SCIENCE msspecimens. We scoredcharacters includingmantle color, tail pattern, andhead pattern; sketched head and rectrixpatterns; and took measure- COOKILARIAPETRELS mentsofculmen length, bill depth, andtail length,and measured indi- vidual rectrices to determine tail shape.Wing lengthswere obtained INTHE EASTERN fromthe literature and from speci- mentags, although it islikely these werenot all taken by the same meth- PACIFICOCEAN' ods. Biometrics from this review will appearin PartII of thispaper. Both authors have studied Cook's Petrels IDENTIFICATIOANDoff California, and Bailey participat- ed in an April 1989 cruisethat recorded113 Cook's Petrels (Bailey et DISTRIBUTION al. 1989). Roberson observed in the eastern Pacific, August-December1989, on a NOAA- PartI ofa Two-PartSeries sponsoredsurvey. He obtainedexpe- rience with hundreds of Cook's, White-winged,and Black-winged petrels,and a few Stejneger'sand byDon Roberson and "Collared"petrels. Illustrator Keith StephenE Bailey Hansen, whose color plate will appearin PartII, alsohas experience THE SMALL PTERODROMA PETRELS and known distribution of all small withmost of thesespecies in theeast- of the subgenusCookilaria are Pterodroma in the eastern Pacific. We ern Pacific. amongthe least understood seabirds review six species:Cook's Petrel, Neither authorhas field experi- In the world. Two species,Cook's Defilippe'sPetrel, Pycroft's Petrel, encewith Defilippe'sor Pycroft's Petrel (P. cookii)and Stejneger's Stejneger'sPetrel, White-winged petrels.We discussedthese species Petrel(P. longirostris),have been Petrel(P. leucoptera, including "Col- withobservers who had field experi- recorded off the west coast of North laredPetrel" [P. (l.) brevipes]),and ence(e.g., J. A. Barde,C. Corben,B. America;others have been tentative- Black-wingedPetrel (P. nigripennis). Haase, P. Meeth, R. L. Pitman, P. ly reported.Knowledge of theirsta- Twoother species, Chatham Petrel Pyle,L. Spear),and reviewed pho- tushas been clouded by thelack of (P. axillaris) and Bonin Petrel (P. tographsand the literature. While we identification criteria separating hypoleuca),are often included in believe that our conclusions will Cook'sPetrel from Defilippe's Petrel Cookilaria.They do not generally proveof value, they remain open to (P.defilippiana) and Pycroft's Petrel P. occurin theeastern Pacific, and they revision. pycroj•i).Indeed, the California havedistinctive underwing patterns; Records Committee, accepting seeHarrison (1983, 1985, 1987) and Historyand records of cookii, has used a dis- Pratt et al. (1987). Althoughwe Taxonomyof Pterodromapetrels is claimerthat "defilippiana and pycroj•i reviewthe taxonomic history of these far from settled,and much of the lit- wereconsidered eliminated solely on forms,we havenot includedthem in eratureis confusing. The firstspeci- knownrange and not on plumage" themain body of this paper. menswere described by Gray (1843) (Roberson1986, Dunn 1988).Tyler under the name cookit. andBurton (1986) thought defilippi- Methods Bonaparte(1855) first used the ana was"nearly identical" to cookii We examineda largepercentage of generic names Cookilaria and in the field. The purposesof this the Cookilariaspecimens in Amer- Pterodroma,placing Cook's Petrel paperare to developidentification ican and New Zealand collections, and alliesin Cookilaria,but he soon criteriafor the Cook's/Defilippe's/ studying100 cookii, 34 defilippiana,moved them to RhantistesKaup Pycroft's/Stejneger'sgroup, and to 37 pycroj•i,95 1ongirostris,95 leu- (Bonaparte1856). Numerous other summarize identification features coptera(of all races), and 79 nigripen-species were described in the late

