NOTES A MASKED BOOBY AT ISLAS LOS CORONADOS, BAJA CALIFORNIA, MEXICO WILLIAM T. EVERETT, Department of Birds and Mammals, San Diego Natural History Museum, P. O. Box I390, San Diego, California92112 SHERRY TERESA, California Department of Fish and Game, California Research Station, 2140 Eastman Avenue, Suite I00, Ventura, California 93003 On 23 April 1988 we observeda juvenileMasked Booby (Sula dactylatra) roosting on a smallrock off the northend of IslaCoronado Sur, Baja California,Mexico. Islas LosCoronados are situated 6 nauticalmiles (nm) off the westcoast of northernBaja Californiaand 4 nm southof the UnitedStates/Mexico boundary. We first noticed the bird at 1250 as we cruised around the north end of the island. We slowlyapproached and observedit for 25 minutesat distancesas closeas 6 meters (photographson fileat the San Diego Natural History Museum). Throughout our observa- tionthe birdseemed oblivious to our presence,despite several attempts to flushit by soundingour air horn. It remainedin the samespot, at timestucking its bill underits wing. Using 10 x 50 and 10 x 40 binoculars,we had excellentviews of both front and back. The birdwas immediately identifiable as a sulidby the shapeof itsbill and headand its overall size. A Western Gull (Larus occidentalis)and Double-crestedCormorant (Phalacrocoraxauritus) were on the samerock, allowing close comparison. The dorsal surface,including the wings,back, rump, and tail werea uniformlight brown, approx- imatingthe Army Brown(Color 219B) of Smithe(1975). The head, neck,chin, and upperthroat were a darkershade of brown,close to Dark GrayishBrown (Color 20). This contrastedsharply at the nape with the color of the back. There was no white fieckingin the plumageof the head,whitish feather tips on the mantle,or whiteon the rumpor backof the neck,which would suggest an immatureBlue-footed Booby (S. nebouxii).The underparts,including the vent, abdomen,breast, and sideswere an immaculatewhite. This pure whiteextended up to the throat,where it met the dark brownof the headand chinin a sharplycontrasting shallow inverted V. Accordingto Nelson(1978), thispattern on the throatis diagnosticof juvenileS. dactylatra.In all plumages,Brown Boobies (S. leucogaster)show brownish coloration extending down to thecentral breast. The legs,feet, bill, and facial skin were a dingy,nondescript grayish color.When flying, juvenile Masked Boobies are oftenrecognized by a whitishcollar aroundthe hindneck.This characteristicwas not noted on the birdat LosCoronados, perhapsbecause the neckwas drawnclose to the bodythroughout our observation. Accordingto Nelson(1978), juvenileplumage is retained until the birdis at leastseven monthsold. By the ageof ninemonths the feathersof the headare mostly white, and white fieckingis apparentover most of the mantle. MaskedBoobies, along with Red-lootedBoobies (S. sula),are the mostpelagic of the four sulidspecies occurring in the tropicaland subtropicaleastern Pacific Ocean (Pitman1986). They breedoff southernBaja California at San BenedictoIsland (Jehl andParkes 1982), ClarionIsland (Everett 1988), andAlijos Rocks (Pitman 1985). North of AlijosRocks they are extremely rare. They are unrecorded from Isla Guadalupe (Jehl and Everett1985) and not previouslyknown from IslasLos Coronados(Jehl 1977). Off Alta Californiathere is one recordof an adultobserved on 10 January1977 at CortesBanks, 35 km southwestof the southend of San Clemente Island (Lewisand Tyler 1978). Detailsof a sightingof an adult S. dactylatraon 14 November1987 at San ElijoLagoon in San DiegoCounty (L. Santaella,pers. comm., McCaskie 1988) havebeen sent to buthave not yetbeen evaluated by the CaliforniaBird Records Com- mittee. Western Birds 19:173-174, 1988 173 NOTES We thankJ. B. Nelsonfor confirmingthe identificationof the birdand reviewingthe manuscript,and Victor and Josephine Alleman for providing transportation to Islas Los Coronadosand other southern Californiaislands aboard their yacht the Ballena. LITERATURE CITED Everett,W. T. 1988. Notesfrom ClarionIsland. Condor 90:512-513. gehl,g. R., Jr., and Parkes,K. C. 1982. The statusof the avifaunaof the Revillagigedo Islands, Mexico. Wilson Bull. 94:1-19. Jehl, J. R., Jr., and Everett,W. T. 1985. Historyand statusof the avifaunaof Isla Guadalupe,Mexico. Trans. San DiegoSoc. Nat. Hist. 20:313-336. Lewis,D. B.,and Tyler, W. B. 1978.First record of the Blue-faced Booby from the Pacific Coast of the United States. W. Birds 9:175-176. McCaskie,G. 1988. The autumnmigration. Southern Pacific coast region. Am. Birds 42:134-139. Nelson,J. B. 1978.The Sulidae.Aberdeen Univ. Stud. Set. 154. OxfordPress, London. Pitman, R. L. 1985. The marine birdsof Alijos Rocks,Mexico. W. Birds 16:81-92. Pitman,R. L. 1986. Atlasof seabirddistribution and relativeabundance in the eastern tropicalPacific. Admin. Rep. LJ-86-02C. Southwest Fisheries Center, R O. Box 271, La Jolla, CA 92038. Smithe,E B. 1975. Naturalist'sColor Guide. Am. Mus. Nat. Hist., New York. Accepted28 November 1988 174 o •0 u o o 175 Wing Your Way to... Sabine's Gull Photo fly Bruce Webb Western Field Ornithologists/ Western Bird Banding Association Joint Annual Meeting October 13, 14, and 15, 1989 University of Nevada, Reno 176 .