The Food of Cook's Petrel Pterodroma cookii During Its Breeding Season on Little Barrier Island, New Zealand

Abstract

Food. samples were obtained from 69 Cook's Petrels Pterodroma cookii on Little Barrier Island, New Zealand, during the breeding seasons (October-March) of 1972 to 1977. Food comprised Cephalopoda, fish, Crustacea and Tunicata in that order of importance by volume. Dietary oil formed about 38% by volume of food fed to chicks. The main cephalopods (of 26 species) preyed on were members of the Cranchiidae, Spirulidae (entirely Spirula spirula) and Histioteuthidae (37, 24 and 22% respectively by mass). About 90% by mass of fishes taken were lantern-fshes (Myctophidae), and about 50% by mass of crustaceans were decapod prawns. Seasonal variation was found in the proportion only of the cephalopods Argonauta and Leachia in the diet. Pumice and plastic particles were ingested. The diet revealed by these samples showed extensive reliance on small, mesopelagic, bioluminescent prey, most of which could have been taken by active feeding at night. Selection of prey was related to the petrel's small size: over half of the cephalopods eaten were juvenile or immature.