Peacock Uses ‘Train-Rattling’ Biomechanics

Peacock Uses ‘Train-Rattling’ Biomechanics

When displaying his resplendent plumage to attract a mate, the peacock is working hard behind the scenes to lure his lover.

A study published Wednesday in the journal PLOS ONE found that the male’s colorful display is anything but a stationary exhibition of his iridescent feathers, which feature distinct color patterns and prominent “eyespots” scattered across the semicircular fan.

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Peacock: The rain-rattling display

Actually, the love-hungry bird is shaking his tail feathers systematically, so that the smaller, nondescript ones gently beat the large, attention-getting ones to create a visual and high-frequency audible invitation of courtship, according to the study.

“Peacocks perform a complex, multimodal ‘train-rattling’ display in which they court females by vibrating the iridescent feathers in their elaborate train ornament,” according to the study, titled “Biomechanics of the Peacock’s Display: How Feather Structure and Resonance Influence Multimodal Signaling.”

The train rattling can last up to 25 minutes, which can create a bit of a stamina problem for the male and expose him to danger.

“When a peacock displays, it moves the mass of the train as well as that of supporting muscular, connective and dermal tissue. We often video-recorded peacocks train-rattling for (more than) 25 minutes, suggesting that this behavior may pose a considerable challenge to metabolic stores and short-term muscle power output,” according to the study.

“Assuming sound intensity is proportional to the power required to drive feather vibrations, the acoustic intensity of this multimodal display may allow females to evaluate the power output of different males.”

Risk factors

The tail-feather erection poses other risks, according to the study authored principally by Roslyn Dakin, a researcher at the University of British Columbia.

“When peacocks hold their trains erect, they risk damage to their train feathers caused by wind, assaults by other males, and other causes,” she wrote. At least the impressive feathers are somewhat elastic, protecting against bending and buckling, a sure turn-off for the object of desire.

The peahen also may experience a somewhat hypnotic effect because it appears to her that the male’s large feathers are moving while the dominant eyespots throughout the plumes seem still, hovering in place amid the undulating background, the study found.

Plus, if the peahen is standing about 1 meter from the male, the display practically fills her field of vision, further capturing her attention.

The eyespot itself is an artistic wonder of nature. It has a purple-black center surrounded by concentric blue-green and bronze-gold regions spread across the broad tail fan.

In previous research, Dakin and colleagues confirmed the eyespots played a crucial role in a peahen’s mate-screening process. When the researchers masked some of the eyespots on males, their copulation success plunged to zero. “The blue-green eyespot color overwhelmingly influences peacock mating success,” they reported in 2013.

Darwin noticed it, too

None other than Charles Darwin was among early researchers to find a link between the eyespots and female mate choice, though he went further to dismiss the important effects of the vibrations:

“Peacocks and birds of paradise rattle their quills together, and the vibratory movement apparently serves merely to make noise, for it can hardly add to the beauty of their plumage,” Darwin wrote in his epic study, “The Descent of Man and Selection in Relation to Sex,” published in 1871.

Citing Darwin’s 19th century conclusion, the new study begs to differ.

“On the contrary, our results suggest the possibility that sexual selection (via female choice) has shaped both the biomechanical design of the eyespot feathers and the behaviors that produce visual and audio cues.”

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