Crystals explain the eyes of a peacock's tail is

The secret of the brilliant colours in a peacock's tail have been revealed in a study showing that the tiny crystals within the feathers act like a kaleidoscope, splitting light into the different colours of the spectrum.

Scientists at Fudan University in Shanghai have found that the solid crystals within the iridescent "eyes" of a peacock's tail feathers, rather than the traditional pigments, are used to generate the unusual colours of the male plumage.

Each feather has a central stem with barbs on each side. On each side of a barb there is an array of smaller, flat barbules. The scientists, using an electron microscope, found the outside layer of each barbule consisted of a two-dimensional crystal structure composed of criss-crossing melanin rods.

The number and spacing of the rods differed, depending on the colour of the barbule. Further analysis showed that various lattice patterns produced distinct colours. Two features - the "lattice constant" (rod spacing) and number of "periods" (melanin rod layers) - worked together to produce the peacock's tail-feather display.

Jian Zi and colleagues wrote in the Proceedings of the National Academy of Sciences: "Varying the lattice constant produces diversified colours. Reduction in the number of periods brings additional colours, causing mixed colourations." They said the findings could provide insights into understanding colouration in other organisms and objects.