The discovery made by Mariko Takahashi, a researcher in the Graduate School of Arts and Sciences at the University of Tokyo, shatters the long-held belief that male peacock feathers evolved in response to female mate choice. This directs the researchers to believe that some other features in galliformes, a group that includes turkeys, chickens, grouse, quails and pheasants, as well as peacocks, are not necessarily linked to fitness and mating success. In fact, the researchers studied a free-ranging population of Indian peafowl at Izu Cactus Park, Shizuoka, Japan, and found that male vocalizations appear to do a better job of grabbing female attention than their visually screaming "attire." "We have the idea that peacock calls most influence peahens (female peacocks)," Discovery quoted Takahashi, as saying. Researchers observed male and female mating success during spring periods from 1995 to 2001, from both the male and female perspectives, focusing on "male shivering displays."
At the time of this display, a male shows and shakes its train directly toward a visiting female at close range which produces a distinct rustling noise. And the females seem to keenly solicit shivering displays by running around males they seem to prefer. These behavioural indicators of mating success were taken into consideration and were related to several aspects of peacock train fanciness, including train length and number of eyespots. Later, the researchers also documented the number and duration of shivering displays.
However, the researchers failed to link the elaborateness of a peacock's train with his mating success. However, little train variance was observed among males in the population they studied. Besides, no link was detected between a particular male's fitness and his train.
It was observed that male peacocks shiver in response to female run-arounds. This made the scientists to think that male mating calls, consisting of multiple notes and different in sound than female noises may be responsible for mating success. And on the other hand, they suggest that the trains may just be old-fashioned signals at this point.
According to Louise Barrett, a member of the Faculty of Science and Technology at the University of Central Lancashire in Preston, UK, the reason for their obsolescence may be that the peacock trains are controlled by the female hormone estrogen, rather than testosterone, unlike many other elaborate traits in birds and animals.
"it is the absence of estrogen in the male that produces the train, rather than the presence of testosterone. Traits under the control of estrogen are usually very poor indicators of phenotypic (visible physical attributes) and genotypic (DNA) condition. Accordingly, females are known to disregard estrogen-dependent male plumage cues when choosing mates," said Barrett.
However, she pointed out that this theory, and the rest of the new findings, will certainly prove to be controversial, as the data presented by other researchers indicated that a peacock's train does have an influence irrespective of whether or not a female will choose to mate with him.
"Tests between the two alternate hypotheses now on offer leave students of sexual selection with plenty of work to do," concluded Barrett.