The onager (; ''Equus hemionus''), also known as hemione or Asiatic wild ass,
is a species of the family
Equidae (
horse family) native to
Asia. A member of the subgenus ''
Asinus'', the onager was
described and given its binomial name by German zoologist
Peter Simon Pallas in 1775. Five subspecies have been recognized, one of which is extinct.
The Asiatic wild ass is larger than the
African wild ass at about and (head-body length). They are reddish-brown or yellowish-brown in color and have broad dorsal stripe on the middle of the back. 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). 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.
The onager formerly had a wider range from southwest and central to northern Asian countries, such as
Israel,
Saudi Arabia,
Iraq,
Jordan,
Syria,
Afghanistan,
Russia, and
Siberia, the prehistoric
European wild ass subspecies ranged through Europe until the Bronze age.
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.
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.
Previously listed as
Endangered, onagers have been classified as
Near Threatened by
IUCN in 2015.
Of the five
subspecies, one is extinct, two are endangered, and two are near threatened (their status in China is not well known).
Persian onagers are currently being reintroduced in the Middle East as replacements for the extinct
Syrian wild ass in the
Arabian Peninsula, Israel and
Jordan.
Etymology
The
specific name is
Ancient Greek ἡμίονος (''hēmíonos''), from
ἡμι- (hēmi-), half, and ὄνος (ónos), donkey; thus, half-donkey or
mule. The term onager comes from the ancient Greek ὄναγρος, again from ὄνος ('onos), donkey, and ἄγριος ('agrios), wild.
The species was commonly known as Asian wild ass, in which case the term ''onager'' was reserved for the ''E. h. onager'' subspecies,
more specifically known as the
Persian onager. Until this day, the species share the same name, ''onager''.
Taxonomy and evolution
The onager is a member of the
subgenus ''
Asinus'', belonging to the
genus ''
Equus'' and is classified under the
family Equidae. The
species was
described and given its binomial name ''Equus hemionus'' by German zoologist
Peter Simon Pallas in 1775.
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.
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.
Subspecies
Widely five recognized subspecies of the onager include:
A sixth possible subspecies, the Gobi khulan (''E. h. luteus'',
also called the ''chigetai''
or ''dziggetai'') has been proposed, but may be synonymous with ''E. h. hemionus''.
Debates over the taxonomic identity of the onager occurred until 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.
Characteristics

Onagers are the most horse-like of wild asses. 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 or grayish-brown in the winter. They have a black stripe bordered in white that extends down the middle of the back. The belly, the rump, and the muzzle are white in most onagers, except for the Mongolian wild ass that has a broad black dorsal stripe bordered with white.
Onagers are larger than
donkeys at about in size and in head-body length. Male onagers are usually larger than females.
Evolution

The genus ''Equus'', which includes all extant equines, is believed to have evolved from ''
Dinohippus'' via the intermediate form ''
Plesippus''. One of the oldest species is ''
Equus simplicidens'', described as zebra-like with a donkey-shaped head. The oldest fossil to date is about 3.5 million years old from Idaho, USA. The genus appears to have spread quickly into the Old World, with the similarly aged ''Equus livenzovensis'' documented from western Europe and Russia.
Molecular phylogenies indicate the most recent common ancestor of all modern equids (members of the genus ''Equus'') lived around 5.6 (3.9–7.8) million years ago (Mya). Direct paleogenomic sequencing of a 700,000-year-old middle Pleistocene horse metapodial bone from Canada implies a more recent 4.07 Mya for the most recent common ancestor within the range of 4.0 to 4.5 Mya.
The oldest divergencies are the Asian hemiones (subgenus ''E. (
Asinus)'', including the
kulan, onager, and
kiang), followed by the African zebras (subgenera ''E. (
Dolichohippus)'', and ''E. (
Hippotigris)''). All other modern forms including the domesticated horse (and many fossil
Pliocene and
Pleistocene forms) belong to the subgenus ''E. (
Equus)'' which diverged about 4.8 (3.2–6.5) Mya.
Distribution and habitat

The onagers' favored habitats consist of desert plains, semideserts,
oases,
arid grasslands, savannahs,
shrublands, steppes, mountainous steppes, and
mountain ranges. The Turkmenian kulan and Mongolian wild asses are known to live in hot and colder deserts. The IUCN estimates about 28,000 mature individuals in total remain in the wild.
During the late
Pleistocene era around 40,000 years ago, the Asiatic wild ass ranged widely across Europe and in southwestern to northeastern Asia. The onager has been regionally extinct in Israel,
Saudi Arabia,
Iraq,
Jordan,
Syria, and southern regions of
Siberia.

