We know very little about the nature of color vision in vertebrate animals other than mammals. Humans and some primates have three color pigments in the photoreceptor cells called cones, which are in the retina of the eye. One of these pigments is fairly recently evolved from a gene duplication event. The three pigments provide color vision that is called trichromatic. Birds are one of the non-mammalian groups where many species have excellent color vision, but pigeons are the single species to have been extensive experimental subjects. Birds have maintained four evolutionary ancient lineages of pigments, giving the potential for tetrachromatic color vision that extends into the ultraviolet (UV) region of the visual spectrum. Birds are also unlike mammals in having cone cells that include colored oil droplets within them that can act as color filters, and represent another evolutionary elaboration. This project uses quantitative behavioral testing to study color matches, hue saturation and wavelength discrimination by budgerigars, using narrow wavelength bands of light. The results will address how UV cones participate in color vision, the relation between colored oil droplets and visual pigments, and where the peaks are for optimal wavelength discrimination. This comparative work will be important because color vision often has a major ecological role in communication and foraging. The impact is likely to extend to how other multi-pigment color vision systems work in other animals including invertebrates, and this knowledge could be useful in aspects of molecular evolution, and in design of artificial visual sensors.
