WESTERN BIRDS

Volume 25, Number 4, 1994

IDENTIFICATION OF MANX-TYPE SHEARWATERS IN THE EASTERN PACIFIC

STEVE N. G. HOWELL, LARRY B. SPEAR, and PETER PYLE, Point ReyesBird Observatory,4990 ShorelineHighway, Stinson Beach, California 94970

Recent seabird identificationguides (e.g., Tuck and Heinzel 1978, Harrison 1983, 1987) and articleson the Manx Shearwater(Puffinus puffinus)complex (e.g., Jehl 1982, Bourneet al. 1988), do not satisfacto- rily addressthe problemof separatingthe Manx Shearwater(P. puffinus) from Newell's (P. auricularis newelli) and Townsend's(P. a. auricularis) shearwaters,presumably because Townsend's and Newell'sare Pacific Ocean specieswhile Manx is essentiallya bird of the AtlanticOcean. The Manx, however,is a long-distancemigrant that has occurredin the Pacific off Australiaand New Zealand(Kinsky and Fowler 1973, Lindsey1986, Tennyson1986) and off Washingtonstate, in September-October1990 and September-October1992 (Tweitand Gilligan1993). In addition,five Californiarecords of the Manx from July to October 1993 have been submittedto the California Bird RecordsCommittee (M. A. Patten pers. comm.). Here, on the basisof museumand literatureresearch, combined with extensivefield experience of thiscomplex, we summarizeidentification charactersof the Manx, Townsend's,and Newell's shearwaters.

METHODS

We examinedspecimens of these three forms, plus the Black-vented Shearwater(P. opisthomelas), at the AmericanMuseum of NaturalHistory (AMNH; n = 35 Manx, 14 Townsend's,1 Newell's),New York, the Bishop Museum (BM; n = 30 Newell's), Honolulu, the California Academy of Sciences(CAS; n = 9 Townsend's),San Francisco, the LosAngeles County Museumof NaturalHistory (LACM; n -- 3 Townsend's),and the Museumof VertebrateZoology, University of California,Berkeley (MVZ; n -- 3 Manx, 1 Townsend's).In addition,personnel at AMNH, BM, LACM, the Carnegie Museumof NaturalHistory (CM; n = 6 Townsend's),Pittsburgh, and the U.S. NationalsMuseum(USNM; n = 8 Townsend's,40 Newell's),Washing- ton, D.C., kindlyprovided further data on specimensat thoseinstitutions. Western Birds 25:169-177, 1994 169 IDENTIFICATION OF MANX-TYPE SHEARWATERS

We researchedpublished literature, as well as unpublished information from Point Reyes Bird Observatory's(PRBO) on-goingresearch on Newell's Shearwatersnesting in Kauai, Hawaii. Our field experiencewith this complexcomprises about 6000 hoursof at-seaand land-basedobservation of thousands of each form.

RESULTS AND DISCUSSION

The onlysmall shearwater occurring regularly off Californiais the Black- vented(A.O.U. 1983), the plumagevariation of whichwas discussedby Loomis(1918) andEverett (1988). The fieldseparation of thisspecies from Townsend's,Newell's, and Manx shearwatersshould not be a problemif the bird is seenwell. Charactersdistinguishing Townsend's and Newelrs fromthe Black-ventedwere discussed adequately by Jehl(1982). The main featuresof the Black-ventedare its lackof white flankpatches and its dark brownishupperparts blending smudgily into whitishunderparts (versus sharplycontrasting blackish upperparts and white underparts of the others). Althoughone birdin morethan 50,000 Black-ventedShearwaters we have seenshowed white flank patches (Pyle pers. obs.), we considerthis to have been an aberrantindividual; in all other respectsit lookedlike a typical Black-ventedShearwater. Howell and Engel (1993) discusseddifferences betweenTownsend's and the easternPacific race of Audubon'sShearwater, P. lherminieri subalaris. Sizeand Shape Manx, Townsend's,and Newelrs shearwatersare all about the same size as the Black-ventedShearwater, and all fourfly in a similarmanner, so size and flightare unlikelyto be usefulidentification points, particularly with a lone bird. Townsend'saverages longer-tailed than Manx, and Newell's averageslonger-tailed than Townsend's,with virtuallyno overlapbetween Newell'sand Manx (Table1). Newell'sgenerally appears fairly long-tailed in the field, although we doubt this would help in separating it from Townsend's(note overlap in Table1). Recentlyfledged Newell's (in October and November)and birdsin worn plumagecan be short-tailed;e.g., the type'specimenof Newell'shas a tail of 76 mm (Kingand Gould1967) or 77

