Latitudinal gradients in avian colourfulness

It has long been suggested that tropical species are generally more colourful than temperate species, but whether latitudinal gradients in organismal colourfulness exist remains controversial. Here we quantify global latitudinal trends in colourfulness (within-individual colour diversity) by collating and analysing a photographic dataset of whole-body plumage reflectance information for >4,500 species of passerine birds. We show that male and female birds of tropical passerine species are generally more colourful than their temperate counterparts, both on average and in the extreme. We also show that these geographic gradients can be explained in part by the effects of several latitude-related factors related to classic hypotheses for climatic and ecological determinants of organismal colourfulness. Taken together, our results reveal that species' colourfulness peaks in the tropics for passerine birds, confirming the existence of a long-suspected yet hitherto elusive trend in the distribution of global biodiversity. After generating a dataset on plumage colouration for over 4,500 bird species, the authors show that tropical species are more colourful than temperate species, confirming a long-held but difficult-to-prove belief.

Automated summary

This study confirms the long-held belief that tropical bird species are more colorful than temperate species by analyzing a dataset of over 4,500 bird species.