干旱区生态环境知识资源中心

Predation in a Massachusetts Common Tern (Sterna hirundo) colony was studied from 1982 to 1984 to identify and quantify its effects on tern reproduction. Prey eaten by Short-eared Owls (Asio flammeus) was determined. The owls caused direct and indirect mortality to terns. Owl foraging activity caused terns to desert their nests during evening twilight and return the following morning. Night desertion exposed tern eggs and nestlings to weather and predators, In 5-6 study plots, 42.0% (N = 290) and 49.7% (N = 280) of the eggs laid (N = 1,254) in 1983 and 1984 seasons, respectively, did not hatch. Nest desertion prolonged incubation periods by six to seven days. Terns accounted for 80.2% (N = 89) of 111 birds killed by the owls. Nestling mortality was exceptionally high, with perhaps only 13 terns fledged of 684 eggs hatched during the two seasons. Techniques for identifying owl predation are described. Management actions directed against the owls are questioned, given this species’ state and regional population status. Standard protocols must be designed to accurately determine and identify predation and predators in colonial waterbird colonies.