The turkey vulture (Cathartes aura), 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] is the most widespread of the New World vultures.[3] One of three species in the genus Cathartes of the family Cathartidae, the turkey vulture ranges 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]
Like all New World vultures, it is not closely related to the Old World vultures of Europe, Africa, and Asia. The two groups strongly resemble each other because of convergent evolution; natural selection often leads to similar body plans in animals that adapt independently to the same conditions.
The turkey vulture is a scavenger and feeds almost exclusively on carrion.[4] It
finds its food using its keen eyes and sense of smell, flying low
enough to detect the gases 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, the vulture receives legal protection under the Migratory Bird Treaty Act of 1918.
Taxonomy
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 that term 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 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 taxonomic placement of the turkey vulture and the remaining six species of New World vultures has been in flux.[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. Some earlier
authorities suggested that the New World vultures were more closely
related to storks.[15] More recent authorities maintained their overall position in the order Falconiformes along with the Old World vultures[16] or place them in their own order, Cathartiformes.[17]
However, recent genetic studies have made it clear that neither New World or Old World vultures are close to falcons, nor are New World vultures close to storks.[18] Both are basal members of the clade Afroaves,[19] with Old World vultures comprising several groups within the family Accipitridae, also containing eagles, kites, and hawks,[20][21] while New World vultures in Cathartiformes are a sister group to Accipitriformes[19] (containing the osprey and secretarybird along with Accipitridae[21]).
There are five subspecies of turkey vulture:
- C. a. aura is the nominate subspecies. It is found from Mexico south through South America and the Greater Antilles. This subspecies occasionally overlaps its range with other subspecies. It is the smallest of the subspecies but is nearly indistinguishable from C. a. meridionalis in color.[22]
- C. a. jota, the Chilean turkey vulture, is larger, browner, and slightly paler than C. a. ruficollis. The secondary feathers and wing coverts may have gray margins.[23]
- C. a. meridionalis, the western turkey vulture, is a synonym for C. a. teter. C. a. teter was identified as a subspecies by Friedman in 1933, but in 1964 Alexander Wetmore separated the western birds, which took the name meridionalis, which was applied earlier to a migrant from South America. It breeds from southern Manitoba, southern British Columbia, central Alberta and Saskatchewan south to Baja California, south-central Arizona, southeast New Mexico, and south-central Texas.[24] It is the most migratory subspecies, migrating as far as South America, where it overlaps the range of the smaller C. a. aura. It differs from the eastern turkey vulture in color, as the edges of the lesser wing coverts are darker brown and narrower.[22]
- C. a. ruficollis is found in Panama south through Uruguay and Argentina. It is also found on the island of Trinidad.[25] It is darker and more black than C. a. aura, with brown wing edgings which are narrower or absent altogether.[25] The head and neck are dull red with yellow-white or green-white markings. Adults generally have a pale yellow patch on the crown of the head.[23]
- C. a. septentrionalis is known as the eastern turkey vulture. The eastern and western turkey vultures differ in tail and wing proportions. It ranges from southeastern Canada south through the eastern United States. It is less migratory than C. a. meridionalis and rarely migrates to areas south of the United States.[22]
Description
The two front toes of the foot are long and have small webs at their bases.[35] Tracks
are large, between 9.5 and 14 cm (3.7 and 5.5 in) in length and 8.2 and
10.2 cm (3.2 and 4.0 in) in width, both measurements including claw
marks. Toes are arranged in the classic, anisodactyl pattern.[36] 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. The black vulture is
relatively shorter-tailed and shorter-winged, which makes it appear
rather smaller in flight than the turkey vulture, although the body
masses of the two species are roughly the same. The nostrils are not
divided by a septum, but rather are perforate; from the side one can see
through the beak.[37] 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.[38] Captive
longevity is not well known. As of 2015 there are two captive birds
over 40 years old: the Gabbert Raptor Center on the University of
Minnesota campus is home to a turkey vulture named Nero with a confirmed
hatch year of 1974,[39] and
another female bird, named Richard, lives at the Lindsay Wildlife
Museum in Walnut Creek, CA. Richard hatched in 1974 and arrived at the
museum later that year.[40] The oldest wild captured banded bird was 16 years old.[4]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).[26][27][28] Birds in the northern limit of the species' range average larger in size than the vulture from the neotropics. 124 birds from Florida averaged 2 kg (4.4 lb) while 65 and 130 birds from Venezuela were found to average 1.22 and 1.45 kg (2.7 and 3.2 lb), respectively.[29][30][31] It displays minimal sexual dimorphism; sexes are identical in plumage and in coloration, and are similar in size.[32] 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.[26] 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.[33] 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.[34]
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, or when fighting with other
vultures over a carcass. Grunts are commonly heard from hungry young and
from adults in their courtship display.
Distribution and habitat
The turkey vulture has a large range, with an estimated global occurrence of 28,000,000 km2 (11,000,000 sq mi). 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.[43] 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.[26]
This bird with its crow-like aspect gave foot to the naming of the Quebrada de los Cuervos (Crows Ravine) in Uruguay, where they dwell together with the lesser yellow-headed vulture and the black vulture.[44]
Ecology and behavior
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.[35]
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.[45] It cools the blood vessels in the unfeathered tarsi and feet, and causes white uric acid to streak the legs.[46] The turkey vulture has few natural predators. Adult, immature and fledging vultures may fall prey to great horned owls, red-tailed hawks, golden eagles and bald eagles, while eggs and nestlings may be preyed on by mammals such as raccoons and opossums.[7][27][47][48][49]Foxes can occasionally ambush an adult but species that can climb are more likely to breach and predate nests than adults.[50] 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.[33] Its life expectancy in the wild ranges upward of 16 years, with a captive life span of over 30 years being possible.[51][52]
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.[33] 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.[53]
Diet
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. They may rarely feed on plant matter, shoreline vegetation, pumpkin, coconut[54] and other crops, live insects and other invertebrates.[43] In South America, turkey vultures have been photographed feeding on the fruits of the introduced oil palm.[55][56][57] They rarely, if ever, kill prey themselves.[58] The turkey vulture can often be seen along roadsides feeding on roadkill, or near bodies of water, feeding on washed-up fish.[4] They 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.[59]
The turkey vulture forages by smell, an ability that is uncommon in the
avian world, often flying 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, black vultures, and condors,
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,[59] but
is displaced in turn by the king vulture and both types of condor,
which make 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.[60]
Reproduction
The breeding season of the turkey vulture varies according to latitude.[61] In the southern United States, it commences in March, peaks in April to May, and continues into June.[62] In more northerly latitudes, the season starts later and extends into August.[63] 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.[43]
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.[43] 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.[43] The young fledge at about nine to ten weeks. Family groups remain together until fall.[43]
Relationship with humans
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.[64] However, the virus that causes hog cholera is destroyed when it passes through the turkey vulture's digestive tract.[33] 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.[65] The droppings produced by turkey vultures and other vultures can harm or kill trees and other vegetation.[66] 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.[67] In captivity, it can be fed fresh meat, and younger birds will gorge themselves if given the opportunity.[33]
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,[68] and by the Convention for the Protection of Migratory Birds and Game Mammals in Mexico.[68]In
the US 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 and
imprisonment of up to six months.[67] 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.
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