How Vegetative Cover Protects Duck Nests from Egg-Eating Birds

Abstract

The importance of vegetative cover in protecting duck nests from egg-eating birds was evalu- ated over two season$ on two is)ands in a lake in central Alberta, Canada. Avian species recorded prey- ing upon the eggs of ducks included ring-billed gulls (Larus deluwarensis), California gulls (L. cali- fornicus), crows (Cortus brachyrhynchus), and black-billed magpies (Pica peca). Apparently egg pilfering occurred when nests were unattended, mainly during the laying stage. No relationship could be demonstrated between egg loss and amount of screening cover at actual duck nests, possibly because all other factors at the nests were not equal. At artificially placed nests, egg loss was inversely correlated with the amount of overhead cover, suggesting that visibility of eggs was a major factor in their destruc- tion. However, avian predators must have used additional visual cues in locating well-hidden nests, the most likely being disturbed vegetation.