NOTES AN ARCTIC WARBLER IN BAJA CALIFORNIA, MEXICO PETER PYLE and STEVE N. G. HOWELL, Point Reyes Bird Observatory,4990 ShorelineHighway, Stinson Beach, California 94970 On 12 October1991 we discoveredan ArcticWarbler (Phylloscopus borealis) on PuntaEugenia, west of GuerreroNegro, Baja California. This sighting constitutes the firstrecord of thisprimarily Old Worldspecies from Mexicoand fromNorth America south of Alaska. The localityof the observationwas Rancho San Miguel,27ø30 ' N, 114ø31' W, at krn-marker122 on the road from EjidoVizcaino to BahiaTortugas and the tip of PuntaEugenia. The ranch,located about 100 m southwestof the road, consistedof two buildingsand a small courtyardcontaining several shrubs and one flowering ornamentalacacia (Leguminosae), 8 m tall. A naturalspring in a canyon 300 m southwestof the buildingsprovided water for the vegetationat the ranch. The outer portionof PuntaEugenia, including the area surroundingthe ranch,is arid, rocky, and barren, devoidof leafyvegetation; Rancho San Migueland the nearbyRancho SantaMonica (2 km southeastof RanchoSan Miguel)were small oases of greenery attractingmigratory landbirds. We studiedthe Arctic Warbler from 1220 to 1255 throughbinoculars, at rangesas closeas 4 m, in sunnylighting. The sparsebranches of the acaciaallowed optimal viewingof the bird and doublechecking of all fieldmarks. Also foragingin the tree were two YellowWarblers (Dendroica petechia), a MagnoliaWarbler (D. magnolia), a Yellow-rumpedWarbler (D. coronata), two Townsend'sWarblers (D. townsendi), and a Painted Redstart(Myioborus pictus). The Arctic Warblerwas similarin body sizeto the Townsend'sWarblers but had a larger head and a shortertail. The bill was significantlylarger than that of the Dendroicawarblers in the tree;its relativesize and the bird'shead shape suggested a LouisianaWaterthrush (Seiurus motacilla). The ArcticWarbler was active,continu- allyhopping and flying short distances, at timesswinging upright on verticalbranches of the acacia.It foragedfor insectsprimarily in the lowto middleportions of the tree and upperportions of the surroundingshrubbery; on one occasionit foragedin the uppermostbranches of the tree. The birdwas in freshplumage. The upperpartswere uniformlydrab olive with a slightgrayish cast. The tipsof four or five outergreater coverts were pale creamy tinged lemon, forminga distinctlower wingbar.One or two mediancoverts had minutepale tips of the samecolor, forming a vagueupper wing bar. The flight featherswere dusky,with narrowgreenish-yellow edges on the outerwebs of the primaries.A prominentwide creamy superciliary extended from the baseof the billto well behindthe eye; its posteriorend curvedup towardthe nape when the bird lookedupward. Below the superciliary was a duskyeyeline extending evenly through the lores.A smallindistinct whitish subocular crescent was present.The auriculars weredirty lemon with diffuse pale dusky streaking concentrated toward the rear.The underpartswere primarily whitish or off-whiteunevenly tinged lemon. The paleness of the lowerthroat extended dorsally, posterior to the auriculars,to the sidesof the nape. Pale duskypatches with diffusedusky streaking were presenton the sidesof Western Birds 24:53-56, 1993 $3 NOTES the breast;a vaguehint of thisstreaking extended across the centerof the breast.The thighfeathers were mixeddusky and pale. The wing tips were long with sevenevenly spaced primary tips visiblebeyond the tertials.The tip of the tenth (outer)primary, visible when the bird droopedits wing, extended1-2 mm beyondthe tips of the primarycoverts. The tips of the undertail covertsfell beyondthe tips of the closedwing. The eye and maxillawere dark; the mandiblewas bright orangish on the basalfour fifths,including the sides,becoming duskyat the tip. The legswere duskyflesh-colored, the solesof the feet slightly brighter.The Arctic Warbler did not vocalizewhile we watchedit. Both of usimmediately recognized the birdas an ArcticWarbler from our previous field experiencewith the speciesin S.outheastAsia, Britain, and Alaska,and with mostof the other migratoryPhylloscopus species in Eurasia.The combinationof the shape, size, plumagecharacters, and the presenceof a tenth primary rulesout all speciesof North American warblersand vireos and is diagnosticof the genus Phylloscopus.Within this genusthe lack of a crownstripe and presenceof a single prominentwingbar rule out all speciesexcept the ArcticWarbler, Greenish Warbler (P. trochiloicles), Green Warbler (P. niticlus), Two-barred Greenish Warbler (P. plumbeitarsus),northern races of the Chiffchaff(P. collybita abietinus and P. c. tristis),and perhaps worn