Table 1 Tail Lengthsand Widthsof DistalBlack Undertail Band (in ram) of Manx, Newelrs, and Townsend'sShearwaters

Tail length Distal black undertail bandb Range(Mean _. SDø) Range(Mean +_ SD)

Manx (n = 38) 68-79 (72.4 +_2.7) 4-21 (9.9 +_4.3) Newelrs(n = 38) 77-89 (83.9 +-3.0) 20-46 (35.2 +_6.8) Townsend's(n = 41) 71-83 (76.3 +_3.0) 43-72 (59.0 +_7.8)

øSD, standarddeviation. bSeeFigure 1. 170 IDENTIFICATION OF MANX-TYPE SHEARWATERS mm (Loomis1918), withinthe rangeof the Manx.Tail lengththus appears of little use in separatingTownsend's from either Manx or Newell'sbut couldbe helpfulin distinguishingbetween Newell's and Manx. Upperpart Coloration As noted above,Manx, Townsend's,and Newell'sare basicallyblackish above and white below. Manx and Newelrs have been described as blacker dorsallythan Townsend's, which is browner(Jehl 1982), and Newell'shas beennoted as blacker dorsally than Manx (Dunn1988). We wereunable to comparesimilarly fresh (blacker) or worn(browner) specimens of all three formsdirectly, although we foundfresh-plumaged Manx as black dorsally as Townsend's,and Loomis(1918) notedthat fresh-plumagedTownsend's are asblack dorsally as Newell's. Because of variablelighting, plumage fading, plumagewear, and poorly known molt schedules of immaturebirds, subtle differencesin the blacknessof the upperpartsappear not to be usefulin identifyinga lonebird at sea.

x

Figure1. Variation(minimum extent of blackabove, maximum extent of blackbelow) in undertailcovert pattern of Townsend's(left), Newell's(center), and Manx (right) shearwaters.The lowerfigure is typicalof Townsend's,whereas most Newelrs have patternsintermediate between the upper and lower figures.Only juvenilesof the Manx showas muchdark asthe lowerfigure. Note that Manx is overallwhite-vented,- Townsend'sis black-vented,with Newelrs intermediatebetween these two extremes. See Table 1 for measurementsof the distalblack undertail band (distanceX). Sketch by Steve N. G. Howell 17i IDENTIFIC^TION OF M^NX-TYPE $HE•RW^TER$

Face and Neck Pattern As Jehl (1982) noted, Newell'sshows a more sharplydefined border betweenthe blackand white throughthe facethan doesTownsend's, which showssome dark freckling in thisregion, making the bordermore diffuse (Figure2). The Manx Shearwaterhas a face and neck patternsimilar to Townsend's(freckled and not sharplydemarcated through the face;Figure 2). We agreewith Jehl (1982) thatthese patterns are likely to be usefulonly at closerange. Another feature that may be helpfulat closerange is the narrowband of palefeathers across the baseof the maxillashown by many ManxShearwaters (e.g., numerous photos, and 20 of 36 specimens;Figure 2). No specimensor photosof Townsend'sor Newell'swe examined showedthis feature; in theseforms the foreheadis solidlyblack (Figure 2). The extentof darkon the sidesof the neckand chest varies considerably in allthree forms. Differences suggested byJehl's (1982) figure 3 arean artifact of the preparation of the specimensshown; specimensof Townsend'sShearwater at CAS match the neck pattern of the upper Newell'sshown by Jehl. Manx Shearwatersalso match the pattern of Townsend's(although the neck sidesof the latter are perhapsslightly blacker),and we considerneck patternof no use in distinguishingthese three forms.

