Pronghorn
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| Pronghorn | ||||||||||||||||||
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 A pronghorn near Fort Rock, Oregon
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| Antilocapra americana Ord, 1815 |
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A. a. americana |
The pronghorn (Antilocapra americana), also pronghorn antelope or prong buck,[2] is a species of ungulate mammal native to interior western North America. It is the only surviving member of the family Antilocapridae.[3]
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[edit] Morphology
Adult males are 1.3–1.5 m (4 1/4-5 ft) long from nose to tail and stand 81–104 cm (2 5/8-3 3/8 ft) high at the shoulder, and weigh 40–60 kg (88-132 lb). The females are as long, but average slightly less heavy, 40–50 kg (88-110 lb). The main color of adults is brown or tan, with a white rump and belly and two white stripes on the throat. A short dark mane grows along the neck, and males also sport a black mask and black patches on the sides of the neck. The tail is short, 7.5–17.8 cm (average 13.5 cm) long. The feet have just two hooves, with no dewclaws. The body temperature is 38.0 °C.[3][4][5][6]
The "horns" of the pronghorn are of special interest. Each horn is comprised of a slender, laterally-flattened blade of bone which grows from the frontal bones of the skull, forming a permanent core. As in the Giraffidae, skin covers the bony cores, but in the pronghorn it develops into a keratinous sheath which is shed and regrown on an annual basis. Unlike the horns of the family Bovidae, the horn sheaths of the pronghorn are branched, each sheath possessing a forward pointing tine (hence the name pronghorn). The horns of males are well developed; in females, they are either small, misshapen, or absent.
The orbits (eye sockets) are prominent and sit high on the skull; there is never an antorbital pit. The feet have only two digits; no dewclaws are present. A gall bladder is present. The teeth are hypsodont, and the dental formula is I 0/3, C 0/1, P 3/3, M 3/3 x 2 = 32.
Both sexes bear a pair of horns on the top of the head, which are made up of an outer sheath of hairlike substance that grows around a bony core; the outer sheath is shed annually. Males have a horn sheath about 12.5–43 cm (mean 25 cm) long with a prong. Females have smaller horns, ranging from 2.5–15 cm (average 12 cm), and sometimes barely visible; they are straight and very rarely pronged.[5] Pronghorns have a distinct, musky odor. Males mark territory with a scent gland located on the sides of the head.[3] They also have very large eyes, with a 320 degree field of vision. Unlike deer, pronghorns possess a gallbladder.
It can run exceptionally fast, being built for maximum predator evasion through running, and is generally accepted to be the fastest land mammal in the New World. The top speed is very hard to measure accurately and varies between individuals; it is variously cited as up to 70 km/h,[4] 72 km/h,[3] or 86 km/h.[5] It is often cited as the second-fastest land animal, second only to the cheetah.[7] It can however sustain high speeds longer than cheetahs. The pronghorn probably evolved its running ability to escape from the recently extinct American cheetah, since its speed greatly exceeds that of extant North American predators. It has a very large heart and lungs, and their hair is hollow. Although built for speed, it is a very poor jumper. Their ranges are often affected by sheep ranchers' fences. However, they can be seen going under fences, sometimes at high speed. For this reason the Arizona Antelope Foundation and others are in the process of removing the bottom barbed wire from the fences, and/or installing a barbless bottom wire.
Gaits used by the pronghorn include the highly distinctive pronk, a leaping gait.
[edit] Distribution
Pronghorns were brought to scientific notice by the Lewis and Clark Expedition, which found them in what is now South Dakota, USA. The range extends from southern Saskatchewan and Alberta in Canada south through the United States (southwestern Minnesota and central Texas west to northeastern California), to Sonora and San Luis Potosí in northern Mexico, with a small disjunct population in northern Baja California Sur.[3] The subspecies known as the Sonoran pronghorn (Antilocapra americana sonoriensis) occurs in Arizona and Mexico.[5] Bands of pronghorns live in open grasslands, forming small single-sex groups in spring and summer, and gathering into large mixed herds, sometimes up to 1,000 strong, in the fall and winter; they may migrate up to 160 km to avoid deep winter snow.[5]
[edit] Diet
Pronghorns live primarily in grasslands but also in brushland and deserts. They eat a wide variety of plant foods, often including plants that are unpalatable or toxic to domestic livestock (sheep and cattle) though they also compete with these for food.[4] In one study forbs comprised 62% of the diet, shrubs 23%, and grasses 15%,[4] while in another, cacti comprised 40%, grass 22%, forbs 20%, and shrubs 18%.[5]
[edit] Reproductive ecology
Pronghorns have a gestation period of 235 days, longer than is typical for North American ungulates. They breed in mid-September, and the doe carries her fawn until late May. This is around six weeks longer than the white-tailed deer. Newborn pronghorns weigh 2–4 kg, most commonly 3 kg. Sexual maturity is reached at 15 to 16 months, though males rarely breed until 3 years old. The longevity is typically up to 10 years, rarely 15 years.[4][5][6]
[edit] Population and conservation
By 1908, hunting pressure had reduced the pronghorn population to about 20,000. Protection of habitat and hunting restrictions have allowed their numbers to recover to 500,000.[5] There has been some recent decline,[4] possibly due to overgrazing by sheep; pronghorn populations cannot maintain themselves successfully where sheep numbers are kept high.[4]
Wolves, coyotes and bobcats are the major predators. Golden eagles have been reported to prey on fawns.
Pronghorns are now numerous enough that they exceed the human population in all of Wyoming and parts of northern Colorado. It is widely hunted in western states for purposes of population control and food, as the meat is rich and lean.
Three subspecies are considered endangered in all (A. a. sonoriensis, A. a. peninsularis), or part of their ranges (A. a. mexicana).
[edit] Other species
During the Pleistocene period, 12 antilocaprid species existed in North America; all but A. americana are now extinct.[3]
[edit] See also
[edit] References
- ^ Antelope Specialist Group (1996). Antilocapra americana. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006.
- ^ Caton, J. D. (1876). The American Antelope, or Prong Buck The American Naturalist 10 (4): 193-205.
- ^ a b c d e f Smithsonian Institution. North American Mammals: Pronghorn Antilocapra americana
- ^ a b c d e f g Mammals of Texas: Pronghorn
- ^ a b c d e f g h Animal Diversity Web: Antilocapra americana
- ^ a b AnAge: Antilocapra americana
- ^ Klessius, M. (2007). Losing Ground. National Geographic 211 (1): 22. ISSN 0027-9358
