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1

RAPTOR RESEARCH

A Quarterly Publication of The Raptor Research Foundation, Inc.

Volume 18, Number 1, Spring 1984
(ISSN 0099-9059)

SMITH

CONTENTS

'■4/

%

V

History and Present Status of Swainson’s Hawks In Southeast Oregon.

Carroll D. Littlefield, Steven P. Thompson and Bradley D. Ehlers f. . .

Nesting Biology of Broad-Winged Hawks in Wisconsin.

Robert N. Rosenfield

Raptor Migration In Northwestern Canada and Eastern Alaska, Spring 1982.

David P. Mindell and Margaret H. Mindell

The Effect of Mining and Blasting On Breeding Prairie Falcon (Falco
mexicanus) Occupancy In the Caballo Mountains, New Mexico.

James C. Bednarz

Results Of A Helicopter Survey Of Cliff Nesting Raptors In A Deep

Canyon In Southern Idaho, t.h. Craig and E.H. Craig

Use of Introduced Perches By Raptors: Experimental Results and
Management Implications. Steven E. Reinert

Short Communications

1

6

10

.16

.20

.25

Kleptoparasitism By White-Tailed Hawk ( Buteo albicaudatus) On Black Shouldered Kite ( Elanus caeruleus

leucurus ) In Southern Texas. Borja Heredia and William S. Clark 30

Observations of Nesting Prairie Falcons In the Los Padres National Forest. Wade L. Eakle 31

Barred Owls and Nest Boxes. David H. Johnson and Don G. Follen, Sr 34

Ground-Nesting By Barn Owls. Michael E. Tewfs 36

Unusually Low Nesting Site For American Kestrels ( Falso sparverius). Clark S. Monson 36

Monitoring Bald Eagle Nesting In Baja California, Mexico. Bruce Conant, Albert N. Novara and

Charles J. Henny 36

Thesis Abstracts 37

Instructions For Contributors To Raptor Research 39

The Raptor Research Foundation, Inc.
Provo, Utah

THE RAPTOR RESEARCH FOUNDATION
(Founded 1966)

OFFICERS

PRESIDENT: Dr. Jeffrey L. Lincer, Office of the Scientific Advisor, 2086 Main Street, Sarasota, Florida 33577

VICE-PRESIDENT: Dr. Richard Clark, York College of Pennsylvania, Country Club Road, York, Pennsyl-
vania 17405

SECRETARY: Mr. Ed Henckel, RD 1, Box 1380, Mt. Bethel, Pennsylvania 18343

TREASURER: Dr. Gary E. Duke, Department of Veterinary Biology, 295K Animal Science/Veterinary Medicine
Building, University of Minnesota, St. Paul, Minnesota 55208

BOARD OF DIRECTORS

EASTERN DIRECTOR: Dr. James A. Mosher, Appalachian Environmental Laboratory, University of Maryland,
Frostburg State College Campus, Gunter Hall, Frostburg, Marylnd 21532

CENTRAL DIRECTOR: Dr. Patrick T. Redig, Department of Veterinary Biology, 295 Animal Science/Veterinary
Medicine Building, University of Minnesota, St. Paul, Minnesota 55108

MOUNTAIN & PACIFIC DIRECTOR: Dr. A1 Harmata, Department of Biology, Montana State University, Boze-
man, Montana 59717

EAST CANADA DIRECTOR: Dr. David M. Bird, Macdonald Raptor Research Centre, Macdonald Campus of
McGill University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Quebec H9X ICO

WEST CANADA DIRECTOR: Dr. R. Wayne Nelson, 4218 -63rd Street, Camrose, Alberta T4V 2W2

INTERNATIONAL DIRECTOR: Dr. Martin Bottcher, Postfach 2164, Steinfelder Strass 1 1, 5372 SCHLEIDEN,
Federal Republic of Germany, GERMANY

DIRECTOR AT LARGE # 1 : Dr. Michael Collopy, University of Florida, School of Forest Resources and Conserva-
tion, 118 Newins-Ziegler Hall, Gainesville, Florida 32601

DIRECTOR AT LARGE #2: Dr. Tom Dunstan, Department of Biological Sciences, Western Illinois University,
Macomb, Illionis 61455

DIRECTOR AT LARGE #3: Dr. Mark R. Fuller, U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center,
Laurel, Maryland 20708

Persons interested in predatory birds are invited to join the Raptor Research Foundation, Inc. Dues are $15 per year
in the U.S., $17 per year outside the U.S., $13 per year for U.S. students, and $15 per year for students outside the U.S..
Add $2 to dues if membership is received after 15 February. The Foundation’s journal Raptor Research is distributed
quarterly to all current members. Subscription price to institutions and nonmembers is the same as regulr membership.
Single copies and back issues are available from the Treasurer. A Contributing Membership is $25, a Sustaining
Membership is $100, and a Life Membership is $500. All contributions to The Raptor Research Foundation, Inc., are
tax-deductible.

Send requests for information concerning membership, subscriptions, special publications, or change of address to
the Treasurer. Other communications may be routed through the appropriate Officer or Board member. All inquiries
concerning the journal should be addressed to Dr. Clayton M. White, Editor, Raptor Research , Department of Zoology,
161 WIDB, Brigham Young University, Provo, Utah 84602, U.S.A.

*******************

Published quarterly by The Raptor Research Foundation, Inc. Business Office: Dr. Gary E. Duke, Treasurer,
Department of Veterinary Biology, 295K Animal Science/Veterinary Medicine Building, University of Minnesota, St.
Paul, Minnesota 55108, U.S.A. Printed by Press Publishing Limited, Provo, Utah 84602. Second-class postage paid at
Provo, Utah. Printed in U.S.A.

RAPTOR RESEARCH

A QUARTERLY PUBLICATON OF THE RAPTOR RESEARCH FOUNDATION, INC.

VOL. 18

Spring 1984

No. 1

HISTORY AND PRESENT STATUS OF SWAINSON S HAWKS
IN SOUTHEAST OREGON

arroll D. Littlefield, Steven P. Thompson and Bradley D. Ehlers

Abstract - Similar to other isolated localities, Swainson’s Hawks have declined in southeast Oregon. Formerly, the most
commonly nesting5wteo in the Malheur-Harney Lakes Basin, the species became uncommon after the 1950’s. Population
declines have also been noted during migration. Reasons for the decline are unknown, but several theories are presented.

Declines in Swainson’s Hawk (. Buteo swainsoni )
numbers have been reported from California
(Bloom 1980), Nevada (Herron and Lucas 1968)
and southern Saskatchewan (Houston and Bechard
1983). Here, we report a similar decline in south-
east Oregon. A summary of the species’ nesting and
migratory status is given from 1875 through 1983,
based on U.S. Fish and Wildlife Service (FWS) files,
and reports by early ornithologists who worked in
the Malheur-Harney Lakes Basin. Data were li-
mited in certain periods, but enough accounts have
accumulated to provide a general trend for the
region.

Study Area

Most information has been collected on or near Malheur Na-
tional Wildlife Refuge Harney Co., Oregon (Figure 1). The refuge
consists of 73,219 ha of freshwater marshes, two large lakes and
uplands with big sagebrush (Artemisia tridentata), rabbitbrush
(Chrysothamnus spp.) and/or greasewood (Sarcobatus vermiculatus) .
Many km of riparian habitat are available along water systems,
particularly in the southern portion of the refuge. The main units
are Malheur, Harney and Mud lakes, Double O and Blitzen Val-
ley. The Blitzen Valley contains the most important habitat for
Swainson’s Hawks because of the amount of riparian vegetation
present. The valley extends south from Malheur Lake about 67
km.

Surrounding the refuge are great expanses of shrub-steppe. Big
sagebrush is the dominant plant, but in many regions western
juniper (Juniperus occidentalis ) is characteristic (Franklin and Dyr-
ness 1973). Within this shrub-steppe region the Bureau of Land
Management (BLM), in cooperation with the U.S. Fish and
Wildlife Service, conducted a nesting raptor inventory from 1976
through 1980. Malheur NWR was located within the 26,379 km2
raptor inventory area; however, most of the study area was on
lands administered by the BLM (Figure 1). Information from the
BLM study are included in this report.

Southeast Oregon is within the Basin and Range province, and
is a continuation of this physiological province in Utah, Nevada,
Arizona, New Mexico and California. The province is mostly
about 1200 m elevation, with north-south trending fault-block
mountains and basins of internal drainage (Baldwin 1964). The

highest point in southeast Oregon is Steens Mountain, Harney
Co., which attains an elevation of 2958 m.

Nesting habitat for Swainson’s Hawks has been riparian zones
on Malheur NWR, and widely scattered junipers throughout the
surrounding uplands. In the spring, the species is usually seen
near agricultural areas, while in the fall principle feeding habitat is
newly mowed meadows where an abundance of rodents, particu-
larly montane voles ( Microtus montanus), are left exposed.

Materials and Methods

Most records were obtained from Malheur NWR files and early
documents from ornithologists who worked in the region from
1875 through 1932. From 1940 through 1983 information was
primarily from Malheur NWR Annual Narrative Reports (NR).
Beginning in 1975, 360 km of raptor road counts were initiated on
and surrounding the refuge (Figure 2). During the periods when
Swainson’s Hawks were in the basin, surveys were conducted in
April, June and August 1975, 1977, 1979, 1980, 1982 and 1983.
Transects were driven at 32 kph with stops for 3 min every 1.6 km.
Counts were completed between 10:00 and 15:30.

Results

1875-1939. — Swainson’s Hawks were first
recorded in southeast Oregon in 1875 when
Charles Bendire found the species quite common in
the Malheur-Harney Lakes Basin (Brewer 1875).
Bendire (1877) later considered it a common sum-
mer resident, generally distributed throughout the
basin. They were found nesting in willows ( Salix
spp.) along streams and in isolated junipers and
pine trees on the edge of the forest. He collected 25
egg sets which usually numbered 2, and rarely 3/
clutch.

We know of no additional records until brief
mention was made of several being seen in 1915
(refuge files). Willett (1919) saw 2 individuals near
Malheur Lake on 26 June 1918 and 2 additional
birds on 27 June. The species was considered fairly
common in August 1918, but these could have been
migrants. Willett further reported that between

1

Raptor Research 1 8( 1 ): 1-5

9

Littlefield, Thompson, Ehlers

Vol. 18, No. 1

Figure 1. Location of Bureau of Land Management’s Figure 2. Locations of raptor road transects in the
nesting raptor inventory study area, in respect Malheur-Harney Lakes Basin, Oregon,

to Malheur National Wildlife, Oregon.

Malheur NWR and Klamath Falls, Klamath Co.,
Oregon the species was common along most of the
route, and particularly abudant in canyons and
slopes on Warner Mountains, in Lake Co. On 24
May 1920, 27 were counted as they perched on
fence posts along one side of an alfalfa ( Medicago
sativa) field near Burns, Harney Co. The field con-
tained numerous ground squirrels, and the hawks
were catching rodents for food (Gabrielson 1922).
Based on the lateness of the season, these birds
probably represented locally nesting individuals.
Prill (1922) found the species very common near
Burns and as far south as Wright’s Point ( 1 6 km S of
Burns) from 25 May to 15 June 1921. They were
commonly nesting in trees on the surrounding hills.
In 1922, the Swainson’s Hawk was considered the
most common of the large hawks in the basin dur-
ing the summer months. The species nested in
junipers bordering Harney Valley where it con-
sumed large numbers of 2 species of ground squir-
rels (FWS files).

Jewett (1936) considered the Swainson’s Hawk as
equal in numbers with the Red-tailed Hawk ( B .

jamicaensis ), indicating the species had declined
somewhat between 1922 and 1932. Gabrielson and
Jewett (1940) reported it was once one of the most
common raptorial birds in eastern Oregon, and
could still be considerd a common summer resident
despite a noticeable decrease in numbers during
recent years. Preferred nesting habitat was re-
ported as gnarled, twisted junipers. Forty-two egg
sets collected in Oregon between 1924 through
1960, on deposit at the Western Foundation of
Vertebrate Zoology, showed 64.3% in junipers,
16.6% in willows, and 19.1% in other tree species
(L. Kiff, pers. comm.).

1940-1959. — Swainson’s Hawks were still com-
mon in southeast Oregon in the 1940’s. An esti-
mated 150 individuals were present on Malheur
NWR in the summer of 1941, from which 12 nestl-
ings were banded. At this time some pairs were
nesting in sagebrush in the northern portion of the
Blitzen Valley. This nesting habitat continued to be
used through the mid-1940’s. From 1944 through
1947 the nesting population remained unchanged.

Spring 1984

Swainson’s Hawks In Oregon

3

Table 1. Number of Swainson’s(SW) and Red-tailed(RT) Hawks observed on raptor transects in the Malheur-Harney
Lakes Basin, Oregon.

Month

1975

TOTALS (#(KM)
1977 1979

1980

1982

1983

April

SW

4

(.011)

2

(.006)

1

(.003)

0

(.000)

13

(.036)

2

(.006)

RT

26

(.072)

21

(.058)

16

(.044)

31

(.086)

38

(.106)

56

(.156)

June

SW

2

(.006)

20

(.060)

8

(.020)

18

(.050)

4

(.011)

7

(.019)

RT

14

(.039)

46

(.128)

29

(.081)

67

(.186)

63

(.175)

36

(TOO)

August

SW

7

(.020)

16

(.040)

20

(.060)

30

(.080)

26

(.072)

23

(.064)

RT

46

(.128)

55

(.153)

67

(.186)

96

(.267)

60

(.167)

31

(.086)

In 1947, it was still the most commonly seen raptor
with an estimated 150 individuals. No information
was available from 1948 through 1957, but there
was no indication of change in the species’ status.

In the late 1950’s the population began to de-
cline. In 1958, several pairs nested in willows on
Malheur NWR. A rodent infestation occurred from
May through August, but no Swainson’s Hawk in-
crease was noted on the refuge. However,
neighboring valleys had larger populations of both
Swainson’s and Red-tailed Hawks. In 1959, a re-
duction in the local nesting population was re-
ported (Refuge N.R.)

1960-1983. — In the 1960’s, low populations of
Swainson’s Hawks persisted. The species increased
by 2 pairs on the refuge in 1960, but their numbers
were low compared with those of previous decades.
By 1962 there were only 2 nesting pairs. Pair num-
bers fluctuated through the 1960’s, with the highest
number recorded in 1966 with 5 pairs. Four pairs
were present in 1967, and for the first time in re-
corded history there were no nesting Swaison’s
Hawks on Malheur NWR in 1968. However, in
1969 and 1970, 2 pairs were present, increasing to 3
pairs in 1971. This was the last nesting record in
willows, and the last until 1979 in any habitat on
Malheur NWR. The 1979 nesting effort was in a
juniper and unsuccessful. Eggs were incubated but
did not hatch.

In the BLM study area (Fig. 1), 18 Swainson’s
Hawk breeding territories were located in 1980.
Densities were one pair/1,465 km2 on the BLM
study area. The nearest nesting pair to Malheur
NWR was 9.6 km east. Johnstone, et al. (1980) re-

ported all 18 nests were in western juniper. Mean
tree height was 5.5 m and mean nest height was 5.0
m. Nesting trees were mostly isolated, near or in
stands of low structured vegetation such as crested
wheatgrass ( Agropyron cristatum ), alfalfa, or cheat-
grass ( Bromus tectorum). The majority of nests lo-
cated in the past 7 years has been near sagebrush
removal projects. Prey remains collected at the
nests indicated their major prey was Horned Larks
( Eremophila alpestris ), Western Meadowlarks ( Stur -
nella neglecta), ground squirrels, various small
mammals and insects (Johnstone, et al. 1980).

Swainson’s Hawk numbers have varied on June
raptor transects (Table 1), and consisted of single
individuals or pairs. Single individuals were as-
sumed to have a mate incubating or brooding at the
time the transect was conducted. In 1975, only 2
birds were recorded, but 20 were noted in 1977.
Seven were seen on the 1983 transects. Most of
these birds were associated with agricultural or
crested wheatgrass areas located east and west of
Burns, Oregon. None was recorded in riparian
habitat. Most Swainson’s Hawks seen on the 1977,
1979 and 1980 transects were members of pairs
whose nests had been previously located by BLM
personnel during nesting raptor inventory studies.

Migrational Accounts. — Little historical in-
formation was available on Swainson’s Hawk mig-
ration in southeast Oregon. Leopold (1942) ob-
served 37 (0.58/km) in August 1941 on a single trip
through the Blitzen Valley, and reported the
species as the most commonly seen raptor on
Malheur NWR. A total of 56 individuals was seen
on 1 August and 50 on 1 September 1947 (Refuge
N.R.).

4

Littlefield, Thompson, Ehlers

Vol. 18, No. 1

Road transects conducted in April and August
1975, 1977, 1979, 1980, 1982 and 1983 (Table 1)
indicated Swainson’s Hawks were no longer a
common species during spring and fall migration in
the Malheur-Harney Lakes Basin. Before the
1960’s the species was considered more common
than the Red-tailed Hawk. When comparing the
two from transect data, Red-tailed Hawks were
more common than the Swainson’s Hawk (Table 1).
Discussion

Reductions in the Swainson’s Hawk nesting
population in southeast Oregon, Nevada and nor-
theast California are presently unexplained. In
southeast Oregon, juniper and riparian habitats are
available and appear adequate for nesting sites,
therefore, other factors are apparently involved. A
recent increase in the Great Horned Owl {Bubo
virginianus ) in riparian habitat on Malheur NWR
could be responsible for the disapperance of nest-
ing Swainson’s Hawks in willows. An active nest in
1962 was taken over by a Great Horned Owl pair in
1963. Swainson’s Hawks have not nested in this area
since. Ini 966, there was an active hawk nest 1 .6 km
east of the site and it could have been the displaced
pair. Newton (1979) reported Swainson’s Hawks
nesting close to Great Horned Owls had signific-
antly less success than those nesting in tree clumps
lacking these predators. In Washington, Fitzner
(1980) reported distances between Swainson’s
Hawk and Great Horned Owl nests ranged from
2.2 to 3.1 km indicating less tolerance to Great
Horned Owls than to other raptorial birds. Smith
and Murphy (1973) also found the species nested
far from Great Horned Owls (mean distance 3.54
km). Both of these studies reported a low tolerance
between the two species.

Another possible factor for the species’ decrease
is a reduction in foraging sites within a pair’s territ-
ory. Yensen (1980) reported vegetation in south-
west Idaho was once a mosaic dominated by open
stands of sagebrush with an understory of peren-
nial grasses. The vegetation was severely damaged
by sheep and cattle in the late 1800’s and early
1900’s. Added to a 14-year dry period, culminating
in the severe drought of 1934, the native grass
understory was virtually eliminated. A similar con-
dition occurred in southeast Oregon. As native
grasses disappeared because of overgrazing, sageb-
rush became the dominant plant. Accompanied
with fire suppression by federal agencies, large
monotypic stands of sagebrush have been per-

petuated. Bechard (1980, 1982) reported hunting
sites by Swainson’s Hawks in Washington was not
based on prey density, but more likely on vulnera-
bility of prey to predation. With dense stands of
sagebrush the vulnerability of prey for the species
probably was reduced, resulting in Swainson’s
Hawks abandoning many regions of southeast
Oregon. The 18 territories reported by Johnstone,
et al. (1980) were mostly near low structured vege-
tation and away from dense monotypic shrubs.

Another possibility is the local nesting population
is being limited either in migration or on their win-
tering areas. The species has been reported as hav-
ing difficulty in their Argentine wintering regions
where large scale use of pesticides has been used for
locust control (N. Smith, pers. comm., Olrog 1967).
Locust are apparently an important prey base for
Swainson’s Hawks in Argentina. If this agricultural
activity is occurring in localized regions, the Great
Basin population could be wintering in such an
area. This might account for the decrease in nesting
pairs in southeast Oregon, northeast California and
Nevada when compared with other populations in
western North America. Henny and Kaiser (1979)
found low levels of DDT and its metabolites in
Swainson’s Hawk eggs in northeast Oregon. Low
levels of DDT were also found in eggs collected in
northeast California in 1982 and 1983 (R. Schlorff,
pers. comm.). Therefore, it is reasonable to assume
DDT is not responsible for the decline of Swain-
son’s Hawks in the northern Great Basin, but other
pesticides might be involved. Only 6 years data are
available from raptor transects, but there appears
to have been a decline in spring migrants (except in
1982). However, migrant counts in August have
remained relatively stable since 1979 (Table 1). If
the same migration corridors were used by indi-
viduals in spring (April) and fall (August), a major
loss of Swainson’s Hawks is occurring south of the
Malheur-Harney Lakes Basin.

Acknowledgments

We thank Larry Ditto, Charles Henny, Gary Ivey, Joseph Maz-
zoni and David Paullin for reviewing, correcting and making
suggestions concerning the manuscript, and Dee Dee Ehlers for
typing assistance. Numerous employees of the U.S. Biological
Survey and U.S. Fish and Wildlife Service collected and recorded
data on the species, and to them we are deeply grateful. Lloyd Kiff
provided egg set data from the Western Foundation of Vertebrate
Zoology, Los Angeles, California.

Literature Cited

Baldwin, E.M. 1964. Geology of Oregon. Edward

Bros., Inc. Ann Arbor, Mich. 165 p.

Spring 1984

Swainson’s Hawk in Oregon

5

Bechard, M .J. 1980. Factors affecting nest productivity
of Swainson’s Hawk (Buteo swainsoni) in southeastern
Washington. Ph.D. Thesis, Wash. State Univ.,
Pullman. 75 p.

1982. Effect of vegetative cover

on foraging site selection by Swainson’s Hawk. Condor
84:153-159.

Bendire, C. 1877. Notes on some of the birds found in
southeastern Oregon, particularly in the vicinity of
Camp Harney, from November 1874, to January
1877. Bos. Soc. Nat. Hist. Proc. 19:109-149.

Bloom, P.H. 1980. The status of the Swainson’s Hawk in
California, 1979. Calif. Dept, of Fish and Game Fed.
Aid Wildl. Restoration, Proj. W-54-R-12. 42 p.

Brewer, T.M. 1875. Notes on seventy-nine species of
birds observed in the neighborhood of Camp Harney,
Oregon, compiled from the correspondence of Capt.
Charles Bendire, 1st Cavalry U.S. A. Bos. Soc. Nat. Hist.
Proc. 18:153-168.

Fitzner, R.E. 1978. Behavioral ecology of the Swain-
son’s Hawk (Buteo swainsoni ) in Washington. Ph.D.
Thesis. Washington State Univ., Pullman. 194 p.

Franklin, J.F. and C.T. Dryness. 1973. Natural vege-
tation of Oregon and Washington. U.S.D.A. Forest
Service Gen. Tech. Report PNW-8. 417 p.

Gabrielson, I.N. 1922. Some hawks in Harney Val-
ley, Oregon. Condor 24:33-34.

Gabrielson, I.N. and S.G. Jewett. 1940. Birds of Ore-
gon. Oregon St. Univ. Press, Corvallis. 650 p.

Henny, C.J. and T.E. Kaiser. 1979. Organochlorine
and mercury residues in Swainson’s Hawk eggs from
the Pacific Northwest. Murrelet 60:2-5.

Herron, G.B. and P.B. Lucas. 1978. Population sur-
veys, species distribution, and key habitats of selected
nongame species. Nev. Dept. Fish and Game, Job Per-
form. Report. Proj. W-43-R, Study 1, Jobs 1 and 2.

Houston, C.S. and M.J. Bechard. 1983. Trees and the
Red-tailed Hawk in southern Saskatchewan. Blue Jay
41:99-109.

Jewett, S.G. 1936. Bird notes from Harney County,
Oregon, during May 1934. Murrelet 17:41-47.

Johnstone, R.F., S.P. Thompson and G.
Wing. 1980. Nesting ecology and management of
the raptors in Harney Basin, Oregon. Bur. Land Man-
agement, Unpubl. ms. 95 p.

Leopold, A. 1942. A raptor tally in the northwest. Con-
dor 44:37-38.

Newton, I. 1979. Population ecology of raptors. Buteo
Books, Vermillion, S.D. 399 p.

Olrog, C.D. 1967. Observaciones sobre aves mig-
ratorias del hemisterio norte. Hornero 10:292-298.

Prill, A.G. 1922. Birds of Harney Valley, and Malheur
Lake region, Oregon. Oologist 39:126-131.

Smith, D.G. andJ.R. Murphy. 1973. Breeding ecology
of raptors in the eastern Great Basin in Central Utah.
Biol. Series, Brigham Young Univ. 18:1-76.

Willett, G. 1919. Bird notes from southeastern Ore-
gon and northeastern California. Condor 21:194-207.

Yensen, D. 1980. A grazing history of southwestern
Idaho with emphasis on the Birds of Prey Study Area.
USDI-BLM Snake River Birds of Prey Res. Proj. 82 p.

U.S. Fish and Wildlife Service, Box 113, Burns, OR 97720.

Address of second author: U.S. Fish and Wildlife Service, 100

Brown Farm Road, Olympia, WA 98506.

Received 26 December 1982; Accepted 1 March 1984.

Raptor Research Foundation Meeting. The 1984 annual meeting of the Raptor Research Foundation, Inc., will be held October 25-28
at Virginia Polytechnic Institute and State University, Blacksburg, Virginia. The tentative schedule is:

26-27

October

Paper and Poster Sessions

27

October

Banquet

28

October

Open

For further information, program suggestions, or space requests, contact: Dr. Jim Fraser, Department of Fish 8c Wildl. Sci., VPI 8c
SU, Blacksburg, VA 24061

NESTING BIOLOGY OF BROAD-WINGED HAWKS IN WISCONSIN

Robert N. Rosenfield

Abstract — Seventy-two nestings in 56 Broad-winged Hawk (Buteo platypterus ) nesting areas were investigated in
Wisconsin from 1976 through 1981. Trembling aspen ( Populus tremuloides) and white birch (Betula papyrifera) supported
51% and 29% of all nests, respectively. A reoccupancy rate of 0.60 was found for 16 nesting areas. Mean distances
between nests on an intensive study area were 1.5 km (1976; n = 9), 1.7 km (1980; n = 9), and 1.1 km (1981; n = 10). Density
in 1981 on 23.7 km2 was 1/2.4 km2. Means of 2.4 eggs laid, 1.8 hatched, and 1.5 young fledged were found for 70 active
nests. Fifty-five of 70 (79%) nests fledged young. The major factors reducing productivity occurred before hatching.

Relatively little has been published on the nesting
ecology of the Broad-winged Hawk (. Buteo platyp-
terus). There are few productivity and density data
for this common breeding raptor of North
America’s eastern deciduous forests. The first re-
view of Broad-winged Hawk biology by Burns
(1911) was general, though extensive. Recent
studies of various aspects of Broadwing nesting
ecology have reported data from relatively few
nests: Rusch and Doerr (1972) 5 nests in Alberta;
Fitch (1974) 3 nests in Kansas; and Matray (1974)
14 nests in New York. Keran (1978) presented
habitat data from 29 nests in Minnesota and Wis-
consin. Intensive studies of nest habitat by Titus
and Mosher (1981), and nesting biology by Janik
and Mosher (1982) are based on 24 and 36 nests,
respectively, in Maryland. This paper presents data
from 72 Broad-winged Hawk nests in Wisconsin
from 1976 through 1981. The objectives of my
study were to determine the spacing of nests, de-
nsity of nesting pairs, and productivity.

Study Area and Methods

In 1976, 1980, and 1981, I intensively searched for Broadwing
nests in an area approximately 1 .6 km north of Merrill, Wisconsin,
45°10' lat 89°40'W long. Here, I did not establish study area
boundaries and completely search the interior in 1976 and 1980;
instead, I conducted an intensive nest search and then established
a boundary around the area I was able to inventory, resulting in
18.1 km2 and 17.5 km2, respectively (Fig. 1). In 1981 I established
a 23.7 km2 study area prior to nest searching (Fig. 1). I am confi-
dent that I found all Broadwing nests on the Merrill study area in
1976, 1980, and 1981 (Fig. 1).

In 1977 through 1979 I searched for nests in areas similar to
known nest habitat within 1 0 km east, west and north of the Merrill
study area; in 1977 through 1981 I revisited known nesting areas
to determine reoccupancy. Nests were also found incidental to
other research on the Nicolet National Forest, 1 20 km northeast of
Merrill, and on 2 other areas, one 266 km south and another 190
km northwest of Merrill, respectively. Calling Broad-winged
Hawks led me to nesting areas; fresh greenery on nests indicated
recent use.

The 1981 Merrill study area was nearly level, ranging from 399
to 4 1 2 m in elevation. Its habitat included 39% upland hardwoods,
36% farmland, 10% alder ( Alnus rugosa) thicket, 8% bog, 2.5%
permanent water, 2.5% residential, 1.2% swampland, and 0.7%

red pine ( Pinus resinosa) plantation. Ground moraine soils were
poorly drained, and small (2-10 m2) woodland pools of water were
common throughout spring and summer. The typical upland
hardwood was trembling aspen ( Populus tremuloides) which existed
in pure stands or mixed with white birch ( Betula papyrifera) and
balsalm fir ( Abies balsamea). Black ash ( Fraxinus nigra), black spruce
( Picea mariana), and tamarack ( Larix laricina) were common in
permanently wet areas.

An active nest or nesting attempt was one in which eggs were
laid; an occupied nest was one in which 2 adults were present near
a recently constructed nest with fresh greenery on top (Post-
upalsky 1974). A nesting area was that area within a radius of 250
m of a nest. A nesting area was considered reoccupied if, in
subsequent years, an active or occupied nest was found within 250
m of a previously used Broad-winged Hawk nest, or if a nest was
reused by Broadwings.

Mean distances between nests on the Merrill study area were
determined in 1976, 1980, and 1981 in the manner reported by
Reynolds and Wight (1978). Productivity was determined by
climbing to each active nest once during mid-to-late incubation
and again about 2 w later to record the clutch size and the number
of nestlings, respectively. I returned to nests to determine fledging
rates when I estimated young to be > 30 d old.

Results and Discussion

I found 70 active and 2 occupied Broad-winged
Hawk nests; 28 by intensive searching, 12 by
searching habitat similar to known nest habitat, 17
by revisiting nesting areas in subsequent years, and
15 as incidental finds. Broad-winged Hawks nest in
a variety of hardwood tree species across their
breeding range. The majority of nests in my study
were supportged by trembling aspen (51%) and
white birch (29%). Matray (1974) reported 86% of
14 nests in yellow birch {Betula alleghaniensis) in New
York. In Maryland, Titus and Mosher (1981) found
79% of 24 nests in various oaks, predominantly
white oak ( Quercus alba ) (50%). Burns (1911: 246)
reported American chestnut {Castanea dentata) as
the most “popular” nest tree in the northeastern
United States. Keran (1978) reported 21% of 29
nests in Minnesota and Wisconsin in aspen and 4 1 %
in oak. Diameter at breast height and height of nests
in trees in my study were less than those reported in
other studies (Table 1).

6

Raptor Research 18(1 ) :6-9

Spring 1984

Broad-Winged Hawk in Wisconsin

7

Table 1. Comparison of diameter at breast height (DBH) of nest trees and height of Broad-winged Hawk nests (X ±
S.D., (range) ).

Source

N

DBH

Nest Height (M)

This study

72

31.5 ± 6.3
(21.1 - 48.8)

8.2 ± 2.7
(3.9- 15.4)

Burns (1911)

167

-

10.1

Matray (1974)

14

54.1 ± 8.3
(42.1 - 74.2)

13.3 ± 1.4
(11.0- 15.5)

Titus and Mosher(1981)

24

38.0 ± 9.5

13.7 ± 3.0

(25.0 - 62.0)

(9.5 - 20.6)

Twenty-nine of 56 (52%) Broad-winged Hawk
nesting areas in this study contained 1 or more
other stick nests. This suggests that a nest area, not
just a nest tree, has some important characteristics,
such as the interspersion of habitat types, that may

be related to the high nesting density (see below).
The importance of certain areas for nesting is
further indicated by the reoccupancy rate. I revi-
sited 16 nesting areas (including nest areas on the
Merrill study area) 47 times in subsequent years and

Figure 1. Distribution of Broad-winged Hawk nests on the Merrill, Wisconsin study area. Thickened line indicates
where 2 or more years formed the study area boundary.

8

Robert N. Rosenfield

Vol. 18, No. 1

found them reoccupied on 28 occasions, resulting
in a reoccupancy rate (number reoccupied/number
revisited) of 0.60. Broadwings usually built a new
nest in a different tree in a reoccupied nesting area.
Broad-winged Hawk nests were reused on only 5
occasions; 3 the next year, 2 the second year.

Mean distances between nests on the Merrill
study area were: 1976-1 .5 km (range = 1.1-2. 2 km,
SD = 0.37 km), 1980-1.7 km (range = 0.6-3. 1 km,
SD = 0.72 km), and 1981-1.1 km (range = 0.5-2. 4
km, SD = 0.62 km). The smaller mean distance in
1981 was due to the close spacing of the 6 most
northerly nests (Fig. 1) that were in locally wet
areas.

Density on the Merrill study area in 1981 was 1
pair/2.4 km2. Variously derived densities in other
studies were a maximum of 1 pair/23.3 km2 esti-
mated by Rusch and Doerr (1972) in Alberta, 1
pair/5.2 km2 estimated by Burns (1911: 176) in
Massachusetts, and 1 pair/2 mi2 (this converts to 5.2
km2 rather than 3.2 km2 as stated) reported by
Reran (1978) in Minnesota. Wisconsin density is
high when compared to other studies.

I suggest that the relatively high density of nest-
ing Broad-winged Hawks in 1981 is related to the
interspersion of habitat types on the Merrill study
area, which lies between extensive northern forests
and an intensively farmed central region of Wis-
consin. The partial conversion of forests to farm-
land in this area has created more upland openings
and edge habitat than were originally present.
Reran (1978) suggested that such openings may be
important to nesting Broad-winged Hawks because
they are utilized as primary hunting sites. Fuller
(1979) found Broadwings in field-forest edge more
than would be expected by chance when this habitat
type occurred in their home ranges. Further, 5 of 6
Nicolet Forest nests were within 50 m of roadways,
which perhaps served as primary hunting sites in an
extensively forested area. Titus and Mosher (1981)
indicated that Broad-winged Hawks nested closer
to both water and forest openings than would be
expected by chance. Matray (1974) stated that
Broadwings seemed to prefer nesting on poorly
drained sites. The importance of wet areas is
suggested by the close spacing of the aforemen-
tioned 6 nests which corresponded with the occurr-
ence of wet habitat in the Merrill study area.

Means of 2.4 eggs laid, 1.8 hatched, and 1.5
young fledged per nest attempt were found in this
study (Table 2). A one-way analysis of variance re-
vealed no significant (P > 0.05) differences among

Table 2. Mean number of eggs laid, hatched and young
fledged per nest attempt1.

Year

N

Eggs

laid2

Eggs

hatched

Young

fledged

1976

9

2.2

1.9

1.8

1977

10

2.0

1.3

1.1

1978

14

2.3

1.9

1.7

1979

12

2.3

1.7

1.3

1980

10

2.5

2.1

1.5

1981

15

2.6

2.0

1.7

Total

70

2.4

1.8

1.5

‘A nest attempt was one in which eggs were laid.

2The distribution of clutch sizes was 2 clutches of 1 egg, 43 of 2, 23 of 3, and 2
of 4.

the yearly means, even though there was consider-
able variability. Janik and Mosher (1982) reported
Broad-winged Hawk productivity data for a 3 y
study in Maryland, but they did not report yearly
means. I do not know if the annual fluctuations
found in my study are common for the species or if
they are a function of the relatively small number of
nests analyzed each year.

Fifty-five of the 70 (79%) active nests fledged
young. The major factors that decreased Broad-
winged Hawk productivity occurred before hatch-
ing (38 eggs were lost compared to 20 young). I
could not determine the cause of all egg and nestl-
ing losses, but I suspected mammalian predation of
4 eggs (2 nests) and of 6 nestlings (5 nests), and
avian predation of 3 eggs (1 nest). Destruction of 2
nests by windstorms caused the loss of 2 eggs and 3
nestlings. My extended visit may have caused a
female to desert another nest with 3 eggs. The
incubating adult at 1 nest may have kicked 1 of 2
eggs out of the nest cup, as an ejected egg was found
embedded within the nest structure. Fifteen (14
nests) of the 165 eggs laid, including 2 complete
clutches, did not hatch for unknown reasons. The
cause of loss of 1 0 eggs (6 nests) and 1 1 nestlings ( 1 0
nests) was unknown. Suspected predators of
Broadwing nests were the Raccoon (Procyon lotor )
and Common Crow ( Corvus brachyrhynchos).

My study further supported the importance of
both woodland openings and wet areas to Broadw-
ing nesting habitat. Wisconsin productivity data
provide some basis for understanding the popula-

Spring 1984

Broad-Winged Hawk in Wisconsin

9

tion dynamics of Broad-winged Hawks. However,
the number of young produced in any one year that
is necessary to maintain a stable population is a
factor of the age structure and mortality rates of
nesting adults (Henny and White 1972). Such data
do not exist for the Broad-winged Hawk. Future
studies should include long-term trapping and
marking of breeding adults to determine age
structure and turnover rate of nesting populations.

Acknowledgments

This paper is based in part on a thesis submitted to the College
of Natural Resources, University of Wisconsin-Stevens Point, in
partial fulfillment of the requirements for the Master of Science
degree. My graduate committee, R. Anderson, M. Fuller, and F.
and F. Hamerstrom, greatly improved the manuscript by their
suggestions. S. Postupalsky reviewed an earlier draft. R. Burton
assisted with figure preparation. I am grateful to many field assis-
tants, particularly L. Carson, M. Gratson, C. Harris, A. Kanvik, G.
Kristensen, R. Murphy, and A. Rosenfield. D. Ledger provided
field headquarters. I especially thank my wife, C. Rosenfield, for
both her support and encouragement throughout this study.

Literature Cited

Burns, F.L. 1911. A monograph of the Broad-winged
Hawk (Buteo platypterus). Wilson Bull. 23:139-320.
Fitch, H.S. 1974. Observations on the food and nesting
of the Broad-winged Hawk (Buteo platypterus) in nor-
theastern Kansas. Condor 76:331-333.

Fuller, M.R. 1979. Spatiotemporal relationships of
four sympatric raptor species. Ph.D. diss. University of
Minnesota, Minneapolis.

Henny, C.J., and H.M. Wight. 1972. Population ecol-
ogy and environmental pollution: Red-tailed and
Cooper’s Hawks. Pages 229-250 In Population Ecology
of Migratory Birds. U.S. Department of Interior.
Wildlife Report 2. 278 pp.

Janik, C., and J.A. Mosher. 1982. Breeding biology of
raptors in the central Appalachians. Raptor Res.
16:18-24.

Reran, D. 1978. Nest site selection by the Broad-winged
Hawk in north central Minnesota and Wisconsin.
Raptor Res. 12:15-20.

Matray, P.F. 1974. Broad-winged Hawk nesting and
ecology. Auk 91:307-324.

Postupalsky, S. 1974. Raptor reproductive suc-
cess: some problems with methods, criteria, and ter-
minology. In Hamerstrom, F.N., Jr., B.E. Harrell, and
R.R. Olendorff, eds. Management of Raptors. Raptor
Res. Rep. No. 2 pp. 21-31.

Reynolds, R.T., and H.M. Wight. 1978. Distribution,
density, and productivity of accipiter hawks breeding
in Oregon. Wilson Bull. 90:182-196.

Rusch, D.H., and P.D. Doerr. 1972. Broad-winged
Hawk nesting and food habits. Auk 89:139-145.

Titus, K., and J.A. Mosher. 1981. Nest-site habitat
selected by woodland hawks in the central Appalac-
hians. Auk 98:270-281.

College of Natural Resources, University of Wisconsin-Stevens
Point, Stevens Point, WI 54481.

Received 15 July 1983; Accepted 31 May 1984

Anderson Award. The 2nd annual William C. Anderson Award for the best student paper was presented at the 1983
Raptor Research Foundation meeting in St. Louis, Missouri. The winner was Mr. Jim Duncan of the MacDonald Raptor
Research Center, McGill University. Jim’s paper was entitled “Mate Selection in Captive Kestrels: I. Siblings vs.
Strangers.”

Students wishing to be considered for the 1984 ANDERSON AWARD must indicate their eligibility when submitting
abstracts. Eligibility criteria were published in Raptor Research 16(1): 30-32. Questions regarding the 1984 award should
be directed to: Dr. Robert Kennedy, Director, Raptor Information Center, National Wildlife Federation, 9412 16th
Street, NW, Washington, D.C. 20036.

Attention RRF Members Past and Present!! The Raptor Research Foundation, Inc., is approaching its 20th
Anniversary. In honor of this memorable occasion, I am compiling a twenty-year history of the Foundation to be
presented in Sacramento at the 1985 annual meeting. In addition, plans are to compose a monograph detailing the
Foundation’s history from beginning to present. I request the assistance of you, the membership, both past and present,
in accomplishing this task. Please contact me if you have any pertinent information in your files, such as photographs,
correspondence, etc., that you would be willing to loan to me. All such material will be acknowledged in publications, of
course, and I will make copies of the materials for my use and return the originals immediately. If you have anything you
wish to contribute, please contact me as follows: Jimmie R. Parrish, Department of Zoology, 159 WIDB, Brigham
Young University, Provo, Utah 84602, USA.

°K S RAN®

10

Mindell and Mindell

Vol. 18, No. 1

Figure 1. Map of Canadian and Alaskan observation sites visited during Spring 1982 raptor migration.

RAPTOR MIGRATION IN NORTHWESTERN CANADA AND EASTERN

ALASKA, SPRING 1982

DAVID P. MINDELL AND MARGARET H. MINDELL

Abstract - Searches for migrant raptors in northern British Columbia, southern Yukon Territory and eastern Alaska
were made between 29 March and 29 April 1982 at locations accessible by road along 3 potential, broadfront, migratory
routes. Migration activity occurred within an intermountain route, passing between the Rocky and Pelly Mountains on
the east and Coast and St. Elias Mountains on the west. We saw no migrant raptors coming from a coastal route north over
Chilkat or White passes, or coming from a Canadian prairie route, east of the Rocky Mountains, over the pass along the
Alaska Highway in the Summit Lake vicinity. We found concentrations of migrant raptors along the Lina Range by Atlin
Lake, British Columbia, and at Johnson’s Crossing and in the Takhini River valley of southern Yukon Territory.
Northern Harriers (Circus cyaneus) were most frequently seen, followed in decreasing order by Red-tailed Hawks (Buteo
jamaicensis). Golden Eagles ( Aquila chrysaetos ), Rough-legged Hawks (Buteo lagopus ), Bald Eagles (Haliaeetus leucocephalus) ,
and Peregrine Falcons (Falco peregrinus). Comparison with other studies suggest that migrant buteos and Golden Eagles
make greater use of an intermountain route through northwestern Canada than of a coastal route along the Gulf of
Alaska, while migrant Sharp-shinned Hawks (Accipiter striatus) more frequently use the coastal route.

Migrating raptors seeking the most direct over-
land route to breeding areas in extreme northwest-
ern North America are funneled into areas of
northwestern British Columbia, southwestern
Yukon Territory, southeast and southcentral
Alaska. Movements of migrant raptors to and from
Alaska and northwestern Canada have been little
studied although tens of thousands of raptors pass
through this region biannually.

The north-south oriented ranges of the Rocky,
Cassiar and Coast Mountains along with the Pacific
shoreline delineate 3 broadscale, potential migra-
tion routes (Fig. 1) described as follows: 1) Coastal -
along the west coast of British Columbia, and
southeast Alaska, then either inland over mountain
passes or continuing northwest along the Alaska
coast south of the Chugach Mountains into central
Alaska via the Copper River drainage, Portage Pass
or other overland routes; 2) Intermountain -
through the intermountain trenches in northern
British Columbia and southwestern Yukon Territ-
ory into the Yukon and Tanana River drainages;
and 3) Canadian prairies - through Alberta and
northeastern British Columbia east of the Rocky
Mountains, then crossing the Rocky Mountains,
and heading northwest through British Columbia
and/or Yukon Territory similar to the intermoun-
tain route. These 3 principal routes, all or in part,
have been described previously by West et al. ( 1 968)
as apparent routes for migrating Lapland
Longspurs ( Calcarius lapponicus).

Raptor migration is generally a broadfront pas-
sage, occurring to some degree over nearly all land
regions of the temperate zone. The distribution of
visible migrants, however, is not random, partly
due to topographic features either discouraging or

inducing travel in a particular direction. Gauth-
reaux (1979) has pointed out that despite the
prominence of migration in avian lifestyles, routes,
rates and calendars of migration are known for few
species aside from waterfowl. The purpose of this
study was to learn about distribution of migrant
raptors moving through northwestern Canada and
eastern Alaska, to locate specific areas of migrant
concentration for future study, and to learn about
timing of regional migration.

Study Area and Methods

Between 29 March and 29 April 1982, 3970 km were driven
between Dease Lake on Rt. 37 in British Columbia, Summit Lake
on Rt. 97 in British Columbia and Anchorage, Alaska. Observa-
tions were made in 3 potential, broadscale, raptor migration
routes to compare their relative use. We attempted to observe in
areas physiographically conducive to concentrating migrants,
such as along major rivers, lakes, southeast to northwest trending
ridges, and mountain passes. Observations were made from roads
or within 3 km hiking distance of roads, using binoculars or a 20X
spotting scope to search for and identify migrants. Some of the
most promising areas were rechecked on 2-3 non-consecutive days
to reduce bias associated with varying weather conditions. Once an
area was perceived to be used, we moved to another location. No
attempt was made to count large numbers of birds or to determine
magnitude of the migration.

Raptor migration in interior western North America occurs
along a broader front (Hoffman 1981, and in press) with smaller
local concentrations of birds compared to eastern North America
(Heintzelman 1975) and elsewhere (Smith 1980, Christensen et al.
1982). We use the term “route” to denote a broadscale, dispersed
movement, and do not suggest that lack of sightings in any area
indicates complete lack of use by migrants. We attempted to spend
sufficient time at different locations in each of the 3 possible routes
mentioned, to enable comparison of their relative use.

The possibility of migrants departing from the general coastal
route by moving northward through Lynn Canal and then into

11

Raptor Research 18(1): 10- 1 5

12

Mindell and Mindell

Vol. 18, No. 1

mainland areas was checked by observing at Haines (Lentnikof
Cove, Flat Bay) and Chilkat and White Passes. The intermountain
route was sampled by observing at numerous locations along the
Alaska Highway between Watson and Kluane Lakes (Fig. 1) and
along Rt. 3 to Haines, Rt. 2 to Carcross, and Rt. 7 to Atlin. The
possibility of migrants crossing the Rocky Mountains along the
route of the Alaska Highway was checked from lookouts in the
vicinity of Muncho and Summit Lakes, British Columbia. We
distinguished migrants from possible residents by behavior.
Sedentary birds or birds moving south or east were not counted
unless they were south of their breeding range (e.g., Rough-
legged Hawks ( Buteo lagopus) ).

232,

Results and Discussion

Route Use. — All migrant activity seen occurred
within the intermountain route, passing between
the Rocky Mountains on the east and the St. Elias
and Coast Mountains on the west. No migrant rap-
tors were seen coming from a coastal route north
over Chilkat or White Passes or from east of the
Rocky Mountains over the pass travelled by the
Alaska Highway in the Summit Lake vicinity. Mig-
rant Northern Harriers ( Circus cyaneus), Red-tailed
Hawks ( Buteo jamaicensis ), Rough-legged Hawks
and Golden Eagles (Aquila chrysaetos) were seen in
the intermountain route (Takhini River valley west
of Whitehorse) before, during, and after observa-
tions at Summit Lake and Chilkat and White Passes
(Table 1), suggesting that the lower abundance of
migrants coming over the passes and at Summit
Lake was not due only to timing of observations.

Migrants passing through southern Yukon Ter-
ritory in mid-April were apparently approaching

from northwestern and northcentral British Col-
umbia and the intermountain route rather than
from a coastal or a Canadian prairies route through
northeastern British Columbia. Late April weather
conditions were still severe in Chilkat and White
Passes and along the route of the Alaska Highway
(Rt. 97) through the Rocky Mountains with 1 to 3 m
of snow cover, whereas the T akhini River valley and
much of the intermountain route were more temp-
erate with some bare ground showing by late April.
This is not to imply that no migration occurs
through these passes or areas with snow cover. Sev-
eral groups of 3-6 Sharp-shinned Hawks ( Accipiter
striatus ) were seen heading south through Chilkat
Pass on 7 October 1980. Weather in these mountain
passes may be generally milder during the fall mig-
ration than during the spring, and use by migrants
may be correlated with the difference.

On 27 and 28 March 1982 an apparent vanguard
of the Canada Goose ( Branta canadensis ) migration
(over 440 individuals) was seen resting along the
last unfrozen sections of the Fraser River in central
British Columbia, between Lac La Hache and
Quesnel. Six Red-tailed Hawks were also seen 40 to
30 km south of Quesnel on 28 March 1982. No
migrant raptors or geese were observed during the
subsequent 7 days spent driving north to Watson
Lake and observing in the area between Watson
and Teslin Lakes. On this basis, it seems unlikely
that large numbers of raptors passed through nor-
thwestern British Columbia or southwestern
Yukon Territory before observations began.

Table 1. Observation sites, date, and total raptor sightings for Spring 1982 migration in northwestern Canada and
Eastern Alaska. (B.C. = British Columbia; Y.T. = Yukon Territory.)

Location

Dates

No. migrant
raptors seen

Summit Lake, B.C.

16-18 Apr

0

Johnson’s Crossing, Y.T.

1,14,15,19-21 Apr

73

Atlin Lake, B.C.

21-23 Apr

142

White Pass, B.C.

3, 24, 25 Apr.

0

Chilkat Pass, B.C.

8, 12, 13 Apr.

0

Haines area, Alaska1

9-12 Apr

0

Takhini River valley, Y.T.

5, 6, 13, 14, 26 Apr

53

Other2

5-28 Apr

46

1 Lentnikof Cove, Flat Bay.

2 <3 migrant raptors were seen at any one location, and all locations were within the intermountain route.

Spring 1984

Spring Migration 1982

13

Based on physiographic features, 3 sub-routes
can be distinguished within the broader inter-
mountain route: 1) between the Rocky and Cassiar
Mountains, entering Yukon Territory near Watson
Lake, 2) between the Pelly and Cassiar Mountains
and the St. Elias and Coast Mountains, entering
Yukon Territory near Teslin, and 3) along the east
slope of the Coast Mountains and Atlin or Tagish
Lakes entering the Yukon River drainage near
Whitehorse. Observed migrant activity was greater
in sub-routes 2) and 3).

Recoveries of Alaskan banded birds show that at
least some Peregrine Falcons ( Falco peregrinus)
(Ambrose et al. 1983) and Rough-legged Hawks
(Kessel and Cade 1958) cross the Rocky Mountains,
and many Alaskan breeding Red-tailed Hawks do
so as well. Migrants cross the Rocky Mountains in
many regions, however, Williston Lake west of
Dawson Creek, British Columbia and the Jasper
and Banff areas may be worthy of future study.

A coastal route through southeastern and south-
central Alaska, along the Gulf of Alaska is used by
many raptors based on observations by Islieb and
Kessel (1973) and Swem (1982a, 1982b). Dates of
migrant passage recorded by Swem (1982a) were
such that if large numbers flew from the coastal
migratory route north up Lynn Canal and over
Chilkat or White Passes we would likely have seen
some of them.

Specific Locations of Migrant Activity. — Within
the intermountain route relatively high concentra-
tions of migrants were found at 3 locations. On 22
April we counted 117 raptors in 6 hrs, flying north
along the Lina Range on the east side of Atlin Lake,
British Columbia. This included 65 Northern Har-
riers, 21 Golden Eagles, 18 Red-tailed Hawks, 8
Buteo sp., 4 Bald Eagles ( Haliaeetus leucocephalus),
and 1 Peregrine Falcon. The Lina Range rises 900
m above Atlin Lake, and most of the migrants were

observed from 300 m above the range to half-way
down the slope.

At Johnson’s Crossing, Yukon Territory we
counted 73 raptors during 15.2 total hrs of obser-
vation during portions of 5 days between 14 and 2 1
April. Johnson’s Crossing is at the outlet of Teslin
Lake, a northwest trending lake approximately 80
km northeast of Atlin Lake. In descending order of
abundance the migrants were: Red-tailed Hawks,
Northern Harriers, Buteo sp., Rough-legged Hawks
and Golden and Bald Eagles.

On 13 and 14 April 23 migrants were seen during
5.5 hrs of slow driving and observation in the
Takhini River valley, 10 to 50 km west of
Whitehorse. The Takhini River valley receives mig-
rants that have come northwest along Teslin Lake,
Atlin Lake, and Tagish Lake (intermountain
route). The Takhini River valley is broad, however,
we saw raptors from observation spots on Rt. 1, 3
km east of Champagne, 2 km east of the Kusawa
Lake turnoff and at the Takhini River Crossing. We
saw a total of 1 0 migrants during fast travel through
the Takhini River valley on 5 and 26 April. Mig-
rants proceeding through the intermountain route
could pass along Kluane Lake, however, our obser-
vations there were after the bulk of the Northern
Harrier and Buteo migrations had passed. We saw
only a few migrants along the Tagish River at
Tagish, Yukon Territory, and the Tanana River
near Tetlin Junction, Alaska.

Species Abundances. — The Northern Harrier
was the most frequently seen migrant (Table 2). At
each of the 3 main areas of migrant activity, either
the Northern Harrier or the 2 buteos as a group
were most abundant. The largest flight of Northern
Harriers and Golden Eagles was seen along Atlin
Lake (Lina Range), while the largest flights of
Red-tailed and Rough-legged Hawks were seen at
Johnson’s Crossing.

Table 2. Species percentages of migrant raptors (n = 3 14) seen in northwestern Canada and eastern Alaska 5-18 April
1982.

Red-tailed

Rough-legged

Northern

Golden

Bald

Peregrine

Hawk

Hawk '

Harrier

Eagle

Eagle

Falcon

% of total

sightings

29.1

9.4

40.2

15.7

5.2

0.4

14

Mindell and Mindell

Vol. 18, No. 1

Comparing our study with another conducted
during the spring of 1982 along the Gulf of Alaska
coast at Sitkagi Beach, west of Yakutat Bay (Swem
1982a), the Northern Harrier was the most abun-
dant species along both the intermountain route
and the coastal route passing Sitkagi Beach. Sharp-
shinned Hawks, however, were the second most
abundant species along the coastal route (26.5% of
total) while none were seen in the intermountain
route. Rough-legged and Red-tailed Hawks com-
bined accounted for only 1.8% of the total sightings
along the Gulf of Alaska at Sitkagi Beach,3com-
pared to 38.5% in the intermountain route. Golden
Eagles were also comparatively rare along the
coastal route, comprising 0.4% of total sightings,
compared to 15.7% in the intermountain route.

Greater use of the coastal route by migrant
Sharp-shinned Hawks and greater use of the in-
termountain route by migrant buteos and Golden
Eagles is supported by Swarth (1924, and 1926)
who found that Sharp-shinned Hawks were “never
common in the Atlin, British Columbia region, not
even in the fall after southward migration had
begun”, and by Islieb and Kessel (1973) who de-
scribed Rough-legged Hawks and Golden Eagles as
rare migrants, Red-tailed Hawks as casual migrants
and Sharp-shinned Hawks as fairly common mig-
rants along the Gulf of Alaska and in the Prince
William Sound region. Swarth did observe migrat-
ing Sharp-shinned Hawks at Hazelton in the
Skeena River valley of westcentral British Colum-
bia, although hawks in this area may have been
headed for the coast. A tendency for Sharp-
shinned Hawks to migrate in greater numbers
along the Pacific coast or along the southern edge of
the boreal forest might help to explain the relative
scarcity of migrant Sharp-shinned Hawks in inland
western North America compared to inland sites in
eastern North America such as Hawk Mountain,
Pennsylvania, as suggested by Hoffman (in press).

Islieb and Kessel (1973) also described Red-tailed
Hawks as regular fall migrants in southcentral
Alaska along the Glenn Highway between King and
Sheep Mountains in late September and early Oc-
tober. This corresponds with fall migration obser-
vations we made along the Glenn Highway in 1980
and 1981, and with observations by Bob Dittrick
(pers. comm.).

Peregrines represented 0.8% of the sightings
along the Gulf of Alaska, and 0.4% in the inter-
mountain route. Swarth (1926) also saw migrant
Peregrines within the intermountain route at

Tagish and Teslin Lakes. On the east side of the
Rocky Mountains migrant Peregrines are consis-
tently observed in spring passing through the Ed-
monton, Alberta region (Dekker 1979). The ob-
served fall passage there is considerably less,
suggesting seasonal difference in distribution of
migrant Peregrines. Although no migrant Merlins
(Falco columbarius) were seen during our study they
have been seen both along the coastal route (Swem
1982a) and within the intermountain route (Swarth
1924, and 1926).

Chronology. — The first migrant Rough-legged
Hawks, Red-tailed Hawks and Golden Eagles were
all seen on 5 April in 1982. The first Northern
Harriers were not seen until 14 April. Similarity in
timing of migration for Rough-legged and Red-
tailed Hawks is reflected in similar breeding
chronologies in portions of Alaska (Gabrielson and
Lincoln 1959, Mindell 1983).

Although the present study was not designed to
determine timing of peak migration, the main mig-
ration of buteos in the intermountain route
through southwestern Yukon Territory and
northwestern British Columbia appeared to be over
by 25 April, while some Northern Harriers were
still passing through. This corresponds with aver-
age laying dates over a 4-yr period of 17 May for
Rough-legged Hawks and 16 May for Red-tailed
Hawks along the Kuskokwim River in western
Alaska (Mindell 1983). On 23 April 1982 we ob-
served a Red-tailed Hawk nest building at Tarfu
Lake near the northern end of Atlin Lake. Swem
(1982a) found the peak abundance of migrating
raptors passing Sitkagi Beach near Yakutat Bay to
be on 28 April, with stragglers of 7 species going by
as late as 8 May.

Acknowledgements

We thank Mark Fuller for providing helpful comments on an
earlier draft of this paper.

Literature Cited

Ambrose, R., P. Schempf, and R. Hunter. 1983. Ameri-
can Peregrine Falcon ( Falco peregrinus anatum ) studies
on the upper Yukon River, Alaska, 1983. Unpubl.
report prepared for the U.S. Fish and Wildlife Service,
Office of Endangered Species, Anchorage. 19 pp.
Christensen, S., O. Lou, M. Mueller, and H.
Wohlmuth. 1982. The spring migration of raptors
in southern Israel and Sinai. Sandgrouse 3:1-42.
Dekker, D. 1979. Characteristics of Peregrine Falcons
migrating through central Alberta, 1969-1978. Can.
Field Nat. 93:296-302.

Spring 1984

Spring Migration 1982

15

Gabrielson, I.N. and F.C. Lincoln. 1959. The birds of
Alaska. The Stackpole Co. Harrisburg, Pennsylvania.
922 pp.

Gauthreaux, S.A., Jr. 1979. Priorities in bird migration
studies. Auk 96:813-815.

Heintzelman, D.S. 1975. Autumn hawk flights: the
migration in eastern North America. Rutgers Univ.
Press, New Brunswick, N.J. 398 pp.

Hoffman, S. 1981. Western hawk watching. The News-
letter of the Hawk Migration Assoc, of North America
6(1): 1-5.

Hoffman, S. In press. Raptor movements in inland west-
ern North America: a synthesis. Proceedings of Hawk
Migration Conference IV, Rochester, N.Y., March
24-26, 1983.

Islieb, M.E. and B. Kessel. 1973. Birds of the north
gulf coast - Prince William Sound region, Alaska. Biol.
Papers of the Univ. of Alaska, No. 14.

Kessel, B. and T.J. Cade. 1958. Birds of the Colville
River northern Alaska. Biol. Papers of the Univ. of
Alaska, No. 2.

Mindell, D.P. 1983. Nesting raptors in southwestern
Alaska; status, distribution, and aspects of biology.
BLM-Alaska Technical Report 8. Bureau of Land
Manage., Alaska State Office, Anchorage. 59 pp.
BLM/AK/TR-83/08.

Smith, N.G. 1980. Hawk and vulture migrations in the
Neotropics, pp. 51-65 in Migrant birds in the Neo-
tropics. Keast. A. and F. Morton, eds. Smithsonian
Institution Press, Washington, D.C. 576 pp.

Swarth, H.S. 1924. Birds and mammals of the Skeena
River region of northern British Columbia. Univ. of
Cal. Publ. in Zool. 24(3):3 15-394.

Swarth, H.S. 1926. Report on a collection of birds and
mammals from the Atlin Region, northern British
Columbia. Univ. of Cal. Publ. in Zool. 30(4):51-162.

Swem, T. 1982a. Results of the Sitkagi Beach raptor
migration study, spring 1982. Unpubl. report pre-
pared for U.S. Fish and Wildlife Service, Office of
Endangered Species, Anchorage, Alaska. 21 pp.

Swem, T. 1982b. Results of the Sitkagi Beach raptor
migration study, autumn 1982. Unpubl. report pre-
pared for U.S. Fish and Wildlife Service, Office of
Endangered Species, Anchorage, Alaska. 14 pp.

West, G.C., L.J. Peyton, and L. Irving. 1968. Analysis
of spring migration of Lapland Longspurs to Alaska.
Auk 85:639-653.

Department of Zoology, Brigham Young University, Provo,

Utah 84602. Address of second author: 1 1 South 200 East, Lin-

don, UT 84062.

Received 2 December 1982; Accepted 1 May 1983

Position Available - NATURALIST/STAFF BIOLOGIST. Hawk Mountain Sanctuary Association seeks a
naturalist/staff biologist for a two-year position beginning in August 1984. Responsible for all field studies, including
fall raptor migraton count. Will also participate as resource person in education program. Excellent opportunity to
initiate new studies and analyze migration statistics. Computer system available. Minimum qualifications are M.S. in
biology or related field, experience in conducting field studies and data analysis/write-up, experience with raptor
identification, and ability and interest in working with volunteers and general public. Computer experience strongly
preferred. Salary plus housing on grounds. Apply to Stanley E. Senner, Executive Director, Hawk
Mountain Sanctuary Association, Rt. 2, Kempton, PA 19529.

Hawk Mountain Research Awards. The Hawk Mountain Sanctuary Association is accepting applications for its eighth
annual award for raptor research. To apply for the $500 award, students should submit a description of their research
program, a curriculum vita, and 2 letters of recommendation by 30 September 1984, to James J. Brett, Curator, Hawk
Mountain Sanctuary, Rt. 2, Kempton, Pennsylvania 19529. The Association’s Board of Directors will make a final
decision late in 1984. Only students enrolled in a degree-granting institution are eligible. Both undergraduate and
graduate students are invited to apply. The award will be granted on the basis of a project’s potential to improve
understanding of raptor biology and its ultimate relevance to conservation of North American raptor populations.

THE EFFECT OF MINING AND BLASTING ON BREEDING PRAIRIE FALCON
(Falco mexicanus) OCCUPANCY IN THE CABALLO MOUNTAINS, NEW MEXICO

James C. Bednarz

Abstract - I surveyed 3 small isolated mountain ranges in southcentral New Mexico for the presence of breeding
Prairie Falcons ( Falco mexicanus). Of these, the Caballo Mountains were intensively impacted by mining and blasting
activity, while the other 2 were essentially undisturbed. No falcons were found in the disturbed mountain range, but a
total of 8 nests were documented in the 2 control ranges. The 3 areas were extremely similar in all respects except for the
number of mining claims.

Almost no published information is available
concerning the impacts of mining and blasting on
birds of prey. The limited data available are re-
stricted to observation of short-term impacts on
actively nesting raptors (Stahlecker and Alldredge
1976). Several works (Allen 1979, Call 1979, Becker
and Ball 1981) contain speculation about the im-
pending impacts of mining operations on raptors
and offer suggestions to minimize potentially ad-
verse effects. Follow-up or controlled experimental
studies of such impacts are virtually nonexistent.

Herein I report the numbers of breeding Prairie
Falcons observed during a survey of 3 small and
very similar mountain ranges in southcentral New
Mexico. One of these ranges, the Caballo Moun-
tains, has been intensively impacted by mining op-
erations and associated human intrusions for sev-
eral years. The other 2, the Fra Cristobal and
Florida mountains, have minimal or no disturbance
from mining. If mining and the associated blasting
has no influence on Prairie Falcon nest occupancy, I
would expect the numbers of breeding falcons at all
3 study areas to be similar. The habitat and number
of cliffs at all 3 mountain ranges seems comparable.

Study Areas and Methods

I surveyed the Fra Cristobal Mountains on 15-18 April and
19-23 May 1980, the Florida Mountains on 21-25 April 1980, and
the Caballo Mountains on 5-9 May 1980. These ranges were
searched for raptors as part of a larger statewide survey with
emphasis on endangered raptors on lands administered by the
Bureau of Land Management (BLM). These 3 ranges are isolated,
but located in relatively close proximity (Fig. 1). The climate of all
3 ranges is similar; all are extremely dry with summer daytime
temp often exceeding 38° C and winter temp commonly dropping
below 0° C at night. The vegetation in all 3 study areas can be
characterized as creosote bush ( Larrea tridentata) dominated
shrubland on the lower slopes grading into a sparse juniper-oak
(Juniperus spp.; Quercus spp.) woodland on the summits and
upper, north-facing slopes (Table 1). Elements of Chihuahuan
desert vegetation (e.g . Prosopis glandulosa, Yucca spp ,,Opuntia spp.)
are more common in the Florida Mountains. Suitable cliff habitat,
elevation and topographic relief above basins are comparable for
all 3 study areas (Table 1). Area of suitable cliff habitat (Table 1)

includes only that contiguous mountain habitat that contains cliffs
potentially usable as nest sites. Foothill habitats without cliffs sur-
rounding mountain ranges were not included in this area mea-
surement.

Geologically, the Fra Cristobal and the Caballo mountains are
nearly identical, consisting primarily of marine sedimentary rock
resulting from an uplift along the Rio Grande Rift (Kelly and
Silver 1952). The Florida Mountains differ in this respect as they
are of a rhyolitic formation.

Field surveys in all 3 areas emphasized the most prominent
cliffs, which in my experience are preferred by Prairie Falcons for
nest sites. I have found that cliffs < 50 m in height are generally
used only in New Mexico when larger cliffs are not available.
During this study I examined numerous smaller cliffs (< 50 m in
height) but none contained active Prairie Falcon nests. Surveys
were accomplished by climbing to an observation point that al-
lowed observation of 1 or more large cliffs ( > 50 m of vertical or
near vertical rock). I studied cliffs for falcon-like excrement
(“whitewash”) with binoculars and spotting scope and watched for
falcon activity for periods of several hours as outlined by Bond et
al. (1977) and Call (1978). Cliff observations were made in the
early morning or late afternoon. After cliffs were watched for at
least 2 h without success, I approached from below and attempted
to disturb (by shouting and clapping hands) any previously unob-
served raptor. Observations were discontinued at cliff sites when
nests of the Golden Eagle (Aquila chrysaetos) or Prairie Falcon were
located. Field examinations in all areas were conducted when
falcons were expected to be incubating or possibly tending small
young.

Accessibility of mountain ranges differed considerably. The
Caballo range had numerous roads on talus slopes providing easy
access to excellent observation perches close to prominent cliffs.
On the other hand, the Fra Cristobal range was extremely remote
and almost no roads approach the foothills. Although I spent
nearly twice as many field days in this area, most of the additional
time was used in travel. Access roads circled around the Florida
Mountains, but generally stopped at the base of the talus. Search
and observation effort at all 3 ranges was comparable (Table 2).

Results and Discussion

I located 5 active Prairie Falcon nests in the
Florida range and 3 active sites in the Fra Cristobal
range (Table 2). No nests or large falcons were
observed in the Caballo Mountains. I also found 2
Golden Eagle nests in the Fra Cristobal range. In all
observable physical and ecological characteristics,
except for the intensity of mining, the 3 mountain

16

Raptor Research 18( 1): 16-19

Spring 1984

James C. Bednarz

17

Table 1. Characteristics of 3 mountain study areas in southcentral New Mexico.

Fra Cristobal
Mountains

Caballo

Mountains

Florida

Mountains

Approx, area of
suitable cliff
habitat (km2)

36

26

34

Maximum elevation (m)

2083

2301

2270

Elevation relief
above basin (m)

730

1000

915

Primary rock type

marine

sedimentary

marine

sedimentary

rhyolite

Dominant vegetation
community on slopes

creosote

shrubland

creosote

shrubland

creosote-mesquite

shrubland

Dominant vegetation
community at summit

juniper-oak

woodland

juniper-oak

woodland

juniper-oak

woodland

ranges appeared to be extremely similar (Tables 1
and 2).

The area I surveyed (26 km2) in the Caballo
Mountains contained 125 active mining claims
(mining claim records dt 21 June 1980, BLM State
Office, Santa Fe, New Mexico). I witnessed blasting

during 1 of my 5 field survey days in this area.
Numerous shallow shafts were blasted into rock
walls and talus slopes throughout the range. These
blast shafts were concentrated at or just above the
base of both large and small cliffs examined. In
addition, several ladders were bolted to the vertical

Table 2. Results of field survey for Prairie Falcon nests and active mining claims in 3
southcentral New Mexico.

mountain study areas in

Fra Cristobal
Mountains

Caballo

Mountains

Florida

Mountains

Field days

9

5

5

Cliff observation (time h)

25.9

25.0

25.0

# of major cliffs
examined ( > 50 m in height)

10

8

9

# of major cliffs

not examined ( > 50 m in height)

3

3

4

# nests located

3

0

5

Mining claims recorded at BLM office

0

125

29

Mining activity observed

none

intense

none

18

Prairie Falcon in New Mexico

Vol. 18, No. 1

0 100

I 1

k m

Fig. 1 . Location of 3 mountain tudy areas in southcentral
New Mexico.

rock walls and 2 compressors were parked high on
the talus slopes adjacent to cliffs.

In the Florida Mountains, with 29 mining claims
in the area surveyed (34 km2), I observed no evi-
dence of active mining. I did note 1 probable min-
ing road leading up the talus slope on the north side
of the mountain range. No evidence of mining ac-
tivity was observed in the Fra Cristobal range.

The absence of nesting Prairie Falcons from the
Caballo range was an unexpected Finding. Promi-
nent cliffs in the 2 control study areas provided
habitat for 8 pairs of breeding falcons. Evidence of
mining activity and related human disturbance was
obvious in the Caballo Mountains, but minimal in
the 2 control ranges.

Breeding falcons may have occurred in the
Caballo Mountains in 1980, but if so, they must
have occupied the smaller, less preferred cliffs.
Given that I did not observe any Prairie Falcons,
during the field survey, I suspect that few, if any,
breeding falcons were present. No historical data
on raptor breeding populations are available for
any of the 3 ranges surveyed.

A possible alternative explanation is that low
numbers of available prey made the Caballo range
unsuitable as falcon breeding habitat in 1980. I feel,

however, this is unlikely because the Fra Cristobal
Range 30 km to the north and the Florida range 90
km to the south provided enough prey to support at
least 8 pairs. The vegetative cover in the vicinity of
all ranges was extremely similar in all appearances.
An absence of Prairie Falcons from the Caballo
Mountains could only be caused by an extreme
depression in prey populations in a very localized
area around these mountains, which seems highly
improbable.

The Florida Mountains were used by almost twice
as many falcon pairs (5 vs 3) as the Fra Cristobal
Mountains. This difference may be due to the dis-
persion of cliffs in the respective ranges. Prominent
cliffs in the Florida range were uniformly distri-
buted along the west face, whereas in the Fra Cris-
tobal range, cliffs were aggregated in 2 relatively
small parts of the range (1 aggregation in the north
portion and the other in the south). The uniform
cliff dispersion probably enables more falcons to
use a small mountain range without intruding into
defended areas around neighboring eyries. The
cliffs in the Caballo range are distributed in a man-
ner similar to that found in the Florida Mountains.
Therefore, I would expect to find between 3-5
Prairie Falcon nests if the Caballo Mountains were
undisturbed.

All raptors have individual differences in the
amount of disturbance that will be endured. I am
aware of 1 case in Wyoming where a pair of Prairie
Falcons tolerated intensive coal mining activity in-
cluding blasting, heavy equipment operation, and
settling pond construction within 75 m of the nest
(S. Platt, pers. comm.). Falcons returned to the
same general area for 3 consecutive years (1981-
1983) following the disturbance. These birds were
not successful in producing young in any of the
years monitored, but adverse weather conditions
may have been a factor (S. Platt, pers. comm.). In
this case the primary disturbance was limited to 1
breeding season and was apparently of similar in-
tensity throughout the disturbance period. Toler-
ant falcons may more readily habituate to a steady,
predictable intensity of disturbance. In contrast,
mining and blasting activity in the impacted range
surveyed during this study was probably of a highly
variable and unpredictable nature.

Blasting and mining operations in the Caballo
Mountains are primarily the endeavaors of indi-
vidual prospectors or small part-time mining
partnerships. One larger corporation was mining
barite at the time of my survey, but this mining was

Spring 1984

James C. Bednarz

19

in the foothills >3 km from the area of suitable
nesting cliffs. Since the climate in this area is rela-
tively mild and there are no restrictons on blasting,
I assume that all active claims are worked periodi-
cally throughout the year. All mining in the survey
area seemed to be on a part-time basis. Placer gold
was probably the principle mineral that was being
extracted. Also, much of the mining activity is sus-
pected to be treasure hunting in search of legen-
dary “Spanish gold” thought to be hidden in the
Caballo Mountains (T. Custer, BLM Geologist,
White Sands Resource Area; pers. comm.). Trea-
sure hunters may pursue their hobby under the
facade of a mining claim which allows them to leg-
ally blast natural cliff faces. The combination of
mining and treasure hunting has resulted in an
extremely high intensity of blasting in the Caballo
Mountains.

In conclusion, I believe the data presented here
suggest that there is a difference in Prairie Falcon
nest occupancy between the Caballo Mountains and
the 2 control ranges most likely due to blasting and
mining or associated human activities. To my
knowledge, no study has examined the long-term
effects of mining or blasting on occupancy of raptor
nest sites, but short-term impacts have been
documented (Stahlecker and Alldredge 1976). Ellis
(1981), based on a 2 y study of simulated sonic boom
noise, implied that both adverse short-term and
long-term impacts of such activities were probably
negligible on nesting raptors. My results indicate
that this conclusion cannot be extended to more
intensive blasting and mining activities, and I urge
further observation, and particularly, controlled
experimental studies to address the long-term im-
pacts of such disturbances on breeding raptors.

Acknowledgements

I thank Gregory Schmitt, Marshall C. Conway, and John P.
Hubbard for providing encouragement during the course of field
surveys. Pat L. Kennedy, George Anne Thibodeau, Buck Cully,
Dale W. Stahlecker, and John P. Hubbard thoroughly reviewed
earlier drafts. Steve Platt shared with me some of his data and
thoughts on the impacts of mining on raptors. Mr. Joe Williams,
Mr. Crawford, and other ranchers gave me permission to enter
and camp on their land. This work was supported by the Bureau
of Land Management and the New Mexico Department of Game
and Fish, Endangered Species Program.

Literature Cited

Allen, G. T. 1979. Assessment of potential conflicts
between nesting raptors and human activities in the
Long Pines area of southeastern Montana — with spe-
cial emphasis on uranium development. M.S. Thesis,
Washington State University, Pullman. 109 pp.

Becker, D. M., and I. J. Ball. 1981. Impacts of surface
mining on Prairie Falcons: recommendations for
monitoring and mitigation. Unpubl. m.s., Montana
Cooperative Wildlife Research Unit, Montana State
University, Missoula. 38 pp.

Bond, F. M., C. R. Craig, J. H. Enderson, A. W. Heggen,
C. E. Knoder, J. V. Kussman, M. W. Nelson, R. D.
Porter, D. L. Wills. 1977. American Peregrine Fal-
con recovery plan (Rocky Mountain and Southwest
populations). U.S. Fish and Wildl. Serv. 183 pp.

Call, M. W. 1978. Nesting habitats and surveying
techniques for common western raptors. U.S.D.I.,
Bureau of Land Management Technical Note TN-
316. 115 pp.

Call, M. W. 1979. Habitat management guidelines for
birds of prey. U.S.D.I., Bureau of Land Management
Technical Note TN-338. 67 pp.

Ellis, D. H. 1981. Responses of raptorial birds to low
level military jets and sonic booms. Unpubl. m.s., In-
stitute for Raptor Studies, Oracle, Arizona. 59 pp.

Kelly, V. C., and C. Silver. 1952. The geology of the
Caballo Mountains: with special reference to regional
stratigraphy and structure and to mineral resources,
including oil and gas. University of New Mexico Publ.
in Geology No. 4. 286 pp.

Stahlecker, D. W., and A. W. Alldredge. 1976. The
impact of an underground nuclear fracturing experi-
ment on cliff-nesting raptors. Wilson Bull. 88:151-
154.

Department of Biology, University of New Mexico, Albuquer-
que, NM 87131.

Received 17 December 1983; Accepted 27 April 1984

RESULTS OF A HELICOPTER SURVEY OF CLIFF NESTING RAPTORS
IN A DEEP CANYON IN SOUTHERN IDAHO

T. H. Craig and E. H. Craig

Abstract - In 1 980 a helicopter survey of cliff nesting raptors was conducted along Salmon Falls Creek, a deep canyon
in southern Idaho. The most numerous species recorded was the Red-tailed Hawk (Buteo jamaicensis) followed by the
Golden Eagle ( Aquila chrysaetos), Prairie Falcon ( Falco mexicanus ), and Common Raven ( Corvus corax). Great Horned Owls
( Bubo virginianus) , Barn Owls ( Tytoalba ), and Turkey Vultures (Cathartes aura) were recorded when they flushed from cliff
faces. Numbers of Prairie Falcon nests and Barn Owls flushed may have been related to land use practices near the
canyon. Inter-nest distances, productivity, nest exposure and the behavioral response of nesting adults are presented for
the 4 principle nesting raptors. A comparison of the results of a simultaneous boat survey revealed that the helicopter
survey was faster and more accurate in determiningitotal active and inactive nests.

Nesting densities of raptors in the intermountain
west have been determined for several locations
(Platt 1971, Smith and Murphy 1973, Howard et al.
1976, Seibert etal. 1976, Thurow et al. 1980). How-
ever, except in the Snake River Birds of Prey Area
(BPSA), few nesting surveys have been conducted
in deep canyons in this region (USDI 1979a). The
data reported herein were gathered in 1980 during
a helicopter survey of Salmon Falls Creek, a deep
canyon in southern Idaho.

Study Area and Methods

The northern part of Salmon Falls Creek flows for approxi-
mately 103 km from the Nevada border north to its confluence
with the Snake River in Idaho. The creek is small with a mean daily
flow in water-year 1980 of 4.59 m3/sec (provisional information
from the U.S. Geological Survey, Boise, Idaho). The area around
the creek is cool desert (Odum 1971) dominated by shrubs where
native vegetation remains. Native habitat has largely been re-
placed by introduced grass seedings (primarily Agropyron cristatum)
or agriculture over large portions of the study area.

The study area was divided into 4 segments based on vegetation
and physiographic features, and distances (creek-km) were mea-
sured beginning at the Nevada border. The southernmost seg-
ment ( 1 ) is characterized by a meandering stream and a 20 km long
reservoir contained within a relatively shallow (50 ± 1 1 m) cliff-
lined boundary. It is surrounded by Artemesia arbusculal grass
seedings. The Salmon Falls Creek Dam marks the northern end of
segment 1. Beginning at the dam, the creek flows through a deep
(145 ± 26 m) gorge to creek-km 62 (segment 2) and is surrounded
predominantly by Artemesia tridentatal grass seedings to at least 3.5
km away from its rim. In the succeeding segment (3) the vegeta-
tion bordering the east side of the creek is agriculture, while the
west side is covered with A. tridentatal grass seedings. The final
segment (4) begins at creek-km 81 and is bordered on the east
predominantly by agriculture and on the west by a mixture of A.
tridentatal grass seedings and agriculture.

In 1980 from 28-30 May and on 5 June we flew in a Hiller 12E
helicopter for about 16 h inventorying cliff nesting raptors in the
gorge. Nesting data were collected on all raptor species except
American Kestrels (Falco sparverius). Nest location, status (an active
nest was one where adults or young were present or which obvi-
ously had recently fledged young), estimated exposure, and the
behavior of adults toward the helicopter were recorded. To

minimize flight time and disturbance to raptors, nest parameters
were not recorded for every inactive nest, and we did not tarry at
active nest sites if we were unable to count nestlings immediately.

Because cavity nests are difficult to find, we did not attempt to
determine nest sites of Barn Owls, Great Horned Owls, or Turkey
Vultures, but did record them when we flushed these birds from
cliffs. Nests of Prairie Falcons were recorded when adults were
flushed near a pothole or ledge (usually with white-wash beneath
it), when young were observed, or when adult(s) defended against
the helicopter.

Nest site characteristics and distances between nests were mea-
sured on topographic maps, and nest elevations were determined
on maps at a point on the canyon rim above the nest. It should be
noted that when 2 nests were close together and neither was close
to another, the effect on our data was to double the inter-nest
distance in calculation of the mean. Because we recorded nest
exposure in 16 directions our sample size was too small for statisti-
cal analysis. Therefore, we lumped this information into 4 general
directions to increase sample size.

Gross vegetational patterns were determined by placing a grid
of 144 randomly selected spots (after Marcum and Loftsgaarden
1980) on aerial photographs of the study area in each major
vegetation type. The percents of spots falling on: 1) agriculture,
2) A tridentatal grass seeding, 3) A. arbusculal grass seeding, and 4)
other (roads, canyon, water) were then calculated. The grid used
to select the 144 random spots covered a square area (approxi-
mately 92.16 km2), the corners of which (farthest random point
possible) were about 6.8 km from the center of the canyon.

Results and Discussion

Nesting Density. — The most numerous nesting
raptors in the canyon were Red-tailed Hawks, Gol-
den Eagles, Prairie Falcons, and Common Ravens
(Table 1). A comparison with the BPSA reveals that
Salmon Falls Creek is an area of lower raptor de-
nsity. The diversity of nesting raptors is also lower
since no Ferruginous Hawks (Buteo regalis ) were
found nesting on cliffs in Salmon Falls Creek (Table
2). The density of nesting raptors in Salmon Falls
Creek is, however, larger than reported for the Rio
Grande River Gorge (Ponton 1980).

20

Raptor Research 18(l):20-25

Spring 1984

Craig and Craig

21

Table 1. Distribution of Raptor Nests/km (N), Raptors Flushed/km (F) and Vegetational Coverage in Salmon Falls
Creek, Idaho.

Estimated Vegetational Cover

Artemesia Artemesia

Segment

Golden
Eagle (N)

Prairie

Falcon(N)

Red-Tailed

Hawk(N)

Common

Raven(N)

Great-Horned Barn
Owl(F) Owl(F)

Turkey

Vulture(F)

Agri-

culture

tridentata /
seedings

arbusculal

seedings

Other

1

0.13

0.7*

0.13

0.13

0.10

0.00*

0.03

0%

0%

88%

12%

2

0.28

0.27*

0.15

0.12

0.09

0.00*

0.00

0%

92%

0%

8%

3

0.21

0.31*

0.31

0.16

0.21

0.16*

0.00

29%

61%

0%

10%

4

0.10

0.05*

0.33

0.05

0.14

0.19*

0.00

70%

21%

0%

9%

Total

0.18

0.17

0.21

0.12

0.13

0.07

0.01

Total Observations:

19 18 22 12 13 7 1

*Statistical significance (P< 0.05), X2 test.

There were more active eagle nests in the parts of
the canyon bordered by A. tridentata! g rass seedings,
but more Red-tailed Hawk nests in the part of the
canyon bordered by agricultural lands, although
neither were significantly higher (P > 0.05). An
important prey of Golden Eagles near our study
area is the Black-tailed Jack Rabbit (Lepus calif or-
nicus) (Seibert et al. 1976, USDI 1979a), a
lagomorph that is dependent upon native sageb-
rush communities (USDI 1979a) like those in seg-
ments 2 and 3. Red-tailed Hawks, on the other
hand, are a more diverse feeder and may be better
able to utilize areas of the canyon bordered by ag-
riculture.

There was a significant difference in the number
of Prairie Falcon nests and Barn Owls flushed in
different segments of the creek. Prairie Falcons

were noted more frequently in areas bordered by A
tridentata/ grass seedings than in parts bordered by
A. arbusculalg rass seedings or agriculture. Barn
Owls on the other hand, were flushed from the
canyon walls only in segments bordered by ag-
ricultural lands. These results may reflect a re-
sponse to some environmental factor, such as cli-
mate, since segment 1 is higher and cooler than
segment 4. However, Prairie Falcons feed on small
mammals which can be adversely affected by ag-
riculture (USDI 1979a), while Barn Owls may pre-
fer nest sites near agricultural lands (USDI 1979b).
There was no significant difference in the numbers
of Great Horned Owls and Turkey Vultures
flushed or Common Raven nests and vacant stick
nests seen in different segments of the canyon.

Inter-nest distances. — Distances between con-

Table 2. A Comparison of Nesting Density (Nests/km) of Selected Raptors and Total Raptor Diversity Among 3 River
Gorges in the western United States.

Salmon Falls
Creek
Idaho

Snake River
Birds of Prey
Study Area
Idaho

Rio Grande Gorge
Colorado and
New Mexico

Golden Eagle

0.18

0.19

0.04

Prairie Falcon

0.17

1.32

0.10

Red-tailed Hawk

0.21

0.37

0.18

Common Raven

0.12

0.76

0.12

Total

0.68

2.64

0.44

# of species found

9

10

5

22

Helicopter Survey of Nesting Raptors

Vol. 18, No. 1

Table 3. Straight-Line Inter-nest Distances in Km of Adjacent Conspecific Raptor Nests in Salmon Falls Creek, Idaho,
and Average Inter-nest Distances in Km for Adjacent Conspecifics in the Snake River Birds of Prey Study
Area Over 8 years (After USDI 1979a).

Salmon Falls Creek
X ± S.D. (min.)

BPSA

Inter-nest distance
(smallest min.)

Golden Eagle

4.39 ± 2.3(1.56)

3.46(0.97)

Prairie Falcon

4.13 ± 3.7(0.58)

0.65(0.09)

Red-tailed Hawk

3.91 ± 3.0(0.32)

2.08(0.35)

Common Raven

7.48 ± 7.3(0.10)

Not recorded

specific nests were variable (Table 3). Mean and
min. inter-nest distances, especially for Prairie Fal-
cons, are larger than observed in the BPSA and
reflect the difference in raptor densities of the 2
areas (USDI 1979a). It should be noted that because
the Snake River Canyon is comparatively wide, ter-
ritorial spacing of raptors along the canyon is prob-
ably minimized.

The greatest mean conspecific inter-nest distance
in our study area was among Common Raven nests.
Ravens also showed the smallest min. nesting dis-
tance (0.1/km) of any conspecific nesting pair,
perhaps reflecting weak intraspecific territoriality
in ravens as noted by Knight and Call (1980).
Common Ravens also nested close to Red-tailed
Hawks and Prairie Falcons (Table 4). Close nesting
of ravens to raptors has been noted elsewhere,
hypothesizing a commensal relationship (Knight
and Call 1980). Golden Eagles displayed the
greatest X distances to their nearest neighbors in
Salmon Falls Creek.

Productivity. — - We recorded the number of young
(most were late nestlings) in nests of 2 species. The
mean number of young in 16 Golden Eagle nests
was 1.94 T 0.68 (range 1-3) which is comparable to
the mean number of young fledged per successful
nesting attempt (1.62) of Golden Eagles in the
BPSA and comparison area (USDI 1979a). We ob-
served a mean of 2.79 T 0.79 (range 2-4) young for
19 Red-tailed Hawk nests. A similar figure (# of
young fledged/successful nesting attempt = 2.70)
has been noted in the BPSA (USDI 1979a).

Nest Exposure. — Nest exposures for all active and
many vacant stick nests are contained in Table 5.
The 2 rows of data resulted when we arbitrarily
lumped the observed 16 exposures into quadrants
which correspond nearly to NW, NE, SE, SW and
then rotated the boundaries of our quadrants 45° so
that the easterly and northeasterly exposures were
not divided.

In the first treatment of the data, nests were
oriented significantly more to the quadrant bet-

Table 4. Inter-nest Distances (X km + S.D.) of nearest neighboring raptor nests in Salmon Falls Creek, Idaho.

Species:

Golden Eagle

Red-tailed Hawk

Prairie Falcon

Common Raven

Nearest Neighbors:

Golden Eagle 0

Prairie Falcon

Red Tailed Hawk

0.75 ± 0.17
N = 7

1.53 ± 0.77
N = 8

0.18 ± 0.63
N = 4

1.46 ± 0.80
N = 4

0.73 ± 0.51
N = 6

0.84 ± 0.45
N = 6

0.48 ± 0.32
N = 6

1.06 ± 0.54
N = 5

0.73 ± 0.25
N = 2

0.75 ± 0.55
N = 8

0.75 ± 0.38
N = 3

1.68 ± 0.73
N = 4

0.35
N = 1

0.58 ± 0.32
N = 5

0.10
N = 2

Common Raven

Spring 1984

Craig and Craig

23

Table 5. Exposures of Active and Inactive Stick Nests in 4 Segments of Salmon Falls Creek as Determined by 2 arbitrary
analyses.

060

Segment 1 Segment 2 Segment 3 Segment 4

N

NNE

8

5

17*

8

I

N

NNE

6

10

12

10

N

4

NNE

9

8

4

N

NNE

7

13

6

13

*Statistically significant (P— 0.05), Chi-square test.

ween south and west-northwest in segment 1.
Therefore, it appears that the Red-tailed Hawks
and Golden Eagles, which built most of these nests,
oriented them in a southwesterly direction. When
the quadrant boundaries were rotated, a significant
number of nests in segment 4, the lowest part of the
canyon (elevations in segment 4 are about 500 m
lower than in segment 1) are oriented nearly to the
east. This may indicate that nest exposure and ele-
vation (and thus temp) are related in Salmon Falls
Creek. Seibert et al. (1976) found that Golden
Eagles in northern Nevada avoided building nests
with a northern exposure in a significant number of
cases. Similarly, Mosher and White (1976) have
shown that exposure of Golden Eagle nests at
higher elevations, or in more northerly latitudes,
are exposed to the south, while the reverse is true
for nests at lower elevations, or in southerly
latitudes.

Behavioral Response to the Helicopter. — Be-
havioral responses were observed at 29 Golden
Eagle, Red-tailed Hawk, and Prairie Falcon nests.
No adults were seen at the remaining 30 active
nests.

We observed Golden Eagles near active nest sites
on 6 occasions, always perching almost motionless
while watching the helicopter pass-by. Page and
Seibert (1973) have reported similar behavior in
nesting Golden Eagles. Prairie Falcons, by contrast,
flew about the helicopter calling 9 times (we could
see their mouths open and close) or on 6 occasions
flushed from the cliff and flew away. Once we ob-
served Prairie Falcons near a nest diving on a
Black-billed Magpie (Pica pica) perched well away
from the cliff. This activity may have been redi-
rected behavior (Wallace 1 979) induced by our pre-
sence. Red-tailed Hawks exhibited the greatest
variability in their responses to the helicopter.

24

Helicopter Survey of Nesting Raptors

Vol. 18, No. 1

Adults either defended by circling and calling
(once), perched near the nest and watched the
helicopter (on 4 occasions) or sat tightly on the nest
(on 3 occasions). The latter response may have oc-
curred due to adults still brooding young, since
Carrier and Melquist (1976) observed a similar re-
sponse to helicopters by incubating Osprey ( Pand -
ion haliaetus). Lee (1980) found that most raptors
which were perched or nesting on transmission to-
wers were tolerant of a helicopter used in nest sur-
veys, although some Red-tailed Hawks tried to at-
tack the helicopter as it approached their nest site.
He also noted that birds which were on nests con-
taining eggs or young remained on the nest when
the helicopter flew past.

The Helicopter Survey and a Boat Survey Com-
pared. — Two other biologists surveyed Salmon
Falls Creek Reservoir by boat (Alan Sands and Sam
Mattise, pers. comm.) while we surveyed the reser-
voir by helicopter. In addition to being a faster
technique, other advantages of the helicopter in
raptor surveys are reflected in comparison of sur-
vey results. We observed 40 active and inactive
raptor nests from the helicopter, while from the
boat only 31 were noted. Five different locations
were thought to be possible Prairie Falcon nests by
the boat survey team because of the presence of
white-wash. From the helicopter these were found
to be either perches or stick nests not visible from
the boat due to the low angle of observation. The
same 3 Red-tailed Hawk nests and 3 Golden Eagle
nests were found by both survey techniques, but the
boat surveyors mistook an alternate nest site for the
actual Golden Eagle nest. Four raven nests were
found by the boat survey while 3 were located from
the helicopter. Both survey techniques produced 1
active Prairie Falcon nest, although they were at 2
different locations, illustrating the difficulty in de-
tecting active cavity nests from the air. The greatest
disparity in the results of the 2 techniques is that
only 15 of 30 vacant stick nests observed from the
helicopter were found by the boat survey team.
Three of the stick nests recorded on the boat survey
were not found from the air, but 1 1 recorded from
the helicopter were not found by boat.

The angle of observation is the most important
factor in differences between the 2 techniques.
However, since the boat survey took longer, more
time was allowed to see and hear nesting raptors, so
that the same number of active stick nests and an
additional cavity nest was found by the boat survey
team.

Acknowledgments

The field work for this report was funded by the Bureau of
Land Management, Burley District Office, Burley, Idaho,
through a contract to Western Environmental Research As-
sociates, Pocatello, Idaho. We acknowledge K. Lynn Bennett, Wil-
lis Bird, Mike Kochert, Sam Mattise, Linda Parsons, Fred Rose and
Alan Sands for help with aspects of this field work and/or manus-
cript preparation. We also thank Tim Zarkos for piloting the
helicopter with extraordinary skill, Alan Sands and Sam Mattise
for allowing us to use their boat survey data, and Fred Dauter-
mann for his help with computer analysis of nest distances.

Literature Cited

Carrier, W.D. and W.E. Melquist. 1976. The use of a
roto-winged aircraft in conducting nesting surveys of
Ospreys in northern Idaho. Raptor Res. 10:71-83.
Howard, R.P. L.O. Wilson, and F.B. Renn. 1976. Re-
lative abundance of nesting raptors in southern Idaho.
Raptor Res. 10:120-128.

Knight, R.L. and M.W. Call. 1980. The Common
Raven. Tech. Note No. 344, U.S. Bureau of Land
Management, Denver Service Center, Denver, Col-
orado.

Lee, J.M. Jr. 1980. Raptors and the BPA transmission
system. In: Proceedings of a workshop on raptors and
energy developments. R.P. Howard and J.F. Gore
(eds). Idaho Chapter; The Wildl. Sc., Boise, Idaho, pp
41-55.

Marcum, C.L. and D.O. Loftsgaarden. 1980. A non-
mapping technique for studying habitat preferences.
J. Wildl. Manage. 44:963-968.

Mosher, J. A. and C.M. White. 1976. Directional expo-
sure of Golden Eagle nests. Can. Field-Nat. 90:356-
359.

Odum, E.P. 1971. Fundamentals of Ecology. W.B.

Saunders Co., Philadelphia, Pennsylvania. 574 pp.
Page, J.L. and D.J. Seibert. 1973. Inventory of Golden
Eagle nests in Elk County Nevada. Cal-Nev Wildl.
Trans. 1973:1-8.

Platt, J.B. 1971. A survey of nesting Hawks, Eagles,
Falcons and Owls in Curlew Valley, Utah. Great Basin
Natur. 31:51-65.

Ponton, D. A. 1 980. Raptor use of the Rio Grand Gorge.
Rep. prepared by Los Alamos Scientific Laboratory,
WX-1-80-390. 34 pp.

Seibert, D.J., R.J. Oakleaf, J.M. Laughlin, and J.L.
Page. 1976. Nesting Ecology of Golden Eagles in
Elko County, Nevada. Tech. Note No. 281 Bureau of
Land Management, Denver Service Center, Denver,
Colrado. 17 pp.

Smith, D.G. and J.R. Murphy. 1973. Breeding ecology
of raptors in the eastern Great Basin of Utah. Brigham
Young Univ. Sci. Bull. 18:1-76.

Thurow, T.L., C.M. White, R.P. Howard, and J.F. Sul-
livan. 1980. Raptor ecology of Raft River Valley,
Idaho. EG&G-2054. Natl. Tech. Inf. Ser., Springfield,
Virginia. 45 pp.

Wallace, R.A. 1979. The ecology and evolution of ani-
mal behavior. Good Year Publ. Co., Santa Monica,
California. 284 pp.

U.S.D.I. 1979a. Snake River Birds of Prey Special Re-
search Report to the Secretary of the Interior. Bureau
of Land Management, Boise District, Boise, Idaho.
142 pp.

U.S.D.I. 1979b. Snake River Birds of Prey Annual Re-
search Report. Bureau of Land management, Boise
District, Boise, Idaho. 60 pp.

Department of Biology, Northwest Nazarene College, Nampa,
ID 83651.

Present address: Box 1, Lee Creek Road, Leadore, ID 83464.

Received 10 May 1983; Accepted 16 April 1984

USE OF INTRODUCED PERCHES BY RAPTORS: EXPERIMENTAL RESULTS
AND MANAGEMENT IMPLICATIONS

Steven E. Reinert

Abstract - Fourteen dead trees and 9 man-made perches were placed in the Sachuest Point National Wildlife Refuge,
Rhode Island between 1977 and 1979 for use by the open country raptor community that inhabits the area during fall
and winter. On 120 days during fall and winter 1978-79 and 1979-1980 raptors were observed on the introduced perches
525 times. American Kestrels {F alco sparverius) , Short-eared Owls {Asia flammeus) and Northern Harriers ( Circus cyaneus )
in that order were the most frequent users. In all, 10 raptor species used the dead trees and 4 species used man-made
perches. Kestrels displayed a preference for trees over constructed perches in 1979-80, but not in 1978-79. Kestrels used
the perches for hunting, resting and prey consumption, but other raptors used them mostly for resting. These results
suggest that introduced perches could play an important role in raptor conservation efforts.

Elevated perches are a habitat requirement of
most birds of prey for hunting, resting and feeding
(Brown and Amadon 1968, Brown 1976). The im-
portance of perches has been documented by sev-
eral investigators who noted the activity of raptors
when first seen (Schnell 1968, Craighead and
Craighead 1969, Marion and Ryder 1975, Bildstein
1978). The Red-shouldered Hawk (Buteo lineatus),
Red-tailed Hawk (Buteo jamaicensis), Rough-legged
Hawk ( Buteo lagopus), Golden Eagle (Aquila
chrysaetos ) and American Kestrel (Falco sparverius)
were perched during 50% or more of the observa-
tions of 1 or more of these authors. The importance
of perches as a hunting substrate has been shown
most clearly for American Kestrels. Several authors
(Sparrowe 1972, Collopy 1973, Cruz 1976, Bilds-
tein 1978) have found that kestrel attacks on prey
were initiated from a perch in 71% or more of the
attempts, and that the attacks initiated from a perch
were more successful than attacks initiated from
flight.

The erection of man-made perches, especially
utility-line towers, has served as a passive raptor
management tool by opening up millions of acres of
habitat to hunting from stationary perches (Olen-
dorff et al. 1980). For example, in Colorado,

Stahlecker (1978) documented a concentration of
raptors in the area immediately surrounding a
newly constructed transmission line. Such findings
have led to the introduction of elevated perches in
suitable hunting range where tall perches are lack-
ing (Christensen 1972, Snow 1974, White 1974,
Steenhof 1977, Stumpf 1977, Hall et al. 1981). He-
rein I report the use of 2 types of raptor perches
introduced into the Sachuest Point National
Wildlife Refuge on the Rhode Island coastline.
Study Area and Methods

Sachuest Point is an 86 ha peninsula extending into the Atlantic
Ocean from the southeast corner of Aquidneck Island, Rhode
Island. The vegetated interior of the point is bordred by a 5 km
perimeter of rocky shoreline and cobble beaches. Shrub and her-
baceous communities, which dominate the peninsula, are inter-
rupted by a network of roads and scattered buildings abandoned
by the U.S. Navy. Bayberry (Myrica pensylvanica) is the dominant
shrub species. It reaches 3 m in height in the northern section of
the point where it occurs in clumps (ca 100-300 m2) which are
interspersed with shorter, mixed stands of goldenrod ( Solidago
tenuifolia) and blackberry ( Rubus sp.). In the southern part of the
peninsula, bayberry from 0.5 to 1.5 m tall forms dense, isolated
stands 0.5 to 3.0 ha in area which are surrounded by an herbace-
ous community. Grasses, especially Autumn Bent (Agrostis peren-
nans) and Red Fescue (Festuca rubra), are common and occur either
alone or beneath a forb layer dominated by goldenrod ( Solidago
spp.) and Black Knapweed ( Centauria nigra). Shrubs provide the
cover throughout 52% of the vegetated region of the study area

25

Raptor Research 18ce1):25-29

26

Steven E. Reinert

Vol. 18, No. 1

and herbs cover the remaining area. Elevated perches were absent
or scarce within all habitats on the refuge prior to the initiation of
this study.

Five dead trees (+ height = 4.8 m, range = 3. 7-8.5 m) with
numerous horizontal branches were erected on the refuge in the
summer of 1977, and 9 more (+ height = 4.8 m, range = 3.6-6. 1
m) in the summer of 1979. Two trees were erected within the tall
shrub community and 5 within the shorter, bayberry stands. The
remaining 7 were erected within herbaceous habitats. In the
summer of 1978, 9 man-made perches were erected. Each man-
made perch consisted of a 6-m board, 5 cm x 1 0 cm size, fitted with
two 2.5 cm dia. dowels. The dowels were cut into 65 cm lengths
and centered through holes in the boards so that 30 cm of perch
space was available on either side. The dowels were placed on each
structure at heights of 2.25 m and 4.5 m above ground. Length of
board in excess of 4.5 m was buried. Two perches were placed
within tall shrubs, 3 within short shrubs, and 4 within herbaceous
communities.

Raptors were observed for 1 h periods on 88 d between 1
September 1978 and 12 March 1979, and on 32 d between 12
November 1979 and 29 January 1980, from the roof of a 6 m high
abandoned building near the center of the refuge. Thirty-five
visits were made at various times in the morning; 85 were made
from 1500 to 1700 h. For each observation of a perched raptor a
record was made of species, perched height, individual perch
number, and purpose for which the perch was used whenever this
was apparent.

Results

Five species of raptors were seen during the 2
years (Table 1). During both periods, the Northern
Harrier (Circus cyaneus), American Kestrel, and
Short-eared Owl (Asio flammeus ) were dominant.
Harriers and kestrels were present in varying num-
bers throughout both study periods. Four Short-

eared Owls arrived in November of 1978 and 1 in
December of 1979; each remained until the end of
the study period each year. The Sharp-shinned
Hawk (. Accipiter striatus) and Merlin (Falco colum-
barius ) occured only as migrants; they were seen on
perches in September and October 1978. Raptors
were more abundant during the 1978-79 period,
averaging 3.7 individuals/hr observation (range =
0-3 1 ). An average of 2.6 individuals/hr (range = 0-6
were seen during the shorter, 1979-80 period.

During the 120 h of observation, I made 525
sightings (4.4 sightings/hr) of raptors using the in-
troduced perches (Table 1). All species except
Sharp-shinned Hawks used both perch types at
least once; sharp-shins used only dead trees. In
addition, the Cooper’s Hawk (Accipiter cooperii),
Red-tailed Hawk, Rough-legged Hawk, Peregrine
Falcon (Falco peregrinus), and Snowy Owl (Nyctea
scandiaca) were also sighted on the dead trees.

Chi-square (X2) tests were conducted using each
of the 3 dominant raptor species to determine
whether the more natural, dead-tree perches were
used more than might have been expected by
chance. During 1978-79, there were no significant
differences (P = 0.05) in the use of natural vs.
constructed perches for any of the 3 species. In
1979-80, kestrels used dead trees significantly more
than expected (P < 0.001) (X2 = 15.3, df = 1).

Raptors nearly always perched as high as possible
on a perch. On man-made perches, the higher of 2

Table 1. Raptor Perch-Use Statistics.

Species

Individuals/Day

Percent of
Days Present

# Perches Used
# Perch Observations*

-t-

range

Dead Trees

Constructed

Sharp-shinned Hawk

0.2

0-10

7

1- 3

-

Northern Harrier

1.4

0- 5

68

6- 35

6- 32

American Kestrel

1.2

0-21

67

14-190

8-149

Merlin

-

0- 1

2

3- 7

1- 1

Short-eared Owl

1.5

0- 4

43

11- 47

8- 61

Total

282

243

*Based on 88 h of observation of 5 dead trees and 9 man-made perches in 1978-79 and 32 h of observation of 14 dead trees
and 9 man-made perches in 1979-80.

Spring, 1984

Raptor Perch Introduction

27

Table 2. Reported Perch Introduction Experiments.

Source and State

# Perches

Target Species

Raptors Using Perches

Christenson 1972
Utah

3

All Raptors

Swainson’s Hawk ( Buteo swainsoni )
Red-tailed Hawk
American Kestrel

Great Horned Owl ( Bubo virginianus)
Long-eared Owl ( Asio otus)

White 1974

8

Golden Eagle

Golden Eagle

Utah

Snow 1974
Colorado

2

All Raptors

Red-tailed Hawk
Ferruginous Hawk (Buteo regalis )
Golden Eagle
Northern Harrier

Harrison 1977
Michigan

50

Grassland Birds

American Kestrel
Short-eared Owl

Steenhof 1977

4

Bald Eagle

Bald Eagle

South Dakota

Steenhof 1977

1

Bald Eagle

Bald Eagle

Oregon

Stumpf 1977
Arizona

12

Bald Eagle

Red-tailed Hawk

Harris’ Hawk ( Parabuteo inicinctus)

Hall etal. 1981
California

36

All Raptors

White-tailed Kite (Elanus leucurus )

Red-tailed Hawk

Northern Harrier

American Kestrel

Common Barn-Owl (Tyto alba)

Short-eared Owl

Great Horned Owl

Burrowing Owl (Athene cunicularia)

This study
Rhode Island

23

All Raptors

Northern Harrier
Sharp-shinned Hawk*
Cooper’s Hawk*
Red-tailed Hawk*
Rough-legged Hawk*
American Kestrel
Merlin

Peregrine Falcon*
Snowy Owl*
Short-eared Owl

*Used dead trees only.

available perches was selected in 97% of 32 harrier
observations, 99% of 149 kestrel observations, and
85% of 61 Short-eared Owl observations. Except
when eating prey, raptors perched within the up-
permost branches.

I did not see harriers or owls attack prey from, or
consume prey on, an introduced perch. These 2

species apparently used the introduced perches as
resting sites between hunting forays. I witnessed 16
prey attacks by kestrels, 14 from man-made perches
and 2 from dead trees. Six of the attacks from
man-made perches and both from trees were suc-
cessful. Kestrels were observed eating prey on trees
and on man-made perches 10 times each. Kestrels

28

Steven E. Reinert

Vol. 18, No. 1

perched more frequently per individual/hr than
Short-eared Owls, and owls perched more fre-
quently than harriers.

Discussion

A total of 20 raptor species, representing 2 orders
and 4 families, have used perches introduced speci-
fically for their use (Table 2). Although these num-
bers are impressive, not all attempts at raptor man-
agement by perch introduction have been success-
ful. Perches introduced as part of Bald Eagle
( Haliaeetus leucocephalus) management programs by
the U.S. Bureau of Land Management (BLM)
(Steenhof 1977) and the U.S. Bureau of Reclama-
tion (Stumpf 1977) were little used by the target
species. The BLM had better success with perches
introduced for Golden Eagle management;
numerous eagles were seen on the perches during
the first year after their placement (White 1974).
Snow (1974) reports that 4 raptor species used
perches placed in a Colorado grassland community,
and perches erected in agricultural fields by Hall et
al. (1981) received extensive use by 8 species (Table
2).

To determine if introduced perches would serve
as a means for enhancing biological control of un-
desirable rodents, Christensen (1972) placed 3
perches in areas of high pocket gopher ( Thomomys
talpoide^s) density. Five species of raptors used them
(Table 2), and results strongly suggest that gopher
numbers were reduced in the area immediately
surrounding the perches. Over a broad area, how-
ever, the results were inconclusive.

At Sachuest Point I made an average of 1 sighting
of a raptor on an introduced perch during each 14
min of observation. The use of the perches by
hunting kestrels demonstrates a shift in their
hunting strategy as a result of perch introduction,
since prior to perch placement aerial hunting was
the only method available. Furthermore, the
hunting efficiency of kestrels may have improved
following perch introduction since several authors
have shown that kestrels prefer hunting from a
perch rather than hover hunting, and were more
successful when hunting from a perch than when
hunting aerially in general (Sparrowe 1972, Col-
lopy 1973, Cruz 1976, Bildstein 1978). The perches
were also used extensively by kestrels for eating
prey.

Despite the substantial documentation of intro-
duced perch, no study has demonstrated an in-
crease in raptor density within managed areas.

Stahlecker (1978), however, censused wintering
raptors before and after construction of a transmis-
sion line. His results demonstrate that raptor de-
nsity in the area within 0.4 km of the transmission
line (57 km2) became greater than the density in the
area beyond 0.4 km (98 km2) as a result of the
extensive use of transmission line towers as perches.
The increased density within his study area follow-
ing transmission line construction suggests a lack of
perches was limiting raptor use of his study area.

In areas where the scarcity or absence of perches
limits raptor numbers, perch introduction could
play an important role in raptor management, at
least where an increase in density is the goal. Un-
fortunately, perch requirements of raptors are not
well understood, and it is not always evident if a
particular raptor population or community would
benefit from increased available perches. In areas
where habitat destruction threatens raptor popula-
tions, it becomes increasingly important to create
potential for increased densities in unaffected
range. Managers of protected areas (national parks,
public and private wildlife preserves, etc.) should
assess perch availability and consider supplemen-
tation where a scarcity of perches may limit raptor
numbers. Such efforts could help maintain stable
raptor populations, especially wintering popula-
tions, in threatened areas.

Dead trees erected at Sachuest Point were readily
accepted by all raptor species and were preferred
by some over man-made perches. Dead trees are
preferred perches of Bald Eagles (Steenhof 1977,
Stumpf 1977) and were listed as one of the prefer-
red perch types of buteos by Errington and Brec-
kenridge (1938). Thus, trees should be considered
for use in perch introduction projects where a
source is available.

Acknowledgements

This project could not have been completed without the coop-
eration of the staff of the Ninigret National Wildlife Refuge, and
the field help of several volunteers, especially Jeffrey Hall, Jay
Manning and William DeRagon. I also thank Drs. Keith L. Bilds-
tein and Frank C. Golet for carefully reviewing this manuscript.

Literature Cited

Bildstein, K.L. 1978. Behavioral ecology of Red-tailed
Hawks ( Buteo jamaicensis), Rough-legged Hawks ( B .
lagopus ), American Kestrels (Falco sparverius) and other
raptorial birds wintering in south-central Ohio. The
Ohio State University. 364 p. Dissertation.

Brown, L. 1976. Birds of prey: their biologyand ecol-
ogy. New York: Hamlyn Publishing Group Limited.
256 p.

Spring 1984

Raptor Perch Introduction

29

Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. New York: McGraw-Hill Book
Co. 945 p.

Christensen, R.C. 1972. Raptor predation on pocket
gopher populations by the use of hunting perches.
M.S. Thesis. Brigham Young University, Provo, Utah.
87 pp.

Collopy, M.W. 1973. Predatory efficiency of American
Kestrels wintering in northwestern California, Raptor
Res. 7:25-31.

Craighead, J.J. and F.C. Craighead, Jr. 1969. wks,
owls and wildlife. New York Dover Publications. 443
P-

Cruz, A. 1976. Food and foraging ecology of the Ameri-
can Kestrel in Jamaica. Condor 78:409-423.
Errington, P.L. and W.J. Breckenridge. 1938. Food
habits of Buteo hawks in northcentral United States.
Wilson Bull. 50:113-121.

Hall, T.R., W.E. Howard, and R.E.
Marsh. 1981. Raptor use of artificial perches. Wildl.
Soc. Bull. 9:296-298.

Harrison, K.G. 1977. Perch height selection of grass-
land birds. Wilson Bull. 89:486-487.

Marion, W.R. and R.A. Ryder. 1975. Perch-site prefer-
ences of four diurnal raptors in northeastern Col-
orado. Condor 77:350-352.

Olendorff, R.R., R.S. Motroni, and M.W.
Call. 1980. Raptor management — the state of the
art in 1980. Pages 468-523 in R.M. DeGraff and N.G.
Tilgham, eds., Management of western forests and
grasslands for nongame birds. U.S.D.A. For. Serv.
Gen. Tech. Rep. INT-86, 535 p. Intermt. For and
Range Expt. Stn. Ogden, Utah 84401.

Schnell, G.D. 1968. Differential habitat utilization by
wintering Rough-legged and Red-tailed hawks. Condor
70:373-377.

Snow, C. 1974. Ferruginous Hawk ( Buteo regalis). U.S.
Bur. Land Mgmt. Tech. Rep. No. T/N 255. Denver,
Colorado. 23 p.

Sparrowe, R.D. 1972. Prey-catching behavior in the
sparrow hawk./. Wildl. Mgmt. 36:297-308.

Stahlecker, D.W. 1978. Effect of a new transmission
line on wintering prairie raptors. Condor 80:444-446.

Steenhof, K. 1978. Management of wintering bald
eagles. U.S. Fish and Wildl. Serv. FWS/OBS-78/79. 59
P-

Stumpf, A. 1977. An experiment with artificial raptor
hunting perches. Bird Watch 5:1-2.

White, C.M. 1974. Current problems and techniques in
raptor management and conservation. Trans. N. Am.
Wildl. Conf. 39:301-311.

Department of Natural Resources Science, University of Rhode

Island, Kingston, RI 02881. Present Address: 18 Roberta

Drive, Barrington, R.I. 02806.

Received 4 March 1983; Accepted 10 April 1984

Biology and Management of Bald Eagles and Ospreys. A proceedings of 32 refereed papers (325 pp.) by over 50
international experts on topics including taxonomy, distribution, winter and breeding population dynamics, nesting
habitat and nest site selection, nutritional ecology, prey selection, and management of the North American Bald Eagle
and the cosmopolitan Osprey. Typeset and bound with soft cover.

To place orders, write to either David M. Bird, Raptor Research Centre, 21,111 Lakeshore Rd., Ste. Anne de Bellevue,
Quebec H9X ICO or Dr. Gary Duke, Dept, of Vet. Biol., 295K AnSci/Vet. Med. Bldg., Univ. Minnesota, t. Paul, MN
55108. Price per copy: U.S. $15 plus $2.50 handling; Overseas 15$ (U.S.) plus $5 handling; Canada $18 (CDN) plus $3
handling. Send payment with Canadian orders to D.M. Bird and U.S. and overseas orders to the Treasurer, Rapture
Research Foundation, Inc. All profits to Raptor Research Foundation, Inc.

Raptor Collisions with Utility Lines — A Call for Information — The U.S. Bureau of Land Management, Sacramento,
in cooperation with the Pacific Gas and Electric Company, is assembling all available published and unpublished
information concerning collisions of raptors with power lines and other utility lines. Actual case histories — no matter
how circumstantial or fragmentary — are needed. Please acknowledge that you have such information by writing to Dr.
Richard R. (Butch) Olendorff, U.S. Bureau of Land Management, 2800 Cottage Way, Sacramento, California 95825
U.S. A. (Phone (916) 484-4541). A form on which to record your information will then be sent by return mail.

Short Communications

Kleptoparasitism by White-Tailed Hawk (Buteo albicaudatus) on Black-Shouldered
Kite (Elanus caeruleus leucurus ) In Southern Texas

Borja Heredia and William S. Clark

The White-tailed Hawk (Buteo albicaudatus ) is a typical
open and semi-open country raptor, inhabiting prairies
and sparsely forested habitats from southern Texas to
central Argentina. It feeds mainly on mammals [e.g. cot-
tontail rabbits (Sylvilagus floridanus ) and rodents], birds
[largely Bobwhite Quail ( Colinus virginianus\ and
meadowlarks (Sturnella sp.)], reptiles (mostly snakes but
some lizards) and insects (e.g. grasshoppers and crickets)
(Bent 1937, Cottam 8c Knappen 1939, Stevenson 8c Meit-
zen 1946). Its main hunting technique is to search the
ground from a height of 15-50 m (Oberholser 1974) al-
ternating between straight flapping flight, low angle
glides and hovering. It’s habit of congregating at prairie
fires has been recorded on the Texas coast (Stevenson 8c
Meitzen 1946). However, as far as we know, klep-
toparasitism has not been recorded for this species.

We observed kleptoparasitism on 30 December 1982 on
the King Ranch between Kingsville and Falfurias, Texas.
At about 1100 h we spotted a Black-shouldered Kite
(Elanus caeruleus) flying level at a height of 20 m carrying
prey, probably a small mammal. It was pursued by an
immature White-tailed Hawk which was gaining on it. As
the hawk neared the kite, the kite dropped it’s prey and
began to harass the hawk. The kite stooped numerous
times at the hawk, which turned over and presented it’s
talons. Two additional immature White-tailed Hawks ap-
peared and were also harassed by the kite. The kite finally
left and the 3 hawks searched unsuccessfully for the
dropped prey. After they left, we were also unable to find
it.

White-tailed Hawks and Black-shouldered Kites are
sympatric over much of their range in North America.
Recent studies on a Mexican raptor community (Thiollay
1980) showed that there is an 85% overlap in their hunt-
ing habitats. Both select areas of tree cover ranging from
< 10 to 40% and grass length between < 20 cm to 80 cm.
Their hunting techniques also overlap by 90%, both
species being typical searchers and aerial hunters. Both
also hunt from perches (Warner & Rudd 1975). Although
most of their hunting activity occurs late in the day, both
may hunt at any time of day (Thiollay 1980).

Except for the habitual kleptoparasites such as the
Crested Caracara (Polyborus plancus), typical kites (Milvus
sp.), sea and fish eagles (Haliaetus sp.), and the Bateleur
Eagle (Terathopius ecaudatus). Brown 8c Amadon (1968,
p.73) state that piracy is rare among birds of prey. But
piracy has been recorded for 23 other raptor species
(Parmenter 1941, Jeserich 1957, Berger 1958,
Meinertzhagen 1959, Temple 1969, Reese 1973, Bildstein
and Ashby 1975, Hogg 1977, Brockmann 8c Barnard

1979, Dunne 1981), and especially for other species in the
genus Buteo : Red-tailed Hawk (Buteo jamaicensis) on
Peregrine Falcon (Falco peregrinus) (Beebe 1960);
Rough-legged Hawk (B. lagopus) on Northern Harrier
(Circus cyaneus) (Kirby 1958); Red-shouldered Hawk (B.
lineatus) on Common Crows (Corvus brachyrhynchos)
(Kilham 1982); and Common Buzzard (Buteo buteo) on
Merlin (Falco columbarius) and Sparrowhawk (Accipiter
nisus) (Cramp 8c Simmons 1979, p. 182). In addition,
Clark has observed piracy of a Red-tailed Hawk on Prairie
Falcon (Falco mexicanus). The Black-shouldered Kite has
previously been recorded as the victim of piracy, being
robbed by the Lanner Falcon (Falco biarmicus) (Reynolds
1974) and by the Peregrine Falcon (Falco peregrinus) (Lon-
grigg 1981).

Brockmann 8c Barnard (1979) pointed out that regular
association with other raptor species on or near feeding
areas is an ecological factor that appears to promote pi-
racy. Thus the overlap of hunting habitat between the
White-tailed Hawk and the Black-shouldered Kite makes
this interspecific interaction likely. It would be interesting
to know not only how often these encounters occur, but if
they are the regular situation.

Literature Cited

Beebe, F.L. 1960. An instancy of piracy by the Red-
tailed Hawk on the Peregrine Falcon. Condor 62:480-
481.

Bent, A.C. 1937. Life stories of North American birds
of prey. U.S. Nat. Mus. Bull. 167, Part 1. 409 pp.

Berger, D.D. 1958. Marsh Hawk takes prey from
Short-eared Owl. Wilson Bull. 70:90.

Bildstein, K.L. and M. Ashby. 1975. Short-eared Owl
robs Marsh Hawk of prey. Auk 92:807-808.

Brockmann, R.J. and C.J. Barnard. 1979. Klep-
toparasitism in birds. Anim. Behav. 27:487-514.

Brown, L.H. and D. Amadon. 1968. Eagles, Hawks and
Falcons of the World. Vol. 1 Country Life Books. Lon-
don. 414 pp.

Cottam, C. and P. Knappen. 1939. Food of some un-
common North American Birds. Auc. 56:138-169.

Cramp, S. and K.E.L. Simmons (eds). 1979. The Birds of
the Western Paleartic. Vol 2. Oxford Univ. Press. Ox-
ford. 695 pp.

Dunne, P.J. 1981. Kestrel robbing Barn Owl. Raptor Res.
15:22.

Hogg, R.H. 1977. Food piracy by Red-footed Falcons.
Brit. Birds 70:220.

30

Short Communications

31

Jeserich, E. 1957. Baumfalke (Falco subbuteo ) nimmt
Turmfalken (Falco tinnunculus ) beute ab. Die Vogelwelt
88:180.

Kilham, L. 1982. Florida Red-shouldered Hawk robs
American Crows. Wilson Bull. 94:566-567.

Kirby, R.P. 1958. Rough-legged Hawk takes prey from
Marsh Hawk. Wilson Bull. 70:382.

Longrigg, T.D. 1981. Piracy and possible predation by
the Peregrine on the Black-shouldered Kite. Ostrich
52:189.

Meinertzhagen, R. 1959. Pirates and Predators: The
Piratical and Predatory Habits of Birds. Oliver &
Boyd. Edimburgh & London. 230 pp.

Oberholser, H.C. 1974. The Bird Life of Texas. Vol 1.
Univ. of Texas Press. Austin, Texas. 530 pp.

Parmenter, H.E. 1941. Prairie Falcon parasitizing
Marsh Hawk. Condor 43: 157.

Reese, R.A. 1973. Food piracy between Kestrels and
Short-eared Owls. Brit. Birds 66:227-228.

Reynolds, J.F. 1974. Piracy by Lanner. .Bnf. Birds 67:25.

Stevenson, J.O. and L.H. Meitzen. 1946. Behavior and
food habits of Sennett’s White-tailed Hawk in Texas.
Wilson Bull. 58:198-205.

Temple, S.A. 1969. A case of Turkey Vulture piracy on
Great Blue Herons. Wilson Bull. 81:94.

Thiollay, J.M. 1980. Strategies d’exploitation par les
rapaces d’un ecosysteme herbace neotropical. Alauda
48:221-253.

Warner, J.S. and R.L. Rudd. 1975. Hunting by the
White-tailed Hawk Elanus leucurus. Condor 77:226-230.

Museo Nacional de Ciencias Naturales,Castellana 80, Madrid 6,
SPAIN. Address of second author: P.O. Box 1161 Annan-
dale, VA 22003.

Received 26 December 1983; Accepted 30 May 1984

OBSERVATIONS OF NESTING PRAIRIE FALCONS
IN THE LOS PADRES NATIONAL FOREST

Wade L. Eakle

Prairie Falcon (Falco mexicanus) nesting surveys were
conducted by the U.S. Forest Service and California De-
partment of Fish and Game on the Mt. Pinos (MPRD) and
Santa Lucia (SLRD) Ranger Districts, Los Padres National
Forest during April, May and June, 1981. Nine historical
nesting territories were surveyed on the MPRD, of which
4 were active, and 14 historical territories were surveyed
on the SLRD, of which 9 were active. An average of 3.3
young hatched per eyrie (N = 3). Nine nestlings success-
fully fledged from these eyries (X=3.0 young per eyrie).

The goal of this study was to survey 2 Ranger Districts
on the Los Padres National Forest in southwestern
California and determine activity at each eyrie nd pro-
ductivity at 3 eyries. Productivity parameters provide a
measure of reproductive success and allow comparisons
with earlier determinations for the same populations
(Johnson, 1978).

The survey area encompasses prairie falcon nesting
territories in Santa Barbara, Ventura, San Luis Obispo
and Kern counties, California.

Prairie falcon eyries were located and plotted on topog-
raphical maps during 1979 (Alten and Keasler, 1979).
Observation points for viewing the eyries were chosen that
provided viewing directly into nest cavities at distances
ranging from 30 m up to 1 km. Disturbances were
minimized by not climbing to eyries. Observation periods
were restricted to 2 h in length. Observations were made

with Bushnell 10x50 Explorer binoculars and a Bushnell
20-45x Zoom Spacemaster spotting scope.

Prey remains and reguriated pellets were collected
from 2 eyries. Adult Prairie Falcons at BC-1 were ob-
served bringing 1 horned lizard (Phrynosoma sp.), 4
ground squirrels (Spermophilus sp.) and 1 unknown prey
item to the eyrie. At VV-8, adult falcons delivered 3
ground squirrels and 1 western meadowlark (Sturnella
neglecta ) to the eyrie.

Observation points for viewing the eyries were chosen that
provided viewing directly into nest cavities at distances
ranging from 30 m up to 1 km. Disturbances were
minimized by not climbing to eyries. Observation periods
were restricted to 2 h in length. Observations were made
with Bushnell 10x50 Explorer binoculars and a Bushnell
20-45x Zoom Spacemaster spotting scope.

Prey remains and reguriated pellets were collected
from 2 eyries. Adult Prairie Falcons at BC-1 were ob-
served bringing 1 horned lizard (Phi-ynosoma sp.), 4
ground squirrels (Spermophilus sp.) and 1 unknown prey
item to the eyrie. At VV-8, adult falcons delivered 3
ground squirrels and 1 western meadowlark (Sturnella
neglecta) to the eyrie.

Reuse of Nesting Territories and Eyries. — Three of
the 22 known nesting territories have remained active
since 1977. Two have remained occupied for 4 of the 5
years that surveys have been completed. The remaining

32

Short Communications

Table 1 : Summary of Prairie Falcon Nesting Activity. Mt. Pinos and Santa Lucia Ranger Districts, Los Padres National
Forest. 1977-81.

Eyrie

1977

1978

1979

1980

1981

BC-1

NC

NC

A

A

A

HV-2

NC

NC

A

NC

NA

JW-3

NC

NC

A

NC

A

CR-4

NC

NC

A

NA

NA

SB-5

NC

NC

A

NA

NA

DC-6

NC

NC

A 1

A

NA

NA

CC-7

NC

NC

NC

NC

NC

VV-8

NC

NC

A

A

A

LC-9

NC

NC

NC

NC

A

BR-2

A

A

A

A

A

HM-11

A

NA

NA

NA

A

BC-38

A

NC

A

A

A

GM-39

A

A

A

A

A

BT-40

NC

NC

A

A

NC

MM-41

NC

NC

A

A

NC

BR-43

A

NC

NC

NC

NC

BS-45

A

NC

NC

NC

NC

HM-46

A

A

NA

A

A

TC-55

A

A

A

A

A

CC-56

NC

NC

NA

A

A

AC-57

NC

NC

A

A

A

TR-58

NC

NC

NC

NC

A

A - Active; NA - Not Active; NC - Not Counted.

17 were active for 3 years or less (Table 1).

1981 Breeding Season, MPRD. — When surveyed bet-
ween March 1 1-18, 5 eyries were active with adult Prairie
Falcons in the nest territory. Eight historical eyries were
resurveyed in late April and early May. Only 3 eyries,
however, remained active. Young hatched at these 3
eyries during the week of May 3-9. Nestlings fledged
between June 8 and 19.

Productivity. — Clutch size was not determined. As-
suming a minimum clutch size, however, from the brood
size of active eyries (N = 3), a minimum mean clutch size of
3.7 eggs/nest can be inferred. Brood sizes and fledging
success in 1979 and 1981 are summerized in Table 2. For
both years the average fledging success is above the 2.56
needed to maintain a stationary population (Garrett and
Mitchell, 1973).

Mortality. — Two cases of egg loss or prefledging mor-
tality were observed. When VV-8 was observed on May 17,
1 unhatched egg was present in the nest with 3 nestlings.
When observed again on May 31, the egg was no longer
present. A 1-2 day old nestling was found directly below
the JW-3 eyrie in an emaciated condition.

Nesting Activity. — During 1977, both activity and pro-
ductivity at prairie falcon eyries on the SLRD was high.
Activity and productivity dropped in 1978 for some re-
ason. In 1979 the level of activity at the eyries was lower,
but the productivity was higher than the previous year.
Activity during 1980 and 1981 appeared to be fairly high
and when young were seen at the eyries, they were seen in
numbers above the 2.56 fledglings per nest needed to
maintain a stable population (Schlorff, 1979).

Productivity and activity at the prairie falcon eyries on
the MPRD during 1979 was high. A complete survey was
not conducted in 1980, so many eyries that may have been
active were determined to be inactive or not counted.
Activity at the eyries located in 1979 was down in 1981.
Productivity at these active eyries was also lower than the
1979 level.

It is difficult to say why the number of active eyries
observed in 1979 was not seen in 1981 on the MPRD.
Perhaps the falcons are nesting in alernate areas unknown
to the surveyers. Prey did not appear to be limiting. Gar-
rett and Mitchell (1973) stated that the observed rates of
prairie falcon production in California during 1971 and

Short Communications

33

Table 2: Summary of Prairie Falcon Nestling Production. Mt. Pinos Ranger District, Los Padres National Forest. 1979
and 1981.

Eyrie

1979

Brood Size
Fledging Success

1981

Brood Size
Fledging Success

BC-1

4

4

4 4

HV-2

4

4

JW-3

2*

2*

3 2

CR-4

5

0

SB-5

5

5

DC-6

3*

U

CC-7

U

U

VV-8

5

5

3 3

TOTAL

28

20

10

9

Mean

4**

3.3***

3.3

3

* - Number may have been greater, but a complete count was not possible.

** - Mean excluding CC-7.

*** - Mean excluding DC-6 and CC-7.

U - Undetermined.

1972 was below expectation and indicated a declining
population. However, in the Central region of their study,
which includes the area of this study, a production rate in
excess of 2.56 fledglings/total pairs was observed.
Statewide, they determined an average production rate of
1.59 fledglings/pairs studied. They also observed an ex-
tensive shifting of production between eyrie locations in
1970 and 1971, with few of the nesting territories sup-
porting productive pairs in both years. This may be the
case on the MPRD.