Volume45, Number 3' • 1800s,but Mathews (1912) lumped Cookdarta to b•rds with a dehcate bill New Caledoma bird •s best consid- allthese under the single species and skull structure and bluish feet. ereda raceof White-winged Petrel/?. Pterodromacookii. Murphy (1929) Havingreviewed Stejneger's descrip- leucoptera(Imber and Jenkins 1981), reviewed the situation and conclud- tion of thebird off Japan,and the andBourne (in litt.) nowconsiders it edthere were but twospecies: pale- laterspecimens, he concluded that a poorlydefined race, not separable headed birds Pterodroma cookii those in the northeastern Pacific were in the field. Bourne (1983) also (includingthose we now call Cook's, moltingmigrants of theMas Afuera pointedout that Collared Petrel may Black-winged,Chatham, and De- nestingbird and called them all/?. lon- bea formof leucoptera,assuggested filippe'spetrels) and those with dark girostris,this having priority over by Murphy (1929). Our limited crownand nape/?. leucoptera (includ- Murphy'sname masafuera. (The type experiencesuggests it is similarin ing thosenow knownas White- specimen,in Tokyo,remained inac- shapeand flight to White-winged winged, Stejneger's,and Bonin cessibleowing to World War II.) Petrel,and that pale birds are not sep- petrels).He calledthe dark-headed Withinthe Cookilaria subgenus, he arablefrom that species in thefield. birdsnesting in theJuan Fernandez concludedthere were three species:/?. We followJouanin and Mougin islandsoff Chile the "MasAfuera longirostris(Stejneger's and Pycroft's (1979)in consideringit a raceof P. Petrel"(P. l. masafuera),and used petrels), P. cookii (Cook's and leucoptera.[Ainley and Boekelheide "MasAtierra Petrel" for the pale- Defilippe'spetrels), and/?. leucoptera (1983) mistakenly used the name "P headedform here,/?. [c.] defilippiana. (White-winged Petrel). There re- l. gouldi"for17. l. brevipes(D. Ainley, He also describeda new race, orien- mainedBonin, Black-winged, and pers.comm.). The term '•ouldi'qs talis,for birds that were very like the Chathampetrels; these had stout bills notavailable for anypopulation of Cook'sPetrels nesting around New andusually flesh-colored feet. He thesepetrels, as "Pterodroma gouldi" Zealand, but which occurred off decidedthey wereone species:P. (Hutton) isnow consideredthe New Chile;these had a scalyback pattern hypoleuca.Fleming (1941 ) consid- Zealandrace of Great-winged Petrel formedby whitish feather tips. He eredCook's and Pycroft's separate (17.macroptera). ] wasunable to placethe taxonlon- species,and lumped Black-winged The popularliterature has tended girostrisdescribed from seas off Japan andChatham petrels as one species,/?. to discussall taxaas separate species, byStejneger (1893), not having seen axillaris, within the Cookilaria sub- but it is not without its own confu- thetype specimen, but he thought it genus.Later, Falla (1962) received sion.Harper and Kinsky (1978) spht likely belongedto the leucopteranotes on/?. longirostrisfrom Kuroda in Pycroft'sfrom Stejneger'sand group.Soon thereafter he referred Japan,supporting his conclusion that Collaredfrom White-winged, asd•d fiveother specimens from the north- it wasa migrantfrom the Mas Afuera Harrison (1983), who greatly eastern Pacific to longirostrisislands; the species has been known as improvedon earlierdiscussions of (Murphy1930). Moffitt (1938)fol- Stejneger'sPetrel ever since. field identification. However, lowed Murphy's taxonomyand Jouaninand Mougin reviewed the Harrison(1983) confused defilipp•- referredthe 1908specimens far off Procellariiformesin 1979. Among anawith Murphy's discredited orien- California(Loomis 