Opportunistic feeding in lamp-light by Brown-hooded Gulls (Larus maculipennis) in Puerto Madryn harbour, Argentina

LEOPOLD, M.F.; PHILIPPART, C.J.M; YORIO, P.

El Hornero

Asociación Ornitológica del Plata

Año: 2010 vol. 25 p. 55 - 60

0073-3407

This note describes nocturnal, marine feeding behaviour in Brown-hooded Gulls (Larus maculipennis) in November 2009. The gulls assembled at night at the end of a long pier, running 800 m offshore into the Golfo Nuevo, at Puerto Madryn, Argentina. Here, powerful lights predictably lighted the water around the pier?s end and attracted many small prey animals to the surface. Several hundreds of gulls, presumed to be local breeders, came every night to feed on this bounty, using various feeding techniques and taking several prey species and sizes. Potential prey were caught to be identified by vertical plankton hauls. The gulls most likely took relatively large Isopoda (Idothea sp.), Annelida (Platynereis sp.) and fish larvae (Patagonotothen sp.) as well as smaller crustaceans, mostly Amphipoda (Phoxocephalidae) and Mysidacea. The gulls caught small prey items while swimming, by rapid surface pecking, while they hunted the larger prey species by flying low over the water and performing shallow, vertical plunge-dives. During daylight, only few gulls ventured from land into the bay, indicating that they took advantage of the nocturnal feeding opportunity, facilitated by artificial lighting. The clear short-term gain of exploiting this novel foraging opportunity may, however, be offset by potential threats such as increased vulnerability to predators or contamination by an oil spill from a ship moored along the pier.