WESTERN

Volume 19, Number 3, 1988

BIOLOGY OF THE BLACK-VENTED

WILLIAM T. EVERETT, Departmentof Birdsand Mammals,San DiegoNatural History Museum, P.O. Box 1390, San Diego, California92112

In light of newly availableinformation and the recent trend toward con- sideringthe Black-ventedShearwater (Puffinusopisthomelas) and its close relativesas distinctspecies, not subspeciesof the Manx Shearwater( puffinus),it seemsappropriate to summarizecurrent knowledge of the Black- vented Shearwater'sbiology. For this study, I drew informationfrom the literature,data on specimensin the San Diego Natural History Museum (SDNHM), WesternFoundation of VertebrateZoology, Los Angeles (WFVZ), Museumof VertebrateZoology, University of California,Berkeley (MVZ), Los AngelesCounty Museumof NaturalHistory (LACM), CaliforniaAcademy of Sciences,San Francisco(CAS), CarnegieMuseum of NaturalHistory, Pitts- burgh (CMNH), British Columbia ProvincialMuseum, Victoria (BCPM), AmericanMuseum of NaturalHistory, New York (AMNH), the UnitedStates NationalMuseum, Washington, D.C. (USNM), my own field notesof more than 10 yearsfrom islandsand watersoff Californiaand Mexico,and com- municationwith knowledgeableobservers.

BREEDING DISTRIBUTION

The known breedinggrounds of the Black-ventedShearwater are confined to Isla Guadalupe, Isla Natividad, and Islas San Benito off the Pacificcoast of BajaCalifornia, Mexico (Figure 1). The specieswas described (Coues 1864) from a specimen(USNM 16990) taken at seanear Cabo San Lucasby John Xantuson 20 July 1859. In early1886, W. E. Bryant(1887) heardnumerous birdscalling at nightand found a decayedspecimen on top of IslaGuadalupe, but occupiednests were not found there until 1892 (Anthony1896). Other nestingsites remained undiscovered until 1897, when A. W. Anthonyfound a few nestson IslasSan Benito (Anthony 1900a) and discoveredthe vast colonyat Isla Natividad (Anthony 1900b, Kaeding 1905). At Isla Guadalupe,the birdshave been reportedas "rathercommon" at severalsites but at no place in any largecolony (Anthony 1900b). In 1906, they were "abundantat night about the perpendicularcliffs near the north WesternBirds 19:89-104, 1988 89 BIOLOGY OF THE BLACK-VENTED SHEARWATER end of the island"(Thayer and Bangs1908). Nestswere found in naturalholes in the lavaor underlarge boulders (Anthony 1896). More recently,colonies werefound and studiedby Carl L. Hubbson smalloffshore islets at the south end of the island (Jehl and Everett 1985). Little is known of the extentof the breedingpopulation at IslasSan Benito. As at IslaGuadalupe, nesting birds inhabit a few smallcaves and crevicesscat- tered aboutthe islandsand are "not very abundant"(Anthony 1900a). On 14 April 1968, J. R. Jehl, Jr. (pers.comm.) found 20 activenests on San

California

181a8 _.• Los Coronado8 Arizona 181a8Todo8Santos-•:•

isis SanRoque -- • • • iei,Aeunclon• •• Pacific•n • 0 1• KiloSere : : ', 0

Figure 1. Principalseabird breeding islandsof Baja California'sPacific coast, with documentedbreeding locales of P. opisthornelascircled.

