Evaluating the light environment as a contributor to colour differences among related bird species.

This article investigates the role of ambient light environment in driving plumage colour variation among 12 closely related, sexually monomorphic species of Phylloscopus warblers in the western Himalayas. Despite measurable differences in irradiance spectra across five forested habitats and between sun and shade conditions, the study finds little evidence that these light environment variations influence the chromatic contrast or colour of plumage patches, including signalling features like wing bars and tail patches. The authors suggest that relational colour constancy in avian vision maintains consistent perception of colour contrasts across different light conditions, reducing the impact of habitat irradiance on colour evolution. Alternative explanations for plumage diversification include camouflage, background contrast, sensory biases, and stochastic evolutionary processes rather than direct adaptation to ambient light spectra.