Might Charles Darwin have been wrong about the sexual attraction of the peacock’s tail?

A controversial new study from Japan has found no evidence for the traditional view that peahens choose their sexual partners based on the quality of a peacocks’ feather train.

This runs counter to 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 turkeys, chickens, grouse, quails and pheasants, as well as peacocks, are not necessarily linked to fitness and mating success.

For Indian peafowl (Pavo cristatus), which the researchers studied, male vocalisations appeared to do a better job of getting the attention of females than their visually screaming “attire.”

Mariko Takahashi, an animal behaviourist at the University of Tokyo in Japan, and her team, studied a free-ranging population of Indian peafowl at Izu Cactus Park, Shizuoka, Japan, from 1995 to 2001. They photographed each male during the tail-fanning display ritual, and counted the number of eyespots (a measure of tail quality). Next they examined whether females chose mates with the best-quality tails.

During spring periods, the scientists observed male and female mating success, from both 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 towards a visiting female at close range. The shaking produces a distinct rustling noise, and females appear to actively solicit shivering displays by running around the males they seem to prefer.

The scientists took these behavioural 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.

Over the seven years of observation, Takahashi’s team observed 268 successful matings. But surprisingly they found that females mated with drab-tailed peacocks as often as with flashy males. Therefore, they concluded that the peacock’s train is not the object of female sexual preference.

In fact, researchers were unable to link any single male trait with his mating success, and 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.

So, 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 train might originally have served as a sign to females; hypothesizes Takahashi, but like last year’s fashions, they have now become obsolete.

The findings are published in the journal Animal Behaviour.

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Posted by Jonathan in Biology, Sociobiology

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