J smrrui! b£ Udii ptsfthnlogBli ftMWmi. Gur MeCnWe \fcmhi' rrhip S*crmttfy t GP«f v ri* v&wmitttr- Jem Wlmm 1 EJitixr Alan M_ Criig f j'ij [i rw p! J Uimtt . A h rt lUUi*iL%!: s Wlflls«(| li SetsLe. A flitidw j , Ber^' r u r*nt!e (L iliilTord. Pi ml F* priftiult, Li}rtH i. ttwjHna f JCmrpft ^rcMtfxrt; Ston. P. IftvJil Siltf, Am.il I hmW, It j i^bard W. llAviil rhag m G* Shumm LI. tJ.h-nEk M i I nm, Tisirrwn IF Wuhlf Ratenii IJ Wauer, LifUiJe Webb. Dulc A- Ztmiitftraajtt Ho Volume 5 , Number 1 , 1974 Age, Sex, Mall artd MigLirbn • 'f Dimlim Jt Buliniu Lag tfMn Gary fine Rjang^ F*jw m>i.-.n md Activity Fattcfui in. TOiLnottrot AukkM J^Mkbtwl Stott, W-tytm HufftftvW Our j./ iwfep fifld €. Ft’itJ' jSp^n^ihr i 13 NO'UiS \lttifciu ft^ck Wriii OitriJ S jfiiwfPrijmtt Erie l-\ Strrcihng Rmurd for th? Srtnifulrtmnl 41 Ouctn Shw***, Jtsm& H- Wank, Jr, A Vellyw-bslkii Lomj in K,ij'4 i ijlifarnia, Mexico Rfpid 1 .SVmcit J' Siiw.oji 2 ! 2 : 23 Ljypui tm| eovtr iio-ifTn 2 ~iy Vfcflnii| i* Imh^wn WESTERN BIRDS' Volume 5, Number 1, 1974 AGE, SEX, MOLT AND MIGRATION OF DUNLINS AT BOLINAS LAGOON GARY PAGE, Point Reyes Bird Observatory, Box 321, Bolinas, California 94924 Various aspects of the winter biology of Dunlins ( Calidris alpina) have been studied in California by Storer (195 1), Recher (1966), Holmes (1966a, b, 1971), Gerstenberg (1972) and Jurek (1973). Recent studies at Bolinas Lagoon provide information that supplements and in certain details, contradicts previously published accounts. This paper reports on age and sex ratios, molt and migration of Dunlins at Bolinas Lagoon. STUDY AREA AND METHODS Bolinas Lagoon is a 570-hectare estuary at the southern edge of the Point Reyes peninsula on the central California coast. It is shallow with extensive sand and mud flats on which large numbers of shorebirds can be found during most of the year. To estimate the number of shorebirds on the estuary, six censuses per month were taken from June 1971 through May 1972, and usually three but occasionally six censuses per month from June 1972 through May 1974. On each census the estuary was divided into three areas and the birds in each area were counted or estimated simultaneously by three observers. Some censuses included numbers of small sandpipers that could not be separately identified as Dunlin, Least Sandpiper ( Cali- dris minutilla) or Western Sandpiper ( Calidris mauri), but in no census did such observations exceed 20% of the total number. These birds were incorporated into a census total as Dunlins, Least Sandpipers and Western Sandpipers according to the relative abundance of firm identi- fications of these species in the census. Most censuses were taken on flood or ebb tides 1.1 m to 1.7 m above mean low water. Western Birds 5:1-12, 1974 1 DUNLINS AT BOLINAS LAGOON Between October 1971 and April 1972, Dunlins were trapped after dusk in mist nets set across channels and pools in salt marsh where the birds roosted. Trapped birds were weighed to the nearest gram on Peso- la spring balances. The culmen (length from the tip to where the feathers meet the center of the upper mandible) was measured to 0.1 mm with dial calipers. Each bird was banded with a numbered aluminum band on the tarso-metatarsus and a blank aluminum band on the tibiotarsus. Both bands were covered with colored plastic tape to indicate fj^e location and the season of banding and the age of the bird. Birds were considered immature if they had buffy edges on their innermost tertial or inner middle wing coverts, and adult if these feathers were white- or grey- tipped. Molt was recorded for six body regions (crown, upper back, rump, throat, breast and abdomen). The number of growing feathers was estimated in each body area and the molt was scored from 0 to 3 as described in Page (1974, Table 1). The molt score for the entire body is the sum of the different body regions. The flight feathers of the wing were grouped into 10 primaries, 10 secondaries and 5 tertials, including as a tertial the small innermost feather that Holmes (1966a) apparently did not consider a tertial in the Dunlins he examined. Each flight feather was recorded as growing or not growing. In this paper, “season” as used under the heading “Return Rate” refers to the period from June to May of the following year. SEASONAL ABUNDANCE Although the pattern of Dunlin occurrence varied during the study (Figure 1), the birds consistently arrived in late September and were present in the greatest numbers in November. During the period of peak abundance Dunlins were about twice as numerous in 1971 as in 1972 and 1973. During January and February of 1972 and 1974, the Dunlin population ranged from 1000 to 1600 individuals. In January 1973 the Dunlin population decreased from approximately 1000 at the beginning of the month to 300 at the end, probably because of very heavy rains (15 inches in 14 days). During periods of heavy rain, Dun- lins and other shorebirds leave the lagoon at moderate and high tides and feed or roost in nearby pastures. In January 1973 heavy rains ap- parently drove most Dunlins out of the area entirely. Spring migratory waves of Dunlins were apparent in April 1973 and 1974 although not in April 1972 (Figure 1). The magnitude of these waves was small in comparison to those in other species such as the dowitchers (Limnodromm spp) and the Western Sandpiper (Page, Fearis and Jurek 1972). 