It is evident that the colors that different birds have are, in reality, a complex calculation of nature, not only to beautify them, but to give them strength, protect them from light, and in some cases, also choose their mates! This is evident from a research which found that North Cardinals choose their mates based on the darkness of color. Females usually choose males with darker shades, as these shades are produced by carotenoids. So, the better the color, the better is the male at finding food sources rich in carotenoid. This also means that the male has the best of genes and skills.