Onager

This article is about the horse species. For the weapon, see Onager (siege weapon).
Onager
A Persian onager (Equus hemionus onager) at Rostov-on-Don Zoo, Russia.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Perissodactyla
Family: Equidae
Genus: Equus
Subgenus: Asinus
Species: E. hemionus
Binomial name
Equus hemionus
Pallas, 1775
Subspecies

E. h. hemionus
E. h. kulan
E. h. onager
E. h. khur
†E. h. hemippus

Equus hemionus range

The onager, also known as hemione or Asiatic wild ass[2] (Equus hemionus) is a large equid of the family Equidae (horse family) native to Asia. Unlike most horses and donkeys, onagers have never been domesticated. They are among the fastest mammals, as they can run as fast as 64 km/h (40 mph) to 70 km/h (43 mph). Previously listed as Endangered, they have been classified as Near Threatened by IUCN in 2015.[1]

The onager is closely related to the African wild ass, as they both shared the same ancestor. The kiang, formerly considered a subspecies of Equus hemionus, diverged from the Asiatic wild ass and has been acknowledged as a distinct species.[3]

The onager formerly had a wider range from southwest and central to northern Asian countries, such as Israel, Saudi Arabia, Iraq, Syria, Afghanistan, Russia, and Siberia. During early 20th century, the species lost most of its ranges in the Middle East and Eastern Asia. Today, onagers live in deserts and other arid regions of Iran, Pakistan, India, and Mongolia, including in Central Asian hot and cold deserts of Kazakhstan, Uzbekistan, Turkmenistan, and China.[4] Other than deserts, it lives in grasslands, plains, steppes, and savannahs.

Like many other large grazing animals, the onager's range has contracted greatly under the pressures of poaching and habitat loss.[2] Of the five subspecies, one is extinct, one is critically endangered, and three are endangered[2] (their status in China is not well known[2]). Persian onagers are currently being reintroduced in the Middle East as replacement for the extinct Syrian wild ass.

Etymology and taxonomy

The specific name is Ancient Greek ἡμίονος (hēmíonos), from ἡμι- (hēmi-), half, and ὄνος (ónos), donkey; thus, half-donkey or mule. In Persian the archaic word gur preserves the second syllable of the common Indo-European term that includes ona/ono (donkey) and ger/gur (swift).

The species was commonly known as Asian wild ass, in which case the term "onager" was reserved for the E. h. onager subspecies,[2] more specifically known as the Persian onager. Until this day, the species share the same name, "onager".

Subspecies

Widely recognized subspecies of the onager include:[2]

A sixth possible subspecies, the Gobi khulan (E. h. luteus,[1] also called the chigetai[5] or dziggetai) has been proposed, but may be synonymous with E. h. hemionus.

Debates over the taxonomic identity of the onager occurred until in 1980. As of today, four living subspecies and one extinct subspecies of the Asiatic wild ass have been recognized. The Persian onager was formerly known as Equus onager, as it was thought to be a distinct species.

Evolution

The Asiatic wild ass, among Old World equids, existed for more than 4 million years. The oldest divergence of Equus was the onager followed by the zebras and onwards.[6] A new species called the kiang (E. kiang), a Tibetan relative, was previously considered to be a subspecies of the onager as E. hemionus kiang, but recent molecular studies indicate it to be a distinct species, having diverged from the closest relative of the Mongolian wild ass's ancestor less than 500,000 years ago.[7]

Syrian wild ass (E. h. hemippus)

Persian onager (E. h. onager)


Indian wild ass (E. h. khur)

Turkmenian kulan (E. h. kulan)

Mongolian wild ass (E. h. hemionus)





Physical description

Onagers are larger than donkeys at about 290 kg (640 lb) and 2.1 m (6.9 ft) (head-body length), and are a little more horse-like. They are short-legged compared to horses, and their coloring varies depending on the season. They are generally reddish-brown in color during the summer, becoming yellowish-brown in the winter. They have a black stripe bordered in white that extends down the middle of the back. Male onagers are usually larger than females.

