EGG PREDATION IN THE HERRING GULL LARUS-ARGENTATUS - WHY DOES IT VARY SO MUCH BETWEEN NESTS

We studied egg loss in Herring Gulls Larus argentatus on the Dutch Frisian Island of Terschelling. Conspecific egg predation was the main cause of egg loss. Late breeding, a small inter-nest distance and a low vegetation cover enhanced egg predation. Predation was more frequent in nests with small eggs than in nests with large eggs. The effect of egg volume on predation was experimentally investigated by exchanging clutches between pairs. Increasing differences in egg size between original and adopted clutches increased progressively the predation rate. Egg predation was strongly correlated to the original clutch volume (control and experimental pairs combined). No correlation was observed between egg predation and the volume of the adopted clutches. This excludes a possible predator-linked selection mechanism. It is suggested that lower quality birds not only lay smaller eggs but also exhibit less efficient parental care during the incubation period, resulting in an increased predation risk.