You've probably caught a glimpse of them on the side of the road. Turkey vultures. They're our outdoor cleaning crew, ridding the landscape of road kills and other carcasses, an important yet thankless service. It's even reflected in their scientific name, Cathartes aura. Cathartes is from the Greek word, katharsis meaning to purge or cleanse.

Turkey vultures are common from southern Canada, throughout most of the United States and South America. Northern birds are migratory, leaving colder areas in September and October for warmer climates. They either migrate in flocks or join up with others of their kind en route south.

Turkey vultures are not terribly attractive: They have a brownish black body, two-tone black wings and a naked red head.

But when it comes to flight, these large birds are quite graceful. Using their 6-foot wingspan, they can soar for hours on updrafts and rising columns of warm air called thermals. Turkey vultures extend their wings into a V-shape, lightly rocking from side to side.

Their diet consists almost entirely of carrion from fresh to putrid, although they will occasionally feed on decaying vegetation, insects or fish. Efficient scavengers, turkey vultures quickly dispose of carcasses. They can consume the bodies of animals that died of illness or infection without being adversely affected. They are most likely to be found soaring over open or semi-open country, including fields, lightly wooded areas, deserts and foothills.

Turkey vultures often congregate in large trees, known as roosts, to rest.

They are late risers and will wait for the sun to warm them. They pose with wings slightly drooped, known as a spread wing posture. This helps to dry their wings and regulate their body temperature. Wing spreading in the morning absorbs solar energy, passively raising the bird's temperature to its daytime level.

Pairs are monogamous and both parents incubate the eggs, as well as feed and care for the young. Nest sites consist of little or no nest at all. The eggs are laid on debris inside a hollow tree or log, in crevices of cliffs, in caves, in dense thickets or in old buildings.

Usually, two whitish eggs, blotched with brown and lavender, are laid. Incubation lasts 34-41 days. The young are born with a coat of down and their eyes open. Their parents feed them by regurgitation. If the nest is disturbed, parents will protect it by violently vomiting. Immature turkey vultures look similar to their parents except they have black heads and beaks. The young are able to fly when they are about 9-10 weeks old. The beaks turn to adult white or ivory by the age of 4.

Because they have no syrinx or voice box, turkey vultures cannot sing like other birds. Instead, they hiss, grunt and huff.

If threatened or disturbed, turkey vultures throw up. Some ornithologists believe that this is because the predators will consume the regurgitated material and leave the turkey vulture alone. Most believe, though, that it is simply a defensive reaction caused by fright.

Turkey vultures also excrete down their legs. One theory suggest that because their excrement contains a lot of ammonium, it helps to kill any bacteria picked up from their food. Another theory is that this helps to keep the birds cool.

While they may not be on everyone's list of favorite birds, turkey vultures do help to remove carcasses quickly. With an increase in development comes an increase in road kills. Scavengers like turkey vultures keep the surrounding environment clear of unsightly and decaying animal bodies.

So remember when watching one circling overhead: Without vultures, every day would be like a garbage strike.