90 BIOLOGY OF THE BLACK-VENTED SHEARWATER

BenitoEste before he stoppedsearching. In 1975, Boswall(1978) found birds in sevenlocations, three of whichhad largedowny chicks. R. L. DeLongand R. S. Crossin(unpubl.), during their work with the PacificOcean Biological SurveyProgram in 1968, estimatedup to 150 breedingpairs on the island group.In February1981, duringthe breedingseason, I observedup to 350 birds near the islands at dusk. The fine sandysoil of the southand eastportions of IslaNatividad seems to bestsuit the burrowinghabit of thesebirds, for the islandclearly has been the strongholdof the .Anthony (1900b) reportedfinding "thousands of burrows... likea honeycomb."In 1930 J. R. Pembertoncollected eggs at Natividad (WFVZ) and noted "an immense colony...probably 250,000 occupiedburrows." This figureis undoubtedlya greatexaggeration. In April 1968 DeLongand Crossin(unpubl.) estimated 5000 burrowson the island. Duringmy stayon the islandin July 1987 I estimated,in areasof apparent highestdensity of burrowentrances, an averageof 25 burrowentrances per 100 square'meters.If the majorcolony is not largerthan 4 squarekilometers, whichis my bestestimate, this suggests not morethan 10,000 burrows.The actualfigure is probablysomewhere between 5000 and 10,000 burrows,but thisdoes not necessarily reflect population size or potential,since many burrows could be unoccupiedor occupied by Cassin'sAuklets (Ptychoramphus aleuticus).Also, the extent to which Black-ventedShearwaters inhabit areas on Natividad other than the main colony is unknown. Banks (1964) saw "thousands"of birdsnear the islandon 21 April 1963 and notedthat burrows wereabundant and "mostwere occupied." In lateMarch 19811 saw500-1000 birdsstaging at dusknear the southend of the island.In February1987 1saw severalhundred during a dusktransit 10 km westof Natividad.On 25 April 1987 R. L. Pitman (pers.comm.) saw"thousands... probably10,000" near the south end of the island in the Canal de Dewey. No censushas been attempted,but it seemslikely this island gave rise to the enormousflocks of this speciesthat were formerlyreported at sea (seebelow).

UNCONFIRMED BREEDING REPORTS

There havebeen several erroneous reports of breedingby thisspecies at otherlocales. The recordof eggscollected by CaptainC. M. Scammonat Santa Barbara Island (Brewster1902) off southernCalifornia was later cor- rectedby A. B. Howell (1917). Nelson (1921) reportedshearwater burrows at Isla San Geronimo,near Punta Baja, but thesewere probablymade by Cassin'sAuklets, which breed abundantlythere but had desertedthe island by the time of his visitin August 1905. The A.O.U. Check-list(1957) listed IslaAsuncion (south of Natividad)as a breedinglocale, perhaps on the casual commentof G. D. Hanna (1925), who reported"burrows of Cassin'sAuklet or someshearwater everywhere." Hanna and A. W. Anthony (1923) again mentionedshearwater burrows on Asuncionand Isla San Roque, but I can findno additionalevidence to supportthese claims. Although the mostrecent edition of the Check-list(A.O.U. 1983) has deleted the referenceto Asun- cion,it perpetuatesthe ideathat Isla San Martin, off San Quintin,is a known breedingsite. This idea probablyresulted from the reportsof A. B. Howell

