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Excerpts from Jim Conrad's
Naturalist Newsletter
from the October 6, 2008 Newsletter written in Sabacché; ~N20.66°, ~w89.37°, elev. ~10m (~63ft); issued from a ciber in Mérida, Yucatán, MÉXICO
BLACK-VULTURE CENOTE
A water-filled sinkhole, or cenote, near my casita is a roosting spot for Black Vultures. They overnight there, spend mornings in dead tree snags preening and basking in the sunlight, in the afternoons circle in convection currents above us, then as the sun sets they return to the cenote. The cenote provides a sheltered, humid, lush habitat very different from the surrounding arid, cattle-stomped, hacked-for-firewood scrub, so Tuesday morning I went there looking for special plants and animals. But before entering I had to sit awhile to admire those Black Vultures. One of them is shown below, spreading his wings while basking in the sunlight:
I arrived before convection currents begin forming and soon it was clear that the vultures abhorred the idea of taking to the air so early. Getting airborne seemed to be a dreaded chore for them so, if you approach them halfway non-threateningly, you can get fairly close. I drew near them like a lumbering cow, then sat and waited for them to get used to me. Their sounds fascinated me. Vultures are usually described as mostly silent, limiting their vocalizations to grunts and hisses, but the sound that got my attention was one like the woof! of a small, Schnauzer-type dog who can't make up his mind whether he needs to bark or not, so he barks halfheartedly as he looks away.
Tuesday morning sunlight was intermittent, so for long periods all the twenty or so vultures perched preening or just resting, but the moment sunlight broke through, in unison, they'd all unfurl their wings like the one in the photo, and keep them open until the next cloud covered the sun.
Perches were important to those vultures, and birds at the top of the pecking order got the best perches. If Alpha Vulture wanted a perch occupied by a lower-ranked bird he'd simply fly to the lower-ranked bird's perch. If the lower-ranked bird didn't get out of the way automatically, a few pecks would be exchanged, but then the lower-ranked bird would quickly abandon his perch anyway.
The above photo shows the whiteness typical of a Black Vulture's major wing feathers. Howell in A Guide to The Birds of Mexico and Northern Central America describes the Black Vulture's plumage as "black overall, white shafts above and webs below of outer 6 primaries form contrasting whitish wing panels." You can see yourself whether the white is limited to the outer six primaries. When Black Vultures are soaring overhead, their white wing-spots, or "panels," are easily discerned.
In the photo you can also see the vulture's long, stout legs. When I started birding back in the 60s, field guides always placed vulture illustrations among those of hawks and falcons, because vultures were regarded as most closely related to them. Now our New World Vultures are accepted as most closely related to storks, not raptors or even Old World Vultures. Those long legs make their stork affinities easy to believe.
Later that day as I hiked through the scrub suddenly a loud, wind-ripping, whooshing noise tore through the space above me. At first I thought it was a low-flying jet with his engines off, but then I saw two Black Vultures displaying high in the sky. One vulture would dive at the other from high up, then pull up near the other so sharply that the whooshing sound was tremendous. You can see how this display would serve its purpose during courtship: The stronger the bird, the faster he's able to dive, the sharper he can make his pull-up, and the louder the resulting whoosh. The louder the whoosh, then, the healthier and stronger the prospective mate.
By the way, you can see the difference in silhouettes between an overhead Turkey Vulture and a Black Vulture below:
