Global biogeographical patterns in the diet of a cosmopolitan avian predator

Aim: The investigation of biogeographical patterns in the diet of widely distributed predators is essential to understand their ecology, life history traits and local adaptations. However, it is particularly challenging because of their wide distribution, broad trophic spectra and high ecological plasticity. Here, we described patterns of trophic ecology in a cosmopolitan nocturnal raptor, the common barn owl group, from a biogeographical perspective. We then compared variation in diet between barn owls living in the Americas (T. furcata), and those inhabiting Europe, Middle-East and Africa (T. alba), thus hunting on different assemblages of prey types. Location: World. Taxon: Barn owl species complex. Methods: We reviewed 790 studies reporting diet information of 971 locations (3,733,902 individual vertebrate prey), and investigated the variation in different diet parameters, reflecting taxonomic diversity, size of the prey and frequency of certain prey types according to geographical and climatic variables. Results: While confirming that the barn owl is a selective mammal hunter with variable taxa constituting its staple food in different regions, we also found significant geographical and climatic trends in several diet parameters. Although prey composition differed among continents, most of the patterns, including an increase in proportion of mammal prey in cold environments, an increase in diet diversity with elevation, a decrease in small prey consumption from high to low latitudes and at increasing temperature, and a decrease in rodent predation in humid habitats, were similar between T. furcata and T. alba. A strong island effect was observed for all diet parameters. Main conclusion: Our results indicate a generalized pattern of variation in barn owl diet across biogeographical regions, suggesting that similar prey communities occur in habitats with comparable ecological conditions and/or that different barn owl populations living in similar climate convergently evolved similar food preferences and hunting strategies.