91 BIOLOGY OF THE BLACK-VENTED SHEARWATER

(1910, 1911), who inferredbreeding on IslasLos Coronadosand Isla San Martinfrom sightingsof birdsnear the islandsduring breeding season. Grin- nell (1928) correctlyquestioned Howell's suppositions, which Friedmann et al. (1950)apparently accepted without question. This inclusion on the Mexican check-listwas the solereason (B. Monroe pets. comm.) for the retentionof the islandas a breedinglocale on the NorthAmerican check-lists (A.O.U. 1957, 1983). I know of no reportor evidenceof Black-ventedShearwaters nesting on IslaSan Martin.I foundno burrowson the islandduring several visits since 1979,but crevices and caves abound. Large flocks are frequently seen at nearby banks and at Cabo Colnett, north of the island. Fetal cats are now well establishedat San Martin (pers.obs.), so it is unlikelythat shearwaterswill successfullybreed there in the near future. Wilbur(1987) reported Isla Cedros (near Isla Natividad) as a breedinglocale, on the basisof informationpublished by Banks(1964) and observationsby K. Garrett.Both Banks(1964) and Garrett(pers. comm.) reported only birds seennear the islandduring the breedingseason; neither suggested the birds were actuallynesting. At one time lslaRaza, in the Sea of Cortez,was identified as a nestingsite on the basisof the presenceof "old shearwaterburrows" (Bancroft 1927). A. J. van Rossera(1945), who was with Bancroftwhen they found these burrows,was not totally convinced that they were of Black-ventedShearwaters, and the reportwas subsequently discarded (Palmer 1962). Recentwork on Raza (Boswalland Barrett1978) has not revealedany Black-ventedShear- watersbreeding. The referenceby Leigh(1941, p. 157) to shearwatersnesting on George'sIsland, in the northernSea of Cortez, was unsupportedand appearsto be an assumption.Sightings in the northernSea of Cortezduring the breedingseason in the last few yearshave led to speculationof local breeding(Anderson 1983), which awaitsconfirmation. Many potentialnesting sites exist in Baja California.It is possiblethat P. opisthomelasformerly bred at someof the islandsmentioned above but was extirpatedor desertedthe colonies.Other localeswhere breeding is suspected, on the basisof sightingsof birdsin the immediatevicinity, include Rocas Alijos (Pitman 1985) and Isla San Geronimo(Pitman pers. comm.).

BREEDING SEASON

Currentinformation allows the breedingphenology of the Black-vented Shearwaterto be outlinedas follows:At IslaNatividad birds begin nocturnal visitsto nestsat asearly as November(Lamb 1927). At IslaGuadalupe fresh eggshave been found by 5 March{Jehl and Everett1985) and as late aslate June {J.R. JehlJr., R. S. Crossin,unpubl.). These dates can vary somewhat fromyear to year,and evenfrom colony to colonyin the sameyear {Crossin unpubl.).Typically, colonies are welloccupied by earlyJanuary and the peak of layingis in earlyApril {Anthony 1900b, Kaeding 1905, Banks1964). Young havebeen found as early as lateApril, and by mid-Junemany burrows have a chick{Jehl and Everett1985). Fullygrown young have been found in early July {pets.ohs.) and early August (Anthony 1925). By mid-Augustmost col- onieshave been vacated.The breedingseason appears to be slightlylater than that of Townsend'sShearwater {P. auricularis){Jehl 1982), but this 92 BIOLOGY OF THE BLACK-VENTED SHEARWATER hypothesisshould be tested after further studieson both species.At Isla Natividadfrom 4 to 8 July 1.9871 found several occupied burrows with large downyyoung and freshcarcasses of juvenileswith smallamounts of down stillclinging to the body.

DISTRIBUTION AT SEA

Black-ventedShearwaters are found commonly from the breedinggrounds northto PointConception (34 ø 50' N) and southto Cabo San Lucas (23ø N) and are possiblyregular south along the coastof mainlandMexico (Jehl 1.974)to near the Gulf of Tehuantepec(Figure 2). Lack of field work in the

Figure2. Distributionof Puffinusopisthomelas. Star indicatesthe only localityof extralimitaloccurrence documented with specimens.

