Ecogeographical patterns in owl plumage colouration: climate and vegetation cover predict global colour variation

Aim: Ecogeographical rules link animal colours, especially those produced by melanin pigments, with variation in environmental conditions over wide geographical scales. In particular, Gloger’s rule, coined in two versions for endothermic animals, suggests that tegument darkness would increase at high temperature, as well as in highly humid environments. On the other hand, the thermal melanism hypothesis, predicts that darker colourations should be more frequent in colder areas given their thermoregulation benefits. Location: Global Time period: Contemporary Major taxa studied: Strigiformes Methods: Here, we provide a global comparative test of these contrasting expectations in all extant owls (n = 198 species), a group of nocturnal birds displaying huge variability in the degree of melanin-based plumage colouration and environmental specialization. Combining analyses at both species and assemblage level, we assessed the climatic and environmental variables explaining variati...