Another Look at the Western and Yellow-Footed Gulls

ANOTHER LOOK AT THE WESTERN AND YELLOW-FOOTED GULLS

GUY McCASKIE, San Diego NaturalHistory Museum, P. O. Box 1390, San Diego, California 92112

With recognitionof the Yellow-looted Gull (Larus livens) as a distinct species,separate from the Western Gull (Larusoccidentalis) (American Or- nithologistsUnion 1982), there is renewed interestin the dark-mantledgulls of westernNorth America.In orderto correctlyidentify these birds it is impor- tant to understandhow they progressfrom juvenal to adult plumage, and when molts occur. JonathanDwight's definitive work, The Gullsof the World (1925), includes much valuableinformation on plumagesand molts, but was designedfor museumworkers with specimensin hand, and is now difficultto obtain,being longout of print. Recently,Peter Grant (1982) provideda masterpieceon all the gullsknown to occur in the westernPalearctic, Gulls: A Guide to Iden- tification, with emphasison field identification.It is from this book that the chartshowing the sequenceof plumagesand molts,as well asthe topograph- ical terminology,is taken. Mostgulls molt twice a year, with a completemolt in late summerand early fall, and a partialmolt involving only head and body feathers in latewinter and earlyspring. The time takento advancefrom juvenalto adultplumage varies amongspecies but, in general,the largerthe birdthe longerit takesto attain adult plumage. Small gulls reach adult plumage in their second winter, medium-sizedgulls in their third winter, and largegulls in their fourth winter. Needlessto say, there are exceptions(e.g., some large gulls reach adult plumagein third winter). In addition,some individuals, particularly among the larger species,show signsof immaturityduring the first year as adults (e.g., adult-plumagedbirds with dark markingsretained in the tail), while othersadvance towards adult plumagein a more rapid or retardedrate than expected(e.g., a largespecies of gull in third-winterplumage could possibly be in itssecond winter if progressingat a more rapid rate than expected,or in itsfourth winter if retarded),and sickor injuredbirds may failto molt at the ap- propriatetimes. Figure 1 indicatesthe typicalsequence of plumageand the approximateseasons of moltsfor the three sizesof gullsas they advancefrom juvenileto adult. It also includesthe age terminology(e.g., first-winter)in commonuse, which is usedthroughout this paper. A basicknowledge of the variousplumages of WesternGulls is necessary to identifyYellow-looted Gulls with certainty,and is essentialto thoseinterested in the differencesthat helped establishthe Yellow-looted Gull as a distinct speciesin the mindsof those studyingthe bird. Consequently,a complete review of WesternGull plumagesis in order.

WESTERN GULL Larus occidentalis

This speciesis the commondark-mantled gull of the Pacificcoast of North America, nesting from the vicinity of Destruction Island in northern Washingtonsouth to Guadalupe Island off the west coast of central Baja Western Birds 14: 85-107, 1983 85 WESTERN AND YELLOW-FOOTED GULLS WESTERN AND YELLOW-FOOTED GULLS

California.There are two races,the nominateform occidentalis,nesting from the Farallon Islandsoff central California northward, and the darker-mantled form wymani, nestingfrom the vicinityof MontereyBay southward(Figure 2). At the northernlimit of the rangeWestern Gulls interbreed with the closely related Glaucous-wingedGull (Larus glaucescens),resulting in many inter- grades(Scott 1971, Hoffman et al. 1978). In winter somebirds move northward into coastalsouthwestern British Columbia, with a stragglerrecorded as far north as near Chignik on the Alaska Peninsula (Kesseland Gibson 1976:46), while others move as far south as the southerntip of the Baja Californiapeninsula, with stragglershaving reached Guaymas, Sonora, on the coastof mainland Mexico (Devillerset al. 1971). However, the speciesas a whole is mostlysedentary, remaining in the immediatevicinity of the coast. Feedingareas (e.g., garbagedumps) and bathingspots attract flocks a few milesinland along the coastalplain, and spawningsalmon have been reported to attract individualsup major rivers (LaFave 1965, Weber 1981), but the speciesis otherwiseaccidental inland.

L. o. occidentalis

L. o. wymani

L. livens

Figure2. Breedingrange of WesternGull (Laruso. occidentalisand L. o. wyrnani)and Yellow-looted Gull (L. liuens).

