The ornamental feathers that fan out into a spectacular display belong exclusively to the male bird, the peacock. This bird is part of the peafowl group, which are recognizable members of the pheasant family. The male’s elaborate plumage, known as a train, evolved to attract a mate. The female, or peahen, possesses a subdued appearance that allows her to remain camouflaged while nesting.
Clarifying the Terminology
The collective term for the species is peafowl, referring to both male and female birds. A male is specifically called a peacock, while a female is a peahen. This distinction is important because the dramatic difference in appearance between the sexes is a classic example of sexual dimorphism. Peafowl include three species: the Indian, the Green, and the Congo peafowl.
The Male’s Display
The stunning structure a peacock fans out is not its tail but its train, made up of elongated upper-tail covert feathers. These feathers grow over the shorter tail feathers, which serve as a support structure during display. The Indian Peafowl’s train can reach up to 2.3 meters, and each feather is tipped with an iridescent eyespot, known as an ocellus.
The vibrant colors of the ocelli—purple-black, blue-green, and bronze-gold—are not the result of pigment but of structural coloration. This effect is created by the microscopic arrangement of keratin nanostructures within the feather barbules. These tiny structures cause light to scatter and interfere, producing the shimmering, metallic iridescence that changes with the viewing angle. The typical train contains between 180 and 200 ocellated feathers.
The Evolutionary Purpose of the Train
The peacock’s train is a trait driven by sexual selection. The function of this immense structure is to serve as an honest signal of the male’s genetic quality and health to the peahen. Growing and maintaining such a large, cumbersome train requires significant energy, making it a biological handicap. Only the fittest males can survive while carrying such an extravagant burden, signaling superior foraging skills and relative freedom from parasites.
During courtship, the peacock performs a display by erecting the train into an enormous fan and engaging in “train-rattling.” This involves vibrating the feathers at approximately 25 times per second, creating a shimmering effect designed to hold the peahen’s attention. Peahens prefer males whose trains have a greater number of symmetrical and highly iridescent eyespots, which correlates directly with mating success.
Species Diversity in Peafowl
While the Indian Peafowl (Pavo cristatus) is the most recognized species, two others exist with distinct features. The Green Peafowl (Pavo muticus), native to Southeast Asia, is physically larger and has metallic green and bronze body plumage, contrasting with the Indian species’ blue neck.
The Congo Peafowl (Afropavo congensis) is found only in the Democratic Republic of Congo and presents a less dramatic appearance. The Congo peacock possesses a much shorter train and primarily uses its actual tail feathers for display. Its plumage is a deep blue with green and violet iridescence, but the ocelli on its train are significantly less pronounced than those of its Asiatic relatives.