Sincere appreciation is extended to Cliff Fox and Gary
Smith, U.S. Forest Service, and Jim Davis, California De-
partment of Fish and Game, for advice and assistance and
to Dr. Stanley W. Harris, Humboldt State LJniversity, for
directing the field problem.

Literature cited

Alten, G.R. and G.L. Keasler. 1979. Priarie Falcon
Study, 1979, Mt. Pinos Ranger District, Los Padres
National Forest, U.S. Forest Service, Frazier Park, CA.
7pp.

Garrett, R.L. and D.J. Mitchell. 1973. A Study of
Prairie Falcon Populations in California. California
Department of Fish and Game. Wildlife Management
Branch Administrative Report No. 73-2, Sacramento,
CA. 15pp.

Johnson, D.R. 1978. The Study of Raptor Populations.
The University Press of Idaho. Moscow, Idaho. 57pp.

Schlorff, R. 1979. 1979 Prairie Falcon Survey Summary
Data Sheet. California Department of Fish and Game
Interagency Memo.

Department of Wildlife Management, College of Natural Re-
sources, Humboldt State University, Areata, CA 95521.
Current Address: USD A Forest Service, Rocky Mountain
Forest and Range Experiment Station, Forestry Sciences
Laboratory, Arizona State University Campus, Tempe,
AZ 85287.

Received 2 November 1981; Accepted 1 March 1984.

34

Short Communications

Barred Owls and Nest Boxes

David H. Johnson and Don G. Follen, Sr.

The use of artificial nesting structures by the Barred
Owl ( Strix varia) has long been assumed. This is due in part
to the use of man-made structures by a closely related
species, the Tawny Owl ( Strix aluco) in Europe (Davey
1969). Hamerstrom (1972) gave recommended but un-
tested Barred Owl box dimensions. A literature search
reveals 3 published accounts (Johnson 1980, Follen 1982,
Synder and Drazkowski 1981) of Barred Owls using artifi-
cial structures for nesting. We briefly discuss Barred Owl
use of various types of semi-natural and artificial nesting
structures in Minnesota, Wisconsin, and Michigan.

Minnesota: Table 1 shows use of artificial and natural
cavity nest sites by Barred Owls in north-central Min-
nesota (Hubbard, Wadena, and Crow Wing counties)
during the breeding seasons of 1980, 1981, and 1982. All
nesting attempts were successful in fledging from 1 to 4
young. A “# nesting attempts” column is shown as some
nests were used in 2 and 3 consecutive years. Average
production from 12 nesting attempts in artificial struc-
tures was 2.75 young fledged/nesting attempt. Average
production in 4 natural cavity nests was 2.00 young
fledged/nesting attempt. This difference in production is
likely related to the prey abundance/availability within the
owls’ territory than to a function of nest site quality. How-
ever, larger sample sizes are needed to better assess this
evaluation. Figure 1 shows the design of the Barred Owl
nest box currently being used by the First author. This box
is a slightly enlarged Wood Duck (Aix sponsa) box with a

17.8 cm diameter entrance hole. Thirty-five of these are
currently being field tested in various forest habitats in
north-central Minnesota. Heights of nest boxes and top-
less Wood Duck boxes used by owls have ranged from
3.73-6.70 m (measured from bottom of entrance hole to
ground level). Both back-mounted and side-mounted nest
boxes (see Fig. 1) have been used by owls (N = 2 and N =5
respectively, based on number of nesting attempts).

Table 1. Minnesota Records.

Type of nest

# nests
used

# nesting
attempts

young

fledged

Barred Owl nest box

5

7

18

Topless Wood Duck box

2

4

12

Wood Duck box (with top)

1

1

3

Natural cavity

4

6

12

Wisconsin: In 1966, 3 young Barred Owls were
fledged from a topless Wood Duck box, located on Goose
Island, La Crosse County. In 1967, this same box con-
tained 2 young. Additional boxes of this type were suc-
cessful in subsequent years, but unfortunately the par-
ticular nesting data were not recorded (J. Rosso pers.
comm., F. Lesher pers. Comm.).

A large Barred Owl nest box was established in 1979 by
I Bill Drazkowski along the Mississippi River backwaters in

FRONT VIEW

Back-mounted Box

Figure 1. Barred Owl nest box made of wood (1.3 cm thick). All dimensions are in cm.

Short Communications

35

Figure 2. Semi-natural (hollow log) Barred Owl nest cavity. All dimensions are in cm.

Trempealeau County. In 1980 this box contained 2
young, and 3 in 1981. The dimensions of this box
were: entrance hole 22.2 x 21.0 cm, bottom of entrance
hole to floor of box 33.0 cm, inside floor 33.6 x 36.2 cm.
Mr. Drazkowski found the birds to be nesting in the
corner of the box, indicating that perhaps such a large box
was not required.

In 1981, owls fledged 3 young from a semi-natural nest
structure established by Follen in Wood County (Follen
1982). This structure (Fig. 2) consists of a section of a
hollow log, with top, bottom and backing plate added. In
this structure a 15.2 cm diameter entrance hole was used.

Michigan: In 1977 and 1978 Barred Owls nested in a
Red-shouldered Hawk ( Buteo lineatus) nest in Alpena
County. It was unsuccessful, as eggshells and dead young
were found beneath the nest. Lewis Scheller (pers. comm.)
then established a reconditioned topless Wood Duck box
in the area on 2 March 1979. It was used in 1979 and
young owls successfully fledged. In 1980 owls again used
it, as evidenced by a single infertile egg. In 1981 owls
fledged 2 young from 2 eggs, and 3 young from 3 eggs in
1 982. This box is approximately 57 cm deep with a bottom
of about 31x31 cm. Scheller has also established 5 other
slightly larger nest boxes, all with open tops. At the time of
this writing, none of these have been used by owls.

The availability of suitable nest sites is reported to be a
limiting factor for cavity nesting species (Thomas et al.
1979). With current forest management directives of
short rotations, intensive culture, etc., this situation is
becoming more severe. Although Barred Owls have
nested in old hawk or squirrel nests in northeastern US
(Bent 1938:183) and in Michigan (L. Scheller per.
comm.), in Minnesota they have been recorded only as a
cavity nester (Johnson 1982). Beginning in 1980, a five
year project was initiated in north-central Minnesota to
address the question of artificial nest structures (design,
placement, and suitability) for Barred Owls. A project of a

similar nature has also been started in Wisconsin. Our
findings thus far indicate that Barred Owls do succes fully
nest in various types of man-made and semi-natural nest
cavities in Minnesota, Wisconsin, and Michigan. A nest
box project has also been started in New Jersey by
Leonard J. Soucy, Jr.

We thank Catherine M. Fouchi, Douglas Reran, Con-
rad Schmidt, Jon Carter, Fred Lesher, Dennis Seevers,
Bill Drazkowski, Lewis Scheller, Jerry R. Rosso, and
Leonard J. Soucy Jr. for their field assistance or other
input into this project.

Literature Cited

Bent, A. C. 1938. Life histories of North American birds
of prey, Part II. Dover publ., Inc. New York. 482 pp.
Davey,J.H. 1969. Nest boxes for birds of prey. R.S.P.B.
(2): 174-174.

Follen, D.G., Sr. 1982. The barreds of the big house.

Passenger Pigeon 44(1):20;22.

Hamerstrom, F. 1972. Birds of prey of Wisconsin. Dep.
Nat. Res., Madison, 64 pp.

Johnson, D.H. 1980. Barred Owls use nest box. Loon
52(4): 193-194.

1981. Raptors of Minnesta - Nesting

distribution and population status. Loon 54(2):73-104.
Synder, B., and B. Drazkowski. 1981. (newsletter).

Hiawatha Valley Bird Notes 18(7): 2.

Thomas, J.W., R.J. Anderson, C. Maser, and E.L. Bull.
1979. Snags/A J.W. Thomas, ed. Wildlife habitats in
managed forests - the Blue Mountains of Oregon and
Washington. USDA Handbook 553.51 1 pp.

Red Lake Wildlife Management Area, Box 100, Roosevelt,
MN 56673. Address of second author: 9201 Rock Inn
Road, Arpin, WI 55410.

Received 1 January 1983; Accepted 1 March 1984.

36

Short Communications

Ground-Nesting by Barn Owls

Michael E. Tewes

While trapping small mammals on the Aransas National
Wildlife Refuge in south Texas, I flushed some Common
Barn-Owls ( Tyto alba) from the ground in a dense stand of
gulf cordgrass ( Spartina spartinae). There were 3 separate
tunnel-like pathways through the cordgrass which were
apparently being used for roosting. Each cordgrass tunnel
was about 1 m long, terminating in a small chamber be-
neath the grass. The floor of each chamber was littered
with owl pellets and skulls of rodents and shrews.
Between November 1980 and January 1981, owls were
regularly observed using these cordgrass tunnels for
roosting, and in January an abandoned clutch of 4 eggs
was found in 1 concealed compartment. I suspected the
nest was abandoned after having been flooded during a
rainstorm (gulf cordgrass communities normally occur on
areas that are periodically flooded). I could not find addi-
tional nests or roosts. The grass community had a domin-
ant Baccharis shruf influence except for a small 3 ha
shrub-free area in which the owl tunnels were located.

These observations are of interest because they provide
additional evidence that Common Barn-Owls will nest
and roost on the ground. Quigley (Condor 56:315, 1954)
found young barn owls in a box with an open top, sunk
flush with the surface of the ground in a marsh. It is
possible, however, that owls resort to such areas for nest-
ing and roosting only if there is no alternative. The
nearest tree or man-made construction that could serve as
a nest or roost site was located ovr 4 km away.

Raptor management has received increased attention in
recent years. If particular management objectives for an
area include enhancing the raptor populations, then at-
tempts should be made to preserve roost and nest sites by
not altering selected mature cordgrass stands. Erection of
nest boxes (Marti et al., Wildl. Soc. Bull. 7:145-148, 1979)
over cordgrass meadows may attract barn owls and sup-
port more successful nesting attempts than ground nests.
Otteni et al. (Wilson Bull. 84:434-448, 1972) and Delnicki
and Bolen (Southwest. Natural. 22:275-277, 1977) pro-
vide additional instances of Common Barn-Owl use of
nest boxes in marsh areas.

I acknowledge Ray Anderson and his students, Univer-
sity of Wisconsin at Stevens Point, for assistance. J ames G.
Teer and Bruce C. Thompson critically reviewed the
manuscript. Support for this research was provided by the
Edwards H. and Winnie H. Smith Fellowship and the Rob
and Bessie Welder Wildlife Foundation.

Welder Wildlife Foundation Contribution No. 155. Rob and
Bessie Welder Wildlife Foundation, P.O. Drawer 1400, Sinton,
TX 78387. Present address: Caesar Kleberg Wildlife Research
Institute, Box 218, Texas A&I University, Kingsville,
TX 78363.

Received 20 January 1983; Accepted 2 May 1984.

Unusually Low Nesting Site For
American Kestrels ( Falco sparverius )

Clark S. Monson

Two American Kestrel (Falco sparverius) nests found in
extreme northern Utah were located in small pine stumps
on a steep canyon hillside. The nests were less than 45 m
apart and both nest holes were only 64 cm above the
ground. Higher and seemingly more suitable holes were
common in nearby trees but were not occupied by nesting
kestrels.

The low nest holes that were occupied did not appear to
make the birds more sensitive to human disturbance. On
one occasion, I was able to walk directly up to one of the
nests and temporarily remove the incubating female be-
fore she made an attempt to fly.

543 East 2600 North, Provo, UT 84602.

Received 15 May 1983; Accepted 15 May 1984.

Monitoring Bald Eagle Nesting
in Baja California, Mexico

Bruce Conant, Albert N. Novara and Charles J. Henny

Henney et al. (Auk 95:424, 1978) discussed Bald Eagle
(Haliaetus leucocephalus) sightings and nesting activity in
the vicinity of Bahia Magdalena in Baja California. They
confirmed 2 nesting pairs in 1977, apparently the first
published record of Bald Eagle nesting in Baja California
during the last 50 years.

During an aerial survey of wintering waterfowl on 18
January 1983, the first and second authors found 3 nests
(2 occupied) on Isla Creciente. Two were close together
(one occupied) at the location (24°22'N, 111°39'W;
hereafter abbreviated as 2422-1 1 139) reported by Henny
et al. (op.cit.) and an additional one occupied at 2422-
11133 also on Isla Creciente. At the latter nest there was
an adult eagle incubating 2 eggs with another adult
perched nearby. One of the other 2 nests had an incubat-
ing adult, but we were unable to flush it off the nest.
Assuming an incubation period of 35 days, the eggs seen
would not have been laid before mid-December. All nests
were made of sticks and located in the crowns of man-
grove, but were readily visible from the air. The location
of the other nesting pair found by Henney et al. (op.cit.) in
1977 (near San Jorge 2534-11206) was not checked in
detail in 1983.

The west coast winter waterfowl survey was conducted
by the U.S. Fish and Wildlife Service in cooperation with
the Direccion General de la Fauna Silvestre of Mexico as
part of the U.S.-Mexico Joint Agreement. Bald Eagle ob-
servations were made incidental to the waterfowl survey.
We expect to fly annual winter surveys in this area in the
future and plan to monitor the status of Bald Eagle nests
at both general locations.

Thesis Abstracts

Addendum

The nests on Isla Creciente were checked again the
following year on 16 January, 1984 during the 1984
Mexico winter waterfowl survey. An incubating adult was
found in each of 2 nests (2422- 11139 and 2422- 11133) but
we were unable to obtain an egg count. One flying adult
was sighted near San Jorge (2534-1 1206) but the nest was
not located.

U.S. Fish and Wildlife Service, P.O. Box 1287, Juneau, AK
99802. Address of second author: U.S. Fish and Wildlife Ser-
vice, P.O. Box 1747, Jamestown, ND 58401. Address of third
author: U.S. Fish and Wildlife Service, 480 West Airport Road,
Corvalis, OR 97333.

Received 30 June 1983; Accepted 8 March 1984.

The Seasonal Abundance, Habitat Use and Foraging
BehaviorOf Wintering Bald Eagles Haliaeetus
leucocephalus, IN WEST-CENTRAL ILLINOIS

The season abundance, habitat use and foraging behavior of
bald eagles wintering near Lock and Dam 19, Mississippi River,
were investigated by regular census taking and intensive be-
havioral sampling during the winters 1978-79 and 1979-1980.
The ultimate objectives of the study were to provide information
necessary for an Environmental Impact Analysis of a proposed
Mississippi River bridge and highway corridor on wintering bald
eagles and to obtain information useful to management of winter
bald eagle habitat.

The two study seasons contrasted greatly in weather severity.
During the severe winter of 1978-79, 8263 eagles were recorded
on 59 censuses. The peak count for this season was 454 eagles on
January 18. During the mild winter of 1979-80, 4230 eagle? were
recorded on 97 censuses. The peak count this season was 127
eagles on February 1 8. Eagle abundance varied considerably each
season; the greatest numbers were recorded during the coldest
periods of each winter. The effects of weather severity on the eagle
population of the study area are discussed. Overall, adult eagle
outnumbered immatures by 2.28 to 1 ; however, age class compos-
ition varied over the course of each season. Immatures comprised
a greater proportion of the eagle population during the early and
late parts of the season.

The daily activities of eagles included foraging and eating, fly-
ing, loafing and night-roosting. Eagles typically used different
portions of the study area for each of these activities, especially
when the eagle population was large. Habitat use data were ob-
tained from 10,710 locations of perched eagles plotted on census
forms. Ice cover, wind exposure, human activity and local food
concentrations were the most important factors determining the
daily use of suitable perching habitat. Eagle dispersion was most
clumped when ice cover on the river was at a maximum, and most
uniform when the river was ice-free.

Eagles use of foraging areas was greatest in the morning and
diminished as the day progressed; however, when large numbers
of eagles were present, eagles were observed foraging during all
daylight hours. Use of loafing areas peaked in the middle of the
day.

The prey base of eagles in the study area was dead or injured
fish, primarily gizzard shad ( Dorosoma cepedianum). Six behavior-

ally distinct foraging strategies were identified and are described.
By far the most commonly used, and the most intensively studied
of these was Strategy 1, an aerial search, swoop and capture of
prey. Eagles fishing via this method were successful approxi-
mately 70% of the time and averaged less than 5 minutes of flight
time per fish captured. Adults were significantly more successful
in capturing fish and averaged shorter flight duration per fish
captured than immatures. Approximately 70% of the fish cap-
tured were small (15 cm. or less) and the size of fish taken was
similar for both age classes. Over 97% of small fish captured by
eagles were successfully consumed. Most small fish (71.0%, N =
1181) were consumed in flight. Nearly 37% of large fish (greater
than 15 cm) captured by eagles were lost (pirated or accidentally
dropped) prior to being consumed. Most large fish (51.5%, N =
504) were eaten at tree perches.

Eagles readily attempted to steal prey from other fish predators,
even though food was generally abundant. Eagles attempting
interspecific piracy were relatively more successful (55.4%, N =
65) than eagles attempting intraspecific piracy (14.3%, N - 154).
Eagles carrying large fish were more vulnerable to piracy, and
were more likely to be attacked than were eagles carrying small
fish. Intraspecific piracy increased in frequency as foraging eagles
became more concentrated. Foraging eagles exhibited many be-
haviors designed to prevent the loss of procured prey to other
eagles. These pirate avoidance and pirate defense strategies are
discussed. — Fischer, David Lawrence. 1982. M.S. Thesis.
Western Illinois University, Macomb.

Ecology of Bald Eagles Wintering
in Southern Illinois

The population size, food habitats, distribution, and habitat of
wintering Bald Eagles ( Haliaeetus leucocephalus) were investigated
in Illinois at Union County and Horseshoe Lake conservation
areas during 1979-1981. Crab Orchard National Wildlife Refuge
was examined also during 1980-1981.

Eagles arrived in southern Illinois during late October with
estimated peak populations of 180-200 occurring, dependent
upon weather conditions, in January and February; eagles de-
parted by early March. Immature eagles predominated in win-
tering populations, but adult and immature subpopulations dis-
played similar patterns of fluctuations in numbers. Morning and
evening roost counts provided an accurate estimate of total popu-
lation size and automobile transact counts provided data on eagle
distribution and habitat utilization patterns.

Diurnal perch sites near shallow water areas were utilized most
during early winter. Occurrence of ice cover caused eagles to shift
to areas of open water where waterfowl also concentrated. Canada
Goose ( Branta canadensis) carcasses appeared to be the principal
food at this time, though unsuccessful eagle attacks were witnessed
on injured or dying waterfowl. During late winter, eagles ap-
peared less reliant on refuges for feeding. This may have been
associated with spring migration.

Food availability was considered the major influence on the
selection of diurnal perch sites. Protection from winds and insula-
tion from human disturbance appeared to be of secondary im-
portance. Communal roosts offered shelter from prevailing winds
by surrounding vegetation and were associated with standing
water. Most eagles left the roost by sunrise and returned by 20 min
after sunset. Times of vocalization and movement were similar to
those of entrance and departure. — Sabine, Neil. 1981. M.S.
Thesis, Southern Illinois University, Carbondale.

37

“The Peregrine Falcon At Reelfoot Lake”

By Murrell Butler
Limited Edition Print of 2,500

A tree-nesting “Duck Hawk” populated the Mississippi and Ohio River areas in times past. A remnant nesting
population was first documented during the 1930’s at Tennessee’s Reelfoot Lake by the late Albert F. Ganier. During
the 1940’s a new nest site was discovered on the west side of the lake by Dr. Walter R. Spofford, then Professor of
Anatomy at Vanderbilt University. Dr. Spofford and a few carefully selected observers made yearly nesting observa-
tions until the early 1950’s.

Mr. Thomas S. Butler was privileged to have been among those who spent many days recording the events of each
year’s breeding season beneath the enormous cypress tree that served as the falcons’ nest site. During the late 1970’s a
happy circumstance led Tom to meet Murrell Butler, a distant cousin from Louisiana. Murrell was an accomplished
wildlife artist and became enthralled by the tales of a Peregrine Falcon that once nested in the snag of the mammoth
cypress tree. A subsequent trip to the nest site (the cypress still stands!), the relocation of old photographs and
consultation with friends and fellow falconers culminated in this magnificent painting by Murrell Butler.

“The Peregrine Falcon at Reelfoot Lake” portrays the last known North American tree nest of the Peregrine.
Available in a 16" by 20" limited edition print of 2500, the introductory price is $65.00 for prints #1 - #500. The
introductory price includes postage within the fifty states and a $10.00 donation to The Raptor Research Foundation,
Inc. The price will advance to $125.00 per print for #2001 - 2500, according to the following schedule: #1 - 500,
$65.00; #501 - 1000, $75.00; #1001 - 1500, $85.00; #1501 - 2000, $95.00; #2001 - 2500, $125.00; Arkansas residents
will need to add state, city and /or county sales tax). Prints may be ordered directly from Mr. Thomas S. Butler, Butler
Galleries, 28 Fairmont Street, Eureka Springs, Arkansas 72632, USA. Payment may be made by check, money order,
VISA or MASTERCARD.

38

INSTRUCTIONS FOR CONTRIBUTORS TO RAPTOR RESEARCH
Effective with Volume 18, 1984

The editorial office of the Raptor Research Foundation, Inc.,
welcomes original reports, short communications and reviews
pertaining to the ecology and management of both diurnal and
nocturnal predatory birds for publication in Raptor Research . Pub-
lication in the journal is open to anyone, regardless of current
membership in the Raptor Research Foundation, Inc. Contribu-
tions are welcomed from throughout the world but must be writ-
ten in English. Submit all contributions to the Editor, Clayton M.
White, Department of Zoology, 161 WIDB, Brigham Young Uni-
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York, 1968), or Nelson (Raptor Res. 16(4):99, 1982). If more than

39

40

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RAPTOR RESEARCH

A QUARTERLY PUBLICATION OF THE RAPTOR ReSEARCHFoUNDATION, INC.

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RAPTOR RESEARCH

A Quarterly Publication of The Raptor Research Foundation, Inc.

Volume 18, Number 2, Summer 1984
(ISSN 0099-9059)

CONTENTS

Heptachlor Seed Treatment Contaminates Hawks, Owls and Eagles of Columbia
BASIN Oregon. Charles J. Henny, Lawrence J. Blus and T. Earl Kaiser 41

Breeding Ecology of Barred Owls in the Central Appalachians.

James G. Devereaux and James A. Mosher 49

Telemetry of Heart Rates in Large Raptors: A Method of Transmitter and

ELECTRODE Placement. Kevin T. Patton, Walter C. Crawford, Jr. and William Sawyer 59

Electroretinograms and Retinal Structure of the Screech Owl ( Otus asio) and Great
Horned Owl (Bubo virginianus). Steven J. Ault 16

Footprinting of Raptors For Identification. Erik H. Stauber 67

Pseudomenbraneous Gastritis Compatible with (Clostridium sp.) in a Captive

Peregrine Falcon. James H. Enderson and Morgan Berthong, M.D 72

Biotelemetered Daily Heart Rate Cycles in the Red-tailed Hawk (Buteo jamaicensis).
David E. Busch, William A. deGraw and N.C. Clampitt 74

Short Communications

Status of a Population of Bald Eagles Wintering in Western Connecticut.

Steven D. Faccio and Howard I. Russock 77

Nest Defense by Northern Harriers Against the Coyote in Southwestern Idaho.

Leon R. Powers, Timothy H. Craig and John Martin 78

News and Reviews 79

The Raptor Research Foundation, Inc.
Provo, Utah

THE RAPTOR RESEARCH FOUNDATION
(Founded 1966)

OFFICERS

PRESIDENT: Dr. Jeffrey L. Lincer, Office of the Scientific Advisor, 2086 Main Street, Sarasota, Florida 33577

VICE-PRESIDENT: Dr. Richard Clark, York College of Pennsylvania, Country Club Road, York, Pennsyl-
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BOARD OF DIRECTORS

EASTERN DIRECTOR: Dr. James A. Mosher, Appalachian Environmental Laboratory, University of Maryland,
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CENTRAL DIRECTOR: Dr. Patrick T. Redig, Department of Veterinary Biology, 295 Animal Science/ Veterinary
Medicine Building, University of Minnesota, St. Paul, Minnesota 55108

MOUNTAIN & PACIFIC DIRECTOR: Dr. A1 Harmata, Department of Biology, Montana State University, Boze-
man, Montana 59717

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161 WIDB, Brigham Young University, Provo, Utah 84602, U.S.A.

;

Published quarterly by The Raptor Research Foundation, Inc. Business Office: Dr. Gary E. Duke, Treasurer,
Department of Veterinary Biology, 295K Animal Science/ Veterinary Medicine Building, University of Minnesota, St.
Paul, Minnesota 55108, U.S.A. Printed by Press Publishing Limited, Provo, Utah 84602. Second-class postage paid at
Provo, Utah. Printed in U.S.A.

RAPTOR RESEARCH

A QUARTERLY PUBLICATON OF THE RAPTOR RESEARCH FOUNDATION, INC.

Vol. 18

Summer 1984

No. 2

HEPTACHLOR SEED TREATMENT CONTAMINATES HAWKS,
OWLS, AND EAGLES OF COLUMBIA BASIN, OREGON

Charles J. Henny, Lawrence J. Blus and T. Earl Kaiser

Abstract - We evaluated organochlorine residues in 12 species of hawks, owls, and eagles from the Columbia Basin of
Oregon between 1978 and 1981. Companion studies showed that heptachlor epoxide (HE) induced adult mortality and
reduced productivity of the Canada Goose ( Branta canadensis) and American Kestrel ( Falco sparverius) . In this study, brain
tissue from raptors found dead and sample eggs from 90 nests were analyzed for organochlorines. The primary concern
was HE that entered raptor food chains through the ingestion of heptachlor-treated seed by their prey. HE residues were
detected in eggs from 9 of 10 species and ranged as high as 4.75 ppm (wet wt), but no definite effects of HE on
productivity were readily apparent from the limited series of nests. However, the hazard of heptachlor seed treatments to
birds of prey was demonstrated by the occurrence of lethal residues of HE in brain tissue of 3 Golden Eagles ( Aquila
chrysaetos ) and 1 Rough-legged Hawk ( Buteo lagopus). Other organochlorine pesticides were present in the eggs and
significant relationships were found between DDE and eggshell thickness for the Swainson’s Hawk (Buteo swainsoni) and
Western Screech-Owl (Otus kennicotti), although shell thinning (9.6% and 7.4%) was below the generally accepted range

where reproductive problems have been known to occur.

The history of heptachlor as a wheat seed treat-
ment to control wireworms in Umatilla and Morrow
counties, Oregon, is poorly understood. Through
1970, it was listed in th e Pacific Northwest Insect Con-
trol Handbook (Anon., various dates) after aldrin and
dieldrin, with an application rate on seed of 1 oz/bu
(about 1,000 ppm). It was not listed in 1971, 1972,
and 1973. Then from 1974, heptachlor was listed at
2 oz/bu (about 2,000 ppm). In 1979, heptachlor
seed treatments were banned in a 1700 km2 area
near the Umatilla National Wildlife Refuge (NWR),
and by 1981, there appeared to be a nearly com-
plete changeover from heptachlor to lindane as a
seed treatment in our study area. As of September
1982, production of heptachlor for use as a seed
treatment in the United States was prohibited;
however, there was a provision for using up existing
stocks.

In 1976 and 1977, die-offs of several species of
birds occurred in Umatilla and Morrow counties,
Oregon. Residues of HE that are considered lethal
(Stickel et al. 1979) were found in brain tissue of the
Ring-necked Pheasant ( Phasianus colchicus ),
California Quail ( Callipepla calif ornica), Canada
Goose, Black-billed Magpie {Pica pica), and Golden
Eagle (Blus et al. 1979). This history of wildlife
mortality associated with heptachlor seed treatment
of wheat prompted a detailed study of Canada

Geese nesting at Umatilla NWR (Blus et al. 1979),
and a study of American Kestrels nesting through-
out the region (Henny et al. 1983). Both studies
showed heptachlor-induced adult mortality. Fur-
thermore, although HE did not thin eggshells, re-
duced nesting success was correlated with increased
HE residues in eggs of both species. The kestrel was
more sensitive to HE residues in eggs than was the
Canada Goose (i.e., reduced productivity occurred
at >1.5 ppm [wet wt] in kestrel eggs vs. >10 ppm
in Canada Goose eggs).

We reasoned that Canada Geese were obtaining
heptachlor directly from the ingestion of treated
seeds; however, the diet of American Kestrels is
mainly insects (especially grasshoppers) but in-
cludes mice, small birds and some lizards and am-
phibians (Fisher 1893). Therefore, the presence of
HE in kestrel eggs indicated contamination of the
food chain of at least one species of hawk.

This study was designed (1) to determine if HE
entered food chains of other species of hawks and
owls nesting in the region, and (2) to evaluate the
success or failure of each nesting attempt in re-
lationship to organochlorine residues in the sample
egg collected. The egg data provides insight into
residue concentrations that affect reproductive
success of the various species although more infor-
mation of this type is needed. Also, brain tissue of

41

Raptor Research 1 8(2) :4 1-48

42

Henny, Blus, Kaiser

Vol. 18, Number 2

birds of prey found dead were analyzed to deter-
mine if mortality was related to organochlorine
contaminants.

Methods

We collected a sample egg from 90 raptor nests located in
Umatilla and Morrow counties, Oregon in 1978-81. The remain-
der of the eggs were monitored for hatchability and fledging rates.
Since a sample egg was collected from each nest for or-
ganochlorine analysis, some productivity values were not directly
comparable to other published studies. Nest boxes were placed in
the region to attract American Kestrels, but Western Screech-Owls
and the Northern Saw-whet Owl (Aegolius acadicus) also used them.
The Burrowing Owl ( Athene cunicularia ) used artificial burrows
(Henny and Blus 1981).

The sample eggs were refrigerated until opened. Contents were
placed in a chemically cleaned jar and frozen for later analysis.
Shell thickness (shell and shell membranes) was measured at 3 sites
on each egg equator with a micrometer graduated in units of 0.01
mm. Historical eggshells (pre-1947) were measured at 3 museums
in Oregon and Washington. One randomly selected egg from each
clutch was measured.

Samples were homogenized and subsamples extracted by a
Soxhlet apparatus and cleaned by Florisil-column chromatog-
raphy. Polychlorinated biphenyls (PCB’s) were separated from
pesticides by silicic acid column chromatography (Cromartie et al.
1975 and Kaiser et al. 1980). All samples were analyzed for DDE,
DDD, DDT, dieldrin, heptachlor epoxide, mirex, oxychlordane,
m-chlordane, cw-nonachlor, tram-nonachlor, endrin, toxaphene,
hexachlorobenzene, and PCB’s. Additionally, samples in 1978,

1980 and 1981 were analyzed for lindane, samples in 1978 and

1981 for^-BHC, and samples in 1978 for pentachloronitroben-
zene (it was not detected).

Residues were quantitated by electron-capture gas-liquid
chromatography using either a 1.5/1.95% OV-17/QF-1 or a 1.5/
1.95% SP-2250/2401 column. Recoveries from fortified chicken
eggs ranged from 83-104%. Residue levels were not corrected for
recovery. A few samples from 1978 were analyzed at the Denver
Wildlife Research Center (Peterson et al. 1976). Residues in 8% of
the samples were confirmed on a Finnigan 4000 series gas
chromatograph/mass spectrometer (Kaiser et al. 1980). The lower
limit of residue quantification was 0.1 ppm for pesticides and 0.5
ppm for PCB’s. For statistical purposes, the lower limit of quantifi-
cation was divided in half and that value assigned to samples in
which the contaminant was not detected. Statistical calculations
were not performed unless 75% of the samples contained detecta-
ble residues. Contents of eggs were converted to an approximate
fresh wet wt by use of egg volume (Stickel et al. 1973); residue
concentrations were then expressed on an estimated fresh wet wt
basis. A t-test was used to determine significant (P < 0.05) changes
in eggshell thickness. The mean clutch size and mean number of
young fledged was not calculated unless > 6 nest records were
available.

O'

Results and Discussion

The largest series of eggs was obtained from the
Swainson’s Hawk (25 nests) and Long-eared Owl
(Asio otus) (21 nests), but because the preponder-
ance of data pertain to either 1978 or 1979, a statis-

tical analysis of the residue changes over time was
not advisable. A ban on heptachlor seed treatments
near the Umatilla NWR in 1979 resulted in an im-
mediate lowering of HE concentrations in kestrel
eggs the following year (Henny et al. 1983).

Hawk Eggs. — Heptachlor epoxide was detected
in the majority of eggs sampled among the buteos,
i.e., Swainson’s Hawk (21 of 25, 84%), Ferruginous
Hawk (Buteo regalis ) (9 of 10, 90%), and Red-tailed
Hawk (B. jamaicensis) (5 of 6, 83%) (Table 1). DDE
was detected at about the same frequency as HE in
all 3 species: Swainson’s Hawk (23 of 25, 92%),
Ferruginous Hawk (8 of 10, 80%), and Red-tailed
Hawk (5 of 6, 83%). Dieldrin was frequently de-
tected in Swainson’s Hawk eggs (13 of 25, 52%), but
was virtually absent from the Ferruginous Hawk (0
of 10) and Red-tailed Hawk (1 of 6) eggs.

Residues in sample eggs were tabulated from the
highest to the lowest to ascertain if residues influ-
enced nesting success. Although sensitivity to con-
taminants varies from species to species, we know
American Kestrel nesting success declined when
HE egg residues increased above 1.5 ppm (Henny
et al. 1983). With the Swainson’s Hawk, 15 of 21
nests (71%) with <1.5 ppm HE were successful
with 26 young fledged (1.24 per nesting attempt)
which was judged good to excellent. (Note: 1 egg
was collected which reduced the number fledged).
Only 4 nests contained >1.5 ppm HE (2 were
successful and fledged 4 young or 1.00 per nesting
attempt). Four of 5 Swainson’s Hawk nests with the
highest DDE residues (5 to 10 ppm) in eggs were
successful and produced 10 young (2.00 young/
nest). Two successful Swainson’s Hawk nests in
1976 contained DDE residues of 4.35 and 7.13 ppm
and produced 3 young and 1 young, respectively
(Henny and Kaiser 1979). When the 10 nest records
from 1976 were combined with 25 nests in this
study, regression analysis indicated a significant
logarithmic relationship between DDE and eggshell
thickness (Y = 0.393 - 0.022 logioX, r = - 0.40, P <
0.02). The same method showed no significant re-
lationship between HE and eggshell thickness (Y =
0.393 + 0.002 logioX, r = 0.04, P > 0.05). Eggshell
thickness (X ± SE) during this study was
0.387±0.007 mm which was 9.6% thinner (P <
0.01) than the pre-DDT era (before 1947) mean of
0.428±0.005 mm in the Pacific Northwest (Henny
and Kaiser 1979). This amount of thinning was less
than the generally accepted 18-22% range where
reproductive problems occur (Lincer 1975).

Summer 1984

Heptachlor Contamination in Oregon

43

Bechard (1981) collected a sample egg from 6
Swainson’s Hawk nests in nearby southeastern
Washington in 1977 and 1978. At least 1 young was
fledged from each nest. Low DDE residues (ppm
wet wt) were reported in 5 eggs (0.20, 0.68, 1.2,1 .4,
2.9) and low HE residues in 2 eggs (0.11, 0.35).

Neither the Ferruginous nor the Red-tailed
Hawk eggs contained HE above 1 .5 ppm (the effect
zone observed for the American Kestrel), and DDE
residues were generally low. Shell thickness for the
Red-tailed Hawk was identical (0.420±0.017 mm)
to pre-1947 thickness from the northern prairies
(Anderson and Hickey 1972); whereas, the small
series of Ferruginous Hawk eggs showed a signific-
ant (P < 0.01) shell thickness increase

(0.485±0.006 mm, n = 10 vs. 0.451 ± 0.008 mm, n
= 14) in comparison to eggs collected in Oregon
and Washington before 1947. Ferruginous Hawk
eggs collected from 6 nests in southcentral Idaho in
1979 contained low residues (ppm wet wt) of DDT
and its metabolites (highest value 0.65) and low
residues of HE (highest value 0.10) (Thurow et al.
1980). HE residues in Swainson’s and Ferruginous
Hawk eggs from this study were higher than re-
ported from eggs collected in adjacent states during
the same time period.

Four Northern Harrier ( Circus cyaneus ) eggs and
2 Prairie Falcon (Falco mexicanus ) eggs all contained
HE and DDE (Table 1).

Owl Eggs. — Heptachlor epoxide was detected

Table 1 . Clutch size, fledging success, eggshell thickness, and organochlorine residues (ppm wet wt) in eggs of hawks
nesting in Umatilla and Morrow counties, Oregon, 1978-80.

Year

Clutch

sizea

Fledged

Shell

Thickness

(mm)

HE

OXY

DDE

Dieldrin

HCB

TRNO

Swainson’s

Hawk

1979

4

1

0.480

2.95

0.31

0.76

0.49

0.19

0.10

1978b

4

3

0.383

2.93

2.16

1979

2

0

0.372

2.82

0.23

10.34

1.03

1979

3

0

0.360

2.52

0.28

1.15

0.52

2.62

0.58

1979

2

0

0.418

1.42

0.21

1979

2

1

0.391

1.31

0.14

1.87

0.14

1979c

4

3

0.365

1.20

0.11

10.41

0.11

1979

4

3

0.430

0.93

0.66

0.14

1979

3

0

0.417

0.67

0.21

0.45

1980

p

1

0.429

0.64

0.13

0.10

1979

3

0

0.353

0.50

0.45

1979c

4

3

0.335

0.36

8.74

1.34

1979d

3

0

0.378

0.35

0.13

1.28

0.33

1979

3

0

0.398

0.26

0.10

1980

2

0

0.351

0.25

0.28

0.17

1979e

4

3

0.370

0.23

7.50

0.10

1979

3

1

0.359

0.23

1.41

1979

3

1

0.388

0.19

2.66

0.15

1979

4

2

0.377

0.14

2.96

1979

3

1

0.430

0.13

0.56

1978b

p

1

0.371

0.10

0.15

1978b

3

1

0.346

5.00

1979

4

2

0.381

1.56

1979

3

1

0.404

1.32

0.13

1979f

4

2

0.397

0.23

3.22§

1.20§

0.3878

0.38h

0.98h

(Table 1 Continued)

44

Henny, Blus, Kaiser

Vol. 18, No. 2

(Table 1 Concluded)

Year

Clutch

sizea

Fledged

Shell

Thickness

(mm)

HE

OXY

DDE

Dieldrin

HCB

TRNO

Ferruginous Hawk

1978b

4

3

0.475

1.32

3.88

1979

2

0

0.493

1.08

0.12

2.25

1979

2

0

0.509

0.56

0.11

0.28

1978b

2

1

0.457

0.49

1.05

1979

4

2

0.455

0.40

0.65

1979

4

2

0.512

0.38

1978b

4

3

0.497

0.17

0.29

1978b

4

0

0.477

0.14

0.10

1978b

5

0

0.496

0.10

0.32

1980

4

2

0.475

1.31

0.30

3.50?

1.30?

.485?

0.3 1 h

0.42h

Red-tailed Hawk

1979

4

0

0.353

1.44

0.17

0.20

1980

?

2

0.477

1.34

0.14

0.15

1978b

3

?

0.417

1.22

3.58

1979

3

2

0.441

0.87

0.22

0.24

0.43

1978b

?

2

0.407

0.14

0.32

1979

3

2

0.424

0.420?

0.49h

0.27h

Northern Harrier

1979

6

o[

0.315

1.90

0.18

3.61

0.22

1978b

p

O1

0.317

1.06

5.24

1978

?

01

0.55

0.14

4.15

0.13

1979

?

o1

0.289

0.25

0.61

0.307?

0.73h

2.63h

Prairie Falcon

1979

5

3

0.372

4.75

0.33

0.86

0.21

0.22

1978b

4

?

0.319

1.84

1.11

0.346?

2.96h

0.98h

Vote: HE = heptachlor epoxide, OXY = oxychlordane, HCB = hexachlorobenzene, and TRNO = frans-nonachlor.

lBefore sample egg removed. ^ Analyzed at Denver Wildlife Research Center. cAlso, 0.36 or 0.66 ppm toxaphene. ^Also, 0.13 ppm DDD. eAlso, 1.0 ppm
PCB’s. ^Recycled after first nest abandoned. ^ Arithmetic mean. ^Geometric mean. Nests destroyed by farm mowing operations.

less frequently in eggs of the 5 species of owls (T able
2) than in hawk eggs: Western Screech-Owl (5 of 7,
71%), Short-eared Owl {Asio flammeus) (3 of 5, 60%),
Long-eared Owl (7 of 21, 33%), Burrowing Owl (2

of 6, 33%), and Northern Saw-whet Owl (0 of 4).
Our criteria for calculating geometric means (75%
of samples with detectable amounts) was not met
for HE in any of the owl species. DDE occurred in

Summer 1984

Heptachlor Contamination in Oregon

45

eggs at greater frequencies than HE: Western
Screech-Owl (6 of 7, 86%), Burrowing Owl (5 of 6,
83%), Long-eared Owl ( 1 7 of 2 1 , 8 1 %), Short-eared
Owl (4 of 5, 80%), and Northern Saw-whet Owl (1
of 4, 25%). However, the DDE concentrations in
owls were low.

Long-eared Owls experienced excellent repro-
ductive success; 16 of 19 nests (84%) were success-
ful. The 3 nests that failed did not contain higher
residue concentrations than the successful nests. A
test for the logarithmic relationship between DDE
and eggshell thickness was not statistically signific-
ant (P > 0.05). The mean eggshell thickness
(0.237±0.003 mm, n =21) was similar to the pre-
1947 mean (0.238±0.002 mm, n = 11) from Ore-
gon and Washington.

Western Screech-Owl eggs contained some of the
higher DDE residues among the owls (Table 2).
Although only 7 Western Screech-Owl eggs were
collected, a highly significant logarithmic relation-
ship existed between DDE and eggshell thickness ( Y
= 0.2 1 1 - 0.025 logioX, r = - 0.92, P < 0.01). There
was no significant relationship (P > 0.05) between
HE and eggshell thickness. Mean Western
Screech-Owl eggshell thickness of 0.2 12 ±0.007
mm was 7.4% thinner (P < 0.01) than the pre-1947
mean (0.229±0.004 mm, n = 1 1) from Oregon and
Washington. Laboratory studies showed that 2.8
ppm (wet wt) of DDE in the diet reduced Eastern
Screech-Owl (Otus asio) eggshell thickness by an av-
erage of 12% (McLane and Hall 1972). Residues of
DDE in Eastern Screech-Owl eggs from Ohio in

Table 2. Clutch size, fledging success, eggshell thickness, and organochlorine residues (ppm wet wt) in eggs of owls
nesting in Umatilla and Morrow counties, Oregon, 1978-81.

Shell

Clutch

Thickness

Year

sizea

Fledged

(mm)

HE

OXY

DDE

Dieldrin

HCB

PCB’s

Long-eared Owl

1979

5

4

0.237

1.92

0.25

0.14

0.10

1979

5

3

0.250

0.65

0.11

0.16

1079

6

5

0.236

0.61

0.45

1.49

1979

6

5

0.242

0.49

0.15

1980

5

p

0.243

0.45

0.19

1.04

0.22

1980

5

4

0.240

0.15

0.16

0.39

1978

5

0

0.265

0.14

1980

5

4

0.218

3.32

1979

7

5

0.221

1.58

1979

8

0

0.228

0.90

1980

5

3

0.250

0.56

0.18

1980

6

4

0.218

0.44

1978b

7

2+

0.247

0.42

1980

5

p

0.236

0.26

0.48

1980

6

0

0.234

0.25

1979

6

5

0.208

0.16

1980

4

3

0.264

0.12

1980

7

6

0.254

0.10

1980

5

4

0.231

1980

5

4

0.231

1980

5

4

0.218

0.24d

5.62c

(Table 2 Continued)

3.42c

0.237c

46

Henny, Blus, Kaiser

Vol. 18, Number 2

(Table 2 Concluded)

Shell

Clutch Thickness

Year sizea Fledged (mm) HE OXY DDE Dieldrin HCB PCB’s

Western Screech-Owl

1979

5

4

0.225

3.15

1979

le

X

0.189

2.57

1980

4

0

0.204

1.03

1978b

p

2

0.206

0.46

1979f

3

0

0.201

0.30

1980

5

4

0.215

1981

4

3

0.243

0.39

0.55

0.39

2.76

0.73

3.94

0.15

oil

1.01

0.13

0.60

1.98

0.28

3.43

0.50

0.10

1.06

4.20c 2. 1 7C 0.212c 0.90d

Burrowing Owl

1981

6

0

0.178

0.19

0.66

1981

5

os

0.182

0.16

0.24

1979

10

7

0.172

0.18

1980

8

7

0.174

0.14

1980

10

?

0.180

0.11

1980

12

10

0.192

8.50c 0.180c

Short-eared Owl

1979

6+

3

0.246

1980

4

?

0.277

1978b

?

0h

0.216

1979

8

5 +

0.235

1979

9

3 +

0.258

0.1 7d

1.70

0.33

0.20

0.51

0.99

0.35

0.29

0.24

0.61

1.08

0.74

0.26

0.85

0.246c 0.30d

Northern Saw-whet Owl

1978

5 +

3

0.185

0.11

1979

6

5

0.197

1981

7

3

0.192

1981

6

2

0.191

0. 1 9 lc

Note: HE= heptachlor epoxide, OXY = oxychlordane, HCB = hexachlorobenzene, PCB’s = polychlorinated biphenyls. ^

aBefore sample egg removed. “Analyzed at Denver Wildlife Research Center. cArithmetic mean. “Geometric mean. eLone egg found in nest box. Also, 0.96
ppm eis-chlordane. ^Four hatched but depredated by a Badger (Taxidea taxus ). ^Nest destroyed by farm mowing operation.

Summer 1984

Heptachlor Contamination in Oregon

47

1973 were generally low (arithmetic X 1.29 ppm
wet wt, range 0.33-2.8) and no relationship was
found between hatching failure and presence of
organochlorine residues (Klaas and Swineford
1976). For comparison, the arithmetic mean for
DDF in this study was 1.65 ppm.

The shell thickness of 6 Burrowing Owl eggs
averaged 0.1 80 ±0.003 mm which was not signific-
antly different from 6 eggs collected in Oregon and
Washington before 1947 (0.191 ±0.009 mm).
Short-eared Owl eggs showed a mean shell thick-
ness of 0.246 ±0.0 10 mm which was nearly identical
to the 0.245 ±0.006 mm from 3 eggs collected in
Oregon and Washington prior to 1947. Northern
Saw-whet Owl eggs had a mean shell thickness of
0. 191 ±0.003 mm; however, no historical eggs were
available from the region for comparison. DDE re-
sidues were generally < 1 ppm in eggs of these 3
species of owls.

Eagles and Hawks Found Dead. — Although
eggs from Golden Eagle nests in the region were
not collected, 8 eagles found dead were analyzed
(Table 3). Residues of HE in brain tissue of 3 Gol-
den Eagles (7.9, 10, and 13 ppm) were diagnostic of
HE poisoning (i.e., > 8 ppm established for ex-
perimental birds [Stickel et al. 1979]). The eagle
with 4.7 ppm HE died under suspicious cir-

cumstances; it was observed gliding and then fatally
diving straight into the ground! Rough-legged
Hawks nest in the Arctic and winter in the region,
but 1 bird accumulated lethal residues of HE. A
nesting American Kestrel died in its nest box with
28 ppm HE in her brain; an egg she laid contained
the highest HE concentration among the 261 kes-
trel eggs collected during a 4-year study (Henny et
al. 1983). The birds with lethal HE residues died in
March, April, May, and June which is considerably
after the fall planting time for heptachlor-treated
wheat seeds.

Acknowledgments

Biological technicians collecting field data for this study in-
cluded E.G. Huff, R.R. Sheehy, G.A. Green, B.E. Forman, K.D.
Hansen, and R. A. Grove. J.E. Kurtz and G.M. Constantino, refuge
managers at Umatilla NWR, kindly allowed use of refuge facilities
as our field operations center. S.A. Rohwer, Thomas Burke
Memorial Museum, Seattle; G.D. Alcorn, University of Puget
Sound Museum, Tacoma; and the staff of the University of Ore-
gon Museum, Eugene, assisted in obtaining measurements from
pre-DDT era eggs housed at their facilities. E.F. Hill and D.H.
White of the Patuxent Wildlife Research Center and G.A. Fox of
the Canadian Wildlife Service improved the manuscript with their
thoughtful reviews. We thank all who assisted in this effort.

Addenda

A Barn Owl ( Tyto alba) found dead in the study area on 1
January 1984 had the following residues (ppm wet wt) in its

T able 3 . Organochlorine residues (ppm wet wt) in brain tissue of eagles and hawks found dead in Umatilla and Morrow
counties, Oregon, 1977-80.

Species Wt (g) Age Sex Date HE OXY DDE Dieldrin TRNO HCB PCB’s

Golden Eaglea

2640

Adult

Golden Eagle*3

3600

Adult

Golden Eagle

4825

Adult

Golden Eagle

4500

SAd

Golden Eagle

3350

SAd

Golden Eagle

3225

Adult

Golden Eagle

4025

Adult

Golden Eagle

2900

SAd

Red-tailed Hawk

1050

Juv

Rough-legged Hawk
American Kestrel0

728

Juv

Adult

M

30 April 1977

10

0.62

M

May-June 1978

13

0.69

F

Winter 78-79

F

Winter 78-79

M

Winter 78-79

0.10

M

Early 1979

1.5

0.12

F

3 May 1980

4.7

0.30

M

17 June 1980

7.9

0.67

M

10 Feb 1980

F

20 March 1980

20

2.4

F

11 June 1979

28

2.5

1.1

0.75

0.40

0.29

0.61

0.49

0.43

0.21

0.11

1.8

0.12

0.89

1.5

0.26

0.31

1.6

0.42

0.34

7.4

0.35

0.95

0.21

Note: SAd = subadult (has white on tailor wings; seeSteenhof etal. 1983), Juv (in second calendar year of life; juvenal plumage); HE =
heptachlor epoxide, OXY = oxychlordane, TRNO = tozm-nonachlor, HCB = hexachlorobenzene, PCB’s = polychlorinated
biphenyls.

aFell from sky, hit ground and began convulsing. ^Found alive; no coordination and some muscle twitching. cSee Henny et al. (1983) for
details.

48

Henny, Blus, Kaiser

Vol. 18, No. 2

brain: heptachlor epoxide 1.1, oxychlordane 0.31, trans-

nonachlor 0.10, and DDE 0.18. Thus, another raptor species in

the area accumulated residues of heptachlor epoxide.

Literature Cited

Anderson, D.W. and J.J. Hickey. 1972. Eggshell
changes in certain North American birds. Proc. Inter-
natl. Ornithol. Cong. 15:514-540.

Anon, (various dates). Pacific Northwest Insect Control
Handbook. Compiled and edited annually by Exten-
sion Entomologists of Oregon State Univ.,
Washington State Univ., and Univ. of Idaho. Oregon
State Univ. Book Stores, Inc., Corvallis.

Bechard, M. 1981. DDT and hexachlorobenzene re-
sidues in southeastern Washington Swainson’s Hawks
( Buteo swainsoni). Bull. Environ. Contain. Toxicol.
26:248-253.

Blus, L.J., C.J. Henny, D.J. Lenhart and E. Cromartie.
1979. Effects of heptachlor-treated cereal grains on
Canada Geese in the Columbia Basin. In: Manage-
ment and Biology of Pacific Fly way Geese: A Sym-
posium. R.L. Jarvis and J.C. Bartonek (eds.). Oregon
State Univ. Book Stores, Inc., Corvallis, pp. 105-1 16.

Cromartie, E., W.L. Reichel, L.N. Locke, A.A. Belisle,
T.E. Kaiser, T.G. Lamont, B.M. Mulhern, R.M.
Prouty and D.M. Swineford. 1975. Residues of or-
ganochlorine pesticides and polychlorinated
biphenyls and autopsy data for Bald Eagles, 1971-72.
Pestic. Monit. J. 9:11-14.

Fisher, A.K. 1893. The Hawks and Owls of the United
States in Their Relation to Agriculture. U.S. Dept.
Agric., Div. Ornithol. Mammal. Bull. 3.

Henny, C.J. and L.J. Blus. 1981. Artificial burrows
provide new insight into Burrowing Owl nesting biol-
ogy. Raptor Res. 15:82-85.

Henny, C.J. and T.E. Kaiser. 1979. Organochlorine
and mercury residues in Swainson’s Hawk eggs from
the Pacific Northwest. Murrelet 60:2-5.

Henny, C.J., L.J. Blus and C.J. Stafford. 1983. Effects
of heptachlor on American Kestrels in the Columbia
Basin, Oregon./. Wildl. Manage. 47:1080-1087.

Kaiser, T.E., W.L. Reichel, L.N. Locke, E. Cromartie,
A.J. Krynitsky, T.G. Lamont, B.M. Mulhern, R.M.
Prouty, C.J. Stafford and D.M. Swineford.
1980. Organochlorine pesticide, PCB and PBB re-
sidues and necropsy data for Bald Eagles from 29
states — 1975-77 .Pestic. Monit. J. 13:145-149.

Klaas, E.E. and D.M. Swineford. 1976. Chemical con-
tent and hatchability of Screech Owl eggs. Wilson Bull.
88:421-426.

Lincer, J.L. 1975. DDE-induced eggshell thinning in
the American Kestrel: A comparison of the field situ-
ation with laboratory results./. Appl. Ecol. 12:781-793.

McLane, M.A. R. and L.C. Hall. 1972. DDE thins
Screech Owl eggshells. Bull. Environ. Contain. Toxicol.
8:65-68.

Peterson, J.E., K.M. Stahl and D.L. Meeker.
1976. Simplified extraction and cleanup for deter-
mining organochlorine pesticides in small biological
samples. Bull. Environ. Contain. Toxicol. 15:135-139.

Steenhof, K., M.N. Kochert, and J.H.
Doremus. 1983. Nesting of subadult Golden Eagles
in southwestern Idaho. Auk 100:743-747.

Stickel, L.F., S.N. Wiemeyer and L.J. Blus. 1973. Pes-
ticide residues in eggs of wild birds: Adjustment for
loss of moisture and lipid. Bull. Environ. Contain. To-
xicol. 9:193-196.

Stickel, L.F., W.H. Stickel, R.D. McArthur and D.L.
Hughes. 1979. Chlordane in birds: A study of lethal
residues and loss rates. In Toxicology and Occupa-
tional Medicine. W.B. Deichmann (organizer).
Elsevier/North Holland, New York. pp. 387-396.

Thurow, T.L., C.M. White, R.P. Howard, and J.F. Sul-
livan. 1980. Raptor ecology of Raft River Valley,
Idaho. U.S. Dept. Energy, Idaho National Engineer-
ing Laboratory, EGG-2054, Idaho Falls, Idaho. 45 pp.

U.S. Fish and Wildlife Service, Patuxent Wildlife Research

Center, 480 SW Airport Road, Corvallis, OR 97333. Address of

third author: U.S. Fish and Wildlife Service, Patuxent Wildlife

Research Center, Laurel, MD 20708

Received 10 March 1984; Accepted 9 May 1984.

BREEDING ECOLOGY OF BARRED OWLS IN
THE CENTRAL APPALACHIANS

James G. Devereux and James A. Mosher

Abstract - Eight pairs of breeding Barred Owls (Strix varia) in western Maryland were studied. Nest site habitat was
sampled and quantified using a modification of the James and Shugart (1970) technique (see Titus and Mosher 1981).
Statistical comparison to 76 random habitat plots showed nest sites were in more mature forest stands and closer to forest
openings. There was no apparent association of nest sites with water. Cavity dimensions were compared statistically with
41 randomly selected cavities. Except for cavity height, there were no statistically significant differences between them.

Small mammals comprised 65.9% of the total number of prey items recorded, of which 81.5% were members of the
families Cricetidae and Soricidae. Birds accounted for 14.6% of the prey items and crayfish and insects 19.5%. We also
recorded an apparent instance of juvenile cannibalism.

Thirteen nestlings were produced in 7 nests, averaging 1.9 young per nest. Only 2 of 5 nests, where the outcome was
known, fledged young.

The Barred Owl ( Strix varia ) is a common noc-
turnal raptor in forests of the eastern United States,
though few detailed studies of it have been pub-
lished. Most reports are of single nesting occurr-
ences and general observations (Bolles 1 890; Carter
1925; Henderson 1933; Robertson 1959; Brown
1962; Caldwell 1972; Hamerstrom 1973; Appel-
gate 1975; Soucy 1976; Bird and Wright 1977;
Leder and Walters 1980). Habitat was described
qualitatively by Nicholls and Warner (1972) and
Fuller (1979). Barred Owl food habits were re-
ported by Cahn and Kemp (1930), Errington
(1932), Errington and McDonald (1937), Wilson
(1938), Mendall (1944), Hamerstrom and
Hamerstrom (1951), Blakemore (1960) LeDuc
( 1 970), and Korschgen and Stuart (1972). The food
habits studied, however, were all from midwestern
states, except Mendall’s (1944) study from Maine.
Dunstan and Sample (1972) reported the number
of fledglings from 1 cavity each year for 5 years, but
provided no other productivity information.
Clutch sizes in various geographic regions can be
found in Bent (1961) and Murray (1976).

This study was conducted in an area where 4
diurnal raptor species, the Red-shouldered Hawk
(Buteo lineatus), Broad-winged Hawk (B . platypterus) ,
Red-tailed Hawk (B. jamaicensis) and Cooper’s
Hawk ( Accipiter cooperi), were also under study (see
Titus and Mosher 1981, Janik and Mosher 1982).
Our objectives were to quantitatively describe veg-
etation structure at Barred Owl nest sites and com-
pare it with surrounding habitat, measure and
compare dimensions of cavities used by them with
those from randomly selected cavities, describe
their food habits for this geographic region, and
determine their breeding chronology and produc-
tivity.

Study Area and Methods

The study was conducted in Green Ridge State Forest (GRSF),
Allegany County, Maryland. It is within the Ridge and Valley
physiographic region (Stone and Matthews 1977), characterized
by narrow mountain ridges oriented northeast to southwest sepa-
rated by steep narrow valleys (see Titus 1980).

About 74% of the county and nearly all of GRSF is forested
Major forest types were described by Brush et al. (1980). Predom-
inant tree species include white oak ( Quercus alba), red oak (£).
rubra), chestnut oak (Q. prinus), scarlet oak (Q. coccinea), red maple
{Acer rubrum), and pignut and mockernut hickories ( Carya glabra
and C. tomentosa). Predominant understory species include flow-
ering dogwood ( Corntis florida), sassafras {Sassafras albidum), ser-
viceberry {Amelanchier spp.), and saplings of the dominant trees.

The study area was systematically searched for active nests from
late February through May in 1981 and 1982. During 1982, tape
recorded Barred Owl calls were broadcast in order to elicit re-
sponses and help localize nesting pairs.

Nest sites were plotted on 7.5 min USGS topographic maps and
County Soil Conservation Service maps. A nest site was defined as
a 0.4 ha plot (1 1.3 m radius) centered on the nest tree. This size
plot was considered more time and field efficient than either
smaller or larger size plots when making quantitative estimates of
the vegetation (Lindsey et al. 1958, James and Shugart 1970).

Nests were checked periodically each season to obtain nesting
chronology and productivity information. At the same time, re-
gurgitated pellets found in the cavities were collected and any prey
remains were noted.

At the end of the nesting season, vegetation at each active nest
site was sampled using a modificaton of the James and Shugart
technique (1970), as described by Titus and Mosher (1981).
Thirty-four variables were measured or derived at each site (Table
1). The type of cavity in which a pair nested (hollow tree stub, hole
from disease, excavated hole, or hole from broken limb) and
successional stage of the cavity tree (Fig. 1) were recorded.

Height to cavity entrance was measured with a meter tape for
trees climbed, otherwise height measurements and percent slope
were measured with a Haga altimeter. Percent canopy, understory
and ground covers were based on 40 ocular tube readings, 10
along each of 4 transects starting at the nest tree and extending in
each of the cardinal compass directions.

We compared nest site data with random habitat samples col-
lected by Titus and Mosher (1981) to determine if vegetation
structure around nest trees differed from surrounding habitat.
Variables measured at random plots are listed in Table 1 except

49

Raptor Research 18(2):49-58

50

Devereaux and Mosher

Vol. 18, No. 2

Table 1. Qualitative habitat variables and cavity characteristics used in analysis of Barred Owl nest site habitat

1. ALTITUDE

2. SOIL

3. SITINDX

4. WATER

5. DISFOROP

6. PERSLOP

7. CANHT

8. CANEVER

9. CANTOT

10. UNDEVER

11. UNDTOT

12. GRNDEVER

13. GRNDTOT

14. SHRUBDEN

15. SHRUBIND

16. NOSPTREE

17. NOSPSHRB

18. NOTREES

19. UND14

20. UND58

21. UNDGT8

22. DBHLT26

23. DBH2650

24. DBHGT50

25. BASAL

26. DBH*

27. TREEHT*

28. CAVHT*

29. %CAVHT*

30. TREEDIAM*

31. HORIZONT*

32. VERTICAL*

Altitude of plot in meters; taken from U.S.G.S. 7.5-min. quadrangles

Soil-woods suitability; measures suitability for tree productivity; class 1 indicates high produc-
tivity and class 6 indicates low productivity (Stone and Matthews 1977)

Site index; based on SOIL and the tree species present in the plot (Stone and Matthews 1977)

Distance to water in meters

Distance to the nearest forest opening in meters; measured to the nearest break in forest
continuity, such as created by trail, road, field, etc.

Percent slope of plot

Canopy height of the plot in meters; the mean of 5 measurements taken to the top of the canopy

Percentage evergreen canopy cover

Percentage total canopy cover

Percentage evergreen understory cover

Percentage total understory cover

Percentage evergreen ground cover

Percentage total ground cover

Shrub density (James and Shugart 1970, James 1978)

Shrub index (Titus 1980)

Number of species of overstory trees in the plot

Number of species of shrubs and saplings in the plot

Number of overstory trees in the plot

Number of understory stems 1-4 cm diameter in the plot

Number of understory stems 5-8 cm diameter in the plot

Number of understory stems greater than 8 cm diameter in the plot

Number of overstory trees less than 26 cm dbh in the plot

Number of overstory trees 26-50 cm dbh in the plot

Number of overstory trees greater than 50 cm dbh in the plot

Basal area in m2/ha for overstory trees

Diameter at breast height of nest tree

Height of cavity tree in meters

Height to lowest point of cavity entrance in meters

Percentage cavity height; calculated as: (CAVHT/CANHT) (100) = %CAVHT
Diameter of cavity tree at cavity height
Horizontal length of cavity opening in cm
Vertical length of cavity opening in cm

(Table 1 continued)

Summer 1984

Appalachian Barred Owls

51

(Table 1 concluded)

33. CAVDIAM* Inside diameter of cavity in cm; measured from inside of entrance to back wall; for hollow tree

stubs, the largest diameter is recorded

34. CAVDEPTH* Cavity depth in cm; measured from lowest point of cavity entrance to base of cavity.

(* = variables unique to cavities and cavity trees).

for the cavity and cavity tree specific variables.

Dimensions of 41 randomly selected, unoccupied cavities were
measured and compared with nest cavities to provide a measure of
cavity sizes availble to Barred Owls and assess cavity selection. The
random sampling of cavities was stratified. Transects, approxi-
mately 100 m apart, 1.6 km long extending on both sides of a road
running the length of the study area, were randomly chosen. A
coin flip determined which side of the road the transect was
walked. Every third cavity encountered was measured but no
more than 3/transect to avoid measuring too many within a single
habitat type. The criteria for accepting a random cavity was that it
be at least 2 m from the ground and have at least a 1 5 cm diameter
opening, or, for a hollow tree stub, a 25 cm dbh.

Minimum sample sizes were calculated for each variable to
determine if random sampling was adequate. Sample sizes were
considered adequate if they met the criteria of remaining within
20% of the mean for 95% of the samples. Twenty of 25 variables
pertaining to habitat structure met this criteria with < 76 samples.
Seven of 9 cavity and cavity tree variables met this criteria with
sample sizes of < 41.

Habitat data were subjected to nonparametric statistical
analyses conducted on the Statistical Package for the Social Sci-
ences (SPSS) computer program (Nie et al. 1975, Hull and Nie
1981). Two sets of Kruskall-Wallis one-way analysis of variance

(Siegal 1956) tested for similarity between nest site habitat and
random habitat plots, and nest site cavity and random cavity di-
mensions. Spearman rank correlation coefficients (Siegal 1956)
were calculated to determine the extent of correlation among
structural features of habitat and among cavity characteristics.
X2 goodness-of-fit tests were used on pooled samples of nest site
and random cavities to determine if differences existed among the
number of each cavity type found and number of cavity trees in
each successional stage. Test results were considered significant if
P < 0.05.

Results and Discussion

Habitat. — Eight-Barred Owl nests were located.
The 4 found in 1981 were not reused in 1982. Nest
site habitat and random habitat plots were signific-
antly different between groups for 7 of 25 variables
(Table 2). Nest sites were found significantly closer
to forest openings than random sites, in habitats
with well developed understories. Percent under-
story cover and the number of stems greater than 8
cm diameter, both positively correlated with each

Table 2. Means ± standard deviations and ranges of habitat variables at Barred Owl nest sites and random habitat plots,
and results from Kruskal-Wallis one-way ANOVA (chi-square statistic) testing for significant differences
between groups.

Habitat

variable3

Barred owl
nest sites
(N = 8)

Random

sites

(N = 76)

Kruskal-
Wallis
X2 value

ALTITUDE

1239 ± 517

1356 ± 613

0.084

(820 - 2420)

(560 - 2860)

SOIL

3.6 ± 1.4

3.9 ± 1.3

(1 - 6)

(1 - 6)

0.093

SITINDX

65 ± 11.7

61.4 ± 12.5

0.410

(45 - 85)

(40 - 90)

WATER

218 ± 222

320 ± 243

1.860

(15 - 675

(35 - 1050)

(Table 2 continued)

52

Devereaux and Mosher

Vol. 18, No. 2

(Continuation of Table 2)

Habitat

variable3

Barred owl
nest sites
(N = 8)

Random

sites

(N = 76)

Kruskal-
Wallis
X2 value

DISFOROP

85 ± 116

221 ± 209

7.481**

(4 - 350)

(8 - 1 1 10)

PERSLOP

9.4 ± 12.9

21.6 ± 13.3

0.107

(0 - 40)

(3 - 80)

CANHT

23.5 ± 3.3

20.6 ± 4.5

2.991

(19 - 28)

(10 - 31)

CANEVER

7 ± 13

6 ± 14

0.019

(0 - 32)

(0 - 53)

CANTOT

68 ± 21

75 ± 9

0.230

(30 - 98)

(43 - 90)

UNDEVER

0

2 ± 7

0.535

(0 - 37)

UNDTOT

67 ± 14

53 ± 14

5.120*

(50 - 90

(17 - 80)

GRNDEVER

0

.5 ± 3

0.059

(0 - 30)

GRNDTOT

43 ± 13

38 ± 16

0.893

(23 - 68)

(10 - 75)

SHRUBDEN

23 ± 19

24 ± 11

1.074

(5 - 68)

(3 - 64)

SHRUBIND

42 ± 23

50 ± 21

1.220

(10 - 83)

(14 - 115)

NOSPTREE

4.5 ± 1.7

4.6 ± 1.8

0.046

(3 - 7)

(1 - 10)

NOSPSHRB

11.4 ± 2.8

10.1 ± 2.9

1.395

(8 - 16)

(5 - 17)

NOTREES

10.9 ± 3.6

19.5 ± 10)

7.315**

(4 - 17)

(7 - 48)

UND14

69.8 ± 34.9

74.3 ± 33.3

0.245

(28 - 131)

(9 - 154)

UND58

17.5 ± 8.8

12.7 ± 8.7

2.874

(3 - 33)

(1 - 45)

(Table 2 continued)

Summer 1984

Appalachian Barred Owls

53

(Table 2 concluded)

Habitat

variable3

Barred owl
nest sites
(N = 8)

Random

sites

(N = 76)

Kruskal-
Wallis
X2 value

UNDGT8

9.5 ± 3.7

5.9 ± 3.6

5.870*

(4 - 16)

(0 - 14)

DBHLT26

5.1 ± 3.2

14.7 ± 11.6

6.554**

(0 - 10)

(0 - 48)

DBH2650

3.9 ± 2.2

4.6 ± 2.8

0.665

(2 - 8)

(0 - 12)

DBHGT50

1.8 ± 1.2

0.2 ± 0.6

12.714***

(0 - 4)

(0-3)

BASAL

28.4 ± 5.8

20 ± 5.5

11.755***

(21.7 * 40.1)

(3.9 - 34.2)

aMnemonic names defined in Table 1.

(* = P < 0.05; ** = P < 0.01; *** = P < 0.001).

other (r = 0.24, P = 0.03, N = 84), were signific-
antly higher at nest sites. There were fewer over-
story trees, because of fewer trees in the < 26 cm
dbh size class. There were significantly more trees
> 50 cm dbh at nest sites (45/ha vs 5/ha at random
sites), nnd greater basal area.

These results' are in general agreement with the
qualitative habitat descriptions provided by previ-
ous authors (i.e., Barred Owls utilize forest stands
mature enough to provide suitable nesting cavities).
Craighead and Craighead (1969) suggested one of
the reasons Barred Owls were absent from part of
their study area was a lack of mature basswoods
(Tilia sp.) and a lack of heart rot fungus in woodlots
that had mature trees. However, owls are known to
nest in old hawk or squirrel nests, as did 1 pair in
this study, and 23 of 38 pairs reported by Bent
(1938). Bent suggested that they choose alternative
nests because of lack of cavities. Hilden (1965) and
Temple (1977) indicated that birds may shift from
their traditional nesting sites by imprinting on the
type of nests from which they fledge. If this occurs
in Barred Owls, those raised in old hawk or squirrel
nests may subsequently use these nest types re-
gardless of cavity availability.

Much literature on Barred Owls indicates an ap-
parent association with wet areas (Carter 1925, Er-
rington and McDonald 1937, Bent 1938, Appelgate

1975, Soucy 1976), perhaps because such areas are
often inacessible or too wet to be logged, thereby
providing old growth timber and abundant nesting
cavities. We found no difference in the proximity to
water between nest sites and random habitat plots.
The average distance to water was 218m with only 1
nest located on a stream “floodplain”. Further-
more, Nicholls and Warner (1972) and Fuller
(1979), both radiotelemetry studies, reported that
Barred Owls utilized oak-upland habitat more fre-
quently and consistently than any other habitat type
including white cedar ( Thuja occidentalis) swamps,
alder ( Alnus spp.) swamps, and marshes. Nicholls
and Warner (1972) suggested that owls used up-
land sites because of more suitable nest sites, abun-
dance of hunting perches, open understory for
hunting, and the opportunity to hear prey better in
dry areas.

Bent (1938) reported that distribution of Barred
Owls in southern New England coincides with
Red-shouldered Hawks and noted they are often
found in the same woodlot. In this study, forest
structure around Barred Owl nest sites was similar
to that of sympatric Red-shouldered Hawks, both
species utilizing old growth timber for nesting. Six
of the 7 significant variables listed in Table 2 were
also significant for the Red-shouldered Hawk
(Titus and Mosher 1981). Apparent differences

54

Devereaux and Mosher

Vol. 18, No. 2

between them were that Red-shouldered Hawk
nests were no closer to forest openings than ran-
dom habitat plots, but were significantly closer to
water, and there was a higher shrub density at Red-
shoulder occupied sites.

Cavities. — Six Barred Owl nests were in the top
of hollow tree stubs, 1 in a cavity created by disease
and 1 in an old stick nest. The high incidence of
hollow tree stubs as nest sites is probably a reflection
of cavity type availability in this area. Sixty-nine
percent of the total number of cavities measured
were hollow tree stubs, significantly more than the

other 3 types (X2 = 54.17, 3 df, P < 0.05).
Twenty-three percent were holes, resulting from
broken limbs and 8% were holes created by disease.
No excavated holes were found that met the criteria
to be included in the random cavity sample. Four of
the 7 nesting cavities were in trees in the second
successional stage (see Fig. 1) and 1 each in the
third, fourth and fifth stages. There was no statisti-
cal difference in the total number of cavity trees in
each of the 5 successional tree stages (X2 = 9.29, 4
df, P < 0.05).

There was a significant difference between ran-

Table 3. Means ± standard deviation and ranges of cavity and cavity tree dimensions for Barred Owl nest site cavities
and random cavities, and results from Kruskal- Wallis one-way Anova (chi-square statistics) testing for
similarity between groups.

Cavity

variable2

Nest site
cavities

N

Random

cavities

N

Kruskal-

Wallis

X2square

value

DBH

61 ± 15

7

53 ± 13

41

1.652

(42 - 88)

(26 - 90)

TREEHT

15.4 ± 5.8

7

12.9 ± 7.1

41

1.137

(10 - 25)

(3 - 24)

CAVHT

9.1 ± 2.9

7

6.3 ± 3.1

41

5.5999*

(4 - 14)

(2 - 17)

%CAVHT

39 ± 11

7

30 ± 14

41

2.724

(17 - 50)

(10 - 71)

TREEDIAM

46 ± 8

4

48 ± 11

33

0.048

(36 - 54)

(25 - 69)

HORIZONT

15 ± 0

1

21 ±8

12

2.571

(12 - 40)

VERTICAL

45 ± 0

1

49 ± 35

12

2.571

(20 - 140)

CAVDIAM

33 ± 8

6

30 ± 10

33

0.985

(22 - 41)

(11 - 60)

CAVDEPTH

54 ± 44

6

167 ± 203

33

0.767

(3 - 130)

(0 - 800)

aMnemonic names defined in Table 1.
(* = P < 0.05).

Summer

Appalachian Barred Owls

55

Figure 1 . Successional stages for describing Barred Owl cavity trees: 1 . LIVE - tree is apparently healthy except for
cavity; 2. DECLINING - tree is obviously declining; losing leaves; some dead branches; 3. DEAD; NO APPARENT
DECOMPOSITION - no leaves; tree still has all or most of bark; some branches may be broken; no apparent rotting of
wood; 4. DECOMPOSING; EARLY STAGE - many broken branches; bark falling off; wood becoming soft in spots;
5. DECOMPOSING; LATE STAGE - little or no bark on tree; very soft wood; broken tree stub is often all that remains

dom and nest site cavity dimensions for only 1 of 9
variables (Table 3). Cavities used by owls averaged 3
m higher than random cavities. Cavity depth of nest
site cavities was highly variable, ranging from 3 -
130 cm. Bent (1938) recorded a depth for 1 Barred
Owl cavity of 244 cm.

The cavity data suggest that most cavities, given
certain minimum dimensions, may be suitable for
nesting. Nest trees generally have at least a 25 cm
dbh and those with cavities 9 m or more above
ground may be preferred. Most reported dimen-
sions (Bent 1938; Allin 1944; LeDuc 1970; Dunstan
and Sample 1972; Soucy 1976 Leder and Walters
1980) are less than the maximum cavity dimensions
we found. Few data exist on the length and/or width
of cavity openings. Hamerstrom (1972) recom-
mended a 20 cm dia opening when constructing a
nest box for this species but did not indicate the
basis for this measurement. Forsman (1975) re-
ported a range of cavity entrance widths of 15.2 -
55.9 cm for 10 cavities used by the closely related
Spotted Owl ( Strix occidentalis).

Food Habits. — Barred Owl food habits in the
GRSF region are summarized in Table 4. The per-

cent occurrence of mammals and birds is fairly typi-
cal of what has been reported in the literature. Fish,
reptiles, amphibians, and arthropods have also
been recorded as prey items but are probably more
important to individual owl pairs than to a regional
population. The majority of crayfish recorded as
prey in this study, for example, were from 2 nests.

Jaksic (1982) hypothesized that temporal segre-
gations of falconiform and strigiform raptors may
not reduce competition for food between groups.
However, his data for Barred Owls revealed little
dietary overlap with falconiform species, except
with the American Kestrel (Falco sparverius). We
also observed little overlap. Sciuridae mammals
were clearly the major prey for the 4 hawk species
on the study area (Janik and Mosher 1982), while
Cricetidae and Soricidae species, which accounted
for 81.5% of the mammals and 53.7% of the total
number of prey items, were the predominant prey
for owls. Furthermore, Flying Squirrels and
Crayfish, both nocturnal and not recorded as prey
items for the hawks, comprised 8.5% and 12.2% of
the total number of prey items recorded, respec-
tively.

56

Devereaux and Mosher

Vol. 18, No. 2

Table 4. Food habits of Barred Owls in the Central Appalachians3.

Prey Species

Occurrence

%

Mammals

Southern Flying Squirrel ( Glaucomys volansi )

7

Shorttail Shrew (Blarina brevicauda)

7

Peromyscus spp.

5

Meadow Vole (Microtus pennsylvanicus)

4

Eastern Chipmunk ( Tamias striatus)

2

Red Squirrel (Tamiasciurus hudsonicus )

1

Unidentified Cricetidae sp.

16

Unidentified Soricidae sp.

12

Total

54

65.9

Birds

Scarlet Tanager ( Piranga olivacea )

3

Eastern Phoebe (Sayornis phoebe)

2

Blue Jay ( Cyanocitta cristata)

1

Unidentified

6

Total

12

14.6

Arthropods

Crayfish (Cambarus sp.)

10

Unidentified insects

6

Total

16

19.5

Total Items

82

100.0

aBased on prey remains and analysis of pellets from seven nests.

One nestling, about 28 d old, was cannabilized by
its sibling. Most of its body was eaten; legs, and skin
and feathers of the back were all that remained.
Based on growth measurements being taken every
3 to 4 d, both nestlings appeared healthy and were
of relatively equal size at 27 d old. The cause of
death was unknown but fratricide in raptors usually
occurs shortly after the second young hatches (Stin-
son 1979) and among nestlings of considerable size
difference (Ingram 1959), neither of which were
the case in this incident. Juvenile cannibalism is not
an uncommon occurrence among raptors, but to
our knowledge has not previously been
documented for Barred Owls.

Nesting Chronology and Productivity. — Nesting
chronology and productivity parameters are sum-
marized in Table 5. Hatch dates were fairly consis-
tent among nests, 5 out of 6 hatching within 7 d of
each other. Mean egg dates indicate Barred Owls

begin nesting about 1 wk before Red-tails (Janik
1980), the earliest nester of the hawk species for this
area.

Average clutch size/nest was 2.3, slightly higher
than the 2.0 reported by Murray (1976) for Barred
Owls in this region and latitude. A total of 13 nestl-
ings were produced in 7 nests, averaging 1.9
young/active nest. The outcome of 5 nests was
known. Of these, only 2 fledged young. The eggs
rolled out of 1 nest and the nestlings in the other 2
were preyed upon, perhaps as a result of human
activity at the nest sites.

The 2 young in successful nests emerged from
their cavities when 3 1 ± Id and 30 ± 1 d old,
respectively. At this age, Barred Owls are essentially
flightless. Primary remiges and rectrices of these 2
owls were only 50 and 1 2% of adult size, respectively,
within 2 d of fledging. Bent (1938) also reported
nestling Barred Owls climbing out of their cavities

Summer 1984

Appalachian Barred Owls

57

Table 5. Nesting chronology and productivity of Barred Owls in the central Appalachians, 1981-1982 (# of nests in
parentheses).

Mean egg datea (6)

Mean hatch date (6)

Mean nest departure date (2)

20 March
10 April
24 May

Mean clutch size (7)

2.3

Total eggs producted^ (8)

19.0

% hatching success (8)

68.4

# of nestlings per active nest (7)

1.9

Total number fledged (5)

2.0

# fledged/successful nest attempt (2)

1.0

% nesting attempts successful (2/5)

40.0

aEgg dates based on back dating from hatch dates using a 28-day incubation period (Bent 1938)
^Minimal number of eggs produced based on # of hatchlings and/or eggs found in nests

at 28-35 d old. Forsman (1975) reported Spotted
Owls leaving their cavities at 34-36 d old. Dunstan
and Sample (1972) and Soucy (1976), however, re-
ported Barred Owls not leaving nests until about 49
d old. The age at which owls emerge may be a factor
of cavity size. Those in small, cramped cavities, un-
able to spread and exercise their wings, may emerge
at an earlier age.

Leaving the nest early is a disadvantage from a
development standpoint because additional energy
is required to compensate for that lost to environ-
mental stress and increased activity. This was
suggested by measurements of 1 of the owls that
weighed the same 2 d after leaving the nest as 2 d
before leaving. However, mobility vs sitting in the
nest may be advantageous in terms of predator
avoidance. Birds in cavities are especially vulnera-
ble to predation because there is usually only 1
escape route. Young Barred Owls that do leave
nests at a preflight stage are not totally helpless.
Adult Barred Owls will continue to feed and defend
their young throughout the summer, even after
they can fly (Henderson 1933, Bent 1938, Dunstan
and Sample 1975, Bird and Wright 1977). Also,
young Barred Owls have the ability to climb trees
using their beaks and talons (Dunstan and Sample
1972). Thus, they are able to move about, first by
gliding or fluttering to the ground, then climbing a
nearby tree. Tree climbing has also been reported
for Great-horned Owl (Bubo virginianus), Screech
Owl (Otus asio) (Dunstan and Sample 1972) and
Spotted Owl (Forsman 1975).

Conclusions

Secondary cavity nesting birds, including the
Barred Owl, cannot choose a location within a
habitat to “place” their nests. They are limited to
what is already available. The data indicate that
differences exist between Barred Owl nest site
habitat and surrounding habitat, but do not indi-
cate whether cavities are selected based on those
differences. Further study is needed to answer this
question.

Acknowledgements

We thank J. Coleman, L. Garrett, M. Kopeny, D. Lyons, F.
Presley, R. Whetstone and K. Titus for their time and assistance.
We also thank S. Postupalsky for comments on an earlier version
of the manuscript. This study was supported, in part, by grants
from Sigma Xi, the Maryland Ornithological Society, and the U.S.
Fish and Wildlife Service (FWS 14-16-0009-80-007). This is Scien-
tific Series No. 1549-AEL of the Appalachian Environmental
Laboratory and Technical Report- 10 of the Central Appalachian
Raptor Ecology Program.

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Soucy, L., Jr. 1976. Barred owl nest. North Am. Bird
Bander 1:68-69.

Stinson, C.H. 1979. On the selective advantage of frat-
ricide in raptors. Evolution 33:1219-1225.

Stone, K.M. and E.D. Matthews. 1977. Soil survy of
Allegany County, Maryland. USDA, Soil Cons. Ser-
vice. 234 pp.

Temple, S. A. 1977. Manipulating behavioral patterns of
endangered birds. A potential management
technique. Pp. 435-443 In S. A. Temple (ed.), En-
dangered birds. Management techniques for pre-
serving threatened species. Univ. Wise. Press, Madi-
son.

Titus, K. 1980. Nest site habitat selection by woodland
hawks in the central Appalachians. M.S. thesis,
Frostburg State College, Maryland. 67 pp.

and J.A. Mosher. 1981. Nest site habitat

selection by woodland hawks in the central Appalac-
hians. Auk 98:270-281.

Wilson, K.A. 1983. Owl studies in Ann Arbor, Michi-
gan Auk 55:187-197.

Cooperative Wildlife Rsh. Lab, Southern Illinois Univ. Carbon-
dale, IL 62901. Address of second author: Appalachian En-
vironmental Lab, Univ. of Maryland, Frostburg State College
Campus, Frostburg, MD 21532. Present address of second au-
thor: Savage River Consulting, Box 71, Frostburg, MD 21532.

Received 8 March 1983; Accepted 10 May 1984.

TELEMENTRY OF HEART RATES IN LARGE RAPTORS:

A METHOD OF TRANSMITTER AND ELECTRODE PLACEMENT

Kevin T. Patton, Walter C. Crawford, Jr., and William Sawyer

Abstract - Heart rates of the Red-tailed Hawk (Buteo jamaicensis) and Barred Owl ( Strix varia) were monitored
telemetrically. The most acceptable data were received from devices whose electrodes were anchored within the
thoracoabdominal space near the apex of the heart (primary lead) and dorsum (reference lead). Easily assembled plastic
backpacks and leather harnesses were designed to be comfortable to birds and also to be resistant to damage from beaks
and talons.

Previously developed methods for monitoring
heart rate telemetrically (Sawby et al. 1974; Busch
et al. 1978; Kanwisher et al. 1978) proved unsuc-
cessful for large raptors for several reasons. First,
unsuitable arrangement of electrode leads gave un-
reliable results (Sawby et al. 1974) and were too
difficult and time-consuming to place to be of prac-
tical value (Busch et al. 1978). Secondly, an easy,
reliable method of attaching the transmitting de-
vices to the dorsum of each bird has been lacking. In
addition, Kanwisher, et al. (1978) described a
method which was vague on electrode placement
and included an unprotected backpack. Our objec-
tives were, therefore, to develop a more satisfactory
placement of electrodes and a safe, economical
backpack and harness for transmitter attachment.
Materials and Methods

Electronics. — Two electrodes, 1 acting as primary lead and the
other as reference lead, were surgically implanted. The primary
lead consisted of a 34 cm strand of Teflon-E insulated 7 x 40 cm
silver coated copper wire (Beldon Electronics, Geneva, IL 60134)
terminating at 1 end with a 1 mm round pin (Vector Electronic
Co., Inc., Sylmar, CA 91342) and a No-Knot Eyelet fish hook
(Wilson- Allen Corp., Windsor, MO) at the other end (Sawby et al.
1974), constituting a barbed-needle electrode (Fig. 1). The refer-
ence lead was constructed with the same material except that the
No-Knot Eyelet was replaced with a 0.5 cm loop of uninsulated
wire, constituting a circle electrode (Fig. 1). These electrodes de-
tected action potential of high amplitude S-waves of the elec-
trocardiogram of the raptor and the attached transmitter module
converted information into short RF pulses which were transmit-
ted in the range of 148-149 MHz (J. Stuart Enterprises, Grass
Valley, CA 95945). The transmitter had a mass of 20 g and mea-
sured 2.0 x 1.5 x 8.5 cm (Fig. 1).

Surgical Procedure. — Subjects wre anesthetized with an in-
tramuscular injection of Ketamine Hydrochloride (Fowler 1978)
and Acepromazine Maleate into the muscles of the leg. The Acep-
romazine Maleate reduces the muscle spasms resulting from the
use of Ketamine Hydrochloride as the principal anesthetic
(Fowler 1978). Satisfactory dosages were 15-25 mg/kg of a 10:1
Ketamine/ Acepromazine solution.

A 1 cm incision was made along the abdominal midline 0.5 cm
posterior to the sternum, roughly following the method proposed
by Sawby et al. (1974). Using a curved hemostat, the barbed-
needle electrode of the primary lead was inserted cranially
through the incision into the abdominal cavity (Fig. 2) and ad-

vanced along the peritoneal surface of the keel, to a position as
close as possible to the apex of the heart, then imbedded into the
sternum. The remainder of the lead was passed laterally from the
incision subcutaneously to a point just posterior to the left wing. It
was usually necessary to open this track with a blunt probe before
pushing the lead through. A 0.5 cm incision was made to allow the
lead to exit. This lead was similarly tunneled from the point of
lateral incision to a point on the median of the dorsum. Another
incision was made to allow exit of the lead and removal of the slack.
All incisions were closed with 3-0 gut suture.

The circle electrode on the reference lead was anchored sub-
cutaneously with 3-0 gut suture to muscle tissue at the point of the
dorsal incision (Fig. 2). This incision was then closed with 3-0 gut
suture, leaving both leads protruding out of the skin. The proce-
dure usually lasted about 20 min.

Salvaged raptor carcasses were dissected prior to this study to
practice locating heart and surrounding structures before begin-
ning on a live bird. Also, domestic fowl ( Gallus sp.) were implanted
with electrodes to perfect surgical technique and electrode place-
ments.

Backpack and Harness. — A backpack was constructed of 10 cm
of2.6cm (i.d.)clear plastic tubing (Kirkill, Inc., Downy, CA 90241)
and end-caps consisting of plastic 35 mm film canisters. A leather
harness was made by riveting 2 strips of leather (each 1.5 cm wide)
to the dorsal wall of the backpack (Fig. 3). The contact pins of both
leads were passed through a hole in the ventral wall of the plastic
tubing and connected to the transmitter inside of the tubing.
Leather straps were passed around the wings of the bird to the
ventrum and riveted together (Fig. 2).

Data Collection. — Signals were received by a portable unit
consisting of 3 components: a hand-held antenna, a radio re-
ceiver, and a strip-chart recorder (J. Stuart Enterprises, Grass
Valley, CA 95945). The receiver was a Telonics Model TR-2
direct-frequency reading, synthesized triple heterodyne, AC/DC
receiver which measured 11. 5x5. lxl 8.0 cm. The recorder was a
Gulton Model 288 DC recorder which utilized pressure sensitive
strip-chart paper to record an instantaneous average of heart rate
in beats/min at 2-sec intervals. This unit measured 15.3 x 22.9 x
19. 1. The normal DC mode of the recorder was converted to AC
by the use of a current transformer. A programmable household
timer (Radio Shack/Tandy, Ft. Worth, TX 76113) was used to turn
on the recorder at previously determined intervals. The graphs
produced resembled that in Fig. 4.

Two Red-tailed Hawks, 1 Great Horned Owl {Bubo virginmnus)
and 1 Barred Owl were affixed with transmitters. All were victims
of crippling injuries to 1 wing and thus incapable of flight and had
been received from the rehabilitation unit of the Raptor Rehabili-
tation and Propagation Project, Inc. Each bird was housed in an
outdoor enclosure (2.5 x 5.0 x 2.5 m) after implantation and
recovery.

59

Raptor Research 18(2):59-61

60

Patton, Crawford, Sawyer

Vol. 18, No. 2

B

Figure 1. A and C: Bottom and side views of
transmitting device; B: Primary
lead and reference lead.

Results and Discussion

Signals from the heart rate transmitter were re-
ceived up to a distance of 1 km. Lithium batteries in
each of the 3 units used were in continuous opera-
tion for over 1 yr, with no apparent reduction in
performance. The backpacks and leads, when
properly placed, remained functional for at least 1
mo. The backpacks and leads were checked daily
for damage. We believe that the method of record-
ing was less complex to operate and more easily
monitored than day-to-day methods previously re-
ported (Sawby et al. 1974, Busch et al. 1978, Kan-
wisher et al. 1978).

Difficulty in implanting the barbed-needle elec-
trode of the primary lead was encountered with
older birds whose skeletons had undergone more
ossification. Implanting the electrode in the lateral
edge of the sternum may prove adequate if normal
implantation is not possible.

Placement of the leads proved critical. The prim-
ary lead did not respond satisfactorily if placed
outside the abdominal cavity or if placed loosely
inside the abdominal cavity. The barbed-needle
electrode on the primary lead provided a secure
long-lasting anchor inside the body cavity in pro-
ximity to the apex of the heart. Care was taken
during the implantation to prevent accidental in-
jury to internal structures, especially pericardium.

Figure 2. A: Ventral insertion of internal (primary) lead near end of keel; B: Side view of barbed-needle electrode of internal lead
being pushed into dorsal side of keel through ventral incision; C: Subdermal insertion of internal lead toward dorsal exit
point; D: Dorsal view showing exit of internal lead and surgical implantation of external (reference) lead; E: Enlarged view
of subdermal attachment of reference lead and exit of primary lead; F: Attachment of harness containing transmitter.

Spring 1984

Raptor Heart Rates

61

Figure 3. Construction of Backpack and Harness; A: Plastic film
canisters; B: Leather straps; C: Metal rivet; D: Clear
plastic tubing; E: Hole for exit of leads.

1 HOUR

300-

1 0 0-

Figure 4. Heartrate data (heartbeats/min) obtained from a cap-
tive Red-tailed Hawk (Buteo jamaicensis) at a distance of
15 m.

The reference lead, if anchored in any area but the
surface of dorsal muscles, did not provide adequate
grounding for a proper response of the system.
Interference by the electromyogram of the pectoral
muscle tissue was assumed to have prevented satis-
factory ventral placement of this lead, since diffi-
culty was encountered only when that muscle was
contracting. Obviously, this would be unacceptable
in applications involving birds in flight. The
method described might possibly be used to
monitor the heart rate of birds in flight, however,
given the lack of electromyogram interference and
range of signal transmission.

Construction of the backpack/harness assembly
was very simple and economical. Total cost was
under $1 US. The plastic materials utilized en-
dured the efforts of the birds to remove or disman-
tle them with beak or talon without contributing
excessive mass. A very snug fit is required to pre-
vent the bird from gaining access to the leads where
they exit the dorsal incision and enter the backpack.

Acknowledgements

Artwork was done by David Huth. Equipment was funded
through a cooperative aid agreement with the North Central
Forest Experiment Station, USD A Forest Service. Dr. Gary Duke
kindly provided constructive criticism of our preliminary drafts.

Literature Cited

Busch, D.E., W.A. deGraw and N.C. Clam-
pitt. 1978. Effects of handling disturbance stress on
heartrate in the Ferruginous Hawk (Buteo regalis).
Raptor Research 12:122-125.

Fowler, M.E. 1978. Restraint and handling of wild and
domestic animals. Iowa State University Press. Ames,
IA 332 pp.

Kanwisher, J.W., T.C. Williams, J.M. Teal and K.O.
Lawson, Jr. 1978. Radiotelemetry of heart rates
from free-ranging gulls. Auk 95:288-293.

Sawby, S.W. and J.A. Gessaman. 1974. Telemetry of
electrocardiograms from free-living birds: a method
of electrode placement.

Raptor Rehabilitation and Propagation Project, Inc., Tyson Re-
search Center, Eureka, MO 63025.

Received 25 August 1983; Accepted 27 April 1984.

ELECTRORETINOGRAMS AND RETINAL STRUCTURE OF THE
EASTERN SCREECH OWL ( Otusasio ) AND GREAT HORNED OWL (Bubo virginianus)

Steven J. Ault

Abstract — Electro retinograms (ERGs) were recorded from 2 species of owls: Eastern Screech Owl (Otus asio) and
Great Homed Owl (Bubo virginianus). Dark adaptation and flicker stimuli were used to determine retinal activity and to
infer retinal structure. The dark adaptation results showed typical patterns associated with retinas composed primarily of
rods. This was indicated by the late regeneration of the scotopic b-wave. Flicker ERGs, however, also indicated a residual
cone component. This was indicated by the one-to-one response at high luminance levels and high flicker frequencies.
The ERG data confirm existing histological observations of high rod numbers and few cones in the retinas of nocturnal
owls.

Owl retinas have been examined histologically by
a number of investigators (Bornshein and Tansley
1961; Hocking and Mitchell 1961; Oehme 1961;
Fite 1973; Yew et al. 1977; Bowmaker and Martin
1978). All reported retinas with high concentra-
tions of rods, as would be expected for basically
nocturnal animals. However, Fite (1973) and
Oehme (1961) point out that owl retinas do possess
very small concentrations of cones, even in the most
nocturnal species.

Few electroretinographic studies have been per-
formed on owls. Bornshein and Tansley (1961)
obtained ERGs from Short-eared Owl (Asio flam-
meus ) and compared response of the retina to that
of the pigeon. These authors also correlated the
ERG results with histological preparations of the
owl and pigeon retinas. The ERGs and the his-
tological examination revealed a retina composed
predominantly of rods in the Short-eared Owl.
Martin and Gordon (1975) recorded ERGs from
the nocturnal Tawny Owl (Strix aluco ) to determine
its retinal spectral sensitivity. The ERG data sup-
ported earlier findings (Martin 1974; Martin and
Gordon 1974) that the Tawny Owl possesses a re-
tina with cone receptors that are present in large
enough numbers to contribute to the visual re-
sponse.

The purpose of this investigation was to record
electroretinographic activity of the Eastern Screech
Owl and Great Horned Owl, two species not previ-
ously investigated. Correlation of the ERG data
with retinal structure of these species was made in
an attempt to better define the relative role of the
rods and cones in the visual process of these owls.

Materials and Methods

Subjects and Anesthesia. — One Eastern Screech Owl and one
Great Horned Owl were used for electroretinography. Both were
anesthetized with an anesthetic mixture containing Ketamine (10

mg/ml), Acepromazine (0.1 mg/ml), and Xylazine (1.0 mg/ml).
Dosage was 1 ml/kg body weight, administered IM. Average dura-
tion of anesthesia was approximately 1 h.

Each subject was placed into a light-tight, electrically grounded
box, and a corneal electrode was placed on the eye. Space between
the cornea and electrode was flooded with a saline (0.9% NaCl)
conducting solution. A reference electrode was placed in the skin
of the ear flap or in the skin of the ear canal. A ground electrode
was inserted in the wing skin. A fiber optic light guide was hlaced a
few mm from the cornea.

Electrorednograph. — The light source was a 300 watt
tungsten-halogen lamp that could deliver steady, single-flash, or
flickering stimuli. Flicker stimuli were produced by a motor-
driven disc that interrupted the light to give equal time on and off.
The light beam was focused upon a fiber optic light guide which
delivered light to the subject’s eye in Maxwellian view (Armington
1974). The light beam wavelength and intensity were adjusted by
the use of various color and neutral density filters. Unfiltered light
intensity from this apparatus was approximately 1.076 x 104 mil-
lilamberts (mL) (1 mL = 0.001 lumens/cm2).

The recording electrodes used were silver pedestal corneal
contact lens systems. Reference and ground electrodes were silver
skin needle probes. Signals from the electrodes were channeled
through a Tektronix TM 504 pre-amplifier. The signal was
amplified and displayed on a Tektronix 51 03N dual-trace storage
oscilloscope. Traces were permanently recorded by Polaroid
photography.

Procedure. — Two tests commonly used in electroretinography,
dark adaptation and flicker stimuli, were used. Dark adaptation
tests were used to observe changes in the ERG as the retina ad-
justed to darkness. The eye was first pre-adapted to light for 5 min
to insure bleaching of the photopigments. Pre-adaptation retinal
illuminance was approximately 1.076 x 103 mL for the Eastern
Screech Owl and 1.076 x 101 mL for the Great Horned Owl.
Different intensities were used for both owls to assess the effec-
tiveness of such intensities for pre-adaptation, single-flash (20
msec duration) stimuli attenuated with a Kodak #2 neutral density
filter and a Kodak #26 gel film red filter, were delivered at widely
spaced intervals (see Figs. 1-3) to the eye to observe the retina’s
increasing sensitivity to darkness. After 20-30 min, full-intensity
single- flash stimuli of red (Kodak #26 gel film), blue (Kodak #47,
47A, 47B gel film) and white (no filters) were given successively to
assess the degree of photopic (cone) and scotopic (rod) recovery.

The second test utilized flickering stimuli of various intensities
and flicker frequencies. Various neutral density filters, but no
color filters, were used.

Histology. — The retinas of a Great Horned and Eastern

62

Raptor Research 18(2):62-66

Summer 1984

Owl Electroretinograms

63

time (min)
0

030
I 00
300
500
1000

n

100 /J v \ |

50 msec

1500
20.00
25 00
30100

red

blue

white

Figure 1. ERGs during dark adaptadon in the Eastern Screech Owl. Time indicates minutes into dark adaptation.

Stimulus: 1.076 x 104 mL attenuated with #2 neutral density filter and #26 red filter; 20msec duration, a)
Slight regeneration of photopic b-wave after 1 minute into dark adaptation, b) Slight regeneration of
scotopic b-wave after 30 minutes into dark adaptation.

Screech Owl were examined histologically. The Great Horned was
the same animal used in the ERG study. The subjects were
euthanized with lethal injection of Ketamine and enucleated. The
posterior portion of the eye was cut away and fixed in Bouin’s
solution. The tissue was dehydrated in a graded ethanol series and
cleared in cedarwood oil. Portions of peripheral retina were em-
bedded in paraffin, sectioned meridionally at 5 m on a rotary
microtome and stained with Hematoxylin and Eosin.

Results

Dark Adaptation. — The ERGs from dark adap-
tation tests for both subjects showed very early
low-amplitude responses which peaked at around
1-2 min into dark adaptation (Figs, la, 2a). Also,
late appearing (between 20 and 30 min into dark

lime (min)

0 ^ —

0.30 V

I 00 1

a

1

2,00 ~ ~

3 00

5 00 —

adaptation) low-amplitude waveforms were ob-
served (Figs, lb, 2b). The final red, blue, and white
stimuli produced waveforms of low amplitude.

Flicker Stimuli. — A change in waveforms were
observed as the flickering stimuli were increased
from low to high intensities and flicker frequencies;
this was best demonstrated by the Eastern Screech
Owl. At low intensities and low flicker frequencies,
waves were evident as they followed the stimuli on a
1:1 basis (Fig. 3a). There was a fusion of this re-
sponse as intensities and flicker frequencies in-
creased, with a subsequent waveform taking over at
high intensities and high flicker frequencies (Fig.
3b). The Great Horned Owl also displayed the
above pattern, but with less clarity (Fig. 4).

1000

: j 1 5: oo

a

Figure 2. ERGs during dark adaptation in the Great Horned Owl. Time indicates minutes into dark adaptation.

Stimulus: 1 .076 x 104 mL attenuated with #2 neutral density filter and #26 red filter; 20 msec duration, a)
Slight regeneration of photopic b-wave after 1-2 minutes into dark adaptation, b) Slight regeneration of
scotopic b-wave after 20-30 minutes into dark adaptation.

64

Steven J. Ault

Vol. 18, No. 2

neutral denelty
filter

Ar-

A/~-

500 msec

'/•vLh

12 Hi T 30 Hi

100/jV J

100 mtec

Figure 3. Flicker ERGs of the Eastern Screech Owl. a) Arrows indicate one-to-one response of waveforms to individual
flickers at low intensity and low flicker frequency, b) Arrows indicate one-to-one response of waveforms to
individual flickers at high intensity and high flicker frequency. 1.076 x 104 mL light source attenuated with
indicated neutral density filters.

Histology. — The retinal layers of the Eastern
Screech Owl could be clearly discerned histologi-
cally (Fig. 5). Retinas were composed primarily of
rods; indicated by the elongated and cylindrical
morphology of their outer segments in the receptor
layer. The nuclei in the outer nuclear layer were
also identified as rod nuclei because they were typi-
cally more elongated and were fairly evenly distri-
buted throughout the outer nuclear layer (Walls
1942; Duke-Elder 1958). The rod nuclei of the
Great Horned Owl were extremely elongated and
closely packed.

A few cones were also seen in owl retinas. These
were identified by their nuclei, which are typically
rounder than rod nuclei and lie adjacent to the
external limiting membrane. In all sections, cones
were always few in number and were greatly out-
numbered by the high density of rods.

Discussion

The typical ERG waveform is composed of the a,
b and c waves. The initial negative deflection (a-
wave) is followed by a positive deflection (b-wave)
normally of greater amplitude. The late-occuring

neutral density
filter

2

7\ - 5 — -

yv — —

30 Hz

Figure 4. Flicker ERGs of the Great Horned Owl. a) Arrows indicate one-to-one response of waveforms to individual
flickers at low intensity and low flicker frequency, b) Arrows indicate one-to-one response of waveforms to
individual flickers at high intensity and high flicker frequency. 1.076 x 104 mL light source attenuated with
indicated neutral density filters.

Summer 1984

Owl Electroretinograms

65

Figure 5. a). Layers of the Eastern Screech Owl retina. A) cartilaginous cup; B) pigment epithelium; C) receptor layer;

D) external limiting membrane; E) outer nuclear layer; F) outer plexiform layer; G) inner nuclear layer; H)
inner plexiform layer; I) ganglion cell layer; J) nerve fiber layer; and K) internal limiting membrane (200x);
b) Eastern Screech Owl and c) Great Horned Owl retinas, cn = cone nuclei; onl = outer nuclear layer
(primarily rod nuclei). (787. 5x and 500x respectively).

positive deflection (c-wave) is not commonly
evaluated in comparative studies. Brown (1968)
explained that the a-wave is produced in the re-
ceptor cell layer, the b-wave through bipolar cell
activity, and the c-wave by metabolic activity of the
pigment epithelium. The a- and b-waves can be
further subdivided into photopic (cone generated)
and scotopic (rod generated) components. In gen-
eral, the photopic components have shorter laten-
cies and steeper slopes than scotopic components
(Armington 1974). These patterns were evident in
the owls studied (Figs. 1, 2)

The dark adaptation results revealed typical
patterns associated with retinas composed predo-
minantly of rods. The late regenerating wave forms
were most likely scotopic b-waves suggesting that
rods were regenerating after having been bleached
during light adaptation. Latency of these b-waves
suggested the response was from the scotopic sys-
tem. Longer latency or implicit time (approxi-
mately 100 msec) is indicative of a scotopic rather
than photopic b-wave (approximately 50-70 msec).
Earlier low-amplitude responses were probably
cone responses because of their early appearance
during dark adaptation. Latency of these responses
was also shorter than the scotopic responses, again

suggesting generation by a cone component. As
dark adaptation progressed, these early responses
diminished and were replaced by the scotopic re-
sponses. After 25-30 min, there was still no com-
plete regeneration of the scotopic responses in
either owl, denoting that many of the rods were not
yet adapted to the dark. The reduced effect of the
blue light on the scotopic system also verified this
since blue light is primarily a rod stimulator. These
observations suggested a retina predominated by
rods, but with a small cone component. However, it
could mean that the initial light adapting intensity
was too high. This seems unlikely since an absence
of complete regeneration of the scotopic response
was also observed in the Great Horned Owl which
was exposed to a lower light-adapting intensity.

The shift from scotopic to photopic systems
during the flicker procedures was indicated by a
decrease in latency and an increase in amplitude of
the initial b-wave as flicker frequencies and inten-
sities were increased. The initial a-wave also became
more prominent at higher flicker frequencies and
intensities, providing further indication of the shift
to the photopic system (Armington 1974). The rods
and cones were also able to follow the individual
flickering stimuli. At low intensities and low flicker

66

Steven J. Ault

Vol 18, No. 2

frequencies, rods were able to follow individual
flickers, having not yet exceeded their critical
flicker fusion frequency. As intensity and/or fre-
quency was increased, rods “fused” the stimuli. Fu-
sion occurred when the receptors could no longer
respond to individual flickers on a 1:1 ratio but
instead responded to them as if there was one con-
stant stimulus. At high intensities and high flicker
frequencies, cone response became dominant and
was able to follow individual flickers since they pos-
sess a higher critical flicker fusion frequency than
rods (Armington 1974). Histological results in
combination with the ERG data indicated that the
retinas were predominantly composed of rods.
This supports the findings of previous workers
(Bornshein and Tansley 1961; Hocking and
Mitchell 1961; Oehme 1961; Fite 1973; Yew et al.
1977; Bowmaker and Martin 1978) who histologi-
cally demonstrated a retina composed predomin-
antly of rods in the Great Horned Owl and other
owl species. However, histological results and ERG
data also demonstrated the presence of a cone
component that was small but active.

My results and those of Bowmaker and Martin
(1978) and Martin and Gordon (1975) verify that
the retina of owls, even the most nocturnal species,
possess cones in numbers large enough to contri-
bute to the visual process. Existence of such a cone
component could be the remnants of an ancestral
cone-dominated retina. Nocturnal owls such as
screech and Great Horned Owls are occasionally
active during the day. It is reasonable to assume that
the few cones that are present contribute to the
owl’s visual process in the brighter illumination of
daylight hours.

Acknowledgments

I extend special thanks to Charles J. Parshall, Animal Specialty
Clinic, Richfield, Ohio, for help and expertise with electroretinog-
raphy and to Richard F. Nokes, The University of Akron, who
assisted with anesthesiology. F. Scott Orcutt, John H. Olive, Steven
P. Schmidt, Edwin W. House, and Carolyn Wilson made positive
critical comments on the manuscript. This study was supported in
part by a Grant-in- Aid of Research from Sigma Xi, The Scientific
Research Society.

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Bornshein, H. and K. Tansley. 1961. Elektroretinog-
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Bowmaker, J.K. and G.R. Martin. 1978. Visual pig-
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(Tawny owl). Vision Research 18: 1 125-1 130.

Brown, K.T. 1968. The Electroretinogram: Its Com-
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Duke-Elder, S. 1958. System of Ophthalmology. Vol.
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Fite, K. 1973. Anatomical and Behavioral Correlates of
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Hocking, B. and B.L. Mitchell 1961. Owl Vision. Ibis.
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Martin, G.R. 1974. Color Vision in the Tawny Owl
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Martin, G.R. and I. Gordon 1974. Increment-
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1975. Electroretinographically Deter-
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Oehme, H. 1961. Vergleichend-histologiche Unter-
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Walls, G.L. 1942. The Vertebrate Eye. Cranbrook In-
stitute of Science. Bulletin #19.

Yew, D.T., H.H. Woo and D.B. Meyer 1977. Further
Studies on the Morphology of the Owl’s Retina. Acta
Anatomica 99:166-168.

Department of Biology, The University of Akron, Akron, Ohio

44325. Present address: Department of Biology, Idaho State

University, Pocatello, Idaho 83209.

Received 8 March 1984; Accepted 1 July 1984.

FOOTPRINTING OF RAPTORS FOR IDENTIFICATION

Erik H. Stauber

Abstract - The feet of 15 Peregrine Falcons ( Falco peregrinus) and 25 Red-tailed Hawks (Buteo jamaicensis) were
photographed for evaluation of the dorsal scale patterns of their toes. Visual analysis of the middle toes (digit #3) showed
recognizeable scale pattern differences between toes from individual birds as well as for all related and unrelated birds.
Scale patterns remained unchanged for birds that were available in successive years. It is suggested that the toe scale
pattern is unique for any Peregrine Falcon or Red-tailed Hawk and could be used for permanent individual identifica-
tion.

Methods of differentiating individuals within
certain species, including man, have been explored
and used for many decades. Artificial markers con-
sisting of either bands, tags, tatoos or hot or cold
brands are used to identify individuals when readily
identifiable and unalterable natural markers do not
exist. However, there are a few species in which
each individual has unique, unchanging markings
which can be recorded and used effectively for
purposes of identification. The most notable
example is the use of fingerprinting in humans.
Other examples where unique markers have been
used for individual identification are the stripe
patterns of zebras, the reticulation on the pelage of
giraffes, the noseprints on bovine animals, or the
dorsal fin shapes and spots on killer whales.

Most birds have scale patterns on their feet and
legs, but there is no evidence that the scale pattern
of any species has ever been analyzed for the pur-
pose of developing an identification system. The
foot scale patterns of Peregrine Falcons {Falco
peregrinus) and Red-tailed Hawks {Buteo jamaicensis)
were characterized to determine their usefulness in
individual identification.

Materials and Methods

Individual birds represendng 2 raptor species were chosen for
photographic evaluation of the scale pattern of the dorsal aspects
of their toes. Birds included in the study were 15 Peregrine Fal-
cons and 25 Red-tailed Hawks. Several were siblings and three
were compared in successive years.

Feet were placed so that the entire dorsal aspect of the 3 forward
pointing toes (digits # 2,3,4) could be photographed with a
close-up lens. Black and white prints (5"x7") were developed and
the scale patterns of the toes of all birds were visually analyzed.
Only the middle toes (#3) were considered in this study. For
evaluation and comparison among individuals, scales of corres-
ponding areas on each toe were characterized according to size,
arrangement of scales in relation to adjacent scales, and network
of interscale spaces. For convenience of comparison, the area
occupied by the dorsal scale(s) closest to the talon was designated
as row 1L3 (scale row 1 , left foot, digit #3) for the first scale of the
middle toe of the left foot and 1 R3 for the right foot. Subsequent
scales were designated 2L3, 2R3, etc. depending on how many
rows of scales were discernible.

Results

Evaluation of photographs taken of the dorsum
of the middle toes of 15 Peregrine Falcons and 25
Red-tailed Hawks clearly showed that the scale
patterns of each bird differed from the corres-
ponding scale arrangement of all other birds (Fig.
1-4). The number of scale rows varied between the
2 species studied. The evaluation included compari-
son of 2 sibling (male) Red-tailed Hawks (Fig. 3) and
4 sibling (3 females, 1 male) Peregrine Falcons (Fig.
1 and 2 showing related females E.S., C.F., L.B.).
Comparison between right and left foot of each
individual bird further revealed that scale patterns
were never identical.

Birds which were available the year following the
first evaluation and had completed a full molt of
their plumage were re-evaluated and shown to have
unchanged scale patterns in 2 successive years (Fig.
1 and 4).

Obvious differences for scale patterns for Pereg-
rine Falcons were frequently noted between rows 6
to 8 and commonly between rows 11 to 18 and
beyond. The differences in the scales of rows 1-5
and 9 and 10 were more subtle relating primarily to
scale size and the ratio of width to length (Fig. 1 and
2). Readily visible differences of scale patterns for
Red-tailed Hawks started at rows 5 or 6 and re-
mained distinct for all following rows (Fig. 3 and 4).

Discussion

The principal objective of this study was to de-
velop an identification system for Peregrine Fal-
cons. It was important that the system be simple and
could be used for identification of individual birds.
Red-tailed Hawks were included primarily because
they are a common raptor with a prominent foot
scale pattern and were readily accessible for study
through the raptor rehabilitation facility at
Washington State University.

All birds were identified by the use of photo-
graphy and by visually comparing the scale patterns

67

Raptor Research 18(2):67-71

68

Erik H. Stauber

Vol. 18, No. 2

Peregrine Falcon

C.F.

Right Foot

Peregrine Falcon

E.S.

Right Foot

Summer 1984

Raptor Identification

69

Peregrine Falcons

Figure 2.

70

Erik H. Stauber

Vol. 18, No. 2

Red Tailed Hawks

22555-033
Left Foot

22555-034
Left Foot

Figure 3.

Summer 1984

Raptor Identification

71

Red Tailed Hawk 8411-131

Left Foot

Figure 4.

and shapes of only the middle toe of both feet. In
most instances, a mere glance at the scale patterns
revealed distinct differences between left and right
middle toe of individual birds as well as any 2 birds
(including siblings) and these differences remained
constant over an extended period.

While it was not difficult to identify birds by
photography of the toe scale pattern, it became
apparent that magnification of feet and scales was
not always uniform since the camera was held at
varying distances and angles in the first year of the
study. For purposes of this study, measurement of
scales was considered unimportant, but scale size
and dimensions should certainly be considered in
perfecting a reliable identification system. This
could be accomplished by making a clay print or by
placing the foot on a grid with known dimensions.
A study exploring the use of some techniques which
will yield a good estimate of the scale size and di-
mensions is currently underway.

The availability of a reliable identification system
for Peregrine Falcons would be of considerable
value in light of the status which this bird has oc-
cupied in the history of civilization, in general, and in
its contemporary management in particular. Pro-
per identification of individual Peregrines held in
captivity has been a concern of state and federal

wildlife officials for many years. Illegal substitution
of lost or deceased birds by replacement of federal
bands or the switching of federal bands on stolen
birds has been known to occur but nearly impossi-
ble to prove. The system of identification described
herein would preclude the substitution of one fal-
con for another and thereby greatly facilitate the
management of Peregrine Falcons held in captivity
or other bird species to which the system would be
applicable. Regardless of whether analysis of foot
scale patterns by photography or another system
will prove to be the simplest and most feasible ap-
proach to the identification of Peregrine Falcons
(and other birds), a “footprinting” system offers
great promise to document the uniqueness of a
raptor so identified.

Acknowledgments

The author acknowledges the assistance of Dennis Cancellare
and Jerry McCollum (photography), Amy Werner (medical illus-
trator), arid William Geoffroy and Lester Boyd for their sugges-
tions. This study was supported in part by funds from the Ag-
ricultural Experiment Station, University of Idaho, Moscow. Pub-
lished with the approval of the Director of the Idaho Agricultural
Experiment Station, Moscow, as Research Paper No. 83819.

Department of Veterinary Sciences and WOI Regional Program
in Vet. Med. Ed., Univ. of Idaho, Moscow, ID 83843.

Received 30 March 1984; Accepted 25 June 1984.

PSEUDOMEMBRANEOUS GASTRITIS COMPATIBLE WITH ( Clostridium sp.)
IN A CAPTIVE PEREGRINE FALCON

James H. Enderson and Morgan Berthrong, M.D.

Abstract - There have been several instances where the Peregrine Falcon (Falco peregrinus) used for captive-
breeding for many years have died rapidly after being removed from the breeding lofts (W. Burnham, J. Weaver, C.
White pers. comm.). This is an account of such an instance where the benefit of a complete necropsy is available and
reveals one possible explanation for these losses.

A female Peregrine in captivity over 19 y had
produced nearly 100 eggs during the last 10 y while
in the loft with a male. Because no eggs were pro-
duced in the last year the bird was hooded and
transported to a new location. She appeared calm
after subsequently consuming a portion of a thawed
quail. She seemed relaxed and normal the next
morning, but at 1000 h was lethargic. By 1200 h she
was breathing heavily and rapidly, and was very
weak. She died within the hour.

Pathologic Observations

Complete autopsy revealed a good state of nutri-
tion. Body weight was 860g. The lateral air sacs
were smooth and glistening without parasitic
worms or fungi. The oral cavity, crop, esophagus,
trachea, lungs and heart were entirely normal. The
stomach was empty and contracted with resulting
thickening of its mucosal folds. A gray-green exu-
date was adherent to the mucosl surface. No ulcer-
ations were noted. The remainder of the intestinal
tract was grossly normal. The adrenal glands were
smaller in comparison to a wild peregrine. The
spleen was slightly enlarged. The ovary was small
and nodular without developing ova. The kidneys,
pancreas, and brain appeared grossly normal.

Histologic examination revealed a fibrinopuru-
lent layer which covered the gastric mucosa where
only the most superficial mucosal cells were necro-
tic and only a superficial mucosl infiltrate of in-
flammatory cells was observed. The mucosal capil-
laries were dilated. Gram stains revealed swarms of
gram positive rods, large, straight with slightly
rounded ends and numerous oval subterminal and
central spores, characteristic of a clostridial species
within the fibrinopurulent membrane (Fig. 1 and
2). These organisms were not found in the mucosa
itself or in the muscularis of the stomach. Large
numbers of bacilli, mostly gram positive and similar
to those in the stomach, were found in the lumina of
both small and large intestine but no mucosal alter-
ations or pseudomembranes were seen. The spleen

showed plasmacytoid cells in the red pulp consis-
tent with an immunologic reaction, a so-called
“acute splenic tumor”.

Kidney sections showed small cysts of a possible
congenital cystic disease but large areas of normal
glomeruli and tubules suggested normal renal suf-
ficiency. Minimal osteoarthritis was found in the
upper humeral joint surface. A small para-adrenal
microscopic nodule was found, thought to be a be-
nign neoplasm resembling a human neoplasm
known as a carcinoid. Several cysts were found in
one of a number of sections of skeletal muscle rec-
ognized as those of quiescent avian malaria, possi-
bly Plasmodium relictum. These cysts were not sur-
rounded by any tissue reaction and the liver, spleen,
bone marrow and heart showed no evidence of
active malaria.

Discussion

The development of a pseudomembranous en-
terocolitis of the intestinal tract with toxic shock,
often fatal, has been well recognized in man
(Goulston et al. 1965). It was known to occur during
the post-opertive period, usually after abdominal
surgery, before the advent of antibiotics. Presuma-
bly because of an alteration of the bacterial envi-
ronment, pseudomembranous enteritis or colitis
became much more common after widespread use
of antibacterial agents in man. At first, cases may
have been the result of highly virulent staphylococci
but in recent years evidence indicates that most
human cases are now the result of overgrowth of
clostridial species in the gastrointestinal tract
(Bartlett et al. 1978). Epidemics of this condition
occurred in Germany immediately after World War
II (MacLenan 1962), and in New Guinea (Murrell et
al. 1966) from Clostridium perfringens , presumably
due to ingestion of food massively contaminated
with this organism. Recently, most human cases
have been shown to be the result of overgrowth of
the antibiotic-resistant Clostridium difficile, the
exotoxin of which has a potent cytotoxic effect and

72

Raptor Research 18(2):72-74

Summer 1984

Gastritis in Peregrine Falcon

73

Figure 1 . Low power photomicrograph of gastric mucosa
covered by a fibrinopurulent pseudomem-
brane containing swarms of bacteria but with
only superficial erosion of the glands.

after absorption has frequently lethal action (George
et al. 1978). Most human cases are seen in patients
on antibiotics, after serious surgical procedures, in
newborn infants, and in patients in whom, for many
different reasons, immunosuppression exists. Es-
sentially identical pseudomembranous enterocolitis
can be produced experimentally in rabbits (Kataet
al. 1978) and hamsters (Rifkin et al. 1978). This
falcon developed acute pseudomembranous gas-
tritis histopathologically identical to human cases.
That the bird died of resulting clostridial toxemia is
suggested although not confirmed by culturing the
suspected etiologic agent. It is possible the falcon
ingested food with large numbers of clostridial or-
ganisms, a bacterium known to multiply with great
rapidity under proper circumstances and that the
stress of moving led to the rapid growth of those
organisms in the gastrointestinal tract resulting in
pseudomembranous gastritis. It is of interest that
some birds and mammals are known to carry C.
difficile in the intestinal track (McBee 1960).

Of some clinical importance, while most clostri-
dial species are susceptible to penicillin, C. difficile is

Figure 2. High power photomicrograph of the
pseudomembrane with large grampositive
rods characteristic of a clostridial species.

sensitive only to Vancomycin. Furthermore, the
oral administration of cholestyramine resin, which
apparently binds the toxin in the lumen of the gut,
has proven efficacious in human cases of
pseudomembranous gastronintestinal disease due
to Clostridium difficile (Kreutzer and Mulligan 1978).

Literature Cited

Bartlett, J.G., Chang, T.W., Gurwith, M., Gorbach,
S.L. and Onderdonk, A.B. 1978. Antiobiotic-
associated pseudomembranous colitis due to toxic
producing Clostridia. N. Eng. J. Med. 298:53 1-4.

George, R.H., Symonds, J.M., Domock, F., et
al. 1978. Identification of Clostridium difficile as a
cause of pseudomembranous colitis. Brit. Med.
J. 1:695. >

Goulston, S.J.M. and V.J. McGovern. 1965.
Pseudomembranous colitis. Gut 6:207-212.

Katz, L., J.T. Lamont, J.S. Trier, E.B. Sounenblick,
S.W. Rothman, S.A. Broitman and S. Rieth.
1978. Experimental Clindamycin-associated colitis in
rabbits. Gastroent. 74:246-252.

Kreutzer, E.W. and F.D. Mulligan. 1978. The treat-
ment of antibiotic-associated pseudomembranous col-
itis with cholestyramine resin. The Johns Hopkins Medi-
cal Journal 143:67-72.

MacLennan, J.D. 1962. The histotoxic Clostridial in-
fections of man. Bac. Rev. 26:177-276.

McBee, R.H. 1960. Intestinal flora of some Antarctic
birds and mammals./. Bacteriology 79:311-312.

Murrell, T.G.C., L. Roth, J. Egerton and P.D.
Walker. 1966. Pigbel: enteritis necroticans. Lancet
1:217-222.

Rifkin, G.D., J. Silva and R. Fekety. 1978. Gastroint-
stinal and systemic toxicity of fecal extracts from
hamsters with clindamycin-induced colitis. Gastroent
74:52-57.

Department of Biology, The Colorado College, Colorado
Springs, CO 80903. Address of second author: Penrose Hos-
pital, 2215 N. Cascade Ave., Colorado Springs, CO 88907.

Received 12 November 1983; Accepted 15 August 1984

BIOTELEMETERED DAILY HEART RATE CYCLES IN THE
RED-TAILED HAWK (Buteo jamaicensis)

David E. Busch , William A. deGraw and N.C. Clampitt

Abstract - Daily fluctuations in resting heart rate (HR) were studied in a captive ? Red-tailed Hawk (Buteo jamaicensis)
using radiotelemetry. HR’s were recorded hourly during 10 consecutive days while the hawk was housed in an outdoor
pen. Daytime HR’s averaged 202 beats/min and were significantly higher than the average nocturnal HR of 134
beats/min (P<0.001). Maximum HR’s ( >200 beats/min) occurred crepuscularly, just after sunrise and before sunset.

Daily cycles of several physiological factors have
long been known for a number of birds and mam-
mals. In birds for example, marked nocturnal de-
pression of body temperature has been de-
monstrated in Snowy Owls (Nyctea scandiaca ) and
Short-eared Owls (Asio Jlammeus) by Irving (1955).
Odum (1941) commented on the marked changes
in heart rate (HR) occuring between day and night
in avian species. Smith et al. (1976) reported that
telemetered HR is lower and less variable during
darkness in the domestic Mallard Duck ( Anas
platyrhynchos ). One method, that of telemetered
HR, allows physiological study of unrestrained
birds under near-natural conditions. This method
has also been promoted as a suitable indicator of
relative metabolic rate in homeotherms (Johnson
and Gessaman 1973; Gessaman 1980).

Indications that HR can be a good relative
metabolic indicator come from studies in which HR
and O2 consumption were measured simultane-
ously (Morhardt and Morhardt 1971; Lund and
Folk 1976). Similarities between HR-ambient
temperature curves and metabolism-ambient
temperature curves have been demonstrated for
birds such as the Burrowing Owl (Athene cunicularia)
(Coulombe 1970) and Blue-winged Teal (Anas dis-

cors) (Owen 1969). Because of circulatory adjust-
ments occurring during more intense locomotor
activity, HR is only considered a valid metabolic
indicator when an animal is unstressed and at rest,
or exercising moderately (Jones and Wang 1976).
We have used telemetered HR’s to demonstrate
stress in the Ferruginous Hawk (Buteo regalis)
(Busch et al. 1978), but in order to use HR as a
metabolic indicator, activity levels must be low and
stress minimal.

Little of the aforementioned types of research
have focused on birds of prey in spite of the em-
phasis on raptor conservation, rehabilitation and
captive breeding. Our goal was to assess diurnal
fluctuations in resting HR’s of the Red-tailed Hawk
via telemetry. Changes in HR were also compared
with time of day and with extrinsic factors such as
ambient temperature and elevation of the sun.

Methods

The subject of this study, a $ Red-tailed Hawk, was considered
non-releasble by rehabilitation personnel because of an unmend-
able broken wing. This disability did not conflict with the study’s
goals since the bird’s feeding and perching were not affected, and
since our focus was on daily variations in resting HR.

The hawk was maintained in an outdoor pen measuring 56 m2

74

Raptor Research 18(2):74-77

Summer 1984

Red-Tailed Hawk Heart Rate

75

Figure 1. (A) Mean heart rates (HR) and (B) mean ambient temperatures during 10 consecutive days of recording.
Vertical bars depict standard deviations for each hourly sample period (n = 10 d).

located on the Allwine Prairie Preserve of the University of Neb-
raska at Omaha. Sources of disturbance were few at this rural site.
A small building adjacent to the pen provided portholes for ob-
serving the bird, as well as electrical power and housing for the
recording instruments. The desirability of such conditions was
highlighted by Owen (1969) who measured significantly higher
HR’s in Blue-winged Teal under semi-natural conditions than
under controlled laboratory conditions. Food for the hawk con-
sisted of freshly killed laboratory rats placed in the cage at ran-
domly selected times which did not coincide with hourly data
collection.

Electrocardiogram electrodes were surgically implanted on the
pleural surface of the bird’s sternum through a mid-line abdomi-
nal incision, using a modification of the method of Sawby and
Gessaman (1974). Leads from these electrodes provided the input
to a Narco FM 1 10-E4 HR telemetry transmitter. The transmitter,
packaged in dental acrylic and worn by the bird as a “backpack”,
weighed 109g with its harness. The transmitter assembly weighed
7.5% of bird’s body wt (1.45 kg). This was within the 10% limit
considered valid for electrocardiogram telemetry devices (Gessa-
man 1973).

The telemetered signal was detected with a Narco FM 1100-7
receiver. A switching device was designed to record a 2-min seg-
ment from each h of the day. This device also operated a tape
recorder on which data were recorded in digital format as audible
“clicks.” Each click represented 1 QRS complex from the elec-
trocardiogram (1 heart beat). High heart rates made counting

audible clicks impractical so these data were coverted to an
analog format using a Physiograph Cardiotach. The resulting
chart records were analyzed to determine X HR for each 2-min
sampling period, and to evaluate changes between hourly X HR’s
for more than 240 sample times. Data were collected continuously
for 10 d between 9 and 18 April 1977. During this period daily X
max. temp, was 24.1 ± 3.7°C (n = 10), while the X min. temp, was
12.4 ± 3.1°C (n— 10).

Results and Discussion

The pattern of changes in X HR is displayed in
Fig. 1 A. The bimodality of the cycle, exemplified by
2 daytime peaks, prevented the use of sophisticated
biorhythm analysis. However, simpler methods
such as t-Tests are considered sufficient to de-
monstrate existence of daily biological cycles
(Koukkari et al 1974). In this instance, one way
ANOVA confirmed the existence of highly sig-
nificant variation in HR (F=6.589; df = 23, 216;
P<0.001). Furthermore, the diurnal X HR (202
beats/min) for the 14 h between sunrise and sunset
was significantly greater than the nocturnal X (134
beats/min) (t-Test, P<0.001). Resting HR’s were

76

Busch, DeGraw, Clampitt

Vol. 18, No. 2

highest in periods just after sunrise and just before
sunset.

Variability (i.e., standard deviation) in instan-
taneous HR was greatest near sunrise and sunset
(Fig. 1A). For example, the average coefficient of
variation was 80% between 0600-0900 but was only
28% during mid-day (1000-1400). Bartlett’s test re-
vealed highly significant heterogeneity in variances
(P<0.001). Hourly changes in X HR were also
greatest in the early morning and late afternoon.
When hourly changes in HR’s during the 5 h
around sunrise (0500-1000) were grouped with
those during the 5 h near sunset (1500-2000), mean
changes in HR for these 10 h were significantly
greater (P<0.01) than changes during the other 14
h of the day.

Although daily metabolic or HR cycles are not
unusual for raptors (Coulombe 1970), bimodal
patterns such as reported herein have been de-
scribed infrequently (Nastosescu et al. 1975). The
adaptive value of this crepuscular HR pattern is
somewhat puzzling.

Parallel changes in X HR’s and X ambient temp
should not be regarded as a casual relationship,
despite the well-established inverse relationship
between avian metabolism and air temp outside of
the thermoneutral zone. There is strong evidence
that metabolic rhythms are more closely linked to
photoperiod (Folk 1974) and that daily changes in
HR coincide somewhat with those of ambient temp
only because of their common relationship to solar
periodicity. The distinctly bimodal peaks we ob-
served contrast with the curve for ambient temp
(Fig. IB).

