Predator effect and behavioral patterns in arctic terns (Sterna paradisaea) and Sabine's gulls (Xema sabini) during a failed breeding year

Little is known about the factors influencing the breeding decisions of Arctic breeding seabirds and their behavior in afailed breeding year. Here we present the behavioral patterns observed in a year with late sea ice break-up and regular predator visits to the colony. We found that breeding initiation of Arctic Terns and Sabine's gulls was delayed until the breeding attempt was given up and the colony abandoned. However, the birds did not leave the region but returned to the colony soon after sea ice break-up continuing bonding behavior although egglaying was not initiated. In 2006, the period 11-15 July seemed important for the breeding decision, as birds gradually gave up breeding and left the colony during that period.