| Turkey Vulture | |
|---|---|
| At Santa Teresa County Park, San Jose, California, USA | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Incertae sedis (disputed) |
| Family: | Cathartidae |
| Genus: | Cathartes |
| Species: | C. aura |
| Binomial name | |
| Cathartes aura (Linnaeus, 1758) |
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Approximate range map:
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The Turkey Vulture (Cathartes aura) is a bird found throughout most of the Americas. It is also known in some North American regions as the Turkey Buzzard (or just Buzzard), and in some areas of the Caribbean as the John Crow or Carrion Crow.[2] One of three species in the genus Cathartes, in the family Cathartidae, the Turkey Vulture is the most widespread of the New World vultures,[3] ranging from southern Canada to the southernmost tip of South America. It inhabits a variety of open and semi-open areas, including subtropical forests, shrublands, pastures, and deserts.[1]
The Turkey Vulture is a scavenger and feeds almost exclusively on carrion.[4] It finds its meals using its keen vision and sense of smell, flying low enough to detect the gasses produced by the beginnings of the process of decay in dead animals.[4] In flight, it uses thermals to move through the air, flapping its wings infrequently. It roosts in large community groups. Lacking a syrinx—the vocal organ of birds—its only vocalizations are grunts or low hisses.[5] It nests in caves, hollow trees, or thickets. Each year it generally raises two chicks, which it feeds by regurgitation.[6] It has very few natural predators.[7] In the United States of America, the vulture receives legal protection under the Migratory Bird Treaty Act of 1918.[8]
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The Turkey Vulture received its common name from the resemblance of the adult's bald red head and its dark plumage to that of the male Wild Turkey, while the name "vulture" is derived from the Latin word vulturus, meaning "tearer," and is a reference to its feeding habits.[9] The word buzzard is used by North Americans to refer to this bird, yet in the Old World this word refers to members of the genus Buteo.[10] The generic term Cathartes means "purifier" and is the Latinized form from the Greek kathartēs/καθαρτης.[11] The species name, aura, is Latinized from the Native Mexican word for the bird, auroura.[9] The Turkey Vulture was first formally described by Linnaeus as Vultur aura in his Systema Naturae in 1758, and characterised as V. fuscogriseus, remigibus nigris, rostro albo ("brown-gray vulture, with black wings and a white beak").[12] It is a member of the family Cathartidae, along with the other six species of New World vultures, and included in the genus Cathartes, along with the Greater Yellow-headed Vulture and the Lesser Yellow-headed Vulture. Like other New World vultures, the Turkey Vulture has a diploid chromosome number of 80.[13]
The exact taxonomic placement of the Turkey Vulture and the remaining six species of New World Vultures remains unclear.[14] 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.[15] More recent authorities maintain their overall position in the order Falconiformes along with the Old World Vultures[16] or place them in their own order, Cathartiformes.[17] 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.[14]
There are five subspecies of Turkey Vulture:
A large bird, it has a wingspan of 160–183 cm (63–72 in), a length of 62–81 cm (24–32 in), and weight of 0.8 to 2.3 kg (1.8 to 5.1 lb).[22][23][24] While birds in the Northern limit of the species' range average around 2 kg (4.4 lb), vulture from the neotropics are generally smaller, averaging around 1.45 kg (3.2 lb).[25][26] It displays minimal sexual dimorphism; sexes are identical in plumage and in coloration, although the female is slightly larger.[27] The body feathers are mostly brownish-black, but the flight feathers on the wings appear to be silvery-gray beneath, contrasting with the darker wing linings.[22] The adult's head is small in proportion to its body and is red in color with few to no feathers. It also has a relatively short, hooked, ivory-colored beak.[28] The irises of the eyes are gray-brown; legs and feet are pink-skinned, although typically stained white. The eye has a single incomplete row of eyelashes on the upper lid and two rows on the lower lid.[29]