2 5000 40 00 3 000 2000 1000 2000 1000 0 200 0 1000 0 ire 1 . N Dunl: DUNLINS AT BOLINAS LAGOON umbers of Dunlins at Bolinas Lagoon from September 1971 to May ns are absent from late May until late September. 3 DUNLINS AT BOLINAS LAGOON DETERMINING THE SEX FROM THE BILL MEASUREMENT MacLean and Holmes (1971) found a culmen range of 34.0 mm to 41.0 mm with a mean of 37.2 mm for male Dunlins, and a range of 34.5 mm to 45.0 mm with a mean of 40.5 mm for female Dunlins wintering in western North America. I measured Dunlin specimens in breeding plumage from California at the Museum of Vertebrate Zoology, Berke- ley, and the California Academy of Sciences and obtained similar results. Bill lengths of 87 males were in the range of 33.1 mm to 41.3 mm with a mean of 36.9 mm (S.D.=1.7 mm) and those of 82 females in the range of 35.7 mm to 44.6 mm with a mean of 40.5 mm (S.D.=1.6 mm). Most if not all of these 169 specimens must also have been used by MacLean and Holmes. From these statistics the normal distributions of male and female bill lengths were determined (see Page and Fearis 1971). I found that 70% of the male and 4% of the female Dunlins had a bill length <37.7 mm and 67% of the females and 4% of the males had a bill length >39.8 mm. Twenty-five percent of the males and 28% of the fe- males had a bill length between 37.8 mm and 39.7 mm. If Dunlins with culmens < 37.7 mm are considered males and those >39.8 mm females, in a normally distributed sample with a 1:1 sex ratio the result would be 35% of the birds sexed correctly as males, 34% correctly as females, 2% incorrectly as males, and 2% incorrectly as females. Twenty-seven percent of the birds in the sample would be unsexed, of which 13% are expected to be males and 14% females. In the birds trapped from Oc- tober 1971 to April 1972 the culmens of 24% of the adults and 23% of the immatures were between 37.8 mm and 39.7 mm. As my data suggest that approximately the same number of males and females will remain unsexed if Dunlins with bill lengths <37.7 mm are considered males and >39.8 mm females, I have used these divisions to separate the sexes in this paper. AGE AND SEX COMPOSITION Adult Least Sandpipers and Western Sandpipers leave the breeding grounds before they begin the bulk of their prebasic molt and arrive in California well before the immatures. In contrast, Dunlins undergo most of the prebasic molt on the breeding grounds and the adult and immature Dunlins arrive together in California. Holmes (1966b) states that adult and immature Dunlins arrive in about equal numbers in Calif- ornia. This was based on the occurrence of approximately equal num- bers of Dunlins of both age classes in museum collections (Holmes pers. comm.). But in birds trapped at Bolinas Lagoon in October 1971, im- 4 DUNLINS AT BO LINAS LAGOON matures markedly outnumbered adults (Figure 2). Adults made up 17% of the birds trapped from October to December 1971, 40% from Janu- ary to February 1972, and 45% from March to April 1972. A possible explanation is that immatures are more easily trapped early in the season and are less wary of nets than adults. Later in the season adults and young may perhaps be trapped with similar ease. Differential mortality rates or movements of the two age classes could also affect the observed age ratio change in the Dunlin population between the spring and fall. Male and female Dunlins arrived simultaneously at Bolinas Lagoon in October but males outnumbered females (Figure 2). Of birds trapped and sexed between October and December 1971, only 37% of the adults and 34% of the immatures were females; between January and February 1972, 25% of the adults and 18% of the immatures were females; and between March and April 1972, 46% of adults and 32% of immatures were females. Assuming that there is not an unequal sex ratio in the C. alpina pacifica population as a whole, the uneven sex ratios at Bolinas may indicate geographic or ecological segregation by sex of Dunlins on the wintering grounds. I was unable to trap enough birds to determine when males and females left the lagoon in the spring. MOLT The Dunlin lingers on or near the breeding grounds and molts into its basic plumage (Holmes 1971) whereas the Western Sandpiper (Holmes 1972) and Least Sandpiper (Page 1974) migrate south before molting. Holmes (1971) reported that Dunlins leave the breeding grounds before the prebasic molt is complete but, except for a few early birds, have completed molt on arrival in California. I found some Dunlins in light molt at Bolinas Lagoon in October 1971 but body molt was most in- tense between late October and the third week of November (Figure 3). Growing feathers were apparent in many birds in most or all body areas I examined. Evidently body molt is not complete by the time many Dunlins arrive in California. Molt of flight feathers differed in one respect between Least and Western Sandpipers and Dunlins. None of the 258 immature Dunlins captured between October and December 1971 had new or growing tertials or rectrices. Between 28 September and 6 November, during the height of the first prebasic molt of Least and Western Sandpipers at Bolinas, 8.2% of 61 Western Sandpipers trapped had new or growing ter- tials and 3.3% had new or growing tail feathers, as compared to 78.3% and 30.0% respectively for 217 Least Sandpipers. During the prealter- 5 CL, O O LlI o > O I- o o SQdia Q3ddVdl !N33d3d s: | u C- o x W 39.8 mm females. During much of the 1971-72 season males outnumbered females about 2:1. Immatures were much more abundant than adults from October to December; but in March and April adults and immatures were almost equally abundant. In autumn 1972 at least 32% of the adults and 15% of the immatures banded the previous season returned to Bolinas Lagoon. 