Data: Generalized evidence for Bergmann’s rule body size variation in a cosmopolitan owl genus

Aim: The eco-geographic Bergmann’s rule predicts that animals have smaller body size in warmer regions than in cold environments because of thermoregulatory reasons. Although this rule has been widely investigated, intraspecific analyses on cosmopolitan taxa are rare. We examined whether geographic variation in wing length, a proxy of body size, shows a Bergmannian pattern and can be explained by three mechanisms known to affect animal body size (heat conservation, resource availability and starvation resistance) in seven species of nocturnal raptors of the genus Tyto. Location: World. Taxon: Genus Tyto. Methods: We measured wing length of 9033 museum specimens covering the entire distributional range of each species and linked it with geographic (absolute latitude, elevation) and climatic predictors associated with heat conservation, resource availability and starvation resistance hypotheses of spatial variation in body size. Results: All the species show a trend of increas...