1918) to/?.leu- thesepetrels, they lumped Pycroft's talis, and thus failed to include copteramasafuera. Although "masa- with Stejneger'sand Collared with Defilippe'sPetrel in hisguide. Th•s fuera"later proved to belongirostris, White-winged. All were placed in the waspartly remediedin Harrison and these specimenswere of subgenusCookilaria and considered (1985), who called it "at best an Stejneger'sPetrel, the original label of a superspecies.Black-winged and allopatricform of Cook'sPetrel"; but leucopterapersisted and the records Chatham were considered another hegave a rangeof"to 12øN,"again weremistakenly attributed to White- superspecies,but Boninwas termed confusingDefilippe's with specimens wingedPetrel (e.g., Pough 1957). "distinct."The A.O.U. (1983)large- of theold "orientalis" (all specimens Duringthis period Falla (1933) ly followedthis taxonomy, though taken north of the equator are describedPycroft's Petrel (P. pycrofi•). they restricted the superspecies to Cook's).In Harrison(1987), deftlip- Falla also discussed an immature cookii/defilippiana.Bourne (1983) piana(under the name "Masatierra Cook'sspecimen that hada scaly reviewedthe entire group and used Petrel")metired full textand illustra- backand wondered if Murphy's ori- the subgenusCookilaria for all tions,and the range was somewhat entalismightbe a youngCook's on speciesexcept Black-winged, Chat- reduced(though still mapped too far migration.This interpretation isnow ham, and Bonin. He treated all dis- north),but the painting of defilippi- generallyaccepted, and "orientalis" is tinctive populationsas separate anashowed an incorrect tail pattern. not considered valid. species,including the recently dis- Plate 129 in Harrison (1987), also In a subsequentreview, Falla covered birds from New Caledonia appearingin L•fgren (1984) and (1942) restrictedthe subgenus (de Naurois 1978). However, the Lindsey(1986), labelled"Cook's

400. AmericanBirds, Fall 1991 Petrel,"is actuallya fine photoof "white-winged,"and that the name 1990), in the centralPacific (Gould Defilippe'sPetrel taken by Lars White-wingedPetrel is used widely 1983),and offBaja California (pers. L6fgrenoff Chile. Harrison'splate by researchersin the Pacific(e.g., obs.),but in generalmost individuals 135,labelled "Pycroft's Petrel," taken Pitman 1986). foragealone. Any Cookilariamay be byPier Meeth north of NewZealand, attracted to flotsam, and we have is actuallya Cook'sPetrel in worn GroupCharacteristics seenmost species drop onto the plumage.Harrison, L/3fgren, and Cookilaria Petrels are small, fast- watersurface to investigateobjects. Meeth (in litt.) now concurwith our flying Pterodroma,approaching All arepartial to deep,warm, open reidentificationsof thesephotos, Bonaparte'sGull (Larusphiladelphia) ocean, and we are aware of extremely whichwill bothbe printed in PartII in size.All aregray above, with a dark fewrecords of shore-basedsightings of thispaper. carpal-ulnarbar and dark primaries awayfrom the breeding grounds. Exceptfor considering"Cale- formingan "M" patternacross the The specieswith whichwe have donian"and "Collared" petrels as mantle, and mostlywhite below experiencefly in rapid,mostly shal- racesof White-winged, we use (exceptfor melanistic White-winged lowarcs, contouring over the waves. Bourne'sselection of Englishnames. Petrels). Important characters In highwinds, exceeding 15 knots, "Defilippe'sPetrel" is muchbetter include tail pattern, presenceor Cookilariaare prone to arcup quick- for P. defilippianathan the name absenceof a prominentunderwing ly and high, in very rapid roller- "MasatierraPetrel" used by Harrison carpal-ulnarbar, and overall size and coasterfashion; but