Breeding season diets of sympatric White-tailed Eagles and Golden Eagles in Scotland: no evidence for competitive effects

Capsule The breeding season diets of White-tailed Eagles and Golden Eagles in western Scotland were different, and there was no evidence of competition between the two species. Aim To test the hypothesis that the reintroduced White-tailed Eagles will have an adverse effect on Golden Eagles through competition for food. Methods Collections of prey remains at nests and regurgitated pellets during the breeding season were analysed. Temporal change in Golden Eagle territory occupancy and breeding productivity where the influence of White-tailed Eagles should be most evident was also examined. Results Diet breadth was similar between species but diet composition was significantly different, with White-tailed Eagles taking more sheep and aquatic or coastal food items, whereas Golden Eagles took more gamebirds (Galliformes), lagomorphs and other terrestrial prey. Diet overlap comparisons, between species-pairs that nested close together or far apart, rejected a hypothesis that there was competition for food, but partially supported an alternative hypothesis that diet overlap indicated abundant shared food. There was no indication that White-tailed Eagles have had any long-term effect on the breeding productivity or abundance of territorial Golden Eagles. Conclusions There is no evidence that reintroduced White-tailed Eagles are having an adverse effect on Golden Eagles through competition.