Burrowing Petrels as Dominant Trophic Resources for Raptors on a Rodent-free Island in the Southwestern Atlantic Ocean.

Seabird colonies can sustain high-density populations of raptors, but few studies have focused on studying raptor guilds subsidized by seabirds in the southern hemisphere. Here, we studied the food habits of the three most abundant raptor species during the breeding season on a 300-ha, rodent-free island on a subantarctic archipelago in the southwestern Atlantic Ocean. We studied the Short-eared Owl (Asio flammeus), the Peregrine Falcon (Falco peregrinus), and the Striated Caracara (Phalcoboenus australis). Analysis of prey remains and pellets suggest a guild-wide dependence on burrowing petrels that breed on the island, particularly the Common Diving-Petrel (Pelecanoides urinatrix) and the Slender-billed Prion (Pachyptila belcheri). The three raptor species tended to differ in the consumption level of their low-ranking prey items. Peregrine Falcons fed exclusively on burrowing petrels, Short-eared Owls took terrestrial prey such as passerines and insects in addition to burrowing petrels, and Striated Caracaras also fed on other seabirds such as penguins and cormorants. Our results suggest that the local presence of breeding colonies of burrowing petrels explain the high density and species richness of breeding raptors in this small insular system. [ABSTRACT FROM AUTHOR]