PlumaDevariation and hybridizationin Black-footedand LaysanAlbatrosses Tristan McKee P.O. Box631 Ferndale,California 95536 (eraall:bertmckee•yahoo.com) PeterPyle 4990Shoreline Highway SUnsonBeach, California 94970 (email:[email protected]) INTRODUCTION Black-footed(Phoebastria nigripes) and Laysan (P. immutabilis) Albatrosses nest sideby sidein denseisland colonies. Their breeding populations center in the northwesternHawaiian Islands, with smaller colonies scattered across the subtrop- icalNorth Pacific. Both species visit nutrient-rich waters off the west coast of North Americathroughout the year to forage. Black-footeds concentrate in coastal waters fromnorthern California tosouthern Alaska, while Laysans frequent more offshore andnortherly waters in thisregion. Bkders on pelagic trips off the West Coast often encountersignificant numbers of oneor bothof thesespecies, and searching for other,rarer albatrosses among them has proven to be a worthwhile pursuit in recen! years(Stallcup and Terrill 1996, Cole 2000). Albatrossesidentified as Black-looted x Laysan hybrids have been seen and studiedon MidwayAtoll and other northwestern Hawaiian Islands since the late 1800s(Rothschild 1900, Fisher 1948, 1972). In addition,considerable variation in appearanceis found within both species, indMduals with strikinglyaberrant plumageand soft part colors occasionally being encountered (Fisher 1972, Whittow 1993a).Midway Atoll hosts approximately two-thirds of the world'sbreeding A presumedhybrid Laysan x Black-lootedAlbatross tends a chickat Midway LaysanAlbatrosses (Fig. 1) andone-third of theworld's breeding Black-footed Atoll, 14 February2000. Photographby PeterPyle. Albatrosses.These populations have provided us with many opportunities tostudy andphotograph presumed hybrids and unusual individuals. In this paper, we dis- BLACK-FOOTEDALBATROSS cussvariation in theplumages of bothspedes and the appearances of aberrant Worldwide,the Black-looted Albatross isthe less common of thetwo species, with indMdualsand probable hybrids, as well as the potential pitfalls to identificationpopulation estimates ranging from 200,000 to 300,000 individuals (Whittow 1993a, thatsuch birds may pose. Our observations arebased on a collective21months on Cousins& Cooper 2000). Adults arrive at colonies in lateOc!ober, fledging takes Midwayfrom 1997 to 2000,in additionto the study of thousandsof Black-footed place in late June and July, and adults have an incomplete tocomplete molt during andhundreds of LaysanAlbatrosses at sea off California. April(non-breeding individuals) or July (breeders) through October. This species islargely dark brown at all ages, with white shafts to the outer primaries. Juveniles havewhitish bases to the feathers encircling the bill and to those feathers in a cres- centimmediately under the eye. The resulting pale areas are obscured at fledging, resultingin wholly dark plumage (Fig. 2) butquickly become visible with wear. Fledglingsusually show well-developed white areas on the face by the time they reachNorth America in latesummer. We have seen one or twobreeding adults that lackedthe eye crescent and showed limited white around the bill, but these features areobvious on the vast majority of individualsafter fledging. Feather edges on the headbecome very frayed and bleached on birds of alllater ages in the summer, and thewhite area can encompass most of thehead on some birds in thisstate (Fig. 3). Adultswith heavily bleached heads from April to August likely represent breeding individualsthat have spent significant time at subtropical latitudes, whereas those showingless bleaching probably are prebreeders (ages 2-10 or moreyears) or birds thatskipped breeding that year and remained attemperate or subarcticlatitudes, thusbeing exposed toless intense sunlight. Feather edges throughout the neck and underpartsalso become bleached and frayed, and on manybirds the edges contrast distinctlywith dark feather bases and create a scalloped look of tanon brown (see Miller 1940). Figure1. MidwayAtoll hosts significant portions of thebreeding populations of Whiteleathering develops on therump, uppertail coverts, lower belly, vent, and bothBlack-looted and Laysan Albatrosses. Presumed hybrids and aberrant indi- undertailcoverts, and its extent has been linked to age and sex (Streets 1877, Bourne vidualsare found regularly in thesedense colonies. Photograph byPeter Pyle. 1982,Pyle unpubl. data), old males being whitest. Birds showing areas of white VOLUME 56 (2002), NUM.ER 2 131 Figure2. JuvenileBlack-tooted Albatross near fledging. Pale areas are Figure3. Anexceptionally worn and bleached adult Black-tooted Albatross. alreadydeveloping on the face,before all the downis lost.Midway Atoll, Thebill is nearthe paleextreme for the species.Photographed