Flank Patch The whiteflank patch of Townsend's(formed by cleanwhite longest flank feathers)was first noted by Jehl (1982) as a fieldmark distinguishing it from the Black-vented and Audubon's shearwaters. Newell's also shows white flankpatches like Townsend's, although the patches on bothforms can be inconspicuous(Howell and Engel 1993; pers. obs.).Furthermore, up to 30% of severalhundred Manx Shearwatersstudied critically in April and May (offWales and England;Howell), in August(off New Brunswick;J. L. Dunn,photos), in September(off Maine; Pyle), and in November(off Chile; Howell)showed distinct white flank patches, with some birds being similar to a typicalTownsend's or Newell's.Also, 18 of 38 specimensof the Manx had.rnosfiy white flanks that probably would appear as patches, although the flank feathersare not as long as on Townsend's;in the other 20 specimens,the flanks were marked with blackish and at seaprobably wo•ld not looklike white patches. Thus, extensive white flank patches strongly suggestTownsend's or Newell'sbut may not eliminatethe Manx. A bird clearlylacking white flank patches is mostlikely a Manx but couldbe a Townsend'sor Newell'smolting its flankfeathers. Evaluatingthe presenceand extent of whiteflank patches demands care. If viewedfrom the sideor above,with the wingsheld bowed (as on the bottomof a downstroke),all three forms show a whiteflank patch between theblack upperwing and the black thighs. The extentto whichthese white patchesextend up ontothe sidesof the rump,as in typicalTownsend's and Newell's,is best seen when the bird is flying slightly away from the observer. Criticalprior experience with one or moreforms is desirablein evaluating the extentof whiteflank patches.

172 IDENTIFICATION OF MANX-TYPE SHEARWATERS

Figure2. Comparisonof Townsend's(left), Neweil's (center), and Manx(right) shearwaters.Note the longer tail of Neweli'srelative to theManx (but see Table 1) andthe different undertail covert patterns of allthree forms (also see Figure 1). See text for other differences. Sketchby SteveN. G. Howell 173 IDENTIFICATION OF MANX-TYPE SHEARWATERS

Undertail Covert Pattern The best featurefor distinguishingthe three forms is the pattern of the undertail coverts.The undertailcoverts of these shearwatersare long, reachingalmost to the tip of the tail and coveringmost of the undersideof the closedtail. Becauseclear views from directlybelow are seldompossible at sea, and becauseblack undertailcoverts often cannot be distinguished from black rectrices,it is usuallyeasier to determinethe extent of black distallyon the undertail(Figures 1 and 2, Table 1). ManxShearwaters older than one year have white undertail coverts, with blackrestricted to the outer websof the lateralundertail coverts (Figure 1, upper).Birds in juvenalplumage (identified by axillarpattern; Baker 1993) alsoshow dusky markings at the tipsof the longestundertail coverts, which are stillmostly white (Figure1, lower).In the field, therefore,the Manx looks white-vented(Figure 2). If a bird is seen from above, however, shadowingcombined with the blackishthighs can suggestthe dark vent of Townsend'sShearwater, and from the sidethe undertailpattern can appear whitebasally and blackdistally, like that of Newell'sShearwater. With birds on the water,the whiteappears as an extensivewedge under the tail (Figure 2). For Townsend'sShearwater, Jehl (1982) indicatedthat "the undertail covertsare uniformlyblackish." In freshplumage, some undertail coverts of Townsend'shave smallwhite tips unlikelyto be visibleother than in the hand. Loomis(1918) also noted that someTownsend's have white proxi- mal undertail coverts and concluded "there are no constant characters differentiatingthe Hawaiian form from the Revilla Gigedo birds."Two specimens(CAS 810, 811; Townsend'sby tail lengthand locality)confirm thisvariation in undertailcovert pattern (Figure 1, upper).However, while a Townsend'swith white proximalundertail coverts may approachthe pat- tern of someNewell's, the whiteproximal coverts of Townsend'sare patchy and do not form such a noticeable and solid white area as on Newell's (Figure 1). Also, in the absenceof molt, the white centralarea on the undertailcoverts of Newell'sis typicallytapered, or V-shaped,while on Townsend'sit is more roundedor irregular(Figure 1). On the water, Townsend'stypically appears all dark underthe tail (Figure2). Descriptionsof the undertailcoverts of Newell's have varied. For ex- ample, figure 3 in Jehl (1982) showstwo specimensof Newell'swith undertailcoverts white proximallyand blackdistally (the feet obscurethe exact extent of white). On the other hand, Harrison (1987) noted that Newell's differs from Townsend's in its "white or mixed black and white undertail-coverts,"and Pratt et al. (1987) said "undertailcoverts whi*.e" for Newelrs. We know of no evidence that Newell's ever has all-white undertail coverts.Museum specimens, photographs, live birds we havehandled, and birdsseen clearly at sea all showedundertail coverts about half white and halfblack (Figures 1, 2), as notedby Jehl(1982). Priorconfusion may have resultedfrom observers'being unfamiliarwith the extent of undertail covertscovering the undersideof the tail (seeabove). Superficially, how- ever, Newell'sappears "white-vented"because the centralwhite area is

