While riding my bike to Mesilla Park, just outside Las Cruces, one afternoon, I glanced up at the sky and skidded to a stop, head tilted upwards in astonishment. Just above the tops of the mulberry trees, the air was filled with huge, silent black birds with bare, wrinkled heads and wings held stiffly in a V as they teetered on the air currents – turkey vultures. I watched the flock of about 40 birds as they caught a thermal and spiraled upwards, coasted south towards the horse farm, then turned and rode the waves of southerly winds towards me, bouncing, teetering and coasting as if riding a giant water slide.
Ungainly on land, vultures excel in the air. These master gliders can soar gracefully for hours with nary a beat of their 6-foot-wide wings, riding thermals – rising columns or bubbles of warm air – or coasting on the streams of wind. With broad wings and a low wing loading (the ratio of body weight to wing area), vultures can soar at extremely slow speeds without sacrificing maneuverability. By soaring with their wingtip feathers spread wide like the fingers on a hand, vultures counteract the large amount of drag produced by their wide wings, reducing wingtip turbulence and lowering their stalling speed. When soaring slowly, vultures actually glide downward to maintain forward thrust, but they stay aloft because the rising warm air propels them upwards faster than they sink.
The ability to ride the air slowly to great heights and for great distances with little energy expenditure allows vultures to search efficiently for their randomly-occurring and often widely-dispersed food – carrion, rotting carcasses. Vultures also save energy by cooperating, searching in groups, and descending en masse when one spies a carcass.
Vultures often get bad press for their diet. But the scientific name of their family, Cathartidae, from the Greek word for “cleanser,” commemorates their role in Southwest ecosystems: they dispose of potential sources of disease, and recycle the nutrients contained in the carcasses. Vultures are well-designed for sanitarians. Sophisticated immune systems protect them from disease-causing organisms, and their unfeathered heads are easily cleaned of rotten meat and potential pests. The odor-processing area of a vulture’s brain is much larger than in other birds of comparable size, suggesting that the stench of carcasses helps them locate their food from long distances.
When we lived in Mesilla Park, we saw this flock of turkey vultures frequently. Communal birds, turkey vultures roost and nest together. In winter, they migrate south to Mexico, often in flocks of several hundred birds, returning in March. Since we moved to another part of town, I’d forgotten how awesome is the sight of these huge black birds passing silently overhead just above the treetops, teetering on the air currents as they go about their business.