The
Mongolian wild ass lives in deserts, mountains, and grasslands of Mongolia and
Inner Mongolian region of northern China. A few live in northern Xinjiang region of northwestern China, most of which live mainly in
Kalamaili Nature Reserve. It is the most common subspecies, but its populations have drastically decreased to a few thousand due to years of poaching and habitat loss in
East Asia. The
Gobi Desert is the onager's main stronghold. It is regionally extinct in eastern Kazakhstan, southern Siberia, and the
Manchurian region of China.
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 in Turkmenistan and has been reintroduced in southern Kazakhstan and Uzbekistan.
Biology and behavior
Asiatic wild asses are mostly active at dawn and dusk, even during the intense heat.
Social structure

Like most equids, onagers are social animals.
Stallions are either solitary or 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.
The social behavior of the Asian wild ass can be very different, depending on different habitats, ranges, and even threats by predators and humans. In
Mongolia and
Central Asia (''E. h. hemionus'' and 'E. h. kulan''), a stove onager stallion can adopt harem-type social groups with several mares and foals in large home areas in the southwest and territory-based social groups in the south and southeast. Also, annual large hikes occur to , where hiking in summer is more limited than in the winter. Partially, onagers also form large group associations of 450 to 1,200 individuals, but this usually only takes place on locations with food or water sources. Since dissolving these major units within one day again, no overarching hierarchy next to the ranking of the individual herds seems to exist. Also, young male onagers frequently form "bachelor groups" during the winter. Such a lifestyle is also seen in the wild horse, the
plains zebras (''E. quagga'') and
mountain zebras (''E. zebra'').
Southern populations of onagers in the Middle East and South Asia tend to have a purely territorial life, where areas partly overlap. Dominant stallions have home ranges of , but they can also be significantly larger. These territories include food and rest stops and permanent or periodic water sources. The waters are usually at the edge of a coalfield and not in the center. Mares with foals sometimes find themselves in small groups, in areas up to , which overlap with those of the other groups and dominant stallions. Such features are seen in Grévy's zebras (''E. grevyi'') and the African wild asses.
Reproduction
The Asian wild ass is sexually mature at two years old, and the first mating usually takes place at three to four years old.
Breeding is seasonal, and the
gestation period of onagers is 11 months; the birth lasts a little more than 10 minutes. Mating and births occur from April to September, with an accumulation from June to July. The mating season in India is in the rainy season. The foal can stand and starts to nurse within 15 to 20 minutes. Females with young tend to form groups of up to five females. During rearing, a foal and dam remain close, but other animals and her own older offspring are displaced by the dam. Occasionally, stallions in territorial wild populations expel the young to mate with the mare again. Wild Asian wild asses reach an age of 14 years, but in captivity, they can live up to 26 years.
Diet

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 onager digs holes in dry riverbeds to reach subsurface water. The water holes dug by the onagers 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 form an important component of the diet of the Mongolian wild ass.
Predation
The onager is preyed upon by predators such as
Persian leopards and
striped hyenas. A few cases of onager deaths due to predation by leopards were recorded in Iran. Though leopards do not usually feed on equids as in
Africa, this may be because Persian leopards are larger and strong enough to prey on Asiatic wild asses.
In the Middle East and the Indian subcontinent,
Asiatic lions and
tigers were the main predators of onagers. They were also formerly preyed upon by
dholes,
Asiatic cheetahs, and possibly
bears, though they may have mostly preyed only on onager
foals. In India,
mugger crocodiles can be great threats to onagers during migratory river crossings.
Currently, the main predator for onagers are
gray wolves. However, like most equids, they are known to have antipredator behaviour. Groups of stallions cooperate and try to chase off predators. If threatened, onagers defend themselves and violently kick at the incoming predator.
Threats
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 also vulnerable to
diseases. A disease known as the "South African horse sickness" caused a major decline to the Indian wild ass population in the 1960s. However, the subspecies is no longer under threat to such disease and is continuously increasing in number.
Conservation

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,
whilst the Persian onager alone has been reintroduced to Jordan and the deserts of Saudi Arabia.
Interaction with human beings
Onagers are notoriously untamable. Equids were used in ancient
Sumer to pull wagons c. 2600 BC, and then
chariots on the
Standard of Ur, c. 2550 BC. Clutton-Brock (1992) suggests that these were
donkeys rather than onagers on the basis of a "shoulder stripe".
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.
In literature
In
La Peau de Chagrin by
Honoré de Balzac, the onager is identified as the animal from which comes the ass's skin or
shagreen of the title.
References
*
External links
"Ass"''
Encyclopædia Britannica''
''Equus hemionus'' bibliographyat The Biodiversity Heritage Library
{{Authority control
Category:Donkeys
Category:EDGE species
Category:Equus (genus)
Category:Extant Pliocene first appearances
Category:Fauna of the Middle East
Category:Fauna of Iran
Category:Fauna of Iraq
Category:Fauna of Western Asia
Category:Mammals described in 1775
Category:Mammals of Afghanistan
Category:Mammals of Central Asia
Category:Mammals of Mongolia
Category:Mammals of Pakistan
Category:Near threatened biota of Asia