Foraging strategies of Antarctic fulmarine petrels

During breeding, procellariiform seabirds are typical central-place foragers, depending on distant pelagic resources. Especially in polar environments, where there is only a short time window to complete the breeding season, high chick provisioning rates are needed to allow chicks to fledge successfully. The duration of the chick period and of chick growth are linked to provisioning parameters such as the frequency and quantity of the chick meals, but probably also to the quality of the food delivered. We studied the provisioning and growth of chicks of Southern Fulmars Fulmarus glacialoides and Antarctic Petrels Thalassoica antarctica on Ardery Island (66°S, 110°E) near the Australian Antarctic station Casey. During two seasons (1998, 1999) we deployed artificial nests to collect data on chick provisioning. Southern Fulmars delivered meals more frequently (one per 14 hours) than did Antarctic Petrels (one every 25-26 hours). In 1998, the mass of meals brought to chicks of both species was not significantly different and averaged around 128 g. In 1999, the meal mass of Southern Fulmars remained the same, but that of the Antarctic Petrel was 28 g heavier. Chick provisioning rates calculated from meal frequencies and masses were significantly different between Southern Fulmars (254 g/day) and Antarctic Petrels (151 g/day), even after correction for body size. Because growth rates for the two species were not significantly different we suggest that Antarctic Petrels deliver meals of higher nutritional value, probably related to food reaching a higher density in the parents' stomach during their longer foraging trips.