,  Humboldt  State 
Univ.,  Areata. 

Osborne,  T.  O  and  J.  G.  Reynolds.  1971.  California  seabird 
breeding  ground  survey.  Wildl.  Mgmt.  Branch  Admin. 
Rept.  71-73.  Calif.  Dept.  Fish  Game,  Sacramento. 


464 


LITERATURE  CITED 


Otvos,  I.  S.  and  R.  W.  Stark.  1985.  Arthropod  food  of  some 
forest-inhabiting  birds.  Can.  Ent.  117:971-990. 


Page,  G.  W.,  F.  C.  Bidstrup,  R.  J.  Ramer,  and  L.  E.  Stenzel. 
1986.  Distribution  of  wintering  Snowy  Plovers  in  Califor- 
nia and  adjacent  states.  W.  Birds  17:145-170. 

Page,  G.  W.,  H.  R  Carter,  and  R.  G.  Ford.  1990.  Numbers 
of  seabirds  killed  or  debilitated  in  the  1986  Apex  Houston 
oil  spill  in  California.  In  S.  G.  Sealy,  ed.  Auks  at  sea, 
164-174.  Studies  Avian  Biol.  14. 

Page,  G.  W.  and  J.  G.  Evens.  1987.  The  sizes  of  Clapper  Rail 
populations  at  Corte  Madera  Ecological  Reserve,  Muzzi 
Marsh,  San  Clemente  Creek,  and  Triangle  Marsh.  Point 
Reyes  Bird  Obs.  Rept.  to  Marin  Audubon  Soc.  PRBO 
Contrib.  367. 

Page,  G.  W.,  P.  L  Quinn,  and  J.  C.  Warriner.  1989. 
Comparison  of  the  breeding  of  hand-  and  wild-reared 
Snowy  Plovers.  Conserv.  Biol.  3:198-201. 

Page,  G.  W.  and  L  E.  Stenzel,  eds.  1981 .  The  breeding  status 
of  the  Snowy  Plover  in  California.  W.  Birds  12:1-40. 

Page,  G.  W.,  L  E.  Stenzel,  and  C.  A.  Ribic.  1985.  Nest  site 
selection  and  clutch  predation  in  the  Snowy  Plover.  Auk 
102:347-353. 

Page,  G.  W.,  L  E.  Stenzel,  W.  D.  Shuford,  and  C.  R.  Bruce. 
1991 .  Distribution  and  abundance  of  the  Snowy  Plover  on 
its  western  North  American  breeding  grounds.  J.  Field 
Ornithol.  62:245-255. 

Page,  G.  W.  and  M.  Walter.  1988.  Petition  to  list  the  coastal 
population  of  the  Western  Snowy  Plover  as  threatened. 
Point  Reyes  Bird  Obs.  Rept.  to  U.S.  Fish  Wildl.  Serv. 

Page,  G.  W.  and  D.  F.  Whitacre.  1975.  Raptor  predation  on 
wintering  shorebirds.  Condor  77:73-83. 

Palmer,  R  S.,  ed.  1962.  Handbook  of  North  American  Birds. 
Vol.  I:  Loons  through  Flamingos.  Yale  Univ.  Press,  New 
Haven. 

.  1967.  Species  accounts.  In  G.  D.  Stout,  ed.  The  Shore- 
birds  of  North  America,  143-267.  Viking,  New  York. 

.  1968.  Pine  Siskin.  In  O.  L  Austin,  Jr.,  ed.  A.  C.  Bent 

et  al.'s  Life  histories  of  North  American  cardinals,  gros- 
beaks, buntings,  towhees,  finches,  sparrows,  and  allies. 
U.S.  Nad.  Mus.  Bull.  237  (Part  1):  424-447. 

,  ed.  1976a.  Handbook  of  North  American  Birds.  Vol.  2: 


Waterfowl  (Part  I).  Yale  Univ.  Press,  New  Haven. 
-,  ed.  1976b.  Handbook  of  North  American  Birds.  Vol.  3: 


Waterfowl  (Part  2).  Yale  Univ.  Press,  New  Haven. 
,  ed.  1988a.  Handbook  of  North  American  Birds.  Vol.  4-' 

Diurnal  Raptors  (Part  I).  Yale  Univ.  Press,  New  Haven. 
,  ed.  1988b.  Handbook  of  North  American  Birds.  Vol.  5: 

Diurnal  Raptors  (Part  2).  Yale  Univ.  Press,  New  Haven. 
Palmer,  T.  K.  1973.  The  House  Finch  and  Starling  in  relation 

to  California's  agriculture.  In  S.  C.  Kendeigh  and  J.  Pi- 

nowski,  eds.  Productivity,  Population  Dynamics,  and  System- 

atics  of  Granivorous   Birds,   275-290.   Polish  Sci.   Publ., 

Warsaw. 
Parsons,  J.  J.  1960.  Fog  drip  from  coastal  stratus,  with  special 

reference  to  California.  Weather  (London)  15:58-62. 


Paszkowski,  C  A.  1982.  Vegetation,  ground,  and  frugivorous 
foraging  of  the  American  Robin.  Auk  99:701-709. 

.  1984-  Macrohabitat  use,  microhabitat  use,  and  foraging 

behavior  of  the  Hermit  Thrush  and  Veery  in  a  northern 
Wisconsin  forest.  Wilson  Bull.  96:286-292. 

Paterson,  R.  L,  Jr.  1984.  High  incidence  of  plant  material  and 
small  mammals  in  the  autumn  diet  of  Turkey  Vultures  in 
Virginia.  Wilson  Bull.  96:467-469. 

Pattee,  O.  H.  and  S.  R.  Wilbur.  1989.  Turkey  Vulture  and 
California  Condor.  In  National  Wildlife  Federation.  Proc. 
Western  Raptor  Mgmt.  Symp.  and  Workshop,  61-65. 
Nad.  Wildl.  Fed.  Sci.  and  Tech.  Ser.  12. 

Patton,  C.  P.  1956.  Climatology  of  summer  fogs  in  the  San 
Francisco  Bay  Area.  Univ.  Calif.  Publ.  Geogr.  10:113- 
200. 

Payne,  R.  B.  1969.  Breeding  season  and  reproductive  physi- 
ology of  Tricolored  and  Red-winged  blackbirds.  Univ. 
Calif.  Publ.  Zool.  90:1-114. 

Peakall,  D.  B.  and  L  F.  Kiff.  1988.  DDE  contamination  in 
Peregrines  and  American  Kestrels  and  its  effect  on  repro- 
duction. In  T  J.  Cade,  J.  H.  Enderson,  C.  G.  Thelander, 
and  C.  M.  White,  eds.  Peregrine  Falcon  Populations:  Their 
Management  and  Recovery,  337-350.  The  Peregrine  Fund, 
Boise,  Idaho. 

Pearson,  O.  P.  1963.  History  of  two  local  outbreaks  of  feral 
house  mice.  Ecol.  Monogr.  44:540-549. 

Peck,  G.  K.  and  R.  D.  James.  1983.  Breeding  Birds  of  Ontario: 
Nidology  and  Distribution.  Vol.  1:  Nonpasserines.  Royal 
Ontario  Museum,  Toronto. 

Peeters,  H.  J.  1962.  Nuptial  behavior  of  the  Band-tailed 
Pigeon  in  the  San  Francisco  Bay  Area.  Condor  64:445- 
470. 

Perring,  F.  H.  and  S.  M.  Walters.  1962.  Atlas  of  the  British 
Flora.  Botanical  Soc.  British  Isles.  T.  Nelson,  London. 

Peterson,  R.  T.,  G.  Mountfort,  and  P.  A.  D.  Hollom.  1954. 
A  Field  Guide  to  the  Birds  of  Britain  and  Europe.  Collins, 
London. 

Petit,  D.  R,  K.  E.  Petit,  and  L  J.  Petit.  1990.  Geographic 
variation  in  foraging  ecology  of  North  American  insectivo- 
rous birds.  In  M.  L  Morrison,  C.  J.  Ralph,  J.  Verner,  and 
J.  R  Jehl,  Jr.,  eds.  Avian  foraging:  Theory,  methodology, 
and  applications,  254-263.  Studies  Avian  Biol.  13. 

Phelps,  J.  H.,  Jr.  1968.  Oregon  Junco,  Pink-sided,  Northwest- 
ern, and  Point  Pinos  Oregon  juncos.  In  O.  L  Austin,  Jr., 
ed.  A.  C.  Bent  et  al.'s  Life  histories  of  North  American 
cardinals,  grosbeaks,  buntings,  towhees,  finches,  sparrows, 
and  allies.  U.S.  Nad.  Mus.  Bull.  237  (Part  2):  1050-1089. 

Phillips,  A.,  J.  Marshall,  and  G.  Monson.  1964.  The  Birds  of 
Arizona.  Univ.  Arizona  Press,  Tucson. 

Phillips,  J.  C  1922-1926.  A  Natural  History  of  the  Ducks.  4 
vols.  Houghton  Mifflin,  Boston. 

Piatt,  J.  F.  and  D.  N.  Netdeship.  1985.  Diving  depths  of  four 
alcids.  Auk  102:293-297. 

Pickwell,  G.  1930.  The  White-tailed  Kite.  Condor  32:221- 
230. 

Pickwell,  G.  B.  1931.  The  prairie  Horned  Lark.  St.  Louis 
Acad.  Sci.  Trans.  27:1-153. 


465 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Pierotti,  R.  1981.  Male  and  female  parental  roles  in  the 
Western  Gull  under  different  environmental  conditions. 
Auk  98:532-549. 

Pinkowski,  B.  C.  1979.  Foraging  ecology  and  habitat  utiliza- 
tion in  the  genus  Sialia.  In  J.  G.  Dickson,  R.  N.  Conner, 
R  R.  Fleet,  J.  A.  Jackson,  and  J.  C.  Kroll,  eds.  The  Role  of 
Insectivorous  Birds  in  Forest  Ecosystems,  165-190.  Academic 
Press,  New  York. 

Pinowska,  B.  1975.  Food  of  female  House  Sparrows  (Passer 
domesticus)  in  relation  to  stages  of  the  nesting  cycle.  Polish 
Ecol.  Studies  1:311-325. 

Pitelka,  F.  A.  1951a.  Ecologic  overlap  and  interspecific  strife 
in  breeding  populations  of  Anna  and  Allen  humming- 
birds. Ecology  32:641-661. 

.  1951b.  Breeding  seasons  of  hummingbirds  near  Santa 

Barbara,  California.  Condor  53:198-201. 

.  1951c.  Speciation  and  ecologic  distribution  in  Ameri- 
can jays  of  the  genus  Aphelocoma.  Univ.  Calif.  Publ.  Zool. 
50:195-464. 

Planck,  R.  J.  1967.  Nest  site  selection  and  nesting  in  the 
European  Starling,  Stumus  \nilgaris  L,  in  California.  Ph.D. 
thesis,  Univ.  Calif.,  Davis. 

Piatt,  S.  W.  and  J.  H.  Enderson.  1989.  Falcons.  In  National 
Wildlife  Federation.  Proc.  Western  Raptor  Mgmt.  Symp. 
and  Workshop,  111-117.  Nad.  Wildl.  Fed.  Sci.  and  Tech. 
Ser.  12. 

Pleasants,  B.  Y.  1979.  Adaptive  significance  of  the  variable 
dispersion  pattern  of  breeding  Northern  Orioles.  Condor 
81:28-34. 

Point  Reyes  Bird  Observatory.  1985.  The  impacts  of  the  T/V 
Puerto  Rican  oil  spill  on  marine  birds  and  mammal  popu- 
lations in  the  Gulf  of  the  Farallones,  6-19  November 
1984.  Point  Reyes  Bird  Obs.  Spec.  Sci.  Rept. 

Porter,  D.  K.,  M.  A.  Strong,  J.  B.  Giezentanner,  and  R.  A. 
Ryder.  1975.  Nest  ecology,  productivity,  and  growth  of  the 
Loggerhead  Shrike  on  the  shortgrass  prairie.  Southwestern 
Nat.  19:429-436. 

Portnoy,  J.  W.  and  W.  E.  Dodge.  1979.  Red-shouldered 
Hawk  nesting  ecology  and  behavior.  Wilson  Bull.  91: 
104-117. 

Poston,  H.  J.  1974-  Home  range  and  breeding  biology  of  the 
Shoveler.  Can.  Wildl.  Serv.  Rept.  Ser.  2. 