10 DUNLINS AT BO LINAS LAGOON In autumn, birds of both age classes underwent some body molt af- ter arriving at Bolinas Lagoon. Adults and immatures underwent a par- tial prenuptial molt in spring in which very few birds replaced any flight feathers. Evidence suggesting migration is much more pronounced in the in- terior of California in spring than in fall conflicts with the previously held view and points out the need for further studies of Dunlin migra- tion in California. ACKNOWLEDGMENTS Many volunteers of Point Reyes Bird Observatory participated in various ways to make this study possible. I would particularly like to thank Lynne Stenzel, Barbara Fearis, Alice Williams, Bev McIntosh and Libby Meyers for helping with the field work on Bolinas Lagoon, Leo Karl, Jane Flurry and Margaret Redwine for helping with the data an- alysis, and Phil Henderson, Pam Kruskal and Bob Stewart for censusing shorebirds in the Point Reyes area. R. T. Holmes, J. R. Jehl, Jr., El- marie Hutchinson, John Smail and Deanna Page read the manuscript and made many helpful suggestions. Logistic support was provided by Craig Hansen through the College of Marin. This is Contribution 100 of Point Reyes Bird Observatory. LITERATURE CITED Gabrielson, I. N. and S. G. Jewett. 1940. Birds of Oregon. James, Kerns and Abbott Co., Portland, Oregon. Gerstenberg, R. H. 1972 . A study of shorebirds (Charadrii) in Humboldt Bay, California. M. S. Thesis, California State Univ. at Humboldt, Areata, Ca. Holmes, R. T. 1966a. Molt cycle of the Red-backed Sandpiper ( Calidris alpina) in western North America. Auk 83 : 5 1 7-5 33. Holmes, R. T. 1966b. Breeding ecology and annual cycle adaptations of the Red-backed Sandpiper ( Calidris alpina ) in northern Alaska. Condor 68: 3-46. Holmes, R. T. 1971. Latitudinal differences in the breeding and molt schedules of Alaskan Red-backed Sandpipers (Calidris alpina). Condor 73:93-99. Holmes, R. T. 1972. Ecological factors influencing the breeding season schedule of Western Sandpipers ( Calidris mauri) in subarctic Alaska. Am. Midi. Nat. 87:472-491. Jewett, S. G., W. P. Taylor, W. T. Shaw, and J. W. Aldrich. 1953. Birds of Wash- ington State. Univ. of Washington Press, Seattle. Jurek, R. M. 1973. California shorebird study. Final report. California Depart- ment of Fish and Game. MacLean, S. F., Jr. and R. T. Holmes. 1971. Bill lengths, wintering areas, and taxonomy of North American Dunlins, Calidris alpina. Auk 88:893-901. Page, G. 1974. Molt of wintering Least Sandpipers. Bird-Banding 45:93-105. 11 DUNLINS AT BO LINAS LAGOON Page, G. and B. Fearis. 1971. Sexing Western Sandpipers by bill length. Bird- Banding 42:297-298. Page, G., B. Fearis, and R. M. Jurek. 1972. Age and sex composition of Western Sandpipers on Bolinas Lagoon. Calif. Birds 3:79-86. Page, G. and D. F. Whitacre. 1975. Raptor predation on wintering shorebirds. Condor 77: (in press). Recher, H. F. 1966. Some aspects of the ecology of migrant shorebirds. Ecology 47:393-407. Strauch, J. G., Jr. 1967. Spring migration of Dunlin in interior western Oregon. Condor 69:210-212. Storer, R. W. 1951. The seasonal occurrence of shorebirds on Bay Farm Island, Alameda County, California. Condor 53:1 86-19 3 . 12 RANGE EXPANSION AND ACTIVITY PATTERNS IN RHINOCEROS AUKLETS J. MICHAEL SCOTT, Department of Zoology, Oregon State University, Corvallis, Oregon 97331 (Present address: P. O. Box 44, Hawaii National Park, Hawaii 96718) WAYNE HOFFMAN, Department of Zoology, Oregon State University, Corvallis, Oregon 97331 DAVID AINLEY, Point Reyes Bird Observatory, Box 321, Bolinas, California 94924 C. FRED ZEILLEMAKER, U. S. Fish and Wildlife Service, William L. Finley National Wildlife Refuge, Corvallis, Oregon 97330 The AOU Check-list (1957) lists Destruction Island in northern Wash- ington as the most southerly known breeding site of the Rhinoceros Auk- let ( Cerorhinca monocerata). Since then and particularly since the late 1960s, several new breeding sites of this species have been discovered in British Columbia, Oregon and California. The status of C. monocerata in the southern part of its range is either changing or at least becoming better known. In this paper we wish to 1) report some additional breed- ing sites in the southern part of this species’ range, 2) summarize all the new records of the past ten years, and 3) comment on the significance of these records. We also compare Rhinoceros Auklet activity patterns during the breeding season in the new southern extreme of their range with their activity patterns farther north. NEW BREEDING SITES FOR RHINOCEROS AUKLETS Browning and English (1968) suspected but could not confirm the nesting of C. monocerata on Goat Island, Curry County, in southern Oregon. On 2 July 1973 we (JMS, WH, CFZ) found a dead nestling on the grassy north slope of Goat Island; a search of several burrows in deep top soil produced two additional nestlings which were photographed (Figure 1). These burrows were situated among those of Tufted Puffins ( Lunda cirrhata) on the same north slope of the island. At sunset on 2 July, Rhinoceros Auklets in breeding plumage began gathering