FEEDING ECOLOGY OF THE DARK-RUMPED PETREL IN THE GALAPAGOS-ISLANDS

During a study of Dark-rumped Petrel (Pterodroma phaeopygia) breeding biology in the Galapagos Islands, we collected over 80 samples of food regurgitated by petrel chicks. We identified the prey to the lowest possible taxonomic level and determined the relative importance of each food class in the petrel's diet. We also monitored the daily changes in mass of 14 chicks on Floreana Island to determine the quantity of food delivered as well as the food delivery rate. Dark-rumped Petrel hatchlings were fed a mixture of stomach oils, semi-digested fish, cephalopods and crustaceans. On the basis of mass composition, about 46% of the diet was cephalopods, about 37% fish, and about 17% crustaceans. Cephalopods, of at least 16 families, occurred with the greatest regularity. Fish were present in the samples more frequently than Crustacea: seven and five families, respectively. Feeding rates were highest in the month after hatching and lowest before fledging. Estimated food loads averaged 68 g and did not increase in size over the growth period. Dark-rumped Petrels fed on mainly mesopelagic prey, taken presumably at night, while ranging up to 2,000 km from the colonies, largely southwards.