The two front toes of the foot are long and have small webs at their bases.[30] Tracks are large, between 3.75 and 5.5 inches in length (9.5–14 cm) and 3.25 and 4 inches in width (8.2–10.2 cm), both measurements including claw marks. Toes are arranged in the classic, anisodactyl pattern.[31] The feet are flat, relatively weak, and poorly adapted to grasping; the talons are also not designed for grasping, as they are relatively blunt.[3] In flight, the tail is long and slim, in contrast to that of the Black Vulture. The nostrils are not divided by a septum, but rather are perforate; from the side one can see through the beak.[32] It undergoes a molt in late winter to early spring. It is a gradual molt, which lasts until early autumn.[6] The immature bird has a gray head with a black beak tip; the colors change to those of the adult as the bird matures.[33] How long turkey vultures can live in captivity is not well known. While 21 years is generally given as a maximum age, the Gabbert Raptor Center on the University of Minnesota campus is home to a turkey vulture named Nero with a confirmed age of 37. The oldest wild captured banded bird was 16 years old.[4]
Leucistic (sometimes mistakenly called "albino") Turkey Vultures are sometimes seen.[34] The well-documented records come from the United States of America, but this probably reflects the fact that such birds are more commonly reported by birders there, rather than a geographical variation. Even in the United States, white Turkey Vultures (although they presumably always turned up every now and then) were only discussed in birder and raptor conservation circles and are not scientifically studied.[35]
The Turkey Vulture, like most other vultures, has very few vocalization capabilities. Because it lacks a syrinx, it can only utter hisses and grunts.[5] It usually hisses when it feels threatened. Grunts are commonly heard from hungry young and from adults in their courtship display.
The Turkey Vulture has a large range, with an estimated global occurrence of 28,000,000 km². It is the most abundant vulture in the Americas.[3] Its global population is estimated to be 4,500,000 individuals.[1] It is found in open and semi-open areas throughout the Americas from southern Canada to Cape Horn. It is a permanent resident in the southern United States, though northern birds may migrate as far south as South America.[4] The Turkey Vulture is widespread over open country, subtropical forests, shrublands, deserts, and foothills.[36] It is also found in pastures, grasslands, and wetlands.[1] It is most commonly found in relatively open areas which provide nearby woods for nesting and it generally avoids heavily forested areas.[22]
The Turkey Vulture is gregarious and roosts in large community groups, breaking away to forage independently during the day. Several hundred vultures may roost communally in groups which sometimes even include Black Vultures. It roosts on dead, leafless trees, and will also roost on man-made structures such as water or microwave towers. Though it nests in caves, it does not enter them except during the breeding season.[6] The Turkey Vulture lowers its night-time body temperature by about 6 degrees Celsius to 34 °C (93 °F), becoming slightly hypothermic.[30]
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. It is practiced more often following damp or rainy nights. This same behavior is displayed by other New World vultures, by Old World vultures, and by storks.[7] Like storks, the Turkey 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.[37] It cools the blood vessels in the unfeathered tarsi and feet, and causes white uric acid to streak the legs.[38]
The Turkey Vulture has few natural predators. Adult, immature and fledging vultures may fall prey to golden eagles, bald eagles and great horned owls, while eggs and nestlings may be preyed on by mammals such as raccoons, virginia opossum and foxes.[23][7] Its primary form of defense is regurgitating semi-digested meat, a foul-smelling substance which deters most creatures intent on raiding a vulture nest.[6] It will also sting if the predator is close enough to get the vomit in its face or eyes. In some cases, the vulture must rid its crop of a heavy, undigested meal in order to take flight to flee from a potential predator.[28] Its life expectancy in the wild ranges upward of 16 years, with a captive life span of over 30 years being possible.[39][40]
The Turkey Vulture is awkward on the ground with an ungainly, hopping walk. It requires a great deal of effort to take flight, flapping its wings while pushing off the ground and hopping with its feet.[28] While soaring, the Turkey Vulture holds its wings in a shallow V-shape and often tips from side to side, frequently causing the gray flight feathers to appear silvery as they catch the light. The flight of the Turkey Vulture is an example of static soaring flight, in which it flaps its wings very infrequently, and takes advantage of rising thermals to stay soaring.[41]