on the water within 200 m of the island and by dark their numbers had in- creased to 30 birds. One hour after dark (22:00) an adult in breeding plumage (but without a brood patch) was caught in a mist net. In addi- tion, Rhinoceros Auklets were observed flying from the center of the island just before dawn. From these observations we estimated a breed- ing population of at least 20 pairs. Observations summarized in Table 1 indicate the probable breeding of Rhinoceros Auklets at Sea Lion Caves, Lane County, and at three other Oregon localities. The observations of adults in nuptial plumage Western Birds 5:13-20, 1974 13 RHINOCEROS AUKLETS and carrying fish in their bills at Sea Lion Caves is evidence of nesting short only of finding an egg or chick. The latter may never be possible at this site because of its inaccessibility. Table 1. Summary of observations of breeding and possibly breeding Rhinoceros Auklets in Oregon 1968-73. DATE LOCALITY 25 March 1968 Goat Island, Curry County July-August 1969 Cape Foulweather, Lincoln County May-August 1969 Yaquina Head, Lincoln County June 1969 Sea Lion Caves, Curry County July-August 1970 Cape Foulweather Summer 1970 Sea Lion Caves Summer 1970, 1971, 1972 Yaquina Head 7 August 1972 16 July 1972 Cape Meares, Tillamook County Sea Lion Caves June 1973 Yaquina Head June 1973 Sea Lion Caves 2 July 1973 Goat Island COMMENTS AND REFERENCE OR OBSERVER One breeding plumage adult in burrow, remains of other breeding plumaged adults (Browning and English 1968). Up to five breeding plumaged adults foraging and resting, photographed from the beach (Hoffman pers. obs.). Groups of up to 25 breeding plumage adults flying in circles immediately off Yaquina Head at dusk (J. M, Scott pers. obs.). At least 20 in caves, 1 with fish in mouth; all in breeding plumage (Crowell and Nehls 1969). Breeding plumaged birds foraging and resting (Hoffman pers. obs.). Rhinoceros Auklets inside Sea Lion Caves (Crowell and Nehls 1970). Breeding plumaged adults observed throughout the summer; evening passing flights in 1971 and 1972 (J. M. Scott pers. obs.). Four breeding plumaged birds flying near Cape at dusk (Hoffman pers. obs.). Three birds carrying food into caves (Crowell and Nehls 1972). Eleven or more breeding plumaged adults flying around Head at dusk (J. M. Scott, W. Hoffman pers. obs.). Three adults in breeding plumage flying into caves at 0900 (R. Olson, P. Rothlis- berg pers. obs.). Two live chicks taken from burrows and photographed, 1 dead chick on ground, up to 30 adults circling at dusk (W Hoff- man, W. Pearcy, J. M. Scott, C. F. Zeillemaker pers. obs.). 14 RHINOCEROS AUKLETS Breeding by C. monocerata at the three other Oregon sites (Table 1) is not as certain as at Sea Lion Caves. At Yaquina Head, Lincoln Coun- ty, where six other species of seabirds nest (Scott 1973), as many as 25 adult Rhinoceros Auklets in breeding plumage were observed for the entire summer in five consecutive years (1969-1973). During these years they were frequently observed in the evenings as they made “passing flights” near the cliffs, a behavioral characteristic of the breeding birds at nesting sites in Washington (Richardson 1961, Scott pers. obs.). Late evening passing flights suggest breeding of Rhinoceros Auklets at Cape Foulweather, Lincoln County, and Cape Meares, Tillamook County. Figure 1. Photograph of nestling Rhinoceros Auklet (Cerorbinca monocerata) taken from burrow on Goat Island, Oregon 2-3 July 1973. Photo by C. Fred Zeillemaker 15 RHINOCEROS AUKLETS In 1966 and 1967 large breeding populations of Rhinoceros Auklets were discovered at two islands in southern British Columbia. Intensive investigation of the seabirds at these islands carried out some years earlier had failed to reveal this species. First, in 1966 Hancock (1970) estimated that 3 ,000 pairs of Rhinoceros Auklets bred at Triangle Island at the northern end of Vancouver Island. The species was not reported in 1949 or 1950 when extensive ecological surveys were conducted there. It seems that such a large population, if present earlier, would have been difficult to miss. Second, in 1967 Campbell and Stirling (1967) estimated that about 50 pairs of Rhinoceros Auklets nested on Cleland Island at the southern tip of Vancouver Island. Previous in- tensive avifaunal work had been conducted on this 8.5 ha island as well, the latest being in 1961, but the breeding of C. monocerata had only been suspected (Hancock 1970). We know of no recently discovered Rhinoceros Auklet colonies in Washington, but there have been in- creases in the population size at Smith Island (D. Manuwal pers. comm.). Osborne (1973) estimated that between 50 and 75 pairs bred on Castle Rock, Del Norte County, California in 1970. This is the first report for breeding Rhinoceros Auklets at that site and is only the second breeding locality for California. At the other California site, South Fara- llon Island (San Francisco Co.) in central California, two and possibly more pairs of Rhinoceros Auklets occupied burrows during the sum- mers of 1972 and 1973 (Ainley and Lewis 1974). Possible disturbance of large numbers of nesting murres and cormorants prevented a search for eggs or chicks. Historically, the Farallon Islands have been the southernmost breeding site of the species. However, the breeding popu- lation was exterminated in 1862 (Grinnell 1926, Ainley and Lewis 1974). The nesting of Rhinoceros Auklets in recent