Peacock tails may be hard to miss, but humans are unaware of the noise created by the bird's pretty plumage. Scientists have shown that peacocks shake their tails to make a noise that is too low for us to hear. Male birds may make the infrared rumble to scare off an approaching rival or to attract a mate. Scientists have shown that peacocks shake their tails when displaying (stock image) to make a noise that is too low for us to hear. Male birds may make the infrared rumble to scare off an approaching rival or to attract a mate across dusty scrub land, the study claims . Researchers at the University of Manitoba in Winnipeg, Canada, have shown that the birds make infrasound noises - below 20 hertz - using their tails and that other peacocks respond to them. Most humans hear noises between 20 and 20,000 hertz. Dr James Hare noticed a peacock displaying and shaking its tail at a wall in a zoo, which he noted looked like a satellite dish and made him question whether the bird was listening to itself, BBC Earth reported. This sparked a study, leading him and graduate student Angela Freeman to record the sound of 46 peacocks shaking their feathers while displaying. Male and female peacocks became more alert and moved around when the low noises were played back to them by researchers, with males (stock image) shrieking out . Charles Darwin first suggested that a peacock’s train serves to attract females and studies have since shown that females tend to prefer males with the most exaggerated male characteristics. Amotz Zahavi said the train indicates a male’s fitness. Males with impressive trains have been shown to be healthier, suggesting that the ornament indicates a male’s ability to survive. His ‘handicap principle’ says that since males with particularly brightly coloured or large plumes will attract the attention of predators, they must be extra fit to survive. Females are thought to choose mates with good genes, so males with more exaggerated sexual characteristics, such as a big train, tend to have better genes in a peahen’s eyes. Marion Petrie tested whether the displays signal a male’s generic quality by studying a feral population of peafowl in Whipsnade Wildlife Park in England. She found the number of eyespots in the train predicted a male's mating success and that she could manipulate a male’s chances of mating success by cutting off some of his eyespot tail feathers. In the experiment, females lost interest in pruned males and became attracted to untrimmed ones. Furthermore, chicks fathered by males with impressive trains weighed more than those sired by less ornamented birds. Humans hear a rustling sound when this happens, but the experts found that the birds hear a loud sound of between 70 and 108 decibels, according to the study published in the journal Animal Behaviour. Male and female peacocks became more alert and moved around when the low noises were played back to them by researchers, with males shrieking out in response. Experts are unsure how the birds detect infrasound, but know that some can feel vibration through their legs. Ms Freeman said that the birds may simply hear the noises through their ears, the inner part of which seems to be the right shape to detect very low noises. Other animals, such as elephants, have long been known to produce such infrasound, which humans can’t hear. And although a type of grouse called the capercaillie produces infrasound, it seemingly doesn't use it to communicate, meaning that the bird either can’t hear it itself or they just doesn't care about it. Ms Freeman believes that male peacocks may use infrasound to maintain their territory and warn off approaching rivals. But the noises could also be a way of attracting a mate. She observed that male peacocks were most likely to make the low sounds when they showed off their train feathers, producing two displays which she called the ‘shiver train’ and the ‘pulse train’. The shiver train is produced by vibration of the train feathers from the centre feathers to the outside of the array and is used by males when females are far away. Ms Freeman believes that male peacocks may use infrasound to maintain their territory and warn off approaching rivals. But the noises could also be a way of attracting a mate. Here, a male displays for a brown, female peahen, hoping she will be impressed by his show of strength . The pulse train is produced by a vibration emanating from the base of all the train feathers and it is used when the female is nearby. Peacocks’ tails are a sign of strength and good genes, so a strong noise may reinforce a message of virility, Ms Freeman said. This could be especially useful as the birds live in scrubby woodland, where high noises can only travel over short distances and birds sometimes can’t see each other. ‘We think that possibly these signals could signal to females and males who are out of sight behind a bush or over the hill,’ she added.
Researchers at the University of Manitoba, Canada, have shown that peacocks make infrasound noises - below 20 hertz - using their tails . Females were more alert when they heard the sound and males shrieked . Male peacocks may use infrasound to maintain their territory . They could also use the noise to attract a mate across scrubby woodland .