DAN L. REINKING and STEVE N. G. HOWELL, Point Reyes Bird Observatory, 4990 ShorelineHighway, StinsonBeach, California94970 (currentaddress of Reinking:George M. SuttonAvian ResearchCenter, P.O. Box 2007, Bartlesville, Oklahoma 74005-2007)
At 1415 on 2 November 1991 we found an Arctic Loon (Gayla arctica sensustricto) at Abbott'sLagoon, Point ReyesNational Seashore, in Marin County,California. We observedthe bird for aboutan hour at rangesdown to about250 m with binocularsand spottingscopes. It wasa clearday, and we had the sunat our backs.After completingfield notes and sketches,we returned home to consultthe literature and notify other birders. We returned the following morning and, with several other birders, soon located the loon and observed it for over 2 hours. Additional notes were taken as the bird swamintermittently to within 100 m and then farther out into the fog. The followingdescription and Figures2 and 3 are derivedfrom our notes and sketches taken from 1415 to 1515 on 2 November and from 0845 to 1100 on 3 November.The bird was last reliablyreported on 17 November.Other observersphotographed and videotaped(Figure 1) the bird, and the identificationhas been acceptedby the California Bird Records Committee. The bird initiallysuggested a Common Loon (G. iramet), owing to its steepforehead, somewhat flattened crown, and largishbill, but was obvi- ouslysmaller with plumagemore variegatedthan a CommonLoon, two of whichwere presentduring the observation.The crown,nape, and hindneck were pale slaty gray in contrastto the blackishupperparts and forehead. Pale-tippedmantle feathersformed whitish barring on the upperparts, which is characteristicof juvenalplumage. On 2 November,and for much of the time on 3 November,the lower face, throat, foreneck, and chest appearedwhite. From closerviews on 3 November,however, we noted that the throatand foreneckwere cloudedwith palegray; seen in goodlight, the white face contrastingsubtly with the pale gray throat recalledthe pattern of an Arctic Tern (Sterna paradisaea).The chest and underbodywere white, with head-onviews revealing a slightcontrast between the dusky foreneckand white chest.Shadowing suggested a chinstrap,but seenin directlight the forenecklacked this feature. The moststriking feature of the birdwas the amountof whiteshowing on its flanks.When it wasactively swimming and diving,the whitewas limited to patchesflaring up at the rear,suggesting those of a Townsend'sShearwa- ter (Puffinusauricularis) or Violet-greenSwallow (Tachycineta thalassina), as shownin Figures1 and 2, figure1 of McCaskieet al. (1990), figure4 of Applebyet al. (1986), and plate 42 of Harrison(1987). When the bird was more relaxedor sleeping,its wholeside up to and alongthe foldedwing showedwhite abovethe waterline,like a TuftedDuck (Aythyafuligula), as shownby Figure3, plates187 and 190 of Applebyet al. (1986), and plate 10 of Walsh(1988). Thispattern was in obviouscontrast to that shownby relaxedor sleepingPacific Loons (G. pacifica),one adultand one juvenile of whichwere also present on the lagoon.These only rarely showed any white Western Birds 24:189-196, 1993 189 ARCTIC LOON IN CALIFORNIA
abovethe waterline,and that wasrestricted to a relativelysmall area of their midsection. The crown, nape, hindneck,and upperpartsof the Arctic Loon were noticeablydarker than thoseof the juvenilePacific Loon, with the Pacific Loon also showing less contrast between the hindneck and back. The upperpartsof the adult Pacific Loon were similarin shadeto those of the Arctic Loon. On one occasion the Arctic Loon could be seen with the two Pacific Loons in the same spottingscope field, allowinga direct sizecomparison. The ArcticLoon appearedabout 10% largerthan the juvenilePacific Loon, butwas only slightly larger than the adult.The headand billappeared larger in the ArcticLoon butthe differenceswere not striking.perhaps because of a similarbill-to-head proportion. McCaskie et al. (1990) noted that this differencewas not a particularlyuseful one for separatingArctic and Pacific loons.