in lightwinds (1983, 1985, 1987) or "MasAtierra proportions.Facial pattern is also many species(especially White- Petrel"used by Murphy (1936). The important,and some species show a wingedand Black-winged) glide low bird breeds on a number of islands "half-collar"up the sides of theneck, over the water in shallow arcs outsidethe Mas a Tierra group. anda dusky pectoral patch of variable betweenbuoyant, rapid, shallow "Masatierra"iseasily confused with extent.Unfortunately, it is generally wingbeats.In highwinds, the arcs of "Masafuera,"Murphy's old name for notpossible to obtaindecent views at the slimmerspecies are rapid and Stejneger'sPetrel, while "Defilippe's" sea of birdsmore than 300 m distant, ascendto sharp,high apexes, recall- is easilyreferable to the Latin P. andfor manyfeatures, such as tail ing a fastsee-saw. Often the ventral defilippiana.Finally, all the other patternor bill size,it isoften neces- surfaceis quickly turned to the speciesin its subgroup(Cook's, saryto approachthe bird within at observer,then the bird banks down Stejneger's,Pycroft's) are known by least100 m. Throughoutthis paper quickly,to reappearwith the ventral patronyms,and the name Defilippe's weconsider what an observer might surfaceagain, making it quite is in worldwide use. The A.O.U. seethrough 8 or 10power binoculars difficult to observe dorsal features. (1989) addedto the confusionby froma reasonableheight above the The wingslook thin andstiff. All proposingto usethe name"Juan sea.Observers restricted to viewing speciesappear quite maneuverable, FernandezPetrel" (long established from near sea level may not see details unlike the heavier, more deliberate for P.externa externa) for P. defilippi- well evenat the distanceswe cite, and glidesof larger Pterodroma. ana, but this was withdrawn may need to have even closer Eachspecies has a subtlycharac- (A.O.U. 1990) andthey now also encounterswith thesefrustrating teristicshape owing to differingwing usethe name Defilippe's Petrel. [The birds. andtail proportions; these will likely spelling"Defilippe's" istechnically None of the speciesseem to be belearned only with experience. The incorrect;because the professor for ship-followers,and many avoid observer faced with a Cookilaria whom the bird is named was de ships. The Cook's Petrels off should concentrateon (1) under- Filippi (Giglioli and Salvadori California in April 1989 did not wingpattern, (2) presenceor absence 1869).To ourknowledge, no author come to cod-liver oil slicks as did of nape/backcontrast, (3) exacthead hasused the correctspelling. We Murphy'sPetrels, although slicks pattern,(4) tail pattern,and (5) bill proposethat the spelling "De- attractCookilaria in thetropics (P. size/shape.Underwing and head pat- filippe's"be conserved to avoidfur- Pyle,L. Spearin litt.). In theeastern ternsmay be noted at fairdistances, ther confusion.] tropicalPacific, only White-winged but tail patternor bill sizeare not Asto thechoice of White-winged Petreltypically joins mixed bird likelyto be useful until one is at dose Petrelover "Gould's Petrel" (used by flocksfeeding over tuna, but less so range(although these may often be Harrison 1983, 1985, 1987), we thanthe larger Juan Fernandez Petrel studiedlater if photosare obtained). notethat the polytypic species P./eu- (P. externa)(Au and Pitman 1986, There may be differencesin foot coptera needs a group name pers.ohs.). Loose feeding flocks of color (seeFalla 1933), but we have ("Gould's"is often restrictedto one Cookilariaand other species have never seen the feet of a Cookilaria population),that leucopterameans beenreported off Australia(Wood petrelin thefield.

