Predation on reptiles and birds by the common buzzard,Buteo buteo, in relation to changes in its main prey, voles

It has commonly been assumed that predators whose main prey are voles reduce their predation on other prey when voles are abundant. This assumption may, however, not be valid for slow-moving and ground-dwelling prey species with habitat demands similar to those of voles. In southern Norway, the field vole, Microtus agrestis, is an important prey for the common buzzard, Buteo buteo. Two other important groups of prey are birds and reptiles. In a forested study area with cyclic vole populations, prey remains and pellets were collected from buzzard nest sites in 2 peak vole years and 3 low vole years. Birds were most important as prey when vole populations were low. Reptiles, on the other hand, were most common as prey in peak vole years, possibly because the buzzards then concentrated on hunting ground-dwelling prey in habitats with high vole populations. In the study area, this was mainly clearcuts, which were commonly used also by basking reptiles. The vole-hunting adder, Vipera berus, may be especially vulnerable to buzzard predation in peak vole years because it is probably attracted to the vole-rich patches utilized by the buzzard.