Foraging niche partitioning by sympatrically breeding Antarctic and snow petrels

Breeding in sympatry may increase competition among closely related species, especially when these species are colonial central-place foragers. Niche partitioning, for example through segregation in space, time, habitat or diet, can help mitigate such competition. Here, we tested for differences in the movement, space use and habitat selection of 2 closely related pelagic seabirds, the Antarctic petrel Thalassoica antarctica and the snow petrel Pagodroma nivea, breeding sympatrically in Antarctica. To do so, we tracked the foraging movements of breeders from a large colony at Svarthamaren, Dronning Maud Land, using GPS loggers. We found that during incubation, Antarctic petrels travelled faster and trips were longer in duration and travel distance than those of snow petrels. Antarctic petrels foraged predominantly northeast of the colony, whereas snow petrels foraged farther west, closer to the coastline. This led to spatial segregation, with <15% mean overlap between foraging areas of the 2 species. Snow petrels foraged more frequently among sea ice, and closer to the sea-ice edge than Antarctic petrels. These results support the hypothesis that the foraging niches of the 2 species are differentiated in geographical space and habitat, possibly mediated by differences in size and therefore flight performance. Our results imply that foraging snow petrels are more directly dependent on sea ice than Antarctic petrels, and consequently more immediately affected by loss of sea ice due to climate change.