87 WESTERN AND YELLOW-FOOTED GULLS

The only occurrencesfrom the true interiorin the westernUnited Statesare one (L.o. occidentalis)collected along the ColoradoRiver above Parker Dam (Monsonand Phillips1981) and four seenon the Salton Sea in southeastern California(a third-winterbird along the southshore between 17 Januaryand 13 February1965, anotherthere on 29 March1969, an adultjudged to be u•yrnaniat Salton City on 26 September1982, and a third-winterbird, also judgedto be u•yrnani,there on 11 and 28 November1982--McCaskie pers. obs.).Reports of one seennear Denver,Colorado (Am. Birds32:1038 , 1978) and anotherseen on Lake Mead, Nevada (Am. Birds35:210, 1981) lacksubstantiating details, and all otherpublished records from the SaltonSea are now believed to have been L. livens. The WesternGull is a largegull, takingabout 31/2 years to acquireadult plumage.It isabout the size of a HerringGull (Laru$argentatu$), possibly a bit larger,but stockier,with a stouterbill and shorterwings, having much the bodysize and shapeof a Glaucous-wingedGull. The southernform u•yrnaniis darkermanfled than the northernbirds at all ages,and acquiresa paleeye as an adult. The nominate form occidentalismore closely resemblesthe Glaucous-wingedGull, normallyhaving a darkeye as an adult,and having some darknesson the head and neck in winter plumage.However, the distinctionbetween the southernbirds and the northernbirds is not obvious, therebeing more of a clinaltrend, with the darkest-mantledbirds in the south andthe lightest-mantledbirds in the north,the latterbeing quite similar in ap- pearanceto the moresouthern Glaucous-winged Gulls. The followingdiscus- sionand detaileddescriptions apply to the southernbirds. In juvenalplumage the WesternGull appears much like a juvenileHerring Gull, but is darker,the overallcoloration being sooty-gray rather than gray- brown,and the paleedges to the feathersof the upperparts being narrower, givingthe bird a lessmottled appearance than juvenileHerring Gulls. The rumpof the WesternGull appearswhiter than that of the HerringGull, there beinga greatercontrast between the backand rumpthan on a HerringGull. The tailis also darker, helping to emphasizethe pale rump. The flight feathers on bothspecies are blackish,but WesternGulls lack pale areason the inner websof theinner primaries that form pale windows in thewings of youngHer- ring Gulls. First-winterWestern Gulls are similarto the juveniles,but have more con- spicuouswhite in therump, and lack the patterning on the upperparts formed by the pale edgesto the mantleand scapularfeathers on the juvenile,the overallappearance being streaked and smudged.First-winter Western Gulls do not exhibitthe pale-headedappearance evident on mostfirst-winter Her- ring Gulls. First-summerWestern Gulls are similarto first-winter,but tend to bepaler about the headand underparts,with the now 1-year-oldwing and tail feathersshowing evidence of wearand fading,varying from littleto extensive (someindividuals of all gullspecies have primaries and rectricesthat appearto be mere feather-shaftsin summer). The minor differencesthat separate juvenileWestern and Herringgulls hold true throughthe firstsummer. In second-winterthe head and bodyare mostlywhite, and the mantleand scapularsshow much of thedark gray worn by the adult.The birdacquires the eye colorof the adultlate in the winter(pale yellow or grayto whitishfor most u•yrnani,but dark brown to blackishfor mostoccidentalis). The wingsappear 88 WESTERN AND YELLOW-FOOTED GULLS

much as they did in first-winter,with only a minimal amount of dark gray leatheringon the wingcoverts, but the primariesremain entirely blackish. The tail showsa little more white at the basethan in first-winter,but is nonetheless mostlydark, contrastingsharply with the whitishrump. From this stageon- wardthe colorationof the mantleand scapularsmakes differentiating Western and Herringgulls much easierthan in first-winterand first-summer.Second- summerbirds are whiter aboutthe head and underpartswith relativelycon- spicuouswhite rumps. The darkgray on the upperparts becomes a littlemore extensive,but the wingsand tail are the same as in second-winter,though showingthe effectsof wear. Third-winterbirds look more similarto adults, havingthe dark gray of the upper parts extendingacross the wing coverts.However, the primariesare uniformblackish without the whitemirrors. There is normally some brown col- orationevident on the wing coverts,and someblack is alwayspresent in the tail. The bill may startto acquiresome of the yellow color of the adult, but is morenormally pinkish with blacktowards the tip (billcolor is variableon most immature gulls, and is not recommended for use in aging individuals, especiallyafter the firstwinter). Third-summer birds look muchthe same,but never show any duskycoloration about the head and neck, and many in- dividualshave bare partsmatching those of the adult. Adult Western Gulls in the winter are entirely white about the head and throughoutthe underparts.The mantleand uppersides of the wingsare dark graymerging into the blackprimaries. White tipsto the primariesand second- ariesform a prominentwhite trailingedge to the wing, and the outermost primary containsa small white mirror. The dark flight featherscontrast noticeablywith the whiteunderwing coverts, and the whitetrailing edge to the wingis quiteevident from below. The rumpand tail are entirelywhite. The bill isyellow with a reddish-orangespot at the gonys.Southern birds have only a minimalamount of duskyspotting about the headand neck (difficultto seeon many individuals),but thismottling is more evidenton winteradults from the more northern populations, and is most evident on those hybrids with Glaucous-wingedGulls. Summer adultsare similar, but normallylose the whitetips to the primariesdue to wear, and the bareparts are more brightly coloredat the onsetof the breedingseason. All duskymarkings about the head and neck are gone. A more detailed descriptionof each plumage follows. Juvenile (Figures3A, 4, 5, and 7A). HEAD Ratheruniform sooty-gray, darkest immediately ahead of the eye and on the ear-coverts,with diffusedpale gray streakingon the crown, nape and neck. BODY Underpartssooty-gray flecked with white, the individualfeathers dark sooty-grayfinely edged with pale gray to white, the lower belly and vent being somewhatpaler than the restof the underparts.Mantle and scapularsdark sooty-gray liberallyflecked with white, the individualfeathers blackish finely edged with white, the largerscapulars presenting a "scaled"appearance. Rump and uppertailcoverts whitish liberallyflecked with black,appearing paler than the back, but not strikinglyso. WINGS Wing covertssooty-gray flecked with white much as the mantle and scapulars,the individualfeathers being sooty-gray edged with white, but alsohaving extensivepale brownblotches, this brown coloration being most evident on the greater coverts and tertials. Primaries blackish and secondaries dark brown to blackish with a narrowline of pale gray at the very tip of the innerprimaries, and more noticeablepale

