March 26, 2008 -- The feather train on male peacocks is among the most striking and beautiful physical attributes in nature, but it fails to excite, much less interest, females, according to new research.
The determination throws a wrench in the long-held belief that male peacock feathers evolved in response to female mate choice. It could also indicate that certain other elaborate 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.
For Indian peafowl, which the researchers studied, male vocalizations appear to do a better job of grabbing the attention of females than their visually screaming "attire."
"We have the idea that peacock calls most influence peahens (female peacocks)," lead author Mariko Takahashi told Discovery News.
Takahashi, a researcher in the Graduate School of Arts and Sciences at the University of Tokyo, and her colleagues studied a free-ranging population of Indian peafowl at Izu Cactus Park, Shizuoka, Japan.
During spring periods from 1995 to 2001, the scientists observed male and female mating success, from both the male and female perspectives, with a focus on what are known as "male shivering displays."
During such a display, a male shows and shakes its train directly toward a visiting female at close range. The shaking produces a distinct rustling noise.
Females seem to actively solicit shivering displays by running around males they seem to prefer.
The scientists took these behavioral indicators of mating success and related them to several aspects of peacock train fanciness, including train length and number of eyespots. The researchers also documented the number and duration of shivering displays.
Across the board, the researchers were unable to link the elaborateness of a peacock's train with his mating success. In fact, Takahashi and her team found little train variance among males in the population they studied. They also couldn't detect any link between a particular male's fitness and his train.
The findings have been accepted for publication in next month's Animal Behavior journal.
Since male peacocks appear to shiver in response to female run-arounds, the scientists think that male mating calls, which consist of multiple notes and sound very different than the noises females make, could affect mating success. The trains, on the other hand, may just be obsolete signals at this point, they suggest.
Louise Barrett, a member of the Faculty of Science and Technology at the University of Central Lancashire in Preston, U.K., thinks the reason for their obsolescence could be that, unlike many other elaborate traits in birds and animals, peacock trains are dictated by the female hormone estrogen, rather than testosterone.
Barrett said that "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," she explained. "Accordingly, females are known to disregard estrogen-dependent male plumage cues when choosing mates."
Barrett, however, mentioned that this theory, along with the rest of the new findings, is bound to be controversial, since other researchers have presented data suggesting that a peacock's train does influence 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," Barrett concluded.
Related Links:
Jennifer Viegas' blog: Born Animal
San Diego Zoo's Animal Bytes: Peafowl