Turkey vulture

Name and taxonomy

Carl Linnaeus described the bird in 1758, in the tenth edition of Systema Naturae. He gave it the name Vultur aura. The word vulture comes from a Latin word meaning tearer, which points at how the bird feeds. North Americans often call it a buzzard, though in the Old World that word means a hawk of the genus Buteo.

In parts of the Caribbean the bird is a John crow or a carrion crow. The Jamaican name is old enough to have been given to a mountain range. The genus Cathartes holds three species, and the other two are the yellow-headed vultures. Authorities count five or six subspecies, which differ mainly in where they live. The family Cathartidae holds seven species in all.

Evolution and relatives

New World vultures are not close relatives of the vultures of Europe, Africa and Asia. The two groups look alike because they took up the same trade, an example of convergent evolution. Where the family belongs has moved about for more than a century. Some earlier authors placed the New World birds close to the storks.

Genetic work rejects that idea, and it also rejects any close tie to the falcons. Cathartiformes now sits as the sister group to the Accipitriformes. That second group holds the eagles, kites, hawks, the osprey and the secretarybird. The Old World vultures sit inside it, in the family Accipitridae. Like other birds in this family, the turkey vulture carries 80 chromosomes.

Appearance

The body feathers are brownish-black. Seen from below, the flight feathers look silver-grey against dark wing linings. The head is small, bare and red, and the bill is a short ivory hook. A young bird has a grey head and a black bill tip, and the colours change as it matures. The legs and feet are pink, but they are usually stained white. The upper eyelid carries a single broken row of lashes, and the lower lid carries two.

The feet are flat and weak, and the talons are blunt. This bird cannot grip or carry prey the way a hawk does. Males and females match in colour, pattern and size. Northern birds average larger than tropical ones. A sample of 124 birds in Florida averaged 2 kilograms, while two samples from Venezuela averaged 1.22 and 1.45 kg. Pale leucistic birds turn up now and then.

Habitat and range

The turkey vulture uses open and half-open country across the Americas. The estimated range covers about 28 million square kilometres. The bird is resident in the southern United States, and northern birds may travel as far as South America. It favours open ground beside woodland, because it needs trees for roosting and nesting. Closed forest is a problem, because a heavy bird cannot get airborne inside it.

Ground with no trees at all is little better, so parts of the Great Plains hold few vultures. Hills and low mountains suit the species, because the air there lifts a heavy bird cheaply. Pasture and other low-input farmland are key feeding and roosting habitat. Row-crop fields draw only passing flyovers. Vultures cross towns and cities regularly, mostly outside the breeding season.

The northern edge of the range has moved north over recent decades. Limits on hunting may explain part of that spread. The species also uses deserts, wetlands, shrubland and tropical forest. It is recorded in 52 countries on GBIF.

Diet and feeding

Carrion makes up almost the whole diet. The bird takes everything from mice and shrews to dead cattle and deer. It prefers a fresh body and turns away from one that has gone rotten. Small carcasses are the usual meal, and roadkill is a large part of the supply. Fish stranded in a drying pool or washed up on a shore are taken as well. The bird kills very rarely, and then only eggs, nestlings or a sick animal.

Smell leads the search, which sets this bird apart from most others. It flies low and picks up ethyl mercaptan, a gas released as a body begins to break down. The part of the brain that handles scent is unusually large. That lets the vulture find a carcass hidden below a forest canopy. Black vultures, king vultures and condors watch turkey vultures and follow them down.

The bill cannot cut the hide of a large animal. So the vulture waits for a condor or a king vulture to open the body first. The two kinds of bird therefore depend on each other at a big carcass. Black vultures arrive in numbers and push the turkey vulture off the food. In Peru, though, turkey vultures won such contests in 56 percent of cases. Hawks, falcons, caracaras and eagles all outrank the vulture at a carcass.

Behaviour and social life

Turkey vultures roost together and forage alone. Several hundred may share one roost, and black vultures often join them. Favourite roosts are dead trees, thin stands of conifer, water towers and masts. The bird lets its body temperature drop by about 6 degrees Celsius overnight. It becomes slightly hypothermic as a result.

In the morning it stands with the wings spread wide, a posture called the horaltic pose. The pose probably dries the feathers, warms the body and bakes bacteria off the wings. Birds use it most after a damp or rainy night. The vulture also empties its bowels onto its own legs, and the liquid cools them as it evaporates. Uric acid streaks the legs white as a result.

