Peacock. Peafowl is a common name for three species of birds in the genera Pavo and Afropavo of the Phasianidae family, the pheasants and their allies. Male peafowl are referred to as peacocks, and female peafowl as peahens, though peafowl of either sex are often referred to colloquially as peacocks. The two Asiatic species are the blue or Indian peafowl originally of the Indian subcontinent, and the green peafowl of Southeast Asia; the one African species is the Congo peafowl, native only to the Congo Basin. Male peafowl are known for their piercing calls and their extravagant plumage. The latter is especially prominent in the Asiatic species, which have an eye-spotted tail or train of covert feathers, which they display as part of a courtship ritual. The functions of the elaborate iridescent colouration and large train of peacocks have been the subject of extensive scientific debate. Charles Darwin suggested they served to attract females, and the showy features of the males had evolved by sexual selection. More recently, Amotz Zahavi proposed in his handicap theory that these features acted as honest signals of the males' fitness, since less-fit males would be disadvantaged by the difficulty of surviving with such large and conspicuous structures. The Indian peacock has iridescent blue and green plumage, mostly metallic blue and green, but the green peacock has green and bronze body feathers. In both species, females are as big as males, but lack the train and the head ornament. The peacock tail, known as a train, consists not of tail quill feathers, but highly elongated upper tail coverts. These feathers are marked with eyespots, best seen when a peacock fans his tail. Both sexes of all species have a crest atop the head. The Indian peahen has a mixture of dull grey, brown, and green in her plumage. The female also displays her plumage to ward off female competition or signal danger to her young. Green peafowl differ from Indian peafowl in that the male has green and gold plumage and black wings with a sheen of blue. Unlike Indian peafowl, the green peahen is similar to the male, only having shorter upper tail coverts, a more coppery neck, and overall less iridescence. The Congo peacock male does not display his covert feathers, but uses his actual tail feathers during courtship displays. These feathers are much shorter than those of the Indian and green species, and the ocelli are much less pronounced. Females of the Indian and African species are dull grey and/or brown. Chicks of both sexes in all the species are cryptically coloured. They vary between yellow and tawny, usually with patches of darker brown or light tan and dirty white ivory. Hybrids between Indian and Green peafowl are called Spaldings, after the first person to successfully hybridise them, Mrs. Keith Spalding. Unlike many hybrids, spaldings are fertile and generally benefit from hybrid vigor; spaldings with a high-green phenotype do much better in cold temperatures than the cold-intolerant green peafowl while still looking like their green parents. Plumage varies between individual spaldings, with some looking far more like green peafowl and some looking far more like blue peafowl, though most visually carry traits of both. In addition to the wild-type blue colouration, several hundred variations in colour and pattern are recognised as separate morphs of the Indian Blue among peafowl breeders. Pattern variations include solid-wing/black shoulder, pied, white-eye, and silver pied. colour variations include white, purple, Buford bronze, opal, midnight, charcoal, jade, and taupe, as well as the sex-linked colours purple, cameo, peach, and Sonja's Violeta. Additional colour and pattern variations are first approved by the United Peafowl Association to become officially recognised as a morph among breeders. Alternately-coloured peafowl are born differently coloured than wild-type peafowl, and though each colour is recognisable at hatch, their peachick plumage does not necessarily match their adult plumage. Occasionally, peafowl appear with white plumage. Although albino peafowl do exist, this is quite rare, and almost all white peafowl are not albinos; they have a genetic condition called leucism, which causes pigment cells to fail to migrate from the neural crest during development. Leucistic peafowl can produce pigment but not deposit the pigment to their feathers. This results in the complete lack of colouration in their plumage and blue-grey eye colour. Pied peafowl are affected by partial leucism, where only some pigment cells fail to migrate, resulting in birds that have colour but also have patches absent of all colour; they, too, have blue-grey eyes.