Zi's motivation to study peacock coloration came after a trip to the marketplace in southern China's Yunnan province, where he bought a bundle of peacock feathers from Banna (a town renowned for its wild peacocks) as a souvenir. "When I watched the eye pattern against the sunshine, I was amazed by the stunning beauty of the feathers," said Zi.
To uncover the basis of that color, Zi and colleagues used very powerful electron microscopes to examine the barbules of the green peacock, Pavo rnuticus. The barbules are the tiny feather tip structures that come off of barbs on either side of the central stem of peacock feathers.
When viewed under a microscope, they revealed a repetitive two-dimensional structure of small crystalseach with a width hundreds of times thinner than a human hair. Optical measurements and calculations showed that variation in the spaces between repeats of the crystals causes the structures to reflect light in slightly different ways and leads to variation in color.
Dressed to Impress
"Structural colors are often found in animals that wear the color as a function to be conspicuous," commented Andrew Parker, an evolutionary biologist and coloration expert at the University of Oxford in England. Such color mechanisms are often much brighter and visible over longer distances than pigments.
Charles Darwin was one of the first scientists to argue that female peacocks prefer the males with the boldest and most attractive ornaments, and subsequent work has shown that brightly decorated males enjoy greater mating success. Studies have also shown that the quality of ornamentation in peacocks is an accurate reflection of the state of the immune system, so females are picking those males genetically predisposed for tip-top health.
Discovering so-called photonic crystals in peacock feathers could allow scientists to adapt the structures for industrial and commercial applications, said Parker. These crystals could be used to channel light in telecommunications equipment, or to create new tiny computer chips. We can take advantage of "millions of years of evolutionary trial and error," for new technologies, he said.
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