89 WESTERN AND YELLOW-FOOTED GULLS

buffy-graytips to the secondaries,forming a narrowpale trailingedge to the wing. Underwingcoverts and axillariesblackish, appearing darker than the undersideof the flightfeathers. TAIL Blackishwith pale bully-grayterminal stripe formed by lighttips to feathers. BARE PARTS Irisblackish. Orbital ring dark grayto black.Bill entirely black. Legs andfeet blackishwith traces of dirtypink throughout, the extentof pinkvarying from individual to individual. First-winter (Figure 3B). Acquired by post-juvenalhead and body molt between Augustand November.There is muchvariation in the lengthof time individualsretain juvenalplumage, some havingacquired first-winter plumage by early Octoberwhile othersare stillin juvenal plumagein November. HEAD AND BODY Head sootygray-brown, slightly paler than in juvenile,with the area immediatelyahead of the eye and ear-covertsbeing the darkest,and the nape and hindnecktending to be the palest.Underparts smudged sooty gray-brown, the whitefiecking of the juvenilenow appearingmore diffused. Mantle and scapularssooty gray-brownsmudged with lightgray, the "scaled"appearance of thejuvenile gone, the individualfeathers being sootygray-brown with diffusedpale gray edges. Rump and uppertailcoverts whitish liberally flecked with sootygray-brown, still appearing paler than the back. WINGS AND TAIL Wing covertssooty gray-brown matching the colorationand patternof the mantleand scapulars.Primaries and secondariesdark brown to blackish, underwingcoverts and axillariesblackish, and tail blackishas in juvenile. BARE PARTS Irisblackish. Orbital ring dark gray to blackish. Bill black with varying amountsof dirtypink at the extremebase, particularly at the baseof the lower mandi- ble. Legs and feet dirty pink. Flrst-surnrne• (Figure3C). Acquiredby headand bodymolt between February and April, with wing and tail feathersof the juvenileretained. HEAD AND BODY Head muchas in first-winterbut somewhatlighter, with the dark area aroundthe eye retained.Body muchas in first-winterwith underpartstend- ingto be somewhatpaler, and the markingson the upperpartsappearing smudged. WINGS AND TAIL Wing covertsdark gray-brown like the mantleand scapulars. However,wear and bleachingaffects the appearanceand colorof the feathers,particularlythe greatercoverts which can be anythingfrom pale brownto almostwhitish. The primariesand secondaries,now a year old, tend to showthe effectsof wear, and are decidedlybrownish. The tail, alsoa year old, matchesthe primaries. BARE PARTS Irisnow detectablypaler than the pupil, but stillquite dark. Orbital ringdark gray. Bill much as in firstwinter, but with more dirty pink at thebase. Legs and feet pinkishwith a gray tone. $e½ond-wl•te• (Figure3D). Acquiredby a completemolt between July and October. HEAD Mostlywhite with varyingamounts of dusky-graysmudging and spotting, particularlyaround the eye, and mostnoticeably ahead of the eye. BODY Underpartsmostly white with varying amounts of dusky-grayscalloping on the breastand belly,the lowerbelly and vent tendingto look cleanerthan the breast. Mantle and scapularsmostly uniform dark gray, but containingsome gray-brown leathering.Tips of the longestscapulars pale brownto whitishforming pale scapular crescents,and the tipsof the longesttertials whitish forming pale tertial crescents. Rump and uppertailcoverts white with a minimalamount of darkflecking and smudging. WINGS Wing covertsmuch as in first-winter,but havinga littlemore of the dark grayleathering on the lessercoverts, contrasting sharply with the muchmore uniformly coloredback. Primariesblackish with no traceof whitemirrors, though inner primaries tippedpale gray to white.Secondaries dark brownish-gray tipped with pale gray forminga pale line alongthe trailingedge of the wing.Underwing coverts and axillariesdirty brownmottled with white, appearingquite dark, and matchingthe colorof the undersideof the flightfeathers. 9O WESTERN AND YELLOW-FOOTED GULLS

B. First-winter

C. First-sum A. Juvenile

D. Second-winter F. Adult

E. Third-winter

Figure 3. Western Gull (Larus occidentalis). 91 WESTERN AND YELLOW-FOOTED GULLS

TAIL Mostlyb•ackish, but somewhite mottlingtowards the base,particularly at the baseof the outertai• feathers. and narrowpale terminal band formed by pa•egray tips to the individual feathers. BARE PARTS Iris pale gray-brown. Orbita• ring gray. Bill pink with varying amountsof b•ackon the tip, thoughthe very tip is normallywhitish, the blackmerging into the pink rather than appearingsharply separated as in first-winterCalifornia Gulls (La•'u$½ali•fomicu$). Legs and feet dusky-pink. $e•:or•cl-$,•mmer. Acquired by head and body mo•tbetween February and April, the wing and tail feathersof second-winterbeing retained. HEAD AND BODY Much as in second-winter,but head and underpartswhiter, and mantle and scapularsacquiring more of the uniform dark gray associatedwith the adult. WINGS AND TAIL Much as in second-winter.but wing covertsacquiring a •itfie more of the dark gray, and the underwingcoverts and axillariesappearing a little whiter. The flight feathersare normallypaler due to wear and b•eaching. BARE PARTS The orbital ring may show a trace of yellow and the bill can show some yellow tones in the areas of pink, with the black at the tip becoming more restricted. Tl•irc!-•ir•te• (Figures3E and 6). Acquired by complete molt between July and Oc- tober. HEAD White with dusky mottling, particularlyaround the eye, and on the nape and hindneck, the extent of this motfling being more than that present in adult, but much •essthan that of a Herring Gull.

