Contrasting foraging tactics by northern gannets (Sula bassana) breeding in diVerent oceanographic domains with diVerent prey Welds

In order to forage and to provision oVspring eVectively, seabirds negotiate a complex of behavioural, energetic, environmental and social constraints. In Wrst tests of GPS loggers with seabirds in North America, we investigated the foraging tactics of free-ranging northern gannets (Sula bassana) at a large and a mediumsized colony that diVered in oceanography, coastal position and prey Welds. Gannets at Low Arctic colony (Funk Island) 50 km oV the northeast coast of Newfoundland, Canada provisioned chicks almost entirely with small forage Wsh (capelin Mallotus villosus, 89%), while at boreal colony (Bonaventure Island) 3 km from shore in the Gulf of St. Lawrence, Quebec, Canada, large pelagic Wsh dominated parental prey loads (Atlantic mackerel Scomber scombrus 50%, Atlantic herring Clupea harengus 33%). Mean foraging range and the total distance travelled per foraging trip were signiWcantly greater at the larger inshore colony (Bonaventure) than at the smaller oVshore colony (Funk Island; 138 and 452 km vs. 64 and 196 km, respectively). Gannets from Funk Island consistently travelled inshore to forage on reproductive capelin shoals near the coast, whereas foraging Xights of birds from Bonaventure were much more variable in direction and destination. Birds from the Low Arctic colony foraged in colder sea surface water than did birds from the boreal colony, and dive characteristics diVered between colonies, which is concordent with the diVerence in prey base. DiVerences between the colonies reXect oceanographic and colonysize inXuences on prey Welds that shape individual foraging tactics and in turn generate higher level colony-speciWc foraging “strategies”.