Pronghorn

Pronghorn
A Pronghorn near Fort Rock, Oregon
Conservation status

Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Suborder: Ruminantia
Infraorder: Pecora
Family: Antilocapridae
Gray, 1866
Genus: Antilocapra
Species: A. americana
Binomial name
Antilocapra americana
Ord, 1815
Subspecies[2]

A. a. americana
A. a. mexicana
A. a. oregona
A. a. peninsularis
A. a. sonoriensis

The Pronghorn (Antilocapra americana), is a species of artiodactyl mammal endemic to interior western and central North America. Though not an antelope, it is often known colloquially in North America as the Prong Buck, Pronghorn Antelope, Speedgoat, or simply Antelope,[3] as it closely resembles the true antelopes of the Old World and fills a similar ecological niche due to convergent evolution.[4] It is the only surviving member of the family Antilocapridae.[5]

Contents

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 36–70 kg. The females are the same heights as males but weigh 41–50 kg. The feet have just two hooves, with no dewclaws. The body temperature is 38.0°C.[5][6][7][8]

Pronghorns in Montana, United States.

Each "horn" of the Pronghorn is composed of a slender, laterally flattened blade of bone that 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.

The orbits (eye sockets) are prominent and sit high on the skull; there is never an antorbital pit. The teeth are hypsodont, and the dental formula is:

Dentition
0.0.3.3
3.1.3.3
PronghornDetail.jpg

Males have a prominent 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.[7] Males are further differentiated from females in that males will have a small patch of black hair at the corner of the jawbone. Pronghorns have a distinct, musky odor. Males mark territory with a scent gland located on the sides of the head.[5] 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,[6] 72 km/h,[5] or 86 km/h.[7] It is often cited as the second-fastest land animal, second only to the cheetah.[9] It can, however, sustain high speeds longer than cheetahs. University of Idaho zoologist John Byers has suggested that the Pronghorn evolved its running ability to escape from extinct predators such as the American cheetah, since its speed greatly exceeds that of extant North American predators.[10] It has a very large heart and lungs, and hollow hair. 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.

Distribution

Pronghorns in Fort Rock, Oregon, United States.

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.[5]

The subspecies known as the Sonoran Pronghorn (Antilocapra americana sonoriensis) occurs in Arizona and Mexico.[7] Other subspecies include the Mexican Pronghorn (A. a. mexicana), the Oregon pronghorn (A. a. oregona), and the critically endangered Baja California Pronghorn (A. a. peninsularis).

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. An ongoing study by the Lava Lake Institute for Science and Conservation and the Wildlife Conservation Society, shows an overland migration route that covers more than 160 miles.[11] The migrating pronghorn start travel from the foothills of the [Pioneer Mountains] through [Craters of the Moon National Monument] to the Continental Divide. Dr. Scott Bergen of Wildlife Conservation Society says, ""This study shows that pronghorn are the true marathoners of the American West. "With these new findings, we can confirm that Idaho supports a major overland mammal migration--something that is becoming increasingly rare in the U.S. and worldwide."[12]

Diet

Pronghorn herd, Yellowstone National Park

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.[6] In one study forbs comprised 62% of the diet, shrubs 23%, and grasses 15%,[6] while in another, cacti comprised 40%, grass 22%, forbs 20%, and shrubs 18%.[7]

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.[6][7][8]

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 an estimated population of between 500,000 and 1,000,000.[13] There has been some recent decline in a few localized populations,[6] due to blue tongue disease which is spread from sheep; however the overall trend has been positive since conservation measures were put in place.

Cougars, wolves, coyotes and bobcats, are the major predators. Golden Eagles have been reported to prey on fawns.

Pronghorn migration corridors are threatened by habitat fragmentation and the blocking or traditional migration routes. In a migration study conducted by Lava Lake Institute for Science and Conservation and the Wildlife Conservation Society, at one point the migration corridor bottlenecks to an area only 200 yards wide.[14]

Pronghorns are now quite numerous and outnumbered people in Wyoming and parts of northern Colorado until just recently. 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).

Other species

During the Pleistocene period, 12 antilocaprid species existed in North America. About 5 existed when humans entered North America 13,000 years ago; all but A. americana are now extinct.[5]

See also

References

  1. ↑ Hoffmann, M., Byers, J. & Beckmann, J. (2008). Antilocapra americana. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 10 April 2009. Database entry includes a brief justification of why this species is of least concern.
  2. ↑ Wilson, Don E.; Reeder, DeeAnn M., eds (2005). Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press, 2 vols. (2142 pp.). ISBN 978-0-8018-8221-0. OCLC 62265494. http://www.bucknell.edu/msw3/browse.asp?id=14200468. 
  3. ↑ Caton, J. D. (1876). The American Antelope, or Prong Buck The American Naturalist 10 (4): 193-205.
  4. ↑ Farb, Peter (1970). Ecology. Time Life Books. pp. 126, 136
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Smithsonian Institution. North American Mammals: Pronghorn Antilocapra americana
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Mammals of Texas: Pronghorn
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Animal Diversity Web: Antilocapra americana
  8. ↑ 8.0 8.1 AnAge: Antilocapra americana
  9. ↑ Klessius, M. (2007). Losing Ground. National Geographic 211 (1): 22. ISSN 0027-9358
  10. ↑ Byers, John (1998). American Pronghorn: Social Adaptations and the Ghosts of Predators Past. Chicago University Press. p. 318. ISBN 978-0226086996. http://books.google.com/books?id=iFQgW0Mf5VoC&source=gbs_navlinks_s. 
  11. ↑ "Pronghorn Antelope Migration Route: 160 Miles Plus : Discovery News". News.discovery.com. http://news.discovery.com/animals/pronghorn-antelope-migration-route-160-miles-plus.html. Retrieved 2010-07-21. 
  12. ↑ "Pronghorn migration circuit found in Idaho - NatGeo News Watch". Blogs.nationalgeographic.com. 2009-11-02. http://blogs.nationalgeographic.com/blogs/news/chiefeditor/2009/11/pronghorn-migration-found-in-idaho.html. Retrieved 2010-07-21. 
  13. ↑ Antilocapra americana, International Union for Conservation of Nature and Natural Resources
  14. ↑ New Long Distance Migration Route for Pronghorn Found in Idaho by WCS and Lava Lake Institute, November 2, 2009