Ambient light influences the evolution of colour signals

In light-contrasted ecosystems, ambient light and background colours influence the evolution of animal coloration. Because maximal conspicuousness is achieved for signals which are rich in the colours of ambient light but poorly reflected by background, different signals will be cryptic or conspicuous at different heights in tropical rainforest.

In the forthcoming issue of Ecology Letters, Gomez and Théry compare plumages of 40 species living in French Guiana. They demonstrate that predators exert an important pressure on coloration: birds are well camouflaged with colours similar to their habitat, light green in canopy and dark brown in understorey. On the contrary, ultraviolet is more likely used in conspicuous signals to select mates. Both sexes present similar coloration at each height, but males display more conspicuous sexually selected patterns than females.

Colours of light and background are also likely to influence the evolution of visual signals in other light-contrasted ecosystems.