Abstract

A long-term study of the Common Buzzard Buteo buteo population on the islands of Colonsay and Oronsay, Argyll, was carried out during 1988–2019. Until 2010, the islands held between 18 and 28 occupied territories. Subsequently, numbers dropped to 8–9 pairs while, at the same time, there was an increase in the number of Golden Eagles Aquila chrysaetos and White-tailed Eagles Haliaeetus albicilla present on the islands. Competition for food and nest sites and direct predation are believed to be factors in the decline of Buzzard numbers on the islands. The study also found a reduction in the proportion of crag-nesting pairs of Buzzards, as well as an advance in hatching dates. Buzzards switched their principal prey away from European Rabbits Oryctolagus cuniculus in response to declining prey availability during the study period. An increase in the diversity of diurnal raptors was noted with the increasing density of eagles and the decline in Buzzards.