On the ground the turkey vulture is clumsy and hops rather than walks. Taking off costs it real effort, and it flaps hard while pushing away with its feet. Once up, it holds the wings in a shallow V and rocks from side to side. Light wing loading keeps the bird up on weak thermals. Vultures defend no territory, and a home range grows or shrinks with the food supply.

Communication and senses

The turkey vulture has no syrinx, the organ that other birds sing with. It can only hiss, grunt and bark. Most of those sounds warn a rival or a predator away. Displays carry the rest of the message.

In courtship, several birds gather on the ground and hop in a ring with half-open wings. In the air one bird follows another closely, flapping and diving as it goes. Scent leads the search for food, and sight backs it up. Few birds anywhere lean on smell as heavily. Chicks hiss at anything that reaches the nest site.

Reproduction and life cycle

The breeding season shifts with latitude. In the southern United States it opens in March, peaks between April and May, and runs into June. Further north it starts later and can last into August. A pair stays together through the season, and often through the whole year.

The birds build no nest at all. Eggs go straight onto the floor of a cave, a rock crevice, a burrow, a hollow tree or a thicket. An old building will serve just as well. A female usually lays two eggs, sometimes one and rarely three. The eggs are cream, with brown or lavender spots at the broad end. Each one measures 6.5 to 7.5 centimetres long.

Both parents sit on the clutch, and the chicks hatch after 30 to 40 days. A chick hatches helpless. Both adults feed it several times a day by bringing food back up. The young fly at about nine to ten weeks and stay dependent for a week or so more. Families hold together until the autumn. One study found that about a fifth of adults die each year.

Predators and threats

Adults have few natural enemies, and attacks are rare. Great horned owls take the most, followed by golden eagles and bald eagles. Red-tailed hawks may take one now and then. Raccoons and opossums raid eggs and chicks, and a fox can ambush an adult. Dogs sometimes kill a vulture on the ground.

A cornered vulture vomits half-digested meat at the attacker. The smell drives most raiders off, and the spray stings the eyes. A bird with a full crop may need to empty it before it can take off. Adults may also flee the nest or feign death.

Most recorded deaths come from people. Vultures collide with vehicles and buildings, and they get caught in fences and traps. Lead is the other danger. A vulture that feeds on an animal shot with lead pellets swallows the metal. Even small doses bring disease, nerve damage and breeding failure.

Population and conservation

The IUCN lists the turkey vulture as Least Concern. The world population is put near 18 million birds. The trend looks steady, and the species is far from the threshold for a threatened listing. That threshold needs a fall of more than 30 percent over ten years or three generations. The bird rivals the black vulture as the most numerous raptor on earth. Naturalists have logged 268,834 records on iNaturalist.

Three national laws protect the species. The Migratory Bird Treaty Act of 1918 covers it in the United States. Canada and Mexico protect it under their own migratory bird conventions. Taking a vulture, an egg or even a feather without a permit is illegal. A person can be fined up to $100,000 and jailed for a year. Lead ammunition in carcasses remains the main pollution risk.

Relationship with humans

The turkey vulture removes dead animals that would otherwise breed disease. That service matters most beside farms and roads. The bird settles near people easily and takes little notice of them. Ranchers still suspect it of carrying anthrax or hog cholera on its feet or bill. The virus behind hog cholera does not survive a trip through the vulture's gut.

Black vultures do kill newborn calves, and the turkey vulture gets the blame by association. A turkey vulture at a dead calf has almost always arrived after the fact. Droppings under a large roost can damage or kill trees. Farmers try noise, carcass removal and moving stock, with little success. Like other wild scavengers, it needs carrion and open space, so it makes a poor pet. Keeping one in the United States is illegal in any case.

In culture and myth

In Cherokee tradition, the Great Buzzard shaped the land itself. The story says the earth was still soft mud when the bird flew low over it. Its wingbeats cut the valleys and threw up the mountains of Cherokee country. In Jamaica the bird is the John crow. That name was written down in the 1820s and passed to the John Crow Mountains. Before that, people called the range Carrion Crow Ridge, using a still earlier name for the vulture.

In Uruguay, a gorge called the Quebrada de los Cuervos takes its name from these dark birds. Across much of the United States the bird is simply the buzzard. Two captive turkey vultures became well known teaching birds in that country. One of them, Nero, hatched in 1974 and lived to 47. Another, Lord Richard, hatched in the same year and reached 51.