White-rumped storm petrel (Oceanodroma sp) 
White-rumped storm petrels were the most evenly distributed group in 
the survey area. Two species were identified: Leach (0. leucorhoa ) and 
Galapagos (0. tethys ). The latter was confined to the vicinity of the 
Galapagos Islands and was distinguished by its distinctly triangular 
white rump patch. All but four of the closely observed Oceanodroma in this 
area were of this species. 
Leach T s constituted 100 percent of all the black, white-rumped storm 
petrels that were closely observed in the remainder of the survey area. 
Identification was based on the black line through the white rump. 
White-tailed Tropicbird ( Phaethon lepturus ) 
All individuals of this species were observed closely as they circled 
and/or followed the ship. A single bird was recorded at 7°N 88°W, two 
single birds were recorded on consecutive days at l8°S 92°W and 20°S 93°W, 
and a "pair" was recorded at 13°N 99°W. 
Red-tailed Tropicbird ( Phaethon rubricauda ) 
Nearly 65 percent of the total number of this species observed were 
recorded south of 5°S. Individuals were observed daily between 20°S and 
5°S along 98°W. 
Brown Booby (Sula leucogaster ) 
This species was observed only north of the equator. Eighty percent 
of the total number observed were recorded on a single day (l February) at 
5 N. Eighty-four percent of the total number observed were immature birds. 
Columbian Brown Boobies (S. 1. brewsteri ) were noted only in the vicinity 
of Cocos Island. The male of this race is characterized by the distinct 
