In some passerines, parents allocate more food to offspring with the brightest red gapes, but the function of parental decisions based on offspring gape coloration is unknown. We hypothesize that gape coloration is part of a communication system where nestlings reveal their condition to...

Structural coloration has been hypothesized to play a role in sexual selection, and we tested whether this was the case in a field study of the barn swallow Hirundo rustica. The dorsal iridescent plumage of barn swallows has a strong reflectance in the ultraviolet (UV) region, with adult males...