years on this island represents a re-establishment of a former breeding population. The fact that Rhinoceros Auklets nest in burrows, approach their nesting areas only under cover of darkness (Richardson 1961, Bent 1919 but see below) and occur in small numbers in Oregon and California may account for the previous lack of documentation of this species breeding in that area. However, several of the new breeding localities for Rhinoceros Auklets have been well known for an appreciable period prior to the reports summarized in this paper. This is especially true of sites in British Columbia; Goat Island, Oregon; Castle Rock, California (Gabrielson and Jewett 1940, Grinnell and Miller 1944); and the Farallon Islands (Ainley and Lewis 1974). Occurrences at these sites suggest that there has been a real expansion in the range of this species and, in the case of the Farallones, a reoccupation of formerly suitable habitat. Con- struction of a housing development adjacent to a large nesting colony of Rhinoceros Auklets on Protection Island may have caused the relocation of breeding birds to other areas in the Pacific Northwest. In fact, 16 RHINOCEROS AUKLETS Glaucous-winged Gulls ( Larus glaucescens ) banded as nestlings on Pro- tection Island have been found breeding at sites 37 km distant. The range of a species may expand and contract with changing en- vironmental conditions. This has probably occurred and may now be occurring with C. monocerata in the southern extreme of its breeding range. The possible effect of changes in prey species abundance on the numbers of C. monocerata and closely related species in California is discussed elsewhere (Ainley and Lewis 1974). DIURNAL VS. NOCTURNAL ACTIVITY PATTERNS IN BREEDING RHINOCEROS AUKLETS Observations of C. monocerata during daylight on Goat Island (Scott, Hoffman and Zeillemaker pers. obs.) and on South Farallon Island (Ain- ley and Lewis 1974 and below) and of them bringing food to suspected nest sites at Sea Lion Caves during daylight (Table 1) conflict with our previous observations at Destruction Island, Washington (1970-73), and those made elsewhere by others. Historically, C. monocerata has been reported to be strictly nocturnal at the breeding grounds (Bent 1919, Richardson 1961, Cody 1973). Nocturnal activity in small auklets, in- cluding Rhinoceros Auklets, is supposedly a strategy to avoid predation or piracy by gulls while food is being carried to chicks (Lack 1966, Cody 1973). However, the occurrence of diurnal activity in C. monocerata brings to question the factors selecting for nocturnal activity in this species. If this behavior is to avoid predation or piracy, one might ex- pect a relationship between diurnal activity in the auklets and charac- teristics of the predator, perhaps size or temperament. Observations of Rhinoceros Auklet/gull interactions on South Fara- llon were made a few hours daily for two months in 1972. There, even though as many as five Rhinoceros Auklets carried on diurnal activity within 4 m of active Western Gull ( Larus occidentalis ) nests, no preda- tion attempts were made toward them. There was, however, interaction, but only after the gull chicks hatched when the adult gulls become very territorial. During this time gulls were observed displacing Rhinoceros Auklets a total of six times. However, during the same period Rhinoc- eros Auklets were displaced four times by Tufted Puffins, four times by Brandt’s Cormorants (Phalacro corax penicillatus ) and once by Common Murres ( Uria aalge). Gulls also displaced Tufted Puffins once, Pigeon Guillemots ( Cepphus columba ) four times, and were unsuccessful in two attempts to displace Brandt’s Cormorants. On one occasion gulls reached into a cavity to pull out a Rhinoceros Auklet; on another they pulled an adult Pigeon Guillemot from its cavity. In neither case was the vic- tim harmed. In contrast, Western Gulls on the Farallones actively pur- sue and capture smaller Cassin’s Auklets ( Ptychoramphus aleuticus ) and storm-petrels ( Oceanodroma sp.) that expose themselves during daylight (Manuwal 1972, Ainley et al. 1974). 17 RHINOCEROS AUKLETS We observed no interaction of the diurnal Rhinoceros Auklets with Western Gulls at Sea Lion Caves. In this locality the auklets can ap- proach their nest sites directly from the sea and at least 15 m below the level of the gull colony. Gull harassment is further reduced because the flight of Rhinoceros Auklets into the caves is swift and close to the water, and because gulls do not frequent the dark interior of the caves. It is of interest that diurnal activity in the auklets has been observed only in that part of their range where Western Gulls and not Glaucous- winged Gulls are known to breed. Glaucous-winged Gulls average some- what larger in size than Western Gulls, and there is a tendency in both species for birds in the northern part of the breeding range to be larger; however, there is considerable variation in size even at a single colony (Dwight 1925, Ridgway 1919). From British Columbia south to the Farallones there is an almost complete overlap in the size of these two species, and no significant differences in body or bill size were noted at the sites sampled (Table 2). Overlap is greatest on Destruction Island where they interbreed (Scott 1971, Scott and Wiens unpublished data). This lack of difference in predator size at the different sites suggests that some other factor must be responsible for the observed differences in Rhinoceros Auklet nocturnal/diurnal activity patterns. Bent (1919) in- Table 2. Body measurements of Western Gulls ( Larus occidentalis) and Glaucous- winged Gulls (L. glaucescens) from several sites where they are known to occur syntopically with Rhinoceros Auklets ( Cerorhinca monocerata). SPECIES & LOCALITY WEIGHT, g BILL DEPTH, mm CULMEN LENGTH, mm Glaucous-winged Gull: Mandarte Island, British Columbia 1 x=1010 S.D.