The possibility that higher heart rates near sun-
rise might represent elevation of metabolic rate re-
quired to raise the bird’s body temp from a slightly
torpid nocturnal condition was examined using the
Van’t Hoff relationship. Assuming a Qio equal to
2.3, we calculated that a difference of 4.95°C would
be required to account for the difference between
nocturnal and daytime X HR. A change in body
temp of this magnitude is unlikely in view of reports
of body temp cycles in large raptors (Coulombe
1970; Gessaman 1978) and would not explain the
evening peak at all.

We might expect to find an explanation for the
bimodal pattern in HR in Buteo behavior, however
Red-tailed Hawks do not seem especially crepus-
cular in their activities in the wild. Their soaring
activity is greatest near midday when thermal con-

vective currents are most favorable (Henty 1977).
For most buteos many potential prey species are
crepuscular. Since the foraging success of Red-
tailed Hawks has been linked to behavior of prim-
ary prey species (Stinson 1980), the possibility can-
not be discounted that the HR cycle demonstrated
here parallels activity patterns of prey.

Acknowledgements

This research was completed by the senior author in partial
fulfillment of the requirements for the M.A. degree in Biology at
the University of Nebraska at Omaha. It was made possible by the
cooperation of the Raptor Rehabilitation Society, Lincoln, Neb-
raska, and assistance from R.A. Lock of the Nebraska Game and
Parks Commission. We are particularly indebted to L. Phillips who
assisted with surgery and to L. Simmons, Director of the Henry
Doorly Zoo, Omaha, NE, who generously provided facilities and
support equipment for the surgery.

Literature Cited

Busch, D.E., W.A. deGraw, and N.C. Clam-
pitt. 1978. Effects of handling-disturbance stress on
heart rate in the Ferruginous Hawk ( Buteo regalis ).
Raptor Res. 1 2:(3 14) 122-1 25.

Coulombe, H.N. 1970. Physiological and physical as-
pects of temperature regulation in the Burrowing Owl
(Speotyto cunicularia). Comp. Biochem. Physiol. 35:307-
337.

Folk, G.E. 1974. Environmental Physiology. Lea and
Feibiger. Philadelphia. 452 p.

Gessaman, J.A. 1973. Ecological Energetics of
Homeotherms. Utah State University Press. Logan.
155 p.

1 97 8. Body temperature and heart rate of

the Snowy Owl. Condor 80:243-245.

1980. An evaluation of heart rate as an

indirect measure of daily energy metabolism of the
American Kestrel. Comp. Biochem. Physiol. 65A:273-
289.

Henty, C.J. 1977. Thermal soaring of raptors. Brit.
Birds 70:471-475.

Irving, L. 1955. Nocturnal decline in the temperature
of birds in cold weather. Condor 57:362-365.

Johnson, S.F., and J. A. Gessaman. 1973. An evaluation
of heart rate as a monitor of free-living energy
metabolism. In: Ecological Energetics of
Homeotherms, J. A. Gessaman, Utah State University
Press. Logan. 155 pp.

Jones, D.L., and L.C.H. Wang. 1976. Metabolic and
cardiovascular adaptations in the western chipmunks,
genus Eutamius. J. Comp. Physiol. 105:219-231.
Koukkari, W.L., S.H. Duke, F. Halberg, and J.K.
Lee. 1974. Circadian rhythmic leaf movements; a
student exercise in chronobiology. Chronobiologia
1:281-302.

Short Communications

77

Lund, F.L. and G.E. Folk. 1976. Simultaneous mea-
surement of heart rate and oxygen consumption in
Black-tailed Priarie Dogs ( Cynomys ludovicianus) . Comp.
Biochem. Physiol. 55:201-206.

Morhardt, J.E., and S.S. Morhardt. 1971. Correla-
tions between heart rate and oxygen consumption in
rodents. Am. J. Physiol. 221:1580-1586.

Nastosescu, Gh., I. Ceausescu, Gh. Ignat, and A.
Vadineanu. 1975. Ritmul circadian al metabolis-
mului energetic la Anas platyrhynchos . St. Si Cere. Biol.,
Seria Biol. Anim. 27(2): 131 -135.

Odum, E.P. 1941. Variations in the heart rates of birds; a
study in physiological ecology. Ecological Monographs
11:299-326.

Owen, R.B. 1969. Heart rate, a measure of metabolism
in the Blue-winged Teal. Comp. Biochem. Physiol.
31:431-436.

Sawby, S.B., and J.A. Gessaman. 1974. Telemetry of
electrocardiograms from free-living birds: a method
of electrode placement. Condor 76:479-481.

Smith, F.N., C. Peterson and K. Thigpen. 1976. Body
temperature, heart rate, and respiration rate of an
unrestrained domestic Mallard Duck (Anas platyrhincos
domesticus). Comp. Biochem. Physiol. 53:19-20.

Stinson, C.H. 1980. Weather-dependent foraging suc-
cess and sibling aggression in Red-tailed Hawks in
central Washington. Condor 82:76-80.
Wooley,J.B.,Jr., and R.B. Owen. 1977. Metabolic rates
and heart rate-metabolism relationships in the Black
Duck (Anas rubripes). Comp. Biochem. Physiol. 57A:363-
367.

Departments of Biology and Chemistry, University of Nebraska
at Omaha, Omaha, Nebraska 68182-0040. Current address of
first author: Bureau of Reclamation, Box 427, Boulder City,
NV 89005.

Received 17 May 1983; Accepted 10 April 1984

Short Communications

Status of a Population of Bald Eagles Wintering in Western Connecticut

Steven D. Faccio and Howard I. Russock

In a previous study (H.I. Russock, Raptor Research
13(4): 112-115, 1979) a population of 4 Bald Egles
(Haliaeetus leucocephalus) was observed on wintering
grounds in western Connecticut during the winter of
1976-1977. The eagles congregated below a hydroelectric
dam on the Housatonic River. The dam’s generators kept
the otherwise frozen river open and killed or injured large
numbers of fish which the eagles preyed upon. This paper
presents the results of subsequent observations made
during the winter of 1 982- 1 983 on the same population of
eagles which grew to 17 individuals.

Eagles were observed in the vicinity of the Shepaug
Hydroelectric Dam, Housatonic River, approximately 4.6
km north of Newtown, Connecticut. Above the dam, and
created by it, is Lake Lillinoah with a surface area of 769
ha. Directly west, across Lake Lillinoah, is the Upper
Pauggessett State Forest extending for 3 km north along
the western shore of the lake. On the south side of the
river, below the dam, is a large privately owned wooded
hillside where eagles congregated. North, across from the
hillside, is a hydroelectric plant owned by Connecticut
Light and Power Company.

Most observations were made from the top of the dam
and from a canvas blind constructed on the south side of
the river, approximately 25 m from a frequent perching
area. Other observations were made from a road running

parallel to the north side of the river and from several
locations northwest of the dam (when attempting to de-
termine roosting sites). Observations were made with field
binoculars (7x35) and a 600 mm photographic lens and
were results dictated into a taperecorder or handwritten.
A total of 178 h of observation were made between 8
December 1982 and 8 April 1983. Trips were made to the
dam on 52 separate days, 34 of which resulted in sighting
of eagles.

The first eagle observed was on 3 January 1983; 9
observation days in December did not result in any sight-
ings. Eagles were last observed on 24 March 1983; during
6 observation days in late March and early April none
were seen.

Due to unusually mild weather, the Housatonic River
remained virtually free of ice during the entire winter.
Therefore, the departure of eagles could not be corre-
lated with the opening of the river in spring as it was
during the winter of 1976-1977. It was not determined if
the greater availability of open water elsewhere affected
the number of eagles wintering in the vicinity of the
Shepaug Dam. However, due to the abundance of fish at
the dam, it is likely that all eagles wintering in the area
frequented the dam.

Seventeen individuals were positively identified using
plumage characteristics and other outstanding features;

78

Short Communications

Vol. 18, No 2

10 were adults and 7 immature. Eight (4 adults, 4 imma-
tures) were observed frequently from early January to
early or mid-March. Two other immatures were observed
between 6 and 24 February 1983. Seven others (5 adult, 2
immatures) were seen on 1 or 2 observation days each,
between 13 January and 12 March 1983.

Night Roosts — Three night roosts were tentatively
2. 5-7. 5 km north and northwest of the Shepaug Dam. All
3 were located in undeveloped mixed hardwood forest.
The first 2 sites were located by direct observation of
eagles leaving or returning in early morning and early
evening, respectively. The third was located with a police
scanner by tracking a radio-tagged eagle.

Breeding grounds — The 17 eagles wintering in the
vicinity of the Shepaug Dam can be divided into 2 groups,
8 observed throughout the winter and 9 observed over a
period of 1 to 18 d. It is reasonable to assume that the
latter group is made up of transient birds. Three of these
have been traced to breeding areas in Maine. Two imma-
tures observed only during February were identified by
leg bands as hatch year birds from Maine. A third imma-
ture, observed on 1 d in February, had both leg bands and
a backpack transmitter which identified it as coming from
a nest in the Cobscook Bay area of the Main coast. Two
others (1 adult, 1 immature), seen on 1 or 2 d each, also
had leg bands, but could not be further traced.

There is no direct evidence of an active nest in the area.
However, 7 of the 8 eagles observed throughout the
winter could be divided into 2 groups which virtually
always moved as separate units. One group consisted of 2
adults and 1 immature and the other group consisted of 2
adults and 2 immatures. This suggests that there were 2
family groups. The senior author observed a single adult

on 3 separate occasins during the first week of June 1983,
approximately 7 km north of the Shepaugh Dam.

Feeding — Eagles arrived at the dam area 5-15 min
before sunrise; they remained perched until the hy-
droelectric plant smarted operation at 0700 when they
began feeding on fish killed or injured by the plant’s
turbines. Feeding continued for 1-3 h after which the
birds perched or soared over the hills on the south side of
the river. Feeding often resumed in early afternoon be-
fore the birds returned to their roosts.

Eagles were observed making dives to the river to catch
fish on 232 occasions, 170 (73%) of which were successful.
Adults were successful on 103 (75.7%) of 136 attempts
while immatures were successful on 67 (69.8%) of 96
attempts (NS, X2 Test). Fish caught included trout ( Sal -
velinus spp.), bass ( Micropterus spp.), catfish ( Ictalurus spp.),
and shiner ( Notropis spp.).

We thank Connecticut Light and Power Company for
allowing access to their property. We also thank Lawrence
Fisher, Janet Mitchell and Stewart Mitchell for their help
and personal observations of Bald Eagles in western Con-
necticut and Francis Gramlich, NSBERT, for his help in
tracing several eagles to Maine. Dr. Frank Dye and Dr.
Susan Maskel, Western Connecticut State University,
commented on an earlier version of this manuscript.

Department of Biological and Environment Sciences, Western
Connecticut State University, Danbury, Connecticut 06810.

Received 8 March 1983; Accepted 10 May 1984.

* Please send reprint requests to H.I. Russock

Nest Defense by Northern Harriers Against the Coyote in Southwestern Idaho

Leon R. Powers, Timothy H. Craig and John Martin

Predation on Northern Harrier ( Circus cyaneus ) by
Striped Skunk {Mephitis mephitis). Badger (Taxidea taxus ),
foxes ( Fulpes sp.) and Mink {Mustella vision) has previously
been reported. (Craighead and Craighead 1956;
Hamerstrom 1969; Watson 1977). Although Murie
(1940) reported that Coyotes {Canis latrans) prey on the
Short-eared Owl {Asio flammeus), an ecological equivalent
of the Northern Harrier, we are not aware of reports of
Coyote predation on Northern Harriers. Herein we re-
port several Northern Harrier — Coyote interactions ob-
served during 1 98 1 in the Snake River Birds of Prey Study
Area in southwestern Idaho.

On 29 March at 1020, T.C. observed a pair of nesting
harriers perched in a small tree {Crataegus sp.) near a
spring bordering the Snake River. Riparian habitat sur-
rounded the spring for a distance of 15 m with senescent

reed {Phragmites communis) and stinging nettle {Urtica sp.)
the predominant vegetation. Beyond the spring, big
sagebrush {Artemesia tridentala) and June grass {Bromus
tectorus) covered the nearby canyonside. Shortly, the
female harrier flew from the tree followed by the male,
and both began emitting a call usually associated with
agnostic displays. The male then started diving repeatedly
at the edge of the riparian growth. By the male’s changing
position it was obvious that the object of his dive was
moving toward the center of the riparian vegetation. As
the hawk completed a dive, a Coyote rose on its hind legs
above the vegetation and snapped its jaws at it. The
Coyote again attempted to grab the harrier, and then
stopped with his back visible. It appeared that it was mov-
ing its head near the ground as if eating. The female
harrier circled and called overhead while the male con-

Summer 1984

News and Reviews

79

tinued to call and dive, although not as closely. After about
5 min, T.C. approached the spring and the coyote fled
with the male harrier in close pursuit, diving with both
feet swung forward attempting to grab the coyote. A
single, pale-blue, harrier egg was found in the nest at the
spot where the coyote had appeared to be eating. Both
harriers circled and called over the human intruder but
neither dived. A single adult male harrier was observed
near the nest area on 24 April but on 2 subsequent visits no
birds were seen. On 7 July the nest was visited again and
only a few bits of egg shell were found; however, no
harriers were present.

On 30 May at 1146 L.P. observed a male harrier escort a
Golden Eagle ( Aquila chrysaetos) from the harrier’s territ-
ory. The harrier circled back toward its nest in a shallow
undulating flight and began to vocalize and dive at some-
thing on the sagebrush slope above the nest site. As the
male continued its vigorous dives, the object of the attack,
a Coyote, appeared. A female harrier soon began circling
over the area, occasionally making shallow dives at the
Coyote. Shortly, a second male harrier flew into the area
from a neighboring nesting territory to the east andjoined
the pair. The second male appeared to “sky dance”
(Hamerstrom 1969) around the female at first but soon
began to vocalize and dive at the Coyote also. The Coyote,
followed by the defending hawks, gradually moved out of
view toward the neighboring harrier territory. At 1 155 a
male harrier reappeared from the east and soared above
the original harrier’s territory.

Later that day at the same harrier territory, a male flew
across the river from its nest area and dove several times at
a Coyote that trotted eastward. After 1 to 2 min the harrier
veered off, perched on a sagebrush briefly and then flew
at an angle away from the Coyote and intercepted a sec-
ond male harrier which was approaching the Coyote from
the northeast. The first male briefly chased the invading
hawk which attempted to dive at the Coyote. Soon, the
first harrier flew back toward its territory and began to
hunt. Within 5 min he captured a small prey item and
delivered it to his mate at the nest across the river. When
we visited the nest on 7 June, 1 egg and 2 nearly-hatched
nestlings were found. Twenty-seven days later on a sec-
ond visit the nest had been destroyed and only pin feath-
ers of juveniles remained. The adjacent harrier nest to the
east successfully fledged at least 3 young.

J.M. frequently saw Coyotes in the vicinity of harrier
nests on the study area, and observed both male and
female harriers, individually and jointly, diving at

Coyotes. More often the male was the lone defender. As in
the previously described observations, J.M. also observed
a Coyote leap into the air after a defending adult male and
at times observed several harriers cross well defined ter-
ritorial boundaries to pursue a Coyote. Newton (1979)
reports such communal nest defense among Marsh Har-
riers {Circus aeruginosus) . In one location J.M. found a
Coyote den at one end of a large marsh which contained 7
harrier nests. Five of those 7 nests failed, and 3 showed
evidence of Coyote predation.

Although eye-witness accounts of predation at raptor
nests are not common, our observations indicate that
Coyotes do prey on Northern Harrier nests, especially in
desert areas, perhaps where sparse riparian habitat at-
tracts both animals. Furthermore, our report suggests a
danger of leading this predator to harrier grounds nests
by investigator scent trails (Fyfe and Olendorff 1976) as
reported by Craighead and Craighead (1956) for a farm
dog (Canis familiaris) .

We thank Drs. F. and F.N. Hamerstrom for helpful
comments on the manuscript.

Literature Cited

Craighead, F.C. and J.J. Craighead, Jr. 1956. Hawks,
owls and wildlife. Harrisburg, Stackpole Co.

Fyfe, R.W. and R.R. Olendorff. 1976. Minimizing the
dangers of nesting studies to raptors and other sensi-
tive species. Canadian Wildlife Service, Occasional
Paper Number 23.

Hamerstrom F. 1969. A harrier population study.
Pages 367-383. In J.J. Hickey, (Ed.). Peregrine Falcon
Populations: their biology and decline. University of
Wisconsin Press, Madison, Milwaukie, and London.
Murie, A. 1940. Ecology of the coyote in Yellowstone.

U.S. Dept. Int., Natl. Park Serv., Fauna Ser. 4.
Newton, I. 1979. Population ecology of raptors. Buteo
Books. Vermillion, S.D.

Watson, D. 1977. The hen harrier. T. and A. D. Poyser,
Ltd., Berkhamstead, Herts., England.

Department of Biology, Northwest Nazarene College, Nampa,
Idaho 83651. Address of second author: Box 1, Lee Creek
Road, Leadore, Idaho 83464. Address of third author: 6702
East 950 South, Huntsville, Utah 84317.

Received 26 December 1983; Accepted 10 May 1984

NEWS AND REVIEWS

Behavior of Fledgling Peregrines by Steve K. Sherrod; drawings by Karen Lynn Allaben-Confer. 1983. Fort Collins,
Pioneer Impressions, xi + 202 pp., 59 figures, 23 tables. Price $10.00. Available from the Peregrine Fund, Inc., Ithaca, New York.

Peregrine Falcons are renowned for their spectacular aerial broods of fledglings, 2 broods from Australia and 2 from Green-

feats. How they develop this unique behavior is unfolded as 4 land, are followed from first flight to dispersal. The book’s sequ-

80

News and Reviews

Vol. 18, No. 2

ence of chapters follows the development of fledgling behavior.
Initial sections cover simple perch-to-perch flight behavior, fol-
lowed by behavioral descriptions of soaring, stooping, pursuits of
parents and siblings, pursuits of inanimate and animate objects,
play, and development of the ability to kill. Later, types of food
transfers from adults to offspring and various types of aggression
are described. The final section covers the length of post-nestling
dependency, including a discussion of stimulus for dispersal and
parental care during migration.

The 1 overriding observation that leaps out to the reader is the
aggressiveness of the young. Sherrod states “Aggression is a com-
ponent common to the behavioral repertoire of the peregrine, and
it is incorporated into many of the displays of this bird”. A com-
mon phrase “don’t bite the hand that feeds you” is scoffed at by
fledglings. Parents are bitten, footed, bumped off their perches
and chased relentlessly by juveniles seeking food — even when
there is none to be had. Such aggressiveness provides the basis for
the author’s reinterpretation of the “luring” behavior reported by
early observers of peregrine behavior. It has been thought that
when adults flew by their nests with prey they were “luring” their
young to fly from the nest. The author, however, provides many
observations to indicate that adults are simply reluctant to land
because they “fear” being rushed by thier young, bitten, footed or
pushed off the ledge itself.

In addition to fledgling behavior of wild peregrines, extremely
valuable behavioral comparisons were made with broods of
fledglings without parents that are “hacked” from artificial nests.
Most behaviors observed in wild young also recurred in hacked
young but distinctions were present. For example, “Although
hacked fledglings instinctively recognize other raptors, wild
offspring probably learn which predators are an immediate threat
in their natal territory by observing the defensive behavior of their
parents”.

I found this book valuable because it 1) provides a wealth of
background information for future comparative behavioral
studies of congeners, 2) provides a clear picture of the develop-
ment of fledgling peregrine behavior (and associated adult be-
havior) for people who have never had the opportunity to observe
nests, 3) provides descriptions of behavior that fill in gaps of
knowledge for even experienced observers who are not fortunate
enough to observe, uninterruptedly, fledgling behavior from first
flights to dispersal and 4) focused attention on aspects of my own
behavioral observations of peregrines that I did not put into con-

text until after reading the book. For example, while I watched
shorebirds at high tide on 3 November 1975 at the northern end of
Humboldt Bay, California, 2 peregrines flew by and the adult
male captured a small shorebird, Western Sandpiper ( Calidris
mauri) size, killed it, and then dropped it 10 m and recaught it.
Meanwhile the female-struck a shorebird that fell into the water.
She made several passes at it but was unable to pick it up. When the
2 falcons rejoined in flight the male dropped his kill to the female
below him but she failed to catch it. Moments later she captured a
Willet ( Catoptrophorus semipalmatus) sized shorebird but then drop-
ped it into the bay. The male then caught another small shorebird,
carried it out over the bay, accompanied by the female and head-
ing south where they eventually disappeared. After reading
Chapter 9, it occurred to me that what I may have observed was
parental care during migration or, continuation of the adult pair
bond after leaving the nesting cliff, although I could not be sure if
the female was an adult.

Numerous format irregularities were distracting. When I first
opened the book I was immediately struck by the contrast in type
sizes, and then by the narrow margins. The feeling of being
squeezed was further compounded by the narrow bar widths in
Figures 3, 26a & b, 33a-e, and 56. Table and figure captions in the
text are inconsistent with those given at the beginning of the book.
The drawings ranged from excellent to extremely poor. (Fig. 48
looks more like a Potoo (Nyctibius) than a Peregrine. Some figures
seem irrelevant (Figs. 1, 20, 21) and 1 figure (38) appears to have
been printed upside down. The eyes are virtually obscured in all
Peregrine drawings. In defense of the book, however, all drawings
do illustrate what is being demonstrated behaviorally.

The author seemed (understandably) reluctant to summarize
much of his data because juvenile Peregrines show wide variation
in the initiation of a behavior and its expression. Instead, numer-
ous bar graphs are presented to visually depict the variation and
midpoint of the data. A valuable addition would be a single
timeline, summarizing when the mean onset of each behavior
occurs in terms of fledgling age or time on the wing since first
flight.

Despite a few shortcomings in the format, I highly recommend
the work. It has immediate appeal to raptor biologists for be-
havioral descriptions. There is also a broader appeal because
Sherrod makes numerous behavioral correlations between the
offspring of Peregrines and the offspring of mammalian carni-
vores. — Douglas A. Boyce Jr.

Temporary Position - Research Associate - Department of Veterinary Biology, University of Min-
nesota. Ph.D. degree with experience in teaching and research at the college level is required. Must have
experience working with raptors and must be interested in gastrointestinal (GI) physiology and energetics.
Individual who holds or has held a university faculty position is preferred. Duties include conducting
research on regulation of GI function in raptors and assisting in teaching physiology to veterinary medical
students as time permits. Application deadline: 15 November 1984. Position is available for four months
from 1 December 1984 through 31 March 1985. Salary $1,608 per month. Send curriculum vitae and
three references to: Dr. Gary E. Duke, Department of Veterinary Biology, University of Minnesota, 295
AnSci/Vet. Med. Bldg., 1988 Fitch Ave., St. Paul, MN 55108, USA.

The University of Minnesota is an equal opportunity educator and employer and specifically invites and
encourages the applications of women and minorities.

RAPTOR RESEARCH

A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCHFOUNDATION, INC.

EDITOR: Dr. Clayton M. White, Department of Zoology, 161 Widtsoe Building, Brigham Young University, Provo,
Utah 84602

ASSISTANT EDITOR: Mr. Jimmie R. Parrish, Department of Zoology, 159 Widtsoe Building, Brigham Young
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EDITORIAL BOARD: Dr. Fredrick N. Hamerstrom, Jr. (Principal Referee); Dr. Byron E. Harrell (Editor of
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INTERNATIONAL CORRESPONDENT: Dr. Richard Clark, York College of Pennsylvania, Country Club Road,
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INSTRUCTIONS FOR CONTRIBUTORS: Submit a typewritten original and two copies of text, tables, figures and
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Raptor Research

A Quarterly Publication of The Raptor Research Foundation, Inc.

Volume 18, Number 3, Fall 1984

(ISSN 0099-9059)

Contents

The Peregrine Falcon (Falco peregrinus macropus) Swainson in Southeastern

Queensland. G.v. Czechura 81

Spring and Fall Migrations of Peregrine Falcons in Central
Alberta, 1979-1983, with Comparison to 1969-1978.

Dick Dekker 92

Winter Habitat Selection of Diurnal Raptors in Central Utah.

David L. Fischer, Kevin L. Ellis and Robert J. Meese 98

Do Northern Harriers Lay Replacement Clutches?

Robert Edward Simmons 103

Unusual Predatory and Caching Behavior of American Kestrels in Central

Missouri. Brian Toland 107

Short Communications

1981 - An Extraordinary Year for Golden Eagle “Triplets” in the Central Rocky Mountains.

M. Alan Jenkins and Ronald A. Joseph Ill

Food Piracy Between European Kestrel and Short-eared Owl.

Erkki Korpimaki 113

An Unusual Observation of ‘Homing’ to Prey By a Migrating Immature Peregrine Falcon.

Carl Safina 115

News and Reviews 91, 97, 102, 115, 1 16

The Raptor Research Foundation, Inc.
Provo, Utah

THE RAPTOR RESEARCH FOUNDATION, INC.
(Founded 1966)

OFFICERS

PRESIDENT: Jeffrey L. Lincer, Office of the Scientific Advisor, 2086 Main Street, Sarasota, Florida 33577

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BOARD OF DIRECTORS

EASTERN DIRECTOR: James A. Mosher, Appalachian Environmental Laboratory, University of Maryland,
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CENTRAL DIRECTOR: Patrick T. Redig, Department of Veterinary Biology, 295 Animal Science/ Veterinary
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MOUNTAIN 8c PACIFIC DIRECTOR: A1 Harmata, Department of Biology, Montana State University, Bozeman,
Montana 59717

EAST CANADA DIRECTOR: David M. Bird, Macdonald Raptor Research Centre, Macdonald Campus of McGill
University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Quebec H9X ICO

WEST CANADA DIRECTOR: R. Wayne Nelson, 4218 -63rd Street, Camrose, Alberta T4V 2W2

INTERNATIONAL DIRECTOR: Martin Bottcher, Postfach 2164, Steinfelder Strass 11, 5372 SCHLEIDEN,
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DIRECTOR AT LARGE #2: Tom Dunstan, Department of Biological Sciences, Western Illinois University, Macomb,
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DIRECTOR AT LARGE #3: Mark R. Fuller, U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center,
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Send requests for information concerning membership, subscriptions, special publications, or change of address to
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Published quarterly by The Raptor Research Foundation, Inc. Business Office: Gary E. Duke, Treasurer, Depart-
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Utah. Printed in U.S.A.

RAPTOR RESEARCH

A QUARTERLY PUBLICATON OF THE RAPTOR RESEARCH FOUNDATION, INC.

VOL. 18

Fall 1984

No. 3

THE PEREGRINE FALCON (Falco peregrinus macropus ) Swainson
IN SOUTHEASTERN QUEENSLAND

G. V. CZECHURA

Abstract - Most studies of Peregrine Falcon ( Falco peregrinus) biology have been conducted in Europe and North
America (Hickey and Anderson 1969; Ratcliffe 1980; Cade 1982). Information concerning southern hemisphere
Peregrines is restricted to the studies of Clunie (1972, 1976) on Fiji, reviews by Cade (1969), Brown (1970) and Steyn
(1982) of African populations, while Chaffer (1944), Jones and Bren (1978), Norris et al. (1977), Olsen and Olsen (1979),
Olsen et al. (1979), Olsen (1982), Pruett-Jones et al. (1981 a, b), Walsh (1978) and White et al. (1981) provide important
contributions for Australia.

Declines in some nothern hemisphere popula-
tions due to the effects of pesticides (Hickey 1969;
Bijleveld 1974; Newton 1979; Ratcliffe 1980; Cade
1982) have served to focus considerable attention
on the distribution and dynamics of regional Pereg-
rine Falcon {Falco peregrinus) populations. Concern
has been expressed about the potential affects of
pesticides on populations of this falcon within Au-
stralia (Olsen and Olsen 1979, 1981; Pruett-Jones et
al. 1981b). Existing studies on the status of the
peregrine within Australia have been conducted in
the southeastern corner of the continent (Olsen and
Olsen in press) and little is known of the status of
northern and western populations. The following
reviews the present state of knowledge of the
peregrine in southeast Queensland. A more
detailed, long-term study is underway.

Materials and Methods

Information for this review was obtained from Queensland
Museum records, literature, and previously unpublished obser-
vatios of both myself (1968 to present) and others. Geographic
units referred to as southeastern Queensland and Moreton and
Wide Bay — Burnett region follow Roberts (1979) and Mather
(1976), respectively. Note that a bias toward the Moreton region
exists - reflecting distribution of observers. Sufficient information
is available for the presentation of a broad outline of distribution,
breeding, hunting and conservation problems of peregrines over
southeastern Queensland as a whole. Vegetation terminology
follows Groves (1981).

Distribution

Peregrine Falcons have been recorded over
much of southeastern Queensland (Fig. 1 ; Table 1).
In addition, they have been recorded in the im-

mediate vicinity of the regional boundary (Broad-
bent 1889; Barnard and Barnard 1925; Longmore
1978; Passmore 1982). Vegetation type appears to
exert little or no influence on the overall distribu-
tion here, as closed-forests, open-forests, wood-
lands, wetlands and agricultural areas are all fre-
quented by falcons. For example, Dwyer et al.
(1979) recorded peregrines from 8 of 12 habitat
types found across Cooloola. The vegetation types
represented here included vine forest, various
forms of open forest and woodland as well as heath,
herb and sedgeland. Wide occupation of vegetation
types has been noted also in the Rockhampton area
to the north (Longmore 1978).

Vernon (1976) and Roberts (1979) both note that
peregrines favour mountainous areas with exten-
sive cliffs and rocky outcrops. Examination of re-
cords used to construct Fig. 1 indicates that this is
essentially correct with some modification. Cer-
tainly peregrines are well represented in moun-
tainous areas as they have been seen on 1 1 of the 14
major mountain systems. However, they are also
frequently observed in coastal districts where they
may be locally abundant (Cooloola; Roberts and
Ingram 1976). Examination of inland localities
where peregrines are regularly encountered indi-
cates an association with cliffs, gorges, and out-
crops. Similarly, coastal records involve areas where
eroded high dunes/coastal cliffs (Fraser, Moreton
and North Stradbroke Islands), subcoastal high-
lands (MacPherson Range-Gold Coast) or isolated
peaks (Mt. Cooroy-Peregian, Pumicestone Passage -
Glasshouse Mountains) are found nearby.

81

Raptor Research 18(3):81-91

82

G.V. CZECHURA

Vol. 18, No. 3

Figure 1. Distribution of Falco peregrinus macropus in southeastern Queensland based on both published and unpub-
lished sightings.

Breeding, Density and Movements

Twenty-four active eyries (eggs and/or adults
plus young present) are known from southeastern
Queensland. In addition, several areas containing
suspected eyries have yet to be examined and 1
eyrie previously known to be active was inactive.
Most eyries were located within major range sys-
tems although 6 outlying sites are known. With the
exception of 1 eyrie located on a high coastal
foredune, vertical or subvertical rock faces along
exposed cliffs or along gorges were utilized. Rock
faces were variously composed of granite, trachyte,
basalt or sandstone. The dune nest was situated on
exposed sandrock-fossil hardpan. Individual eyries
were placed on ledges, crevices or shallow caves
(Fig. 2 A,B) between 30-270 m above ground level.
The surrounding vegetation was either subtropical
rainforest, open-forest or woodland.

Most eyries appeared to have been active for
some time. One located within the northern More-
ton region was active since the early 1940’s, al-
though peregrine records within this area indicate
at least 50 yr occupation of the site. Activity as-

sociated with another Moreton region eyries indi-
cates that it has been active for about 60 yr. The
earliest records available for the southern Moreton
region are from the early 1940’s, and mid-1950’s
for the western Moreton region. Only very recent
records are available for the Wide Bay-Burnett re-
gion.

Observations made wihin the northern Moreton
region suggest that breeding starts mid- August or
early September. Beruldsen (1980) records a nest-
ing season of “July to October, sometimes
November in the south, and April to June in the
north”. The earliest known egg-laying occurred in
late July (1980) and the latest early November
(1968). The latter cases appears somewhat anoma-
lous and may represent either a late breeding or a
replacement clutch. Display was noted during Oc-
tober and 2 fledglings were present during De-
cember. Little activity had been detected during
September of that year. Pre-egg-laying display
flights were typical of those used by peregrines
elswhere and consists of mixtures of components
such as High-circling, Figure-of-eight, Flight-
rolling and Z-flight (Cramp and Simmons 1980;

Fall 1984

Peregrine Falcon in Queensland

83

Table 1. Summary of available published sightings of Peregrine Falcons in Southeastern Queensland.

Locality

Source

Callide Dam

Zillman 1974

Sandy Cape

Makin 1968

Fraser Island

Vernon and Barry 1972

Mt. Walsh

Frauca 1970

Maryborough

Anon. 1972, Jones 1981

Auburn River

Darling Downs Naturalist Dec. 1978:43*

Cooloola

Roderick 1975, Roberts and Ingram 1976;
Dwyer et al. 1977

Teewah Creek

Ingram 1972

Noosa Heads

Wheeler 1959 (probable)

Jimna

Q.O.S. July 1978:2*

Kilcoy Shire

McEvoy et al. 1979

Blackall Range

Czechura in press

Maleny

Czechura 1970, Q.O.S. Jan. 1975:2

Conondale Range

Roberts 1977; Czechura in press

Glasshouse Mountains

Jack 1941; Fien 1966; MacArthur 1978

Pumicestone Passage

Mayo 1934; MacArthur 1978

Redcliffe

Q.O.S. May 1974:3

Crows Nest

Q.O.S. Oct. 1977:3

D’ Aguilar Range

Illidge 1923; Vernon 1976

Pinkenba

Q.O.S. Nov. 1982:4

Lytton

Q.O.S. Nov. 1982:2

Bardon

a.S. May 1974:3

Stones Corner

Q.O.S. Nov. 1982:2

Murphy’s Creek

Lord 1956

Pt. Lookout

Q.O.S. May 1977:4

North Stradbroke Is.

Vernon and Martin 1975

Cecil Plains

Q.O.S. June 1979:2

Cooper’s Plains

Q.O.S. March 1976:3

Redwood Park

Q.O.S. July 1978:3

Cunningham’s Gap

Vernon 1976

Dalrymple Ck.

Q.O.S. June 1977:2

Tweed R. District

Keast 1944

Warwick district

Kirkpatrick 1967

Emu vale

Q.O.S. Sept. 1977:2

Stanthorpe

Passmore 1982

Lamington N.P.

Robertson 1948

Binna Burra

Wheeler 1973; Q.O.S. July 1979:4

* Newsletters are cited in table only. ‘Q.O.S.’ refers to Queensland Ornithological Society Newsletter.

Monneret 1974; Ratcliffe 1980). In addition, a
flight termed herein the V-flight, has been ob-
served in which a circling or flying peregrine sud-
denly stoops with wings closed, terminates the stoop
by spreading its wings and regains altitude using a
combination of momentum and flapping flight

(Fig. 3). The speed at which the stoop is terminated
and altitude regained often leaves the impression of
a stoop followed by a ‘bounce’. The V-flight usually
followed a period of High-circling, linear flight or
undirected activity. Several flights may be con-
ducted in quick succession. All display flights were

84

G.V. CZECHURA

Vol. 18, No. 3

C D

Figure 2: A. Ledge eyrie (e), eastern Moreton region; adjacent roosts (r) are also indicated. B. Cave eyrie (2), eastern
Moreton region; perched peregrine (1) and adjacent roosts are indicated. The location of this eyrie is
shown by its entrance. C-D. Peregrine hunting area (approx. 4 km SW Maleny). This area has been
regularly used since 1970. Note different vegetation types present (r- rainforest, t-tall open-forest,
p-pasture, w-regrowth).

Fall 1984

Peregrine Falcon in Queensland

85

Figure 3. The ‘V-flight’ display. The display commences
(A) from earlier circling or similar activity. The
falcon abruptly stoops with wings closed (B),
terminates the flight (C) by spreading the wings
and regains altitude (D) using momentum and
later flapping flight.

accompanied by much vocalization. Copulation
usually occurred late during the display period and
on areas surrounding the nest (ledges, projections
of the cliff-face or adjacent trees).

Little information is available concerning clutch
size. P. Olsen (pers. comm.) has examined 3
clutches ( 1 questionably from sotheastern Queens-
land). All consisted of 3 eggs. Indirect evidence,
such as the number of fledglings at active eyries,
suggests that a clutch size of 3 is usual (G. Geruldsen
pers. comm.; pers. obs.). Typically 2 young fledge
(Table 2). The maximum number of fledglings ob-
served at a number of sites is 3 (pers. obs.; P. Slater
pers. comm.; D. Evans pers. comm.,) suggsting
either high productivity or occasional larger
clutches. Olsen and Olsen (1979) record a mean
clutch size for Queensland peregrines of 2.5 pre-
1947 and 3. 1 post- 1947. Savidge (in Mathews 1916)
records cliff-face nesting in the Clarence River dis-
trict of northeastern New South Wales and col-
lected the following successive clutches from 1 pair

of falcons; 16 August, 3 eggs; 13 September, 3 eggs;
14 October, 2 eggs.

Data from southeastern Queensland appear con-
sistent with similar data from southeastern Au-
stralia. The presumed clutch size of 3 in southeast-
ern Queensland compares favourably with both the
State means (above) and the combined means for
New South Wales, Victoria, South Australia and
Tasmania (pre-1947, 3.0; post- 1947, 2.7; data from
Olsen and Olsen 1979). Olsen (1982) did not find
any significant correlation between clutch size and
latitude, longitude or temperature. Similarly, com-
parison of the mean numbers of fledglings of the 2
Moreton region eyries (2.13, 2.25; Table 2) indi-
cates that these values are within the range for
numbers of young at successful eyries in New South
Wales (2.2), Victoria (2.1), South Australia (2.2) and
Tasmania (2.5) (data from Pruett-Jones et al. 1981 ;
Olsen and Olsen in press).

Pending the completion ot survey work currently
in progress, only approximate values of peregrine
density over the entire region are available. Esti-
mates, based on known pairs in the Moreton region,
indicate a density of about 1 pair/2600 km2, while
taking suspected pairs into consideration a value of
1 pair/ 1500 km2 is suggested. These values com-

Table 2: Fledgling number at 2 adjacent northern
Moreton Region Eyries 1968 - 1982.

Numbers of Fledglings Observed

Year

Eyrie A Eyrie B

1968

2

*

1969

2

*

1970

3

*

1972

3

*

1976

2

*

1977

1

*

1979

2

2

1980

*

3

1981

*

2

1982

2

2

Mean

2.13

2.25

* - No data available

86

G.V. CZECHURA

Vol. 18, No. 3

pare with a density of 1 pair/ 100 km2 for one area
under study. Distances between neighboring eyries
range from 4.8 - 65 km (mean 40.9, N = 221 km).
The above density values are tentative. This un-
certainty reflects the difficulty in locating alternate
nesting sites (e.g., stick nests) in dense forest (rain-
forest, tall open-forest) and poor accessibility to
some highland areas supporting suitable cliff faces.
The current estimates indicate a nesting density
well below that of Victoria (1 pair/600 - 800 km2,
White et al. 1981) and slightly higher than Tas-
mania (Olsen and Olsen in press).

Storr (1983) considers F. p. macropus to be
nomadic and evidently migratory over much of
Queensland. He noted that most records involved

the period April-October. Monthly observations at
several more accessible Moreton region eyries
strongly suggested that breeding birds are rela-
tively sedentary with roosts being maintained
around the eyrie outside the breeding season. Ob-
servations made by Jones and Bren (1978) and
Olsen and Olsen (in press) indicate the same in
southeastern Australia. Hunting is less frequent but
conducted over much the same area as used dur-
ing the breeding season. In general, it seems that
the apparent nomadism of peregrines may be at-
tributable to the inconsicuousness of adults
around eyries outside the breeding season and
movements of immature birds. Locally high de-
nsities have been reported (Elks in Roberts and

Table 3. Prey recorded for the Peregrine Falcon ( Falco peregrinus macropus) in Southeastern Queensland.

Prey Items Source

Insects

Orthoptera

Odonata

Birds

Prion ( Pachyptila sp.

Cormorants ( Phalacrocorax spp.)

Sacred Ibis (Threskiornis aethiopicus)

Black Duck ( Anas superciliosa)

Grey Teal ( Anas gibberifrons)

Australian Kestrel (Falco cenchroides)

Stubble Quail ( Coturnix novaezelandiae)

Brown Quail ( Coturnix australis)

Red-kneed Dotterel (Erythrogonys cinctus)

Red-necked Stint ( Calidris ruficollis)

Feral Pigeon (Columba liva)

Crested Pigeon ( Ocyphaps lophotes)

Bar-shouldered Dove ( Geopelia humeralis)

Rainbow Lorikeet (Trichoglossus haematodus)

Scaly-breasted Lorrikeet (Trichoglossus chlorolepidotus)
Pale-headed Rosella (Platycercus adscitus)
White-throated Needle-tail ( Hirundapus caudacutus)
Black-faced Cuckoo-shrike (Coracina novae ho llandiae)
Lewin Honeyeater (Meliphaga lewinii)

Noisy Friar-bird (Philemon corniculatus)

Noisy Miner (Manorina melanocephala)

Yellow-faced Honeyeater (Lichenostomus chrysops)
Common Starling (Sturnus vulgaris)

P. Slater pers. comm.

Pers. obs.

C. Corben pers. comm.

Mayo 1934

Czechura 1971, pers. obs.

R. Lutkins pers. comm.

R. Lutkins pers. comm.

B. Cowell and G. Czechura obs.1
Czechura 1979

Czechura 1979
G. Roberts pers. comm.

C. Corben and G. Czechura obs.

C. Corben pers. comm., D. Evans pers. comm.
P. Veerman pers. comm,
pers. obs.

pers. obs., D. Evans pers comm., C. Corben
pers. comm.

pers. obs.1, D. Evans pers. comm.

Prey remains at eyrie
G. 8c R. Czechura obs.1
pers. obs.
pers. obs.1
pers. obs.1
pers. obs.1
pers. obs.
pers. obs.1

1 Includes observations made at eyrie during breeding season.

Fall 1984

Peregrine Falcon in Queensland

87

Ingram 1976) but as with most reports, it is not
known if these involve adults or immatures. Im-
matures once independent, rarely remain in the
vicinity of the eyrie for longer than 4-8 weeks
approximately, although lone birds may take up
residence in areas rarely frequented by the adults
(pers. obs.). Otherwise little is known of movements
or fate of the majority of immature birds.

Hunting and Prey - Peregrines were observed
hunting in a variety of habitat and landscape types.
Some regularly hunted over both very open
(mudflats, waterways, pastureland) and densely
vegetated (rainforest, tall open-forest, heathland)
areas (Fig. 2 C, D). Presumably, hunting areas were
determined by the location of nesting sites.

Prior to the advent of European settlement in
southeastern Queensland, peregrines were largely
assocated with forested habitats. Rainforest vegeta-
tion was more extensive in coastal and subcoastal
districts than at present (Illidge 1925; Francis
1970). Indeed, Cade (1982) noted that Australian
populations of F. peregrinus show modifications of
the feet and beak typical of “forest” races of the
peregrine, F. p. peregrinator (India), F. p. ernesti
(New Guinea) and F. p. nesiotes (Figi) and the two
large, forest-dwelling species, Orange-breasted
Falcon (Falco deiroleucus) and New Zealand Falcon
(Falco novaeseelandiae) . Similarly, Pruett-Jones et
al. (1981a) have commented on modifications of
hunting techniques for dense woodland and
forests in Victoria.

Birds were the chief prey (Table 3). Brief de-
scriptions of some hunting flights are given by
Mayo (1934) and Czechura (1970, 1971). Compari-
son of published and unpublished observations
with the descriptions of Treleaven (1977), Ratcliffe
(1980) and Cade (1982) indicate most hunting con-
sists of a period of “still hunting” or “waiting on”
followed by the traditional stoop or direct pursuit.
“Still hunting” (Fig. 4-1 A) involves the falcon
launching an attack from a perch, such as an emer-
gent tree in rainforest, on passing birds. On leaving
the perch, the peregrine either gained altitude and
then stooped onto the prey, made a level dash to-
wards it (Mayo 1934; Czechura 1971) or stooped
directly onto it. “Waiting On” (Fig. 4- IB) involves
the raptor initially spending some time circling
and/or engaged in active flight before stooping.
The actual stoop (Fig. 4-2 B) is usually conducted
with wings closed or partly closed in a rather shal-
low angle of attack. The Final stages of the stoop

may result in complex aerial manoeuvres as prey
attempts to evade the falcon (Fig. 4- IB). Once the
prey is struck by the peregrine, a loop may be per-
formed to retrieve the body (Fig. 4-2 B) or the bird
may be simply seized and carried. Direct pursuit
usually culminates in the peregrine seizing the
prey.

Under special circumstances other hunting
techniques were employed. “Solitary flushing” may
be employed against ground-dwelling quail
(Czechura 1979). The peregrine will make rapid,
low-level passes above the vegetation sheltering the
quail. If quail flush, direct pursuit will result.
Peregrines, at other times, will “hawk” flying insects
by leisurely circling amongst the insects and
snatching them out of the air or snatch birds shel-
tering on the ground as they pass overhead, e.g.,
waders on mudflats.

It is difficult to determine hunting efficiency of
peregrines. On many occasions a falcon will indulge
in numerous attacks for up to an hour before a
successful kill is made. Many attacks, however, do
not appear to be pressed with determination (low
intensity attacks, Treleaven 1977) e.g., the falcon
breaks off early, stoops are short and relatively
slow. During such times, and sometimes after
feeding, “playful” attacks are made on large birds
such as ibis (' Threskiornis spp.) and Torrsian Crow
(Corvus orru ). Under the circumstances, lone crows
or ibises are stooped on, with the peregrine often
looping around the intended victim and then flying
away. Similarly, flocks may be attacked with the
apparent objective of breaking them up into smal-
ler units. Bouts of such playful behaviour are in-
terspersed with periods of soaring, slow flying and
perching. Attacks on flocks of birds are .usually
unsuccessful if the flocks maintain their structure
(Fig. 4- 1C). Lone birds that attempt to leave the
flock often are very quickly captured (Fig. 4-2C).
Fruit pigeons and lorrikeets will often attempt to
out-manoeuvre the falcon and seek shelter in the
canopy of nearby trees by perching or flying
through them. Frith (1942) reported such be-
haviour among fruit pigeons in northern New
South Wales but notes one case where the pursuing
peregrine pressed its attack below the forest
canopy. While successful attacks have been ob-
served on lorikeets (Trichoglossus spp.) and hon-
eyeaters, no successful attacks have been reported
on either Topnot Pigeon ( Lopholaimus antarcticus) or
White-headed Pigeon (Columba leucomela ) flocks.

88

G.V. CZECHURA

Vol. 18, No. 3

Figure 4. Peregrine Falcon ( Falco peregrinus ) hunting behavior.

4. 1 Hunting over rainforest and pasture-regrowth area near Maleny (profile taken from transect across part of the
hunting area shown in Plate 1 C-D). A. Unsuccessful (Plow intensity) attack on a flock of Topknot Pigeons (flight
path C) leaving rainforest canopy. The adult female peregrine was perched in an emergent Ficus sp. and
returned after this attack. B. Successful attack on an unidentified honey-eater (D) after a period of soaring. The
honeyeater attempted to climb, then dive away from the falcon prior to its capture (x). Plucking and feeding was
conducted on the perch atop the emergent Ficus sp. This attack was conducted approximately 15 mins after
attack A.

4.2 Successful hunt over woodland - pasture - low riverine rainforest near Woodford. A. Feeding flock of lorikeets
were attacked by an adult female peregrine (B) after leaving the central tree. The flock, except one bird (C) fled
through the canopy of adjacent trees. Bird C was struck by the falcon, caught after a rapid loop, then carried.

Fall 1984

Peregrine Falcon in Queensland

89

Although very little is known of hunting and prey
species of peregrines in the region during early
settlement, observations made by Savidge (in Mat-
thews 1916) in the Clarence River district of north-
eastern New South Wales suggest little change has
taken place. Savidge records the followng prey,
Black Duck ( Anas superciliosa) , Rainbow Lorikeet
(Trichoglossus haematodus), Pale-headed Rosella
(Platycercus abscitus), Australian Magpie-lark (Gral-
lina cyanoleuca ) Feral Pigeon (Columba livid) and
Feral Chicken ( Gallus gallus). All but G. cyanoleuca
and G. gallus have been recorded among prey from
southeastern Queensland (Table 3).

Interactions with Other Raptors - Interaction
between the Australian Hobbie (Falco longipennis )
and peregrines occur in many areas with the excep-
tion of heavily timbered and some upland areas
(Czechura in press). Both falcons may be found
hunting in the same areas on occasion (e.g., Wood-
ford, Caboolture), especially when lorikeets are
abundant. At these times peregrines largely hunt
the Rainbow Lorikeet ( Trichoglossus haematodus) and
Scaly-breasted Lorikeet ( Trichoglossus chlorolepi-
dotus ), while Australian hobbies hunt T.
chlorolepidotus and the smaller Little Lorikeet ( Glos -
sopsitta pusilla). The Brown Falcon (Falco berigora)
occurs with peregrines in many areas with the ex-
ception of densely timbered country. Interactions
between Brown and Peregrine Falcons appear to be
mildly aggressive. Brown Falcons will often leave
hunting areas after the appearance of peregrines.
At other times peregrines may make 1 or 2 casual
stoops at flying Brown Falcons or Brown Falcons
may stoop at perched peregrines. The Australian
Kestrel (Falco cenchroides ) comes into contact with
peregrines in the same habitats as Brown Falcons.
Kestrels readily mob perched peregrines, while
Czechura (1970) has reported a possible ‘play’ en-
counter. On one occasion a kestrel was among prey
brought to an eyrie (Table 3).

Peregrines have been observed mobbing the
Whistling Kite (Haliastur sphenurus) on 2 occasions
along Pumicestone Passage. Both of these involved
the same immature female peregrine. Otherwise
observations are restricted to encounters near
eyries. On several occasions the Wedge-tailed Eagle
(Aquila audax ) and once a Grey Goshawk (Accipiter
novaehollandiae) were mobbed by one or both fal-
cons as they approached eyries.

Mortality and Conservation - Little is known of
natural mortality among peregrines in southeast-

ern Queensland, although one was found dead
after a hailstorm in the Brisbane area (Q.M. or-
nithological records). The most significant cause of
mortality appears to be human persecution. Pigeon
fanciers have destroyed adults and interfered with
eyries in the eastern Moreton region. Some falcons
certainly fall victim to general persecution of rap-
tors. Disturbance at eyries also results from sight-
seers, bushwackers and illegal egg-collectors.

The nature and extent of pesticide effects within
the region are poorly known. Olsen and Olsen
(1979) found greater than 20% eggshell thinning
attributable to D.D.T. in clutches from southeast-
ern Queensland; this compares with a State mean of
3.6%. Shell thinning of 15-20% is critical - affected
eggs would not be expected to withstand incubation
(Newton 1979; Ratcliffe 1980). No peregrines have
come to the Small Animal Clinic, Department of
Veterinary Science, University of Queensland, suf-
fering from pesticide poisoning (W. Rooke pers.
comm.), but the Clinic has received other diurnal
raptors suffering from pesticide poisoning.

Some recent developments in the patterns of
pesticide use in southeastern Queensland are of
concern. Heliothis moths are serious crop pests
(Broadley 1977) and recent failure of a number of
synthetic pyrethrins used in their control has led to
renewed use of organochlorines in a number of
areas, while serious outbreaks of armyworms
(Pseudaletia spp., Spodoptera sp.; Broadley 1978,
1979) in southern subcoastal pasturelands have
necessitated use of pesticides (particularly via aerial
application), where their usage has traditionally
been of a low level.

Although a number of eyries are within the
existing national park-reserve system, there are no
specific conservation/management programmes in
operation. The species is protected under the pro-
visions of the Fauna Conservation Act of 1974.

Acknowledgments

I thank Victor Bushing, David Evans, Peter Hughes, Ted
Johansen, Kathleen MacArthur, Gary Norwood, Tony Palliser,
Chris Pollitt, Gary Silk, Peter Slater, Phillip Veerman, Ian Vena-
bles and Eric Zillmann for information used herein. For field
assistance, I thank Robin Czechura and Gunter Maywald. Assis-
tance in manuscript preparation was kindly provided by Gordon
Beruldsen, Chris Corben (Department of Forestry, Queensland),
Glen Ingram (Queensland Museum), Scott Mooney (National
Parks and Wildlife Service, Tasmania). Jerry Olsen, Penny Olsen
(Division of Wildlife Research, C.S.I.R.O.), Greg Roberts and
Clayton White (Brigham Young University).

90

G.V. CZECHURA

Vol. 18, No. 3

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Beruldsen, G. 1980. ‘A Field Guide to the Nests and
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Bijleveld, M. 1974. ‘Birds of Prey in Europe’ (Macmil-
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Broadbent, K. 1889. Birds of the central part of
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Broadley, R.H. 1977. Heliothis . . . serious agricultural
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Broadley, R.H. 1978. The lawn armyworm ... a seri-
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1979. Year of a massive armyworm

problem. /fod. 105(6):573.

Brown, L.H. 1970. ‘African Birds of Prey’.
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Cade, T.J. 1969. The status of the peregrine and other
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and Decline’. (University of Wisconsin Press, Madison.
596 pp.)

Cade, T.J. 1982. ‘Falcons of the World’ (Cornell Univer-
sity Press, Ithaca. 192 pp.).

Chaffer, N. 1974. Black-cheeked Falcon. Emu
43(4):251-253.

Clunie, F. 1972. A contribution to the natural history of
the Fiji Peregrine. Notomis 19:302-22.

1976. A Fiji Peregrine (Falco peregrinus)

in an urban-marine environment. Ibid 23(1): 8-28.

Cramp, S. and Simmons, K.E.L. 1980. ‘Handbook of the
Birds of Europe, the Middle East and North Africa.
Vol. 2. Birds of Prey to Bustards’. (Oxford University
Press, Oxford. 570 pp.).

Czechrua, G.. 1970. The Peregrine Falcon {Falco pereg-
rinus) at Maleny (S.E.Q.). Sunbird 1(4): 102-3.

1971. Field notes on hunting methods

of falcons. Ibid. 2(4):68-72.

1979. Observations on quail-hunting

strategies in some Australian raptors. Ibid.
10(3°4):59-66.

in press. The raptors of the Blackall-

Conondale Ranges and adjoining lowlands.

Dwyer, P.D., Kikkawa, J. and Ingram,
G.J. 1979. Habitat relations of vertebrates in sub-
tropical heathlands of coastal southeastern Queens-
land. pp. 281-99. In R.L. Specht (ed.). ‘Ecosystems of
the World 9A. Heathlands and Related Shrublands.
Descriptive Studies. (Elsevier, Amsterdam. 497 pp.).

Fien, I. 1966. Falcon at Glasshouse Mountains. Queens-
land Bird Notes 2(5): 4.

Francis, W.D. 1970. ‘Australian Rainforest Trees’. (Au-
stralian Government Printer, Canberra. 468 pp.).

Frauca, H. 1970. Some notes on the mammals and birds
of Mount Walsh National Park, Biggenden, Wide Bay
area, Queensland. Wambaliman 4(5): 4- 13.

Frith, H.J. 1942. Noteson the pigeons of the Richmond
River, N.S. W. Emu 89-99.

Groves, R.H. (ed.) 1982. ‘Australian Vegetation’.
(Cambridge University Press, Cambridge, 449 pp.).

Hickey, J.J. (ed.) 1969. ‘Peregrine Falcon Populations.
Their Biology and Decline’ (University of Wisconsin
Press, Madison, 596 pp.).

Illidge, R. 1923. Insects and birds observed during
Cedar Creek and D’ Aguilar Range excursion. Qd Nat.
4(2): 34-5.

1925. The Blue-faced Lorilet also cal-
led Coxen’s Fig Parrot. Ibid 4(6): 133-4.

Ingram, G.J. 1972. Notes on the feeding of White-
browed Woodswallows ( Artamus superciliosus). Sunbird
3:64-5.

Jack, N. 1941. Some birds and mammals of the Glassh-
use Mountains district. Qd Nat. 1 1(6): 127-32.

Jones, M.V. 1981. Birds of the Maryborough district,
Queensland, 1972-1980. Aust. Bird Watcher 9(1): 1-13.

Jones, S.G. and Bren, W.M. 1978. Observations on the
winterig behaviour of Victorian Peregrine Falcons.
Ibid 7(6): 198-203.

Keast, A. 1944. A inter list from the Tweed River dis-
trict, N.S.W., with remarks on some nomadic species.
Emu 43:177-87.

Kirkpatrick, T.H. 1967. Mammals, birds and reptiles
of the Warwick district, Queensland. 2 Birds. Qd. J.
Agric. Animal Sci. 24:81-91.

Longmore, N.W. 1978. Avifauna of the Rockhampton
area, Queensland. Sunbird 9(3/4) :25-53.

Lord, E.A.R. 1956. The birds of Murphy’s Creek dis-
trict, southern Queensland. Emu 56:100-28.

McEvoy, J.S., McDonald, K.R. and Searle,
A.K. 1979. Mammals, birds, reptiles and amphibians
of the Kilcoy Shire, Queensland. Qd J. Animal Sci.
36(2): 167-80.

Mac Arthur, K. 1978. ‘Pumicestone Passage. A Living
Waterway’ (Author, Caloundra. 141 pp.).

Makin, D. 1968. Birds of Sandy Cape, Fraser Island. Qd.
Nat. 19:31-42.

Mather, P. (ed.) 1976. ‘The National Estate. Moreton
and Wide Bay-Burnett Regions’. (Queensland
Museum, Brisbane 272 pp.).

Matthews, G.M. 1916. ‘The Birds of Australia. Vol. 5’
(Witherby, London. 440 pp.).

Mayo, W.M. 1934. Bird notes of Bribie Island and
Pumice Stone Passage. QdNat. 9(1): 12-6.

Monneret, R.J . 1974. Repertoire comportmental du Faucon
pelerin. Falco peregrinus. Hypothese explicative des Man-
ifestations Adversives. Alanda 42:407-28.

Newton, I. 1979. ‘Population Ecology of Raptors’
(Poyser, Calton. 430 pp.)

Norris, K.C., Emison, W.B. and Bren, W.M. 1977. A
preliminary survey pf the population of Peregrine Fal-
cons in Victoria. Emu. 77:86-7.

Fall 1984

Peregrine Falcon in Queensland

91

Olsen, J., Olsen, P. and Jolly, J. 1979. Observation on
interspecific conflict in the Peregrine Falco peregrinus
and other Australian falcons. Aust. Bird Watcher
8(2):51-7.

Olsen, P.D. 1982. Ecogeographic and temporal varia-
tion in the eggs and nests of the Peregrine, Falco pereg-
rinus, (Aves Falconidae) in Australia. Aust. Wildl. Res.
9:277-91.

Olsen, P. and Olsen, J. 1979. Eggshell thinning in the
Peregrine, Falco peregrinus, in Australia. Ibid. 6:217-26.

1981. D.D.T. Peregrines in peril.

RAOU Newsletter 49:1-3.

in press. Population studies of the

Peregrine in Australia. (Proceedings of the I.C.B.P.
Conference on Birds of Prey, Thessaloniki, Greece,
1982).

Passmore, M.D. 1982. Birds of Stanthorpe, Queens-
land, and its northern environs, 1972-1981. Amt Bird
Watcher 9(7):277-237.

Pruett -Jones, S.G., White, C.M. and Devine,
W.R. 1981a. Breeding of the Peregrine Falcon in
Victoria, Australia. Emu 80 suppl: 253-269.

Pruett-Jones, S.G., White, C.M. and Emison,
W.B. 1981b. Eggshell thinning and organochlorine
residues in eggs and prey of Peregrine Falcons from
Victoria, Australia. /fod. 281-287.

Ratcliffe, D. 1980. ‘The Peregrine Falcon’ (Payser,
Calton, 416 pp.).

Roberts, G.J. (ed.) 1977. ‘The Conondale Range - the
case for a National Parks’ (Queensland Conservation
Council, Brisbane, 86 pp).

1979. ‘The Birds of South-east

Queensland’ (Queensland Conservation Council,
Brisbane. 50 pp.).

and Ingram, G.J. 1976. An annotated

list of the land birds of Cooloola. Sunbird 7:1-20.

Robertson, J.S. 1948. Birds of the 1947 Queensland
camp-out at Binna Burra, Queensland. Emu
47:373-88.

Roderick, G. 1975. Bird observations in the Cooloola
area, 12-20 August 1972. Qd Nat. 21:58-9.

Steyn, P. 1982. ‘Birds of Prey of Southern Africa’
(David Philip, Cape Town. 309 pp.).

Storr, G.M. 1973. List of Queensland birds. Spec. Publ.
W. Aust. Mus. 5:1-177.

Vernon, D.P. 1968. ‘Birds of Brisbane and Environs’
(Queensland Museum, Brisbane 131 pp).

1976. Birds pp. 74-97. In Mather, P.

(ed.) ‘The National Estate. Moreton and Wide Bay-
Burnett Region’ (Queensland Museum, Brisbane. 272

pp.).

and Barry, D.H. 1972. Birds of

Fraser Island and adjacent waters. Mem. Qd Mus.
16(2):223-32.

and Martin, J.H.D. 1975. Birds of

Stradbroke Island. Proc. R. Soc. Qd 86(1 1):61-72.
Wash, B.P. 1978. Observations on Peregrine Falcons
nesting in Werribee Gorge, Victoria. Aust. Bird Watcher
7(5): 138-142.

Wheeler, R. 1959. The R.A.O.U. camp-out at Noosa
Heads, Queensland, 1958. Emu 59:229-249.

1973. The birds of ‘Green Mountains’.

Aust. Bird Watcher 4(8):257-269.

White, C.M., Pruiett-Jones, S.G. and Emison,
W.B. 1981 . The status and distribution of the Pereg-
rine Falcon in Victoria, Australia. Emu 80 suppl. : 270-
280.

Zillmann, E.E. 1974. Birds at Callide Dam. Wambaliman
8(5):6-8.

Queensland Museum, Gregory Terrace, Fortitude Valley. Q.
4006.

Received 15 June 1983; Accepted 1 June 1984.

Attention RRF Members Past and Present!! The Raptor Research Foundation, Inc., is approaching its 20th
Anniversary. In honor of this memorable occasion, I am compiling a twenty-year history of the Foundation to be
presented in Sacramento at the 1985 annual meeting. In addition, plans are to compose a monograph detailing the
Foundation’s history from beginning to present. I request the assistance of you, the membership, both past and present,
in accomplishing this task. Please contact me if you have any pertinent information in your files, such as photographs,
correspondence, etc., that you would be willing to loan to me. All such material will be acknowledged in publications, of
course, and I will make copies of the materials for my use and return the originals immediately. If you have anything you
wish to contribute, please contact me as follows: Jimmie R. Parrish, Department of Zoology, 159 WIDB, Brigham
Young University, Provo, Utah 84602, USA.

SPRING AND FALL MIGRATIONS OF PEREGRINE FALCONS IN
CENTRAL ALBERTA, 1979-1983, WITH COMPARISONS TO 1969-1978

Dick Dekker

Abstract - In central Alberta, 1979-1983, 339 sightings of migrating Peregrine Falcons ( Falco peregrinus) were
recorded between 15 April and 31 May. Mean sightings per hour afield were 0.23 for the entire period and 0.29 for the
main migration period 4-23 May, respectively 1 1 and 19% lower than for 1947-1978. Mean early dates, mid-dates and
mean late dates for adults were respectively 6, 7 and 2 days in advance of immatures, and nearly identical to 1969-1978.
Fall sightings were similarly scarce as in 1969-1978, totalled 24, and occurred from 1 7 September to 3 October. In fall, the
ratio of adults to immatures was roughly 1:3 and in spring 1:1. The success rate of 191 hunting attempts was 9.4%.

Since the 1950’s, the Peregrine Falcon (Falco
peregrinus ) has suffered serious population declines
in North America (Hickey 1969). As a breeding
bird it was extirpated in southern and central Al-
berta by the early 1970’s (Fyfe et al. 1976), although
captivity-raised and released falcons nested in Ed-
monton and Calgary in 1982 and 1983 (G.
Erickson, Alberta Fish and Wildlife Division, pers.
comm.). In spring and fall, northern peregrines
migrate through central Alberta (Dekker 1979).
Field surveys along the Atlantic and Texas coasts
have recently shown substantial increases in the
number of peregrines sighted during fall migra-
tions (F.P. Ward, pers. comm.). This paper presents
data on the characteristics of migrating peregrines
in central Alberta from 1979 to 1983. Pooled data
for these 5 yrs can be juxtaposed to data from 1969
to 1978 when I did similar field studies (Dekker
1979), although data for 1969-1973 are incomplete
and based on less expertise. The most recent 10 yrs
allow valid comparisons of number of sightings/h,
age ratios and timing of migrations.

Study Area and Methods

The study area was a crescent-shaped strip of grainfields and
open pastures, roughly 10x2 km in size, bordered by Beaverhill
Lake, that attracted numerous waterfowl and shorebirds in mig-
ration. In searching for peregrines no set procedures were fol-
lowed, although methods were similar to those of 1969-1978. Each
day afield I hiked 5-25 km, frequently pausing to scan through
10x50 binoculars. I often sat in a parked car and used a20-40X
telescope as well as binoculars. Many resting peregrines sitting on
fence posts or on the ground were watched until they left of their
own accord. Flying peregrines were observed for as long as they
remained visible. Alarm behaviour of prey species often alerted
me to the arrival of peregrines. The study area was visited from
early March to early December. Pooled for 5 yrs, field days totalled
167 and 79 respectively during 15 April -31 May and 1
September- 15 Ocotber. Field days lasted 3-17 and averaged 9 h
within varying time frames. About 85% of peregrines sighted in
spring were positively identified; distant large falcons that I could
not identify were assumed to be peregrines unless I suspected

them of being Prairie Falcons {Falco mexicanus), that are occasion-
ally seen in the study area in spring (Dekker 1982). During fall,
when peregrines are uncommon in the study area and both the
Prairie Falcon and the Gyrfalcon {Falco rusticolus) occur (Dekker
1983), all sightings of unidentified large falcons were deleted. (For
criteria used in field identification see Dekker 1977). I paid little
attention to the problem of duplicate sightings other than to delete
obvious ones. For 1969-1978 I tabulated maximum and minimum
sightings that show a duplication rate of 2.4. This indicates the
magnitude of the problem but is only an estimate. The so-called
maximum numbers of 1969-1978 “include duplicate counts ex-
cept the most obvious ones”, (Dekker 1979:297) and correspond
to sightings in this study. Data on hunting are for 1980-1983 only;
1979 observations were presented elsewhere (Dekker 1980).
Methods in recording foraging behavior were the same as in
1969-1978. Observations were written down during or at the end
of the day.

Results and Discussion

Numbers Sighted and Timing of Migrations - In
spring, peregrines were seen from 20 April to 31
May (Fig. 1). Sightings pooled for 5 yrs ranged from
0 to 21/d and totalled 339 (Table 1). Mean numbers
of sightings/h were 40-60% higher in morning and
evening than between 1200Hand 1500H (Table 2).

Earliest dates ranged from 20 to 30 April. Mean
early dates for adults and immatures respectively,
ranged from 20 April to 7 May and from 1 to 9 May.
Early arriving falcons appeared to pass quickly.
They often hunted over the still-frozen lake and
rested on the ice far from shore. I suspect that all
April sightings of unidentified falcons involved
adults. That assumption would advance their mean
early date to 25 April, 9 d ahead of immatures
(Table 3). Mean late sightings of adults and imma-
tures respectively, ranged from 17 to 27 and 19 to
31 May. Mean late dates and mean mid-dates (half
of total sightings) were nearly equivalent to those of
1969-1978 (Table 3).

To check for the presence of summering falcons,
the study area was visited about 4 times/month

92

Raptor Research 18(3):92-97

Fall 1984

Peregrine Falcon Migration

93

10-

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rfT

fh "

1—1

10-

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1 5~

p-tT

Tlrf

'4b

f

— |

HT

bh

20-
*) -

, 15-

M

5-:

-TU r

-Tlrf

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20 April 25 1 May 5 10 15 20 25 30

Figure 1. Peregrines sighted during spring migration
unidentified age class.

(range 3-7) in June, July and August. One pereg-
rine each was seen on 19 July 1980 and 2 June 1982.
Both were immatures. The June sighting probably
involved a late migrant, but the July bird may have
originated from a captive-breeding program with
releases in central and southern Alberta (G.
Erickson, Alberta Fish and Wildlife Division, pers.
comm.). I saw no evidence that captive-bred pereg-
rines occurred in the study area during spring mig-
ration. Data for the autumn were similarly limited
as in 1974-1978 and ranged from 1 7 September to 3
October.

Age and Sex Ratios - The proportion of adults
and immatures in spring differed from 1974-1978
(Table 4). I attribute that difference to the follow-
ing change in my criteria for identification. In
1969-1978 I differentiated the age groups mainly
by dorsal coloration; adults are ashy-blue, imma-
tures brownish. However, I have found that dorsal
color is not always a reliable fieldmark as some adult
peregrines look blackish-brown dorsally, resembl-
ing the spring immatures that are often light-
chested (Dekker 1979). Since 1979, 1 have included
all dorsally blackish falcons in the unidentified

in central Alberta. Total sightings include peregrines of

category unless I saw their ventral markings, barred
in the adult, streaked in the immature. The more
typically-colored adults are easily identified in
flight under good conditions. The proportion of
adults (29%) was remarkably close to that of 1974-
1978 (28%) but differed from 1969-1973 (38%).
The adult and immature percentages for fall dif-
fered from 1969-1973 and 1974-1978, but sample
size was small (Table 4).

The smallest males are about two-thirds the size
of the largest females (Godfrey 1966). However, I
was unable to determine the sex of 54% of sight-
ings. Under some conditions, especially when flying
falcons interacted with other birds, their relative
size could be assessed with confidence. Large
peregrines outnumbered small ones by a factor of
3:1 in the adults and 9:1 in immatures. Although
females outnumbered males also in 1969-1978,
values differed substantially, probably reflecting
the unreliability of basing sex ratios on sightings.
Females outnumbered males by a factor of 3:1 or
more in coastal migration surveys (Hunt et al. 1975;
Ward and Berry 1972).

Behavior - I saw falcons attack prey species 254

94

Dick Dekker

Vol. 18, No. 3

Table 1. Days and hours afield, and peregrines sighted, 15 April -31 May 1969-1983. (figures in brackets represent
the main migration period 4-23 May, when respectively 79, 85 and 79% of pooled sightings occurred in 3
groups of 5 years).

Year

Days Afield

Hours Afield

Sightings

Mean Sightings/Hr

1969

22(12)

_

20(9)

.

1970

25(16)

-

15(11)

-

1971

27(17)

-

33(27)

-

1972

25(16)

-

26(21)

-

1973

23(16)

-

41(39)

-

Sub-Totals

122(77)

-

135(107)

-

1974

26(16)

251(166)

46(43)

0.18(0.26)

1975

29(16)

284(171)

41(35)

0.14(0.20)

1976

30(17)

307(196)

66(53)

0.21(0.27)

1977

38(19)

378(216)

163(153)

0.43(0.71)

1978

34(19)

358(229)

90(64)

0.25(0.28)

Sub-Totals

157(87)

1570(978)

406(348)

0.26(0.36)

1979

31(16)

289(179)

57(46)

0.20(0.26)

1980

34(18)

323(194)

94(55)

0.29(0.28)

1981

34(19)

308(193)

67(59)

0.22(0.31)

1982

33(18)

276(172)

58(53)

0.21(0.31)

1983

35(19)

302(197'

63(56)

0.21(0.28)

Sub- Totals

167(90)

1498(035)

339(269)

0.23(0.29)

times. The success rate of 191 hunting attempts of
which the outcome was known was 9.4%, not sig-
nificantly different from the 7.7% reported for
1965-1979 (Dekker 1980). Prey captured included
9 ducks of 7 species and 9 shorebirds of 4 species.

In the first 2 h after daybreak, when I was rarely
in the field (Table 2), I only once saw a falcon attack
ducks, but I found falcons feeding on ducks 7 times.
In one case the prey was a Gadwall {Anas strepera ) I
had seen killed by a falcon the previous evening at
dusk. In the others, sunken eyes of ducks and
amount of meat taken from the carcasses led me to
suspect that they had been killed the previous
evening, during the night or near dawn. On several
occasions I saw peregrines attack ducks 0.5-1 h after
sundown, and they hunted sandpipers or pas-
serines very late in the evening. Crepuscular

foraging activity of peregrines has been reported by
several observers (Beebe 1960; Clunie 1976; De-
kker 1980). Some falcons that I watched at nightfall
stayed on posts until it was too dark to see them and
they probably roosted there. Their locations were
not only over water but also on open pasture. All
roosting falcons (n=9) were gone next morning at
dawn.

Most resting falcons that I watched in the morn-
ing from 1 h after sunrise remained inactive until
0900-1100 H when some began to hunt; others
soared to great heights and sailed away in a nor-
therly direction, apparently resuming migration.
In 1969-1978, falcons under observation left the
study area in late morning by soar and sail flight at
great altitudes (Dekker 1979). Each spring, 1 or 2
recognizable peregrines stayed in the study area for

Fall 1984

Peregrine Falcon Migration

95

Table 2. Percent of total field time for 5 daily periods, 15 April-31 May (figures in brackets represent main migration
period 4-23 May). Data pooled for periods of 5 years. Mean sightings per hour afield not available for
1974-1978 when the exact time of most sightings was not recorded.

% of Total Hours Afield

Mean Sightings/Hr

Time Period

1974- 1978 1979- 1983

1979- 1983

0500 - 0900

6.7 (7.7)

8.3 (10.5)

0.28 (0.33)

0900- 1200

19.3 (21.6)

17.8(19.1)

0.28 (0.36)

1200- 1500

24.8 (24.3)

20.5 (20.5)

0.17(0.21)

1500- 1800

26.9 (24.1)

27.0(23.7)

0.20 (0.26)

1800- 2200

22.4 (22.3)

26.4 (26.2)

0.24 (0.31)

TOTALS

100 (100)

100 (100)

0.23 (0.29)

3-8 d, no doubt causing duplication of sightings.

Conclusions - Although mean numbers of
sightings/h in spring were 11-19% lower in 1979-
1983 than in the preceding 5 yrs, most yearly
figures have remained similar, suggesting that no
change has occurred in the size of the spring popu-
lation migrating through central Alberta. An ex-
ceptional year was 1977 when sightings/h were
65-95% higher than the 5 yr mean (Table 1). The

spring of 1977 was characterized by dry climatic
conditions when peregrines and their prey con-
centrated on the lakeshore where they were readily
located.

Why peregrines were much scarcer in fall than in
spring in the study area is not clear. Perhaps some
peregrine populations breeding in the northwest
migrate in fall via a flight path east of Alberta to the
Atlantic coast, but return in spring by a more direct

Table 3. Mean early dates, mid-dates (half of total sightings) and mean late dates for adult and immature peregrines
sighted during spring migration in central Alberta. Data pooled for 3 groups of 5 years, 1969-1983. (“All
sightings” include falcons of unidentified age).

Mean Early Dates Mid-Dates Mean Late Dates

Years

Adult Immatures

All

Sightings

Adult Immatures

All

Sightings

Adult Immatures

All

Sightings

28

3

29

8

15

13

19

25

25

1969-1973

April

May

April

May

May

May

May

May

May

25

7

24

7

14

12

19

25

25

1974-1978

April

May

April

May

May

May

May

May

May

28

4

25

9

16

11

22

24

25

1979-1983

April

May

April

May

May

May

May

May

May

96

Dick Dekker

Vol. 18, No. 3

Table 4. Age composition of peregrines in percent of total sightings during spring and fall. Data pooled for 3 groups
of 5 years, 1969-1983.

Years

Sightings

% Adult

% Immature

% Unidentified

Spring

1969-1973

135

38

36

26

1974-1978

406

28

47

25

1979-1983

339

29

32

39

Sub-Totals

880

32

38

30

Fall

1969-1973

10

50

30

20

1974-1978

17

6

65

29

1979-1983

24

21

58

21

Sub-Totals

51

26

51

23

route through the continent. Differentiation of
spring and fall migration routes has been
documented for some shorebird species (Godfrey
1966).

Early and late dates of fall and spring sightings in
the study area were respectively 16 and 41 d apart
in 1979-1983 and 24 and 45 d in 1969-1978. Why
the spring passage lasts so much longer than the fall
migration is not known. Perhaps spring migrant
peregrines, especially subadults, linger in the study
area attracted by the concentrations of migrating
shorebirds, which are more numerous in May than
at any time during fall.

Although the number of fall migrating pereg-
rines was too small for comparisons, the number of
sightings/d increased from 0.24 in 1969-1978 to
0.30 in 1979-1983, consistent with increases in
sightings per unit effort during fall migrations
along the Atlantic and Texas coasts (F.P. Ward,
pers. comm.).

Acknowledgment

This study was financed by the Alberta Fish and Wildlife Divi-
sion, the World Wildlife Fund (Canada), and the Alberta Recrea-

tion, Parks and Wildlife Foundation. I thank W. Wishart for

support. A.J. Erskine, R.W. Nelson and F.P. Ward read the man-
uscript. Denise Fitz did the typing.

Literature Cited

Beebe, F.L. 1960. The marine peregrines of the
Northwest Pacific Coast. Condor 62:145-189.

Clunie, F. 1976. A Fiji peregrine in an urban environ-
ment. Notornis 23:8-28.

Dekker, Dick. 1977. Field identification of Peregrines,
Prairie Falcons and Gyrs in southern and central Al-
berta. Alberta Naturalist 7(1): 1-5.

Dekker, Dick. 1979. Characteristics of Peregrine Fal-
cons migrating through central Alberta, 1969-1978.
Can. Field-Nat. 93:296-302.

Dekker, Dick. 1980. Hunting success rates, foraging
habits, and prey selection of Peregrine Falcons mig-
rating through central Alberta. Can. Field-Nat.
94:371-382.

Dekker, Dick. 1982. Occurrence and foraging habits of
Prairie Falcons, Falco mexicanus, at Beaverhill Lake,
Alberta. Can. Field-Nat. 96:477-478.

Dekker, Dick. 1983. Gyrfalcon sightings at Beaverhill
Lake and Edmonton, Alberta, 1964-1983. Alberta
Naturalist 13(3): 103.

Fyfe, R.W., S.A. Temple, and T.J. Cade. 1976. The
1975 North American Peregrine Falcon survey. Can.
Field-Nat. 90:228-273.

Fall 1984

Peregrine Falcon Migration

97

Godfrey, W.E. 1966. The Birds of Canada. National
Museum of Canada Bulletin 203. 428 pp.

Hickey, J.J. (Editor). 1969. Peregrine Falcon popula-
tions: their biology and decline. University of Wiscon-
sin Press, Madison. 596 pp.

Hunt, W.G., R.R. Rogers, and D.J. Slowe. 1975. Mig-
rations and foraging behaviour of Peregrine Falcons
on the Texas coast. Can. Field-Nat. 89: 111-123.

Ward, F.P. and R.B. Berry. 1972. Autumn migrations
of Peregrine Falcons on Assateague Island, 1970-
1971./. of Wild. Mgt. 36:484-492.

3819-112 A Street, Edmonton, Alberta, Canada T6J 1K4.

Received 20 November 1983; Accepted 15 April 1984

Biology and Management of Bald Eagles and Ospreys. A proceedings of 32 refereed papers (325 pp.) by over 50
international experts on topics including taxonomy, distribution, winter and breeding population dynamics, nesting
habitat and nest site selection, nutritional ecology, prey selection, and management of the North American Bald Eagle
and the cosmopolitan Osprey. Typeset and bound with soft cover.

To place orders, write to either David M. Bird, Raptor Research Centre, 21,111 Lakeshore Rd., Ste. Anne de Bellevue,
Quebec H9X ICO or Dr. Gary Duke, Dept, of Vet. Biol., 295K AnSci/Vet. Med. Bldg., Univ. Minnesota, St. Paul,
MN 55108. Price per copy: U.S. $15 plus $2.50 handling; Overseas 15$ (U.S.) plus $5 handling; Canada $18 CDN)
plus $3 handling. Send payment with Canadian orders to D.M. Bird and U.S. and overseas orders to the Treasurer,
Raptor Research Foundation, Inc. All profits to Raptor Research Foundation, Inc.

WINTER HABITAT SELECTION OF DIURNAL RAPTORS
IN CENTRAL UTAH

David L. Fischer, Kevin L. Ellis and Robert J. Meese

Abstract - A total of 525 observations of 10 species was recorded during a winter roadside survey of raptors around Utah
Lake, Utah Co., Utah. Six species; Red-tailed Hawk (Buteojamaicensis), Rough-legged Hawk (Buteo lagopus ) , American Kestrel
(Falco sparverius), Northern Harrier {Circus cyaneus ), Golden Eagle {Aquila chrysaetos), and Bald Eagle ( Haliaeetus leucocephalus)\
accounted for 493 (94%) of the observations. Red-tailed Hawks, Rough-legged Hawks and American Kestrels were found in
greater than expected numbers in grassland habitat, Northern Harriers and Golden Eagles in sage/greasewood desert, and
Bald Eagles in riparian/lakeshore habitat. Rough-legged Hawks predominantly used utility pole rather than tree perches;
American Kestrels predominantly used wire perches; Red-tailed Hawks used tree and pole perches according to availability.
All species, except American Kestrels, used areas away from centers of human activity more often than expected.

Ornithological literature contains relatively little
information on the winter ecology of diurnal rap-
tors (Newton 1979). Road surveys taken over sev-
eral months can provide information on distribu-
tion, relative abundance and habitat use (Craighead
and Craighead 1956; Bildstein 1978). This infor-
mation may provide a basis for making land use
decisions. Although many raptor road surveys have
been conducted (Enderson 1965; Johnson and En-
derson 1972; Craig 1978; Bauer 1982; Gessaman
1982), few have studied habitat or perch use in
relation to availability, a prerequisite for making
inferences concerning species preference or selec-
tion. Here, we conducted a road survey of winter-
ing raptors and sampled the availability of general
habitat types, specific perch types and proximity of
centers of human activity along a 125 km census
route. We then tested the (null) hypothesis that
raptor use is in proportion to habitat availability.
Where use of a particular habitat type was found to
be significantly greater than expected, we infer
selection or preference on the part of the species
involved. Some argue that selection can only be
demonstrated by detailed behavioral observations
in which an active choice on the part of the animal is
shown (see Morse 1980). We assume, however, that
raptors are highly mobile organisms capable of
moving from one habitat or perch type to another
in a matter of minutes. Therefore, we infer an
active choice on the part of the species if it occupies
a particular habitat type significantly more often
than could be expected by chance.

Study Area and Methods

A 125 km loop around Utah Lake, beginning near Provo and
terminating near Lindon, defined the census route (Fig. 1). Aver-
age elevation of Utah Valley is 1371 m. Mean annual precipitation
ranges between 30.4 and 40.6 cm. Daily mean temperature during
the period December-March ranged from approx. - 15°C to 10°C.
Vegetation was a mosaic of agricultural lands (irrigated and dry),

Figure 1. Map of census route, Utah County, Utah.

sagebrush {Artemesia tridentata ) mixed with greasewood ( Sarcobatus
vermiculatus) desert, grassland/pasture, orchard, and riparian/
lakeside woodland. Topography of the census strip was generally
flat.

Twelve censuses totalling 42 h were conducted weekly from 8
January to 27 March 1983. Direction of travel along the census
route was alternated each week. Roads on the east side of the lake
were driven at speeds of 40 kph or less. Those on the west side,
where there is little vegetation to impair vision and there are fewer
potential raptor perch sites, were driven at speeds of 72 kph or
less. Brief stops to identify birds and record data were sometimes
made. Mean speed of travel per census was 36 kph. Mean time to
complete a census was 3.45 h. The number of observers was
usually 2, with 3 observers present on 2 occasions and a single
observer present on 1 occasion.

Only those birds seen initially with the unaided eye were tallied.
Binoculars and a 20x spotting scope were used to aid identifica-
tion. For each sighting we recorded location, habitat type, be-
havior (flying, perched, hovering, soaring, coursing), perch site
and distance from centers of human activity (farmyards, resi-
dences, commercial establishments, etc.). Habitat categories used
were (1) cultivated farmland, (2) sage (cold desert including some
greasewood), (3) grassland (including pasture and grass domi-
nated rangeland), (4) riparian (including lakeside woods), (5) or-
chard, and (6) residential (including urban and commercial areas
and the immediate area around farm and ranch houses). Perch

98

Raptor Research 18(3):98-102

Fall 1984

Winter Habitat Selection in Utah

99

■ sage H CULTIVATED S RESIDENTIAL S other

n GRASSLAND EE RIPARIAN □ ORCHARD

N=49 N=26 N=78

Figure 2. Percent deviation from expected number of raptor sightings by habitat type.

categories were (1) utility pole, (2) fence post, (3) wire, (4) tree, (5)
shrub and (6) ground. Distance to human activity was recorded as
(1) < 0.16 km, (2) 0.16 to 0.8 km, or (3) > 0.8 km.

Habitat and perch availability were quantified by assuming a
census strip width of 1 km (0.5 km each side of road) for that
portion of the route on the east side of the lake, and a width of 2
km (1 km each side of road) on the west side of the lake (Fig. 1).
These strip widths reflected the maximum lateral distances at
which we assumed nearly all raptors present could be spotted with
the unaided eye. A random sample of 30, 200-m radius circular
plots was taken to estimate the availability of each habitat and
perch type within the census strip.

Data were analyzed using non-parametric Chi-square methods
in which expected values were calculated from the estimates of
relative availability of habitat factors. For example, if 25% of the
census strip is cultivated farmland, we expect 25% of the sightings
of Red-tailed Hawks to be in this habitat. Categories were lumped
when expected values were less than 5 (Cochran 1954).

Results and Discussion

A total of 525 raptor sightings was recorded on
12 censuses. Most frequently observed species with
sample size sufficient to analyze were Red-tailed
Hawk (Buteo jamaicensis), American Kestrel ( Falco
sparverius). Rough-legged Hawk {Buteo lagopus),
Bald Eagle {Haliaeetus leucocephalus), Northern

Harrier {Circus cyaneus), and Golden Eagle {Aquila
chrysaetos). Species observed in smaller numbers
were Prairie Falcon {Falco mexicanus ), Merlin {Falco
columbarius ), Ferruginous Hawk {Buteo regalis) and
Cooper’s Hawk {Accipiter cooperii).

Habitat Use - Red-tailed Hawks were not ran-
domly distributed among the 6 habitat types
(P<0.01). (Fig. 2). The observed number of birds in
sage/greasewood desert was approximately a third
of that expected, while the number found in grass-
land habitat was over twice that expected.

Rough-legged Hawks were also not randomly
distributed among habitat types (P<0.1). They
were found at approximately the expected fre-
quency in sage, more often than expected in grass-
lands and far less often than expected in developed
areas (residential, etc.) (Fig. 2). This species breeds
in remote, nearly treeless areas of the far north
(Brown and Amadon 1968). Consequently it is not
surprising that it prefers open habitat and shuns
areas of intensive human activity.

Kestrels were also distributed non-randomly
among habitat types (P<0.01). They were found

100

Fischer, Ellis, Meese

Vol. 18, No. 3

Figure 3. Percent deviation from expected number of
raptor sightings by perch type.

twice as often in grassland as expected, but only
one-third as often as expected in sagebrush (Fig. 2).

Of 4 habitat categories that could be considered
(riparian, residential and orchard habitats lumped
due to low expected numbers), Northern Harriers
and Golden Eagles occurred more frequently than
expected in sagebrush and less frequently than ex-
pected in all other habitats (Fig. 2).

Bald Eagles showed the most restricted habitat
use pattern (Fig. 2). They were observed almost
exclusively along the west shoreline of Utah Lake,
and only where open water was nearby. Though the
affinity of wintering Bald Eagles for open water is
well documented (Fawks 1960; Southern 1963;
Steenhof et al. 1980), most wintering Bald Eagles in
Utah occur in sagebrush dominated desert valleys
and subsist largely on carrion (Edwards 1969; Platt
1976). The narrow habitat choice found in this
study is atypical of the normal habitat use pattern of
the species in Utah.

Rough-legged Hawks, harriers, kestrels and, to a
lesser extent, Red-tailed Hawks are known to prey
heavily on cricetine and microtine rodents
(Craighead and Craighead 1956). Only Northern
Harriers occurred in expected or greater than ex-

pected numbers in the sagebrush habitat. The
other species used grasslands more often than ex-
pected. Though we attempted no investigation of
abundance and distribution of prey species, a pre-
vious study in central Utah reported similar num-
bers of rodents in sage-greasewood as in grassland
habitat (Woodbury 1955). Thus, it appears the prey
base of the grassland habitat supports more species
and greater numbers of wintering raptors than
does the prey base of the sagebrush desert. This
may be due to greater vulnerability of prey to pre-
dation by diurnal raptors in grasslands than in the
sagebrush. Furthermore, in the desert, where ele-
vated perches are scarce, the aerial foraging of har-
riers may be more efficient than the perch and
hover hunting strategies employed by Rough-
legged Hawks and kestrels.

Perch Use - Raptor perches were primarily (83%)
in trees or on utility poles. Rough-legged Hawks
used poles more than expected (P<.01) whereas
Red-tailed Hawks used tree and pole perches
roughly according to their availability (Fig. 3).
Schnell (1968) and Weller (1964) reported that
Rough-legged Hawks tend to perch on poles and
lone trees, while Red-tailed Hawks tend to select

Rpole
Entree
□ wire

-MOO-

+75-

+50-

+25-

0-

-25-

-50-

-75-

-100-

1

RED-TAILED HAWK
N = 137

ROUGH-LEGGED HAWK AMERICAN KESTREL
N=65 N=74

Figure 4. Percent deviation from expected number of
raptor sightings by distance from centers of
human activity.

Fall 1984

Winter Habitat Selection in Utah

101

perches in groves of trees and along wood edges.

Wires, a frequent (77% of total) perch of kestrels,
were crudely quantified as being equal in availabil-
ity to poles. Although the number of potential
perch sites along an interpole length of wire is far
greater than on a single pole top (or cross arm), we
assume that the choice facing an individual kestrel
is essentially a dichotomous one — pole or wire?
Kestrels used wire perches more and poles and
trees less frequently than expected (P<.01, Fig. 3).
Bildstein (1978) also reported a preference of kes-
trels for wire perches.

Sixty-five of 66 perched Bald Eagles were in
trees. Too few sightings of perched Golden Eagles
and Northern Harriers were recorded to permit a
statistical analysis of perch site preference.

Human Disturbance - Red-tailed and Rough-
legged Hawks used undeveloped areas more than
developed areas (P<0.01, Fig. 4). Over twice as
many Red-tailed Hawks were seen more than 0.8
km from human disturbance as would have been
expected by chance alone. Only 12 of 79 (15%)
observations of Rough-legged Hawks were within
0.8 km of human habitation. Interestingly, slightly
more Red-tailed Hawks than expected were re-
corded within 0. 16 km of centers of human activity.
Large trees were often present around farmyards
and ranch houses, whereas trees were often lacking
nearby. The greater than expected number of
Red-tailed Hawk sightings close to potential human
disturbance may be due to a greater availability of
perches. Rough-legged Hawks appeared not to use
trees as readily as pole perches, and thus, did not
perch as often as expected near centers of human
activity. Alternatively, Rough-legged Hawks may
be less tolerant of human disturbance than are
Red-tailed Hawks, and the Rough-legged Hawk’s
use of poles may be due, at least in part, to the
proximity of a large proportion of the study area’s
trees to human activity.

American Kestrels were distributed non-ran-
domly also(P <0.01). Almost twice as many kestrels
were seen <0.16 km from human activity as were
expected (Fig. 4). Bildstein (1978) found that kes-
trels used areas nearer centers of human activity
than did other raptors wintering in Ohio.

Northern Harriers, Golden and Bald Eagles were
seen almost exclusively in undeveloped areas.
Therefore, no statistical analysis of this trend was
performed. These species seem to avoid developed
habitat.

Acknowledgments

We thank our wives, Darlene Fischer and Barbara Ellis, who

either spent weekends looking for hawks or spent them alone.

Chris Ellis and Pam Thompson assisted on the censuses. Michael

Kochert and Clayton White provided editorial comments which

greatly improved this manuscript.

Literature Cited

Bauer, E.N. Winter roadside raptor survey in El Paso
County, Colorado, 1962-1979. Raptor Res. 16:10-13.

Bildstein, K.L. 1978. Behavioral ecology of Red-Tailed
Hawks, Rough-legged Hawks, Northern Harriers,
American Kestrels and other raptorial birds wintering
in south central Ohio. Ph.D. Dissertation. Ohio State
Univ., Columbus.

Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill, New York.

Cochran, W.G. 1954. Some methods for strengthening
the common chi-square test. Biometrics 10:417-451.

Craig, T.H. 1978. A car survey of raptors in southeast-
ern Idaho 1974-1976. Raptor Res. 12:40-45.

Craighead, J.J. and F.C. Craighead. 1956. Hawks,
owls and wildlife. Stackpole Company. Harrisburg,
Pennsylvania.

Edwards, C.C. 1969. Winter behavior and population
dynamics of American Eagles in western Utah. Ph.D.
Dissertation, Brigham Young University, Provo, Utah.

Enderson, J.H. 1965. Roadside raptor count in Col-
orado. Wilson Bull. 77:82-83.

Fawks, E. 1960. A survey of wintering Bald Eagles. Iowa
Bird Life 30:56-58.

Gessaman, J.A. 1982. A survey of raptors in northern
Utah, 1976-79. Raptor Res. 16:4-10.

Johnson, D. and J.H. Enderson. 1972. Roadside raptor
census in Colorado - winter 1971-72. Wilson Bull.
84:489-490.

Morse, D.H. 1980. Behavioral mechanisms in ecology.
Harvard University Press, Cambridge, Massachusetts.

Newton, I. 1979. Population ecology of raptors. Buteo
Books, Vermillion, South Dakota.

Platt, J.B. 1976. Bald Eagles wintering in a Utah de-
sert. Amer. Birds 30:783-788.

Schnell, G.D. 1968. Differential habitat utilization by
wintering Rough-legged and Red-tailed Hawks. Con-
dor 70:373-377.

Southern, W.E. 1963. Winter populations, behavior
and season dispersal of Bald Eagles in northwestern
Illinois. Wilson Bull. 75:42-55.

Steenhof, K., S.S. Berlinger and L.H. Fred-
rickson. 1980. Habitat use by wintering Bald Eagles
in South Dakota./. Wild l. Man. 44:798-805.

Weller, M. W. 1964. Habitat utilization of two species of
buteos wintering in central Iowa. Iowa Bird Life
34:58-62.

Woodbury, L. 1955. An ecological and distributional
study of small mammals in Cedar Valley, Utah County,

102

Fischer, Ellis, Meese

Vol. 18, No. 3

Utah. M.S. Thesis, Brigham Young University, Provo,
Utah.

Department of Zoology, Brigham Young University, Provo,
Utah 84602. Current address second author: Colorado Di-
vision of Wildlife, 6060 Broadway, Denver, Col-

orado 80216. Current address third author: Department of
Wildlife and Fisheries Biology, University of California,
Davis, California 95616.

Received 3 February 1984; Accepted 1 July 1984

Request for Information

Information is being gathered on the post-release behavior and survival of captive-reared and rehabilitated birds and mammals. The
objectives of this study are to assess the amount and type of work that has already been done, to summarize the available data and evaluate
techniques, and define the reasons for the survival or mortality of released animals.

Published and unpublished reports and raw data would be appreciated. For additional information, individuals willing to cooperate
please contact Daniel R. Ludwig, Ph.D., Willowbrook Wildlife Haven, Forest Preserve District of DuPage County, P.O. Box 2339, Glen
Ellyn, IL 60138.

Raptor Collisions with Utility Lines — A Call for Information — The U.S. Bureau of Land Management, Sacramento,
in cooperation with the Pacific Gas and Electric Company, is assembling all available published and unpublished
information concerning collisions of raptors with power lines and other utility lines. Actual case histories — no matter
how circumstantial or fragmentary — are needed. Please acknowledge that you have such information by writing to Dr.
Richard R. (Butch) Olendorff, U.S. Bureau of Land Management, 2800 Cottage Way, Sacramento, California 95825
U.S. A. (Phone (916) 484-4541). A form on which to record your information will then be sent by return mail.

DO NORTHERN HARRIERS LAY REPLACEMENT CLUTCHES?

Robert Edward Simmons

Abstract - An ecological difference between North American and European populations of Circus cyaneus is the
apparent lack of replacement clutches laid by the North American form (the Northern Harrier) on the failure of the first
clutch. I present several lines of evidence that Northern Harriers do lay replacements, but only if their clutches are
disturbed during laying or shortly thereafter. Two of the five females that renested were successful in their attempts and
the quality of the new nest sites was higher, despite most renests being within 200 m of the old sites.

In 2 detailed and long term ( > 20 y) studies of
Circus cyaneus , one in Orkney, Scotland (where it is
called the Hen Harrier), and one in Wisconsin,
U.S.A., a major ecological difference is evident.
Harriers in Scotland may lay 1 and occasionally 2
replacement clutches following the failure of their
original clutch (Balfour 1957), while harriers in
Wisconsin have never been recorded as laying a
replacement (Hamerstrom 1969, pers. comm.
1981 ; Schmutz and Schmutz 1975). Since Simmons
and P.E. Barnard (MS) found few behavioural dif-
ferences in a comparison of the 2 continents’
populations, other than migratory habits, then this
apparent difference warrants attention and expla-
nation.

Here, I present evidence that harriers in a large
Canadian population laid replacement clutches in
all 3 y in which they were studied, and that renest-
ing females picked higher quality sites for their
second attempts.

Study Site and Methods

One of North America’s largest assemblages of breeding har-
riers was studied on the 60 km2 Tantramar Marsh (45°53'N,
64°20'W), New Brunswick. The objectives were to document
breeding and feeding ecology of the population in relation to
polygyny. In so doing, the location of each nest was mapped and its
history detailed; the date of settling, habitat type, courtship dis-
plays, clutch size, and male and female activity (see Simmons 1983
for details). About 2500 h of observation were made, of which 562
h were specific nest watches to record feeding rates.

As no birds were marked, the evidence presented here consists
of the followng categories: (a) recognition of plumage charac-
teristics and voice; (b) identical reaction to human disturbance at
both nests, which varied significantly among females; (c) short
relaying period; (d) lack of “sky dancing” (Hamerstrom 1969)
from any male involved following nest predation; (e) close
proximity of nest and renest; and (f) alarm-calling at the nest up to
2 d after nest failure.

To determine nest site quality, I recorded dominant vegetation,
moisture level, and visibility at each of 64 nests found. Moisture
was ranked as Dry if no water existed within 1 m of the nest, Wet if
water appeared due to my weight, and Very Wet if water was
already present at the site. Vegetation was ranked as cattail ( Typha
spp.), marsh grasses (Spartina pectinata or Calamagrostis canadensis),
Spirea ( Spirea latifolia and other low shrubs), and alder {Alnus spp.
and willow Salix spp.). Visibility, which was later found to have no

effect on the success or failure of each nest (Simmons and Smith
1985), is disregarded here since it does not affect quality. Quality
reflects the probability of success, and the quality score for each
nest site is a combination of the percentage success of moisture and
vegetation categories arcsine transformed, and summed (see
Simmons and Smith 1985).

Results and Discussion

Suspected renesting occurred twice among 30
nests in 1980, and in 3 of 22 nests in 1981. The
original nest of a suspected renest in 1982 was not
found, and details of 2 renests in 1983 (R.B.
MacWhirter and G.L. Hansen in litt .) were not
taken, and are not discussed further here.

In the first case in 1980, a yellow-eyed female
distinguished by a very dark terminal tail band had
just completed a clutch of 5 eggs (determined by
egg colour: Sealy 1967; Hamerstrom 1969, pers.
obs.) in Cattails. She reacted to me by flying 300-400
m east and circled at low altitude while alarm
calling. On my next visit, a bird already 300-400 m
east of me started cackling. Later, the same bird
flew to the new nest and was recognized by her eye
and rectrix colour. The fact that she alarm-called
near her new nest on my first visit would have been
unusual for any other harrier with no prior
experience of my activities. In my experience at 59
other first nests, a female never called until I was
closer than approximately 80 m on my first visit.

The second nest-renest evidence in 1980
(“Alders”: Table 1) consisted of (a) close circling
and calling but Ao stooping by the female, (b) a 7-d
relaying interval, (c) a lack of sky dancing by her
polygynous mate who otherwise performed a
greater number of displays than any other male
(Simmons 1983), and (d) a renest only 160 m from
the original site. She was 1 of 2 polygynous females
(Table 1) who relaid with the same male
(polygynous males were identified by watching
them feed one, then another female in succession).

In 1981, in an effort to gain accurate data on egg
laying and incubation periods, I disturbed several
females with 0- or 1-egg clutches. Five of 6 females

103

Raptor Research 18(3):103-106

104

Robert Edward Simmons

Vol. 18, No. 3

Table 1. Factors associated with 5 renests located on the Tantramar Marsh of New Brunswick, 1980-1981.

Renesting Factors*

Nest

I

II

III

IV

Va

VIb

VII

Midgic 1

8

320

9 May 1980

Just completed

5

144

clutch

Renest

27 May 1980

5

140

S

Alders y

7

160

18 May 1980

Egg-laying

4

117

Renest

31 May 1980

4

114

pc

Midgic 2

11

100

14 May 1981

First egg

1

92

Renest

25 May 1981

2

133

S

Alders ft

4

120

14 May 1981

First Egg

1

92

Fd

Renest

18 May 1981

5

118

Phoebe

7

200

1 June 1981

First egg

1

140

Renest

8June 1981

4

140

pe

* — I = days between failure and relaying; II = proximity of nests (m); III = clutch initiation dates; IV = stage at failure; V = clutch size;
VI = quality score of nest site; VII = outcome of renest attempt: S = successful, F = failed.

aAll renest clutches were full clutches and hatched.

bBased on moisture and vegetation at the nest site (see text); range of scores 92-144.
cDiseased chicks
^Observer induced
e Predation

deserted, and 2 of 5 relaid. A third female, whose
1-egg clutch was taken by a lone Common Raven
(Corvus corax), also relaid. In each case, a renest was
established using 2 or more of the categories out-
lined in Methods. One ft female continued to de-
fend her destroyed renest for 2 d following its de-
struction. This is in contrast to evidence presented
by Hamerstrom (1969) for Wisconsin harriers
which left the area within 24 h of nest loss, and
indicates the potential for a female to remain and
renest on the Tantramar Marsh.

Three characteristics common to all 5 renesters
emerge from their histories: (1) all failed while in
the process of egg-laying or shortly thereafter; (2)
the distance between the nests was, in 4 of 5 cases,
closer than the minimum distance recorded bet-
ween concurrently occupied nests (260 m); and (3)
the period between failure and relaying was short,
averaging 7.4 (± 3) d. Morrison and Walton (1980),
in their review of replacement clutches in raptors,
reported that the frequency of relaying was greater
among birds whose clutches were disturbed early in

the breeding attempt, and that renesting generally
took place within “several hundred metres”. These
facts concur with (1) and (2) in this study. The
significance of the short relaying period (3) can be
seen in light of the fact that on the Tantramar
Marsh, females settling into new territories (i.e.
courting and preparing to lay eggs) required at least
1 wk and usually longer (Simmons 1983) to put on
sufficient fat/protein reserves (cf. Newton et al.
1983, Hirons et al. 1984) before laying their first
egg. Since the average relaying interval was only 1
wk for renesters, this implies that a female part way
through laying finds it easier to begin a new clutch,
having not fully depleted her protein reserves, than
a female starting afresh. This may explain the short
relaying interval (Table 1). It is also significant in
this regard that the female with the longest relaying
interval (Midgic 2) also produced the smallest re-
peat clutch (Table 1), and was fed very little by her
monogamous mate (Simmons 1983).

A related but paradoxical fact arises from a
comparison of relaying intervals reported for other

Fall 1984

Northern Harrier Replacement Clutches

105

small falconiforms (12-18 d : Morrison and Walton
1980) and those found in this study (7.4 d). This
difference may be related to the fact that many of
the falcons and accipiters cited {ibid. ) were
deliberately double-clutched and therefore “failed”
after producing a full clutch, while the harriers
failed earlier in their attempts. The relaying
intervals (Table 1) concur with those found by
Balfour (1957) who stated that replacements were
often completed within a fortnight by Hen Harriers
in Orkney. The frequency of renesting (8 nests in
96: 8% [Simmons 1983, 1983a; G.L. Hansen and
R.B. MacWhirter in lift.]) over 4 y on the Tantramar
Marsh is also similar to that found in Orkney (N.
Picozzi, pers. comm.).

Newton (1979:136) argued that the proportion
of relaying raptors in 4 population is determined by
food supply; evidence from this study does not
support this hypothesis. Microtines and shrews
(Sorex spp.), principal prey of the harriers on the
Tantramar Marsh (Barnard 1983), were sampled
each year {ibid, and G.L. Hansen in litt .) and related
to the proportion of renesters. Spring vole
abundance could be ranked from highs in 1980 and
1983 to lows in 1981 and 1982, yet renests
accounted for 6.3%, 6.6%, 13.6% and 8.3% of all
nests in these years respectively. Several factors
(other than my research activities) therefore must
have been operating over and above food
abundance to produce these results.

Further evidence which does not support the
food-related hypothesis comes from a survey of
other records of renesting among Northern
Harriers. Riendahl (1941) reported 1 nest among 5;
Craighead and Craighead (1956) reported 1 renest
among 9 in a year of low vole abundance, but none
in a “high” year; Smith (1971) recorded 1 among 5
nests, and Duebbert and Lokemoen (1977)
reported 1 among 3 nests. If low numbers of nests
were indicative of a low vole population (cf.
Hamerstrom 1979; Simmons et al. in prep.) in these
studies, then none of them support the
food-related renesting hypothesis (Newton 1979).

If nests are destroyed by predators, it is
surprising that the harriers studied generally
renested within 200 m of their original sites; their
mates often held territories up to 1 km in diameter
(Simmons 1983), and suitable nesting substrate
appeared to be relatively unlimited. This unusual
situation was investigated through an estimation of
the quality of the nest and renest in terms of

anti-predator adaptations. This was based on the
knowledge that Very Wet cattail sites were
significantly more successful than most other
combinations (Simmons and Smith 1985). The
results indicate that harriers could afford to locate
their renests close to their original nests, since on
average they chose better quality sites. Four of the 5
renests stayed in high quality sites or increased in
quality, while overall the quality scores increased by
an average of 12 points; this was not significant,
however (Wilcoxson test, U = 10, P = 0.3). Even so,
all 5 renesters hatched eggs; 2 raised flying young
and only 1 renest failed again due to predation.

I conclude that North American harriers do lay
replacement clutches if their original clutch fails
early in the attempt, at about the same frequency as
their European conspecifics. As the Northern
Harrier is behaviourally very similar to the Hen
Harrier, the fact that they both lay replacement
clutches adds to the contention that they are also
ecologically very similar.

Acknowledgments

This study was made possible through 2 graduate fellowships
from Acadia University and financial support through my
supervisor Dr. P.C. Smith. I thank P.E. Barnard and the Canadian
Wildlife Service, Sackville, New Brunswick, for their assistance,
and Frances Hamerstrom and Nick Picozzi for their interesting
discussions. Mark Fuller helped clarify the paper through
constructive criticism, and Bruce MacWhirter and Gay Hansen
kindly supplied unpublished material.

Literature Cited

Balfour, E. 1957. Observations on the breeding biology
of the Hen Harrier in Orkney. Bird Notes 27:1 77-183.
Barnard, P.E. 1983. Foraging behaviour and energetics
of breeding Northern Harriers Circus cyaneus (L.) B.Sc.
(Hons) thesis, Acadia Univ., Nova Scotia.

Craighed, J.J. and F.C. Craighead. 1956. Hawks, owls
and wildlife. Dover Publ. Inc., New York.

Duebbert, H.F. and J.T. Lokemoen. 1977. Upland
nesting of American Bittern, Marsh Hawk and
Short-eared Owl. Prairie Nat. 9:33-40.

Hamerstrom, F. 1969. A harrier population study. Pp.
367-385 in: J.J. Hickey (ed.) Peregrine Falcon
populations: their biology and decline. Univ. of
Wisconsin Press, Milwaukee.

Hamerstrom, F. 1979. Effect of prey on
predator: voles and harriers. Auk 96:370-374.
Hirons, G.J.M., A.R. Hardy, and P.I.
Stanley. 1984. Body weight, gonadal development
and moult in the Tawny Owl {Strixaluco).J. Zool., Lond.
202:145-164.

Morrison, M.L. and B.J. Walton. 1980. The laying of

106

Robert Edward Simmons

Vol. 11, No. 3

replacement clutches by Falconiformes and
Strigiformes in North America. Raptor Res. 14:79-85.

Newton, I. 1979. Population Ecology of Raptors. T. and
A.D. Poyser, Berkhamsted, Hertfordshire, England.

Newton, I., M. Marquiss, and A.
Village. 1983. Weights, breeding and survival in
European Sparrowhawks. Auk 100:344-354.

Riendahl, E. 1941. A story of Marsh Hawks. Nature
Mag. April: 191-194.

Schmutz, J.K. and S.M. Schmutz. 1975. Primary molt
in Circus cyaneus in relation to nest brood events. Auk
92:105-110.

Sealy, S.G. 1967. Notes on the breeding biology of the
Marsh Hawk in Alberta and Saskatchewan. Blue Jay
25:63-69.

Simmons, R.E. 1983. Polygyny, ecology and mate choice
in the Northern Harrier Circus cyaneus (L.). M.Sc.
thesis, Acadia University, Nova Scotia.

Simmons, R.E. 1983a. The harriers of the Tantramar.
New Brunswick Nat. 12:9-12.

Simmons, R.E. and P.C. Smith. 1985. Do Northern
Harriers Circus cyaneus choose nest sites adaptively?
Can. J. Zool. (in press).

Smith, D.G. 1971. Population dynamics, habitat
selection and partitioning of the breeding raptors in
the Eastern Great Basin of Utah. Ph.D. thesis,
Brigham Young Univ. Utah.

Department of Biology, Acadia Univ., Wolfville, Nova Scotia
BOP IXO. Present address: Department of Zoology, Univ. of
Witwatersand, Johannesburg, South Africa.

Received 27 December 1983; Accepted 1 August 1984

UNUSUAL PREDATORY AND CACHING BEHAVIOR OF
AMERICAN KESTRELS IN CENTRAL MISSOURI

Brian Toland

Abstract - Caching behavior of the American Kestrel ( Falco sparverius) was studied 1981-1983 in Boone County,
Missouri. Both wild prey and quarry thrown from car windows were cached. Kestrels cached food 116 times and
retrieved it 77.5% of the time. Males cached food in elevated sites (at least 4 m high) 64% of the time while females did so
only 20%. During spring and summer, 93% of the prey items were cached uneaten. During fall and winter, only 42% of
the food cached was uneaten. When a surplus of prey was created by releasing several mice at a time, kestrels killed them
while flying to their cache sites. These prey items were stored in the same cache site. Apparently, caching behavior of
American Kestrels is not directly correlated with the length of time between feedings, and caching behavior operates
independently of food deprivation, especially in spring and summer.

Many reptors have been observed caching prey.
Mueller (1974) provided a review of food storing in
several captive species. Among the falconiforms,
prey caching seems to be most developed and wide-
spread in falcons. Published records of caching in-
clude those for the Merlin ( Falco colwmbarius )
(Greaves 1968; Oliphant and Thompson 1976;
Pitcher et al. 1982), American Kestrel ( F . sparverius)
(Pierce 1937; Tordoff 1955; Roest 1957; Stendell
and Waian 1968; Balgooyen 1976; Collopy 1977),
Prairie Falcon (F. mexicanus) (Peterson and Sitter
1975; Oliphant and Thompson 1976), Peregrine
Falcon (F. peregrinus ) (Beebe 1960; Brown and
Amadon 1968; Nelson 1970; Cade 1982), Gryfal-
con (F. rusticolus ) (Jenkins 1978; Cade 1982) and
many others.

Study Area and Methods

Data reported here are from a 48 km2 area in Boone County,
Missouri, where farmlands are interspersed with woodlots, old
fields, meadows and residential areas.

I observed kestrels from September 1981 through August 1983
using a 30x spotting scope and 9x binoculars at distances of 5-200
m. For each observation I recorded species cached, location of

cache, weather conditions, time of day, and duration of caching
sequence. Additional live prey was thrown from my car window to
kestrels perched within 25 m of roads. The prey thrown were
brown, gray, white and black House Mouse {Mus musculus ) and
House Sparrows ( Passer domesticus) with several primaries pulled to
ensure their capture by kestrels.

Results and Discussion

During the 2 yr study 1210 h of observation of
kestrels were made and 30 kestrels were seen cach-
ing prey a total of 116 times. They subsequently
retrieved food successfully 77.5% of the time. Prey
cached were 95% rodents and 5% birds. Both wild
and provided prey were cached. Kestrels captured
95% of the prey thrown from car windows and
cached 46 (48%). The remaining 70 (60%) prey
cached consisted of 55 Prairie Vole ( Microtus oc-
hrogaster ), 6 house mice, 3 White-footed Mouse
( Peromyscus leucopus ) 2 Western Harvest Mouse
( Reithrodontomys megalotis), 2 House Sparrows, 1
Grasshopper Sparrow ( Ammodramus savannarum)
and 1 Eastern Meadowlark ( Sturnella magna ).

Cache sites were of 8 kinds (Table 1). Males
cached prey in elevated sites significantly more

Table 1. Cache sites used by American Kestrels in Boone County, Missouri 1981-83.

Location and Height of Caches

Sex

Grass
clumps
(0-0.1 m)

Hollow

railroad

ties

(0-0.1 m)

Tree
roots
(0-0.1 m)

Bushes
(0. 5-1.0 m)

Fence Building
posts gutters
(1.0 m) (4.0 m)

Tree limbs
and holes
( 4.5 m)

Tops of
power poles
(10.0-20.0 m)

Total

M

16

3

1

1

6

2

44

3

76

F

27

0

0

2

3

0

8

0

40

107

Raptor Research 18(3): 107-1 10

108

Brian Toland

Vol. 18, No. 3

often than did females (Table 1). Males cached prey
4 m or more above the ground 64% of the time,
while females did so only 20% (X2 = 22.16, P<0.01,
df=l).

During the breeding season kestrels have special
courtship feeding ceremonies (Fox 1979; Cade
1982). Food transfer often begins as remote food
passing (Nelson 1977) when the male deliberately
caches prey within view of the female. When he
leaves, she flies to the cache, retrieves apd eats the
food. I observed that all copulation and courtship
activities including hitched wing-displays, food
begging, courtship feeding and remote food pas-
sing occurred at elevated sites, on or near favorite
-plucking or hunting perches. Because males alone
cache prey at these elevated sites during courtship
they may be predisposed to cache in elevated sites
during the rest of the year.

Partially eaten carcasses were always decapitated
before being cached and only the posterior 2/3 to
1/2 of the body of the prey was placed in the cache.
However, kestrels cached 78% (36 of 46) of the
presented prey and 69% (48 of 70) of wild prey
completely uneaten. Of all prey items cached,
only28% (32 of 116) were decapitated. In contrast
Stendell and Waian (1968) reported that 14 of 15
small mammals cached by a single female kestrel
were decapitated and Collopy (1977) reported that
10 female kestrels decapitated 13 of 17 (76.5%)
small animals cached. In Missouri kestrels cached
more (58%, 27 of 48) partly-eaten prey during the
fall and winter than the 7% (5 of 68) during spring
and summer, which may be explained by the lack of
hunger during the breeding season due to greater
availability of food and warmer temperatures.

Kestrels hiding food approached the cache site
furtively, then thrust, pushed, or nudged the prey
into position with the beak (see Balgooyen 1976;
Collopy 1977). Sometimes sites apparently were
selected before the flight started, and kestrels flew
directly to the cache spot. Prey was not placed in any
preferential position such as belly-down (as if to
take advantage of the prey’s protective coloration)
as reported by Balgooyen (1976) and Collopy
(1977). I found items lying on back or sides as often
as on the belly. Kestrels sometimes did make several
attempts at repositioning prey until it was better
concealed. In all cases when prey was stored on the
ground in grass clumps, kestrels chose sites next to
fence posts, utility poles, sign posts, or other mar-
kers. Tordoff (1955) observed that a captive kestrel

which cached prey used objects nearby to memorize
the location of the cache site.

When retrieving prey, kestrels flew to the cache
site and if unable to find stored prey, hovered above
the area or walked to adjacent grass clumps to
search. In several instances kestrels appeared to
give up their search when they flew to a nearby
perch, only to return and resume the search. One
female kestrel spent 15 min investigating grass
clumps both on foot and in brief hovers before
giving up.

Because my field observations were evenly distri-
buted throughout the day, I assumed that there was
no difference in the probability of observing either
prey storing or retrieval (see Collopy 1977). On this
assumption, I considered my caching data as a rep-
resentative sample of the relative frequency of prey
caching and retrieving and calculated a recovery
efficiency of about 78%, similar to the 70% re-
ported by Collopy (1977).

1 observed that presenting kestrels with live prey
stimulated a response that simulates the reactions
of kestrels to natural prey. The typical response was
to fly from the perch toward the prey within 20 sec
of its detection. Kestrels then would either (1) bind
to the quarry on the ground and kill it with a bite to
the neck immediately (or after having flown to a
nearby perch) or, (2) snatch the prey from the
ground without landing and fly to a nearby perch to
dispatch it with a bite to the neck.

On 6 March 1982 at 1430H I observed a female
through binoculars from a distance of 100 m. The
weather was 38°C, calm and clear. I approached in
my car to within 25 m, threw a white mouse out the
window and waited. Within 2 min the kestrel ap-
proached within 4 m of my car, hovered, and then
retreated to a wire 20 m away. I then threw out 2
more mice and backed the car 25 m away. At 1440 H
the kestrel again flew toward the mice but after
hovering above them and looking at my car, again
retreated to the wire only 15 m distance. I then
presented 4 more white mice for a total of 7, all of
which were conspicuous against a recently mowed
lawn. At 1445 H the kestrel flew to a wire only 5 m
from the mice and after hesitating for 15 or 20 sec
flew down and captured a mouse. However, she
immediately flew west 75 m during which flight I
saw her bend over several times in midair to bite the
neck of the mouse. She immediately landed on the
ground and cached the prey in a grass clump at the
base of a fence post. She quickly returned to cap-

Fall 1984

American Kestrel Caching Behavior

109

ture and dispatch in flight the remaining mice in
rapid succession. All 7 mice were cached in 1 or 2
grass clumps 1 m apart. None of the 7 mice were
eaten at this time.

A month later at the same time of day a male took
7 mice in the same fashion, killing them midair as it
flew to the cache site in a white oak tree (Quercus
alba).

I was able to elicit the capture and caching of as
many as 10 mice in sequence by both captive and
wild kestrels when presenting them with prey one at
a time, over 2 to 8 h periods. Nunn et al. (1976)
reported that 1 wild female took 20 white mice
thrown from a car window one at a time, over an
hour. I found no literature reports of American
Kestrels responding to a sudden increase in prey
availability by mid-flight killing and caching of suc-
cessive prey items uneaten.

Caching has been described as a behavorial
mechanism to exploit a seasonal or daily abundance
of prey, thereby maximizing food intake and dam-
pening the effects of fluctuations in prey availability
(Balgooyen 1976; Collopy 1977). My studies agree
with other researchers that kestrels, like other fal-
cons, store extra food for periods of a few hours to
several days, especially when the capture of suffi-
cient prey may be difficult (i.e., inclement weather,
snow cover, or brood rearing).

Although winter food storing in kestrels may be
stimulated by a “hunger drive” (see Mueller 1973,
1974) in part, my observations agree with Collopy
(1977), Fox (1979) and Cade (1982) that Lorenz’
(1937) model of instinctive behavior operating in-
dependently of food deprivation occurs in kestrels
during the nesting season. Mueller’s (1973)
laboratory findings, in which the predatory be-
havior of kestrels was directly correlated with
length of time between feedings, was not substan-
tiated. Fifty-eight percent of the prey cached in fall
and winter was partially eaten, but only 7% during
the nesting season. This indicates that hunger drive
does not explain caching behavior of courting
males or parental food storing behavior during
nesting.

When presented with a surplus of easily captured
prey (both in late winter and spring) kestrels killed
prey as they flew to a cache site, thus expediting
capture of an ephemeral abundance of prey.

The accompanying caching of multiple prey
items in the same cache or nearby appears to be yet
another example of the flexible behavior of kestrels

attempting to hurriedly exploit sudden surpluses in
prey availability. Because I saw kestrels caching 7
prey items together in a 5-min period, I cannot
support Mueller’s (1973) statement that “excessive
killing resulted from the falcon “forgetting” that it
had cached food when it was exposed to the prey
stimulus.” Kestrels cache several consecutive prey
items in the same spot in a period of minutes or
days, and later retrieve them (Stendell and Waian
1968).

Acknowledgments

I appreciate the guidance of William H. Elder. Tim Haithcoat
and Dave Scarbrough provided valuable field assistance. Thomas
S. Baskett and Curtice Griffin provided constructive criticism of
the manuscript. The Natural History Section of the Missouri De-
partment of Conservation funded this study, and the Missouri
Cooperative Wildlife Research Unit (U.S. Fish and Wildlife Ser-
vice, Missouri Department of Conservation, Wildlife Management
Institute, and School of Forestry, Fisheries and Wildlife, Univer-
sity of Missouri-Columbia, cooperating paid publication costs.

Literature Cited

Balgooyen, T.G. 1976. Behavior and ecology of the
American Kestrel in the Sierra Nevada of California
Univ. California Publ. Zool. 103:1-83.

Beebe, F.L. 1960. The marine Peregrines of the nor-
thwest Pacific coast. Condor 62:145-189.

Brown, L.H. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill, New York.

Cade, T.J. 1982. The falcons of the world. Cornell Univ.
Press, Ithaca, New York.

Collopy, M.W. 1977. Food caching by female American
Kestrels in winter. Condor 79:63-68.

Fox, N. 1979. Nest robbing and food storing by New
Zealand Falcons. Raptor Res. 13:51-56.

Greaves, J.W. 1968. Food concealment by Merlins.
British B irds 61:310-311.

Lorenz, K. 1937. Uber die Bildung des Instinkt begrif-
fes. Die naturwissenschaften, 25, Heft 19. (as found in
studies in animal and human behavior, Vol. I, pp.
259-312. Translated by Robert Martin, Cambridge,
Mass., Harvard Univ. Press).

Mueller, H.C. 1973. The relationship of hunger to
predatory behavior in hawks (Falco sparverius and Buteo
platypterus). An. Behav. 21:513-520.

1974. Food caching behavior in the

American Kestrel. Z. Tierphycol. 34:105-114.

Nelson, R.W. 1970. Some aspects of the breeding be-
havior of Peregrine Falcons on Langara Island, B.C.
MS Thesis, Univ. Calgary, Alberta.

1977. Behavioral ecology of Coastal

Peregrines (Falco peregrinus pealei). Ph.D. Dissertation,
Univ. Calgary, Alberta.

Nunn, G.L., P. Klem, Jr., T. Kimmel and T. Merri-
man. 1976. Surplus killing and caching by American

110

Brian Toland

Vol. 18, No. 3

Kestrels. An. Behav. 24:759-763.

Oliphant, L.W. and J.P. Thompson. 1976. Food cach-
ing behavior in Richardson’s Merlin. Can. Field-Nat.
:364-365.

Peterson, S.R. and G.M. Sitter. 1975. Raptor nesting
and feeding behavior in the Snake River Birds of Prey
Natural Area, Idaho: An Interim Report. Snake
River Birds of Prey Research Proj. Ann. Rep.
1975:179-185.

Pierce, W.M. 1937. A pet Sparrow Hawk. Condor
39:137-143.

Pitcher, E., P. Widener and S.J. Martin. 1982. Winter
food caching by the Merlin. Raptor Res. 13:39-40.

Roest, A.L. 1957. Notes on the American Sparrow
Hawk. Auk 74:1-19.

Stendell, R.C. and L. Waian. 1968. Observations of
food-caching by an adult female Sparrow Hawk. Con-
dor 70:187.

Tordoff, H.B. 1955. Food storing in the Sparrow
Hawk. Wilson Bull. 67: 139- 140.

Department of Forestry, Fisheries and Wildlife, University of

Missouri, Columbia, MO 65201.

Received 8 March 1984; Accepted 18 September, 1984.

Fall 1984

Short Communications

111

Short Communications

1981 - An Extraordinary Year for Golden Eagle “Triplets” in the Central Rocky Mountains

M. Alan Jenkins and Ronald A. Joseph

The clutch size of the Golden Eagle (Aquila chrysaetos)
ranges from 1 to 4 eggs with a mean near 2 (Brown 1977).
Clutches of 3 are unusual, occurring less than 1 0% of the
time (Table 1). Normally, 1 to 3 young fledge/successful
nest with a mean of 1.2 to 1.4 (Brown 1977).

and Collopy 1983). We are unable to assess the influence
of these factors on the high number of triplets in 1981
with the possible exception of the influence of high prey
densities. Clutch size, and therefore, ultimate productivity
(number of fledged young/successful nest), are partly in-

Table 1. Frequency of 3-egg clutches in the Golden Eagle.

Study Area

Year(s)

No. OF
Clutches

No. of 3-egg
Clutches

% OF 3-egg

Clutches Reference

California

21

3

14.3

Slevin, in Arnell 1971

Scotland

82

8

9.8

Gordon 1955

Colorado

5

0

0.0

Jollie, in Arnell 1971

Montana

1963-1964

60

4

6.7

McGahan 1966

Montana

1963-1968

30

1

3.3

Reynolds 1969

Utah

1957-1958

5

0

0.0

Hinman [no date]

Utah

1967-1968

23

1

0.4

Murphy et al. 1969

Utah

1969-1970

26

8

30.8

Arnell 1971

Idaho, Oregon

1966

15

1

6.7

Hickman [no date]

TOTALS

267

26

MEAN

9.7

Various factors, from failure to lay eggs to mortality of
nestlings, reduce the probability of a pair of eagles fledg-
ing 3 (“triplets”) from a nest. Table 2 compares data on the
frequency of 3 fledgling nests from various studies of
Golden Eagles in the western United States.

In 1981, we independently surveyed eagle nests for
productivity and recorded nests with 3 nestlings. We sub-
sequently discovered that other investigators, in Utah
especially, found 5 nestling nests. The mean percentage
(3.8%) of nests fledging triplets in 1981 in Utah, Col-
orado, and Wyoming is significantly higher P < 0.10)
than the mean percentage of triplets for other years in the
western United States (Table 2). We assumed that mortal-
ity of the nearly-grown nestling eagles observed in 1981
was low and that most nearly-grown nestlings fledged.
Most studies with which we compared our data also made
that assumption by counting nearly-grown nestlings as
fledglings.

Many factors can influence productivity in Golden
Eagles as reviewed by Newton (1979); also see Edwards

fluenced by the quantity of food adult females eat before
egg-laying affecting her nutritional state of health (New-
ton 1979). Newton (1979) pointed out that rodent-eating
raptors lay clutches that can vary directly in size with
rodent densities in the nest area. This allows raptors to
exploit rodent and other cyclic prey species in high density
years by increasing productivity. Evidence suggest that
this is true of Golden Eagle-prey relationships, because
the eagle’s diet in North America is mainly (74%)
lagomorphs and rodents (Olendorff 1976) that exhibit
cyclic populations (Murphy 1975). This relationship may
be moderated by other factors.

In the western United States lagomorph populations
appear to have increased in the years leading up to 1981 .
In southwestern Idaho populations of Black-tailed Jack-
rabbits ( Leus califomicus) reached plague proportions in
the winter of 1981-82, as reported in the popular press
(e.g., Trueblood 1982). Jackrabbit densities were the
highest in 9 y in 1981 in the Snake River Canyon of Idaho
(Steenhof et al. 1983). In Utah, jackrabbit censuses con-

12

Short Communications

Vol. 18, No. 3

Table 2. Frequency of three-fledgling (triplet) Golden Eagle nests in the western U.S.

Study Area

Year

Total No. Successful No. with
Throughout Study Triplets

% Successful
w/T riplets

Reference

Years Other Than 1981

Idaho, Oregon

1966

17

0

-

Hinman, no date

Utah

1957-1958

5

0

-

Hinman, no date

Utah

1967-1968

18

0

-

Camenzind 1968

Utah

1969-1970

19

3

15.8

Arnell 1971

Wyoming, Colo.

1964-1980

882

1

0.1

Den. Wildl. Res. Ctr.

data

Wyoming

1979

11

0*

-

Lockhart et al. 1980

Wyoming, Mont.

1975-1978

34

0*

-

Lockhart et al. 1978

Montana

1963-1964

55

3

5.5

McGahan 1966

Montana

1962-1968

22

0

-

Reynolds 1969

Oklahoma

1974-1975

6

0

-

Lish 1965

Texas

1974-1975

5

0

-

Lockhart 1976

TOTALS

1,074

7

MEAN

0.7

1981 Data

Utah

1981

95

6

6.3

Present study

Colorado

1981

94

3

3.2

Pearson, Grode pers.

comm.

Wyoming

1981

46

0

0

Phillips and Beske 1981

TOTALS

235

9

MEAN

3.8

♦Data gathered by personal communication with the author.

ducted by the Department of the Army (R. LeClerc pers.
comm.) showed that densities were high(though decreas-
ing thereafter) in autumn 1980 at 3 northwestern Utah
study sites, moderate populations at 3 others, and low at 1
Nevada site. Data from both Steenhof et al. (1983) and the
Army show similar high densities in 1971 supporting the
hypothesis of a 10 yr jackrabbit population cycle in these
areas.

Increased prey availability for nesting eagles is probably
an important cause for higher than normal frequency of
triplets in the western United States in 1981. The only
other instance of a high frequency of triplets is the study
of Arnell 11971) in Utah. He noted hierh lagomorph
populations in 1971, 10 yr before the high number of
triplets in 1981.

Acknowledgment is due to Dugway Proving Grounds
(Dept, of the Army), J.M. Lockhart, E.W. Pearson, B.
Waddell, P.W. Wagner and the Grand Junction office of
the Colorado Division of Wildlife for contributing data.

An earlier draft of the manuscript was reviewed and im-
proved by M.A. Bogan, W.R. Dryer, and R.L. Phillips.

