Retarded Wing Molt in Black-Legged Kittiwakes

NOTES

RETARDED WING MOLT IN BLACK-LEGGED KITTIWAKES

STEVE N. G. HOWELL, Point ReyesBird Observatory,4990 ShorelineHighway, StinsonBeach, California 94970 CHRIS CORBEN, P.O. Box 2323, Rohnert Park, California 94927

Prebasicmolt of the primariesin mostspecies of northernhemisphere gulls occurs betweenApril and December(Dwight 1925, Grant 1986, Cramp and Simmons 1983, pers.obs.). Exceptions are mainlytransequatorial migrants, both those that molt primariesafter they have reachedtheir southernhemisphere winter grounds (e.g., Sabine'sGull, Xema sabini;Grant 1986) and thosethat suspendprimary molt betweenthe summerand winter grounds (e.g., Baltic Lesser Black-backed Gull, Larus fuscusfuscus; Jonsson 1998). The completesecond prebasic molt of the Black- leggedKittiwake (Rissa tridactyla) reportedly occurs from May to November,the adult prebasicmolt from June to December(Cramp and Simmons 1983, Baird 1994). Duringthe springof 1999 we notedadult Black-legged Kittiwakes in central Californiathat had not completedtheir prebasicprimary molt. Here we document and discussthis phenomenon. On 21 April 1999, off BodegaHead, SonomaCo., Corbennoted a kittiwakethat appearedto havean outerprimary only partially grown and that showeda largeblack patchalong the leadingedge of the underwing,anterior to the blackwing tip. We thoughtlittle of thisuntil, on 2 May 1999, we examineda kittiwakespecimen found freshlydead on SoutheastFarallon Island, San Francisco Co., on 11 March1999. On thisbird, primaries9 and 10 (P9-10) on the rightwing were worn and retainedand the new P8 was slightlyless than full length;on the left wing P10 was retained,P9 missing(presumed shed), and P8 full length.The tertialsand outer secondarieshad beenreplaced, while the middlesecondaries were retainedand worn;the innertwo subscapulars(nearest the body)had beenreplaced, while the outertwo were old and worn. Rectrix5 on eachside was old and frayedin contrastto the othertail feathers, whichhad beenreplaced. We detectedno activemolt (i.e., pin feathers)on the head, body,or scapulars.The patternof the retainedfeathers on thisbird indicatedthat it wasat ]eastin itsfourth calendar year (CY4), andthe specimenhas been deposited at the CaliforniaAcademy of Sciences(CAS 5507). Subsequentto thisdiscovery we recordedmolt data on 33 CY3 andolder kittiwakes observedduring May 1999: singlebirds off BodegaHead, Sonoma Co., on 10 and 11 May, one birdin MontereyBay, MontereyCo., on 15 May, and 30 birdsat Pescadero Creek,San Mateo Co. (nineon 15 May, 21 on 17 May).Of thesebirds, only two were CY3, both of which had full-grownnew primaries.None of the remaining31 birds hadfull-grown outer primaries: one hadP9-10 retainedon bothwings (and P8 about 85% grown),seven had P10 retainedon bothwings (P9 65-100% grown),four had P10 retainedon one wing and shedon the otherwing, and the other birdshad P10 growingbut not full length.Of the 19 birdswith P10 growing,this featherwas 90- 95% of its full lengthon nine birds(with P9 full grown)and 40-70% grownon the other ten birds(P9 90-100% grown).The retainedouter primariesof five birds studiedcarefully on 17 May had a patterntypical of a secondbasic or older(versus juvenal)feather, and thusthese individuals were at leastin their fourthcalendar year. The headpatterns of birdswith retardedmolt varied considerably, but no birdhad the cleanwhite headtypical of alternateplumage. All birdswith retainedprimaries had head markingstypical of basicplumage (with a dark auricularsmudge and a variabledusky wash to the crown and nape). All birdswith P10 growinghad white headswith scattereddusky gray feathers on the auriculars,hindcrown, and nape:at