The Turkey Vulture feeds primarily on a wide variety of carrion, from small mammals to large grazers, preferring those recently dead, and avoiding carcasses that have reached the point of putrefaction. It may rarely feed on plant matter, shoreline vegetation, pumpkin and other crops, live insects and other invertebrates.[36] In South America, it has been seen (and photographed) feeding on the fruits of the introduced Oil Palm.[42][43] It rarely, if ever, kills prey itself.[44] The Turkey Vulture can often be seen along roadsides feeding on roadkill, or near bodies of water, feeding on washed-up fish.[4] It also will feed on fish or insects which have become stranded in shallow water.[6] Like other vultures, it plays an important role in the ecosystem by disposing of carrion which would otherwise be a breeding ground for disease.[45]
The Turkey Vulture forages by smell, an ability that is uncommon in the avian world. It often will fly low to the ground to pick up the scent of ethyl mercaptan, a gas produced by the beginnings of decay in dead animals.[7] The olfactory lobe of its brain, responsible for processing smells, is particularly large compared to that of other animals.[7] This heightened ability to detect odors allows it to search for carrion below the forest canopy. King Vultures and Black Vultures, which lack the ability to smell carrion, follow the Turkey Vulture to carcasses. The Turkey Vulture arrives first at the carcass, or with Greater Yellow-headed Vultures or Lesser Yellow-headed Vultures, which also share the ability to smell carrion.[7] It displaces the Yellow-headed Vultures from carcasses due to its larger size,[45] but is displaced in turn by the King Vulture, which makes the first cut into the skin of the dead animal. This allows the smaller, weaker-billed, Turkey Vulture access to food, because it cannot tear the tough hides of larger animals on its own. This is an example of mutual dependence between species.[46]
The breeding season of the Turkey Vulture varies according to latitude.[47] In the southern United States, it commences in March, peaks in April to May, and continues into June.[48] In more northerly latitudes, the season starts later and extends into August.[49] Courtship rituals of the Turkey Vulture involve several individuals gathering in a circle, where they perform hopping movements around the perimeter of the circle with wings partially spread. In the air, one bird closely follows another while flapping and diving.[36]
Eggs are generally laid in the nesting site in a protected location such as a cliff, a cave, a rock crevice, a burrow, inside a hollow tree, or in a thicket. There is little or no construction of a nest; eggs are laid on a bare surface. Females generally lay two eggs, but sometimes one and rarely three. The eggs are cream-colored, with brown or lavender spots around their larger end.[36] Both parents incubate, and the young hatch after 30 to 40 days. Chicks are altricial, or helpless at birth. Both adults feed the chicks by regurgitating food for them, and care for them for 10 to 11 weeks. When adults are threatened while nesting, they may flee, or they may regurgitate on the intruder or feign death.[6] If the chicks are threatened in the nest, they defend themselves by hissing and regurgitating.[36] The young fledge at about nine to ten weeks. Family groups remain together until fall.[36]
The Turkey Vulture is sometimes accused of carrying anthrax or hog cholera, both livestock diseases, on its feet or bill by cattle ranchers and is therefore occasionally perceived as a threat.[50] However, the virus that causes hog cholera is destroyed when it passes through the Turkey Vulture's digestive tract.[28] This species also may be perceived as a threat by farmers due to the similar Black Vulture's tendency to attack and kill newborn cattle. The Turkey Vulture does not kill live animals but will mix with flocks of Black Vultures and will scavenge what they leave behind. Nonetheless, its appearance at a location where a calf has been killed gives the incorrect impression that the Turkey Vulture represents a danger to calves.[51] The droppings produced by Turkey Vultures and other vultures can harm or kill trees and other vegetation.[52] The Turkey Vulture can be held in captivity, though the Migratory Bird Treaty Act prevents this in the case of uninjured animals or animals capable of returning to the wild.[53] In captivity, it can be fed fresh meat, and younger birds will gorge themselves if given the opportunity.[28]
The Turkey Vulture species receives special legal protections under the Migratory Bird Treaty Act of 1918 in the United States,[8] by the Convention for the Protection of Migratory Birds in Canada,[54] and by the Convention for the Protection of Migratory Birds and Game Mammals in Mexico.[54] In the USA it is illegal to take, kill, or possess Turkey Vultures, and violation of the law is punishable by a fine of up to 15,000 US dollars and imprisonment of up to six months.[53] 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 percent in ten years or three generations.[1]
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