Breeding biology of the Peruvian Diving-Petrel Pelecanoides garnotii on La Vieja Island, central coast of Peru

Abstract

Breeding adults were found all around the year; however two peaks were identified. The first and most noticeable, occurs during the summer from December through March. The second, occurs in winter from May through September. Incubation period was estimated to last 50 to 60 days. Rearing period takes 70 to 80 days for complete development. Higher growth rates were found during winter, probably due to a better quality of food. In winter Peruvian Diving-petrels feed mostly on fish larvae, while in summer they feed mostly on planktonic crustaceans. During the El Niño event 1997-98, the first breeding peak occurred normally. Variations were noticed during the second peak. The proportion of incubating adults dropped from 45,25% in May to 17,5% in July. The proportion of nests with chicks dropped from 15% in May and July to less than 5% in September. All this suggests a low hatching success and a high chick mortality. A census conducted during November of 1997 showed a population of 12.800 pairs of birds and does not differ from censuses conducted before. Incubating adults were found in at least 38,41% of the surveyed nests, 66.27% of them were previously banded birds.