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.