=136.12 Range=7 30-1400 n=110 No data No data Destruction Island, Washington 2 x=1006 S.D.=330.4 Range =8 60-1 190 n=5 x=19.31 S.D.=1.28 Range=17.7-21.5 n=9 x=53.9 S.D.=4.29 Range=47.0-59.8 n=9 Western Gull: Destruction Island, Washington 2 x=979 S.D.=73.29 Range=9 00-1 150 n=10 x=20.1 S.D.=1.6 Range=17.3-22.5 n=30 x=55.5 S.D.=3.2 Range=5 1.5-62.5 n=30 Farallon Islands, California 2 x=1019 S,D.=59.43 Range=800-1 190 n=38 x=20.72 S.D.=1.66 Range=18.2-23.0 n=30 x=55.8 S.D =3.09 Range=48 .0-5 9.5 n=30 1. John Ward pers. comm. 2. J. M. Scott and John A. Wiens unpublished data. 18 RHINOCEROS AUKLETS dicates that Western Gulls are more predaceous on marine birds at breed- ing colonies than are Glaucous-winged Gulls. This would suggest that if gull interference or predation were the primary factor selecting for nocturnality in Rhinoceros Auklets, they would be least likely to be di- urnal where they were syntopic with Western Gulls. In fact, just the opposite was true. However, the fact that Rhinoceros Auklets were observed carrying food to young only at the Sea Lion Caves site, where harassment by gulls can be avoided, indicates that piracy by gulls may restrict Rhinoceros Auklets to nocturnal feeding of their young. The diurnality of Pigeon Guillemots, despite their being somewhat smaller than Rhinoceros Auklets and the fact that they too carry food in their bills to their nestlings, may be explainable by Guillemots being quicker and more maneuverable in flight, perhaps as a result of their lower wing- loading. Thus the lack of diurnal feeding of young by Rhinoceros Auklets at all but one site seems to be the result of piracy on the adults by gulls. However, the diurnality of adults without food in their bills in the south- ern extreme of their breeding range and their complete nocturnality in the north remains unexplained. The answer may lie in regional differ- ences in the offshore distribution and availability of food resources. ACKNOWLEDGMENTS We wish to thank the U. S. Coast Guard and the Oceanic Society for logistics to the Farallones and to Destruction Island. The Farallon Re- search Station work in 1972-73 was made possible by generous financial support from the Dean Witter Foundation, the Charles E. Merrill Trust, the Lucius Beebe Foundation and many private individuals. The co- operation of the U. S. Fish and Wildlife Service and particularly R. D. Bauer at the Farallons was appreciated. T. J. Lewis and S. Morrell con- tributed observations on the Farallones. This is Contribution 82 of Point Reyes Bird Observatory. The work in Washington and Oregon was fund- ed by a grant from the Frank M. Chapman Fund to the senior author. LITERATURE CITED Ainley, D. G., and T. J. Lewis. 1974. The history of Farallon Island marine bird populations, 1854-1972. Condor (In press). Ainley, D. G., S. Morrell, and T. J. Lewis. 1974. Annual cycles of storm-petrels on the Farallon Islands. The Living Bird (In press). American Ornithologists Union. 1957. Check-list of North American birds. Fifth ed. Am. Ornithol. Union, Baltimore, Md. Bent, A. C. 1919. Life histories of North American diving birds. U. S. Natl. Mus. Bull. 107. 19 RHINOCEROS AUKLETS Browning, M. R., and W. English. 1968. A breeding colony of Cassin’s Auklets and possible breeding of the Rhinoceros Auklet on Goat Island, southeastern Oregon. Condor 70:88. Campbell, R. W., and D. Stirling. 1967. Notes on the natural history of Cleland Island, British Columbia, with emphasis on the breeding bird fauna. Rept. Provincial Mus., 1967, Victoria. Pp. 32-41. Cody, M. 1973. Coexistence, coevolution and convergent evolution in seabird communities. Ecology 54:3 1-44. Crowell, J. B., and H. B, Nehls. 1969. Nesting season. Northern Pacific Coast re- gion. Audubon Field Notes 23:84-88. Crowell, J. B., and H. B. Nehls. 1970. Nesting season. Northern Pacific Coast re- gion. Audubon Field Notes 24:708-711. Crowell, J. B. s and H. B. Nehls. 1972. Nesting season. Northern Pacific Coast re- gion. Birds 26:893-897. Dwight, J., Jr. 1925. The gulls (Laridae) of the world: Their plumages, moults, variations, relationships and distribution. Bull. Am. Mus. Nat. Hist. 52:63-401. Gabrielson, I. N., and S. W. Jewett. 1940. Birds of Oregon. Oregon State Mono- graphs, Studies in Zoology No. 2. Grinnell, J. 1926. The evidence as to the former breeding of the Rhinoceros Auk- let in California. Condor 28:37-40. Grinnell, J., and A. H. Miller. 1944. The distribution of the birds of California. Pac. Coast Avif. No. 27. Hancock, D. 1970. New Rhinoceros Auklet colony for British Columbia. Con- dor 72:491. Lack, D. 1966. Population studies of birds. Clarendon Press, Oxford. Manuwal, D. A. 1972. The population ecology of Cassin’s Auklet on Southeast Farallon Island, California. Ph.D. Dissertation, Univ. California, Los Angeles. Osborne, T. O, 1973. Recent nesting of the Rhinoceros Auklet in California. Condor 75:463-464. Richardson, F. 1961. Breeding biology of the Rhinoceros Auklet on Protection Island, Washington. Condor 63:456-473. Ridgway, R. 1919. The birds of North and Middle America, Part VIII. U. S. Natl. Mus. Bull. 50, Scott, J. M. 1971. Interbreeding of the Glaucous-winged Gull and Western Gull in the Pacific Northwest. Calif. Birds 2:129-133. Scott, J. M. 1973. Resource allocation in four syntopic species of marine diving birds. Ph.D. Dissertation, Oregon State University, Corvallis. 