About
The peafowl include two Asiatic bird species (the blue or Indian peafowl originally of India and Sri Lanka and the green peafowl of Myanmar, Indochina, and Java) and one African species (the Congo peafowl native only to the Congo Basin) of bird in the genera Pavo and Afropavo of the Phasianidae family, the pheasants and their allies, known for the male's piercing call and, among the Asiatic species, his extravagant eye-spotted tail covert feathers which he displays as part of a courtshipritual. The term peacock is properly reserved for the male; the female is known as a peahen, and the immature offspring are sometimes called peachicks.1
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 signalsof the males' fitness, since less fit males would be disadvantaged by the difficulty of surviving with such large and conspicuous structures.
Plumageedit
Peacock in Wagga Wagga Zoo
The Indian peacock has iridescent blue and green plumage. 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.
The green peafowl differs from the Indian peafowl in that the male has green and gold plumage with black wings with a sheen of blue. Unlike the 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.
Occasionally, peafowl appear with white plumage. Although albino peafowl do exist, this is quite rare and almost all white peafowl are not, in fact, albinos; they have a different condition called leucism which causes an overall reduction in different types of pigment. This can result in the complete lack of colouration of their plumage, however preserving normal eye colour. By contrast, true albino peafowl have a complete lack of melanin, resulting in the albino's characteristic red or pink eyes. Leucistic peachicks are born yellow and become fully white as they mature.
Iridescenceedit
Further information: Iridescence and Structural coloration
As with many birds, vibrant iridescent plumage colours are not primarily pigments, but structural colouration. Opticalinterference Bragg reflections based on regular, periodic nanostructures of the barbules (fiber-like components) of the feathers produce the peacock's colours. Slight changes to the spacing of these barbules result in different colours. Brown feathers are a mixture of red and blue: one colour is created by the periodic structure and the other is created by a Fabry–Pérot interference peak from reflections from the outer and inner boundaries. Such structural coloration causes the iridescence of the peacock's hues. Interference effects depend on light angle rather than actual pigments.2
Evolution and sexual selectionedit
Charles Darwin first theorised in On the Origin of Species that the peafowl's plumage had evolved through sexual selection. This idea was expanded upon in his second book, The Descent of Man and Selection in Relation to Sex.
The sexual struggle is of two kinds; in the one it is between individuals of the same sex, generally the males, in order to drive away or kill their rivals, the females remaining passive; whilst in the other, the struggle is likewise between the individuals of the same sex, in order to excite or charm those of the opposite sex, generally the females, which no longer remain passive, but select the more
agreeable partners.3
Sexual selection is the ability of male and female organisms to exert selective forces on each other with regard to mating activity.4 The strongest driver of sexual selection is gamete size. In general, eggs are bigger than sperm and females produce fewer gametes than males. This leads to eggs being a bigger investment, and therefore to females being choosy about the traits that will be passed on to her offspring by males. The peahen's reproductive success and the likelihood of survival of her chicks is partly dependent on the genotype of the mate.5 Females generally have more to lose when mating with an inferior male due to her gametes being more costly than the male's.
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