TAXONOMY AND DISTRIBUTION
Until recently,the Pacificand Arcticloons have usuallybeen considered conspecific,with the breedingranges of the three subspeciesdistributed in a brokenring aroundthe North Pole: (3. a. arctica, breedingfrom northern Europeto westernSiberia. (3. a. viridigularis,breeding in easternSiberia and locallyin westernAlaska. and (3. a. pacifica, breedingin northwestern North America (westfrom Hudson Bay) and northeasternSiberia (AOU 1983, Cramp and Simmons 1977, Walsh 1988). Thus viridigularis and pacifica are sympatricin eastern Siberia and western Alaska (Walesand Cape Krusenstern,Douglas and Sowl 1993).
Figure1. ArcticLoon at Abbott'sLagoon, Marin County,California, 4 November 1991 Note headshape and whiteflank patch. Videotape by Leslie Lieurance
190 ARCTIC LOON IN CALIFORNIA
Portenko (1981) reported no intergradesbetween oiridigularisand pacificain their zone of sympatryin easternSiberia, although he recog- nizedthat the two formsoccur "under different ecological environments," the former occupyingmore inlandlocations in the forestbelt and tundra, the latterareas close to the coast.Bailey (1943) reportedboth •iridigularis and pacifica from westernAlaska but notedtwo specimensthat "are not typicaland may be intergrades."Storer (1978) discussedreasons for not consideringpacifica specifically distinct, including evidence of intergrades between •iridigularis and pacifica. The general trend, however,since Portenko(1981) has beento considerpacifica specifically distinct, a view adoptedby the AOU (1985). In winter,Arctic Loons occur south to southwesternEurope, the Aral Sea (nominatearctica), and Japan (viridigularis)(AOU 1985, Cramp and Simmons1977, Dement'evand Gladkov1951; seemap in Walsh1988). We believethe ArcticLoon at Abbott'sLagoon to representthe firstvalid recordof the speciesin NorthAmerica south of Alaska,except possibly for
Figure2. Arctic Loon at Abbott'sLagoon, Marin County, California,3 November 1991.
Sketch by Steve N. G. Howell
191 ARCTIC LOON IN CALIFORNIA one sketchedand describedfrom Massachusetts(Evered 1985). The only previousvalid extralimital record for theArctic Loon is of onecollected near AdmiraltyIsland, Alaska, in 1948 (Walsh1988). The identificationof supposedArctic Loons from British Columbiahas been discredited (Campbellet al. 1990). A secondArctic Loon was reportedfrom Morro Bay, California,from 7 to 23 December1991 (T. Edelland G. Smithpers. comm.). This record is still under considerationby the CaliforniaBird RecordsCommittee (McCaskie1992).
IDENTIFICATION SUMMARY
Loon identificationhas been the subjectof numerouspublications in recent years (e.g., Stallcup1983, Walsh 1984, 1988, Evered 1985,
Figure3. Comparisonof sleepingjuvenile Arctic Loon (upper)and juvenilePacific Loon (lower)at Abbott'sLagoon, 3 November 1991. Sketch by Steve N. G. Howell
192 ARCTIC LOON IN CALIFORNIA
Applebyet al. 1986, Harrison 1987, Harris et al. 1989, Roberson1989, Schulenberg1989, Kaufman1990, McCaskieet al. 1990). Separationof Arcticand Pacificloons, however, has remainedsomewhat poorly defined. We here discussseparation of these two forms in juvenal and basic plumages. The ArcticLoon averageslarger than the Pacific,but the two do overlap (Walsh1988, Schulenberg1989). Size, therefore,is of limiteduse for field identification,although when severalbirds of two or more speciesare togetherit may be of somevalue. The head of an Arctic Loon tends to be flatter than that of a Pacific, which is puffy and rounded(McCaskie et al. 1990). This characteristicis ephemeral,however, depending on the activityof an individualbird (such as neck-craningbefore a dive),but often may be useful. In alternateplumage, the crownand nape of the PacificLoon appear pale silverygray, paler than in the ArcticLoon. Whetheror not thistrait is of use for separationof birdsin juvenal or basicplumages has not been addressedin the literature,although such a differencebetween the juvenile Arcticand juvenilePacific loons at Abbott'sLagoon was apparent. The most strikingplumage feature distinguishing the Arctic and Pacific loonis the extentand purity of whitevisible on the flanks:in all comparable postures,significantly more white is visibleon ArcticLoons. A PacificLoon
