Northern Prairie Wildlife Research Center
The authors tested whether avian predators are attracted to islands in southern Sweden where observers flush incubating common eiders (Somateria mollissima). The abundance of hooded crows (Corvus cornix) was slightly lower after disturbance than before, although many common eider nests were exposed after disturbance. Crows did not increase their foraging effort or success in finding nests on the islands following disturbance. Herring gulls (Larus argentatus) and great black-backed gulls (L. marinus) were slightly attracted to the disturbed islands and tended to increase their foraging effort and success. Although we observed more depredations after disturbance than before, clutch size and frequency of robbed nests did not differ (P > 0.10) on disturbed and undisturbed islands. All nests were covered by the observers, and this probably protected the nests; simulated nests with exposed eggs experienced much higher predation than those covered with down.