Literature Cited

Arnell, W.B. 1971. Prey utilization by nesting Golden
Eagles ( Acquila chrysaetos ) in central Utah. MS Thesis.
Brigham Young University, Provo, Utah.

Brown, L. 1977. Eagles of the world. Universe Books,
New York. 244 pp.

Camenzind, F.J. 1968. Nesting ecology and behavior of
the Golden Eagle in west central Utah. Unpbl. Master’s
Thesis. Brigham Young University, Provo, Utah. 40

pp.

Edwards, T.C., Jr., and M.W. Collopy. 1983. Obligate
and facultative brood reduction in eagles: an exami-
nation of factors that influence fratricide. Auk
100:630-635.

Fall 1984

Short Communications

113

Gordon, S. 1955. The Golden Eagle. Collins, London.
246 pp.

Hickman, G.L. [no date.] Life history and ecology of the
Golden Eagle in southwestern Idaho and southeastern
Oregon. U.S. Fish and Wildlife Service Rep. 104 pp.

Hinman, R.A. [no date.] Antelope populations in
southwestern Utah with special reference to Golden
Eagle predation. Completion Rep., Fed. Aid. Proj.
W-65-R-6. 61 pp.

Lish, J.W. 1975. Status and ecology of Bald Eagles and
nesting of Golden Eagles in Oklahoma. MS Thesis.
Oklahoma State University, Norman, OK. 98 pp.

Lockhart, J.M. 1976. The food habits, status and ecol-
ogy of nesting Golden Eagles in the Trans-Pecos re-
gion of Texas. MS Thesis. Sul Ross State University,
Alpine, Texas. 65 pp.

, T.P. McEneaney, and R.L. Phil-
lips. 1978. The effects of coal development on the
ecology of birds of prey in southeastern Montana and
northern Wyoming. Annual Progress Rep. 1978., Sec-
tion of Wildlife Ecology on Public Lands, Denver
Wildlife Research Center, Denver, Colorado pp. 9-14.

, D.W. Heath, and C.L. Be-
litsky. 1980. The status of nesting Peregrine Fal-
cons and other selected raptor species on the Black
Butte Mine Lease and adjacent lands. U.S. Fish and
Wildlife Service - Final Rept. to the U.S. Bureau of
Land Management and Peter Kiewit Sons’ Co. 59 pp.

McGahan, J. 1966. Ecology of the Golden Eagle. MS
Thesis. University of Montana, Missoula, MT. 78 pp.

Murphy, J.R. 1975. Status of a Golden Eagle population
in central Utah, 1967-1973. In: J.R. Murphy, C.M.
White and B.E. Harrell (eds.) Population status of
raptors . Raptor Res. Rep. No. 2. pp. 91-96

Murphy, J.R., F.J. Camenzind, D.G. Smith, and J.B.
Weston. 1969. Nesting ecology of raptorial birds in
central Utah. Brigham Young Univ. Sci. Bull., Biol. Ser.
10:1-36.

Newton, I. 1979. Population ecology of raptors. Buteo
Books, Vermillion, South Dakota. 399 pp.

OlendOrff, R.R. 1976. The food habits of North
American Golden Eagles. Amer. Midi, Nat. 95:231-236.

Phillips, R.L., and A.E. Beske. 1981. Golden Eagles
and coal development in the eastern Powder River
Basin of Wyoming. Unpubl. Rep. U.S. Fish and
Wildlife Service, Denver Wildlife Research Center,
Denver, Colorado. 55 pp.

Reynolds, H.V., III. 1969. Population status of the
Golden Eagle in south-central Montana. MS Thesis.
University of Montana, Missoula. MT. 61 pp.

Steenhof, K., M.N. Kochert, and J.H.
Doremus. 1983. Nesting of subadult Golden Eagles
in southwstern Idaho. Auk 100:743-747.

Trueblood, T. 1982. The great rabbit roundup. Field
and Stream 86(12): 1 1,14, 16.

White, C.M., and T.L. Thurow. 1984. Reproduction of
Ferruginous Hawks exposed to controlled distur-
bance. Condor (in press).

U.S. Fish and Wildlife Service, Denver Wildlife Research
Center, Building 16, Federal Center, Denver, CO 80225. Ad-
dress of second author: U.S. Fish and Wildlife Service, Federal
Building, Room 1311, 125 South State Street, Salt Lake City,
UT 84138.

Received 27 December, 1983; Accepted 11 June 1984.

Food Piracy Between European Kestrel and Short-eared Owl

Erkki KoRPiMaki

I studied a raptor community of the large field plain of
Alajoki in Southern Ostrobothnia, western Finland (63°
05 'N, 22°55'E), from 1977 through 1982 (see Korpimaki,
etal. 1977, 1979). The most numerous raptor on the study
area was the Short-eared Owl ( Asio flammeus) (315 total
pairs, 39.4%), followed by European Kestrel ( Falco tin-
nunculus) (36.2%), Long-eared Owl (A. otus) (20.0%),
Northern Harrier {Circus cyaneus) (2.5%), Boreal Owl
{Aegolius funereus) (1.6%) and Sparrow Hawk (Accipiter
nisus) (0.3%); for addition details see Korpimaki

1984a). Although the 4 most common species comprise
the guild of open-terrain hunting birds of prey in the
study area (Korpimaki 1978, 1981), inter- and intra-
specific food piracy or kleptoparasitism (see Brockmann
and Barnard [21979] for additional details on the terms)
was observed only once. Consequently this case may be of
some interest.

On 16 May 1982 at 2130 H, I saw a Short-eared Owl in
the northern part of Alajoki flying over the field at the
height of about 120 m and carrying a vole in its talons. The

114

Short Communications

Vol. 18, No. 3

owl passed a male European Kestrel sitting on the roof of a
barn. The kestrel chased the owl and struck it in the back.
It attacked 3 times and the owl took shelter in high vegeta-
tion near a ditch. The kestrel stopped attacking and re-
turned to the roof of the same barn. The owl waited for a
few minutes on the ground and then started to fly and
hunt again. When I examined the location where the owl
took shelter, I found a whole Common Vole ( Microtus
arvalis), which was still warm, but no owl nest. The nest in
this territory was found on 5 June, when the young were
just hatching. Consequently the female was incubating in
the middle of May, and the owl observed was probably the
hunting male. The kestrel does not breed in the vicinity
and was apparently not defending a nest.

The proportion of Microtus voles (M. agrestis and M.
arvalis) in the diets of raptors was studied in 1977, when it
was 95.5% for Long-eared Owl, 97.6% for Short-eared
Owl and 87.7% for European Kestrel (Korpimaki et al.
1977). As rodents are central also in the diet of Northern
Harrier (in Norway 57%, Hagen 1952), voles are the most
important prey item for raptors of Alajoki, although there
are also some alernative prey groups available (e.g.,
shrews, mice, birds, lizards, frogs and insects; Korpimaki
1984b). Consequently, one might expect a keen inter- and
intraspecific competition for food among these birds,
especially when voles are scarce. Vole populations crashed
in 1980-81 and were in the increase phase in 1982 (Kor-
pimaki 1984a), wherefore a lack of food may have been
the reason for piratical behaviour of the kestrel. Also,
Brockmann and Barnard (1979) pointed out that klep-
toparasitism occurs more frequently during years of a
food shortage. The hunting Short-eared Owl flies near
the ground and locates its prey by hearing and sight. The
hunting technique of the owl is adapted to catching of
prey animals in the high grass (for example in unculti-
vated fields) better than that of the kestrel, which flies or
hovers high in the air over the field (Korpimaki 1978).
The Short-eared Owl is a vole specialist, while the kestrel
preys opportunistically on shrews, birds, lizards, frogs and
insects when voles are scarce (Korpimaki 1984b). Thus the
Short-eared Owl can probably catch voles of lower
densities compared with the kestrel, and it may be advan-
tageous for the kestrel to rob food from Short-eared Owl,
which is quite a slow flyer.

Food piracy between the European Kestrel and Short-
eared Owl is quite rare. I have found only 6 earlier cases
described in literature (from Sweden, Mascher 1963,
Nilsson 1975 and from Great Britain, Balfour 1973, Reese
and Balfour 1973, Boyle 1974, Clegg and Henderson
1974). Dickson (1971) has described also an interaction of
Short-eared Owl, European Kestrel and Northern Har-
rier on same pipit prey. All above mentioned cases were
observed from the end of winter to the beginning of
summer when vole populations were at their lowest and
the competition for food may have been keenest. Food
shortage enhances kleptoparasitism among birds, espe-

cially in falconiforms and charadriiforms (Brockmann
and Barnard 1979).

Food piracy is more general between open-country
predators in central and western Europe than in my
northern study area, because harriers can also take prey
from Short-eared Owls (11 cases in Great Britain, Watson
1977 and in the United States, Berger 1958, Clark 1975).
On the other hand, Short-eared Owl may sometimes
adopt piratical behaviour. Wood (1976) has observed that
the owl tried to take a small rodent from a Stoat ( Mustela
erminea)-, Bildstein and Ashby (1975) saw the owl robbing
prey from Northern Harrier and Gordon Riddell (ac-
cording to Mikkola 1983) described a Short-eared Owl
attempting to take prey from a kestrel. This apparent
difference in frequency of piratical behaviour between
regions may be due to the cyclic fluctuations of the vole
populations in northern Europe causing a higher degree
of nomadism among raptors compared with a more stable
food production in more southern areas where raptors
tend to be resident. Most raptors migrate from my study
area when voles are scarce (Korpimaki 1984a), and this
behaviour decreases the competition for food.

Acknowledgment

I thank Mikko Hast for help in the field work, Clayton M. White
and an anonymous reviewer for useful comments on my manus-
cript as well as the Finnish Cultural Foundation, the Oulu Student
Foundation, the Jenny and Antti Wihuri Foundation, the Emil
Aaltonen Foundation and the Academy of Finland for financial
support of my raptorial studies.

Literature Cited

Balfour, E. 1973. Food piracy between kestrel, short-
eared owl and hooded crows. British Birds 66:227-228.

Berger, D. 1958. Marsh hawk takes prey from short-
eared owl. Wilson Bull. 70:90.

Bildstein, K.L., and M. Ashby. 1975. Short-eared Owl
robs Marsh Hawk of prey. Auk 92:807-808.

Boyle, G.L. 1974. Kestrel taking prey from short-eared
owl. British Birds 67:474-475.

Brockmann, H.J., and C.J. Barnard. 1979. Klep-
toparasitism in birds. Animal Behaviour 27:487-514.

Clark, R.J. 1975. A field study of the short-eared owl,
Asio flammeus (Pontoppidan), in North America. Wildl.
Monogr. 47:1-67.

Clegg, T.M., and D.S. Henderson. 1974. Kestrel taking
prey from short-eared owl. British Birds 64:317.

Dickson, R.S. 1971. Interaction of Short-eared Owl,
Kestrel and Hen Harrier over pipit prey. British Birds
64:543.

Hagen, Y. 1952. Rovfuglene og viltpleien. Oslo.

KoRPiMaki, E. 1978. Observations from hunting habits
of seven raptorial species. Suomenselan Linnut
313:40-44, 86-89.

Fall 1984

Short Communications

115

1981. On the ecology and biology of

Tengmalm’s Owl (Aegolius funereus) in Southern Os-
trobothnia and Suomenselka, western Finland. Acta
Univ. Ouluensis ser. A. Sci. rerum not. 118 Biol. 13:1-84.

. 1984a. Population dynamics of birds

of prey in relation to fluctuations in small mammal
populations in western Finland. Annales Zoologici Fen-
nici 21 (in print).

. 1984b. Optimal diet of the Kestrel

Falco tinnunculus in breeding season. Ornis Fennica 61
(in print).

. 1984c. Prey choice strategies of the

Kestrel Falco tinnunculus in relation to small mammal
abundance and Finnish birds of prey. Annales Zoologici
Fennici 21 (in print).

, S. Ikola, R. Haapoja, and J.

KiRKKOMaki. 1977. On the ecology of Long-eared,
Short-eared and Tengmalm’s Owls as well as Kestrel
and Hen Harrier in Alajoki in 1977. SuomenselUn Lin-
nut 12:100-117.

, E., S. Ikola, R. Haapoja, and O. Hem-

minki. 1979. On the occurrence and breeding of
raptors in Alajoki in 1978. SuomenselUn Linnut
14:44-51.

Mascher, J.W. 1963. Torn falk (Falco tinnunculus) over-
tar byte fr&n jorduggla {Asio flammeus) i flykten. Vdr
FAgelvarld 22:293-294.

Mikkola, H. 1983. Owls of Europe. T & A D Poyser,
Calton. 397 pp.

Nilsson, I. 1975. Tornfalk poarasiterar pa jorduggla.
Anser 14:133.

Reese, R.A., and E. Balfour. 1973. Food piracy bet-
ween kestrels and short-eared owls. British Birds
66:227-228.

Watson, D. 1977. The Hen Harrier, T & A D Poyser,
Calton. 307 pp.

Wood, C.R. 1976. Piratical short-eared owl. British Birds
69:272.

Kp.4, SF-62200 Kauhava, FINLAND

Received 17 December 1983; Accepted 4 June 1984

An Unusual Observation of ‘Homing’ To Prey By A
Migrating Immature Peregrine Falcon

Carl Safina

On 6 October 1981 at 10:05 EST, while operating a
raptor banding station on the Long Island, New York
barrier beach, I saw a hatching year female Peregrine
Falcon (. Falco peregrinus) land approximately 50 m from
my blind and begin eating a small passerine (probably a
White-throated Sparrow (Zonotrichia albicollis, based on
feathers). The falcon was on a low, beach heather (. Hud -
sonia) covered rise in a broad, open rolling area. Soon after
the falcon began eating, an Osprey ( Pandion haliaetus),
carrying a fish, came over the falcon, vocalizing. The
Peregrine flew up and chased the Osprey over the bay to
the north, stooping repeatedly at it before flying out of
sight. Within 5 min the falcon reappeared on its kill. As
the prey was small, cryptically colored, and in a broad,
non-descript area of the beach, and since the Peregrine
was not seen searching for it, apparently the falcon re-
membered exactly where it had left its kill and was able to
return there from a point out of sight.

Falcons frequently return to cached prey. What is in-
teresting about this incident is that the falcon was a first
year migrant and the topography was almost certainly not
familiar (the banding station had been manned daily for 3
w prior, and no Peregrines appeared to have been staying
in the area). Enderson (Auk. 81 :332-352, 1964) described
wintering Prairie Falcons ( Falco mexicanus ) leaving their
prey on the ground and driving off other rapors in a
similar manner. His falcons seldom had difficulty re-
locating the prey, but this is not surprising because they
were familiar with the area.

National Audubon Society, Scully Sanctuary, 306 South Bay
Avenue, Islip, NY 11751.

Received 30 March 1983; Accepted 30 April 1984

Errata - Raptor Research 18(2)

Page 44 (Table 1 concluded), 0.420& should appear in the column for shell thickness, 0.49*1 should appear in the
column for HE and 0.27*1 should appear in the column for DDE; page 47, paragraph 3, line 6, > 8 ppm should appear
as >8 ppm; page 6 1 , Literature Cited, the Sawby et al. reference appeared in Condor 76:479-481 ; page 70, photographs
are reversed.

116

News and Reviews

Vol. 18, No. 3

“The Peregrine Falcon At Reelfoot Lake”

By Murrell Butler
Limited Edition Print of 2,500

A tree-nesting “Duck Hawk” populated the Mississippi and Ohio River areas in times past. A remnant nesting
population was first documented during the 1930’s at Tennessee’s Reelfoot Lake by the late Albert F. Ganier. During
the 1940’s a new nest site was discovered on the west side of the lake by Dr. Walter R. Spofford, then Professor of
Anatomy at Vanderbilt University. Dr. Spofford and a few carefully selected observers made yearly nesting observa-
tions until the early 1950’s.

Mr. Thomas S. Butler was privileged to have been among those who spent many days recording the events of each
year’s breeding season beneath the enormous cypress tree that served as the falcons’ nest site. During the late 1970’s a
happy circumstance led Tom to meet Murrell Butler, a distant cousin from Louisiana. Murrell was an accomplished
wildlife artist and became enthralled by the tales of a Peregrine Falcon that once nested in the snag of the mammoth
cypress tree. A subsequent trip to the nest site (the cypress still stands!), the relocation of old photographs and
consultation with friends and fellow falconers culminated in this magnificent painting by Murrell Butler.

“The Peregrine Falcon at Reelfoot Lake” portrays the last known North American tree nest of the Peregrine.
Available in a 16" by 20" limited edition print of 2500, the introductory price is $65.00 for prints #1 - #500. The
introductory price includes postage within the fifty staites and a $10.00 donation to The Raptor Research Foundation,
Inc. The price will advance to $125.00 per print for #2001 - 2500, according to the following schedule: #1 - 500,
$65.00; #501 - 1000, $75.00; #1001 - 1500, $85.00; #1501 - 2000, $95.00; #2001 - 2500, $125.00; Arkansas residents
will need to add state, city and /or county sales tax). Prints may be ordered directly from Mr. Thomas S. Butler, Butler
Galleries, 28 Fairmont Street, Eureka Springs, Arkansas 72632, USA. Payment may be made by check, money order,
VISA or MASTERCARD.

RAPTOR RESEARCH

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EDITOR: Clayton M. White, Department of Zoology, 161 Widtsoe Building, Brigham Young University, Provo,
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ASSOCIATE EDITORS

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INTERNATIONAL CORRESPONDENT: Richard Clark, York College of Pennsylvania, Country Club Road,
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Raptor Research (ISSN 0099-9059) welcomes original manuscripts dealing with all aspects of general ecology, natural
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INSTRUCTIONS FOR CONTRIBUTORS: Submit a typewritten original and two copies of text, tables, figures and
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Raptor Research

A Quarterly Publication of The Raptor Research Foundation, Inc.

Volume 18, Number 4, Winter 1984

(ISSN 0099-9059)

Contents

Raptor Community Structure of a Primary Rain Forest in French Guiana
and Effect of Human Hunting Pressure. Jean-Marc Thiollay 117

Biological and Etho logical Notes On Falco peregrinus cassini in

CENTRAL ARGENTINA. Wenceslao Guillermo Vasina and Roberto J. Straneck 123

Behavior of the African Peregrine During Incubation.

Warwick Tarboten 131

Roost Selection and Behavior of The Long-Eared Owl (Asio otus)

Wintering in New Jersey. Thomas Bosakowski 137

Factors Influencing Differential Predation on House Mouse (Mus musculus)

by American Kestrel (Falco sparverius). James R. Bryan 143

Habitat Selection by the American Kestrel (Falco sparverius) and Red-tailed Hawk
(Buteo jamaicensis) Wintering in Madison County, Kentucky.

N ancy J . Sferra 148

Short Communications
A Clutch of Unusually Small Peregrine Falcon Eggs.

M. Alan Jenkins 151

Eyrie Aspect as a Compensator for Ambient Temperature Fluctuations: A Preliminary

Investigation. Richard N. Williams 153

Successful Breeding of a Pair of Sharp-shinned Hawks in Immature Plumage.

David L. Fischer 155

Thesis Abstracts 157

News and Reviews 158, 159, 160

The Raptor Research Foundation, Inc.
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RAPTOR RESEARCH

A QUARTERLY PUBLICATON OF THE RAPTOR RESEARCH FOUNDATION, INC.

VOL. 18

Winter 1984

No. 4

j ' )

RAPTOR COMMUNITY STRUCTURE OF A PRIMARY RAIN FOREST
IN FRENCH GUIANA AND EFFECT OF HUMAN HUNTING PRESSURE

Jean-Marc Thiollay

Abstract - The diurnal raptor community of a primary rain forest in French Guiana was studied, both around a small
isolated village and far from any human settlement. Twenty species were found in large areas of unbroken forest and 6
additional species only near edges and clearings around the village. The comparison between hunted and non-hunted
patches of otherwise similar virgin forest showed that even a moderate hunting pressure (i.e., for food by few people)
significantly reduces both mean species richness of sample counts and density of most primary forest raptors. The largest
species may eventually disappear.

Other than regional avifaunas and local anno-
tated lists, including birds of prey, I found no
studies on any entire raptor community of a par-
ticular primary Neotropical rain forest. Most pap-
ers are restricted to short observations on feeding
(Haverschmidt 1962; Greenlaw 1967; Smith 1969;
Lamm 1974; Lemke 1979; Boyce 1980; Fontaine
1980) or breeding behavior (Laughlin 1952; Smith
1970; Strauch 1975). Very few are longer, be-
havioral (Peeters 1963; Fowler and Cope 1964;
Skutch 1965; Rettig 1968; Gochfeld et al. 1978), or
ecological studies (Voous 1969; Smith and Temple
1982).

The number of falconiform species is much
higher in tropical American forests than in similar
forests of other continents (Thiollay 1984). How-
ever, their overall density does not seem to be
higher (pers. obs. in Africa, Asia and Central
America). Tropical forest raptors are exceedingly
difficult to see in their natural habitat, so much so
that only one nest of Micrastur (5 species), probably
the most widespread genus of Neotropical rain
forest raptors, has ever been found (Mader 1979).

The avifauna of French Guiana is poorly known
(see Tostain 1980), though type specimens of many
species (including raptors) coming from this coun-
try were described nearly 200 y ago. This paper
presents the preliminary results of a larger study
designed for a rain forest national park in French

Guiana, and the effect of human hunting pressure
on the non-game bird community of primary forest.
The objectives were to determine: ( 1 ) the composi-
tion of the diurnal raptor community of a truly
virgin Neotropical rain forest, (2) the closest esti-
mate of the structure (relative abundance of species)
of such a community, (3) the forest species occur-
ring only near the edge of large clearings or as-
sociated secondary forest and not around smaller
natural opening in otherwise unbroken forest, and
(4) the result of a moderate human hunting pres-
sure (mostly on non-raptor species) on the raptor
community richness and species’ abundance.

Study Area and Methods

The study site was in southcentral French Guiana (3° 35 'N - 53°
10'W) near the small village of Saul (50 inhabitants, mainly
goldminers). There are no other settlements or clearings within a
100 km radius. The country was hilly (200 to 500 m) and com-
pletely covered with high, dense, primary rain forest. The rich
flora (ca. 500 tree species) was described by Granville (1978) and
the forest structure by Oldemann (1974). The mean canopy
height was 30-40 m with the highest trees up to 60 m. Numerous
tree fall gaps and small streams (but no large rivers) increase
habitat diversity. Mean annual rainfall was 2400 mm, occurring
mainly from December to February and April to July. Precipita-
tion was 96 mm in November (17 d) and 206 mm (24 d) in
December 1983.

The village was surrounded by about 150 ha of plantations, old
re-growth, secondary forest and an airfield. A network of 120 km
of small trails helped when searching the forest within about 5 km
around the village. Local people hunted there for food. Nearly all

117

Raptor Research 18(4): 117-122

118

Jean-Marc Thiollay

Vol. 18, No. 4

medium-size or large mammals and birds were hunted. The fol-
lowing raptors were killed during my 6 wk study: 1 Harpy Eagle
{Harpia harpyja), 1 Ornate Hawk Eagle ( Spizaetus ornatus ), 1 White
Hawk (Leucoptemis albicollis), 2 Red-throated Caracara (Daptrius
americana) and 1 Bat Falcon (Falco rufigularis). According to the
villagers, about 50 rapors/yr are killed. Hunting has begun there
since the first gold miners settled less than 50 y ago.

The second area was located in the Massif des Emerillons, 50 km
south of Saul. It is uniformly covered by a strictly virgin rain forest,
similar to that of Saul but completely devoid of any human settle-
ment (the nearest is Saul), even of nomadic indians, and never
hunted. The study site was around a bare rocky outcrop which
provided the only opening in the forest. Only faint markings were
made along line transects which radiated in every direction.

In both areas, only primary, structurally intact forest was consi-
dered, but tracks, small openings and edges, from which soaring
birds were searched, were included. In Saul this had an influence
on the species composition since wider ranging soaring raptors
coming from neighboring secondary habitats were recorded
above the primary forest canopy.

After a preliminary survey in December 1981 — January 1982,
counts were made from 22 November 1983 to 2 January 1984.
The Saul area, studied in 31 d, extended over about 100 km2,
against less than 10 km2 in the Massif des Emerillons, which was
surveyed during 1 1 d. This period covered the end of the dry
season and the beginning of the rainy season and little time was
lost because of afternoon rains.

In spite of numerous attempts in other tropical forests, I have
found no single method which can give an accurate figure of a
whole tropical forest raptor community. Therefore, the following
two complementary methods were used;

1 - The number of birds seen or heard within < 1 00 m on each side
of the line transect, per 2 h spent slowly walking with frequent
stops inside the forest, was recorded. Very noisy flocks of
caracaras were more often heard than seen, and their flock size
could not always be accurately assessed. Therefore, only the
number of flocks was computed, irrespective of the actual
number of individuals. No significant differences were found
among times of day, so all hours have been lumped (rainy
periods excluded). This careful search is the only way to detect
all the non-soaring species, although more specialized methods
(tape records, traps) may help to detect a higher proportion of
some species.

2 - From edges, natural gaps on ridges or rocky outcrops
dominating the forest, the minimum number of different
individual birds seen flying over the canopy, or even sitting
on exposed branches, was recorded during 2-hr periods,
spent on the same spot in non-rainy weather. To account for
the hourly variation of the species’ soaring activity, the day
was divided into 4 periods. Only birds within < 1 km (the
range of visibility of a small raptor to the naked eye) were
recorded.

Pooling the data from the 2 methods does not give an accurate
figure of the entire community because of very different degrees
of conspicuousness, and hence detectability, among species,
hours, weather, etc. In spite of this, a rough and tentative estimate
of the numerical proportion of each species in the raptor com-
munity will be made. The percentages were calculated on the
maximum frequency recorded in any of the 2 methods (i.e., mean
number of individuals seen per 2-hr period, either under or above
the canopy, during the most favourable time of day). Such a
treatment obviously underestimates the relative importance of
inconspicuous species which rarely, if ever, soar (forest falcons
( Micrastur sp.), Black-faced Hawk ( Leucoptemis metanops), etc.

Results and Discussion

The first striking result was the higher mean
species richness per sample count and abundance
of raptors in non-hunted vs hunted areas, even
when the natural primary forest in hunted area
suffered no other disturbance than the occasional
presence of a few hunters and goldminers. From
the hunted to the non-hunted forest, the mean
number of species per 2-hr sample increased both
under (+ 53.6%, Table 1) and above the canopy ( +
40.9%, Table 2). The frequency of encounters with
caracara flocks was 69.4% higher in non-hunted vs
hunted area (Table 1). Similarly, the abundance of
other raptors increased from the hunted to the
protected forest by 46.6% (Table 1) to 93.9% (Table
2). This change in mean number of individuals seen/

Table 1. Mean number of individuals (or whole flocks of Daptrius) and species seen/2-hr periods of careful search
within a 200 m wide strip under the primary rain forest canopy in hunted (Saul) and not hunted (Emerillons)
areas. Vultures and kites seen soaring above the canopy are not included.

2-Hr

counts

Flocks (X) of
Daptrius americanus

Individual (X) raptors
other than Daptrius

Species (X)
including Daptrius

Hunted

128

0.36

0.15

0.56

Not hunted

28

0.61

0.22

0.86

Winter 1984

Raptor Community Structure - Tropics

119

Table 2. Mean number of individuals and species of raptors seen/2 hr period sitting in the upper canopy (excluding
Daptrius), or most often soaring. Observations are within 1 km of the still observer, during the 4 periods of the
day in hunted (Saul) and not hunted (Emerillons) areas.

0600 H -

0900 H

0901 H -

1200 H

1201 H-

1500 H

1501 H-

1800 H

Counts

Individuals Species

Individuals

Species

Individuals

Species

Individuals

Species

(X)

(X)

(X)

(X)

(X) ■

(X)

(X)

(X)

Hunted

33

2.20

1.24

11.90

7.18

4.33

3.25

2.02

1.55

Not hunted

12

1.50

1.50

20.33

9.33

6.83

3.80

11.00

4.00

2-hr period is the closest estimate available of actual
density fluctuations. All the differences were
statistically significant (Mann Whitney U-test, P <
0.01) for both the pooled four hourly periods (as
above) and when computing them separately (ex-
cept for the 6-9 hr period of Table 2). Such a con-
stant trend, whatever the method used or the set of
species considered, strongly suggests that a “nor-
mal” human hunting pressure from a small isolated
village on both raptors (which are killed for food or
fun) and more traditional game animals may deeply
impoverish the raptor fauna.

Table 3 gives a tentative figure of the whole rap-
tor community in the 2 forest areas. Table 3 takes
into account only the highest value of the mean
number of individuals recorded for each species
either under or above the canopy in any set of the
same 2 h samples. Indeed, highly conspicuous
soaring species recorded over a 1000 m radius are
mixed with smaller, very inconspicuous species of
the understory, detectable over a much shorter
range. Therefore, percentages cannot be rep-
resentative of the actual relative densities and they
are given only as long as better estimates are not
available. The main goal was to compare two areas
with the same methods in similar habitats at the
same season. In this respect Table 3 shows that all
species, except the Accipiter-Micrastur group (rarely
soaring and thus badly sampled), reach a higher
abundance in non-hunted than in hunted areas.
However, excluding 4 species linked to secondary
habitats (see below) and 4 species not recorded in
the virgin forest (probably because of too short a
survey or too small an area studied). The 2 com-
munities have a rather similar diversity (H' = 2.37

in non-hunted vs 2.28 in hunted zone) and equita-
bility index (J ' = H 7H ' max = 0.59).

Among the 26 species identified, 6 were as-
sociated with clearings and secondary growths
around Saul and 4 occured in the samples when
soaring (Black Hawk Eagle (Spizaetus tyrannus).
Tiny Hawk (Accipiter superciliosus) or hunting
Plumbeous Kite (Ictinia plumbea ), Bat Falcon) over
the unbroken primary forest, but never far from its
edge. The last 2 species of this group, the Crane
Hawk ( Geranospiza caerulescens) and the Gray Hawk
( Buteo nitidus ) have only been recorded at the edge
of the primary forest and hence are not included in
any count. The lack of species around Saul such as
the Roadside Hawk (Buteo magnirostris ) or the
Laughing Falcon (Herpetotheres cachinnans ), com-
mon in secondary habitats at the northern edge of
the Guianan forest, reflects the small size of the
local clearing and the absence of other gaps over a
huge surrounding area. Hereafter, all species will
be typical of the undisturbed primary forest, even if
most of them also occurred elsewhere in secondary
habitats.

Three species continuously soaring high above
the forest have a relative density obviously overes-
timated. The Greater Yellow-headed Vulture
(Cathartes melambrotus) is the only Cathartes iden-
tified within the vast expanses of unbroken virgin
forest. The two other congeneric species are com-
mon in northern Guiana around clearings, savan-
nas and marshes. The King Vulture ( Sarcoramphus
papa) is as widespread as the previous species but it
is proportionally more abundant in non-hunted
areas (ratio Cathartes /Sarcoramphus = 1.1 vs 1.9 in
hunted forest). The last very conspicuous species is

120

Jean-Marc Thiollay

Vol. 18, No. 4

Table 3. Relative abundance of raptors in hunted (Saul) and not hunted (Emerillons) primary forests. N max =
highest frequency (mean number of individuals seen/2 h) obtained in any method and time period. % =
proportion of the species in the community (percentage of the total number) computed from the above
frequency. Names are from the A.O.U. checklist, 1983.

Hunted

N Max %

Not hunted
N Max %

Greater Yellow-headed Vulture, Cathartes melambrotus

1.66

13.6

3.00

14.0

King Vulture, Sarcoramphus papa

0.88

7.2

2.66

12.5

Gray-headed Kite, Leptodon cayanensis

0.11

0.9

?

a

Hook-billed Kite, Chondrohierax uncinatus

0.44

3.6

?

a

Swallow-tailed Kite, Elanoides forficatus

1.60

13.2

4.00

18.7

Double-toothed Kite, Harpagus bidentatus

1.66

13.7

2.00

9.4

Rufous-thighed Kite, Harpagus diodon

0.22

1.8

0.33

1.5

Plumbeous Kite, Ictinia plumbea

0.90

7.4

b

Tiny Hawk, Accipiter superciliosus

0.11

0.9

b

Bicolored Hawk, Accipiter bicolor

0.22

1.8

0.08

0.4

White Hawk, Leucopternis albicollis

0.99

8.1

1.33

6.2

Black-faced Hawk, Leucopternis melanops

0.04

0.4

p

V

Great Black Hawk, Buteogallus urubitina

0.33

2.7

2.00

9.4

Crested Eagle, Morphnus guianensis

0.11

0.9

0.50

2.3

Harpy Eagle, Harpia harpyja

c

1.00

4.6

Black and White Eagle, Spizastur melanoleucus

0.88

7.2

1.33

6.2

Black Hawk Eagle, Spizaetus tyrannus

0.44

3.6

b

Ornate Hawk Eagle, Spizaetus ornatus

0.33

2.7

1.33

6.2

Red-throated Caracara, Daptrius americanus ^

0.44

3.6

1.66

7.8

Barred Forest Falcon, Micrastur ruficollis

p

a

0.03

0.2

Lined Forest Falcon, Micrastur gilvicollis

0.22

1.8

0.07

0.4

Slaty-backed Forest Falcon, Micrastur mirandollei

0.01

0.1

?

a

Collared Forest Falcon, Micrastur semitorquatus

0.02

0.2

0.03

0.2

Bat Falcon, Falco rufigularis

0.55

4.5

b

a = may exist but not identified

b = not seen and probably lacking

c = formerly known, but now a rare vagrant

d = number of flocks heard within a 1 km radius from vantage points used for the census of soaring species

the Swallow-tailed Kite (Elanoides forficatus ) grace-
fully flying over the forest in flocks of 3 to 8 and
roosting in high, emergent dead trees.

Two medium size kites, the Gray-headed (Lepto-
don cayanensis ) and the Hook-billed are very local
and might be associated with forest openings. The
Double-toothed Kite ( Harpagus bidentatus ) is the
most likely of all small forest raptors to soar over the
canopy or spend long periods in upper exposed
branches and it appears much more abundant than
other similar sized species. It has certainly a higher

density than the congeneric Rufous-thighed Kite
(Harpagus diodon) (6-7 times higher in the counts)
which has only a slightly less conspicuous behavior.
These 2 Kites may co-exist since I have seen them in
the same patch of forest at two different localities.
On the other hand, the Bicolored Hawk (Accipiter
bicolor ) is probably commoner than suggested by the
results (see Table 3) since it rarely soars and is
restricted to low levels of the understory.

The White Hawk is mostly found on the edge of
clearings or natural gaps and often soars, whereas

Winter 1984

Raptor Community Structure - Tropics

121

the congeneric Black-faced Hawk has only been
seen in dense undergrowth at medium height.
Their conspicuousness is very different and their
actual relative frequencies might be closer to each
other than suggested by Table 3. The Great Black
Hawk (. Buteogallus urubitinga) is a conspicuous rap-
tor (pairs often perform noisy displays) but patchily
distributed along some forest streams or rocky
openings.

The Harpy Eagle is the only species not recorded
from the hunted forest (although one was shot just
outside the study area). Thus, it appears to be the
species most sensitive to human hunting pressure,
directly and through lack of prey. During this
study, I have never seen it soaring, unlike Morphnus,
but adults are easily seen in the morning from gra-
nite outcrops dominating the forest, when they
perch on exposed branches of the upper canopy.
The Crested Eagle {Morphnus guianensis ) has prob-
ably a higher overall density or a wider distribution
than the Harpy. One pair of each of these species
was followed from a vantage point above the
Emerillons virgin area. From the distribution of
their perch sites and display flight circuits, their
respective territories seemed to be contiguous but
not overlapping. No interspecific aggressive be-
havior was observed.

The Black and White Hawk-eagle ( Spizastur
melanoleucus ) is the commonest eagle (but also the
one which most often soars). The Ornate Hawk
Eagle is the only Spizaetus in pure primary forest
where it may be more abundant than Harpia and
Morphnus together, but slightly less than Spizastur.

The Red-throated Caracara {Daptrius americanus )
is by far the most noisy and conspicuous raptor, but
it never soars. Nevertheless, it actually reaches the
highest density of all raptors both in hunted and
virgin primary forest, if the number of individuals,
and not only flocks, is taken into account. They are
always in territorial flocks of 3-9 birds often loosely
associated with Toucans (mainly Ramphastos vitel-
linus) and Oropendolas (mainly Psarocolius viridis).
Around Saul, on 6000 ha intensively surveyed,
there were 12 flocks (at least 71 individuals).
Elsewhere, the Yellow-throated Caracara {Daptrius
ater ) has been recorded only along rivers, and the
lack of any sizeable river in the study area may
explain why this species has never been seen there.

The 4 species of Micrastur (forest falcons) are
exceedingly secretive and inconspicuous (unless

their voices are known). They are probably more
abundant than suggested by the results and may be,
together, as abundant or more than Accipiter and
Harpagus because, among small raptors, they are
the most frequently seen in the understory. The
commonest species is the Lined Forest Falcon (M.
gilvicollis). The Barred Forest Falcon (M. ruficollis),
if accepted as a separate species (according to the
criteria given in Meyer de Schauensee and Phelps
[1978] and Schwartz [1972]) was definitely iden-
tified only once. The Collared Forest Falcon (M.
semitorquatus ) is widespread and the Slaty-backed
Falcon (M. mirandollei) seems to be the rarest species
of the genus.

Conclusion

The virgin state over several million ha of the
forest in French Guiana affords a fair opportunity
to answer the main question of this study which was
to ascertain the influence, on the raptor commun-
ity, of a small human settlement, with associated
clearings and hunting pressure, within a large tract
of primary rain forest. Although it is difficult to
assess the accurate structure of a rain forest com-
munity, because o' very different degrees of con-
spicuousness between species, the results strongly
suggest that (1) small clearings of shifting cultiva-
tion and secondary growths attracted 6 additional
species, apparently very rare and local (large gaps)
in natural conditions and thus increased the overall
species diversity, and (2) hunting pressure, though
mainly on a few game animals, lowers the density of
most primary forest raptors, especially the large
species, some of which may eventually disappear
(Harpy Eagle).

Hunting may depress raptor density both
through occasional direct killing of sensitive hawk
species (the largest ones which are likely to have the
lowest natural density and reproductive rate),
through reduction of their food resources (game
species as well as other components of the disrupted
food chains), or disturbance of shy species. Hunting
pressure is the most widespread form of human
activity in tropical countries, which usually adds its
effects to those of forest destruction (logging, culti-
vation). Raptors are among the first non-game
species to disappear in the process of human
population growth and exploitation of the rain-
forest and are thus suitable indicators of habitat
disturbance.

122

Jean-Marc Thiollay

Vol. 18, No. 4

Acknowledgments

This program was supported by a grant from the French
Ministry of Environment and the Ministry of Defense Nationale
(helicopter transportation). I am grateful toJ.L. Dujardin, experi-
enced ornithologist, for his invaluable help both in the field and in
preparing the expedition.

Literature Cited

A.O.U. 1983. Checklist of North American birds. 6th
edition. American Ornithologists’ Union.

Boyce, D.A., Jr. 1980. Hunting and pre-nesting be-
havior of the Orange-breasted Falcon. Raptor Res.
14:22-39.

Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the World. Country Life Books.

Fontaine, R. 1980. Observations on the foraging associ-
ation of Double-toothed Kites and White-faced
Capuchin monkeys. Auk. 97:94-98.

Fowler, J.M. and J.B. Cope. 164. Notes on the Harpy
Eagle in British Guiana. Auk 81:257-273.

Gochfeld, M., M. Kleinbaum and G. Tudor. 1978. Ob-
servations on behavior and vocalizations of a pair of
wild Harpy Eagles. Auk. 05:192-194.

Granville, J.J. (de). 1978. Recherches sur la flore et la
v6g6tation guyanaises. Ph.D. Dissertation, University
du Languedoc, Montpellier.

Greenlaw, J.S. 1967. Foraging behavior of the
Double-toothed Kite to association with White-faced
monkeys. Auk. 84:596-597.

Haverschmidt, F. 1962. Notes on the feeding habits
and food of some hawks of Surinam. Condor 64:154-
158.

Lamm, D.W. 1974. White Hawk preying on the Great
Tinnamou. Auk 91:845-846.

Laughlin, R.M. 1952. A nesting of the Double-toothed
Kite in Panama. Condor 54:137-139.

Lemke, T.O. 1979. Fruit eating behavior of Swallow-
tailed Kites ( Elanoides forficatus ) in Colombia. Condor
81:207-208.

Mader, W.J. 1979. First nest description for the genus
Micrastur (forest falcons). Condor 81:320.

Meyer De Schauensee, R. and W.H. Phelps,
Jr. 1978. A guide to the birds of Venezuela. Prince-
ton Univ. Press.

Oldeman, R.A. 1974. L’architecture de la fordt
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Rettig, N.L. 1978. Breeding behavior of the Harpy
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Schwarz, P. 1972. Micrastur gilvicollis, a valid species
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Smith, N.G. 1969. Provoked release of mobbing. A
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Smith, N.G. 1970. Nesting of King Vulture and Black
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Smith, T.B. and S.A. Temple. 1982. Feeding habits and
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Received 11 March 1984; Accepted 1 November 1984

BIOLOGICAL AND ETHOLOGICAL NOTES ON Falco peregrinus cassini IN

CENTRAL ARGENTINA

Wenceslao Guillermo Vasina and Roberto J. Straneck

Abstract - We describe the hunting range of a pair of Peregrine Falcon ( Falco peregrinus cassini) near Cordova
Argentina. Main food was the Eared Dove ( Zenaida auriculata) and of 9 food pursuits seen the success was 66%. The
hunting strategies used are outlined. The cliff used by the peregrines was also used by several other species and of these
only the raptorial species were attacked aggressively while such species as the Ringed Kingfisher ( Ceryle torquata) was
attacked as displacement activity.

The subspecies of Peregrine Falcon (Falco pereg-
rinus cassini) (Plate 1) has been found nesting with
greater frequency in southern Argentina than in
northern Argentina. Thus, finding a pair nesting in
the centre of the country (Province of Cordoba) was
important for us, inasmuch as it is the most north-
ern nest we are aware of, located in Los Reartes
Valley (31°60' S-64°50')1, and it provided at the
same time an excellent opportunity to study the
species. The synthesis of our observations that fol-
lows occurred on 1 2 regular visits that spanned the
breeding period (our first visit was on 20 July 1977,
our last on 15 January 1978).

Materials

Photos were taken from a hide situated 12 m
from the nest. (Plate 2). The falcons became per-
fectly accustomed to it immediately. Super 8 film
and voice recordings were also made.

Results

Daily Non-Breeding Cycle - While most hunting
took place at distant hunting grounds, the rest
their activities take place around the breeding cliff.
Our observations indicate that the pair was resident
from at least July until the end of January, and
perhaps they were there year round. As the sun
first struck the cliff (ca. - 0900 H in August), each
bird left its separate overnight roost and flew to
stumps or sticks about 400 m in front of the cliff
where they preened or sunned themselves. These
preening roosts were about 150 m apart.

As they flew towards roosts, the Southern Lap-
wing ( Vanellus chilensis ), common in the area, gave
alarm calls (in spite of the fact that the peregrines
never preyed on them). After 30 min of sunning

*Ed. Note -F.p. cassini is now (1984) known to nest several
hundred km northward in Salta province, the nor-
thernmost province in Argentina. The authors have since
located several pairs of peregrines in the Cordova region.

and preening, they set out to hunt. The basic food
for this pair consisted of the Eared Dove (Zenaida
auriculata ), which was ubiquitous. The falcons
hunted independently or as a cooperative pair.

After feeding they roosted at a shaded spot on
the cliff for the remainder of the day, or would
bathe, until departing shortly before sunset to hunt
again. At twilight their activity ceases completely,
each one going to separate night roosts.

Uneaten prey was frequently cached on a ledge to
be eaten the following day. They were a particularly
noisy pair in their relationship, and the occasions
when they were not connected in some way, either
by vocalizations or visually, were rare. When 1 of
the 2 returned to the gully, the 1 perched on the
cliff always gave a characteristic call. Of the 2, the
male disappeared from the cliff for longer periods,
both in midwinter and during breeding time, when
it provided the female with prey. In every case, its
absences were never more than 2 h.

Territory and Home Range - The home range
could be divided into 3 areas of defense in which
they showed different reactions. The greatest area
“defended” was the hunting ground, which co-
vered several square kilometers and included the
other 2 areas. The second was the territory they
defended near the nest, of some 300 m (radius)
starting from the nest. The third area was the
breeding cliff, formed by the nest and its sur-
rounding shelves. In the province of Cordoba, the
limiting factor for the number of established pairs
seems to be the distribution of cliffs with a suffi-
ciently difficult approach so as to enable them to
nest with relative security and not be disturbed; the
other possible limiting factor, food (doves), is more
than plentiful in all localities. In their “hunting
ground” they displaced other competitive species
[the male pursued and severely attacked an Ap-
lomado Falcon (Falco femoralis) until it was expelled
from the territory] or other unpaired peregrines;
but they didn’t attack other species that were appar-

123

Raptor Research 18(4): 123-130

124

Vasina and Straneck

Vol. 18, No. 4

Plate 1 : Falco peregrinus cassini at nest ledge in Cordova Province, Argentina.

Winter 1984

Argentine Peregrine Falcon

125

Plate 2: Female Falco peregrinus cassini with young at nest in Cordova Province, Argentina.

126

Vasina and Straneck

Vol. 18, No. 4

Figure 1 . Cliff nest site characteristics for a pair of Falco peregrinus cassini nesting in Cordova, Argentina. Site 1 - Prey
transfer area; Site 2 - Male’s roost; Site 3 - Female’s roost; Site 4 - Male plucking perch site; Site 5 - additional
perch site also used for sunning.

ently non-competitive or did not serve as food
(lapwings, gulls (Larus sp.), herons, Chimango
Caracara ( Milvago chimango), or American Kestrel
(Falco sparverius). In attacks of other species in the
“defended area”, in all cases the female carried out
the most aggressive defense and passed closest to
the intruder. The male fulfilled the task of “sup-
port” by joining in calling, but his stoops were less
decided and he nearly always watched the action
flying above the female. The cliff had several
characteristic points (Fig. 1) which were: the nest
(1); a main eating and plucking ledge for the trans-
ference of prey(2); the male’s sleeping roost (3); the
female’s sleeping roost (4); and a plucking and
resting ledge of the male (5) also used for sunning
Food and Hunting - The principal prey remains
found below the plucking perch was the Eared
Dove. Below the male’s roost we found the remains
of Monk Parakeet ( Myopsittia monachus) and
Screaming Cowbird (Molothrus rufoaxilaris ) as well
as those of the dove. Undoubtedly the male caught
smaller birds ( Sicalis , Passer, Zonotrichia, etc.), but we
didn’t find their remains.

Hunting - The principal hunting ground was in
front of the nest on low-lying flat ground, partly
bordered by the river that was a flying route of
pigeons and doves. This hunting ground was where
we observed most captures. At the height of the
breeding season when large young were in the nest,
we witnessed the pair hunting in a highly effective
method (in 9 pursuits they achieved 6 captures =
66% success). The hunting method, used with very
fast flying, medium sized prey, consisted of the
following: in a succession of stoops at the pigeon
(one after the other), the female falcon generally hit
the pigeon as it tried to watch the male, who cut off
its retreat while the pigeon looked for a refuge on
the cliff or in the scrub (Fig. 2).

We were particularly impressed by the syn-
chronization of movement they showed when
hunting as a pair, from the first moment until they
finally caught the prey. A sequence which we fre-
quently observed was the following: they both flew
over the cliff at a height of ca. 50 m, soaring against
the wind (50-60 m apart); and while making notable
head movements they searched the horizon for pi-

Winter 1984

Argentine Peregrine Falcon

127

9

FRONTAL PAIR ATTACK

Figure 2. Hunting methods of Falco peregrinus cassini.

128

Vasina and Straneck

Vol. 18, No. 4

geons. The male always soared some 10 to 15 m
above the female. When the male began to flap his
wings, the female followed him at a distance of 30
m, beating her wings in the same rhythm. In an
oblique flight, the female began to gain height,
ready to stoop onto the prey which dodged the
male’s first dive. Most times, in the second dive, the
female caught the prey. Out of 6 captures observed
in 1 day, only 1 was made by the male, and the rest
by the female. Similar strategies have been de-
scribed and diagramed by Hustler (1983).

Young Eared Doves were more easily captured
(most feathers found were from young). Some
doves, nevertheless, were not able to be caught after
a combined chase of more than 500 m, in which the
male and female made a succession of stoops; until,
to save themselves, the doves flung themselves like
stones against the scrub of the cliff, while the pereg-
rine gained height again, and, with repeated stoops
to the ground tried to make the dove fly again.

Adaptation to the Surroundings and Relations
with Other Species - The cliff face housed several
species in addition to the peregrines. Each species
seemed to coordinate their activities relative to the
peregrines’. For example, a pair of the Ringed
Kingfisher (Ceryle torquata) nesting near the falcons
had to leave the cliff to save their lives when the
female peregrine, molested by our presence, di-
rected her attacks at whatever was below her.
when very near, turned in the air and took the prey.

We also observed another very effective com-
bined attack: a dove approached flying towards
the falcons, in an oblique direction. The male flew
out to meet it and the female, flying behind him but
lower (about 5 m above the ground) made her much
lower than the dove’s line of flight. The dove was
apparently unable to see the female falcon, but
could see the male.

As it neared the male, the dove turned sharply,
descending and practically hitting the female, who
had by now gained sufficient speed flying low, that
she only had to attack from below, rising upwards to
catch her prey (Fig. 2). On this occasion the female
killed and partly plucked the dove while still on the
wing. Of several prey captured in 1 day, only 1 was
killed on the ground, the rest in flight by biting the
neck.

During the time we observed the cooperative
hunting described, the nestlings were about 20 d
old and the female left the nest for long periods to
join the hunting male. When the male brought food

to the female, he usually perched 30 m from the
nest and called to the female. They were very vocal
at the food exchange with a characteristic call (Fig.

3).

Considerations of Food Habits - Of several
checks for food on the plucking perches, we only
found remains of Zenaida auriculata. One, recently
killed (still warm) and intact, weighted 130 g. Com-
paratively, the Spotted Pigeon (Columba maculosa ),
also frequent in the area, must be difficult to hunt;
and it is our opinion (which we could not confirm in
the field) that the male peregrine (cassini) could not
transport in flight one of these pigeons that weighs,
on average, 260 g.

All the doves were hunted and caught by direct
pursuit because their size and agile flight enabled
them to successfully evade a stoop. Larger prey that
were difficult to carry in flight (ducks, etc.) were
hunted by stooping perpendicularly from a consid-
erable height and striking the prey. We found that
the “waste factor” of this pair was high. Usually only
the breast was gone from the dove. They caught
about 3 doves a day and ate about 1/3 of each (40 g
of muscles).

Based on the followng scenario some calculations
can be made. They daily consumed the equivalent
of 12% or 15% of their body weight (according to
temperature and activity level). The female
weighed about 900 g, the male 650 g, and a dove
weighed 125 g. During the rearing period each
nestling consumed the equivalent of a little more
than 1 dove/d (only about 5% of this pair’s diet was
not doves). Thus, we calculate that the pair and the
4 nestlings raised ate approximately 1750 doves
annually. On a kg basis this value is in line with that
derived independently by Ratcliffe (1980).

Adaptation to the Surroundings and Relations
with Other Species - The cliff face housed several
species in addition to the peregrines. Each species
seemed to coordinate their activities relative to the
peregrines’. For example, a pair of the Ringed
Kingfisher (i Ceryle torquata) nesting near the falcons
had to leave the cliff to save their lives when the
female peregrine, molested by our presence, di-
rected her attacks at whatever was below her.

Several times we observed these attacks. These
were not attacks to kill and eat the kingfishers. On
one occasion the kingfisher came in from down
river, flying low over the water directly to its nest
located about 50 m from the peregrine nest. The
female peregrine started a sudden vertical dive-

Winter 1984

Argentine Peregrine Falcon

129

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Figure 3. Miscellaneous sonogram patterns of Falco peregrinus cassini in central Argentina.

Pattern 1 : Alarm call of nesting female. The female was stooping at us near the nest. She made the calls (chitters) only
when near us. The first vocal stanza is more dense than the other two because she was close by. The call
ranges from 900-4100 Hz.

Pattern 2. Contact call of the male. This call was given ( Eechip , sometimes accompanied by ledge display) from the main
eating ledge. Call frequency is from 600 - 5,000 Hz. Of note is that when the female approached him, the
number of voices doubled in the same time lapse (ledge display). The latter is easily found in 1.5 sec of the
sonogram from left to right. Then, when the female left, the call became more spatial after the 4th sec.

Pattern 3: Anti-aggression call of perched male. This is also a submission call, since the female, while flying, will disturb
or attack the male to make him fly. From the 5.25 sec, the female was close to the male, flying over him. His
voice resembles total submission to the point of being like that of the young in front of their mother (compare
1st sec of Pattern 6).

Pattern 4: Alarm call of the female with young. This sonogram reveals a more definite and persistent voice, more than
when the nest contains only eggs (compare to Pattern #1). The call went from 1,000 - 5,000 Hz. In the same
sonogram we found that young joined the female in the alarm call. This is noted in the difference in time
between their voices, at 3.5 sec and from 4.75 sec, remaining even as the single voice at the end.

Pattern 5: Alarm call of the male. Note the difference between the alarm calls of male and female. The male call was a
mixture of a wail and a typical alarm call. The wail is a single frequency call lasting 14 sec and the alarm call, a
great variation of frequencies in !4 sec. Both male and female alarm calls range in the same frequency
(compare Patter #3).

Pattern 6: Call of nestlings. Their alarm call varied from 900 - 4,200 Hz. and resembled the alarm call of the adults in
structure but not in the frequency range. The calls befoare 2.5 sec were the typical submission voice, that the
male performs while the female is excited, aggressive or closeby (compare Pattern #3).

Notes: a) On the horizontal scale of the sonogram, each 4 divisions is one second (sec); b) Every character found in the

sonogram below the 400 Hz range identifies parasitic and background noises from the wind.

130

Vasina and Straneck

Vol. 18, No. 4

attack the instant the kingfisher passed just below
her, which caused the kingfisher to dive violently
and loudly into the water. What impressed us most
was the stoop of the peregrine, with a sudden
movement of the wings, the body down in an almost
vertical position, gyrated around the body axis. The
wings accelerated the speed and the body returned
to its normal position only at the end of the plunge.
After passing just a few centimeters over the water,
with a movement of the tail and due to the high
speed the peregrine gained elevation to get into
position for a second attack. The kingfisher sur-
faced and changed its flight direction, but the sec-
ond attack forced it back into the water again. After
repeating the maneuver several times, the falcon
finished the game, allowing the kingfisher to leave
the area.

Something very similar happened with a Speck-
led Teal (Anas flavirostris) that nested on the cliff
about 30 m from the peregrines. Several times,
flying to its nest, it had to enter the water because of
the peregrines’ attacks. However, unlike the
kingfisher, once in the water it did not take wing to
avoid the second attack, but swam away. Despite
these attacks, the teal fledged a brood of young.

A group of swallows (the Southern Martin, Pro-
gne modesta, and Grey-Breasted Martin, Progne
chalybea) also shared the cliff. They nested near the
night roost of the male, and their presence was
noticeable whenever the peregrines were resting or
far away from the cliff. We used the swallows as
indicators of the presence of the falcons because
when the falcons were present, the swallows flew
near the bush — protected cliff. Their alarm-call
told us when the male came back to the cliff with
prey.

Due to changes in the environment (swelling
river after heavy rainfalls that floods lower lands),
some species disappear temporarily. Among them,
the Southern Lapwings ( Vanellus chilensis ) and
Brown-Hooded Gulls (Larus maculipennis) made
considerable noise whenever the peregrines were
flying near despite the fact that they were never
attacked.

The peregrine vehemently attacked Common
Caracaras (Polyborus plancus) to a radius of 300 - 400
m from the nest. On the other hand, the Chimango
Caracara ( Milvago chimango) was not attacked, even
when coming as near as 10 m to the nest.

Once we observed the male soaring about 800 m
from the cliff. Suddenly he stooped at a Common

Caracara that was flying in front of the nest. On
another occasion he pursued and drove away an
Aplomado Falcon (Falco femoralis) that passed at a
very high altitude over the cliff. We can confirm,
however, that they do not attack either the Ameri-
can Kestrel (Falco sparverius ) or the White-tailed
Kite (Elanus leucurus). A pair of the former nested in
a hole of the cliff about 500 m from the peregrines.
The kite occupied two little woods of Eucaliptus and
conifers about 400 m from the cliff.

Acknowledgment

We owe special gratitude to Walter Cerban, Cristian Henschke,
and Christopher Clark for their collaboration in this note and to
Clayton M. White for comments on the manuscript.

Literature Cited

Hustler, K. 1983. Breeding biology of the peregrine
falcon in Zimbabwe. Ostrich 54:161-171.

Ratcliffe, D. 1980. The peregrine falcon. T 8c AD
Poyser, Calton, England.

Museo Argentino de Ciencias Naturales, Av. Angel Gallardo
470, 1405 Buenos Aires, Republica Argentina.

Received 15 August 1982; Accepted 10 May 1984

BEHAVIOR OF THE AFRICAN PEREGRINE DURING INCUBATION

Warwick Tarboton

Abstract - Dawn-to-dusk watches were made during 5 d at a Peregrine Falcon ( Falco peregrinus ) nest with eggs in the
Transvaal and all activity was recorded. The male incubated 35% of the day and the female 65%. Their incubation shifts
averaged, respectively, 1 h 30 min and 2 h 25 min. Eggs were covered for 98% of the day. The female slept on the nest at
night. The non-incubating bird was absent from the nest-cliff for periods averaging 2 h at a time and totalling about 3 h
each day. It may have hunted during this time. Hunting by chasing and ‘flushing’ is described. Twenty-one prey items
from 3 eyries were all birds, especially pigeons and doves (46%). The high share of the incubation done by the male, the
abnormal hunting by the female during incubation, and the apparent rarity of Peregrines in the T ransvaal are discussed.

The status of the African race of the Peregrine
Falcon ( Falco peregrinus minor )is poorly
documented, though it appears to be scarce and
very localized throughout its range (Cade 1969;
MacWorth-Praed and Grant 1957, 1962; Snow
1978). It is described as being a rare breeding resi-
dent and possibly threatened in South Africa (Sieg-
fried et al. 1976). During a 3-yr survey of fal-
coniforms in the Transvaal only 10 breeding pairs
were located in 286,300 km2 (Tarboton and Allan
1984). Data herein may give insight into the factors
contributing to its rarity in South Africa, and may
provide useful comparative data for similar studies
being done on the Lanner Falcon (. Falco biarmicus )
(Kemp, in prep).

Detailed observations were made during 5 d at an
eyrie in the eastern Transvaal Escarpment Region
(Site 1). This paper describes observed breeding
and hunting behavior of this pair and includes ob-
servations made at 2 other eyries (Sites 2 and 3).
Obviously the behavior of a single pair may not
represent the species as a whole; in the absence of
other published data on the biology of the African
Peregrine, these observations are given.

Study Area and Methods

The peregrine pair at Site I laid eggs in 1979 on an old nest
probably built by the Black Stork ( Ciconia nigra) on a ledge 40 m
from the base of a 140 m east-facing cliff overlooking a long,
sloping valley extensively planted under pines and eucalyptus.
When first located in May 1979 a single male peregrine was seen at
the nest-cliff. Observations were made between 5-11 September
when the site was occupied by a pair incubating 3 eggs. On 2
November the pair was accompanied by 2 just-fledged young.
Both male and female were adult and they could be distinguished
by their size difference and the male’s noticeably brighter-yellow
eye ring, cere and feet.

The nest-cliff was observed continuously from dawn to dusk for
5 d (5-8 and 1 1 September) totaling 61 h with an additional 2 h 5
min on 10 September. Three observers watched in rotation from a
vantage point on the slope directly below the nest. Two tripod-
mounted telescopes were used, one trained on the nest and the

other following the movements of the non-incubating bird. All
activity, including nest change-overs, agonistic behavior, activities
while perched (e.g. preening), vocalizations, and flights were re-
corded. During periods of rapid action a cassette recorder was
used to record activity.

Local sunrise and sunset at the site were, respectively, 0600 H
and about 1745 H during the observation period, but it became
too dark for observations after 1800 H and before 1530 H. The
nest was shaded after 1330 H and the nest-cliff after 1550 H.
During 3 d weather was cloudless and warm with little or no wind,
and on 2 d it was cold, overcast and windy. No behavioral differ-
ence by the birds on clear and overcast days were noticed.

Results

Eggs were incubated for 97.9% of the daytime (n
= 61 h); on 4 d this averaged 99.3%, whereas on 1 d
the eggs were covered for only 92.2% of the time.
Both sexes incubated during daytime, but only the
female spent the night on the nest (n = 5). Overall
the female did the greater share of incubation, al-
though on 1 d the male’s exceeded the fe-
male’s. The respective proportion of incubation
(X/s.d.;range) during 5 d was, for the male: 34.7/
17.5; 11.6-59.5, and for the female: 65.3/17.5;
40.5-83.4. If the female’s overnight incubating is
included, the respective male: female proportion of
the incubation is 17.7:82.3.

Daytime incubating shifts by the female averaged
2 h 25 min (s.d. = 1 h 6 min, range = 29 min - 4 h 3
min, n = 1 1) and those of the male averaged 1 h 30
min. (s.d. = 1 h 17 min, range = 8 min - 4 h 14 min,
n = 14) (the difference is not significant). The male
had both the longest and shortest daytime incubat-
ing shifts (respectively, 4 h 14 min and 8 min),
although if the female’s overnight shifts are in-
cluded, these would exceed the longest shifts by the
male. Her longest continuous incubation shift in
this case was 15 h 52 min.

Most observed nest change-overs (n = 27) were
similar in that the relieving bird flew unannounced
to the nest and alighted beside the incubating bird.
One or both birds then uttered a series of 'tjak-ak ’

131

Raptor Research 18(4): 131-136

132

Warwick Tarboton

Vol. 18, No. 4

Table 1 . Total time during 5 d, given in min and as a percentage, in which the non-incubating bird was present at, and
absent from, the nest-cliff.

Whereabouts of

NON-INCUBATING BIRD

time (min)

(

%

MALE

FEMALE

MALE

FEMALE

Present at nest-cliff

562

735

42.0

30.7

Absent from nest-cliff

777

1637

58.0

68.3

Unknown

0

26

1.0

Totals

1339

2398

100.0

100.0

notes before the incubating bird flew off and the
relieving bird incubated. Occasionally other vocali-
zations (e.g. whining ‘weee-e-k’) were used at
change-overs. The male often (10/15 times) ap-
peared to be reluctant to give up incubating when
relieved by the female. On such occasions one or
both birds called much longer than usual, uttering
25-30 ‘ tjak-ak ’ notes. Invariably the female
supplanted the male in these instances, whereas the
male frequently (n = 10) came to the nest to relieve
the incubating female but was unable to dislodge
her. Occasionally (n = 3) the female had already left
the nest when the male arrived to incubate and he
took over silently.

There was no regular pattern of shifts by sex
during the 5 d, apart from the first and last shift
each day by the female. The male relieved her be-
fore sunrise (averaging 28 min before sunrise) on 4
of the 5 d. The female’s last shift continued over-
night and commenced at various times between 47
min - 3 h 59 min before sunset (X = 1 h 54 min).

Activity of the Non-incubating Bird — Often the
non-incubating bird left the vicinity of the nest-cliff,
presumably to hunt since both birds returned after
absences with bulging crops. When not incubating,
the male was absent a significantly greater propor-
tion of the time than the female (P < 0.0001, see
Table 1). On average, the non-incubating bird was
absent from the nest-cliff for about two-thirds of
each day (X/s.d. = 8 h 3 min/1 h 35 min; range = 5 h
17 min - 9 h 7 min, n = 5). The incubating bird was
alone at the nest-cliff for 71 % of the day (female) or
62% of the day (male).

The Crowned Eagle ( Spizaetus coronatus ), Jackal
Buzzard ( Buteo rufofuscus), Gymnogene

( Polyboroides radiatus ) and the White-necked Raven

(Corvus albicollis) were invariably chased and harras-
sed by the non-incubating bird if they passed the
nest-cliff when he or she was present. The incuba-
ting bird was never seen to leave the nest and assist
its mate during these pursuits, nor did it attempt to
chase off passing birds of prey when the mate was
absent. On 1 occasion the nest-cliff and eggs were
left entirely unattended for 55 min when the female
left the nest to pursue, catch and eat a passing
pigeon (see Hunting Behavior). Black Storks, which
came and went continuously from an active nest
about 500 m away on the cliff were not molested.

Typically both birds, at the end of an incubating
shift, flew to a favored perch, defecated, and com-
menced preening, and later started other mainte-
nance activities such as stretching, scratching or
(occasionally) casting a pellet. On average, male and
female spent, respectively 86 and 90 min/day (s.d. =
29 and 39 min respectively) actively preening on a
perch (about 12% of each day). After a period of
preening they usually became alert, looking about,
making perch-changes or ‘flush-hunting’ (see
Hunting Behavior) before taking flight, soaring high,
and going out of view behind the nest-cliff.

Hunting Behavior — Most hunting and eating of
prey apparently occurred away from the nest-cliff
since only 2 successful prey strikes were observed in
5 d. In one of these the female left the nest to catch a
passing pigeon which it ate away from the nest-cliff.
In the other instance the male caught a small bird
which it took back to the nest-cliff to eat. There was
little prey pluckings below favored perches, and
none at the nest, suggesting that during incubation
prey was not frequently brought back to the nest-
cliff to eat. During 5 d the male never brought food
to offer the female and she appeared to provision

Winter 1984

African Peregrine Falcon

133

herself entirely. In the instance where the male
returned to the nest-cliff to eat prey, the female left
the nest and attempted to take the remains from
him after he had eaten for 10 min. They grappled
for the prey on the male’s perch before it fell and
was lost in the forest below.

In addition to 2 successful strikes, 5 unsuccessful
chases (2 by female, 3 by male) and 1 probably
successful strike (female) were initiated from the
nest-cliff. Three of these 8 attempts (all by the
female) involved chasing birds, twice pigeons,
which were flying past at least 2-3 km distant. In one
case she soared briefly to gain height before at-

tacking passing birds, flying with rapid wingbeats to
a point ahead of the birds so as to intercept them. In
one unsuccessful chase the 2 pursued pigeons
changed direction as she approached, then dived
downwards. She stooped unsuccessfully at them 3
times before they reached shelter in trees. In a
second apparently successful chase the female’s
flight from take-off to strike lasted 120 ± 5 sec. It
followed the same pattern in which the prey at-
tempted to evade the peregrine by diving and the
female spiralled down after it.

At site 2 a male stooped at and caught a swift
(probably Apus melba) which was one of a large flock

Table 2. Peregrine prey recorded at 3 Transvaal eyries. Sites 1 and 2 are in the Escarpment Region, Sites 3 is in the
Low veld.

Source of data

Prey species

No.

1 . Prey remains

found below perches on nest-cliffs;

Site 1

Domestic Pigeon, Columba livia

4

Red-eyed Dove, Streptopelia semitorquata

1

Laughing Dove, Streptopelia senegalensis

1

Cuckoo, Chrysococcyx sp.

1

Site 3

Red-eyed Dove Streptopelia semitorquata

1

Green Pigeon, Treron australis

1

Burchell’s Coucal, Centropus superciliousus

1

Swift, Apus sp.

1

Red-faced Mousebird, Colius indicus

1

Lilabreasted Roller, Coracias caudata

1

African Hoopoe, Upupa epops

1

Rock Martin, Hirundo fuligula

1

Blackheaded Oriole, Oriolus larvatus

1

Starling, Lamprotornis sp.

1

Small passerine

1

2. Prey observed being caught

Site 1

Domestic pigeon, Columba livia

1

Small bird

1

Site 2

Swift, probably Apus melba

1

3. Unsuccessful

prey strikes

Site 1

Rock Pigeon, Columba guinea

1

Pigeon, Columba sp.

2

Redwinged Starling, Onychognathus morio

1

Small bird

2

Site 2

Rock Pigeon, Columba guinea

1

134

WARWICK Tarboton

Vol. 18, No. 4

spiralling around in the valley below the nest-cliff.
The stoop lasted about 10 sec. The bird covered
about 1 km and dropped about 300 m during the
strike. It took the swift in its feet as it passed
through the flock.

In a second hunting method peregrines attemp-
ted to flush prey (‘flush-hunting’) from the nest-
cliff and then pursue it. Both male and female
frequently did this, though never successfully. In
‘flush-hunting’ the peregrine changed its perch on
the cliff frequently, doing small aerial circuits be-
fore re-alighting, sometimes flying up into small
crevasses, clinging there briefly, and flying out
again. Flushed birds which were unsuccessfully
chased included a Rock Pigeon ( Columba guinea),
Redwinged Starling ( Onychognathus morio) and two
smaller birds. ‘Flush-hunting’ was also observed
being used by the female peregrine at Site 2. In this
case she flushed, but failed to catch, a Rock Pigeon.
This method was frequently used by immature
peregrines in the Aleutian Islands, Alaska, and by
adults in Argentina (C.M. White, pers. comm.).

The non-incubating bird’s frequent absences
from the nest-cliff may have been for the purpose
of hunting. These absences lasted, on average,
about 2 h (respectively, X/s.d.; range, for male: 2 h
8 min/55 min; 1 h - 3 h 40 min; n = 9, and female: 1
h 50 min/1 h 30 min; 33 min - 4 h 1 min; n = 7). On
at least 2 occasions returning birds had bulging
crops.

Prey — Prey data frotn 3 Transvaal peregrine
eyries are given in Table 2. These include items
identified from plucking found below perches on
the nest-cliffs (18), prey observed being caught (3)
and potential prey unsuccessfully chased (7). In all
cases prey was avian, and in the wt. -range 25-300 g.
Thirteen (46%) were pigeons and doves. The sam-
ple from Site 3, a low veld eyrie, includes several
bird-species which are absent from the escarpment
region.

Discussion

Of special interest was the high proportion of
incubation done by the male (35%) and indepen-
dence of the female in obtaining food during incu-
bation. This compares with the findings of Hustler
(1983) in Zimbabwe. In some peregrine popula-
tions (e.g. in Alaska, Enderson et al. 1972) males
may share up to a third of the incubation, but it is
usual for females to take the major share (Cramp
1980). The independent hunting by the female at

Site 1 is exceptional, since other studies indicate
that she is provided with most or all of her food by
the male during incubation (Brown and Amadon
1968; Cramp 1980). It would be instructive to de-
termine whether these observations reflect an iso-
lated occurence or occur generally in populations
of F.p. minor.

These two features are at variance with a general
pattern in falconiforms where reversed size di-
morphism is closely correlated with rapaciousness,
a difference in prey size taken by the sexes and
often with the nature of parental roles (Selander
1966; Reynolds 1972; Amadon 1975). Thus bird-
catching hawks which are the most rapacious tend
to have the greatest size dimorphism, take prey in 2
size-classes according to sex and, during breeding,
partition parental duties such that the female does
most of the incubation while the male does most or
all of the provisioning (Newton 1979). Peregrines
have a large size dimorphism and are highly rapa-
cious, yet the observations recorded here do not
conform to the predicted model of partitioned pa-
rental roles. The behavior of the pair at Site 1 may
have been atypical.

The rarity of the peregrine in the Transvaal (and
elsewhere in southern Africa) has not yet been
adequately accounted for. The Lanner Falcon, by
contrast, is a relatively common bird (McLachlan
and Liversidge 1978). A measure of the relative
abundance of the two species in the Transvaal is
shown by the number of breeding sites of each
recorded during the survey of birds of prey during
1975-1981 when 14 peregrine and 151 lanner
eyries were located (Tarboton and Allan 1984). I
believe that indirect competition between the two
species is partly responsible for the peregrine’s rar-
ity, and that the following contribute to this situa-
tion:

( 1 ) Prey — Whereas peregrines take almost ex-
clusively avian prey, lanners, that prey largely on
birds, also take a variety of non-avian prey, includ-
ing rodents, bats, lizards and locusts (Brown and
Amadon 1968; Cramp 1980, pers. obs.).

(2) Hunting Methods — The peregrine is a
specialized hunter, securing avian prey in the air by
stooping on it at great speed, and it requires suffi-
cient air-space in order to chase and catch its prey.
The lanner often hunts by stooping, but also hunts
from perches and frequently chases avian prey in
level flight, pursues prey flushed by vehicles, ani-
mals or persons on foot, and snatches prey such as

Winter 1984

African Peregrine Falcon

135

young gamebirds and poultry from the ground
(Brown and Amadon 1968; Cramp 1980, pers.
obs.).

(3) Nest-sites — All 14 Transvaal peregrine eyries
were on high cliffs (mean height 187 m), only one
being on a cliff lower than 140 m. Most recorded
lanner nest-sites in the Transvaal (n = 175) were
similarly on cliffs (57%), but mainly on small cliffs
(45%) less than 60 m in height. Many were also in
crow nests on pylons (25%), on crow or eagle nests
in trees ( 1 4%), and on buildings or in quarries (4%).

Lanners, with a broad feeding niche, may out-
perform peregrines (on an energy/time-cost basis)
in some situations, while in other situations the op-
posite will occur. During breeding, when food de-
mands are greatest, this difference between the two
species will reflect their choice of breeding sites and
their reproductive output. It is predicted that opti-
mal breeding sites for peregrines will be on high
cliffs overlooking airspace through which there is a
steady passage of high-flying birds within striking
range. In such situations a breeding pair can search
for prey while perched on the nest-cliff and simul-
taneously be able to defend the nest from pre-
dators. Lanners, less specialized in making high-
speed, long-range stoops, may not match the per-
formance of peregrines breeding in such cir-
cumstances. However, on progressively lower cliffs
(which offer peregrines a less effective striking
height) or in situations where there is less prey
passing within range of the cliffs, breeding sites
become marginal for peregrines, and a threshhold
would be reached where lanners, with their wider
prey range and more diverse means of taking prey,
outperform peregrines.

Peregrines breeding at marginal sites may incur
higher energy costs than those breeding at optimal
sites; both hunting away from the nest-cliff (neces-
sitating frequent climbing in order to make stoops)
and transporting food back to the nest, may be
more time and energy consuming. Such disadvan-
tages could leave nests exposed to potential pre-
dators and may result in a reduced provisioning
rate, affecting reproductive performance nega-
tively. The site observed may have been marginal
since most hunting was done away from the cliff,
and once during the 5-day watch the cliff was left
entirely unattended for 55 min. This may also be
why the female hunted for herself during incuba-
tion.

Elsewhere in the world the peregrine’s prefer-

ence for high cliffs has been noted (Hickey 1942;
Ratcliffe 1962); and during the extirpation of F. p.
anatum from northeastern America through pes-
ticide contamination in the 1950’s it was noted that
the first eyries to be deserted were those on low
cliffs, and the last to go were those on the highest
cliffs (Hickey 1969). This supports the hypothesis
that occupation of high cliffs has energy/time-cost
benefits for peregrines breeding there. In areas
where lanners (or other Falco species filling the
‘lanner-niche’) are absent, peregrines may occupy a
wider range of breeding sites than otherwise, al-
though the reproductive performance of pairs at
marginal sites may not match that of pairs at opti-
mal sites. Where lanners occur in sympatry, pere-
grines are excluded from many marginal sites by
lanners because of the latter’s more generalized
hunting capabilities and efficiency at low sites.

Thus it is hypothesized that the rarity of pereg-
rines in the Transvaal is the result of (1) the general
scarcity of optimal breeding sites (i.e. high cliffs
overlooking airspace offering sufficient prey-
capture opportunities), and (2) the presence of lan-
ners which outcompete them (on an energy/time-
cost basis) and exclude them from marginal sites.
Lanners are generally much more common, since
by far the greater part of the Transvaal is a plateau
with little or no relief. However, in parts of the
Transvaal Escarpment Region where conditions
favor peregrines, lanners are outnumbered by
them. In one such area 4 peregrine eyries are
known, compared with only 2 of lanners.

Acknowledgments

I thank David Allan and Guggi Tarboton for help in all aspects
of the fieldwork, the Department of Forestry for cooperation and
provision of many facilities, and the Transvaal Division of Nature
Conservation who supported this work.

Literature Cited

Amadon, D. 1975. Why are female birds of prey larger
than males? Raptor Research 9:1-11.

Brown, L.H. and D. Amadon. 1968. Eagles, hawks and
falcons of the world, Vol. 2. Feltham: Country Life.
Cade, T.J. 1969. The status of the Peregrine and other
Falconiformes in Africa, pp 289-321, in Hickey, J.J.
(ed) Peregrine Falcon populations, their biology and
decline. Madison: Univ. Wise. Press.

Cramp, S. 1980. Handbook of the birds of Europe, the
Middle East and North Africa, Vol. 2. Oxford: Ox-
ford Univ. Press.

136

Warwick Tarboton

Vol. 18, No. 4

Enderson, J.H., S.A. Temple and L.G. Swartz. 1972.
Time-lapse photographic records of nesting Peregrine
Falcons. Living Bird 11:113-128.

Herbert, R.A. and K.G.S. Herbert. 1965. Behaviour
of Peregrine Falcons in the New York City Region. Auk
82:62-94.

Hickey, J.J. 1942. Eastern populations of the Duck
Hawk. Auk 59:176-204.

Hickey, J.J. (ed). 1969. Peregrine Falcon populations,
their biology and decline. Madison: Univ. Wise. Press.
Hustler, K. 1983. Breeding biology of peregrine falcon
in Zimbabwe. Ostrich 54: 161-171.

McLachlan, G.R. and R. Liversidge. 1978. Roberts’
birds of South Africa, 4th ed. John Voelcker Bird
Book Fund: Cape Town.

Macworth-Praed, D.W. and C.H.B. Grant. 1957.

Birds of eastern and northeastern Africa, Ser. 1 , Vol.
1. London: Longmans.

Macworth-Praed, C.W. and C.H.B. Grant. 1962.

Birds of the southern third of Africa, Ser. 2, Vol. 1.
London: Longmans.

Newton, I. 1979. Population Ecology of Raptors. Buteo
Books, Vermillion, South Dakota.

Ratcliffe, D.A. 1962. Breeding density of the Pereg-
rine Falco peregrinus and Raven Corvus corax. Ibis
104:13-39.

Reynolds, R.T. 1972. Sexual dimorphism in the accip-
iter hawks: a new hypothesis. Condor 74: 191-197.
Selander, R.K. 1966. Sexual dimorphism and the diffe-
rential niche utilization in birds. Condor 68:1 13-151.
Siegfried, W.R., P.G.H. Forst, J. Cooper, and A.C.
Kemp. 1976. South African Red Data Book: Aves. S.
Afr. National Sci. Prog. Rep. 7. Pretoria: CSIR.

Snow, D.W. (ed). 1978. An atlas of speciation in African
non-passerine birds. London: Trustees Brit. Mus.
(Nat. Hist.).

Tarboton, W.R. and D.G. Allan. 1984. A survey of
birds of prey in the Transvaal. Tvl. Mus. Monogr. No.
3.

Transvaal Division of Nature Conservation, P.O. Box 327,
Nylstroom 0510, South Africa.

Received 15 August 1982; Accepted 15 august 1983

ROOST SELECTION AND BEHAVIOR OF THE LONG-EARED OWL
(Asio otus) WINTERING IN NEW JERSEY

Thomas Bosakowski

Abstract - Roosting Long-eared Owls ( Asio otus) selected conifers with dense foliage that concealed all or most of the
main trunk with no apparent regard to tree species. Roosts were established only in clumps of 2 or more closely-spaced
conifers (3-15 m in height), always near a variety of open habitats. Communal roosts of 2-4 owls were significantly
preferred to solitary roosts. Strong fidelity for a single roosting tree was observed within each winter, although the owls
shifted to a new main roost site each yr. Owls concealed themselves in dense foliage; when approached, they would hide
or freeze and flush only at close distances. Evidence indicated that these owls had habituated to remarkably close human
activity, although they were readily able to detect an intruder. The 2 most frequented roosts were within 8 m of large
buildings which may have provided wind protection and increased shade for hiding. The owls remained at roosts well
into darkness and when flushed during the day, showed strong aversion to daylight activity.

While the food habits of wintering Long-eared
Owls (Asio otus ) have been extensively studied (see
reviews by Marti 1976; Voight and Glenn-Lewin
1978), the literature on roosting sites and attendant
behavior is limited and few of the observations have
been systematic (Glass and Nielsen 1967; Smith
1981). Here, I document systematic counts of
roosting Long-eared Owls in man-made habitat
where all vegetation was landscaped and planted in
orderly patterns (i.e., an industrial park and a
cemetery). This eliminated many of the habitat
variables normally encountered in natural ecosys-
tems and facilitated the identification of essential
roost-site requirements.

Study Area and Methods

Observations on roosting Long-eared Owls were made from 18
January 1981 to 10 March 1984 in the Hackensack Meadowlands
District, New Jersey. This area contains estuarine marshes that
border the lower Hackensack River. These extensive open
marshes are dominated by common reed ( Phragmites communis),
interspersed with small tidal channels and creeks. Ornamental
conifers were distributed in a nearby industrial park (office and
warehouse buildings).

In 1981, all conifers within 1 km of the originally-discovered
roost were checked for owls and/or their sign (pellets, prey re-
mains, feathers, urates). I found that all roosting activity was
limited to one 22 ha block of the industrial park. In 1982, I
systematically searched this block for roosting owls with 9 flush
counts (Craighead and Craighead 1956), by closely inspecting 77
conifers on each census date. These conifers were 2-6 m high and
were the following: 73 Austrian pine ( Pinus nigra), 2 eastern
hemlock ( Tsuga canadensis), and 2 Atlas cedar ( Cedrus atlantica).
The number of flush counts was kept to a minimum and their
timing was designed to obtain the most information with the least
amount of disturbance to the owls (Table 1). At approximately
monthly intervals, other conifers within 1 km were checked but
signs of roosting were not revealed. After the snow cover had
melted in early February of 1982, pellets were found and collected
on each of the last 6 flush counts. A record of the number and
location of pellets provided an additional measure of roost-site

use, for each owl ejects approximately 1 pellet per day at the roost
(Craighead and Craighead 1956; Birkenholz 1958; Graber 1962).
Analysis of these pellets was reported previously (Bosakowski
1982). During the winter of 1982-83, neither owls nor pellets were
found during 17 systematic searches. In the winter of 1983-84 the
roosts became active again and 9 systematic searches (including
pellet collections) were conducted.

Results and Discussion

Roost Trees. — In the study block, I observed
Long-eared Owls roosting in 4-6 m ornamental
Austrian pines (36 times) and once in a 2 m hemlock.
A few additional observations were made at a
cemetery about 2 km from the study block during
the second winter. Here, 1-3 Long-eared Owls
roosted in a planted row of 4-5 m ornamental ar-
borvitae (Thuja spp.) and in a row of 10-15 m hem-
locks. Although Long-eared Owls typically exhibit a
strong preference for roosting in conifers, a pre-
ference for certain species has not yet been indi-
cated (Randle and Austing 1952; Smith 1981; this
study). Density of foliage is probably of most im-
portance since it provides protection from wind-
chill, precipitation, predators, and mobbing birds.
In this study the trees selected for roosting were
those that offered the greatest foliage density and
concealment of the main trunk. Smith (1981) noted
that roost trees had extensive branching to within 2
m of the ground.

Roost-site Use and Characteristics. — In the
study block, virtually all roosting was confined to 2
roost sites (Fig. 1). In 1981, the owls showed a
strong fidelity for roost 1 as demonstrated by the
lack of sightings and pellets elsewhere in the study
area. In 1982, 1 or 2 owls stayed in roost 1 for a
short period (10 pellets) and joined other owls
(maximum = 3) at roost 2 for the remaining winter

137

Raptor Research 18(4):137-142

138

Thomas Bosakowski

Vol. 18, No. 4

Table 1. Systematic flush counts of Long-eared Owl roosts.

Roost 1

Roost 2

Date

Owls Pellets

Owls Pellets

First Winter

20 January

1981

1

+a

0

0

31 January

1981

2

+

0

0

Second Winter

01 January

1982

0

0

0

0

24 January

1982

1

NCb

3

NC

26 January

1982

2

NC

1

NC

04 February

1982

0

10

3

85

10 February

1982

0

0

3

15

23 February

1982

0

0

3

9

02 March

1982

0

0

1

8

1 8 March

1982

0

0

1

14

24 March

1982

0

0

1

1

Third Winterc

31 October 1982- 4 April 1983

0

0

0

0

Fourth Winter

1 8 December

1983

0

0

0

0

31 December

1983

4

27

0

0

07 January

1984

0

26

0

0

20 January

1984

4

NC

0

NC

28 January

1984

3

52

0

0

04 February

1984

2

25

0

0

20 February

1984

2

32

0

0

04 March

1984

0

1

0

0

10 March

1984

1

3

0

0

Totals:

22

176 +

15

132

apellets present but not collected during first winter.
b pellets not collected because of snow cover.
ca total of 17 counts were made during this period.

(132 pellets) (Table 1). In 1983 there was no evi-
dence of roosting during the entire winter season.
This may have been the result of mild temperatures
during December and January as compared to
other years (Fig. 2). In 1984 only roost 1 was used by
1-4 owls.

Roost 1 consisted of a cluster of two 4 m Austrian

pines that were 2 m apart, three 1 m evergreen
shrubs, a 2 m hemlock, and a 6 m white birch (. Betula
pendula ). The trees were planted on a 0.5 m mound,
bordered with small boulders. Roost 2 was a row of
ten 3-5 m Austrian pines that were planted so that
the foliage met between almost every tree. The
preference of Long-eared Owls to select roost trees

Winter 1984

Long-Eared Owl in New Jersey

139

Figure 1. Map of study area with inset maps showing close-up views of two Long-eared Owl roosts. Small arrows
indicate most frequently-used roost trees. Systematic searches were conducted in the center block (study
block).

from among clumps of two or more conifers was
also noted by Bent (1938: 153), Randle and Austing
(1952), and Birkenholz (1958).

The two roosts that were selected represented 2
of 4 apparently-suitable pine plantings in the study
block, yet the other pine groups showed virtually no
signs of use during the study (2 and 6 pellets
found). The two favored sites were closer to build-
ings (6-8 m as compared to 19-25 m) and as a result,
received less direct sunlight. Protection from the
prevailing northwesterly winds was apparent at
roosts 1 and 2 but not at the little used pine groups.
While the eastern site (roost 1) was shielded directly
by the adjacent building, the western site (Roost 2)
was also protected by being on the southeastern side
of the pine row (Fig. 1).

Roost-site Fidelity. — The fidelity of Long-eared
Owls to certain trees within the favored roost sites
was evident, e.g., in 1982 there were 119 pellets
under one tree in roost 2 and only 27 pellets under
7 additional trees. In 1984 the results were similar

at roost 1 with 147 pellets under 1 tree and 67
pellets under 9 other trees. Some pellets found at
alternate roost trees were the result of owls tem-
porarily moving after I flushed them. The
Craigheads (1956:88) mentioned the habit of
Long-eared Owls to return to the same roost tree
and noted one owl on the same perch on 9 consecu-
tive roost counts. I observed 1-3 owls roosting in the
same tree on 7 consecutive roost counts (54-day
period). Smith (1981) reported the fidelity of
Long-eared Owls to certain groups of trees over a
period of many years, but no reference was made to
Fidelity to individual trees.

While I observed a strong fidelity to one roost site
during each winter, it was surprising that the owls
established their main roost at a different site each
year, alternating between roost 1 and roost 2 (Table
1). These data seem to indicate that the initial selec-
tion between two suitable roosts is a rather fortuit-
ous event and that a strong site-tenacity develops
thereafter. Similarly, Klopfer and Hailman

140

Thomas Bosakowski

Vol. 18, No. 4

q December mean temperature

0 January mean temperature

— ^ maximum number of owis/winter

mean number of owls/day

Figure 2. Inverse relationship between mean winter
temperatures (°C) and owl numbers occurring
in the study area. Weather data was obtained
from National Weather Service at Newark
International Airport located only 1 3 km from
the study site.

(1965:291) have postulated that in their study only
one of several available sites was occupied by gulls
because of social stimulation.

Proximity to Hunting Areas. — According to the
literature, Long-eared Owl roosts are almost always
located near open habitats. The significance of this
association was revealed by Randle and Austing
(1952) who found a “preponderance” of open-field
prey species in the pellets. A review of numerous
food habits studies (Marti 1976) confirms this
finding and suggests that the majority of hunting
occurs in open country. In the present study, both
roosts were within 200 m of large Phragmites tidal

marshes. In addition, five man-made habitats were
also present: a few small weed-covered fields (total
15 ha), 2 bulldozed construction sites (8 ha), park-
ing lot and road edge, lawns surrounding the
roosts, and large sanitary landfill mounds (70 ha).
Hunting in these “disturbed” habitats may have
accounted for the unusual dominance of Mus mus-
culus in the pellets (Bosakowski 1982).

Roosting Behavior. — In most cases owls con-
cealed themselves completely in a dense portion of
the conifer and were not visible until flushed or an
intention movement was made. Consequently, it
was not always possible to accurately note informa-
tion such as roosting height, distance from trunk, or
individual distances.

On one occasion, a Long-eared Owl was perched
on a completely exposed branch, but when I ap-
proached, it hopped along several branches and hid
behind the tree trunk while keeping a continuous
watch in my direction. Similar hiding behaviors
were observed on 3 other roost counts. On 2 other
occasions, owls were seen trying to avoid detection
by elongating their posture, erecting their ear tufts
and closing their eyelids nearly completely. The
resultant motionless form was maintained unless I
approached closer than 3-4 m; then the owls
flushed. This concealing posture was identical to
the “broken branch” appearance described in Bent
(1938:163). Another time, I observed a person, un-
aware of the owl roost, walk within 4 m of an owl
that was roosting on an exposed branch, but the owl
remained undisturbed. However, when I ap-
proached within 9 m and looked directly at the
same owl, it began staring intently, quickly rotated
its head back and forth, and then flushed. These
contrasting observations suggest that Long-eared
Owls will habituate to nearby human traffic, but are
readily able to discriminate when they are being
watched. Such selective attention to a predator’s
eyes (in this case, the author’s) can have considera-
ble survival value (Suarez and Gallup 1983) in that
prey species can monitor the direction of a pre-
dator’s visual focus and may be able to take advan-
tage of better escape opportunities (Gagliardi et al.
1976). Randle and Austing (1952) reported a simi-
lar ability of Long-eared Owls to discern scattered
members of a searching party and change the di-
rection of their escape flight accordingly.

Communal Roosting. — In general, these owls
roosted or flushed between 2 to 3 m above ground.
When 2-4 owls roosted communally, they were

Winter 1984

Long-Eared Owl in New Jersey

141

typically distributed on different branches at vary-
ing heights. Only once were 2 owls seen roosting
together on the same branch. When more than one
owl was present in the study block, communal
roosting was significantly preferred (x2 = 18.0, d.f.
= 1, P < 0.001) with only 4 solitary roostings ob-
served. Fleming (1981) lists the five most accepted
explanations for communal roosting: (1) a shor-
tage of roost sites, (2) huddling for body heat con-
servation, (3) predation risks, (4) a tendency to ex-
change information on patchy food locations, and
(5) to assess population size in relation to resources.
Although suitable roost sites were not plentiful in
the study area (hypothesis 1 , Fleming 1981) my data
show that a major roost can be totally ignored in
successive years with the owls clustering at another
nearby site. Clustering is not related to huddling
(hypothesis 2, Fleming 1981), for the closest indi-
vidual distance observed was 0.4 m. Reduction of
predation risks (hypothesis 3, Fleming 1981) has
probably been a major ‘ultimate’ factor in favor of
these owls forming communal assemblages. During
many flush counts, one owl would usually detect me
first, and then the others apparently were alerted
by either intention movements or by the sound of
the first bird flushing. Furthermore, when several
owls flush simultaneously, momentary confusion
may be experienced by an advancing predator. Post
(1983) speculated that in a solitary hunting species,
communal winter roosts have probably evolved as
an anti-predator mechanism. However, hunting by
Long-eared Owls may not be a completely solitary
event since some owls may follow others to profita-
ble hunting grounds. Therefore, the effect of
hypothesis 4 (Fleming 1981) remains unknown for
the Long-eared Owl. Finally, I agree with Schnell
(1969) that the plausibility of hypothesis 5 (Fleming
1981) is questionable and not likely to be tested in
the field.

Flushing Behavior. — The view of the owls was
frequently obstructed by dense cover or they were
dozing with closed or partially closed eyes. Hence
the flushing distance was usually between 2 to 4 m
with a quiet approach (no crusty snow or leaves).
During the study period, the owls were flushed a
total of 22 times, either singly or in groups. On 8
occasions, some owls immediately returned to the
same roost site within a period of several min. Two
owls attempted to return repeatedly (4 and 6 times)
to the same roost tree within 10 min of being
flushed. Apparently disturbed by my presence,

these owls were unable to resettle at each return.
This reluctance to leave the roost has not been
previously described, but was probably related to
the scarcity of roosting cover in the study area. Owls
that did not attempt an immediate return to the
roost were generally seen perched in the nearest
available conifers. This further attested to the
strong aversion of Long-eared Owls for daylight
activity. Like the observations of Randle and Aust-
ing (1952), the owls I studied were often clumsy and
disoriented when flushed, and twice were observed
to fly into black non-reflective windows of an adja-
cent building. Apparently, the dark windows were
mistaken for large cavities. No injuries were evident
and the owls continued to seek cover immediately.
The tendency of Long-eared Owls to hide, freeze
and flush only at close distances explains why this
raptor is able to roost very close to human habita-
tions.

Roost Departure. — The nocturnal inclination of
the Long-eared Owl was further characterized by
their late emergence at dusk. On 2 evenings, owls
were still roosting 26 and 40 min after sunset at
roost 2, but on 2 other evenings, could not be found
at this roost 49 or 81 min after sunset. From these 4
evenings, it appears that roost departure is most
likely to occur between 40 and 49 min after sunset.
Similarly in England, Armitage (1968) observed a
group of Long-eared Owls on one night departing
from the winter roost 35 min after sunset. In De-
nmark, Glass and Nielsen (1967) observed depar-
tures of Long-eared Owls from a winter roost on 40
nights and found a departure time of 39 ± 8 (X ±
S.D.) min after sunset.

Acknowledgments

I thank Robert Speiser and Richard Kane for valuable discus-
sions throughout the course of the study and for their critical
reading of the manuscript. Appreciation is also extended to Drs.
John H. Edgcomb, Frances N. Hamerstrom, Kevin L. Keim, Carl
D. Marti, and Clayton M. White for reviewing various drafts of the
paper. Robert Pitler provided encouragement and suggestions
about the project. Dr. Arthur A. Levin assisted with graphics.

Literature Cited

Armitage, J.J. 1968. A study of a Long-eared Owl roost.

Naturalist No. 905:37-46.

Bent, A.C. 1938. Life histories of North American birds

of prey. U.S. Natl. Mus. Bull. 170:482 pp.

Birkenholz, D. 1958. Notes on a wintering flock of

Long-eared Owls .III. Acad. Sci. Trans. 51:83-86.

142

Thomas Bosakowski

Vol. 18, No. 4

Bosakowski, T. 1982. Food habits of wintering Asio owls
in the Hackensack Meadowlands. Records of N.J. Birds
8:40-42.

Craighead, J.J. and F.C. Craighead, Jr. 1956. Hawks,
owls and wildlife. Stackpole Co., Harrisburg, Pa.

Fleming, T.H. 1981. Winter roosting and feeding be-
havior of Pied Wagtails Motacilla alba near Oxford,
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Academic Press, New York.

Marti, C.D. 1976. A review of prey selection by the
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Rough-legged Hawks (Buteo lagopus). Auk 86:682-690.

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Dept, of Zoology and Physiology, Rutgers University, Newark,
NJ 07102. Present address: Dept, of Toxicology and Pathol-
ogy, Roche Research Center, Nutley, NJ 07110.

Received 6 September 1984; Accepted 21 January 1985

FACTORS INFLUENCING DIFFERENTIAL PREDATION ON HOUSE MOUSE
( Mus musculus) BY AMERICAN KESTREL (Falco sparverius )

James R. Bryan

Abstract - Due to the sexual size dimorphism of raptors, it was thought that a preference for different sized prey might
be evidenced between male and female American Kestrel ( Falco sparverius). A modified bal-chatri trap was used which
gave kestrels a choice of 2 types of mice. In the first experiment, wild birds in the field were given a choice between a large
mouse (35 - 40g) and a small mouse (22 - 27g). The results of the summer season were compared to those of the fall-winter
season. The preferred prey size between the males and the females was not significantly different in fall-winter (X2 =
0.036, P >0.05). During breeding season, the preferred prey size shifted dramatically; males chose predominately small
mice, females predominately large ones (X2 = 20.55, P < 0.001). The second experiment showed the influence of hunger
on preference for a particular sized mouse. The birds that were determined to have a higher hunger level chose
predominately the large mice (X2 = 5. 1 8, P < 0.025). The third experiment showed the effect of a conspicuous, but odd,
color of prey (white mouse) compared to that of the normal, agouti color. The agouti color was chosen by 82% of the
birds. The difference between the actual preference and a random choice was highly significant (X2 = 1 8. 85, P < 0.005).

There are many aspects to the selection of prey by
predators. Lack of protective coloration (Dice 1947 ;
Kaufman 1974a), prey activity (Kaufman 1974b)
and oddity (Mueller 1971) play important roles.
The roles of predator experience (Mueller and Be-
rger 1970), specific search image (Tinbergen 1960;
Mueller 1971) and hunger (Mueller 1973) have also
been demonstrated. Several authors have investi-
gated the role of size in the selection of prey by
storks (Ogden et al. 1976), shrikes (Slack 1975) and
several species of raptors (Storer 1966; Mueller and
Berger 1970; Synder and Wiley 1976; Marti and
Hogue 1979).

The American Kestrel ( Falco sparverius) shows
only a slight size dimorphism with the male being,
on the average, 8% smaller by weight than the
female (Brown and Amadon 1968). The kestrel
must select prey with an efficiency such that the
energy expended to find, catch and kill the prey is
less than the energy obtained. Predation efficiency
is even more important during the breeding season
when the male feeds the female and young, as well
as himself. Certain prey must exist that are more
efficiently found and subdued (Emlen 1968). One
aspect of this efficiency is size of prey. This study
attempts to show a preferred size of prey by kestrels
which corresponds to the sex of the bird, hunger of
the bird and color of the prey, as well as seasonal
variation.

Methods and Materials

A modified bal-chatri trap (Mueller and Berger 1959), consist-
ing of 2 compartments (each 13 cm x 25 cm) separated by 15 cm
and made of lA- in hardware cloth was used. Capture loops were
made using 12# + cst monofilament line with approximately 20
loops attached to each compartment. Two size categories of the
agouti colored House Mouse ( Mus musculus) were used: large
(35-40g) and small (22-27g). All agouti mice were inbred genetic

strain C2H. Small mice were randomly placed in 1 cell and large in
the other. Whenever possible, the 2 mice used had a 15g weight
difference. When a perched kestrel was sighted the trap was tossed
to the ground from a slowly moving vehicle at a distance of 10-40
m from the bird. The trap was removed after 5 min unless some
type of response from the kestrel was observed. When the bird was
trapped, its sex was noted as well as which mouse (large or small) it
attacked. Any time a bird switched from one side of the trap to the
other, the trial was discounted. This happened on only 10 of 149
trials and only in the fall-winter season. The fall-winter season
included the months September, October, November and De-
cember 1980 & 1981. No switches were made during the summer
season of May, June and July, 1981, 1982, 1983 (see Tables 1 and
2). Males and females were compared for prey size preference as
well as difference between the 2 seasons. Independent and semi-
independent young birds were separated from adults on the basis
of whether flight feather molt was occurring during the breeding
season (see Table 2). During fall-winter season the immature birds
were combined with the data for adults.

A second part of the study concerned the determination of
hunger in birds which might have influenced preference for a
particular sized mouse. Hunger was determined by computing
ratio of average wing chord to the cube root of average body wt.
Any bird with a ratio above the average was considered under-
weight and any bird with a below average ratio was considered
overweight. Overweight and underweight kestrels were then sub-

Table 1 . Comparison of the number of female and male
kestrels that chose either the large or the small
mouse during the fall-winter “season”. The
category “switched mice” denotes that the kes-
trel attacked one size mouse and then switched
and attacked the other.

Switched

Large Mouse

Small Mouse

Mice

Males

23

26

4

Females

41

49

6

143

Raptor Research 18(4): 143- 147

144

James R. Bryan

Vol. 18, No. 4

Table 2. Comparison of the number of female and male
kestrels that chose either the large or the small
mouse during the “summer” season. The categ-
ory “switched mice” denotes that the kestrel at-
tacked one size mouse and then switched and
attacked the other.

Large Mouse

Small Mouse

Switched

Mice

Males

5

23

0

Females

Immature

21

4

0

Females

Immature

3

10

Males

1

1

0

jected to Chi-square (X2) analysis to determine if both preferred
the same or different sized mice.

Finally, I determined if a conspicuous, but odd-colored, mouse
(white) was preferred over the more natural color (agouti). The
white mouse could be seen, when it moved, up to approximately
300 m away, whereas the agouti mouse could be seen up to ap-
proximately 200 m. These distances were determined by objective
analysis by the author. The background did not appear to make
much difference in discerning the white mouse unless the sub-
strate was very light in color. The experiment was similar to the
large and small mouse experiment, except the trap contained only
1 white and 1 agouti mouse with no more than 3 g difference in wt.

Comparison of wing chord was done between summer and
fall-winter kestrels to determine if 2 populations of kestrels (mig-
ratory and non-migratory) were being sampled in fall-winter ver-
sus 1 population in summer (non-migratory). A t-Test was used to
compare means and a F-test for variance.

Results and Discussion

Fifty-three adult birds were trapped during the
summer season when young were in the nest or still
on the territory being fed. In the fall- winter season
1980 and 1981, 149 birds were trapped. Eighty-
nine birds were trapped for the white mouse/agouti
mouse experiment in the fall-winter season, 1982
and in January 1983. Kestrels were trapped in open
habitat in Los Angeles, Orange, Riverside and Kern
counties, southern California. During fall-winter,
more females were trapped than males. This may
have been due to sexual habitat preference (Koplin
1973). Females tend to prefer open habitat while
males prefer woodland margins.

The data are shown in Tables 1-5. The preferred
prey size between males and females was not sig-
nificantly different in fall-winter ( X 2 = 0.036, P >
0.05; see Table 1). During the breeding season,
preferred prey size shifted dramatically; males

predominately chose small mice, females predomi-
nately large mice (see Table 2). This difference was
highly significant (X2 = 20.55, P < 0.001) and was
reflected in seasonal comparisons within each sex.
Males shifted from a random choice in fall-winter to
a strong preference for small mice in the breeding
season (X2 = 5.32, P < 0.025). Females shifted from
a random choice in fall-winter to a strong prefer-
ence for large mice in the summer season (X2 =
10.14, P < 0.001).

Table 3. The number of overweight and underweight
females that chose either the large or small
mouse during the fall-winter “season”.

Large Mouse

Small Mouse

Overweight

12

13

Underweight

11

13

Relationship of hunger to preferred prey size was
apparent with females. During the fall-winter, un-
derweight females predominately chose the large
mouse while overweight females chose the small
mouse (see Table 3). This difference in the prefer-
red prey size was significant (X2 = 5.18, P < 0.025).
However, there seemed to be no relationship of
hunger to preferred prey size in males (X2 = 0.018,
P > 0.05) (see Table 4). Average wing chord for 49
males and 90 females was 188 mm and 196 mm,
respectively. Wing chord means and variance val-
ues did not differ significantly from summer to
fall-winter seasons (t-Test, P > 0.05; F-test, P >
0.05). Average weight was 1 08 g for males and 1 22 g
for females.

Table 4. The number of overweight and underweight
males that chose either the large or small
mouse during the fall-winter “season.”

Large Mouse

Small Mouse

Overweight

12

13

Underweight

11

13

Winter 1984

Predation Factors

145

Effect of a conspicuous, but odd, color of prey
(white mouse) is seen in Table 5. There was no
significant difference between male and female
selection for color (X2 = 0.272, P >0.05), therefore
they were combined. Eighty-two percent of kestrels
chose agouti mice. The difference between the ac-
tual preference and a random choice was highly
significant (X2 = 18.85, P < 0.005).

Table 5. The number of males and females that chose
either the white or agouti colored mouse dur-
ing the fall-winter “season”. The category
“switched mice” denotes that the kedtrel at-
tacked one size mouse and then switched and
attacked the other.

White

Agouti

Switched

Mouse

Males

4

26

1

Females

12

47

2

Behavior of kestrels toward the trap led me to
believe that each bird was preferentially selecting
one of the mice. The kestrels exhibited several types
of behavior. In one type the bird flew toward the
trap and hovered over it for several seconds before
attacking one side. In another pattern the kestrel
flew to a position over the trap (telephone lines or
poles, trees, etc.) and sat examining the trap for
some time before attacking. In the third, and most
convincing, type of behavior, the bird was not
caught on initial attack, flew away, and consistently
returned to attack the same mouse. This pattern
continued until the kestrel either was caught or
gave up. In the last, the bird attacked one side of the
trap, then attacked the other or it attacked one side,
flew away, and returned to attack the other. This
was rare, occurring 6.7% of the time, during fall-
winter and was excluded from data analysis.

The results clearly show a preference for size of
prey in spring for kestrels. The reasons for this
preference are not as clear The first possible reason
was advanced by Storer (1966). He hypothesized
that due to sexual size dimorphism, sexes take dif-
ferent size prey serving to reduce competition bet-
ween them so that the pair can feed in a smaller
territory. This may work well when the prey is
birds. Young birds (after fledging) are essentially

the same size as adults, so preying on different size
birds means preying on different species. This
would seem to reduce competition between sexes
and increases the number of potential prey. How-
ever, in rodent species young are smaller than
adults. Preying on different sizes (hence difference
ages) of the same species would not seem to increase
available prey, although it would allow some reduc-
tion in competition between sexes. If male and
female kestrels prey on different sizes of the same
species, the prey population would be reduced as
quickly as if both sexes preyed on both sizes equally.
This hypothesis should not be quickly discarded,
however, as even a subtle avoidance of competition
is an advantage.

An alternative is that males chose the smaller
mouse because there are simply more small mice at
that time of the year. The males may have formed a
specific search image (SSI) for smaller mice on the
basis of availability. The females, on the other hand,
do little hunting for much of the season and may
not have a strong SSI formed and thus choose the
larger mouse for a larger reward.

Another alternative deals with the energetics of
carrying a mouse to the nest cavity. The female does
little hunting for most of the breeding season while
the male procures food for himself, the female and
young. He must carry prey to the nest for distances
up to 1 km (Balgooyen 1976). It may be less
energetically demanding to carry more small mice
to the nest than fewer large mice. The female, on
the other hand, hunts infrequently near the nest,
and does not have far to carry prey; therefore, it
seems most advantageous for her to attack the
largest prey possible. Studies of the energetics of
flying with varying weights are needed to confirm
this hypothesis.

During winter, the males and femals are feeding
only themselves and would not need to be as selec-
tive with the size of prey. The prey does not have to
be carried far and both sexes should be able to kill
the large category mouse with almost equal skill.
Males do not have the same bulk as females, how-
ever males do have a lighter wingloading and feet
and beaks which are not significantly different in
size (Balgooyen 1976). The male should be able to
transport prey as easily as the female due to lighter
wingloading. The only advantage seems to be that
females have more bulk to subdue larger prey. A
flaw in this hypothesis is that it would seem most
advantageous to prey on the largest mouse because

146

James R. Bryan

Vol. 18, No. 4

of the larger gain. This was not, however, indicated
by the data. The birds selected a large proportion of
small mice in winter. This may be explained by the
hunger of the bird. A kestrel that is underweight
might be more inclined to attack a larger mouse
than a kestrel that is overweight.

The influence of hunger in predation was shown
by Mueller and Berger (1970). They trapped
Sharp-shinned Hawks (Accipiter striatus ) in 2 man-
ners. One in which the hawks actually struck lure
birds [pigeons, starlings or House Sparrows (Passer
domesticus)], and the other in which the hawks flew
near, but did not attack, and were trapped in a net.
Although the data were not statistically significant
in all cases, a tendency existed in which lighter
hawks actually struck prey more frequently. This
suggested to them that hunger influences a hawks
tendency to kill. Mueller (1973) demonstrated the
relationship of predatory behavior to hunger in
American Kestrels. Kestrels were deprived of food
for intervals of 1, 5, 10, 20, 25, 30 or 35 h. In his
experiment on deprivation interval to food con-
sumption the curve was almost linear. On the aver-
age, kestrels consumed 2% of their body wt after 1 h
of deprivation and about 13% after 35 h. In the
experiment on deprivation interval to killing ten-
dency the curve was only a little less linear. After 1 h
of deprivation kestrels killed mice 14% of the op-
portunities and 92% after 35 h. Mueller (1973:519)
felt that all his data “indicate a complete correlation
between food consumption and predatory be-
havior, suggesting that predation is a direct re-
sponse to hunger.”

In this paper it was assumed that an underweight
bird is more hungry than an overweight bird. The
effect of hunger is seen in Tables 3 and 4. Table 3
shows the effect of female hunger in which 32 of 48
(67%) of the overweight females chose the large
mouse. Table 4 shows this not to be the case with
males. There is no difference in preferred prey size
from underweight to overweight males. There may
be other factors that override the effect of hunger
in males. The data for females suggest that hunger
influences the selection for prey, which is contrary
to Lorenz’s (1966) generalization that killing in-
stinct of predators is unitary and driven indepen-
dently of hunger. However, my study supports the
contention of Mueller (1973) and Mueller and Be-
rger (1970) that hunger plays an important role in
the tendency to kill.

The results of the white mouse/agouti mouse ex-

periment clearly show a preference for the natural
agouti color although there is a definite selection
for the odd color (white) at times. This was espe-
cially evident when kestrels attacked the white
mouse, was not caught, and returned to the same
mouse before getting caught. The selection of ag-
outi mice seems to show an SSI for agouti color
whereas the selection of white mice may show a
tendency of a kestrel to vary its diet (Tinbergen
1960; Mueller 1974). I believe the existence of an
SSI is supported by this study, although there ap-
pear to be many variables that can alter the SSI.
Several authors believe that predators carefully
evaluate their chances of success with each pros-
pective prey (Cushing 1939; Errington 1967; Cade
1967). When this evaluation encompasses the SSI,
the predator will decide whether to attack or not
(e.g., if the mouse is the correct size, color and
species but the distance to the prey is too far and the
cover is too dense, the bird will not attack).

The selection of odd mice in my experiment is
consistent with the results of Mueller (1974:716) in
which “some birds showed a tendency to select a
reasonably constant proportion of mice of a given
color throughout a series regardless of the relative
abundance of the mouse, suggesting that the bird
seeks a fixed amount of novelty or variety.” Mueller
contended that in most prey populations odd prey
is probably unfit and, therefore, would be actively
selected from the environment (see Mueller 1974
for a listing of references to support the conten-
tion).

There are inherent problems in any study that
attempts to relate an artificial situation to the real
world, and this study is no exception. A choice
between 2 mouse sizes probably rarely occurs in
nature and it seems unlikely that the kestrel would
not kill a mouse of the non-preferred size. How-
ever, the birds probably have an SSI for a preferred
size and when all factors are considered (i.e., dis-
tance from prey, visibility of prey, etc.) they are
more likely to attack the preferred size than
another. This does not mean that either sex will not
attack the non-preferred size mouse. The kestrel is
an opportunistic predator and will attack anything
within certain broad limits. It does mean that they
have an SSI for a size prey that they will aggressively
pursue over long distances and more adverse con-
ditions than other size prey. Another problem to
consider is the activity of the 2 mouse sizes, as
Kaufman (1974b) showed that active rats were

Winter 1984

Predation Factors

147

preyed upon more than inactive rats. Marti and
Hogue (1979) found that small mice may move
faster than large mice, but they do not move longer
distances in the same time period. If the kestrels
preferred a faster (smaller) mouse or a slower
(larger) mouse, it would not be expected that they
would switch this preference seasonally as is the
case in this study.

A third potential problem is with fall-winter data
which dealt with hunger in females where 2 popu-
lations of females were sampled (migratory and
non-migratory). Although wing chord analysis
showed no difference in the size of these 2 popula-
tions, it may be that migratory females are, on the
average, lighter in wt than non-migratory females.
Migratory females may have a previous SSI formed
for large mice. This would bias the data toward the
results achieved based on hunger. In the fall-winter
data, part of the population were immature birds
which were not distinguished from adults. Mueller
and Berger (1970) showed that inexperienced
raptors tend to take inappropriate prey. However, I
have a strong feeling that by winter young birds
have formed an SSI.

Literature Cited

Balgooyen, T.B. 1976. Behavior and ecology of the
American Kestrel ( Falco sparverius). Univ. Calif. Publ.
Zool. 102:1-85.

Bond, R.M. 1943. Variation in western Sparrow Hawks.
Condor 45(5): 168-1 85.

Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill.

Cade, T.J. 1967. Ecological and behavioral aspects of
predation by the Northern Shrike. Living Bird 6:43-86.
Cushing, J.E. Jr. 1939. The relation of some observa-
tions upon predation to theories of protective colora-
tion. Condor 41:1 00- 111.

Dice, L.R. 1947. Effectiveness of selection by owls of
deer mice ( Peromyscus maniculatus) which contrast in
color with their background. Contrib. Lab. Vert. Biol.
Univ. Michigan, Ann Arbor. 34:1-20.

Emlin, J.M. 1968. Optimal choice in animals. Amer.
Natur. 102:385-389.

Errington, P.L. 1967. Of predation and life. Ames,
Iowa State Univ. Press.

Kaufman, D.W. 1974a. Adaptive coloration in Peromys-
cus polionotus: experimental selection by owls. J.
Mammal 55:271-283.

1974b. Differential predation on active

and inactive prey by owls. Auk 91:172-173.

Koplin, J.R. 1973. Differential habitat use by sexes of
American Kestrels wintering in northern California.
Raptor Res. 7(2):39-42.

Lorenz, K.Z. 1966. On aggression. Chicago, Univ.
Chicago Press.

Marti, C.D. and J.G. Hogue. 1979. Selection of prey by
size in Screech Owls. Auk 96:319-327.

Mueller, H.C. 1971. Oddity and specific search image
more important than conspicuousness in prey selec-
tion. Nature 233:345-346.

1973. The relationship of hunger to

predatory behavior in hawks ( Falco sparverious and
Buteo platypterus). Anim. Behav. 2 1 :5 13-520.

1974. Factors influencing prey selec-
tion in the American Kestrel. Auk 91:705-721.

, and D.D. Berger. 1959. The bal-

chatri; a trap for the birds of prey. Bird Banding
30:18-26.

1970. Prey preferences in the Sharp-

shinned Hawk: the roles of sex, exprience and moti-
vation. Auk 87:542-547.

Ogden, J.C., et. al. 1976. Prey selectivity by the Wood
Stork. Condor 78:324-330.

Slack, R.S. 1975. Effects of prey size on Loggerhead
Shrike predation. Auk 92:812-814.

Snyder, N.F.R. and J.W. Wiley. 1976. Sexual size di-
morphism in hawks and owls of North America. Or-
nith. Monog. 20:1-95.

Storer, R.W. 1966. Sexual size dimorphism and food
habits in three North American accipiters. Auk
83:423-436.

Tinbergen, L. 1960. The natural control of insects in
pinewoods. 1. Factors influencing the intensity of
predation by songbirds. Arch. Neerl. Zool. 13:265-343.

2120 National Ave., Costa Mesa, CA 92627.

First Received 24 December 1983; Accepted 1 December 1984

HABITAT SELECTION BY THE AMERICAN KESTREL (Falco sparverious)
AND RED-TAILED HAWK (Buteo jamaicensis) WINTERING IN
MADISON COUNTY, KENTUCKY

Nancy J. Sferra

Abstract - Habitat selection by the American Kestrel {Falco sparverius) and Red-tailed Hawk {Buteo jamaicensis) in
Madison County, Kentucky, was determined for the winter of 1980-81. Results showed that there was significant
non-random use of 6 habitat types (Kestrels: x2 = 629.5, P < 0.05, d.f. = 5; Red-tailed Hawks: x2 = 124.8, P < 0.05, d.f. =

5) with old field sites being used most frequently by both species.

The American Kestrel (Falco sparverius ) and
Red-tailed Hawk (Buteo jamaicensis) are the most
numerous diurnal raptors wintering in Madison
County (Sferra 1 984). Mengel ( 1 965) reported that,
in Kentucky, kestrels preferred open areas. Along
highways in West Virginia, kestrels most often
hunted in pasturelands, or open areas planted with
Lespedeza spp. (Ferris 1974). However, near high-
ways in the Texas panhandle, kestrels frequented
wooded areas (Allan and Sime 1943).

Red-tailed Hawks were most commonly as-
sociated with woodlots in Iowa and the Texas
panhandle (Allan and Sime 1943; Weller 1964).
Petersen (1979) reported that Red-tailed Hawks
seldom used internal portions of woodlots, sup-
porting Schnell’s (1968) observation that the species
preferred perching at woodlot edges. In Michigan,
open areas were heavily utilized (Craighead and
Craighead 1956), lone trees being favored as perch
sites (Chamberlain 1974).

High winter densities of these raptors in Madison
County (Sferra 1984) may result from the amount
of open habitat available for hunting, as well as the
presence of adjacent, heterogeneous edge habitat.
Many open areas are bordered by fencerows of
trees or are bisected by power lines, providing
perching sites from which hawks can search for
prey. The purpose of the present study was to de-
termine the relative extent to which wintering kes-
trels and Red-tailed Hawks frequented various
habitats found in Madison County.

Study Area and Methods

Madison County encompasses parts of 4 physiographic regions
in central Kentucky: the Hills of the Bluegrass, the Outer Blueg-
rass, the Knobs Section of the Cumberland Plateau, and the
Mountains (Soil Conservation Service 1973). Terrain ranges from
rolling, upland plains to long, narrow ridge tops separated by
steep valleys with the maximum relief being 335 m (Jillson 1928).
Madison County is composed predominantly of pastureland and
hayfields with forest stands being confined mainly to stream mar-
gins, field edges, and rugged regions of the Cumberland Plateau
and Mountains.

Birds were located by means of an automobile road count
(Craighead and Craighead 1956) covering secondary roads of the
county. The count routes were chosen so that each of the physiog-
raphic regions in the county were represented. One road count
was run weekly from late December 1980 to March 1981 for a total
of 10 counts. Each covered the same 235 km and were not run
when visibility was hampered by snow, fog, or rain. A driver/
observer and passenger/observer were present during each cen-
sus. Routes were driven at speeds between 32-48 kph, and all
raptor sightings on both sides of the road were recorded. The
maximum distance of sightings on each side of the road was
approximately 440 m.

Habitats directly beneath raptors in flight, and areas overlooked
by perched birds formed the basis for determining species-specific
habitat utilization. Six habitat categories were distin-
guished: pastureland (both grazed pasture and mowed
hayfields), cropland, urban areas, old fields, woodlots and plowed
fields. Actual habitat use was tested against their relative occurr-
ence. Proportion of occurrence was quantified from randomly
selected aerial photographs representing 10% of the entire
county.

Results and Discussion

The six habitat types occurred in the following
proportions: 57% pastureland and hayfields, 33%
woodlots, 3% cropland, 3% urban areas, 2% old
fields and 2% plowed fields. Kestrels and Red-
tailed Hawks utilized certain habitats to a greater
extent than that predicted by their relative availa-
bility. Chi-square (x2) tests showed significant non-
random habitat use by kestrels and Red-tailed
Hawks wintering in Madison County (Table 1).

Table 1. Results of Chi-square (x2) analysis of habitat
selection and utilization based on habitat av-
ailability in Madison county.

Species

x2

American Kestrel

629. 5a

Red-tailed Hawk

124. 8a

aP < 0.05; d.f. = 5

148

Raptor Research 18(4): 148-150

Winter 1984

Winter Habitat Selection in Kentucky

149

Table 2. Total number of American Kestrel and Red-tailed Hawk sightings and % deviation from expected Chi-
square values for their occurrence in each of 6 habitat types. A positive sign indicates habitat use greater than
expected and a negative sign indicates use less than expected.

American Kestrels

Red-tailed Hawk

Habitat

N

% DEVIATION

N

% DEVIATION

Pastureland

276

+ 38

117

+ 28

Old Field

66

+ 790

21

+525

Cropland

15

+ 76

1

- 59

Plowed Fields

5

- 31

1

- 70

Woodlots

3

- 98

28

- 65

Urban Areas

0

-100

0

-100

Kestrels habitat use was as follows: pasture land
76.9%, old field 1 8.4%, cropland (consisting mainly
of corn stubble) 4.2%, plowed field 1.4%, woodlots
0.8% and urban areas 0%. Percent deviations from
expected values of the chi-square test showed that
kestrels utilized woodlots and urban areas less, and
all other habitats more than expected. Selection of
old fields was most pronounced (Table 2).

The nature and distribution of perching sites in a
given surveyed area probably introduced bias into
road count data. In the Texas panhandle, for in-
stance, frequent utilization of woodlots by kestrels
(Allan and Sime 1943) could have been directly
related to lack of perching sites in open habitat. In
Madison County, the majority of kestrels were seen
perching on utility lines, many of which run parallel
to the census route. On the other hand, birds hid-
den behind trees, buildings and signs may have
resulted in low utilization estimates for woodlot and
urban area use.

Winter habitat separation by sexes has been re-
ported as common among kestrels in Texas,
California, Arizona, Mexico (Mills 1976; Koplin
1973) and Georgia (Stinson et al. 1981). Chi-square
test showed male kestrels were significantly more
numerous than females (58% males, P < 0.05).
However, sex-specific differences in habitat were
not significant in Madison County (P < 0.05).

Habitat selection by Red-tailed Hawks was as
follows: pastureland 69.9%, woodlots 16.7%, old
field 12.5%, cropland 0.6%, plowed fields and
urban areas 0%. Use of pastureland and old field
sites was greater than expected; all other habitats

were frequented less than expected (Table 2). The
majority of Red-tailed Hawks associated with
woodlots were perched along margins overlooking
open areas. Similarly, Petersen (1979), using a road
count in Wisconsin, found that internal portions of
woodlots were seldom used.

Of all habitat types, old field site use by hawks
deviated the most from the expected values. Selec-
tion for old field sites by kestrels, and to a lesser
degree by Red-tailed Hawks, may have been in-
duced by higher prey populations, specifically
Meadow Vole ( Microtus pennsylvanicus). Austing
(1964) found Meadow Voles to be staple prey for
Red-tailed Hawks during winter months, and vole
population density has been suggested as the major
factor determining hawk distribution (Bart 1977).
Kestrels also depend heavily upon Meadow Voles
during winter (Craighead and Craighead 1956). In
Madison County, matted vegetation used by voles
for runways will not accumulate on intensively
grazed pastureland and mowed hayfields, resulting
in decreased population density. Old field sites,
based on presumed prey density, have the greatest
potential for supporting large numbers of winter-
ing kestrels and Red-tailed Hawks.

Acknowledgments

Special thanks are extended to those who helped in obtaining
field data: R. Altman, G. Barels, P. Mastrangelo, G. Murphy, J.
Schafer, C. Schuler, T. Towles, and especially J. Colburn.

Literature Cited

Allan, D.F. and P.R. Sime. 1943. A hawk census on
Texas panhandle highways. Wilson Bull. 55:29-39.

150

Nancy J. Sferra

Vol. 18, No. 4

Austing, G.F. 1964. The world of the Red-tailed Hawk.

J.B. Lippincott Co., Philadelphia. 128 pp.

Bart, J. 1977. Winter distribution of Red-tailed Hawks
in New York State. Wilson Bull. 89:623-625.
Chamberlain, M.L. 1974. Fall hunting behavior of the
Red-tailed Hawk (Buteo jamaicensis) in Central Michi-
gan. Jack-pine Warbler 52:2-9.

Craighead, J.J. and F.C. Craighead, Jr. 1956. Hawks,
owls and wildlife. Stackpole, Harrisburg, Pa. 443 pp.
Ferris, C.R. 1974. Effects of highways on Red-tailed
Hawks and Sparrow Hawks. M.S. Thesis. West Va.
Univ., Morgantown, W. Va.

Jillson, W.R. 1928. The geology and mineral resources
of Kentucky. Ky. Geol. Survey, Frankfort, Ky.
Koplin, J.R. 1973. Differential habitat use by sexes of
American Kestrels wintering in Northern California.
Raptor Res. 7:39-42.

Mengel, R.M. 1965. The birds of Kentucky. Omithol.

Mono. No. 3, Am. Ornithol. Union, Lawrence, Kansas.
Mills, G.S. 1976. American Kestrel sex ratios and
habitat separation. Auk 93:740-748.

Petersen, L. 1979. Ecology of the Great Horned Owl
and Red-tailed Hawk in southeastern Wisconsin. Wise.
Dept. Nat. Res. Tech. Bull. No. Ill, Madison, Wise. 63
pp.

Schnell, G.D. 1968. Differential habitat utilization by
wintering Rough-legged and Red-tailed Hawks. Con-
dor 70:373-377.

Sferra, N.J. 1984. Population densities of diurnal rap-
tors wintering in Madison County, Kentucky. Trans.
Ky. Acad. Sci. 45 (3-4): 128-131.

Soil Conservation Service. 1973. Soil survey of Madi-
son County, Kentucky. U.S.D.A. and Ky. Agri. Exp.
Sta., Lexington, Ky.

Stinson, C.H., D.L. Crawford and J. Lauth-
ner. 1981. Sex differences in winter habitat of
American Kestrels in Georgia./. Field Ornith. 52:29-35.

Weller, M. W. 1 964. Habitat utilization of two species of
Buteos wintering in central Iowa. Iowa Bird Life
34:58-62.

Dept, of Biol. Sci., Eastern Ky. Univ., Richmond, Ky. 40475.
Present address: Dept, of Zoology, Mich. State Univ., E. Lans-
ing, Mich. 48824.

Received 15 July 1984; Accepted 30 January 1985

Winter 1984

Short Communications

151

Short Communications

A Clutch Of Unusually Small Peregrine Falcon Eggs

M. Alan Jenkins

Unusually small (dwarf or runt) eggs are rare, occurring
at a frequency of 0.05-0.09% in the Domestic Chicken
(Gallus gallus) (Romanoff and Romanoff 1949), 0.08% in
the Common Grackle ( Quiscalus quiscula ), and 0.18% in
the Red-winged Blackbird (Agelaius phoeniceus) (Rothstein
1973). More than one small egg in a clutch is even rarer.
Pearl and Curtis (1916 cited in Romanoff and Romanoff
1949) found only 1 1 % of chickens that laid any small eggs
laid more than one, i.e. about 0.0055-0.0099% over all.

Small Peregrine Falcon (Falco peregrinus) eggs, here de-
fined as those less than 40 ml in estimated volume, are also
rare (Table 1). Although accurate frequency data from
the wild are not readily available, Burnham (pers. comm.)
found only 1 small egg in about 350 (0.3%) he has hand-
led. Most small eggs occur as runts, an odd egg in an
otherwise normal clutch (Ratcliffe 1980). The 2 eggs of
the clutch described here are smaller than any noted in the
literature for North American peregrines. That both eggs
were small suggests a “normal” egg size for this female
rather than odd eggs. I found the clutch in a Sonoran
eyrie on 8 May 1981. This site was first known to be
occupied in 1978 when an adult was seen there in mid-
March. A pair of adults vigorously defended this area in
late April of 1980, but the exact eyrie location was not
found. The eyrie site used in 1981 was a small cave (ca. 2 X
2 X 2 m in size and hemi-conical in shape) near the top of
an igneous cliff. There were 2 eggs in a scrape near the
back wall of the cave. The eggs were cool to the touch and
their contents sloshed when gently shaken, indicating they
were addled. On 8 May successful eyries in this area
should have contained nestlings, as had 10 other eyries
previously visited. The estimated mean hatching date for
Gulf of California peregrines is 12 April (n = 31), the latest
known hatching date is 15 May (Porter et al. in prep.).

I measured the 2 eggs with a caliper having a Vernier
scale marked in increments of 0.1 mm; the results are
given in Table 1 as eggs A and B. Table 1 also compares
the size of these 2 eggs with some published dimensions of
small and average-sized Peregrine Falcon eggs.

Several factors have been given as causes for abnor-
mally small bird eggs. Chickens may occasionally lay yolk-
less eggs which weigh only a few grams (Romanoff and
Romanoff 1949). The only known yolkless peregrine egg
from the wild, also from the Gulf of California, was noted
by Risebrough (1971). This egg was small but its dimen-
sions were not given. In captivity, yolkless eggs occur
about once in 300 eggs; one measured 33.2 X 25.0 mm

(Burnham pers. comm.). The sizes of eggs laid by indi-
vidual peregrines may also vary with age; small eggs are
produced by young females laying for the first time (Blair
1 967) but also by old females (Ratcliffe 1 980). The eggs of
one female reported by Ratcliffe (1980) from Britain de-
creased in size in an 8-y period from almost normal eggs
averaging 50.0 X 39.5 mm (39.7 ml) to the smallest re-
corded size of 4 eggs averaging 46.5 X 32.5 mm (25.0 ml).

Racial differences in egg size occur but are not great
(Brown and Amadon 1968). The small-bodied subspecies
babylonicus (considered by some to be a separate species)
has the smallest mean egg size according to Brown and
Amadon (1968) and is similar in body and egg size to the
small F. p. minor (Table 1). Egg size variation due to racial
differences are probably related to female body weight
differences. Romanoff and Romanoff (1949) state that
the smallest chicken eggs are produced by the lightest
females.

The first egg of a cycle (clutch) in the chicken is gener-
ally the heaviest, decreasing thereafter (Romanoff and
Romanoff 1949). Physical condition, nutrition, and
climatic conditions can also affect egg size (Romanoff and
Romanoff 1949).

Olsen (1982) found that peregrine egg size increased
with increasing latitude (in the southern hemisphere), use
of tree hollows as nests, and decreasing temperatures.
These relationships disappeared in certain areas after the
1940s, a period corresponding with the introduction of
DDT and intensification of land use. Olsen (1982) found
no significant difference in egg size between the first and
replacement clutches from the same nest site, nor any
correlation between clutch size and egg size.