93 BIOLOGY OF THE BLACK-VENTED SHEARWATER southern range and problems of identificationwhere the range of P. opisthornelasoverlaps that of P. auricularisaccount for the uncertainty. The speciestypically occurs within 25 km of the coast (except at Isla Guadalupe),but wanderingindividuals have been noted far offshorefrom Baja Californiaat RocasAlijos (24 ø 57 • N, 115ø 45 • W) (Pitman 1985) and in California waters off San Clemente, Santa Cruz (Howell 1917, G. McCaskie pers.comm.), and San Miguel islands(Jehl 1973a). It has alsoentered large bayson the westcoast of BajaCalifornia, such as Bahia San Bartolome(Town- send 1923) and Bahia Magdalena (Bancroft1932, specimensSDNHM). After breeding,some birds move north into the SouthernCalifornia Bight, where they reachpeak numbersfrom Novemberto January (Ainley 1976). Extrapolationsof densityestimates from fall 1977 surveys(Briggs et al. 1987) indicate peak numbers of 20,000 to 30,000 individualsduring this season. This patterndiffers from that reportedearlier (Anthony 1896, Howell 1917, Grinnell and Miller 1944), which suggestedpeak abundancefrom July to September.This discrepancycan be accountedfor only by tremendousflex- ibilityin the breedingand migrationschedule or insufficientfield data during the early part of this century.In recentyears, however, very few birdshave been seen in late summer off southernCalifornia (pets. ohs.). Dispersalnorth of PointConception is irregular,varying from year to year. In someyears, large numbers can be seenin fall as far northas the Monterey Bay region(Stallcup 1976, Beck 1910), but in other yearsthe speciesis absent there.North of MontereyBay verifiedrecords are few. There is one published observationfrom SoutheastFarallon Island off San Francisco(three birdsseen on 28 October1975, DeSanteand Ainley 1980). Briggset al. (1987) reported "one record of three probable Black-vented Shearwatersnear Eureka in December1981." Anthony (1896) reportedBlack-vented as "not uncommonon severaloccasions off the ColumbiaRiver duringthe summer monthsand in Novemberand January."Anthony, who wasa reliableobserver, unfortunatelydid not publishadditional information on thesesightings. On 29 August1929, smallwhite-bellied shearwaters "possibly... Black-vented" wereobserved just off Newport,Oregon (Gabrielson et al. 1930). The species is includedon the Oregon check-list(Crabtree and Nehls 1981) on the basis of a more recentsight record; it isconsidered hypothetical in Washington(Wahl 1975, Mattockset al. 1976) and regarded as very rare in BritishColumbia on the basisof a few midsummersightings (e.g., Martin 1942, Guiguet 1953, Martin and Myres 1969, Guzman and Myres 1983) and five fall and winter specimenstaken near Albert Head, Vancouver Island, in the late 1800s (Kermode 1904, Fannin 1898). I have examined three of these (BCPM 89, 1494, and 1495) and confirmed their identification. Recentmidsummer sightings of smallblack and whiteshearwaters in Alaska (Kesseland Gibson 1978), as well as some of the BritishColumbia reports, may pertainto the Manx Shearwater(Pu•nus puffinus,sensu A.O.U. 1983) whichis a long-distancemigrant whose propensity for occasionalwandering is well established(Palmer 1962, Slater 1970, Kinskyand Fowler1973). The Manx Shearwater'snormal migration places it in higherlatitudes in the north- ern summer, and it is more accustomed to cooler water than is the Black- ventedShearwater (Ainley 1976). Harrison(1983) suggestedthat thesenorth- ern sightingsmay pertainto the Newell'sShearwater of Hawaii (P. auricularis

94 BIOLOGY OF THE BLACKsVENTED SHEARWATER neweili), but in light of its tropical distribution(King and Gould 1967) this appearsless likely. Specimens will be requiredto settlethe questionof origin of these North Pacificvagrants. South of Cabo San Lucas, the statusand distributionof P opisthomelas arepoorly known. Additionally, there is potential for confusionbecause mixed- species(opisthomelas/auricularis) flocks occur in the region(Jehl 1974, 1982, Pitman 1986). Although the fifth edition of the A.O.U. Check-list{1957) reported Isla Clarion as a locationof occurrence,I know of no supporting evidence. In any case, this was deleted from the sixth edition (1983), presumablyas a resultof the Black-ventedShearwater's absence from Jehl and Parkes' (1982) list of birdsof the RevillagigedoIslands. Helbig (1983) reported "about2000" near Puerto Vallarta, Jalisco,on 27 November 1980. Willetttook two specimens{LACM 18954, 86400) at Bahia Tenacatita,Jalisco, on 18 February1938. Pitman (unpubl.),during several cruises off southwest Mexico, has identified Black-vented Shearwaters on three occasions: a flock of 26 on 13 February1980 about30 nauticalmiles (nm) westof BahiaNavidad,

Figure3. Puffinusopisthomelas in wornplumage, photographed 16 August1984 in the centralregion of the Sea of Cortez,near Bahia de Los Angeles.

Photo by Bernie Tershyand Craig Strong

95 BIOLOGY OF THE BLACK-VENTED SHEARWATER

Jalisco, 1 on 4 June 1982 40 nm off Manzanillo, Colima, and 3 on 29 September1986 about40 nm off the southerncoast of Michoacan.His notes for the region contain numerousother sightings,which becauseof viewing conditionscould be identifiedonly as "Manx-type"shearwaters. Murphy (1958) reported"many [Black-ventedShearwaters] seen feeding... about40 miles off Punta San Telmo,southeast of Manzanilld'on 13 November 1956. R. G. B. Brown (unpubl.)reported two individualsoff Oaxaca on 16 April 1981. The southernmostspecimen that I am aware of (SDNHM 38461) was taken off Guerreroby J. R. Jehl, Jr. on 6 April 1973 at 17 ø 25 f N, 101ø 17 f W. Jehl (1974) reported"two brownishbirds (opisthomelas?) in the southernpart of the Gulf of Tehuantepec"on 10 April 1973. Murphy (1952) reportedon sup- posed Black-ventedShearwaters taken off Cabo Blanco, Costa Rica. These were misidentified,as he eventuallyrealized; the specimens,now in AMNH, are Wedge-tailedShearwaters (P. pacificus)(Slud 1964). Bourne and Dixon (1975) reportedsightings of 288 opisthomelason 21 January 1971 off El Salvador.This and reportsof sightingsbetween Hawaii and the Galapagos Islands(King and Pyle I957) are interestingbut more likelypertain to either race of P. auricularis (Pitman 1986). There are sightingsand photographs(Figure 3) but no specimensof this speciesfrom the Sea of Cortez. Helbig (1983) reportedthree birdsbetween Topolobampoand La Pazon 4 June 1980. Jehl (1974) recordedthree "prob- able" opisthomelasnear Isla Cerralvo on 29 March 1973. In March 1887, M. A. Frazarsaw "a largenumber of medium sized,white-breasted and dark- backed shearwaters" between Islas Carmen and Monserrat and near Isla EspirituSanto that were"probably" this species (Brewster 1902). Farthernorth, near Isla Tiburon, D. R. Dickey (in van Rossem1945) reportedshearwaters in June 1928 that were "very probably"but "not certainly"this species.In late December 1931 van Rossem(1933, 1945) noted about a dozen Black- vented Shearwaters between Isla San Pedro Nolasco and Bahia Kino. Between 1983 and 1986 D. Breese,B. Tershy,and C. Strong(pets. comm.) recorded manysightings of Black-ventedShearwaters near Bahia de LosAngeles. These recentsightings suggest this speciesoccurs regularly in the Sea of Cortez.

FEEDING

Littleis knownof thisaspect of the biologyof the Black-ventedShearwater. Rollo H. Beck (field notes, MVZ) reportedsardines ($ardinops sp.) in the stomachsof specimenshe collectedin MontereyBay in December1910. Stephens(1921) reported Black-vented Shearwaters feeding on sardinesnear IslasLos Coronados. Anthony (1896) saysherring (C!upea sp.) and othersmall are the main diet, with bait or refusebeing ignored. In my experience, the birdsare not ship-followersand are not attractedto any type of chum. They havebeen observed feeding "just outside the breakers"at LagunaSan Ignacio (Huey 1927). North of Isla San Martin at Cabo Colnett, Anthony (1896) observedthem plunging after prey in the foamycrests of breakingsurf, althoughthis is apparentlyquite unusual. A flockof nearly12,000 birds(the largestflock reportedin many years)was seen off La Jolla, California,in November1979 feedingon a vast schoolof spawningsquid (Unitt 1984).

