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Birds 25:169-177, 1994 169 IDENTIFICATION OF MANX-TYPE SHEARWATERS We researchedpublished literature, as well as unpublished information from Point Reyes Bird Observatory's(PRBO) on-goingresearch on Newell's Shearwatersnesting in Kauai, Hawaii.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 somebirds 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 flankswere 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 flankpatches 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