Figure4. Categoriesof chinstrapon basicand juvenai-plumaged loons. A, indistinct (two examples);B, distinct. Sketch by Steve N. G. Howell
193 ARCTIC LOON IN CALIFORNIA
ridinghigh in the water or preeningcan showa moderateamount of white abovethe waterline(see figure 3 in McCaskieet al. 1990), but its flanksare mostlysooty brownish, in contrastto the cleanunbroken white flanksof the Arctic Loon, in which the white extendsup to the line of the closedwing. Note alsothe upwardflaring of the white at the rear of Arctic Loon (see plate 10 in Walsh 1988). The bird's posturemust be assessed,as loons often roll on the water and then may appear to show extensivelywhite sides. Other plumagecharacteristics separating the Arcticand Pacificloons are the band of dark feathersforming a chinstrapon most PacificLoons in basicplumage, absent on most if not all Arctics,and the dark band across the vent of the PacificLoon in all plumages,faint or absentin the Arctic Loon (Walsh 1988). Roberson's(1989) photographsof Pacific and Arctic loon specimens illustratethese features.We found, however,that one of the "Arctic" Loons in thesephotographs is actuallya PacificLoon. This bird is the top "Arctic" Loon in figures1 and 4, the bottom "Arctic"Loon in figure2, and the right- hand "Arctic"Loon in figure 3. We reidentifiedthe bird by usingWalsh's (1988) measurements.Its exposedculmen measured 55.3 mm, closerto Walsh'smean of 52.7 mm for G. pacifica than to that of 64 mm for G. a. viridigularis.The bill depth of 13.6 mm approximatesthe mean of 14 mm givenby Walsh for the Pacificwhile fallingbelow the range (15-
A B C F•õure5. Cateõodesof ve•tstrapon basica•d juve•ile-plumaõed1oo•s. A, partial;B, complete(pale brown); C, complete(dark brown). Sketch by Steve N. G. Howell 194 ARCTIC LOON IN CALIFORNIA
20 mm) listedfor the Arctic.Similarly, the tarsusmeasurement of 71.6 mm agreeswith the meanof 70 mm for the Pacificand falls just below the range (72-91 mm)for viridigularis.Also note the indistinctchinstrap on thisbird in Roberson's(I989) figure2 and the partialventstrap visible in figure3. His figure2 andespecially figure 4 showthat the birdalso lacks white flank patches. Our examinationof nearlyI50 PacificLoon and 6 ArcticLoon speci- mens at the California Academy of Sciences,San Francisco,and the Museumof VertebrateZoology, University of California,Berkeley, sheds furtherlight on the usefulnessof the chinstrapand ventstrap for identifica- tion. (Determiningthe presenceor absenceof a ventstrapon a loon is extremelydifficult in the field.)We classifiedbirds in juvenal,basic, and alternateplumages as having no, indistinct,or distinctchinstraps, as well as havingno, partial,complete pale brown, or completedark brown ventstraps (Figures4 and5). We foundthat 91% of PacificLoons in basicplumage and 54% of thosein juvenalplumage had indistinctor distinctchinstraps. All PacificLoons examined had at leasta partialventstrap, and 90% of these showeda completeventstrap; 93.5% of juvenileshad a completepale brown ventstrap,whereas 69.5% of Pacific Loons in basic or alternate plumagehad a completedark brown ventstrap. No ArcticLoons had even an indistinctchinstrap, whereas 5 of 6 showeda partialstrap at the sidesof the vent.Table I summarizesthe presenceand extent of thesecharacteris- ticson the specimenswe examined. Now that criteria for the identification of Pacific and Arctic Loons in all plumageshave been established, it will be interestingto seeif ArcticLoons are more regular on the West Coast than the two recordsfrom late fall I99I would indicate.
