Geographic range.—Throughout tropical Pacific area and south to Australia. In Micronesia: Mariana Islands—Asuncion, Uracas, Pagan, Medinilla, Saipan, Rota, Guam; Palau Islands—exact locality unknown; Caroline Islands—Grimes, West Fayu, Truk, Kusaie; Marshall Islands—Jaluit, Eniwetok.
Characters.—Adult: A heavy sea bird dark brown except for white lower breast, belly, under tail, and auxillars; bill heavy and light bluish; face, gular pouch and feet greenish yellow.
Immature: Resembles adult, but lower breast, belly and under tail mottled with brown; feet light yellow.
Measurements.—Two adult males (Rota, Guam) measure: wing 386, 408; tail 194; exposed culmen 93, 98; tarsus 45, 49; two adult females (Rota, Kusaie): wing 380, 487; tail 193, 217; exposed culmen 94, 99; tarsus 45, 50.
Weights.—The author (1948:41) records one immature female from Rota weighing 1042 grams.
Specimens examined.—Total number, 6 (3 males, 3 females), as follows: Mariana Islands, USNM—Rota, 3 (Oct. 24); AMNH—Guam, 1 (July 23); Palau Islands, AMNH—exact locality not given, 1 (Dec. 1); Caroline Islands, AMNH—Kusaie, 1 (April 19).
Nesting.—Few records have been published concerning nesting of the Brown Booby in Micronesia. Yamashina (1932a: 407) reports the taking of 12 eggs at Medinilla in the Mariana Islands on February 19, 1931. At Palau, Coultas (field notes) obtained reports that the bird nests at Kiangat, a small islet north of Babelthuap.
Parasites.—Uchida (1918:487, 493) obtained bird lice (Mallophaga), Menopan brevipalpe and Lipeurus potens, from the Brown Booby from the "sea off Mariana Islands."
Remarks.—The Brown Booby has not been found abundantly by observers in the Micronesian area. Coultas and Kubary, who spent considerable time in this region, observed the bird at only a few of the islands. Probably the bird does not nest abundantly in Micronesia, although small colonies may be present. The NAMRU2 party observed a flock of twelve brown boobies on high cliffs at Taipingot Peninsula at Rota on October 24, 1945. Birds were seen also at Guam in May, July and November, 1945, and at Truk in December of the same year. Coultas obtained a single specimen at Kusaie; the natives told him that it was not a resident of the island. The writer observed several Brown Boobies approximately twenty miles east of Eniwetok in the Marshall Islands on January 7, 1945. These were in the company of other sea birds.