Pough,  R.  H.  1957.  Audubon  Western  Bird  Guide:  Land, 
Water,  and  Game  Birds.  Doubleday,  Garden  City,  N.Y. 

Pratt,  H.  M.  1972.  Nesting  success  of  Common  Egrets  and 
Great  Blue  Herons  in  the  San  Francisco  Bay  region. 
Condor  74:447-453. 

.  1974-  Breeding  of  Great  Blue  Herons  and  Great  Egrets 

at  Audubon  Canyon  Ranch,  California,  1972-73.  W. 
Birds  5:127-136. 

1980.  Directions  and  timing  of  Great  Blue  Heron 


foraging  flights  from  a  California  colony:  Implications  for 

social  facilitation  of  food  finding.  Wilson  Bull.  92:489- 

496. 
.  1983.  Marin  County  California  heron  colonies:  1967- 

81.  W.  Birds  14:169-184. 
Pray,  R.  H.  1950.  Cowbirds  in  the  Bay  Area.  Gull  32:38. 

466 


Prestt,  I.  and  A.  A.  Bell.   1966.  An  objective  method  of 

recording  breeding  distributions  of  common  birds  of  prey 

in  Britain.  Bird  Study  13:277-283. 
Price,  F.  E.  and  C.  E.  Bock.  1973.  Polygyny  in  the  Dipper. 

Condor  75:457-459. 
.  1983.  Population  ecology  of  the  Dipper  fCindus  mexi- 

canus)  in  the  Front  Range  of  Colorado.  Studies  Avian  Biol. 

7. 
Pmett-Jones,  S.  G,  M.  Pruett-Jones,  and  R  L  Knight.  1980. 

The  White-tailed   Kite  in  North  and  Middle  America: 

Current  status  and  recent  population  trends.  Am.  Birds 

34:682-688. 

R 

Rabenold,  P.  P.  1983.  The  communal  roost  in  Black  and 

Turkey  vultures— an  information  center?  In  S.  R  Wilbur 

and  J.  A.  Jackson,  eds.  Vulture  Biology  and  Management, 

303-321.  Univ.  California  Press,  Berkeley. 
Raley,  C.  M.  and  S.  H.  Anderson.  1990.  Availability  and  use 

of  ardrropod  food  resources  by  Wilson's  Warblers  and 

Lincoln's  Sparrows  in  southeastern  Wyoming.  Condor 

92:141-150. 
Ralph,  C.  J.  and  C.  A.  Pearson.  1971 .  Correlation  of  age,  size 

of  territory,   plumage,   and   breeding  success   in  White- 
crowned  Sparrows.  Condor  73:77-80. 
Ralph,  C.  J.  and  C.  L  Ralph.  1958.  Notes  on  the  nesting  of 

egrets  near  San  Rafael,  California.  Condor  60:70-71. 
Randle,  W.  and  R.  Austing.  1952.  Ecological  notes  on  the 

Long-eared   and   Saw-whet  owls   in   southwestern  Ohio. 

Ecology  33:422-426.  > 

Raphael,  M.  G.  1985.  Orientation  of  American  Kestrel  nest 

cavities  and  nest  trees.  Condor  87:437-438. 
Raphael,  M.  G.   and  M.  White.   1984-   Use  of  snags  by 

cavity-nesting  birds  in  the  Sierra  Nevada.  Wildl.  Monogr. 

86. 
Rauzon,  M.  J.  and  H.  R.  Carter.   1988.  Observations  of 

nesting  waterbirds  in  the  San  Francisco  Bay  Area  in  1988. 

Point  Reyes  Bird  Obs.  Rept.,  Contrib.  432. 
Ray,  M.  S.  1904.  Spring  notes  from  bay  counties.  Condor 

6:139. 
Raynor,  G.  S.  1983.  A  method  for  evaluating  quality  of 

coverage  in  breeding  bird  adas  projects.  Am.  Birds  37: 

9-13. 
Reichel,  W.   L   et  al.   1969.   Pesticide  residues  in  eagles. 

Pesticides  Monitor  Jour.  3:142-144- 
Remsen,  J.  V.,  Jr.  1978.  Bird  species  of  special  concern  in 

California:  An  annotated  list  of  declining  or  vulnerable 

bird  species.  Wildl.  Mgmt.  Branch  Admin.  Rept.  78-1. 

Calif.  Dept.  Fish  Game,  Sacramento. 
Reynolds,  J.  D.  and  R.  W.  Knapton.  1984.  Nest  site  selection 

and  breeding  ecology  of  the  Chipping  Sparrow.  Wilson 

Bull.  96:488-493. 
Reynolds,  R.  T.  1983.  Management  of  western  coniferous 

forest  habitat  for  nesting  Accipiter  hawks.  U.S.  For.  Serv. 

Gen.  Tech.  Rept.  RM-102.  Rocky  Mtn.  For.  and  Range 

Exp.  Sta.,  Fort  Collins,  Colo. 


LITERATURE  CITED 


.  1989.  Accipiters.  In  National  Wildlife  Federation.  Proc. 

Western  Raptor  Mgmt.  Symp.  and  Workshop,  92-101. 
Nad.  Wildl.  Fed.  Sci.  and  Tech.  Ser.  12. 

Reynolds,  R.  T.  and  E.  C.  Meslow.  1984.  Partitioning  of  food 
and  niche  characteristics  of  coexisting  Accipiter  during 
breeding.  Auk  101:761-779. 

Reynolds,  R.  T.,  E.  C.  Meslow,  and  H.  M.  Wight.  1982. 
Nesting  habitat  of  coexisting  Accipiters  in  Oregon.  J.  Wildl. 
Mgmt  46:124-138. 

Reynolds,  R.  T.  and  H.  M.  Wight.  1978.  Distribution, 
density,  and  productivity  of  accipiter  hawks  breeding  in 
Oregon.  Wilson  Bull.  90:182-196. 

Reynolds,  T.  E.  1942.  Unusual  location.  Gull  24:24. 

Rice,  D.  L  and  B.  Peterjohn.  1986.  Considerations  in  estab- 
lishing adequacy  of  coverage  standards.  In  S.  M.  Sutcliffe, 
R.  E.  Bonney,  Jr.,  and  J.  D.  Lowe,  comps.  Proc.  2nd 
Northeastern  Breeding  Bird  Adas  Conference,  13-15. 
Lab.  Ornithology,  Cornell  Univ.,  Ithaca,  N.Y. 

Rich,  T.  1986.  Habitat  and  nest-site  selection  by  Burrowing 
Owls  in  the  sagebrush  steppe  of  Idaho.  J.  Wildl.  Mgmt. 
50:548-555. 

Richardson,  F.  1961.  Breeding  biology  of  the  Rhinoceros 
Auklet.  Condor  63:456-473. 

Richmond,  S.  M.  1953.  The  attractions  of  Purple  Martins  to 
an  urban  location  in  western  Oregon.  Condor  55:225- 
249. 

Rigney,  M.  and  T.  Rigney.  1981.  A  breeding  bird  survey  of 
the  south  San  Francisco  Bay  salt  pond  levee  system  1981. 
Rept.  by  members  of  the  South  Bay  Institute  for  Avian 
Studies  for  the  S.  F.  Bay  Nad.  Wildl.  Refuge,  Newark. 

Risebrough,  R.  W.  and  J.  G.  Monk.  1989.  Toxic  chemicals 
and  birds  of  prey:  A  perspective  in  1987.  In  National 
Wildlife  Federation.  Proc.  Western  Raptor  Mgmt.  Symp. 
and  Workshop,  245-255.  Nad.  Wildl.  Fed.  Sci.  and  Tech. 
Ser.  12. 

Risebrough,  R.  W.  and  D.  B.  Peakall.  1988.  Commentary- 
The  relative  importance  of  the  several  organochlorines  in 
the  decline  of  Peregrine  Falcon  populations.  In  T.  J.  Cade, 
J.  H.  Enderson,  C  G.  Thelander,  and  C.  M.  White,  eds. 
Peregrine  Falcon  Populations:  Their  Management  and  Recov- 
ery. The  Peregrine  Fund,  Boise,  Idaho. 

Ritchison,  G.  1981.  Breeding  biology  of  the  White-breasted 
Nuthatch.  Loon  53:184-187. 

.  1983.  Breeding  biology  of  the  Black-headed  Grosbeak 

in  northern  Utah.  W.  Birds  14:159-167. 

Ritter,  L  V.  1983.  Nesting  ecology  of  Scrub  Jays  in  Chico, 
California.  W.  Birds  14:147-158. 

Ritter,  L  V.  and  K.  Purcell.  1983.  Cavity-nesting  Brewer's 
Blackbirds.  W.  Birds  14:205. 

Ritter,  W.  E.  1929.  The  nutritional  activities  of  the  California 
Woodpecker  (Balanosphyra  formicivora).  Quart.  Rev.  Biol. 
4:455-483. 

.  1938.  The  California  Woodpecker  and  l.  Univ.  Califor- 
nia Press,  Berkeley. 

Robbins,  C.  S.  1973.  Introduction,  spread,  and  present 
abundance  of  the  House  Sparrow  in  North  America.  In  S. 
C.  Kendeigh,  chairman.  A  symposium  on  the  House 
Sparrow  (Passer  domesticus)  and  European  Tree  Sparrow 


(P.  montanus)  in  North  America.  Ornithol.  Monogr.  14: 
3-9. 

1982.  Overview  of  international  adasing.  In  S.  D. 


Laughlin,  ed.  Proc.  of  the  Northeastern  Breeding  Bird 
Adas  Conference,  3-10.  Vermont  Inst.  Nat.  Sci.,  Wood- 
stock, Vt. 

Robbins,  C.  S.,  B.  Bruun,  and  H.  S.  Zim.  1966.  Birds  of  North 
America.  Golden  Press,  New  York. 

Robbins,  C.  S.,  D.  Bystrak,  and  P.  H.  Geissler.  1986.  The 
Breeding  Bird  Survey:  Its  first  fifteen  years,  1965-1979. 
U.S.  Fish  Wildl.  Serv.  Resource  Publ.  157. 

Roberson,  D.  1985.  Monterey  Birds.  Monterey  Peninsula 
Audubon  Soo,  Carmel,  Calif. 

Robertson,  I.  1974-  The  food  of  nesting  Double-crested  and 
Pelagic  cormorants  at  Mandarte  Island,  British  Columbia, 
with  notes  on  feeding  ecology.  Condor  76:346-348. 

Robertson,  R.  J.  and  R.  F.  Norman.  1977-  The  function  and 
evolution  of  aggressive  host  behavior  towards  the  Brown- 
headed  Cowbird,  Molothrus  ater.  Can.  J.  Zool.  55:508- 
518. 

Rodgers,  T.  L  1937-  Behavior  of  the  Pine  Siskin.  Condor 
39:143-149. 

Roest,  A.  I.  1957.  Notes  on  the  American  Sparrow  Hawk. 
Auk  74:1-19. 

Root,  R.  B.  1964-  Ecological  interactions  of  the  Chestnut- 
backed  Chickadee  following  a  range  extension.  Condor 
66:229-238. 

.  1967.  The  niche  exploitation  pattern  of  the  Blue-gray 

Gnatcatcher.  Ecol.  Monogr.  37:317-350. 

.  1969a.  Interspecific  territoriality  between  Bewick's  and 

House  wrens.  Auk  86:125-127. 

.  1969b.  The  behavior  and  reproductive  success  of  the 

Blue-gray  Gnatcatcher.  Condor  71:16-31. 

Roselaar,  C.  S.  1980.  Moorhen.  In  S.  Cramp,  chief  ed. 
Handbook  of  the  Birds  of  Europe,  the  Middle  East,  and  North 
Africa:  The  Birds  of  the  Western  Palearctic.  Vol.  2:  Hawks  to 
Bustards,  578-588.  Oxford  Univ.  Press,  Oxford. 

Rotenberry,  J.  T.  1980.  Dietary  relationships  among  shrub- 
steppe  passerine  birds:  Competition  or  opportunism  in  a 
variable  environment7  Ecol.  Monogr.  50:93-110. 

Rodistein,  S.  I.  1975.  An  experimental  and  teleonomic  inves- 
tigation of  avian  brood  parasitism.  Condor  77:250-271. 

.  1977-  Cowbird  parasitism  and  egg  recognition  of  the 

Northern  Oriole.  Wilson  Bull.  89:21-32. 

