THE FOOD OF COOKS PETREL PTERODROMA-COOKII DURING ITS BREEDING-SEASONON LITTLE BARRIER-ISLAND, NEW-ZEALAND

Food samples were obtained from 69 Cook's Petrels Pterodroma cookii on Little Barrier Island, New Zealand, during the breeding seasons (Octo ber-March) or 1972 to 1977. Food comprise Cephalopoda, fish, Crustacea and Tunicata in that order of importance by volume. Dietary oil forme d about 38% by volume of food fed to chicks. The main cephalopods (of 26 species) preyed on were members of the Cranchiidae, Spirulidae (ent irely Spirula spirula) and Histioteuthidae (37, 24 and 22% respectivel y by mass). About 90% by mass of fishes taken were lantern-fishes (Myc tophidae), and about 50% by mass of crustaceans of decapod prawns. Sea sonal variation was found in the proportion only of the cephalopods Ar gonauta and Leachia in the diet. Pumice and plastic particles were ing ested. The diet revealed by these samples showed extensive reliance on small, mesopelagic, bioluminescent prey, most of which could have bee n taken by active feeding at night. Selection of prey was related to p etrel's small size: over half of the cephalopods eaten were juvenile o r immature.