Color vision and its functions

Vision is the primary sense for many birds, and the avian eye is probably the most complex of any vertebrate. I commence with an overview of avian eye design, concentrating on the photoreceptors hypothesized to underlie color vision, examples of amino acid substitutions generating the different opsins variants found in avian cones, and methods used to infer differences in spectral sensitivity at a photoreceptor and whole animal level. I then summarize the evidence for the functions of avian color vision. This concentrates on the functions of UV sensitivity in birds for two main reasons: there have been substantial advances in our understanding of this topic in the last decade; and wavelength dependent properties of light, and spectral sensitivity of receiver and signaller, predispose the uses to which wavebands can be put. The section deals with the roles of avian spectral sensitivities in mate choice displays, predation and foraging.