.  1980.  The  preening  invitation  or  head-down  display  of 

parasitic  cowbirds:  II.  Experimental  analyses  and  evidence 
for  behavioural  mimicry.  Behaviour  75:148-184- 

Rothstein,  S.  I.  and  R.  C  Fleischer.  1987.  Vocal  dialects  and 
their  possible  relation  to  honest  status  signalling  in  the 
Brown-headed  Cowbird.  Condor  89:1-23. 

Rothstein,  S.  I.,  J.  Verner,  and  E.  Stevens.  1980.  Range 
expansion  and  diurnal  changes  in  dispersion  of  the 
Brown-headed  Cowbird  in  die  Sierra  Nevada.  Auk  97: 
253-267. 

.  1984.  Radio-tracking  confirms  a  unique  diurnal  pattern 

of  spatial  occurrence  in  the  parasitic  Brown-headed  Cow- 
bird. Ecology  65:77-88. 


467 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Rothstein,  S.  I.,  J.  Verner,  E.  Stevens,  and  L  V.  Ritter.  1987. 

Behavioral  differences  among  sex  and  age  classes  of  the 

Brown-headed  Cowbird  and  their  relation  to  the  efficacy  of 

a  control  program.  Wilson  Bull.  99:322-337. 
Rothstein,  S.  I.,  D.  A.  Yokel,  and  R  C.  Fleischer.  1986. 

Social  dominance,  mating  and  spacing  systems,  female 

fecundity,  and  vocal  dialects  in  captive  and  free-ranging 

Brown-headed  Cowbirds.  Current  Ornith.  3:127-185. 
Rothwell,  B.  S.  1959.  Pioneering  in  Marin  County.  Unpubl. 

manuscript.   California   Room,   Marin  County  Library, 

Civic  Center,  San  Rafael. 
Rudolph,  S.  G.  1978.  Predation  ecology  of  coexisting  Great 

Horned  and  Barn  owls.  Wilson  Bull.  90:134-137. 
Rundle,  W.  D.  and  M.  W.  Sayre.  1983.  Feeding  ecology  of 

migrant  Soras  in  southeastern  Missouri.  J.  Wildl.  Mgmt. 

47:1153-1159. 
Rush,  D.  H.,  E.  C.  Meslow,  P.  D.  Doerr,  and  L  B.  Keith. 

1972.   Response  of  Great  Horned  Owl  populations  to 

changing  prey  densities.  J.  Wildl.  Mgmt.  36:282-295. 
Russell,  D.  N.  1971.  Food  habits  of  the  Starling  in  eastern 

Texas.  Condor  73:369-372. 
Rust,  H.  J.  1920.  The  home  life  of  a  western  Warbling  Vireo. 

Condor  22:85-94. 
Ryser,  F.  A.,  Jr.  1985.  Birds  of  the  Great  Basin:  A  Natural 

History.  Univ.  Nevada  Press,  Reno. 


Sakai,  H.  F.  1988.  Breeding  biology  of  Hammond's  and 
Western  flycatchers  in  northwestern  California.  W.  Birds 
19:49-60. 

Sakai,  H.  F.  and  B.  R.  Noon.  1990.  Variation  in  the  foraging 
behaviors  of  two  flycatchers:  Associations  with  stage  of  the 
breeding  cycle.  In  M.  L  Morrison,  C.  J.  Ralph,  J.  Verner, 
and  J.  R.  Jehl,  Jr.,  eds.  Avian  foraging:  Theory,  methodol- 
ogy, and  applications,  237-244.  Studies  Avian  Biol.  13. 

Salt,  G  W.  1952.  The  relation  of  metabolism  to  climate  and 
distribution  in  three  finches  of  the  genus  Carpodacus.  Ecol. 
Monogr.  22:121-152. 

Salyer,  J.  C.  and  K.  F.  Laglar.  1946.  The  eastern  Belted 
Kingfisher,  Megaceryle  alcyon  alcyon  (Linnaeus),  in  relation 
to  fish  management.  Trans.  Amer.  Fish  Soc.  76:97-1 17. 

Samuel,  D.  E.  1971.  The  breeding  biology  of  Barn  and  Cliff 
swallows  in  West  Virginia.  Wilson  Bull.  83:284-301 . 

San  Francisco  Bay  Conservation  and  Development  Commis- 
sion and  T.  E.  Harvey.  1983.  Aquatic  and  wildlife 
resources  of  Richardson  Bay.  Special  Area  Plan  Study. 
Sept.  1983. 

Sander,  T.  G  1986.  Aspects  of  the  breeding  biology  and 
recolonization  history  of  Rhinoceros  Auklets  (Cerorhinca 
monocerata)  on  Southeast  Farallon  Island,  California. 
Rept.  of  Point  Reyes  Bird  Obs./Evergreen  State  Coll., 
Olympia,  Wash. 

Santee,  R.  and  W.  Granfield.  1939.  Behavior  of  the  Saw-whet 
Owl  on  its  nesting  grounds.  Condor  4:3-9. 

Sappington,  J.  N.  1977.  Breeding  biology  of  House  Sparrows 
in  north  Mississippi.  Wilson  Bull.  89:300-309. 


Sayre,  M.  W.  and  W.  D.  Rundle.  1984.  Comparison  of 

habitat  use  by  migrant  Soras  and  Virginia  Rails.  J.  Wildl. 

Mgmt.  48:599-605. 
Schaefer,  V.  H.  1976.  Geographic  variation  in  the  placement 

and  structure  of  oriole  nests.  Condor  78:443-448. 
.  1980.  Geographic  variation  in  the  insulative  qualities  of 

nests  of  the  Northern  Oriole.  Wilson  Bull.  92:466-474. 
Schorger,  A.  W.  1952.  Introduction  of  the  domestic  pigeon. 

Auk  69:462-463. 
.  1966.  The  Wild  Turkey:  Its  History  and  Domestication. 

Univ.  Oklahoma  Press,  Norman. 
Schranti,  F.  G  1943.  Nest  life  of  the  eastern  Yellow  Warbler. 

Auk  60:367-387. 
Schreiber,  R.  W.  1970.  Breeding  biology  of  Western  Gulls 

(Larus   occidentalis)   on   San   Nicolas   Island,  California, 

1968.  Condor  72:133-140. 
Scott,  D.  M.  and  C.  D.  Ankney.  1983.  The  laying  cycle  of 

Brown-headed  Cowbirds:  Passerine  chickens?  Auk  100: 

583-592. 
Scott,  J.  M.,  W.  Hoffman,  D.  Ainley,  and  C.  F.  Zeillemaker. 

1974-  Range  expansion  and  activity  patterns  in  Rhinoceros 

Auklets.  W.  Birds  5:13-20. 
Sealy,  S.  G.  1982.  Rough-winged  Swallows  scavenging  adult 

midges.  Wilson  Bull.  94:368-369. 
.  1984.  Capture  and  caching  of  flying  carpenter  ants  by 

Pygmy  Nuthatches.  Murrelet  65:49-51. 
Seibert,  M.  L  1942.  Occurrence  and  nesting  of  some  birds 

in  the  San  Francisco  Bay  region.  Condor  44:68-72. 
Selander,  R.   K  and  C.  J.   LaRue,  Jr.   1961.   Interspecific 

preening  invitation   display  of  parasitic  cowbirds.   Auk 

78:473-504. 
Selleck,  D.  M.  and  B.  Glading.  1943.  Food  habits  of  nesting 

Barn  Owls  and  Marsh  Hawks  at  Dune  Lakes,  California, 

as  determined  by  the  "cage  nest"  method.  Calif.  Fish  Game 

29:122-131. 
Serie,  J.  R  and  G  A.  Swanson.  1976.  Feeding  ecology  of 

breeding  Gadwalls  on  saline  wedands.  J.  Wildl.  MgmL 

40:69-81. 
Sharrock,  J.  T.  R,  ed.  1976.  The  Atlas  of  Breeding  Birds  in 

Britain  and  Ireland.  British  Trust  for  Ornithology,  Tring, 

England. 
Shields,  W.  M.  1984.  Factors  affecting  nest  and  site  fidelity 

in  Adirondack  Barn  Swallows  (Hirundo  rustica).  Auk  101: 

780-789. 
Shuford,  W.  D.  1982.  Field  checklist  of  the  birds  of  Marin 

County,  Alta  California.  PRBO,  4990  Shoreline  Hwy., 

Stinson  Beach,  CA  94970. 
.    1985.   Acorn  Woodpecker  mutilates   nesding  Red- 
breasted  Sapsuckers.  Wilson  Bull.  97:234-236. 
.   1986.  Have  ornithologists  or  breeding  Red-breasted 

Sapsuckers  extended  their  range  in  coastal  California?  W. 

Birds  17:97-105. 
Shuford,  W.  D.,  G  W.  Page,  J.  G  Evens,  and  L  E.  Stenzel. 

1989.  Seasonal  abundance  of  waterbirds  at  Point  Reyes:  A 

coastal  California  perspective.  W.  Birds  20:137-265. 
Shuford,  W.  D.  and  I.  C.  Timossi.  1989.  Plant  Communities 

of  Marin  County.  Calif.  Native  Plant  Soc.  Spec.  Publ.  10. 


468 


LITERATURE  CITED 


Shy,  E.  1984.  Habitat  shift  and  geographical  variation  in 

North  American  tanagers.  Oecologia  63:281  -285. 
Sibley,  C.  G.  1952.  The  birds  of  the  South  San  Francisco  Bay 

region.  Published  by  the  author.  Available  at  PRBO  library, 

4990  Shoreline  Hwy.,  Stinson  Beach,  CA  94970. 
.  1955.  Nesting  of  the  Western  Tanager  in  the  Santa 

Cruz  Mountains,  California.  Condor  57:307. 
Sibley,  C.  S.  and  L  L  Short,  Jr.  1959.  Hybridization  in  the 

buntings  (Passerina)  of  the  Great  Plains.  Auk  76:443-463. 
Siegfried,  W.  R  1973.  Summer  food  and  feeding  of  the 

Ruddy  Duck  in  Manitoba.  Can.  J.  Zool.  51:1293-1297. 
.   1976a.   Social  organization   in   Ruddy  and   Maccoa 

ducks.  Auk  93:560-570. 
.  1976b.  Breeding  biology  and  parasitism  in  the  Ruddy 

Duck.  Wilson  Bull.  88:566-574. 
.  1977.  Notes  on  the  behavior  of  Ruddy  Ducks  during 

the  brood  period.  Wildfowl  28:126-128. 
Siegfried,  W.  R,  A.  E.  Burger,  and  P.  J.  Caldwell.  1976. 

Incubation  behavior  of  Ruddy  and  Maccoa  ducks.  Condor 

78:512-517. 
Simberloff,  D.  1987.  The  Spotted  Owl  fracas:  Mixing  aca- 
demic, applied,  and  political  ecology.  Ecology  68:766-772. 
Sisson,  R   F.   1974.  Aha!   It  really  works!   Nad.   Geogr. 

145:143-147. 
Skaar,  P.  D.  1967.  Long  range  changes  in  the  avifauna  of  the 

Bozeman,  Montana  region.  Proc.   Montana  Acad.   Sci. 

27:55-66. 

.  1969.  Birds  of  the  Bozeman  Latilong,  Bozeman,  Montana. 

Published  by  the  author,  501  S.  Third,  Bozeman,  Mon- 
tana. 

1975,    1980.    Montana   Bird   Distribution:    Preliminary 


Mapping  b}  Latilong.  Published  by  the  author,  501  S. 
Third,  Bozeman,  Montana. 

Skinner,  J.  E.  1962.  An  historical  review  of  the  fish  and 
wildlife  resources  of  the  San  Francisco  Bay  Area.  Water 
Projects  Branch  Rept.  1.  Calif.  Dept.  Fish  Game,  Sacra- 
mento. 

Skinner,  M.  P.  1938.  Rocky  Mountain,  California,  Vancou- 
ver, and  Coast  Pygmy  owls.  In  A.  C.  Bent,  ed.  Life  histories 
of  North  American  birds  of  prey  (Part  2).  U.S.  Nad.  Mus. 
Bull.  170:401-434. 

Skorupa,  J.  P.,  R  L  Hothem,  and  R  W.  DeHaven.  1980. 
Foods  of  breeding  Tricolored  blackbirds  in  agricultural 
areas  of  Merced  County,  California.  Condor  82:465-467. 

Slack,  R  S.  1975.  Effects  of  prey  size  on  Loggerhead  Shrike 
predation.  Auk  92:812-814. 

Slobodchikoff,  C  N.  and  J.  T.  Doyen.  1977.  Effects  of 
Ammophila  arenaria  on  sand  dune  arthropod  communi- 
ties. Ecology  58:1171-1175. 