Some of the above causes of small eggs can be elimi-
nated as factors in the Gulf of California clutch. The
female defending the nest was seen clearly at close range
and was in full adult plumage with no immature feathers
remaining. She probably was at least in her third calendar
year of life and had probably laid other clutches. How-
ever, it is possible that she was a very old female. Racial
differences in egg size can be eliminated because the eggs
of this clutch are far smaller (ca. 35% less in estimated
volume) than average eggs of the small subspecies F. p.
babylonicus. The order of laying was not a factor because
both eggs were unusually small. Whether or not the eggs
were yolkless is not known, but it is unlikely that 2 such
eggs would occur together. The effects of low latitude and
warm temperatures as found by Olsen (1982), could be

Table 1 . Dimensions of Peregrine Falcon eggs. Maximum length (L) and breadth (B) are in mm ; estimated volume (V) was calculated according to Hoyt
(1979) and is in ml.

152

Short Communications

Vol. 18, No. 4

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Winter 1984

Short Communications

153

important because the eyrie is near the southern limit of
peregrine distribution for the northern hemisphere, and
is in an area that has mild temperatures during the time
peregrines nest. Nevertheless, it is unlikely that even both
of these effects in combination could produce such a large
reduction from the average.

Thanks are due to M.A. Bogan, W.A. Burnham, L.F.
Kiff, R.L. Phillips, R.D. Porter, and D.Q. Thompson for
review and suggestions on an earlier draft of the manu-
script. S. Sumida measured eggs from Baja California,
Mexico, in the Western Foundation of Vertebrate Zoology
collection. The 1981 field work would not have been pos-
sible without the cooperation and help of R. A. Graham,
R.S. Ogilvie, J.R. Swift, and Alfonso de Anda T. of the
Direccion General de Fauna Silvestre of Mexico.

Addendum

An additional record of a small peregrine egg was recently
brought to my attention. Charles Bendire (Smith. Inst. Spec. Bull.
No. 1 , 1 892) noted an egg with dimensions of 38.5 mm x 30 mm (L
x B). This egg is smaller than any I could find recorded, but it was a
single example (a runt) and not a clutch as in the case of the
Sonoran eggs.

Literature Cited

Bannerman, D.A. and G.E. Lodge. 1956. The birds of
the British Isles, Vol. 5, Oliver & Boyd, Ltd., Edin-
burgh and London.

Bent, A.C. 1938. Life histories of North American birds
of prey. Part 2. U.S. Nat. Mus. Bull. 170.

Blair, H.M.S. 1967. On two exceptional clutches of
peregrines’ eggs. Oologists' Record 41:6-7.

Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill Book Co., New
York.

Cramp, S. (ed.). 1980. Handbook ofthe birds of Europe,
the Middle East, and North Africa, Vol. 2 Oxford
Univ. Press, Oxford.

Glutz von Blotzheim, U.N., K.M. Bauer, and E. Bezzel
(eds.). 1971. Handbuch der Vogel Mitteleuropas,
Vol. 4. Akademische Verlegsgesellschaft, Frankfurt
am Main.

Hoyt, D.F. 1979. Practical methods of estimating vol-
ume and fresh weight of bird eggs. Auk 96:73-77.

Olsen, P.D. 1982. Ecogeographic and temporal varia-
tion in the eggs and nests of the peregrine, Falco pereg-
rinus. (Aves: Falconidae) in Australia. Aust. Wildl. Res.
9:277-291.

Ratcliffe, D. 1980. The Peregrine Falcon, Buteo Books
Co., Vermillion, S.D.

Risebrough, R. 1971. Baja California. Pp. 126-127 in
Research planning conference on peregrines and
other birds of prey, Cornell University, Ithaca, New
York, November 7-9, 1969-part 2, K. Hodson, (ed.).
Raptor Res. News 5:123-131.

Romanoff, A.L. and A.J. Romanoff. 1949. The avian
egg. John Wiley and Sons, Inc., New York.

Rothstein, S.I. 1973. The occurrence of unusually
small eggs in three species of songbirds. Wilson Bull.
85:340-342.

USFWS, Denver Wildlife Res. Ctr., Bldg. 16, Fed. Ctr., Denver,

CO 80225. Present Address: George Miksch, Sutton Avian Res.

Ctr., Inc., P.O. Box 2007, Bartlesville, OK 74005-2007.

Received 20 February 1983; Accepted 28 April 1984

Eyrie Aspect as a Compensator for Ambient Temperature Fluctuations:
A Preliminary Investigation

Richard N. Williams

Raptor ecologists have long recognized that nest site
characteristics may influence reproductive success for
many birds of prey (Olendorff 1973; Porter and White
1973; Ogden and Hornocker 1977). However, few studies
have demonstrated relationships between nest site
characteristics and physical factors that may provide
energetic or reproductive advantages.

It has been suggested that the Prairie Falcon {Falco
mexicanus) prefers nest sites with a southerly exposure
(Enderson 1964; Olendorff 1973; Porter and White 1973;
Denton 1975; Ogden and Hornocker 1977). Additionally,

Leady (1972) and Williams (1981) noted a component of
easterly-facing eyries. McGahan (1968) speculated that an
easterly eyrie aspect in Golden Eagle {Aquila chrysaetos ) in
Montana may negate early morning chill and temper af-
ternoon heat, however, he did not test this prediction.

In 1980, 1 studied the reproductive phenology of a local
population of Prairie Falcons nesting at high elevations ( X
= 2720 ± 199 m) in central Colorado (Williams 1981). Of
the 1 4 eyries examined, 7 had east or southeasterly aspects
between 93-165°. I initiated a preliminary investigation
using one of these eyries to estimate the relationship bet-

154

Short Communications

Vol. 18, No. 4

HOUR (MDT) (x ioo)

Figure 1. Eyrie and ambient temperatures for eyrie No. 2, 10-1 1 June 1980. Solid line denotes eyrie temp. Dashed line
denotes ambient temp. Thin lines represent time periods when data were not collected.

between eyrie aspect, eyrie temperature and ambient
temperature.

I collected eyrie and ambient temperatures over a 23 h
period (2100 H MDT 10 June 1980 - 2000 H MDT 11
June 1980) from eyrie No. 2 (Williams 1981) in North
Park, Colorado (eyrie aspect = 95°, cliff aspect = 80°,
elevation = 2650 m). Temperatures were recorded using
a Yellow Springs Thermistor Unit with wire temperature
probes. Eyrie temp was monitored via a wire probe taped
to the rear wall of the eyrie. The probe was in the shade at
all times, placed 0.4 m above and behind the nestlings in
the center rear portion of the eyrie. I do not believe the
probe was close enough to the nestlings to have been
influenced by their metabolic heat. The nestlings were 16
d old at this time. Ambient temperatures were collected in
the shade at the cliff base. Temp was recorded at 15 min
intervals from a secluded spot 30 m from the eyrie where
my presence seemed to have no affect on the behavior of
the adult birds. Weather during the 23 h period was clear
with winds between 12-18 kph.

Minimum and maximum eyrie and ambient temp and
ranges during the study period are shown in Figure 1.
Eyrie temp was higher than ambient temp from 0100-
0930 H, whereas ambient temp was higher than eyrie
temp from 21 15-0100 H and 0930-2000 H. Paired t-Tests
were used to compare ambient temps higher and lower
than eyrie temps. Both tests were significant: higher (t =
7.07, df31,P<0.01)andlower(t= 10.9, df 17, P< 0.01).

Ambient temp fluctuated 21.2° C, whereas eyrie temp
fluctuated only 7.4° C during the 23 h sampling period
(Fig. 1), suggesting that a microclimate exists within
easterly-facing eyries which buffers nestlings from am-
bient temp extremes. This buffering is most readily seen
where early morning and late afternoon ambient temps

varied greatly from eyrie temp. Eyrie and ambient temps
were equal ( 1 3° C) at 1 000 H. Eyrie temp increased only 4°
C during the next 8 hours, whereas, ambient temp in-
creased 14° C. Platt (1974) noticed a 5-8° C difference
between ambient and eyrie temperatures, with the eyrie
invariably cooler during the hottest time period of the
day. Clayton M. White (pers. comm.) also noted clear
differences between ambient and cliffside temperatures
while entering Gyrfalcon ( Falco rusticolis) and Peregrine
Falcon (Falco peregrinus ) eyries in Alaska.

In the cold climates of both Alaska and high elevation
Colorado, environmental temperature fluctuations are
apparently ameliorated by the action of solar radiation
falling on the cliff surface. The cliff functions as a heat
sink during the day, slowly absorbing heat from solar
radiation and serves as a heat source at night, slowly losing
the absorbed heat to the cooler night air. This keeps the
cliff-face warmer than the minimum ambient temp at
night and cooler than the maximum ambient temp during
the day. Nesting falcons were able to utilize the moderated
environment to initiate reproductive activities (courtship
and egg-laying) while ambient conditions were still quite
harsh. In both Alaska (C.M. White pers. comm.) and Col-
orado (Williams 1981), this was necessary so that nestling
phenology was timed with peak abundances of prey
species.

The relatively moderate microclimate of eyries should
enhance nesting success. Adult falcons can devote less
time to brooding and shading of young during daylight
hours, thereby providing increased time for predator de-
tection, eyrie defense and hunting. Increased prey de-
liveries would greatly benefit the youngest nestlings, who
often do not survive the nestling period during times of
food shortage. All of these factors could increase the

Winter 1984

Short Communications

155

probability of nesting success and the number of young
fledged by reducing nestling mortality.

Further studies are needed to define the role of eyrie
aspect in nest site selection by Prairie Falcons. Data on
eyrie and ambient temperatures from the courtship to
fledging phases of nesting phenology should be collected
from north, south, west, and east facing eyries across a
spectrum of elevational and latitudinal locations. Such
information could be coupled with existing data on nest
site selection and productivity to identify general trends
(and local patterns) in nest site selection of Prairie Falcons
throughout their breeding range.

Acknowledgments

I would like to thank C.M. White and J.R. Parrish for
their input and encouragement during the preparation of
this manuscript. Financial assistance was provided by the
Frank M. Chapman Memorial Fund and the Colorado
Division of Wildlife through Federal Aid in Wildlife Re-
storation Project W-124-R.

Literature Cited

Denton, S.J. 1975. Status of prairie falcons breeding in
Oregon. M.S. thesis. University of Oregon, Eugene,
Oregon.

Enderson,J.H. 1964. A study of the prairie falcon in the
central Rocky Mountain region. Auk 81:332-352.

Leedy, R.R. 1972. The status of the prairie falcon in
western Montana: emphasis on possible effects of
chlorinated hydrocarbon pesticides. M.S. thesis. Uni-
versity of Montana, Missoula, Montana.

McGahan, J.E. 1968. Ecology of the golden eagle. Auk
85:1-12.

Ogden, V.T. and M.G. Hornocker. 1977. Nesting de-
nsity and success of prairie falcons in southwestern
Idaho./ Wildl. Mgt. 41:1-11.

Olendorff, R.R. 1973. Ecology of the nesting birds of
prey of northeastern Colorado. U.S. I.B.P. Grasslands
Biome Technical Report 211.

Platt, S.W. 1974. Breeding status and distribution of
the prairie falcon in northern New Mexico. M.S. thesis.
Oklahoma State University, Stillwater, Oklahoma.

Porter, R.D. and C.M. White. 1973. The peregrine
falcon in Utah, emphasizing ecology and competition
with the prairie falcon. Brigham Young University
Science Bulletin 28:1-74.

Williams, R.N. 1981. Breeding ecology of prairie fal-
cons at high elevations in central Colorado. M.S. thesis.
Brigham Young University, Provo, Utah.

Department of Zoology, Brigham Young University, Provo,

UT 84602.

Received 1 November 1984; Accepted 15 December 1984

Successful Breeding of a Pair of Sharp-shinned Hawks in Immature Plumage

David L. Fischer

Adult plumage in Accipiter is usually acquired during an
individual’s second summer (1 year after hatching). Since
this molt is not completed until the following fall, nesting
accipiters can be easily identified as immature (yearling)
or adult (2 or more years) on the basis of plumage. Al-
though Bent (1937) stated that each of the three North
American Accipiter species may breed as yearlings, pub-
lished accounts of such breeding, particularly of yearling
males, are uncommon. In the Northern Goshawk (A. gen-
tilis atricapillus) and the Cooper’s Hawk (A. cooperii ),
yearling females are known to occasionally pair with adult
males and breed (Meng 1951; McGowan 1975; Reynolds
and Wight 1978). I could find no published account of
such pairing in the Sharp-shinned Hawk (A. striatus).
However, K. Tuttle (pers. comm.) observed this at 1 of 26
nests found in Utah and Idaho during the 19-y period
1963-1981, and C.M. White (pers. comm.) saw this at
another Utah nest in 1963. Breeding by yearling males is
apparently a rare event. Two cases each of breeding by
yearling male Cooper’s Hawk (Kline 1975; Rosenfield and
Wilde 1982) and European Goshawk (A.g. gentilis) (Glutz

von Blotzheim 1971) have been reported. R. Rosenfield
(pers. comm.) has recently observed this at 2 additional
Cooper’s Hawk nests. To my knowledge, breeding by
yearling male Sharp-shinned Hawks has not been
documented. K. Tuttle (pers. comm.) observed this in
1973 at a Utah nest site at which an adult male had been
shot and killed the previous year. This note documents
the successful breeding of a pair of Sharp-shinned Hawks,
“both in immature plumage.

On 23 May 1983, while searching for nests as part of a
breeding ecology study of accipiters in central Utah, I
encountered an immature female Sharp-shinned Hawk in
what later proved to be the nest stand. The male was first
observed on 3 June and appeared virtually identical to the
female in plumage and eye color. It was easily separable by
its smaller size and higher pitched call.

The nest stand was at an elevation of @ 2000 m on a
gentle, north-facing slope in the Uinta National Forest, 8
km northeast of Provo, Utah County. A partially con-
structed nest was found during the initial observation of
the female. The nest was located 4 m above ground near

156

Short Communications

Vol. 18, No. 4

the trunk of a small white fir ( Abies concolor ) within a stand
dominated by bigtooth maple (Acer grandidentatum) and
Gambel oak ( Quercus gambelii). No old nests were found in
the stand. On 7 June the nest contained 3 eggs. All eggs
hatched, but 1 chick disappeared the first wk after hatch-
ing. The 2 remaining young fledged by 15 August and
were last seen in the nest stand on 23 August.

During incubation the female could be approached to
within 3 m and could have been hand-netted on numer-
ous occasions. With the exception of this extreme toler-
ance of the female to close approach, the behavior of the
pair was similar to neighboring pairs. The immature
female noted by White in 1963 could be touched while on
the nest incubating.

Newton et al. (1981) reported that in a relatively stable
population of the European Sparrowhawk (A. nisus ),
yearlings formed 17% of the breeding males and 16% of
the breeding females. In A. striatus and A. cooperii, year-
lings (especially males) appear to comprise a much smaller
proportion of the breeding population than in A. nisus,
though the reasons for this are not clear. Meng (1951),
Hennessy (1978) and Reynolds and Wight (1978) re-
ported that yearlings formed 6% (N=36), 20% (N = 15)
and 6% (N = 34), respectively, of breeding females of
Cooper’s Hawk populations in New York, Utah and Ore-
gon. Though males were not observed at every nest, all
seen by these authors were adult. On the basis of exami-
nation of testes of 10 immature male Goshawks, Hoglund
(1964) concluded that immature males are normally in-
capable of breeding. This may also be true of yearling
males in A. cooperii and A. striatus, but to my knowledge,
has not been studied. Reynolds (1972) discussed the gen-
eral lack of nesting by yearling male Goshawks, Coopers
Hawks and Sharp-shinned Hawks and hypothesized that
since males are the principal food providers during the
nesting season, foraging experience may be a prerequisite
for successful nesting. Reynolds and Wight (1978)
suggested that an immature male, lacking experience,
may be subject to greater risk of predation or accident
while foraging, and therefore, deferring the age of first
breeding may increase its future fitness. A concommitant
of deferred breeding is delayed sexual maturity. How-
ever, a similar argument should apply to the ecologically
similar A. nisus, yet considerable numbers of European
Sparrowhawks, and at least as many males as females,
breed successfully their first year (Newton et al. 1981).
Furthermore, the relatively larger proportion of yearling
breeders is found in both stable and recovering popula-
tions, though it may be accentuated in the latter (Newton,
pers. comm.). The breeding biology of the closely related
Sharp-shinned Hawk has not been intensely studied, and
breeding by yearlings, including males, may not be as rare
as might be concluded from existing observations.

I thank R.L. Yergensen and K. Ellis for assistance in the
field and Robert Redford and Brigham Young University
for financial support. K. Tuttle, R. Rosenfield and I.

Newton graciously provided unpublished data. J.R. Mur-
phy, C.M. White, R.T. Reynolds, R. Fitznerand D.H. Ellis
reviewed the manuscript.

Literature Cited

Bent, A.C. 1937. Life histories of North American birds
of prey, Part 1. U.S. Nat. Mus. Bull. 167.

Glutz von Blotzheim, N. 1971. Handbuch der Vogel
Mitteleuropas. Vol. 4. Falconiformes. Akademische
Verlagsgesellschaft, Frankfurt am Main.

Hennessy, S.P. 1978. Ecological relationships of Ac-
cipiters in Northern Utah — with special emphasis on
the effects of human disturbance. M.S. thesis. Utah
State University, Logan.

Hoglund, N. 1 964. Der habicht Accipiter gentilis Linne in
Fennoskandia. Viltrevy 2:195-270.

Kline, R. 1976. An eagle and a hawk./. Calif. Hawking
Club 1975:16-17.

McGowan, J.D. 1975. Distribution, density and pro-
ductivity of Goshawks in interior Alaska. Alaska Dept,
of Fish and Game. P-R Proj. Rep., W- 17-445.

Meng, H.K. 1951. The Cooper’s Hawk Accipiter cooperii
(Bonaparte). Ph.D. Thesis, Cornell University, Ithaca,
New York.

Newton, I., M. Marquiss and D. Moss. 1981. Age and
breeding in Sparrowhawks./. An. Ecol. 50:839-853.
Reynolds, R.T. 1972. Sexual dimorphism in accipiter
hawks: A new hypothesis. Condor 74:191-197.
, and H.M. Wight. 1978. Distribution, de-
nsity and productivity of accipiter hawks breeding in
Oregon. Wilson Bull. 90:182-196.

Rosenfield, R.N. and J. Wilde. 1982. Male Cooper’s
Hawk breeds injuvenile plumage. Wilson Bull. 94:2 1 3.

Department of Zoology, Brigham Young University, Provo,
UT 84602.

Received 28 September 1984; Accepted 1 October 1984

Aegyptius Monachus Carrying Food In Its Claws

Miguel A. Pons and Francisco Lillo

On 24 September 1983, while taking a census of the Black
Vulture (Aegyptius monachus) on the island of Mallorca (Balearic
Islands) for ICONA (Ministerio de Agricultura), we observed an
adult of this species flying with a relatively large, whitish object in
its claws. The bird approached our observatory (Alfabia, 1,067 m
above sea level) following the area’s mountain crests at a height of
approximately 30 - 50 m above the terrain. We could not deter-
mine where it came from — possibly from far away. After observ-
ing its flight — straight — for about 5 min, we saw it land on a rocky
promontory 500 m from our position. It began to peck at the
object in its claws. With the aid of binoculars (8 & 9x) we confirmed
the fact that the bird was eating. With almost complete certainty
the vulture had transported a part of a sheep (Ovis aries) which
constitutes its basic diet on the island (70% according to Mayol
(Soc. Hist. Nat. Bal., 22:150-178, 1976.))

Winter 1984

Thesis Abstracts

157

Our observation is of ethological interest, since no author cites
this bird’s ability to carry food in its claws (Bernis Ardeola,
12:45-99, 1966), Valverde ( Ardeola , 12:101-115, 1966), Cramp
and Simpson (Handbook of the Birds of Europe, the Middle East
and North Africa, Vol II, Hawks to Bustards, R.S.P.B., Oxford
University Press, 1980)). We must nevertheless mention the ob-
servation of Hiraldo ( Donana acta vertebrata 3(1): 19-31, 1976) re-
ferring to a Black Vulture presumably capturing a lizard ( Lacerta
sp.). These observations confirm the fact that the Black Vulture,

the only species of Palearctic vulture known to us to have this
behavior, maintains the grasping capacity of its claws to a greater
extent than other species of the group.

Unidad de Vida Silvestre, ICONA, Pasaje Guillermo de Torrela
no. 1, Palma de Mallorca, Baleares.

Received 20 August, 1984; Accepted 1 September 1984

Thesis Abstracts

Ecology of Breeding Burrowing Owls in the
Columbia Basin, Oregon

The ecology of breeding BurrowingOwl ( Athene cunicularia) was
studied in northcentral Oregon during the spring and summer of
1980 and 1981. Pairs began arriving on the study areas as early as
the first week of March; however, most arrivals were during April.
Egg-laying began the first week of April and continued into the
first week of May. Whole family groups left the nesting areas as
early as the first week in July while members of other families
remained until at least the end of September.

Nest success was 57% for 63 nests in 1980 and 50% for 76 nests
in 1981. Desertion was the major reason for nest failure and may
have been related to the proximity of other nesting pairs. Badgers
{Taxidea taxus) were the major nest predtors. Nests which were
lined with cow or horse dung were significantly less prone to
predation than nests not lined, suggesting dung masks odors of
nest occupants.

Diets were determined by pellet analysis. Arthropods com-
prised 91.6% of the total prey by number; however, they contri-
buted only 22.0% of the total biomass. Vertebrates, mostly small
mammals, comprised the balance. Perognathus parvus (Great Basin
Pocket Mouse) was the most important vertebrate prey and
Stenopelmatus fuscits (Jerusalem Cricket; Gryllacridadae) was the
most important arthropod. Coleoptera were preyed upon very
heavily, but they were dominated by very small ( < 1 0 mg) beetles
and, therefore, contributed little to the total biomass. Burrowing
Owls preyed on mammals during the spring then shifted to insects
during the summer. Burrowing Owl diets were influenced by soil
type, and owls selected mammals in proportion to their occurr-
ence in the environment.

Burrowing Owls selected 3 of 5 habitats for nesting. Hole avail-
ability and possibly food availability as important prerequisites
function analysis indicated variables responding to horizontal
visibility and possibly food availability as important prerequisites
for nest selection. Soil texture greatly influenced re-use and
longevity of nest burrows. — Green, Gregory A. 1983. M.S.
thesis, Oregon State Univ., Corvallis.

Reproductive Ecology and Habitat Utilization
of Richardson’s Merlins in Southeastern Montana

Reproductive ecology, food habits, habitat utilization, and
eggshell quality of Richardson’s Merlin ( Falco columbarius
richardsonii) in southeastern Montana were examined. Breeding
activity spanned five months. Clutch size, brood size, and fledging
success at active nests were similar (P > 0.05%) among four years.
Birds comprised >90% of individual prey items, and 6 1 % of avian
prey species were typically associated with predominantly open
habitats. Horned Lark ( Eremophila alpestris), Lark Bunting
(Calamospiza melanocorys), and Vesper Sparrow ( Pooecetes
gramineus) collectively comprised 57% of all prey. Home ranges of
three breeding male Merlins encompassed approximately 13, 23,
and 28 km2, and each male traveled a maximum of 8 to 9 km from
his nest. These home ranges encompassed five physiognomic
habitat types. Percentages of total observations by habitat type
indicated greatest us of sagebrush and grassland habitats. Sage-
brush, riparian, and pondrosa pine habitats were used more (P <
0.05) than expected, but grassland and agriculture habitats re-
ceived less (P < 0.05) use than expected. Comparisons of Montana
eggshells with pre-pesticide (pre-1946) eggshells indicated 12%
and 20% reductions in eggshell weight and eggshell thickness
indices, respectively. These reductions were significant (P <).
Seven organochlorine compounds were detected in eggs collected
on the study area. The overall management goal should be
maintenance of a viable Merlin population and the habitat fea-
tures essential for its continued existence. Management recom-
mendations include limitation of alteration of ponderosa pine
sideslope habitat, restriction of activities from 10 March through
20 July, rescheduling of activities, establishment of 400 m zones of
no disturbance surrounding nests, limiting loss of prairie habitat
and sagebrush removal, limiting use of organochlorine com-
pounds, reviewing potential impacts of activities prior to their
occurrence, and maintaining confidentiality of nest locations. —
Becker, Dale M. 1984. M.S. Thesis, University of Montana, Mis-
soula.

158

News and Reviews

Vol. 18, No. 4

THE RAPTOR RESEARCH FOUNDATION, INC., YEAR-END REPORT

This was another year of firsts! We broke the 700 member number for starters and, for the first time distributed a
comprehensive Membership Directory (named “The Kettle”, of course). Dick Clark and his crew did an especially good
job on that directory and we thank them for their efforts above and beyond the call of duty. As usual, the annual meeting
(in Blacksburg, Virginia, this year) was the highlight of the year’s activities. Roughly 300 raptor enthusiasts attended a
very well-organized and smoothly-run conference held at the Donaldson Brown Center for Continuing Education at
the Virginia Polytechnic Institute and State University. Papers ranged from topics on Condors to Screech Owls and the
workshops provided valuable hands-on technique experience, e.g. transmitter attachment to eagles, etc.

The banquet was well-attended and lots of fun, with full credit going to Jim Fraser and his fellow organizers. A special
thanks goes to Jim’s wife for the music and dancing of an Appalachian fiddle-plucking and boot-stomping ensemble.
The Andersen Award for Best Student Paper, again, went to the east Canadians working out of McGill University. Reed
Bowman won the honor this year for his presentation of his M. Sc. results entitled “Behavior of Widow and Replacement
Mates in Wild American Kestrels.” Congratulations also go to the runners-up, Andre Lavigne (“Growth of Nestling
Kestrels in Relation to Dietary Facts”) and Nicole Vanderheyden (“Investigations into the Hematology of Captive
American Kestrels”). And no, their major Professor, David Bird, wasn’t on the selection committee!

Next year’s RRF conference to be held in Sacramento, California promises to be one of the biggest ever. But don’t let
the length of the conference scare you. The program has been arranged in such a way as to allow participants to pick and
choose the various symposia and meetings of particular interest. Frankly, sunny California at that time of year, i.e.
November 2 - 1 0, 1 985, is enough to entice most folks for the duration. It promises to be a momentous occasion in raptor
conservation history. For more information, write to: Dr. Richard R. Olendorff, U.S. Bureau of Land Management,
2800 Cottage Way, Sacramento, California 95825.

The Conference Guidelines Committee composed of Toni and Dave Bird, myself, Ed and Judy Henckel, Butch
Olendorff, Nancy Venizelous and Jim Fraser has been very active in promoting excellence in RRF meeting organiza-
tional efforts. A manual and questionnaire on this subject are now in rough draft format and we are very interested in
your comments. Please send them to Dr. Bird (at Macdonald Raptor Research Centre, Macdonald Campus of McGill
Univeristy, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Quebec H9X 1 CO). I am pleased to announce that the 1 986
RRF meeting will be in Gainesville, Florida, under the direction of Dr. Michael Collopy. We are now looking for bids for
the 1987 conference from places located in either the mid-west or far west. Applicants will need: a central meeting
place capable of housing roughly 500 participants; easy access to major transportation centers, and; a good pool of
hard-working volunteers. Send your bid to Dr. Bird at the above address.

One of the topics of intense discussions, especially among Board members was the journal, both as to format and
timing. Specific changes have been implemented, including the formation of a working committee of associate editors,
which will help with the manuscript review process. I am confident that by early 1985, Raptor Research will be going out
on time. Furthermore, I personally like the new professional format, thanks to the efforts of our volunteer editor, Dr.
Clayton White and his part-time Assistant Editor, Jimmie Parrish.

I am more than pleased to tell you that RRF memberships have reached 770, our highest ever, with more and more
international members joining us each year. It is not just the journal publication you support with your annual dues, but
also a strong voice in raptor conservation, encouragement of young scientists to pursue excellence in raptor research
and management, and the establishment of research grants and awards for dedication to raptor conservation. Most
important, your involvement supports a solid network of diverse individuals and organizations with identical objectives
in mind and heart. Let’s shoot for a thousand members for the end of 1985. Join (or rejoin) our swelling ranks!

As an update on Directors and Officers, the Board decided to keep me around for another year, as your President.
Sadly, we could not cajole our hard-working, devoted Secretary for the past two years, Ed Henckel, to renew his post,
but happily for RRF, Jim Fraser has consented to take on this tedious task. The results of your ballots are in: Jim
Mosher and Martin Bottcher remain in their positions of Eastern and International Directors, respectively, and Rich
Howard won his bid for the At-Large #3 Director’s slot. Congratulations to all and a hearty thanks to our outgoing
At-Large Director, Mark Fuller, for a job well-done and his encouragement for “new blood” in the organization.

Warmest wishes for success in the new year. See you in Sacramento next fall!

Jeff Lincer
President

Winter 1984

News and Reviews

159

Membership Recognition

The Raptor Research Foundation, Inc., expresses sincere appreciation to the following individuals for
their continued support of the Foundation and its objectives.

HONORARY MEMBERS — Founders of The Raptor Research Foundation, Inc.

Byron Harrell

George Jonkel

Don Hunter

Paul Springier

LIFE MEMBERS

Dean Amadon

Friedrick O.P. Hechtel

SUSTAINING MEMBERS FOR 1984

Daniel!. Brimm

Robert M. Weintraub

James E. Doyle

CONTRIBUTING MEMBERS FOR 1984

Jae Abel

Paul Kerlinger

Leslie P. Arelt

Michael A. Lavelle

R.T. Bell

Library, Smithsonian Tropical Research Institute

Karen S. Bollinger

Lee Merrick

Gary Bounholdt

Bill Meyer

Jim Brett

Carl D. Mitchell

Michael P. Coffeen

E. Stuart Mitchell

William G. Coleman

Virginia Moede

Eric B. Cummins

James A. Mosher

Stuart Elliott

Joseph R. Murphy

Joseph Eoff

Michael J. Murray

Albert Ferwerda

New Jersey Raptor Association

Roy A. Geiger, Jr.

National Zoological Park Library

Nancy F. Green

Bruce N. Pikaard

Carrie A. Griffith

Richard N. Roberts

Claire H. Hager

Carol F. Smith

David Harlow

C. Pierre Thoumsin

Victoria S. Johnsen

Richard F. Waechter

Jacquelyn L. Katzmire

Donald Yarnell

THE RAPTOR RESEARCH FOUNDATION CONFERENCE — NOVEMBER 1985. The 1985 Raptor Research
Foundation International Meeting and Symposium on the Management of Birds of Prey will be held at the capital Plaza
Holiday Inn in Sacramento, California, November 2 - 10, 1985. Highlights of this 20th anniversary meeting of the
Foundation will include 1) the Second RRF Conference on Raptor Conservation Techniques — Twelve Years of
Progress, 1973-1985, 2) a Western Hemisphere Meeting of the World Working Group on Birds of Prey (ICBP), 3) the
Second International Vulture Symposium, 4) a Western North America Osprey Symposium, 5) a Workshop on North
American Candidate Endangered Raptors, 6) an International Symposium on Raptor Reintroduction, and 7) a
Symposium on Raptor Rehabilitation, Captive Breeding and Public Education. For more information contact Dr.
Richard R. Olendorff, U.S. Bureau of Land Management, 2800 Cottage Way, Sacramento, California 95825, or Nancy
Venizelous, San Francisco Zoological Society, Stoat Boulevard at the Pacific Ocean, San Francisco, California 94132.

160

News and Reviews

Vol. 18, No. 4

Reviewers for Raptor Research, 1984

The subject matter of manuscripts received for publication in Raptor Research is very diverse. Numerous individuals
throughout the year have generously given of their time and expertise by acting as reviewers for manuscripts submitted
for publication. The Editorial Staff expresses its sincere appreciation to the individuals listed below, who, through their
efforts as reviewers, have helped to raise the standards and quality of the journal. Those individuals who have
contributed reviews of two or more manuscrips are indicated by an asterisk.

David M. Bird*, Douglas A. Boyce, Tom J. Cade*, Richard Clark*, William S. Clark, Michael W. Collopy, Gary E.
Duke*, James H. Enderson*, Philip K. Ensley*, David L. Fischer, Glen A. Fox, Mark R. Fuller*, James A. Gessaman,
Frances Hamerstrom, Frederick Hamerstrom*, A1 Harmata*, Steve Herman, Jerome A. Jackson, James R. Karr*,
Lloyd Kiff, Michael N. Kochert*, Carl Marti*, David P. Mindell, James A. Mosher*, Helmut C. Mueller*, Joseph R.
Murphy, Richard R. Olendorff*, Lynn W. Oliphant*, David B. Peakall, David T. Rogers, Jr., Steve K. Sherrod*, Joseph
K. Scheiring, Gordon R. Ultsch, F. Prescott Ward, Robert C. Whitmore*, Stanley N. Weimeyer, E. William Wischusen*,
Neil Woofinden.

ANDERSEN AWARD — The third annual William C. Andersen Memorial Award for the best student paper was
presented at the Raptor Research Foundation Annual Meeting in Blacksburg, Virginia, on 27 October 1984. The
winner was Mr. Reed Bowman of the Macdonald Raptor Research Centre of McGill University for his paper “Behavior
of Widow and Replacement Mates in Wild American Kestrels.”

Students wishing to be considered for the 1985 Andersen Award must indicate their eligibility when submitting
abstracts. Eligibility criteria were published in Raptor Research 16(l):30-32. Questions regarding the 1985 award should
be directed to: Dr. Robert Kennedy, Director, Raptor Information Center, National Wildlife Federation, 9412 16th
Street, NW, Washington, D.C. 20036.

The Macdonald Raptor Research Centre of McGill University is offering 4 to 6 non-salaried summer student
internships with free residence (not board). Internships provide exerience in public education, care and rehabilitation
of captive raptors as well as an opportunity to pursue personal research. Interested candidates should submit two
letters of recommendation, a resume of experience and interests, and an unofficial transcript of college academic
records by April 1 , 1985 to: Dr. David M. Bird, Director, Macdonald Raptor Research Centre, 21,111 Lakeshore Road,
Ste-Anne de Bellevue, Quebec H9X ICO, Tel: 1-514-457-2000, ext. 345.

Biology of the Peregrine and Gyrfalcon in Greenland. By William A. Burnham and William G. Mattox.
Meddelelser om Gronland, Bioscience 14, 1984: 25 pp., 12 figs., 12 tables. Dkr. 46.75 excl. of VAT and postage. — This paper presents
the results of 1 0 years of study ( 1 972- 1 98 1 ) in .western Greenland that took place primarily in the region of Sondre Strom fjord. The study
is still ongoing. Much of the data were hard won, especially in the early years. Frequently the researchers had to make week long treks
with 25-35 kilos of gear in back packs just to gather data on 2-3 eyries. I still have vivid memories of trudging over the landscape with the
survey crew in 1975; backpack so heavy and feet so sore I could hardly walk after a one week trek. Over 40 researchers were involved in
data gathering and 9 organizations provided some support. Within this report the bulk of the data deals with the Peregrine Falcon (Falco
peregrinus). Of the 17 pages containing biological data 9 were devoted to peregrine biology, 3 to Gyrfalcon ( Falco rusticolus ) and the
remaining 5 to such topics as migration, banding recoveries, chemical pollutants, and interspecific competition. The biologies presented
are not unlike that of both species elsewhere in their circumpolar ranges with but a couple of exceptions. The 2 species were not found to
occupy the same cliff simultaneously (although they did in 1984). Part of their discussion attempts to explain why this would have
developed in the historical sense. They speculate that food densities as well as the distribution of nests of the Common Raven ( Corvus
corax), which Gyrfalcons usurp for nesting, have been important factors in the dispersion of the 2 species.

A second departure from general peregrine biology was the findings on food habits. While peregrines are noted for their catholic diets
this was not the case in Greenland. Four species made up about 90% of the diet in 1973. This probably results from the fact that therejust
are not large populations of many species to prey on at inland localities. In some ways it is disappointing that so much data were lost by not
checking food remains in eyries more thoroughly. For all years of the study productivity was recorded at each eyrie and in most cases
young were banded. 1973 was the only year reported with food data. Why weren’t food remains systematically collected while in the
eyrie? Had such data been collected a better idea of regional food differences, yearly prey fluctuation and biomass consumption at each
eyrie may have emerged. Overall, considering the physical and logistic restraints encountered by field parties, this study is a credit to the
authors and an important addition to raptor biology. — Clayton M. White.

RAPTOR RESEARCH

A Quarterly Publication of The Raptor Research Foundation, Inc.

EDITOR: Clayton M. White, Department of Zoology, 161 Widtsoe Building, Brigham Young University, Provo,
Utah 84602

ASSISTANT EDITOR: Jimmie R. Parrish, Department of Zoology, 159 Widtsoe Building, Brigham Young Univer-
sity, Provo, Utah 84602
ASSOCIATE EDITORS

Jeffrey L. Lincer - Environmental Chemistry and Toxicology
Richard Clark - Order Strigiformes
Ed Henckel - Family Cathartidae
Gary E. Duke - Anatomy and Physiology

Patrick T. Redig - Pathology, Rehabilitation and Reintroduction
Jim Mosher - General Ecology and Habitat Analysis m

INTERNATIONAL CORRESPONDENT: Richard Clark, York College of Pennsylvania, Country Club Road,
York, Pennsylvania 17405

Raptor Research (ISSN 0099-9059) welcomes original manuscripts dealing with all aspects of general ecology, natural
history, management and conservation of diurnal and nocturnal predatory birds. Send all manuscripts for considera-
tion and books for review to the Editor. Contributions are welcomed from throughout the world, but must be written in
English.

INSTRUCTIONS FOR CONTRIBUTORS: Submit a typewritten original and two copies of text, tables, figures and
other pertinent material to the Editor. Two original copies of photographic illustrations are required. Raptor Research is
published in a double-column format and authors should design tables and figures accordingly. All submissions must
be typewritten double-spaced on one side of 814 x 1 1-inch (2 1 14 x 28cm) good quality, bond paper. Number pages
through the Literature Cited section. The cover page shoulcfcontain the full title and a shortened version of the title (not
to exceed 30 characters in length) to be used as a running head. Author addresses are listed at the end of the Literature
Cited section. Authors should indicate if present addresses are different from addresses at the time the research was
conducted. When more than one author is listed, please indicate who should be contacted for necessary corrections and
proof review. Provide an abstract for each manuscript more than 4 double-spaced typewritten pages in length. Abstracts
are submitted as a separate section from the main body of the manuscript and should not exceed 5% of the length of the
manuscript. Acknowledgements, when appropriate, should immediately follow the text and precede the Literature
Cited. Both scientific and common names of all organisms are always given where first appearing in the text and should
conform to the current checklists, or equivalent references, such as the A.O.U. Checklist of North American Birds (6th
ed., 1983). Authors should ensure that all text citations are listed and checked for accuracy. If five or fewer citations
appear in the text, place the complete citation in the text, following these examples: (Brown and Amadon, Eagles,
Hawks and Falcons of the World. McGraw-Hill, New York. 1968), or Nelson {Raptor Res. 16(4):99, 1982)). If more than
five citations are referenced, each should include author and year (e.g., Galushin 1981)), or in a citation with three or
more authors, the first author and year (e.g., (Bruce et al. 1982)). Citations of two or more works on the same topic
should appear in the text in chronological order (e.g., (Jones 1977, Johnson 1979 and Wilson 1980)). Unpublished
material cited in the text as “pers. comm.,” etc., should give the full name of the authority, but must not be listed in the
Literature Cited section. If in doubt as to the correct form for a particular citation, it should be spelled out for the Editor
to abbreviate.

Metric units should be used in all measurements. Abbreviations should conform with the Council of Biology Editors
(CBE) Style Manual, 4th ed. Use the 24-hour clock (e.g., 0830 and 2030) and “continental” dating (e.g., 1 January 1984).

Tables should not duplicate material in either the text or illustrations. Tables are. typewritten, double-spaced
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Raptor Research

A Quarterly Publication of The

Volume 19, Number 1, Spring 1985

(ISSN 0099-9059)

Highwall-to-Pole Golden Eagle Nest Site Relocations.

Robert A. Fala, Arthur Anderson and John P. Ward 1

Biology of Eleonora’s Falcon ( Falco eleonorae ): 7. Variability of Clutch Size,

Egg Dimensions and Egg Coloring. Michael Wink, Dietrich Ristow and Coralie Wink V. 8

Nesting Behavior of Peregrine Falcons in West Greenland During the
NESTLING Period. Julie Hovis, Thom D. Snowman, Virginia L. Cox,

Raymond Fay and Keith L. Bildstein 15

The Hunting Ranges of Two Female Peregrines Towards the End of a

Breeding Season. Richard Mearns 20

How Effective Are Hunting Peregrines? Rune Roalkvam 27

Dissertation Abstracts 30

News and Reviews 14, 29,32

Instructions for Contributors to Raptor Research 35

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RAPTOR RESEARCH

A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC.

VOL. 19

Spring 1985

No. 1

HIGHWALL-TO-POLE GOLDEN EAGLE NEST SITE RELOCATIONS

Robert A. Fala, Arthur Anderson andJohnP. Ward

Abstract - Golden Eagles (Aquila chrysaetos) constructed nests and produced young at 2 cliff-like mine highwalls at a
southcentral Wyoming surface coal operation. The nests were in areas formerly unoccupied by nesting eagles, a result of
the mining process creating suitable nesting habitat. Nest site availability is believed to be a local limiting factor on Golden
Eagle productivity. Existing state and/or federal reclamation laws require the elimination of highwalls. Other laws,
however, forbid the removal of Golden Eagle nests. To resolve this conflict and improve management of eagles, the
nestling relocation technique was implemented to move nest sites to man-made nesting platforms mounted on poles.
Behavioral responses of the adult eagles to the relocations indicated a high degree of parental attachment to young as well
as nesting adaptability. Management implications of the technique are promising, particularly as they relate to mitigation
for highwall nesting eagles and possibly other raptor species. However, further research is needed for this practice to be
of predictive value for eagle behavior and response after relocation.

Golden Eagle (Aquila chyrsaetos) nests are often
threatened by surface coal mining operations in the
western United States. Because Golden Eagles and
their nests are also protected by the Bald Eagle Act,
mining and reclamation are sometimes impeded.

Errington (1932) first indicated that certain rap-
tor nestlings, tethered away from the nest, would be
cared for and fed by adult birds. This technique was
adapted by Postovit et al. (1982) to affect a success-
ful tree-to-pole Golden Eagle nest site relocation in
northeastern Wyoming by moving nestlings pro-
gressively further away from their original nest. Sub-
sequent successful tree-to-pole Golden Eagle nest
relocations were performed and reported for the
same region (Phillips and Beske 1982, 1983). These
authors stress the importance of locating artificial
nesting structures within the home ranges of mated
pairs while also taking into account the territories of
adjacent nesting pairs. The demonstrated use of
alternate nest sites (Lockie and Ratcliffe 1964;
McGahan 1968; Boeker and Ray 1971; Call 1978)
also indicates some flexibility by Golden Eagles in
their adaptability to new nest locations. Postovit et
al. (1982) and Phillips and Beske (1982, 1983) also
report the use of artificial nesting structures by
Golden Eagles in years subsequent to their initial
relocation, indicating the potential long-term value
of this technique.

The directed nest relocations performed in
northeastern Wyoming were: from tree to pole,
tree to tree, and pole to pole. Success in simulating
tree nest sites suggests that the simulation of other
types of nest sites may be successful, especially for
highwall nesting eagles. A conflict with highwall
nesting eagles arose in the Hanna Basin surface coal
mining region of southcentral Wyoming. A high-
wall is the exposed face of rock or overburden,
often nearly vertical, in an open cut of a surface
mine; this substrate simulates cliff nesting raptor
habitat (Figs. 1 and 2). Golden Eagles constructed
nests and successfully fledged young on the high-
walls of 2 mined-out pits: Bed 24 and Bed 51 East.
Bed 24 highwall nest was first observed in 1979 and
has fledged at least 1 eaglet during each of the past
4 yr (1979-1982). Bed 51 East nest was observed
first in 1981 and has produced at least 1 eaglet in
each of the past 2 yr (1981 and 1982).

Both nests were constructed beneath overhangs
on highwalls with angles approximately 55 from
the horizontal. Bed 24 nest faced SW and was 12 m
below the top of the highwall, 60 m in height; Bed
51 East nest faced SSW and was 10 m below the top
of a highwall, 40 m in height.

Unlike the situation in northeastern Wyoming
where nests were impeding coal development, the 2
highwall nests in southcentral Wyoming were im-

Raptor Research 19(1): 1-7

2

Fala et al.

Vol. 19, No. 1

Figure 1. Golden Eagle and nest (arrow) at Bed 51 East mine highwall. Note the cliff-like nesting habitat.

Figure 2. Close-up of Bed 51 East mine pit highwall nest with a nestling visible just below the adult eagle.

lilSte

Spring 1985

Golden Eagle Nest Relocations

3

Figure 3. Bed 5 1 East pole nesting structure with 1 large nestling visible on the platform. Adult perch sites are indicated
by arrows.

peding reclamation. State and/or federal laws re-
quire timely reclamation and the elimination of all
mine highwalls for safety reasons. Regulations also
forbid the disturbance of eagle nests. Therefore,
reclamation in southcentral Wyoming could not
occur within the legal time limit. To resolve the
dilemma, state and federal agencies cooperatively
developed a mitigation strategy using the research
provisions of applicable laws. Citing tree-to-pole
nest relocations as a precedent, relocation of the 2
highwall nests was made during the 1982 nesting
season.

The intent of the highwall-to-pole strategy was to
allow the pits and highwalls to be reclaimed while
providing alternate nesting sites for the eagles. This
paper describes the 2 highwall-to-pole relocations
and some associated behavioral responses of the
adult eagles.

Study Area and Methods

This study was conducted in the Hanna Basin coal region,
southcentral Wyoming. Vegetation is typical of semi-arid plains
with sagebrush ( Artemisia spp.) and grassland communities
dominating, except for drainages that are ephemeral where
greasewood ( Sarcobatus spp.) prevails. Lack of trees of appreciable
height precludes tree nesting by eagles. The topography is
primarily gentle with dissection drainage patterns and numerous

minor rock outcrops. Nesting habitat is limited to a few rimrocks
or cliff-like outcrops. These rimrocks contain the only other oc-
cupied or alternate Golden Eagle nests within the study area.

Beginning in September 1981, eagle pairs were monitored once
a month to determine the approximate location of their home
ranges. Home ranges were determined by direct observations of
the eagles. Prospective locations of artificial nest structures were
within the home ranges. Artificial nesting structures were con-
structed according to McEneaney and Phillips (1981) and erected
with platform bases 7 m above ground level (Fig. 3). Platforms
were installed in December 1981, to lure eagles into using the
artificial structure over their actual nest site and to familiarize
them with the structure. Leafless or dead sagebrush twigs and
straw were then wired atop each artificial platform to construct a
nest bowl.

Bed 24 artificial nesting structure was erected on a reclaimed
area 575 m from the highwall nest (Fig. 4), and Bed 51 East
artificial structure was placed in a sagebrush site 470 m from the
highwall nest site (Fig. 5). The latter was later moved to within 1 00
m of the highwall nest. Both structures were in direct line of sight
of their respective highwall nests.

The highwall nests were monitored bi-weekly beginning 1
March 1982, to document incubation, hatching, and number of
nestlings. Monitoring was from 800 m with a 1 5 - 60X spotting
scope to minimize disturbance during the sensitive incubation
period (Fyfeand Olendorff 1976). Exact dates of nest events, such
as hatching, were not determined since this was not critical. The
main prerequisites for relocation was to do so when nestlings were
present.

Golden Eagle nestlings developed the ability to fast when ap-
proximately 20 d old (Ellis 1979). To provide a margin of safety,

4

Fala et al.

Vol. 19, No. 1

SURFACE HIRED AREA

a • unreclaimed
b • reclaimed

Figure 4. Location of Bed 24 highwall nest and artificial
nesting platform.

attempts to move eaglets were made only after they were 4 to 5 wk
old. On 8 June 1982 we removed 4 nestlings from the highwalls, 2
from each nest. They were fed about 0.3 kg of White-tailed Jack-
rabbit (Lepus townsendii) and placed on the platforms of the artifi-
cial structures. A jackrabbit carcass was provided on the platform
as potential food for the adults to feed the young. Relocating and
feeding of the young birds were accomplished within 2 h for each
nest. Dawn to dusk monitoring of adults and nestlings resumed
from 800 m distance as soon as relocations were completed.
Nestlings were hand fed again on the platforms every 24 to 26 h
until the adults began feeding them. Once the eaglets were ac-
cepted at the artificial structures, monitoring was reduced to 15
min observation periods every 1 - 2 d. Both highwalls were re-
leased for reclamation in August 1982 and eliminated before the
1983 breeding season.

Results and Discussion

Bed 24 Nest. — Bed 24 artificial structure was
utilized by perching eagles between erection in De-
cember 1981 and nestling relocation in June 1982,
as indicated by actual observations of eagles and
whitewash. Once the nestlings were placed on the
artificial structure, the adult eagles were usually
observed perched atop nearby spoil piles or along
the Bed 24 highway, except for occasional hunting
or soaring away from the site.

During the 50 h between relocation and accept-

ance of the nestlings, one adult flew in an anxious
manner and alighted frequently at the highwall
nest and at other perches along the highwall. The
sex of this bird could not be determined at the time.

In the interim between adult acceptance of the
Bed 24 nestlings and fledging of the eaglets (28 d),
24 observations (6 h total) were made on 21 differ-
ent days. The adult female was very attentive to the
artificial structure, as exhibited by her perching on
the structure during 5 of the 24 observations (or
1.25 h). Attentiveness decreased as fledging ap-
proached. On 3 of the 5 occasions the female was
observed on the platform feeding the young, but
only during the first 5 d after acceptance of the
nestlings at the artificial structure and not later than
a nestling age of about 44 d. This is consistent with
known natural eagle behavior (Ellis 1979). As was
also noted by Postovit et al. (1982), no adult from
the mated pair was ever observed at the former nest
site once the new artificial site was accepted by both
adults.

In addition to the recommendations of Postovit
et al. (1982) concerning enhancing the success of
Golden Eagle nest site relocations, we believe that
other interrelated factors contributed to the Bed 24
relocation success: the relative serenity and lack of
human related activities within 3 km of the reloca-

■ — ■ GOLDEN EAGLE TERRITORY

SURFACE MINED AREA

a = unreclaimed
b = reclaimed

Figure 5. Location of Bed 5 1 East highwall nest and arti-
ficial nesting platforms.

Spring 1985

Golden Eagle Nest Relocations

5

tion site; familiarization with and use of the artifi-
cial structure during the period between erection
and nestling relocation; and the amount of time the
adult bird(s) spent in line of sight of the relocated
nestlings at the relocation site; i.e., response time.

A few twigs were added to the platform nest by
the adults in February 1983. Ultimately, this pair
constructed a new nest 0.8 km to the NW at an
adjacent mine property highwall. At the new high-
wall nest site the adults hatched 1 eaglet in 1983.
This nest was relocated a distance of 1340 m SE to
the existing platform on 31 May 1983. The adult
male came to the platform 13 min prior to the
female, about 26 h after relocation of the eaglets. It
was felt that if intentional disturbance had occurred
early on (under USFWS permission) at the highwall
before incubation commenced, the adults may have
been forced to use the artificial structure. Inten-
tional disturbance was not used in this instance,
because the nest was discovered late in the nesting
cycle and disturbance may have resulted in nest
failure.

Bed 51 East Nest. — The pair of adult eagles at
Bed 5 1 East did not perch on the artificial structure
in the interim between erection and nestling relo-
cation. However, both adults were often seen flying
in the general area. This relocation site was subject
to reclamation disturbances involving use of heavy
equipment within 0.8 km of the structure during
the nestling relocation.

Once the Bed 51 nestlings were placed on the
artificial structure, the adults spent considerable
time away from the relocation site. Direct line of
sight between adult perches and the relocated
nestlings was broken at places by topographical re-
lief and the close proximity (100 m) of spoil, thus
response time of the adults was reduced.

After 54 h with little or no response by the adult
eagles to the artificial structure, the nestlings were
returned to their original highwall nest. No prey
items had been placed at the artificial platform by
the adult eagles, though a Desert Cottontail ( Syl -
vilagus auduboni ) and a Wyoming Ground Squirrel
(Spermophilus elegans) had been delivered to the
highwall nest during the eaglets’ absence. Within 5
h after returning the nestlings to the Bed 5 1 high-
wall nest, the adult female alighted at this site.

One objective in this study was to habituate the
mated pair to the artificial structure prior to recla-
mation of the Bed 51 East pit and highwall. The
intention was to familiarize the pair with the plat-

form in hopes of encouraging them to nest there in
succeeding years. With this in mind, we felt that the
best course of action after returning the nestlings to
their highwall nest was to wait a few days, then move
the artificial structure closer to the highwall nest
(from 470 m to 100 m) and make a second reloca-
tion attempt. The adult female responded to the
new location and frequented the nearest perch atop
a spoil pile (100 m distant) in direct line of sight of
the platform for several hours at a time. This en-
hanced association with the platform resulted in
acceptance of the platform by an adult 31 h after
the second relocation of the nestlings.

In the interim between adult acceptance of the
Bed 51 nestlings at the artificial structure and the
last fledging date of the young (35 d), 31 observa-
tions (or 7.45 h) were conducted on 23 different
days. An adult eagle was not sighted during 15 of
these observations. However, 7 of these times an
adult was observed perched atop the nearby spoil
pile (100 m). Two sightings (30 min total) of adults
on the artificial structure were made. One adult was
observed atop the structure, and the other was of an
adult on the platform with the young. These 2
observations were noted during the first 2 d after
adult acceptance of the structure but not later than
a nestling age of about 41 d.

In contrast to Postovit et al. ( 1 982) and the Bed 24
case, we documented use of the former highwall
nest site on 2 occasions. This occurred on the first 2
evenings after acceptance, when the adult female
returned without prey and alighted at the highwall
nest to roost. It was never postively determined that
the adult male alighted on the artificial structure.

Because the adult female returned to the high-
wall nest, and seemed to lack attentiveness to the
artificial structure after the apparent acceptance of
the nestlings, there was concern over the seemingly
tentative nature of the acceptance. Because we were
not certain that the young were being fed, we
climbed the platform structure and inspected the
nest 20 h after acceptance. A Desert Cottontail had
been delivered to the platform and picked clean by
an adult. Despite the somewhat secretive and cau-
tious acceptance of the artificial structure, there
were no apparent ill effects to the eaglets, which
developed normally and fledged.

Both adults added material to the artificial nest
during the next nesting season (March 1983), and
incubation began at this site on 26 March 1983. One
eaglet was hatched at the platform nest site in May.

6

Fala et al.

Vol. 19, No. 1

The original highwall was not available at this time,
but there was an adjacent highwall 100 m to the
west. Since the desired relocation site was not at-
tained in 1982, a platform-to-platform relocation
was preformed at a distance of 914 m on 31 May
1983. This relocation elicited an adult male re-
sponse after 79.5 h, however the female did not
accept the new platform. After 122.5 h the project
was aborted due to concern for the nestling. The
nestling was adopted out and fledged at a surrogate
nest.

Both Nests. — As signified by the survival and
ultimate fledging of the young at the respective
artificial nest structures in 1982, the nestling relo-
cation efforts at Bed 24 and Bed 51 East met with
comparable results. However, the degree of diffi-
culty in the relocation efforts and adult behavior
after acceptance were distinctly different. We con-
clude that the differences in adult behavior were
instigated primarily by the inherent behavioral or
tolerance differences of the eagle pairs to man re-
lated manipulations. Also, Bed 51 East highwall
nest site was located below ground level and not in
view of mine related activities, whereas the artificial
structure was located above ground level and in line
of sight of mining activities. Conversely, the Bed 24
adults did not encounter human related distur-
bances to within about 3 km of the relocation area,
and apparently the eagles responded favorably and
fledged young.

We feel other possible explanations of the varied
adult responses are related to the proximity of the
artificial structure to suitable perches, the adults
familiarity with and previous use of the platforms,
and the amount of time the adults spent in direct
line of sight of the structure once the nestlings were
relocated (i.e., response time).

Management Implications. — As a result of the
successful highwall-to-pole nestling relocations, the
Bed 24 and Bed 51 East pits were released for
reclamation grading activities in August 1982, soon
after eaglets fledged. All reclamation activities were
completed by 1 February 1983, so that spatial buf-
fer zones around the platform could be honored,
thereby increasing the likelihood of nesting by
adult pairs at the respective structures in succeed-
ing years.

Of paramount importance to nest manipulations
of this type is whether the artificial structures will be
used in subsequent years. Postovit et al. (1982) and
Phillips and Beske (1982, 1983) reported use of

artificial structures in years following tree-to-pole,
pole-to-pole, and tree-to-tree eaglet relocations. In
the case of the Bed 51 East nest site in this study,
and a Wyoming uranium mine highwall case
(Beske, pers. comm.), it appears that the same is
possible for highwall-to-pole or cliff-to-pole reloca-
tions. However, we recommend that this technique
be utilized only on a temporary or emergency basis,
or when other more permanent or natural nesting
habitat cannot be created or enhanced (i.e., modifi-
cation of natural cliff areas, preserving mine high-
walls, tree planting, etc).

In summary, the difference in response at the
respective relocation sites for these 2 pairs of eagles
represent some degree of adaptability for accepting
and fledging young at an artificial, and drastically
different, nest substrate under varying conditions.
Due to the small sample size in this study, any
generalizations about the nature of adaptability of
Golden Eagle populations would be presumptuous.
However, this study may be an indicator that relo-
cation practices may prove beneficial in solving an
important management dilemma currently faced
by coal mine biologists and the USFWS.

Acknowledgments

This project was funded primarily by Arch Mineral Corpora-
tion with assistance from the U.S. Fish and Wildlife Service,
Wyoming Cooperative Fishery and Wildlife Research Unit, and
the Wyoming Game and Fish Department. We thank M. Lockhart
and R. Joseph for assisting with the field work and W. Dyer, U.S.
Fish and Wildlife Service, for reviewing the manuscript. We thank
S. Mikol-Ritter for assistance with the field work and L. Parker,
Wyoming Game and Fish Department, for providing the photo-
graphs used in the figures. Pacific Power and Light, Inc., assem-
bled, erected and relocated the artificial nesting structures. A.
Beske, Wyoming Cooperative Fisheries and Wildlife Research
Unit, aided with both the manuscript and field work.

Literature Cited

Boeker, E.L. and T.D. Ray. 1971. Golden Eagle popu-
lation studies in the southwest. Condor : 463-467.
Call, M.W. 1978. Nesting habitats and surveying
techniques for common western raptors. BLM Tech.
Note TN-316. Bureau of Land Management. Denver,
Colorado.

Ellis, D.H. 1979. Development of behavior in the gol-
den eagle. Wildl. Monogr. 70. 94 pp.

Errington, P.L. 1932. Technique of raptor food habits
study. Condor 34:75-86.

Fala, R. A. 1982. The development of a mine highwall as
wildlife habitat - highwall variance proposal. For Bed
51 West of Arch Mineral Corporation. Seminoe No. 1

Spring 1985

Golden Eagle Nest Relocations

7

Mine, approved by WDEQ and OSM, Hanna, Wyom-
ing. 50 pp.

Fala, R.A. 1982a. An eagle dilemma. Wyoming Wildlife
46:31-33.

Fyfe, R.W. and R.R. Olendorff. 1976. Minimizing the
dangers of nesting studies to raptors and other sensi-
tive species. Can. Wildl. Serv. Occas. Paper No. 23. 16 pp.

Lockie,J.D. andD.A. Ratcliffe. 1964. Insecticides and
Scottish Golden Eagles. Brit. Birds 57(3):89-102.

Mariah Associates. 1979. Final baseline wildlife study
report. Prepared for the Arch Mineral Corporation
Seminoe No. 1 Mine, Laramie, Wyoming. 88 pp.

McEneaney, T. and R. Phillips. 1981. Golden eagle
artificial nesting platform. (Design and Construction
Criteria). U.S. Fish and Wildlife Service. Sheridan,
Wyoming Field Station. 5 pp.

McGahan, J. 1968. Ecology of the golden eagle. Auk
85:1-12.

Phillips, R.L. and A. E. Beske. 1982. Golden eagles and
coal development in Eastern Powder River Basin of

Wyoming. Annual Report for 1981. U.S. Fish and
Wildlife Service, Denver Wildlife Res. Center. 55 pp.

. 1983. Golden eagles and coal de-
velopment in Eastern Powder River Basin of Wyom-
ing. Annual Report for 1982. U.S. Fish and Wildlife
Service, Denver Wildlife Res. Center. 55 pp.

Postovit, H.R., J.W. Grier, J.M. Lockhard andJ. Tate,
Jr. 1982. Directed relocation of a golden eagle nest
site./. Wildl. Manag. 46:1045-1048.

Arch Mineral Corporation, Environment Group, Box 490,
Hanna, WY 82327. Address of second author: USFWS,
2120 Capitol Avenue, Room 7010, Cheyenne, WY 82002.
Address of third author: Wyoming Cooperative Fish and
Wildlife Research Unit, P.O. Box 3166, University of
Wyoming, Laramie, WY 82071.

Received 8 March 1984; Accepted 30 January 1985

BIOLOGY OF ELEONORA’S FALCON ( Falco eleonorae ):

7. VARIABILITY OF CLUTCH SIZE, EGG DIMENSIONS
AND EGG COLORING

Michael Wink, Dietrich Ristow and Coralie Wink

Abstract — The variation of egg size, egg coloring and clutch size was studied in an Aegean colony of Eleonora’s
Falcon (Falco eleonorae). Egg-laying occurs between mid-July and early August with laying intervals of 2.6 and 2.9 d
between first and second, and second and third egg, respectively. Mean clutch size was about 2.28. Three-egg clutches are
started earlier than 2-egg or 1-egg clutches, which results in a negative correlation between laying date and clutch size.
Within a laying sequence, third eggs are significantly smaller than first and second eggs. Egg breadth has a higher
interclutch variation than intraclutch variation. A positive correlation can be established between female weight and egg
breadth. Egg color corresponds to laying order; the second and third eggs show many dark spots, the first egg is pale
brown. Clutch size was correlated with the weight of the male falcon but not with female weight. A correlation between
the hunting success of a male falcon and its weight is assumed. Food availability is a limiting factor in the colony studied,
and since the female falcon relies entirely upon the food supplied by the male, a correlation between male hunting success
and clutch size is suggested.

Variability in clutch size and egg parameters
has been studied in many birds, especially in species
breeding colonially (gulls, terns, swallows), or
species using nest boxes (tits, flycatchers, sparrows)
(Lack 1966; Klomp 1970; Drent 1975). Birds of
prey, except for the European Kestrel (Falco tin-
nunculus) (Cave 1969), the Red-footed Falcon (Falco
vespertinus ) (Horv&th 1955), and the European
Sparrowhawk (Accipiter nisus) (Newton 1979), have
not been studied extensively, probably because of
difficulties in acquiring sufficiently homogeneous
data.

Since the Eleanora’s Falcon (Falco eleonorae)
breeds colonially and shows rather synchronized
breeding, studies on reproductive biology and
ecology are facilitated. On the other hand, field
work is difficult to carry out because breeding col-
onies are usually situated on rocky, uninhabited
islands of the Mediterranean Sea.

We studied a large breeding colony of Eleonora’s
Falcon in the Aegean Sea for 8 seasons and report
here on the variability of clutch size, egg dimensions
and egg coloring with respect to laying sequence
and weight of the corresponding parent falcons.

Materials and Methods

The present study was carried out in July/ August 1975 and in
August/October 1977 near Crete in an Aegean colony of Eleo-
nora’s Falcon of about 250 breeding pairs. A few data were de-
rived from a study in August/September 1979 (Ristow et al. 1980;
Wink et al. 1980b). About 40 nests were monitored daily during
the egg-laying period of 1975, and all eggs were marked individu-
ally with pencil so that the exact dates of laying and their sequence
within a clutch were known.

Altogether, 240 eggs were measured. Egg weight was deter-

mined with a gauged spring balance to the nearest g. Egg length
(L) and egg breadth (B) were measured with a micrometer to the
nearest 0.1 mm. Egg volume was calculated as V = (7tL-B2)/6, in
analogy to the volume formula of a globe (Rheinwald, pers.
comm.). The weight of captured adult falcons was measured with
a spring balance to the nearest 5 g.

Results

Egg Dimensions. — The measurements of 240
eggs made in 1975 and 1977 are summarized in
Table 1. The data of both yrs are pooled, since the
parameters L, B and volume did not differ signifi-
cantly (P > 0.05, /-Test) between years. Third eggs
are significantly smaller (P < 0.02, /-Test) than first
or second eggs (Table 1), whereas first and second
eggs cannot be distinguished by size. The mean egg
shape index (L/B) decreases from first egg ( 1 .29) to
second egg (1.25) to third egg (1.23); third eggs
sometimes give the impression of being spherical.

Relationship With Female Weight. — The range
of B for 3 1 three-egg clutches was 5.6 mm, whereas
the range was only 1.7 mm within the respective
clutches themselves. To quantify the degree of in-
traclutch and interclutch variation (Vaisanen et al.
1972), 30 sequenced three-egg clutches were sub-
jected to a one-way analysis of variance (ANOVA)
(Table 2). The proportion of interclutch variation
was 15% higher in L and 52% higher in B than
intraclutch variation. The strong interclutch varia-
tion of B suggests that the anatomy and physiology
of the female might be of importance. Unfortu-
nately, these factors are difficult to measure, and
the only factor that could be determined for the
incubating female was weight.

8

Raptor Research 19(1):8-14

Spring 1985

Egg Variation in Eleonora’s Falcon

9

Table 1. Dimensions (X ± S.D.) of the first, second and
third egg of Eleonora’s Falcon. The third egg
differs significantly in breadth (P < 0.02, t-
Test), length, weight and volume (P < 0.001,
t-Test) from the first and second egg.

Parameter

N

Dimensions

Egg Length

Total

240

42.14 ± 1.61

First Egg

23

42.63 ± 1.03

Second Egg

21

42.16 ± 1.40

Third Egg

23

40.41 ± 1.37

Egg Breadth

Total

240

33.54 ± 1.01

First Egg

23

33.61 ± 0.98

Second Egg

21

33.80 ± 0.74

Third Egg

23

32.90 ± 0.72

Egg Weight

Total

163

26.37 ± 2.32

First Egg

23

27.13 ± 1.89

Second Egg

21

26.57 ± 1.85

Third Egg

23

23.54 ± 1.74

Egg Volume

Total

240

24.78 ± 2.56

First Egg

23

25.24 ± 1.62

Second Egg

21

25.26 ± 1.63

Third Egg

23

22.88 ± 1.40

The relationship between female weight and
egg dimensions is illustrated in Figure 1 . Breadth,
volume, but not L, are the most influenced
parameters, and in consequence, egg weight also.
The heavier the female, the heavier the resulting
eggs and probably the hatching young also.

Evaporative Water Loss. — Egg weight is sub-
jected to a steady reduction during incubation due
to H2O evaporation and CO2 production (Bezzel
1977). Sixty-four eggs weighed 22.8 ± 2.09 g ( X ±
S.D.) at the end of incubation in 1977. Taking 30 d
as incubation period and 26.4 g as initial egg weight,
a daily loss of 116 mg occurred. On this basis, a
13.3% total loss occurred which may be influenced
by climatic conditions at the breeding site (Table 3)
with its relatively high temp and low humidity dur-
ing daytime.

Relationship With Laying Period. — Egg-laying

Table 2. Results of one-way analysis of variance
(ANOVA) of inter- and intraclutch differences
in egg breadth of 30 sequenced three-egg
clutches of Eleonora’s Falcon. The figures in-
dicate percentage estimates of variance com-
ponents. Significance of F-test is shown with
stars (actual F-values not given).

Percent of Variance

Variables Intraclutch Interclutch

Egg Length 25.3*** 39.8*

Egg Breadth 16.2*** 68.5***

* - P < 0.05; *** - P < 0.001.

was rather synchronized and occurred between
mid-July to early August with an interval of 2 or 3 d
between each egg being laid (Table 4). The sizes of
54 eggs ordered by their date of laying show a
negative correlation for L and weight, but not for B
(Table 5). This effect can be easily explained by the
fact that third eggs were smaller than preceding
ones and laid about 5 to 6 d later than the first egg.
Consequently, only slight negative correlations
were established for first and third eggs analyzed
separately.

Egg Coloring. — First eggs are pale brown with
numerous small dots, whereas second or third
eggs are dark brown with many dots, usually larger,
which are concentrated at the blunt poles of the
eggs (Table 6). Therefore, egg sequence of any
clutch can be determined according to egg color

Table 3. Temperature and relative humidity (X ± S.D.)

measured with a thermohygrograph at 15

Eleonora’s Falcon nests in
1977.

August/September

Time

Temp (°C)

Rel. Humid. (%)

Night

20.92 ± 2.5

85.00 ± 6.7

Middaya

32.00 ± 4.5

49.50 ± 9.2

a 6 - 8 h after sunrise.

10

Wink et al.

Vol. 19, No. 1

FEMALE WEIGHT Igl

Figure 1. Linear regression analysis between weight of parent female Eleonora’s Falcons and egg breadth
(*** . P < 0.001).

and egg size, as is also the case in eggs of the Red-
footed Falcon (Horv&th 1955).

Clutch Size. — Clutch size data are summarized
in Table 7. Only data obtained at the beginning of

the incubation period (i.e., as soon as clutches are
completed) were considered in order to avoid ar-
tifacts due to loss of eggs or clutches during incuba-
tion. A negative correlation (P < 0.001) existed

Table 4. Date of egg laying (X ± S.D.; Range) and interval (X ± S.D.) in days between laying of first and second egg
and laying of second and third egg in an Aegean colony of Eleonora’s Falcon.

Egg Sequence

Laying Date

N

Interval (d)

First Egg

24.5 July ± 3.3 d
18 July - 27 July

21

Second Egg

27.1 July ± 3.3 d
21 July - 2 August

22

2.61 ± 0.92

(Between 1st & 2nd egg)

Third Egg

29.1 July ± 3.3 d
24 July - 7 August

17

2.91 ± 2.12

(Between 2nd & 3rd egg)

Spring 1985

Egg Variation in Eleonora’s Falcon

1

Table 5. Correlation values resulting from a linear regression analysis between sequence of laying and egg size in
Eleonora’s Falcon.

Parameter

N

R

Y = A - b(x)*

All Eggs

Length

54

-0.43**

Y = 46.15 - 0.16(d)

Breadth

54

-0.11

Weight

54

-0.36**

Y = 31.54- 0.21(d)

First Eggs

Length

21

-0.19

Weight

21

-0.36

Third Eggs

Length

16

-0.06

Weight

16

-0.17

* - Sadis 1972; ** - P < 0.01.

between the date of laying and clutch size (i.e.,
3-egg clutches were started earlier than 2-egg or
1-egg clutches).

Looking for an explanation, we studied the
weight of the corresponding parent falcons. Clutch
size was independent of female weight (r = 0.53, P
< 0.01). The implication of this phenomenon was
dealt with in detail in another paper (Wink et al.
1980a). We conclude that male weight and hunting
efficiency are correlated; probably the mates of
large males (which usually have 3-egg clutches) start
laying at an earlier date than the mates of younger
and smaller males.

Discussion

In Eleonora’s Falcon and all lands hitherto
studied (Lundberg and Vaisanen 1979) egg size
decreases with laying sequence. The opposite has
been found in several passerines (Svensson 1978)
[e.g., the Song Thrush (Turdus philomelos) (Pitelka
1971), the Eastern Bluebird (Sialis sialis) (Pinkowski
1 975], as well as waders (Vaisanen et al. 1 972 ; Miller
1979), and the Red-footed Falcon (Horvath 1955)
whose egg size increases with laying order. Pas-
serines start incubation with the last egg and an
adaptive value can be assumed for the observed egg
size variation. Since the probability of predation is
higher for the first than for the last egg, it is of
advantage if the last eggs are bigger. The loss of a
small first egg would be less costly than the loss of a
large last egg (Miller 1979). This assumption de-

mands that in the opposite case (i.e., Eleonora’s
Falcon) the female should start incubation with the
first egg in order to minimize the probability of a
loss of the first and largest egg, and this is exactly
what happens.

Is there any adaptive value of the third egg being
the smallest and darkest? In order to answer this
question it should be recalled that the interval be
tween laying of the first and the third egg is about 5
to 6 d, but that incubation starts with the first egg.
Hatching takes place within a 2 to 3 d (seldom 4 d)

Table 6. Observed numbers of eggs and color in relation
to egg color and laying sequence in Eleonora’s
Falcon. A = all eggs individually known; B =
includes data from eggs which were
categorized by their size.

Egg

Color

First

Egg

Second

Egg

Third

Egg

A. Pale Brown

21

1

1

Dark Brown

1

17

18

B. Pale Brown

90

2

Dark Brown

4

91

36

12

Wink et al.

Vol. 19, No. 1

20 30 9

JULY AUGUST

Figure 2. Linear regression analysis between laying dates of first egg and clutch size of Eleonora’s Falcon
(*** . P < 0.001).

interval, however. To explain the gain of 2 to 3 d in
laying time several factors have to be considered.
The female may incubate the first egg less inten-
sively during the first 3 days. “Clicking” calls of the
young birds prior to hatching, which occurs in Falco
eleonorae, can speed up hatching of an embryo to
some extent (Drent 1975). Incubation time is posi-
tively correlated with egg weight and incubation

temp. According to basic physics, a dark body col-
lects more radiation energy than a light one, thus
we assume that a small and darker egg (i.e., the
third egg in Falco eleonorae) would need a shorter
incubation period. This would be of advantage,
since the first young to hatch is the largest and the
last young the smallest, which reduces the latter’s
chances of survival.

Table 7. Mean clutch size in an Aegean colony of Eleonora’s Falcon. Initial clutch size data were derived from the
beginning of the incubation period (July/ August) in 1975.

Clutch Size (n)

Parameter

Mean

1 Egg

2 Eggs

3 Eggs

4 Eggs

Initial Size

2.28

5

45

26

Post-Incubation Size^

1.97

21

76

18

(l)a

aIn 1982 a 4-egg clutch was found, but according to egg size measurements it was derived from 2 females.

^Most data were collected in 1 977. If clutch size is determined at the end of the incubation period, clutch size is biased by egg loss due to
predation.

Spring 1985

Egg Variation in Eleonora’s Falcon

13

Comparing the clutch size in different colonies of
Eleonora’s Falcon, the highest values are reached in
the western Mediterranean: 2.55 eggs/clutch in the
Balearic Islands (Mayol 1977), 2.85 - 3.05 eggs/
clutch in Morocco (Conant and de Naurois 1958;
Vaughan 1961; Walter 1968; Clark 1981) com-
pared with 2.28 eggs/clutch in the Aegean region
for our study period. Clutches of 4 eggs are more
common in the Moroccan colonies (the mode being
3-egg clutches, Clark 1981) than in the eastern
Mediterranean where 4-egg clutches are uncom-
mon. It remains to be studied whether this gradient
in clutch size from eastern to western Mediterra-
nean regions is primarily due to a better food sup-
ply, or due to other factors such as climate, aridity,
or genetic differences (Ojanen et al. 1979).

The clutch size within a colony seems to depend
on the hunting success of the male, who supplies the
female and the young with food during the breed-
ing period. A larger falcon generally has a better
hunting efficiency than a small one (Bezzel 1977;
Newton 1979). Since food availability is a limiting
factor for Eleonora’s Falcon, it is not surprising that
the clutch size is positively correlated with the
weight of the male (Wink et al. 1980a). The physical
condition of the female does not influence clutch
size, but seems to be important for egg size and, in
consequence, for the weight of the hatching young.
The heavier a hatchling, the better its chances of
survival (LeCroy and LeCroy 1974; Coulson and
Thomas 1978; Lundberg and Vaisanen 1979; Par-
sons 1970). Consequently, the offspring of a larger
female may have an advanage over the young of a
smaller female.

Acknowledgments

We thank our friends in Germany and Greece for help and
support, and the Studienstiftung des deutschen Volkes for grants
(to MW and CW). We are thankful to Dr. R. A. Vaisanen for critical
comments on an earlier draft of this paper and to Dr. L. Kiff for
refereeing and linguistic help.

Literature Cited

Bezzel, E. 1977. Ornithologie. Eugen Ulmers Verlag,
Stuttgard.

Cave, A.J. 1968. The breeding of the kestrel, Falco tin-
nuculus, in the reclaimed area Oostelijk Flevoland.
Metherl. J. Zool. 18:313-407.

Clark, A.L. 1981. Ecology of the Eleonora’s Falcon in
Morocco. Ph.D. Dissertation, Cornell Univ., Ithaca,
NY.

Conant, M. and R. de Naurois. 1958. Observations sur
les especes nicheuses des iles de Mogador. Alauda
26:196-198.

Coulson, J.C. and C. Thomas. 1978. The significance
of egg size in gulls. Ibis 120:407.

Drent, R. 1975. Incubation. In Avian Biology, D.S.
Farner andJ.R. Kingeds., Vol 5:333-420.

HoRv£th, L. 1955. Red-footed Falcons in Ohat-Woods,
near Hortobagy. Acta Zool. Acad. Sci. Hungar. 1:245-
287.

Klomp, H. 1970. The determination of clutch size in
birds. A review . Ardea 58:1-124.

Lack, D. 1966. Population studies of birds. Oxford,
Clarendon Press.

LeCroy, M. and S. LeCroy. 1974. Growth and fledging
in the Common Tern (Sterna hirundo). Bird Banding
45:326-340.

Lundberg, C.A. and R. A. Vaisanen. 1979. Selective cor-
relation of egg size with chick mortality in the Black-
headed Gull (Larus ridibundus). Condor 81:145-156.

Mayol, J. 1977. Estudios sobre el Halcon de Eleonor,
Falco eleonorae, en las islas Baleares. Ardeola 23:103-
136.

Miller, E.H. 1979. Egg size in the Least Sandpiper,
Calidris minutella, on Sable Island, Nova Scotia,
Canada. Ornis. Scand. 10:10-16.

Newton, I. 1979. Population ecology of raptors. T. and
A.D. Poyser, Berkhamsted.

Ojanen, M., M. Orell and R. A. Vaisanen. 1979. Role of
heredity in egg size variation in the Great Tit Parus
major and the Pied Flycatcher Ficedula hypoleuca. Ornis
Scand. 10:22-28.

Parsons, J. 1970. Relationship between egg size and
post hatching chick mortality in the Herring Gull
( Larus argentatus). Nature 228:1221-1222.

Pikula, J. 1971. Die VariabilitatderEierder Population
T urdus philomelos Brehm 1831 in der CSSR. Zool. Listy
21:69-83.

Pinko wski, B.C. 1975. Growth and development of
Eastern Bluebirds. Bird Banding 46:273-289.

Ristow, D., B. Conrad, C. Wink and M.
Wink. 1980. Pesticide residues of failed eggs of
Eleonora’s Falcon from an Aegean Colony. Ibis
122:74-76.

Sadis, L. 1972. Statistische Answertupmethoden. 3rd
Ed., Springer, Berlin-New York.

Svensson, B.W. 1978. Clutch dimensions and aspects of
the breeding strategy of the Chaffinch Fringilla coelebs
in northern Europe: a study based on egg collections.
Ornis Scand. 9:66-83.

Vaisanen, R.A., O. Hilden, M. Soikkeli and S. Vuo
lanto. 1972. Egg dimension variation in five wader
species: the role of heredity. Ornis Fenn. 14: 1-25.

Vaughan, R. 1961. Falco eleonorae. Ibis 103:114-128.

Walter, H. 1968. Eie Abhangigkeit des Eleonorenfal-

14

Wink et al.

Vol. 19, No. 1

ken ( Falco eleonorae) vom mediterranen Vogelzug. Dis-
sertation, Bonn University.

Wink, M., C. Wink and D. Ristow. 1980a. Biologie des
Eleonorenfalken ( Falco eleonorae ) 8. Die Gelegegro/3e
in Relation zum Nahrungsangebot, Jagderfolg und
Gewicht der Altfalken./. Orn. 121:387-390.

. 1980b. Biologie des Eleonorenfalken

9. Eitemperaturen und Korpertemperatur juveniler

und adulter Falken Wahrend der Brutzeit. Vogelwarte
30:320-325.

Institut fur Pharmzaeutische Biologie dr Technischen Univer-
sitat Mendelssohnstr. 1, 3300 Braunschweig, Federal Re-
public of Germany. Address of second author: Pappelstr.
35, 8014 Neubiberg, Federal Republic of Germany.

Received 18 April 1983; Accepted 27 September 1984.

THE RAPTOR RESEARCH FOUNDATION CONFERENCE — NOVEMBER 1985. The 1985 Raptor Research
Foundation International Meeting and Symposium on the Management of Birds of Prey will be held at the capital Plaza
Holiday Inn in Sacramento, California, November 2 - 10, 1985. Highlights of this 20th anniversary meeting of the
Foundation will include 1) the Second RRF Conference on Raptor Conservation Techniques — Twelve Years of
Progress, 1973-1985, 2) a Western Hemisphere Meeting of the World Working Group on Birdsof Prey (ICBP), 3) the
Second International Vulture Symposium, 4) a Western North America Osprey Symposium, 5) a Workshop on North
American Candidate Endangered Raptors, 6) an International Symposium on Raptor Reintroduction, and 7) a
Symposium on Raptor Rehabilitation, Captive Breeding and Public Education. For more information contact Dr.
Richard R. Olendorff, U.S. Bureau of Land Management, 2800 Cottage Way, Sacramento, California 95825, or Nancy
Venizelous, San Francisco Zoological Society, Stoat Boulevard at the Pacific Ocean, San Francisco, California 94132.

NESTING BEHAVIOR OF PEREGRINE FALCONS IN WEST GREENLAND
DURING THE NESTLING PERIOD

Julie Hovis, Thom D. Snowman, Virginia L. Cox,

Raymond Fay and Keith L. Bildstein

Abstract - Time-lapse photography was used to study adult and nestling behavior at 2 Peregrine Falcon ( Falco
peregrinus) eyries in West Greenland during July and August 1974. During the first 10 d after hatching, nestlings at both
eyries were brooded > 80% of the time. Brooding activity declined gradually during d 11-15 and was not recorded at
either eyrie following d 20. The length of each feeding bout at 1 eyrie (Rings </>) diminished steadily throughout the
nestling period. In contrast, the length of each feeding bout at the other eyrie (Lone Female) remained relatively
constant. The rate of food delivery was consistently greater at Rings</> than at Lone Female. The Rings</> nestlings began to
wander from the nest scrape on d 9-10, but spent most of their time on the scrape until d 24. The Lone Female nestlings
also spent most of their time on the scrape during d 1-20, but they spent less time in bodily contact with one another than
did the Rings</> nestlings.

Although the Peregrine Falcon {Falco peregrinus )
has been the subject of numerous scientific investi-
gations, few studies had been conducted in the
Arctic prior to the 1970s. Following the reproduc-
tive decline of the peregrine throughout much of
North America during the 1950s and 1960s (Hic-
key 1969), however, the need to evaluate the status
of Arctic populations became apparent (Cade
1969).

In response, an intensive study was initiated in
West Greenland in 1972. The primary focus of this
long-term investigation was to determine the dis-
tribution, density and reproductive success of a
nesting population of Peregrine Falcons (see Mat-
tox et al. 1972; Walker et al. 1973; Burham et al.
1974; Mattox 1975; Mattox et al. 1980 and Burn-
ham and Mattox 1984 for the results of this por-
tion of the project). An additional effort was made
to study the breeding behavior of the birds. Here,
we present one aspect of that behavioral investiga-
tion: the use of time-lapse photography to record
the activities of adult and nestling Peregrine Fal-
cons at 2 eyries.

Materials and Methods

The study was conducted on the west coast of Greenland at 2
cliffs located approximately 6 km WNW and 24 km WSW of
Sondrestrom fjord Air Force Base. The region ranges in elevation
from sea level to 590 m, has a low-arctic climate, and is charac-
terized by expanses of tundra interspersed with shallow ponds and
lakes.

Two Peregrine Falcon eyries were studied intensively during
July and August 1974 by T.D. Snowman and V.L. Cox, who
established a base camp near the Rings </> eyrie. The Rings</> eyrie
was two-thirds of the way up a 45-60 m cliff and overlooked 2 large
and several smaller bodies of water to the SSE; there were 4
nestlings (2 S i and 2 $ $ ) at the eyrie. The Lone Female eyrie, 20
km to the WSW of Rings</>, was two-thirds of the way up a 24-30 m
rock outcropping and overlooked a large lake to the S. On 23 July,

1 live (a <?) and 2 dead nestlings were discovered at the latter eyrie.
Because we believed there was little chance the single nestling
would survive without the warmth of another bird, a second male
nestling of about the same age was transplanted to the nest from a
nearby eyrie on 29 July. At that time, both nestlings were ap-
proximately 12-13 d old.

Minolta super-8 movie cameras, housed within waterproof
metal and Plexiglas cases, were secured with climbing pitons and
slings 5 m from the nest scrape at Rings</> and 3-4 m from the nest
scrape at Lone Female. Filming at Rings</> began 1 7 J uly, about 5 d
after the eggs hatched, and continued through 6 August. During
the first \Fh d, the camera exposed 1 frame/min; during the last
3V2 d, the rate was increased to 1 frame/15 sec. From 13 July
through 5 August, additional observations of adults and nestlings
were made with an 8-25X spotting scope from a hidden location
1 40 m from the nest scrape. Filming at Lone Female began 23 July ,
about 6 d after the original clutch hatched, and ended 5 August.
The camera exposed 1 frame/min throughout the period. The
film at the Lone Female eyrie had to be changed every 60 h,
requiring a 6-h, 20-km walk from Rings </>; incidental observations
were made during these visits.

R. Fay, J.A. Hovis and K.L. Bildstein transcribed observations
from the film using a film-editing machine and microfiche reader.
Four adult behavioral patterns were recognized: 1) brooding,
including close sitting or standing over the nestlings (Jenkins
1978); 2) feeding, including feeding bouts and food deliveries; 3)
adult on eyrie but inattentive, including observations in which at
least 1 adult was on or near the nest scrape but was not brooding or
feeding the young; 4) adult not at eyrie, including observations in
which neither adult was in view. We excluded from analysis adult
behavioral patterns influenced by human activity when the film
was changed.

We also recorded the absolute (on or off scrape) and relative (in
contact with at least 1 other sibling or alone) location of nestlings.

Results and Discussion

Adult Behavior. — Nestlings at the Ringst/) eyrie
were closely brooded during the first 10 d after
hatching (Table 1). As the young began to acquire
their second down at 10-14 d of age (Bent 1938),
there was a gradual decline in brooding activity,
with most brooding occurring at night or during

15

Raptor Research 19(1): 15-19

16

HO VIS ET AL.

Vol. 19, No. 1

Table 1. Percent of time adult Peregrine Falcons engaged in various activities at 2 eyries in Greenland. Data were
derived from 277 h and 199 h of film time at Rings </> and Lone Female eyries, respectively.

Activity

Age of Nestlings3

3-5

6-10

11-15

16-20

21-24

Brooding

86/NDb’c

80/86

13/37

0/0

O/'ND

Feeding

9/ND

10/4

8/5

6/3

1/ND

On eyrie, inattentive

1/ND

2/5

3/36

1/68

< 1/ND

Not on eyrie

4/ND

8/5

75/22

93/28

98/ND

aDays since hatching.

° Rings*/) Eyrie/Lone Female Eyrie.
CND no data.

periods of extreme temp or rain. No daytime
brooding was recorded following d 15 of the nest-
ling period; brooding at night was last observed
when the young were 19-20 d old and was as-
sociated with cold, rainy and windy weather.

Most brooding activity at the Lone Female eyrie
also occurred when the nestlings were < lOd old
(Table 1). Thereafter, the young were left alone for
increasing amounts of time; no brooding was re-
corded following d 14 of the nestling period.

A similar pattern in brooding activity was ob-
served by Enderson et al. (1972) at 5 peregrine
eyries along the Yukon River, Alaska. Nestlings
were brooded > 90% of the time during the first 6
d after hatching, approximately 88% of the time by
d 10, and < 10% of the time by d 20. The occurr-
ence of increased brooding activity during periods
of inclement weather has been reported for the
peregrine (Nelson 1970; Enderson et al. 1972), the
Gyrfalcon ( F . rusticolus ) (Jenkins 1978) and the
Sparrowhawk (Accipiter nisus) (Newton 1978).

Although adult birds could not be sexed accu-
rately from the film, observations made with a
spotting scope suggested that all brooding at
Rings 4> was done by the female. Other studies also
have found that males play a negligible role in
brooding (Nelson 1970; Enderson etal. 1972; Har-
ris and Clement 1975), a behavioral pattern that in
part may be due to the difference in size between
the sexes. Males apparently are too small to cover
the nestlings properly and are probably less effi-
cient brooders than are females (Nelson 1970),
which are about one-third heavier.

The amount of time the Rings</> adults spent
feeding their young remained relatively constant
throughout the first 20 d of the nestling period
(Table 1). However, average length of each feeding
bout diminished steadily during the period (Table
2). As the nestlings began to tear and shred food on
their own, they probably required decreasing
amounts of time to consume small prey items such
as the Lapland Longspur (Calcarius lapponicus) and
the Snow Bunting (Plectrophenax nivalis), which
comprise the major portion of their diet (Harris
and Clement 1975; Burnham and Mattox 1984).
Also, as the nestlings grew increasingly aggressive
with age, it became difficult for the adults to feed
them at the eyrie. By the fourth wk of the nestling
period, the adults were dropping prey at the eyrie
and allowing the young to feed themselves. The
tendency to avoid the young during the later stages
of the nestling period has been observed for both
peregrines (Sherrod 1983) and Gyrfalcons (Jenkins
1978).

The rate of food delivery at the Rings cf) eyrie was
greatest when the nestlings were 6-20 d old (Table
2). At earlier ages, young took more time to con-
sume lesser amounts of food (Enderson et al. 1972),
were satiated more quickly (Newton 1979) and re-
quired fewer prey items. The limitations of time-
lapse photography probably account for the low
rate of food delivery recorded during the fourth wk
of the nestling period. As the average length of each
feeding bout decreased (Table 2), many food de-
liveries were too brief to be recorded on Film (Jen-
kins 1978).

Spring 1985

Peregrine Falcon in West Greenland

17

Table 2. Rate of food delivery and length of feeding bouts at 2 Peregrine Falcon eyries in Greenland.

Age of Nestlings3

3-5

6-10

11-15

16-20

21-24

Rate of food delivery (prey/hr)
Rings (f)

Lone Female

0.8±0.1(2)b

NDC

1.3±0.2(5)

0.9±0.1(3)

1.2±0.2(5)

0.8±0.3(5)

1.4±0.3(5)

0.6±0.1(5)

0.7 ±0.6(4)
ND

Length of feeding bouts (min)
Rings<£

Lone Female

6.7±5.0(21)

ND

4.9±2.6(85)

2.8±2.3(40)

3.7±2.0(95)

3.5±2.7(61)

2.5± 1.8(97)
3.0±2.2(47)

1.4±0.9(22)

ND

aDays since hatching.

°Mean ± S.D.(N). N = number of days or number of feeding bouts.
CND = no data.

Feeding activity at the Lone Female eyrie re-
mained relatively constant during d 6-20 of the
nestling period (Tables 1 and 2). Both the percent
of time the Lone Female adults spent feeding
young (Table 1) and the rate at which they deli-
vered food to the eyrie, however, were lower (Table
2) than at Rings</>. These findings most likely were
related to differences in the number and sex of the
nestlings at each eyrie. The 2 male and 2 female
nestlings at Rings </> undoubtedly required more
food than the 2 males at Lone Female. That the
average length of each feeding bout at Lone Female
did not diminish as the nestlings matured (Table 2)
is more difficult to interpret. Possible explanations
include: 1) a greater parental diligence on the part
of the Lone Female adults; 2) differences in the
development and behavior of the nestlings at the 2
eyries; or 3) the failure of the cameras to record
accurately the occurrence and duration of each
feeding bout at the 2 eyries.

Nestlings at Rings </> were fed almost entirely by
the adult female. The male was the primary hunter
and provider of food, but was observed feeding the
young only once, when they were 1 2- 1 3 d old. Har-
ris and Clement (1975) observed a similar division
of parental duties for peregrines, whereas Herbert
and Herbert (1965) and Nelson (1970) found that
the male undertook a greater portion of the feeding
responsibilities as the nestlings matured.

The aversion that adult falcons have towards
being on the nest scrape together (Enderson et al.
1972; Harris and Clement 1975; Jenkins 1978) was
further evidenced at the 2 eyries. The Lone Female
adults were never filmed together. All of the 7
instances were the adults at Rings$ were filmed
together occurred within the first 2 wks of the
nestling period, all were associated with a food ex-
change or feeding bout and all lasted less than 1
min. Harris and Clement (1975) suggested that
females may dominate males during the nestling
period, tolerating their presence only in conjunc-
tion with the delivery of food. Neither of the
females observed in this study appeared to be over-
tly aggressive towards their mate and the rea-
son for each pair’s general avoidance of one
another remains unclear.

The Rings </> adults were rarely inattentive while
on the eyrie (Table 1). Until the young were 10-15 d
old, periods of inattentiveness occurred primarily
between periods of brooding and feeding. This be-
havioral sequence also has been recorded for nest-
ing Gyrfalcons (Jenkins 1978). With the cessation of
brooding, the amount of time the Rings </> adults
were on the eyrie and inattentive declined to < 1%,
and they spent 90% of the time away from the eyrie.
In contrast, the Lone Female adults spent an in-
creasing amount of time inattentive on the eyrie as
the nestlings matured (Table 1). This probably re-

18

HOVIS ET AL.

Vol. 19, No. 1

fleets the fact that one of the Lone Female adults
frequently perched away from the nest scrape but
within the field-of-view of the camera.

Nestling Behavior. — Peregrine Falcons are
semi-altricial (Nice 1962). At hatching, young are
sparsely covered with down, and their eyes,
although usually open, are weak and relatively
non-functional (Brown and Amadon 1968). The
young are dependent on their parents for food
throughout the nestling period and for at least 6
wks after their First flight (Nelson 1970; Sherrod
1983). Time of first flight varies, but usually occurs
when the nestlings are appproximately 30 (Herbert
and Herbert 1965) to 43 d old (Nelson 1970).

The young at the Ringst/) eyrie were relatively
helpless and immobile during their first wk. They
were not observed leaving the nest scrape until they
were 9-10 d old (Table 3), at which time they could
sit up and propel themselves short distances by
hopping about on their wings. By the end of the
second wk, the nestlings were actively shifting about
as a group. They had begun to preen themselves
and were able to grab food from the adult as often
as it was offered to them. By d 15, the nestlings were
tearing and shredding prey items and fighting
aggressively over their food. They continued to
spend most of the time in bodily contact with one
another and on the nest scrape (Table 3).
Vocalizations, identified as soft “kaks,” were first
heard at this time. During the fourth wk, the

nestlings became increasingly mobile as they began
to stand and stay off their wings. Thereafter, the
amount of time they spent on the nest scrape and in
contact with one another decreased rapidly (Table
3). When last observed, mid-way through wk 4, the
nestlings appeared healthy and likely to reach
fledging age. They were extremely active and
aggressive, were able to feed themselves and
remained outside of the field-of-view of the camera
for long periods of time.

Transferring the additional nestling to the
Lone Female eyrie did not appear to affect the
development or behavior of either young. The
nestlings, like those at Rings </>, spent the majority of
the time on the nest scrape during d 11-20 (Table
3). The amount of time the Lone Female young
spent in bodily contact with one another during this
period, however, was lower than at Rings </>. The
presence of only 2 nestlings at Lone Female may
explain this difference; at any point in time each of
the 4 Rings (f) nestlings had a greater probability of
being in contact with at least 1 of its siblings than did
either of the Lone Female nestlings.

In conclusion, time-lapse photography proved
an effective means of monitoring the activities of
adult and nestling Peregrine Falcons in West
Greenland. First, the technique generated
relatively large amounts of data with minimal
disturbance of the birds (Enderson et al. 1972).
Second, the information derived from the films

Table 3. Percent of time nestling Peregrine Falcons were on the nest scrape or were in bodily contact at 2 eyries in
Greenland.

Age of Nestlings

a

3-5

6-10

11-15

16-20

21-24

On nest scrape

Rings (f>

100

95

94

90

36

Lone Female

NDb

ND

73

78

ND

In bodily contact

90

80

91

85

28

Rings$

Lone Female

ND

ND

46

54

ND

a

b

Days since hatching.
ND = no data.

Spring 1985

Peregrine Falcon in West Greenland

19

represents an important contribution to our
knowledge and understanding of the Peregrine
Falcon in the Arctic.

Acknowledgments

We thank William G. Mattox and the rest of the 1 974 Greenland
Peregrine Falcon Survey Team for their help in the field and
during the preparation of this manuscript; and Jim Weaver for
assembling our cameras in watertight boxes. The Mellon Fund of
Dartmouth College supported our research and the U.S. Air
Force provided essential logistical support in Greenland. We
thank them both. The Biomedical Laboratory of Edgewood
Arsenal (U.S. Army) — currently the Chemical Research and
Development Center, Aberdeen Proving Ground, MD, supplied
essential funds for travel and field maintenance for the 1974
Greenland Peregrine Falcon Survey.

Literature Cited

Bent, A. C. 1938. Life histories of North American birds
of prey, Part 2. U.S. Natl. Mus. Bull. 167. 482 p.
Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world, Vol. 1, McGraw Hill, New York.
414 .

Burnham, W.A., M.A. Jenkins, F.P. Ward, W.G. Mat-
tox, D.M. Clement and J.T. Harris. 1974. Falcon
research in Greenland, 1973. Arctic 27:71-74.
Burnham, W.A., and W.G. Mattox. 1984. Biology of
the Peregrine and Gyrfalcon in Greenland. Meddelelser
om Gr(fmland, Bioscience 14:1-25.

Cade, T.J. 1969. The northern peregrine poulations.
Pages 502-505 In J.J. Hickey, ed. Peregrine Falcon
populations: their biology and decline. Univ. Wis.
Press, Madison. 596 pp.

Enderson, J.H., S.A. Temple and L.G.
Swartz. 1972. Time-lapse photograhic records of
nesting Peregrine Falcons. Living Bird 11:1 13-128.
Harris, J.T. and D.M. Clement. 1975. Greenland
peregrines at their eyries: a behavioral study of the
Peregrine Falcon. Meddelelser om Gmpnland 205:1-28.
Herbert, R.A. and K.G.S. Herbert. 1965. Behavior of
Peregrine Falcons in the New York City region. Auk
82:62-94.

Hickey, J.J., ed. 1969. Peregrine Falcon popula-
tions: their biology and decline. Univ. Wis. Press,
Madison. 596 pp.

Jenkins, M.A. 1978. Gyrfalcon nesting behavior from
hatching to fledging. Auk 95:122-127.

Mattox, W.G. 1975. Bird of prey research in West
Greenland, 1974. Polar Record 17:387-388.

_ , R.A. Graham, W.A. Burnham, D.M.

Clement and J.T. Harris. 1972. Peregrine Falcon
survey, West Greenland, 1972. Arctic 25:308-311.

, W.R. Heinrich, J. Oar, S.J. Belardo,

K.E. Riddle and T.M. Smylie. 1980. West Green-
land Peregrine Falcon survey, 1978. Arctic 33:199-202.

Nelson, R.W. 1970. Some aspects of the breeding be-
havior of Peregrine Falcons on Langara Island, B.C.
M.S. Thesis, Univ. Calgary, Calgary, Alberta. 306 pp.

Newton I. 1978. Feeding and development of Spar-
rowhawk Accipiter nisus nestlings. J. Zool., London.
184:465-487.

. 1979. Population ecology of raptors.

Buteo Books, Vermillion, S.D. 399 pp.

Nice, M.M. 1962. Development of behavior in precocial
birds. Trans. Linn. Soc. N.Y., no. 8., 211 pp.

Sherrod, S.K. 1983. Behavior of fledgling peregrines.
The Peregrine Fund, Inc., Ithaca, N.Y. 202 pp.

Walker, W., II, W.G. Mattox and R.W. Rise
brough. 1973. Pollutant and shell thickness deter-
minations of peregrine eggs from West Greenland.
Arctic 26:256-258.

Caesar Kleberg Wildlife Research Institute, Texas A&I Univer-
sity, Kingsville, TX 78363. Address of second author: 4
Stagecoach Road, Amherst, MA 01002. Address of third
author: P.O. Box 132, McGrath, AK 99627. Address of
fourth and fifth authors: Department of Biology, Winthrop
College, Rock Hill, SC 29733.

Send reprint requests to Keith L. Bildstein.

Received 6 September 1984; Accepted 4 January 1985

THE HUNTING RANGES OF TWO FEMALE PEREGRINES TOWARDS THE

END OF A BREEDING SEASON

Richard Mearns

Abstract - Radio transmitters were fitted to two female Peregrine Falcon (Falco peregrinus) at adjacent territories in
South Scotland, and each was tracked during the late nestling and early post-fledging period. Whilst the young were on
the nest ledge, and for a week after leaving,, both females remained close to the eyrie. Occasionally they left to hunt,
probably within 5 km. Later the females began to range more widely. Eighteen days after the young had left the nest, one
female regularly traveled 8-14 km, sometimes more, and once 1 8 km from the eyrie. The second female was not studied
at this later stage. The territories of the two females did not apparently overlap. One female, next to a Golden Eagle
{Aquila chrysaetos) territory, tended to avoid that area. Although birds hunted often over coniferous forest this was mainly
for domestic pigeons and few ‘woodland’ species were recorded. One pair took a larger proportion of waders than the
other and this was consistent with the observed ranges of the females, which included areas of low marshy ground for
one, but not for the other.

During the breeding season, the male Peregrine
Falcon (Falco peregrinus) is responsible for almost all
the hunting for himself, the female and young
nestlings. As the food demands of young increase,
the female may have to take a more active hunting
role. This may be especially so if the brood is large
(Weir 1978).

For a pair of radio-tracked peregrines in Califor-
nia, the female made proportionately fewer hunt-
ing flights than the male, but when she did leave the
vicinity of the eyrie, she appeared to go as far as the
male and was tracked up to 8 km away (Enderson
and Kirven 1983). Other peregrines, of undeter-
mined sex, have been recorded hunting (not by
radio telemetry) at 20 km and 27 km from their
eyries (Porter and White 1973; Kumari 1974).

This study was an attempt to assess the foraging
areas of two female peregrines with young.

Study Area and Methods

The 2 eyries, A and B, were 4.5 km apart, about 300 m a.s.l., and
had alternative cliffs 2.5 km and 3.0 km to the north, which had
rarely been used. Eyrie A was easily observed from a road below;
Eyrie B was 1 km from a road but was less easily observed because
of trees close to the eyrie and beside the road. Both eyries were in
areas planted with exotic conifers, mainly Sitka spruce ( Picea
sitchensis), Norway spruce (Picea abies) and larch ( Larix sp.), but also
various other tree species. Most of this new forest was 20-25 y old,
but some small areas had trees over 50 y old (Fig. 1). Most of the
remaining ground in the study area was open, mainly heather
(Calluna) moorland or rough pasture, though some parts had
recently been ploughed and planted with trees. To the east was a
mixture of pasture, rough grazing and arable land, with scattered
small clumps of coniferous or deciduous woodland. The valley
bottoms had numerous small lochs and marshy areas.

Both eyries were on the edge of an upland area where several
other peregrine pairs bred. Eyrie A had other pairs 9 km south-
west and 9 km west, while eyrie B had other pairs 1 0 km south-west
and 7 km west-northwest. There were none to the east or southeast
within 30 km. A Golden Eagle ( Aquila chrysaetos) reared 1 young

about 1 1 km southwest of eyrie A and an unsuccessful eagle pair
nested 6 km southeast.

The 2 eyries were chosen because of their previous good
breeding success and the good network of roads nearby. The
females were trapped at the nest during incubation and 10 g
radio-transmitters were fitted to their central tail feathers. On
non-breeding Goshawks (Accipiter gentilis), transmitters of com-
parable weight and fitted in the same fashion did not interfere
with prey capture, nutritional condition or tendency to leave an
area (Kenward 1978). The transmitter signals could be detected
from more than 10 km away when birds were soaring, but from
much shorter distances when birds were perched. Reception was
severely restricted by intervening hills.

Female A was monitored for a total of 1 78 h over 24 d, between 1
June and 25 July (Fig. 2). Female B was monitored for a total of 86
hover 16 d between 2 June and 30 June. Each was monitored until
transmissions ceased to be heard, probably because of battery
failure or because the central tail feathers were moulted. Both
broods left the nest between 23 June and 27 June; 4 young (2 <? <?,
2 9$ ) at eyrie A, and 3 young (1 <3\ 2 $ $ ) at eyrie B.

Both females were occasionally lost for up to 90 m (once 1 80 m);
usually, I was away searching when a bird returned to the eyrie so
exact times away were not known.

To begin with, I followed birds from the eyrie, but later it was
more efficient to station myself at elevated points 5-10 km away
and wait for the birds to appear. It was difficult to get cross
bearings on a flying bird unless it was soaring, when precise
location was usually possible.

Prey remains were collected after the young left the eyrie, as well
as when eyries were visited to ring young. Additional data on prey
were collected in other years, when these eyries were occupied by
the same females.

Results

Telemetry - Throughout the period when the
young were on the nest ledge, female A spent 93%
of the observed time at the cliff, either perched or
feeding young (Table 1). She made several short
flights and often soared above the eyrie. Longer
trips were rare (only 1% of the time observed) but
increased in number and duration after the young
had left the nest (Table 2).

20

Raptor Research 19(l):20-26

Spring 1985

Peregrine Falcon in Scotland

21

N

Hunting Ranges of Two Female Peregrines

Figure 1. Ranges of two female Peregrine Falcons in the British Isles. ® = Peregrine Falcon eyrie, occupied; O =
Peregrine Falcon eyrie, unoccupied; H = Golden Eagle eyrie; P = regular perch; D = dispute with Golden

Eagle; range limits: = largely nestling period, = up to 18 d after fledging, = over 18

days after fledging. □ □ = open country. □ □ = trees over 20 yr (within hunting range only).

When the young had been out of the nest a week,
the female extended her range slightly to include
two hills, one 2.5 km to the southwest, the other 3.8
km to the northeast of the eyrie (Fig. 1). The tops of
the hills where she perched (once for 300 min) were
mainly heather and boulders, but only one offered
a view directly towards the eyrie. Also at this time
the female was recorded on 4 occasions in the gen-
eral area of the alternative nesting cliff, 2.4 km
northward, and once was seen perched there,
alone. Not until 18 d after the young left the nest
was she recorded more than 8 km from the eyrie.
She then travelled 8-18 km on each of the remain-
ing 9 d that she was monitored; each day to the same
general area to the southeast, usually between 8 km
and 14 km, though twice when lost and relocated
(after 40 min and 150 min) at about 14 km she may
have been returning from a longer trip or she may
have been perched on the ground (perhaps on a
kill).

Female B also remained close to the eyrie when
young were on the nest ledge but had a larger
recorded range (22 km2) than bird A (9 km2), at this
time (Fig 1). On 8 occasions the signal was lost for
up to 90 min, during which time the bird could have

was on the hill opposite the eyrie on a perch that I
later discovered, from which no signal could be
heard on the road.

For 5 d after the young left the nest (the radio
stopped working on the 5th day) the range of
female B did not increase in size, though observa-
tion time was limited. The maximum recorded
range of female B (23 km2) did not overlap that of
female A ( 1 1 7 km2).

Activity - At all stages there was little activity for
long periods and both females were often on their
same perches for over 2 h at a time. After the young
had left the nest, hunting trips by the females
seemed to occur at any time of day, but were regular
in the late afternoon to early evening period, and
probably the early morning, because on 5 or 6 occa-
sions female A was absent at about 0700 H when
monitoring commenced (Fig. 2). This female was
also often away from the eyrie at mid-day, but at this
time was more usually perched elsewhere. Hunting
flights varied in length; female A was 8 times away
for 2-3 hrs, but may not have been actively hunting
all of this time. She sometimes left the cliff and
returned with prey in 20 min or less (Table 2). I had
no information on the proportion of food brought

Time Spent Near Eyrie (within 2 km) Total Trips > 2 km Lost

From Eyrie

22

Richard Mearns

Vol. 19, No.

1 1
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Grouped together because observations were made by telemetry from 10 km away.

Spring 1985

Peregrine Falcon in Scotland

23

I >2 Km FROM EYRIE
LOST
AT EYRIE

JUNE T]

§

14

-15

is]

20

21

27

28

m

JULY 2

h-

3

<

Q

10

11

12

13

14

16

17

18

19

20

21

HOUR OF DAY

Figure 2. Peregrine Falcon nesting activity in the British Isles study area during continuous monitoring periods (Bird A
only).

to the young by the two females.

There was little or no activity after 2000 H when
continuous monitoring ceased; both females
roosted on their cliffs close to their eyries.

Sight Observations - Despite radio-location, ac-
tual sightings of birds away from their eyries were
few. On 6 occasions when female A was seen clearly,
she was apparently alone, but once she was seen
together with a male (probably her mate) 3 km from
the eyrie. Bird B was seen 3 times alone and twice

with a male at 3 km and 4.5 km away from the eyrie.
There was no indication of cooperative hunting in
these instances.

At other times, I witnessed 5 attempts to catch
prey, 4 of them above forest; twice this involved
Domestic Pigeon ( Columba livid) flocks, once a flock
of unidentified birds and twice probably a small
passerine. Each attempt was unsuccessful and was
between 0.5 km and 4 km from the eyrie.

Adults were often pursued by their young beg-

24

Richard Mearns

Vol. 19, No. 1

Table 2. Length of time (min) spent > 2 km from eyries.*

BIRD A BIRD B

Time away Time away

No Av Min Max No Av Min Max

Nestling period

3

5

2

10

2

38

15

60

Young out of nest - 1 week

4

43

5

93

2

53

15

90

- 2-3 week

9

90

10

300

-

-

-

-

- 4 week

9

77

20

150

-

-

-

-

♦Excludes trips when birds were lost, if birds returned to eyries while I was away searching.

ging for food even if not carrying prey; no young
peregrines were seen more than 2 km from either
eyrie.

Interactions with Other Birds - On 1 occasion
female A was seen in aerial dispute with one of the
neighboring Golden Eagles, together with a Merlin
( Falco columbarius). The dispute continued for 6
min, after which the peregrine flew off towards her
eyrie 3 km away. The Merlin pursued the eagle for
2 min longer, until the eagle moved south.

The general vicinity of the eagle eyrie to the
southeast seemed to be avoided, and once when

returning to her eyrie from 15 km away the pereg-
rine took a course that avoided flying directly over
the eagle nest, even though this would have been
the shortest route.

Bird A (and her mate) also briefly mobbed a
Common Buzzard (. Buteo buteo) when it was 3.5 km
from the eyrie, and chased away a Carrion Crow
(Corvus corone) from the front of the breeding cliff,
though with no serious attempt to strike it.

Diet - The prey recorded at both eyries were
predominantly Domestic Pigeons and few ‘wood-
land’ species were taken in 1978 or in other years;

Table 3. Proportion of main prey groups in the large nestling and early post fledgling periods.

TERRITORY A

TERRITORY B

1978

1977-79

1978

1977-80

(38 items)

(66 items)

(17 items)

(76 items)

Game bird

3

1

0

3

Wader

31

26

12

13

Pigeon

47

53

53

49

Passerine*

16

17

35

34

Gulls, terns, ducks

3

3

0

1

‘Woodland’ species

5

4

12

8

♦Including Cuckoo and Great Spotted Woodpecker.

Spring 1985

Peregrine Falcon in Scotland

25

most passerines were Meadow Pipit (. Anthus praten-
sis) or Starling ( Sturnus vulgaris). More waders were
recorded for eyrie A than B (Table 3).

Discussion

The activity of the adult peregrines clearly varied
from day to day depending upon hunting condi-
tions. It might also vary according to brood size, age
and sex of young, success of prey capture and aver-
age weight of prey generally available. Even with 3
or 4 young, the adults did not appear hard-pressed
to obtain food and much time was spent in leisurely
soaring or perching. In southwest England, Tre-
leaven (1977) also noted long periods of inactivity
by both sexes, in all the later stages of breeding;
birds would often remain perched for hours, and
twice birds were on the same perches for over 6 h at
a time.

During the nestling period both females re-
mained within the general vicinity of their eyries
almost all the time. This was consistent with obser-
vations by Parker (1979) at one Welsh coastal eyrie
where the female spent 89% of the time observed at
the nesting cliff. Occasionally she hunted pigeons
out over the sea when she sometimes “could hardly
be seen with binoculars”. It is also consistent with
the general observation that the female is almost
invariably present when peregrine eyries are visited
at this stage.

Adult peregrines elsewhere have been observed
seeking out perches either not obvious to their
young or away from the nesting cliff, in response to
increased and persistent aggression by their young
in demanding food (Sherrod 1983). This may
partly explain the extension of range for female A
which took place when young had been out of the
eyrie for a week and the long periods she spent
perched on nearby hills.

Ranges for all raptors are likely to be larger in the
late nestling and post-fledgling periods than at
other times in the breeding cycle, as food demands
increase and the need to defend young decreases
(see e.g. Marquiss and Newton 1982, for Spar-
rowhawks ( Accipiter nisus )). In the breeding season
the distances travelled must ultimately be limited by
the need to return with heavy prey, itself a tiring
feat. The maximum recorded distance from the
eyrie of 1 8 km is intermediate between some other
observations on peregrines. Outside the breeding
Season, when there is no need to return with prey,

the range could be larger still.

The 2 ranges did not apparently overlap, but
they may have done so outside the breeding season.
One adult female known to have been from the
eyrie 7 km WNW of eyrie B was found dead, within
the breeding season range recorded for bird B in
1978. This was in December 1980, when the bird
flew into a stone wall. Other untagged peregrines
breeding nearby could have hunted in the same
areas or flown over them in order to get to low
ground, though no intruding peregrines were seen
during the telemetry work.

Golden Eagles are dominant over peregrines in
choice of eyrie (Ratcliffe 1980) and probably over at
least part of a hunting range. Flying around a Gold-
en Eagle territory, rather than directly over it,
would involve less expenditure of energy and time
if it avoided a dispute with an eagle, especially when
carrying prey. Meinertzhagen (1959) once saw a
peregrine robbed of a grouse kill by a Golden Eagle.

Throughout, both females apparently hunted
over all types of habitat within their recorded
ranges, including both young and mature conifer
plantations. Catching prey, such as Domestic Pi-
geons, above forest is unlikely to be a problem
(Mearns 1983), but the trees offer immediate re-
fuge for prey being chased and could reduce the
success rate.

Some of the waders recorded as food could have
been taken as they flew past on migration and some
may have come from upland breeding areas, but
most were probably from low ground. Even though
there was less information on the range of female B,
she (and her mate) did not apparently hunt over the
lower ground as much as the birds at eyrie A, as
fewer waders were recorded as prey.

Acknowledgments

I thank the Forestry Commission for permission to work on
their ground and various members of their staff for help that they
gave, in particular the late Alec Marshall. I also thank A. Allison
and Dr. M. Marquiss for help with identification of prey; and Dr.
M. Marquiss and Dr. I. Newton for constructive comments on the
original drafts of this paper.

Literature Cited

Enderson, J.H. and M.N. Kirven. 1983. Flights of

nesting Peregrine Falcons recorded by telemetry.

Raptor Res. l7(2):33-37.

26

Richard Mearns

Vol. 19, No. 1

Kenward, R.E. 1978. Radio transmitters tail-mounted
on hawks. Ornis Scand. 9:220-223.

Kumari, E. 1974. Past and present of the Peregrine Fal-
con in Estonia. In Estonian wetlands and their life.
Valgus, Tallinn, pp 230-253.

Marquiss, M. and I. Newton. 1982. A radio tracking
study of the ranging behaviour and dispersion of
European Sparrowhawks Accipiter nisus. ]. Anim. Ecol.
51:111-33.

Mearns, R. 1983. The diet of the Peregrine in south
Scotland during the breeding season. Bird Study
30:81-90.

Meinertzhagen, R. 1959. Pirates and Predators: The
piratical and predatory habits of birds. Oliver and
Boyd, Edinburgh and London.

Parker, A. 1979. Peregrines at a Welsh coastal eyrie.
Brit. Birds 72:104-114.

Porter, R.D. and C.M. White. 1973. The Peregrine
Falcon in Utah, emphasizing ecology and competition
with Prairie Falcon. Brigham Young University Sci-
ence Bulletin 18:1-74.

Ratcliffe, D.A. 1980. The Peregrine Falcon. Berk-
hamsted. pp 416.

Sherrod, S.K. 1983. Behavior of Fledgling Pereg-
rines. The Peregrine Fund, Inc., Colorado, pp 202.

T releaven, R.B. 1977. Peregrine. The private life of the
Peregrine Falcon. Headline Publications, Penzance.

Weir, D.N. 1978. Wild Peregrines and Grouse. The Fal-
coner 7:98-102.

Connansknowe, Kirkton, Dumfries, SCOTLAND.

Received 28 January 1983; Accepted 15 April 1984

HOW EFFECTIVE ARE HUNTING PEREGRINES?

Rune Roalkvam

Abstract - Data on Peregrine Falcon {Falco peregrinus) hunting success are reviewed. Breeding adults have a mean
success rate of 34.9%, significantly higher than adults in the non-breeding season which have a rate of 12.7%. Juveniles
have a success rate of 7.3%, significantly lower than non-breeding adults. Factors affecting hunting success rates are
discussed.

Since Rudebeck (1950-51) published his results
on the hunting efficiency of some migrating rap-
tors, the hunting abilities of the Peregrine Falcon
(Falco peregrinus) have been widely discussed. I have
analyzed available data on this subject in order to
trace any differences in hunting success between
different categories of peregrines.

Results

Data on peregrine hunting efficiency are pre-
sented in Table 1. In addition, Monneret (1973)
found a success rate of a. 10% (37 out of a. 400
attacks) for peregrines in a French mountain area.

Table 1. Studies on Peregrine Falcon hunting success

The variation in hunting performance is enor-
mous (7 - 83% success rate). Juveniles are significantly
less successful than adults outside the breeding sea-
son, with success rates of 7.3 and 12.7%, respec-
tively (X2 = 7.2 , P < 0.01, sources 1,7,12 and
3,5,7,15 (Table 1)). A few of Rudebeck’ s (1950-51)
birds may be adults, so the difference is probably
slightly greater.

Breeding adults are more successful (34.9%)
than adults outside the breeding season (12.7%) (X2
= 149.1, P < 0.001, sources 2,3,4,6,9,10,11,13,14
and 3,5,7,15 (Table 1)).

Data on sexual differences in hunting efficiency

Author

Hunting Success %

N

Comments

1. Rudebeck 1950-51

7.3

260

Migration

2. Hantge 1968

17.0

69

Breeding $

"

11.0

121

Breeding <?

3. Lindberg 1975

13.7

350

Winter, ad.$

4.

13.7

51

Breeding

5. Clunie 1976

9.6

62

Winter, ad. 9

6. Parker 1979

15.0

83

Breeding $

"

17.0

30

Breeding <?

7. Dekker 1980

7.7

674

Migration

"

9.8

215

Adults

"

7.1

363

Juveniles

8. Hantge 1980

10.8

529

All year (only adults?)

9. Treleaven 1980

69.0

45

Breeding, “High Intensity”

"

30.0

10

Breeding, “Low Intensity”

10. Bird & Aubry 1982

35.0

197

Breeding pair

11. Cade 1982

83.2

183

Breeding <? (“Red Baron”)

12.

40.0

25

Subadults

13.

31.0

32

Breeding

14. Thiollay 1982

25.4

318

Breeding Pair

"

16.5

<?

"

23.3

9

"

37.8

Co-operative

15. Olsen & Roalkvam(unpub.)

13.7

453

Winter, ad. 9

27

Raptor Research 19(1 ):27-29

28

Rune Roalkvam

Vol. 19, No. 1

in breeding peregrines are too scarce to warrant an
analysis, but Thiollay (1982) found that co-
operative hunts were significantly more successful
than when either bird hunted alone.

Discussion

Although there is great variation in recorded
hunting success, most studies reveal a success rate
of 10 - 40%. This rather low rate is to be expected
when predation is an important mortality factor for
the prey species involved. The “life - dinner princi-
ple” has been put forward by Dawkins and Krebs
( 1979) to explain this: rabbits run faster than foxes
because the rabbit runs for its life while the fox is
only running for its dinner. Selection pressures are
therefore stronger in improving the prey’s anti-
predator strategies than on the ability of predators
to make successful hunting attempts. It is also to be
expected that the success rate is lower for a pre-
dator (e.g. a peregrine) hunting evasive and agile
prey than for a predator hunting less evasive prey,
e.g. some fish species or insects (see Curio
1976: 193).

That juveniles are less able hunters than are
adults is not surprising, as learning is very impor-
tant in shaping hunting efficiency. Newly fledged
peregrines often make attacks on flowers and in-
sects as well as on more relevant prey. For a detailed
account of the ontogeny of the behavior of young
peregrines, see Sherrod (1983).

The higher hunting efficiency of breeding
peregrines relative to birds outside the breeding
season is interesting and has been noted by several
authors, e.g. Dekker (1980) and Bird and Aubry
(1982). This is often explained by a presumed
higher motivation to make successful kills when
hunting for young (Dekker 1980), resulting in
more persistant pursuits by these birds than by
non-breeding adults. There are other factors which
may be equally important in explaining the differ-
ence: birds often form flocks in the non-breeding
season, while they space out in the breeding season.
Flocks are more vigilant and individuals harder to
catch than lone birds (Kenward 1978). Further,
there are large numbers of young, inexperienced
birds during summer which should be easier to
catch. It may also be that the difference in available
prey species between seasons may affect the overall
success rate. It is well documented that hunting
success varies with prey species (Bird and Aubry

1982; Thiollay 1982). Finally, cooperative hunting
which yields a higher success rate (Thiollay 1982) is
restricted to the breeding season at least in areas
where the peregrines are migratory.

Individual differences in hunting ability also
occur. A notable exception in Table 1 is the “Red
Baron”, a released tiercel hunting from high
perches over coastal marshes. In 1979 the Baron
caught 95 birds in 102 hunts, a success rate of 93%
(Cade 1982).

The availability of large open areas, e.g. coastal
marshes, lakes or sea, is presumably favorable for
hunting peregrines. Hunt et al. (1975) noted that
peregrines sometimes missed intentionally and re-
peatedly in their stoops on released pigeons. When
the pigeon took to the air, the falcon would guide it
toward the ocean where escape possibilities were
less. Also, the availability of suitable perches to hunt
from is important. Treleaven (1980) observed that
“still hunting” from a perch was more successful
than when hunting “waiting on” on the wing.

Treleaven (1961, 1980), Hantge (1968), Dekker
(1980) and Ratcliffe (1980) agree that a large por-
tion of the peregrine’s hunting attacks are not
“serious”. Hantge states that 20-40% of the attacks
are of this category. Treleaven (1980) introduces
the terms “Low Intensity” and “High Intensity”
hunting to distinguish between the serious hunts
and the others, with a success rate of 30% and 69%,
respectively. The distinction between the two
modes of hunting is however subjective and of little
use in many situations. Even serious hunts may be
given up long before contact is made. When the
falcon is hunting from a perch, the hunt often lasts
for only some seconds. In such instances it is virtu-
ally impossible to assess the “seriousness” of the
hunt.

Playful hunting is well documented for young
peregrines (Parker 1979; Sherrod 1983) where it
occurs regularly when learning to hunt. In adults,
“non-serious” attacks may be involved when 1)
teaching the young to hunt, 2) chasing away intrud-
ers in the nesting area and mobbing birds, 3) testing
a flock of birds before deciding to attack. Stoops
meant to drive prey toward open areas, or to single
out an individual from a flock should be considered
part of the ordinary “serious” hunting process. The
existence of “practice” attacks only meant to perfect
hunting skills cannot be excluded, but it seems un-
likely, especially in the breeding season, that a
peregrine deliberately should avoid making a kill.

Spring 1985

Peregrine Hunting Success

29

Food is a limiting factor that influences the breed-
ing success (e.g. Thiollay 1982), and each extra prey
(which can be cached for later use) reduces the
possibility that the young may starve before fledg-
ing.

Acknowledgments

I want to thank the reviewers for valuable comments on an
earlier draft of this paper.

Literature Cited

Bird, D.M. and Y. Aubry. 1982. Reproductive and
hunting behaviour in Peregrine Falcons, Falco pereg-
rinus, in southern Quebec. Can. Field-Nat. 96:167-171.
Cade, T.J. 1982. The falcons of the world. Cornell Univ.
Press, Ithaca. 192 pp.

Clunie, F. 1976. A Fiji Peregrine (Falco pregrinus) in an
urban-maritime environment. Notornis 23:8-28.
Curio, E. 1976. The ethology of predation. Zoophysiol-
ogy and ecology 7. Springer-Verlag, Berlin. 250 pp.
Dawkins, R. and J.R. Krebs. 1979. Arms races between
and within species. Proc. R. Soc. Lond. B. 205:489-51 1.
Dekker, D. 1980. Hunting success rates, foraging habits,
and prey selection of Peregrine Falcons migrating
through central Alberta. Can. Field-Nat. 94:371-382.
Hantge, E. 1968. Zum Beuteerwerb unserer Wander-
falken. Orn. Mitt. 20:211-217.

Hantge, E. 1980. Untersuchungen uber den Jagder-
volgr mehrerer europaischer Greifvogel. J. Orn.
121:200-207.

Hunt, W.G., R.R. Rogers, and D. Slowe. 1975. Migrat-
ory and foraging behavior of Peregrine Falcons on the
Texas coast. Can. Field-Nat. 89:1 1 1-123.

Ken ward, R. 1978. Hawks and doves: attack success
and selection in Goshawk flights at Woodpigeons./.
Anim. Ecol. 47:449-460.

Lindberg, P. 1975. Pilgrimsfalken i Sverige. Svenska
Naturskyddsforeningen, Stockholm. 94 pp.

Monneret, R.-J. 1973. Techniques de chasse du Faucon
Pelerin Falco peregrinus dans une region de moyenne
montagn e.Alauda 41:403-412.

Parker, A. 1979. Peregrines at a Welsh coastal eyrie.
Brit. Birds 72:104-1 14.

Ratcliffe, D. 1980. The Peregrine Falcon. Poyser,
Calton. 416 pp.

Rudebeck, G. 1950-51. The choice of prey and modes of
hunting of predatory birds with special reference to
their selective effect. Oikos 2:65-88, 3:200-231.

Sherrod, S.K. 1983. Behavior of fledgling Peregrines.
Pioneer Impressions, Ft. Collins. 202 pp.

Thiollay, J.-M. 1982. Les ressources alimentaires, fac-
teur limitant la reproduction d’une population in-
sulaire de Faucons Pelerins, Falco peregrinus brookei.
Alauda 50:16-44.

Treleaven, R.B. 1961. Notes on the Peregrine in
Cornwall. Brit. Birds 54:136-142.

Treleaven, R.B. 1980. High and low intensity hunting
in raptors. Z.fur Tierpsychol. 34:339-345.

Department of Animal Ecology, Museum of Zoology, N-5014
Bergen University, Norway. Present Address: Rosenli 15,
N-4000 Stavanger, Norway.

Received 20 April 1983; Accepted 1 August 1984

POSITION ANNOUNCEMENT -- POSTDOCTORAL ASSOCIATE (70%) — Location: Department
of Veterinary Biology, College of Veterinary Medicine, University of Minnesota. Requirements: Ph.D. in
Physiology and one year of research experience working with avian species required. Two years research
experience to include an interest and experience in fields of digestive function or avian energetics is
desirable. Duties: The individual in this position would be expected to perform studies on neutral and/or
hormonal regulation of avian GI motility and secretion. Salary: $ 1 4,000/9 months (70% time). Application
Deadline: 15 July 1985. Beginning Date: 1 September 1985.

Contact: Dr. Gary E. Duke, Department of Veterinary Biology, College of Veterinary Medicine, Univer-
sity of Minnesota, 295 AnSci/Vet Med Bldg., St. Paul, MN 55108.

The University of Minnesota is an Equal Opportunity Educator and Employer and Specifically
Invites and Encourages Applications from Women and Minorities.

30

Vol. 19, No. 1

Dissertation Abstracts

A Study of the Black-shouldered Kite Elanus caeruleus

Colour-marked Black-shouldered Kites {Elanus caeruleus ) were studied during 1977-1978 in a 6900 ha area near
Settlers (24° 572S; 28° 33E) in the Springbok Flats, South Africa. Most of the annual rainfall of 601 mm fell during the
summer months. About 75% of the area was cultivated. Results from ringing and moult studies during 1970-1976 in a
wider area of the Transvaal Province were incorporated into the present work.

The study aimed to describe the basic biology of kites and to investigate the role of food supply in their behaviour and
breeding. About 97% (n = 3408) of prey found in pellets were small mammals (Mendelsohn, J.M. 1982. African J. Zool.
17:197-210). Three rodents, Otomys angoniensis, Rhadbomys pumilio and Praomys natalensis, formed about 92% of the
weight of the kites’ prey. Regular trapping suggested that rodent densities changed substantially during the study.
Measures of the food intake of kites showed changes that closely matched variation in rodent numbers (Mendelsohn,
J.M. 1982. Durban Mus. Novitates 13:75-1 16).

The birds usually caught 1-3 prey items each day by hovering and perch-hunting. The proportions of hovering
(about 30%), perch-hunting (70%) and the duration of hunting each day varied greatly. Non-breeders probably hunted
for average periods of about 2 h each day while breeding males hunted for about 4 h. The 2 hunting methods differed in
several ways; when hovering, prey was caught more rapidly than when perch-hunting, but hovering was energetically
more expensive. Hovering was probably used to obtain prey as rapidly as possible, while perch-hunting helped
minimize energy costs. It would be important to economize on daily energy expense since the unpredictability of prey
capture means that excessive energy spent in hunting could not be replaced with certainty.

Individual kites showed a high degree of variability in their social behaviour and dispersion (Mendelsohn, J.M. 1983.
Ostrich 54:1-18). Residents were unpaired, paired or breeding birds; unpaired kites experienced the poorest, and
breeders the best, feeding conditions. Males usually established territories and remained resident as long as food supply
allowed. Territories with good feeding conditions were at a premium and nomadic males probably spent long periods
searching for suitable vacancies. Females seldom occupied territories alone but usually settled with territorial males.
Most females settled to pair with males when most pairs were starting to breed. Females also deserted territories more
readily than males and moved around probably in search of those males with territories holding the best breeding
prospects. There were always more males than females in the study area and this could have allowed females to change
territories often.

