Train-Rattling Peacocks Are Biomechanical Wonders

A peacock unfurls his magnificent train feathers. (Credit: Roslyn Dakin) When you see a peacock shake a train feather, you’re watching finely tuned natural engineering at work. When a peacock wants to woo a peahen, he unfurls his glorious, iridescent feathers and furiously vibrates them in what’s called a “train-rattling” display. The vibrations make the bird’s signature eyespots appear to float, motionless atop a swirling sea of wispy feather barbs. In his book on sexual selection, Darwin believed peacocks vibrated their colorful tails “merely to make noise,” because the motion could “hardly add to the beauty of their plumage.” This, coming from a man who said the sight of a peacock feather was enough to make him sick — peacocks, with their clumsy, massive feathers, didn’t fit nicely into Darwin’s “survival of the fittest” framework. They sort of forced him to develop the idea of sexual selection as an additional mechanism of evolution.