Smail,  J.,  D.  G.  Ainley,  and  H.  Strong.  1972.  Notes  on  birds 
killed  in  the  1971  San  Francisco  oil  spill.  Calif.  Birds 
3:25-32. 

Smallwood,  J.  A.  1988.  A  mechanism  of  sexual  segregation 
by  habitat  in  American  Kestrels  (Falco  sparverius)  wintering 
in  south-central  Horida.  Auk  105:36-46. 


Smith,  C  F.  and  C  L  Hopkins.  1937.  Notes  on  the  Barn 
Owls  of  the  San  Francisco  Bay  region.  Condor  39:189- 
191. 

Smith,  C.  R  1982.  Thoughts  on  adequate  coverage,  random 
sampling,  auxiliary  data  collection,  and  data  analysis  for 
breeding  bird  adas  projects.  In  S.  B.  Laughlin,  ed.  Proc. 
Northeastern  Breeding  Bird  Adas  Conference,  80-89. 
Vermont  Inst.  Nat.  Sci.,  Woodstock,  Vt. 

,  ed.    1990.    Handbook  for  Atlasing  American   Breeding 

Birds.  Vermont  Inst.  Nat.  Sci.,  Woodstock,  Vt. 

Smith,  D.  G.,  C.  R  Wilson,  and  H.  H.  Frost  1974-  History 
and  ecology  of  Barn  Owls  in  Utah.  Condor  76:131-136. 

Smith,  J.  N.  M.  1978.  Hycatching  by  male  Song  Sparrows, 
Melospiza  melodia.  Can.  Field-Nat.  92:195-196. 

Smith,  J.  N.  M.,  P.  Arcese,  and  I.  G.  McLean.  1984.  Age, 
experience  and  enemy  recognition  by  wild  Song  Sparrows. 
Behav.  Ecol.  Sociobiol.  14:101-106. 

Smith,  K.  C.  and  D.  C  Anderson.  1982.  Food,  predation, 
and  reproductive  ecology  of  the  Dark-eyed  Junco  in  north- 
ern Utah.  Auk  99:650-661. 

Smith,  R.  L.  1963.  Some  ecological  notes  on  the  Grasshopper 
Sparrow.  Wilson  Bull.  75:159-165. 

.  1968.  Grasshopper  Sparrow.  In  O.  L  Austin,  Jr.,  ed. 

A.  C.  Bent  et  al.'s  Life  histories  of  North  American 
cardinals,  grosbeaks,  buntings,  towhees,  finches,  sparrows, 
and  allies.  U.S.  Nad.  Mus.  Bull  237  (Part  2):  725-745. 

Smith,  R.  L  and  L.  D.  Flake.  1985.  Movements  and  habitats 
of  brood-rearing  Wood  Ducks  on  a  prairie  river.  J.  Wildl. 
Mgmt.  49:437-442. 

Smith,  S.  M.  1967.  An  ecological  study  of  winter  flocks  of 
Black-capped  and  Chestnut-backed  chickadees.  Wilson 
Bull.  79:200-207. 

.  1972.  The  ontogeny  of  impaling  behavior  in  the  Log- 
gerhead Shrike,  Lanius  ludovicianus  L.  Behavior  42:  232- 
247. 
-.  1973.  A  study  of  prey-attack  behavior  in  young  Logger- 


head Shrikes,  Lanius  ludovicianus  L  Behavior  44:1 13— 

141. 
Smidi,  W.  A.  1968.  The  Band-tailed  Pigeon  in  California. 

Calif.  Fish  Game  54:4-16. 
Smith,  W.  J.  1966.  Communications  and  relationships  in  the 

genus  T^rannus.  Nutt.  Ornithol.  Club  Publ.  6. 
Snapp,  B.  D.  1976.  Colonial  breeding  in  the  Barn  Swallow 

(Hirundo  rustica)  and  its  adaptive  significance.  Condor 

78:471-480. 
Snyder,  D.  E.   1954.  A  nesting  study  of  Red  Crossbills. 

Wilson  Bull.  66:32-37. 
Snyder,  N.  F.  R,  H.  A.  Snyder,  J.  L  Lincer,  and  R.  T. 

Reynolds.  1973.  Organochlorines,  heavy  metals,  and  the 

biology  of  North  American  accipiters.  BioSci.  23:300-305. 
Snyder,  N.  F.  R.  and  J.  M.  Wiley.  1976.  Sexual  size  dimor- 
phism in  hawks  and  owls  of  North  America.  Ornithol. 

Monogr.  20:1-96. 
Soriano,  P.  S.  1931.  Food  habits  and  economic  status  of  the 

Brewer  and   Red-winged   blackbirds.   Calif.   Fish  Game 

17:361-395. 


469 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Southern,  H.  N.  1945.  The  economic  importance  of  the 
House  Sparrow,  Passer  domesticus  L,  a  review.  Ann.  Appl. 
Biol.  32:57-62. 

Sowls,  A.  L,  A.  R.  DeGange,  J.  W.  Nelson,  and  G.  S.  Lester. 

1980.  Catalog  of  California  seabird  colonies.  USDI,  Fish 
and  Wildl.  Serv.  Biol  Serv.  Progr.  FWS/OBS  37/80. 

Sowls,  A.  L,  S.  A.  Hatch,  and  C.  J.  Lensink.  1978.  Catalog 

of  Alaskan   seabird  colonies.   USDI,   Fish  Wildl.   Serv. 

FWS/OBS-80/37. 
Spear,  L  B.,  T.  M.  Penniman,  J.  F.  Penniman,  H.  R.  Carter, 

and  D.  G.  Ainley.  1987.  Survivorship  and  mortality  factors 

in  a  population  of  Western  Gulls.  In  J.  L  Hand,  W.  E. 

Southern,  and  K.  Vermeer,  eds.  Ecology  and  behavior  of 

gulls,  44-56.  Studies  Avian  Biol.  10. 
Speich,  S.  M.,  H.  L  Jones,  and  E.  M.  Benedict.  1986.  Review 

of  the  natural  nesting  of  the  Barn  Swallow  in  North 

America.  Amer.  Midi.  Nat.  115:248-254. 
Spofford,  W.  R  1964.  The  Golden  Eagle  in  the  Trans-Pecos 

and  Edwards  Plateau  of  Texas.  Audubon  Conserv.  Rept. 

I.  Nad.  Aud.  Soc.,  New  York. 

Sprunt,  A.  S.,  Jr.  1942.  Purple  Martin.  In  A.  C.  Bent,  ed.  Life 
histories  of  North  American  flycatchers,  larks,  swallows, 
and  their  allies.  U.S.  Nad.  Mus.  Bull.  179:489-509. 

Squires,  W.  A.  1917.  Some  field  notes  for  1917.  Condor 
19:185-186. 

Stacey,  P.  B.  and  R.  Jansma.  1977.  Storage  of  pinon  nuts  by 
the  Acorn  Woodpecker  in  New  Mexico.  Wilson  Bull. 
89:150-151. 

Stallcup,  P.  L  1968.  Spatio-temporal  relationships  of  nut- 
hatches and  woodpeckers  in  ponderosa  pine  forest  of 
Colorado.  Ecology  49:831-843. 

Stanback,  M.  T.  1991.  Autumnal  breeding  in  the  Scrub  Jay. 
J.  Field  Omithol.  62:94-96. 

Stendell,  R  C.  and  P.  Meyers.  1973.  White-tailed  Kite  preda- 
tion  on  a  fluctuating  vole  population.  Condor  75:359- 
360. 

Stenzel,  L  E.  and  S.  C.  Peaslee.  1979.  Part  II:  The  California 
mainland  coast.  In  G.  W.  Page  and  L  E.  Stenzel,  eds.  The 
breeding  status  of  the  Snowy  Plover  in  California,  II-l  to 
11-23.  Nongame  Wildl.  Invest.  Rept.  Calif.  Fish  Game, 
Sacramento. 

Stenzel,  L  E,  S.  C.  Peaslee,  and  G.  W.  Page.  1981.  Results 

II.  Mainland  Coast.  In  G.  W.  Page  and  L.  E.  Stenzel,  eds. 

1981.  The  breeding  status  of  the  Snowy  Plover  in  Califor- 
nia, 6-16.  W.  Birds  12:1-40. 

Stephens,  A.  B.  1931.  Audubon  notes.  Gull  13,  No.  7. 

Stephens,  L  A.  1936.  Birds  of  Marin  County,  California. 
Gull  18,  No.  6. 

.  1941.  June  field  trip.  Gull  23:24-25. 

.  1945.  White-tailed  Kite.  Gull  27:36-37. 

Stephens,  L  A.  and  C.  C.  Pringle.  1933.  Birds  of  Marin 
County.  Audubon  Assoc,  of  the  Pacific,  San  Francisco. 
Available  at  PRBO  library,  4990  Shoreline  Hwy.,  Stinson 
Beach,  CA  94970. 

Stern,  R.  J.  A.  1959.  Mockingbird  observed  on  the  southern 
tip  of  Tiburon  Peninsula,  Marin  County,  California.  Con- 
dor 61:59. 


Stewart,  B.  S.,  P.  K  Yochem,  and  R  W.  Schreiber.  1984. 

Pelagic  red  crabs  as  food  for  gulls:  A  possible  benefit  of  El 

Nino.  Condor  86:341-342. 
Stewart,   R.   E.   1953.  A  life  history  of  the  Yellow-throaL 

Wilson  Bull.  65:99-115. 
.  1975.  Breeding  Birds  of  NortK  Dakota.  North  Dakota 

Inst.  Reg.  Studies,  Fargo. 
Stewart,  R  M.  1972.  Nesding  mortality  in  swallows  due  to 

inclement  weather.  Calif.  Birds  3:69-70. 
.  1973.  Breeding  behavior  and  life  history  of  the  Wilson 

Warbler.  Wilson  Bull.  85:21-30. 
Stewart,  R  M.  and  K.  Darling.  1972.  Breeding  biology  of  the 

Wilson's  Warbler  in  the  high  Sierra  and  on  the  coast 

Point  Reyes  Bird  Obs.  Newsl.  24:3-5. 
Stewart,  R  M.,  R.  P.  Henderson,  and  K.  Darling.  1977. 

Breeding  ecology  of  the  Wilson's  Warbler  in  the  high 

Sierra  Nevada,  California.  Living  Bird  16:83-102. 
Stiehl,  R  B.  1985.  Brood  chronology  of  the  Common  Raven. 

Wilson  Bull.  97:78-87. 
Stiles,  F.  G.,  III.  1973.  Food  supply  and  the  annual  cycle  of 

the  Anna  Hummingbird.  Univ.  Calif.  Publ.  Zool.  97: 

1-109. 
Stine,  S.  MS.  Fat,  furs,  feathers,  and  flesh:  The  game  trade  in 

early  California.  Unpubl.  manuscript 
Stinson,  C.  H.,  D.  L  Crawford,  and  J.  Lauthner.  1981.  Sex 

differences  in  winter  habitat  of  American  Kestrels  in  Geor- 
gia. J.  Field  Ornithol.  52:29-35. 
Stocek,  R  F.  1970.  Observations  of  the  breeding  biology  of 

the  Tree  Swallow.  Cassinia  52:3-20. 
Stokes,  A.  W.  1950.  Breeding  behavior  of  the  goldfinch. 

Wilson  Bull.  62:107-127. 
Stoner,  E.  A.  1934.  Recent  occurrences  of  the  American  Egret 

in  the  San  Francisco  Bay  region.  Condor  36:57-59. 
.  1947.  Food  of  White-tailed  Kites  in  Suisun  Marsh. 

Condor  49:84-85. 
Stophlet,  J.  J.   1959.  Nesting  concentration  of  Long-eared 

Owls  in  Cochise  County,  Arizona.  Wilson  Bull.  71:97- 

99. 
Storer,  R.  W.  1951 .  The  seasonal  occurrence  of  shorebirds  at 

Bay  Farm  Island  Alameda  County,  California.  Condor 

53:186-193. 
.  1966.  Sexual  dimorphism  and  food  habits  in  three 

North  American  accipiters.  Auk  83:423-436. 
Storer,  T.  I.  1926.  Range  extensions  by  the  Western  Robin 

in  California.  Condor  28:264-267. 
.   1927.  Three  notable  nesting  colonies  of  the  Cliff 

Swallow  in  California.  Condor  29:104-108. 
Strohmeyer,  D.  L  1977.  Common  Gallinule  (Gallinula  chlo- 

ropus).  In  G.  C.  Sanderson,  ed.  Management  of  migratory 

shore  and  upland  game  birds  in  North  America,  110-117. 