Figure4. A juvenileWestern Gull showingpattern of upperparts.Carmel, Monterey County, California,August 1982. Photoby Don/•o/•er$or•

92 WESTERN AND YELLOW-FOOTED GULLS

BODY Underpartsmostly white with varyingamounts of duskymottling about the sides of the breast, clearest on the center of the breast and upper belly. Mantle and scapularsuniform dark gray with a hint of brown, the ends of the longestscapulars and tertialsbeing white forming scapularand tertial crescents.Rump and uppertailcoverts white. WINGS Similarto adult in winter, the entire upper surfacebeing uniform dark gray merginginto the blackof the primaries,and the white tipson the secondariesand •nner primariesforming a bold white line along the trailingedge of the wing. However, the outer primarieslack the white tipsand there isno mirroron the outer primary, and varyingamounts of blackishcoloration are present along the leadingedge of the outerwing. includingthe primary covertsand alula. Most individualsretain some brown leathering on the wing covertsthat disruptswhat would otherwisebe the uniform appearanceof the adult. Underwing covertsand axillarieswhite flecked with dark brown, appearing mostly white. TAIL White with black subterminalmarks of highly variable extent and pattern forming an i•regularblack band toward the tip of the tail. BARE PARTS Like adult except for bill which is typicallypinkish with varying amountsof black towardsthe tip and which often lacksred at the gonys. Tl•ir•!-summer. Acquiredby head and body molt between Februaryand April. the wing and tail feathersbeing retained. Similarto third-winter,except head and underpartsentirely white, all duskymottling having been lost. Flight feathers, particularlythe primaries,show evidenceof wear

Figure 5. A juvenile Western Gull in flight. Carmel, Monterey County, California, August 1982. Compare this with the juvenile Yellow-looted Gull in Figure 10. Photo by Don Roberson

93 WESTERN AND YELLOW-FOOTED GULLS

(white tips to primarieslost). Bill frequently containsred at the gonys along with the black near the tip and is now decidedlyyellow (someindividuals have adult bill coloration in third-summer). Adult winter (fourth winter) (Figure3F). Acquiredby completemolt between July and October. HEAD AND BODY Head entirelywhite with faint dusky mottlingevident on most individuals(this mottling can be somewhatrestricted and difficultto see unlesscarefully lookedfor). Underpartsentirely white. Mantle and scapularsuniform dark gray. White tips to longestscapulars and tertialsform bold white scapular and tertial crescents. Rump and uppertailcoverts entirely white. WINGS AND TAIL Upper surfaceof wing uniformdark gray merginginto black primaries. White leathering at the marginal covertsform a thin white line along the

Figure6 A third-winterWestern Gull in flightshowing typical tail pattern. A second- winter Yellow-looted Gull looks similar, but would have much more black in the tail, and would lackdusky markings about the head. Photo by Don Roberson

94 WESTERN AND YELLOW-FOOTED GULLS leadingedge of the inner wing. White tips to thesecondaries and inner primaries form a boldwhite trailing edge to the wing. Outerprimaries black with smallwhite tips and somewhatrestricted white mirror on outer primary (white mirror presenton second primaryin someindividuals). Underwing coverts and axillariespure white, contrasting sharplywith black underside of primaries and dark gray underside of secondaries (white trailingedge to the wingis a prominentfeature on WesternGulls viewed from below). Tail entirelywhite. BARE PARTS Iris pale gray to white. Orbitalring pale yellow.Bill yellowwith orange-redspot at gonysand whitishtip. Legsand feet darkpinkish. Adult summer. Acquiredby head and body molt betweenFebruary and April, the wing and tail feathersbeing retained. As adultwinter, except all tracesof duskymarking about the headlost, the birdap- pearingclean white throughout with dark graymantle and upperwings merging into the blackprimaries. White tips to outerprimaries invariably lost due to wear.Coloration of bareparts more intense at the onsetof nesting,the yellowof the orbitalring being brighter,and the colorof the bill deeper.

A. Western Gull

B. Yellow-looted Gull

Figure7. Juvenalplumage of Western Gull (Larus occidentalis) and Yellow-looted Gull (L. livens).

95 WESTERN AND YELLOW-FOOTED GULLS

YELLOW-FOOTED GULL Larus livens

This speciesis the large clark-backeclgull that is resiclentin the Gulf of California.A historicreview of thisspecies, ancl the WesternGull with whichit had until recentlybeen consiclereclconspecific, illustrates the state of confu- sion surrounclingthis bircl. John James Auclubon (1839) first clescribedthe WesternGull from two specimenscollectecl near the mouth of the Columbia River in southernWashington in early October 1836, ancl nameclthe bird Larusoccidentalis. Subsequent ornithologists believecl the rangeto be the entire westcoast of North Americafrom Washingtonto the tip of Baja California and throughoutthe Gulf of California.Dwight (1919) pointeclout that the more southernWestern Gulls had noticeablyclarker mantles, and on the basis of a specimencollectecl on San JoseIslancl in the Gulf of California,clescribecl the clarkermanfled birclsas a new race Larus occidentalislivens, retaining Larusoccidentalis occidentalis for the more northernpaler-mantled birds, and stateclthat bothforms have yellowfeet. Larusoccidentalis livens was believecl to range from central California south to the tip of Baja California and throughoutthe Gulf of California. FollowingDwight's clescription of livensthere wasa perlociof clisagreement among authoritiesas to the color of the legsand feet of WesternGulls, with Allan Brooks(1922) statingthat all WesternGulls along the Pacificcoast have pink legs. However, in 1925 A. J. Van Rosseracorrectly assessecl the situa- tion, pointingout the fact that all WesternGulls on the Pacificcoast have pink legs,while those in the Gulf of Californiahave yellowlegs. This observation led to the separationof the WesternGull into three races,the nominateform occidentalisoccurring along the Pacific coast from Washington to central California,a newlyclescribecl dark-mantled, pink-leggecl form wymanioccur- ring from central Californiato the Pacificcoast of Baja California, and the yellow-leggeclbircls of the Gulf of Californiaretaining the name livens(Dickey and Van Rossera1925). DonalclDickey and A. J. Van Rossemsuggestecl the yellow-leggeclbircls of the Gulf of Californiamight be specificallyclistinct, but lackeclcurrent knowleclge about the breeclingclistribution in Baja California, and the possibleintergraclation between wymani and livens. We now know that the vocalizations of Yellow-looted Gulls cliffer from those of Western Gulls, in particularin the "long call" of livens, which is noticeablylower pitchecl, justifying suggestions that the Yellow-lootedGull be treateclas a separatespecies from the Pacificcoast bircls (Hanoi 1981). In addition, breeclingcolonies of Yellow-looted Gulls clifferfrom those of Western Gulls. Yellow-looted Gulls place their nestson beachesin a row roughly parallelingthe ticleline, allowingthem unimpecleclaccess to the waterwithout havingto crossother territories (Hanoi et al. 1981); in sharpcontrast, Western Gullsform clustereclcolonies high above the water.These clifferences support the suggestionthat livens is a clistinctspecies. It is also believeclthat the Yellow-lootedGull isconfinecl to the Gulf of Californiaas a breeclingbircl, and that the WesternGull breeclsno farthersouth than halfway clownthe Pacific coastof Baja California (Figure 2); thus nestingareas do not overlap. In ac- tuality, there is very littlecontact between these two speciesat any time of the year, sincefew Western Gulls enter the Gulf of California, and the Yellow- footeclGull is acciclentalalong the Pacificcoast. 96 WESTERN AND YELLOW-FOOTED GULLS

