Dietary carotenoid availability affects avian color discrimination

Carotenoid pigments are found in the retinas of many vertebrate species, where they serve a range of functions. In birds, carotenoid-containing retinal oil droplets act as optical filters, modifying the light reaching the underlying visual pigment and thereby enhancing color vision. Dietary carotenoid manipulation is known to affect the allocation of carotenoids to the retina, although the effects this has on vision are less well understood. Using dietary manipulations, in which juvenile Japanese quail (Coturnix japonica) received either a high- or a low-carotenoid diet, we tested the effects of carotenoid availability on the ability to perform a color discrimination task. Birds on both diet treatments were able to make a relatively coarse discrimination between colors that appeared to humans as yellow-orange and orange; however, only high-carotenoid diet birds were able to make a finer-scale discrimination involving intermediate colors, showing that dietary carotenoid availability can ...