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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Blue or black? Colors are produced when light bounces off the grooves and ridges on feathers. © Stephen J. Lang
Blue or black? Colors are produced when light bounces off the grooves and ridges on feathers.

© Stephen J. Lang

February 2003

What color is a bluejay?

Looks deceive.

Anita Carpenter

Bluejays are feisty, incessant talkers that frequent our neighborhoods. They announce their arrival at bird feeders with loud, raucous calls. Watchful for roosting owls, the jay's piercing "jay-jay" alerts all others to the potential predator's dive-bombing harassment. Devilish bluejays can mimic screaming red-shouldered hawks, while loving bluejays will "tea-kettle" to each other.

Early taxonomists appropriately named bluejays Cyanocitta cristata, meaning "crested blue chattering bird." What the taxonomists didn't realize was that bluejays aren't really blue! We perceive their feathers as blue, but they are actually black. So what phenomenon produces the blue of bluejays? It's the same science that explains why the sky is blue.

Feather colors are determined either by pigments, called pigmented colors, or by light refraction called structural colors. Feathers contain two types of pigments. The melanins are sharply outlined, microscopic particles we see as black, dull yellow, red and brown. The lipochrome pigments are diffused in fat droplets and produce brighter yellows, reds and oranges.

When light strikes a pigment, it absorbs all the other wavelengths of the color spectrum except the color we see, which is reflected back to our eyes. Black is produced when all color wavelengths are absorbed and no color is reflected.

Structural colors, produced by selective light reflection, are mostly the blues, greens and violets. Shimmering iridescent colors are produced when light bounces off the grooves and ridges on feathers. The distance between these surface irregularities influences which colors we see. These structural colors change with the angle of view. Most blue structural colors are produced when particles smaller than a light beam scatter light. These blues do not change hue when viewed from different angles.

John Tyndall, a British physicist of the late 1800s, first described how minute particles, usually less than 0.6 microns, absorb the longer red wavelengths of light but reflect or scatter the shorter blue wavelengths. This phenomenon became known as "Tyndall scattering" and accounts for the sky's blue color that is sometimes called "Tyndall blue."

In bluejays, the color-producing units are found in feather barbs. These barbs consist of three layers. A colorless, transparent horny outer layer covers box cells, which cover a dark layer of melanin-containing cells. The box cells contain irregularly shaped air-filled cavities that scatter light. When sunlight strikes a bluejay feather, the beam passes through the barb's transparent outer layer to the air-filled cavities that scatter the blue light and absorb the longer red wavelengths. Any transmitted light that remains after passing through the box cells is completely absorbed by the melanin. The blue we perceive is actually enhanced in intensity by the underlying melanin-rich black layer.

Admire a bluejay from different angles. Its blue color remains pure and is one of the most striking blues we find in Wisconsin. Let's thank those early taxonomists, for I prefer a neighborhood sentinel named bluejay rather than blackjay!

Anita Carpenter eyes the colors of winter from Oshkosh.