There are three vultures in the United States, the California Condor, the Turkey Vulture, which has the widest range, extending from Canada down into South America, and the Black Vulture, the smallest of the three. If I wanted to see a black vulture twenty five years ago, I went to the Everglades or the Texas Gulf Coast. About fifteen years ago, I saw some in New Jersey in a large swampy area behind Raptor Trust, and, with warming climate, they’re now showing up in the southern Adirondacks.
The black vulture probably evolved out of a relative from the Pleistocene, which was about 15% larger, while in their current form, black vultures are no different from the fossilized remains of those from at least ten thousand years ago. Black vultures are stubbier than turkey vultures, two to two and a half feet in length, have a wing span of up to five and a half feet, and weigh in between four and a half to six and a half pounds. Perhaps following Bergman’s rule, northerly vultures are larger than their tropical counterparts. Black vultures have grayish heads and black feathers, long weak feet with blunt talons, and somewhat flattened bills for tearing at decaying flesh.
Black vultures are basically carrion eaters, but they will grab new born animals and eggs as opportunity presents itself. Black vultures often hunt together, and may mob victims, even going after new born calves and other relatively defenseless animals, pecking at the eyes. Black vultures seem to be less discriminating in their ingestion of decaying flesh, with turkey vultures preferring carrion not more than four days dead. The featherless heads appear to be an adaptation to prevent the buildup of bacteria on vulture heads, which are frequently inside the body of a decaying animal. The liquid and solid wates of birds form uric acid, and both turkey and black vultures defecate on their legs, as a way of cooling off the blood vessels in the unfeathered tarsi and feet, through the evaporation of the liquid portion of the uric acid, a process called urohidrosis. Neither vulture has a syrinx, so the only vocalizations are grunts and hisses.
While the turkey vulture roosts in groups, they tend to be individually solitary hunters, though other turkey vultures mayh be drawn to a carcass where an individual turkey vulture is already feeding. There is a dead tree on the western bank of the West Branch of the Ausable, maybe 100 yards north of the Adirondack Wildlife Refuge, which flanks the east side of the river, where turkey vultures frequently roost in groups.
Both vultures are frequently seen roosting in sunny weather with wings spread, probably absorbing warmth, drying their wings or baking off bacteria accumulated while feeding. Both vultures ride rising thermals to get to heights where they can glide to other thermals, the lazy birds way of getting from one area to another with minimal wing flaps. Circling vultures are called a kettle, and may be riding a rising thermal, or in the case of turkey vultures, dropping to locate the odor of ethyl mercaptan. Turkey vultures have longer wings, and are more efficient gliders than the stubbier-winged black vulture.
Black vulture mating depends on climate and latititude, so black vultures in the northern range mate around March, while those in southern ranges many months earlier. There is a courtship ritual involving strutting, bobbing, and sometimes flights over nesting sites, which may be on the ground, in a log or a cavity no more than ten feet up above the ground. The vultures may decorate a nesting site with a ring of colorful manmade products, bottle caps, as well as shards of plastic and glass, but no special gathering of nesting materials. What did they do before homo sapiens showed up, and is this sort of decoration not a sign of intelligence? Both parents sit on one to three eggs, and the hatching period is between 28 and 40 days. The chicks leave the nest and can fly after about two and a half months. Eggs and young may be scavenged by racoons and other small mammals. Like turkey vultures, black vulture migration only occurs in colder northern climates.
The turkey vulture and the smaller lesser and greater yellow headed vultures of South America, are the only vultures with a sense of smell, with relatively big nostrils, as well as an enlarged olfactory lobe in the brain, dedicated to detecting ethyl mercapatan, the strong oder arising from the body of a dead animal. Turkey vultures can be fooled by leaking propane tanks, as ethyl mercaptan is that offensive odor mixed in with propane, which has no odor, as a warning signal to home owners of a leaky tank or propane line.
One advantage of roosting with turkey vultures, or following their flight, is that black vultures may be able to steal carcasses by mobbing or bullying outnumbered turkey vultures. Alex and I have observed turkey vultures and black vultures roosting in the same tree in the Santee Wildlife Refuge in South Carolina.
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Adirondack Wildlife Refuge & Rehabilitation Center
Steve & Wendy Hall
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