96 BIOLOGY OF THE BLACK-VENTED SHEARWATER

MOLT AND PLUMAGES

Accordingto Anthony (1896), Black-ventedShearwaters undergo a com- plete molt from July to Augustand a "moreor less"complete molt of head and bodyfeathers in Januaryand February.Loomis (1918), after examining I39 specimens,concluded that the birdsundergo a protractedpostnuptial molt with great variationin timingamong individuals.He also suggeststhe speciesmay have a seconddowny plumage,as is well known in the closely relatedManx Shearwater(Lockley 1942), but sucha plumageis so far uncon- firmed for the Black-vented.Figure 4 shows a downy young on lsla Natividadphotographed on 7 July 1987. Loomis (1918) believedbirds with extensivegray mottlingon the under- partswere "apparently immature." This has not beenverified. The "melanistic" specimen(MVZ 18691) picturedby Loomis(1918, plate 15) is actuallya typical Short-tail•d Shearwater(P. tenuirostris)(pers. ohs.). This specimenwas col- lectedby the experiencedRollo H. Beck at MontereyBay on 19 December 1910 and tentatively identified by him as a ChristmasShearwater nativita•is)(field notes MVZ). The reasonLoomis reidentified the specimenas opis•homelasis unknown. Leucismand partial albinism,which have been reportedfor other speciesof Puffinus(Mackrill and Yesou 1988), are so far unrecordedfor opisthomelas.

Figure 4. Downy young Pu•finu$

Photo by W. T. Everett

97 BIOLOGY OF THE BLACK-VENTED SHEARWATER

IDENTIFICATION

Jehl (1982) comparedcharacters of Puffinusspecies normally found in the easterntropical and temperatePacific. Since P. puffinusof the North Atlantic is a possiblewanderer, it is worthpointing out that it is similarto P. auricularis (bothsubspecies) in generalappearance. Manx Shearwaterscan even show the conspicuouswhite flankstypical of both racesof auricularis(Hoskins et al. 1979) and alsopresent on the Fluttering(P. gavia) and Hutton's(P. huttoni) Shearwatersof the southernhemisphere (Jehl 1982). The dark vent of opisthomelasmay be the mostreliable field mark. Observers should pay par- ticularattention to face and underwingpatterns, since these characters are poorlyknown but may be useful(G. McCaskie,pers. comm.). The complexity of this situationis illustratedby Figure5, which showsa range of variation in ventral colorationwithin opisthomelas,and Figure 6, which compares opisthomelas,gayla, and huttoni. Becausemany measurementsand charactersin this complexof species overlap,and there are plumagechanges resulting from feather wear and also muchindividual variation, great care should be takenin identificationof species out of their known range. Clear photographsare helpful,but presentknowl- edge suggeststhat only specimenscan documentextralimital records ade- quately. Specimensshould be prepared with one wing extendedto allow examinationof the underwing.

DISCUSSION

Clearly,much remainsto be learnedabout this interesting and little-studied species.It is probablethat unknown coloniesexist on Isla Guadalupe (Jehl and Everett 1985). The currentstatus and abundanceof breedingbirds on Islas San Benito and Isla Natividad also needs elucidation. Little is known of the voiceof the Black-ventedShearwater. Information on behavior,breeding biology,and feedingecology may providedetails useful in settlingthe still unresolvedquestion of systematicrelationships of thisand othersimilar species of the genus Puffinus. Finally,there may be conservationproblems for thisspecies. Feral cats were alreadydestroying birds on IslaGuadalupe in 1892 (Anthony1896), and by 1922 feralcats were established on all knownbreeding islands (Anthony 1925). Sincethat time, all visitorsto Isla Natividad have reported widespreadpreda- tion by cats (Bancroft1927, Banks 1964, Jehl 1973b, 1984, DeLong and Crossinunpubl., Karl Kenyon unpubl.). During my visit in July 1987 I saw no live feral cats, but dried scatswere abundant. Dogs, kept as pets in the fishingvillage at Natividad, occasionallyenter the colony and attempt to excavateburrows. The extent of predationdeserves further study. In recent years, monofilamentgill netting has increasedsubstantially along the coast of Baja California.Nothing is known of the impact on Black-ventedShear- watersof this potentiallydevastating method of fishing. In the early 1890sAnthony (1896) observedoff Baja Californiaa flockof Black-ventedShearwaters consisting of not lessthan 50,000 birds.Grinnell (1897) recorded"immense numbers" of these birdsin the San Pedro Channel in May 1897. Enormousflocks such as theseare no longerseen. In addition 98 BIOLOGY OF THE BLACK-VENTED SHEARWATER

