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About the cover
D e s e r t E x p o s u r e July 2013
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?
birds 1
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
Sand covers only about 20 percent of the Earth's deserts. Most of the sand is in sand sheets and sand seas--vast regions of undulating dunes resembling ocean waves "frozen" in an instant of time.
Nearly 50 percent of desert surfaces are plains where eolian deflation--removal of fine-grained material by the wind--has exposed loose gravels consisting predominantly of pebbles but with occasional cobbles.
The remaining surfaces of arid lands are composed of exposed bedrock outcrops, desert soils, and fluvial deposits including alluvial fans, playas, desert lakes, and oases. Bedrock outcrops commonly occur as small mountains surrounded by extensive erosional plains.
Oases are vegetated areas moistened by springs, wells, or by irrigation. Many are artificial. Oases are often the only places in deserts that support crops and permanent habitation.
Underground channels carry water from nearby mountains into the Turpan Depression of China. If the channels were not covered, the water would evaporate quickly when it reached the hot, dry desert land.