Female blue-footed boobies prefer males with the bluest feet.

Found along the coasts of the Galápagos Islands, Peru, and Mexico, blue-footed boobies are famous for their vividly colored feet. During their summer breeding season, the male birds make sure those feet are on full display with an elaborate courtship dance: They slowly lift one foot, then the other, stepping and strutting around in an effort to impress potential mates.

The brighter the blue, it seems, the better his chances; the pigments that give the feet their vivid color come from the male’s diet, and those pigments also tend to fade with age, so the intensity of the blue is thought to demonstrate his health and vitality and thus make him more attractive to females.