B. First-winter

A. Juvenile

E. Adult C. First-summer

D. Second-winter

Figure8. Yellow-looted Gull (Lotuslivens). Sketchesby Tim Manolis

97 WESTERN AND YELLOW-FOOTED GULLS

The Salton Sea in southeasternCalifornia is the only localityin the United Stateswhere Yellow-looted Gulls regularly occur, and their occurrencethere isa relativelyrecent phenomenon. The firstrecord was of an adultfound near SaltonCity on 22 August1965 (Devillerset al. 1971). Numbersgradually in- creasedthrough the 1960s, with as many as 45 individualsa day recorded duringJuly 1969. Thisincrease continued through the 1970s, and todaythe Yellow-lootedGull is a relativelycommon late summer visitor (e.g., 250 + on 7 August1982), presentbetween late June and the end of September,with smallernumbers (15 maximum)remaining through the winter, and an occa- sionalstraggler found in springand earlysummer. Most are foundalong the bare sandyshores and aroundrocky jetties, as at Salton City, beingmuch scarceron mudfiats,as at the mouthof the WhitewaterRiver, but occasionally foundin irrigatedfields, as southof the SaltonSea. Mostindividuals found in winterand springare in first-yearplumage, there being no recordsof adultsat thistime of the year. Juvenilesappear in earlyJuly (10 July 1976, 1977 and 1982 are the earliestarrival dates for juvenilesin the past 10 years)at the time the speciesis mostnumerous on the SaltonSea. There are only four recordsfrom alongthe coastof California,all in San DiegoCounty: a second-summerfemale collected in San Diegoon 23 June 1966 (San DiegoNatural History Museum 36001); an adultseen in the Im- perial Beach/Otay area on 7 December1978 and 19 January 1979 (Am. Birds 33:314, 1979); and two adults (one a third-winterbird showingsome blackin the tail) seenaround Otay between13 and 28 February1981 (Am. Birds 35:336, 1981). The Yellow-looted Gull is one of the largergulls occurring along the west coastof North America,being on averageslightly larger than the similarap- pearingWestern Gull, but witha heavierbill. However,unlike all otherlarge gullsoccurring in North America,the Yellow-lootedGull acquiresadult plumagein only 21/2years. Yellow-looted Gulls nest early in the year, with eggslaid by earlyApril, and young fledged by late June. The complete molt of late summer occursearlier than that of the more northern large gulls, and startsas early as May, beingvirtually complete by September.The partialmolt of late winter also occurs earlier, with birds showing evidence of molt in December;this molt is completedby March. The juvenileYellow-looted Gull is strikinglydifferent from the juvenile WesternGull, havingmore boldly patterned upperparts, conspicuous white underparts,and a whiterrump. The overallcolor is quitedark about the head and neck, thoughpaler than a juvenileWestern Gull, and not as brownas a Herring Gull. The back is more boldlypatterned than that of a juvenile WesternGull, the feathersbeing broadly edged with lightgray-buff, adding a slightbrownish tone, thoughstill extremely dark. The belly and undertail covertsare mostlywhite, strikingly different from the sooty-grayunderparts of thejuvenile Western Gull, andthe rumpis conspicuously whiter (less spotted with dark flecking)than that of a juvenileWestern Gull, contrastingsharply with the dark tail and back. In the first winter the Yellow-looted Gull acquiresmuch white about the head and neck, but losesmuch of the bold patterningon the upperparts,the backbeing a moreuniform gray-brown. At thisstage it moreclosely resembles a second-winterWestern Gull, but lacksany of the darkgray leathering on the

98 WESTERN AND YELLOW-FOOTED GULLS mantle.The darkgray leathering like that worn by adultsis presenton the mantlein first-summerplumage, and the bird now resemblesa second- summerWestern Gull, but havingmore black in the tail and withthe legs showingtraces of yellow. Second-winterbirds look muchmore similar to adults,having the darkgray ofthe mantleextending across the wing coverts and merging into the black of the primaries.However, the primarieslack white mirrors,and the wing covertsshow a definitebrownish cast. At this stagethe bird most closely resemblesa third-winterWestern Gull, but hasmuch more black in the tail, the billis yellowwith a blacktip, andlegs and feet are yellow. Second-summer birdslook muchthe same,but are whiterabout the headand showsigns of wearon the wingsand tail. Many second-summer birds have the full colored bill of an adult. Adult Yellow-lootedGulls in winterare entirelywhite about the head and underparts,with dark gray mantle and uppersides to the wingsmerging into theblack of the primaries, looking similar to the Western Gulls found along the coastof southernCalifornia. However, theseadults appear to lack dusky markingson the head in winter, and have bright yellow legs and feet instead of thepink legs and feet of thePacific coast birds. In summerthe white tips to the primariesare lost due to wear,and the color of thebare parts is brighter, but theplumage is otherwiseidentical to winter.A moredetailed description of each plumagefollows.

