Colour-variable birds have broader ranges, wider niches and are less likely to be threatened

Coloration fulfils a variety of adaptive functions in animals. Colour variability, both between and within species, can be caused by different colours being favoured for different functions and in different environments. Thus, species with highly variable coloration may have greater potential to persist in new and changing environments. As a consequence such colour variable species may be more able to adapt, colonize new areas and niches, occupy larger ranges, speciate more readily and in general be less vulnerable to environmental change and extinction. These predictions have been supported by comparative analyses on amphibians and reptiles. However, since coloration in ectotherms plays a key role in thermoregulation, it is unclear whether these results can be generalised to endotherms, such as birds and mammals. Here we test the hypothesis that more colour variable endotherms occupy larger ranges/niches and are less vulnerable to the threat of extinction by focusing on colour variatio...