Aquatic Bird Predation by Antarctic and Subantarctic Pinnipeds Vagrants Off Argentina

Abstract

Antarctic and Sub-Antarctic pinnipeds are well-known seasonal visitors of the Southwest Atlantic Ocean. According to the literature, at their breeding grounds they feed mainly on a variety of fish, cephalopods, and crustaceans. During the non-breeding period and far away from its breeding colonies, little is known about their feeding habits. Here, we present records of predation on aquatic birds by Antarctic and Sub-Antarctic pinnipeds off northern Argentinian coast (37°27′ S, 57°06′ W to 41°50' S 65°02' W). We examined the gastrointestinal contents of 22 specimens by four pinnipeds species (Arctocephalus gazella [n = 10], A. tropicalis [n = 10] and Hydrurga leptonyx [n = 1]) collected from 1996 to 2023. Remaining of aquatic birds were found in the gastrointestinal tracts of three individuals (13.64%) of two A. gazelle and one H. leptonyx. We identified feathers, and other bird parts by comparing them to specimens from scientific collections and descriptions/illustrations from the literature. Two of the three aquatic birds found in the gastrointestinal tracts were most probably Magellanic Penguins (Spheniscus magellanicus); whereas the other one was a Great grebe (Podiceps major). To our knowledge, this is the first study reporting predation on aquatic birds by Antarctic pinnipeds far from their breeding colonies.