Three peafowl species, and estrogen that keeps trains female
Three birds go by the name peafowl: the Indian and green species of Asia and the Congo peafowl of central Africa. Peacocks are famous for their eyespotted trains, yet peahens have been seen growing male feathers late in life, because showy plumage appears unless hormones hold it back.
The Asian species differ in how alike the sexes look. Indian males shine in metallic blue and green, while their hens are dull grey and brown; green peafowl males wear green and bronze with blue-sheened black wings, and their hens resemble them apart from shorter coverts and less shimmer. The long train of both Asian species is made not of true tail feathers but of greatly lengthened coverts above the tail. The Congo peacock instead fans its real tail, which is much shorter and carries fainter eyespots. All three wear crests, nest on the ground, roost in trees and are thought to be polygamous.
Much of the dazzle is not pigment at all. Evenly spaced nanostructures in the tiny barbules of each feather reflect light so that particular colours reinforce one another, and small changes in that spacing shift the hue. Displaying males make the most of it, typically angling the train about 45 degrees to the right of the sun while the hen faces it head-on.
Why the train exists is still argued. Charles Darwin saw it as the product of females repeatedly choosing the most beautiful males. Marion Petrie, studying feral birds at Whipsnade in England, found that the number of eyespots predicted a male’s mating success, but a seven-year Japanese study by Mariko Takahashi found no sign that hens favoured longer, more symmetrical or more eyespotted trains. Amotz Zahavi argued the burden of such plumage proves a male’s fitness, and another idea holds that train, loud call and boldness warn off predators and rivals.
The group has a long Asian history. The earliest named member of the tribe, Eopavo, lived on a high-altitude savanna in Gansu, northwestern China, during the late Miocene, and still older unnamed fossils from the Himalayan region date to about 13.6 million years ago.
Source: Peafowl
