Black vulture

Appearance

The black vulture is a fairly large bird of prey, measuring 56–74 cm in length, with a 1.33–1.67 m wingspan.

Weight for black vultures from North America and the Andes ranges from 1.6 to 3 kg but in the smaller vultures of the tropical lowlands it is 1.18–1.94 kg. The extended wing bone measures 38.6–45 cm, the shortish tail measures 16–21 cm and the relatively long tarsus measures 7–8.5 cm.

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.

Distribution

The black vulture has a Nearctic and Neotropic distribution. Its range includes the mid-Atlantic States, the southernmost regions of the Midwestern United States, 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 Peru, central Chile and Uruguay. It also is found as a vagrant on the islands of the Caribbean.

Status

It receives special legal protections under the Migratory Bird Treaty Act of 1918 in the United States, by the Convention for the Protection of Migratory Birds in Canada, and by the Convention for the Protection of Migratory Birds and Game Mammals in Mexico. In the United States it is illegal to take, kill, or possess black vultures without a permit and violation of the law is punishable by a fine of up to US$15,000 and imprisonment of up to six months.

It is listed as a species of Least Concern by the IUCN Red List. Populations appear to remain stable, and it has not reached the threshold of inclusion as a threatened species, which requires a decline of more than 30% in ten years or three generations.

Behavior

The black vulture 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 wing area.

Like all New World vultures, the 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 urohidrosis. 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 black vulture, like other New World vultures, has very few vocalization capabilities. It is generally silent, but can make hisses and grunts when agitated or while feeding.

The black vulture is gregarious, and roosts in large groups. In areas where their ranges overlap, the black vulture will roost on the bare branches of dead trees alongside groups of turkey vultures. The black vulture generally forages in groups; a flock of black vultures can easily drive a rival 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.

Habitat

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.

Reproduction

The timing of black vultures' breeding season varies with the latitude at which they live.

Pairs are formed following a courtship ritual which is performed on the ground: several males circle a female with their wings partially open as they strut and bob their heads. They sometimes perform courtship flights, diving or chasing each other over their chosen nest site.

The black vulture lays its eggs on the ground in a wooded area, a hollow log, or some other cavity, seldom more than 3 m above the ground.

While it generally does not use any nesting materials, it may decorate the area around the nest with bits of brightly colored plastic, shards of glass, or metal items such as bottle caps. Clutch size is generally two eggs, though this can vary from one to three.

The egg is oval and on average measures 7.56 cm × 5.09 cm. The smooth, gray-green, bluish, or white shell is variably blotched or spotted with lavender or pale brown around the larger end.

Both parents incubate the eggs, which hatch after 28 to 41 days. Upon hatching, the young are covered with a buffy down, unlike turkey vulture chicks which are white. Both parents feed the nestlings, regurgitating food at the nest site.

The young remain in the nest for two months, and after 75 to 80 days they are able to fly skillfully. Predation of black vultures is relatively unlikely, though eggs and nestlings are readily eaten if found by mammalian predators such as raccoons, coatis and foxes.

Food

In natural settings, the black vulture eats mainly carrion. In areas populated by humans, it may scavenge at garbage dumps, but also takes eggs and decomposing plant material and can kill or injure newborn or incapacitated mammals.

Like other vultures, it plays an important role in the ecosystem by disposing of carrion which would otherwise be a breeding ground for disease. The black vulture locates food either by sight or by following New World vultures of the genus "Cathartes" to carcasses.

These vultures—the turkey vulture, the lesser yellow-headed vulture, and the greater yellow-headed vulture—forage by detecting the scent of ethyl mercaptan, a gas produced by the beginnings of decay in dead animals. Their heightened ability to detect odors allows them to search for carrion below the forest canopy.

The black vulture is aggressive when feeding, and may chase the slightly larger turkey vulture from carcasses.

The black vulture also occasionally feeds on livestock or deer. It is the only species of New World vulture which preys on cattle. It occasionally harasses cows which are giving birth, but primarily preys on newborn calves. In its first few weeks, a calf will allow vultures to approach it. The vultures swarm the calf in a group, then peck at the calf's eyes, or at the nose or the tongue. The calf then goes into shock and is killed by the vultures.

Black vultures have sometimes been observed removing and eating ticks from resting capybaras and Baird's tapir.

Like other birds with scavenging habits, the black vulture presents resistance to pathogenic microorganisms and their toxins. Many mechanisms may explain this resistance. Anti-microbial agents may be secreted by the liver or gastric epithelium, or produced by microorganisms of the normal microbiota of the species.

Predators

Due to its aggressiveness and size, few predators can threaten the fully-grown vulture. However, various eagles may kill vultures in conflicts and even the ornate hawk-eagle, a slightly smaller bird than the vulture, has preyed on adult black vultures.

Cultural

The 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 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.

Black vultures are an important cultural symbol in Lima, Peru.

This vulture has appeared on two stamps: those of Suriname in 1990 and Nicaragua in 1994.