Multidimensional Diet Diversity in Nine European Owl Species: Integrating Taxonomic, Functional, and Phylogenetic Perspectives

Diet diversity of owls has traditionally been studied using prey taxonomic composition, but species identities alone do not necessarily capture ecological roles, energetic dominance, or evolutionary breadth of prey. Here we quantified diversity across taxonomic, functional, and phylogenetic dimensions of prey of nine European owl species: Aegolius funereus, Asio otus, Athene noctua, Bubo bubo, Glaucidium passerinum, Otus scops, Strix uralensis, Strix aluco, and Tyto alba. Using a unified Hill-number framework we estimated richness- and evenness-sensitive diversity and evaluated prey assemblage structures using standardized effect sizes from richness-controlled null models. Prey diversity varied strikingly among owls. Diet strongly relied on a limited set of functionally and phylogenetically similar prey. Bubo bubo showed high richness but low evenness, Otus scops specialization, Glaucidium passerinum high evenness, and Athene noctua high phylogenetic breadth. Large differences in taxonomic richness were frequently decoupled from functional or evolutionary breadth, for example in Bubo bubo and Athene noctua. Structural analyses revealed phylogenetic overdispersion in Athene noctua and Otus scops, clustering in Glaucidium passerinum, and extreme functional clustering in Tyto alba and Asio otus. Together, these results show that owl diets are structured along multiple, partially independent axes, best revealed by combining Hill-number profiles with null-model analyses.