WesternBirds 31:123-125, 2000 123 NOTES longrange, a fewappeared to haveall-white heads. This suggests that those birds with the least retardedprimary molt may have been attainingalternate head plumage concurrentlywith the completionof their prebasicprimary molt. Howell examinedwinter throughspring specimens of kittiwakesat the CAS to determinewhether or not the spring1999 birdswere anomalous. Two of 21 CY3 and olderbirds collected in centralCalifornia from February to April 1907 exhibitretarded molt:CAS 10873 (18 February)with P8-10 retainedon the rightwing, P9-10 on the left with P8 shed,and CAS 10822 (13 March)with P10 80% grown.Three of eight CY3 and older birdscollected from December1907 to February1908 also show ongoingprimary molt, althoughtwo of theseprobably would have completed molt in January.The third specimen(CAS 10888, 17 January)has P8-10 retained,P7 5% grown,and P6 fulllength. An additionalspecimen (CAS 21944, 22 March 1899) also hasretarded molt of the outerprimaries: P9-10 retained,P8 85% grown,and P7 full length.All of theselate-molting birds appear to be CY4 or older,from the patternof the primary covertsand retainedouter primaries(Grant 1986, pers. obs.), and they constituted20% (4 outof 20) of the Januaryto AprilCAS specimensof thisage group. None of the Januaryto Marchspecimens shows suspended molt, i.e., full-grown innerprimaries adjacent to retainedouter primaries. Rather, they suggest a protracted over-wintermolt, with a givenprimary not sheduntil the precedingfeather is almost or completelyfull grown. The retardedbut relatively synchronized schedules of birdsin May 1999, however,suggest that their primary molt may have been suspended earlier in the winter,as hasbeen documented for somespecies of shorebirdswintering in northern temperate latitudes.For example, adult Black-belliedPlovers (Pluvialis squatarola) winteringin northwesternEurope start primary molt in Augustand September.Birds unableto completemolt before the adventof adversewinter weather suspend molt and retaintheir outer one to three primariesuntil the followingspring, when they may completethe molt from Marchto May (Crampand Simmons 1983). A combinationof factorscould be responsiblefor retardedmolt in kittiwakes, ultimatelyreflecting reduced energy intake. The most direct factor might be a particularlybad storm, or storms,in early winter before birds completedmolt. Environmentalconditions during preceding seasons might also contribute to a pattern of retardedmolt. For example,following particularly stormy winters birds might be weakenedand unable to startmolt until later than usual. Consequently, they might not completemolt beforethe next winter.During a strongEl Nifio, wintersof 1996-97 through1998-99 wereunusually stormy in the northeasternPacific Ocean, and the food supplyof manyseabirds was reducedthrough summer 1998, as evidencedby widespreadbreeding failures of many species(PRBO unpubl.data; pers. obs). A combinationof any or all of thesefactors could have contributed to the retardedmolt schedulesof the kittiwakeswe observedduring spring 1999. In conclusion,at leastduring some yearssuspended or very protractedwing molt occursin a proportionof the adultBlack-legged Kittiwakes wintering off California.In somebirds, primary molt doesnot finishuntil May or June, takingalmost a year to complete. We thankDiana Humpie and Mike Lynesfor salvagingthe Farallonbird, Douglas J. Longfor allowingaccess to specimensat CAS, DebraL. Shearwaterfor enabling Howell to observekittiwakes in MontereyBay, and PeterPyle, Sophie Webb, and an anonymousreviewer for commentson the manuscript.This is contributionnumber 913 of Point ReyesBird Observatory.

LITERATURE CITED

Baird,P. H. 1994. Black-leggedKittiwake (Rissa tridactyla), in The Birdsof North America(A. Pooleand F. Gill, eds.),no. 92. Acad. Nat. Sci., Philadelphia.

124 NOTES

Cramp,S., and Simmons, K.E. L. (eds.). 1983. Handbook ofthe Birds of Europe, the MiddleEast, and North Africa, vol. 3. OxfordUniv. Press, Oxford, England. Dwight,J. 1925.The gulls (Laridae) ofthe world: Their plumages, molts, variations, relationships,and distribution.Bull. Am. Mus. Nat. Hist. 52:63-408. Grant,P. J. 1986.Gulls: A Guideto Identification. Academic Press, San Diego. Jonsson,L. 1998. BalticLesser Black-backed Gull Larus fuscus fuscus--moult, ageing,and identification. Birding World 11:295-317.

Accepted3 May 2000

,." " ': --_ •':'.•. ..•..:'.".'•C'. "

t. ', ß .". 'ø. :•. '•:-'(.'-Z::'-•:::::::'t•'::'•'.:•.•'5 ß "• •ß ' ß. ' .....- :.' •.- •:..•.• :-7..?f•"'..':..:.]"-:•.:.:;•;:•.• c•W----• •i•.... • ß ' ' ß4e ' ßß.' ß. - -ß., - '. ß '. ß-: , ' .. .."-•':;;• • "....'.'- ':4-'-.:c.'•?, • -:•:•? ;• '...... ß . -. -. ...-'- .. '- -.. '..... -..•,. !•.'-.•.•.• ..'.•;'.•.r..•o'•',•.•.•;;. .x-'•:'..•'.•:,•:•:"• ...... I;,.....-:. :...... ::.. •,.'ßß ß ß - ß '.' '-1 '-?....'.. ß"¾ :•E:':"'", • •' . , .. ,,. . •.. ß'?- .; ,; ß ,•"'• '.'•' .:.': ;:.:- .'•:.a . •-;...:,' . •.•'.-'i "':'•,..i...'• :x:,! -., .. • '..

Bonaparte'sGull Sketch by Sven Achtermann

125