Distribution and range

An Indian wild ass in Little Rann of Kutch, Gujarat

The onagers' favored habitats are deserts, semideserts, arid grasslands, shrublands, and mountain steppes. The Turkmenian kulan is known to live in hot and colder deserts.

During the late Pleistocene era around 40,000 years ago, the Asiatic wild ass ranged widely across Europe to northeastern Asia. The onager have been regionally extinct in Israel, Saudi Arabia, Iraq, Jordan, Syria, and southern regions of Siberia.

Onagers at Wadi Lotz, Negev Mountains, Israel

The Mongolian wild ass lives in deserts of Mongolia and northern China and is the most common subspecies, but its populations have decreased to a few thousand due to years of poaching and habitat loss. It is regionally extinct in eastern Kazakhstan and Siberia. The Indian wild ass was once found throughout the arid parts and desert steppes of northwest India and Pakistan, but about 4,500 of them are found in a few very hot wildlife sanctuaries of Gujarat. The Persian onager is found in two subpopulations in southern and northern Iran. The larger population is found at Khar Turan National Park. However, it is extinct in the wild of Afghanistan. The Turkmenian kulan used to be widespread in central to north Asia. However, it is now found only in Turkmenistan and has been reintroduced in southern Kazakhstan.

Diet

Indian wild ass herd feeding on grasses

Like all equids, onagers are herbivorous mammals. They eat grasses, herbs, leaves, fruits, and saline vegetation when available, but browse on shrubs and trees in drier habitats. They have also been seen feeding on seed pods such as Prosopis and breaking up woody vegetation with their hooves to get at more succulent herbs growing at the base of woody plants.

During the winter, onagers also eat snow as a substitute for water. When natural water sources are unavailable, the Asiatic wild ass digs holes in dry riverbeds to access subsurface water. The water holes dug by the wild asses are often subsequently visited by domestic livestock, as well as other wild animals. Water is also found in the plants on which the onagers feed.

During spring and summer in Mongolia, the succulent plants of the Zygophyllaceae family form an important component of the diet of the Mongolian wild ass.

Biology and behavior

Asiatic wild ass are mostly active at dawn and dusk, even during the intense heat.

Breeding is seasonal, and the gestation period of onagers is 11 months, and most births occur from April to September. The mating season in India is in the rainy season. Females with young tend to form groups of up to five females.

Like most equids, onagers are social animals. Stallions are either solitary or they live in groups of two or three. The males have been observed holding harems of females, but in other studies, the dominant stallions defend territories that attract females. Differences in behaviour and social structure likely are the result of changes in climate, vegetation cover, predation, and hunting. In Mongolia alone, the onager can adopt harem-type social groups in the southwest and territory-based social groups in the south and southeast.

The onager is preyed upon by leopards, gray wolves, and hyenas (formerly by tigers and lions), but they are known to have antipredator protection. Groups of stallions cooperate and try to chase off predators. If threatened, onagers defend themselves and violently kick at the incoming predator.

Onagers are notoriously untamable. Equids were used in ancient Sumer to pull wagons circa 2600 BC, and then chariots on the Standard of Ur, circa 2550 BC. Clutton-Brock (1992) suggests that these were donkeys rather than onagers on the basis of a "shoulder stripe".[8] However, close examination of the animals (equids, sheep and cattle) on both sides of the piece indicate that what appears to be a stripe may well be a harness, a trapping, or a joint in the inlay.[9][10]

Threats

An Asiatic lion attacking an onager (Roman, circa AD 150)

The greatest threat facing the onager is poaching for meat and hides, and in some areas for use in traditional medicine. It is the one of highest threats for the Mongolian wild ass. The extreme isolation of many subpopulations also threatens the species, as genetic problems can result from inbreeding. Overgrazing by livestock reduces food availability, and herders also reduce the availability of water at springs. The cutting down of nutritious shrubs and bushes exacerbates the problem. Furthermore, a series of drought years could have devastating effects on this beleaguered species.

Habitat loss and fragmentation are also major threats to the onager, a particular concern in Mongolia as a result of the increasingly dense network of roads, railway lines, and fences required to support mining activities.

