Bold…striking…varied…the colors of the visible light spectrum are well represented in avian coloration. For example,
Violet—Costa’s Hummingbird’s gorget
The astounding array of bird colorations and patterns is part of what draws many people into birding. Later, as one develops more birding skills, he or she finds mottled grey and brown colors and patterns equally intriguing.
Color is the major identification criterion used by birders and non-birders. If a non-birder were asked the names of the birds in the photographs above, he or she would probably answer correctly. Coloration can be simply observed, as in this example, but is actually much more complex than I imagined.
Several months ago, I read Geoffrey E. Hill’s book, National Geographic Bird Coloration to expand my birding knowledge and skills. The topic I found most interesting was how bird coloration is produced.
The most common pigments are melanins and caroteniods, which produce black, brown, rufous, red, yellow, and orange. Melanin, the animal world’s universal colorant, is found in both the plumage and skin of most birds. This pigment is made in the body by amino acids. Melanin produces caps, rings on bills, and markings such as masks, bars, spots and stripes; these give the bird its characteristic appearance. If a bird is lacking melanin, those places that would normally be colored are non-pigmented, making it an albino bird. There are two classes, eumelanin, and phaeomelanin.
Eumelanin is found on both feathers and bare parts (unfeathered areas such as legs and bills). Shades range from light gray to deep black. It is what makes Red-winged Blackbirds black and the Gray Catbird gray. Hill explains how eumelanin is like the toner in a copy machine: the more toner, or eumelanin, that is deposited, the blacker the area.
Phaeomelanin is found on feathers and probably colors bare parts as well, but scientists have never isolated it. It is usually deposited on feathers in combination with eumelanin, imparting earth tones, such as rufous, chestnut, golden, and yellowish hues. Like eumelanin, the amount of pigment deposited on the feathers determines the intensity of the color. Together, eumelanin and phaeomelanin can produce complex feather patterns in birds such as Marbled Godwits.
Carotenoids are the second most common pigments. They produce yellow, the most common, red, and orange. There are more than twelve types of carotenoids; contrast this with melanin, with only two forms. Unlike melanin, carotenoids cannot produce elaborate patterns within feathers. Another difference between the two common pigments is that carotenoids cannot be made by the body like melanin can. Carotenoids are in the food birds consume; after digestion, these pigments are absorbed into the circulatory system and carried to the appropriate places. Some are carried unchanged, but some are chemically altered before being deposited. If a certain pigment is absent or deficient in a bird’s diet, plumage of that pigment will be drabber or even a different color.
Pigments are not the only ways feathers are colored. Structural coloration is the other way, the structure being the microscopic layers, specifically barbs and barbules, of the feather. Barb microstructure creates non-iridescent coloration, while iridescent coloration is created by the barbules. There are three types of structural coloration: white, non-iridescent and iridescent coloration. This type of coloration is the result of how light interacts with the feather structure: how wavelengths of light are reflected, absorbed, amplified, or interfered with.
Many birders think of white as being produced by pigments, a default “color”, but white is actually created by feather structure. Non-iridescent colors are short wavelength colors, blue, indigo, violet, and ultraviolet. These colors are non-glossy and visible in all lights and angles. For example, no matter at what angle you view a Blue Jay, it is always the same royal blue.
In birds such as Common Grackles, iridescence is produced by layers of light-transmitting substances and melanin, which reflect light in the barbules. The more layers involved, the brighter the display. Display colors, as birders know, depend on light; without the right lighting conditions and viewing angles, iridescent plumage is dark.
Coloration can also be a mixture of the two coloration methods. For example, when pigments such as yellow caroteniods are deposited on feathers with non-iridescent structural coloration, green or olive coloration is produced.
As I discovered from reading this book, coloration is not as simple as selecting a crayon from the box and depositing color in the desired location on the bird. Whether colored by pigments or microstructures, each species has its own kind of beauty. As the kaleidoscope mesmerizes with its variation of colors and patterns, bird coloration can produce the same fascination. From the violet gorget of the Costa’s Hummingbird to the red of the Vermilion Flycatcher, the avian rainbow offers a beautiful palate for our enjoyment. Take time to carefully observe and enjoy the colors and patterns of birds and read this book for yourself. There are many more fascinating topics included that I think young birders (actually any birder) will enjoy.
About the author: Alexandria Simpson is an avid, sixteen-year-old birder from Santa Anna, Texas. While she wishes she could say she has been birding all of her life, instead she has spent the last four years making up for lost time. She wants to become an ornithologist and someday read scientific papers without falling asleep. Her photography, illustrations, and writings have won awards at local, state, and national levels. She currently serves as one of the student blog editors for The Eyrie.