Volume 45, Number 3- light. Underthese conditions, the darkmargins of theunderwings may belost against the background, espe- ciallyat a distance.The effectis that the width of dark marginsor the strengthof the carpal-ulnarbar are underestimated when a bird is seenat a distanceor in stronglight, a phe- nomenoncalled "sea glare illusion." Cook'sPetrel, for example,often looks"uniformly bright white" on theunderwings ata distance,but dis- tinctdark margins and a thin, short carpalbar are seen in flatlighting or at closerange (see Figure 2). An observerwho seesdistant Cook's, and thena doseone, might be tempted to Figure1. Cook'sPetrel in molt,with fresh beck but heavilyworn and moltingwings, off Baja California,March 23,1980. Photograph/RobertL. Ir•tman. thinktwo spedes were present, based uponthe margins and carpal bar seen Molt, Wear,and Lighting crown,especially contrasting against on the near individual. Even the The appearanceof a bird at seais thedark cap of species like Stej neger's broadunderwing margins of White- affectedby molt, wear, and lighting. Petrel.As the plumage wears, these wingedand Black-winged petrels All Cookilaria become darker as the whitetips are worn off, reducing the may seemreduced under strong featherswear. This ismost apparent extent of the white forecrown and lightingat a distance. on theback: a palegray mantle may givingway to a motfledappearance. Lightingcan also affect percep- wearto adingy gray-brown, redudng Littlehas been published on molt tionsof molt.In a strongglare, fresh thecontrast between nape and back of Cookilaria.In thespecies accounts, plumagemay reflect less light than (Stejneger'sand White-winged we summarize what we have learned wornplumage. In thesesituations, a petrels).Wear mayalso affect the abouttiming of molt by reviewing wornBlack-winged Petrel, for exam- prominenceof the "M" pattern specimensand photos; a full analysis ple,may look paler than a freshbird across the mantle. Some birds with isnot possible, as specimens from all (P.Gould in litt.),although the feath- very worn upperwingcoverts may seasonsare often lacking. ersare actually darker. Observers lookessentially black-winged at sea; Lightingand distance play impor- shouldalways take environmental moltmay also account for irregular tant roles in Cookilaria observations. conditions into account. whitepatches on wingsor tail (see Thesesmall, pale seabirds are usually PartH will appearin theWinter Figure1). The palehead of Cook's, seenagainst adark sea, and contrast is issueof American Birds, lOlume 45, Defilippe's,Pycroft's, and Black- heightenedin glareor strongsun- No. 5. wingedpetrels becomes duskier as it becomesworn. Thesespecies may showa suggestionof a darkcap when these worn feathers contrast with either less-wornor newlymolted backfeathers. Body wear often seems correlated with remix and rectrix wear, so that the entire bird looks ragged.At thesetimes, one should reduce reliance on head/back con- trast.Characteristic shape features maybe altered when the wing or tail feathersare growing. In all species, the extent of a white forecrown is affectedby wear. New feathersof the mid-foreheadare tipped white, Figure2. Cook'sPetrel in molt,off BajaCalifornia in July1980. appearingas a broadwhite fore- Photograph/RobertL. Pittma,.

402-American Birds,Fall 1991 Literature Cited Mus.,vol. 1, no. 4: 173-180. 2, no. 12: 1-187. AINLEY, D. G., and R. J. --. 1942. Review of the smaller MATHEWS, G. M. 1912ßThe Birds BOEKELHEIDE.1983ß An ecolog- Pacific forms of Pterodroma and of Australia.Vol. 2. Witherby& ical comparisonof the Cookilaria. Emu42:111-118. Co., London. communities of the southern ß1962. New Zealand records of MOFFITT, J. 1938. Two southern PacificOceanß In Tropicalseabird Pterodromalongirostris and a new petrelsin the north Pacific. (R. W. Schreiber,ed.), recordof Pterodromaleucoptera. 