the many ornithologists who have visited 

 islands W of Mexico. I find no mention 

 of them in availahle texts. They prove, 

 however, to he the probahle northernmost 

 breeding station in the Eastern Pacific 

 of three wide-ranging tropical ocean birds, 

 namely this species, the masked booby, and 

 the American man-o'-war bird. 



The tropic-birds at Alijos Rocks were en- 

 gaged in active courtship, twos and threes 

 joining in swift pursuit flight and keeping 

 up an excited trill of their boatswain 

 whistles. A male collected wa6 at the 

 physiological peak of breeding. It dis- 

 gorged a 25-cm. fish ( Colalabis saira ) . 



Surface temperatures in the neighborhood 

 of the Alijos Rocks were as low as 20.6°C. 

 The tropic-birds appeared to be nesting on 

 each of the three stacks of the group. 



Pelecanus occidentalis . Brown pelican. 

 This is a continent-hugging species, of 

 little interest in an oceanographic campaign. 

 It has reached only one group of remote 

 oceanic islands- the Galapagos - where the 

 resident colony is isolated and racially 

 endemic . 



We encountered two subspecies, californicus 

 of the northerly and relatively arid coast, 

 and carolinensis of the moist tropical 

 Middle American coast of both Atlantic and 

 Pacific. Nothing was learned about dis- 

 tribution boundaries or possible inter- 

 gradation of these two forms. 



Sula dactylatra . Masked booby. This 

 largest of the tropical pelagic boobies is 

 to a great extent a flying fish-eater. White 

 adults, dark young, and birds in transitional 

 plumage were seen regularly after we had 

 reached the newly discovered nesting station 

 at Alijos Rocks. The species avoids forested 

 islands and continental coasts. It was not 

 present at Cocos Island, for example, although 

 common enough over the surrounding ocean 

 within a distance of a few hours' sail. 



Discovery of the Alijos colony, where breeding 

 boobies appeared to be confined to the eastern- 

 most of the three stacks, rounds out our 



knowledge of the nesting stations in the 

 Eastern Pacific. These extend from the 

 Alijos Rocks S to San Ambrosio Island, off 

 northern Chile, and include Malpelo (Colombia) 

 and La Plata (Ecuador). The LaPlata colony 

 is the only one within sight of the continent. 

 Malpelo has by far the largest booby 

 population. 



At sea this booby showed marked curiosity 

 regarding conspicuous flotsam such as our 

 skiff and the radar reflector above bottle- 

 floats. The birds would swoop around them 

 again and again, and even attempt to alight. 

 As noted above, the masked booby also makes 

 regular and prolonged use of sea turtles as 

 rafts for resting on the ocean. Substantial 

 flotsam, such as logs, is used in the same 

 way, but it is likely that turtles offer the 

 mo6t plentiful opportunities for perching 

 throughout vast areas off soundings . 



At any rate, on Nov. 15, some 90 miles off 

 the Gulf of Tehuantepec, I saw eight of these 

 boobies standing peacefully on turtles. 

 Again, on Dec. 8, much farther off the coast, 

 six more were observed resting in the same 

 manner. Lone turtle-perchers were noted on 

 numerous other occasions, in some instances 

 apparently sleeping, with the bill tucked 

 among the feathers of the back. 



Sula sula . Red-footed booby. This is the only 

 tree-and shrub-nesting member of its family. 

 In breeding and feeding habits it occupies a 

 somewhat different ecological niche from other 

 boobies inhabiting the same area, thus avoid- 

 ing or reducing interspecific competition. 



Like the masked booby, the red-foot is an 

 offshore and pelagic bird, rarely found near 

 continental coasts. We entered its strong- 

 hold only at Cocos Island, a well -populated 

 nesting station, and found it at sea only 

 within UO0 miles of that island, chiefly 

 toward the NW. It was the only booby that 

 followed the ship, played around the mastheads, 

 and alighted on the superstructure. 

 Approaching Cocos, one was caught on a fish- 

 hook. Others were collected at the island. 



Throughout the tropical oceans this species 

 has several plumage phases, the taxonomic 



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