Int.  Assoc.  Fish.  Wildl.  Agencies  and  U.S.  Fish  Wildl. 

Serv. 
Stull,  W.  D.  1968.  Eastern  and  Canadian  Chipping  spar- 
rows. In  O  L  Austin,  Jr.,  ed.  A.  C.  Bent  et  al.'s  Life 

histories  of  North  American  cardinals,  grosbeaks,  bun- 
tings, towhees,  finches,  sparrows,  and  allies.  U.S.  Nad. 

Mus.  Bull.  237  (Part  2):  1166-1184. 


470 


LITERATURE  CITED 


Sturman,  W.  A.  1968.  The  foraging  ecology  of  Parus  atri- 
capillus  and  P.  rufescens  in  the  breeding  season,  with 
comparisons  with  other  species  of  Parus.  Condor  70: 
309-322. 

Sullivan,  J.  O.  1966.  A  Dipper  nest  away  from  water.  Condor 
68:107. 

Summers-Smith,  J.  D.  1963.  The  House  Sparrow.  Collins, 
London. 

Sumner,  E.  L,  Jr.  1935.  A  life  history  study  of  the  California 
Quail,  with  recommendations  for  conservation  and  man- 
agement. Calif.  Fish  Game  21:167-256,  277-342. 

Sutcliffe,  S.  M.,  R.  E.  Bonney,  Jr.,  and  J.  D.  Lowe,  eds.  1986. 
Proceedings  of  the  2nd  Northeastern  Breeding  Bird  Adas 
Conference.  Lab.  Ornithology,  Cornell  Univ.,  Ithaca, 
NY. 

Sutton,  G.  M.  1976.  On  the  feeding  behavior  of  the  Red 
Crossbill.  Bull.  Okla.  Ornithol.  Soc.  9:3-6. 

Swanson,  G.  A.,  G.  L  Krapu,  and  J.  R.  Serie.  1979.  Foods 
of  laying  female  dabbling  ducks  on  the  breeding  grounds. 
In  T.  A.  Bookhout,  ed.  Waterfowl  and  wedands— an  inte- 
grated review,  47-57.  Proc.  Symp.  1977,  N.  Cent.  Sec, 
The  Wildl.  Soc. 

Swanson,  G.  A.,  M.  I.  Meyer,  and  J.  R.  Serie.  1974.  Feeding 
ecology  of  breeding  Blue-winged  Teals.  J.  Wildl.  Mgmt. 
38:396-407. 

Swanson,  G.  A.  and  A.  B.  Sargeant.  1972.  Observation  of 
nightime  feeding  behavior  of  ducks.  J.  Wildl.  Mgmt.  36: 
959-961. 

Swanton,  H.  1933.  The  Snowy  Egret  in  Marin  County, 
California.  Condor  35:73. 

Swarth,  C.  W.  1983.  Foraging  ecology  of  Snowy  Plovers  and 
the  distribution  of  d^eir  arthropod  prey  at  Mono  Lake, 
California.  M.S.  thesis,  Calif.  State  Univ.,  Hayward. 

Swenson,  J.  E.  1979.  The  relationsip  between  prey  species 
ecology  and  dive  success  in  Ospreys.  Auk  96:408-412. 

.  1981.  Status  of  the  Osprey  in  soudieastern  Montana 

before  and  after  the  construction  of  reservoirs.  W.  Birds 
12:47-51. 

Swenson,  J.  E.  and  P.  Hendricks.  1983.  Chick  movements  in 
Common  Poorwills.  Wilson  Bull.  95:309-310. 

Swisher,  O.  D.  1978.  Poor-wills  nesting  in  southwestern 
Oregon.  N.  Am.  Bird  Bander  3:152-155. 

Sydeman,  W.  J.  1989.  Effects  of  helpers  on  nesding  care  and 
breeder  survival  in  Pygmy  Nuthatches.  Condor  91:147- 
155. 

Sydeman,  W.  J.  and  M.  Giintert.  1983.  Winter  communal 
roosting  in  the  Pygmy  Nuthatch.  In  J.  W.  Davis,  G.  A. 
Goodwin,  and  R.  A.  Ockenfels,  tech.  coords.  Snag  habitat 
management:  Proceedings  of  the  symposium,  121-124- 
U.S.  For.  Serv.  Gen.  Tech.  Rept.  RM-99. 

Sydeman,  W.  J.,  M.  Giintert,  and  R.  P.  Balda.  1988.  Annual 
reproductive  yield  in  the  cooperative  Pygmy  Nuthatch 
(Sitta  p-ygmaea).  Auk  105:70-77. 

Szaro,  R.  C,  J.  D.  Brawn,  R.  P.  Balda.  1990.  Yearly  variation 
in  resource-use  behavior  by  ponderosa  pine  forest  birds.  In 
M.  L  Morrison,  C.  J.  Ralph,  J.  Verner,  and  J.  R.  Jehl,  Jr., 
eds.  Avian  foraging:  Theory,  methodology,  and  applica- 
tions, 226-236.  Studies  Avian  Biol.  13. 


Taber,  W.  J.  and  D.  W.  Johnston.  1968.  Indigo  Bunting.  In 
O.  L  Austin,  Jr.,  ed.  A.  C.  Bent  et  al.'s  Life  histories  of 
North  American  cardinals,  grosbeaks,  buntings,  towhees, 
finches,  sparrows,  and  allies.  U.S.  Nad.  Mus.  Bull.  237 
(Parti):  80-1 11. 

Tait,  W.  W.,  H.  M.  Johnson,  and  W.  D.  Courser.  1972. 
Osprey  carrying  a  small  mammal.  Wilson  Bull.  84:341. 

Takekawa,  J.  E.,  H.  R.  Carter,  and  T.  E.  Harvey.  1990. 
Decline  of  the  Common  Murre  in  central  California, 
1980-1986.  In  S.  G.  Sealy,  ed.  Auks  at  sea,  149-163. 
Studies  Avian  Biol.  14- 

Tangren,  G.  V.  1977.  Climatic  effects  on  the  seasonality  of 
California's  avifaunas.  Am.  Birds  31:960-965. 

Tate,  J.,  Jr.  1973.  Mediods  and  annual  sequence  of  foraging 
by  the  sapsucker.  Auk  90:840-856. 

.  1981.  The  Blue  List  for  1981:  The  first  decade.  Am. 

Birds  35:3-10. 

.  1986.  The  Blue  List  for  1986.  Am.  Birds  40:227-236. 

Tate,  J.,  Jr.  and  D.  J.  Tate.  1982.  The  Blue  List  for  1982.  Am. 
Birds  36:126-135. 

Tatschl,  J.  L  1967.  Breeding  birds  of  the  Sandia  Mountains 
and  their  ecological  distributions.  Condor  69:479-490. 

Taverner,  P.  A.  1933.  Purple  Martins  gathering  leaves.  Auk 
50:110-111. 

Taylor,  D.  M.  and  C.  D.  Litdefield.  1986.  Willow  Hycatcher 
and  Yellow  Warbler  response  to  catde  grazing.  Am.  Birds 
40:1169-1173. 

Taylor,  H.  R.  1905.  The  nest  and  eggs  of  the  Vaux  Swift. 
Condor  7:177  6k  179. 

Taylor,  P.  D.  and  S.  M.  Smidi.  1986.  Multi-species  clusters 
of  birds  in  soudiern  Ontario.  In  M.  D.  Cadman,  P.  F.  J. 
Eagles,  and  F.  M.  Helleiner,  comps.  Atlas  of  the  Breeding 
Birds  of  Ontario,  576-580.  Univ.  Waterloo  Press,  Water- 
loo. 

Taylor,  W.  K.  1965.  Nesting  heights  of  some  Louisiana  birds. 
Wilson  Bull.  77:146-150. 

Tenaya,  K.  and  R.  Tenaya.  1966.  First  report  of  the  Starling 
in  San  Francisco,  California.  Condor  68:600. 

Thelander,  C.  G.  1974.  Nesting  territory  utilization  by 
Golden  Eagles  (Aquila  chrysaetos)  in  California  during 
1974.  Wildl.  Mgmt.  Branch  Admin.  Rept.  74-7.  Calif. 
Dept.  Fish  Game,  Sacramento. 

Thomas,  J.  W.,  E.  D.  Forsman,  J.  B.  Lint,  E.  C.  Meslow,  B. 
R.  Noon,  and  J.  Verner.  1990.  A  conservation  strategy  for 
the  Northern  Spotted  Owl.  Rept.  of  the  Interagency  Sci. 
Coram,  to  Address  the  Conservation  of  the  Northern 
Spotted  Owl.  U.S.  For.  Serv.,  Portland,  Oregon;  Bur. 
Land  Mgmt.;  U.S.  Fish  Wildl.  Serv.;  U.S.  Nad.  Park  Serv. 

Thompson,  S.  P.,  C.  D.  Litdefield,  and  R.  A.  Ryder.  1979. 
Historical  review  and  status  of  colonial  nesting  birds  on 
Malheur  National  Wildlife  Refuge,  Oregon.  Proc.  1979 
Conf.  Colonial  Waterbird  Group  3:156-164. 

Thompson,  W.  L  1960.  Agonistic  behavior  in  the  House 
Finch.  Part  1:  Annual  cycle  and  display  patterns.  Condor 
62:245-271. 


471 


MARIN  COUNTY  BREEDING  BIRD  ATIt\S 


Thomsen,  L  1971.  Behavior  and  ecology  of  Burrowing  Owls 

on  the  Oakland  municipal  airport.  Condor  73:177-192. 
Thut,  R.  N.  1970.  Feeding  habits  of  the  Dipper  in  soudiwest- 

ern  Washington.  Condor  72:234-235. 
Tinbergen,  J.  1981.  Foraging  decisions  in  Starlings  (Sturnus 

vulgaris  L).  Ardea  69:1-67. 
Tinbergen,  J.  M.  and  R.  H.  Drent.  1980.  The  Starling  as  a 

successful  forager.  In  E.  N.  Wright,  I.  R.  Inglis,  and  C.  J. 

Feare,  eds.  Bird  Problems  in  Agriculture,  83-101.  Lamport 

Gilbert,  Reading,  Great  Britian. 
Titman,  R.  D.  1983.  Spacing  and  three-bird  flights  of  Mal- 
lards breeding  in  pothole  habitat.  Can.  J.  Zool.  61:839- 

847. 
TordufT,  H.  B.  1954-  Social  organization  and  behavior  in  a 

flock  of  captive,   nonbreeding   Red   Crossbills.   Condor 

56:346-358. 
Townsend,  C.  W.  1926.  Virginia  Rail.  In  A.  C.  Bent,  ed.  Life 

histories  of  North  American  marsh  birds.  U.S.  Nad.  Mus. 

Bull.  135:292-301. 
.  1 929.  Killdeer.  In  A.  C.  Bent,  ed.  Life  histories  of  North 

American  shore  birds  (Part  2).  U.S.  Nad.   Mus.   Bull. 

146:202-217- 
.  1938.  Short-eared  Owl.  In  A.  C.  Bent,  ed.  Life  histories 

of  North  American  birds  of  prey  (Part  2).  U.S.  Nad.  Mus. 

Bull.  170:169-182. 
Tramontano,  J.  P.  1964.  Comparative  studies  of  die  Rock 

Wren  and  the  Canyon  Wren.  M.S.  diesis,  Univ.  Ariz., 

Tucson. 
Travis,  J.  1977.  Seasonal  foraging  in  a  Downy  Woodpecker 

population.  Condor  79:371-375. 
Tremblay,  J.  and  L  N.   Ellison.   1979.  Effects  of  human 

disturbance  on  breeding  of  Black-crowned  Night  Herons. 

Auk  96:364-369. 
Troetschler,  R  G.  1976.  Acorn  Woodpecker  breeding  strat- 
egy as  affected  by  Starling  nest-hole  competition.  Condor 

78:151-165. 
Turner,  A.   K.   1982.   Optimal   foraging  by  the   swallow 

(Hirundo  rustica  L.):  Prey  size  selection.  Anim.   Behav. 

30:862-872. 
Tyler,  W.  M.  1929.  Spotted  Sandpiper.  In  A.  C.  Bent,  ed. 

Life  histories  of  North  American  shore  birds  (Part  2).  U.S. 

