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

We studied egg loss in Herring Gulls Larus argentatus on the Dutch Fri sian Island of Terschelling. Conspecific egg predation was the main ca use of egg loss. Late breeding, a small inter-nest distance and a low vegetation cover enhanced egg predation. Predation was more frequent i n nests with small eggs than in nests with large eggs. The effect of e gg volume on predation was experimentally investigated by exchanging c lutches between pairs. Increasing differences in egg size between orig inal and adopted clutches increased progressively the predation rate. Egg predation was strongly correlated to the original clutch volume (c ontrol and experimental pairs combined). No correlation was observed b etween egg predation and the volume of the adopted clutches. This excl udes a possible predator-linked selection mechanism. It is suggested t hat lower quality birds not only lay smaller eggs but also exhibit les s efficient parental care during the incubation period, resulting in a n increased predation risk.