Juvenile (Figures7B, 8A, 9 and 10). HEAD Top of headand hindneckgray-brown finely streaked with white,the individual feathersbeing gray-brownfinely edged with white. Eye-crescentand ear covertsdarker gray-brown,lacking white streaking,giving the bird a dark facialap- pearance.Chin, throat and foreneckwhite liberallymarked with diffusedelongated spotsof gray-brown,the individualfeathers being mostly white mottledwith gray- brown, these diffusedspots terminating in a somewhatwell-defined line acrossthe lowerbreast, forming an obviousline of demarcationbetween the darkbreast and the white belly. BODY Underpartsmostly white with some diffusedgray-brown mottling on the flanks,and widely spaced spots on the undertailcoverts. Mantle and scapulars relative- ly boldlypatterned, the individualfeathers being dark gray-brown boldly edged with palewhitish-buff, the entireupperparts appearing fresh and unworn.Rump and uppertailcoverts white with limited dark gray-brownfiecking throughout, this flecking being noticeablyreduced from that found on juvenile and first-winter Western Gulls, resulting in a whitishrump that contrastssharply with the blackishtail and darkback. WINGS Wingcoverts dark gray-brown boldly patterned with whitish-buff matching the mantle and scapulars•However, greatercoverts (includingprimary coverts)are darkerwith pale edgingsmore restricted.Primaries and secondariesuniform blackish with no obviouspale edgeson the primaries,but narrowpale tips on the secondaries forma narrowline alongthe trailingedge of the wing. Underwingcoverts and axillaries dark gray-brown,with a minimalamount of whiteflecking visible, appearing almost blackishin the field, and lookingdarker than the undersidesof the flightfeathers. TAIL Entirelyblackish with pale gray tips to the individualfeathers forming a nar- row terminal band. BARE PARTS Irisdark. Orbitalring dark gray.Bill entirely black with small amount of whiteat the verytip (someindividuals show small amount of pink at the verybase of the lowermandible). Legs and feeta dirty-lookingpinkish with no indicationof yellow at this early stageof development. 99 WESTERN AND YELLOW-FOOTED GULLS

First-winter (Figures8B, 11 and 12). Acquired by post-juvenalmolt of head and body feathersbetween Ju]y and September,the wing and taftfeathers being retained. HEAD AND BODY Head and neck much whiter than in juvenile, there being no contrastin colorbetween the breastand be]]ybecause most of the diffusegray-brown e]ongatedspotting has been ]ost.]n addition.much of the darknessaround the eye and on the ear coverts is ]ost, the facial area being mosfiy whitish with dark featbering restrictedto the area immediate]yaround the eye (most]yahead of the eye). Manfie and scapu]arsmore uniform dark gray-brown.having a definitegray cast: mostof the bold whitishedgings to the feathersare now gone. Light gray-browntips on the longestter- tia]sform pa]e diffusedtertia] crescents. Rump and uppertaftcoverts white with on]y a ]imitedamound of gray-brownf]ecking, appearing whiter than in the juveni]e. WINGS AND TAIL Wing covertsgray-brown similar to the mantleand scapulars, most of the pa]e edgesto the individua]feathers having been ]ost. Underwing coverts and axi]]ariesmuch as in juvenile. Primaries,secondaries and taft feathersare thoseof the juvenile. BARE PARTS Iris remainsdark and the orbitalring remainsdark gray. Bill mostly b]ackwith varyingamounts of pinkish-ye]]owat the base,particu]ar]y on the ]owerman- dib]e,and sma]]amount of whitepresent on the verytip. Legsand feetpinkish, much as in juvenile. First-summer (Figures8C, 13 and 14). Acquiredby partialmolt involvingonly head and body feathersbetween December and March. the juvenalwing and tail feathersbeing retained.

I .'

Figure9. A mixedgroup of Yellow-footedGulls including four juveniles.one bird in transitionfrom first-summerto second-winterplumage (the adult-like bird in the center) andtwo full adults. Salton City on the SaltonSea, July1982. Photo by Richard E. Webster

100 WESTERN AND YELLOW-FOOTED GULLS

HEAD AND BODY Appearancemuch as in first-winter,except head and under- partsnow generally whiter with diffusebrown streaking confined to hindneck,and a limited amount of brown spottingin the immediatearea of the eye. Mantle and scapularsnow mostlyuniform dark graywith a brownishcast, the feathersthemselves being dark gray with a trace of brown_Rump and uppertailcoverts white, virtually devoid of dark flecking. WINGS AND TAIL Wing covertsremain much as in first-winterplumage, con- l•astingwith the uniformgray appearanceof the mantleand scapulars,but due to wear are nowpaler, the greatercoverts often showing much abrasion. Primaries and secondaries,along with the tail feathers,are thoseworn in juvenalplumage, but now appear brownerdue to wear and bleaching.Underwing coverts and axillariesshow more white fieckingthan in first-winter.but remain quite dark.