Nad.  Mus.  Bull.  146:78-97. 
.  1937.  Turkey  Vulture.  In  A.  C.  Bent,  ed.  Life  histories 

of  North  American  birds  of  prey  (Part  1).  U.S.  Nad.  Mus. 

Bull.  167:12-28. 
.  1942.  Tree  Swallow.  In  A.  C.  Bent,  ed.  Life  histories  of 

North  American  flycatchers,  larks,  swallows,  and  their 

allies.  U.S.  Nad.  Mus.  Bull.  179:384-400. 
.  1948a.  Red-breasted  Nuthatch.  In  A.  C.  Bent,  ed.  Life 


histories  of  North  American  nuthatches,  wrens,  thrashers, 
and  their  allies.  U.S.  Nad.  Mus.  Bull.  195:22-35. 
— .  1948b.  White-breasted  Nuthatch.  In  A.  C.  Bent,  ed. 
Life  histories  of  North  American  nuthatches,  wrens, 
thrashers,  and  their  allies.  U.S.Nad.  Mus.  Bull.  195:1-12. 
1948c.  Brown  Creeper.  In  A.  C.  Bent,  ed.  Life  histories 


.  1949.  Eastern  Robin.  In  A.  C.  Bent,  ed.  Life  histories 

of  North  American  dinishes,  kinglets,  and  their  allies. 
U.S.  Nad.  Mus.  Bull.  196:14-45. 

U 

Unglish,  W.  E.  1929.  The  Texas  Nighthawk  in  Santa  Clara 
County,  California.  Condor  31:223. 

Unitt,  P.  1977.  The  Litde  Blue  Heron  in  California.  W.  Birds 
8:151-154. 

.  1984-  The  Birds  of  San  Diego  County.  San  Diego  Soc. 

Nat.  Hist.  Memoir  13. 

U.S.  Fish  and  Wildlife  Service.  1987a.  The  Northern  Spotted 
Owl  status  review.  Portland,  Oregon. 

.  1987b.  Migratory  nongame  birds  of  management  con- 
cern in  the  United  States:  The  1 987  list.  Office  Migratory 
Bird  Mgmt.,  USFWS,  Washington,  D.C. 

.  1989a.  Endangered  and  threatened  wildlife  and  plants. 

50CFR17.11  and  17.12. 

.  1 989b.  Endangered  and  threatened  wildlife  and  plants; 

animal  notice  of  review.  50  CFR  Part  17. 

.  1989c.  The  Northern  Spotted  Owl:  A  status  review 

supplement.  Portland,  Oregon. 

.  1 991 .  Endangered  and  threatened  wildlife  and  plants; 

animal  candidate  review  for  listing  as  endangered  or  threat- 
ened species.  50  CFR  Part  17. 

U.S.  Forest  Service.  1988.  Final  supplement  to  the  environ- 
mental impact  statement  for  an  amendment  to  the  Pacific 
Northwest  Regional  Guide.  Spotted  Owl  guidelines.  2 
vols.  USFS,  Portland. 

U.S.  Weather  Bureau.  1934.  Climatic  summary  of  the 
United  States. 


Van  Beet,  C.  C.  1919.  A  short  paper  on  the  Hutton  Vireo. 
Condor  21:162-165. 

Verbeek,  N.  A.  M.  1967.  Breeding  biology  and  ecology  of  the 
Horned  Lark  in  alpine  tundra.  Wilson  Bull.  79:208-218. 

.  1970.  Feeding  ecology  of  two  coexisting  corvids.  In  N. 

A.  M.  Verbeek.  The  exploitation  system  of  the  Yellow- 
billed  Magpie.  Ph.D.  thesis,  Univ.  Calif.,  Berkeley. 

.   1973.  The  exploitation   system  of  the  Yellow-billed 

Magpie.  Univ.  Calif.  Publ.  Zool.  99:1-58. 

.  1975a.  Comparative  feeding  behavior  of  three  coexist- 
ing tyrannid  flycatchers.  Wilson  Bull.  87:231-240. 

1975b.  Northern  wintering  of  flycatchers  and  the  resi- 


of  North  American  nuthatches,  wrens,  thrashers,  and  their 
allies.  U.S.  Nad.  Mus.  Bull.  195:56-70. 


dency  of  Black  Phoebes  in  California.  Auk  92:737-749. 
Verheyan,  R.  F.  1980.  Breeding  strategies  of  the  Starling.  In 

E.  N.  Wright,  I.  R.  Inglis,  and  C.  J.  Feare,  eds.  Bird 

Problems  m  Agriculture,  69-82.  Lamport  Gilbert,  Reading, 

Great  Britain. 
Vermeer,  K.  1979.  Nesting  requirements,  food,  and  breeding 

distribution  of  Rhinoceros  Auklets,  Cerorhinca  monocerata, 

and  Tufted  Puffins,  Lunda  cirrhata.  Ardea  67:101-110. 
. .  1980.  The  importance  of  timing  and  type  of  prey  to 

reproductive   success   of  Rhinoceros  Auklets   Cerorrtinca 

monocerata.  Ibis  122:343-350. 


472 


LITERATURE  CITED 


Vermeer,  K.  and  L  Cullen.  1982.  Growth  comparison  of  a 
plankton-  and  a  fish-eating  alcid.  Murrelet  63:34-39. 

Vermeer,  K.  and  S.  J.  Westrheim.  1984.  Fish  changes  in  diets 
of  nesding  Rhinoceros  Auklets  and  their  implications.  In 

D.  N.  Nettleship,  G.  A.  Sanger,  P.  F.  Springer,  eds.  Marine 
birds:  Their  feeding  ecology  and  commercial  fisheries 
relationships,  96-105.  Proc.  Pac.  Seabird  Group  Symp., 
Seattle,  Washington,  6-8  Jan.  1982.  Canadian  Wildl. 
Serv.  for  P.S.G. 

Verner,  J.  1963.  Song  rates  and  polygamy  in  the  Long-billed 
Marsh  Wren.  Proc.  XIII  Int.  Omithol.  Congr.  1 :299-307. 

.  1964.  Evolution  of  polygamy  in  the  Long-billed  Marsh 

Wren.  Evolution  18:252-261. 

.  1965.  Breeding  biology  of  the  Long-billed  Marsh  Wren. 

Condor  67:6-30. 

Verner,  J.,  E.  C.  Beedy,  S.  L  Granholm,  L  V.  Ritter,  and 

E.  F.  Toth.  1980.  Birds.  In  J.  Verner  and  A.  S.  Boss,  tech. 
coordinators.  California  wildlife  and  their  habitats:  West- 
em  Sierra  Nevada,  75-319.  Gen.  Tech.  Rept.  PSW-37. 
Pac.  Southwest  Forest  and  Range  Exp.  Stn.,  Forest  Serv., 
Berkeley,  Calif. 

Verner,  J.  and  G.  H.  Engelson.  1970.  Territories,  multiple 
nest  building,  and  polygyny  in  the  Long-billed  Marsh 
Wren.  Auk  87:557-567. 

Verner,  J.  and  T.  A.  Larson.  1989.  Richness  of  breeding  bird 
species  in  mixed-conifer  forests  of  the  Sierra  Nevada, 
California.  Auk  106:447-463. 

Verner,  J.  and  L  V.  Ritter.  1983.  Current  status  of  the 
Brown-headed  Cowbird  in  the  Sierra  National  Forest.  Auk 
100:355-368. 

Verner,  J.  and  M.  F.  Willson.  1969.  Mating  systems,  sexual 
dimorphism,  and  the  role  of  male  North  American  passer- 
ine birds  in  the  nesting  cycle.  Ornithol.  Monogr.  9. 

Voous,  K.  H.  1960.  Atlas  of  European  Birds.  Nelson,  Amster- 
dam. 

.  1988.  Owls  of  tke  Northern  Hemisphere.  M.IT.  Press, 

Cambridge,  Mass. 

w 

Wagner,  J.  L  1981.  Seasonal  change  in  guild  structure:  Oak 
woodland  insectivorous  birds.  Ecology  62:973-981. 

Wahl,  J.  R.  1975.  Seabirds  in  Washington's  offshore  zone. 
W.  Birds  6:117-134. 

Waian,  L  B.  and  R.  C  Stendell.  1970.  The  White-tailed  Kite 
in  California  with  observations  of  the  Santa  Barbara  pop- 
ulation. Calif.  Fish  Game  56:188-198. 

Walkinshaw,  L  H.  1937.  The  Virginia  Rail  in  Michigan.  Auk 
54=464-475. 

.  1938.  Life  histories  of  the  eastern  goldfinch,  Part  I. 

Jack-Pine  Warbler  16:3-11,  14-15. 

.  1940.  Summer  life  of  the  Sora  Rail.  Auk  57:1 53-168. 

.  1944.  The  eastern  Chipping  Sparrow  in  Michigan. 

Wilson  Bull.  56:193-205. 

Walkinshaw,  L  H.  and  D.  A.  Zimmerman.  1961.  Range 
expansion  of  the  Brewer  Blackbird  in  eastern  North  Amer- 
ica. Condor  63:162-177. 


Walsberg,  G.  E.  1981.  Nest-site  selection  and  radiative  envi- 
ronment of  the  Warbling  Vireo.  Condor  83:86-88. 

Walsh,  H.  1978.  Food  of  nesding  Purple  Martins.  Wilson 
Bull.  90:248-260. 

Walters,  R.  E.,  ed.  1983.  Utah  bird  distribution— latilong 
study.  97  pp.  mimeo. 

Walton,  B.  J.  1978.  The  status  of  the  salt  marsh  Song 
Sparrows  of  the  San  Francisco  Bay  system,  1974-1976. 
M.A.  thesis,  San  Jose  State  Univ.,  San  Jose. 

Walton,  B.  J.  and  C.  G.  Thelander.  1988.  Peregrine  Falcon 
management  efforts  in  California,  Oregon,  Washington, 
and  Nevada.  In  T.  J.  Cade,  J.  H.  Enderson,  C.  G.  Thelan- 
der, and  C.  M.  White,  eds.  Peregrine  Falcon  Populations: 
Their  Management  and  Recovery,  587-597.  The  Peregrine 
Fund,  Boise,  Idaho. 

Walton,  B.  J.,  C.  G.  Thelander,  and  D.  L  Harlow.  1988.  The 
status  of  Peregrines  nesting  in  California,  Oregon,  Wash- 
ington, and  Nevada.  In  T.  J.  Cade,  J.  H.  Enderson,  C.  G. 
Thelander,  and  C.  M.  White,  eds.  Peregrine  Falcon  Popula- 
tions: Their  Management  and  Recovery,  95-104.  The  Pere- 
grine Fund,  Boise,  Idaho. 

Warner,  J.  S.  and  R.  L  Rudd.  1975.  Hunting  by  the  White- 
tailed  Kite  (Elanus  leucurus).  Condor  77:226-230. 

Warriner,  J.  S.,  J.  C.  Warriner,  G.  W.  Page,  and  L  E.  Stenzel. 
1986.  Mating  system  and  reproductive  success  of  a  small 
population  of  polygamous  Snowy  Plovers  (Charadrius  alex- 
andrinus).  Wilson  Bull.  98:15-37. 

Watson,  J.  R.  1910.  The  impaling  instincts  in  shrikes.  Auk 
27:459. 

Wauer,  R.  H.  1969.  Recent  bird  records  from  the  Virgin 
River  Valley  of  Utah,  Arizona,  and  Nevada.  Condor  71: 
331-335. 

Weathers,  W.  W.  1983.  Birds  of  Southern  California's  Deep 
Canyon.  Univ.  California  Press,  Berkeley. 

Weaver,  R.  L  1939.  Winter  observations  and  a  study  of  the 
nesting  of  English  Sparrows.  Bird-Banding  10:73-79. 

.  1943.  Reproduction  in  English  Sparrows.  Auk  60:62- 

74. 

Webster,  C.  G.  1964.  Fall  foods  of  Soras  from  two  habitats 
in  Connecticut.  J.  Wildl.  Mgmt.  28:163-165. 

Webster,  J.  D.  1941a.  The  breeding  of  the  Black  Oyster- 
catcher.  Wilson  Bull.  53:141-156. 

.  1941b.  The  feeding  habits  of  the  Black  Oyster-catcher. 

Condor  43:175-180. 

Weitzel,  N.  H.  1988.  Nest-site  competition  between  the 
European  Starling  and  native  breeding  birds  in  northwest- 
ern Nevada.  Condor  90:515-517. 

Welch,  W.  R.  1928.  Quail  shooting  in  California  today  and 
fifty  years  ago.  Calif.  Fish  Game  14:122-128. 

