Copulation Behavior in the Osprey in Relation to Breeding Density

We studied Osprey (Pandion haliaetus) copulation behavior in two geographically separated subpopulations with different breeding densities. In the low density area, the nearest neighbor distance between nests was 7 km, and in the high density area 1.4 km. The frequency of successful copulations was significantly higher in the high density area, 0.65 hr−1 as compared to 0.30 hr−1. Extra-pair copulations were recorded only in the high density area, and extra-pair visits by intruding Ospreys also were more frequent there. There was no relation between copulations and delivery of food or nest material. Our results support the idea that copulation behavior is related to breeding density, but whether or not this is a result of sperm competition or some other social factor remains undetermined.