The spectacular sight of a peacock's tail has made the animal synonymous with vanity. Researchers knew that the brilliant colors result from so-called structural coloration--that is, the interaction of light with features of the feathers--instead of pigmentation, but the precise mechanism of color production was unknown. New findings published online this week by the Proceedings of the National Academy of Sciences unveil the creature's beauty secrets.
A team led by Jian Zi of Fudan University in Shanghai examined peacock tail feathers using both an optical microscope and a scanning electron microscope. The scientists determined that each feather has a central stem with a number of barbs on each side. These barbs, in turn, have smaller flat structures dubbed barbules protruding from them. The microscope images showed that regardless of the feather color, the barbules all had a two-dimensional lattice made up of melanin rods as their outside layer. The number of rods and the spacing between them was not consistent, however. "These differences," the scientists note, "are the cause of the diversified colors."
The researchers used numerical simulations to show that the different lattice patterns found in the barbules shift the light waves that pass through them to produce the tail's vibrant blues, greens, yellows and browns. "The strategies for color production in peacock feathers," they conclude, "are very ingenious and rather simple."