The onager (Equus hemionus ), also known as hemione or Asiatic wild ass, is a species of the family Equidae 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.
Unlike most horses and donkeys, onagers have never been domesticated. This species is closely related to the African wild ass, as they both shared the same ancestor.
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. Male onagers are usually larger than females.
The natural range of this species covers a huge area from the Black Sea to the Yellow River in China, including Mongolia, which holds nearly half of the total population of this species. Onagers prefer to live in desert plains, semideserts, oases, arid grasslands, savannahs, shrublands, steppes, mountainous steppes, and mountain ranges.
Onagers are social animals. Males are either solitary or live in groups of 2-3 individuals. The males have been observed holding harems of females, but in other studies, the dominant stallions defend territories that attract females. Onagers also occasionally form large group associations of 450 to 1,200 individuals, but this usually only occurs in places with food or water sources. As these larger groups dissolve again within a day, no overarching hierarchy apart from the ranking of the individual herds seems to exist. Young males also frequently form "bachelor groups" during the winter. 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 9 km2 (3.5 sq mi), but they can also be significantly larger. These territories include food and rest stops and permanent or periodic water sources. Onagers are mostly active at dawn and dusk, even during the intense heat. They are among the fastest mammals, as they can run as fast as 64 km/h (40 mph) to 70 km/h (43 mph).
Onagers are herbivorous animals that eat grasses, herbs, leaves, fruits, and saline vegetation when available but browse shrubs and trees in drier habitats. They also eat seed pods and break up woody vegetation with their hooves to get at more succulent herbs growing at the base of woody plants. During the winter, they 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.
Males of this species exhibit different breeding behaviors, but all of them tend to primarily defend resources and only then mate. With the onset of the reproductive season, dominant males begin to control areas along water sources. Hence, they can visit and mater with all females of the area, which can be described as a polygynous mating system. However, this shouldn't be confused with a harem-based system. Some females may travel between the home ranges of males, while others prefer staying in the same area until the end of the reproductive season. They breed and yield offspring between April and September, generally - in June-July. Meanwhile, the population in India breeds during the rainy season. The gestation period lasts for 11 months, after which one foal is born. Weaning occurs between 1 and 2 years of age, while the age of reproductive maturity is 3-4 years old.
Presently, onager populations as a whole are primarily threatened by poaching for consumption. Other human activities include river diversion for crop irrigation, because of which their arid, desert habitat becomes even drier and more barren. On the other hand, these mammals heavily suffer from excessive grazing by livestock, leading to food shortages and making onagers compete for water sources as well. Additionally, they are often left without suitable food due to the removal of shrubs and bushes within their range. Further, some populations of this species live in isolation for a long period of time. As a result, they often have serious problems, associated with continuous interbreeding. Two small populations of these animals are negatively affected by disease and drought.
According to the IUCN Red List, the global population of onagers is 55,000 animals. This includes 40,000 individuals in Mongolia with an additional 1, 500 individuals in the Transaltai Gobi; around 5,000 Onagers are believed to occur in adjacent China, primarily in Xinjiang province; around 4, 000 animals are found in the Little Rann of Kutch, India; around 3, 100 Onagers live in Kazakhstan; around 790 animals occur in Iran; around 920 - in Turkmenistan and adjacent Uzbekistan; and 250 live in the Negev, Israel. At present, there have been accomplished two projects of Onager re-introduction into semi-reserves, which are large enclosures. One of these semi-reserves is the Dzheiran Ecocentre, located in Uzbekistan and holding a population of 98 individuals. The other one is on the Birjutschii peninsula (Ukraine), which is home to 91 Onagers. Nevertheless, none of these populations was reported on the IUCN Red List. Overall, Onagers are currently classified as Near Threatened (NT), but their numbers remain stable.
Due to their diet habits, onagers may impact vegetation communities. The water holes dug by the onagers are often subsequently visited by domestic livestock, as well as other wild animals.