174 IDENTIFICATION OF MANX-TYPE SHEARWATERS generallyV-shaped, the sameshape as the undertailcoverts overall, and the blackishdistal and lateralundertail coverts do not differobviously from the rectrices(Figure 2). The pattern of the undertailcoverts of Newell'sis actuallyintermediate between that of Manx and Townsend's.Those Newell'swith the most white approachthe pattern of the Manx, but the lateraland mostdistal tail covertsare more extensivelyblack, contributing to a broaderblack distal area underthe tail (Figures1 and 2; Table 1). In summary,most birds can be separatedby the widthof the darkdistal undertailband formed by the rectricesand dark undertailcoverts. This is generally5-20 mm wide on the Manx Shearwater,25-45 mm wide on Newell'sShearwater (30 mm on the type specimen),and 50-70 mm wide on Townsend'sShearwater (67 mm on the type specimen).These differ- encesare detectableat sea under most condiditonswhen, in directflight, the feetof shearwatersare tuckedin andnot visible, enabling clear views of the undertailpattern. The feetof birdsalighting on, or takingoff from,the water,however, can blockthe undertailpattern. This may alsooccur rarely in directflight, leaving an impressionof darkundertail coverts on the Manx- Shearwater.Observers should also take into accountthe effectsof lighting, suchas brightsun reflecting off the water and makingwhite areaslook more extensivethan they actuallyare, or shadowsmaking white areas appeardark. Also, molt of the the longestcentral undertail coverts of a ManxShearwater may cause the undertailto showmore black than usual at the tip. UnderwingPattern Dunn (1988) pointedout that Newell'sshows more contrastof flight feathersto underwingcoverts than doesthe Manx Shearwater.While both Townsend'sand Newell'shave the undersurface of their remigesblackish gray, versusa paler,more silverygray in the Manx, we agreewith Dunn (1988; pers. comm.) that this characteris subjectto variationsin lighting and couldbe of useonly underideal conditions. The underwingcoverts of all three formsare mostlywhite, with a dark or duskybar on the proximallesser coverts. This bar generallyshows up most stronglyon Townsend'sShearwater but is also present on Manx and Newell's.Thus underwing pattern is not likelyto be usefulfor distinguishing these three forms at sea.

SUMMARY

Fieldseparation of Manx, Newelrs,and Townsend'sshearwaters is not alwayseasy and requires clear and preferably prolonged views of a bird.The effectsof lighting,wear, and molt shouldalways be considered,and an evaluationof, all possiblefeatures should be used. The pattern of the undertail coverts is the most useful feature: Townsend'-s has black undertail coverts, Manx has white undertail coverts, while Newell's has a pattern intermediate between these two extremes, with black distal and lateral covertsand white central proximal coverts (Figures 1 and 2). Differencesin face patternare usefulbut requireclose-range views: look for the cleaner- 175 IDENTIFICATION OF MANX-TYPE SHEARWATERS cutblack and whitefacial division of Newelrsand the narrowpale band over the bill of Manx (Figure2). Birdswith prominentwhite flank patchesare most likelyTownsend's or Newell's;those lackingthem are more likely Manx. The longertail of Newell'scompared with Manx may be a useful feature;the tail lengthof Townsend'sis intermediatebetween that of the Manx and Newell's.

