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A Possible Brown Skua (<I>Stercorarius Antarcticus</I>) On

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A Possible Brown Skua (<I>Stercorarius Antarcticus</I>) On lan McLaren mer (June-August)specimens in Canadi- in both publishedarticles and material an museumscollected prior to 1980 in At- postedon the WorldWideWeb,has indicat- BiologyDepartment lantic Canada have been critically identi- edto us thatthe Sable Island bird strongly fied as South Polar Skuas (Michel resembledBrown Skua, although deficien- DalhousieUniversity Gossefin, National Museum of Canada, cies in this information lead us to leave it pers. comm.;University of WesternOn- formallyunidentified. Halifax,Nova Scotia B3H 4J1 tario [seebelow]). All GreatSkua speci- mens have come from the Grand Banks: an ([email protected]) BACKGROUND ON CONFIRMED AND immature in late August 1961 (D. POSSIBLE BROWN SKUAS IN THE McAlpine,New Brunswick Museum, pers. NORTH ATLANTIC Zoe Lucas comm.)and severaladults in September Even after Chilean (S. chilensis)and South (M. Gossefin,pers. comm.). The Great Polar Skuaswere recognizedas distinct P.O.Box 64, Halifax CRO Skuaslisted for SableIsland by McLaren species,the three other skua taxa in the (1980)were not criticallyidentified. Nova Southern Hemisphere continued to be Halifax,Nova Scotia B3J 2L4 Scotianobservers have attemptedto dis- classifiedas formsof GreatSkua (e.g., tinguishthe two speciessince at leastthe Devillers1977). BrownSkna, however, has early 1980s.Since 1992, Lucas has studied becomegenerally recognized as a distinct six live Great Skuas on Sable Island at fair- specieswith threesubspecies (e.g., Olsen ABSTRRCT ly closerange and has found five tideline and Larsson 1997): Falkland Skua, nomi- This paperconsiders characters of a skua carcasses(two salvageableas specimens), nate antarcticus, of the Falklands Islands photographed13 May 1996on SableIsland, all betweenSeptember and January. These and southernArgentina; Tristan Skua, NovaScotia, which the authors identify as a wereidentified by theirbulk, presenceof hamiltoni,of Tristanda Cunhaand Gough possibleBrown Skua (Stercorarius antarcti- distinctlycinnamon or rufousunderparts, Islands in the South Atlantic; and Sub- cus), a speciesnot yet confirmedin the and pale or rufousstreaks on backs.She antarcticSkua, lonnbergi, of the Antarctic westernNorth Arianticbut recentlydocu- has also found two dead South Polar Skuas Peninsulaand islands from South Georgia mentedby molecularevidence in the east- and closelyobserved a live one,all in late across the Southern Ocean to New ern North Atlantic. May.These were typicallight- or interme- Zealand.The futuremay bring further re- diate-morphbirds, dark-backed,evenly arrangementsin systematicsof the south- FIELDENCOUNTER brownishgray below. and with pale nuchal ern skuas(Blechschmidt et al. 1993), and In mid-dayon 13 May 1996,Lucas found a areas. McLaren has similarly identified the evolutionary relationshipbetween skuasitting on the beachat SableIsland, a SouthPolar Skuas off Seal Island in August GreatSkua and PomarineJaeger (Sterco- 45-kin long crescenticsandbar some I60 1983,Great Skuas during a pelagictrip off rarius pomarinus)is apparently close km from the nearest mainland of Nova Sco- Halifax, Nova Scotia, in October 1990. and enough(Braun and Brumfield1998) that tia. This skuawas approachable, to within bothspecies during a pelagictrip offHali- the American Ornithologists' Union about5 m, allowingtwo photographs to be fax in late Scptcmbcr1990, and on a re- (Banks2000) hasrecently merged genus takenin full sunlightbe[ore it stoodup, search cruise on the qcotian Shelf in late Catharactainto genus Stercorarius,al- tookoff, circled and flew away. Because of September1997. thoughthis reclassificationhas not been itsoverall bulk and dark ventral plumage-- Becausethe photographsof the Ma) madeuniformly in the worldornithologi- with what appearedto be warmer tones 1900bird on SableIsland do noteasily ac- cal community than had been observed on South Polar cordwith either of thetwo regularly occur- Brown Skua has long been known to Skuas (Stercorarius macconmcki)--it was ring skuaspecies, we havebeen led to con- wandernorth of the equatorin the Indian initially identifiedin the field as a Great sider other possibilities. For several Ocean(Higgins and Davies1996), but in Skua (S. skua). decades,skuas outwardly similar to the thc wcstern North Atlantic, our lack of Sable Island bird have led observers in the specimensand limited criteriafor the dis- DISCUSSION North Atlantic to suspectthat a third criminating skuas within the antarcticu•/ SKUAS IN CANADIAN species,Brown Skua (Stercorariusantarcti- lonnbcrgi/hamiltonicomplex have thwarted ATLANTIC WATERS cus) wanders to thc North Ariantic. This identificationof severalsuspected Brown Balch (19151) focussedattention of birders suspicionhas been