The American Black Vulture

American Black Vulture

The American Black Vulture, Coragyps atratus, also known as the Black Vulture, is a bird in the New World vulture family whose range extends from the southeastern United States to South America. Although a common and widespread species, it has a somewhat more restricted distribution than its compatriot, the Turkey Vulture, which breeds well into Canada and south to Tierra del Fuego. Despite the similar name and appearance, this species is unrelated to the Eurasian Black Vulture. The latter species is an Old World vulture in the family Accipitridae (which includes eagles, hawks, kites and harriers), whereas the American species is a New World vulture. It is the only extant member of the genus Coragyps, which is in the family Cathartidae. It inhabits relatively open areas which provide scattered forests or shrublands. With a wingspan of 1.5 m (5 ft) the American Black Vulture is a large bird though relatively small for a vulture. It has black plumage, a featherless, grayish-black head and neck, and a short, hooked beak.

The American Black Vulture is a scavenger and feeds on carrion, but will also eat eggs or kill newborn animals. In areas populated by humans, it also feeds at garbage dumps. It finds its meals either by using its keen eyesight or by following other (New World) vultures, which possess a keen sense of smell. Lacking a syrinx - the vocal organ of birds - its only vocalizations are grunts or low hisses. It lays its eggs in caves or hollow trees or on the bare ground, and generally raises two chicks each year, which it feeds by regurgitation. In the United States, the vulture receives legal protection under the Migratory Bird Treaty Act of 1918.

Taxonomy

The common name "vulture" is derived from the Latin word vulturus, which means "tearer" and is a reference to its feeding habits. The species name, atratus, means "clothed in black", from the Latin ater 'black'. The genus name, Coragyps means "raven-vulture". The family name, Cathartidae, means "purifier".

The exact taxonomic placement of the American Black Vulture and the remaining six species of New World vultures remains unclear. Though both are similar in appearance and have similar ecological roles, the New World and Old World vultures evolved from different ancestors in different parts of the world. Just how different the two are is currently under debate, with some earlier authorities suggesting that the New World vultures are more closely related to storks. More recent authorities maintain their overall position in the order Falconiformes along with the Old World vultures, or place them in their own order, Cathartiformes. The South American Classification Committee has removed the New World vultures from Ciconiiformes and instead placed them in Incertae sedis, but notes that a move to Falconiformes or Cathartiformes is possible.

There are three subspecies of American Black Vulture:

• C. a. atratus, named by the German ornithologist Johann Matthäus Bechstein in 1793, is known as the North American Black Vulture. It is the nominate subspecies. It is approximately the same size as C. a. foetens, but its plumage is not as dark. Its range stretches from northern Mexico through Texas and the southern United States north to the Carolinas.
• C. a. brasiliensis, named by Charles Lucien Jules Laurent Bonaparte in 1850, is known as the Southern American Black Vulture. It is smaller than C. a. atratus and C. a. foetens. The light markings on the undersides of the primaries are whiter and broader than those of the other subspecies, and the underwing coverts are lighter than those of C. a. foetens. It is found in Central America and northern South America. To the south, the range extends to the coastal regions of Peru on the west and the lowlands of Bolivia on the east. To the north, it stretches to Sonora in western Mexico and San Luis Potosí in eastern Mexico. It is not found in high-altitude regions.
• C. a. foetens, named by Martin Lichtenstein in 1817, is known as the Andean Black Vulture. It is approximately the same size as C. a. atratus. The markings on the undersides of the primaries are smaller than those of the other subspecies, and the underwing coverts are darker. It is found in the Andes range, from northern Ecuador through Peru, northern Bolivia, Paraguay, Uruguay, and the lowlands of Chile.

Evolutionary history of Coragyps

From the Early to the Late Pleistocene, a prehistoric species of Black Vulture, Coragyps occidentalis, known as the Pleistocene Black Vulture or - somewhat in error - the "Western Black Vulture", occurred across the present species' range. This bird did not differ much from the American Black Vulture of today except in size; it was some 10-15% larger, and had a relatively flatter and wider bill. It filled the same ecological niche as the living form, and indeed seems to have evolved into it by decreasing in size during the last ice age. Well documented from fossil bones, the genus Coragyps gives a rare glimpse in the evolutionary dynamics of two chronospecies. The final stages of this evolutionary transformation must have been witnessed by humans: a subfossil bone of the extinct species was found in an Paleo Indian to Early Archaic (9000-8000 years BCE) midden at Five Mile Rapids near The Dalles, Oregon.

