It turns out that Black Vultures are different in several interesting ways. For one, they hunt only visually and therefore are commonly found in open territory rather the wooded hills like ours. They do however keep their eyes open for congregating Turkey Vultures which usually means a free meal. They are more aggressive and will run Turkey Vultures off, taking over their dinner.
Turkey vultures are a common sight, circling over Bull Creek or settling down over a nice dead carcass. In addition to being common, they are readily identifiable by their bald red heads. Since they hunt both with their keen vision and acute sense of smell, they forage over forested land where they don't have to compete with Black Vultures as often.
Since both vultures rely of dead animals for their food they may go days without eating. They make up for this with a Henry VIII habit of gorging prodigiously when food is available. They appear to be immune to the bacteria infesting dead animals, although they do prefer to have their meals recently dead. Their bald heads help in plunging head first into the body cavities to get to the good stuff.
Turkey vultures will glide on thermals with their wings held still in a V shape as they tip from side to side. Black vultures tend to fly with alternating a series of flaps, then gliding with their wings out straight. The difference has to do with their design. While weighing approximately the same, Turkey Vultures have a low wing load, meaning they have the longer wingspan in proportion to their weight. This allows them to ride the thermals with much less effort. For this reason, Black Vultures tend to start out later in the morning when the sun warmed earth creates stronger thermals to lift them up.
Like turkey, deer and raccoon, vultures have adapted to the expanding human population. They frequent highways looking for road kill and are now known to sometimes drop in on unguarded picnic food. So the next time you are out and see the "buzzards" circling, just remember that they are probably just curious - it doesn't signify a personal health risk.
The January 13 News-Leader MDC article on Black Vultures is at this site.