supportedby recent Skuas.Single skuas photographed at the on summerpresence of SouthPolar Skuas molecularevidence froin the UnitedKing- HudsonCanyon off New York/NewJersey in North Atlanticwaters. Although earlier dom (Scott2002, Moon and Carrington on 28 May 1977 (photographin American fitemture indicates otherwise, three sum- 2002). Informationon skuaidentification, Birds32: 1108;Balch 1981) and 29 May 622 NORTH AMERICAN BIRDS 1987 (Brady 1988) were thought to be BrownSkuas, the formera probableSub- antarctic Skua, while the latter bird was identifiedby world authoritiesat the time as a Tristan Skua. Off North Carolina, recordsfrom 22 May 1992(Brinkley 1994) and 29 May 1993 (M. O'Brien,pers. comm.; seeFigures 6, 7) perhapspertain to Sub- antarctic Skua. Several more recent candi- dates from the Gulf Stream off North Car- olina have also been postedto websites (<www.patteson.com/skuas/skuas.htm>, and <www.magikcircle.com/birds/image. asp?title_id=457>).At present,no North American bird records committee has ad- mitted any taxonof skuaother than mac- cormicki and slma to its official list, al- thoughthe North CarolinaBird Records Committee has consideredreports of BrownSkua (H. LeGrand,pers. comm.). In the eastern North Atlantic, Brown Figure1. Skoa on Sable Island, Nova Scotia, 13May 1996. œhotooraphbyZoeLucas. Skua has now been confirmed twice: on the ScillyIslands, 7 October2001 (Scott 2002) Skuas(Newell et al. 1997), but othershave essary.The May 1996bird on SableIsland is andin Glamorgan,3 February2002 (Moon raised the possibility of Brown Skuas thereforedescribed here as a plausiblebut andCartington 2002). The identification of amongsome of themore robust intermedi- unconfirmedrecord, in part to advancethe these skuas from mitochondrial DNA did ate- and dark-plumagedindividuals 0iguet questionof skuaidentification. not excludethe possibility of eitherbeing a 1997). hybridwith paternalSouth Polar Skua, but We can no longerassume that all skuas APPEARANCE OF THE thiswas deemed very unlikely from popu- in the North Atlantic are either Great or SABLE ISLAND SKUA lationestimates and morphology(Votier el South Polar, and records committees In diagnosingthe Sable Island bird (Figure al. 2004). There are no other confirmed shouldnow review all pastreports of skuas, 1, 2), we consultedphotographs, illustra- records of Brown Skuas from North Atlantic just as theydid in the 1970s,when South tions, and descriptionsof the various waters,but moremay come from the east- PolarSkua was accorded species status. Un- speciesand subspeciesof skuasby James ern AtlanticOcean off Senegal,where only til more is known about the identification (in Higginsand Davies1996), Olsenand Great Skuashad been thought to occur of BrownSkua from observationsor photo- Larsson(1997), and Shirihai(2002), along Numbersfrom that regionhave been pho- graphs,morphometric or geneticdetermi- with numerousweb-posted photographs. tographicallyidentified as South Polar nation from birds in the hand remains nec- ß Ageing The reference taxa for the Sable Island skua were naturally Great and South Polar Skuas.At this time of year,a GreatSkua born in 1995 would be at least almost one year old, whereas any southern-hemi- sphere skua could be considerably younger. The lack of pale featbering around the bill, the uniformly dark bill (somepaleness apparently from figh! re- flection), and the blackish rather than grayishor mottledtarsi indicate that it is a post-juvenile.No matterwhat the species, there are no indications that this individual wasunder one year of age.Beyond that, it is not possibleto age this bird on present knowledge,although we suspectthat this individual is not in the "definitive" plumageof an adultof anytaxon, given its rather uniform dorsalplumage. The bird might therefore best be considereda subadult,an impreciselabel but onesuited to the uncertainties surrounding skua plumages(see comments based on molt below). Figure2.5kua on Sable Island, Nova •otia, 13 May 1996. &oto•ro•byloeLucos. ß Comparisonwith plumagesof Great Skua The lackof stronglyrufous tones below or VOLUME 58 (2004) NUMBER 4 623 lesserand greatercovert feathers are vari- ably raggedand othersfresh. This indi- catesthat the bird had only partiallyre- newed its wing plumage,which would better fit a SouthernHemisphere sched- ule, althoughtiming of molt is not fully understood,especially among subadult skuas.(Steve N. G. Howell [pets.comm.] conjecturesthat one very worn featherin the lessercoverts may be a retainedjuve- nile feather,indicating three generations of covertsand suggestingthat the bird is starting its secondprebasic molt, in its third calendaryear.) Iypical GreatSkuas observedin watersoff Virginia,Maryland, and North Carolina in late February throughApril have all completedwing molt and showuniforml) freshremiges and covertsby late winter (J. B. Patteson,
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