Weller,  M.  W.  and  L  H.  Fredrickson.  1973.  Avian  ecology 
of  a  managed  glacial  marsh.  Living  Bird  12:269-291. 

Wells,  P.  V.  1958.  Indigo  Buntings  in  Lazuli  Bunting  habitat 
in  southwestern  Utah.  Auk  75:223-224. 

Welter,  W.  A.  1935.  The  natural  history  of  the  Long-billed 
Marsh  Wren.  Wilson  Bull.  47:3-34. 

Welty,  J.  C  and  L  Baptista.  1988.  TKe  Life  of  Birds.  4th  ed. 
Saunders,  New  York. 


473 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


Wemmer,  C.  1969.  Impaling  behaviour  of  the  Loggerhead 
Shrike,  Lanius  ludovicianus  Linnaeus.  Z.  Tierpsychol.  26: 
208-224. 

Werschkul,  D.  F.,  E.  McMahon,  and  M.  Leitschuh.  1976. 
Some  effects  of  human  activities  on  the  Great  Blue  Heron 
in  Oregon.  Wilson  Bull.  88:660-662. 

West,  M.  J.,  A.  P.  King,  and  D.  H.  Eastzer.  1981.  The 
cowbird:  Reflections  on  development  from  an  unlikely 
source.  Amer.  Sci.  69:56-66. 

Weston,  H.  G.,  Jr.  1947.  Breeding  behavior  of  the  Black- 
headed  Grosbeak.  Condor  49:54-73. 

.  1948.  Spring  arrival  of  summer  residents  in  the  Berke- 
ley area,  California.  Condor  50:81  -82. 

Wetmore,  A.  1925.  Food  of  American  phalaropes,  avocets, 
and  stilts.  U.S.  Dept.  Agri.  Bull.  1359. 

Wheeler,  R.  J.  1965.  Pioneering  Blue-winged  Teal  in  Califor- 
nia, Oregon,  Washington  and  British  Columbia.  Murrelet 
46:40-42. 

White,  H.  C.  1953.  The  eastern  Belted  Kingfisher  in  the 
Maritime  Provinces.  Fish.  Res.  Board  Can.  Bull.  97. 

White,  J.  M.  1973.  Breeding  biology  and  feeding  patterns  of 
the  Oregon  Junco  in  two  Sierra  Nevada  habitats.  Ph.D. 
thesis,  Univ.  Calif.,  Berkeley. 

Whitmore,  R.  C.  1975.  Indigo  Buntings  in  Utah  with  special 
reference  to  interspecific  competition  with  Lazuli  Buntings. 
Condor  77:509-510. 

.  1979a.  Temporal  variations  in  the  selected  habitats  of 

a  guild  of  grassland  sparrows.  Wilson  Bull.  91:592-598. 

.  1 979b.  Short-term  change  in  vegetation  and  its  effect  on 

Grasshopper  Sparrows  in  West  Virginia.  Auk  96:621- 
625. 

.  1981.  Structural  characteristics  of  Grasshopper  Spar- 
row habitat  J.  Wildl.  Mgmt.  45:811-814. 

Widrlechner,  M.  P.  and  S.  K.  Dragula.  1984.  Relation  of 
cone-crop  size  to  irruptions  of  four  seed-eating  birds  in 
California.  Am.  Birds  38:840-846. 

Wieloch,  M.  1975.  Food  of  nesding  House  Sparrows,  Passer 
domesticus  L,  and  Tree  Sparrows,  Passer  montanus  L,  in 
agrocenoses.  Polish  Ecol.  Studies  1:227-242. 

Wiens,  J.  A.  1969.  An  approach  to  the  study  of  ecological 
relationships  among  grassland  birds.  Ornithol.  Monogr. 
8. 

.  1973.  Interterritorial  habitat  variation  in  Grasshopper 

and  Savannah  sparrows.  Ecology  54:877-884- 

.  1974-  Climatic  instability  and  the  "ecological  satura- 
tion" of  bird  communities  in  North  American  grasslands. 
Condor  76:385-400. 

.  1989.  The  Ecology  of  Bird  Communities.  Vol.  1:  Founda- 
tions and  Patterns.  Vol.  2:  Processes  and  Variations.  Cam- 
bridge Studies  Ecol.,  Cambridge  Univ.  Press,  Cambridge, 
England. 

Wiens,  J.  A.  and  M.  I.  Dyer.  1977.  Assessing  the  potential 
impact  of  granivorous  birds  in  ecosystems.  In  J.  Pinowski 
and  S.  C.  Kendeigh,  eds.  Granivorous  Birds  in  Ecosystems: 
Their  Evolution,  Populations,  Energetics,  Impact,  and  Control, 
15-51.  InL  Biol.  Progr.  12.  Cambridge  Univ.  Press,  Lon- 
don. 


Wiggins,  I.  L  and  B.  L  Wiggins.  1939.  An  unusual  nesting 
site  of  die  Western  Tanager.  Condor  41 :80-81 . 

Wilbur,  S.  R  1973a.  The  Red-shouldered  Hawk  in  the 
western  United  States.  W.  Birds  4:15-22. 

.  1973b.  The  California  Condor  in  the  Pacific  North- 
west Auk  90:196-198. 

.  1974.  The  literature  of  the  California  Black  Rail.  U.S. 

Fish.  Wildl.  Serv.  Spec.  Sci.  Rept.  Wildl.  179. 

.  1978.  Turkey  Vulture  eggshell  thinning  in  California, 

Florida  and  Texas.  Wilson  Bull.  90:642-643. 

.  1983.  The  status  of  vultures  in  the  Western  Hemi- 
sphere. In  S.  R.  Wilbur  and  J.  A.  Jackson,  eds.  Vulture 
Biology  and  Management,  1 13-123.  Univ.  California  Press, 
Berkeley. 

Wilde,  M.  L  C.  1897.  Nesting  of  the  Parula  Warbler  (Com- 
psothlypis  americana)  in  Cape  May  County,  New  Jersey. 
Auk  14:289-294. 

Wiley,  J.  W.  1975.  The  nesting  and  reproductive  success  of 
Red-tailed  Hawks  and  Red-shouldered  Hawks  in  Orange 
County,  California,  1973.  Condor  77:133-139. 

Wiley,  J.  W.  and  F.  E.  Lohrer.  1973.  Additional  records  of 
non-fish  prey  taken  by  Ospreys.  Wilson  Bull.  85:468-470. 

Willett,  G  1912.  Birds  of  the  Pacific  slope  of  southern 
California.  Pac.  Coast  Avifauna  7. 

.   1933.  A  revised   list  of  the  birds  of  southwestern 

California.  Pac.  Coast  Avifauna  21. 

Williams,  J.  B.  1975.  Habitat  utilization  by  four  species  of 
woodpeckers  in  a  central  Illinois  woodland.  Am.  Midi. 
Nat.  93:354-367. 

.  1980.  Intersexual  niche  partitioning  in  Downy  Wood- 
peckers. Wilson  Bull.  92:439-451. 

Williams,  L  1927.  Notes  on  the  Black  Oyster-catcher.  Con- 
dor 29:80-81. 

.  1940.  The  status  and  preservation  of  the  White-tailed 

Kite  in  California.  Gull  22:29-32. 

.   1942.  Display  and  sexual  behavior  of  the  Brandt's 

Cormorant.  Condor  44:85-104. 

.  1952.  Breeding  behavior  of  the  Brewer's  Blackbird. 


Condor  54:3-47. 

1958.  Brewer's  Blackbird.  In  A.  C.  Bent,  ed.  Life 


histories  of  North  American  blackbirds,  orioles,  tanagers, 
and  allies.  U.S.  Nad.  Mus.  Bull.  211:302-334. 

Williams,  L,  K  Legg,  and  F.  S.  L  Williamson.  1958. 
Breeding  of  the  Parula  Warbler  at  Point  Lobos,  California. 
Condor  60:345-354. 

Williams,  L  W.  1929.  Notes  on  the  feeding  habits  and 
behavior  of  the  California  Clapper  Rail.  Condor  31:52- 
56. 

Williams,  M.  L,  R.  L  Hothem,  and  H.  M.  Ohlendorf.  1989. 
Recruitment  failure  in  American  Avocets  and  Black- 
necked  Stilts  nesting  at  Kesterson  Reservoir,  California, 
1984-1985.  Condor  91:797-802. 

Williams,  P.  L  1982.  A  comparison  of  colonial  and  non-colo- 
nial nesting  by  Northern  Orioles  in  central  coastal  Califor- 
nia. M.A.  thesis,  Univ.  Calif,  Berkeley. 


474 


LITERATURE  CITED 


— .  1988.  Spacing  behavior  and  related  features  of  social 
organization  in  Northern  Orioles  of  central  coastal  Califor- 
nia. Ph.D.  thesis,  Univ.  Calif.,  Berkeley. 
-.  1990.  Use  of  radiotracking  to  study  foraging  in  small 


terrestrial  birds.  In  M.  L  Morrison,  C.  J.  Ralph,  J.  Verner, 
and  J.  R.  Jehl,  Jr.,  eds.  Avian  foraging:  Theory,  methodol- 
ogy, and  applications,  181-186.  Studies  Avian  Biol.  13. 

Williamson,  F.  S.  L  1956.  The  molt  and  testis  cycles  of  the 
Anna's  Hummingbird.  Condor  58:342-366. 

Williamson,  P.  and  L  Gray.  1975.  Foraging  behavior  of  the 
Starling  (Stumus  vulgaris)  in  Maryland.  Condor  77:84-89. 

Willson,  M.  F.  1966.  Breeding  ecology  of  the  Yellow-headed 
Blackbird.  Ecol.  Monogr.  36:51-77. 

.  1970.  Foraging  behavior  of  some  winter  birds  of  decid- 
uous woods.  Condor  72:129-132. 

Wilson,  S.  W.  1978.  Food  size,  food  type,  and  foraging  sites 
of  Red-winged  Blackbirds.  Wilson  Bull.  90:511-520. 

Wilson,  U.  W.  and  D.  A.  Manuwal.  1986.  Breeding  biology 
of  the  Rhinoceros  Auklet  in  Washington.  Condor  88: 
143-155. 

Wittenberger,  J.  F.  1978.  The  breeding  biology  of  an  isolated 
Bobolink  population  in  Oregon.  Condor  80:355-371. 

Wolford,  J.  W.  and  D.  A.  Boag.  1971.  Food  habits  of 
Black-crowned  Night  Herons  in  southern  Alberta.  Auk 
88:435-437. 

Wolinski,  R.  A.  1980.  Rough-winged  Swallow  feeding  on  fly 
larvae.  Wilson  Bull.  92:121-122. 

Wood,  A.  K.  and  J.  D.  Brotherson.  1981.  Microenvironment 
and  nest  site  selection  by  Ring-necked  Pheasants  in  Utah. 
Great  Basin  Nat.  41 :457-460. 

Woods,  R.  S.  1940.  Anna's  Hummingbird.  In  A.  C.  Bent, 
ed.  Life  histories  of  North  American  cuckoos,  goatsuckers, 
hummingbirds,  and  their  allies.  U.S.  Nad.  Mus.  Bull. 
176:371-387. 

.  1942.  Black  Phoebe.  In  A.  C.  Bent,  ed.  Life  histories  of 

North  American  flycatchers,  larks,  swallows,  and  their 
allies.  U.S.  Nad.  Mus.  Bull.  179:154-164. 

.  1948.  California  Thrasher.  In  A.  C.  Bent,  ed.  Life 

histories  of  North  American  nuthatches,  wTens,  drrashers, 
and  their  allies.  U.S.  Natl.  Mus.  Bull.  195:402-410. 


.  1968.  House  Finch.  In  O.  L  Austin,  Jr.,  ed.  A.  C.  Bent 

et  al.'s  Life  histories  of  North  American  cardinals,  gros- 
beaks, buntings,  towhees,  finches,  sparrows,  and  allies. 
U.S.  Nad.  Mus.  Bull.  237  (Part  1):  290-314. 

Woolfenden,  G.  E.  and  J.  W.  Fitzpatrick.  1984.  The  Horida 
Scrub  Jay:  Demography  of  a  cooperative-breeding  bird. 
Monogr.  Pop.  Biol.  20.  Princeton  Univ.  Press,  Princeton. 

Wright,  E.  N.,  I.  R.  Inglis,  and  C.  J.  Feare,  eds.  1980.  Bird 
Problems  in  Agriculture.  Lamport  Gilbert,  Reading,  Great 
Britain. 


