Lead author Roslyn Dakin and her team wrote that the male's careful motions allow "the colorful iridescent eyespots - which strongly influence female mate choice - to remain nearly stationary against a dynamic iridescent background."
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The researchers watched the male peacock displays in slow motion and Dakin, a zoologist at the University of British Columbia, and her team studied the structure and movement of individual male peacock feathers.
The iridescent trains are actually located, not at the tail, but on the backs of males. The displays, however, involve rear end shaking, wing shaking and what the researchers call "train rattling." During the latter, the male birds may strum their tail feathers against the back of the train.
Humans only hear rustling, which seems rather dull. Prior research, however, found that the movement produces infrasound, meaning that the sound waves are too low-pitched for us to properly detect. Female peacocks known as peahens are hard-wired to hear such sounds, however, and appear to often be captivated by them.
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The eyespots account for at least 50 percent of the male peacock's wooing success, though, according to the researchers. Scanning electron microscopy showed that the eyespot barbs - consisting of the hair-like branches on the feather shaft - are locked together with microhooks. This gives each eyespot greater density than the surrounding loose barbs, keeping them essentially in place as the loose barbs shimmer in the background.
The movement of the feathers, according to the authors, has properties similar to that of a guitar string. Both are flexible and produce particular sounds depending on how they are manipulated.
The scientists further determined that the longer a male's train feathers are, the faster the hopeful males shook them during courtship displays. This requires more muscular effort, and suggests the dynamics of feather vibrations could also signal male muscle power to choosy females.
British naturalist Charles Darwin documented the male peacock's remarkable display in his book on sexual selection, "The Descent of Man and Selection in Relation to Sex." He was not very impressed with the sound produced during the peacock's effort, though.
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Darwin wrote: "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 the plumage."
The new paper counters the view that the sound is just meaningless "noise," as the produced sound, the mesmerizing eyespots, shimmering feathers and other features of the display appear to all work in concert.
"Charles Darwin observed that peacocks vibrate their feathers during courtship," co-author Suzanne Kane said in a press release, "but it took this multidisciplinary team of scientists to characterize the dynamics of this behavior."
Photo: Male peacock courting a female. Credit: Roslyn Dakin PLOS ONE e0152759