Mary Syrett - December 2007

The Function of Feathers
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 the charcoal-gray of a great blue heron soaring in flight. A person might think about birds in one way or another every day, but how often does a Chesapeake Bay nature lover contemplate a bird’s feathers?
      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. Beaks and eyes have no feathers, and most birds have featherless legs and feet.
      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 perhaps 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. These are the feathers that birds are born with that act as insulation, keeping the 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 has a tapering shaft bearing a flexible vein 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 is sealed off.
      Feathers play diverse roles in the lives of birds, including mating. In some species, the colors of the male have a direct impact on how attractive he appears to a female, and, therefore, to his mating success. In some instances, the roles are reversed, with the male seeking clues to a female’s value as a mate by examining the coloration of her feathers.
      Territorial Dominance. Biological research suggests that birds in good 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 others should 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 tightly overlap to form a waterproof outer shield.
      Feathers help provide camouflage from predators. For example, the winter plumage of a ptarmigan is pure white, which matches 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.
      Flight. Feathers obviously play a crucial role in flight, lending an airfoil shape to wings that provides lift. Hummingbirds are particularly adept at controlling their feathers and thus the shape of the wing when they hover while feeding.
      Water birds have specialized 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, which spectacle you have undoubtedly witnessed if you have ever visited the Everglades.
      If clothes make the man, 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.
      Color is important in mating. Birds, unlike 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 absolutely critical to a bird’s survival, much time is spent maintaining them. In fact, much of a bird’s day is spent cleaning and grooming feathers by applying oil, bathing and preening.
      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 them to fly and hunt. Flight feathers of some predatory birds last two to three years. Other birds 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 but think of “feathers.” Plumage is the most prominent feature of a bird’s anatomy. Every bird has feathers and everything that has feathers is a bird.
      Feathers 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 many societies since the dawn of time. While feathers have been used for a variety of human purposes, feathers do look best on and are most useful to birds. Let’s keep it that way and enjoy the magnificent sights to be seen at birding hotspots throughout Chesapeake Bay country.