Many males and females were resident for short periods and, as a result, the average monthly turnover of residents
was about 26%. These short-term residents and records of great concentrations of kites suggest that kites are often
eruptive and nomadic, particularly when rodent densities vary erratically. Information concerning changes in food
supply is probably exchanged at communal roosts; kites roosted communally when feeding conditions were poor. Such
itinerant behaviour contrasts with the site-tenacity of some individuals that remained resident for most or all of the
census period.

Residents bred repeatedly and opportunistically at any time of the year. Some males made up to 7 breeding attempts
in 19 months but most failed, particularly at early stages of the cycle. The average duration of breeding was: pre-laying
(24 d), incubation (31 d), nestling period (35 d) and post-nestling period (82 d). Most adult females deserted soon after
the young left the nest and probably searched for unpaired males to attempt breeding again. The flying young were fed
by adult males for the remaining part of the post-nestling period. For males, each successful breeding cycle lasted on
average 172 d. Some males started breeding again immediately after the young became independent, and thereby
breeding twice in one year. Females, with a shorter participation in each breeding cycle, could breed three times each
year.

Breeding females seldom hunted. Males supplied them and the young with food. Many breeding attempts failed,
probably because of frequent food shortages. Females accumulated energy reserves during the pre-laying period which
helped them produce eggs and probably withstand food shortages later in the cycle. Other adaptations to future feeding
conditions are indicated. Kites might stop breeding if poor feeding conditions early in the cycle indicate that greater
food demands are unlikely to be met later during the nestling period. They may also time breeding on the basis of the
amount of breeding activity in their rodent prey, again as an indication of expected food availability (Mendelsohn, J.M. ,
In press. Proc. 5th Pan- African Ornith. Congr.).

It is suggested that breeding females do not hunt and remain largely inactive at the nest so that they can conserve
energy reserves. Further, the fact that females are larger than males enables them to store proportionately greater
reserves. Males probably do not store energy because the increased weight of reserves would hinder their flying ability
in catching prey.

30

Spring 1985

Dissertation Abstracts

31

Residents in the study area defended territories (feeding and breeding) against all conspecific intruders. Tail wagging
was probably an aggressive display to warn other kites away. The most violent conflicts, sometimes involving physical
contact, were between neighbouring residents; intruding nomads were repulsed more readily.

Kites showed several responses to excessive heat and cold. They usually perched in the shade of trees during the hot,
midday period, or soared sporadically if they were hunting. Most nests were built in the SW sectors of trees where
incubating females and nestlings were protected from direct sun. In the early morning kites usually perched low above
the ground where they were less exposed to cold wind. Similarly, they roosted within the foliage of trees during winter,
where they were more protected from cold wind than on perches on the outermost branches of trees, their roost sites at
other times.

Most kites moulted during summer and this seasonality contrasted with the variable timing of their breeding. Primary
feathers moulted in a single sequence from the inner wing outwards, but sequences in the secondaries and rectrices were
variable, as in many raptors.

Several size differences were found between males and females and between adults and 2 age groups of subadults.
Changes in the weights of subadults during the year, and probably in those of adults, corresponded to changes in food
supply. Males that remained resident for long periods were probably morphologically more ‘typical’ than short-term
residents. The physical features of males may therefore in part determine their ability to catch prey and consequently to
pair and breed successfully. The performance of females, however, may depend more on their ability to choose mates
and territories which will provide the best feeding conditions.

In conclusion, I suggest that unpredicted fluctuations in feeding conditions play a central role in the biology of kites.
Such fluctuations occur at 2 levels, one on an hourly or daily basis and the other on a weekly or monthly scale. The
capture of large and irregularly spaced prey is an unpredictable event and several aspects of hunting behaviour and
daily activity are geared to meeting the general requirement of obtaining prey as rapidly and at the least possible energy
expense.

Many social, spatial and breeding strategies are probably adaptations to feeding conditions that fluctuate over longer
periods. While kites often survive and occasionally breed in situations of moderate food supply, the ‘slumps’ and ‘gluts’
in prey numbers are the periods when selection is most severe. It is then that kites will either manage to survive or will so
capitalize on a superabundant food supply that they leave great numbers of offspring. Mendelsohn, J.M. 1981. Ph.D.
Dissertation. University of Natal, Pietermaritzburg, South Africa. 285 pp.

Uniformity in Relative Habitat Selection by Buteo lineatus and B. platypterus
in Two Temperate Forest Regions

I have examined nest site habitat use and selection by 2 woodland hawk species, Buteo platypterus (Broad-winged
Hawk, BWH), and B. lineatus (Red-shouldered Hawk, RSH). The hypothesis tested was that species select similar
nesting habitat in dissimilar regions after accounting for differences in habitat availability.

Study sites were located in northeast Wisconsin (WI) and in western Maryland (MD). Twenty-seven characteristics
were measured at active nest sites from 1978 through 1982. Also, random samples were collected to estimate habitat
availability. Sample sizes were: 87 MD BWH, 34 WI BWH, 30 MD RSH, 22 WI RSH, 100 MD random, and 73 WI
random. The two regions differed in structural features of the available habitat, and both species selected only portions
of the available habitat within each region. Also, habitat use by BWH and RSH differed between regions.

To determine whether relative habitat selection differed between regions for each hawk species, I adjusted for
regional differences using a series of ‘Z’ score rescalings of the availability data. Study area differences were eliminated
by these transformations. The resultant data vectors were then applied to the specific hawk data sets for tests of habitat
selection uniformity. Relative habitat selection was uniform between regions. For the BWH, only 2 of 18 rescaled
variables were different between regions. Three of 18 rescaled variables were different between regions for RSH.

I contend that these two species have uniform patterns of habitat selection. Differences in habitat use between regions
may merely reflect habitat availability related to differences in scale between regions. Titus, Kimberly. 1984. Ph.D.
Dissertation, Univ. of Maryland, Cantonsville. Dissertation directed by James A. Mosher, Appalachian Environ-
mental Laboratory.

32

Vol. 19, No. 1

News and Reviews
RESOLUTIONS

At the 1984 annual meeting held in Blacksburg, Virginia, the following resolutions were adopted by the Board of
Directors of The Raptor Research Foundation, Inc.

RE: In Appreciation of the Hawk Mountain Sanctuary Association

WHEREAS, in 1934, the Hawk Mountain Sanctuary Association established the first formal sanctuary
for birds of prey anywhere in the world; and

WHEREAS, the programs initiated by the Hawk Mountain Sanctuary Association 50 years ago have
grown considerably, providing many educational and research opportunities; and

WHEREAS, the hard work of the people in the Hawk Mountain Sanctuary Association has facilitated
the viewing and appreciation of raptors during migration and at other times by approximately 50,000
people annually; and

WHEREAS, the staff at the Hawk Mountain Sanctuary has taken an active role in many raptor
conservation issues and programs outside the sanctuary;

NOW, THEREFORE, BE IT RESOLVED that The Raptor Research Foundation, Inc., commends the
Hawk Mountain Sanctuary Association for its foresight in recognizing the importance of habitat preserva-
tion for birds of prey and for their ongoing efforts to provide educational and research opportunities for
the public; and

BE IT FURTHER RESOLVED that The Raptor Research Foundation, Inc., encourages the Hawk
Mountain Sanctuary Association to continue in its leadership role in raptor conservation.

THE RAPTOR RESEARCH FOUNDATION, INC.

Jeff Lincer

President, The Raptor Research Foundation, Inc.

WITNESS my hand and official seal, this 28th day of January, A.D. 1985

Ruth K. Trembath

Notary Public, State of Florida

RE: In Support of Steel Shot for Migratory Game Bird Hunting

WHEREAS, lead poisoning has been documented in waterfowl since 1900; and

WHEREAS, the U.S. Fish and Wildlife Service estimates that approximately 2 to 3 million waterfowl die
annually from lead poisoning; and

WHEREAS, lead poisoning has been documented in our national symbol, the endangered Bald Eagle;
and

WHEREAS, a growing body of evidence indicates that many Bald Eagles die annually from lead
poisoning; and

Spring 1985

News and Reviews

33

WHEREAS, lead presence and/or poisoning has also been documented in a number of raptors,
including Prairie Falcons, kestrels, Red-tailed Hawks, and California and Andean Condors; and

WHEREAS, steel shot is non-toxic when ingested and an acceptable substitute for toxic lead shot;

NOW, THEREFORE, BE IT RESOLVED that The Raptor Research Foundation, Inc., supports the
complete conversion to steel shot for all migratory game bird hunting; and

BE IT FURTHER RESOLVED that The Raptor Research Foundation, Inc., requests that the Depart-
ment of the Interior and the U.S. Fish and Wildlife Service establish nationwide non-toxic steel shot
regulations for all migratory game bird hunting as soon as possible, but no later than 1989.

THE RAPTOR RESEARCH FOUNDATION, INC.

Jeff Lincer

President, The Raptor Research Foundation, Inc.

WITNESS my hand and official seal, this 28th day of January, A.D. 1985

Ruth K. Trembath

Notary Public, State of Florida

RE: Biological Survey of the United States

WHEREAS, there exists both scientific and public awareness of the effects of acid rain, pesticides, and
industrial pollutants on the environment; and

WHEREAS, no systematic national survey has been conducted to collect basic information on the
existing composition of our flora and fauna; and

WHEREAS, without more extensive knowledge of the various species of biota and their interaction, it is
virtually impossible to understand and, effectively, mitigate human impacts on natural habitats; and

WHEREAS, several other countries, including Australia, Hungary, India, Israel, New Zealand, and the
Soviet Union, have recognized the need and initiated comprehensive biological surveys to address similar
issues;

NOW, THEREFORE, BE IT RESOLVED that The Raptor Research Foundation, Inc., supports the
establishment of a comprehensive Biological Survey of the United States; and

BE IT FURTHER RESOLVED that this program be designed to (1) describe the plants and animals of
the United States, (2) fund basic taxonomic research of the biota, and (3) produce needed publications
including identification manuals, species catalogues, and atlases of biotic surveys.

THE RAPTOR RESEARCH FOUNDATION, INC.

Jeff Lincer

President, The Raptor Research Foundation, Inc.

WITNESS my hand and official seal, this 28th day of January, A.D. 1985

Ruth K. Trembath

Notary Public, State of Florida

34

News and Reviews

Vol. 19, No. 1

Proceedings — Second Symposium On African Predatory Birds. — The proceedings of this symposium, held in
August 1983 at Golden Gate National Park, South Africa, are now available. The volume contains 25 full papers and 1 8
abstracts, presenting a wealth of new information and several reviews. A limited edition of 200 copies is available for sale
R22,00 (postage included). Orders should be sent to the Natal Bird Club, % Durban Natural History Museum, P.O. Box
4085, Durban 4000, South Africa.

Guide to Owl Watching in North America. Donald S.
Heintzelman, 1984. Winchester Press, Piscataway, New Jersey.
Xiii + 193 pp., 65 photos, 2 figures, 2 tables. Paperback: $8.95.
Geographic scope: North America south to Mexico. — The stated
purpose of this book is to stimulate interest in owl study and
conservation via recreational owl watching, and in this the author
has succeeded. Functionally, the book consists of three parts. The
first part is an owl watching primer containing species accounts,
chapters on owl watching methods and equipment, pellets and
food habits, migrations, survival adaptations and conservation.
The second part contains lists of field marks and abundant photos
as further aids in identification, while the final part comprises state
by state (and province by province for Canada) accounts of where
to go to observe owls. The text is well written with a timely
conservation-minded undertone, which reflects the author’s
background.

The species accounts include information on size, field recogni-
tion, flight style, voice, nest and eggs, food, habitat and distribu-
tion presented in a clear, concise manner. Their brevity is desira-
ble considering the intended audience and those desiring further
details can consult any of a number of sources, some of which
Heintzelman refers to in the suggested reading list. However,
several of the range descriptions could be updated. For instance,
no mention is made of the Boreal Owl in northern Wyoming and
Colorado, where breeding populations are known to occur, and
the range description for the Flammulated Owl leads one to be-
lieve it is absent from Colorado.

Heintzelman’s discussion of owl watching methods is diverse,
but too brief. In particular I thought the section on nocturnal owl
watching could be expanded. Mention is made that tapes of owl
calls should be played for at least 2 min for each species. This
statement is open-ended and should be considered further. While
censusing Eastern Screech Owls in Connecticut, my mean re-
sponse time for 271 owls was slightly over 3 min, while thus far for
Great Horned Owls in Utah it is over 6 min, with some birds not
responding until several minutes after the tape is shut off.
Siminski (unpublished M.S. Thesis, Bowling Green University,
1976) found mean responses in Ohio for male Great Horned Owls
occurred after 25 played vocalizations and for females after 28
played vocalizations. These studies indicate that while some
species and individuals respond quickly to the tape, others are

considerably slower and for these, 10 min of tape playback fol-
lowed by a 5-10 min listening period might be appropriate. The
author drives home a good point regarding police relations while
observing owls at night, as any owl enthusiast can attest to the time
he’s been checked-out by the local Gendarmes for conducting
suspicious activities.

In the section on owl pellets there is a guide to their identifica-
tion that lists owl species, pellet size and pellet characteristics. The
pellet descriptions range from quite detailed for the Great
Horned Owl to extremely vague for the Barred Owl, whose pellets
are characterized as “compact”. I found some of the terminology
ambiguous: large versus very large, gray versus dark gray, and I
contend that use of this guide will result in a high proportion of
misidentifications. To a great extent this ambiguity reflects the
within species variability of pellets, with pellet shape, size, color
and composition depending on diet, season and age of the bird.
Perhaps photographs illustrating an assortment of pellets for each
species would be more helpful, although identification of pellets
from an unknown source is almost always questionable. Heintzel-
man’s stand on taking detailed locality data at the pellet collection
site and using a reference skull collection in identifying prey is to
be commended. A table of nest box dimension, based primarily on
the work of Hamerstrom (Birds of Prey of Wisconsin, Dept, of
Natural Resources, Madison, 1972) is presented, but entrance
width for the Saw-whet Owl is given as 2.75 in, which differs from
Hamerstrom’s value of 2.5 in.

Photographs are black and white and of adequate quality, but
the lists of field marks opposite them are at times repetitive. The
list of owl watching sites is extensive, containing 224 entries, each
with a brief habitat description, access routes and list of species to
be on the lookout for. State and national parks and wildlife areas
are heavily represented. Finally, there are appendices of acciden-
tal occurrences of owl species, conservation organizations and an
owl pellet data form. I question the appropriateness of the first of
these because it contains only a single species entry which could
have been included in the species accounts. Despite its shortcom-
ings, this book presents a wide variety of information of definite
value for the beginning owl student and I wish it had been availa-
ble some years ago when I first began to observe owls. — D.T.
Walsh.

INSTRUCTIONS FOR CONTRIBUTORS TO RAPTOR RESEARCH
Effective with Volume 19, 1985

The editorial office of the Raptor Research Foundation, Inc.,
welcomes original reports, short communications and reviews
pertaining to the ecology and management of both diurnal and
nocturnal predatory birds for publication in Raptor Research. Pub-
lication in the journal is open to anyone, regardless of current
membership in the Raptor Research Foundation, Inc. Contribu-
tions are welcomed from throughout the world but must be writ-
ten in English. Submit all contributions to the Editor, Clayton M.
White, Department of Zoology, 161 WIDB, Brigham Young Uni-
versity, Provo, Utah, 84602, USA. Referees and associate editors
review each manuscript submitted for originality of data, ideas or
interpretation, for accuracy, conciseness, and clarity. With the
exception of abstracts, manuscripts submitted for consideration
must not have been published or concurrently be under consid-
eration for publication elsewhere.

Manuscript Preparation

Submit a typewritten original and four copies of the text, tables,
figure headings and all other materials for use by the referees.
Submit four copies of all illustrations. All typewritten material
must be double-spaced on one side of 8lA> x 1 1-inch (2 1 Vi x 28cm),
good quality, bond paper, with at least 1 inch (2lA cm) margins. Do
not use erasable, mimeo, or light-weight bond paper. Copies may
be Xerox or carbon reproductions of good, clear quality. Number
pages through the Literature Cited section of the manuscript.
Type the author’s name in the upper right-hand corner of every
page. Submit each table on a separate unnumbered page; combine
legends for illustrations on one unnumbered page whenever pos-
sible. Material submitted in tables or illustrations should not be
repeated in the text of the manuscript. Write mathematical for-
mulas on one line whenever possible. Each manuscript should
include a cover page containing a concise, informative, full title, a
shortened version of the title (not to exceed 35 characters in
length) to be used as a running head, and the name(s) of the
author(s) as it should appear in print. Avoid footnotes and hyphen-
ation.

Address for each author at the time the research was conducted
should be listed at the end of the manuscript following the Litera-
ture Cited section. Present address of author(s), if different,
should be listed, as well as name and full address to whom proof is
to be sent. If you are no longer associated with the institution
where the research was conducted, but you wish to credit that
institution, it may be mentioned first.

Provide an abstract for each manuscript more than four
double-spaced typewritten pages in length. Abstracts are submit-
ted as a separate section from the main body of the manuscript and
should not exceed 5% of the length of the manuscript. The
abstract should recapitulate the overall findings of the research
and should be suitable for use by abstracting services.

Authors should cite the scientific and (if any) common names of
all species at first mention in both the abstract and the main text of
the manuscript. Names for birds should follow those in the A. O.
U. Check-list of North American Birds (sixth ed., 1983), or an
appropriate equivalent. Subspecific identification should only be
cited when pertinent to material presented in the manuscript. In
all cases where the scientific and common names are cited to-
gether, the common name should be placed first.

Metric units should be cited for all measurements in accordance
with Systeme International D’Unite (SI) notation and conventions.
Abbreviations of statistical terminology and mensural units should
conform with the Council of Biology Editors (CBE) Style Manual
(fourth ed., 1978, American Institute of Biological Sciences, 1401
Wilson Blvd., Arlington, Virginia, 22209, USA). Use the 24-hour

clock (e.g., 0830 and 2030) and “continental” dating (e.g., 1
January 1984). Consult the CBE Style Manual and current issues
of Raptor Research on particular matters of style.

Raptor Research is published in a double-column format. There-
fore, authors should consider whether a table or illustration can
best be presented in a single-column, with the vertical axis of the
table or illustration longer than the horizontal, or covering an
entire page width.

Tables should not duplicate material in either the text or illustra-
tions. Tables are typewritten, double-spaced throughout, in-
cluding title and column headings, should be separate from the
text and be assigned consecutive Arabic numerals. Each table must
contain a short, complete heading. Footnotes to tables should be
concise and typed in lower-case letters.

Illustrations (including coordinate labels) should be on 8V2 x
1 1-inch (2 1 V2 x 28cm) paper and must be submitted flat. Copies
accompanying the original should be good quality reproductions.
The name of the author(s) and figure number should be penciled
on the back of each illustration. All illustrations are numbered
consecutively using Arabic numerals. Include all illustration
legends together, typewritten double-spaced, on a single page
whenever possible.

Line illustrations (i.e., maps, graphs, drawings) should be ac-
complished using undiluted india ink and designed for reduction
by 1/3 to V2. Drawings should be accomplished using heavy weight,
smooth finish, drafting paper whenever possible. Use mechanical
lettering devices, pressure transfer letters or calligraphy. Type-
written or computer (dot matrix) lettering is not acceptable. Let-
tering should be large enough when submitted that it will be as
large as text type (7-10 point) when reduced by 50%. Avoid bold,
heavy or ornate letters that would tend to distract from the illus-
tration. Use a pattern of lines and dots for shading that will not
appear as a solid tone when reduced. Include a key to symbols
used within an illustration, unless the symbols are best explained
in the legend. Measurement scales (e.g., distance) should be given
in the illustration itself.

Some special symbols cannot be typeset by the printer. There-
fore, if a magnification scale is needed in connection with a
photomicrograph, for instance, the scale should be placed on the
photo itself and not in the legend.

Use of photographic illustrations is possible but requires that
prior arrangements be made with the Editor and the Treasurer.
Photographs should be glossy prints of good contrast and sharp-
ness, preferably mounted on an artist’s mounting board and sub-
mitted in approximately the same size as they should appear in
print. Photographs should be made from monochrome (“black
and white”) film whenever possible. On the back of each photo-
graph, write the author’s name and the figure number using a
special marking (“felt tip”) pen. Composite photographs should be
mounted touching one another and squared on all sides. Separate
portions of such illustrations should be identified as necessary
using adhesive transfer letters. Color photographs cannot be pub-
lished unless completely subsidized by the author(s).

Faulty illustrations may be returned to the author. If they are
fixed by a scientific illustrator under the Editor’s direction, the
author will be charged.

Literature Cited in the manuscript should be listed alphabetically
at the end of the text and Acknowledgements. Authors should
ensure that all text citations are listed and checked for accuracy. If
five or fewer citations appear in the text, place the complete
citation in the text, followng these examples: (Brown and Ama-
don. Eagles, hawks and falcons of the World. McGray-Hill, New
York, 1968), or Nelson {Raptor Res. 16(4):99, 1982). If more than

35

36

Instructions for Contributors

Vol. 19, No. 1

three citations are referenced, each should include author and
year (e.g., (Galushin 1981)), or, in a citation with three or more
authors, the first author and year (e.g., (Bruce et al. 1982)). Cita-
tions of two or more works on the same topic should appear in the
text in chronological order (e.g., (Jones 1977; Johnson 1979 and
Wilson 1980). Unpublished material cited in the text as “pers.
comm.,” etc., should give the full name of the authority, but must
not be listed in the Literature Cited section. Authors should follow
the BIOSIS List of Serials (1974, Biosciences Information Service
of Biological Abstracts) as a guide for abbreviations and forms of
titles of serial publications. If in doubt as to the correct form for a
particular citation, it should be spelled out for the Editor to ab-
breviate.

Editorial review and revision processes will be conducted on man-
uscripts submitted for publicaton as regular articles or Short
Communications. Manuscripts will be critically reviewed by ref-
erees selected for competency in the subject matter of the manus-
cript. Acceptance of a manuscript for publication will depend
upon scientific merit, originality, timeliness, and suitability for the
journal. The referee’s comments and Editor’s suggestions will be
conveyed to the author. Manuscripts will generally be published in
order of receipt, although publication may be advanced or de-
layed in order to maintain balance or to group manuscripts deal-
ing with closely related subjects. Each published paper will show
the date of receipt in the Editorial Offices and the date of accep-
tance of the final revision. Excessive time taken by authors in
revising manuscripts will generally result in a delay in publication.

Proofs, typescript and reprint order forms will be sent to the senior
author unless indicated otherwise. Please inform the Editor well in
advance of any change in address or system for handling proofs.
The corrected proofs and the original typescript should be re-
turned to the Editor within 3 days of receipt. Corrections will be
made without charge but revisions done by authors will be charged
at the rate of $20.00 per hour of additional typesetting.

Commentary on articles published in Raptor Research is invited by
the Editor. Comments should be in letter form submitted in dupli-
cate to allow one copy to be forwarded to the author whose work is
being addressed. The recipient will be invited to reply. All submis-
sions should be typed, double-spaced, signed, and be as brief as
possible. Contributions to the Commentary section will be re-
viewed by the Editorial Board, which will select contributions for
publication that are most pertinent to the interests of our reader-
ship.

Announcements of noncommercial raptor news, requests for as-
sistance, etc., are invited by the Editor. Items submitted should be
typed double-spaced in Raptor Research format. Announcements
that carry a dead-line should be submitted at least six months in
advance to allow enough time for publication and response. Ad-
vertisement notices will be published free of charge providing
15% of the proceeds requested are donated to The Raptor Re-
search Foundation, Inc. All other advertisements will be charged
at a rate consistent with current publication costs in effect at the
time the ad request is received. The journal also publishes notices
about selected new books, booklets, reports, etc., that are received
in the editorial office. Authors and publishers are encouraged to
submit a copy of their material for consideration and not just an
announcement. Insure that price and source for all such material
is given. A review of material when appropriate will be requested
by the Editor and published in the journal.

Publicaton Policy

The cost of producing an issue of Raptor Research is expensive,
and membership dues alone do not meet the publication costs. In
order to defray some of the costs of publishing the journal, it is the

policy of The Raptor Research Foundation, Inc., to expect authors
of manuscripts accepted for publication to contribute to these
costs through the use of institutional, grant or contract, or other
funds available to them for this purpose. Those authors who are
able to completely subsidize publication of their papers will be
scheduled for publication in the earliest available issue of Raptor
Research following approval of galley proofs. Authors who are
members of The Raptor Research Foundation, Inc., but do not
have access to institutional, grant or contract, or other funds may
request a waiver of contributions toward publication costs. Au-
thors of lengthy manuscripts are especially encouraged to help
defray the costs of publication. It is unlikely that articles of more
than 10 printed pages (i.e., 18 typewritten, double-spaced pages of
manuscript including tables and illustrations) can be published
without a significant contribution. The ability to contribute toward
publication costs does not enter into the editorial decision re-
garding the acceptability of a manuscript.

There are some costs of publishing papers that are fixed and
cannot be waived. These include costs of alterations or redrafting
of figures, changes in proofs other than those correcting printing
errors, and changes made necessary after type has been set as a
result of excessively complicated text, or numerous tables or fig-
ures, or inclusion of color or black and white plates. Such charges
will be billed to the author by the Treasurer.

Reprint charges will be forwarded to authors at the same time as
the article galley for proofing. The Raptor Research Foundation,
Inc., will not waive the cost of reprints of articles requested by
authors. Payment in full for requested reprints must be forwarded
to the Treasurer before reprints can be mailed. However, authors
employed by government agencies, universities, or other firms
that will meet their reprint costs, may forward an intent to pay to
the Treasurer in the form of an agency voucher/purchase order.
Upon receipt of a voucher/purchase order, reprints can be mailed
to the author. The Treasurer will then bill the appropriate agency
for the reprints with the understanding that payment will be made
within 30 days.

All funds should be made payable to The Raptor Research
Foundation, Inc., and forwarded directly to the Treasurer: Dr.
Gary E. Duke, Department of Veterinary Biology, 295K Animal
Science/Veterinary Medicine Building, University of Minnesota,
St. Paul, Minnesota 55108, U.S.A. All personal contributions to-
wards publication costs, as well as other personal costs of prepar-
ing papers for publication, are tax-deductible.

Copies of these instructions are available upon request from
the Editor, to whom correspondence regarding contributions to
Raptor Research should be forwarded.

RAPTOR RESEARCH

A Quarterly Publication of The Raptor Research Foundation, Inc.

EDITOR: Clayton M. White, Department of Zoology, 161 Widtsoe Building, Brigham Young University, Provo,
Utah 84602

ASSISTANT EDITOR: Jimmie R. Parrish, Department of Zoology, 159 Widtsoe Building, Brigham Young Univer-
sity, Provo, Utah 84602
ASSOCIATE EDITORS

Jeffrey L. Lincer - Environmental Chemistry and Toxicology
Richard Clark - Order Strigiformes
Ed Henckel - Family Cathartidae
Gary E. Duke - Anatomy and Physiology

Patrick T. Redig - Pathology, Rehabilitation and Reintroduction
Jim Mosher - General Ecology and Habitat Analysis

INTERNATIONAL CORRESPONDENT: Richard Clark, York College of Pennsylvania, Country Club Road,
York, Pennsylvania 17405

Raptor Research (ISSN 0099-9059) welcomes original manuscripts dealing with all aspects of general ecology, natural
history, management and conservation of diurnal and nocturnal predatory birds. Send all manuscripts for considera-
tion and books for review to the Editor. Contributions are welcomed from throughout the world, but must be written in
English.

INSTRUCTIONS FOR CONTRIBUTORS: Submit a typewritten original and two copies of text, tables, figures and
other pertinent material to the Editor. Two original copies of photographic illustrations are required. Raptor Research is
published in a double-column format and authors should design tables and figures accordingly. All submissions must
be typewritten double-spaced on one side of 8V2 x 1 1-inch (2 W2 x 28cm) good quality, bond paper. Number pages
through the Literature Cited section. The cover page should, contain the full title and a shortened version of the title (not
to exceed 30 characters in length) to be used as a running head. Author addresses are listed at the end of the Literature
Cited section. Authors should indicate if present addresses are different from addresses at the time the research was
conducted. When more than one author is listed, please indicate who should be contacted for necessary corrections and
proof review. Provide an abstract for each manuscript more than 4 double-spaced typewritten pages in length. Abstracts
are submitted as a separate section from the main body of the manuscript and should not exceed 5% of the length of the
manuscript. Acknowledgements, when appropriate, should immediately follow the text and precede the Literature
Cited. Both scientific and common names of all organisms are always given where first appearing in the text and should
conform to the current checklists, or equivalent references, such as the A.O.U. Checklist of North American Birds (6th
ed., 1983). Authors should ensure that all text citations are listed and checked for accuracy. If five or fewer citations
appear in the text, place the complete citation in the text, following these examples: (Brown and Amadon, Eagles,
Hawks and Falcons of the World. McGraw-Hill, New York. 1968), or Nelson (Raptor Res. 16(4):99, 1982)). If more than
five citations are referenced, each should include author and year (e.g., Galushin 1981)), or in a citation with three or
more authors, the first author and year (e.g., (Bruce et al. 1982)). Citations of two or more works on the same topic
should appear in the text in chronological order (e.g., (Jones 1977, Johnson 1979 and Wilson 1980)). Unpublished
material cited in the text as “pers. comm.,” etc., should give the full name of the authority, but must not be listed in the
Literature Cited section. If in doubt as to the correct form for a particular citation, it should be spelled out for the Editor
to abbreviate.

Metric units should be used in all measurements. Abbreviations should conform with the Council of Biology Editors
(CBE) Style Manual, 4th ed. Use the 24-hour clock (e.g., 0830 and 2030) and “continental” dating (e.g., 1 January 1984).

Tables should not duplicate material in either the text or illustrations. Tables are typewritten, double-spaced
throughout, including title and column headings, should be separate from the text and be assigned consecutive Arabic
numerals. Each table must contain a short, complete heading. Footnotes to tables should be concise and typed in
lower-case letters. Illustrations (including coordinate labels) should be on 8*/2 x 1 1-inch (2 1 V2 x 28cm) paper and must be
submitted flat. Copies accompanying the original should be good quality reproductions. The name of the author(s) and
figure number should be penciled on the back of each illustration. All illustrations are numbered consecutively using
Arabic numerals. Include all illustration legends together, typewritten double-spaced, on a single page whenever
possible. Line illustrations (i.e., maps, graphs, drawings) should be accomplished using undiluted india ink and
designed for reduction by 1/3 to V2. Drawings should be accomplished using heavy weight, smooth finish, drafting paper
whenever possible. Use mechanical lettering devices, pressure transfer letters, or calligraphy. Typewritten or computer
(dot matrix) lettering is not acceptable for illustrations. Use of photographic illustrations is possible but requires that
prior arrangements be made with the Editor and the Treasurer.

A more detailed set of instructions for contributors appeared in Raptor Research, Vol. 18, No. 1, Spring 1984, and is
available from the Editor.

THE RAPTOR RESEARCH FOUNDATION, INC.
TREASURER’S OFFICE
3292 Richmond Avenue
Shoreview, MN 55112

NON-PROFIT ORG.

U.S. POSTAGE

PAID

PERMIT #66
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Raptor

A Quarterly Publication of The Raptor Research Foundation, Inc.

Number 2/3, Summer/Fall 1985

(ISSN 0099-9059)

Contents

North American Merlin Breeding Survey. Lynn w. Oliphant .'7\\ . . . .37

Food Habits and Breeding Biology of Merlins in Denali National

Park, Alaska. Karen Laing 42

Breeding Chronology and Reproductive Success of Richardson’s
Merlins in Southeastern Montana. Dale M. Becker and

Carolyn Hull Sieg 52

Productivity, Population Density and Rate of Increase of an

Expanding Merlin Population. Lynn W. Oliphant and Elizabeth Haug 56

Breeding Behavior of the Merlin: The Courtship Period.

John W. Feldsine and Lynn W. Oliphant 60

Captive Breeding of the European Merlin (Falco columbarius aesalon ).

William Ruttledge 68

Growth Rates and Food Consumption of Hand-raised Merlins.

Lynn W. Oliphant and Stacey V. Tessaro 79

Migration of the Merlin Along the Coast of New Jersey.

William S. Clark 85

Merlins and the Behavior of Wintering Shorebirds. Douglas A. Boyce, Jr 95

swithsoK^.
AUG 17 1987

ptfftARIES

Research

(Continued Inside Front Cover)

The Raptor Research Foundation, Inc.
Provo, Utah

Notes on Wintering Merlins in Western Montana. Christopher Servheen

97

Observations of Winter Food Caching by the Richardson’s Merlin.

Ian G. Warkentin and Lynn W. Oliphant 100

i

Early Nesting Records for Merlins in Montana and North Dakota.

Dale M. Becker 102

Merlin Feeding on Road-kills. Elizabeth Haug 103

Meadow Vole Predation by a Merlin Wintering in Saskatoon, Saskatchewan.

Ian G. Warkentin .104

News and Reviews .106

Persons interested in predatory birds are invited to join The Raptor Research Foundation, Inc. Dues are $1 5 per year
in the U.S., $17 per year outside the U.S., $13 per year for U.S. students, and $15 per year for students outside the U.S..
Add $2 to dues if membership is received after 15 February. The Foundation’s journal Raptor Research is distributed
quarterly to all current members. Subscription price to institutions and nonmembers is the same as regular member-
ship. Single copies and back issues are available from the Treasurer. A Contributing Membership is $25, a Sustaining
Membership is $100, and a Life Membership is $500. All contributions to The Raptor Research Foundation, Inc., are
tax-deductible.

Send requests for information concerning membership, subscriptions, special publications, or change of address to
the Treasurer. Other communications may be routed through the appropriate Officer or Board member. All inquiries
concerning the journal should be addressed to Clayton M. White, Editor, Raptor Research, Department of Zoology, 161
WIDB, Brigham Young University, Provo, Utah 84602, U.S. A.

Published quarterly by The Raptor Research Foundation, Inc. Business Office: Gary E. Duke, Treasurer, Depart-
ment of Veterinary Biology, 295K Animal Science/Veterinary Medicine Building, University of Minnesota, St. Paul,
Minnesota 55108, U.S. A. Printed by Press Publishing Limited, Provo, Utah 84602. Second-class postage paid at Provo,
Utah. Printed in U.S. A.

The Merlin

“This is one of the most dashing of all birds of prey, pursuing its

QUARRY WITH A SINGLE-MINDED TENACITY AND FEROCITY THAT CANNOT BE
BETTERED BY MANY A LARGER AND MORE SPECTACULAR RAPTOR.”

L.H. Brown, 1976.

This Issue of Raptor Research is devoted to the Merlin ( Falco columbarius) — Ed.

Adult male Richardson’s Merlin with House Sparrow — Saskatoon, Saskatchewan

Photo by L. W. Oliphant

RAPTOR RESEARCH

A QUARTERLY PUBLICATON OF THE RAPTOR RESEARCH FOUNDATION, INC.

Vol. 19

Summer/Fall 1985

No. 2/3

NORTH AMERICAN MERLIN BREEDING SURVEY

Lynn W. Oliphant

Abstract - A total of 864+ North American nestings of the Merlin ( Falco columbarius) are summarized by state and
province. Of these nestings, 812+ occurred since 1950. Productivity figures are presented for 526 successful nests. The
number of nestings of the prairie race of Merlin ( F.c . richardsonii) far outnumbered the other two subspecies and also
exhibited the highest reproductive rate.

The Merlin (Falco columbarius) has been poorly
studied in comparison to the other 4 species of
falcons common to Canada and the United States.
Trimble’s (1975) review of the status of the Merlin
concluded that “All North American Merlins have
recently decreased in reproductive success”. He
also concluded that the great plains population (F.c.
richardsonii ) was “in the greatest trouble”. Because
the studies that led to these conclusions were based
upon very limited sample sizes and more recent
data on Merlins nesting in Saskatchewan indicated
a rather healthy breeding population (Oliphant
and Thompson 1978), I felt that an attempt to
gather more information on the breeding status of
this poorly studied falcon was in order.

Methods

A “Merlin Working Group” was formed at the 1976 Raptor
Research Meeting in Ithaca, New York, and a decision to sum-
marize the breeding status of the Merlin was made at the 1977
meeting in Tempe, Arizona. Letters were mailed to over 60 per-
sons known to have an interest in Merlins, soliciting information
on the historic (pre-1950) and present (post-1950) breeding status
of the Merlin. Summaries were made for each state or province
with person(s) compiling the information indicated. The followng
criteria were used to edit submissions:

1 . Minimum accepted evidence for a “nesting” was a defending
pair seen during the breeding season.

2. Nestings at the same site in different years were counted as
separate nestings (i.e. counted as a nesting for each year).

3. Only banding age nestlings or accurate counts of newly
fledged young (branchers) were accepted for calculation of
young/successful pair.

4. Published accounts of individual nestings (usually in local
natural history journals) were included in the totals but not
generally cited individually.

Results and Discussion

Table 1 summarizes the results of the informa-
tion submitted. Almost 75% of all recorded nestings
since 1950 were Merlins (F.c. richardsonii) nesting on
the northern great plains. Of these, approximately
85% were from the Canadian prairies. Reproduc-
tive success of this population was generally good
(3-4 yg/successful nest) with the exception of the 7
nests reported for North Dakota that averaged only
2.0 yg/successful nest. Although no attempt was
made to extract information from museum collec-
tions, a cursory examination of several large in-
stitutions confirmed that the majority of Merlin
eggs collected during the late 1800’s and early
1900’s were also from the Canadian prairies. To
what extent these data reflect the true distribution
and breeding density of the Merlin or merely the
relative ease of access to breeding areas by humans
is difficult to assess. In any case, concern regarding
the recent reproductive success of F.c. richardsonii
(Fox 1971; Trimble 1975) can perhaps be allayed
somewhat on the basis of the data presented here.
Loss of suitable habitat is perhaps the most critical
factor that is presently affecting Merlins on the
prairies.

In comparison to the data on F.c. richardsonii,
breeding information on the Merlins inhabiting the
boreal forest (F.c. columbarius) is rather meager
(Craighead and Craighead 1940; Lawrence 1946;
Temple 1972). Recent reproductive success of this
population is lower than that of richardsonii (2-3
yg /successful nests in most areas). Although there
has been a decline in fall Merlin sightings at the

37

Raptor Research 19(2/3): 37-41

38

L.W. Oliphant

Vol. 19, No. 2/3

Table 1. Summary of Merlin nesting attempts and productivity.

Young/

Area and Compiler

# Nestings

Successful Pair

Details

1. Newfoundland

5 (pre-1950)

4/1

= 4.0

Includes 2 ground nests

(David Bird)

6 (1963-79)

4/1

= 4.0

20 (1969)

5/19

= 3.0

Temple, 1972. (David Bird visited
6 of these sites in 1977 - none
were occupied.)

2. Maritimes and

7 (1955-79)

7/3

- 2.3

No breeding records for New

adjacent islands
(David Bird)

Brunswick

3. Quebec

10 (1974-79)

At least 5 of these nests hatched

(David Bird)

1 (1965)

yg. and one fledged at least 4 yg.
Fyfe (pers. comm.)

4. Ontario

20(pre-1950)

Eggs or young noted at 16 of these

(Gerry McKeating)

sites.

5. N.W.T.

11 (1950-78)

16/6

= 2.7

(Richard Fyfe)

17 (1972-74)

26/6

= 4.3

6. Yukon

No nesting records

(Dave Mossop)

pre-1950
13 (1973-79)

4/2

= 2.0

8 possible additional nestings
where only single adult observed;
Nest sites new each year (not
rechecks of old sites).

7. Manitoba

2 (pre-1950)

(Bob Nero)

5 (1954-77)

4/1

= 4.0

Eggs at 3 of 4 sites where-
production not recorded;
Casual observations of another

estimated 5-6 pair in Northern
Man. (1977-79).

(Dave Mossop)

3 (1956-61)

3 fledged yg. at one site.

8. Saskatchewan

27 (1958-65)

38/11’

= 3.5

6 of the 27 known successful with

(Lynn Oliphant)

96 (1970-77)

187/47

= 4.0

unknown production and 1 known
unsuccessful.

Oliphant and Thompson, 1978.

70+(1978-82)

214/51

= 4.2

Urban Nestings

(Richard Fyfe)

14 (1967-76)

31/8

= 3.9

Includes one nest in woodpecker
hole.

9. Alberta

300 + (1968-79)

911/281

= 3.3

A single egg was taken from

(Alan Smith)

many of these nests for pesticide
analysis. Productivity is re-
ported without correction for
this bias.

10. British Columbia

4 (pre-1950)

~

F.c. suckleyi

(Keith Hodson)

2 females collected, one with

eggs; other 2 nests with un-
recorded number of young.

11 (1969-1977) 7/2 = 3.5 F.c. suckleyi

At least 5 nests where production
was not recorded were successful
(fledged young seen)

(Table 1 continued)

Summer/Fall 1985

Merlin Breeding Survey

39

(Continuation of Table 1)

Young/

Area and Compiler

# Nestings

Successful Pair

Details

11. Alaska

2 (1960’s)

5/1

= 5.0

Other nest unsuccessful. Adolphson.

(Doug Weir)

1969.

21 (1974-79)

6/2

= 3.0

Several other probable nestings
where only single bird was seen.

5-6 (1980)

--

Fledged broods

12. Washington

1 (pre-1950)

F.c. suckleyi

(Clifford Anderson)

3 (1978-79)

Unconfirmed reports of F.c.
suckleyi. One nest with a minimum
of 3 fledged yg.

13. Idaho

3 (pre 1950)

Craig and Renn, 1977

(Timothy Craig)

1 (1973)

--

1 (1975

3/1

= 3.0

4 eggs June 1

5 eggs June 5

All hatched, 2 died

1 (1977)

Same site as 1975 - unsuccessful

14. California

—

-

No known historical records -

(Jim Adamson)

All “Merlin eggs” are American
Kestrel. Recent - Merlins

observed in N. Calif, in June
and July; no nests found.

15. Nevada

__

No confirmed nestings.

(Bob Oakleaf)

16. Wyoming

1 (pre-1950)

Bent (1938)

(Bob Oakleaf)

21 (1961-79)

20/7

= 2.9

2 nests known to have failed

17. Montana

8 (1970-74)

15/5

i 3.0

Ellis (1976)

(David Ellis)

3 nests known to be unsuccess-

ful although 5 young hatched
at one site and died subsequently

(Dale Becker)

10 (1977)

4/1

- 4.0

Only one nest located, other
sites (9) had active pairs

8 (1978)

24/7

| 3.4

18 (1979)

60/17

= 3.5

All sites successful

15 (1980)

49/14

= 3.5

16 (1981)

38/10

= 3.8

18. Colorado

2 (pre 1950)

1877 and 1887

(Alan Jenkins)

19. Utah

2 (pre-1950)

Eggs collected inl868 and 1869

(Alan Jenkins)

20. North Dakota

5 (1977-78)

9/5

= 1.8

2 yg. killed by Weasel at one

(Howard Postovit)

nest; 2 other nests with addled
eggs (1 yg. and 4 addled eggs
and 2 yg. and 2 addled eggs).

(Bill Cornatzer)

5+ (pre- 1950)

5/2

I 2.5

2 (1977)

(Table 1 continued)

40

L.W. Oliphant

Vol. 19, No. 2/3

(Continuation of Table 1)

Young/

Area and Compiler

# Nestings

Successful Pair

Details

21. South Dakota

7 (1970)

15/4

= 3.8

Unknown # yg. fledged in re-

(Steve Duecker)

3 (1971)

mainting 3 sites.

2 nests checked had 2 and 4

small downies.

22. Nebraska

No historical records

(Ross Lock)

5 (1975-78)

One additional site with male

only. 1 nest with 4 newly hatched
young and 1 egg.

3 (1980)

~

2 nests with 5 yg. each (less
than 1 week old).

23. Wisconsin

3 (1966-68)

2/1

= 2

Sindelar and Jacobson 1981.

24. Michigan

3 (pre 1950)

All 3 successful

(Sergej Postupalsky)

19 (1955-67)

24/8

= 3.0

1 (1979)

-

25. New York, Penn.

-

-

No authenticated records

New England

although some recent and

(Mark Fuller and

historic sightings during

Janet Parte low)

the breeding season.

26. Minnesota

4 + (pre- 1950)

Johnson 1982 - 3 nests con-
tained 4, 4 and 2 yg. less
than 1 week old.

13(1950-64)

4/1

= 4.0

Beer, 1966

4 (1952-81)

5/1

= 5.0

Johnson, 1982

(P.B. Hofslund)

6+(1951-60)

Cedar Grove Ornithological Station in Wisconsin
(D.D. Berger, unpub. obs.) the Merlins migrating
along the east coast have increased over the past
10-15 years (W.S. Clark, F.P. Ward pers. comm.)
despite the rather low productivity figures pre-
sented here. This discrepancy between the recent
migration data and reproductive data is also true of
the Peregrine Falcon (Falco peregrinus) and needs to
be addressed.

The darkest Merlin (F.c. suckleyi) remains the
least well studied of the three North American sub-
species. Only 14 nestings potentially attributable to
this subspecies since 1950 are reported here and
production figures were available for only 2 nests
(3.5 yg./successful nest). Conclusions as to the status
of this population must await further study.

Acknowledgments

The enthusiasm and work of Bud Anderson, Chris Servheen
and Dale Becker was largely responsible for the initiation of the
“Merlin Working Group” and the publication of this special Mer-

lin issue and is gratefully acknowledged. The effort of all those
making contributions to this survey is greatly appreciated. The
author takes full responsibility for any residual errors in the re-
port.

Literature Cited

Adolphson, D. 1969. Raptor populations committee
report for 1969. Raptor Res. News 3:43-57.

Beer, J.R. 1966. The pigeon hawk in Minnesota. The
Loon 38:129-132.

Bent, A.C. 1938. Life histories of North American birds
of prey, Vol. II. U.S. Natl. Museum Bull. 170, Wash.
D.C. pp. 70-90.

Craig, T. and F. Renn. 1977. Recent nestings of the
merlin in Idaho. Condor 79:392.

Craighead, J.J. and F.C. Craighead, Jr. 1940. Nesting
pigeon hawks. Wilson Bull. 59:241-248.

Ellis, D.H. 1976. First breeding records of merlins in
Montana. Condor 78:112-114.

Fox, G.A. 1971. Recent changes in the reproductive
success of the pigeon hawk./. Wildlife Mgt. 35:122-128.

Summer/Fall 1985

Merlin Breeding Survey

41

Johnson, D.H. 1982. Raptors of Minnesota - Nestings
distribution and population status. The Loon 54:73-
104.

Lawrence, L. de K. 1949. Notes on nesting pigeon
hawks on Pimisi Bay, Ontario. Wilson Bull. 61 : 15-25.

Oliphant, L.W. and W.J.P. Thompson. 1978. Recent
breeding success of Richardson’s merlin in Saskatche-
wan. Raptor Res. 12:35-39.

Sindelar, C. and A. K. Jacobsen. 1981. Wisconsin’s sec-
ond recorded merlin nest. Pass. Pigeon 43:107-108.

Temple, S.A. 1972. Chlorinated hydrocarbon residues
and reproductive success in eastern Northern Ameri-
can merlins. Condor 74:105-106.

Trimble, S.A. 1975. Report No. 15, Merlin -Falcocolum-
barius. Habitat management series for unique or en-
dangered species. U.S. Bureau of Land Management.
41 pp.

Department of Veterinary Anatomy, Western College of Veteri-
nary Medicine, University of Saskatchewan, Saskatoon, Sas-
katchewan S7N OWO CANADA.

FOOD HABITS AND BREEDING BIOLOGY OF MERLINS IN DENALI

NATIONAL PARK, ALASKA

Karen Laing

Abstract - Four pairs of the Merlin ( Falco columbarius ) were studied during the 1983 breeding season in Denali
National Park, Alaska. Additional observations were made of a fifth pair and a family discovered after young hatched.
Observations began 30 April, during the courtship period, and ended 1 September, when Merlins had dispersed from
nesting territories. To determine food habits, prey remains were collected and identified, and prey delivery behavior was
recorded. Productivity was determined by checking nests during incubation and after young hatched. Breeding
behavior, including sex roles and nest defense, was also documented during 125 h of observation.

Little is known about the status of the Merlin
{Falco columbarius ) in Alaska. During the past 2 de-
cades some attention was given the decline of
breeding populations in other parts of the range
(Fox 1971; Hodson 1976; Newton et al. 1978;
Oliphant and Thompson 1978; Newton et al. 1981 ;
Williams 1981; Roberts and Green 1983). In con-
trast; information on Merlins in Alaska is limited to
general surveys (Gabrielson 1944; Kessel and Cade
1958; Gabrielson and Lincoln 1959; Murie 1963;
White et al. 1977; Ritchie 1982, 1983; Mindell
1983). The objective of this study was to gather
preliminary information on their productivity,
food habits, and breeding behavior in Alaska.

Study Area and Methods

Merlin nests were studied in the Alaska Range, Denali National
Park, Alaska, at 63 'N. All nests were within 200 m of the park’s
only road, at elevations ranging from 770 m to 1230 m.

Merlins often nest in strips of white spruce ( Picea glauca) wood-
land at treeline, (Figure 1). Below 770 m, spruce forest dominates,
while above treeline willow ( Salix spp.) and dwarf birch (Betula
nana and B. glandulosa) give way to alpine tundra at about 1230 m.
Between April and September the park receives most of its 37 cm
annual precipitation. Rain accounts for most precipitation, but
occasional snowfall may also occur in summer. Temperature
ranges from 0° to 20°C. Daylength varies from 12 h in late March
and September to 22 h in late June.

Field Observations - Four nest sites were located in April and
May 1983. A fifth pair was observed in May, but a nest was not
located. An additional family was observed in late July and early
August.

One hundred twenty-five h were spent observing Merlins be-
tween 30 April and 1 September, when they are in the park.
Approximately half the observation time was spent at 1 nest.
Between 1 5 and 20 h were spent at each of the other 3 nests, and 9
h were spent observing other Merlins. Observations were made
using 7 x 35 binoculars and a 20-45x zoom spotting scope. Obser-
vations at 2 nests were made from the road. The third nest was
observed from atop a human food cache located 60 m from the
nest, while the fourth was observed from the ground.

Nest trees were climbed once during the third week of incuba-
tion and twice after young hatched. On the third visit, young birds
at 3 nests were banded.

Food Habits - Information on food habits was obtained largely
from discarded prey remains found at plucking perches near
nests. Remains were collected at least weekly at 2 nests, and at least
bi-weekly at other sites.

Prey remains were identified by comparing prey items with
study skins in the University of Alaska Museum. Mean prey
weights were obtained from museum specimens and records. If
remains of the same species were found at several locations near 1
nest on the same day, they were considered to be from a single
individual except when feathers of juveniles could be differen-
tiated from those of adults.

Aging Merlins - Dorsal plumage of juveniles closely resembled
that of adult females, varying in color from medium brown to dark
brownish gray. At close range, juveniles were identified by the
upper tail coverts and rump feathers, which were the same color as
the back. In contrast, the upper tail coverts and rump feathers of
females were slate brown against the darker back (Temple 1972).
The color of the cere, eyelids, legs and feet proved a more useful
field character. In adults all were bright yellow. Ceres and eyelids
of juveniles were pale blue-gray to pale yellow, and legs and feet
were pale yellow.

Sexing Merlins - Adults were usually separated in the field by
their marked sexual dichromatism. Dorsal plumage in males was
slate blue, and in females, brownish gray. In some males the buffy
background color of the breast and belly gave way to orange at the
throat and flanks, a character never observed in females. Adults
perching together were more easily sexed since males were smaller
than females. In some pairs vocalizations helped distinguish bet-
ween sexes.

Juveniles were difficult to sex. When perched together, they
could usually be sexed by size as in adults. At close range, they were
sexed by the color of their light tail bands, which are gray in males,
and buffy in females (Temple 1972).

Results and Discussion

Food Habits — Prey - Bird prey remains were the
only remains found near nests (Table 1). Although
Merlins were observed to bite at insects near
perches, predation on insects could not be con-
firmed since pellets were not analyzed. Snyder and
Wiley (1976) note that studies of prey remains and
pellets often give biased estimates of diets for rap-
tors. Their data from stomach analyses, based on
the number of prey items found, indicate that Mer-

42

Raptor Research 19 (2/3): 42-51

Summer/Fall 1985

Breeding Merlins in Alaska

43

Figure 1. Typical habitat occupied by the Merlin in Denali National Park, Alaska.

lins take 74. 1 % insects, 25.2% birds, 0.5% mammals
and 0.2% lower vertebrates. However, most of their
data were from migrants. Brown and Amadon
(1968) estimate that, by weight, Merlins take 80%
birds, 15% insects and 5% mammals.

Merlins preyed on 22 species of birds (Table 1).
The main species were the American Tree Sparrow
( Spizella arborea), Dark-eyed Junco (Junco hyemalis ),
Lapland Longspur ( Calcarius lapponicus ), Fox Spar-
row (Passerella iliaca ) and White-crowned Sparrow
( Zonotrichia leucophrys ), in decreasing order of oc-
currence. These 5 species formed approximately
49% of the numerical total remains collected.

The 5 species also made up 48% of the prey
biomass, with the Fox Sparrow contributing most
substantially (13.3%, Table 1). The Varied Thrush
( Ixoreus naevius), Snow Bunting ( Plectrophenax
nivalis), and Catharus thrushes were not numerically
important prey species, but did contribute substan-
tially to total prey biomass (Table 1).

By contrast, the variety of major prey species
taken by breeding Merlins elsewhere is much smal-
ler. The Horned Lark ( Eremophila alpestris) alone
formed approximately 50% of the numerical prey

remains collected on the Canadian prairies by both
Fox (1964) and Hodson (1976). Newton et al.
(1978) in Northumberland, Great Britain, found
the Meadow Pipit (Anthus pratensis) comprised 48%
of numerical remains collected. Finally, Merlins at
an urban site in Saskatoon, Saskatchewan, took an
estimated 90% House Sparrows {Passer domesticus)
(Oliphant 1974).

Habitat preferences of major prey species at De-
nali Park indicate that Merlins do not confine
hunting to a particular habitat. Juncos are found
primarily in spruce forest, while Tree, Fox and
White-crowned Sparrows are common in willow
and birch shrubland and spruce woodland, and
Lapland Longspurs are found in alpine tundra.

Forty-five percent of prey items collected bet-
ween 10 July and 6 August were identified as
juveniles. Juveniles taken included the American
Tree Sparrow, Lapland Longspur, White-crowned
Sparrow, Dark-eyed Junco, Snow Bunting, Savan-
nah Sparrow {Passerculus sandwichensis), Rosy Finch
{Leucosticte arctoa ) and Ptarmigan ( Lagopus sp.).

Frequency of Prey Delivery - According to Krull
(1976) and Daniel Gibson (pers. comm.), northern

44

Karen Laing

Vol. 19, No. 2/3

Table 1 . Prey remains found at 4 Merlin nests in Denali National Park, Alaska.

Species

%a

% BlOMASSb

Ptarmigan ( Lagopus sp.)

0.9

.

Semipalmated Plover ( Charadrius semipalmatus )

1.8

3.4

Least Sandpiper (Calidris minutilla)

0.9

0.9

Horned Lark ( Eremophila alpestris)

1.8

2.7

Tree Swallow ( Tachycineta bicolor)

0.9

0.7

Catharus thrushes (C. ustulatus, C. guttatus, C. minimus)

0.8

9.0

Varied Thrush (Ixoreus naevius)

2.8

8.6

Water Pipit (Anthus spinoletta)

6.2

5.4

Orange-crowned Warbler ( Vermivora celata)

2.8

1.0

Yellow Warbler (Dendroica petechia)

1.8

0.7

Northern Waterthrush (Seiurus noveboracensis)

0.9

0.6

Wilson’s Warbler (Wilsonia pusilla)

1.8

0.6

American Tree Sparrow ( Spizella arborea)

11.5

8.5

Savannah Sparrow (Passerculus sandwichensis)

3.6

2.6

Fox Sparrow ( Passerella iliaca)

8.9

13.3

Golden-crowned Sparrow (Zonotrichia atricapilla)

1.8

2.4

White-crowned Sparrow (Zonotrichia leucophrys)

8.0

7.9

Zonotrichia sp.

0.9

1.0

Dark-eyed J unco (Junco hyemalis)

10.6

8.1

Lapland Longspur (Calcarius lapponicus)

9.8

10.7

Snow Bunting (Plectrophenax nivalis)

5.3

8.3

Rosy Finch (Leucosticte arctoa)

2.8

3.1

Common Redpoll (Carduelis flammea)

0.9

0.5

Unidentified small bird

5.3

-

Total

100.0

100.0

aTotal prey items = 113.

bTotal calculated prey biomass = 2748 g; mean weights could not be determined for unidentifiable prey remains and Ptarmigan of
unknown species and age.

Frequency of Prey Delivery - According to Krull
(1976) and Daniel Gibson (pers. comm.), northern
passerines rest 3 to 4 H daily, usually between 2300
H and 0300 H, despite long summer photoperiods.
Since Merlins were observed hunting between 0400
H and 2330 H, a 20-H day was assumed for the
purpose of estimating frequency of prey delivery.

During incubation, 18 May to 19 June, males
delivered prey to females at a rate of 0.15 birds/h
(3.0 birds/d). Between 19 June and 25 July, when
young were being fed, males delivered prey to
females at a rate of 0.48 birds/h (9.6 birds/d). Prey
capture by females during breeding was not
documented. In a study of a wintering female Mer-
lin, Page and Whitacre (1975) estimated prey con-
sumption at 2.2 birds/d. The Dunlin ( Calidris al-

pina ), the major prey species in that study, weighs
approximately twice as much as major Denali Park
prey species.

Hunting Behavior - Fast, low, horizontal flight
from a perch has been described previously for
Merlins (Bent 1938; Page and Whitacre 1975; Cade
1982). On 5 June a male departed its nest area and
flew to an adjacent shrub-covered slope. He flew
rapidly and close to the vegetation, gaining altitude
only when he approached a rise, where he turned
and swept back over the brush. He then perched
without prey. Frederick Dean (pers. comm.) ob-
served a similar low, fast flight along a ditch parallel
to the park road. In this case the bird flew so low
that it was level with the road bed. In another obser-
vation a male left his perch, flying fast over an

Summer/Fall 1985

Breeding Merlins in Alaska

45

adjacent river valley. When he was about 1 km from
the nest he began to dive at several small birds. Both
the falcon and the pursued birds dipped and rose
several times. Within 2 min, the falcon returned to
the nest area with prey.

On several occasions females were observed to
dive at a steep angle into brush below their perches
near nests. Whether they were hunting or collecting
cached prey could not be determined.

Feeding and Caching Behavior - Merlins re-
moved the head and wings of prey and plucked
most of the feathers before eating. Merlins usually
prepared prey on snags, stumps or fallen logs
within 150 m of the nest, using favorite perches
repeatedly throughout the season.

Merlins sometimes cached prey in the vicinity of
plucking perches. One Rosy Finch was found entire
and unplucked. Four other birds were found par-
tially plucked, with heads and wings removed. In 1
instance, following a food transfer, a female flew
low toward an unseen perch for 10 sec, then ap-
peared on a perch without prey. On another occa-
sion, a female flew toward an unseen perch and
then returned to the nestlings with prey. In this
instance, the male had been absent from the area
for 2 h.

Habitat and Nest Sites - Breeding Merlins at
Denali Park favored sloping white spruce forest
within 1 km of treeline. All 4 nests were in white
spruce trees (Tables 2,3). One nest tree was living
and undamaged, while a second had little green
foliage. A third was living but was missing many
branches on one side, where an old telephone cable
was attached to the trunk with a glass insulator
(Figure 2). The fourth nest was in a snag (Figure 3).
Merlins nested only in abandoned nests of Black-
billed Magpies (Pica pica) (Table 4). There was no
evidence that Merlins altered the structure of Mag-
pie nests.

Nesting habits vary throughout the Merlin’s
range. All nests recorded in Denali Park were in
trees, and most Merlins in Norway and North
America nest in trees (Fox 1964; Oliphant 1974;
Oliphant and Thompson 1976; Hodson 1976;
Cramp and Simmons 1980; Evans 1982). Near
Arctic treeline in Alaska and Canada, Merlins nest
on the ground (Bent 1938, Ritchie 1983, Clayton
White, pers. comm.). Ground nesting is the norm in
Great Britain. Seventy-seven percent of 96 nests in
Northumberland (Newton et al. 1978), and 64% of
90 nests in Wales (Williams 1981) were on the
ground.

Table 2. Description of 4 Merlin nest sites in Denali National Park, Alaska.

Nest

Vegetation Type21

Description

1

Open needleleaf
forest; white
spruce

Nest tree was on a slope in open forest
with a low, closed understory. Tree was
located about 100 m from low, closed shrub
scrub and 120 m from the road.

2

Open needleleaf
forest: white
spruce

Nest tree was in flat forest with low, open

understory. Tree was located 50 m from

low, closed shrub scrub and about 150 m from the road

3

Closed tall shrub
scrub: willow

Nest tree was on a slope dominated by tall
willows ( > 1.5 m). Area was formerly open
spruce forest; almost all mature spruce
trees were destroyed by porcupines during
the 1950s, leaving many snags. Tree was
10 m from the road.

4

Open needleleaf
forest: white
spruce

Nest tree was on a slope in spruce forest
with a tall, open understory. Tree was
500 m from shrub, 100 m from
a river, and 90 m from the road.

aVegetation nomenclature and classification follows Viereck et al. (1982).

46

Karen Laing

Vol. 19, No. 2/3

Table 3. Measurements of white spruce nest trees used by Merlins in Denali National Park, Alaska during 1983.

Nest

Tree

Height

(m)

Tree Diameter
at Nest Height
(cm)

Tree Diameter
at Breast Height
(cm)

Height of Nest
Above Ground
(m)

1

9.3

18.8

37.6

5.5

2

7.5

12.9

22.2

5.5

3

9.0

18.8

26.9

4.1

4

10.0

21.8

28.3

4.1

X

8.9

18.1

28.8

4.8

S.D.

1.1

3.7

6.5

0.8

Nesting Chronology - Spring arrival dates have
not been documented for the Alaska Range, but
records for interior Alaska indicate arrivals during
the last 2 weeks of April. Occasionally individuals
arrive in Fairbanks as early as late March (Brina
Kessel, unpubl. data).

Merlins were first observed in Denali Park on 30
April, and engaged in breeding activity between
that date and 15 May. During this period Merlins
were extremely vocal. They were observed inves-
tigating Magpie nests, and on 10 May a female was
flushed off a nest in which she later laid eggs.
Harassment of other bird species near nests was
first observed 7 May. All observed copulation at-
tempts occurred between 30 April and 15 May.
After 1 5 May females at all nests were observed only
when they left nests to take prey from males, indi-
cating that they began incubating during the third
week of May.

Since Merlins incubate for 28-32 d (Cramp and
Simmons 1980), it was assumed that Merlins in De-
nali Park hatched during the third and fourth
weeks of June. On 29 June, nestlings at all nests
were downy white, and were unable to grasp with
their feet. On 10 July all young were able to grasp
well. Nestlings at 1 nest had remiges over 6 cm long
on this date. Their backs, wings and heads were well
feathered, although down still projected through
the plumage in tufts (Figure 4). Nestlings at 2 other
nests visited on 10 July were still downy, with re-
miges 2-4 cm long (Figure 5).

The fourth nest visited 10 July was empty. The
young left sometime after 5 July, when the adult
female was last seen carrying prey to the nest. Mer-

lins at the other 3 nests fledged between 1 1 and 19
July. Merlins fledged about 32 d after hatching
(Fox 1964; Newton et al. 1978).

After 20 July adults were only occasionally seen
in nest areas, the last being a male on 16 August.
Juveniles were first observed away from nest areas
on 7 August. Merlins continued to be observed
throughout the park until the first week of Sep-
tember.

Nest Success - All 4 nests contained 5 eggs, which
compared to mean clutch sizes in Canada and Wales
of 4.1 to 4.7 eggs (Fox 1971 ; Hodson 1976; Roberts
and Green 1983). Fifteen of 20 eggs produced
hatched, 2 did not hatch, and 3 were not accounted
for, yielding a mean of 3.75 hatchlings/nest (range
2-5). A minimum hatching success of 75% was ob-
tained on this basis. By contrast, Fox (1971) re-
corded 49% success in a Canadian population ap-
parently affected by pesticide contamination, and
92-98% success in unaffected populations there.

Successful nests at Denali Park appear to be pro-
ducing as many fledglings as reported for other
areas. One nestling died soon after hatching, but all
others fledged, giving a mean of 3.5 fledglings/nest.
Hodson (1976) reported a mean of 3.2 fledglings/
nest with young, while Oliphant and Thompson
(1978) reported a mean of 4.0 fledglings/nest.

Courtship and Copulation Behavior - Merlins
were observed investigating potential nests on 3
occasions. On 7 May, a female called “ki-ki-ki-keee”
as she flew around the perched male. While the
male remained perched, the female disappeared
among the boughs of a spruce tree, where she ut-
tered a “tick” call, and remained for 2 min. On 10

Summer/Fall 1985

Breeding Merlins in Alaska

47

Figure 2. Magpie nest in White Spruce tree used by Mer-
lins in 1983.

May, a female entered a Magpie nest and uttered
“ki-ki-ki-kee”, while a male flew in circles nearby,
also calling. The female walked back and forth
through the nest, then flew to an unseen perch and
uttered a “chrrr” call, which often preceded copu-
lation. The male flew toward her, also out of sight.

Food exchanges during courtship were usually
slow and tentative. On 10 May, a paired male
brought an unplucked Snow Bunting to the female

Figure 3. Magpie nest in dead spruce used by Merlins in
1983.

and perched beside her. The male transferred the
bird to his bill as the female bit at it with her bill. The
male then allowed the female to take the bunting,
and she left the perch. The male remained on the
perch an additional 5 min, gave a “tick” call twice,
then flew in the same direction as the female. On 19
May, the male at another nest brought a bird to the
nest area and perched. He uttered the “ki-ki-ki-
kee” and “tick” calls, and bit at the prey. After 5 min

Table 4. Measurements (cm) of magpie nests occupied by Merlins in Denali National Park, Alaska during 1983.

Nest

Nest

Diameter

Bowl

Diameter

Bowl

Depth

Cavity

Height

1

64.0

30.0

8.0

50.0

2

61.0

25.0

10.0

37.0

3

46.0

25.0

8.0

55.0

4

44.0

20.0

9.0

40.0

X

44.0

20.0

9.0

40.0

S.D.

10.2

4.1

1.0

8.4

48

Karen Laing

Vol. 19, No. 2/3

Figure 4. Nestling merlin in Alaska, age ± 21 d.

the female perched on the same snag. The male
crouched, transferring the prey to his bill, while the
female stepped slowly down the branch toward the
male. When she was close enough, the male allowed
her to take the prey. The pair appeared to tug at the
prey a moment before the male relinquished it. The
female remained on the perch as the male flew to
the nest tree and called.

Copulation attempts were observed 1 1 times
during 16.3 h of observation between 30 April and
12 May. In one instance, Merlins attempted copu-
lation twice in a 2 min period. One male mounted 3
times in a 2V6 h period. Females often appeared to
solicit copulation. Typically, a female called “ki-ki-
ki-keee”, flew low through the forest and perched
near the male. The female then crouched on the
perch and leaned forward so that her body was
horizontal. While in this position, the female spread
and lifted her tail to one side. The male then flew to
the female, hovered momentarily above her, and
uttered the “chrrr” call. In 2 instances a male ap-
proached a perched female and uttered the “chrrr”
call before the female assumed the crouch position.

Figure 5. Nestling merlin in Alaska, age 10 - 14 d.

Sex Roles During Incubation - Females per-
formed the majority of incubation. During 30 h of
observation during incubation, males incubated
approximately 15% of the time. This estimate is
based on direct observation of undisturbed males
entering and leaving nests. Both Temple (1972)
and Newton et al. (1978) estimated that males incu-
bate 33% of the time. However, their estimates were
obtained by flushing birds from nests and then
sexing them.

Males generally took over incubation for periods
of 10 min to 1 h after bringing food to females.
Females indicated readiness to resume incubation
by calling and flying to perches near nests, at which
time males vacated the nests. While 1 bird incu-
bated the other often remained perched within 150
m. Perched males usually dozed or looked about,
while perched females stretched and preened ac-
tively.

Males apparently did all hunting during the in-
cubation period. Food transfer was accomplished in
a more rapid and aggressive manner than was usu-
ally observed during courtship. When a male en-

Summer/Fall 1985

Breeding Merlins in Alaska

49

tered the nest area and called, the incubating
female left the nest. She quickly took the prey from
the male and flew to a perch to feed. On only 1
occasion did a male appear reluctant to relinquish
prey.

Sex Roles During the Nestling Period - Merlins
apparently removed or ate eggshells and dead
nestlings. When all nests were checked after
hatching, 2 entire eggs were found, while 3 others
were unaccounted for. No eggshells were found.
Cramp and Simmons (1980) state that eggshells are
removed or eaten by females. On 18 June, a dead
nestling was found atop a 2 m stump commonly
used as a plucking perch.

My observations indicate that females brood
young only during the first week after hatching.
Even then females were observed off nests for
progressively longer periods. Feeding young,
which generally required 10-20 min, was ac-
complished only by females. When the nestlings at 1
nest fledged at approximately 2 wk old, the female
continued to feed them on the ground.

During the nestling period, males were away
from nests more often, yet delivered food to
females more frequently than during courtship or
incubation. While females may have taken prey
near nests, they did not appear to make a major
contribution to food collection. This finding is con-
sistent with studies by Rowan (1921) and Oliphant
(1974). However, Temple (1972) found evidence
suggesting that females do hunt soon after brood-
ing.

Behavior of Young Merlins - On 29 June, nest-
lings called weakly, and did not react to an ap-
proaching hand. By 10 July, all young were alert
and active. For example, 1 nestling perched at a
nest entrance for 30 min, preened, watched passing
vehicles, bobbed its head and snapped at insects.

During the first week after fledging, young did
not fly often. When they did, flights were low and of
short duration. After the first week, fledglings be-
came more active. They called frequently, and
often in unison. They chased each other, and mob-
bed adults returning to the nest area with prey.

By early August, juveniles were observed chasing
other birds. While not observed hunting success-
fully, they were seen pursuing small birds. More
often, they chased other raptors. On 16 August, 3
juveniles were observed chasing 2 American Kes-
trels (Falco sparuerius) and 2 juvenile Northern Har-
riers (< Circus cyeneus ) simultaneously. On other occa-

sions, these same juveniles chased a Golden Eagle
(Aquila chrysaetos ), a Sharp-shinned Hawk (Accipiter
striatus) and 2 Black-billed Magpies. All these chases
appeared playful. Pursued birds, particularly kes-
trels and Sharp-shinned Hawks, sometimes turned
and chased Merlins, and frequently remained in
the area following a chase. Kestrels and Merlins
sometimes perched together in the same tree. Cade
(1982) has observed similar associations of juvenile
Merlins and Sharp-shinned Hawks in interior
Alaska.

Territorial and Nest Defense - Merlins at Denali
Park generally chased intruders when found within
150 m of nests, females behaving more aggressively
than males. Merlins were particularly aggressive
toward raptors and other large birds. Golden
Eagles, Northern Harriers, Common Ravens ( Cor -
vus corax ) and a Gyrfalcon (Falco rusticolus) were
chased on different occasions. Merlins were also
observed diving at Black-billed Magpies and Willow
Ptarmigan (Lagopus lagopus ). In one instance, a
female called vigorously for 10 min after a small
airplane passed low over the area.

During courtship, Merlins were chased by birds
already present in nest areas. On 1 occasion, a Mew
Gull ( Larus canus ) chased a female Merlin just after
the Merlin dove at a magpie. Gray Jays (Perisoreus
canadensis) displayed aggression toward Merlins in
early May, but were ignored.

Red Squirrels (Tamiasciurus hudsonicus) may pose
a threat to nestlings. The nest vacated by young
Merlins between 5 and 10 July contained spruce
cones and scales in mid -July, indicating that squir-
rels were using it. Squirrels may have displaced the
Merlins. Red Squirrels at Denali Park have been
observed to feed on American Robin ( Turdus mig-
ratorius) nestlings.

While they ignored Moose (Alces alces ) and
Grizzly Bear ( Ursus arctos), Merlins were intolerant
of human presence near nests. My searches for prey
remains were commonly interrupted by a Merlin
calling and diving at me, and this harassment con-
tinued until I moved at least 100 m from the nest.
Perched males sometimes allowed me to pass with-
out disturbance, but when visible to a female, I was
always pursued.

The proximity of the park road to all 4 nests
required Merlins to adjust to human activity. In 3
cases, nests were between 90 and 150 m from the
road. Merlins at these nests appeared to regard the
road as a territorial boundary, ignoring vehicles

50

Karen Laing

Vol. 19, No. 2/3

and pedestrians on the road, but diving and calling
at pedestrians off the road in the direction of nests.
The fourth nest was located 10 m from the road.
Plucking perches were located across the road, so
the road bisected the nest territory. In May, adults
called at any human activity on the road. By June,
they ignored road activity, but pursued pedestrians
off the road in either direction.

Nest checks elicited a strong response. Merlins
often flushed from nests when humans approached
to within 5 m of nest trees, and always flushed when
nest trees were climbed. They called from nearby
perches, diving frequently to within 2 m of the
intruder, and were joined by their mates, when
present.

Acknowledgments

Permission to study Merlins in Denali National Park was
granted by John Dalle-Molle of the U.S. National Park Service,
which also provided equipment. Philip S Tiempf and Robin
Hunter, U.S. Fish and Wildlife Service suggested the study and
provided banding assistance. Kenneth Kertell, Michael Britten,
Joseph Van Horn, Barbara O’Donnell, Marti Loew and Gary
Lester assisted in the field. Stephen Herman, The Evergreen State
College, provided guidance throughout the study, and Kenneth
Kertell and Francis Singer reviewed earlier drafts. Daniel Gibson,
University of Alaska Museum, identified many prey remains. I am
grateful to these people, as well as to the many residents of
McKinley Park, Alaska, who provided me with Merlin sightings.

Literature Cited

Beebe, F. 1974. Field studies of the Falconiformes of
British Columbia. Occasional paper of the British Col-
umbia Provincial Museum No. 17.

Bent, A.C. 1938. Life histories of North American birds
of prey, part 2. Smithsonian Inst., U.S. Natl. Mus. Bull.
170.

Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world, Vol. 2. McGraw-Hill Book Co.
Cade,T.J. 1982. The falcons of the world. Cornell Univ.
Press, Ithaca, N.Y.

Cramp, S. and K.G.L. Simmons. 1980. Handbook of the
birds of Europe, the Middle East, and North Africa:
the birds of the western palearctic, Vol. II, hawks to
bustards. Oxford Univ. Press, Oxford, London, New
York.

Evans, D.L. 1982. Status report on twelve raptors. U.S.
Dept, of Interior, Fish and Wildl. Service Special Sci-
entific Report — Wildlife No. 238. Washington D.C.
Fox, G.A. 1964. Notes on a western race of the pigeon
hawk .Blue Jay 22:140-147.

. 1971. Recent changes in the reproductive

success of the pigeon hawk./. Wildl. Manage. 35(1)
122-128.

Gabrielson, I.N. 1944. Some Alaskan notes. Auk
61:122-128.

and F.C. Lincoln. 1959. Birds of Alaska.

The Stackpole Co., Harrisburg, Pa.

Hodson, K.A. 1976. Some aspects of the nesting ecology
of Richardson’s merlin ( Falco columbarius richardsonii)
on the Canadian prairies. M.Sc. Thesis. Univ. of Brit.
Col., Vancouver.

Kessel, B. and T.J. Cade. 1958. Birds of the Colville
River, northern Alaska. Biological paper of the Univ.
of Alaska No. 2.

Krull, F. 1976. Zeitgebers for animals in the continuous
daylight of high arctic summer. Oecolgia (Berlin)
24:149-157.

Mindell, D.P. 1983. Nesting raptors in southwestern
Alaska: status, distribution and aspects of biology.
U.S. Dept, of Interior, Bureau of Land Management
Technical Report 8, Anchorage, Alaska.

Murie, A. 1963. Birds of Mt. McKinley National Park,
Alaska. Mt. McKinley Natural History Assoc.

Newton, I., E. Meek and B. Little. 1978. Breeding
ecology of the merlin in Northumberland. Br. Birds
71:376-398.

__ , J.E. Robson and D.W. Yalden. 1981. De-

cline of the merlin in the Peak District. Bird Study
28:225-234.

Oliphant, L.W. 1974. Merlins - the Saskatoon falcons.
Blue Jay 32:140-147.

and W.J.P. Thompson. 1976. Food cach-
ing behavior in Richardson’s merlin. Can. Field-Nat.
90(3): 364-365.

Page, G. and D.F. Whitacre. 1975. Raptor predation
on wintering shorebirds. Condor 77:73-83.

Ritchie, R.J. 1982. The results of raptor surveys along
the Porcupine River, Alaska, 1982. Unpubl. final re-
port by Alaska Biological Research, Fairbanks, for U.S.
Fish and Wildlife Service, Endangered Species Office,
Anchorage.

. 1983. The results of raptor surveys along

the Porcupine River, Alaska, 1983. Unpubl. final re-
port by Alaska Biological Research, Fairbanks, for U.S.
Fish and Wildlife Service, Endangered Species Office,
Anchorage.

Roberts, J.L. and D. Green. 1983. Breeding failure and
decline of merlins on a north Wales moor. Bird Study
30:193-200.

Rowan, W. 1921. Observations on the breeding habits
of the merlin. Br. Birds XV(6): 122-129; XV(9):194-
202; XV(10):222-231; XV(1 1):246-253.

Snyder, N.F.R. and J.W. Wiley. 1976. Sexual size di-
morphism in hawks and owls of North America. Or-
nithol. Monogr. No. 20.

Temple, S.A. 1972. Sex and age characteristics of North
American merlins. Bird-Banding 43:191-196.

Viereck, L.A., C.T. Dyrness and A.R. Bat-
ten. 1982. 1982 revision of preliminary classification
for vegetation of Alaska. Unpubl. revision of U.S.
Dept. Agri., Forest Service General Tech. Rep. PNW-

Summer/Fall 1985

Breeding Merlins in Alaska

51

106, 1980. Institute of Northern Forestry, Univ. of Division of Wildlife and Fisheries Biology, University of
Alaska, Fairbanks. California, Davis, Davis , California 95616.

Williams, G.A. 1981. The merlin in Wales: breeding
numbers, habitat and success. Br. Birds 74:205-214.

BREEDING CHRONOLOGY AND REPRODUCTIVE SUCCESS OF
RICHARDSON’S MERLINS IN SOUTHEASTERN MONTANA

Dale M. Becker and Carolyn Hull Sieg

Abstract - Breeding chronology and reproductive success of the Merlin ( Falco columbarius richardsonii) were studied in
southeastern Montana from 1978 - 1981 . Breeding activity spanned 5 mo from the earliest observation of adults to the latest
dispersal of adults and young from nesting areas. Clutch size, brood size and fledging success at active nests were similar (P >
0.05) among the 4 yrs. Mortality tended to be highest before the hatching stage. Breeding chronology and reproductive
success were similar to results of studies in Canada.

The Merlin ( Falco columbarius) is 1 of 6 species of
falcons that occur in North America. Three sub-
species of the Merlin in North America are recog-
nized (Temple 1972). F.c. richardsonii, the sub-
species of interest in this study, occurs in the prairie
parklands of the Northern Great Plains.

Data pertaining to the ecology of F.c. richardsonii
have been generated primarily from studies in the
prairie provinces of Canada. The life history of
Canadian Merlins, including breeding chronology
and reproductive success, was documented by Fox
(1964,1971). In Alberta and Saskatchewan, Hod-
son (1976) reported that reproductive success at
Merlin nests that fledged young was high, but net
productivity was variable. An apparent increase in
reproductive success over that reported by previous
studies was discussed for Merlins in Saskatchewan
by Oliphant and Thomson (1978).

Information on F.c. richardsonii in the United
States is lacking, although local populations or
scattered breeding pairs occur in several western
states (Oliphant, this issue). This study was initiated
to document the reproductive ecology of a popula-
tion of richardsonii in Montana.

Study Area and Methods

Breeding chronology and reproductive success were examined
on a 39,448-ha study area in southeastern Montana. Sandstone
buttes and hills ranging to 300 m above the adjacent prairies and
farmlands are common on the study area. Maximum elevation is
1,282 m above sea level. Vegetation consists of approximately 27%
forest cover and 67% grassland. The dominant forest species is
ponderosa pine (Pinus ponderosa). Aspen (Populus tremuloides), box
elder (Acer negundo ), green ash ( Fraxinus pennsylvanica), and a
variety of shrubs grow in more mesic sites. Major grassland species
are western wheatgrass (Agropyron smithii), blue grama (Bouteloua
gracilis), prairie junegrass (Koeleria cristata), and needle-and-
thread grass (Stipa comata).

The climate in southeastern Montana is characterized by fre-
quent winds, hot summers, cold winters, and a semi-arid moisture
regime. Annual precipitation averages 39 cm, of which 70% falls
from May - September. Monthly mean temp during the Merlin
breeding season range from -8°C in March to 33°C in July.

Breeding chronology and reproductive success were studied
from March - September, 1978-1981. Breeding territories were
located by traversing potential breeding habitat (i.e., ponderosa
pine stands) during April and May. Nest sites were detected when
adults were flushed or exhibited aerial and vocal defense be-
havior. When flushing was not observed but defensive adult Mer-
lins were present, Black-billed Magpie (Pica pica ) nests in the
vicinity were examined.

Timing and duration of breeding activities were determined by
observing Merlins from early spring through late autumn. Obser-
vations of courtship, hatching, growth of young, fledging, and
dispersal were documented at all active nests. Number of eggs,
young and fledglings were recorded during 3 visits to each
nest: during incubation, shortly after hatching, and just prior to
fledging. Precautions were taken to avoid disturbance of adults
and young (Fyfe and Olendorff 1976).

Data collected during nest visits were used to calculate percen-
tages of eggs hatched, young fledged, and eggs resulting in
fledglings. Fledging success was calculated for active nests (“nests
in which eggs have been laid”) and successful nests (“occupied
nests from which at least 1 young fledged during the breeding
season under consideration”) (Postupalsky 1974). Sex of nestlings
was determined at approximately 2 weeks of age. Larger foot size
and larger, less fully developed bodies (Fox 1964), along with
greater tarsal diameter were generally reliable characteristics of
females.

Student t-Tests were used to compare reproductive success
among years. Paried t-Tests were used to compare average clutch
size, brood size and number of fledglings/ active nest within yrs.
Clutch size, brood size and number of fledglings/active nest for the
4 yrs combined were compared using combination of probabilities
from tests of significance (Fisher 1950). Unless otherwise noted,
differences were considered significant at a = 0.05.

Results

Breeding Chronology. — The earliest observation
of an adult Merlin on the study area was 1 1 March
1978. Breeding activities spanned approximately 5
mo from the earliest observation of an adult until
the latest dispersal of adults and young (Fig. 1).

Males were observed at breeding territories be-
fore females. Courtship began shortly after the ar-
rival of the females in early April and continued
until late-May (Fig. 1). Eggs were layed from mid-
April through mid-June. Females usually incu-

52

Raptor Research 19(2/3): 52-55

Summer/Fall 1985

Breeding Merlins in Montana

53

11 Mar

23 Apr

Courtship

Egglaying

5 Apr

26 May

15 Apr

j 7 Jun

1

Incubation

Hatching

15 Apr

27 Jun

24 May

1 27 Jun

24 May

1

4 Jul

Brooding

Nestling

24 May

26 Jul

Fledging

24 Jun | 18 Jul

Dispersal

1 . .

!iil

i i 1 i

10 Jul | 9 Aug

. 1 . . 1 i

1 10 20

30 10 20 30

10 20 30 10

20 30 10 20 30 10

Month March April May June July August

Figure 1. Nesting chronology of F.c. richardsonii in southeastern Montana. Horizontal lines indicate ranges of activity,
vertical lines indicate means.

bated eggs, although males were occasionally ob-
served on nests for short periods.

Earliest observed hatching occurred on 24 May
1980, and the latest on 27 June 1979. Nestlings
were brooded 3 - 5 d, and remained in the nest 12 -
17 d before beginning to spend time on top of the
nest canopy and/or in nearby branches. Young
Merlins fledged from 26 - 33 (X = 29) d after
hatching. Fledging dates ranged from 24 June - 18
July. Fledglings remained in the vicinity of the nest
from 7 - 19 (X =13)d after fledging. The latest
dispersal of young and adults from a breeding ter-
ritory occurred on 9 August 1979.

Reproductive Success. — Forty-eight active
Merlin nests were located during the study, of
which 43 (90%) were ultimately successful in pro-
ducing fledglings. All nests were originally Black-
billed Magpie *nests located in ponderosa pine trees

on sideslopes of buttes.

The number of eggs laid per nest did not vary
significantly from year to year during this study
(Table 1). Brood sizes were also similar among
years. Sex ratios of 157 nestlings indicated a slightly
greater proportion of females (53%) than males
(47%). Numbers of fledglings per active nest did
not differ significantly among years, and for 4 yrs
combined, was higher than the average number per
successful nest (Table 2).

In 3 of the 4 yrs, and for the 4 yrs combined,
significant mortality was observed from the time
the eggs were laid until the Merlins fledged (Table
1). Average clutch size varied significantly from
average brood size in 1978, 1979 and 1980, while
clutch size was similar to brood size in 1981. Aver-
age number of fledglings per active nest was smaller
than average brood size in 1979 (P 0.08) and
1980. In 1978 and 1981, the number of fledglings
per active nest did not differ significantly from

54

Becker and Sieg

Vol. 19, No. 2/3

Table 1. Reproductive success for Richardson’s Merlins in southeastern Montana, 1978 - 1981.

Year

Sample

size

Clutch

size

(X ± SE)1

Brood

size

(X ± SE)

Fledglings/
Active Nest
(X ± SE)

Eggs

Hatched

(%)

Young

Fledged

(%)

Eggs

Fledged

(%)

1978

8

4.1 ± 0.2a

3.3 ± 0.4b

3.0 ± 0.6b

79

92

73

1979

18

4.3 ± 0.2a

3.6 ± 0.4b

3.3 ± 0.4C*

84

92

78

1980

15

4.5 ± 0.2a

3.5 ± 0.4b

3.3 ± 0.4C

79

94

75

1981

7

4.3 ± 0.4a

4.3 ± 0.4a

3.3 ± 0.9a

100

77

77

Combined

data

48

4.3 ± 0.8a

3.6 ± 1.4b

3.3 ± 1.6C

84

90

76

xMean ± standard error

a,b,cMeans within rows (clutch size, brood size, fledglings per active nest) with the same superscript are not significantly different (P >
0.05)

*In 1979, fledglings/ active nest was smaller than brood size at a *£ 0.08.

average brood size. For the 4 yrs combined, clutch
size, brood size and number of fledglings per active
nest were different.

Discussion

Breeding Chronology. — The presence of male
Merlins in early March when the study area was first
visited indicated that some males may have arrived
earlier, or possibly over-wintered in the area. Male
F.c. richardsonii in Saskatchewan arrived at breeding
sites as early as late February or early March, up to a
month before females (Fox 1964).

The chronology of Merlin breeding activities in
southeastern Montana was similar to breeding

chronology of captive F.c. richardsonii in Alberta
(Campbell and Nelson 1975) and wild Merlins in
Saskatchewan (Fox 1964; Oliphant 1974) and Al-
berta (Hodson 1976). However, some breeding ac-
tivities began earlier in the spring in Montana than
in Canada. As an example, the peak egg-laying date
in Saskatchewan was 20 May (Fox 1964), while
Merlins in Montana had generally completed laying
by this date.

Reproductive Success. — Reproductive success
remained relatively consistent throughout the
study, as evidenced by the low year-to-year varia-
bility of clutch size, brood size and number of
fledglings per active nest. Average clutch size,

Table 2. Reproductive success of Richardson’s Merlins in various areas in the Northern Great Plains of the United
States and Canada (sample sizes in parentheses).

Study

Location

X

Clutch

Size

X

Brood

Size

X

Fledglings/
Successful Nest

Fox 1964
Fox 1971

Saskatchewan
Great Plains

4.5(10)

2.7(10)

...

Fox 1971

(forested)
Great Plains

4.1(9)

4.0(16)

—

Hodson 1976

(prairie)
Alberta and

4.5(10)

2.7(17)

2.8(6)

Oliphant and

Saskatchewan

4.6(156)

3.5(107)

3.2(108)

Thompson 1978

Saskatchewan

...

4.0(47)

Fox and Donald 1980

Alberta

4.1(10)

3.7(10)

...

Fox and Donald 1980

Alberta

3.4(10)

1.9(10)

...

This study

Montana

4.3(48)

3.6(48)

3.7(43)

Summer/Fall 1985

Breeding Merlins in Montana

55

brood size and number of fledglings per successful
nest for the 4 yrs combined are similar to results
reported by Fox (1964, 1971); Fox (1964, 1971);
Hodson 1976; Fox and Donald (1980); and
Oliphant and Thompson (1978) (Table 2). Average
clutch and brood sizes for our study are towards the
upper range of reported values, and although
fledging data from other studies are limited, the
average number of fledglings in this study is gener-
ally higher.

Percentages of eggs which hatched and resulted
in fledglings in southeastern Montana are within
the range of reported values. The hatching success
rate of the Merlin in Montana is higher than the
60% and 58% hatching rates reported by Fox
(1964) and Hodson (1976), respectively. In Alberta,
85% of the young Merlins fledged (Hodson 1976),
while 96% fledged in Saskatchewan (Fox 1964).
The percentage of nestlings which fledged during
this study is within this range.

Mortality tended to be highest prior to hatching
for Montana, as evidenced by the significant loss of
eggs before the nestling stage. However, post-
hatching mortality was common during each year,
and for the 4 yrs combined, resulted in a significant
loss of Merlins before they fledged. Causes of mor-
tality in this study were not specifically identified,
but could be attributed to predation of eggs and
nestlings and inclement weather around hatching
time. Cold, rainy weather in Alberta during the
hatching stage resulted in severe losses of active
nests (Hodson 1976). Human disturbance did not
appear to be a major cause of nest failures. Precau-
tions were taken by study personnel to minimize
disturbance of breeding Merlins and nestlings, and
the isolation of most nests made harassment from
other human activities unlikely.

Results of this study indicate that the sequence
and duration of Merlin breeding activities in south-
eastern Montana were similar to the breeding
chronology reported in Canada, although breeding
activities appeared to begin earlier in the spring.
Reproductive success rates in southeastern Mon-
tana were generally higher and consistent among
years when compared to other studies. Mortality
was highest before hatching, followed by the period
between hatching and fledging. Although human
disturbance from research activities did not appear
to be a cause of mortality, extensive human ac-
tivities, such as energy development and mineral
exploration, and development of more extensive

agricultural practices may disrupt breeding ac-
tivities. Data provided by this study will be useful in
monitoring the status of this Merlin population in
light of future land development activities.

Acknowledgments

Research in 1978 and 1979 was funded by the USDA Forest
Service, Custer National Forest. Research in 1980 and 1981 was
funded by the USDA Forest Service, Rocky Mountain Forest and
Range Experiment Station in Rapid City, South Dakota. We thank
George T. Allen, Daniel W. Carney, Richard LeVesque and
Stephen L. Mackey for assistance in data collection in the field.
Gene Hoff provided housing for field personnel during the study.
Critical comments on an earlier draft of the manuscript were
provided by I.J. Ball, Richard L. Hutto, B. Riley McClelland,
Christopher Servheen and Daniel W. Uresk.

Literature Cited

Campbell, J.A. and R.W. Nelson. 1975. Captive
breeding and behavior of Richardson’s Merlins, 1974.
J. N. Am. Falconer s Assoc. 14:24-31.

Fisher, R.A. 1950. Statistical methods for research
workers. Hafner Pub. Co. New York, N.Y. 354 pp.
Fox, G.A. 1964. Notes on the western race of the Pigeon
Hawk. Blue Jay 12:140-147

1971. Recent changes in the reproduc-
tive success of the Pigeon Hawk. f. Wildl. Manage.
35:122-128.

Fox, G.A. and T. Donald. 1980. Organochlorine pol-
lutants, nest-defense behavior and reproductive suc-
cess in Merlins. Condor 82:81-84.

Fyfe, R.W. and R.R. Olendorff. 1976. Minimizing the
dangers of nesting studies to raptors and other sensi-
tive species. Can Wildl. Serv. Occas. Paper No. 23. Can.
Wildl. Serv., Ottawa, Ont. 7pp.

Hodson, K.A. 1976. The ecology of Richardson’s Mer-
lins on the Canadian prairies. M.S. Thesis. Univ. of
British Columbia, Vancouver, B.C. 83 pp.

Oliphant, L.W. 1974. Merlins: the Saskatoon falcons.
Blue Jay 32:140-147.

Oliphant, L.W. and W.J.P. Thompson. 1978. Recent
breeding success of Richardson’s Merlins in Sas-
katchewan. Raptor Res. 12:35-39.

Postupalsky, S. 1974. Raptor reproductive suc-
cess: some problems with methods, criteria and ter-
minology. Pages 2 1-32 in Hamerstrom, F.N.,Jr., B.E.
Harrell and R.R. Olendorff (eds.). Management of
raptors. Raptor Res. Rep. No. 3.

Temple, S.A. 1972. Systematics and evolution of the
North American Merlins. Auk. 89:325-338.

USFWS, Montana Cooperative Wildl. Rsh. Unit, Univ. of Mon-
tana, Missoula, MT 59812. Address of second au-
thor: USDA Forest Service, Rocky Mtn. Forest and Range
Exp. Sta., South Dakota Sch. of Mines and Tech., Rapid City,
SD 57701.

PRODUCTIVITY, POPULATION DENSITY AND RATE OF INCREASE
OF AN EXPANDING MERLIN POPULATION

Lynn W.Oliphant and Elizabeth Haug

Abstract - The growth of a newly established population of the Merlin ( Falco columbarius) in the city of Saskatoon,
Saskatchewan, was monitored from 1971 to 1982. Each year nesting pairs were located and their young were counted and
banded. The breeding population increased from one pair to sixteen pairs over the twelve year period. The calculated
rate of increase (r) of this population was 0.233. Productivity averaged 4.2 young/successful nest and 3.7 young/nest
attempt. The density of this population in 1982 was the equivalent of 55.2 pair/ 100 km2.

Man’s activities have often been the cause of long
term declines in many raptor populations (Newton
1979). In contrast, the urban environment of a few
cities on the Canadian Prairie-parkland have pro-
vided a new and highly suitable man-made envi-
ronment for the Merlin {Falco columbarius)
(Oliphant 1974; Smith 1978). Following a few
nestings in the 1960’s and early 1970’s, the Merlin
population in the city of Saskatoon, Saskatchewan,
exhibited a dramatic increase. This population ex-
pansion has provided a unique opportunity to mea-
sure the actual rate of increase (r) of a raptor popu-
lation in a previously unused environment.

Methods

Surveys of suitable nesting habitat within the city were made
each spring. Taped calls of Merlin vocalizations, which were
utilized during the last 5 years, greatly reduced the effort needed
to detect breeding pairs. Reports of Merlin sightings were investi-
gated and often resulted in discovery of nests. In most years
(1974-82) the nests were not climbed until the last half of June
when the young were counted and banded.

A “breeding pair” was defined as a pair at a nest site at least into
the time of incubation. This criterion was necessary because many
pairs relocated in new territories even up to a week or two prior to
egg laying. A “successful nest” was one which produced at least
one advanced nestling of banding age. The number of young
produced was not known for some sites (nest not climbed or

Table 1. Numbers of breeding pairs of Merlins and production of young in Saskatoon from 1971-1982.

Year

No.

Breeding Pairs

Minimum No.
Young Produced

Estimated No.
Young Produced

Average No.
Young /Successful
Nest

Average No.
Young/Nest
Attempt

1971

1

3

3

3.0 ( 1)

3.0

1972

2

5

5

5.0 ( 1)

2.5

1973

4

4

8*

4.0 ( 1)

2.0*

1974

2

9

9

4.5 ( 2)

4.5

1975

3

14

14

4.7 ( 3)

4.7

1976

5

15

19*

3.8 ( 4)

3.8*

1977

6

22

22

4.4 ( 5)

3.7

1978

7

30

30

4.3 ( 7)

4.3

1979

10

37

37

4.1 ( 9)

3.7

1980

12

40

40

4.0 (10)

3.3

1981

14

57

61*

4.4(13)

4.4*

1982

16

50

54*

4.2 (12)

3.4*

Totals

Or

X ± SE

82

286

302

4.2 ± 0.03
(n = 68)

3.7 ±0.07
(n = 82)

* Productivity of one nest estimated as described in Methods section.

56

Raptor Research 19 (2/3): 56-59

Summer/Fall 1985

Population Growth of Merlins

57

YEAR

Figure 1. Growth of breeding population of Merlins in Saskatoon from 1971 to 1982.

number of young fledged unknown). Production at these sites was
estimated by assuming a successful nest produced young equal to
the average of all successful nests for that year and a nest with
unknown outcome produced young equal to the average of all
nests (successful and unsuccessful) for that year.

The actual rate of increase (r) per year of the breeding popula-
tion was estimated by taking the regression coefficient of loge of
the number of breeding birds versus year (Caughley and Birch
1971). Analysis of variance was used to test the significance of the
regression coefficient.

Results

Prior to 1 97 1 there were 3 Merlin nest records for
Saskatoon (1963, 1965 and 1970). Of the 82 known
nestings between 1971 and 1982, 71 were success-
ful, 10 failed and the outcome of one nest was
unknown. All of the nest sites were in old American
Crow (Corvus brachyrhynchos ) or Black-billed Magpie
{Pica pica) nests which, with three exceptions, were
in large spruce {Picea sp.) trees. Table 1 summarizes

the numbers of pairs and production of young
from 1971-82.

The growth of the breeding population is shown
in Figure 1 . Other than a decline in 1974, there has
been a steady exponential growth over the study
period. Regression analysis revealed a rate of in-
crease (r) per year of 0.233 ± 0.022. This linear
relationship was highly significant (F = 1 16.9; df =
1, 10; P < 0.001) and represents a 26% increase in
the breeding population per year.

Although Saskatoon has a total area of 122 km2,
only the older parts of the city have mature trees
offering suitable nesting habitat for Merlins. All of
the nest sites (1971 -82) were located within a 35 km2
core area. In 1982 all 16 pair nested within a 29 km2
area. The distance of each 1982 nest site to the
nearest adjacent nest site averaged 1.2 km and var-
ied from 0.7 km to 2.3 km.

58

Oliphant and Haug

Vol. 19, No. 2/3

Discussion

Several factors contribute to making the urban
environment of Saskatoon a suitable nesting habitat
for the Merlin. A primary factor is the presence of
spruce trees which were planted early in the history
of the city. As these trees matured they provided
suitable nesting habitat for Crows and Black-billed
Magpies. Houston (1977) has documented a major
influx of these two species into Saskatoon between
1968 and 1972. Until the large stick nests of these
corvids were present there were no suitable nesting
sites for Merlins which, like other falcons, do not
build their own nests.

Another important factor is prey availability. The
large urban population of House Sparrows (Passer
domesticus ) provides an abundant prey base heavily
utilized by the Merlins (Oliphant 1974; Oliphant
and McTaggert 1977). Prey density is probably the
most important factor responsible for the current
high breeding density of the Merlin.

A third factor is the proximity of the South Sas-
katchewan River which runs through the middle of
the city. The urban population was most probably
derived from the Merlins that occur naturally along
the major river systems on the prairies (Oliphant
and Thompson 1978; Houston and Schmidt 1981).

Nesting habitat, prey availability and intras-
pecific competition do not appear to be limiting
population growth in Saskatoon at this time. Given
these conditions, the calculated rate of increase (r)
of this population should approximate the
maximum rate of increase (r max) for this situation
(Caughley and Birch 1971). This assumes that the
population is closed (no ingress or egress). Al-
though this assumption is certainly not valid in the
strictest sense, we believe that the majority of birds
nesting in the city were indeed fledged from city
nests.

Opportunities to estimate the capacity for in-
crease of a wild raptor population are rare. Ratcliffe
(1980) describes the decline and resurgence of the
Peregrine Falcon (Falco peregrinus ) in Britain first
due to shooting and secondly to pesticides. Rates of
increase of the population were not calculated,
however.

The Merlins of Saskatoon have already achieved
the highest recorded nesting density for this
species. The overall breeding density for 1982 was
equal to 55.2 pairs/ 100 km2. The densest group of
nests was a group of 5 nests contained within 1.3
km2 (384.6 pairs/100 km2). Newton et al. (1978)

reported maximum Merlin densities of 10 and 13
pairs/ km2 in two study areas in northern Britain.
The closest nestings they recorded were 3 pairs at
the corners of a triangle 1.0 - 1.1 km apart. This is
very similar to the average distance between nearest
neighbors in the 1982 Saskatoon population. In
Wales (Williams 1981) the highest Merlin density
recorded was 9 pairs in 35 km2 (25.7 pairs/ 100 km2)
with 7 of these pairs found within 6 km2 (116.7
pairs/100 km2).

This high density in Saskatoon far exceeds re-
corded non-urban density on the Canadian
prairies. During a population study of Ferruginous
Hawks (Buteo regalis ) in southern Alberta, a
minimum Merlin nesting density of only 1 .9 pairs/
100 km2 was recorded (Schmutz 1982). In limited
areas of good habitat, however, non-urban Merlin
densities may be higher and occasionally pairs may
nest less than 1 km apart (A. Schmidt, pers. comm.)

Acknowledgments

Coordination of the Merlin survey was done by John Poison in
1980 and 1981 and by John Feldsine in 1982. We also thank Paddy
Thompson, Stacey Tessaro, Jane Jenkins, Adam Schmidt, Bob
Rafuse, Stuart Houston, Al Smith, Jim Slimmon, Bruce Hanbidge
and John Hanbidge for help with the survey or information on
Merlin nestings. Andy Didiuk and Dick Neal made constructive
comments on an earlier draft of this paper.

Literature Cited

Caughley, G. and L.C. Birch. 1971. Rate of increase./.
Wildl. Mgmt. 35:658-663.

Houston, C.S. 1977. Changing patterns of the Corvidae
on the prairies. Blue Jay 35:149-156.

Houston, C.S. and A. Schmidt. 1981. History of
Richardson’s Merlin in Saskatchewan. Blue Jay
39:30-37.

Newton, I., E.R. Meek and B. Little. 1978. Breeding
ecology of the Merlin in Northumberland. Brit. Birds
71:376-398.

Newton, I. 1979. Population ecology of raptors. Buteo
Books, S. Dakota. 399 pp.

Oliphant, L.W. 1974. Merlins - The Saskatoon falcons.
Blue Jay 32:140-147.

Oliphant, L.W. and S. McTaggert. 1977. Prey species
utilized by urban nesting Merlins. Can. Field-Nat.
91:280-286,

Oliphant, L.W. and W.J.P. Thompson. 1979. Recent
breeding success of Richardson’s Merlin in Saskatche-
wan. Raptor Res. 1 2 : 35-39.

Schmutz, J.K. 1982. An estimate of Ferruginous Hawks
in Alberta and the relationship between their density
and land use. Unpublished report for the Fish and
Wildlife Division of Alberta Energy and Natural Re-
sources.

Summer/Fall 1985

Population Growth of Merlins

59

Smith, A.R. 1978. The Merlins of Edmonton. Alberta
Naturalist 8:188-191.

Williams, G.A. 1981. The Merlin in Wales: breeding
numbers, habitat and success. Brit. Birds 74:205-214.

Department of Veterinary Anatomy, Western College of Veteri-
nary Medicine, University of Saskatchewan, Saskatoon, Sas-
katchewan, S7N OWO CANADA. Address of second au-
thor: Department of Biology, University of Saskatchewan,
Saskatoon, Saskatchewan, S7N OWO CANADA.

BREEDING BEHAVIOR OF THE MERLIN:
THE COURTSHIP PERIOD

John W. Feldsine and Lynn W. Oliphant

Abstract - Behavioral observations were made on an urban population of the Merlin ( Falco columbarius richardsonii)
nesting in the city of Saskatoon, Saskatchewan. Fourteen distinct behavioral displays and four vocalizations were
identified during the courtship period. The behavior of the birds was remarkably similar in most respects to large falcons
such as the Peregrine Falcon ( F . peregrinus), Prairie Falcon (F. mexicanus) and Gyrfalcon (F. rusticolus ), which have been
studied more thoroughly.

Information on the breeding behavior of the
Merlin is scanty and sometimes contradictory.
Brown (1976), referring to the British Merlin (F.c.
aesalon), states that “Merlins do not perform spec-
tacular aerial display flights” while Cramp and
Simmons (1980) briefly mention such aerial dis-
plays. Most of the literature dealing with Merlin
breeding behavior focuses on the nesting and rais-
ing of young (Rowan 1921-22; Craighead and
Craighead 1940; Lawrence 1949; Campbell and
Nelson 1975) with little information on behavior
during the courtship period. This study was de-
signed to compile an ethogram of the behavior of
the Merlin from pair formation to the time of egg
laying.

Methods

Most of the observations were made on a population of Merlins
nesting in Saskatoon, Saskatchewan, a city of 1220 ha. and a
population of 1 55,000 (see Oliphant 1974 and Oliphant and Haug
1984 for details of this Merlin population). Data were obtained
during a behavioral study conducted in 1982 and 1983 by John
Feldsine supplemented by casual observations between 1971 and
1 984 by Lynn Oliphant (estimated 800 h). During the 2 yr study 1 6
nest sites were visited each year from mid-January to the end of
April. A tape recording of Merlin vocalizations was played at each
site to draw out concealed birds and to initiate behavioral displays.
Scattered observations were made at several nest sites throughout
the day but the majority of observations was made between sunrise
and 1100 H. In addition, intensive observations of 2 pairs of
Merlins were made in 1982. A total of 1 75 h of observations were
made on these birds between February 17 and April 30 from a
parked vehicle using binoculars and a spotting scope between
sunrise and 1400 H. Casual observations were also made In 1982
on a pair of Merlins that raised young in captivity.

Results

We were able to recognize 14 courtship displays
and 4 primary vocalizations. The displays are in
some cases comprised of several components,
which may be employed in more than one display.
Not all of the displays described were seen in both
of the intensively studied pairs. These 2 pairs rep-
resented the seasonal extremes in terms of appear-
ance on territory; 1 pair was first observed courting
on territory on 16 February, the other not until 14

April. The early pair was not as elaborate or expres-
sive in its displays as was the late arriving pair, nor
did it display so frequently.

Vocalizations

1. Ki-ki-kee (Kek-kek-kek). This is the most
commonly heard call and takes on several different
forms, which vary in intensity, speed, rhythm and
number of syllables according to the situation. It is
used by both sexes with the male’s call higher in
pitch and more rapidly delivered. This call accom-
panies several courtship displays and territorial or
other aggressive encounters, although in an aggres-
sive context, it is deeper and resembles a kac-kac-
kac sound (Craighead and Craighead 1940).

2. Tic (Chip). Used by both sexes in almost all
courtship rituals and is typically repeated several
times at intervals of a few seconds. Again, the male’s
call is higher in pitch than the female’s. Often this
call is given alternately by the pair, especially when
near each other but not in visual contact.

3. Copulation Chutter (Copulation Bleat,
Chrrr). Somewhat like the sound made by a short
blast on a police whistle. When used by the male,
this call indicates a desire to copulate. Females occa-
sionally use it in encounters involving food, e.g.,
when the male returns with prey but fails to signal
for a food transfer. This may indicate an extremely
hungry female. Also used by non-resident birds of
either sex when approaching a resident female.

4. Food Begging Whine. Used strictly by the
female and consists of a series of monotonous
whining notes resembling a very slow ki-ki-kee. It
apparently tells the male either “give me the food
that you have” or “go get me some food”. Occasion-
ally females gave this call before, during and after a
copulation sequence. It resembles and is presuma-
bly derived from the begging call of the young.

Courtship Displays

1. Power Flying. One of the earliest male
courtship displays and may continue throughout

60

Raptor Research 19 (2/3): 60-67

Summer/Fall 1985

Breeding Behavior of the Merlin

61

the courtship period. It consists of a strong flapping
flight with deep wingbeats accompanied by rolls
which alternately display the dorsal and ventral as-
pects of the plumage when viewed from the side
(Fig. 1.1). Power Flying may be terminated by a
Slow Landing Display, Power Dive or a Rocking
Glide usually past a perched female and/or poten-
tial nest tree. Power Flying is used as a territorial
display to a rival or potential or existing mate.
When performed in the presence of a rival male it
reaches its greatest intensity. We have observed 2
males from adjoining territories Power Flying past
each other at their common boundary. The Tic-Tic
vocalization is usually given during this display.
Volume and frequency of the vocalization and
snappiness of the rolling vary with the intensity of
the display. One male was observed Power Flying
repeatedly over a period of about 1 wk followng the
death of his mate just prior to egg laying. No other
birds were observed in the area during these dis-
plays suggesting that Power Flying may be used to
attract potential mates into a male’s territory.

2. Power Diving. Another male display which
appears to be a more intense variation of Power
Flying with the only major difference being the
angle of flight (Fig. 1.2). This display may be in-
itiated by a direct high-level climb over the territory
or preceded by Power Flying at heights which may
reach several hundred meters. The steepness of the
dive may vary from about 45° to near vertical. Flap-
ping flight may continue throughout the dive ac-
companied by 180° rolls. As speed increases the
wings are partially folded. The dive may be termi-
nated with a U-shaped climb or often by Power
Flying or a Rocking Glide display past a potential
mate or nest site. The context of this display is one
of territory defense and advertisement. This dis-
play was most often precipitated by one or more
rival males on the resident male’s territory. As many
as 4 birds were present on some occasions, and we
suspect that the female copulated with one of the
rivals as well as the resident male. Cramp and Sim-
mons (1980) report that pairs were observed Power
Diving together. We have never observed females
Power Flying or Power Diving.

3. Rocking Glide. A less intense version of
Power Flying (Fig. 1.3). The components of the 2
displays are similar except that there is no flapping
flight with the Rocking Glide. The falcon initially
flaps to build up speed or comes out of a Power Dive
and then sets'the wings to glide. It then performs

90° - 1 80° rolls depending upon the speed attained
beforehand. As in the previous 2 displays the rol-
ling component of this display alternately flashes
the blue back and contrasting lighter underparts of
the male. The plumage contrasts are not so obvious
when the display is performed by females or im-
matures. Probably as a result of the slower flight
speed, the tail and wing feathers are somewhat
more flared than when Power Flying.

This is a fairly common display and was fre-
quently indulged in by both sexes, although more
often by males. Males may use this display to attract
mates to their territories or upon return to an es-
tablished territory. In the latter situation the male
begins rocking and sounding the Tic-Tic call when
passing by a perched female. The use of this display
by females was more aggressive and was most often
observed in response to a taped female call. Females
are often more aggressive than males in defense of
the nest site, and intruding females often elicited a
Rocking Glide display from a resident female. This
display was often terminated with a Slow Landing
display at the nest tree.

4. Flutter Flying. A common aerial display and
may be observed almost daily at an active nest site.
The flight pattern is usually circular or Figure-eight
shaped (Fig. 1.4). Flight speed is slow with rapid
shallow wing beats generally below the level of the
body. It is similar to the fluttering flight of the
Eastern Kingbird (Tyrannus tyrannus). The flight
often terminates in a Slow Landing display. Flutter
Flying probably functions as a mild territorial ad-
vertisement and/or display to a perched mate. The
Ki-ki-kee and/or Tic-Tic vocalizations are usually
given by the flying male, and the female often
answers.

5. High Circling/Soaring. Although the Mer-
lin is often reported as never soaring, we often
observed 1 or more (up to 4) birds circling at heights
up to several hundred meters. These birds often set
their wings and soared if conditions were favorable.
Circling/Soaring was seen by both resident and
non-resident birds of both sexes. In the former it
probably served as a mild territorial display while
for the latter it may serve as a means for surveying
another territory from an advantageous position.

6. Slow Landing Display (Hitched
Wing). Commonly a terminal component of other
displays, the Slow Landing display is a male display
made while coming in to perch (Fig. 1 .5). The flight
pattern when approaching the perch is similar to

62

Vol. 19, No. 2/3

Figure 1 . Diagramatic representations of twelve major courtship displays of the Merlin. Symbols ( <? 9 ) indicate the sex
of the bird typically making the display.

Summer/Fall 1985

Breeding Behavior of the Merlin

63

1-11

1-12

Copulation Solicitation

0" Nest Display

(Continuation of Figure 1.)

64

Feldsine and Oliphant

Vol. 19, No. 2/3

the flight when approaching for copulation. The
body attitude varies from about 45° to nearly verti-
cal and the legs are dropped. Movement is almost
entirely confined to the outer wing, and the tail is
generally fanned. Forward progress is slow and
owl-like. The bird alights stiff legged with head
bowed. Slow Landing may occur immediately be-
fore or after copulation and may also be a terminal
component of other aerial displays. When used be-
fore copulation, the copulation chutter may im-
mediately precede the Slow Landing display. On
other occasions the Ki-ki-kee call is given during the
flight or no vocalization is given.

7. Food Begging. A female display generally
made from a perch. When perched, the bird sits
with puffed out plumage (Fig. 1.6) and emits a
series of monotonous whines or wails, very much
like a slow Ki-ki-kee. Intensity and duration of the
call is probably a good indication of hunger level. If
very hungry she may flit from perch to perch emit-
ting the wails constantly. Often the male responds
by initiating a food transfer. If he is without food,
he may leave the territory, presumably to hunt. If
he does not respond and has food, she may fly to
him and initiate a Forced Food Transfer by
snatching the prey from him. If he is without food
she may supplant him from his perch. When
supplanted, the males usually left the territory pre-
sumably to hunt. The begging call is given almost
constantly during all of these actions and sometimes
continues after the male has disappeared. This dis-
play is performed exclusively by the female and is
very similar to the begging behavior of nestlings. It
reaches its maximum intensity a few weeks prior to
egg laying.

8. Food Transfers. We have observed 3 forms
of this display: air-to-air, perched, and air-to-
perch. Air to air transfers occur with the female
flying out to meet the male as he returns to the nest
site with food (Fig. 1.7). The birds fly toward one
another and rise in a simultaneous, nearly vertical
stalling climb until they are nearly breast to breast.
The male will often have transferred the food to his
beak. As they pass closely in the air the female
reaches out with a foot and grabs the prey. Rowan
(1921-2) calls this behavior Courtship Feeding and
considers it to occur only rarely. Aerial transfers are
much more common after the young have hatched
than during courtship period. Perched food
transfers take place much as described by Wrege
and Cade (1977) for the Peregrine (Falco peregrinis)

with bowing and sounding of the Ki-ki-kee and/or
Tic calls by both birds. The female sometimes
makes the Food Begging whine during the entire
ritual. On occasion the females seemed irritated,
aggressive and probably hungry. They flew quickly
to the male’s perch, often running towards him
upon landing, grabbed the food without display or
ceremony (a Forced Food Transfer). A variety of
calls was heard during these encounters, a very
excited and aggressive sounding Ki-ki-kee, a
Copulation Chutter, or the Food Begging whine
from the female, and a rapid, high pitched Ki-ki-
kee from the male. During Air to Perch Transfers
either bird may remain perched. If the male
perches he transfers the prey from foot to beak and
the female flies by and grabs it with a foot. Food
transfers begin rather late in courtship and increase
in frequency towards the time of egg laying.

Food caching is common throughout the breed-
ing cycle and is performed by both sexes (Oliphant
and Thompson 1976). Ritualized caching of prey
by the male within sight of the female followed by
retrieval by the female is commonly observed in
captive peregrines. Although we did not observe
this in the Merlin, it may well occur.

9. Supplanting. During supplantations, 1 bird
flies to another perched individual (generally a
male) and drives that bird from its perch (Fig. 1.8).
This behavior occurred in 3 different contexts: ( 1 )
a resident male supplanting a rival male, (2) the
resident female supplanting her mate and (3) one
or both resident birds supplanting an intruder such
as an American Crow ( Corvus brachyrhynchos) or
Blacked-billed Magpie (Pica pica). An aggressive
Ki-ki-kee call was usually heard during these en-
counters.

In all contexts this behavior may be interpreted as
a display of aggression and when used against in-
truders or rivals it also appears to be a defense of
territory. When occurring between the mated pair,
expression of female dominance seems the likely
motivation and may be used to encourage the male
to begin hunting.

10. Tail Chasing (Fig. 1.9). This behavior was
only observed on a few occasions. Once a female
was observed vigorously chasing her mate who had
just returned with prey. While chasing him she
repeatedly called using the Copulation Chutter. He
eventually dropped the prey. At another location a
female was observed chasing a male at great speed.
He appeared and sounded as if his life was in grave

Summer/Fall 1985

Breeding Behavior of the Merlin

65

danger. The chase coursed around trees and
shrubs 2 or 3 m off the ground. The pair soon
disappeared and the outcome was not determined.
Cramp and Simmons (1980) report that tail chases
often end in copulation. Captive female Merlins
have been observed to pursue actively their mates.
These tend to be very aggressive interactions, and
when this occurs in confinement, the male is some-
times killed (Campbell and Nelson 1974). The
female from our captive pair caught and grappled
with her mate on several occasions in 1 982 just prior
to egg laying. Clipping her primaries reduced her
flight ability and normal mating occurred soon
after. In 1983 this female killed the male in spite of
having her primaries clipped. Apparently it is
necessary for the male to have plenty of space in
order to avoid being caught by the female.

11. Prominent Perching. Merlins often perch
on a high vantage point near the nest site for long
periods of time (Fig. 1.10). This is probably a ter-
ritorial advertisement, but often appears to be sim-
ply loafing. The bird surveys the surrounding area
constantly and occasionally may preen or sound the
Ki-ki-kee or Tic-Tic calls. This was a commonly
observed behavior most often involving the male,
but occasionally the female. A large high rise
building was often used by both sexes and acted as a
focal point for many aerial displays by the males.
Television antennas and certain trees (spruce and
weeping birch particularly) also offered favored
perch sites in Saskatoon.

12. Male Precopulation Display. The male has
a number of ways in which he signifies readiness to
copulate. He most often perches in a tree close to
the tree where the female is perched and may call
frequently (Ki-ki-kee and/or Tics). He may also bow
and fan his tail. J ust prior to flying to the female he
stands tall, stares intently at the female and utters
the Copulation Chutter one or more times perhaps
in response to a mild solicitation by the female or
perhaps attempting to initiate solicitation. When
flying towards the female he uses the Flutter Flight
with his legs dangling, often continuing to give the
Copulation Chutter. Copulation ensues if the
female is receptive with the final mounting of the
male being similar to the Slow Landing Display.

13. Female Copulation Solicitation (Fig.
1.11). The female signals readiness to copulate by
bowing deeply and fanning her tail. This often fol-
lows an exchange of vocalizations with the male and
Precopulation Displays by the male. Both birds

typically vocalize during copulation. The female
makes a modified hoarse Ki-ki-kee call and often
makes a slow drawn out Ki-ki-kee immediatly fol-
lowng copulation while the male Chutters. The
male often makes a Slow Landing Display following
copulation. Copulation may occur very early dur-
ing courtship (up to 3 or more months prior to egg
laying) but becomes much more frequent (up to
several times an hour) as egg laying approaches.

We have not considered copulation as a courtship
display in itself, but it is obvious that copulations
that precede egg laying by several weeks to months
do not function in fertilization but rather to cement
the pair bond.

14. Male Nest Display (Fig. 1.12). Both sexes
enter potential nests and often make Tic vocaliza-
tions during the courtship period. Since it was gen-
erally impossible to observe the birds when on the
nest, our only observations of this display (3) are
from our captive pair which were watched from
behind one-way glass looking into the nest. In this
display the male lowered himself on the nest as if he
were settling on eggs. He then extended his wings
and drooped them and fanned his tail nearly verti-
cal. He extended his head forward and then with-
drew it while arching his back. The drooping wings
were trembled throughout the display. As the head
was extended forward, the tail and lower back were
raised above the horizontal so as to display the fan-
ned tail and dorsal plumage. The female was a
passive observer on the edge of the nest during the
entire display with the male facing the female. No
vocalizations were given. This display is very similar
to that of a juvenile House Sparrow {Passer domes-
ticus ) begging food from an adult, and was First
reported by Fyfe (in Trimble, 1975).

Discussion

In describing the behavior of the Merlin, we have
drawn somewhat arbitrary lines between individual
displays or vocalizations as well as between what we
classified as a complete display and what was simply
a display component. Many behavioral actions
(rocking in flight, bowing, tail flashing) were thus
considered components of displays rather than dis-
plays in themselves. We have attempted to follow
accepted terminology and classification from pre-
vious descriptions of falcon behavior although
some deviation was necessary. For example, Wrege
and Cade (1977) and Nelson (1977) consider the
Head Low Bow to be a major display of the pereg-

66

Feldsine and Oliphant

Vol. 19, No. 2/3

rine. We do not consider it well developed enough
in the Merlin to be considered any more than a
component of other displays.

The difficulties of assigning a particular func-
tional significance to displays that are probably
often, if not always, multifunctional should also be
recognized. The primary functions of behavioral
displays during the courtship period include the
establishment and defense of a nesting territory,
attraction of a suitable mate and the establishment
of a strong pair bond, all of which are necessary for
successful breeding. Determining which of these
functions are the primary focus of a given display is
difficult to ascertain simply from the context of the
situation without experimental manipulation.

Vocalizations

The courtship vocalizations used by Merlins are
similar both in structure and context to those of the
large falcons with which we are familiar (the Pere-
grine, Gyrfalcon and Prairie Falcon). They differ
mainly in having a higher pitch associated with their
smaller body size. The Tic call is the most divergent
and is a short stacatto version of the large falcons’
“Eechip” call. It is the most like the shortened
“Chup” version of this call not having the high
pitched initial segment. The Female Begging call or
“Treble Whine” (Nelson 1977) and Copulation
Chutter are almost identical to those of the large
falcons, and the Ki-ki-kee is the equivalent of the
large falcons’ deeper Kac-kac-kac. In general, the
Merlin is more vocal than large falcons with the
possible exception of the Gyrfalcon which appears
to have a more varied and frequently used vocal
repertoire.

Courtship Displays

The courtship behavior of the Merlin and espe-
cially aerial displays has been largely overlooked
in the literature (Rowan 1921-22; Trimble 1975;
Cramp and Simmons 1980). In contrast to the con-
clusion of Cramp and Simmons that display flights
are “rather inconspicuous and rarely observed,” the
Merlins we observed regularly performed complex
aerial courtship flights that were nothing short of
awesome. The Power Flying and Power Diving
flights with side to side rolls are essentially identical
to those described for the peregrine by Nelson
(1977) and are presumably similar to other large
falcons (Cade 1982). The impression given by the
Merlin, while performing these displays, is one of a

much larger, heavier and more powerful falcon.

Other behavioral displays that the Merlin shares
in detail with the peregrine include the Slow Land-
ing Display, High Circling/Soaring, Prominent
Perching, Flutter Flying, Female Begging, Food
Transfers and Supplanting. Bowing is much less
prominent in the Merlin than large falcons, al-
though it is present as a low intensity component of
several displays. Rarely is the deep bowing, typical
of large falcons, seen in Merlin displays. The Nest
Ledge displays typical of both sexes of large falcons
(which include much bowing) may be absent in the
Merlin, being replaced by the very different male
nest display, possibly as a result of the spacial limi-
tations imposed by the stick nests typically used by
Merlins in North America. Nest displays in ground
nesting populations of Merlins may be different.
Although we did not describe it as a separate dis-
play, scraping movements similar to those of cliff-
nesting falcons were made by our captive pair as
evidenced by a well-developed nest scrape on a
gravel ledge their first year (1981). Cramp and
Simmons (1980) describe a Female Nest Display
similar to the motions of settling on eggs, and we
observed both sexes of wild pairs repeatedly visiting
potential nests and could hear Tic-Tic vocaliza-
tions. Scraping on the stick nest cup may well be
occurring at these times or possibly mild forms of
the Nest Ledge Displays typical of large falcons.

Fanning or flashing the tail appears to be much
more common in the Merlin than large falcons. It is
often seen as a component of male displays and is
typical of Copulation Solicitation of the female
where the tail is kept fanned until actual mounting
by the male. The sharply contrasting tail of the
Merlin makes this a potentially strong visual
stimulus. Merlin courtship behavior is decidedly
more complex than that of the American Kestrel (F.
sparverius), although the displays which are com-
mon to both species are similar. Two distinct aerial
displays have been described for the kestrel, the
Flutter Glide and the Dive display (Willoughby and
Cade 1964). The Flutter Glide is performed by
kestrels in much the same manner as Flutter Flying
in Merlins. In the kestrel this type of flight is per-
formed mainly by the female, while in Merlins it is
more commonly performed by males. The kestrels’
Dive Display is similar to the Undulating Flight
Display of the peregrine and Gyrfalcon as de-
scribed by Nelson (1977) and Cramp and Simmons
(1980). We have not observed it in the Merlin al-

Summer/Fall 1985

Breeding Behavior of the Merlin

67

though it is somewhat similar to Power Diving. The
overall behavioral repertoire and intensity of dis-
plays of the Merlin is markedly more similar to the
large falcons than to the kestrel.

Our lack of observations of overt intraspecific
aggression directed toward non-resident birds was
somewhat surprising as most falcons are thought of
as being highly aggressive and territorial (Wrege
and Cade 1977; Nelson 1977; Cade 1982). We have
observed only 2 cases where actual physical contact
between the resident bird (both males) and non-
resident birds (also males) was made and both of
these occurred in the fall. Only one case of overt
aggression was observed during the courtship
period when an adult male swooped on another
male from a great height near a territorial bound-
ary. The attacked bird screamed and was visibly
upset, but no further interaction ensued. Non-
resident birds (both adult and immature) were reg-
ularly seen on established nesting territories. In-
teraction ranged from completely ignoring the in-
truder to a variety of territorial displays, including
Power Flying and Diving, Rocking Glide and Slow
Landing Displays by the resident male. Earlier in
courtship, before nest site selection and final estab-
lishment of territorial boundaries, group displays
by several birds are not uncommon. Once such
group display involved 4 adult males and at least 1
female (W.J.P. Thompson, pers. comm). Although
it is often difficult to keep track of individual birds
when several are present, we feel that copulation
attempts (some successful) by non-resident males
may occur relatively frequently.

Given the lack of intraspecific aggression di-
rected towards non-resident birds by a territorial
pair, it is somewhat surprising that the female of a
pair is sometimes so aggressive towards her mate.
At least in captivity, high proportions of females
regularly attack their mates and often succeed in
killing them. This appears to be much more fre-
quent among Merlins than larger falcons. Similarly

interspecific aggression directed towards other

raptors, crows, etc., is often intense and is carried

out by both sexes.

Literature Cited

Brown, L. 1976. British birds of prey. London, Collins.

Cade, T.J. 1982. The Falcons of the world. New York.
Comstock/CoRNELL Univ. Press.

Campbell, J.A. and R.W. Nelson. 1975. Captive
breeding and behavior of Richardson’s merlin, 1974.
J. N. Am. Falconers Assoc. 14:24-31.

Craighead, J. and F. Craighead. 1940. Nesting pigeon
hawks. Wilson Bull. 52:241-248.

Cramp, S. and Simmons, K.E.L. (Eds.) 1980. Handbook
of the birds of Europe the Middle East and North
Africa. The birds of Western Palearctic. Vol. II. Hawks
to Bustards. Oxford Univ. Press.

Lawrence, L. de K. 1949. Notes on nesting pigeon
hawks at Pimisi Bay, Ontario. Wilson Bull. 61:15-25.

Nelson, R.W. 1977. Behavioral ecology of coastal
peregrines ( Falco peregrinus pealei). PhD. thesis, Univ.
Calgary, Calgary, Alberta.

Oliphant, L.W. 1974. Merlins — The Saskatoon fal-
cons. Blue Jay 32:140-147.

Oliphant, L.W. and W.J.P. Thompson. 1976. Food
caching behavior in Richardsons merlin. Canadian
Field-Natur. 90:364-365.

Oliphant, L.W. and E. Haug. 1984. Productivity
population density and rate of increase of an expand-
ing merlin population. Raptor Research (This Issue).

Rowan, W. 1921-2. Observations on the breeding habits
of the merlin. British Birds 15:122-129; 194-202; 222-
231; 246-253.

Trimble, S.A. 1975. Report No. 15, Merlin -Falcocolum-
barius. Habitt management series for unique or en-
dangered species. U.S. Bureau of Land Management.

Willoughby, E.J. and T.J. Cade. 1964. Breeding be-
havior of the American Kestrel (Sparrow hawk). Living
Bird 3:75-96.

Wrege, T. and T.J. Cade. 1977. Courtship behavior of
the large falcons in captivity. Raptor Research 11:1-27.

Department of Veterinary Anatomy, Western College of Veteri-
nary Anatomy, University of Saskatchewan, Saskatoon, Sas-
katchewan, S7N OWO CANADA.

CAPTIVE BREEDING OF THE EUROPEAN MERLIN (Falco columbarius aesalon)

William Ruttledge

Abstract - Two pairs of the European Merlin (Falco columbarius aesalon) were established in two contiguous Hurrell-
type skylight and seclusion breeding pens in 1 977. One male had been taken from the wild, the other 3 were captive-bred
Fi’s. Both males were in adult plumage but the females were sub-adult. All had been manned and were tolerant of limited
intrusion that became necessary. A choice of nest site between an artificial crow’s nest and a roofed open nest-box was
provided in each pen. The crow’s nest was chosen in one pen, the nest-box in the other. Provision of ground sites was
considered to be unnecessary. Nest-site selection, food passing, mating, egg-laying, incubation and hatching are
described, followed by feeding and development of the young. One pair laid 4 eggs; 1 hatched. The other laid 5 eggs; all
hatched. Owing to the apparent initial inefficiency of the parents in feeding newly hatched young because of interference
by the male, the singleton and 2 of the brood of 5 were removed to a brooder and hand-fed until about 8 d old. The
former was returned to its parents, and the other 2 were fostered with that pair. All young were reared successfully and
five were issued on loan to falconers. Incubation period was between 3 1 and 32 d. The earliest to roost away from the nest
were 2 males in their 25th d, and the latest a female in its 28th d. The males were hard-penned at about 40 d. The diet
comprised half-grown surplus laboratory white mice, of which an ample deep-frozen supply was available.

This work was done at Beckhampton, Marlborough, Wiltshire.

