Group feeding of Northern Fulmars Fulmarus glacialis on the hydrozoan Sarsia princeps on Svalbard

Northern Fulmars Fulmarus glacialis are considered generalist feeders, eaGng whatever the ocean surface offers. Their prey includes (but is not restricted to) fish, squid, fisheries offal, discard and bait, polychaetes, small crustaceans, carcasses floaGng on the water surface (Mallory et al. 2012) and debris such as plasGcs (Kühn et al. 2022). Most diet studies in seabirds rely on stomach content analyses and are biased towards hard prey items, such as fish otoliths, eye lenses and bones, squid beaks, crustacean carapaces, bird feathers and polychaete jaws (Barre et al. 2007). So prey digests o]en too quickly to be recognised in stomach contents and may therefore be underreported in most studies. The ingesGon of so] prey may therefore be common, but is difficult to prove in tradiGonal diet studies, although e.g., Phillips et al. (1999), Byers et al. (2010) and Mallory et al. (2010) report the occasional uptake of so]-bodied pteropods by Fulmars from ArcGc Canada and Greenland. On Svalbard, Fulmar stomachs mainly contained hard prey remains of fish (e.g., Polar Cod Boreogadus saida, Redfish Sebastes marinus and Capelin Mallotus villosus), squid (e.g., Gonatus fabricii), polychaete (e.g., Nereis irrorate), crustaceans (e.g., amphipods, gammarids, euphausiids, etc.), but also here, pteropods were described (Lydersen et al. 1989; Erikstad 1990; Mehlum & Gabrielsen 1993). This current study provides evidence for the ingesGon of hydrozoans by Fulmars on Svalbard, extending their known broad prey spectrum by another invertebrate group.