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 strongly fied as South Polar (Michel resembledBrown , 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 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 (, and ).At present,no North American bird records committee has ad- mittedany 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 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, pets. comm.;Brinkley 1994).

ß Comparisonwith plumagesof Chilean and The markedlyrufous , which Figure3.An apparent intermediate orpale/intermediate juvenileGreat Skua, captured byLucas onSable Island, Nova Scotia, alsoalmost always has a strongcap, has on2 January 1995 and brought tothe mainland forrehabilitation. Hatethe dark hood, tawny underparts, andpale rufous neverbeen reported in the North Atlantic markingswithin covert feathers, alltypical ofjuvenile Great Skuas (but see text). Photograph byl.l•claren. and is ruled out on plumage,at leaston presentknowledge. However, nonadult in dorsalstreaking and the lack of darkcap appearto be, at most,ve D' narrowpaler plumagesof BrownSkua are more difficult or stronglymarked hood on the headis at marginson somefresh covert feathers. to distinguishfrom darker plumagesof variancewith mostGreat Skua plumages at Ihe mosttelling evidence against Great SouthPolar Skua (particularlypresumed anyage (e.g., Figure3). However,the pos- Skua may be the condition of bird's subadults).the blackish-brownwings do sibilityof dark-morphGreat Skua is impor- plumage.What can be seenof the flight resemble those of South Polar Skua. but tant to consider.Bearhop el al. (1998) not- feathers(Figure 4) suggeststhat primar- there was no hint in the field (nor in the ed that some captive juveniles froin ies, secondaries,and median coverts are photographs)of the pale nape and fore- Orkneyin Scodandhad "verydark, sooty moderatelyfresh. but somescapular and mantle generallyfound in intermediate plumage,with very little contrastbetween in tone between their head, neck and un- derparts,or betweentheir wings and body," and that "some of the darker birds show[callIn addition,virtually the "theno two-toned ru[oustones [brill at all."pat-

tern becameless evident as the juveniles becameolder and by February(ca. seven months)was hardlydetectable on several birds_"Votier et al. in a 2002 web-posted essayon the Scilly IslandsBrown Skua (www.sur fbirds.com/mb/ Features/skua-identificafion.html>) stated that dorsalfeathers of "all of the juvenile GreatSkuas that we haveclosely examiued (probably1500+ birds) show a ratherdis- tinctive internal pattern.. althoughthis maybe restrictedto the medianaud lesser covertsof thedarkest birds, [consisting] of a seriesof complexfine pale speckles, usu- ally just short of the tip of the feather." They further commented:"almost all all- dark sub-adult Great Skuas showed a small amountof paler,mid-brown edging to the greatercoverts...' No such markingsare evidentin Lucas'sphotographs (Figure 4). Rather,there are narrowpale areasalong Figure4.Wing area enlarged fromFigure 1and much brightened tohighlight contrasting details. Hate the apparently fresh shaftsof somescapulars, ending in ex- primariesandsecondaries, themix of worn and fresh scapulars andcoverts, thewhite, exposed shafts onsome worn scapular posedquills on someworn ones,and what feathers,andthe lack of pale internal markings onfresh covert feathers. Photograph byZoeLucas.

624 NORIH AMERICAN BIRD (e.g., Figure 5) and dark-intermediate birds,and often in dark-morphindividuals (photographsin Howell2004). Also,the chestnutcast to the ventralplumage, with whitishfleckings and feathermargins, are not characteristic of South Polar Skuas. A dark-morphSouth Polar Skua should show lessapparent contrast between the blackish upperpartsand paler underparts (e.g., Fig- ure 3 in Howell 2004) than the SableIsland bird. Its apparentrobustness, long, flat- crownedhead, and large bill wouldalso ar- gueagainst South Polar Skua, and the tar- sus,even from the angle shown in Figure2, seemsrelatively longer than expectedfor that species.

