The Science Behind Bird Feather Colors

Every bird feather and its colors tell a story of adaptation and survival, making the beauty of feathers complex and captivating. Bird feathers are not only beautiful due to their hues, but also because of the intricate combination of pigments and structures that comprise them.

Birds come in all color tones, which are either pigmented, or the result of microscopic structures that reflect a select portion of wavelengths. Let’s find out more about how birds get their amazing colors.

The purple-wine color of the Pompadour Continga (Xipholena punicea) is the result of a minor alteration of Carotenoid colors structuring. Photo: Anselmo D’Afonseca.

Pigments in Bird Feathers

There are three types of pigments in feathers that create their color; melanins, carotenoids, and porphyrins.

Melanins

red-winged-blackbird-
The dark color of the Red-winged Blackbird (Agelaius phoeniceus) is rich in melanin pigments.

These pigments are the most common and create earth tones, blacks, browns, and buff colors. Melanins are made from tyrosine, an amino acid, by pigment cells called melanoblasts that move about in the dermis layer of the skin. 

During feather development, the melanoblasts insert melanin granules into specific cells that become specific barbs and barbules. The birds’ shades of brown or gray depend on the density of melanin deposition. 

Two forms of melanins, eumelanins which produce dark brown, gray, and black and phaeomelanins, which create tans, reddish-browns, and some yellows, dominate the barbs and barbules. 

Melanins serve several functions; they help protect feathers from wear and tear, absorb radiant energy, and assist thermoregulation.


Carotenoids

house-finch-northeast-region


Carotenoids are responsible for bright yellows, oranges, reds, and certain blues and greens. 

These pigments dissolve quickly in lipids or organic solvents, which is why they are often stored in egg yolk, body fat, and the secretions of oil glands. Growing feathers’ cells accumulate these pigments in droplets of lipid and become embedded in the barbs and barbules when fat solvents disappear. 

There are two forms of carotenoids, carotenes, and xanthophylls. Xanthophylls have oxygen atoms attached to their carbon and hydrogen molecules. Bright red pigments include canthaxanthin and astaxanthin, while lutein is a common pigment that produces bright yellow feathers.

Image: The plumage of the House Finch (Haemorhous mexicanus) contains slightly different versions of carotenoids that results in brown, tan, and red-like colors.


Porphyrins


Porphyrins are related to hemoglobin and liver bile pigments and are the third type of pigment that shows intense red fluorescence under ultraviolet illumination. 

Porphyrins are commonly found in red or brown feathers of at least 13 bird orders, like owls and bustards. These pigments are chemically unstable and easily destroyed by sunlight, found mostly in new feathers. 

Turacin, a unique copper-containing pigment, produces the bright magenta in the wings of turacos, which are spectacular crow-sized birds of African forests.

Image: The redish-brown in the Barred Owl (Strix varia) may look similar to other brown colors in birds, but it is the result of Porphyrin pigments. One would need a color-metering device to really differentiate the uniqueness of the brown color of this owl. Photo: Guenter Weber.


Biochrome’s Function in Birds

Biochrome is a coloring matter that can be extracted from a plant or animal, serving as a natural pigment. It is a type of biological pigment produced by living organisms, which acquire color through selective absorption of certain wavelengths.

Biological pigments are found in specialized cells called chromatophores. Biochromes are chemically formed microscopic pigments that occur naturally. They are designed to absorb specific colors of light and reflect the remaining wavelengths.

Birds use biochromes for several functions. Melanin makes feathers resistant to wear and tear while also helping protect feathers from sand abrasion and promoting drying of damp feathers. 

Carotenoids help protect feathers by absorbing ultraviolet radiation. Porphyrin mixed with turacoverdin creates bright green colors in turacos’ feathers.

Structural Colors 

Some of the most vibrant colors in bird feathers come from structural features on the surface of the feathers.

Structural colors are created by the physical alteration of incident light on the feather surface. This means that the color of the feather is not due to any pigment, but rather the way that the light interacts with the surface structure of the feather.

For example, blues and greens in birds such as parrots, bluebirds, and hummingbirds are structural colors that result from the scattering of short (blue) wavelengths of light by tiny melanin particles in the surface cells on the feather barbs.  The other longer wavelengths of light pass through the surface layer to an absorbent melanin layer below, leaving only the blue color visible.

The Peach-faced Lovebird, a small African parrot, has both blues and greens on its feathers that result from another process based on interference among different wavelengths of incident light.


Altering Colors

Carotenoid pigments can convert structural blues to green or violet.  Wild Budgerigars, for example, are green because of an association of  yellow pigment with structural blue. Mutant parakeets with a single recessive gene that blocks carotenoid pigment deposition are blue rather than green.

If the carotenoid pigment is red rather than yellow, violet or purple results, as in the Pompadour Cotinga. 

The purple head feathers of the Blossom-headed Parakeet are actually made from structural blue from the barbs plus red pigment in the barbules.


Iridescence

The brilliant iridescences gorget of this Purple-collared Woodstar (Myrtis fanny) come from 7 to 15 closely stacked layers of tiny melanin granules located on the feather barbules. Photo: Ale Telleria.


Iridescence is the phenomenon of glistening colors that vary with the angle of incidence of illumination. Directional iridescence is seen from only one angle of view, from other directions the feather appears black.

The iridescent colors of the “eyes” on a Peacock’s tail and the quetzal’s back feathers result from interference of light waves reflected from the outer and inner surfaces of a reflecting layer. 

The brilliant iridescences of hummingbird feathers come from 7 to 15 closely stacked layers of tiny melanin granules located on barbules. Each granule is a flat, hollow platelet with two reflecting layers that create particular colors by light interference and reinforcement. The intensity of the iridescence increases with the number of granule layers.

Other Reflection Systems

Other types of reflecting layers have evolved in starlings and trogons. African starlings have iridescent colors caused by reflections from the interfaces between melanin granules and keratin layers.

Four different systems are known to produce the iridescent colors of five genera of trogons. These controlling microstructures, which include air-filled melanin plates and hollow melanin tubes, are arranged in precise layers.

 Colors and patterns result from small variations in the refractive indices of keratin and melanin, the shape and measurements of the pigment granules, and the spacing within and between layers of granules.

These factors are subject to closely controlled variation in every part of every iridescent feather on a bird. 

Conclusion

The science behind bird feather colors is fascinating and complex. Bird feathers are beautiful not only for their colors, but also for the pigments and intricate structures that create them. 

The colors of feathers serve many functions. Not only do they help us identify different species of birds, but they also allow them to survive by camouflaging themselves, helping in thermoregulation, and even finding mates. Understanding the science behind these colors is important for both scientists and bird enthusiasts alike.

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