A peacock’s display is not only about colour – it is about sound and motion too.
And a collaborative study between biologists and physicists suggests that the birds’ famous train feathers are built to move so as to accentuate the colours.
The team used high-speed video to analyse the motion of the rattling train.
“The feathers move as standing waves, like the strings of a guitar,” said Roslyn Dakin of Canada’s University of British Columbia, who led the research.
Their calculations revealed that the feathers are vibrated in such a way as to create maximum movement for minimal energy expenditure, depending on their length, weight and thickness.
What’s more, while the feathers are vibrating back and forth, the eyespots remain almost stationary.
That’s because the feather barbs in the eyespots are locked together with tiny hooks, much like those in flight feathers, while the rest hang free and loose.
This endows the eyespots with greater density and therefore inertia, which keeps them still as the train vibrates around them.
The result is a mesmerising effect in which the iridescent eyespots appear to hover motionless against a blurred background.
“It’s neat to think about what this display must be like from the peahen’s point of view,” said Dakin. “Close to the ground, the peacock’s 1.75m-long train would virtually fill her field of view with undulating, rattling, glittering feathers.”
The team has yet to establish how the motion component of the display influences females’ choices. One approach might be to manipulate the feathers so that the eyespots become more or less stationary during displays.
“We could add small weights on the shaft of the eyespot feathers to change the weight distribution along the length of the feather,” Dakin told BBC Wildlife.
“This would not affect the look of the eyespots, but it would affect how the feathers move. It would be harder to get the feathers moving with a greater amplitude or speed – we might need a robotic peacock.”
Did you know?
Much of the sound that is produced by a peacock rattling its tail is pitched too low for human ears to hear, though peahens and rivals can sense and respond to the noise.
Source PLoS ONE
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