Yahner,  R.  C.  1983.  Site-related  nesting  success  of  Mourning 
Doves  and  American  Robins  in  shelterbelts.  Wilson  Bull. 
95:573-580. 

Yocum,  C.  F.  and  S.  W.  Harris.  1975.  Status,  habits,  and 
distribution  of  birds  of  northwestern  California.  Hum- 
boldt State  Univ.  Bookstore,  Areata,  Calif. 

Yokel,  D.  A.  1986.  Monogamy  and  brood  parasitism:  An 
unlikely  pair.  Anim.  Behav.  34:1348-1358. 

Yokel,  D.  A.  and  S.  I.  Rothstein.  1991.  The  basis  for  female 
choice  in  an  avian  brood  parasite.  Behav.  Ecol.  Sociobiol. 
29:39-45. 

Young,  H.  1955.  Breeding  behavior  and  nesting  of  the 
eastern  Robin.  Am.  Midi.  Nat.  53:329-352. 


Zarn,  M.  1974-  Burrowing  Owl  (Speotyto  cunicularia  hypu- 
gaea).  Habitat  management  series  for  Endangered  species. 
U.S.  Bur.  Land  Mgmt.  Tech.  Notes  250. 

Zimmerman,  D.  A.  1970.  Roadrunner  predation  on  passer- 
ine birds.  Condor  72:475-476. 

.  1973.  Range  expansion  of  Anna's  Hummingbird.  Am. 

Birds  27:827-835. 

Zimmerman,  J.  L  1977.  Virginia  Rail  (Rallus  limicola).  In  G. 
C.  Sanderson,  ed.  Management  of  migratory  shore  and 
upland  game  birds  in  North  America,  46-56.  Int.  Assoc. 
Fish  Wildl.  Agencies  and  U.S.  Fish  and  Wildl.  Serv. 

Zusi,  R.  L  and  R.  W.  Storer.  1969.  Osteology  and  myology 
of  the  head  and  neck  of  the  Pied-billed  Grebes  (Podilym- 
bus).  Misc.  Publ.  Mus.  Zool.  Univ.  Mich.  139. 


475 


INDEX 


Abbreviations   77 

Abundance  data  48 

Adequacy  of  coverage,  determining 

46 
Arrival  dates,  landbirds   39 
Adas  coverage   51 
Auklet,  Rhinoceros   199 
Avocet,  American   1 87 

B 

Beach-dune  vegetation,  coastal   23 
Bishop  pine  forest   21 
Bittern,  American  91 
Blackbird 

Brewer's    398 

Red-winged   392 

Tricolored   394 

Yellow-headed     434 
Block  assignments   42 
Bluebird,  Western   316 
Bobolink  434 

Breeding  Bird  Census,  list  444 
Breeding  bird  communities   61 
Breeding  Bird  Survey  data   443 
Breeding  code  criteria   44 
Breeding  distribution,  Marin    76 
Bunting,  Lazuli   367 
Bushtit  292 


Canvasback  430 

Chaparral    24 

Chat,  Yellow-breasted    360 

Chickadee,  Chestnut-backed    288 

Climate   1 1 

climatic  extremes    1 6 

ocean  air  and  current  cycles    1 2 

precipitation   1 1 

seasonality   1 1 

summer  fog   16 

temperatures    1 1 
Coastal  scrub,  northern   24 
Composition  of  breeding  avifauna    56 


Condor,  California   430 
Conservation  applications   69 
Coot,  American    1 74 
Cormorant 

Brandt's   85 

Double-crested    83 

Pelagic  89 
County  adas  projects   4 
Cowbird,  Brown-headed   401 
Creeper,  Brown    301 
Crossbill,  Red  414 
Crow,  American   284 
Cuckoo,  Yellow-billed   432 

D 

Data  summary  48 
Dipper,  American   312 
Distribution  map  data     73 

blocks  recorded   75 

breeding  criteria  categories    75 

breeding  status    73 

Confirmation  Index  (CI)  75 

Fine-Scale  Abundance  Rating 
FSAR)   75 

Overall  Population  Index  (OPI)    75 

Relative  Distribution  Index  (RDl)    75 

seasonal  status   73 
Distributional  highlights    55 
Dove 

Mourning   207 

Rock  203 
Duck 

Fulvous  Whisding-  430 

Ruddy  122 

Wood   106 

E 

Eagle 

Bald   430 

Golden   148 
Ecological  requirements    76 
Egret 

Catde  430 

Great   96 

Snowy  98 


Evergreen  forest,  mixed    19 
Exotic  plants   27 


Falcon 

Peregrine   1 54 

Prairie   431 
Finch 

House    412 

Purple  411 
Flicker,  Northern   252 
Flycatcher 

Ash-throated   264 

Olive-sided    255 

Pacific-slope   258 

Willow  433 
Freshwater  marsh    26 


G 

Gadwall    118 

Gathering  additional  information 

45 

Geology    1 0 

Gnatcatcher,  Blue-gray    314 

Goldfinch 

American   422 

Lawrence's   420 

Lesser  418 
Goose,  Canada    104 
Grackle,  Great-tailed  434 
Grassland   22 
Grebe 

Clark's  429 

Eared   429 

Pied-billed   79 

Western   429 
Grid  system   41 
Grosbeak,  Black-headed   364 
Guillemot,  Pigeon   197 
Gull 

California   432 

Heermann's   432 

Western    191 

477 


MARIN  COUNTY  BREEDING  BIRD  ATLAS 


H 

Habitats,  Breeding  bird    19 

additional   28 

plant  communities     19 
Harrier,  Northern    1  36 
Hawk 

Cooper's   141 

Red-shouldered    144 

Red-tailed   146 

Sharp-shinned    1 39 
Heron 

Black-crowned  Night-     101 

Great  Blue    92 

Green-backed    100 

LitdeBlue   429 
Historical  Background   1 
Historical  trends/population 

threats   76 
Historical  Studies 

California   2 

Marin  County    3 
Hummingbird 

Allen's   240 

Anna's   237 

Black-chinned  433 

J 

Jay 

Scrub  282 

Steller's   280 
Junco,  Dark-eyed   390 

K 

Kestrel,  American    151 
Killdeer   179 
Kingbird 

Cassin's    265 

Western   266 
Kingfisher,  Belted   241 
Kinglet,  Golden-crowned   313 
Kite,  Black-shouldered    133 


Land  use,  history  of  31 
Lark,  Horned    268 

M 

Mallard    109 
Martin,  Purple   269 
Meadowlark,  Western   397 
Merganser,  Common    1 20 


Methods  of  adas   41 

abundance  data   48 

adequacy  of  coverage  46 

data  summary   48 

gathering  additional  information   45 

grid  system  41 

participant  instruction   42 
Mockingbird,  Northern    327 
Moorhen,  Common    1 72 
Murre,  Common    194 
Murrelet,  Marbled   432 

N 

Night-Heron,  Black-crowned     101 
Nuthatch 

Pygmy  298 

Red-breasted    294 

White-breasted    296 

o 

Oak  savannah    21 
Oak  woodland    21 
Observers  cited     77 
Origin  of  atlas  project  6 
Oriole 

Hooded   405 

Northern   409 
Osprey   1 29 
Owl 

Barn    210 

Burrowing   219 

Great  Horned    215 

Long-eared   226 

Northern  Pygmy-    217 

Northern  Saw-whet   231 

Short-eared   229 

Spotted   222 

Western  Screech-    213 
Oystercatcher,  Black   181 


Participant  instruction   42 
Parula,  Nordiern    343 
Pewee,  Western  Wood-   256 
Phalarope,  Wilson's   431 
Pheasant,  Ring-necked   158 
Phoebe 

Black  261 

Say's   262 
Pigeon,  Band-tailed   205 
Pintail,  Northern    1 1 1 
Plant  communities    19 


Plover,  Snowy    1  76 
Poorwill,  Common    233 
Puffin,  Tufted   201 
Pygmy-Owl,  Northern     217 


Q 

Quail,  California    161 


R 

Rail 

Black   164 

Clapper   1 66 

Virginia    169 
Raven,  Common    286 
Redhead   430 
Redstart,  American   433 
Redwood  forest,  coast  22 
Remarks,  content  of  species 

account  text    77 
Results    51 

adas  coverage   51 

composition  of  breeding 
avifauna     56 

distributional  highlights    55 

patterns  of  species  richness   51 
Riparian  forest,  coastal    26 
Roadrunner,  Greater   209 
Robin,  American   322 


Salt  marsh,  coastal   25 
Sandpiper,  Spotted    189 
Sapsucker,  Red-breasted    245 
Scaup,  Lesser  430 
Screech-Owl,  Western    213 
Seabird  breeding  numbers, 

Marin   87 
Shoveler,  Northern   116 
Shrike,  Loggerhead   330 
Siskin,  Pine   41  7 
Soils    10 
Sora    171 
Sparrow 

Black-chinned   376 

Chipping   374 

Grasshopper   382 

House  424 

Lark   378 

Rufous-crowned   372 

Sage  379 


478 


INDEX 


Savannah   380 
Song    385 
White-crowned    388 

Species  account  text,  content  of    76 

abbreviations   77 

ecological  requirements   76 

historical  trends/population 
threats   76 

Marin  breeding  distribution   76 

observers  cited    77 

remarks   77 
Species  accounts,  content  of  73 
Species  of  special  concern, 

identification  of  69 
Species  richness 

factors  limiting  61 

patterns  of    51 
Spring  Bird  Count  data  435 
Starling,  European   333 
Stilt,  Black-necked   184 
Storm-Petrel 

Ashy  81 

Fork-tailed   429 

Leach's  429 
Swallow 

Bank  433 

Barn  278 

Cliff    276 

Northern  Rough-winged    275 

Tree   272 

Violet-green   273 
Swift 

Chimney  433 


Vaux's    234 
White-throated   236 


Tanager,  Western   362 
Teal 

Blue-winged   113 

Cinnamon   115 

Green-winged  430 
Tern 

Caspian   432 

Forster's   432 

Least  432 
Thrasher,  California   329 
Thrush 

Hermit  320 

Swainson  s   318 
Timing  of  breeding   37 
Titmouse,  Plain   290 
Topography,  Marin  County   7 
Towhee 

California    371 

Rufous-sided   369 
Turkey,  Wild  431 


Vireo 

Hutton's   338 
Solitary   337 
Warbling   340 

Vulture,  Turkey    125 


w 

Warbler 

Black-throated  Gray   350 

Hermit   352 

MacGillivray's    353 

Orange-crowned    342 

Wilson's   358 

Yellow   346 

Yellow-rumped   348 
Waxwing,  Cedar  433 
Whisding-Duck,  Fulvous  430 
Wigeon,  American   430 
Woodpecker 

Acorn   243 

Downy  248 

Hairy  250 

Nuttall's   246 

Pileated   253 
Wood-Pewee,  Western   256 
Wren 

Bewick's   305 

House  307 
Marsh  310 
Rock  303 

Winter    309 
Wrentit   324 


Yellowthroat,  Common    355 


479 


The  Marin  Count}  Breeding  Bird  Atlas  was  composed  into  type  using  Ventura  Publisher  and  a 
Hewlett-Packard  LaserJet  III  printer  with  LaserMaster  controller  in  Goudy  Old  Style  set  10.5/1 1.5. 


BUSHTIT     BOOKS 


BOLINAS,      CALIFORNIA 


THE  MARIN  COUNTY 
BREEDING  BIRD  ATLAS 

•  The  first  breeding  bird  atlas  in  western 
North  America 

•  Provides  species  accounts,  with 
distribution  maps,  for  163  species  of 
breeding  birds,  most  of  which  occur 
throughout  the  West 

•  Explains  the  climate,  ocean  cycles, 
and  vegetation  communities  that 
influence  breeding  birds  in  coastal 
California 

•  Details  the  habitat  needs,  nesting 
sites,  food  requirements,  and  foraging 
strategies  for  all  species 

•  Traces  historical  trends  of  all  species 
with  reference  to  California  as  a 
whole 

•  Suggests  how  to  use  atlas  data  for 
conservation 


Biologist/field  ornithologist  Dave  Shuford  has  lived  in  Marin  County,  California  since  1975. 
He  is  a  member  of  the  scientific  staff  of  Point  Reyes  Bird  Observatory.  For  over  20  years, 
Dave  has  passionately  studied  the  distribution,  abundance,  habitat  needs,  and  natural  history 
of  California's  diverse  birdlife . 


$24.95 


ISBN  0-9633050-0'X