Abstract

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 directly affect the ability of birds to make chromatic discriminations. This finding has implications for our understanding of trade-offs in carotenoid allocation between vision and other key functions such as sexual ornamentation and health maintenance, and suggests that variation in dietary carotenoid availability may affect the ability of animals to make ecologically pertinent color discriminations, such as between sexual signals or cryptic food items.