Southernmost Records of Western and Yellow-Footed Gulls

NOTES

SOUTHERNMOST RECORDS OF WESTERN AND YELLOW-FOOTED GULLS

STEVE N. G. HOWELL and SOPHIE WEBB, Point ReyesBird Observatory,4990 ShorelineHighway, Stinson Beach, California 94970

On 27 April 1988 we visitedthe coastallagoons at La Ventosa,5 km eastof Salina Cruz,Oaxaca,Mexico. Scanningthrough a flockof about800 LaughingGulls (Larus atricilla) and 200 Franklin'sGulls (L. pipixcan) we were surprisedto see two adult Yellow-lootedGulls (L. livens). While we were watchingthese, a third large dark- backedgull flew over us and landedin the flock. As it appearedsmaller, slighter, and paler-backedthan the Yellow-footeds,the possibilityof a LesserBlack-backed Gull (L. fuscus)crossed our minds. Closer examination,however, showed this bird to be a WesternGull (L. occidentalis).We approachedthe gullsto within 50 m and watched them at rest and in flight over the courseof three hours.The followingdescriptions are taken from our field notes. Yellow-lootedGulls: very large and heavily built (obviouslylarger than nearby CaspianTerns). Heavy bill orange-yellowwith red gonysspot; legs and feet bright orange-yellow.Head and underpartswhite. Upperparts blackish slate; wingtips blackerwith smallinconspicuous white tips to outer primaries.Rump and tail white with no trace of dark tail band. As seen when the birds flew overhead, undersideof primariesand secondariesdark. The two birds appearedsimilar in size and stayed closetogether at all times. WesternGull: a large gull, clearlylarger than CaspianTern but noticeablysmaller thanthe Yellow-lootedGulls (therefore perhaps a smallfemale?). Bill relatively heavy (butless so than the Yellow-footeds'),yellow with red gonysspot; legs dull pink. Head and underpartswhite. Upperpartsslaw gray, similarin shadeto thoseof an adult LaughingGull, and very worn; wing-covertsfrayed and faded,blackish wingtips worn and fadedwith no white tips visible.Rump and tail white, rectrixtips veryworn. As seen when the bird flew overhead, undersideof primariesand secondariesdark, thoughsecondaries slightly paler. Although at timesstanding near the Yellow-looted Gulls,the WesternGull stayed mostly apart and at one pointflew off alonetoward the coast, returning some 30 minuteslater. We are very familiarwith both species,and the identificationswere facilitatedby the birds' being adults.The relativelypale gray upperpartsof the Western Gull suggestthe northern-breedingsubspecies, L. o. occidentalis,for which, surprisingly, there appear to be no Mexican records(Friedmann et al. 1950, Wilbur 1987). The small size, however,suggests the darker-backedsouthern subspecies L. o. wymani (LeValley1980). Binford(1989) did not listeither speciesfrom Oaxaca, and we are aware of no other records from the state. AlthoughYellow-looted Gulls have been recordedfrom Guerrero,in November 1983 (Pitman 1986), April 1973 (Jehl 1974), and on 23 May 1990 (an adult at Bahia Papanoa,pers. obs.), we havefound no confirmedrecords of the WesternGull southof the tip of Baja California,although "a report from the RevillagigedoIslands (lsla Clari6n) probablypertains to this species"(American Ornithologists' Union 1983). The sourceof reportsof the WesternGull from Sinaloaand Nayarit(A.O.U. 1983) is unclear,and these reports more likely refer to the Yellow-lootedGull (Friedmannet al. 1950). In addition,Stiles and Skutch (1989) mentioneda Western Western Birds 23:31-32, 1992 31 NOTES or LesserBlack-backed Gull from Costa Rica, althoughthe observerconsiders the bird to have been a LesserBlack-backed Gull (S. Perkinspers. comm.). Our Oaxaca recordsthus appear to representthe southernmostrecords of both species,and are remarkable for their coincidence. Other interestingbirds present at the Salina Cruz lagoons on 27 April 1988 included11 HudsonianGodwits (Limosa haemastica), 18 daysearlier than Binford's earliestrecord, eight adultGull-billed Terns (Sterna nilotica), apparentlypaired, and two immature SandwichTerns (Sterna sandvicensis). We thank Laurence C. Binford, Ron LeValley, and Philip Unitt for helpful commentson an earlier versionof this manuscript.This is contributionnumber 509 of Point ReyesBird Observatory.

LITERATURE CITED

AmericanOrnithologists' Union. 1983. Check-listof North AmericanBirds, 6th ed. Am. Ornithol. Union, Washington,D.C. Binford,L. C. 1989. A distributionalsurvey of the birdsof the Mexicanstate of Oaxaca.Ornithol. Monogr.43. Friedmann, H., Griscom, L., and Moore, R. T. 1950. Distributionalcheck-list of the birds of Mexico. Part 1. Pac. Coast Avifauna 29-1-202. Jehl, J. R. 1974. The nearshore avifauna of the Middle American west coast. Auk 91:681-699. Pitman, R. L. 1986. Atlas of seabird distribution and relative abundance in the EasternTropical Pacific. Natl. Marine FisheriesService Admin. Rep. LJ 86- 02C, SouthwestFisheries Center, P.O. box 271, La Jolla, CA 92038. Stiles,F. G., and Skutch,A. F. 1989. A Guide to the Birds of Costa Rica. Cornell Univ. Press, Ithaca, NY. Wilbur,S. R. 1987. Birdsof BajaCalifornia. Univ. Calif. Press,Berkeley.

Accepted 18 April 1991