55: 255-259. StudiesinAvia n Biology 8: 2 -23. Notornis9: 275-277. MURPHY, R. C. 1929. On AMERICAN ORNITHOLOGISTS' FLEMING, C. i. 1941. Notes on Pterodroma cookii and its allies. UNION. 1983. Check-list of Neozelanicforms of thesubgenus Amer. Mus. Novatares370. North American Birdsß 6th ed. Cookilaria. Emu 41: 69-80. --.. 1930. Birdscollected during A.O.U., Washington,D.C. GRAY, G. R. 1843. "Birds." inE. the Whitney SouthSea expedi- ß1989. Thirty-seventh supple- Diffenbach, Travels in New tion. Amer. Mus. Novatares419. ment to the A.O.U. Check-list of Zealana•2: 199. ß1936. Oceanic Birds of South North American Birds. Auk 106: GIGLIOLI, H.H., andT. SALVADORI. America. Vol. 2. Amer. Mus. Nat. 532-538. 1869. On some new Procellaridae Hist., NewYork. --; 1990.Errata to the thirty-sev- collectedduring a Voyageround PITMAN, R. L. 1986. Atlas of enth supplementto the A.O.U. theWorld in 1865-68by H.I.M.'s seabird distribution and relative Check-list of North American S. 'Magenta.'Ibis, New Series, 5: abundancein theeastern tropical Birds. Auk 107: 274. 61-68. Pacific. NOAA, NMFS, South- Au, D. W. K., and R. L. PITMAN. GOULD, P. J. 1983. Seabirds west Fisheries Center Admin. 1986. Seabird interactions with between Alaska and Hawaii. Rept.LJ-86-02C, LaJolla, CA. dolphinsand tuna in the eastern Condor85: 286-291. POUGH, R. H. 1957. Audubon tropicalPacific. Condor88: 304- HARPER, P. C., and F. C. KINSKY. lgOsternBird Guide.Doubleday, 317. 1978. Southern and GardenCity, N.Y. BAILEY, S. F., P. PYLE, and L. B. petrels:an identificationguide. PRATT,H. D., BRUNER,P. L., and SPEARß 1989. Dark Pterodroma VictoriaUniv. Press, Wellington, BERRET, D. G. 1987. A Field petrelsin theNorth Pacific: iden- N.Z. Guide to the Birds of Hawaii tification, status, and North HARRISON, P. 1983. Seabirds:an and the Tropical Pacific. American occurrence. Am. Birds identificationguide. Houghton Princeton Univ. Press, Prince- 43:400-415. Mifflin, Boston. ton, N.J. BONAPARTE, C. L. 1855. ---. 1985. Seabirds: an iden- ROBERSON,D. 1986.Ninth report Conspectusgenerum avium. II: tificationguide. Rev, 2nd print- of the California Records Bird 190-191. ing.Houghton Mifflin, Boston. Committee. l•st. Birds 17: 49-77. 1856. Especesnouvelles ß1987. Seabirds of the world: a STEJENGER, L. 1893. Notesona d'Oiseauxd'Aise et d'Amerique, et photographicguide. Christopher thirdinstallment of Japanese birds tableaux paralleliques des Helm.Bromley, England. in the ScienceCollege Museum, Pelagiensou Gaviae.Comptus IMBER,M. J., andJ.A. F.JENKINS. Tokyo,Japan, with descriptions of Rendus Acad. Sci. Paris trans. 42: 1981. The New Caledonia Petrel. new species.Proc. U.S. Nat. 764-776. Notornis 28: 149-160. Museum 16:618-620. BOURNE, W. R. P. 1983. The JOUANIN,C., andJ. L. MOUGIN. TYLER, W. B., and K. BURTON. appearanceand classification of 1979. Order . In: 1986.A Cook'sPetrel specimen the Cookilariapetrels. Sea Swallow Check-listof birdsof the world, E. from California. West. Birds 17: 32: 65-71. Mayrand G. W. Cottrell,eds. Vol. 79-84. DE NAUROIS,R. 1978. 1, 2ndEd.: 48-121. Mus.Comp. WOOD, K. A. 1990. Seasonalabun- reproducteursen Nouvelle- Zool.,Cambridge, MA. dance and marine habitats of Caledoniependant l'ete austral. LINDSAY,T. R. 1986. The Seabirds Procellariafulmarine and gadfly Compt. Rend Acad. Sci. Paris ofAustralia. Angus & Robertson, petrelsoff central New South trans. 287: 269-271. NorthRyde, New South Wales. Wales. Notornis37: 81-105. DUNN,J. 1988.Tenth report of the LOFGREN, L. 1984. Ocean Birds. California Bird Records Com- Knopf,New York. -- 282 GroveAcre Avenue, Pacific Grove, mittee. l•st. Birds 19: 129-163. LOOMIS, L. M. 1918. Areviewof Ca93950 (Roberson); Department of FALLA, R. A. 1933. Notes on New Ornithologyand Mammolog 3 Cali•brnia thealbatrosses, petrels, and diving AcademyofSdences, Golden Gate Park, Zealandpetrels. Rec. Auck. Inst. petrels.Proc. Calif Acad. Sci. 2, Pt. SanFrancisco, CA 94118 (Bailey)

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