By Mike Checkett
Plumage colors result from pigments and from the structure and reflective properties of feathers
The development of the feather and the remarkable variation in plumage among bird species are two of nature’s miracles. Feathers are the most distinctive characteristic of a bird and are among the most complex structural organs found in vertebrates. Feathers form the flight surface, improve flight efficiency, and provide exceptional insulation. And they come in an amazing array of colors, which helps birds differentiate species, attract mates, and avoid predators.
Scientists believe feathers are actually a modified version of the scales seen in reptiles, as these two structures have similar chemical composition. Hummingbirds have the fewest feathers (some species have less than a thousand), while some swans have more than 25,000 feathers, 80 percent of which are on the birds’ head and neck.
Feathers grow out of a follicle in the skin. Although highly vascularized (nourished by blood vessels) during growth, mature feathers are nonliving tissue, somewhat like human hair and fingernails.
Ducks have many types of feathers—stiff, glossy ones on the outside to give a water-resistant, streamlined contour, and fluffy down feathers under these for warmth. On the wings, large, stiff feathers form a flexible airfoil, while some feathers in the tail or crest may be enlarged, elongated, or elaborately colored.
Feather colors produce the familiar plumage patterns of each duck species. Birds display virtually every color imaginable, and waterfowl are no different. Colors result from pigments in the feather or from the structure or reflective properties of feathers.
Pigment colorization in birds comes from melanins, carotenoids, and porphyrins. Melanins occur as tiny bits of color in both the skin and feathers of birds. Depending on their concentration and location, melanins can produce colors ranging from black to reddish brown and pale yellow. Feathers that contain melanin are stronger and more resistant to wear. Carotenoids are produced by plants and acquired by eating plants or by eating something that has eaten a plant. Responsible for the bright yellows, reds, and oranges seen in birds, carotenoids can interact with melanins to produce colors like olive-green. Porphyrins are produced in the body and create a range of colors, including pink, brown, red, and green.
Structural coloration in bird plumage is especially important in producing blues, greens, and iridescence. Blues and iridescent colors are generally the result of fine feather structure. There are no blue pigments in feathers (check a feather lit from behind to see for yourself), and most green plumage has no green pigment. Rather, the feather is constructed of layers; one layer reflects the wavelength of light that gives the color we see, while a deeper layer absorbs the other wavelengths.
In some cases, feather colors result from a combination of structural colors and pigment. Yellow pigments overlaying the blue-reflecting structural characteristic of the feathers produce the greens on some ducks.
An example of iridescence in waterfowl is the speculum of many dabbling duck species, such as the blue on a mallard’s wing. The iridescent colors of the speculum are the result of the refraction of light caused by the microscopic structure of the feathers. Refraction works like a prism, splitting the light into rich component colors. At certain angles, little or no light is reflected back to the viewer, and the speculum can appear black. As the viewing angle changes, refracted light becomes visible in a shimmering iridescent display.
Some colors help make feathers stronger and thus occur in areas subject to greater wear. For this reason, many white birds such as snow geese have black wing tips. These feathers contain melanin, which makes them more rigid and less subject to wear and abrasion. Some colors may occur for other physiological reasons, such as absorbing (dark colors) or reflecting (pale colors) light.A bird’s coloration also helps conceal it from predators and aids in recognition, courtship, and other social activities. Signaling by color is important in such activities as species recognition, sexual behavior, flock movements, or warning displays. With so many factors at work, it is difficult to explain the occurrence of any particular color on any particular part of a bird.
Variations in plumage can be based on the sex of the bird, its age, seasonal changes caused by molting, or genetic variation. In ducks, the drake has a neutral “default” plumage. The presence of estrogen suppresses the neutral condition and results in the brown plumages typical of females. In fact, females with damaged ovaries from parasites, shot pellets, or disease can develop a drakelike plumage.
Minor plumage color differences occur in waterfowl because of genetic variability. Different levels of pigments can change the appearance of a bird dramatically. Such color variations occur regularly, but other hereditary abnormalities in plumage occur less frequently. These include excessively dark pigmentation, or melanism, and lack of pigmentation ranging from leucism to albinism.
Animals with leucism have reduced pigmentation in their bodies and colors appear washed out. In waterfowl, leucism can affect plumage, bill, and foot color. This color variation can occur on part or all of the bird. Leucism either is inherited or comes from genetic mutations that occur during development.
Occasionally, totally white individuals, called albinos, occur in the wild. These birds lack coloring because pigments normally found in feathers were not produced during development. Albino birds have no pigment in their skin, feathers, or eyes. Albinism occurs in waterfowl but is much rarer than leucism. In the wild, predators can easily see albino waterfowl, so they seldom live long enough to reproduce and pass on their traits.
Waterfowl feathers not only are beautiful but also serve many important functions that are vital to the birds’ survival. Keep this in mind the next time you bag a duck. Take a moment and have a closer look at the bird’s different kinds of plumage. There are more to feathers than meets the eye.
Mike Checkett is a biologist and communications specialist at DU’s national headquarters in Memphis.