HOW COLOR IS CREATED IN BIRD FEATHERS PART 2

Turkey male fanning tale feathers feathers Kim SmithStructural Color

Have you ever wondered why sometimes you can see the brilliant red gorget (throat feathers) of the male Ruby-throated and Allen’s hummingbirds, and sometimes not at all? Or why iridescent feathers appear green, and then blue, or possibly purple, and then in the next moment look drab and dreary? I think about this when photographing birds such as grackles, buffleheads and hummingbirds. Most recently, the turkeys in our community are currently displaying their wildly varying iridescent feathers when in full courtship mode.

Bufflehead Kim Smith

Bufflehead Iridescence

Iridescent Red Gorget in Male Allen’s Hummingbird, same bird, different angles

Layering

There are two types of structural color, layering and scattering. Iridescence in bird feathers is created by layering. Bird feathers are made of a translucent protein called keratin, which is a very rugged substance. Not only are the feathers made of keratin, but keratin coats the bird’s claws, legs, and bill. Because of the structure of the feather, with its microscopic barbules, when light hits the feather it causes the wave lengths to bend, or refract. Keratin reflects short wave length colors like purples, blues, and violets. The other colors are absorbed by the underlying layer of melanin. The refraction works like a prism, splitting the light into an array of colors. As the viewing angle changes, because of the viewer’s movement or because the bird is moving, the refracted light displays a shimmering iridescence, or none at all. Beautiful color combinations are created when iridescent layers are combined with pigments present.

Turkey male iridescent feathers -2 Kim SmithIn the above photo, the male Turkey’s iridescent feathers surrounding the head make a splendid display in full sun.

These same feathers appear entirely different when back lit.

Turkey male iridescent feathers Kim Smith

Grackle Kim Smith 2016

Iridescence in Grackles

Scattering

Keratin is interspersed with tiny pockets of air of within the structure of the feather filament (called barb). Scattering is created when light hits the pockets of air, which results in specific, non-iridescent color. The color blue in feathers is almost always created in this manner. Feathers of Blue Jays, Bluebirds, and Indigo Buntings are prime examples of scattering.

Here are two graphics found online that I found very helpful in trying to visualize the difference between layering and scattering. The first shows how iridescence is produced and the second, how blue scattering is created.Struct-Color-DIA-Iridescent_Myaedit_coloracrticle-674x441Bird_Biology-Feather_structural_blue-674x450

 

HOW COLOR IS CREATED IN BIRD FEATHERS

In thinking about how colors are created in bird feathers, I wondered if it was similar to how color is formed in butterfly wings. I learned that yes, it is very similar, and that bird feather color has evolved in several ways, from pigmentation present or as a result of light refracting through the layered structure of the feather.

Northern Cardinal Male Kim Smith

Color from Pigment

Pigments are colored material found in plants, animals, and nearly every physical substance in nature. Pigmentation in birds comes from three different sources: melanins, carotenoids, and porphyrines.

Melanins are tiny bits of color in the feathers of birds and in their skin. Melanins produce colors from palest yellow to rusty red browns to the richest black, depending on where the melanin is located and in what degree of concentration. Feathers with melanin are the strongest of all. A bird’s flight feathers are the most susceptible to wear and usually have the highest degree of melanin.

Red-winged Blackbird male Kim Smith

American Robin Kim Smith

Red-winged Blackbirds and American Robins are strong flyers. Their flight feathers have rich concentrations of melanin.

Carotenoids are produced by plants. Birds that eat specific plants, or eat something that has eaten the plant, acquire pigment from carotenoids. A carotenoid-rich diet is responsible for the beautiful vermillion feathers of the Northern Cardinal, as well as the electrifying cadmium yellow of the male American Goldfinch. Another example is the pink feathers of the flamingo, which also have a diet rich in carotenoids that come from the crustaceans that they eat, which ate algae. Melanins and carotenoids can interact to produce feathers such as olive green.

The third group of pigments are called porphyrins and they are the rarest, found only in a handful of bird families. Porphyrins are produced by modified amino acids and all share a common trait, which is to fluoresce bright red when exposed to ultraviolet light. Porphyrins are found in some pigeons, owls, and turacos.

The intensity of the red of the Northern Cardinal is an example of how feather color plays an important role in the survival of a species. Cardinal foods high in carotenoids include rose hips and dogwood berries. The brightest red birds usually have superior breeding territories, with the greatest abundance of their preferred foods. The reddest birds make the most successful parents because of their ability to bring an increased amount of food to the nestlings. When Cardinals are raised in captivity on a diet lacking in carotenoids, with each successive molt, the feathers become paler and paler.

Like butterflies, birds can see color in the ultraviolet spectrum (we humans cannot). Perhaps the way we see birds is entirely different from they way they see themselves!

Part Two Structural Color continued tomorrow.

Red-winged Blackbird in flight male KIm Smith

Male Red-winged Blackbird