Common Name: Black Vulture, American black vulture, Carrion crow, Black buzzard, Jim crow, Charleston eagle – Vellere meaning “tear” in Latin is the etymological root for the word vulturius, the Latin name of the vulture; the metaphor applies to the manner in which the vultures tear at their carrion quarry during feeding. The glossy black plumage is the most obvious characteristic of the species.
Scientific Name: Coragyps atratus – The generic name means “raven vulture” to distinguish the species according to its black, raven-like coloring. In Greek, the word for raven is korax and the word for vulture is gyps – which combine as Coragyps. The species name atratus means clothed in black, particularly when in mourning.
Potpourri: The black vulture, like the turkey vulture, is a member of the family Cathartidae of New World vultures. It is very similar in appearance to the Eurasian black vulture, a member of the family Accipitridae which includes not only the Old World vultures but also hawks, eagles and kites. The family names accentuate their differences: Cathartidae is from the Greek word kathairein meaning “to clean,” indicative of the scavenging removal of dead animal carcasses, and Accipitridae from the Greek acu meaning “fast” and pteron meaning “wing,” flying speed being a notable characteristic of the raptors that dominate the group.
The New World and Old World vultures have essentially separate evolutionary histories that is reflected in several of their key physical characteristics. The Old World accipitrids have strongly hooked feet that are used for grasping their prey, rounded nasal openings and a syrinx, or voice organ that is capable of producing loud screeches. The New World cathartids have weak feet without talons that are not adapted for grasping, a longitudinal nasal passage without a septum and no syrinx so that they are only to make aeration noises likes grunts and hisses. The physical differences and the extant geographic separation of the two vulture groups support the theory of convergent evolution. Convergent evolution is a corollary of the classic Darwinian theory that is based on the observation that animals and plants will gradually evolve the same characteristics in response to similar environments even when geographically separated without intermingling. They converge on the same solution to survival in their given environment. The two groups of vultures both adapted to the eating of dead, decaying flesh as a niche means of survival.
The geologic fossil record does not support separate, convergent evolution; Old World vulture fossils have been found in the New World and vice versa. An avian fossil named Eocathartes (the prefix eo means “dawn” and is used in the sense of very early in time as in the “dawn” of man) found in Germany and dated to the Paleocene Epoch about 65 million years ago (mya) was determined to be a progenitor of New World vultures. Conversely, the Rancho La Brea Tar Pits in California is replete with many avian fossils that consist of ancestors of both the accipitrids and the cathartids. Of the 400,000 avian fossils that have been recovered there, more than fifty percent are vultures. It is hypothesized that there was a large vulture population that evolved and thrived from the Pleistocene Epoch 1.8 mya up to the current Holocene Epoch 10,000 years ago. In North America, this period of geologic history was marked by the emergence of a teeming animal population dominated by large mammals such as the mastodon. The large animal population created a large carcass population; the vultures spread rapidly as the cleansers of the Pleistocene.
The decline of the vultures as one of the predominant avian species to their current limited though resurgent population paralleled the precipitous decline of the large mammal population that occurred at the end of the last Ice Age about 12,000 years ago. There are a number of theories as to why 67 genera of large mammals (more than 50 percent of the total) and many of the vulture species disappeared. The “overkill hypothesis” attributes the decline to the arrival of humans over the Beringian land bridge that connected Eurasia to North America during the period of low ocean level that accompanied the last glaciation. According to the theory, the expanding human population decimated the native mammal populations as part of a nomadic hunting culture. Questions as to the veracity of the overkill theory result from several inconsistencies, such as how the bison and moose survived when many other large mammals were extirpated and why ten avian genera also become extinct. An alternative approach is the “keystone herbivore hypothesis,” which holds that a decline in only a few of the larger mammals due the a natural, but not cataclysmic geologic event could have had a cascade effect; their removal triggering a resurgence of forests that destroyed the habitats of other mammals. However, the most compelling theory of the “late Pleistocene die-off” is climate change that accompanied the retreat of the Wisconsin glaciation, the last and most severe of the glacial periods, about 8,000 years ago. This marked the beginning of a warming trend that must surely have had a major effect on almost all biological communities. The vultures declined in parallel with the carcass population on which they subsisted. There are now just 6 species of New World vulture.
The black vulture and the turkey vulture are the two cathartids that are found in the mid Atlantic region. The major physiological difference is that turkey vultures have the olfactory capacity to detect the presence of an available carrion food source due to the smell of mercaptan, a chemical gas produced by the bacterial decay process and black vultures do not. Therefore, black vultures can locate food only by sight, or by following a turkey vulture to a carcass. This would put them at the same food source for inevitable confrontation where another key difference becomes manifest. Although the turkey vulture is somewhat larger than the black vulture, the latter is more gregarious and more aggressive; groups of black vultures descend on a carrion meal and chase away the frequently singular turkey vulture that likely discovered it. The last key difference affords the observer a means of distinguishing the two species in flight. Turkey vultures hold their longer wings at a dihedral angle and glide in wide circles on the air currents whereas black vultures, with their shorter wings, must frequently flap them 3 to 5 times to maintain altitude with a subsequent glide. Both species use urohydrosis, the expulsion of urine and excrement on the legs, to take advantage of the latent heat of evaporation to lower their body temperature.
The expansion of human activities has contributed to significant increases in the population of black vultures, who thrive on the resultant disturbed ecosystem. They likely constitute the largest bird of prey species in the Americas. It is not uncommon to see hundreds roosting together in trees (though pairs match up and seek more private accommodations for mating and nesting) and as many as 30 or 40, a venue of vultures, at the carcass of a large animal. While they normally feed on carrion, they are opportunistic feeders and will eat eggs and, if stressed, rotten food. It is widely reported that black vultures will also attack and kill livestock, notably defenseless new-born calves. In 1909, it was reported by Baynard that “hundreds of young pigs, lambs, etc., are annually devoured by them… I have had them come into my yard and catch young chickens.” However, actual observations of vultures attacking and killing domestic animals are rare; reports of predation are often submitted based on the discovery of an animal being eaten by vultures, its demise attributed to attack absent an eye-witness validation. Based on reports submitted to the USDA Wildlife Services Division, it was noted that vulture predation was increasing 18 percent annually in the 1990’s. This resulted in the initiation of a study at the Macarthur Agro-Ecology Research Center in Central Florida to examine the interaction between vultures and cattle. It was observed that vultures congregated around pastures where calving was occurring. However, they did not disturb the heifers or their calves, apparently waiting to eat the discarded afterbirth. An actual attempt by the vultures to attach a heifer during birth was observed, but the attacking birds were successfully driven off by the cow. The USDA’s conclusion at this point is that more research is necessary to evaluate the frequency of black vulture attacks on livestock.