ß Comparisonwith plumages of Brown Skua The remaining candidate species is Brown Skua, which the Sable Island bird Figure$.This South Polar Skua (specimen 488,Zology Museum, University ofWestem Ontario) islike others seenin Nova Scotia resemblesin both structureand plumage, watersduring summer. Scott(1959), who collected itoff Lockeport, NovaScotia on7 June 1957, perceptively notedthat its meas- especiallynonadults, which can have lit- urementswere"less thanthe mJnJma recorded forthe... Great Skua..."(the ruler is20 inches, orabout 51 cm) and wondered if tle or none of the paleblotching usually itcould beone ofthe Southern Hemisphere forms.Its small bill, paler around itsbase, cold, brownish-gray underparts, andpale foundon mantleand wings of olderbirds nuthalarea are characteristic ofa pale intermediate-morph, probablysubadult, SouthPolar Skua. Photograph bySarahLee. (James,in Higginsand Davies1996; cf. Figures6, 7). The palefringing of con- Polarx ChileanSkua) nesfiing banded 25 tion, should see that tissueor blood sam- tour feathersis typicalof 1onnbergiBrown January1997 at StationJubany, Antarctic plesare secured from such birds for molec- Skuasphotographed in November-Janu- Peninsula,which was found dead at sea 1 ular-geneticdeterminations. aryon Antarctic breeding grounds 0- Bri- October2000 at the FlemishCap, about an Patteson,E. S. Brinkley,pets. comm.; 600 km eastof St. John's,Newfoundland, ickn0wledõments Figure 8). The narrow, pale streaks some 12,204 km from the nest (Reinhardt We thankcorrespondents Steve N. G. How- around the exposedwhite shafts of et al. 1997,K6ppen and Scheft 2001). The ell, Michel Gossefin,Donald E McAlpine, scapularsand unmarked coverts comport existenceof 1onnbergix maccormickihy- Harry E. keGrand,Jr., Brian Patteson, with the lonnbergiillustrated by Olsen bridsposes a stumblingblock for confir- Michael O'Brien, and David Jamesfor dis- and Larsson(1997: Figures 14, I5). Its mation of Brown Skua In the western cussionsthat improved earlier versions of apparentbulk and long, flat headalso North Ariantic,at leastfor sightand pho- this manuscript. suggestthis largestsubspecies. Nothing tographicrecords such as the Sable Island Literature cited in the photographsis at variancewith individual. In the absence of measure- identification as Subantarctic Skua. In the ments that would confirm Brown Skua-- Balch,L. G. 1982. Identifyingskuas in the photographs,the lack of pale-streaked particularlytarsal length, which in large ABAarea. Birding 13: 190-201. neckor capped/hoodedappearance, typi- femalelonnbergi is much greaterthan in Banks,R. C., chair.2000. Forty-second sup- cal of tamiltoni and antarcticus, makes other taxa--and in the absence of confir- plementto theAmerican Ornithologists' this bird lesslikely to be of thosesub- matorygenetic evidence, we mustconsid- UnionCheck-list of North American Birds. speciesof BrownSkua, although much er this record to be of an unidentified skua Auk 17: 847-858. remainsto be learnedabout SY plumages that resemblesthe known phenotypesof Bearhop,S., R. Furness,and B. Zonfrillo. of these taxa. Brown Skua. 1998. Identification of Catharacta skuas: Hybridskuas must also be considered. More needs to be learned about varia- variabilityin juvenileGreat Skuas. Bird- The incidence of hybridization among tionsin skuaplumages before Brown Skua ingWorld 11: 355-359. southern skua taxa is said to be rather low can be definitivelyclaimed from photo- Blechschmidt,K., H.-U. Peter,J. de Korte, (Parmelee1988, Votier et al. 2004), but re- graphstaken in westernNorth Atlantic wa- M. Winke, I. Seibold,and A. J. Helbig. centstudies by Ritz et al. (2004) indicate ters.Two photographs of a birdon SableIs- 1993. Investigationson the molecular widespread hybridization between land. Nova Scotia,in May 1996 suggest systematicsof skuas (Stercorariidae). Zo- 1onnbergiand maccormicki between 61 ø 05' thatthis species, and in particularthe sub- ologischesJahrbuch ft•r Systematik120: S, 55ø 10' W and 64ø 46' S, 64ø 03' W--ap- specieslonnbergi, may be occurringin the 379-387. parently a broader zone than western North Atlantic. Observers of Brady,A. 1988. Possiblepresence of an known in the 1980s (Parmelee 1988). skuas,of any species,are encouragedto Antarctic Skua in New Jersey waters. Basedon a handingreturn of a lonnbergix make extensivephotographic records of Cassinia 62: 7-11. maccormickihybrid from Brazil, Parmelee their observations and to archive these Braun,M. J., and R. T. Brumfield.1998. (1988) suggeststhat hybrids might tend to with appropriatecommittees. Even varia- Enigmaticphylogeny of skuas:an alter- dispersefarther north in theAtlantic Basin tion in Great Skua plumagesshould be nativehypothesis. Proceedings of the Roy- than do pure BrownSkuas, The only re- documentedexhaustively. Any observer al SocietyB 265: 995-999. coveryof a knownhybrid in the Atlantic fortunateenough to find a skua on the Brinkley,E. S. 1994.Spring migration of Basin north of Brazil is one said to be a sec- beach,especially a tideline corpse or a live off central North Carolina: 22 ond-generationSouth Polar Skua x (South bird in condition suitable for rehabilita- May 1992, with noteson two skua