individualsof the centralAsiatic race of the Yellow-browed Warbler (P. inornatus hurnei) (Dean 1985). Featuresthat distinguishthe Arctic Warbler and the bird we observedfrom theseinclude the combinationof the large Figure1. ArcticWarbler, Rancho San Miguel,Baja California,12 October1991. Drawingderived from field sketches and notes taken at the time of observation. Sketch by Steve N.G. Howell 54 NOTES size and large bill, hint of an upper wing bar, long and prominent superciliarythat tends to curve upward posteriorly, lemon auricularsstreaked with pale dusky, extensiveorange at the baseof the mandibleand, especially,the long wing tip and wing formula (Ticehurst1938, Dement'evet al. 1954, Williamson1967, Marshall and Pantuwattana1969, King et al. 1975, Robertson 1984, Svensson1984, Dean 1985). The similarspecies have more delicate bills, fewer primary tips visible beyond the tertials(4-6; 7 in the GreenishWarbler), and a longer10th primary,extending 4•- 10 mm beyondthe tips of the primarycoverts. We confirmedthese differences and our identificationby examiningmuseum specimens at the CaliforniaAcademy of Sciences(CAS), San Francisco,and the American Museum of Natural History (AMNH), New York. The Arctic Warbler breedsfrom arctic Scandinaviathrough Siberiato western Alaska, southto northern Mongoliaand northern Japan, and wintersprimarily in southeasternChina, the PhilippineIslands, and the Malay Peninsula(Dement'ev et al. 1954, Vaurie 1959). The speciesis a regularvagrant to Britain (Rogers1987); a Julyvagrant collected on PrincePatrick Island, Northwest Territories (Godfrey 1966), representsthe only previousNew World record outsideAlaska. The only other publishedNorth Americanrecords of ?hylloscopuswarblers south of Alaskaare of three DuskyWarblers (P. fuscatus) in centralCalifornia (Pyle et al. 1983, Roberson 1986, Pyle and McCaskie 1992). Vaurie (1959) recognizedsix subspeciesof the Arctic Warbler, includingthe Alaskankennicotti and fiveAsiatic forms. The bird we observedwas large and had a very largebill, drabolive upperparts, lack of extensiveyellow on the underparts,and a relativelylong tenth primary, featuressuggesting one of the northern Asiatic subspecies,borealis or xanthodryas, rather than kennicotti (Ticehurst I938, Dement'ev et al. 1954; Vaurie 1954, 1959; pers. obs.). As the taxonomy of northwesternpopulations of the ArcticWarbler is incompletelyresolved (D. Gibson in Phillips1991), an identificationto subspeciesshould be consideredtentative. We thank Stephen F. Bailey and Mary LeCroy for assistanceand permissionto examine specimensat CAS and AMNH, respectively,and Daniel D. Gibsonand Philip Unitt for commentsthat improvedthe manuscript.We especiallythank the residentsof RanchoSan Miguelfor permissionto roam aroundin their gardenand for theirwarm hospitality,so typicalof BajaCalifornians secluded from majortourist routes.This is contribution527 of the PointReyes Bird Observatory. LITERATURE CITED Dean, A. R. 1985. Review of British statusand identificationof GreenishWarbler. Br. Birds 78:437-451. Dement'ev,G. P., and Gladkov,N. ,A., eds. 1954. Birdsof the SovietUnion. Vol. 4. SovietskaNauka, Moscow. Godfrey,W. E. 1966. The Birdsof Canada.Natl. Mus.Can., Ottawa. King, B., Woodcock,M., and Dickinson,E. C. 1975. A Field Guide to the Birdsof South-EastAsia. Collins,Glasgow, Scotland. Marshall, J. T., and Pantuwattana, S. 1969. Identificationof leaf warblers in Thailand. Nat. Hist. Bull. Siam Soc. 23:1-11. Phillips,A.R. 1991. The Known Birdsof North and MiddleAmerica, part 2. A. R. Phillips, Denver. Pyle, P., DeSante,D. E, Boekelheide,R. J., and Henderson,R. P. 1983. A Dusky Warbler (Phylloscopusfuscatus) on SoutheastFarallon Island, California. Auk 100:995-996. NOTES Pyle, P., and McCaskie,G. 1992. Thirteenth report of the California Bird Records Committee. W. Birds 23:97-132. Roberson,D. 1986. Ninth report of the CaliforniaBird RecordsCommittee. W. Birds 17:49-77. Robertson,I. S. 1984. Mysteryphotographs. 93. ArcticWarbler. Br. Birds77:415- 417. Rogers,M. J., ed. 1987. Report on rare birdsin Great Britain in 1986. Br. Birds 80:516-571. Svensson, L. 1984. Identification Guide to European Passerines. 3rd Ed. L. Svensson,Stockholm. Ticehurst,C.B. 1938. A SystematicReview of the Genus?hylloscopus. Br. Mus. (Nat. Hist.), London. Vaurie, C. 1954. Systematicnotes on Palearcticbirds. No. 9. Sylviinae:The genus ?hylloscopus.Am. Mus. Novitates1685. Vaurie, C. 1959. The Birds of the Palearctic Fauna. Passeriformes.H. F. & G. Witherby, London. Williamson,K. 1967. Identificationfor Ringers2. The Genus?hylloscopus. Rev. ed. Br. Trustfor Ornithol., Oxford, England. Accepted 19 February 1992 .