LAUSR

Birds use spectral information for circadian control, magnetic orientation and phototaxis but most importantly for discriminating the colours of important objects such as food items or mates. Their tetrachromatic colour vision is based on four types of single cones expressing four opsin-based visual pigments and fine-tuned by the carotenoid composition in cone oil droplets. Bird colour vision is not as uniform as previously thought, and single visual pigments have been lost in several bird lineages. Diurnal birds have fine colour discrimination and good colour constancy but can generalize over similar though discriminable colours. Bird colour discrimination is ultimately limited by receptor noise but can be impaired in natural conditions, depending on light intensity and background coloration.