In birds, plumage coloration is an important visual signal involved in communication and survival that varies greatly across species. Plumage colour evolution is influenced by a variety of factors including phylogeny, predation pressure, sexual selection, light and resource availability, and ecological context. Tyrant flycatchers are an interesting group because although there are many monomorphic species with drab plumage, some species are quite colourful. Given the complexity of factors involved, the mechanisms influencing plumage colour evolution in Tyrant flycatchers are likely complex, involving multiple drivers. To account for the fact that differences in the availability of resources and light will result in differences in the acquisition and transmission of plumage signals, we calculated red and blue chromaticity values from red, blue, green scores originally extracted from digitally scanned images from the Birds of the World. Next, we used phylogenetically controlled analyses to assess the influence of a variety of ecological factors on plumage colouration, and dichromatism. Finally, we examined the extent of range overlap among species to test if plumage varies to a greater extent in overlapping species due to reinforcement of pre-mating isolating mechanisms (i.e., for species recognition). We found that diet, precipitation, and temperature all influence colour expression, that precipitation and latitude influence the extent of dichromatism, and finally that the extent of range overlap affects plumage divergence between species. Taken together, our results highlight the complexity of plumage evolution in Tyrant flycatchers and demonstrate that the evolution of plumage colouration is driven by a combination of ecological, geographic, and biological factors.