Figure10. A juvenileYellow-looted Gull in flightshowing the white underparts.Mouth of the WhitewaterRiver at the northend of the SaltonSea, July 1982. Photo by RichardE. Webster

101 WESTERN AND YELLOW-FOOTED GULLS

BARE PARTS Iris is now noticeablypaler than in juvenile, some individualsacquir- ing noticeablywhitish iris by the end of the firstsummer. Orbital ring remainsgray, slightlypaler than in juvenile.Bill pinkish-yellowat the baseand blackat the tip, the pinkish-yellowmerging with the blackat aboutthe mid-pointof the bill, and the verytip of the bill retainingthe smallarea of white. Legsand feet now showstrong traces of yellow. Second-wintext (Figures8D and 15). Acquiredby a completemolt betweenJune and September. HEAD Mostlywhite with fine diffusegray-brown streaking on the crown and ear covertsextending down the nape, and becomingmore conspicuous (long diffuse gray- brown streaks)on the hindneck, and occasionallyextending to the sidesof the breast. BODY Underpartsmostly white, but not appearingclean white as in the adult. Mantleand scapularsuniform dark gray (a shadepaler than the dark grayof the adult) with a trace of brown. White tipsto the longestscapulars and tertialsform prominent scapularand tertial crescents.Rump and uppertailcoverts white. WINGS Wing covertsuniform dark gray matchingthe mantleand scapulars,but containinga trace more brown coloration.The fresh primariesand secondariesare blackish,with paletips to the secondariesand innerprimaries forming a whiteline along the trailing edge of the wing. Underwingcoverts and axillariesdark brown liberally fleckedwith white, with the greaterunderwing coverts being mostly white. TAIL Mostly blackishwith whitishterminal band formed by pale gray tips to the feathers,the individualfeathers being dark gray with broad blackborders, there being only a minimalamount of whitemottling at the verybase of the feathers.and that confined to the inner webs of the feathers. The overall effect is of a uniform blackish tail contrastingsharply with the whiterump. Althoughthe birdnow appearsmost like the third- winterWestern Gull, the tail itselfappears mostly dark, never showingthe white at the base which is so evident on third-winter Western Gulls.

Figure 11. A Yellow-lootedGull in transitionfrom juvenile to first-winterplumage showingthe palenessabout the head and neck. North end of the SaltonSea, August 1982. Photo by Richardœ. Webster

102 WESTERN AND YELLOW-FOOTED GULLS

Figure12. A first-winterYellow-footed Gull in flightshowing the contrastingpale rump. Red Hill at the southend of the Salton Sea, November 1982. Photo by Jerry OIdenettel

Figure13. A first-summerYellow-footed Gull standingamong Ring-billed Gulls (/_arus deloworensis)indicating relative size, and showinguniform dark gray on the mantle. SaltonCity on the SaltonSea. Photo by RichardE. Webster

103 WESTERN AND YELLOW-FOOTED GULLS

BARE PARTS Iris now appearswhitish, but not the pale white of an adult. Orbital ring pale yellowish.Bill yellow with terminalthird black, and the very tip whitish,there being a relativelywell-defined line of demarcationbetween the yellow of the baseand the black of the tip, and a trace of red at the gonydialangle of some individuals.Legs and feet yellow with tracesof pink disappearingas the winter progresses. Second-summer. Acquired by partial molt of head and body feathers between Decemberand March. the wing and tail feathersbeing retained. HEAD AND BODY Head and neckpure white as are the entire underparts.Mantle and scapularsuniform dark gray with a slightbrownish tone. White tips of the longest scapularsand tertialsform prominent scapularand tertialcrescents. Rump and uppertail covertsentirely white. WINGS AND TAIL Wing coverts uniform dark gray matchingthe mantle and scapulars,but showinga little more brown coloration.especially on the greatercoverts (featherwear will exaggeratethe browncoloration). Blackish primaries and secondaries now showingthe effectsof wear. Underwing covertsand axillariesvirtually uniform white with only a minimal amount of dark fleckingconfined to the lesserunderwing coverts.Tail mostlyblackish as in second-winter,but like wing feathers,showing effects of wear. The presenceof varying numbersof all-white rectricesin some individuals resultsin a checkeredpattern, and suggeststhat sometail feathersmay be molted when the gull goes from second-winterto second-summer.

Figure 14. A Yellow-footed Gull in transition from first-summer to second-winter plumage,showing extent of diffusedstreaking on the headand neck. Salton City on the SaltonSea. July 1982. Photoby RichardE •Vebster

104 WESTERN AND YELLOW-FOOTED GULLS

BARE PARTS Iris pale yellow to whitish. Orbital ring pale, showingtraces of yellow. Bill mostly yellow at the base with black near the tip becomingmuch more restricted.and varyingamounts of reddishcolor present at the gonys,with the very tip whitish. Legs and feet yellow. Adult winter (third-winter) (Figure 8E). Acquired by complete molt between June and September. HEAD AND BODY Entire head and underpartspure white, there being no ap- parentdusky markings about the head as in mostother largespecies of gullsin winter. Mantle and scapularsuniform dark gray with prominent white scapular and tertia] crescents.Rump and uppertail covertspure white. WINGS AND TAIL Wing covertsuniform dark graymatching the colorof the mantle and scapulars.merging into the blackof the primaries.White feathersat the marginal covertsform a thin white line along the leading edge of the inner wing. The fresh primariesare blackwith restrictedwhite spotsat the very tips, and a smallwhite mirror near the tip of the outermostprimary. Secondariesdark gray to blackishwith whitetips forminga line alongthe trailingedge of the wing. Underwingcoverts and axi]lariesen- tirely white contrastingwith the blackishcoloration on the undersideof the primaries and secondaries.Tail entirelywhite (a numberof individualsin third-wintershow small amounts of black on the inner webs of some of the feathers). BARE PARTS Iris pale yellowto whitish.Orbital ring pale yellow. Bill yellow with orange-redspot at the gonys. Legs and feet yellow matchingthe bill co]or. Adult summer. Acquiredby head and body molt betweenDecember and March. [denticalto adult winter. However, white tipsto primarieslost due to wear. and the co]orationof the bare partsmore intenseat the onsetof the nestingseason. The orbital ringis brightyellow (someindividuals show a traceof orange).the bill is brightyellow with red spot at the gonys, and the legsand feet matchthe yellow colorof the bill.