The breeding of the European Merlin (Falco col-
umbarius aesalon) in capativity in 1977 described
here was not the first success in a project begun in
1971. A pair allocated to L.H. Hurrell had already
bred in 1975 and 1976. Hurrell had shown a film of
the breeding at the I.C.B.P. Conference on Birds of
Prey, Vienna (1975), the Hawk Trust’s Conference,
Harrow, Middlesex ( 1 976), and at the International
Conference on Falconry and Conservation, Abu
Dhabi (1976). It seemed desirable to publish a de-
tailed account and to recognize the considerable
support given by the Scottish Home and Health
Department in granting a licence, in 3 successive
years, to take a young Merlin from the wild for use
in the project.

Breeding Material Available - Two males and 2
females of the European Merlin were used. They
were a 1974 Scottish-licensed male (Lochan), a 1975
captive-bred Fi male (Brae), and two 1976 captive-
bred Fi females (Myrtle and Corrie) from the first,
kestrel-fostered, and the second, Merlin-reared,
clutch, respectively, from the pair with Dr. Hurrell.
This pair comprised a 1973 flight-impaired male
(wild taken) (Laggan) and a 1973 Scottish-licensed
female (Erica).

It should be noted that whereas the 2 males were
adult approaching 3 and 2 yr old, respectively, the 2
females were not yet 1 yr old. All 4 had been previ-
ously manned and were so up to the breeding sea-
son.

Accommodation - A pair of contiguous Skylight
and Seclusion pens (Hurrell in Mavrogordato,
1973) on a south-facing wall 2.40 m high, topped
with concrete slabs, was used. Sections of the wall
4.50 and 3.30 m long formed the backs of pens 1

and 2, respectively; the sides, each 5.80 m long and
2.40 m high, were of translucent corrugated
polythene, as were the 4.50 m - and 3.30 m - long
south walls (Fig. 1). The roof was 45 mm square-
mesh, heavy nylon netting spread 50 mm below a
layer of 40 mm wire netting.

The timber-walled observation hide was in the SE
corner of pen 1 and SW corner of 2, with access
from outside. Access to each pen was by a small
door, opening outwards from the pen into the hide.

Nest Sites - Each pen had 2 elevated nest sites; an
artificial crow’s (Corvus sp) nest with overhead
shelter from rain, and an open nest-box of a shallow
wooden tray 70 cm long x 35 cm from back to front
x 1 0 cm deep with a rain-proof roof sloping from 40
cm height in front to 30 cm at the back. A landing
board 20 cm wide was along the front. Nest-boxes
were placed in both pens on the north-facing wall
within 1.50 m of the hide in full view. In pen 2 the
crow’s nest was between the hide and nest-box. In
Pen 1 the crow’s nest was left in its 1976 position
under the south-facing wall. Owing to its distance
from the 2-way mirror in the hide it was necessary
for this crow’s nest to be no more than 0.75 m from
the ground for its contents to be visible. All other
sites were 2 m from the ground. Moreover, in order
to see details in the crow’s nest in pen 1 at this
distance (about 5 m) a pair of binoculars with short
range focus were useful.

In Britain Merlins usually nest on the ground in
either heather (Calluna vulgaris) or bracken
(Pteridium aquilinum). Therefore, much time was
spent in 1971 in providing them. This proved un-
necessary, however, as no pair showed any interest
in ground sites. Additionally, an old crow’s nest had

68

Raptor Research 19(2/3): 68-78

Summer/Fall 1985

Falco columbarius aesalon

69

I i I i I i I i I i I

0 1 2 3 4 5

METERS

Figure 1 . Plan of both pen 1 and 2. D or d - door area, H - hide, ft - feeding trays, bb - bath, nb - nest-boxes, c - cairn, cn -
crow nest, at- artificial tree, b - bracken, h - shuttered hatch, v t - vertical tree, i p - isolated post, h b - tree
branch, w a - wall tree.

been placed in the top of an artificial tree (a section
of a pine tree (. Pinus sp) with the top cut out) in the
pen’s NW corner. A prototype of the nest-box, in-
tended to represent a cliff site, had been attached to
the south-facing wall as well.

Before the 1977 season the old crow’s nest was
removed because it was too high for visibility. The
trees, however, continued to be used as a perch. It
appeared that the natural crow’s nest was not dura-
ble enough to withstand the early destructive ac-
tivities of Merlins pulling at twigs and scraping in
the nest cup. By 1977, a more robust artificial crow’s
nest was designed with a very durable cup plastered
with a mixture of silt and rotted farmyard manure.
The cups were partly filled with a mixture of peat
and coarse sand, on the surface of which was scat-
tered a layer of 30 - 40 - mm - long pieces of thin dry
twigs. The tfays of the nest boxes were similarly

treated. The twig chips supplied material for the
female to pick up. We observed incubating Merlins
break off pieces of twig from parts of the nest within
reach and drop these into the nest cup at the bird’s
breast. A female was seen doing this while lying in
the nest long before oviposition; the male also did
so, but less often.

Diet - Half-grown frozen laboratory mice were
fed, but until early April 1977 day-old cockerel
chicks occasionally made up 50% of the daily ration.
On all such occasions the chick’s yolk sac and intes-
tines were removed and feet and tarsi cut off. The
chicks were also roughly skinned and cut up into
head, thoracic and pelvic portions. There were
grounds for thinking that excessive intake of chick
yolk was undesirable and that feet and tarsi, swal-
lowed whole, tended not to be digested.

After early April the diet was 100% laboratory

70

William Ruttledge

Vol. 19, No. 2/3

DATE

Figure 2. Sequence of behavior in No. 1 Pen. (1) a. female harassing male; b. male still mistrusting female; c. male
bonding with female; d. male food caching. (2) a. male nest scraping; b. female nest scraping; c. female in
scrape; d. female starts twig pulling; e. male site display; f. female site display. (3) a. male kwi call; b. male kip
call; c. femal ekwey call; d. femal echup call. (4) a. female responds to male food call; b. beak-to-beak food pass.
(5) a. male mating approach; b. copulation attempt; c. successful copulation; d. oviposition lassitude; e.
female pouchiness; f. eggs laid. (6) eggs hatch - 3 on 20 June, 1 on 21 June, 1 on 23 June.

mice. The adults did not pluck the mice very
thoroughly, although it was noticed that as the
breeding season approached more extensive
plucking was done, particularly by the male when
food passing had begun. Therefore, for the first 10
d after hatching of the young, all mice, except those
put in after dark for the early-morning feeding,
were ‘prepared’ to reduce the ratio of fur to flesh in
each food item. In what came to be known as “Mark
I (MK I) prepared,” the mouse head was removed,
the body skin loosened from the body, which was
pushed further into the skin and the surplus skin
cut off. In “Mark II,” the headless body of a rather
smaller completely skinned mouse was packed in on
top of a MK I preparation, the neck skin of which
was then tied with white cotton thread, thus further
reducing the ratio of fur to flesh.

In the present study, preparation of MK II mice
was used. It seemed that feeding of young ended
when the food item had been distributed to them
rather than when their hunger had been satisfied.
Therefore, the larger size of the MK II mouse was
likely to be beneficial.

Making up of Pairs - The 1975 captive-bred Fi
male (Brae) had been in pen 2 with 2 sibling males
for over 1 yr by 4 December 1976 when the 2 latter
were removed. The 1976 captive-bred Fi female
(Myrtle) was then introduced. They had settled
down together within a week. Circumstances did
not permit the release of the 1974 Scottish male
(Lochan) into pen 1 before the 1976 captive-bred Fi
female (Corrie) had become established there. He
had been familiar with pen 1 and, when introduced

Falco columbarius aesalon

71

Summer/Fall 1985

Figure 3. Sequence of behavior in No. 2 Pen. (1) a. male food caching. (2) a. male nest scraping; b. female nest
scraping; c. female on scrape; d. female twig pulling; e. male site displays. (3) a. mal ekwi call; b. mal ekip call;
c. female kwey call; d. female giving young call. (4) a. female takes food from cache; b. male offering food; c.
attempted male/female food pass; d. successful beak-to-beak food pass. (5) a. male mating flights at female;
b. female deters mating flights; c. apparently successful copulation; d. as in b; e. other successful copulations;
f. oviposition lassitude; g. eggs laid. (6) first egg hatched, (remainder infertile).

on 6 February 1977, seemed at first to hold his own
but soon became nervous of Corrie, particularly
when he had food, on which occasions she was liable
to harass him. Reasonable accord was not achieved
until towards the end of March and full confidence
was not shown until the end of April.

Observations - Regular daily observations on
both pairs were made, particularly at feeding time.
The sequence of the more important steps up to
and including egg hatching is shown separately in
Figures 2 and 3.

Although egg-laying began earlier in pen 2 than
in pen 1, the cycle in pen 1 is shown in Figure 2
before that in pen 2 (Fig 3) because there were more
apparent abnormalities in the latter.

The only apparent irregularity in pen 1 was the
delayed start of caching food by the male (Fig 2, 1 d)

by about 9 d, as compared with pen 2 (Fig 3, la)
which might be attributed to persistence of harass-
ment of the male by the female (Fig 2, la, lb). When
it did take place, it did not initiate the food pass, the
latter taking place on the day following the first
observed occasion of the male’s calling kwi . . . with
food in his beak. The food pass (4b) took place with
its accompanying kwi and kwey calls (3a, 3c) while
nest-site selection (2e, 2f) was still going on. The
food pass was quickly followed by mating approach
flights (5a), the early ones of which were deterred
by the female. A possibly successful mating took
place after 3 d (5b), and probably successful ones 2
d later (5c).

Oviposition lassitude (5d) was evident 3 d after
the first observed possibly successful mating; and
sagging of the abdomen (pouchiness) (5e) on the

72

William Ruttledge

Vol. 19, No. 2/3

following day. On the next day the first of 5 eggs
(5f), laid at 48-h intervals was seen. Dates of laying
were 15, 17, 19, 21, 23 May. Three hatched on 20
June before 1 100 H, 1 on 21 June by midday, and
the final 1 on 23 June. This suggests that incubation
began 1 d before egg No. 4 was laid, giving an
incubation period of 31-32 d.

In pen 2 the breeding cycle was delayed after
nest-site selection by the prolongation of the stage
of food caching by the male and collection by the
female (’’remote food passing” of Nelson 1977,
quoted by Cade, 1982, p. 25). This was due to the
failure of the female to respond adequately for over
a week (4b) to food items offered by the male.
There was a further delay (5a, b, d) before appa-
rently successful mating took place (5e), by which
time oviposition lassitude had been apparent for 5 d
(5f), and two eggs had been laid (5g). This delay
might account for the infertility of 3 of the 4 eggs.

During oviposition lassitude, about 3 d before the
first egg was laid, the female performed a move-
ment (8 in Id), here termed ‘dunking’, similar to
that made when sousing the under-tail coverts
during bathing. It was difficult to be certain when
incubation began, but it probably did not until 1 1
May, the day on which the fourth and last egg was
laid.

Site-Selection Display - On arrival at the scrape
the male held his wings high over his back for a
moment, with the tips pointing upwards. In the
complete pattern the male then partly lowered the
wings and walked about on the nest in a stilted
manner for a short time before starting to bow
towards the female. In this, the head, body, and
partly open wings would be aligned horizontally in
her direction with the tail, usually partly fanned,
cocked up at an angle. At the bottom of the bow, the
wing tips and tail were pointing upwards at an
angle of perhaps 30°. The soft kip call would be
uttered during bowing.

Mutual bowing displays over the nest scrape oc-
curred occasionally. Male bowing in the nest scrape
while holding a mouse in his beak occurred and was
probably part of food-pass display. On 3 May, be-
fore beak-to-beak passing had been achieved in pen
2, the male was doing this, and then deposited the
mouse in a corner of the nest-box. After he had
done so, the female arrived and took the mouse. He
flattened out in the scrape with wings slightly open
and held this position until the female moved slowly
to the front of the nest-box and flew to the other

end of the pen. He had been seen in a similar
position on 2 May with the female standing
alongside and later settling down in a lying position.
She nibbled at his beak.

The crows nest was used in pen 1 and the nest-
box was used in pen 2.

Food Caching by the Male - This might take
place either as initiation of the food pass (“remote
food passing”) or when for any reason the male had
a food item not required by the female.

In the former case the site chosen was where the
female could see what he was doing; in the latter it
was usually in a more concealed position. The food
item, still in the beak, would be deliberately pushed
into the chosen position and left there, after which
the male would stand up tall, looking intently at it,
then back away a few steps before leaving.

Mating Approaches and Mating - The male indi-
cated his intention to make an approach by
stretching his head forward, sleeking his body
feathers and slightly opening the wings in the plane
of the body. The tail was held lower than the plane
of the body, giving an arched-back effect. He stared
in the direction of the female, and on taking off in
flittering flight, uttered a specific, single, rather
drawn-out call, kwark. If the female was prepared to
accept him, she assumed a horizontal position and
remained steady as he mounted; he might maintain
his position by beating his wings. If, however, she
intended to deter him, she uttered a single call, koi,
or gave some unidentified signal, which may have
been failure to adopt the accepting attitude.

On only 2 occasions was a call heard during mat-
ing, uttered by the female, which could only be
recorded as either kwey . . . kwek or something re-
sembling the young food-call (eep . . .eep).

Protest Flying - In April increasing evidence of
territorial awareness was marked by what may be
described as ‘protest flying’ against low overflying
birds. Both of a pair, or both pairs, would suddenly
start flying wildly around the pen, sometimes
throwing themselves feet upwards against the roof
netting, and uttering calls of anger or alarm, (kek,
kek, kek . . . ).

Even after incubation began the sitting bird
would come off and take part. The protests seldom
lasted more than 1 min, and eggs were usually
quickly covered again. The female in pen 1 reacted
more strongly to intruders than did the others.

Feeding of the Female during Incubation -
During incubation the male provided most but not

Summer/Fall 1985

Falco columbarius aesalon

73

all of the female’s food. He took mice from the
feeding tray to a regularly used plucking perch.
When it was adequately plucked he called kwi . . .
kwik and awaited a positive response, the kwey
. . .kwek call of the female and her arrival to receive
it there. Occasionally he transferred food at the
nest. The female ate the item away from the nest
and the male would promptly cover the eggs. After
feeding, the female sometimes did not return to
incubate immediately. If there was no response
from the female to the male’s call, he would either
eat the mouse or cache it.

Hatching - Signs of possible approach of hatch
were noted in pen 2 on 10 June (probably d 31 of
incubation) although no pipping of the eggs could
be seen. The female was doing a greater share of
the incubation, was reluctant to come off when
given a food item, and later would not allow the
male to take over incubation. She was doing an
unusual amount of looking down towards the eggs,
and continued to draw in twig chips. Twice on the
following day both birds were in the nest scrape.
One young was seen at 1500 H.

In contrast, the pair in pen 1 showed no air of
expectancy at the corresponding time and on d 30
of incubation the female left the eggs uncovered,
after having come off to feed, for intervals of 5-7
min.

Feeding of the Young - In pen 1 the first hatch-
ling was seen at 0700 H. The first observed feed
took place at 1030 H, by which time there was a
second young, which also received food. Al-
together, 5 feedings were seen between 1000-2050
H on d 1. Intervals between known consecutive
feedings ranged from 1 to 1 V2 h. At a later date (d
11), 7 feedings were observed. Times between
known consecutive feedings ranging: 3A h, 1 h, 1 h,
1 h.

Interference by the male, usually an interception
and eating of food morsels that were being offered
the young, took place frequently from d 2 until
about d 6, when at least some of the intercepted
morsels were passed to the young.

In pen 2 no further egg hatched after 1 on d 32.
Interference by the male was more disruptive and
on d 3 the young was temporarily removed for
hand-feeding. The parents continued to incubate
the remaining eggs.

By d 4, it seemed that the youngest (No. 4) in pen
1 was not getting enough food in competition with
the 3 older siblings. It was removed to a brooder for

hand-feeding. In anticipation of similar difficulty
with young No. 5, it was removed as soon as possible
after hatching. These 2 young were subsequently
fostered into pen 2 on d 11 and 12.

In spite of the early interference, the males con-
tinued their plucking and offering of mice (now all
MK II prepared) to females as they had done dur-
ing incubation. During the first week, the male
transferred food at the nest, but thereafter she flew
to him on his plucking perch when he called.

In pen 1, full co-operation with the female in
feeding was established by d 11. The male was first
seen feeding alone on May 14, and on d 20, each
parent took a mouse to the nest at the same time and
distributed morsels separately. In contrast, the
male in pen 2 was seen feeding alone only once.
When offering morsels of food, the female used a
single, soft chup call, of which the male’s version was
kip.

Development of the Young - Development of the
young in pen 1 is shown in Table 1. When first
hatched, they were covered with white down
through which body colour was partly visible, giv-
ing the impression that the down was faintly pink in
colour.

The eyes appeared to be sufficiently open for the
young to see and snap at food morsels on d 4. Their
movement in response to temperature coincided
with being left uncovered at intervals from d 8
onwards. Parents shaded them during midday
heat. On d 13 we provided overhead shade for the
nest. This was providential because between d
13-18 a very hot spell occurred with temperatures
reaching 27.5°C.

On d 1 9 a ladder was installed from the ground to
the nest, and it was used on d 24 to 25 by the young
to regain the nest. Within a further 2 d, 2 young
roosted away from the nest. Although they were
able to break up a food item effectively from d
24-26 they were still fed up to d 30. It was expected
that they would be hard-penned soon after primary
No. 9 (counted from carpal joint outwards) was as
long as No. 8. This occurred at about d 38-40. The
rates of growth for Nos. 4 and 5, while being hand-
fed are shown in Table 2, and some weights for all 5
are given in Table 3.

The development of the single female that
hatched in pen 2 is shown in Table 4. The con-
tinued incubation of the remaining eggs facilitated
the return of it after being hand fed from d 3 - 9.
The unhatched eggs were infertile. Although the

74

William Ruttledge

Vol. 19, No. 2/3

hand-fed male young were about 12 d younger
than the female in pen 2 they were adopted. The
female young did not roost away from the nest until
d 28.

The hand-fed young (Table 2) were accommo-
dated in the brooder in a shallow bowl lined with

tissue paper surrounded by a bound ring of twigs.
They were given 8-9 feedings between 0700 and
1300 H of the following day. No. 4 was returned to
parents on its 8th d, but was transferred to pen 2 on
its 11th d. No. 5 was fostered direct from hand-
feeding to pen 2 on its 8th d.

Table 1. Development and progress of the nestlings in No. 1 Pen.

Day number

Feature

(from hatching of Nos. 1-3)

Hatching of Nos. 1-3

1

Hatching of No. 4

2-

Hatching of No. 5

4

No. 4 removed for hand-feeding (aged 2d)

4

No. 5 removed for hand-feeding (aged a few hours)

4

Nestlings left uncovered at intervals

8

Movement of nestlings on nest in response to temp

8 — ►

Wing-flapping and rousing

8

Close ringing

8-9

Parents shade young in midday heat

8, 10, 11

No. 4 returned to pen

9

No. 5 fostered direct from hand-feeding into No. 2 pen

11

No. 4 transferred to No. 2 pen

12

Overhead shade provided for nest

13

Hot spell (shade max. 24-27. 5°C)

13-18

Sitting up on tarsi prolonged

14

White down superseded by smoky grey

11-14

Rectrice tips and remige quills visible

13 - 14

Active interest in movements of parents

15-16 — ►

Standing up on feet; begin to walk

17

Increase in wing-flapping

17

Walking actively on nest

19

Ladder from ground to nest installed

19

Two nestlings perched outside nest in contiguous tree (Fig. 1 wa)

22

One nestling on ground (returned by hand)

23

Parents leave food for nestlings to break-up (with partial success)

23

Two pale bands visible on tails

23

Two nestlings on ground; one bathed; both returned to nest by ladder

24

Nestlings break-up food effectively

24-26

All 3 nestlings on ground; 2 colour-ringed

25

The two more advanced nestlings roost away from nest

25

Flying activity progresses

26 — *

Much time spent lying on nest or elsewhere, apparently asleep

26-38

Last occasion when a parent feeds morsels to a nestling

30

A nestling takes food from tray

29

A nestling caches food item received from parent

30

Nestlings believed to be hard-penned

38-40

Nestlings taken up for training

40 - 41

Summer/Fall 1985

Falco columbarius aesalon

75

Table 2. Routine weighings of two nestlings hand fed up to day eight.

Weight(g) and Time
Day

Nestling 1

1 - 2

2-3

3-4

4-5

5-6

6-7

8

4 *

@21

@25

30

40

50

65

80

2015

0700

0700

0630

0745

0745

0700

5** @10

12

18

25

30

40

50

65

1630

0700

0700

0630

0730

0700

0700

1345

* Nestling 4 removed from parents on day 1 at 1430 H.

** Nestling 5 removed from parents when a few hours old.

Calls - These have already been mentioned in the
text as they occurred and are listed below:

(1) Kip: This soft call, usually repeated rhythmi-
cally at 1 - 2 sec intervals, is used by the male in
several connections in the breeding season:

(a) When he is plucking a food item prepa-
ratory to offering it to the female or eating
it himself and he will continue to call as he
feeds.

(b) When scraping in a nest site.

(c) In nest-site selection bowing display.

(d) When he wants to take over on the nest.

(e) When doing his share in feeding of the
young.

Campbell and Nelson (1975) describe two forms,
‘Chip or Tick’ and ‘Soft Chip or Tick’, attributing
the latter to the female when feeding young. As
shown below, the latter has been represented by
chup, which Campbell and Nelson interpret as a
deterrent used by the female on the nest, but was
not noticed here in this connection. Rowan
(1921-22) mentions a very soft monosyllabic tick
uttered by both birds on arrival at the nest, but he
makes no mention of its use when the female was
feeding young, yet his hide was only 2.5 m from the
nest.

(2) Chup: Believed to be the female’s version of kip
and used:

Table 3. Weights showing rate of growth of nestlings in No. 1 Pen.

Weight(g)

Day

Nestling

8

10

11

12

25

40

41

49

55

1

80

130

@198

178

2

80

—

—

140

@198

—

188

—

—

3

60

—

—

—

—

170

—

—

—

4*

80

—

120

—

177**

—

—

165

5*

65

105

—

—

—

—

—

—

@170

* Nestlings 4 and 5 were hand fed in a brooder for the greater part or all of their first eight days.
** Nestling 4 weighed on day 24.

76

William Ruttledge

Vol. 19, No. 2/3

Table 4. Development and progress of the nestling in No. 2 Pen.

Feature

Day Number

One egg hatched 1

Male disrupts attempts at feeding 1-3

Nestling removed for hand-feeding 3 (evening)

Parents continue to incubate remaining eggs 4-10

Infertile eggs removed and nestling returned to parents 10

Male becoming less disruptive at feeds 1 1

Male sometimes leaves nest after handing over of food 1 1 — ►

Nestling being frequently left alone during day 14

At dusk, female crouching over or beside nestling 14

Remige quills beginning to show on nestling 14

Hand-fed nestling No. 5 of No. 1 Pen fostered 20

Nestling No. 4 fostered from No. 1 Pen 21

All 3 nestlings still huddle together for night 23 - 26

Nestling No. 1 actively playing with twigs, etc. 24

Nestling No. 1 actively wing-flapping 24

For some days male would frequently return to nest and rob female
of food item, which she might retrieve or that he would return 24-28

Nestling No. 1 returned to nest in evening via ladder 27

Two pale bands showing on tail 27

Nestling No. 1 breaks up a mouse, also later accepts morsel 28

Nestling No. 1 to a high perch in evening, probably roosted there 28

Transferred to separate pen 29

Taken up for transfer to a falconer (not yet fully hard-penned) 37

(a) When plucking, and feeding herself, or the
young in the nest.

(b) It is probably used when taking over from
the male on the nest.

(c) In mutual bowing in nest site.

(3) Kwi, kwi, kwi, kwik: A single syllable, rapidly
repeated 4 or 5 times. Used by the male particularly
when he has plucked a food item and intends to
offer it to the female, but sometimes used when he
has no food item. This, and the female’s version,
kwey . . .kwek are undoubtedly the ‘Short Chatter’ of
Campbell and Nelson.

(4) Kwey, kwey, kwey, kwek: Believed to be the
female’s version of kwi . . .kwik and used in response
to it to indicate that she wants to receive the item. It
may be used to draw the attention of the male to her
need for food. The 2 calls were very frequently
used in mutual responses by a pair in a previous
season without food being involved.

It is strange that the female of the pair studied in
the wild by Rowan (1921-22) responded to the

male’s ‘Short Chatter’ with what appeared to be a
form of the young food call, and not with her ver-
sion of the ‘Short Chatter’. The ‘Short Chatter’ of
male and female were the most characteristic and
frequently heard calls during the breeding season
in the present study. There is, however, a very
similar call, but rather shriller in the male and
harsher in the female, that appears to be used to
give the opposite message, “I have food, keep
away.” It was usually heard early in the year. It was
once heard, in May 1974, from a female under
circumstances suggesting territorial advertisement
to another female.

(5) Kwark: A single, drawn-out call uttered by the
male just before flying towards the female in a
mating approach.

(6) Koi: A single, brief call, seldom heard but ap-
parently given by the female to deter the male from
a mating approach. The call had been heard 3 times
in 1975, twice in the context of mating approaches
and once when the male, of a pair in which the

Summer/Fall 1985

Falco columbarius aesalon

77

female had consistently evaded mating, alighted
close to the female without any apparent mating
intent on 23 May. He departed almost at once. On
only 2 occasions was any call heard during mating,
on 7 and 9 May, both after egg-laying began. The
call was given by the female and could only be
recorded as either kwey . . . kwek or the young food
call. It is possible that it may have been something
specific.

(7) Eep, eep, eep . . . : The young food call, heard
after they had left the nest, associated with an adult
having food. Also used by the female in pen 2
occasionally in March and early April, and again in
the succeeding autumn.

(8) Kek, kek, kek . . . : The alarm call, rapidly and
continuously repeated. This is the ‘Aggressive
Chatter’ of Campbell and Nelson.

Discussion

Campbell and Nelson (1975) found their Merlins
(. F . c. richardsoni ) hypersensitive to human interfer-
ence, which caused aggression, sometimes fatal, by
the female towards the male. Campbell (1980)
suggeted that if Merlins were well manned, they
would be less hypersensitive. This was well de-
monstrated in the tolerance in the 2 pairs as
exemplified by the female in pen 2 having had to be
pushed/lifted off the fostered young that she was
brooding in order that a second one might be intro-
duced. None of the Merlins had been given any
occasion to become imprinted on man when young,
but all had been manned at one time or another.
Outside the breeding season they would, given a
few days’ practice, come to the fist in their pens.

Campbell (1980) moots the thought that aggres-
sion he saw might have been due to putting the
Campbell and Nelson (1975) birds together too
early, or leaving them together throughout the
non-breeding season. A little information on this
point was obtained early in 1977, when Heather, a
sibling female of Myrtle (female of pen 2) was re-
turned on 20 February because of aggression to-
wards the male with which she had been paired
elsewhere. She was isolated in a small pen that had a
small, shuttered communicating hatch into pen 2
with watching perches placed within 30 cm of it in
each pen. On 22 April 1977 the blank shutter was
lowered, leaving only a nylon mesh shutter between
the 2 pens. Almost immediately, Brae and Heather
were face to face on opposite watching perches,

evincing interest but no threat, and both at one time
or another tried to get through to the other side.
Myrtle on arrival, made a fierce attack on Heather
across the barrier, to which the latter responded
equally fiercely. The blank shutter had to be hauled
up quickly. On 26 April, Heather was transferred to
be paired with a leg-impaired haggard male.
Breeding did not take place, but nor did harass-
ment.

It seems possible, therefore, that if the introduc-
tion between Lochan and Corrie had been deferred
until March-April and done more gradually, less
aggression might have resulted. A trial in 1975,
aimed at simulating the usually sequential spring
arrival of male and female Merlins on the breeding
grounds (Brown & Amadon 1968; Cade 1982)
showed the feasibility of a 2-stage introduction of a
male, isolated in pen 1 to a female in pen 2 by
manipulating in March-April a double-shuttered
hatch such as that described above.

Corrie, paired with Ben (a sibling of Brae) in
1979 and 1980, reared young, but during the first
week of April 1981 she killed him without warning.
It may be significant that during the breeding sea-
son Corrie reacted more strongly to low over-flying
birds than did the others.

It has been the practice in this project to keep
pairs of Merlins together throughout the year; and,
up till the end of 1982, this was the only fatality of
this kind that occurred. But it appears that there is a
latent danger of violence just before or during the
early stages of the breeding cycle, which might be
triggered by human interference and possibly by
other factors.

The breaking off of pieces of twigs from the
perimeter of the nest and/or the drawing in of twig
chips and dropping them into the nest scrape is of
particular interest, although its purpose is not clear.
When first observed before 1977, it seemed clear
that this could account for the fact recorded in the
ornithological literature that Merlin nests on the
ground in the wild are often lined with heather
stalks and bents. It appears that it was not until the
work in Northumberland (Newton et al. 1978) that
Merlins in the wild were actually recorded as plac-
ing such items, picked up from within reach, into
the nest scrape, beginning before laying and con-
tinuing into incubation. Nibbling of thick heather
stems by the sitting bird also occurred at many
ground nests (Newton et al. 1978). In any case,
whatever the purpose, it seems desirable to provide

78

William Ruttledge

Vol. 19, No. 2/3

twig chips in nest sites.

Flattening out in the scrape, by the male in the
presence of the female, which nibbled at his beak, is
probably a form of ‘Fixed Bow’ derived from
mutual courtship bowing over the nest cup or
scrape. Cade (1982) believed the latter to be condu-
cive to mutual familiarization at close quarters.
Flattening out was seen in a remarkable degree in
1975 between Laggan and Melanie, perhaps be-
cause there seemed to be some obstacle to Melanie’s
acceptance of mating approaches by Laggan. It was
first observed and took place several times on 7
May. By this time beak-to-beak food passing was
well established, with the female frequently passing
the item back to the male. Mutual calling kwi, kwey
was also frequent, but Melanie had consistently de-
terred mating approaches. Flattening out was usu-
ally initiated by the male callin gkip in the crow’s nest
in pen 1 followng which the female would join him,
but sometimes the female might be there already.
They would bow towards each other calling kip and
chup before both birds, the female in the nest cup,
flattened out with the tail partly fanned and
raised at an angle of ca 30°. Both birds might re-
main ‘frozen’ in this position for up to 5 min. The
male would usually stand sooner, remain looking at
the female for up to 1 min, as though doubtful what
to do, before flying away. The female then usually
stood up also. Mating did not follow any of these
sessions. They continued to be seen sometimes up
to 5 or more times a day, until 26 May, 2 d before
Laggan was transferred.

Cade (1982) mentions that a female falcon indi-
cates her readiness to mate by turning away from
the male, which presumably facilitates his mount-
ing. However, this turning away was not seen in the
Merlins. It was noticed that matings appeared to be
more consistently successful when the female was
not perched on a high horizontal perch parallel to
the back wall but on an isolated post, thus permit-
ting the male to approach from any direction.

The Hurrell-type pens proved ideal for their
purpose. The only potential hazard is accumulation

of snow on the roof netting in winter. In the normal
winter climate of southern England all that should
be necessary is to go in with a forked stick and shake
down the snow. In construction of Hurrell-type
pens in the northern hemisphere it would be desir-
able to place the observation hide in the southern
wall and the nest sites adjacent to it in order to avoid
excessive insolation of the latter and provide op-
timum viewing.

Acknowledgements

The author is grateful to the Advisory Committee on the Pro-
tection of Birds for Scotland of the Scottish Home and Health
Department for licences to take wild Merlins. Particularly we
thank the late George Waterston, O.B.E., LL.D., for his interest,
encouragement and support; the Highland Wildlife Park, Ltd.,
for the loan of a flight-impaired Merlin and to D.G. Hunter of the
Agricultural Research Council for making available the deep-
frozen laboratory mice, and to members of his staff, R.J. Taylor
for making the necessary arrangements, and D. Shirt and S. Collis
who handled the mice. A more extensive draft of this paper is on
deposit with the Hawk Trust in Great Britain.

Literature Cited

Brown, L.H. and D. Amadon. 1968. Eagles, Hawks and
Falcons of the World. McGraw-Hill Co., Inc., New
York, NY.

Cade, T.J. 1982. The Falcons of the World. London,
Wm. Collins Sons and Co. Ltd.

Campbell, J. A. 1980. Breeding Merlins in captivity. The
Falconer 7 (3): 184-1 89.

Campbell, J.A. and R.W. Nelson. 1975. Captive
breeding and behaviour of Richardson’s Merlins. J.N.
Amer. Falconers’ Assoc. 14:24-30.

Mavrogordato, J. 1973. A Hawk for the Bush. 2nd ed.
London, Neville Spearman.

Nelson, R.W. 1977. Behavioural ecology of coastal
peregrines (Falco peregrinus pealei). Ph.D. Thesis, Univ.
Calgary, Calgary, Canada.

Newton, I., E.R. Meek, and B. Little. 1978. Breeding
ecology of the Merlin in Northumberland. British Birds
71 (9):376-398.

Rowan, W. 1921-22. Observations on the breeding-
habits of the Merlin.5r. Birds 15:122-129, 194-202,
222-231, 246-253.

10 St. Andrew’s Way, Limpsfield Chart, Oxted, Surrey, ENG-
LAND.

GROWTH RATES AND FOOD CONSUMPTION OF HAND-RAISED MERLINS

Lynn W. Oliphant and Stacey V. Tessaro

Abstract - Growth curves were constructed for two male and two female Merlins that were hand raised. Growth rates
and maximum size of the hand-reared birds appear to be substantially lower than wild birds, possibly due to a lack of
moisture in the diet. Daily food consumption was measured and used to estimate food requirements for a Merlin family
group. For a pair with 4 young, a total of 800 sparrow-sized birds are required for a 120-day breeding season.

Each year hundreds of raptors are hand-raised
by falconers or by the various institutional breeding
projects. This presents a unique opportunity to
gather data on growth rates, food consumption and
general development. Such information is useful
for accurate aging of nestlings, comparisons of
growth rates under different conditions (differing
prey densities, brood size, etc.), determination of
prey requirements of a nesting pair of birds, and
optimizing conditions of hand-rearing. This study
describes observations on the development of 2
pairs of the Merlin (Falco columbarius richardsonii )
that were hand-reared.

Methods

Pair #1 was taken from a nest on 15June 1975 as small downies
of unknown age. Pair #2 was hatched in captivity (Roll-X in-
cubator, 36.7°C) in 1979 from a clutch of eggs taken immediately
after clutch completion. Both pairs were initially maintained in
simple brooder boxes heated by light bulbs. Temperature was
regulated on the basis of behaviour of the young falcons, being
gradually reduced to room temperature.

Diets and feeding regimes for the 2 pairs were slightly different.
Pair #1 was fed a mixture of laboratory mice (head, gastrointesti-
nal tract and skin removed) and day-old chicks (feet, beak and skin
removed) in a ratio of 3 mice to 1 chick. Food was ground in a meat
grinder and frozen in meal-size packages. The birds were fed as
much as they would eat 5 times/d for the first 6 d, 4 times/d for the
next 10 d and 2-3 times/d thereafter. For each feeding the meat
was thawed, brought rapidly to room temp and fed by forceps
until the Merlins could eat from a small saucer. In addition to their
regular fare, they were given a freshly killed House Sparrow
(Passer domestic us) that was minced by hand and fed fresh on 4
occasions.

Pair #2 was fed only freshly-killed Coturnix ( Coturnix sp.). For
the first 3 d after hatching, these Merlins were fed small amounts
of diced breast muscle, heart, liver and small crushed bone frag-
ments. Afterwards they were fed freshly ground whole quail
(beak, gastrointestinal tract and skin removed). This pair was fed 4
times/d for the first 15 d, 3 times/d from the 15th to 22nd d and 2
times/d afterwards. They were fed in the same manner as pair # 1
and allowed to eat as much as they wanted.

Both pair were weighed to the nearest 1/100 g on a Sartorius
electrical balance before and after feeding to determine the weight
of food consumed. Weights used to document daily weight gain
were morning weights prior to the first feeding of the day. Little
casting material was given and weights of the few castings were
ignored.

Pair #1 was placed in a hack box with 2 other Merlins taken

from a nest just prior to fledging which were a few days further
advanced than the hand-reared pair. All 4 fledged together al-
though the hand-reared female, being the youngest, was not cap-
able of sustained flight until 5 d later and was picked up for a final
weighing 2 d after fledging.

Pair #2 was tame hacked for a week after training to a lure
allowing them to be brought in every night. After the hack, this
pair was kept in outdoor mews and both birds flown twice daily for
the next month, primarily at large flocks of House Sparrows
(Passer domesticus ) as part of a crop depredation experiment. Dur-
ing this time they were fed 2 times/d on either Coturnix Quail or
wild birds they had caught, receiving about half a crop in the
morning and a full crop each evening (1 1/2-2 sparrows/d).

Growth curves for both pairs were generated using a computer
program to fit the data to a smooth curve. The growth function
used for this curve is the differential equation of Richards (1959).

Results

Both pairs consisted of 1 male and 1 female. Pair
#2 hatched within an hr of each other on 14 June.
Weights at hatching were 13.0 g and 13.7 g. The
hatching dates for the 1975 pair were estimated to
be 6 June (male) and 9 June (female) using physical
development and weights as compared to pair #2
and wild nestlings of known age. Growth curves for
both pairs are shown in Figs. 1 and 2 with day 0
being hatching day. The growth curves exhibit a
typical sigmoid shape reaching peak weights be-
tween day 23 and 27 with a slight drop in weight
afterwards. The inflection, or point of highest
growth rate, was reached at day 14 or 15.

Pair # 1 was considerably larger than pair #2 and
attained maximum weights of 265 g (female) and
203 g(male) as compared to 226 g (female) and 174
g (male). Maximum weights were 10-30 g higher
than weights at fledging. Pair #2 was flown at
207 ±5 g (female) and 146 ±5 g (male). Their
weights were remarkably consistent from day to
day.

Food consumption (Figs. 3 and 4) showed an
almost straight line increase from hatching to day
12-14 (Fig. 4). Consumption then levelled off and
was maintained at maximum levels with some fluc-
tuation for the remainder of the rapid growth
phase, decreasing when body weight approached

79

Raptor Research 19(2/3): 79-84

80

Oliphant and Tessaro

Vol. 19, No. 2/3

280

260

240

220

200

^ 180
F- 160

2 140

UJ

^ 120

§ 100

00 80

60

40

20

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34

DAYS POST- HATCH

Figure 1. Growth curve for Pair #1,

F-

X

CD

UJ

£

>-

Q

O

m

240

220

200

180

160

140

120

100

80

DAYS POST- HATCH

Figure 2. Growth curve for Pair #2.

Summer/Fall 1985

Growth of Hand-raised Merlins

81

DAYS POST- HATCH

Figure 3. Food consumption - Pair #1.

Figure 4. Food consumption - Pair #4.

DAYS POST- HATCH

82

Oliphant and Tessaro

Vol. 19, No. 2/3

the maximum. The average amount of food con-
sumed during this period was very similar for the
males (40.0 g/d). The female from pair #1 con-
sumed 52.4 g/d as compared to 46.1 g/d for the
other female. Food consumption decreased by day
23-27 to about 30 g/d for both males and females.

General observations on the development of the
4 birds are presented in Table 1. There was a slight
variation in the appearance of various behaviour
patterns with males developing ahead of females.
Post-hatching development is broken down some-

what arbitrarily into 5 major periods: day 0-3 (new-
born); 4-11 (small downy); 12-21 (large downy);
22-28 (brancher); and 29-independence (fledgl-

ing>-

Discussion

Basic growth parameters for Merlins have been
reported (Ricklefs 1968a, b) but are incorrect. The
original data from which these growth parameters
were derived are for the Prairie Falcon ( Falco
mexicanus ) (Fowler 1931) and the reported weights

Table 1. Post-hatching Development

Day

Observations

r *

Hatch; eyes closed, down wet.

Newborn

i

Down dry.

1

l 3

Eyes open.

4-8

Enter period of rapid growth;
Become aware of surroundings;

Small Downy

-

9-11

Second down coat develops.
Sheathed contour feathers appear;
Sitting erect on tarsi;

_

Wing flapping begins.

12-14

Primaries break sheaths;
First casting.

15-17

Rectrices break sheaths;
Egg tooth is lost;

Large Downy

— ■<

18-21

Standing upright.

Cheek and flank feathers develop;
Flight feathers developing rapidly;
Grappling and holding food with feet;
Increased wing flapping;

Leveling off of food consumption and weight gain.

Brancher

"22-28

Maximum weight attained;

Rapid replacement of down by contour feathers

■<

(down visible only on head by 28 days);
Short jumping “flights.”

^29-34

Fledging; become capable of sustained flight.

35-40

First long flights and development of flying abilities;
Interest shown in potential prey (first pursuit

Fledgling

40-50

of bird at 36 days, 1979 (male). First bath.
Hunting begins; first kills on flying insects;
first bird kill [Day 42, 1979 (female)].

Some down still remains on head. Completion of
feather growth.

_ 50-60

Become independent; disperse.

Summer/Fall 1985

Growth of Hand-raised Merlins

83

were incorrectly converted from ounces to grams
and mistakenly reported as Falco columbarius.

The significance of the lower weights at full
growth for pair #2 as compared to pair #1 is dif-
ficult to assess due to small sample size and minor
differences in feeding regimes, handling, etc. Data
collected on weights of wild nestlings of known age
suggest, however, that even pair # 1 was smaller and
exhibited slower growth rates than most wild
nestlings. Weights of 12 wild females between 20
and 28 d old all exceeded 250 g (limit of scales used)
and weights of 5 wild, lid old nestlings (unsexed)
weighed an average of 129.6 g (103-160 g) as com-
pared to 80 g for pair #2 and 90 g for pair #1. It
should be noted that our estimate of the hatching
dates of pair #1 may be as much as 2 d too early
based upon the observed weights of wild nestlings.
The difference in growth rates cannot be attributed
solely to differences in food quality between our
hand-reared birds and wild birds. Weights of 3
captive bred Merlins (2 females, 1 male) raised by
their parents but fed only Coturnix quail averaged
120 g at day 11.

In 1979 we had the opportunity to directly com-
pare our hand-reared pair (#2) with a wild nestling
(male) which had hatched on the same date. The
wild Merlin had fledged prematurely from a nest
site. The birds were 27 d old at the time of compari-
son but on the basis of feather development and
flight capabilities the wild bird appeared to be 4-5 d
more advanced than the hand-reared pair.

There has been recent evidence to suggest that
growth rates and final body size may be less in
falcons reared by people as compared to those
cared for by falcons (The Peregrine Fund; Mac-
Donald Raptor Research Centre, pers. comm.) Jim
Weaver (The Peregrine Fund) suggested that this
difference might be due to fluids added to the food
from the nasal glands of the adult falcon during
feeding. Addition of physiological saline to the food
appears to counteract this slower growth which is
especially apparent during the early stages of de-
velopment (Oliphant, unpub. obs.). Olendorff
(1972) has also noted the potential problem of de-
hydration in hand-reared buteos and, more re-
cently, Wallace at the University of Wisconsin
(Dobbs et al. 1 979) showed that diets containing less
than 55% moisture slowed growth or even halted
growth in young of the Turkey Vulture ( Cathartes
aura). The moisture content of 5 wk old quail given
by Dobbs et al. (1979) is very low (45%) in compari-

son to other whole animal food. It appears that until
further studies are done, it would be prudent to add
water or physiological saline to ground quail being
fed to hand-raised raptors.

There was a noticeable difference in the tarsus,
cere and orbit color of our hand-reared birds as
compared to wild nestlings. Our birds had blue or
blue-green skin as compared to the bright yellow
color of wild nestlings of advanced age. This is
undoubtedly due to the relative lack of carotenoid
pigments in the diet of our hand-reared birds.

Development of vocalizations was retarded in our
hand-reared birds. When pair #1 was placed in the
hack box with the 2 late taken wild young, they only
made food begging cries typical of nestlings. The 2
late taken wild young had already developed a typi-
cal adult call with a rapid stacatto delivery. Even a
wk after fledging this difference was still apparent.
The response of these birds to a wild adult male
Merlin that appeared in the hack area was also very
different. The late taken birds begged for food and
chased the adult male but the hand-reared birds
ignored him.

Based upon our values, the total food require-
ments for 1 Merlin from hatching to fledging are
about 1,000 g. This can be expected to vary slightly
depending on sex and size of the particular nestling
and nutritive value of the food consumed.

Sparrow-sized birds are the principal food of
Merlins (Oliphant and McTaggert 1977; Hodson
1978). Average weights of freshly killed sparrows in
Saskatoon were 28.6 g in summer (n = 15) and 35.6
g in winter (n = 1 0). The weight of a plucked carcass
with head and tarsus removed averaged about 80%
of fresh wt. This gives a value of about 25 g of useful
food per average sparrow kill. The total food re-
quirements per Merlin during the nestling period is
therefore about 40 sparrows. Based upon the food
consumption of pair #2 after fledging, an addi-
tional 38 sparrows would be required from the time
of fledging to independence at day 55. Assuming
similar food requirements for a pair of breeding
adults over an entire 120-d breeding season results
in an additional 210 sparrows required per adult.
The total calculated prey requirements for a
breeding pair and 4 young would therefore be 732
sparrows.

Observations at wild nests in the city of Saskatoon
indicate that these calculations are close, but proba-
bly on the low side. We recorded a total of 5 spar-
rows killed (3-4 expected) during incubation by

84

Oliphant and Tessaro

Vol. 19, No. 2/3

watching at 1 Merlin nest site from dawn to dusk. A
similar watch at a nest site with 5 one wk old young
recorded 10 sparrow kills (8-9 expected). This
slightly higher than calculated kill rate could be due
partially to the occasional loss of some kills during
plucking or food transfers (whole carcasses were
occasionally found at nest sites) and loss of cached
food (Oliphant and Thompson 1976) either stolen
by other birds or simply forgotten. The actual
number of House Sparrow-sized birds killed by a
breeding pair with 4 young is probably close to 800
for a 120-d breeding period. This is somewhat
lower than that estimated by Lawrence (1949)
which would have amounted to a total of 1 , 1 40 for a
brood of 4 young over a 120-d breeding season.

Acknowledgements

We thank Paddy Thompson, Bob Rafuse, Sue McTaggert,
Bruce and John Hanbidge for help in obtaining and rearing
Merlins and gathering data on prey utilization by wild pairs. The
Saskatchewan Department of Tourism and Renewable Resources
issued the necessary permits. Dr. Charles T. Collins kindly
supplied the computer printouts of the growth curves. This study
was supported in part by an NSERC grant to the senior author.

Literature Cited

Dobbs, J.C., N.D. Ahlgren and A.M.
Hayworth. 1979. Examining what raptors eat or are
fed. Hawk Chalk 18(3):34-36.

Fowler, F.H. 1931. Studies of food and growth of the
prairie falcon. Condor 33:193-201.

Hodson, K. 1978. Prey utilized by Merlins nesting in
shortgrass prairies of southern Alberta. Can. Field-
Naturalist 92:76-77.

Lawrence, L. deK. 1949. Notes on nesting pigeon
hawks at Pimisi Bay, Ontario. Wilson Bull. 61:15-25.

Olendorff, R.R. 1972. Comments on rearing young
buteos. Raptor Res. 6:6-10.

Oliphant, L.W. and S. McTaggert. 1977. Prey species
utilized by urban nesting Merlins. Can. Field-Naturalist
91:190-192.

Oliphant, L.W. and W.J.P. Thompson. 1976. Food
caching behavior in Richardson’s Merlin. Can. Field-
Naturalist 90:364-365.

Richards, F.J. 1959. A flexible growth function for em-
pirical use./. Exp. Bot. 10:290-300.

Ricklefs, R.E. 1968a Weight recession in nestling birds.
Auk 85:30-35.

Ricklefs, R. 1968b. Patterns of growth in birds. Ibis
110:419-451.

Department of Veterinary Anatomy, Western College of Veteri-
nary Medicine, University of Saskatchewan, Saskatoon, Sas-
katchewan, S7N OWO CANADA. Address of second au-
thor: Animal Pathology Laboratory, Agriculture Canada,
116 Veterinary Road, Saskatoon, Saskatchewan, S7N OWO
CANADA.

MIGRATION OF THE MERLIN ALONG THE COAST OF NEW JERSEY

William S. Clark

Abstract - Merlins were captured along a migration route in New Jersey from 1968 to 1979. Sixty-one percent of 1550
Merlins captured at Cape May Point in autumn were female. Seventy-six percent of 1 05 Merlins captured at Sandy Hook
in spring were female. Eight percent and 59% of the Merlins captured were adults at Cape May Point and Sandy Hook,
respectively. The dho-gaza was the most effective capture device. Females migrated before males in autumn and vice
versa in spring. Both sexes are captured more frequently after noon in autumn and spring, but many males were
captured in the morning in spring. Timing of spring migration was more compressed. Mean wt and wing chord
measurements were calculated. Adults were significantly heavier than immatures (t-Test, P < 0.001). In spring, Merlins
were considerably heavier than in autumn. Most Merlins can be sexed by wing chord length and wt. Subcutaneous fat
visible beneath the skin was estimated and was not correlated to mean wt. Band recoveries indicate a migration pathway
along the Atlantic Coast with wintering in Florida and the Greater Antilles, but none from Cape May Point have been
recovered in Central America or nothern South America. Some Merlins moved northward in autumn.

The Merlin (Falco columbarius ) is of panboreal
distribution. Most studies of the species have con-
centrated on the breeding season (Fox 1971;
Oliphant and Thompson 1976; Newton et al. 1978)
or systematics (Temple 1972a). Although most
races are migratory (Peters 1964; Dementiev et al.
1966), and a few studies of Merlin migration have
been published (Williamson 1954; Brown 1976;
Thompson 1958), nothing has been published re-
garding migration of populations of eastern boreal
North America F.c. columbarius.

This paper reports Merlin migration from data
gathered during long-term raptor migration re-
search at Cape May Point and Sandy Hook, New
Jersey. Cape May Point is located at the southern tip
of New Jersey where the greatest concentrations of
migrating raptors in North America occur during
the autumn migration (Dunne and Clark 1977;
Dunne 1980). Sandy Hook is located on the south
side of the New York Harbor and has been found to
be a spring concentration point for raptors, espe-
cially small falcons (Clark 1978).

Methods

During 12 autumns, my cooperators and I have operated a
raptor banding station at Cape May Point. During 1977-1980, a

second banding station was operated during spring at Sandy
Hook. Merlins and other species of raptors were captured at both
locations using bownets, mist nets and dho-gaza nets (Clark 1970,
1981). Captured falcons were banded using U.S. Fish and Wildlife
Service bands and in most cases were weighed to the nearest gram
and wing chord measurements in mm were taken. Merlins were
aged and sexed using the technique outlined in Temple (1972b).
Data on wing chord and weight were used to verify sex determina-
tions using the statistical computer program SAS Discriminate
Function Analysis.

During 1978 and 1979, Merlins captured at Cape May Point
were visually checked for subcutaneous fat on the sides of the
breast, in the throat cavity and on the belly by blowing the feathers
out of the way. Presence or absence of fat was recorded according
to the coding scheme in Table 1.

Results and Discussion

Data were obtained for 1550 Merlins captured at
Cape May Point during the years 1968-1979 (Table
2) and 104 at Sandy Hook during the years 1977-
1980 (Table 3).

Age and Sex Ratios. — Only one exception was
found to Temple’s (1972b) key for ageing and sex-
ing Merlins. Many immature plumage males had
both gray and buffy colors in the light tail bands (N
= 577), while immature females had only buffy tail
bands (N = 852). Temple noted that immature
males had only gray color in tail. Immature plum-

Table 1. Coding scheme for subcutaneous fat in captured Merlins.

Fat Class

Side

T HROAT

Belly

0

None

None

None

T (Trace)
1

A trace of fat is noted in any of the areas
Slight-medium bulge

Present

(or)

Present

2

Medium-large bulge

Lined

and

Lined

85

Raptor Research 19 (2/3): 85-93

86

William S. Clark

Vol. 19, No. 2/3

Table 2. Merlins banded Fall, 1968-1979, Cape May
Point, New Jersey

Table 3. Merlins banded Spring, 1977-1980, Sandy
Hook, New Jersey

Males Females Total

Males Females Total

Immature

574

812

1,386

Adult

41

77

118

Unknown

2

44*

46

Total

617

933

1,550

* Includes 43 unknown from 1971

age females also had less well defined tail bands
than those of males.

Merlins are sexually dimorphic with females
larger than males. A plot of wt vs wing chord sepa-
rated the sexes (Fig. 1 ), even though there is a slight
overlap in either measurement between sexes. The
data were also checked for accurate sex determina-
tion using discriminate function analysis. The same
sex was selected by the program and the banders
for every data pair of wing chord and wt.

Immature 3 40 43

Adult 22 39 61

Total 25 79 104

Ninety-two percent of the Merlins captured in
the autumn were first-year birds (Table 2). This age
ratio was consistent with that of other raptors cap-
tured at Cape May Point; American Kestrel (. Falco
sparverius ) 92.5% (N = 8091), Sharp-shinned Hawk
(Accipiter striatus) 94.6% (N = 13,867), and Coopers
Hawk (Accipiter cooperii) 92.7% (N = 756).

Age ratios reported for songbirds banded on
the coast reflect the same phenomena (Robbins
1977).

Figure 1. Comparison of wing chord and weight of migrant Merlins captured at Cape May Point, New Jersey.

Summer/Fall 1985

Migration of the Merlin

87

Table 4. Merlins captured by type of trap.

Trap Type

Cape May Point, N .J.

Sandy Hook, N.J.

Males Females

Total

Males Females

Total

Dho-Gaza

264 (43%)

371 (41%)

638 (43%)

10 (40%)

31 (39%)

41 (39%)

Mist Net

170 (28%)

211 (23%)

381 (25%)

0%

2 (31%)

2 (%)

Bow Net

177 (29%)

333 (36%)

509 (33%)

15 (60%)

46 (58%)

61 (59%)

Other

4

0

Total

611

915

1,532

25

79

104

Presumably the best explanation is that immature
raptors and songbirds are concentrated along the
Atlantic coast during fall migration by the wind
drift and leading line phenomena described by
Mueller and Berger (1967). The higher winter
mortality of immature raptors compared to adults
(Newton 1979) may partially explain the higher
percentage of adults in the spring sample (Table 3).

Capture samples (Tables 2 and 3) showed an
unbalanced sex ratio in favor of females. At Cape
May Point, 61% of the Merlins captured were

females; at Sandy Hook, 76% . These samples are
significantly different (P < 0.001) from each other
and from the expected 50-50 sex ratio (Fox 1964) (P
< 0.001). Possible explanations for the observed
skewed ratios include capture bias, differential
migration and differential survivability. Based on
Merlins being caught and not being caught, there
seems to be little or no sex bias in the capture
techniques. If there is a different migration path-
way for males, it is probably not over land, as no
other raptor banding stations capture many Mer-

Month

Figure 2. Merlins captured at Cape May Point, New Jersey, in the fall (1968 - 1979) by date by sex.

88

William S. Clark

Vol. 19, No. 2/3

Date

Figure 3. Merlins captured at Sandy Hook, New Jersey, in the spring by date by sex.

lins. Merlins have been reported in the fall migra-
ting over water off the eastern coast of North
America (anon. 1979). There are insufficient data
to determine if there is differential survivability
between males and females.

Capture Techniques — Merlins were captured
by 3 types of traps (Table 4). The modified dho-
gaza (Clark 1981) is the most effective trap for
capturing Merlins. There are minor differences in
percentages by capture method among the 4 to 5
different stations at Cape May Point caused by ter-
rain differences. Generally, dho-gazas (and mist
nets) are more effective when there is a dark
background behind them and bow nets are more
effective in more open locations. Differences bet-
ween the capture technique percentages of Cape
May Point and Sandy Hook are probably due to
differences in terrain. The Sandy Hook stations are
in much more open terrain with little backdrop
available.

Diurnal and Seasonal Timing — The Merlin was
one of the earlier autumnal migrants at Cape May
Point, arriving in numbers by September 10, and
completing the passage by mid-October (Fig. 2).
Females migrated earlier in the season than males
and peaked earlier (Fig. 2). Rosenfield and Evans

(1980) theorize that migrating immature female
Sharp-shinned Hawks precede males because of
their dependence on larger avian prey. My data for
Merlins support their hypothesis, as the Merlin also
subsists almost entirely on birds and females mig-
rate first.

Males precede the females in spring (Fig. 3). This
is consistent with behavior of other migrant species
with the adult males arriving on territory first
(Roest 1957). The spring migration period spanned
a shorter time than the autumn period. The au-
tumn migration “season” for Merlins is over a
month while the spring migration period lasts only
about 15 d. In spring they do not appear in num-
bers until after 20 April and most have passed by 5
May.

There is very little difference in the time of day
the sexes are captured at Cape May Point (Fig. 4). In
general, the data support the observation that Mer-
lins are more plentiful in the afternoon.

Migrating Peregrine Falcons ( Falco peregrinus)
have been characterized by having 3 different flight
characteristics during the day (Cochran 1975).
First, from predawn to the time of thermal forma-
tion, they hunt using powered flight in the desired
migration direction at an altitude of around 30m.

Summer/Fall 1985

Migration of the Merlin

89

Hour Interval Beginning

Figure 4. Merlins captured at Cape May Point, New Jersey, in the fall by time of day by sex.

During mid-day, they utilize thermals in the man-
ner of most migrating raptors. In the afternoon,
when thermal production slows down or ceases,
they begin a low-level hunting flight, generally in a
random direction. I believe that the Merlins mig-
rating along the Atlantic Coast use similar
strategies. On many occasions Merlins that had

perched for the night on snags at Cape May Point
were not present the next morning at first light
(Dunne, pers. comm. 1981). The Merlins may have
begun migrating using powered flight hours before
sunrise, changed to thermals later in the morning,
and finally, when thermal formation weakened
later in the afternoon, they dropped to low altitudes

Hour Interval Beginning

Figure 5. Merlins captured at Sandy Hook, New Jersey, in the spring by time of day by sex.

90

William S. Clark

Vol. 19, No. 2/3

Table 5. Mean weight and wing chord of Merlins banded in the Fall at Cape May Point, New Jersey.

Adult*

Immature*

t-TEST FOR

Difference
(P< 6.001)

Weight

Male

158. 6g (40) ± 11.6

152.7 (506) ± 10.7

Yes

Female

217. 7g (72) ± 14.3

211.3 (27) ± 15.6

Yes

Wing

Male

190.4 (40) ± 4.2

190.2 (546) ± 5.0

No

Chord

Female

211.7 (73) ± 3.8

210.4 (759) ± 4.3

Yes

*(Sample size in

parenthesis)Mean

± SD

and. began low-level hunting flight. Merlins were
captured in numbers late in the day, long after
other raptor species have ceased migrating. Merlins
were also captured in numbers on overcast, drizzly
days when thermals, if present, were weak. The
situation is not quite so clear when one looks at the
equivalent data for the spring captures at Sandy
Hook (Fig. 5), probably due to the small sample size.

Measurement Data — Mean wt and wing chord
measurements were calculated for Merlins cap-
tured at Cape May Point (Table 5) and Sandy Hook
(Table 6). Adults of both sexes were significantly
heavier than immatures (t-Test, P < 0.001). Only
for females did adults have significantly longer
wings than immatures. Interestingly, Temple

(1972b) reported no significant differences in age
class measurements of wing chord for F.c. colum-
barius. The mean wing chords reported by Temple
were not significantly different from my data (t-
Test, P > 0.001). The spring data (Table 6) show
almost the identical mean for wing chords as in the
fall, but considerably heavier wt than in the fall.

Fat — There are few references to fat deposition
in raptors (Newton, pers. comm. 1977). Gesseman
(1979) documented and quantified fat deposition
in American Kestrels by sacrificing them and ex-
tracting fat. He attributed changes in fat deposition
to migrational needs.

Merlins were checked for fat deposition during
autumn 1978 and 1979. Of the 279 Merlins in-

Table 6. Mean weight and wing chord of Merlins banded in the Spring at Sandy Hook, New Jersey.

Adult*

Immature*

t-TEST FOR

Difference (P < 0.001)

Male

169.0 (22) ± 13.7

155.9 (3) ± 10.2

No

Weight

Female

243.6 (39) ±21.6

234.4 (40) ± 13.4

Yes

Male

190.1 (22) ± 3.4

188 (3) ± 2.4

No

Wing

Chord

Female

211.9 (39) ± 4.4

210.5 (39) ± 3.8

No

(Sample size in parenthesis) * Mean ± SD

Summer/Fall 1985

Migration of the Merlin

91

Fig. 6 Merlin Band Recoveries from
Cape May Point, N.J.

CAPE MAY POINT

N

\

111 Breeding Range
ITT] Migration Path
[ ] Main Wintering Area

LEGEND FOR BAND RECOVERIES
© September-November
(•) December-February
© March-May

t

c:>

c

^ *

<8 o
<0 _

Figure 6. Map<of recoveries from Merlins banded at Cape May Point, New Jersey.

92

William S. Clark

Vol. 19, No. 2/3

spected, 232 had at least a trace or more of fat.
Weight was not correlated with increasing fat de-
position. A possible explanation for this is that crop
and stomach contents were not measured. Oliphant
(pers. comm. 1981) indicated that Merlins are cap-
able of eating more than 50 g at one time.

Band Recoveries — Band recovery locations of
Merlins from Cape May Point are plotted in Fig. 6.
Breeding range in Fig. 6 was hypothesized based on
the breeding range of the Merlin given by the AOU
Checklist (5th Ed.) and the few recoveries from
breeding areas. This breeding area is the probable
origin for the Merlins occurring at Cape May Point.

The main flight path of Merlins during autumn
migration is along the east coast of North America
based on counts at hawk watches (Dunne 1980).
Few Merlins are encountered on migration in east-
ern North America other than along the Atlantic
coast (Soucy 1976; Field 1978; Holt 1980). Merlins
also migrate across the open ocean (McLean and
Williamson 1958), are regularly encountered at sea
off the east coast of North America in the autumn
(anon. 1979), and are casual in Bermuda (Friedman
1950). It is not known what fraction of the eastern
Merlin population uses an over water migration
pathway in the autumn.

Based on band recoveries, the main wintering
area for eastern Merlins is Florida and the Greater
Antilles (Fig. 6). A few individuals also winter along
the Atlantic coast north to New England. Two re-
coveries of Merlins banded by other studies in au-
tumn along the Atlantic coast and recovered in
Cuba support this theorized winter range. The
AOU Checklist (1957:121) gives the wintering
range of the eastern Merlin as: “. . . from southern
Texas (Brownsville), southern Louisiana (New Or-
leans), Alabama (Anniston), South Carolina and
Georgia south through Mexico, Central America,
and the West Indies to northern Peru, Columbia
and northern Venezuela, casually north to Neb-
raska, Iowa, Illinois, Indiana, Ohio, southern On-
tario, southern Quebec and Maine.”

Since the Cape May Point winter recoveries are
from a much more limited area, Merlins from the
more western part of the breeding range must be
wintering in the other sections. Band recoveries of
this species from Latin America tend to support
this. Three recoveries from Wisconsin bandings
were in northern South America, 2 in Columbia
and 1 in Equador (however, 1 recovery from Wis-
consin was from the Dominican Republic). The

only Central American recoveries are 1 banded in
Ontario and recovered in Honduras and another
banded in the Northwest Territories and recovered
in Costa Rica (data from Bird Banding Lab., U.S.
Fish 8c Wildlife Service).

The majority of the band recoveries were from
females (23 out of 29 or 79% ), but the banding ratio
is 60% female. A possible reason for this could be
due to band retention differences between the
sexes. Females are given a size 4 lock-on band, while
the males have been given size 3A butt-ended
bands. Dunne (pers. comm. 1980 has observed
male Merlins successfully removing bands within
15 minutes after being banded. We have recently
begun to use USFWS size 3 bands on the males,
which are stiffer and should result in better reten-
tion.

These 29 recoveries from a banding sample of
1550 yield a recovery rate of 1.8%. Fyfe and
Banasch (1981) reported a recovery rate of 1.97%
from banding a similar number of Merlins.
Thompson (1958) reported a 15% recovery from
Great Britain banding and Smith (1981) reported a
16.7% rate in Alberta. However, these populations
are non-migratory, and the majority of recoveries
in both studies were within 64 km of the banding
site. Icelandic Merlins migrate through the British
Isles and winter there as well as in southwestern
Europe, but no band recovery percentages have
been reported (Williamson 1954; Brown 1976).

Most band recoveries of Merlins banded at Cape
May Point are from dead birds. Nine had been shot;
7 of these in the Caribbean where it is not against
the law to shoot raptors. Four were found dying,
probably a result of striking windows, buildings or
wires, and 12 were found dead, with the cause of
death not obvious.

Two Merlins were recovered north of Cape May
Point shortly after being banded, 1 in Connecticut.
This may indicate that the autumn migration is not
a simple north to south movement. Another was
captured alive and released 6 days after banding at
Cape Charles, VA. Three were recovered wintering
in the U.S. and 8 in the Greater Antilles. There was
1 spring recovery inland from the coast. There are
few summer recoveries of this species in the breed-
ing range, probably due to remoteness of the
breeding area and the Merlins’ secretive behavior.
There have been no recoveries of Merlins banded
at Sandy Hook and no Merlin recaptures that were
previously banded at Cape May Point.

Summer/Fall 1985

Migration of the Merlin

93

Acknowledgments

This study has been possible because of the efforts of numerous
banders and countless helpers, all of whom put in long hours of
dedicated work. Financial support has been supplied, in part, by
the Raptor Information Center, NWF and by the Army Material
Command through Dr. F. Prescott Ward. Most of the work was
carried out by volunteers. Thanks go to Tom Pierson, who ex-
tracted and manipulated much of the data and carried out most of
the statistical analysis. And special thanks to Sue Artis for retyping
the many drafts. Appreciation is given to Maurice LeFranc, Mark
Fuller, Chris Servheen and Lynn Oliphant for reviewing the draft
MS and making critical comments. The raptor banding project is
one aspect of the raptor migration research being conducted by
the Cape May Bird Observatory.

Literature Cited

Anonymous. 1979. Newsletter . of the Hawk Migr. Assoc, of
N. Am. IV: 16.

Brown, L. 1976. British Birds of Prey. Collins, London.
400 pp.

Clark, W.S. 1970. Migration trapping of hawks (and
owls) at Cape May, N.J. - third year. EBB A News
33:181-189.

, 1978. Spring hawk movement at

Sandy Hook, N.J. - 1977. Occ. Paper No. 133. New
Jersey Audubon 4:43-47.

, 1981. A modified dho-gaza trap for

use at a raptor banding station,/. Wild. Man. 45: 1043-
1044.

Cochran, W.W. 1975. Following a migrating peregrine
from Wisconsin to Mexico. Hawk Chalk XIV:28-37.
Dementiev, G.P., N.A. Gladkov, E.S. Ptushenko, E.P.
Spangenberg, A.M. Sudilovskaya. 1966. Birds of
the Soviet Union. Vol. I, (In English, translated from
the Russian) Israel Program for Scientific Transla-
tions, Jerusalem. 704 pp.

Dunne, P.J. 1980. “Coastal Plain.” Newsletter of the Hawk
Migr. Assoc. ofN. Am. V: 12-16.

- ; ■ _, and W.S. Clark. 1977. Fall hawk

movement at Cape May Point, N.J. - 1976. Occ. Paper
No. 1 30. New Jersey Audubon 3:11 4-124.

Field, M. and W. Rayner. 1978. Hawk Cliff raptor
banding station, sixth annual report. Ont. Bird
Band. 12:1-27.

Fox, G.A. 1964. Notes on the western race of the pigeon
hawk. The Blue jay XXII: 140-147.

, 1971. Recent changes in the repro-
ductive success of the pigeon hawk. J. Wild.
Man. 35:122-128.

Friedman, H. 1950. The Birds of North and Middle
America. Part XI, U.S. Govt. Print. Off., Wash., D.C.
793 pp.

Fyfe, R. and U. Banasch. 1981. Raptor banding in
western Canada . Alberta Nat., Spec. Issue No. 2:57-61.

Gesseman, J.A. 1979. Premigratory fat in the American
kestrel. Wilson Bull 91:625-626.

Holt, J.B., Jr. and R. Frock, Jr. 1980. Twenty years of
raptor banding on the Kittatinny Ridge. Hawk Mt.
News 54:8-2.

McLean, I. and K. Williamson. 1958. Merlins at sea.
Brit. Birds 51:157-158.

Mueller, H.C. and D.D. Berger. 1967. Wind drift,
leading lines, and diurnal migration. Wilson Bull.
73:50-63.

Newton, I. 1979. Population Ecology of Rap-
tors. Buteo Books, Vermillion, S.D. 399 pp.

, E.R. Meek and B. Little. 1978.

Breeding ecology of the Merlin in Northumberland.
Brit. Birds 71:376-398.

Oliphant, L.W. and W.J.P. Thompson. 1978. Recent
breeding success of Richardson’s Merlin in Saskatche-
wan. Raptor Res. 12:35-39.

Peters, J.L. 1964. Check-listof Birds of the World. Mus.
of Comp. Zool. Harvard College, Cambridge Mass.
Vol. I.

Robbins, C.S. (Compiler). 1977. Atlantic flyway re-
view: Reg. V. No. Am. Bird Bander 2:79-85.

Roest, A. I. 1957. Notes on the American Sparrow
Hawk. Auk 74:1-19.

Rosenfield, R.N. and D.L. Evans. 1980. Migration in-
cidence and sequence of age and sex classes of the
Sharp-shinned Hawk. The Loon 52:66-69.

Smith, A.R. 1981. Preliminary results of Merlin band-
ing in Edmonton, Alberta. Alberta Nat., Special Issue
No. 2:38-40.

SoUCY, L.J.,Jr. 1976. Raptor report - Kittatinny Moun-
tains. No. Am. Bird Bander 1 : 108-1 13.

Temple, S. A. 1972a. Systematics and evolution of North
American merlins. Auk 89:325-328.

■' .. ' "" •- ) ■ '■ , , 1972b. Sex and age characteristics of

North American merlins. Bird-Banding 48:181-196.

Thompson, A. L. 1958. The migraton of British falcons
(Falconidae) as shown by ringing results. Brit. Birds
51:179-188.

Williamson, K. 1954. The migration of the Icelandic
Merlin. Brit. Birds 47:434-441.

9306 Arlington Blvd, Fairfax, Virginia 22030.

94

Douglas A. Boyce, Jr.

Vol. 19, No. 2/3

Merlin Chasing Shorebirds

by John Schmitt

MERLINS AND THE BEHAVIOR OF WINTERING SHOREBIRDS

Douglas A. Boyce Jr.

Falcons are commonly reported to associate with
high concentrations of prey (Glue 1968; Roderick
et al. 1968; Scott 1968). Wintering shorebirds, be-
cause of their concentrations near intertidal feed-
ing areas, may be particularly vulnerable to such
predation. Shorebirds, especially juveniles, experi-
ence high mortality rates (Martin-Lof 1961; Boyd
1962; Holmes 1966; Soikkelli 1970; Goss-Custard
1980) and a substantial proportion of which may be
due to predation by raptors — particularly the
Merlin (. Falco columbarius ) (Page and Whitacre 1975;
Kus et al. 1984; Townshend 1984). Goss-Custard
(1980) hypothesized a protective response by
shorebirds to avian predators. Others found that
there are advantages for some small shorebirds to
associate with flocks when under attack (Goss-Cus-
tard 1980; Meyers 1982). Page and Whitacre
(1975:82) found that “small shorebirds in flocks
had less chance of being eaten by the Merlin than
did shorebirds which occurred singly”. Here I re-
port information that shows an additional
mechanism for avoiding predation when in a flock.

I studied the hunting behavior of Merlins on
mixed sho rebird flocks consisting of Dunlin ( Calid -
ris alpina ), Least Sandpiper (Calidris minutilla ), and
Western Sandpiper (Calidris mauri ) during
November through January of 1975 and 1976 at
northern Humboldt Bay, California. Humboldt
Bay is a particularly good place to observe raptor
attacks on shorebirds because incoming tides force
shorebirds to abandon their feeding grounds on
expansive mudflats and to congregate in compact
groups of several thousand at the edge of the bay or
in protected impoundments.

At high tide (± ^ h) falcons, including Merlin,
Peregrine Falcon (Falco per egrinus), and Prairie Fal-
con (Falco mexicanus ), arrived and hunted roosting
shorebirds daily during the study period. Smaller
shorebirds, primarily Dunlin, Least Sandpiper, and
Western Sandpiper, flew and congregated into
tightly knit flocks of several hundred to several
thousand upon the approach of any falcon. Larger
shorebirds, American Avocet (Recurvirostra
americana), Marbled Godwit (Limosa fedoa), and
Willet (Catoptrophorus semipalmatus), showed no re-
sponse to Merlins and only flew when the larger
Peregrine or Prairie Falcon arrived.

Merlins always positioned themselves high over
the water’s surface (30-60m) while shorebird flocks
wheeled back and forth in synchrony over the sur-
face below. Upon attack, the flock shape changed
from spherical to teardrop. Merlins attacked by
diving almost vertically at the flock and chasing
trailing individuals; if unsuccessful in singling out a
member, the falcon regained the original pitch
above the flock and repeated the attack. Flocks of-
ten turned sharply while the Merlin manuevered
for position above. Under careful observation it
appeared that the status of flock members
positioned along the flock’s periphery changed
rapidly (within seconds) between “leaders” and
“trailers” depending on the direction the flock
turned. Since Merlins always attacked the trailing
edge of the escaping flock’s tear-drop or fusiform
shape, shorebirds positioned in the flock interior
were at an advantage because they were rarely trail-
ers during attacks.

I observed individual shorebirds singled out on
10 different occasions. Two of the shorebirds suc-
cessfully outflew the Merlin and rejoined the flock.
Three were captured in mid-air. Three of the other
5 shorebirds were knocked into the water by Mer-
lins and the last 2 were pursued so closely that they
dove directly into the water. Each shorebird that
was stranded in water submerged as the Merlin
swooped down. This was a successful short term
solution but given enough time the Merlin captured
them (2 of 5 captured).

Four of the 5 water-bound shorebirds were ‘as-
sisted’ by the flock from which they had been sepa-
rated. In each case, the flock flew low directly over
the stranded shorebird. The Merlin, as a result,
always rose directly above the approaching flock. In
3 cases the stranded shorebird, within the first few
passes by the flock, left the water and rejoined the
flock as it passed overhead. One of the stranded
shorebirds appeared to have a broken wing and
could not rejoin the flock even though the flock
flew over it many times. The other shorebird was
captured before a flock flew over it.

Others have recorded shorebirds diving into
water in an attempt to escape raptors. John Schmitt
(pers. comm.) observed 3 additional instances at
Humboldt Bay where shorebirds flew into water

95

Raptor Research 19(2/3): 94-96

96

Douglas A. Boyce, Jr.

Vol. 19, No. 2/3

when pursued by Merlins and I observed 9 other
occasions where shorebirds flew into water when
chased by Peregrine Falcons. I also observed a male
Northern Harrier (Circus cyaneus) single out a small
shorebird from a flock and cause it to fly into water.
As with the Merlin, the flock returned and the
shorebird rejoined it. I hypothesize that these birds
are attempting to escape from raptors by purposely
flying at full speed into cover. Neotropical birds, for
example, have been observed to fly at high speed
directly into tree foliage when closely pursued by
the Orange-breasted Falcon (Falco dieroleucus)
(Boyce 1980).

Both the individual and flock benefit when the
raptor slows down to pick up the stranded bird. The
flock is not in danger because of the Merlin’s
changed behavior (i.e., hovering). This allows the
fast flying flock to return with no risk and recover
the stranded member, and escape before the falcon
can regain pursuit speed. The Merlin does not im-
mediately pursue the escaping flock because it con-
tinues searching for the water-bound bird it be-
lieves still remains in the water below.

Shorebirds may experience reduced mortality by
being associated with a flock for 3 immediate
reasons. First, the probability of being the target of
an attack is reduced when other targets are im-
mediately available; second, the tightly whirling
flock makes it difficult for Merlins to select an indi-
vidual for attack; and finally, observations of small
shorebird flocking behavior suggest that flocks will
return over the location of a waterbound bird and
allow the shorebird an opportunity to rejoin the
flock and avoid capture.

A less obvious reason for reduced mortality, by
being associated with a flock, is the position main-
tained by the individual within the flock while
under attack. Kus et al. (1984) reported, at Bodega
Bay, that juvenile Dunlins were over-represented in
Merlin kills compared to the population at large
and suggest that inexperience in maintaining coor-
dinated synchrony with the rest of the flock may
increase their risk. It is possible that shorebirds
located in the flock’s center are experienced adults

and those toward the periphery are inexperienced
juveniles.

I thank Colleen Handle and Jim Sedinger for
reviewing the manuscript.

Literature Cited

Boyce, D.A. 1980. Hunting and prenesting behavior of
the Orange-breasted Falcon. Raptor Research 14:33-39.

Boyd, H. 1962. Mortality and fertility of European
Charadrii. Ibis 104:368-387.

Glue, D.E. 1968. Bird predators feeding at autumn
roosts. British Birds 61 : 526-52 7.

Goss-Custard, J.D. 1970. Feeding dispersion in some
overwintering wading birds, p. 3-35. In: J.H. Cook
(ed.), Social behavior in birds and mammals. Academic
Press, London.

Holmes, R.T. 1966. Breeding ecology and annual cycle
adaptations of the Red-backed Sandpiper ( Calidris al-
pina) in northern Alaska. Condor 68:3-46.

Kus, B.E., P. Ashman, G.W. Page, and L.E.
Stenzel. 1984. Age-related mortality in a wintering
population of Dunlin. Auk 101:69-73.

Martin-Lof, P. 1961. Mortality rate calculations on
ringed birds with special reference to the Dunlin
(Calidris alpina) Ark. Zool. 13:483-491.

Myers, J.P. 1982. Territoriality and flocking by Buff-
breasted Sandpipers: variations in non-breeding dis-
persion. Condor 82:241-250.

Page, G., and D.F. Whitacre. 1975. Raptor predation
on wintering shorebirds. Condor 77:73-83.

Roderick, C.F., R.F. Lee, and J.C. Rolls. 1968. Hob-
bies persistently preying on Starling roost. British Birds
61:134.

Scott, R.E. 1968. Merlins associating with roosting
Starlings. British Birds 61 :527-528.

Soikkelli, M. 1970. Mortality and reproductive rates in
a Finnish population of Dunlin (Calidris alpina). Ornis
Fennica 47 : 1 49- 158.

Townshend, D.J. 1984. The effects of predators upon
shorebird populations in the non-breeding season.
Wader Study Group Bull. 40:51-54.

U.S. Fish and Wildlife Service, Denver Wildlife Research
Center, 1011 E. Tudor Road, Anchorage, Alaska 99503.
Present address: Department of Zoology, 574 WIDB,
Brigham Young University, Provo, Utah 84602 USA.

NOTES ON WINTERING MERLINS IN WESTERN MONTANA

Christopher Servheen

Abstract - Wintering Merlins ( Falco columbarius ) were studied in Missoula, Montana, from 1977 through 1979 where
all 3 North American subspecies winter together. The main food of the Merlins is the Bohemian Waxwing ( Bombycilla
garralus), which congregate in large flocks throughout the winter to feed on fruits of ornamental trees in residential areas
of the city. Possible origins of the 3 subspecies and hunting techniques are discussed.

The Merlin has been considered an uncommon
breeding species throughout its range (L. Oliphant,
this issue) in North America. Many aspects of Mer-
lin biology are unknown including winter habits.
This paper reports on Merlins wintering in an
urban area in western Montana.

Study Area and Methods

Wintering Merlins were studied within Missoula, a city of 36,000
population located in a mountain valley in west-central Montana.
The Missoula valley has an elevation of 950 m and is approxi-
mately 32 km long by 1 6 km wide and is surrounded by precipitous
forested mountains up to 2,900 m in elevation. Missoula is west of
the Continental Divide in the upper Columbia River drainage.
Large ornamental trees are established throughout much of the
residential area of the city. Prior to settlement, the valley was
probably devoid of large trees except those along the Clark Fork
River which bisects the city. The winter climate varies, but much of
the winter is cold with temperatures of — 15°C not uncommon.
Precipitation averages 33 cm per year and snow often covers the
ground throughout the winter. Winds are generally light to mod-
erate.

Observations were made from October through March, 1977
through 1979. Merlins were observed perching, feeding, and
chasing prey. Individual Merlins were trapped, measured, photo-
graphed, and banded with USFWS bands. Prey remains were
collected under perching trees and identified to species. In 1979 a
single Merlin was fitted with a tail-mounted radio transmitter and
tracked for 10 d.

Results and Discussion

Subspecies present. — Seven Merlins were cap-
tured within the city of Missoula during the study.
Of these, 4 were measured and banded with
USFWS bands. The remaining 3 were captured by
falconers and were photographed but not mea-
sured. These 7 Merlins were characterized to sub-
species using the criteria from Temple (1972)
(Table 1).

The identification of F. columbarius suckleyi was
based on the extremely dark plumage with no visi-
ble tail bands on the dorsal surface and 3 very faint
tail bands on the ventral surface. The identification
of F. c. columbarius females was more difficult. Tail
barring was not useful as the percentage of birds
with 4 tail bars is not significantly different between
western taiga F. c. columbarius and coastal forest F. c.
suckleyi (Temple 1972). Tail length and wing chord
measurements were not useful in differentiating F.
c. columbarius from F. c. suckleyi because of probably
feather length differences with age and overlap in
95% confidence intervals for feather length be-
tween coastal forest and taiga populations (Temple
1972). The most useful criterion was the presence
or absence of anterior and posterior web barring of

Table 1. Characteristics of Merlins captured in Missoula, Montana, during the winters of 1976-77 and 1977-78.

Subspecies

Sex

Age3

Wt(g)

Band #

# Tail Bands
(mm)

Wing chord
(mm)

Tail length

F. c. columbarius

M

A

154

1143-57207

4

190

116

F. c. columbarius

F

A

223

1143-57208

4

210

128

F. c. columbarius

F

S

275b

1143-57209

4

213

135

F. c. richardsonnii

F

A

235

793-03903

5

225

137

F. c. richardsonnii

M

S

160

....

4

203

122

F. c. suckleyi

F

A

...

—

3

...

...

F. c. columbarius

F

S

—

—

4

—

—

A = Adult; S = Subadult (estimated based upon plumage and feather wear)
Weight with a full crop; bird was captured with a full crop

97

Raptor Research 19 (2/3): 97-99

98

Christopher Servheen

Vol. 19, No. 2/3

the primaries. All 4 individuals thought to be F. c.
columbarius had no barring on the anterior web and
complete barring on the posterior web. The indi-
vidual F. c. suckleyi had no anterior barring and
incomplete posterior barring.

Tail length measurements agreed with ranges
measured by Temple (1972) (Table 1). The F. c.
richardsonii female was in adult plumage with sev-
eral worn feathers indicating it had gone through at
least 1 molt. Tail length of this bird was within 1
standard deviation of mean adult female tail length
measured by Temple (1972) for F. c. richardsonii.
The F. c. columbarius female with tail length of 135
mm (#1143-57209) was thought to be less than a
year old judged by uniform feather wear. The tail
length was at the high range of western taiga speci-
mens measured by Temple (1972) as would be ex-
pected in a subadult with longer feathers.

Origin of the Wintering Population. — The oc-
currence of all 3 subspecies in Missoula during
winter is unusual because of the separate and dis-
tinct breeding range of each (Temple 1972). West-
ern Montana is one of the few areas in North
America where the breeding ranges of all 3 sub-
species are relatively close together. This juxtaposi-
tion of breeding ranges is probably responsible for
the origin of all 3 subspecies wintering in Missoula.

Breeding of F. c. richardsonii, the priarie race, has
been documented in areas of southern Alberta
(Hodson 1976) and Montana (Becker, this issue)
east of the Continental Divide. No published
breeding records of this subspecies are available
from west of the Continental Divide (those breed-
ing in southwest Wyoming are morphologically
nearest to richardsonii, Ed.), although Craig and
Renn (1977) described two instances of Merlins
(subspecies not defined) nesting in southern Idaho
in cool desert upland habitat more typical of F. c.
richardsonii habitat than that of F. c. columbarius or
suckleyi. The limited data onF. c. richardsonii west of
the Continental Divide suggest thatF. c. richardsonii
individuals wintering in Missoula may have crossed
the Continental Divide (150 km to the east of Mis-
soula) during fall and spring migration.

F. c. columbarius has not been positively
documented as a breeding subspecies in Montana,
although scattered Merlin nesting records from
west of the Continental Divide cited by Ellis (1976)
and Weydemeyer (1973), and documented by other
qualified observers (E. Foss, pers. comm.) are prob-
ably F. c. columbarius based on Temple’s (1972)

maps and the nesting habitats selected. Due to the
difficulty of finding Merlin nests (Ellis 1976; L.
Oliphant, pers. commun.) it is likely thatF. c. colum-
barius may nest in western Montana in greater
numbers than previously thought, although it is still
rare. The boreal forests of western Canada may
support significant numbers of breeding F. c. col-
umbarius, and the Rocky Mountain trench provides
an excellent migratory pathway to funnel migrating
individuals from northern forests into the Flathead
Valley immediately north of Missoula. Thus, F. c.
columbarius individuals wintering in Missoula could
come from local and/or more northerly breeding
populations.

The origin of F. c. suckleyi in Missoula is unusual
in light of its current coastal breeding distribution
from southeast Alaska to southwest British Colum-
bia. Missoula lies approximately 830 km inland
from the Pacific northwest coast. The rich coastal
fauna and relatively stable winter weather condi-
tions result in a reduced seasonal migration for
resident coastal raptors such as the Peregrine Fal-
con (Falco peregrinus pealei) (Beebe 1960, 1974) and
Bald Eagle (Haliaeetus leucocephalus) (Servheen and
English 1979). Such reduced migrational move-
ments would also be expected for F. c. suckleyi which
can prey on large flocks of shorebirds which winter
in Pacific coastal areas (Page and Whitacre 1975; C.
Anderson, pers. comm.). The long distance inland
movement to winter in severe weather conditions
exhibited by F. c. suckleyi in Missoula remains un-
explained.

Food Habits. — Food habits of wintering Merlins
in Missoula are closely associated with large flocks
of Bohemian Waxwings (Bombycilla garrulus) which
winter in Missoula and feed on abundant fruits of
mountain ash ( Sorbus spp .) and crabapple trees
(Malus spp.) which are grown as ornamentals in the
city. This association has also been reported by
Smith (1978). Prey remains under Merlin perching
trees consisted of Bohemian Waxwings.

Hunting flights on waxwings usually were ini-
tiated from high perch trees where the Merlin had a
view of waxwing flocks flying above the open tree
canopy of residential areas. Merlins were observed
attempting to fragment a waxwing flock by direct
flight, and then pursuing an individual separated
from the main group. The pursued waxwing usu-
ally tried to escape by flying to cover, but the Merlin
usually attempted to stay below the waxwing and
thus force it up and away from cover. I have ob-

Summer/Fall 1985

Wintering Merlins in Montana

99

served 2 instances of straight pursuit where the
Merlin was able to out-fly the waxwing. Both times
the waxwing exhibited rapid evasion turns only
when the Merlin was upon it, but I was unable to see
the end of either flight.

Another flight observed involved a single wax-
wing diving for a group of 4 small conifers with the
Merlin approximately 6 m behind. The Merlin en-
tered the conifers after the waxwing, much like a
Sharpshinned Hawk (Accipiter stiatus ), and the 2
moved through 2 other conifers until the waxwing
left the trees. The waxwing then began to fly up-
ward in a spiral with the Merlin flying below in large
circles to gain altitude. The waxwing escaped as the
Merlin did not climb fast enough to attempt cap-
ture. The Merlin eventually gave up pursuit and
flew to a perch in a nearby tree.

Waxwings occur in flocks of up to 2,000 to 3,000
and respond to Merlin attacks by bunching into
tight ball-like formations. They will form dense
evasion clouds when a Merlin appears and smaller
flocks will attempt to join the large group.

Roosting. — In the winter of 1978-79, a tail-
mounted radio transmitter was placed on a Merlin.
That winter was the coldest on record, and wax-
wings were very scarce. The Merlin was tracked for
10 d. It roosted at night inside dense ornamental
spruce ( Picea spp.) trees within 10 to 50 m of houses
and busy streets. Weather severity with tempera-
tures down to -30°C was probably a factor in selec-
tion of dense spruce. On one morning with ex-
tremely cold temperatures, the Merlin did not leave
the night roost tree until between 1 030 and 1 1 30 H.
When the Merlin was in these trees it apparently
was perched close to the trunk in the interior and it
was impossible to see from the outside of the tree.

Acknowledgments

I am grateful to the many individuals whose knowledge, exper-
tise, and interest in Merlins made this work possible. In particular
I would like to thank Pete Jenny, Bob McDonald, Hal Williams,
John Tubbs, and Dale Becker for trapping and observational
assistance. Special thanks to Clifford Anderson and Lynn
Oliphant for insights during many hours of discussion.

Literature Cited

Beebe, F.L. 1974. Field studies of the falconiformes of
British Columbia. British Columbia Provincial
Museum Occasional Paper Series No. 17. Victoria,
B.C. 163 pp.

. 1974. The Marine Peregrines of the nor-
thwest Pacific Coast. Condor 62:145-189.

Craig, T. and F. Renn. 1977. Recent nestings of the
merlin in Idaho. Condor 79:392.

Ellis, D.H. 1976. First breeding records of merlins in
Montana. Condor 78:112-114.

Hodson, K. 1976. Some aspects of the nesting ecology of
Richardson’s merlin ( Falco columbarius richardsonnii) on
the Canadian prairies. M.S. Thesis, Univ. of British
Columbia, Vancouver.

Page, G. and D.F. Whitacre. 1975. Raptor predation
on wintering shorebirds. Condor 77:73-83.

Servheen, C. and W. English. 1979. Movements of re-
habilitated bald eagles and proposed seasonal move-
ment patterns of bald eagles in the Pacific Northwest.
Raptor Res. 13:79-88.

Smith, A.R. 1978. The merlins of Edmonton. Alberta
Naturalist . 8:188-191.

Temple, S.A. 1972. Systematics and evolution of the
North American merlins. A uk 89:325-338.
Weydemeyer, W. 1973. The spring migration pattern at
Fortine, Montana. Condor 75:400-413.

School of Forestry, University of Montana, Missoula, Mon-
tana 59812. Present address: U.S. Fish and Wildlife Ser-
vice, HS 105D, University of Montana, Missoula, Mon-
tana 59812.

OBSERVATIONS OF WINTER FOOD CACHING BY THE
RICHARDSON’S MERLIN

Ian G. Warkentin and Lynn W. Oliphant

Reports of food caching and retrieval are com-
mon in both wild and captive raptors. These be-
havior patterns have been observed in the Ameri-
can Kestrel (Falco sparverius) (Tordoff 1955; Muel-
ler 1974), Northern Goshawk (Accipiter gentilis)
(Schnell 1958), Prairie Falcon (Falco mexicanus)
(Oliphant and Thompson 1976), Lizard Buzzard
(Kaupifalco nongrammicus) Peregrine Falcon (Falco
peregrinus ) and Secretary Bird, (Sagittarius serpen-
tarius) (Brown and Amadon 1968: 78) as well as
many species of owls (Collins 1976). Food caching
by the Merlin (Falco columbarius ) has been reported
during the breeding season (Oliphant 1974;
Oliphant and Thompson 1976) and also during the
winter (Pitcher et al. 1979; Bud Anderson, pers.
comm.).

The observations herein were collected as part of
a wintering ecology study of the Merlin in Saska-
toon, Saskatchewan. Using a mobile null peak an-
tenna system, I.G.W. monitored the activities of 3
Merlins fitted with tail-mounted transmitters
(Model SM-1, AVM Instrument Company): a 2-yr
old male and 5-yr old female banded as nestlings in
Saskatoon and a 2-yr old female banded as a nestl-
ing in Regina, Saskatchewan. The female from Re-
gina was brought to the Western College of Veteri-
nary Medicine in Saskatoon for treatment of an
ulna fracture suffered on 5 December 1983 and
released in the city on 25 January 1984. The 2
others were trapped in Saskatoon, fitted with
transmitters and released within 2 h of capture.
The average temperature in Saskatoon during Feb-
ruary 1984, when these observations were made,
was — 4°C.

The 2-yr old female was monitored for 225 h
over a 49 d period. During this time her food cach-
ing and retrieval activities centered around a linear
grouping of 6 spruce trees ranging in height from 3
m at one end to 5 m at the other. On 3 February
1984 at 0830 H she perched on the second tallest
spruce and began a searching pattern that consisted
of hopping from branch to branch, carefully ex-
amining each one as she worked her way down the
tree. She concentrated her search on one side of the
tree starting on a branch about 3 m high and ending

up on the ground below the tree. After examining
the ground under the tree for 1 min she flew to a
distant perch to begin hunting. During the day she
caught and ate 2 House Sparrow (Passer domesticus),
then returned at 1540 H to perch on the same tree
visited that morning. At 1600 H she twice repeated
her search of the same area of the tree before
perching on an adjacent spruce. From this vantage
point she spotted a rodent on the ground below the
tree that she had presumably cached in the tree
previously. She flew down to pick up the prey and
carried it to a nearby power pole and ate it. Her
return to the same tree and success in finding
cached prey suggests that the behavior exhibited
that morning was an unsuccessful retrieval attempt.

On 5 February 1984 this same female caught and
ate a House Sparrow at 0935. H After 3.5 h she
began to hunt again and at 1 330 H caught a sparrow
and carried it to the tallet spruce tree in the group.
Perched on a branch halfway up the tree and about
1 m from the trunk, she plucked feathers from the
sparrow’s head and neck for 2 min, then used her
beak to carefully place the carcass in a fork of the
branch she was perched on. She left to continue
hunting and at 1 430 H she captured another House
Sparrow. During the remainder of the afternoon,
she made 5 hunting attempts but failed to kill again.
At 1 745 H she retrieved her cache of that afternoon
by flying directly to the fork in the branch used to
support the carcass. She carried it in her feet to a
perch 50 m away to eat. On the morning of 8 Feb-
ruary 1984 the Merlin perched in a spruce tree
making only 1 unsuccessful hunting attempt on a
House Sparrow. At 1 105 H she returned to the tree
used for caching on 3 February 1984 and im-
mediately located a cached House Sparrow on a
branch about 3 m high.

I.G.W. observed the male Merlin on 22 February
1984 at 1 730 H using the same searching pattern as
the female. He began his search on a branch 3 m up
a spruce tree and hopped branch by branch to the
ground twice before flying to a lamp post across the
street. Within a minute he returned to a branch in
the same area of the tree and emerged with the fully
plucked hind quarters of a small bird. Due to

100

Raptor Research 19 (2/3): 100-101

Summer/Fall 1985

Merlin Food Caching

101

transmitter failure this bird was only observed for 8
h over a 2 d period.

During 65 h of observations over an 1 1 d period,
the 5-yr old female was observed to use a cache
once. She flew directly to a branch near the top of a
10 m high spruce at 1430 H on 25 February 1984 to
retrieve a cached House Sparrow that she carried to
a nearby elm to eat.

The 2-yr old female displayed a sequence of
caching followed immediately by a return to hunt-
ing on 5 February 1984. This suggests that she was
hunting in the absence of an immediate food need,
caching food for a period of prey scarcity or greater
caloric demand. The attempted retrieval at 0830 H
on 3 February 1984 may represent such a situation
where the previous night’s temperature was 5°C
lower than the nightly low of the 3 preceding
nights. At least 2 retrievals described above were
caches left overnight. With average nightly temper-
atures of — 8.5°C during February 1984, these car-
casses would have been frozen. There were no ob-
served behavioral changes in the pattern of eating a
frozen carcass but the caloric value of a frozen spar-
row may be less.

During 225 h of observations, the 2-yr old female
used only the 2 spruce trees mentioned for caching
food. This is similar to Tordoff s captive American
Kestrel (1955), which consistently used the same
hiding place for its excess food. Stendell and Waian
(1968) also noted the extended use of one tree for
caching in wild American Kestrels. Oliphant and
Thompson (1976) found that Merlins seldom used
the same tree for caching during the breeding sea-
son. The difference in the pattern of food caching
in Merlins between wintering and breeding periods
may be the result of the degree of piracy by other
birds. Consistent use of the same tree should make
retrieval easier but the dense Black-billed Magpie
{Pica pica) and American Crow {Corvus brachyrhyn-
chos ) populations during the breeding season may

make piracy a greater problem. Individual differ-
ence may also account for the degree of consistency.

All 3 Merlins monitored exhibited food caching
behavior. This, along with the frequent use of
caches by the 2-yr old female, suggests that this
behavior is advantageous and plays an important
role in their wintering ecology.

We thank Paddy Thompson for technical assis-
tance. Support was provided by the Canadian
Wildlife Service University Research Support
Fund, the Frank M. Chapman Memorial Fund, and
the Canadian Plains Research Centre.

Literature Cited

Brown, L.H. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill, New York.
Collins, C.T. 1976. Food caching behavior in owls.
Raptor Res. 10(3):74-76.

Mueller, H.C. 1974. Food caching behavior in the
American Kestrel ( Falco sparverius). Z. Tierpsychol.
34:105-114.

Oliphant, L.W. 1974. Merlins- the Saskatoon falcons.
Blue Jay 32:140-147.

Oliphant, L.W. and W.J.P. Thompson. 1976. Food
caching behavior in Richardson’s Merlin. Can. Field-
Natur. 90(3):364-365.

Pitcher, E., P. Widener, and S.J. Martin. 1979. Winter
food caching by the Merlin {Falco columbarius
richardsonii). Raptor Res. 13(2):39-40.

Schnell, J.H. 1958. Nesting behavior of Goshawks in
the Sierra Nevadas of California. Condor 60:377-403.
Stendell, R. and L. Waian. 1 968. Observations on food
caching by an adult female Sparrow Hawk. Condor
70:187.

Tordoff, H.B. 1955. Food storing in the Sparrow
Hawk. Wilson Bull. 67:139-140.

Department of Biology, University of Saskatchewan, Saskatoon,
Saskatchewan, S7N OWO CANADA. Address of second
author: Department of Veterinary Anatomy, Western Col-
lege of Veterinary Medicine, University of Saskatchewan,
Saskatoon, Saskatchewan, S7N OWO CANADA.

EARLY NESTING RECORDS FOR MERLINS IN MONTANA AND NORTH

DAKOTA

Dale M. Becker

A questionnaire regarding Merlin (Falco columbarius ) eggs sent to several natural history museums in
North America revealed a number of previously unreported sets collected in Montana and North Dakota.
The first breeding records for the Merlin in Montana were recently reported by Ellis ( Condor 78:112-
114. 1976). However, 3 egg sets collected in Montana pre-dated Ellis’ (1976) report. R.B. Hitz collected 2
eggs near Sun River on 5 July 1867 (National Museum of Natural History, USNM 13478). Two eggs were
collected near Helena on 26 May 1882 by A.H. Palmer (Milwaukee Public Museum, MPM 417). The third
set, consisting of 4 eggs collected in Dawson County on 1 1 May 1895, was collected by C.A. Thurston
(Harvard University Museum of Comparative Zoology, MCZ 4285).

Several early nesting records for Merlins in North Dakota were reported by Stewart (Stewart, R.E.
Breeding birds of North Dakota, North Dakota State Univ., Fargo. 1975). Additional nesting records for
North Dakota include sets of 4 and 5 eggs collected in Stark County by R. Dodd on 25 May 1897 and 25
May 1900, respectively (Western Foundation of Vertebrate Zoology, WFVZ 1077684 and 79652-5). A
third set was collected on 13 May 1924 near Columbus by an unknown collector (University of Michigan
Museum of Zoology, UMMZ 190898). Museum records provide useful historical information on nest-
ing Merlins in the United States, yet they are often overlooked as sources of historical range use.

This project was funded by the USDA Forest Service, Rocky Mountain Forest and Range Experiment
Station at Rapid City, South Dakota, under Cooperative Agreement No. 14-16-0009-80-989. J. Hinshaw
(University of Michigan Museum of Zoology), L.F. Kiff (Western Foundation of Vertebrate Zoology), N.
Kracunas (Milwaukee Public Museum), R.A. Paynter, Jr. (Harvard University Museum of Comparative
Zoology), and W.D. Vanko (National Museum of Natural History) provided information on the egg sets.
I.J. BalfJ.S. Marks, C.W. Servheen, C.H. Sieg, andD.W. Uresk provided critical review of an earlier draft
of the manuscript.

U.S. Fish and Wildlife Service, Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, Montana 59812
U.S.A.

102

Raptor Research 19 (2/3): 102

MERLIN FEEDING ON ROAD-KILLS

Elizabeth Haug

In late April, 1979, I was radio-tracking Coyote ( Canis latrans ) near Woodruff, north-central Wisconsin.
While driving along a paved secondary road, at approximately 1000 H, I observed 20-30 dead or crippled
Purple Martin ( Progne subis) in a tight group on the road. They had apparently been attracted to radiated
heat from the paved surface, a behavior previously documented for several bird species (Whitaker, L.M.,
Wilson Bulletin 72:403-404, 1960) and had been run over by a vehicle. Approximately 5 min later, while
engaged in my radio-tracking work approximately 10 m from the accident site, a female Merlin (Falco
columbarius ) landed on the pavement next to a crippled martin. The Merlin appeared to observe the martin
intently for a few seconds. It then reached out, picked up the martin in its talons and flew into adjacent
woods. I remained at the scene for another 10 min during which the Merlin returned twice, each time
picking up a crippled martin and flying into the woods in the same general direction. As no young would
be expected this time of year and considering the short time span in which these observations occurred, I
assumed the Merlin was caching the martins. It is of interest to note that the Merlin appeared to select the
crippled birds, which exhibited varying degrees of movement, rather than dead birds. This incident
apparently represents an example of opportunistic feeding behavior by Merlins. Jenkins (Ontario Bird
Banding 8(2):40-41. 1972) noted a similar behavior where Merlins used moving vehicles to flush potential
prey. This, however, represents the first report of opportunistic feeding by Merlins on prey crippled by a
vehicle.

I wish to thank Lynn Oliphant and Andrew Didiuk for their suggestions on the manuscript.

Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan S7N OWO CANADA. Present Address: Department
of Veterinary Anatomy, University of Saskatchewan, Saskatoon, Sasatchewan S7N OWO CANADA.

103

Raptor Research 19 (2/3): 103

MEADOW VOLE PREDATION BY A MERLIN WINTERING IN SASKATOON,

SASKATCHEWAN

Ian G. Warkentin

The prey of the Merlin (Falco columbarius) is pre-
dominantly birds weighing less than 50 g (Bent
1938; Brown and Amadon 1968; Cade 1982).
Large insects such as dragonflies (Order Odenata),
grasshoppers (Order Orthoptera) and moths (Or-
der Lepidoptera) are commonly reported as part of
the diet but less frequently taken (Allen and Peter-
son 1936; Breckinridge and Errington 1938;
Cushing 1941; Bond 1951; Street 1960; Oliphant
1974). Mammals also make up a smaller proportion
of the prey; Brown and Amadon (1968) suggest
that it is about 5% for Merlins worldwide while
3.4% is reported by Fisher (1893) for Merlins in
North America.

Among mammalian prey, bats (Order Chiropt-
era) are taken more commonly than terrestrial
forms. In the United States, the Merlin is reported
to prey upon Myotis sp. and the Red Bat (Lasiurus
borealis ) (Allen and Peterson 1936; Johnson and
Coble 1967). Stomach and pellet analysis also re-
vealed the remains of rodents (Microtus sp.), pocket
gophers (Family Geomyidae), Thirteen-lined
Ground Squirrel (Spermophilus tridecemlineatus ) and
Least Chipmunk ( Eutamias minimus) (Allen and
Peterson 1936; Bent 1938; Burleigh 1972; Becker
1984). Although Decker (1972) reports a Merlin in
Edmonton, Alberta, catching a brown myotis bat
(Myotis lucifugus) and Oliphant found the skull of a
Least Chipmunk in a Merlin nest in Saskatchewan
(pers. comm.), Fyfe (cited in Trimble, 1975) records
no mammals in the diet of Merlins breeding on the
Canadian Prairies. Oliphant and McTaggart (1977)
listed only small birds and insects for the diet of
breeding Merlins in Saskatoon, Saskatchewan.

As part of a study of Merlins wintering in Saska-
toon, Saskatchewan, I monitored 3 individuals fit-
ted with tail-mounted radio-transmitters (Model
SM-1, AVM Instrument Company) between 25
January and 13 March 1984. Although all of these
birds preyed primarily upon House Sparrow (Pas-
ser domesticus), one Merlin was observed to take
mammalian prey. This bird was a 2-yr old female,
released in the city on 25 January 1984 after treat-
ment for an ulna fracture suffered on 5 December
1983 in Regina, Saskatchewan. She usually hunted

on small unused lots and storage yards in an indust-
rial section on the outskirts of the city. Weather
during the observation period was unseasonably
warm, as all snow in unprotected areas was melted
by the last week of February.

During 225 h of observation, the Merlin con-
sumed 22 House Sparrows and 8 rodents (2 im-
mediately following her release and 6 in early
March). I identified 1 of these rodents as a Meadow
Vole (Microtus pennsylvanicus) by examining the
guard hairs recovered from a plucking perch. The
other 7 rodents were eaten on inaccessible perches
and not positively identified. However, because of
their appearance and location of capture, I as-
sumed that at least 5 of these were also Meadow
Voles. Successful hunting attempts on rodents were
mounted from perches on power poles or building
corners. The Merlin left the perch in a slow, fixed-
wing glide to a point just over the prey followed by a
quick downward plunge with the feet extended.
Several attempts were also made from ground-level
perches but these all proved unsuccessful.

Cade (1982) suggested that young Merlins rely
on non-avian prey more than adults because they
lack the skills to capture birds. Instead, they feed on
insects and rodents which are easier to catch.
Perhaps this female fed on voles during the period
immediately after her release because she had not
yet regained her bird-catching skills. The appear-
ance of rodents, in the Merlin’s diet in early March,
may also represent the opportunistic nature of
raptor hunting. Warm weather during this period
melted most of the snow and thus more easily ex-
posed the voles, which would normally be protected
beneath this cover, and allowed the female to
exploit their availability.

I thank Lynn W. Oliphant for guidance during
the study and helpful comments on earlier drafts.
Harrison B. Tordoff, Stanley A. Temple, Steve W.
Platt and an anonymous reviewer also provided
constructive criticism of the manuscript. Support
was provided by the Canadian Wildlife Service
University Research Support Fund, the Frank M.
Chapman Fund and the Canadian Plains Research
Centre.

104

Raptor Research 19 (2/3): 104-105

Summer/Fall 1985

Merlin Predation on Meadow Vole

105

Literature Cited

Allen, R.P. and R.T. Peterson. 1936. The hawk mig-
ration at Cape May Point, New Jersey. Auk 53:393-404.

Becker, D.S. 1984. Reproductive ecology and habitat
utilization of Richardson’s Merlins in southeastern
Montana. M.S. thesis, University of Montana, Mis-
soula, 62 pp.

Bent, A.C. 1938. Life histories of the North American
birds of prey, Part 2. U.S. Natl. Mus. Bull. 170. Wash.,
D.C. 482 pp.

Bond, R.M. 1951. Pigeon Hawk catching dragonflies.
Condor 53:256.

Breckinridge, W.J. and P.L. Errington. 1938. Food
habits of small falcons in the north central states. Auk
55:668-670.

Brown, L. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill, New York.

Burleigh, T.D. 1972. Birds of Idaho. Caxton Printers,
Caldwell, Idaho.

Cade, T.J. 1982. The falcons of the world. Cornell Uni-
versity Press, Ithaca, New York.

Cushing, J.E. 1941. Notes on the feeding habits of two
species of hawk. Condor 43:70-71 .

Decker, D. 1972. Pigeon Hawk catches bat. Blue Jay
30:256.

Fisher, A. K. 1893. Hawks and owls of the United States
in their relation to agriculture. U.S. Dept, of Agri.
Bull. 3. Gov. Printing Office, Washington, D.C. Cited
by S.K. Sherrod. 1978. Diets of North American Fal-
coniformes. Raptor Res. 12(3/4): 49-121.

Johnson, W.J. and J. A. Coble. 1967. Notes on the food
habits of Pigeon Hawks. Jack-pine Warbler 45:97-98.

Oliphant, L.W. 1974. Merlins-the Saskatoon falcons.
Blue Jay 32:140-147.

Oliphant, L.W. and S. McTaggart. 1977. Prey species
utilized by urban nesting Merlins. Canadian Field-Nat.
91:280-286.

Street, M.G. 1960. Pigeon Hawk catches dragonflies.
Blue Jay 18: 124.

Trimble, S.A. 1975. Habitat management series for
unique or endangered species. Rpt. No. 15, Merlin
( Falco columbarius). Tech. Note T-N-271, U.S. Dept, of
the Interior, BLM.

Department of Biology, University of Saskatchewan, Saskatoon,
Saskatchewan, CANADA S7N OWO.

106

News and Reviews

Vol. 19, No. 2/3

Short Course on Raptors Offered at Hawk Mountain. — The Hawk Mountain Sanctuary Association will offer a
short-course on “The Ecology and Conservation of Raptors” from 2-1 1 January 1986. The course will be based at Hawk
Mountain. Lectures, laboratories and field projects will cover such topics as morphology and flight, behavior and
ecology, population biology and conservation and management. Though academically rigorous it will emphasize
personal instruction. Dr. Paul Kerlinger will be the instructor. Mark Fuller, Jim Brett and others will give guest lectures.
Students may receive 3 hrs of undergraduate or graduate credit through their own institutions or through Cedar Crest
College, Allentown, PA. Cost is $295, including tuition, room and local transportation. Inquire to: RAPTOR
COURSE, HAWK MOUNTAIN SANCTUARY, RT. 2, KEMPTON, PA. 19529. Application must be received by 15
Nov. 1985.

Proceedings of the Southeastern United States and Caribbean Osprey Symposium — published by The International
Osprey Foundation, Inc., edited by Mark A. Westall. Eleven papers, 132 pages. Copies can be ordered from The
International Osprey Foundation, Inc., P.O. Box 250, Sanibel, FL 33957 USA. Price: $16.00 U.S.

A Dictionary of Birds. 195. Bruce Campbell and Elizabeth Lack (eds)., Buteo Books,Vermillion, South Dakota, 704 pp., 500 plus
illustrations. Hardback: $75.00. More than 1,010,000 words. — This is another volume published jointly between a British and United
States firm. The Harrell’s, (Bryon and Joyce) of Buteo Book fame and among the founders of the Raptor Research Foundation, have
done an excellent service by providing a North American printing of many of the books originating in the United Kingdom, such as
books on Peregrines, Barn Owls, Harriers, etc. They have thus made them more readily available in North America. The words of
Frances James, president of the American Ornithologists Union, as written in the preface of this present volume, bare repeating here as
concerns this new Dictionary, “. . . the role the dictionary will play in fostering communications among nations. For students it will serve as
an entrance to the present status of the field. For scientists it will serve as a research tool and bridge between disciplines.” And thus it will
indeed be. More than 2 80 contributors from around the world have written sections for the book. The majority are, of course, European,
actually British; but ornithologists from Africa, Australia, New Zealand, South and Central America, Southeast Asia, and elsewhere are
represented. More than 60 are from the United States and Canada. Thus, the book is truly an international effort.

It is not clear to me exactly when the book was initiated but at least one of the contributors died in 1978. This Dictionary is basically a
modernization of the original Dictionary published in 1895 by Alfred Newton that was revised and enlarged in 1964 in the form of the New
Dictionary of Birds. Most topics have been enlarged and upgraded with current information. I have not had the time to compare how many
additional topics there are, if indeed any, over the 1964 version, but I suggest that there are several. As with any dictionary the topics are
listed alphabetically and cross-referenced. Most topics that are discussed in even the briefest fashion provide a few literature citations that
were consulted in the preparation of the topic. I particularly liked the array of illustrations therein. For example, in the topic of Nest
Function there is a nice series of diagrams on the various nests of the Magpie Goose showing both roosting and courting forms as well. But
what, then, does the book have to offer to a falconphile or strigiphile — membership of Raptor Research?

For the owls, both the Strigids and tytonids are covered in one three-page section entitled Owls; but a considerable amount of the
material in the five-page section on Vision also deals with owls. The main section on Owls is divided into subsections such as: General and
Systematic Characteristics, Habitat, Distribution, Populations, Movements, Food, Behavior, Voice and Breeding. The account was
written by Karel Voous and Heimo Mikkola. The chapter gives a good, albeit cursory, summary of what is known about owls. Unlike the
owls the diurnal raptors are covered in several sections, viz. Falcon, Hawk, Osprey, Secretary-bird and Vulture in addition to a brief
statement under a topic covered by the three ordinal names. While the Osprey is listed as a special category in Birds of Prey, it is in fact
discussed under the Hawks rather than having any lengthy discussion of its own.

Treatment of the four major diurnal raptor groups is not equal nor uniform in the subject matter. The Falcon section is mainly a
taxonomic treatment following Brown and Amadon’s format wherein the primitive neotropical falconids are treated as three separate
groups (Forest Falcons, Laughing Falcons and Caracaras), followed by a majority of the article discussing the True Falcons (lumping with
them the falconets). This section was written by Leslie Brown (who did the falcons for New Dictionary of Birds) and Ian Newton. The Hawk
section is organized somewhat differently, having both topics (i.e. movements, behavior, etc.) and then a survey of the major groups (i.e.
kites, Snake Eagles, etc.). Most of the discussion of groups is done so at the subfamily level. Of interest is the Bat Hawk having been given
its own separate section of treatment rather than being lumped in with the kites as has traditionally been done. This is probably because it
is in a monotypic subfamily. Once again, like the Falcon section, the authors of the Hawk section were Leslie Brown and Ian Newton. The
Secretary-bird has a three quarter page treatment by Alan Kemp. It is discussed on a topical basis but unfortunately has no discussion on
their taxonomy or systematics. Lastly, the Vultures are discussed as two separate contributions — the Old World Vultures written by
David Houston and the New World Vultures by John Ogden. The formats used, topics discussed and length of each is unequal, the Old
World material covers two pages and a good deal of the discussion centers around the differences between the Griffon Vultures (a group
of species in the genus (Gyps) compared with “other Vultures.” The discussion of the Griffons is basically a thumbnail sketch of their “life
history.” Ogden’s discussion of the New World Vultures ocupies about one-half a page and is mainly topical. Here again, a good
discussion of their evolutionary relationships would have been timely and especially informative if compared to the Old World Vultures.

Aside from the above there is also a short two-page discussion on Falconry. This was originally written by A.G.O’C. Scott but has been
redone by Bob Kenward, who most of the readership will know from his fine work on the Goshawk. This chapter is broken into brief
review sections on Birds Used, Basic Equipment, Training, Flying at Quarry and Conservation Aspects.

Overall, the book is very well done and has a wealth of material. Now that the New Dictionary of Birds, done in 1 964, is very hard to get,
the present volume is a good addition to any library. I recommend it highly, and for the cost it is an excellent buy. Regardless of your
interest in the world of birds, this book has something to offer everyone — C.M. White.

RAPTOR RESEARCH

A Quarterly Publication of The Raptor Research Foundation, Inc.

EDITOR: Clayton M. White, Department of Zoology, 161 Widtsoe Building, Brigham Young University, Provo,
Utah 84602

ASSISTANT EDITOR: Jimmie R. Parrish, Department of Zoology, 159 Widtsoe Building, Brigham Young Univer-
sity, Provo, Utah 84602
ASSOCIATE EDITORS

Jeffrey L. Lincer - Environmental Chemistry and Toxicology
Richard Clark - Order Strigiformes
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Jim Mosher - General Ecology and Habitat Analysis

INTERNATIONAL CORRESPONDENT: Richard Clark, York College of Pennsylvania, Country Club Road,
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Volume 19, Number 4, Winter 1985

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Contents V AUG 17 (987

Toward Raptor Community Ecology: Behavior Bases of '^J^Raries _
Assemblage Structure. Fabian M. jaksic

Owl Weights in the Literature: A Review.

John B. Dunning, Jr 113

Evaporative Water Loss in Captive Common Barn-Owls.

Kirk L. Hamilton 122

Peregrine Falcon Semen: A Quantitative and Qualitative

EXAMINATION. John Hoolihan and William Burnham. . .125

Prairie Falcon Prey in the Mojave Desert, California.

Douglas A. Boyce, Jr 128

Perching and Roosting Patterns of Raptors on Power Transmission
Towers in Southeast Idaho and Southwest Wyoming. John c. Smith .135

Short Communications

Relationship Between Prairie Falcon Nesting Phenology, Latitude and Elevation. Richard N. Williams 139

Recapture of a Non-breeding Boreal Owl Two Years Later. Thomas W. Carpenter, d . 142

Fall Raptor Concentration on Henrys Lake Flats. Daniel M. Taylor and Charles H. Trost 143

Bald Eagle (Haliaeetus leucocephalus) Consumption of Harbor Seal ( Phoca vitulina ) Placenta in Glacier Bay,

Alaska. John Calambokidis and Gretchen H. Steiger 1 45

Barred Owl Hunting Insects. Arnold Devine, Dwight S. Smith and Mark Szantyr 145

Northern Harrier Predation on Greater Prairie Chickens in Southwest Missouri. Brian Toland 146

News and Reviews 149, 150

The Raptor Research Foundation, Inc.
Provo, Utah

THE RAPTOR RESEARCH FOUNDATION, INC.
(Founded 1966)

OFFICERS

PRESIDENT: Jeffrey L. Lincer, Office of the Scientific Advisor, 2086 Main Street, Sarasota, Florida 33577

VICE-PRESIDENT : Richard Clark, York College of Pennsylvania, Country Club Road, York, Pennsylvania 17405

SECRETARY: James D Fraser, Virginia Polytechnic Institute and State University, Cheatam Hall, Blacksburg,
Virginia 24061

TREASURER: Gary E. Duke, Department of Veterinary Biology, 295K Animal Science/Veterinary Medicine Build-
ing, University of Minnesota, St. Paul, Minnesota 55108

BOARD OF DIRECTORS

EASTERN DIRECTOR: James A. Mosher, Appalachian Environmental Laboratory, University of Maryland,
Frostburg State College Campus, Gunter Hall, Frostburg, Maryland 21532

CENTRAL DIRECTOR: Patrick T. Redig, Department of Veterinary Biology, 295 Animal Science/Veterinary
Medicine Building, University of Minnesota, St. Paul, Minnesota 55108

MOUNTAIN 8c PACIFIC DIRECTOR: A1 Harmata, Department of Biology, Montana State University, Bozeman,
Montana 59717

EAST CANADA DIRECTOR: David M. Bird, Macdonald Raptor Research Centre, Macdonald Campus of McGill
University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Quebec H9X ICO

WEST CANADA DIRECTOR: R. Wayne Nelson, 4218 -63rd Street, Camrose, Alberta T4V 2W2

INTERNATIONAL DIRECTOR: Martin Bottcher, Postfach 2164, Steinfelder Strass 11, 5372 SCHLEIDEN,
Federal Republic of Germany, GERMANY

DIRECTOR AT LARGE # 1 : Michael Collopy, University of Florida, School of Forest Resources and Conservation,
1 18 Newins-Ziegler Hall, Gainesville, Florida 32601

DIRECTOR AT LARGE #2: Tom Dunstan, Department of Biological Sciences, Western Illinois University, Macomb,
Illinois 61455

DIRECTOR AT LARGE #3: Richard P. Howard, U.S. Fish and Wildlife Service, 4696 Overland Road, Room 566,
Boise, Idaho 83705

Persons interested in predatory birds are invited to join the Raptor Research Foundation, Inc. Dues are $15 per year
in the U.S., $17 per year outside the U.S., $13 per year for U.S. students, and $15 per year for students outside the U.S.
Add $2 to dues if membership is received after 15 February. The Foundation’s journal Raptor Research is distributed
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ship. Single copies and back issues are available from the Treasurer. A Contributing Membership is $25, a Sustaining
Membership is $100, and a Life Membership is $500. All contributions to The Raptor Research Foundation, Inc., are
tax-deductible.

Send requests for information concerning membership, subscriptions, special publications, or change of address to
the Treasurer. Other communications may be routed through the appropriate Officer or Board member. All inquiries
concerning the journal should be addressed to Clayton M. White, Editor, Raptor Research, Department of Zoology, 161
WIDB, Brigham Young University, Provo, Utah 84602, U.S. A.

Published quarterly by The Raptor Research Foundation, Inc. Business Office: Gary E. Duke, Treasurer, Depart-
ment of Veterinary Biology, 295K Animal Science/ Veterinary Medicine Building, University of Minnesota, St. Paul,
Minnesota 55108, U.S. A. Printed by Press Publishing Limited, Provo, Utah 84602. Second-class postage paid at Provo,
Utah. Printed in U.S.A.

RAPTOR RESEARCH

A QUARTERLY PUBLICATON OF THE RAPTOR RESEARCH FOUNDATION, INC.

VOL. 19

Winter 1985

No. 4

TOWARD RAPTOR COMMUNITY ECOLOGY: BEHAVIOR BASES
OF ASSEMBLAGE STRUCTURE

Fabian M. Jaksic

Abstract — Despite definite advantages in comparison to other model systems (e.g. assemblages of passerine birds
and lizards), raptor community ecology is in its infancy. I discuss the adequacy of raptors as model predators for the study
of the relationships between behavioral processes (agonistic interactions and hunting modes) and assemblage-level
patterns (community structure).

Community ecology studies of animals can be
equated with the identification and quantification
of the niche axes along which sympatric species
appear to separate in order to reduce co-use of
resources in limited supply. Schoener (1974) iden-
tified habitat, food, and time as the axes that most
frequently separate vertebrate predators (includ-
ing arthropod consumers such as passerine birds
and lizards, as well as carnivorous vertebrates). In-
deed, the study of insectivorous passerine birds as
model predators has contributed substantially to
the development of community ecology, as attested
by the pioneering studies of MacArthur (1972) and
Cody (1974; Cody and Diamond 1975); (see Strong
et al. 1984 for more recent views). Subsequently,
lizards have gained considerable importance as
model predators ( see Huey et al. 1983 for an over-
view of past and current contributions of her-
petologists to community ecology).

The early findings of Schoener (op. cit. ), although
disputed by some in terms of the underlying causes
(see Strong et al. (op. cit.) for a confrontation of
views), have by and large been held as verified. Both
with passerine birds and lizards it has been shown
that species often segregate along habitat (or mic-
rohabitat) dimensions. However, the data dem-
onstrating food segregation among these or-
ganisms are suspect for reasons described below,
and the adequacy of activity time as a niche differ-
ence is under serious questioning (e.g., Jaksic 1982;
Huey and Pianka 1983, Carothers and Jaksic 1984).
Adding to the confusion is the fact that the three
niche axes are usually correlated (segregation along
one of them leads to segregation along another),

thus making causality difficult to resolve. The
reasons for these correlations are easy to infer. For
example, the trophic structure (patterns of prey
use) of sympatric assemblages, which is described
on the basis of the diets of the component predators
(taxonomic composition, diversity, interspecific
similarity, mean prey size, etc.) is only the outcome
of behavioral processes occurring at the level of the
local population. These processes involve not only
prey selection, but also habitat preferences by the
individual predators, their activity times, foraging
modes and efficiencies, as well as morphological,
physiological, and ecological constraints.

The gap between the summary description of
food-niche patterns in predator assemblages and
the foraging mode of individual predator species
has recently been bridged for passerine birds (Eck-
hardt 1979; Robinson and Holmes 1982) and
lizards (Huey and Pianka 1981). In my view, how-
ever, these two groups of organisms, which seem to
be very suitable for studies of habitat preferences
and microhabitat partitioning, are less suitable for
the study of prey selection and food segregation.
First, prey in their diet often are identifiable only to
the ordinal level, and with some difficulty (at least
for ornithologists) to the familial level, which repre-
sents an important shortcoming. Greene and Jaksic
(1983) have shown that in dietary studies of pred-
ators identification of prey at the ordinal level
(customarily used in passerine and lizard diet
studies) underestimates diet diversity and overes-
timates diet similarity calculated at the species level
of prey identification. Further, Greene and Jaksic
(op. cit. ) have shown that these biases arise in unpre-

107

Raptor Research 19 (4): 107-1 12

108

Fabian M. Jaksic

Vol. 19, No. 4

dictable fashion, so that no reliable correction fac-
tors can be introduced in the computation of di-
etary statistics and consequently the food-niche
patterns so far documented for passerine birds and
lizards are suspect.

A second shortcoming of using passerine birds
and lizards as model predators is that they are sub-
ject to predation themselves. This renders it dif-
ficult to resolve whether they maximize some prey
selection function or compromise the use of opti-
mal prey by minimizing predation risks (an impor-
tant consideration in terms of optimal foraging
theory: see Pyke et al. 1977).

These two shortcomings become especially appar-
ent if one’s intention is to correlate food-niche
statistics (for whole predator assemblages) with the
foraging modes of the constituent species. It is un-
fortunate that this is so, because I think that the
question of how foraging mode is reflected in the
trophic structure of sympatric predators is an im-
portant one in community ecology. Provided that
neither passerine birds nor lizards seem particu-
larly adequate model predators for such an en-
quiry, I contend that raptors (Order Falconiformes
and Strigiformes) may help clarify the relationships
between “basal” behavioral processes and
“epiphenomenic” patterns of assemblage structure.
In the following sections I discuss the pros and cons
of using raptor assemblages as models for
behaviorally-based community analyses and pro-
pose the type of information to be gathered.

Raptor Assemblages as Model Systems

Until recently, raptors have been neglected as
model predators in community ecology. Neverthe-
less they have much to offer toward the clarification
of niche relationships among sympatric consumers.
Segregation of raptors along the habitat axis has
been documented both intra- and interspecifically
(e.g., Newton 1979; Schmutzetal. 1980; Nilsson et
al. 1982; Janes 1984), but this segregation does not
clearly result in access to different prey popula-
tions. Consequently, reduction of exploitative
competition seems an unlikely cause for such
phenomenon, nor does use of the same hunting
habitat lead to compensatory differentiation along
the food axis (Schnell 1968; Baker and Brooks
1981; Steenhof and Kochert 1985) which may be
interpreted as resulting from the functional re-
sponse of essentially opportunistic raptors to high
prey densities (Jaksic et al. 1981 ; Jaksic and Braker

1983; Erlinge et al. 1984). In my impression, where
habitat separation is observed among raptors, the
proximate cause lies on agonistic interactions — a
claim for which both direct (Rudolph 1978; Janes
{op. cit.) and indirect evidence exists {see Newton
1979; Jaksic 1982; Mikkola 1983, for summaries of
predation among raptors, an extreme form of
agonistic interaction). Consequently, the use of
exclusive ranges by raptors relate to reduction of
interference rather than of exploitative competi-
tion.

Something similar may be said of the causes of
temporal segregation. Jaksic (1982) documented
that diurnal and nocturnal raptors do not differ
enough in prey use (i.e., their diets are too similar)
to justify the view that they reduce exploitative
competition by differing in activity period (similar
conclusions were reached by Huey and Pianka
1983). In fact, Jaksic {op. cit.), based on circumstan-
tial evidence, contended that reduction of agonistic
interactions was the likely target of such temporal
segregation of activity. Carothers and Jaksic {op.
cit.), have elaborated this point on more theoretical
grounds, and for a variety of other organisms.
Rudolph {op. cit.) documented temporal segrega-
tion between two sympatric owl species, mediated
by predation of one upon the other. Notice, then,
that where interspecific segregation of raptors
along habitat and time dimensions has been re-
ported, the proximate factor may well be aggressive
exclusion rather than peaceful preemption of
specific resources as accomplished by differential
efficiencies in the exploitation of portions of the
niche axes. The latter has been the general as-
sumption underlying most studies of community
ecology, and I think that the study of raptor as-
semblages can contribute greatly to the under-
standing of the alternative mechanism (interfer-
ence competition) in generating the structure of
communities.

What about food partitioning? Studies ranging in
generality from selected pairs of species through
small groups of related raptors to entire as-
semblages have rendered varied conclusions (e.g.,
Schmutz et al. {op. cit.); Jaksic and Braker {op. cit.);
Knight and Jackman 1984; Marks and Marti 1984).
Results indicate that sometimes prey is partitioned
via size differences between raptors (accipiters are
good examples of this: see Storer 1966; Opdam
1975; Schoener 1984), and that sometimes raptors
differing greatly in body size take essentially the

Winter 1985

Raptor Community Ecology

109

same prey (Schmutz et al. {op. cit.); Jaksic 1983;
Jaksic and Braker {op. cit.)). There is a tendency,
though, for particular raptor groups to “specialize”
on certain general prey categories (e.g., kites and
harriers on small mammals and birds, small falcons
on insects, larger falcons on medium-sized mam-
mals and birds, eagles on hares; buteonines appear
very catholic in diet). These different groups of
raptors share in common similar morphologies and
hunting modes {see Jaksic and Carothers 1985),
which leads me to suggest that the reported trophic
structure of the few raptor assemblages so far
quantified {see Jaksic 1982, 1983; and Jaksic and
Braker {op. cit. )) somehow reflects those similarities.
I do not exactly share the view of Ricklefs and
associates (e.g., Ricklefs and Cox 1977; Bierregaard
1978; Ricklefs and Travis 1980) that it is not neces-
sary to go to the field for studying community ecol-
ogy: morphologic analyses suffice. Instead, I es-
pouse the view {see also Steenhof and Kochert {op.
cit.)) that the study of the hunting behavior of rap-
tors will tell us much about the way assemblages are
structured. That is, how behavioral processes result
in community patterns.

In comparison to both passerine birds and
lizards, the scrutiny of raptor food-niche relation-
ships is facilitated by their greater conspicuousness
and use of prominent roosting and nesting sites,
where detailed information on their diet can be
obtained. However, they also show some
shortcomings as model predators. Despite the fact
of generally being top predators in terrestrial
ecosystems, raptors are not entirely free of preda-
tion. Some species are indeed frequently preyed
upon by other raptors {see Newton op. cit.; Mikkola
op. cit. for summaries), and thus the study of raptor
assemblages does not completely eliminate the dual
constraints of energy maximization and mortality
minimization. But at least in comparison to pas-
serine birds and lizards, raptor behavior should, on
the average, be less affected by predation.