20 NOTES ALBINO ROCK WREN DAVID S. JOHNSTON and ERIC V. JOHNSON, Biological Sciences Department, California Polytechnic State University, San Luis Obispo, California 93401 Albino Rock Wren (Salpinctes obsoletus) photographed 28 May 1974 on a rocky serpentine slope at Laguna Lake Park, San Luis Obispo, California. First noted 17 December 1973 on the Morro Bay Christmas Bird Count, the bird sub- sequently established a territory. From its song and actions we presumed it to be a male. A second albino seen on the same slope the day of the Christmas count was not seen again. The bird pictured was carrying food the day it was photo- graphed, but we were unable to locate a nest. The only marks visible on this bird were extremely pale brownish barring on the wings and tail. It was not pos- sible to get close enough to determine exact soft part color; the eye appeared dark, the bill and feet pale. Western Birds 5:21, 1974 Photo by David S. Johnston 21 NOTES BREEDING RECORD FOR THE SEMIPALMATED PLOVER AT OCEAN SHORES, WASHINGTON JAMES R. MORRIS JR., 1700 Pebble Drive, Greensboro, North Carolina 27410 On 23 June 1973, at Ocean Shores, Grays Harbor County, Washington, Eugene Hunn and I observed an adult Semipalmated Plover (Charadrius semipaltnatus) in breeding plumage calling incessantly and diving at us as close as 15 feet. The bird seemed to be defending a territory in a flat sandy area covered with pebbles and broken seashells, surrounded by sand dunes, and situated near the tip of a mile- long sand spit extending from the southern tip of the Ocean Shores peninsula into the mouth of Grays Harbor. We searched for eggs and young but found none. On 1 July 1973, I returned to the same location and found two adult Semipal- mated Plovers defending the same territory. In the center of the flat sandy area stood one downy young Semipalmated Plover, which immediately ran into the dune grass as I approached. I watched the young plover for approximately 15 seconds with 10 power binoculars from 30 feet. Within one hour after this sight- ing, I made a rough sketch of the young plover from memory. Joseph R. Jehl Jr. has examined this sketch and agreed with the identification. Eighty yards from this first pair of adult Semipalmated Plovers, I observed another pair of adults defending a similar territory, but I could not find eggs or young. On 7 July 1973, I returned with Glen Hoge to confirm my previous findings. We observed the first pair of adults and their one downy young at the same loca- tion. We also observed the second pair of adults defending the same territory as previously, but this time we observed one downy young Semipalmated Plover there also. We estimated that the downy young of this second pair was approximately one week older than the downy young of the first pair. It would have been possible for more than one downy young per pair of adults to have been present, since the young were difficult to see amid the dune grass and the gravel. However the maximum number of young observed was two, one for each pair of adults. Also breeding on the mile-long sand spit were approximately three pairs of Snowy Plovers (C. alexandrinus) and one pair of Killdeer (C. vociferus). The color- ation of the two downy young Semipalmated Plovers precluded any possible con- fusion with the downy young of these other two species of breeding plovers. The brown upperparts of the downy Semipalmated Plovers distinguished them readily from pale-backed downy Snowy Plovers, which both Glen Hoge and I have seen in the area. The downy young Semipalmated Plovers also lacked a black stripe around the neck and a long downy tail characteristic of downy Killdeer (Gabrielson and Lincoln, The Birds of Alaska, 1959). This is the first breeding record for the Semipalmated Plover in Washington. Larrison (Washington Birds, Their Location and Identification, 1968) records the Semipalmated Plover as a migrant and a non-breeding summer resident in Washing- ton. The A.O.U. Check-list of North American Birds (1957) records the southern- most breeding range in western Canada as the Queen Charlotte Islands and north- western British Columbia. Godfrey (Birds of Canada, 1966) cites a breeding record for south-central interior British Columbia. An extralimital breeding record for the Semipalmated Plover for Vancouver, British Columbia in 1967 is described by Campbell (Murrelet 53:11-12, 1972). In late June 1974 I returned with Glen Hoge to check the sand spit for breed- ing Semipalmated Plovers. Numerous dune-vehicle tracks were discovered through both previous nest sites. No Semipalmated Plovers were found. 