Figure15. A second-winterYellow-looted Gull showingsimilarity to adultbirds. Red Hill at the southend of the SaltonSea, November1982. Photoby Jerry Oldenettel

105 WESTERN AND YELLOW-FOOTED GULLS

Althoughthe Yellow-footedGull mostclosely resembles the WesternGull as indicated above, confusionbetween the two is rare since their ranges seldomoverlap. On the SaltonSea HerringGulls are common in winter(mid- October to mid-April), but never show white underparts in first-winter plumageas do all Yellow-lootedGulls, and normally show some pale gray on the mantlewhen more than a year old. CaliforniaGulls are not as largeas Yellow-footedGulls, and havedecidedly smaller bills. However, they can appear dark-mantled,and do haveyellow legs in spring,but all CaliforniaGulls have dark eyes(Yellow-footed Gulls have lighteyes after the firstyear), and never have the very dark mantle of a Yellow-footedGull. Other largegulls found on the Salton Sea includeGlaucous-winged Gulls (rare) and Thayer's Gulls(Larus thayeri) (rare), both having noticeably pale primaries in immature plumages,particularly from the underside,that separatethem from Yellow- lootedGulls. These same species can be found associating with Yellow-looted Gullsin the Gulf of California,and are all relativelycommon winter visitors along the Pacificcoast of southernCalifornia where the occasionalYellow- footed Gull has occurred. Armed withthe aboveinformation, today's observer can confidently go into the field, and not only correctlyidentify adult Western and Yellow-looted gulls,but can also identifyand age thosebirds in immatureplumages, and possiblyattempt to assignsome of the WesternGulls to race. Extralimitaloc- currencesshould be documentedwith carefullytaken notes and/or good photographs.The accumulationof theserecords will aid in our understanding of the distribution and movements of these birds.

ACKNOWLEDGMENTS

PierreDevillers must be acknowledgedas the personsingly responsible for bringingto all our attentionthe mostsignificant fact indicatingthat the Yellow- footed Gull is a speciesdistinct from Western Gull, i.e., that Yellow-looted Gulls,unlike Western Gulls and mostother large gulls, acquire adult plumage in only 21/2years. I alsowish to thank Pierrefor the many enjoyablehours I spentin the field with him from 1967 through1970. I wishto thankRichard E. Webster,Don Robersonand JerryOldenettel for the use of their photographs,Elizabeth Copper for preparingthe map, Jon Dunn, PeterJ. Grant, RichardE. Webster,Joseph R. Jehl, Jr., Don Rober- son and ElizabethCopper for readingearlier drafts of thispaper and making usefulsuggestions, Tim Manolisfor supplyingall the blackand whitesketches, and lastlyPeter J. Grantfor allowinguse of materialsand conceptspreviously publishedby him.

LITERATURE CITED

American Ornithologists'Union Committee on Classificationand Nomenclature. 1982. Thirty-fourthsupplement to the AmericanOrnithologists' Union check-list of North Americanbirds. Supplement to Auk 99(3). Audubon,J. J. 1839. OrnithologicalBiography V:320. Brooks, A. 1922. What color are the feet of the Western Gull? Condor 24:94.

106 WESTERN AND YELLOW-FOOTED GULLS

Devillers,P., G. McCaskie& J. R. Jehl, Jr. 1971. The distributionof certainlarge gulls (Laru$)in southernCalifornia and Baja California.Calif. Birds 2:11-26. Dickey, D. R. & A. J. Van Rossera.1925. A revisionarystudy of the WesternGull. Condor 27:162-164. Dwight, J., Jr. 1919. A new subspeciesof the WesternGull. Proc. Biol. Soc. Wash. 32:11-14. Dwight, J., Jr. 1925. The gulls(Laridae) of the world; their plumage,moults, varia- tions, relationshipand distribution.Bull. Am. Mus. Nat. Hist. 52:63-408. Grant, P. J. 1982. Gulls: a guide to identification.T & A D PoyserLtd., Carlton, En- gland. Hand, J. L. 1981. A comparisonof vocalizationsof WesternGulls (Larusoccidentalis occidentalisand L. o. livens). Condor 83:289-301. Hand, J. L., G. L. Hunt, Jr. & M. Warner. 1981. Thermalstress and predation:influ- enceson the structureof a gull colonyand possiblyon breedingdistributions. Condor 83:193-203. Hoffman, W., J. A. Weins & J. M. Scoff. 1978. Hybridizationbetween gulls (Larus glaucescensand L. occidentalis)in the PacificNorthwest. Auk 95:441-458. Kessell, B. & D. D. Gibson. 1976. Status and distributionof Alaska birds. Studies in Arian Biol. 1. LaFave, L. D. 1965. Revised statusof Laridae in eastern Washington.Murrelet 46:7-11. Monson, G. & A. Phillips. 1981. Annotated checklistof the birdsof Arizona. 2nd ed. Univ. Arizona Press, Tucson. Scott,J. M. 1971. Interbreedingof the Glaucous-wingedGull and WesternGull in the Pacific Northwest. Calif. Birds 2:129-133. Weber,W. W. 1981. The Larusgulls of the PacificNorthwest's interior, with taxonomic commentson severalforms (Part II -- Conclusion). Continental Birdlife 2:74-91.

Accepted 22 February 1983

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