The canonical example of sexual selection, the male peacock (in this image, an Indian blue peacock) is renowned for its iridescent blue-green plumage, elaborate feather train, and iconic "eyes," the colorful markings on its tail feathers. When spread out, those feathers span a diameter that is over 60 percent of the peacock's total body length. The female's appearance, by comparison, is drab: mostly brown, with a bit green iridescence in the neck.

Male "shivering displays," in which a male shows off his train in front of a female to get her attention, and shakes the feathers to produce a distinct rustling noise, play an important role during courtship.