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

Food samples were collected from 29 Herald petrels Pterodroma heraldica, 27 Kermadec petrels P. neglecta and 37 Murphy's petrels P. ultima on the Pitcairn Islands during 1991. 92% of samples were from chicks. Food 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 unidentified decapods, insects-marine water striders Halobates (in 59-66% of 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 enable a comparison of the three petrels' diets. Herald petrels mainly fed on juvenile ommastrephids, whereas Murphy's petrels mainly ate vertically-migrating, bioluminescent cranchiids, histioteuthids and onychoteuthids; Kermadec petrels were intermediate between them. Such differences might have resulted from the different dates when, or different islands where, most samples were collected from each species; or differences in feeding ranges or times of feeding between species; or to species' preferences. (C) 1995 The Linnean Society of London