Covariation between plumage colour polymorphism and diet in the Barn OwlTyto alba

Abstract

Several hypotheses might explain the evolution and maintenance of colour morphs within animal populations. The ‘alternative foraging strategy’ hypothesis states that alternative colour morphs exploit different ecological niches. This hypothesis predicts that morphs differ in diet, either because foraging success on alternative prey species is morph‐dependent or because differently coloured individuals exploit alternative habitats. I examined this prediction in the Barn OwlTyto alba, a bird that varies in plumage coloration continuously from dark reddish‐brown to white. On the European continent, Owls are light‐coloured (subspeciesT. a. alba) in the south and reddish‐brown (T. a. guttata) in the north; in central Europe the two subspecies interbreed, generating many colour variants. If plumage coloration indicates alternative foraging strategies, in sympatry dark‐ and light‐coloured owls should consume prey species that are typical of the diets ofT. a. guttataandT. a. albain allopatry, respectively. In line with this prediction, both in allopatry and in sympatry in SwitzerlandT. a. guttatafed primarily upon Common VolesMicrotus arvalisandT. a. albaupon Wood MiceApodemusspp. Statistical analyses suggest that morph‐dependent diet did not arise from a non‐random habitat distribution of owls with respect to plumage coloration. This suggests that foraging success upon alternative prey is morph‐dependent.