ACKNOWLEDGMENTS

We thankthe followingpersonnel at the museumslisted under Methods for access to and/or data concerningspecimens in their care: Mary LeCroy and Emanuel Levine (AMNH), James Dean and Gary R. Graves (USNM), Robert L. Pyle (BM), KimballL. Garrett (LACM), Robin Panza and Kenneth C. Parkes(CM), Karen Cebra and BetseyCutler (CAS), and CarlaCicero and BarbaraStein (MVZ). We alsothank David Ainley for permissionto examineunpublished photographs and videosof Newell'sShearwaters. Research conducted by PRBO on seabirdecology at sea, coordinatedby Ainleyand ChrisRibic, allowed us to gain extensivefield experience with Newell's and Townsend'sshearwaters. National GeographicSociety grants 3321-86 and 4106-89 and NationalScience Foundation grants OCE 8515637 and OCE 8911125 supportedthis research.Howell thanksRichard Kelton and the KeltonFoundation for sponsoringtwo cruisesto watersoff westernMexico, in 1988 and 1992, which contributedgreatly to HoweIFs experiencewith Townsend's Shearwater.Jon L. Dunn providedphotographs of Manx and Newell'sshearwaters forexamination. David Ainley, Joe Morlan, and Philip Unitt prOVided valuable review of the manuscript.This is contributionnumber 608 of PRBO.

LITERATURE CITED

Baker,K. 1993. IdentificationGuide to EuropeanNon-Passerines: BTO Guide24. BritishTrust for Ornithology,Tring, England. Bourne, W. R. P., Mackrill, E. J., Patterson, A.M., and Yesou, P. 1988. The YelkouanShearwater Puffinus (puffinus?) yelkouan. Br. Birds81:306-319. Dunn,J. L. 1988. Tenthreport of the CaliforniaBird Records Committee. W. Birds 19:129-163. Everett,W. T. 1988. Biologyof the Black-ventedShearwater. W. Birds19:89-104. Harrison,P. 1983. Seabirds,an IdentificationGuide. Houghton Mifflin, Boston. Harrison,P. 1987. Seabirdsof the World,a PhotographicGuide. Christopher Helm, London. Howell,S. N. G., and S. J. Engel.1993. Seabirdobservations off westernMexico. W. Birds 24:167-181. Jehl,J. R., Jr. 1982. The biologyand taxonomy of Townsend'sShearwater. Gerfaut 72:121-135. King, W. B., and Gould, P. J. 1967. The statusof Newell's race of the Manx Shearwater.Living Bird 6:163-186. Kinsky,E C., andFowler, J. A. 1973. A ManxShearwater (Puffinus p. puffinus)in New Zealand. Notornis 20:14•-20. Lindsey,T. R. 1986. The Seabirdsof Australia.Angus and Robertson, North Ryde, N.S.W., Australia.

176 IDENTIFICATION OF MANX-TYPE SHEARWATERS

Loomis.L. M. 1918. Expeditionof the CaliforniaAcademy of Sciencesto the GalapagosIslands, 1905-1906. XII. A reviewof the albatrosses,petrels, and divingpetrels. Proc. Calif. Acad. Sci., Ser. 4., Vol. 2, Pt. 2, 1-187. Pratt, H. D., Bruner,P. L., and Berrett,D. G. 1987. A FieldGuide to the Birdsof Hawaii and the TropicalPacific. Princeton Univ. Press,Princeton, N.J. TennysonßA. J. 1986. Secondrecord of a Manx Shearwaterfrom New Zealand. Notornis 33:59-61. Tuck,G. S., and Heinzel,H. 1978. A FieldGuide to the Seabirdsof Britainand the World. Collins, London. Tweit, B., and GilligamJ. 1993. Oregon/Washingtonregion. Am. Birds47:139- 143.

Accepted 28 Nlay 1994

Manx-typeshearwater, two mileswest of PointJoe, MontereyCounty, 29 August 1993. Photo by Rod Norden

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