Birds have possibly the most advanced visual system of any vertebrate, with a highly developed ability to distinguish colors over a wide range of wavelengths. We have three kinds of cone cells for color vision in our retinas; birds have four. Some species of birds are sensitive to the ultraviolet end of the spectrum, where we’re blind. Moreover, in each of a bird’s cone cells is a drop of colored oil that enhances its ability to detect differences between similar colors.