22 Western Birds 5:22, 1974 NOTES A YELLOW-BILLED LOON IN BAJA CALIFORNIA, MEXICO DAVID SIMON and WINIFRED F. SIMON, 3715 Pattison, Eugene, Oregon 97402 Late in the afternoon of 30 June 1973 we observed a loon offshore at Pete’s El Paraiso approximately 9 miles by road north of San Felipe, Baja California, Mexico. Upon setting up our 20x spotting scope we were amazed to discover that it had a very large, very yellow bill. The bill was pale sulphur or butter yellow becoming white at the tip. There were dark brown markings extending approximately a fourth of the total length of the bill from the base and along the gape as well. The gape markings appeared to be on both mandibles. The bill was very long and high at the base. About a third of the way from the base, the lower mandible began to angle up; the bill thus appeared to come to a long attenuated point. The culmen was straight along most of its length angling up slightly at the tip. The bird seemed very large with a dis- proportionately thick neck. It was assuming a black and white plumage. The head, throat and upperparts were mostly blackish, but some white still remained on the posterior cheek and auricular areas, and the wing coverts and scapulars bore four rows of large white squares. Thus the bird was at least two or more years old. We feel that we conclusively identified a Yellow-billed Loon ( Gavta adamsii) on the basis of the foregoing description. Unfortunately we were unable to photo- graph the bird, nor were we able to relocate it on a return trip there the following weekend. This sighting is remarkable in several respects. It is the southernmost North American record of the species. It is only the second known occurrence in Mexi- co, the first being a specimen taken in extreme northwestern Baja California (Jehl, Condor 72:376, 1970). This sighting in the warm Sea of Cortes is one of the very few records away from the Pacific. The date is unusual in that summer records are scarce in California, Oregon and Washington. Finally, most records in the United States south of Alaska are of birds in brown plumage. Sketch by Tim Manolis Western Birds 5:23, 1974 23 Peregrines at Morro Rock Learn About Falconry . . . Is falconry in California a legitimate and wise use of the raptor resource? Are falconers law abiding, re- sponsible sportsmen? Is there evidence that harvest- ing adversely affects birds of prey? Read how protectionists and falconers answer these questions. . . . THEN DECIDE FOR YOURSELF Send $1 to SPBP, Box 891 Pacific Palisades , CA 90272 USA 24 M-jnincrifiti ihou.ld be wn* 1 b Ahn M. Craig, ilM 9ft NuiUJIjpV SCHtfe, ClilCO, CA 9J926, l : w tn»mi of *syl* tea Ctmt* HVromr Birds (6 jpfi. mimed amilaJil# «’im o».t fmm the fediiorJ arid edit' Slj /*- Marttfaft ini d„ 1922 1-u-niEul’ilf from Americati tn-ftiHjit- of BinJp'gtcil i^-ipnra, 191*1 Wbeoftkln Atft MW t WaahliipEDU, DC 2MU 6 for Sir. (Ji ■ j . i‘ -peci'ire tlrtifft! Iftal air teJ u|hmi field fiiiiitB of hkdi, tbit areboib uadeb BfjTTj ittblf anvl iirHib to iquiteiiri |iu) din- rc’-ik* 1 inulE rii «tle6l(|lc iiicTiuurc, Appropriate copiiia include Jisir ibu don* m%aJri<.m F staH** UdlAtHor, ecology, papulation dynamrci* habitat rcqmrEnlcnta im; eftem elf P>li U lli ion, hm! ic£hwifu«ft for iJenyfy^Bi, ietiMU%, mkia 4 fe,-'i-i mi: nuf pl«ti4> gHphiftjg bffihl to rhe field. PapeRs df grfiCot iniWett 'Will Lie dtraildcferl tegsrdfrttf of [heir gBQ^phk firsgin, bur p .1 r nt 1 1 Fad '. desired are papers dealing with studies leeomp Uijied m at beaeiniK' on Hueky Mountain itate* and prqvkSe* westward, uidikSin>' Alaska anil lUwaiijadjHitTiil! puTrtitfna nf ihe Pkrific Heeid anil Msnii:o. ami ufouin Tcmi, Atjlblvx are ptOvklcd SO free teprmls of eidi ppper . Adibtinn.il re prints tan be ordered si mu bur'* tfijmwe from ilie Editor wfcrn proof k rcwmoJ or earlie r, Good photographs of rare and unusual birds, mu crompanJed by eh in'tide but with option mkliiiling: ipetiin. dalr, IouhImv Ami other pcrcmeni Iftformatloo, ahlJiiid be iubEnktcd t Jti Atu^ld Si 1 i all, OGH N. CauidtJi Dfiw. Revedy ililis. CA $01 IQ, Send -tyre btrd resorts for California Mi Jos Winlei Hriint licvn Hkd Ob Odfi-Elniy, Bo 1 121, ftdlirui, CA 94924 : ict Calii »ird«. irlil^I Kb Fur Arltofu. send re* ports to Ruber 1 A. Wkirfuan,, 4619 E-AumJIll L-uur. A 7 55018. ■ MembffljLlp doe* afill duir®® of MjiJres th-Ould be «nt to l.Uffiiril R, Lyonia TrnsLiEcr k Pen t Of tike. Boa. 369, Del Mar, Cdifomin 9JJPT-4. ClflfilOl Af RieinlW’ ih|p fill tnduiJe -v.i j . >iTi priu n tit Wotzrn Birth- > Pairotl* SKJllrtj Life, £150; Svpskini’il, fftl annually Cu'iitr^uAtu Sin «inua% Regular, $3 annually. Make check* payahtc fp CalK&roifli Field 11m ilhmlog^rl. tttrsi alirj ctuirribulim ni^ ate Miac JeduLrdbic to the rateilt nftb^ed by Saw. FI n'U issiiea of Ciiifnn m Bit AVifm? Kitji lire AvailiblCAT $ 4 iP 0 fur Volume ] iNnirtbrn 2 , J am| 4 lQ7qj, turn for Voltntte I fe* *t>luttn= frt Vdlunse 3 (19723 mm\ Volume I ( 1973 ) Qtiiff from differ^ R l.yons. TrcuHirirr. Pml OfJfiue Bcnfi J 09 , Ueli Mst, CAtlfiwntii $2014 jiavable t o CfrllFimiki Pleld Omit HolsiyiiiiE- . WESTERS HIHDS ADVERTISING RATES AND EPECIF rCATPONS Full P^e 4 \ fid /4 inilift Sfifl per ssue ?ZCn 1 po year Half ^t|r 4 n ? • 1/8 idu E W pet wae A E 30 prr yw QriijirEer Page 4 k i H ] /1 6 cbis- S 30 pet tiraie S 1 1 fl per yea? Offset printing, uik cofumn per page. 4 imdiet- x-tde. tTicrhsy, btack and white phoeoi Me Aveptihlr. katf tone uieeti III line, Pboifr-feady rnpy U re- 4iue$tctl. If iiiin K tucit '.^pwible. extra i-liar^c* for typeeuing will, be made & folloiri: 1 15 fall poge^ Si 0 half pagr + 55 quoTT-cr pogc. Send cupy with rcaih- lance to Clifford tt. L>oai, P. ol Box Dd Mar, CnIET. 92014 , uiid makr- checks piyiitiJc to ("alii'umia iPS«S,i Omuhiriogiftt. A ' S'!*- comiuk-ioo ek allowed for sjJelSele*