Nesting of Brandt's Cormorants in the Northern Gulf of California

NOTES

NESTING OF BRANDT'S CORMORANTS IN THE NORTHERN GULF OF CALIFORNIA

JUAN CERVANTES-SANCHEZ,C/Nueva Zelanda69 6A, 28035 Madrid,Spain ERIC MELLINK, Centro de Investigaci6nCientifica y Educaci6nSuperior de Ensenada,Apdo. Postal 2732, 22860 Ensenada,Baja California, Mexico (U.S. mailingaddress: P.O. Box 434844, San Diego, California92143-4844)

In Mexico, Brandt'sCormorant (Phalacrocoraxpenicillatus) breeds mostly on islandsand offshorerocks along the Pacificcoast of the peninsulaof BajaCalifornia (Everett and Anderson 1991, Grinnell 1928, Wilbur 1987). The southernmost knowncolony on the Pacificcoast is at the north endof IslaMargarita (approximately 24 ø 30' N, 112 øW; Guzmanin Everettand Anderson1991). Coloniesin the Pacific can contain thousands of individuals. In the Gulf of California documentedBrandt's Cormorant breedinghas been restrictedto the Midriff Islands.In this regionit nestsor has nestedon Roca Vela, on islandsin Bahia de los Angeles,including Calavera, Smith, and Flecha, on Roca Partida(near Isla Partida Norte), IslaPartida (or Cardonosa),Isla Salsipuedes, Isla San Esteban,and Isla San Pedro M•rtir (Ainley et al. 1981, Banks 1963, Everett and Anderson1991, Osorio-Tafalland del Toro-Avil•s1945, Tershyand Breese1997, van Rosseraand Hachisuka1937, E. Palaciospers. comm.). In addition,van Rossera (1945) suspectedsome offshorerocks near Guaymasas a breedinglocality for this species.Brandt's Cormorant breedingcolonies in the Gulf of California are small, rarely exceeding250 pairs, and the total populationin this area has been estimated at 500 to 1000 pairs(Everett and Anderson 1991). It is possible,however, that some colonieshave been overlooked,through confusion of this specieswith the Double- crestedCormorant (P. auritus) (Russelland Monson 1998, Wilbur 1987). Here we report a breedingcolony of Brandt'sCormorant on IslaSan Jorgein the northern Gulf of California. Mailliard (1923) and Mellink and Palacios (1993) previouslyreported on the breedingbirds of thisisland, and neitherrecorded nesting Brandt'sCormorants. Isla San Jorge (31 ø 01' N, 113 ø 15' W) comprisesa seriesof smallbare rocky isletslocated in the northeasternGulf of California. On 9 November1999 we founda smallbreeding colony of Brandt'sCormorant on the northeasternside of the southernmostislet (Figure 1). The colony,located on a 30 ø slope, about 10 meters above mean sea level, was surroundedby a small congregationof CaliforniaSea Lions (Zalophuscalifornianus) and some nesting Brown Boobies(Sula leucogaster).Double-crested Cormorants were nestingon the upper ridgesof the islet. We countedabout 40 Brandt'sCormorants, including breedingadults and first-yearbirds, and 24 nests,19 of whichcontained one to four eggs.On 31 January2000 we recorded31 adultsand 13 juveniles.Five adults were stillattending nests. A smallchick, yet to fledge,was visiblein one of these.On 9 January2001 therewere 39 adultsand 26 youngin the colony.Eight of the adults were attendingnests. Our field work was supportedby a grant from Conacyt(Mexico) to Mellink. We thank the SociedadCooperativa Ejidal Bahia de San Jorge for logisticalsupport, Mario Machado and Carmelo Gil for transportationto the island, and Eduardo Palacios and Kimball Garrett for editorial assistance.

LITERATURE CITED

Ainley, D. G., Anderson,D. W., and Kelly, P. R. 1981. Feedinõecolog• of marine cormorants in southwestern North America. Condor 83:120-131.

134 WesternBirds 32:134-135, 2001 NOTES

'::%.. - . •.•. :,,,,• --- • Figure1. Brandt'sCormorant colony at lslaSan Jorge, showing chicks three quarters grownand one incubatingadult. Also visible are Blue-lootedand Brown Boobiesand California Sea Lions.

Photo by Eric Mellink

Banks,R. C. 1963. Birdsof the BelvedereExpedition to the Gulf of California.Trans. San Diego Soc. Nat. Hist. 13:49-60. Everett.W. T., and Anderson,D. W. 1991. Statusand conservationof the breeding seasonson offshorePacific islands of Baja Californiaand the Gulf of California. Int. Council Bird Protection Tech. Publ. 11:116-139. Grinnell,J. 1928. A distributionalsummation of the ornithologyof LowerCalifornia. Univ. Calif. Publ. Zool. 32:1-300. Mailliard,J. 1923. Expeditionof the CaliforniaAcademy of Sciencesto the Gulf of California in 1921. Proc. Calif. Acad. Sci. 12:443-456. Mellink.E., and Palacios,E. 1993. Noteson breedingcoastal waterbirds in northwest- ern Sonora. W. Birds 24:39-37. Osorio-Tafall. B. F., and del Toro-Avil•s. M. 1945. Notas sobre la distribuci6n de Phalacrocoraxpenicillatus (Brandt)en el Golfo de Cortesy la costaoccidental de Baja California.Rev. Soc. Mex. Hist. Nat. 6:85-93. Russell,S. M., and Monson, G. 1998. The Birds of Sonora. Univ. of Ariz. Press, Tucson. Tershy, B. R., and Breese,D. 1997. The birdsof San Pedro M•rtir Island,Gulf of California, Mexico. W. Birds 28:96-107. Van Rossem,A. J. 1945. A distributionalsurvey of the birdsof Sonora. Occ. Pap. Mus. Zool. La. State Univ. 21. Van Rossem,A. J., and Hachisuka,M. 1937. A furtherreport on birdsform Sonora, Mexico, with descriptionsof two new races.Trans. San Diego Soc. Nat. Hist. 8:321-336. Wilbur,S. R. 1987. The Birdsof Baja California.Univ. of Calif. Press,Berkeley.

Accepted 12 February 2001

135