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How the blue jay got blue.

How the blue jay got blue

Scientists may not know how the leopard got its spots, but they are learning how the blue jay, the bluebird and others of that sort got blue. According to Leonard W. Winchester Jr. of the Science and Technology Corp. in Hampton, Va., experiments done more than 100 years ago showed that no pigment can be found in blue jay feathers. Since then, scientists have generally assumed that the blue in the blue jay comes from light scattering, a process of refraction and retransmission of light by tiny transparent objects.

Winchester says he and his research partner, Raymond Leonard of Fairfield (Conn.) University, did not believe this assumption and started spectroscopic experiments with blue jay feathers in the hope of disproving it. Instead, he says, they have proved it.

In the scattering process, because some of the colors in white light are suppressed, others come to predominate in the scattered light. Winchester and Leonard found that the scattering in blue jay feathers is what is technically called Rayleigh scattering, the kind done by spherical objects much smaller than the wavelength of the light. The scatterers are alveolar cells in the barbs of the feathers.

The researchers used tail feathers that had fallen to the bottoms of cages. The Connecticut Audubon Society, which supplied the feathers, refused to pluck live birds.

Scattering is responsible for nearly all of the blue, most of the green and some of the purple in animals, Winchester says. On the other hand, absorption and reflection by a pigment makes canary yellow, and interference of multiply reflected light is responsible for iridescent colors like those in a peacock's tail. Parrot green combines absorption by a yellow pigment with blue due to scattering.

Can all this mean that the bluebird of happiness is an optical illusion?
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Title Annotation:color caused by light scattering
Author:Thomsen, Dietrick E.
Publication:Science News
Date:Nov 1, 1986
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