99 BIOLOGY OF THE BLACK-VENTED SHEARWATER

,

.

lOO BIOLOGY OF THE BLACK-VENTED SHEARWATER to ,overfishing for anchoviesand sardinesin boththe U.S.and Mexico couldhave contributed to an apparentdecline in abundance.

SUMMARY

On the basisof specimencollections, available literature, and personalobser- vations,the Black-ventedShearwater is knownto nestonly at IslaGuadalupe, IslasSan Benito, and Isla Natividad, off the west coastof Baja California, Mexico.Birds occupy the breedinggrounds at leastsix monthsof the year. The northernmostdocumented occurrenceis in British Columbia, Canada, the southernmost,off Guerrero,Mexico. The species'diet includessquid and smallfish. Its molt is complex and not well known. Specimensare essential for documentationof extralimitaloccurrences of thisand otherrelated species. Monitoringof breedingcolonies is recommended to assessor preventa popula- tion decline.

ACKNOWLEDGMENTS

DanielW. Anderson,Joseph R. Jehl, Jr., Guy McCaskie,and RobertL. Pitmanreviewed early draftsof thispaper and providedconstructive comments and additionalinforma- tion. Lloyd Kiff (WFVZ), Amadeo Rea (SDNHM), Ned Johnson(MVZ), and Wayne Campbell(BCPM) graciouslyprovided access to specimens.Douglas Bell (IVFVZ),David Lewis,Karl Kenyon,F. Gary Stiles,Kimball L. Garrett,and Dawn Breesealso provided muchuseful unpublished information. Bernie Tershy and CraigStrong allowed access to and publicationof their photographs.Special thanks to Tom Banksand the Founda- tion for Field Researchfor providingtransportation to Isla Natividad.

LITERATURE CITED

Ainley,D. G. 1976. The occurrenceof seabirdsin the coastalregion of California.W. Birds 7:33-68. American Ornithologists'Union. 1957. Check-listof North American Birds. 5th ed. Am. Ornithol. Union, Baltimore, MD. American Ornithologists'Union. 1983. Check-listof North American Birds. 6th ed. Am. Ornithol. Union, Lawrence, KS. Anderson,D. W. 1983. The ,in IslandBioõeography in the Sea of Cortez (T. J. Caseand M. L. Cody,eds.), pp. 246-264. Univ.of Calif.Press, Berkeley. Anthony, A. W. 1896. The Black-ventedShearwater (Pu•/nu$ opisthorne/a$).Auk

Anthony, A. W. 1900a. A night on land. Condor •-:•-8-•-9. Anthony,A. W. 1900b.Nesting habits of the PacificCoast species of the genusPuf- finus. Auk 17:9_47•9_59_. Anthony,A. W. 19•-5. Expeditionto GuadalupeIsland, Mexico, in 19•-•-.The birds and mammals. Proc. Calif. Acad. Sci., Set. 4, 14:9-77-39-0. Bancroft,G. 1927. Notes on the breedingand insularbirds of cenlralLower California. Condor 29:188-195. Bancroft,G. 193•-. Lower California:A Cruise.The Flight of the Least Petrel.G. P. Putnam's Sons, New York.

lol BIOLOGY OF THE BLACK-VENTED SHEARWATER

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