Table 1 PlumageCharacteristics of Pacificand ArcticLoons
Pacific Loon Arctic Loon
Juv. Basic Alt. Basic Alt. Feature n=46 n=44 n=51 n=5 n= 1
Chinstrapa None 21 4 5 -- Faint 25 14 -- 0 -- Obvious 0 26 -- 0 Ventstrapb None 0 0 0 1 0 Partial 0 4 10 4 c 1c Complete(pale brown) 43 12 3 0 0 Complete(dark brown) 3 28 38 0 0
øSeeFigure 4 for examplesof chinstraps. bSeeFigure 5 forexamples of ventstraps. eVentstrapsin Arctic Loons were limited to 3 cm or lesson the sidesof the vent and were relativelyindistinct.
195 ARCTIC LOON IN CALIFORNIA
ACKNOWLEDGEMENTS
We thank StephenF. Bailey at the CaliforniaAcademy of Sciencesand Ned K. Johnsonat the Museumof VertebrateZoology for accessto loon specimens.Jon Dunn and MichaelPatten providedhelpful comments on an earlier draft of this paper.Leslie Lieurance provided the videotapedimage.
LITERATURE CITED
AmericanOrnithologists' Union. 1983. Check-listof North AmericanBirds, 6th ed. Am. Ornithol. Union, Washington,D.C. AmericanOrnithologists' Union. 1985. Thirty-fifthsupplement to the A.O.U. Check- list of North American Birds. Auk 102:680-686. Appleby,R. H., Madge, S.C., and Mullarney,K. 1986. Identificationof diversin immatureand winter plumages.Br. Birds79:365-391. Bailey,A.M. 1943. The birdsof Cape Princeof Wales,Alaska. Proc. Colo. Mus. Nat. Hist. 18:1-113. Campbell,R. W., Dawe, N. K., McTaggart-Cowan,I., Cooper,J. M., Kaiser,G. W., and McNall, M. C. E. 1990. The Birdsof BritishColumbia, vol. 1. RoyalBr. Columbia Mus., Victoria. Cramp, S., and Simmons,K. E. L. (eds.).1977. Handbookof the Birdsof Europe, the MiddleEast, and North Africa,vol. 1. OxfordUniv. Press,Oxford, England. Dement'ev, G. P., and Gladkov,N. A. 1951. Birds of the Soviet Union. English translation,Israel Program for ScientificTranslations, Jerusalem, 1966. Douglas,H., and Sowl, K. 1993. Northeasternextension of the breedingrange of the Arctic Loon in northwestern Alaska. W. Birds 24:98-100. Evered,D. S. 1985. Pacific(and Arctic) Loon identification:Difficulty, unfamiliarity and a little bit of confusion. Bird Obs. E. Mass. 13:10-14. Harris, A., Tucker,L., and Vinicombe,K. 1989. The MacmillanField Guide to Bird Identification.Macmillan, London. Harrison,P. 1987. Seabirdsof the World. ChristopherHelm, London. Kaufman,K. 1990. A FieldGuide to AdvancedBirding. Houghton Mifflin, Boston. McCaskie,G. 1992. The winter season.Southern Pacific Coast region. Am. Birds 46:313-318. McCaskie,G., Dunn, J. L., Roberts,C., and Sibley,D. 1990. Noteson identifying Arctic and Pacificloons in alternateplumage. Birding 22:70-73. Portenko,L. A. 1981. Birdsof the ChukchiPeninsula and WrangelIsland, vol. 1. Englishtranslation, Amerind Publ., New Dehli, for the SmithsonianInstitution. Roberson,D. 1989. More on Pacificversus Arctic loons. Birding 21:154-157. Schulenberg,T. 1989. More on Pacificversus Arctic loons. Birding 21:157-158. Stallcup,R. 1983. Loons.Point ReyesBird Obs. Newsletter,summer, pp. 8-11. Storer,R. W. 1978. Systematicnotes on the loons(Gaviidae: Aves). Brevoria 448. Walsh, T. 1984. The field identificationof Arctic Loon. Bird Obs. 12:309-314. Walsh,T. 1988. IdentifyingPacific Loons. Birding 20:12-28.
Accepted 6 March 1993
196