Fossil (or subfossil) Black Vultures cannot necessarily be attributed to the Pleistocene or the recent species without further information: the same size variation found in the living bird was also present in its larger prehistoric relative. Thus, in 1968, Hildegarde Howard separated the Mexican birds as Coragyps occidentalis mexicanus as opposed to the birds from locations farther north (such as Rancho La Brea) which constituted the nominate subspecies C. o. occidentalis. The southern birds were of the same size as present-day North American Black Vultures and can only be distinguished by their somewhat stouter tarsometatarsus and the flatter and wider bills, and even then only with any certainty if the location where the fossils were found is known. As the Pleistocene and current American Black Vultures form an evolutionary continuum rather than splitting into two or more lineages, some include the Pleistocene taxa in C. atratus.

Description

The American Black Vulture is a very large bird of prey, measuring 65 centimeters (25.5 in) in length, with a 1.5 meter (5 ft) wingspan and a weight of 2-2.75 kilograms (4.5-6 lb). Its plumage is mainly glossy black. The head and neck are featherless and the skin is dark gray and wrinkled. The iris of the eye is brown and has a single incomplete row of eyelashes on the upper lid and two rows on the lower lid. The legs are grayish white, while the two front toes of the foot are long and have small webs at their bases. The feet are flat, relatively weak, and are poorly adapted to grasping; the talons are also not designed for grasping, as they are relatively blunt.

The nostrils are not divided by a septum, but rather are perforate; from the side one can see through the beak. The wings are broad but relatively short. The bases of the primary feathers are white, producing a white patch on the underside of the wing's edge, which is visible in flight. The tail is short and square, barely reaching past the edge of the folded wings. The subspecies differ in size according to Bergmann's Rule, and the amount of white underwing coloration also varies. As it probably forms a cline over its entire range, the species is often considered monotypic.

A leucistic Coragyps atratus brasiliensis was observed in Piñas, Ecuador in 2005. It had white plumage overall, with only the tarsus and tail as well as some undertail feathers being black. It was not an albino as its skin seemed to have had the normal, dark color and it was part of a flock of some twenty normally-plumaged individuals.

Distribution and habitat

The American Black Vulture has a Nearctic and Neotropic distribution. Its range includes the southern United States, Mexico, Central America and most of South America. It is usually a permanent resident throughout its range, although birds at the extreme north of its range may migrate short distances, and others across their range may undergo local movements in unfavourable conditions. In South America, its range stretches to central Chile and Argentina. It also is found on the islands of the Caribbean. It prefers open land interspersed with areas of woods or brush. It is also found in moist lowland forests, shrublands and grasslands, wetlands and swamps, pastures, and heavily degraded former forests. Preferring lowlands, it is rarely seen in mountainous areas. It is usually seen soaring or perched on fence posts or dead trees.

Ecology and behavior

It soars high while searching for food, holding its wings horizontally when gliding. It flaps in short bursts which are followed by short periods of gliding. Its flight is less efficient than that of other vultures, as the wings are not as long, forming a smaller sail surface. In comparison with the Turkey Vulture, the American Black Vulture flaps its wings more frequently during flight. It is known to regurgitate when approached or disturbed, which assists in predator deterrence and taking flight by decreasing its takeoff weight. Like all New World Vultures, the American Black Vulture often defecates on its own legs, using the evaporation of the water in the feces and/or urine to cool itself, a process known as urohydrosis. It cools the blood vessels in the unfeathered tarsi and feet, and causes white uric acid to streak the legs. Because it lacks a syrinx, the American Black Vulture, like other New World Vultures, has very few vocalization capabilities. It is generally silent, but can make soft hisses and grunts. The American Black Vulture is gregarious, and roosts in large groups. In areas where their ranges overlap, the American Black Vulture will roost on the bare branches of dead trees with groups of Turkey Vultures. The American Black Vulture generally forages in groups; a flock of Black Vultures can easily drive a Turkey Vulture, which is generally solitary while foraging, from a carcass.

Like the Turkey Vulture, this vulture is often seen standing in a spread-winged stance. The stance is believed to serve multiple functions: drying the wings, warming the body, and baking off bacteria. This same behavior is displayed by other New World vultures, Old World vultures, and storks.

Relationship with humans

The American Black Vulture appears in a variety of Maya hieroglyphics in Mayan codices. It is normally connected with either death or as a bird of prey. The vulture's glyph is often shown attacking humans. This species lacks the religious connections that the King Vulture has. While some of the glyphs clearly show the American Black Vulture's open nostril and hooked beak, some are assumed to be this species because they are vulture-like but lack the King Vulture's knob and are painted black.

Copyright: This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on American Black Vulture.