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 nonbreeding 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 of three pinnipeds species (Arctocephalus gazella [n = 10], A. tropicalis [n = 11] and Hydrurga leptonyx [n = 1]) collected from 1996 to 2023. Aquatic birds remains were found in the gastrointestinal tracts of three individuals (13.64%): two A. gazella 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.