The Asiatic wild ass is vulnerable to diseases, as well. A disease known as the "South African horse sickness" caused a major decline to the Indian wild ass population in the 1960s. Fortunately, the subspecies is no longer under threat to such disease and is continuously increasing their numbers.

Onagers were once under threat by apex predators from India, Iran, and Pakistan, as they used to be prey for Asiatic lions, Asiatic cheetahs, tigers, striped hyenas, and dholes. However, until today, the Asiatic wild ass is being strictly protected. However, Asiatic leopards and grey wolves are the current threats of the onagers. A few cases of onager deaths due to predation was recorded in Iran, as a Persian leopard attacked and eaten a Persian onager. It is said that leopards do not usually feed on equids such as in Africa. It may be due that Asian leopards are larger and stronger enough to prey on Asiatic wild ass.

Conservation

A Persian onager in Augsburg Zoo

Various breeding programs have been started for the onager subspecies in captivity and in the wild, which increases their numbers to save the endangered species. The species is legally protected in many of the countries in which it occurs. The priority for future conservation measures is to ensure the protection of this species in particularly vulnerable parts of its range, to encourage the involvement of local people in the conservation of the onager, and to conduct further research into the behavior, ecology, and taxonomy of the species.

Two onager subspecies, the Persian onager and the Turkmenian kulan are being reintroduced to their former ranges, including in other regions the Syrian wild ass used to occur in the Middle East. The two subspecies have been reintroduced to the wild of Israel since 1982, and had been breeding hybrids there,[11] whilst the Persian onager alone has been reintroduced to Jordan and the deserts of Saudi Arabia.

See also

References

  1. 1 2 3 Kaczensky, P., Lkhagvasuren, B., Pereladova, O., Hemami, M. & Bouskila, A. (2015). "Equus hemionus". IUCN Red List of Threatened Species. Version 2015.2. International Union for Conservation of Nature. Retrieved 10 Jan 2016.
  2. 1 2 3 4 5 6 "Asiatic Wild Ass   Equus hemionus". IUCN.org. Gland, Switzerland: IUCN/SSC Equid Specialist Group.
  3. ↑ Ryder, O.A. & Chemnick, L.G. (1990). "Chromosomal and molecular evolution in Asiatic wild asses". Genetica 83 (1): 67–72. doi:10.1007/BF00774690.
  4. ↑ Grubb, P. (2005). "Order Perissodactyla". In Wilson, D.E.; Reeder, D.M. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. p. 632. ISBN 978-0-8018-8221-0. OCLC 62265494.
  5. ↑ Porter, Valerie (ed.); Ian Lauder Mason (2002). Mason's World Dictionary of Livestock Breeds, Types, and Varieties (5th ed.). Wallingford: CABI. ISBN 0-85199-430-X.
  6. ↑ Weinstock, J.; et al. (2005). "Evolution, systematics, and phylogeography of Pleistocene horses in the New World: a molecular perspective". PLoS Biology 3 (8): e241. doi:10.1371/journal.pbio.0030241. PMC 1159165. PMID 15974804. Retrieved 2008-12-19.
  7. ↑ Ryder OA, Chemnick LG. (1990). "Chromosomal and molecular evolution in Asiatic wild asses.". PubLMed.gov. Retrieved 14 October 2015.
  8. ↑ Clutton-Brock, Juliet (1992). Horse Power: A History of the Horse and the Donkey in Human Societies. Boston, Massachusetts, US: Harvard University Press. ISBN 978-0-674-40646-9.
  9. ↑ Heimpel, Wolfgang (1968). Tierbilder in der Sumerische Literatur. Italy: Studia Pohl 2.
  10. ↑ Maekawa, K. (1979). "The Ass and the Onager in Sumer in the Late Third Millennium B.C.". Acta Sumerologica' (Hiroshima) I: 35–62.
  11. ↑ Saltz, D. (1995). "Population dynamics of a reintroduced Asiatic wild ass (Equus Hemionus) herd". Ecological Applications 5 (2): 327–335. doi:10.2307/1942025.
  • Duncan, P. (ed.). 1992. Zebras, Asses, and Horses: an Action Plan for the Conservation of Wild Equids. IUCN/SSC Equid Specialist Group. IUCN, Gland, Switzerland.

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