FOOD OF 3 SYMPATRIC GADFLY PETRELS (PTERODROMA SPP) BREEDING ON THE PITCAIRN ISLANDS

Food samples were collected from 29 Herald petrels Pterodroma heraldic a, 27 Kermadec petrels P. neglecta and 37 Murphy's petrels P. ultima o n the Pitcairn Islands during 1991. 92% of samples were from chicks. F ood items comprised cephalopods (in 86-92% of samples) of 22 species, fish (in 24-41% of samples) of at least four families, crustaceans (in 10-38% of samples) including mysids, an amphipod, an isopod and unide ntified decapods, insects-marine water striders Halobates (in 59-66% o f samples), coelenterates (in 0-8% of samples), tunicates (in 0-7% of samples), and traces of offal (cetacean or shark), plastics and pumice . Only cephalopods were sufficiently numerous and identifiable to enab le a comparison of the three petrels' diets. Herald petrels mainly fed on juvenile ommastrephids, whereas Murphy's petrels mainly ate vertic ally-migrating, bioluminescent cranchiids, histioteuthids and onychote uthids; Kermadec petrels were intermediate between them. Such differen ces might have resulted from the different dates when, or different is lands where, most samples were collected from each species; or differe nces in feeding ranges or times of feeding between species; or to spec ies' preferences. (C) 1995 The Linnean Society of London