The problem of the taxonomic resolution of prey
(Greene and Jaksic {op. cit.)) is important in raptors
that prey primarily on insects; but essentially car-
nivorous raptors abound, and their vertebrate prey
is easily identifiable to the species level, particularly
if mammalian {see Errington 1930; Burton 1973,
for examples). In comparison to passerine birds
and lizards, then, accurate estimates can be made of
raptor diet diversity (= breadth) and interspecific
similarity (= overlap). In addition, open-terrain

raptors are relatively large, conspicuous birds
whose time budget, hunting mode, and hunting
success, can be quantified with minimal equipment
{see Rudebeck 1950, 1951; Warner and Rudd 1975;
Tarboton 1978; Wakeley 1978a, 1978b; Mendel-
sohn 1982; Rudolph 1982). Consequently, the
proportional use that raptors make of differing
hunting modes can be recorded and examined in
light of their diets and hunting success in different
habitat types. In sum, at least as compared to pas-
serine birds and lizards, raptor assemblages are ex-
cellent candidates for the study of food-niche re-
lationships of sympatric predators as related to the
hunting behavior of the component species. In the
following section I propose the type of information
to be gathered for such an aim.

Information Required to Assess
Community-Ecological Correlates of Raptor
Hunting Behavior

I. The use that sympatric raptors make of
different hunting techniques. — Raptor hunting
activities can be dichotomized as either perch- or
aerial-hunting. Within this second category, at least
four techniques can be recognized: a) hovering
flight: a stationary flight that may or may not take
advantage of the wind conditions; used by small
falcons (e.g., Falco sparverius), small kites (e.g.,
Elanus spp.), and by the Burrowing Owl {Athene
cunicularia)’, b) cruising flight: a high-speed, low-
altitude flight; used by large falcons (e.g., Falco
mexicanus) and accipiters {Accipiter spp.); c) quar-
tering flight: a low-speed, to-and-fro flight; used
by harriers {Circus spp.), and some owls {Asio flam-
meus, Tyto alba)-, and d) soaring flight: low-speed,
high-altitude flight that takes advanage of either
thermal or obstruction air currents; used by eagles
{e.g.,Aquila spp.) and buteonine hawks {Buteo spp.),
among others. More detailed descriptions of these
hunting flight techniques can be seen in Brown and
Amadon (1968), Warner and Rudd (1975), Everett
(1977), Tarboton (1978), Wakeley (1978b), Cade
(1982), Rudolph (1982), Collopy (1983a), and Col-
lopy and Koplin (1983). Recognition of these five
techniques seems necessary because there are indi-
cations that they facilitate access to different
habitats and prey types, and also because their
energetic costs differ {see Jaksic and Carothers 1985
for a selective summary). The time allocated to the
different hunting techniques by sympatric raptors
should be evaluated and, noting the prey captured

110

Fabian M. Jaksic

Vol. 19, No. 4

with each, the ecological consequences of raptor use
of differing techniques assessed.

2. The use that sympatric raptors make of dif-
ferent habitat types while hunting. — Here, it is
necessary to evaluate the time spent by raptors
hunting in different habitat types (see Wakeley
1978a; Bechard 1982, for examples), because it is
likely that prey availabilities differ among habitats
(see USDI 1979 et seq.; Baker and Brooks 1981;
Bechard 1982, for such findings). Perhaps only
broad categories of habitat use by raptors need to be
recognized, depending on the physiognomy and
landscape units that characterize the study site. For
interesting examples of ad-hoc habitat categoriza-
tions see USDI (1979 et seq.).

3. The hunting success of sympatric raptors in
different habitat types and in using different
hunting techniques. — The hunting success can
be estimated as the number of successful prey
strikes over the total hunting time spent by the
different raptors. Unsuccessful prey strikes also
should be counted to determine the hunting effi-
ciency (successful strikes/total strikes with known
outcome) of raptors using different hunting
techniques (Collopy 1983a; Collopy and Koplin (op.
cit.)). The prey captured ideally should be iden-
tified to the species level with the aid of adequate
viewing devices. Direct observations are possible
especially during the breeding season, when birds
can be tracked to the nest after a successful prey
strike, and the prey can be identified there if not at
the capture site (e.g., Collopy 1983b). By focusing
attention on open-terrain raptors, the prey cap-
tured in different parts of the habitat can be iden-
tified (e.g., Mendelsohn (op. cit.)).

4. The presumable clues that sympatric raptors
use in choosing hunting habitats. — This is unde-
niably the most difficult part of the proposed re-
search protocol. Judging from recent studies (e.g.,
Jaksic et al. 1981, 1982; Jaksic and Braker (op. cit.)',
Erlinge et al. (op. cit.)), generalist raptors appear to
take prey in about the order of their respective
availabilities in the field. Within characteristic
upper and lower size thresholds scaled to the sizes
of the individual raptor (whatever their abundance,
hares are unavailable prey for American Kestrels
the same way that grasshoppers are for Golden
Eagles). Because prey are taken by raptors on a
one-by-one basis, numerical estimates of the abun-
dance of individual prey may well serve as a crude
estimate of their availability in the different habitat

types recognized in the study site (see Baker and
Brooks 1981; and Bechard 1982, for cautionary
notes). Many techniques exist that can be used (e.g.,
Giles 1971), and examples of their applicability and
relative success can be found in USDI ( 1979 et seq.).
An additional characteristic of the prey species
which may be important in affecting their selection
by — or vulnerability to — raptors is their mobility
(e.g., Huey and Pianka 1981). This feature can be
evaluated as the average displacement in meters
per activity period, with the specifics of the mea-
surement depending on the type of prey. Ideally, a
vulnerability index for the different prey species at
the study site could perhaps be devised by combin-
ing prey characteristics such as density, spatial dis-
tribution (clumped, random, regular), micro-
habitat use, mobility, size, conspicuousness, etc.
How to compute such a complex index I cannot
figure out, because vulnerability is not an inherent
feature of the prey and should vary relative to rap-
tor characteristics (size, habitat preferences, and
hunting mode).

Concluding Remarks

The study of assemblage-level correlates of
hunting behavior in raptors should prove il-
luminating for a number of important questions in
community ecology: To what extent does the
trophic structure of predator assemblages reflect
the hunting behaviors of the component species?,
and — more specifically — provided that fal-
coniforms and strigiforms replace each other dur-
ing the daily cycle, is the similar trophic structure of
these raptor assemblages (Jaksic 1983) based on
behavioral similarities in the hunting modes of their
respective constituent species? To what extent do
the differing hunting modes of sympatric pre-
dators facilitate their coexistence through reduc-
tion of co-use of food resources (exploitative com-
petition)? What is the influence of interspecific
agonistic interactions (interference competition) in
the selection of hunting habitats and of hunting
modes by sympatric raptors?

Autecological studies of raptors are abundant (see
Clark et al. 1978 for a bibliography; Bunn et al.
1982, and Watson 1977, for specific studies), and
raptor population ecology has long reached its
maturity (see Newton 1979; Mikkola 1983, and re-
ferences therein). However, community ecology of
raptors is still in its infancy (see Jaksic and Braker
1983 for a cursory review). Given that raptors com-

Winter 1985

Raptor Community Ecology

111

pare more than favorably to other organisms (pas-
serine birds, lizards) as model predators, I think the
time is ripe for exploring this much neglected as-
pect of raptor ecology.

Acknowledgments

I thank Keith L. Bildstein, Tom J. Cade, John H. Carothers,
Michael W. Collopy, Eduardo R. Fuentes, Harry W. Greene, Jef-
frey L. Lincer, David T. Rogers, Jr., Clayton M. White, Stephen A.
Nesbitt, and an anonymous reviewer for critically reading dif-
ferent versions of the manuscript. I acknowledge the support of
grant DIUC 202/83 from the Pontificia Universidad Catolica de
Chile, and of grant INT-8308032 from the National Science
Foundation.

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Bechard, M.J. 1982. Effects of vegetative cover on
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Burton, J.A. (Ed). 1973. Owls of the world: their
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Cade, T.J. 1982. The falcons of the world. Comstock/
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Carothers, J.H. and F.M. Jaksic. 1984. Time as a niche
difference: the role of interference competition. Oikos
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Clark, R.J., D.G. Smith and L.H. Kelso. 1978. Work-
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Cody, M.L. 1974. Competition and the structure of bird
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Huey, R.B., E.R. Pianka, and T.W. Schoener
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Jaksic, F.M. 1982. Inadequacy of activity time as a niche
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Departamento de Biologia Ambiental, Pontificia Universidad
Catolica de Chile, Casilla 114-D, Santiago, Chile.

First received 7 March 1984; Accepted 20 April 1985

OWL WEIGHTS IN THE LITERATURE: A REVIEW

John B. Dunning, Jr.

Abstract - Published mean body weights of 1 8 species of North American owls are presented and reviewed. Adequate
data are lacking for virtually all species. A pattern of increased weight lability in small owl species is suggested by several
studies of captive and wild birds. One source with large samples of weight data is rejected as its means deviate from
virtually all other published sources.

Mean body weight is an important descriptive
statistic used in many avian studies. Often, how-
ever, researchers do not handle large numbers of
individual birds, and must rely on published mean
weights for the species they are studying. This is
especially true in the case of owls, which are difficult
to capture and weigh in large numbers. In the
course of compiling available weight data for all
North American birds, I searched the literature for
owl weights and noted some inconsistencies. The
purpose of this paper is to review the published
data, assess the reliability of different sources, and
discuss general trends apparent from the data.

Major Sources

Most studies reporting owl weights contain very
small samples, often only a single weight. Two
sources do present weights of all or almost all North
American species. Earhart and Johnson (1970)
(hereafter, E&J) analyzed patterns of size di-
morphism and food habits in owls. They presented
weights (Table 1) and wing lengths for all North
American owls except the Elf Owl (Micrathene whit-
neyi). E&J included 5 subspecies of the Great
Horned Owl {Bubo virginianus ) and 8 subspecies of
Eastern and Western Screech-Owl {Otus asio and
O. kennicottii). These weights were compiled from
various museum collections. The sample sizes were
often the largest reliable weight samples available
for each species. E&J used these data to calculate
the degree of sexual dimorphism for each species,
and examined how various ecological parameters
vary with body size. Snyder and Wiley (1976) also
used this same data set to examine food stress and
female nest defense as factors influencing reversed
sexual dimorphism in hawks and owls. The data
presented in E&J included sample size, mean and
range for both sexes.

The second source with a large series of owl
weights was Karalus and Eckert (1974) (hereafter,
K&E). This is essentially a “coffee table book” with
species accounts of all North American owls. It dif-
fers from the usual book of this type by including

detailed information of species’ and subspecies’
range, weight, linear measurements, voice and
general behavior. The measurements initially seem
attractive since they are based on large samples,
sometimes larger than E&J (Table 1). Unfortu-
nately, the data in this book appear to be completely
unreliable. The acknowledgments imply that most
measurements were taken from museum speci-
mens, but no sources are cited. K&E also presented
sample size, mean and range for at least 1 sub-
species of each species, while an “average weight”
was given for most other subspecies.

Species Accounts

Tyto alba — Single weights of the Common
Barn-Owl are given in Imler (1937) (475g, unsexed
fall bird from Kansas) and Stewart (1952) (457g,
unsexed fall bird from Ohio). Jackson and Dakin
(1982) gave weights of 2 c7 c7 from Mississippi (492,
5 1 2g). Poole ( 1938) reported the mean of 2 birds as
505g, while Haverschmidt (1948) listed the weights
of 1 <7 (485g) and 3 9 9 (446, 498, 558g) from
Surinam. Hartman (1961) collected 4 9 9 (X =
516g) and 4 <7 (X = 439g). His birds were from
Panama, Florida and Ohio, so weights cannot be
ascribed to any one locality with confidence. Marks
and Marti ( 1984) gave the mean of 78 birds as 5 1 1 g.
All these weights were within the range given by
E&J.

Large samples are in Steenhof (1983) and Marti
and Wagner ( 1 985) (T able 1 ). Steenhof ( 1983) cited
unpublished data. Her means were substantially
higher, but within the range presented in E&J.
Marti and Wagner (1985) presented data for live
(Table 1), trauma-killed, and starved owls from
northern Utah in winter. Both starved (9 X =
392g, N = 25; c7 X = 335g, N = 28) and trauma-
killed (9 X = 434g, N = 14; <7 X = 36 lg, N = 7)
birds weighed less than live trapped owls. In addi-
tion, the starved birds weighed less than the
trauma-killed, demonstrating that the manner in
which weight data is collected can affect means re-
corded for a sample. K&E’s data were similar to

113

Raptor Research 19 (4): 1 13-121

Vol. 19, No. 4

114

John B. Dunning, Jr.

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m. occidentals 9 1555(18) 1112-2046 9 1559(9) 1505-1652 Imler 1937

$ 1154(18) 865-1460 S 1269(4) 1230-1360

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v.pacificus 9 1312(23) 825-1668 1384 ave. U 1 166(30) Jaksic & Marti 1984

c? 992(26) 680-1272

(Continuation of Table 1.)

Winter 1985

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Aegolius funereus 9 140(4) 121-160 9 224(23) 199-235 9 167(96) 126-194 Glutz et al. 1979

<J 102(5) 85-119 <? 211(26) 193-227 <? 101(74) 90-1 13

Aegolius acadicus 9 90.8(18) 65-124 9 107(31) 87.9-124 U 91 .2(68) 72-1 12 Mueller & Berger 1967

<? 74.9(27) 54-96 d 102(37) 84.3-1 19

116

John B. Dunning, Jr.

Vol. 19, No. 4

E&J for females, but underestimated the male
weight by 13%. As is true of most other species, too
few data have been published to examine geo-
graphical variation.

Otus flammeolus — Johnson and Russell (1962)
presented mean weights for 13 Flammulated Owls
from California and Nevada (Table 1). The mean
for 11 <? c? is similar to E&J’s mean for 56 <? <$ . The
female mean in Johnson and Russell is substantially
higher, but sample sizes are small. K&E’s data are
widely divergent from both of the above sources,
deviating from E&J by 130 - 140%.

Otus asio and O. kennicottii — Eastern and West-
ern Screech-Owls contain 16 subspecies combined
that are widely divergent in size (A.O.U. 1957, but
see Marshall 1967). The only source covering all 16
subspecies is K&E, but as has been shown for most
other species, these weights are at odds with virtu-
ally all other available sources. E&J provided
weights for 2 subspecies of Eastern Screech-Owl
(: naevius , mccallii ) and 5 subspecies of Western
Screech-Owl ( inyoensis , cinerascens, kennicottii, ben-
direi, quercinus). A large degree of geographic vari-
ation is apparent from this data set.

Other sources of screech-owl weights are few. I
found no data for aikeni, asio, brewsteri, hasbroucki,
maxwelliae, and swenki. Johnson and Russell (1962)
collected 1 9 macfarlanei in California weighing
177g. Miller and Miller (1951) presented data from
Arizona and California for 3 southwestern sub-
species: yumanensis (6 c? X = 103g± 1 1.4S.D.),
inyoensis (2 9 9 , X = 157g); 8 <? <?, X = 131g±9.2),
and quercinus (7 <f d1, X = 1 17g). Miller and Miller’s
inyoensis data were similar to E&J, while the quer-
cinus mean of Miller and Miller was less.

Clench and Leberman (1978) gave a mean of
163g (range 153-176g) for 8 naevius banded in
Pennsylvania. Other naevius weights include
Stewart (1937) (206, 228g unsexed adults) and
Poole (1938) (2 birds averaging I78g). Kelso (1938)
gave weights for naevius (2 <? <?, 133, 156g; 9 9 9 , X
= 20 lg, range 148-244g, New York, some birds
starved), floridans (1 <?, lllg, Florida), and 5
starved unsexed birds from Indiana (X = 139g,
range 1 1 4- 1 62g), which Kelso attributes to swenki
but considering the range must be naevius (A.O.U.
1957). Finally, Imler (1937) collected 4 individuals
in western Kansas (X = 152g, range 153-176g)
which could be either aikeni or swenki.

The only complete analysis of seasonal weight

variation in screech-owls is the Henny and Van-
Camp (1979) study of O. asio naevius in Ohio. Their
means of all birds captured were slightly higher
than E&J for this subspecies (Table 1). Henny and
VanCamp documented a seasonal weight cycle
peaking in late fall. They suggest that this weight
gain reflects an increase in fat reserves which aid
winter survival. They also noted a wide range of
body weights within seasons, suggesting that body
weight was relatively labile. The same possibility has
been discussed in studies of several other small
owls.

Otus trichopsis — The only additional weight
published for the Whiskered Screech-Owl is an es-
timate of 120g (Zar 1969). This figure differs sub-
stantially from E&J. It could be that this estimate
(which Zar did not make himself) was based on the
incorrect assumption that Whiskered Screech-Owls
should weigh approximately the same as the sym-
patric subspecies of Western Screech-Owl (Otus
kennicottii cinerascens). K&E overestimated female
and male means by 84 and 90%, respectively.

Bubo virginianus — With the exception of E&J,
surprisingly little data have been published on
Great Horned Owls. E&J presented weights for 5 of
the 9 North American subspecies. Other published
weights are mostly of virginianus, the eastern sub-
species. Hartman (1955) collected 1 9 (1248g) and
1 c? (1040g) from Ohio. The female weight was
substantially lower than E&J’s minimum for this
subspecies. Poole (1938) gave the mean of 2 vir-
ginianus 9 9 as 1446g. Langenbach and McDowell
(1939) reported large samples of Pennsylvanian
birds (Table 1). They noted a substantial difference
between specimens with full stomachs (Table 1 ) and
with empty stomachs (9 X = 1644g, N = 94; <? X =
1263g, N = 142). The means from birds with full
stomachs closely approximates E&J. The lower
means for birds with empty stomachs show the
amount of error that can be introduced if this factor
is not accounted for.

For the other races, only scattered data are avail-
able. Irving ( 1 960) collected a male lagophonus from
Alaska weighing 1445g, while Williamson (1957)
reported an Alaskan female algistus weighed 2000g.
Poole (1938) gave one unsexed pacificus as 1480g.
Imler (1937) listed a small sample of occidentalis
from western Kansas (Table 1), while Jaksic and
Marti (1984) presented samples for both pacificus
and occidentalis (Table 1). In addition, Siegfried et

Winter 1985

Owl Weights

117

al. (1975) gave the mean weight of 2 9 9 as 1425g.
These were from zoos and unidentified to sub-
species.

By far the most surprising pattern is the lack of
published data. Great Horned Owls are common
throughout North America, and are often among
the most common birds brought to raptor rehabili-
tation centers and museum collections. A large
amount of unpublished data must exist on the vari-
ous subspecies. No reliable data were found for the
subspecies saturatus and heterocnemis.

Nyctea scandiaca — Irving (1960) gave the
weight of 1 Snowy Owl collected in Alaska as 2267g,
while Siegfried et al. (1975) listed 1 unsexed captive
from Minnesota at 1916g. Poole (1938) reported a
single male weighing 1404g, while Hagen (1942)
gave a mean of 2003g for 7 Norwegian birds. Ges-
saman (1978) gave weights of 3 captive 9 9 during
the winter as 1928, 2175 and 2392g. The largest of
these lost 80g during a 5-d fast. All these weights fall
within the range given by E&J.

K&E’s mean for males is close to E&J, but the
female mean in K&E underestimates E&J by 13%.
Even considering the weight loss recorded by Ges-
saman (1978) in a healthy fasting bird, this differ-
ence still may be real.

Sumia ulula — Small samples of Northern
Hawk-Owl weights were found in Irving (1960),
Campbell (1969) and Johnson and Collins (1975).
Campbell (1969) collected 3 $ & (317, 319, 346g)
and 1 9 (41 8g) from Alaska, while Irving (1960)
collected 2 Alaskan <? & (322, 350g) and 4 9 9 (310,
336, 350, 384g). These were slightly heavier than
the ranges in E&J. However, Johnson and Collins
(1975) found a single captive bird’s weight varied
from 293-375g. Thus the above samples agree
fairly well. K&E underestimated male and female
weights by 24 % and 27%, respectively. The varia-
tion recorded by Johnson and Collins reflects the
pattern of weight lability found in smaller owls.

Glaucidium gnoma — Several subspecies of
Northern Pygmy-Owl occur in North America. Lit-
tle data are available and it is impossible to deter-
mine if the wide differences reported are due to
geographic variation or error. Johnson and Russell
(1962) give weights of 8 c? <? (X = 62. 8g, range
57. 3-68. Og) for the subspecies calif ornicum , which
agrees with the californicum weights of E&J. K&E
weights are 34-38% lower than E&J, but are from a
different subspecies (pinacola ). Zar ( 1 969) estimated

Northern Pygmy-Owl weights at 54g, substantially
under the californicum samples, but without reliable
data for the other subspecies, this estimate cannot
be evaluated.

Glaucidium brasilianum — Little additional data
exist for Ferruginous Pygmy-Owls. Prange et al.
(1979) gave the weight of 1 bird as 61.0g. Russell
(1964) collected 2 cT <$ (60.5, 62. 6g) and 4 9 9 (64.4,
74.6, 77.7, 94. 8g) in Belize. These data agree closely
with E&J. K&E overestimate female and male
means by 10 and 28%, respectively. The wide range
of values given by Russell (1964) and E&J may
reflect weight lability in this species.

Micrathene whitneyi — E&J gave no weights for
the Elf Owl. Zar (1969) estimated mean weight as
46g, only slightly larger than the large series mean
of 41. Og in Walters (1981). Lasiewski and Dawson
(1967) estimated the mean as 37. 7g, while Ligon
(1967) gave a range of 35-55g. Johnson (1968)
listed 1 S and 1 9 averaging 37. Og. Finally, Walters
(1981) published a large series of weights based on
banded, unsexed Arizona birds (Table 1).

Athene cunicularia — More data exists for Bur-
rowing Owls than for any other North American
owl. Two subspecies are represented: hypugaea in
the west and floridana in Florida. Some published
weights cannot be safely ascribed to subspecies. For
example, Marti (1974) assembled 8 weights from
literature and museum specimens (X = 140g), but
did not describe his sources more fully.

Most published samples are of hypugaea. Imler
(1937) gave the mean of 7 Kansas birds as 149g
(range 1 1 4- 1 7 1 g). Coulombe (1970) presents sum-
mer and winter weights from the same Californian
population (Table 1). His samples show wide sea-
sonal variation. Thomsen (1971) presents weights
for breeding California birds (Table 1), that were
heavier than E&J by less than 10%. K&E, on the
other hand, overestimate E&J by 28-42%, probably
a very real difference.

Of the published floridana weights, Prange et al.
(1979) listed weights of 3 individuals (179, 182,
185g). Hartman (1955) included weights of 4 9 9
(130, 150, 157, 170g) and 4 dd (130, 150, 170,
1 70g), while Hartman (1961) listed weights of 5 9 9
and 6 <? <3 (Table 1), possibly including the same
data as the earlier paper. Little difference between
the means for the 2 subspecies can be seen.

Strix occidentalis — Johnson and Russell (1962)
collected 2 female Spotted Owls in California

118

John B. Dunning, Jr.

Vol. 19, No. 4

weighing 616 and 648g. No other published
weights were located except for E&J and K&E.
K&E underestimated female weight by 21% and
male weight by 33%. This difference appears very
substantial, but could reflect subspecific differ-
ences. K&E’s sample was based on occidentalis , while
E&J did not give subspecific identification. Three
subspecies of Spotted Owl occur in North America.

Strix varia — Weights are available for 2 sub-
species of Barred Owl. For subspecies varia ,
Hartman (1955) listed weights of 2 9 9 from Ohio
(681, 77lg) and 1 <$ (642g), while Poole (1938) gave
the weight of 1 unsexed bird as 5 1 Og. Both E&J and
K&E samples are of this subspecies. K&E again
seriously underestimated the E&J weights by 37%
(both sexes). Siegfried et al. (1975) gave the weight
of a single captive from Minnesota as 748g.

Hartman (1955, 1961) also gave weights for geor-
gica (“ alleni ” in the 1961 paper). Hartman (1955)
listed 1 9 (875g) and 3 c? d from Florida (681, 750,
800g). Hartman (1961) gave 2 9 9 weights as 850,
875g, and the mean of 6 c? <? as 71 8 + 35. IS. E. These
few weights suggest that georgica might be heavier
than varia , but sample sizes are much too small for
firm conclusions.

Strix nebulosa — Very little data exist for the
Great Gray Owl. Irving (1960) collected 1 9 (1092g)
in Alaska, while Bent (1938) stated that weights of 4
birds ranged “from 1 lb. 15 oz. to 2 lb. 14.5 oz.”
K&E’s male means are substantially overestimated
by 38%, compared to E&J.

Asio otus — Graber (1962) gave the weight of a
captive female and a captive male from Illinois as
310g and 252g, respectively. Poole (1938) listed 2
9 9 as averaging 288g, while Hagen (1942) re-
ported a mean of 285g for 3 Norwegian birds. Marti
(1974) compiled a mean of 262g from 7 weights
found in the literature and museum specimens, and
Marks and Marti ( 1984) gave a mean of 254g for 20
birds. All these weights fall within the range re-
ported by E&J.

Asio flammeus — A number of studies report the
weight of a single Short-eared Owl. Irving (1960)
collected 1 9 weighing 400g from Alaska. Imler
(1937) found one unsexed bird in western Kansas
weighed 270g. Campbell (1969) collected an Alas-
kan male weighing 337g. A captive in California
averaged 385gover 14 d (Page and Whitacre 1975),
while another captive in Illinois averaged 406g over

24 h (Graber 1962). In addition to these single
reports, Clark (1975) reported the mean of 2 9 9 as
392g and 2 cT cT as 304g, while Hagen (1942) gave
the mean of 1 1 Norwegian birds as 37 lg. Clark and
Ward (1974) compiled a relatively large sample for
both sexes (Table 1) which agree closely with E&J.

Aegolius funereus — Irving (1960) collected an
Alaskan male Boreal Owl (A.f. richardsoni) weighing
116g, while Campbell (1969) reported a very fat
Alaskan female weighing 194g. E&J gave weights of
only 9 birds. K&E have a much larger sample, but
their data deviate from E&J by 60% for females and
107% for males and cannot be considered reliable.
The best available sample for this species is Glutz
von Blotzheim et al. (1980). Their sample (Table 1)
is of the European subspecies A. f. funereus, how-
ever, the means and ranges overlap widely with
E&J’s small sample.

Aegolius acadicus — Several small samples of
weights were published for Northern Saw-whet
Owls. Zar (1969) estimated a weight of 124g, which
is very high compared to the following. Single
weights were given by Gatehouse and Markham
(1970) (82. 9g, 1 captive tf), Poole (1938) (108g,
unsexed), and Murray and Jehl (1964) (89. 6g, 1
New Jersey migrant). Graber (1962) weighed 2
captive birds, 1 9 (96g) and 1 c? (75g). Clench and
Leberman (1978) banded 5 unsexed migrants in
Pennsylvania (X = 86. Og, range 72. 6-97. 6g), while
Walkinshaw (1965) banded 10 migrants in Michi-
gan weighing 95. 2g (range 85.1-1 14g). All these
weights agree closely with E&J’s values.

Collins (1963) reported several series of North-
ern Saw-whet Owl weights. Eleven birds of both
sexes from the University of Michigan collection
averaged 81. 8g (range 54.2-1 24g), while 7 banded
birds weighed 82. 7g (range 67.5-1 13g). Collins also
kept 2 9 9 (106, 1 08g) and 1 c? (80g) in captivity. He
noted that the weight of the lighter female varied
daily from 74.1gto 1 14g, suggesting weight lability
in this species.

Mueller and Berger (1967) weighed a large series
of migrants in Wisconsin (Table 1). They
documented a significant weight difference be-
tween adult and immature birds, and discussed
weight change after banding. Their means and
ranges for the unsexed birds agree relatively well
with E&J. K&E overestimated female means by
18% and male means by 36% compared to E&J.

Winter 1985

Owl Weights

119

Discussion

The most apparent pattern in the preceding
species accounts is the lack of published data even
for common species and subspecies of owls. E&J
provide a basic reference sample for most species.
E&J’s data were taken from specimens from several
museums, and are probably adequate if a rep-
resentative mean weight is needed, as in their study
of owl food habits. But since individual specimens
in a collection are often obtained in a wide variety of
ways, the heterogeneity found in these samples
precludes their use in many studies. A single sample
like E&J’s cannot express the seasonal (Coulombe
1970; Henny and VanCamp 1979), daily (Collins
1963) and geographic (Miller and Miller 1951)
variation present in owls. Owls could provide a
good test of ecotypic variation such as Bergmann’s
rule, as they are often permanent residents and
have wide geographic ranges, but the available data
simply do not allow such analyses. Published ac-
counts typically are of small sample size or do not
consider such variables as stomach content
(Langenbach and McDowell 1939) or manner of
collection (Marti and Wagner 1985). Thus, pub-
lished series of weights within and between seasons
for birds handled in a consistent manner are
needed for virtually every species.

This situation is not unique to owls. In a compila-
tion of weight data for all North American birds
(Dunning 1984), I found that adequate data are
lacking for a surprising number of species. This is
especially true for western and southwestern
species. However, I often found that pertinent data
existed in some bander’s log or researcher’s
notebook, but remained unpublished. A single
example of the value of more published data will
suffice. Henny and VanCamp (1979) proposed that
the increase in mean body weight recorded in the
fall reflects an increase in fat reserves allowing
greater winter survival for a population of Eastern
Screech-Owls in northern Ohio. One way to test this
hypothesis would be to examine seasonal weight
cycles in more southerly screech-owl populations.
If a similar fall peak in body weight were found in
screech-owls that lived in a more mild climate, an
alternative explanation might be required. How-
ever, this test is presently impossible to do, as I
could find no weights at all for the more southerly
subspecies in the eastern United States, O. a. asiol

A second pattern of great interest is that of in-
creased weight lability in small owl species. Collins

(1963) reported that the weight of a single captive
female Northern Saw-whet Owl varied from 74. lg
to 1 14g, a variation of 30% from the median. Simi-
larly, Johnson and Collins (1975) reported weight
of a female captive Northern Hawk-Owl varied
from 293g to 375g “without apparent ill effect.” In
comparison, Gessaman (1978) found that a female
Snowy Owl lost only 80g (3.3% of this individual’s
mean weight of 2392g) during a 5-d fast. If this
weight loss had been in the same proportion as the
Northern Saw-whet Owl reported by Collins, the
female Snowy Owl could have lost up to 718g. With
these captivity studies in mind, the wide within-
season range of Eastern Screech-Owl weights re-
ported by Henny and VanCamp (1979) and the
large between-season variation in Burrowing Owl
weights reported by Coulombe (1970) suggest that
weight lability may be common in many smaller
owls.

Finally, it is apparent from this review that
Karalus and Eckert (1974) is totally unreliable. The
mean weights presented in this work deviate from
virtually all other samples by as much as 140%. The
weight lability just discussed could lead to widely
divergent weights sometimes being reported for a
small owl. But the K&E data are supposedly based
on large samples, and the deviations are present in
both large and small species. A spot check of some
of the linear measurements presented for each
species shows that these, too, deviate from pub-
lished references by as much as 20%. Since other
reviewers have found fault with the text, terminol-
ogy, bibliography (Martin 1976) and maps (Bock
1976) in this work, it is apparent that this book
cannot be used as a reliable source of any informa-
tion on owls.

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Bent, A. C. 1938. Life histories of North American birds
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Bock, W.J. 1976. Review — The owls of North America.
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Campbell, J.M. 1969 The owls of the Central Brooks
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Clark, R.J. and J.G. Ward. 1974. Interspecific compe-
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Department of Ecology and Evolutionary Biology, Univ. of
Arizona, Tucson, AZ 85721.

Received 26 December 1983; Accepted 15 April 1985

EVAPORATIVE WATER LOSS OF CAPTIVE COMMON BARN-OWLS

Kirk L. Hamilton

Abstract — Evaporative water loss of the Common Barn-Owl {Tyto alba ) was examined at temp experienced by these
owls during incubation. Water loss increased (P < 0.001) with increasing ambient temp; however, it appeared that
Common Barn-Owls in Utah would not be heat-stressed during incubation.

The Common Barn-Owl (Tyto alba ) readily uses
man-made structures (i.e. , barns, haylofts, aban-
doned water towers) as roosting and nesting sites
and adapts quickly to the use of nestboxes (Otteni et
al. 1972; Marti et al. 1979). The use of nestboxes as
nesting sites provides the barn owl with the advan-
tageous effects of the sheltered nestboxes (i.e., de-
creased forced convection, less direct exposure to
precipitation, and higher than ambient temp) dur-
ing incubation (Hamilton 1982). While there may
be advantages for birds to conduct incubation
within nestboxes, higher ambient temp may be a
potential stressor. Birds may mitigate the effects of
heat stress by panting, gular fluttering, or by post-
ural thermoregulatory behavior (Bartholomew et
al. 1968; Weathers 1972; Bartholomew and Daw-
son 1979; Dawson 1982).

The objectives of this study were to examine
evaporative water loss of barn owls, and to deter-
mine whether water loss plays a crucial role during
incubation at ambient temp below 32°C.

Materials and Methods

Two adult owls were captured in April 1980 at Welder Wildlife
Foundation (Sinton, San Patricio Co., Texas) and a third adult owl
was obtained from a local raptor rehabilitator (S. Ure, Salt Lake
City, Utah). All birds were transported to the Environmental
Physiology Laboratory at Utah State University, Logan, Utah. In
1981, three additional adult owls were captured post-incubation
(April-May, Brigham City, Box Elder Co., Utah) and likewise
transported to the laboratory facilities. All owls (9 ) were housed
in separate 3 x 3 x 2.5 m walk-in environmental chambers. Owls
were fed a laboratory House Mouse ( Mils musculus) diet and
maintained on a 12L:12D photo period during all experimental
trials.

Evaporative water loss of 6 captive barn owls was measured at
temp that simulated nesting temp (2-30°C). An owl was equili-
brated to the test temp for 2-3 d before an experiment and fasted
for 6 h prior to the experiment. Each owl was weighed to the
nearest 1 .0 g on a platform balance and placed in a metabolism
chamber. Owl weights ranged from 527.0-584.4 g with a mean
value of 561.3 g (±27.8, S.D.). Metabolism chambers (56 x 46 x 43
cm) were constructed of plywood (1.3 cm) with a plexiglass sliding
door unit (30 x 22 cm, inside dimensions). All edges of the
chamber and door were sealed airtight with liquid plastic to pre-
vent extraneous air flow. The wood was varnished and the inner
surface of the chamber was covered with a plastic coating to
prevent water vapor from being bound hydroscopically to the
walls of the metabolism chamber. Condensation was never noted

on the walls of a chamber. Air inlet and outlet valves were
positioned on opposite sides of the chamber to allow airflow
through the chamber.

After closure of the sliding door of the metabolism chamber, a
diaphragm pump (dynapump) was started and respiratory gases
were pulled through plastic tubing and then through a series of
preweighed U-tubes which were filled with Drierite and weighed
to the nearest 0.01 g, analytical balance. The weight change in the
Drierite equalled the water vapor expired by the owl plus the
atmospheric water vapor. A second set of Drierite U-tubes was
connected in parallel to measure atmospheric water vapor (same
pump). The rates of air flow from the metabolism chamber and
the second set of tubes were equal. Water vapor expired by the owl
(mg H20/g.h) was calculated as the difference in weight between
the experimental and control tubes.

Air temp inside the metabolism and environmental chambers
was monitored with thermistors (Model No. 1331, Control
Equipment Co., Salt Lake City, Utah) and copper-constantan
thermocouples and recorded on Rustrak chart recorders (Model
No. 2133, Control Equipment Co.) and Wescor thermometers
(Model No. TH50 TC, Wescor Co., Logan, Utah), respectively.
Thermistors and thermocouples were calibrated with a glass mer-
cury thermometer. Temp was recorded every 15 min.

Statistical analysis of data presented here included curvilinear
regression analysis and paired t-Test.

Results and Discussion

Evaporative water loss of barn owls was examined
over a temp regime (2-30°C) which simulated am-
bient temp experienced by incubating barn owls
(Hamilton 1982).

To test the physical effect of the metabolism
chamber in altering the temp experienced by an
owl, ambient (environmental chamber) temp and
temp of the metabolism chamber were monitored
during each experimental trial. Experimental temp
was separated into 3 temp ranges: 0-1 0°C, 1 1-20°C
and 21-30°C. In each temp range, the temp of the
metabolism chamber was significantly higher (P <
0.001, paired t-Test) than the temp of the environ-
mental chamber. The temp difference between the
metabolism chamber and the environmental
chamber was greatest (P < 0.001, 2.0°C) at temp
which ranged between 0-1 0°C, and also was sig-
nificantly higher for temp between 1 1-20°C (0.7°C)
and 21-30°C (0.6°C). Therefore, owls utilizing
nestbox metabolism chambers experience higher
temp than would be seen if using open sites.

122

Raptor Research 19(4): 122-124

Winter 1985

Common Barn-Owl Water Loss

123

Metabolism Chamber Temp(C)

Figure 1 : Water loss (mg FLO/g.h) of 6 captive bam owls.

Eighty-five measurements from 6 captive barn
owls showed that water loss (mg LhO/g-h) increased
significantly (P < 0.001) as ambient temp increased
(Fig. 1). Recent studies by Wunder (1979), Weath-
ers (1979, 1981), and Dawson (1982) have
examined climatic adaptation, physiological ther-
moregulation and water loss from birds and the
data exhibited by the barn owl does not deviate
from established patterns. Water loss of barn owls
at ambient temp from 0-20°C is not different than
data for non-incubating pigeons (Lophophops fer-
ruginea) (Dawson and Bennett 1973) or Burrowing
Owls (Athene cunicularia) (Coulombe 1970).

Coulombe (1970), Dawson and Bennett (1973)
and Weathers (1981) have shown that the pattern of
evaporative water loss of birds is an exponential
function. However, water loss is essentially linear
until approximately 35-40°C at which time birds
become heat-stressed (Dawson 1982) and the water
loss increased exponentially. This is also seen in
Figure 1 ; at temp that mimics incubation temp (up
to 30°C) water loss of barn owls is fairly linear and
not very substantial. However, barn owls in Utah do
not experience nestbox temp greater than 32°C
during incubation (Hamilton 1982); therefore, the

barn owl in Utah may be able to conduct incubation
without an apparent heat stress.

In summary, birds must contend with numerous
environmental stresses during incubation, one of
which is heat stress. Some birds utilize roost sites
with low heat loads (Barrows 1981), while other
incubating birds use postural thermoregulatory
behavior to reduce heat stress (Lustick et al. 1978,
1979; Bartholomew and Dawson 1979). The barn
owl may escape heat stress problems during incu-
bation by using nestboxes and by choosing a loca-
tion where high ambient temp does not occur.
Acknowledgments

This paper is part of a dissertation submitted to the Department
of Biology at Utah State University in partial fulfillment of the
requirements for the Ph.D. degree. I thank members of my
graduate committee: Drs. J.A. Gessaman, K.L. Dixon, R.T. San-
ders, R.P. Sharma and L.C. Ellis. I also thank Dr. A.B. Hamilton
for her help and support through the years. Thanks to Drs. H.E.
Dziuk, J.A. Mosher and one anonymous referee for reviewing an
earlier version of this manuscript. Thanks to Ms. P. Hornbeck and
Ms. J. Thorp for secretarial assistance. This study was funded in
part by an Edwards H. and Winnie H. Smith Fellowship from the
Welder Wildlife Foundation (Dr. J.G. Teer, Director), a Sigma Xi
Grant-in-Aid of Research award, and the Ecology Center, Utah
State University (Dr. F. Wagner, Director). This is Welder Wildlife
Foundation Contribution No. 282.

124

Kirk L. Hamilton

Vol. 19, No. 4

Literature Cited

Barrows, C.W. 1981. Roost selection by Spotted
Owls: an adaptation to heat stress. Condor 83:302-309.

Bartholomew, G.A. and W.R. Dawson. 1979. Ther-
moregulatory behavior during incubation in Heer-
mann’s Gulls. Physiol. Zool. 52:422-437.

Bartholomew, G.A., R.C. Lasiewski and E.C. Craw-
ford. 1968. Patterns of panting and gular flutter in
Cormorants, Pelicans, Owls, and Doves. Condor
70:31-34.

Coulombe, H.N. 1970. Physiological and physical as-
pectsof temperature regulation in the BurrowingOwl
Speotyto cunicularia. Comp. Biochem. Physiol. 35:307-337.
Dawson, W.R. 1982. Evaporative losses of water by
birds. Comp. Biochem. Physiol. 71A:495-509.

Dawson, W.R. and A.F. Bennett. 1973. Roles of
metabolic level and temperature regulation in the ad-
justment of Western Plumed Pigeons ( Lophophops fer-
ruginea) to desert conditions. Comp. Biochem. Physiol.
44A:249-266.

Hamilton, K.L. 1982. The energetic cost of incubation and
bioenergetics of the Bam Owl. Ph.D. Thesis. Utah State
University, Logan, 122 pp.

Lustick, S., B. Battersby and M. Kelty. 1978. Be-
havioral thermoregulation: orientation towards the
sun in Herring Gulls. Science 200:81-83.

. 1979. Effects of insulation on juvenile

Herring Gull energetics and behavior. Ecology
60:673-678.

Marti, C.D., P.W. Wagner and K.W. Denne.
1979. Nest boxes for the management of Barn Owls.
Wildl. Soc. Bull. 7:145-148.

Otteni, L.C., E.G. Bolen and C. Cottam. 1972. Pre-
dator-prey relationships and reproduction of the Barn
Owl in southern Texas. Wilson Bull. 84:434-448.
Weathers, W.W. 1972. Thermal panting in domestic
pigeons, Columba livia, and the Barn Owl, Tyto alba.
J. Comp. Physiol. 79:79-84.

. 1979. Climatic adaptation in avian

standard metabolic rate. Oecologica (Berl.) 42:81-89.
. . 1981. Physiological thermoregula-
tion in heat-stressed birds: consequences of body size.
Physiol. Zool. 54:345-361.

Wunder, B.A. 1979. Evaporative water loss from
birds: effects of artificial radiation. Comp. Biochem.
Physiol. 63 A: 493-494.

Dept, of Biology and the Ecology Center, UMC 53, Utah State
Univ., Logan, UT 84322. Current Address: Dept, of
Physiology and Biophysics, Univ. of Texas Medical Branch,
Galveston, TX 77550.

Received 18 December 1984; Accepted 20 March 1985

PEREGRINE FALCON SEMEN: A QUANTITATIVE AND QUALITATIVE

EXAMINATION

John Hoolihan and William Burnham

Abstract — Collection frequencies and certain characteristics of Peregrine Falcon ( Falco peregrinus) semen were
investigated using semen from a falcon trained to copulate on a specially designed hat. Semen volume increased
significantly when collections were increased from two to three times/day, but cells/ejaculate decreased. No significant
difference in number cells/ejaculate or cells/microliter was detected between morning and evening samples with two
collecdons/day. Three collections/day resulted in decreasing total cell numbers/collections and numbers/microliter with
the most cells collected during the initial morning collection. Semen showed a high motility, with estimated 80 - 100% of
sperm cells alive.

The Peregrine Falcon (Falco peregrinus) continues
to be a focal point of captive propagation efforts
(Cade and Dague 1981). An important technique
used in captive propagation is artificial insemina-
tion, since many captive falcon's do not copulate
(Boyd 1978). The technique of artificial insemina-
tion has been described by Boyd et al. (1977), but
little attention has been directed toward quantita-
tive or qualitative examination of falcon semen. We
report here the affect of increasing frequency of
semen collection upon semen volume and upon
certain characteristics of peregrine semen, includ-
ing concentration of sperm cells, total cells/ejacu-
late, motility and percent of viable sperm cells.

Materials and Methods

We wished to know if daily semen volume could be
increased significantly by collecting semen 3 times/d vs 2
times/d. Two periods were designated near the midpoint
of the semen production cycle (Table 1). Period I com-
prised 9 d when semen was collected 2 times/d, between
0800 H and 1 0 1 5 H, and between 1 7 1 5 H and 1 745 H. A
third collection was accomplished between 1300 H and
1345 H in Period II. Three days separated the two 9-day
collection periods.

All semen in this study was collected from a 10-year-old
peregrine. The falcon was behaviorally imprinted to
humans and copulated on a specially constructed hat
(Cade and Dague 1981). The falcon was handled and
raised as described by Boyd and Schwartz (1981). The
falcon was given the opportunity to copulate on the hat
only during the period when semen was needed for artifi-

Table 1. Means (ranges in parentheses) of semen volume and sperm counts of a 10-year-old Peregrine Falcon.

Time

Vol/Day

Cells//a1 x 103

Cells/Ejaculate x 106

Period I

150(116- 185)

52.86 (38.12 - 81.12)

4.46 (2.55 - 5.84)

(n=9)

(n=8)

(n=8)

0800- 1015 H

59.06 (45.62 - 81.12)

4.97 (3.51 - 5.84)

(n=4)

(n=4)

1715 - 1745 H

46.66 (38.12 - 55.88)

3.95 (2.55 - 4.97)

(n=4)

(n=4)

Period II

192 (175- 208)

37.12 (26.25- 60.62)

2.46 (1.27- 3.88)

(n = l 1)

(n = 15)

(n = 15)

0800 - 1015 H

47.54 (40.00 - 60.62)

3.32 (2.76- 3.88)

(n=3)

(n=3)

1300 - 1345 H

36.47 (30.38- 39.88)

2.61 (1.77- 3.23)

(n=7)

(n=7)

1715 - 1745 H

31.78 (26.25 - 37.38)

1.72 (1.27- 1.90)

(n=5)

(n=5)

125

Raptor Research 19 (4): 125-1 27

126

Hoolihan and Burnham

Vol. 19, No. 4

Volume [/iil/Ejaculate

Figure 1. Semen production of a 10-year-old Peregrine Falcon.

cial insemination. The semen was retrieved from the hat
by use of blood capillary tubes. The capillary tubes were
initially calibrated for volume by using a micropipette.
Each millimeter (mm) of tube length represented 1 micro-
liter (/Ltl) of semen. Volume was therefore easily calcu-
lated by measuring the length of semen in the tube with a
metric rule.

Concentration of spermatazoa per sample was calcu-
lated by the use of a phase contrast hemocytometer. Sepa-
rate means were calculated for the morning and evening
collections since the collections were not evenly spaced
over each 24 hr period.

Standard poultry science methods for determining the
percent of viable sperm were inadequate for peregrine
semen quantification. Use of a live-dead stain was not
helpful in determining fertilization capacity. The nigro-
sin, eosin blue stain (Ernst 1970) which is intended to
darken only dead cells, permeated both live and dead cells
of the falcon semen. This technique needs to be perfected
for falcons.

Motility score of the semen was judged qualitatively.
Samples were taken immediately to the laboratory once
collected and mixed thoroughly in small vials pre-warmed
to 37° C. Semen samples were then placed on pre-warmed
slides which were kept at 37° C in a microscope stage
incubator and viewed through a phase contrast micro-
scope. Motility was judged qualitatively by the progressive
motion and speed of the sperm cells, as well as the esti-
mated percent of moving cells.

Results and Discussion

The 10-year-old male peregrine commenced copu-
lation on 5 March and continued on a daily basis
through 1 June when the opportunity to copulate was
no longer made available to him, thus representing a
semen production period of 95 d. Semen produced
per copulation ranged from 0 (copulation, but no
ejaculation) to 93 ml. Figure 1 compares the volume
produced/ejaculate with frequency of ejaculation for
periods of both 2 and 3 collections/d. Semen volume
rose significantly (28%, P < 0.001, Mann-Whitney
U-test) when collections were increased from 2 to 3
times/d, but cells/ejaculate decreased significantly (P <
0.01) when collection frequency was increased (Table
1).

During Period I, no significant difference (P = 0.20)
in number of cells/pd or cells/ ejaculate be-
tween morning or evening samples was observed
(Table 1). In contrast, in Period II a significant differ-
ence (P < 0.025) existed in number of cells //d and
cells/ejaculate between the 3 collection times. The mean
number of cells/ /id for the morning collection of Period
II of 47.54 x 103 shows a decrease of 19% compared

Winter 1985

Peregrine Falcon Semen

127

with the same time in Period I (Table 1). The midday
and evening collections for Period II had mean values
of 36.47 x 103 and 31.78 x 103 cells//d, respectively, the
latter showing a decrease for the evening collection
times. Total sperm cells/ejaculate (in the morning col-
lections of Period I) averaged 4.97 x 106 (Table 1), and
evening collections averaged 3.95 x 106 cells/ejaculate.
Together, these figures represent a daily total average
of 4.46 x 106 spermatazoa/ejaculate for Period I. In
contrast, the mean for the morning, midday and even-
ing collections of Period II were 3.32 x 106, 2.61 x 106
and 1.72 x 106, respectively (Table 1). We initially pre-
sumed that Period II would show a decrease in
spermatazoa/ejaculate and an overall daily total greater
than Period I. However, fewer total cells were pro-
duced in Period II.

The semen collected showed a high motility value for
more than 92% of the samples (n = 41) analyzed with
an estimated 80 - 100% of the sperm cells alive and
moving in a progressive motion. The speed with which
the sperm cells move is difficult to evaluate with respect
to their apparent fitness. It should be possible to correct
this problem through the examination of samples from
other captive and wild falcons. In this way, comparisons
could be made and the normal speed could be ascer-
tained. Semen from the peregrine tested fertilized eggs
at a level equal to other donors of varying ages.

Acknowledgments

This research was conducted at The Peregrine Fund’s Western Facility

located near Fort Collins, Colorado. Financial support was provided by
The Peregrine Fund, Inc. (T.J. Cade, President). Technical advice was
supplied by R. Amen, Colorado State University Animal Reproduction
Laboratory. D. Konkel, W. Heinrich and C. Sandfort trained the semen
donor and performed most collections. J. Enderson and T. Cade re-
viewed the manuscript and provided statistical assistance.

Literature Cited

Boyd, L.L., N.S. Boyd and F.C. Dobler. 1977. Repro-
duction of prairie falcons by artificial insemination.
J. Wildl. Mgt. 41(2):266-271.

Boyd, L.L. 1978. Artificial insemination of falcons.

Symp. Zool. Soc. London, No. 43, 73-80.

Boyd, L.L. and C.H. Schwartz. 1981. Training im-
printed semen donors. N. Am. Falconers’ Assoc. J.
20:65-69.

Cade, T.J. and P.R. Dague. Eds. 1978. The Peregrine
Fund Newsletter, No. 6, 12 pp.

, Eds. 1981. The Peregrine Fund Newsletter,

No. 9, 16 pp.

Ernst, R.A. and F.X. Ogasawara. 1970. A live-dead
stain to test poultry semen quality. Univ. of Calif. Ex-
tension Service Bulletin OSA, No. 193.

The University of Texas System Cancer Center, Science Park,
Research Division, P.O. Box 389, Smithville, TX 78957.
Address of Second author: The Peregrine Fund, World
Center for Birds of Prey, 5666 West Flying Hawk Lane,
Boise, ID 83709.

First Received 1 April 1982; Accepted 22 April 1985

128

Douglas A. Boyce, Jr.

Vol. 19, No. 4

Adult male Prairie Falcon and young at a typical Mojave Desert nest-site. Artwork by N. John Schmitt.

PRAIRIE FALCON PREY IN THE MOJAVE DESERT, CALIFORNIA

Douglas A. Boyce, Jr.

Abstract — Twenty-five species of birds, 9 species of mammals, 5 species of reptiles and 1 species of insect were
represented in prey remains and castings from 19 Prairie Falcon ( Falco mexicanus) nests in the Mojave Desert, California,
during 1977 and 1978. Reptiles represented a greater proportion in the diet than is reported in most other Prairie Falcon
food studies in the western United States. The Horned Lark ( Eremophila alpestris). Mourning Dove ( Zenaidura macroura ),
Valley Pocket Gopher ( Ttiomomys bottae) and Desert Woodrat (Neotoma lepida) were found in over 50% of the nests.

Eighty-four percent of the prey weighed less than 1 50 g. The
male Prairie Falcons.

The Prairie Falcon (Falco mexicanus) is considered
a generalist in prey selection (Bent 1938: Part 2).
Mammals and birds are the most common prey
taken, with specific prey frequencies varying re-
gionally (Tyler 1923; Fowler 1931; Enderson 1964;
Brown and Amadon 1968; Leedy 1972; Ogden
1973; Denton 1975; Haak 1982). Reptiles and in-
sects are rarely recorded as prey (Table 1 ), although
Snyder and Wiley (1976) reported an unusual re-
liance on insects for food. Types of prey selection by
Prairie Falcons nesting in the Mojave Desert con-
trast sharply with prey previously recorded for this
area. Pierce (1935) and Fowler (1935) reported a
nest in the Mojave Desert where young Prairie Fal-
cons were raised entirely on a diet of reptiles —
mainly Chuckwalla (Sauromalus obesus ) and occa-

mean prey weight was 1 07 g and equals 20% of the weight of

sionally Collared Lizard ( Crotaphytus collaris ), while
Bond (1936) reported exclusively mammalian prey
in 41 castings at another Mojave Desert nest. Be-
cause little is known about food habits of Prairie
Falcons in the Mojave Desert, I studied this aspect
of their biology.

Methods

Prey remains and castings were collected from 19 falcon nests
throughout the Mojave Desert (34° N 1 1 6° W) between March and
June 1977 and 1978 in order to provide a qualitative summary of
Prairie Falcon food habits. Prey remains and castings were also
collected from immediately below the nest site when known to
have come from no other raptor. Prey remains were identified in
the field or compared with specimens at Humboldt State Univer-
sity, Areata, California. Fresh weights for prey items were ob-
tained from the Museum of Vertebrate Zoology, University of
California, Berkeley, California. I used an adjusted weight

Table 1. Frequency (%) of birds, mammals, reptiles and insect prey remains in Prairie Falcon nests in the western
United States.

Source

Location

Mammals

Birds

Reptiles

Insects

Fowler (1931)

California

30c

70

0

0

McKinley unpubl.a

Colorado

55

45

0

0

Marti and Braun (1975)

Colorado

39

61

0

0

Ogden (1973)

Idaho

53

33

14

trace

S.R.B.P.b (1979)

Idaho

22

72

6

0

Platt (1974)

New Mexico

37

54

9

0

Voelker unpubl.a

Oklahoma

8

92

0

0

Porter and White (1973)

Utah

8

92

0

0

Smith and Murphy (1973)

Utah

31

50

0

19

This Study

Mojave Desert

52

38

10

trace

Mata from Sherrod (1978:96, 97)

^Snake River Birds of Prey annual report 1979
crounded to nearest 1 %

129

Raptor Research 19 (4): 128-1 34

130

Douglas A. Boyce, Jr.

Vol. 19, No. 4

of 500 g for rabbit species in Table 2 because, from the available
information, it is unlikely Prairie Falcons are capable of carrying
anything heavier (see discussion below).

Quantifying prey remains and castings collected from hawk
nests duringthe nestingseason is biased and unreliable (Errington
1932; Craighead and Craighead 1956). Some castings and prey
remains may be deposited by falcons before nesting begins and
persist until collection during the nesting season. Furthermore,
Fowler (1931) reported that adult Prairie Falcons remove uneaten
prey and castings from nests. Haak (1982) reported that a larger
variety of prey was found at nests than was hunted, suggesting
over-representation of uncommonly used prey at nests; however,

observations of encounters with some prey species may be difficult
to make. Prey remains may also underestimate the numbers of
small rodents and birds actually captured (Cade 1 960). Because of
numerous potential biases, food habits reported here are qualita-
tive not quantitative.

Delineation of the Mojave Desert boundaries closely parallels
the outer distributional limits of the Joshua Tree ( Yucca brevifolia)
(Jaeger 1957). Cresote (Larrea divaricata) and Burro Bush ( Fanseria
dumosa ) are also characteristic desert flora. Alkali sinks, creosote
bush scrub, shadscale scrub, Joshua Tree woodland, and Pinyon-
Juniper woodland form the major Mojave Desert floral com-
munities (Munz and Keck 1959).

Table 2. Prey items identified at Prairie Falcon nests in the Mojave Desert.

Species

No.a

Nests

%b

Nests

Estimated
Weight (g)

MAMMALS

California Ground Squirrel

(Spermophilus beecheyi )
Mojave Ground Squirrel

2

10.5

565

{Spermophilus mohavensis )

Whitetail Antelope Squirrel

5

26.0

177

{Ammospermophilus leucurus)
Valley Pocket Gopher

4

21.0

113

{Thomomys bottae)
Pocket Mouse

12

63.0

88

{Perognathus sp.)
Kangaroo Rat

5

26.0

19

{Dipodomy sp.)
Deseret Wood rat

5

26.0

41

{Neotoma lepida)
Black-tailed Jack Rabbit

11

58.0

105

{Lepus calif ornicus)
Desert Cottontail

2

10.5

500

(Sylvilagus audubonii )

BIRDS

Chukar

2

10.5

500

{Alectoris chukar )
Western Sandpiper*

3

15.8

500

{Calidris mauri )
Rock Dove

1

5.3

27

{Columba livia)
Mourning Dove

2

10.5

393

(Zenaida macroura)
White-throateed Swift

8

42.1

109

{Aeronaut.es saxatalis)
Western Kingbird

1

5.3

36

{Tyrannus verticalis)
(Table 2 continued)

2

10.5

41

Winter 1985

Prairie Falcon Prey in California

131

(Continuation of Table 2)

BIRDS (cont’d)

Say’s Pheobe*

(. Sayornis say a)

Horned Lark

1

5.3

25

( Eremophila alpestris)
Cactus Wren*

12

63.2

28

{Campy lorhynchus brunneicapillus )
Rock Wren

1

5.3

37

(Salpinctes obsoletus)
Sage Thraasher*

3

15.8

11

{Oreoscoptes montanus)
LeCont’s Thrasher*

1

5.3

44

(Toxostoma lacontei)
Mountain Bluebird

1

5.3

62

(Sialia currucoides)
Loggerhead Shrike

1

5.3

2.7

{Lanius ludovicianus )
European Starling

1

5.3

45

{Sturnus vulgaris)
Black-headed Grosbeak*

2

10.5

77

{Pheucticus melanocephalus)
White -crowned Sparrow

3

15.8

46

( Zonotrichia leucophrys)
Western Meadowlark

1

5.3

2

(Sturnella neglecta)
Red-winged Blackbird

5

26.3

103

(Agelaius phoeniceus)
Brewer’s Blackbird

2

10.5

56

{Euphagus cyanocephalus)
Scott’s Oriole*

3

15.8

58

{Icterus parisorum)
Northern Oriole*

2

10.5

38

{Icterus galbula)
Western Tanager

1

5.3

27

{Piranga ludoviciana )
House Sparrow

4

21.1

31

{Passer domesticus )
House Finch

4

21.1

27

{Carpodacus mexicanus )

REPTILES

Desert Iguana*

1

5.3

20

{Dipsosaurus dorsalis)
Chuckwalla

1

5.3

56

{Sauromalus obesus)

4

21.0

235

Zebra-tailed Lizard*
{Callisaurus draconides)
Desert Horned Lizard

1

5.3

2

{Phrynosoma platyrhinos)
Western Whiptail

4

21.0

22

{Cnemidophorus tigris)

2

10.5

1

aThe number of nests in which a species was recorded.

^The number of nests in which a species was found divided by the number of nests examined (N = 19); times 100 and reported as a
percentage.

*Species not previously recorded in the literature as Prairie Falcon prey.

132

Douglas A. Boyce, Jr.

Vol. 19, No. 4

Results and Discussion

Thirty-nine species representing 3 vertebrate
classes were present in prey collections from 19
nests (Table 2). Twenty-five species of birds, 9
species of mammals and 5 species of reptiles were
identified. Insect parts were rarely noted and only
1 species, Armored Stink Beetle (Eleodes armata) was
identified. The Horned Lark, Valley Pocket
Gopher and Desert Woodrat were present in over
50% of the nests. The Mourning Dove was present
in 48% of the nests.

Although the number of avian species captured
outnumbered mammals by almost 3 to 1, the mean
weight for birds (76 g) was half of the mean weight
for mammals (179 g) suggesting greatest energetic
return results from capturing mammals. Analysis
of 214 pellets provides further evidence that
mammals might be captured more often than birds
or reptiles. Mammals were present in 72%, birds in
24% and reptiles in 4% of the pellets examined.

In contrast to Pierce (1935) and Bond (1936) I
found no instance where all or nearly all prey items
were from just one vertebrate class. No single
species appears as primary prey on a desert-wide
basis (Table 2). Some species were infrequent in
prey remains desert-wide but were locally frequent.
For example, the Black-headed Grosbeak (Pheuc-
ticus melanocephalus ) was collected from 3 nests lo-
cated along the east side of the Sierra Nevada
Mountains but nowhere else in the desert. One nest
had 8 grosbeaks present.

Mammals. The Valley Pocket Gopher and De-
sert Woodrat were found in over 50% of the nests.
They were seldom seen except very early in the
morning or late in the evening when temperatures
were cooler. Their high abundance in the prey re-
mains suggests that they were captured at these
times. Harmata et al. (1978) found that Prairie Fal-
cons forage primarily during early morning and
late afternoon in the Mojave Desert.

Blacktailed Jackrabbit ( Lepus calif ornicus ) and De-
sert Cottontail ( Sylvilagus audubonii ) feet were
found in falcon nests. Adult Blacktailed Jackrabbit
(2,590 g) and Desert Cottontail (1,700 g) weigh 3 to
5 times as much as adult male Prairie Falcons (554 g,
Enderson 1964), making it unlikely that they car-
ried them to their nests. It is probable that only very
young rabbits or portions of them were carried to
nests. Porter and White (1973) noted that Prairie
Falcons prey on White-faced Ibis (Plegadis chihi, 519
g) in Utah. However, since White-faced Ibis were

not found at Utah nests, they concluded that
White-faced Ibis were too heavy for Prairie Falcons
to carry. Adult Chukar (Alectoris chukar) and
California Ground Squirrel ( Spermophilus beecheyi )
weigh between 500-565 g and were the next largest
prey items found in eyrie samples and may have
been brought to the nest by the female (863 g,
Enderson 1964).

Birds. The Horned Lark and Mourning Dove
were found in 63 and 42% of the nests, respec-
tively. The presence of a Western Sandpiper
(Calidris mauri ) (Table 2) demonstrates the oppor-
tunistic hunting nature of Prairie Falcons. The
Mojave River flows through the desert but is sub-
terranean for much of its length. Sandpiper re-
mains were found at a falcon nest 3.2 km from one
of the few points where the river surfaces. The
sandpiper was the only prey item not observed in
the field.

Reptiles. Most Prairie Falcon food studies show
that reptiles are infrequently reported as prey
(Table 1); however, reptiles did constitute a rela-
tively high proportion of the prey in this study
(9.5%). Desert Horned Lizard ( Phrynosoma
platyrhinos ) and Chuckwaila were found at 20% of
the nests. Reptile remains, however, were recorded
in only 4% of the pellets. Reptile scales were found
mixed with mammal hair in castings but no castings
contained both scales and feathers. It seems likely
most reptile scales are so thin that they are digested
and not cast. Usually, the only indication that rep-
tiles were being used was the presence of heads
and tails found around the margin of the nest.
Although only lizards were represented in prey
remains I did observe a male falcon leave its perch
on a power pole and capture a snake.

The 20% Rule. Male falcons usually hunt for
family groups during the nesting season (Newton
1979). Harmata et al. (1978) found that male Prairie
Falcons hunted more frequently than females in
the Mojave Desert. In this study 84% of prey cap-
tured weighed less than 150 g and the mean weight
was 107 g, or 20% of the weight of male Prairie
Falcons. A mean prey weight 20% of mean adult
male falcon weight is also common in other species
of falcons. I noted a high correlation (r = 0.98)
between mean prey weight during the breeding
season and male falcon body weight for 5 species of
falcons (Table 3). Because male falcons are re-
stricted to a definite nesting territory during the
breeding season, and are less restricted in move-
ment during the remainder of the year, it seems

Winter 1985

Prairie Falcon Prey in California

133

Table 3.

Mean weight (g) of male falcons selected to show a weight range and the mean weight of their prey captured
during the nesting season.

Species

Male Weight

Prey Weight
(*)

Source

Falco columbarius

187

26

Laing 1984

Falco eleonorae

350

62

Walter 1979

Falco mexicanus

554

143

This Study

Falco peregrinus pealei

750

199

White 1973

Falco rusticolus

1,170

475

Roseneau 1972

probable that characteristics of prey vulnerability
and density (during the breeding season) have
evolutionarily dictated male falcon size. To test this
hypothesis one needs to compare weight of prey
captured by females when they begin to hunt after
brooding is completed with that caught by males.
An alternative hypothesis is that selection pressure
is highest during winter months and not during the
breeding season. If this were true male and female
falcons should show significant differences in the
weight of prey captured during winter.

Acknowledgments

This manuscript benefited from comments by J. Enderson, S.
England, B. Haak, A. Harmata, J. Hodges, K. Kertell, D. Mindell,
S. Platt, J. Sedinger and C. White. Anne Jacoberger, assistant
curator for the Museum of Vertebrate Zoology, Berkeley,
California and T. Lawler, Humboldt State University, Areata,
California provided specimens. Bill Lehman and B. Hipp assisted
in the field and J. Schmitt helped in identification of prey remains.
The study was supported partially by the U.S. Bureau of Land
Management and U.S. Fish and Wildlife Service.

Literature Cited

Bent, A.C. 1938. Life histories of North American birds
of prey. Part 2. U.S. Natl. Mus. Bull. 167. Dover Publi-
cations, New York.

Bond, R.M. 1936. Some observations on the food of the
Prairie Falcon. Condor 38:169-170.

Brown, L.H. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill, New York, NY.
Cade, T.J. 1 960. Ecology of the peregrine and gyrfalcon
in Alaska. Univ. of Calif. Publ. Zool. 63:151-290.
Craighead, J.J. and F.C. Craighead, Jr. 1956. Hawks,
owls and wildlife. The Stackpole Co., Harrisburg, PA.,
and Wildl. Manag. Inst., Washington, D.C.

Denton, S.J. 1975. Statusof the prairie falcons breeding
in Oregon. M.S. thesis, Oregon State Univ., Oregon.
56 pp.

Enderson, J.H. 1964. A study of the prairie falcon in the

central Rocky Mountain region. Auk 81:332-352.
Errington, P.L. 1932. Technique of raptor food habits
study. Condor 34:75-86.

Fowler, F.H. 1931. Studies of food and growth of the
Prairie Falcon. Condor 33:193-201.

. 1935. Week-ends with the Prairie Fal-
con. Nat. Geog. Mag. 67:610-626.

Haak, B. A. 1 982. Foraging ecology of Prairie Falcons in
northern California. Unpubl. M.S. Thesis, Oregon
State University, 64 pp.

Harmata, A.R., J.E. Durr and H. Geduldig.
1978. Home range, activity patterns and habitat use of
Prairie Falcons nesting in the Mojave Desert. Unpubl.
report U.S. Bureau of Land Management contract No.
YA-512-CT8-43. 89 pp.

Laing, K. 1985. Food habits and breeding biology of
merlins in Denali National Park, Alaska. Raptor Res.
19(2/3):42-51.

Leedy, R.R. 1972. The status of the Prairie Falcon in
western Montana: Special emphasis on possible ef-
fects of chlorinated hydrocarbon insecticides. M.S.
Thesis, Univ. of Montana. 96 pp.

Marti, C.P., and C.E. Braun. 1975. Use of tundra
habitats by Prairie Falcons in Colorado. Condor: 213-
214.

Newton, I. 1979. Population ecology of raptors. Buteo
Books, Vermillion, South Dakota.

Ogden, V.T. 1973. Nesting density and reproductive
success of the Prairie Falcon in southwestern Idaho.
M.S. thesis, Univ. Idaho. 43 pp.

Pierce, W.M. 1935. Experiences with Prairie Falcons.
Condor 37:225.

Platt, S.W. 1974. Breeding status and distribution of the
Prairie Falcon in northern New Mexico. Unpubl. Manus.

68 pp.

Porter, R.D. and C.M. White. 1973. The Peregrine
Falcon in Utah, emphasizing ecology and competition
with the Prairie Falcon. Brigham Young Univ. Sci.
Bull., Bio. Ser. 18:1-74.

Roseneau, D.G. 1972. Summer distribution, numbers

134

Douglas A. Boyce, Jr.

Vol. 19, No. 4

and food habits of the Gyrfalcon (Falco rusticolus ) on
the Seward Peninsula, Alaska. Unpubl. M.S. thesis,
Univ. Alaska. 124 pp.

Sherrod, S.K. 1978. Diets of North American Fal-
coniformes. Raptor Research 1 2:49- 121.

Smith, D.G. and J.R. Murphy. 1973. Breeding ecology
of raptors in the eastern Great Basin of Utah. Brigham
Young Univ. Sci. Bull., Bio Ser. 28:1-76.

Snyder, N.F.R. and J.W. Wiley. 1976. Sexual size di-
morphism in hawks and owls of North America.
A.O.U. Ornithological Monographs 20:1-96.

Tyler, J.G. 1923. Observations on the habits of the
Prairie Falcon. Condor 25:90-97.

U.S. Dept, of Interior. 1979. Snake River Birds of Prey
Research Project Annual Report. U.S. Bureau of Land
Management, Boise District, Boise, Idaho.

Voelker, W.G. 1978. Food habits data for Ferruginous
Hawk, Red-tailed Hawk, Swainson’s Hawk, Broad-
winged Hawk, Golden Eagle and Prairie Falcons. Un-
publ. manuscript. In: Sherrod, S.K. 1978. Diets of
North American Falconiformes. Raptor Research
12:49-121.

Walter, H. 1979. Eleonora’s Falcon. Univ. of Chicago
Press, Chicago, 111.

White, C.M., W.B. Emison and F.S.L. William-
son. 1973. DDE in a resident Aleutian Island pere-
grine population. Condor 75:306-311.

Zoology Dept., Brigham Young University, Provo, Utah 84602.

Received 15 March 1985; Accepted 1 June 1985

PERCHING AND ROOSTING PATTERNS OF RAPTORS ON POWER
TRANSMISSION TOWERS IN SOUTHEAST IDAHO
AND SOUTHWEST WYOMING

John C. Smith

Abstract — As part of an ongoing raptor management program, 45 km of 345 kilovolt (kv) transmission
lines were surveyed from 5 June to 31 September 1983 to determine diurnal and nocturnal raptor use
patterns. The Golden Eagle (Aquila chrysaetos) and Red-tailed Hawk (Buteo jamaicensis) perched mostly on
upper, outer sections of transmission towers during the day and roosted on lower, inner sections at night.
Daytime surveys alone may not accurately represent raptor use of these structures.

In many treeless areas where availability of nest,
perch and roost sites may limit raptor populations,
electrical powerline structures are readily utilized
by many raptor species (Stahlecker 1979; Olen-
dorff et al. 1981). In recent years utility companies
have become more aware that the raptor/ powerline
association is sometimes detrimental to both man
and bird, and have initiated studies to examine
raptor use of powerlines. The most commonly used
technique is daytime aerial surveying (e.g., Wilder
1981; Hansen 1982). Relatively little information
has been gathered concerning raptor roosting be-
havior on powerlines and how it may compare to
perching behavior (Craig and Craig 1984). This

paper presents results of a study funded by Idaho
Power Company in spring and summer of 1983
(Smith 1983), which was designed to collect infor-
mation on nocturnal and diurnal behavior of rap-
tors on electrical transmission towers in southeast
Idaho and southwest Wyoming.

Study Area and Methods

The study area is located 30 km north of the convergence of the
Idaho/Wyomin^Utah borders (Fig. 1 ). Three 345 kv transmission
lines transmit electrical power through the study area from a
coal-fired generating plant near Rock Springs, Wyoming to 3
separate substations bordering the Snake River plain in southern
Idaho.

The 45 km study section is situated on the Idaho/Wyoming border
and traverses mostly rolling, arid, treeless terrain 1800-2100 m in

Figure 1. Transmission line route and study area.

135

Raptor Research 1 9(4): 1 35- 138

136

John C. Smith

Vol. 19, No. 4

h 10m H

Figure 2. Configuration of 345kv transmission tower.

elevation. Three lines in the study area contain a total of 348 guyed
aluminum towers, 25-32 m in height (Fig. 2). Dominant plant species
for most of the area is big sagebrush ( Artemesia tridentata).

Raptors most commonly sighted on towers were the Red-tailed
Hawk {Buteo jamaicensis) and Golden Eagle {Aqvila chrysaetos). During
the post-fledging period (10 July to 31 September), an observed
maximum of 28 fledgling and adult Red-tailed Hawks and 8 fledgling
and adult Golden Eagles used the towers in this area for roost and/or
perch sites. Seven Red-tailed Hawk nests and 2 Golden Eagle nests
were the only occupied raptor nests present on transmission towers
within the study area in 1983.

The study area was surveyed from a vehicle on 45 nights be-
tween 5 June and 31 September 1983. Surveys began at dusk and
usually terminated 1 -2 h before dawn. Each tower was examined using
a hand-held spotlight and binoculars. The reflective property of the
raptors’ retinae aided in locating birds at night. A light amplification
device, or nightscope, was found to be unsuitable for this task due to
inadequate magnification when used alone and poor resolution when
used in conjunction with binoculars or spotting scope. Observations of
birds at specific roost sites were made on 24 nights between 24 June
and 9 September, to determine if movement to and from roost sites
took place during the night. In all cases, Golden Eagles (n = 19 nights
at 14 locations) and Red-tailed Hawks (N=5 nights at 5 locations) did
not move from their roost towers at any time during the night.

Lines were also surveyed from the ground on 15 d between 21
July and 31 September. Day surveys began at 0700 H and were
completed by 1400 H.

Perching/roosting observations were classified according to
time of day, species, and position on tower. “Inside” refers to any
position on the tower that is surrounded on at least 4 sides by tower
members (referring to the 6 sides of a cube). Upper/lower position

designation used in data analysis (Fig. 2) was chosen because very
little perching/roosting occurred in the slanted portions of the
towers (Red-tailed Hawks — less than 10% of all observations, Golden
Eagles — zero observations). Birds were observed perched mainly in 2
regions of the transmission towers, the uppermost horizontal
crossbridge area and the lower horizontal crossarm area (Fig. 2).

Results and Discussion

Most significant observed differences between
diurnal and nocturnal use patterns were as follows:

1. Eagles and hawks showed a significant shift
from using outer tower sections during the day
to using inner tower sections at night.

2. Both species exhibited a shift from using upper
sections of the towers during the day to using
lower sections at night.

Data for Red-tailed Hawks consisted of 99 perch
and 236 roost observations. Data for Golden Eagles
consisted of 46 perch and 124 roost observations.
Frequencies of observations in each category were
used to generate 2x2 chi-square contingency tables
to test the null hypothesis that time of day was
independent of observed perch/roost location on
the towers. Chi-square values (Fig. 3) indicate that

Winter 1985

Raptors and Power Transmission Towers

137

X2= 100.6 (p<.001)

X2 - 1 24.2 (p< .001)

n= 1 70 n= 170

X2- 27.4 (p< .001) X2 = 13.9 (p< .001)

Figure 3. Relative frequencies of perch and roost observations on transmission towers in southeast Idaho and
southwest Wyoming for the period 5 June to 31 September 1983. Chi-square (x2) values were generated
from observed frequencies in each category. Day = 0700-1959 H. Night = 2000-0659 H.

diurnal use patterns differed significantly from
nocturnal use patterns for both species. Results in-
dicate that daytime surveys alone may not accu-
rately represent overall use of towers as perch/roost
structures, and should be supplemented by noctur-
nal observations.

Red-tailed Hawks exhibited larger day-outside/
night-inside differences than did Golden Eagles
(X2 = 78.8, P < 0.001), possibly due to differences in
body size and mobility. The hawks could land and take
off directly from inner tower members, whereas
eagles were required by girder spacing to walk and
hop into and out of some inner locations.

Both Red-tailed Hawks and Golden Eagles ap-

peared to react behaviorally to transmission towers
much as they do to natural substrates such as trees
or cliffs. Upper, outer portions of the towers, used
for diurnal hunting and resting perches, provided
the advantages of an elevated viewpoint and un-
obstructed takeoff and landing flight paths. Lower,
inner portions of the towers afforded what little
cover there was in the area and were used for roost
sites.

Acknowledgments

Special thanks go to Kelly Fulcher for assistance in data collec-
tion, Leon Powers and Morlan Nelson for discussions on raptor
behavior, and Allan Ansell for initiating and supporting the study,
which was funded by Idaho Power Company, Boise, Idaho.

138

John C. Smith

Vol. 19, No. 4

Literature Cited

Craig, T.H. and E.H. Craig. 1984. A large concentration
of roosting Golden Eagles in southeastern Idaho. Auk.
101:610-613.

Hansen, H. 1982. Tripouts, birds and helicopters. Florida
Power and Light Company, P.O. Box 528100, Miami,
FL. 33152.

Olendorf, R.R., A.D. Miller and R.N. Lewhan.
1981. Suggested practices for raptor protection on
power lines. Report No. 4 Raptor Research Founda-
tion, Dept, of Vet. Biol., Univ. of Minnesota, St. Paul,
MN.

Smith, J.C. 1983. Jim Bridger 345 kv transmission system
bird use-fault study. 31 pp. Idaho Power Company, P.O.
Box 70, Boise, ID 83707.

Stahlecker, D.W. 1979. Raptor use of nest boxes and plat-
forms on transmission towers. Wildl. Soc. Bull. 7(l):59-62.
Wilder, S.E. 1981. Jim Bridger 345 kv line raptor use
study. 21 pp. Pacific Power and Light Company, 920 S.W.
6th Ave., Portland, OR. 97204.

Idaho Power Co., Environmental Affairs Dept, P.O. Box 70, Boise,
ID. 83707.

Received 20 November 1984; Accepted 20 April 1985

Winter 1985

Short Communications

139

Relationship Between Prairie Falcon Nesting Phenology,
Latitude and Elevation

Richard N. Williams

The relationship between timing of reproduction,
latitude and elevation is a well known biological
phenomenon: birds in northern areas breed later than
birds in southern ones (Alee et al. 1949; Johnston 1954;
Morton 1978). The Peregrine Falcon (Falco peregrinus tun-
drius) showed delayed nesting in North America with in-
creasing latitude (White 1964). The Prairie Falcon (Falco
mexicanus) in New Mexico (Platt 1974) and Oregon (Den-
ton 1975) showed delayed nesting with increasing eleva-
tion. However, the cumulative effect of latitude and ele-
vation on reproductive phenology has not been examined

for any of the large falcons. It would be of general interest
to know to what extent the variation in timing of repro-
ductive phenology can be influenced by latitude and ele-
vation. Additionally, an analysis of this phenomenon may
elucidate general trends and/or physical limitations that
determine the breeding range of large falcons.

The Praire Falcon presents an ideal study case for an
examination of this phenomenon. It breeds over a wide
range of latitudes, from 25.5° N (Lanning and Lawson
1977) to 54° N (Fyfe pers. comm.), and elevations, from
near sea level (D. Boyce pers. comm.) to 3688 m (Marti

Table 1 . Mean values for latitude and clutch completion date, sample size, and source study for 20 local populations of
the Prairie Falcon.

°N

Latitude

Clutch

Completion

Breeding

Pairs

Source

25.5

23 March

5

Lanning and Lawson 1977

32

10 March

1

Mader pers. comm.

32.5

29 March

1

Porter pers. comm.

34.2

9

1

Porter pers. comm.

35

26 March

24

Boyce pers. comm.

37

14 April

15

Platt 1974

40

13 April

10

Porter and White 1973

40.5

25 April

36

Enderson 1964

40.5

17 April

17

Olendorff 1973

41

1 7 April

9

Craig pers. comm.

41

3 May

23

Williams 1980

42.5

13 April

68

Ogden and Hornocker 1977

43

12 April

5

Johnstone 1980

44.5

16 April

49

Denton 1975

45.5

27 April

66

Becker and Ball 1981

47

6 April

6

Monk 1981

48

28 April

38

Leedy 1972

51

3 May

7

Edwards 1968

52.5

26 April

17

Fyfe pers. comm.

54

10 May

1

Fyfe pers. comm.

GROUP (X ± S.D.)

43.1° ± 4.5°

18 April ± lOd

n = 401

140

Short Communications

Vol. 19, No. 4

Table 2. Mean values for elevation and clutch completion date, sample size, and source study for 20 local populations
of the Prairie Falcon.

Elevation

(m)

Clutch

Completion

Breeding

Pairs

Source

700

6 April

8

Monk 1981

700

13 April

68

Ogden and Hornocker 1977

700

26 April

17

Fyfe pers. comm.

700

10 May

1

Fyfe pers. comm.

1030

26 March

24

Boyce pers. comm.

1100

27 April

66

Becker 1981

1180

29 March

1

Porter pers. comm.

1200

10 March

1

Mader pers. comm

1200

16 April

49

Denton 1975

1200

3 May

7

Edwards 1968

1500

12 April

5

Johnstone 1980

1500

13 April

10

Porter and White 1973

1500

28 April

38

Leedy 1972

1700

17 April

17

Olendorff 1973

1700

1 4 April

15

Platt 1974

1800

25 April

36

Enderson 1964

2000

17 April

9

Craig pers. comm.

. 2510

9 April

1

Porter pers. comm.

2720

3 May

23

Williams 1980

2800

23 March

5

Lanning and Lawson 1977

GROUP (X ± S.D.)

1320 ± 540 m

1 8 April ± 10 d

N = 401

and Braun 1977). However, observations of Prairie Fal-
cons nesting at elevations greater than 3000 m are few and
do not permit analysis of the effects of high elevation on
nesting phenology. Nevertheless, the Prairie Falcon has
been well-studied and data are available from local nesting
populations for latitudes 25.5° - 54° N (Table 1 ) and eleva-
tions 700 - 2800 m (Table 2). Data from the source studies
(Tables 1 and 2) were reported in highly varied forms,
therefore it was not possible to calculate standard devia-
tions or standard errors for many of the mean values
listed. The sequential events in the reproductive phenol-
ogy of large falcons (e.g., territory establishment, copulation,
hatching and fledging) are difficult for the researcher to
observe and to record accurately with regards to time. It is
relatively easy, however, to age young nest-
lings in the eyrie (see Fowler 1931; Moritsch 1983) and
establish hatch dates. Traditionally, clutch completion
dates have been calculated by backdating 30 days from
hatching dates (Olendorff 1973). I employed this method
for studies listed in Tables 1 and 2, unless specific data or
different methods were provided by individual authors.
In this study, therefore, mean clutch completion dates

(Tables 1 and 2) were used as the data base for statistical
analysis and were assumed to be representative of the
timing of the Prairie Falcon’s reproductive phenology in
each locality reported.

On this basis, I tested the prediction that Prairie Fal-
cons nest at higher elevations in southern latitudes and at
lower elevations in northern latitudes by dividing the re-
ported breeding range (25.5° - 54° N latitude, Table 1)
into quartiles. Weighted mean elevations for the quartiles
were compared using ANOVA (SAS 1982) with the
southernmost quartile (X ± s.d. = 2340 ± 786 m) differ-
ing significantly (F = 10.5, P < 0.0001) from the 3 more
northern quartiles. Although the mean elevation of the
northernmost quartile ( X ± s.d. = 1177 ± 376 m) was the
lowest of the means, it did not differ significantly (Dun-
can’s Multiple Range, P < 0.05) from the central 2 quar-
tiles (south-central X ± s.d. = 1344 ± 567 m).

Multiple regression techniques (SAS 1982) for linear
and non-linear models were applied to the combined data
from Tables 1 and 2. A linear model (clutch completion =
5.361 + 2.036 latitude + 0.012 elevation) provided the
best fit (R = 0.85, P < 0.001) with latitude accounting for

Winter 1985

Short Communications

141

Figure 1 . Clutch completion dates by latitude and elevation for 20 breeding populations of the Prairie Falcon. Clutch
completion dates (range 10 March - 10 May) are depicted by circles atop vertical lines where height of line
increases with increasing date. See Tables 1 and 2 for date.

64% of the variation in clutch completion dates and eleva-
tion an additional 21%. A general trend is observable in
Figure 1 in which the mean elevation of nesting Prairie
Falcon populations decrease with increasing latitude. The
strong relationship of clutch completion date with latitude
is easily seen in Table 1. Two studies (Lanning and Law-
son 1977; Williams 1980) that do not appear to conform to
the relationship had mean elevations greater than 2700 m
(Table 2), which may have delayed clutch completion
date.

The relationship of clutch completion date with eleva-
tion is not as apparent (Table 2). It is interesting to note
that the 2 populations nesting north of 52° N latitude
(Fyfe pers. comm.) (Table 1) both nested at 700 m (Table
2), the lowest nesting elevations considered in this study.
Conversely, the southernmost population (25.5°N
latitude (Table 1)) nested at 2800 m, the highest elevation
considered in this study. It seems, therefore, that these
patterns may represent the extremes of the Prairie Fal-
con’s breeding range and nesting phenologies, with birds
in the south using the cool mountain tops in Mexico (Lan-
ning and Lawson 1977) and Canadian prairie birds
utilizing escarpments along low-lying prairie river systems
(Fyfe pers. comm.). In both situations, specific nesting
localities may provide a climate more equitable for
breeding Prairie Falcons than the prevailing climate at
that latitude. Falcons in northern regions may be utilizing
behavioral and ecological adaptations to augment their
nesting attempts, such as choosing south and/or east fac-
ing eyries (see Williams 1984) rather than being restricted
to nesting on low-elevation escarpments along river sys-
tems. Such diversity in nesting phenology could provide a
means of range expansion or a means of utilizing a variety
of habitats to accomplish reproduction.

Acknowledgments

I am grateful to Clayton M. White for his guidance and assis-
tance in this study. I would like to thank J.R. Parrish and Joseph E.
Scheiring for their insightful reviews of the manuscript. Partial
funding was provided by the Department of Zoology, College of
Biological Sciences and the Associated Students of Brigham
Young University and the Frank M. Chapman Fund. The Col-
orado Division of Wildlife provided historical data, lodging and
financial assistance through Federal Aid in Wildlife Restoration
Project W-124-R.

Literature Cited

Allee, W.C., A.E. Emerson, O. Park, and K.P.
Schmidt. 1949. Principles of animal ecology. W.B.
Saunders Co., Philadelphia.

Becker, D.M. and I.J. Ball. 1981. Impact of surface
mining on prairie falcons: recommendations for
monitoring and management. U.S. Fish and Wildlife
Service. Mont. Coop. Wildlife. Res. Unit, Missoula,
Montana.

Denton, S.J. 1975. Status of prairie falcons breeding in
Oregon. M.S. Thesis. University of Oregon, Eugene,
Oregon.

Edwards, B.F. 1973. A nesting study of a small popula-
tion of prairie falcons in southern Alberta. Can. Field-
Nat. 87:322-324.

Enderson, J.H. 1964. A study of the prairie falcon in the
central Rocky Mountain region. A uk 81:332-353.
Fowler, F.H. 1931. Studies of the food and growth of
the prairie falcon. Condor 33:193-201.

Johnston, R.F. 1954. Variation in breeding season and
clutch size in song sparrows of the Pacific coast. Condor
56:268-7$.

Johnstone, R.S. 1980. Nesting ecology and manage-

142

Short Communications

Vol. 19, No. 4

ment of the raptors in Harney Basin, Oregon. Draft
report. B.L.M. Burns, Oregon.

Lanning, D.K. and P.W. Lawson. 1977. Ecology of the
peregrine falcon in northeastern Mexico. Chihuahuan
Desert Research Institute Contribution No. 41.

Leedy, R.R. 1972. The status of the prairie falcon in
western Montana: emphasis on possible effects of
chlorinated hydrocarbon pesticides. M.S. Thesis. Uni-
versity of Montana, Missoula, Montana.

Marti, C.D. and C.E. Braun. 1977. Use of tundra
habitats by prairie falcons in Colorado. Condor
77:213-214.

Monk, J.G. 1976. The raptors of Yakima canyon,
Washington, August 1976. Draft report. B.L.M.
Yakima, Washington.

Moritsch, Marc Q. 1983. Photographic guide for ag-
ing nestling prairie falcons. U.S.D.I., B.L.M., Snake
River Birds of Prey Project, Boise District, Idaho.

Morton, M.L. 1978. Snow conditions and the onset of
breeding in the mountain white-crowned sparrow.
Condor 80:285-289.

Ogden, V.T. and M.G. Hornocker. 1977. Nesting
density and success of prairie falcons in southwestern
Idaho. J. Wildl. Manag. 41:1-11.

Olendorff, R.R. 1973. Ecology of the nesting birds of

prey of northeastern Colorado. U.S. I.B.P. Grasslands
Biome Technical Report 211.

Platt, S.W. 1974. Breeding status and distribution of
the prairie falcon in northern New Mexico. M.S.
Thesis. Oklahoma State University, Stillwater, Ok-
lahoma.

Porter, R.D. and C.M. White. 1973. The peregrine
falcon in Utah, emphasizing ecology and competition
with the prairie falcon. Brigham Young University
Science Bulletin 28:1-74.

SAS Institute Inc. 1982. SAS User’s Guide: Statistics,
1982 Edition. SAS Institute Inc., Cary, North
Carolina.

White, C.M. 1964. Biosystematics of the North Ameri-
can peregrine falcons. Ph.D. dissertation. University
of Utah, Salt Lake City, Utah.

Williams, R.N. 1981. Breeding ecology of prairie fal-
con at high elevations in central Colorado. M.S. thesis.
Brigham Young University, Provo, Utah.

1984. Eyrie aspect as a compensator for

ambient temperature fluctuations: a preliminary in-
vestigation. Raptor Res. 18:155-157.

Department of Zoology, Brigham Young University, Provo,

UT 84602.

Received 15 October 1984; Accepted 15 February 1985

Recapture of a Non-breeding Boreal Owl Two Years Later

Thomas W. Carpenter

On 22 April 1984, while mist-netting owls at Whitefish
Point, Chippewa County, Michigan, I recaptured a Boreal
Owl (Aegolius funereus) that was banded at this location by
Warren A. Lamb on 3 May 1982. There are no known
summer or breeding records for this species in Michigan,
though fair numbers are captured at Whitefish Point
during most springs (Payne 1983). Thus, this bird was
apparently moving north during both years it was cap-
tured following a southward movement during the pre-
ceding fall or winter.

Periodic southward movements of the Boreal Owl have
received previous attention (Anweiler 1960; Bent 1961;
Mysterud 1970; Catling 1972; Evans and Rosenfield
1977). However, to my knowledge this is the first time a
Boreal Owl has been recaptured in North America in a
subsequent year following a southward movement. Re-
capture in a subsequent year of owls banded during mi-
gration is not a common occurrence as shown by the low
recapture rate of the highly migratory Northern Saw-
whet Owl, Aegolius acadicus (Woodford 1959).

Literature Cited

Anweiler, G. 1960. The Boreal Owl influx. Blue Jay
18:61-63.

Bent, A. C. 1961. Life histories of North American birds
of prey, Part 2. Dover, New York.

Catling, P.M. 1972. A study of the Boreal Owl in south-
ern Ontario with particular reference to the irruption
of 1968-69. Can. Field-Nat. 86:223-232.

Evans, D.L. and R.N. Rosenfield. 1977. Fall migration
of Boreal Owls. Loon 49:165-167.

Mysterud, I. 1970. Hypotheses concerning charac-
teristics and causes of population movements in
Tengmalm’s Owl ( Aegolius funereus (L.)). Nytt Mag.
Zool. (Oslo). 18:49-74.

Payne, R.B. 1983. A distributional checklist of the birds
of Michigan. Misc. Publ. Mus. Zool. Univ. Mich. 164.

Woodford, J. 1959. Returns and recoveries of Saw-
whet Owls banded at Toronto, Ontario. Ont. Field Biol.
13:19-23.

Zoology Department, Univ. of Wisconsin-Milwaukee, Mil-
waukee, WI 53201. Present address: 3646 S. John Hix,
Wayne, MI 48184.

Received 20 March 1985; Accepted 20 April 1985.

Winter 1985

Short Communications

143

Fall Raptor Concentration on Henrys Lake Flats

Daniel M. Taylor and Charles H. Trost

In the early 1970’s we became aware of raptor concentrations of
primarily Buteo spp. on Henrys Lake Flats in late summer and
early fall. A concentration of large numbers of raptors on a high
mountain meadow intrigued us, and from 1974 to 1983 we con-
ducted annual roadside surveys to monitor raptor abundance and
gain insight into why they were concentrating in this area.

Henrys Lake Flats is located between 1,950 and 2,000 m in

elevation in Fremont County in the northeast corner of Idaho.
The flats extend from 1 to 8 km from Henrys Lake and are
characterized by large, wet meadows and gently rolling plain
dominated by big sagebrush (Artemesia tridentata). Most of this land
is moderately grazed by cattle with at least a short grass/herb cover
over practically all the land during the period of our surveys. The
flats are surrounded by coniferous stands of primarily lodgepole

Table 1. Total raptor sightings on a 32 km automobile transect around Henrys Lake, Idaho, for the period
1974-1983. All transects conducted between 28 August and 4 September of each year.

Species

Year

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

Mean

Red-tailed Hawk

( B uteo jamaicensis )

12

10

6

14

28

32

114

135

136

39

52.6

Ferruginous Hawk
(Buteo regalis )

46

28

16

7

16

48

67

21

34

31

31.4

Swainson’s Hawk
(Buteo swainsoni )

11

12

3

3

4

15

34

17

19

14

13.2

Unidentified Buteo

2

3

4

1

9

1.9

Sub-total

69

52

25

24

48

98

215

177

190

93

99.1

Northern Harrier

(Circus cyaneus)

11

11

5

9

3

2

6

2

4

5

5.8

Sharp-shinned Hawk

(Accipiter striatus )

2

2

5

2

2

1

1

1.5

Cooper’s Hawk
(Accipiter cooperii)

2

1

1

0.4

Goshawk
(Accipiter gentilis )

2

2

0.4

Osprey

(Pandion haliaetus)

5

2

2

2

8 1

1.2

Bald Eagle

(Haliaeetus leucocephalus )

1

1

3

2

1

2

2

1.2

Golden Eagle
(Aquila chrysaetos)

1

2

1

1

1

0.6

American Kestrel
(Falco sparverius)

33

12

8

9

5

9

5

4

9

9.4

Prairie Falcon

(Falco mexicanus )

2

2

3

4

3

1

1.5

Total

119

83

49

51

62

115

235

187

198

112

121.1

144

Short Communications

Vol. 19, No. 4

pine ( Pinus contorta) extending down from surrounding moun-
tains.

We drove a 32 km automobile transect route around Henrys
Lake once annually in the last few days of August or first week of
September. Heading north, the route started in Section 24, Range
(R) 43 East (E), Township (T) 14 North (N) on a secondary road
which parallels U.S. Highway 20/191. We detoured approx. 1.5
km onto the road to Henrys Lake State Park, where we parked and
walked about 100 m north to a bluff and surveyed the surround-
ing area with a 30 X spotting scope. We returned to U.S. Highway
20/191 and continued north until turning west on U.S. Highway
287. We traveled on U.S. Highway 287 until turning south on a
gravel road in Section 32, R 42 E, T 13 N, where we continued
around the lake and reunited with U.S. Highway 20/191. The
route traveled was mainly through open meadow or sage plain
with the exception of the last few km before rejoining U.S. High-
way 20/191. Using USGS guadrate maps, we estimated surveying
about 68 km2 of open country.

Surveys were conducted on calm, clear mornings and were
generally completed before 1030 H. At least 2 competent obser-
vers conducted each survey. The transect route was traveled at
speeds < 35 kph, and frequent stops were made at good vantage
points or when raptors were sighted. Traffic was minimal on the
route, except sometimes U.S. Highway 20/191 had moderate traf-
fic.

An average of 1 2 1 . 1 raptors/yr were sighted for the 1 0-yr period
(Table 1), of which 99.1 (83%) were buteos, resulting in 4 raptors
sighted/km traveled. Sightings in 1974-75 were near the 10-yr
average, but sightings in 1976-77 were low. Buteos were particu-
larly low in 1976-77. A severe drought in 1976-77 resulted in a
reduction in raptor productivity in the Birds of Prey Natural Area,
near Boise, Idaho (Snake River Birds of Prey Environmental
Statement, 1980, B.L.M., Boise, pp. 2-11), which corresponds with
an ebb in our observations. Perhaps the build-up in subsequent
years is a reflection of raptor recovery from the 1976-77 drought.

The Red-tailed Hawk (B uteo jamaicensis ) was the most common
raptor sighted, averaging 53 birds/survey (Table 1 ) with a range of
6-136 birds. Such a large range for sightings could reflect annual
productivity in the region, since > 90% of red-tail sightings were
of birds in immature plumage. Adult red-tail sightings were con-
fined to small meadows and clear-cuts surrounding the main flats.
Adults may have limited themselves to peripheral areas to avoid
harassment from immatures who often congregated around kills.
Once we observed up to 11 immature red-tails fighting over a
single prey.

The Ferruginous Hawk ( Buteo regalis) was the next most fre-
quently sighted raptor, averaging 31.4 birds/survey (Table 1) with
a range of 7 - 67. Most Ferruginous Hawks sighted were also in
immature plumage. Except for 2 birds perched on the edge of a
clear-cut in 1983, all Ferruginous Hawks were sighted on the main
flats. The observation bluff was a particularly good concentration
spot, with less vegetation, allowing excellent views from ground
level.

Ferruginous Hawks have been known to move to Henrys Lake
Flats from the Raft River Valley along the Utah-Idaho border,
about 250 km to the southeast (Thurow et al. 1980. Raptor Ecol-
ogy of Raft River Valley, Idaho, E.G. and G., Inc., Idaho Falls,
Idaho, and pers. obs.). In late summer food availability becomes
limited in Raft River Valley since Black-tailed Jackrabbits (Lepus
califomicus) become less diurnal to avoid heat (Thurow et al. 1 980).
The Ferruginous Hawks apparently respond by drifting on pre-

vailing wind currents, which move primarily towards the Henrys
Lake area.

The Swainson’s Hawk (Buteo swainsoni) sightings averaged 13.2
birds/survey for the 10-yr period (Table 1) with a peak of 34 in
1980. Unidentified buteos and 9 other diurnal raptors sighted
accounted for an average of 23.9 more sightings/survey.

The heavy concentration of raptors at Henrys Lake Flats is
probably due to the abundance of Richardson’s Ground Squirrels
(Spermophilus richardsoni) . Ground squirrels at lower elevations are
known to estivate in late summer and fall, when hot, dry weather
eliminates or drastically reduces succulent vegetation (Ingles, L.G.
1965. Mammals of the Pacific States. Stanford University Press,
California). The high elevation of Henrys Lake Flats keeps vege-
tation green, and the ground squirrels are active and available as
prey. There may be a general tendency for raptors to move up-
slope as ground squirrels estivate and rabbits become more noc-
turnal. We have observed similar concentrations of buteos in early
fall from 2,000 to 3,000 m elevation on Steens Mountain in south-
east Oregon, where Belding’s Ground Squirrels ( Spermophilus bel-
dingi) were still active. In addition to an abundant food supply, the
Henrys Lake area lies just west of the Continental Divide and may
act as a corridor for migrating birds in general (Larrison, E. 1981.
Birds of the Pacific Northwest: Washington, Oregon, Idaho and
British Columbia. University Press of Idaho, Moscow).

Our automobile surveys indicate that high mountain
meadows are important late summer concentration areas for
buteos, especially those in immature plumage. The Henrys Lake
Flats and other high meadows of the intermountain west have
become increasingly popular recreation areas. Recreation and
other forms of land use may affect high meadow ground squirrel
populations, which in turn may affect raptor concentrations in
those areas.

Acknowledgments

M. DeLate, T. Reynolds, M. Reynolds, S. Trost and C. Webb
helped to conduct surveys. Earlier drafts of this paper were im-
proved by comments from M. Collopy and J. Gessaman.

Department of Biology, Idaho State University, Pocatello,

Idaho 83209.

Received 6 March 1984; Accepted 22 April 1985

Winter 1985

Short Communications

145

Bald Eagle ( Haliaeetus leucocephalus) Consumption of Harbor Seal (. Phoca vitulina)
Placenta in Glacier Bay, Alaska

John Calambokidis and Gretchen H. Steiger

This note reports on the frequent consumption of Harbor Seal
(. Phoca vitulina) placenta by the Bald Eagle (. Haliaeetus leucocephalus)
and a fluctuation in numbers of Bald Eagles in Muir Inlet, Alaska,
in relation to the availability of this food source.

From 30 May to 23 August 1982 and 8 to 1 3 June 1984, we spent
41 d in our study area in the northern portion of Muir Inlet,
located in the northeast corner of Glacier Bay in southeast Alaska.
This recently (within the last 20 yr) deglaciated area is about 20 km
long and an average of 2 km wide. The shoreline rises steeply on
both sides of the inlet and consists of loose rock and glacial debris.
There are no trees and vegetation is extremely sparse. Up to 1 ,000
Harbor Seals rest and give birth to youngon small icebergs formed
by an active tidewater glacier at the head of Muir Inlet. Our
research was focused on the biology and behavior of Harbor Seals
in this area. Our regular censuses and observations of seals re-
quired us to scan the entire inlet with binoculars and spotting
scopes and consequently observe eagles and their interactions with
seals.

On 9 occasions in early June, we observed Bald Eagles feeding
on Harbor Seal placenta; these were the only times we saw eagles
feeding in our study area. In one instance we saw 6 eagles either
feeding on the placenta, chasing after an eagle with placenta, or
perching near a feeding eagle. At each of 3 Bald Eagle perches
visited in early June 1982, we found from 2 to 15 clumps of lanugo
hair (the fetal coat of Harbor Seal pups that is shed before birth
and is expelled with the placenta).

Bald Eagle numbers in our study area changed through the
season and corresponded to the time of Harbor Seal pupping. We
saw a minimum of 4-7 eagles on 5 d between 31 May to 17 June
1982 and a minimum of 5 on 2 d between 8 and 13 June 1984. We
saw fewer eagles during visits later in the season. During the latter
part of June we saw up to 2 eagles. In 16 d of observation in July
and August 1982, we had only one eagle sighting. Bald Eagles in
Muir Inlet consisted about equally of mature and immature birds,
4 of the 7 seen at one time in June 1982 and 3 of the 5 seen at one
time in June 1984 were mature. The majority of Harbor Seal pups
in Muir Inlet are born in late May and early June, the same period
we saw the largest numbers of Bald Eagles. In both 1982 and 1984,
over 300 Harbor Seal pups were born in this portion of Muir Inlet.
Given a minimum weight of 1 kg for a Harbor Seal placenta, this
would mean an excess of 300 kg of food available to eagles.

We concluded that Bald Eagles in this area during late May and
early June subsist largely or entirely on placenta of Harbor Seals
because: 1) our frequent observations of eagles feeding on
placenta and not on other food, 2) the abundance of this food
source and the scarcity of other food sources in this deglaciated
area, 3) the presence of seal lanugo hair found at eagle perches,
and 4) the close parallel between the number of eagles in our study
area and the Harbor Seal pupping season. Eagles appear to use
this area for only a short period; we found no evidence of eagle
nesting.

Sherrod et al. (Living Bird 15:143-182, 1976) reported that
Bald Eagles on Amchitka Island, Alaska consume northern Sea
Lion (Emetopias jubatus) afterbirth. It is the only other report we
know that mentions Bald Eagles feeding on placenta of pinnipeds.
We have observed Bald Eagles feeding on seal placenta and

scavenging on dead seal pups in other parts of Glacier Bay and
Puget Sound, Washington.

Acknowledgments

Funding was by the School for Field Studies, Cambridge, MA.
The National Park Service provided permits and Gary VeQuist
was instrumental in this regard. Staff and students with the School
for Field Studies aided in data collection. Sue Carter and Robin
Butler made additional contributions. Al Harmata and Jon Ger-
rard critically reviewed the manuscript.

Cascadia Research Collective, Waterstreet Bldg., Suite 201,
218% W. 4th Ave., Olympia, WA 98501.

Received 22 January 1985; Accepted 1 May 1985

Barred Owl Hunting Insects

Arnold Devine, Dwight G. Smith and Mark Szantyr

Although the Barred Owl (Strix varia) is partially insectivorous
(Bent, U.S. Natl. Mus. Bull. 170, 1938) its methods of hunting and
capturing insects have not been described. From 1924-2000 H we
observed a Barred Owl hunting insects on 4 April 1984 at Blue
Springs Stake Park, Orange City, Florida. The Barred Owl was
apparently hunting noctuid moths (Lepidoptera) and large vein-
winged insects on the lawn of an historic house in the park. The
owl hunted these insects from a small stump or on a sandy stretch
of lawn beneath a lighted area. In hunting, the owl sat motionless
except for slight head movements to watch the insects. Captures
were attempted only after the insects landed. Capture attempts
were a combination of 3 movements; 1) a bound initiated from a
partially forward leaning position, 2) a single wing flap and 3) a
short glide. Attempts covered 1-2 m distances and the owl was
twice observed to follow missed attempts with 2 or 3 immediate
additional pounces. Insects were captured with the talons and
consumed by bringing the head down to pick the insect from the
talons. One insect not immediately consumed was transferred to
the beak before the owl flew to a nearby tree. At 1949 H the Barred
Owl returned to its hunting perch on the lawn where it unsuccess-
fully attempted two more captures before leaving the area at 2000
H. During the time observed, the Barred Owl was successful in 2 of
18 capture attempts.

Forsman et al., (Wildl. Mongr 87, 1984) reported that the Spot-
ted Owl ( Strix occidentals) diet also includes insects and that these
owls used pounces to capture insects on the ground or on tree
limbs. Also, mid-air captures of flying insects were not observed.

Biology Department, Southern Connecticut State University,
New Haven, CT 06515.

Received 22 March, 1985; Accepted 20 May 1985

146

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Vol. 19, No. 4

Northern Harrier Predation on Greater Prairie
Chickens in Southwest Missouri

Brian Toland

Although habitat preferences of the Northern Harrier (Circus
cyaneus) and the Greater Prairie Chicken (Tympanuchus cupido) are
quite similar (Berger et al. 1963), harriers are rarely reported to
prey upon these galliformes (Yeatter 1943; Schwartz 1945;
Grange 1948; Weller et al. 1955; Ammann 1957; Berger et al.
1963). Other similar-sized avian prey such as Ring-necked Pheas-
ant (Phasianus colchicus ), Sharp-tailed Grouse (T. phasianellus ),
American Bittern (Botaurus lentiginosus), ducks and the Domestic
Chicken (Gallus spp.) are, however, not infrequently taken (Fisher
1893; Peabody 1900; Errington and Breckenridge 1936; Bent
1937; Brown and Amadon 1968) although usually as juveniles
(Peabody op. cit . ; Saunders 1913;Randall 1940; Hecht 1951).

This note reports harrier predation on adult and young Greater
Prairie Chickens in the tail-grass prairie region of southwest Mis-
souri during spring and summer 1984. The study area of 850 ha
consisted of Prairie State Park and surrounding private lands.
Prairie State Park is 1 mi southwest of Liberal, Missouri, in Barton
County. Vegetation consists of bluestem grasses ( Andropogon spp.),
Indian grass ( Sorghastrum nutans) and other native grasses and

forbs, as well as invading cool season grasses such as fescue ( Festuca
sp.). Old and reclaimed strip mines and deciduous woody growth
are scattered throughout the area. Neighboring lands are mostly
crops and fescue (Larson 1982).

A total of 325 h were spent observing harriers and prairie
chickens from 7 April - 7 August 1984. Using techniques de-
scribed by Hamerstrom (1969), I found 7 harrier nests (density of
1 pair/121 ha) clumped in 3 loose aggregations in undisturbed
grasslands.

Approximately 150 prairie chickens were concentrated around
4 booming grounds on the study area during early spring
(April-May) and later scattered throughout the area during nest-
ing (May-July). At least 2 prairie chicken nests were located within
200 m of 2 harrier nests.

Visits to Northern Harrier nests during the nestling stage were
made to collect prey remains and/or pellets. I calculated frequency
of occurrence of prey types from fresh pellets and identified prey
remains. Percent composition of each prey species was calculated
from the number of each type divided by the total. Percent
biomass was estimated by weights given in Schwartz and Schwartz
(1959), Terres (1980) and Steenhof (1983).

Analysis of food items revealed a catholic diet (Table 1). The
diet of nesting Northern Harriers in other regions has been of a
similar euryphagus composition (Randal op. cit. ; Hecht op. cit. ;
Craighead and Craighead 1956; Brown and Amadon 1968; Smith

Table 1. Prey of nesting Northern Harriers at Prairie State Park in southwest Missouri, 1984.

Frequency

of

Prey occurrence

BIRDS

Greater Prairie Chicken
(Tympanuchus cupido )

8

Adults

3

Juveniles

5

Mourning Dove
(. Zenaida macroura )

3

Eastern Meadowlark
(Stumella magna)

6

Common Grackle
(Quiscalus quiscala)

2

Red-winged Blackbird
(Agelaius phoeniceus)

6

Brown-headed Cowbird
( Molothrus ater)

3

Unidentified passerines

11

Total birds
(Table 1 continued)

39

%

COMPOSITION

Average
weight (g)

Estimated

% BIOMASS

6.6

624

22.6

908

12.3

454

10.3

2.5

134

1.8

4.9

95

2.6

1.6

112

1.0

4.9

50

1.4

2.5

41

0.5

9.0

75

3.7

32.0

33.6

Winter 1985

Short Communications

147

(Continuation of Table 1)

MAMMALS

Prairie vole
(Microtus ochrogaster )

24

20.0

8

4.1

Fulvous harvest mouse
(Reithrodontomys fulvescens )

6

4.9

21

0.5

Deer Mouse

( Peromyscus maniculatus)

2

1.6

20

0.2

Cotton rat
(Sigmodon hispidus)

1

0.8

120

0.5

Eastern wood rat
(Neotoma floridana)

1

0.8

255

1.2

Unidentified rodents

7

5.8

30

0.9

Eastern cottontail
( Sylvilagus floridanus )

9

7.4

1200

49.0

Total mammals

50

41.3

56.4

REPTILES

Plains garter snake
(Thamnophis radix)

1

0.8

109

0.5

Unidentified snakes

11

9.1

190

9.5

Total reptiles

12

9.9

10.0

INSECTS

Coleopterans

12

9.9

0.5

tr1

Orthopterans

8

6.6

1

tr

Total insects

20

16.5

tr

TOTAL PREY ITEMS

121

100.0

100.0

fir = trace.

and Murphy 1973; Snyder and Wiley 1976). A total of 7 prairie
chicken remains were collected from the 2 harrier nests closest to
prairie chicken nests. Of these 7 remains, 5 represented half-
grown juveniles and 2 represented adults.

An eighth prairie chicken was captured by an adult female
harrier on 25 July at 0700 H. The hawk hovered briefly 4 m above
a dense stand of bluestem grasses and fescue, before diving into
the vegetation. After waiting about 10 min, I approached the site
and the hawk flushed when I was about 20 m away. I discovered a
dead adult female prairie chicken that was partly deplumed and
still warm. I was unable to find a prairie chicken nest in the
immediate vicinity, but numerous droppings and matted vegeta-
tion (form) indicated that the prairie chicken had been on its roost.
I left the site and watched from a distance of ca 300 m until the

harrier returned to her kill after nearly 20 min. Berger et al.
(1963) observed prairie chickens being captured by raptors (in-
cluding 1 female Northern Harrier) early in the morning.
Campbell (1950) reported an unsuccessful capture attempt of a
Lesser Prairie Chicken ( T . pallidicinctus) during evening hours.
Poor light during early morning and late evening hours may make
approaching raptors more difficult for prairie chickens (or other
quarry) to spot (Berger et al. 1963).

All prairie chicken prey was brought to harrier nests during the
last half of the nestling stage. During this time female harriers
spent as much time hunting for their young as did males. It is
probable that the larger females (50% heavier than adult males)
caught the adult prairie chickens (Berger et al. 1963). I observed
several adult male harriers feeding on mammalian prey among

148

Short Communications

Vol. 19, No. 4

displaying prairie chickens at booming grounds just prior to the
nesting season. The prairie chickens seemed oblivious of these
male harriers. Female harriers, however, usually evoked a re-
sponse from prairie chickens, ranging from a brief squat to an all
out flush. Berger et al. (1963) reported that over a 4-year sample
of harrier-prairie chicken reactions, prairie chickens flushed
nearly 70% of the times female harriers approached, but only 30%
of the times males approached. Of the 33 times that prairie chick-
ens completely ignored approaching harriers, 94% were male
hawks and 6% were females. Female Hen Harriers (C. c. cyaneus )
take significantly more Red Grouse ( Lagopus lagopus) and other
gamebirds than do males (Marquiss 1980).

I have found no evidence of Northern Harriers preying on
Greater Prairie Chickens during winter or on booming grounds in
early spring. However, prairie chickens did comprise a significant
proportion of Northern Harrier diets (22.6% biomass; Table 1)
during the nesting season when female and juvenile prairie chick-
ens in close proximity to harrier nests may be more vulnerable to
raptor predation.

Acknowledgments

Toney Chiles contributed invaluable field assistance. The Mis-
souri Department of Natural Resources provided funding and
technical assistance for this study through a state park research
grant. Nancy Thompson-Toland helped with expenses and field
work. Keith Bildstein, Clayton White and an anonymous referee
made editorial suggestions which improved the manuscript.

Literature Cited

Ammann, G. A. 1957. The prairie grouse of Michigan.

Michigan Dept. Conserv. Tech. Bull. 200 pp.

Berger, D.D., F. Hamerstrom and F.N. Hamer-
strom. 1963. The effect of raptors on prairie chic-
kens on booming grounds. J. Wildl. Manag. 27:778-
791.

Bent, A. C. 1937. Life histories of North American birds
of prey (order Falconiformes). Part 1. U.S. Natl. Mus.
Bull. 167. Dover Publ., New York.

Brown, L.H. and D. Amadon. 1968. Eagles, hawks and
falcons of the world. McGraw-Hill, New York.
Campbell, H. 1950. Note on the behavior of Marsh
Hawks toward Lesser Prairie Chickens. J. Wildl.
Manag. 14:477-478.

Craighead, J.J. and F.C. Craighead, Jr. 1956. Hawks,
owls and wildlife. Stackpole Co., Harrisburg, PA.
Errington, P.L. and W.J. Breckenridge. 1936. Food
habits of Marsh Hawks in the glaciated prairie region
of north-central United States. Aw. Midi. Nat. 7:831-
848.

Fisher, A.K. 1893. The hawks and owls of the United
States and their relation to agriculture. U.S. Dept. Agr.
Bull. 3, Washington, D.C.

Grange, W.B. 1948. Wisconsin grouse problems. Wis-
consin Conserv. Dept. 318 pp.

Hamerstrom, F. 1969. A harrier population study.
Pages 367-383. In J.J. Hickey (Ed.), Peregrine Falcon

populations: their biology and decline. Univ. Wiscon-
sin Press, Madison.

Hecht, W.R. 1951. Nesting of the Marsh Hawk at Delta,
Manitoba. Wilson Bull. 63:167-175.

Larson, L. 1982. Prairie State Park: an introduction to
one of Missouri’s public prairies. Missouri Prairie J.
3:4-11.

Marquiss, M. 1980. Habitat and diet of male and female
Hen Harriers in Scotland in winter. British Birds
73:555-560.

Peabody, P.B. 1900. How a Marsh Hawk grows. Bird
Lore 2:43-49.

Randall, P.E. 1940. Seasonal food habits of the Marsh
Hawk in Pennsylvania. Wilson Bull. 52:165-172.

Saunders, A. A. 1913. A study of the nesting of the
Marsh Hawk. Condor 15:99-104.

Schwartz, C.W. 1945. The ecology of the prairie
chicken in Missouri. Univ. Missouri Studies 20: 1-99.

and E.R. Schwartz. 1959. The wild

mammals of Missouri. Univ. Missouri Press and Mis-
souri Dept. Conserv.

Smith, D.G. and J.R. Murphy. 1973. Breeding ecology
of raptors in the eastern Great Basin of Utah. Brigham
Young Univ. Sci. Bull., Biol. Ser., Vol. 28(3).

Snyder, N.F.R. and J.W. Wiley. 1976. Sexual size di-
morphism in hawks and owls of North America. AOU
Monogr. 20.

Steenhof, K. 1983. Prey weights for computing percent
biomass in raptor diets . Raptor Res. 17:15-27.

Terres, J.K. 1980. The Audubon Soc. encyclopedia of
North American birds. Alfred A. Knoopf, Inc., New
York.

Weller, M.W., I.C. Adams, Jr. and B.J. Rose.
1955. Winter roosts of Marsh Hawks and Short-eared
Owls in central Missouri. Wilson Bull. 67:189-192.

Yeatter, R.E. 1943. The prairie chicken in Illinois. Il-
linois Nat. Hist. Surv. Bull. 22:377-416.

Missouri Department of Natural Resources, Natural History
Program, P.O. Box 176, Jefferson City, MO 65102. Current
address: Route 4, Box 165, Columbia, MO 65201.

Received 8 April 1985; Accepted 15 July 1985.

Winter 1985

News and Reviews

149

The Migration of Birds of Prey in the Northern Red Sea Area: Report of the 1982 Suez Study by David Wimpfheimer, Bertel Bruun,
Sherif M. Bahael Din and Michael C. Jennings with contributions by William S. Clark, Carsten Jensen, Donald Parr and lb Petersen, and
forward by Dean Amadon. Arabic summary by Assad Serhal. 80 pp., 6 Tables, 24 Figures, 2 Appendices, 10 plates. Available from the
Holy Land Conservation Fund, 1825 Eye Street Northwest, Suite 400, Washington, DC 20006. $20.00 U.S.

Whenever the nation of Egypt is mentioned, thoughts come to
mind of the pharaohs, the great pyramids and the sphinx. One
also remembers Egypt’s biblical and more recent history, both
closely tied to the nation of Israel. Thoughts of migrating raptors
do not immediately come to mind. Yet this report has made it
apparent that a spring migration of raptors does occur over the
lands of Egypt, and undoubtedly has done so since before the
great pyramids were built.

The report describes the initial results of the Holy Land Con-
servation Fund’s expedition to Suez, Egypt, in the spring of 1982.
As a result of many individual efforts and outstanding support
from numerous individuals and agencies, both in the United
States and Egypt, the authors have provided students of raptor
migration with a data base for reference and future comparison
for the Middle East. All of the authors except one have previous
experience with Eurasian raptors. Observational data are re-
ported for 124,996 raptors, representing 28 species, sighted dur-
ing the period 23 February - 16 May 1982. The primary goal of the
study was to learn more about the spring migration of raptors at or
near Suez, Egypt, and towards that goal the authors have a good
start. However, there is some question as to whether the report
effectively establishes the Suez area as a concentration point as
stated. Certainly there is a substantial spring overfly in the region,
but the evidence supports the idea that raptors do not initiate
migrations in the immediate vicinity of the city of Suez, and thus
do not concentrate themselves in the area.

A species by species account of sightings by time period and a
seasonal total is provided for each of the 28 species tallied. Com-
parisons by species are made with other regions, particularly Eliat,
Israel. Six species, Buteo b. vulpinus, Aquila nipalensis. A pomarina,
Milvus migrans, Circaetus gallicus and Neophron percnopterus ac-
counted for 90% of total sightings. Sightings of B. b. vulpinus alone
accounted for almost 65% of total numbers, but the vulpinus tally is
biased by the inclusion of all B. buteo sightings with the vulpinus
totals, as pointed out by the authors. Less than 10 individuals were
tallied for 12 species. Observational data for 214 non-raptors are
provided in Appendix A, which includes 3 new sightings for
Egypt. Histograms of related species are provided depicting total
numbers versus date. The figures could have been combined in
many cases, especially Figures 14 and 15 and Figures 17 and 18.
Analysis by 5-day interval would have been most helpful and
welcome, but such was provided only for accipiters, which rep-
resented 0.2% of total sightings.

At least 2 observers were present on most days, and there was a
gap in continuous coverage during early April when no observa-
tions were made. In order to compensate for these gaps, the
authors extrapolated data for observations both before and after
periods of no coverage. On this basis, adjustments were calculated
for selected species, including Aquila sp., A. pomarina and A.
nipalensis. Adjustments were made with the assumption that the
proportions of identified Aquila is the same as unidentified, which
is confusing. However, these adjustment figures do not appear in
final tallies and conclusions. Virtually every individual raptor
sighted was identified at least to genus, and no “unidentified”
category appears in the final tallies. As one who has observed
North American migrations over the years, it is simply not possible
to always pinpoint an individual, though worthy a goal such iden-
tification may represent.

Intermittent observations made in areas adjacent to Suez were
also accomplished. Brief summaries are provided for Hurghada
and surrounding area, for northern Sinai between El Arish and
Nakhl, for Ismalia north of Suez (all observations accomplished by
one or more of the authors), and summaries of previous reports in
the literature for the region and for Eliat, Israel. Previous reports
and more recent studies indicate the migration at Eliat is substan-
tially greater than reported for Suez and surrounding areas (W.S.
Clark, pers. comm.). Also included is a chapter on raptor migra-
tion in the Middle East which provides the reader with a nice
comparison as well as a substantial reference list.

As the authors point out, their attempts to correlate
meteorological factors with their observations needs further
study. Purely qualitative evaluations of wind direction, wind
strength(P) (only for surface winds), and cloud cover are provided
with species tallies. Qualitative assessment carries over into obser-
vations, where individuals are grouped under the heading of
being either an “active” or “passive” migrant based upon convec-
tion current utilization (Table 6) (after studies of raptor migration
in Denmark by B. Bruun and O. Schelde, 1957, Efterarstraekker
pa Stigsnaes, S.V. Sjaelland, D.O.F.T. 51:149-167). The useful-
ness of such categorization seems questionable, since any indi-
vidual of any species may either actively or passively utilize con-
vection currents at any given time.

Appendix B summarizes human threats to migrating raptors.
Although there is little evidence of direct persecution such as
shooting (Plate 4 of a “hunter” displaying 2 recently shot Steppe
Eagles notwithstanding), potential for harm from chemical
dumping and industrial pollution does exist in the Suez area. No
mass kills have been reported, but as with most chemical contam-
inants, raptors that feed, bathe, or drink while enroute through
the region probably pick up harmful compounds which would be
transported back to breeding territories.

Overall, the report provides valuable data to the ever-growing
worldwide raptor migration picture. Sherif Ben el Din’s illustra-
tions evidence a keen familiarity with migrant raptors enroute
through Suez. A more comprehensive assessment of observations
would have been a welcome addition. Nevertheless, an 82-item
literature section is provided which helps to substantiate the re-
port as a basis for comparison with future raptor migration studies
in the Middle East. — Jimmie R. Parrish.

ERRATUM — Volume 18(4), page 159. Paul Springier
should be Paul Springer. The Editorial Staff apologizes to
Paul for failing to catch the misspelling before final
printing.

150

News and Reviews

Vol. 19, No. 4

Announcement

LIT — a Literature Retrieval System Using dBASE II — is a literature cataloguing system for use with personal
computers. While the LIT System ($30.00) can be used for literature on any subject, a prepared Keyworded Data Base is
available including all publications (783 items) of the Raptor Research Foundation, Inc. ($20.00 on disk or hard copy).
New Data Bases are being prepared for all raptor references in Auk, Condor, Wilson Bulletin, etc. Also available is the
LIT Ornithological Keyword List of nearly 900 Keywords ($15.00 on disk or hard copy for use with other systems).
The following is a summary of LIT features and computer requirements:

• Very quick and easy start-up, maintenance and expansion in dBASE II on most MS-DOS computers.

• Rapid menu-driven data base creation, data entry and Keyword management.

• Permanent, efficient and cost-effective generation of Keyworded bibliographies selected by author, title, citation,
subject (Keywords), geographic location, etc.

• Computer must have dBASE II software, but operator need not know how to use dBASE.

• Computer must have a printer and at least two floppy disk drives (or one floppy and a hard disk) capable of reading
360K discs. RAM size must accommodate dBASE.

• All source code is included for dBASE programmers.

• Thorough documentation, sample data entry sheets, suggested data entry formats, and a sample Keyword List are
all included.

• LIT is far more than a computer program; it is also an easy to follow concept for small library/ reprint file
management.

For more information and a free brochure, write Richard R. Olendorff, 6009 Viceroy Way, Citrus Heights, California
U.S.A. Complete documentation (37 pp.) is available for $5.00, which will be deducted from the LIT System purchase
price at the time of purchase.

Proceedings of the Southeastern United States and Caribbean Osprey Symposium — published by The International
Osprey Foundation, Inc., edited by Mark A. Westall. Eleven papers, 132 pages. Copies can be ordered from The
International Osprey Foundation, Inc., P.O. Box 250, Sanibel, FL 33957 USA. Price: $16.00 U.S.

The Southwestern Raptor Management Symposium and Workshop will be held on the University of Arizona
Campus, Tucson, 22-25 May, 1986. The Symposium will focus on raptors in the southwestern United States and
adjacent Mexico. Sessions will cover raptor biology, management and research techniques, impact mitigation, and
population status. There will also be a workshop on research and management priorities. For more information, or if
you are interested in presenting a paper, contact Brian A. Millsap, Raptor Information Center, Institute for Wildlife
Research, National Wildlife Federation, 1412 16th Street, N.W., Washington, D.C. 20036.

Bird Banding by Elliott McClure, The Boxwood Press, Pacific Grove, California. 341 pp., 514 x 814, paper: $15.00. —
While this is a general book on bird banding there are several sections concerning raptors. McClure spent a large
portion of his active professional life in Southeast Asia and much of the material is drawn from his experiences there.
There are 13 distinct sections varying from the geological background of migration routes (the example is from
Southeast Asia), nets and snares, banding nestlings, to the art of record keeping. There are 35 index entries for birds of
prey (1 1 of those are for owls). Under the section, “The Bird and its Banding Idiosyncrasies,” there is a page and a half
devoted to owls and 2 pages to falconiforms. Most of the standard trapping methods used on hawks are discussed (many
variations of the Bal-chatri). An interesting method of snaring the buzzard ( Butastur ) is discussed at some length. This
book has some valuable tips for raptor banders and it is well worth looking at. — C.M. White.

RAPTOR RESEARCH

A Quarterly Publication of The Raptor Research Foundation, Inc.

EDITOR: Clayton M. White, Department of Zoology, 161 Widtsoe Building, Brigham Young University, Provo,
Utah 84602

ASSISTANT EDITOR: Jimmie R. Parrish, Department of Zoology, 159 Widtsoe Building, Brigham Young Univer-
sity, Provo, Utah 84602
ASSOCIATE EDITORS

Jeffrey L. Lincer - Environmental Chemistry and Toxicology
Richard Clark - Order Strigiformes
Ed Henckel - Family Cathartidae
Gary E. Duke - Anatomy and Physiology

Patrick T. Redig - Pathology, Rehabilitation and Reintroduction
Jim Mosher - General Ecology and Habitat Analysis

INTERNATIONAL CORRESPONDENT: Richard Clark, York College of Pennsylvania, Country Club Road,
York, Pennsylvania 17405

Raptor Research (ISSN 0099-9059) welcomes original manuscripts dealing with all aspects of general ecology, natural
history, management and conservation of diurnal and nocturnal predatory birds. Send all manuscripts for considera-
tion and books for review to the Editor. Contributions are welcomed from throughout the world, but must be written in
English.

INSTRUCTIONS FOR CONTRIBUTORS: Submit a typewritten original and two copies of text, tables, figures and
other pertinent material to the Editor. Two original copies of photographic illustrations are required. Raptor Research is
published in a double-column format and authors should design tables and figures accordingly. All submissions must
be typewritten double-spaced on one side of 8V2 x 1 1 -inch (21 V2 x 28 cm) good quality, bond paper. Number pages
through the Literature Cited section. The cover page should contain the full title and a shortened version of the title (not
to exceed 30 characters in length) to be used as a running head. Author addresses are listed at the end of the Literature
Cited section. Authors should indicate if present addresses are different from addresses at the time the research was
conducted. When more than one author is listed, please indicate who should be contacted for necessary corrections and
proof review. Provide an abstract for each manuscript more than 4 double-spaced typewritten pages in length. Abstracts
are submitted as a separate section from the main body of the manuscript and should not exceed 5% of the length of the
manuscript. Acknowledgments, when appropriate, should immediately follow the text and precede the Literature
Cited. Both scientific and common names of all organisms are always given where first appearing in the text and should
conform to the current checklists, or equivalent references, such as the A.O.U. Checklist of North American Birds (6th
ed., 1983). Authors should ensure that all text citations are listed and checked for accuracy. If five or fewer citations
appear in the text, place the complete citation in the text, following these examples: (Brown and Amadon, Eagles,
Hawks and Falcons of the World. McGraw-Hill, New York. 1968), or Nelson (Raptor Res. 16(4):99, 1982)). If more than
five citations are referenced, each should include author and year (e.g., Galushin 1981)), or in a citation with three or
more authors, the first author and year (e.g., (Bruce et al. 1982)). Citations of two or more works on the same topic
should appear in the text in chronological order (e.g., (Jones 1977, Johnson 1979 and Wilson 1980). Unpublished
material cited in the text as “pers. comm.,” etc., should give the full name of the authority, but must not be listed in the
Literature Cited section. If in doubt as to the correct form for a particular citation, it should be spelled out for the Editor
to abbreviate.

Metric units should be used in all measurements. Abbreviations should conform with the Council of Biology Editors
(CBE) Style Manual, 4th ed. Use the 24-hour clock (e.g., 0830 and 2030) and “continental” dating (e.g., 1 January 1984).

Tables should not duplicate material in either the text or illustrations. Tables are typewritten, double-spaced
throughout, including title and column headings, should be separate from the text and be assigned consecutive Arabic
numerals. Each table must contain a short, complete heading. Footnotes to tables should be concise apd typed in
lower-case letters. Illustrations (including coordinate labels) should be on 8V2 x 1 1 -inch (21 V2 x 28 cm) paper and must
be submitted flat. Copies accompanying the original should be good quality reproductions. The name of the author(s)
and figure number should be penciled on the back of each illustration. All illustrations are numbered consecutively
using Arabic numerals. Include all illustration legends together, typewritten double-spaced, on a single page whenever
possible. Line illustrations (i.e., maps, graphs, drawings) should be accomplished using undiluted india ink and
designed for reduction by 1/3 to 1/2. Drawings should be accomplished using heavy weight, smooth finish, drafting
paper whenever possible. Use mechanical lettering devices, pressure transfer letters, or calligraphy. Typewritten or
computer (dot matrix) lettering is not acceptable for illustrations. Use of photographic illustrations is possible but
requires that prior arrangements be made with the Editor and the Treasurer.

A more detailed set of instructions for contributors appeared in Vocmop Pecreapi//^, Vol. 18, No. 1, Spring 1984, and
is available from the Editor.

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