in Monterey June1999. Photographby PeterPyle. Bay,off SantaCruz, California, 15 October2000. Photograph by Michael Donahue. Figure4. A strikingleucistic Black-tooted Albatross in MontereyBay, California,18 September1988. The bill shape eliminates Southern Giant- Petreland Laysan Albatross; the birdalso shows a shadowof the Black-toot- ed'sfacial pattern. Photograph by SergeLaFrance. Figure5. A leucisticBlack-tooted Albatross on Tern Island, Hawaii, January Figure6. Leucismoften appears in patches,as in thisBlack-tooted with 1993. Bocumenteddetails of the wingand tail patternindicate that this is whiteouter primaries and a whitestrip across the belly;note also the pale the sameindividual as presentedin Figure4, photographedseveral years splotchingon lhe feet. The facial pattern is typicalof adults.Midway Atoll, earlier.Photographs from U.S. Fishand Wildlife Service files. 23 June2000. Photograph by PeterPyle. 132 NORTH AMERICAN BIRDS Black-lootedand LaysanAlbatrosses elsewhereonthe body due to leucism are very rare but have been photographed in severallocations (e.•, Figs.4, 5, and6). In extremecases, such as the mostly white birdin Figures4 and 5, this can create an appearance reminiscent of a light-morph SouthernGiant-Petrel (MacroheRes giganteus). The distinctivebill structureof MacroheReswith external nasal tubes atop the culmen, consistently distinguishes thisgenus from all albatrosses (Harrison 1983). Roberson (1980) mentioned white in therectrices and light dusky-yellow feet on some birds. We have seen pale col- orationin theseareas only on obviouslyleudstic Black-footeds, soit doesnot appearto be age-related.Similarly, pale underwings apply only to presumed hybridsand leucistic birds in ourexperience. Such birds were noted by Stallcup (1976),who felt that it wasage-related, and by Roberson (1980), who considered it a featureof aberrantbirds or hybrids.The appearance of indistinct pale areas can alsobe created by the exposure of featherbases of birds in heavymolt in earlysum- meen TheBlack-footed's billis blackish, usually with a pinkishtinge of varyinginten- sityat the base. This color is well developed in some individuals of both sexes, mak- ingthe bill appear fairly bright pink with a blackishor darkgray nail (Fig. 3), espe- Figure7. JuvenileLaysan Albatross, showing white auriculars; adult bill color ciallyin brightsunlight. Pink-billed birds may cause confusion with juvenile Short- beginsto developnear fledging. Midway Atoll, June 1999. Photograph by tailedAlbatross (P.. albatrus), which has a considerablylarger bill. The bill of Short- PeterPyle. tailedis dark at fledging (H. Hasegawa, pers. comm. to Pyle), but eventually it devel- opsa brightpink base and pale blue tip. The timing of thischange is unknown. Largelydark, pink-billed birds photographed off Californiain Octoberto Decemberhave been regarded asjuveniles (e.g., Stallcup and Terrill 1996, N.A.B. 52: 203),but these birds show worn, retained feathers, suggesting that the second pre- basicmolt has taken place. Pink-billed birds photographed in Oregon in March (N..A.B.55: 506) and California in lanuary(McKee and Erickson, in press) may in factbe juveniles, but ageing criteria in thisspedes are still undeaen Short-tailedAlbatrosses slowly acquire an extensively white adult plumage (cf. Roberson1980, Erickson and Hamilton 2001). Pale areas on the upperwing coverts canbe among the first signs of this transition in Short-tailed,but it shouldbe noted that the innermostgreater coverts, tertials, and humeralson Black-looted Albatrosseshave paler inner webs. When worn, this patch of featherscan contrast withthe remainder of theupperwing, creating an appearancesimilar to Short- tailed.Leg and foot color of Black-lootedusually isblackish or darkgray. We have foundseveral individuals with irregular pale splotching on thelegs and feet (e.g., Fig6; thesebirds often show ieucistic plumage as well), but in no casewas this extensiveenough to resemble the entirely pink feet of juvenile Short-taileds. LAYSANALBATROSS Figure8 A Laysanwith rather pale underwings, showing narrow black margins.Midway Atoll, May 1999. Photographby Tristar/McKee. Althoughabout ten times more numerous than the Black-looted Albatross, with a worldpopulation estimated at 2.5 millionbirds (Whittow 1993b), the Laysan Albatrossisnot encountered asfrequently dose to theNorth American continent. Laysansalso arrive at breeding colonies inNovember, fledge young in Julyand early August,and have an annual incomplete tocomplete molt from April to October. Thisspecies was named immutabilis, meaning unchangeable, because of itslack of obviouslydifferent innnature and adult plumages (Jobling 1991). While it is true thatage-related variation is subtle,this species nonetheless shows a considerable