Diet of Herring Gull Larus argentatus chicks in the Gulf and Estuary of the St. Lawrence River, Québec, Canada

Food availability is often an important regulating factor of seabird populations. In the Estuary and Gulf of the St. Lawrence River, most colonies of Herring Gulls are actually decreasing while diet information is lacking. Collection of 635 regurgitations in three areas (Estuary, Corossol Island and Carleton colonies) revealed that the overall diet of Herring Gull chicks was extremely varied and variable over time and space, which is typical of an opportunist species. Nevertheless, capelin, a key species in the food chain in the St. Lawrence Estuary and Gulf, constituted the bulk of gulls’ diet. At Carleton, located in the southern Gulf, capelin was less abundant, and more human waste completed the chicks’ diet, in comparison with the other sites. This study provides baseline data for future investigation of the relationship between trends in Herring Gull populations and food availability in the Estuary and Gulf of the St. Lawrence River.