The Natural World
The Function of Feathers
For birds of the desert Southwest, feathers are essential
for everything from flight to finding a mate.
by Mary Syrett
What comes to mind first when thinking about birds? It might be the brilliant red of a cardinal, the bright hue of a bluebird, the mottled brown of the very spoiled female mallard who lives in my backyard, or a hawk soaring over the Southwest. You might think about birds in one way or another every day, but how often do you contemplate a bird's feathers?
To warm up after a cold desert night, a roadrunner will turn its back to the sun, fluff its back feathers, and expose skin along its back. This skin is black in order to absorb more solar energy.
The most noticeable feature of a bird is in fact its feathers, which are perfectly designed for a multitude of functions. They are light but very strong, and flexible but tough. Feathers do not grow all over a bird. Their beaks and eyes have no feathers and most birds have featherless legs and feet.
If you are a birder who has come for the first time to the American Southwest, you may be in for some surprises. The number of species that have found a desirable place to live in the region's desert basins and mountain ranges may take you aback. You may also be surprised by birds' resourcefulness in coping with an arid and often unforgiving environment.
Among the birds that make their home in the Southwest are the southwestern willow flycatcher, the Gila woodpecker, the Mexican jay, the greater roadrunner (the state bird of New Mexico), the yellow-headed blackbird, great blue herons, the pyrrhulaxia (desert cardinal), and the black-chinned sparrow. Also often seen here are vultures, ibises, quail, wrens, magpies, bald eagles and grebes.
Types of Feathers
Birds have between 1,000 and 25,000 feathers, depending on the species. Larger birds have more feathers; the swan, with its long neck, has the most. Feathers fall into five categories:
- Contour feathers are those that cover the body of a bird and provide the basic color. These overlap like roof shingles to give a bird an aerodynamic shape.
- Flight feathers on the wings are specialized contour feathers. These provide a lightweight, broad surface that pushes against air to make flight possible.
- Down feathers are the fluffy feathers that form the downy plumage of chicks, creatures born with feathers that can move about soon after hatching. Down acts as insulation, keeping birds warm.
- Tail feathers provide lift, balance, steering and braking.
- The powder-down feather is found in only a few birds. It grows continually. The tips break off, forming a water-resistant powder. The metallic sheen of a heron is caused in part by this powder down.
Every feather consists of a tapering shaft bearing a flexible vane on either side. The exposed base of the shaft is called the calamus. An opening at the bottom of the calamus allows blood to enter the young feather during its short growing period. When growth is completed, the feather seals itself off.
The phrase "light as a feather" is no accident. Even birds that seem large, with bulky feathers, don't weigh very much. Consider the common crow, whose range is coast to coast wherever trees grow, including the southwestern desert belt, which is an opportunistic feeder, consuming a great variety of plant and animal foods. It's hard to believe that a seemingly big crow, feathers and all, weighs only about one pound.
Feathers play many roles in the lives of birds, including attracting a mate. In some species, the colors of the male have a direct impact on how attractive he appears to a female and, therefore, on his mating success. In some instances, the roles are reversed, with the male seeking clues to a female's value as a mate by carefully examining the coloration of her feathers.
Fast-moving feathers: Speeds vary by species, but a hummingbird beats its wings about 70 times per second in flight and over 200 times per second while diving. (Photos by Lisa D. Fryxell)
Other ways feathers are important include:
Territorial dominance — Biological research suggests that birds in excellent health produce feathers with super-bright colors. In establishing nesting territory, birds that are brightly colored may be sending a signal that they are especially fit and that it would therefore be wise for others to keep out of "their" territory.
Regulation of body temperature — Feathers help keep birds warm and dry. Penguin feathers, being small and densely packed, are particularly well suited for this purpose. The downy base of each feather traps an insulating layer of air against a penguin's skin. The feather tips overlap to form a waterproof outer shield. Even in the warm and dry Southwest, however, feathers can protect birds in the cold nights and the wet monsoons.
Keeping safe — Feathers help provide camouflage from predators. For example, the winter plumage of a ptarmigan is pure white, the color matching the snow-covered grounds of the bird's winter home. The spring molt produces mottled-brown feathers, making the female virtually invisible as she sits on a nest. In much the same way, it's no wonder the desert Southwest is home to so many brownish-feathered birds, from roadrunners to towhees to doves.
Flight — Feathers obviously play a crucial role in flight, lending an airfoil shape to wings that provides lift. The hummingbirds that zip through New Mexico skies this time of year are particularly adept at controlling their feathers and thus the shape of the wing, as they hover while feeding. A hummingbird's flight speed can average 25-30 miles an hour, and they can dive at up to 60 miles an hour.
Keeping dry — Water birds have special oil glands that make their feathers water-resistant. Exceptions are birds that dive for food; they have no oil glands because they cannot be buoyant. Such birds, including anhingas, must dry their feathers in the sun, a spectacle you have probably witnessed if you have ever visited the Everglades.
Coloration — If clothes make the person, then feathers make the bird. Feathers come in an amazing array of colors, including just about every hue imaginable. All of a bird's feathers are referred to as plumage. Even in the Southwest, where so many birds dress drably to blend into the desert, you will see the brilliant orange of a Bullock's oriole, the electric blue of a blue grosbeak or more subdued blue of an indigo bunting, and the cheery yellow of a goldfinch's feathers.
Color is important in mating. Birds, unlike many creatures including most mammals, can see color. Colorful male plumage is used to attract a female's attention.
Some species, including killdeer, mockingbirds, many shorebirds and most gull species, exhibit a color pattern known as countershading, which features a dark back over light underparts. When viewed from above by a predator, the dark back appears lighter in the sunlight, while the lighter lower half of the bird appears darker as a result of being in its own shadow. The effect is one of a single color, making the bird difficult to spot from a distance.
Because feathers are critical to a bird's survival, much time is spent keeping them well maintained. In fact, a good portion of a bird's day is spent cleaning and grooming feathers by applying oil, bathing and preening.
The male oriole’s bright plumage helps it attract a mate—important since orioles are monogamous.
Feathers do eventually wear out. Molting, the process of losing old feathers and growing new ones, occurs in most birds once or twice a year.
The feathers of predatory birds molt slowly because they need most of their feathers to fly with and hunt. Flight feathers of some predatory birds, including New Mexico's roadrunner, last two to three years. Other birds, including penguins, lose all of their feathers over a two-week period of time, after new ones have begun to grow in.
When you think "birds," you can't help think "feathers." Plumage is perhaps the most prominent feature of a bird's anatomy. Every bird has feathers and everything that has feathers is a bird.
Feathers, regardless of where a bird lives — in the mountains, by the seashore or in the desert — have an exquisite beauty, tenderness and functionality that has captured the imagination of people for untold centuries. These delicate works of nature have been utilized as personal adornments, ritual objects, decorative artifacts and tools by virtually every society since the dawn of time. While feathers have been used for a variety of human purposes, feathers look best on, and are most useful to birds. Let's keep it that way.
To learn more about birds in our area, contact:
Southwestern New Mexico Audubon Society, PO Box 1473, Silver City, NM 88062, (575) 534-1115 firstname.lastname@example.org, www.swnmaudubon.org
Mesilla Valley Audubon Society, Las Cruces, NM, www.mvaudubon.org
Mary Syrett is a freelance writer and long-time bird enthusiast.