VOLUME 58 (2004) NUMBER 4 625 Figures6,7. This large skua, tentatively identified asajuvenile BrownSkua, was observed offNorth Carolina's OregonInlet 29 May 1993. Thetones ofplumage wereuniformly deep,warm brownwitha ruddy castin some parts (especially thecoverts), verydifferent fromthe colder tonesand gray cast ofjuvenile SouthPolar Skua. Theuniformity ofcolor and freshness ofplumage, aswell asthe shape ofthe remige tips,indicate ajuvenile skua,but spring daterules outjuvenile GreatSkua and rules ina skua ofthe Southern Hemisphere. Itsoverall dimensions--particular- lythe heavy body, large, deep bill, and long legs--appeared toorobust for South Polar Skua tothe observers andperhaps evenheavier thanGreat Skua, thought tobe mostly awinter visitor to thesewaters. Other suspected BrownSkuas have been observed 1992-2001 inNorth Carolina waters, butnone has been proved. Photo•]raph bylffichaelO'Brien. (Catharacta) taxa. Chat 58: 94-101. Polarskua. Polar Biology 17: 114-118. d•an Field-Naturalist 77: 15-20. Devillets, P 1977. The skuas of the Ameri- Ritz, M. S., S. Hahn, T. Janicke,K. Rein- Scott, M. 2002. A Brown Skua on the Isles can Pacific Coast. Auk 94: 417-429. hardt,and H.-U. Peter.2004. Hybridisa- of Scilly--thefirst for Europe?Birding Higgins,P. J., and S.J. J. E Davies,editors. tion between South Polar Skua (Cathar- World 15: 383-386. 1996. Handbookof Australian, New acta maccormicki) and Brown Skua Shirihai,H. 2002.Complete guide to Antarc- Zealand and AntarcticBirds. Volume 3, (Catharactaantarctica lonnbergi) in the tic Wildlife.Princeton University Press, Snipesto Pigeons.Oxford University AntarcticPeninsula. Poster and presenta- Princeton,New Jersey. Press,Melbourne, Australia. tion, Scientific Committee on Antarctic Votier,S.C., S. Bearhop,R. G. Newell,K. Howell, S. N. G. 2004. South Polar Skuas Research,XXVIII OpenScience Confer- Orr, R. W. Furhess,and M. Kennedy. off California. Birding World 17: ence,Bremen. Germany 2004. The first record of Brown Skua 288-297. Scott, D. M. 1959. Observations on marine Catharactaantarctica in Europe.Ibis 146: Jiguet,E Identificationof SouthPolar Skua: birds of southwestern Nova Scotia. Cana- 95-102. • theBrown Skua pitfall. Birding World 10: 306-310. K6ppen,U., andS. Scheil.2001. Report on bird-ringingin easternGermany for the years1999 and 2000. Berichte der Vogel- warte Hiddensee 16: 5-61. McLaren, I. A. 1980. The birds of Sable Is- land,Nova Scotia. Proceedings ofthe Nova ScotianInstitute of Science31: 1-84. Moon,S., and D. Carrington2002. A Brown Skuain Glamorgan.Birding World 15: 387-389. Newell, D., R. Porter, and T. Marr. 1997. South Polar Skua--an overlooked bird in the easternAtlantic. B•rding World 10: 229-235. Olsen, K. M., and H. Larsson. 1997. Skuas andJaegers. Yale University Press, New Haven, Connecticut. Parmelee,D. E 1988. The hybridskua: SouthernOcean enigma. Wilson Bulletin 100: 345-356. Figure8.Brown (Subantarctic) Skua($.a./onnbergi) atGrytviken, SouthGeorgia Island, South Atlantic Ocean, 2December Reinhardt,K., K. Blechschmidt,H.-U. Peter, 1995.South ofElephant Islandand north ofPalmer Station onthe Antarctic Peninsula, Subantarctic Skuahybridizes with andD. Montahi.A hithertounknown hy- SouthPolar Skua. Some hybrids resemble Brown Skuas inthe field, enough sothat identification ofvagrant Brown Skuas must bridization between Chilean and South relyon morphometric ormolecular data,at least on present knowledge. Photograph • E•twardS. Brinkley.

626 NORTH AMERICAN BIRD