The Onager is an ass species with a characteristic wide, black colored dorsal band that is fringed with white and absent in the Mongolian wild ass. This ungulate exhibits a white belly, buttocks and muzzle. It's the most horse-like ass species in the world. Coloration of their coat changes with season. Thus, the winter coat of these animals is light brown, whereas the summer coat is reddish brown.
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. Prefer type of habitat is desert or semi-desert. However, Onagers may occasionally be seen in plains as well as high in mountains.
Onagers are highly gregarious creatures, forming troops of 10 - 12 individuals, which include one stallion as well as multiple females with their young. However, older males tend to live alone. During the autumn and winter months, when vegetation is in abundance, these mammals can be seen in large groups of 300 individuals, composed of several smaller troops. This animals are crepuscular with the periods of increased activity at dusk and dawn, when the temperature drops. Onagers prefer living in close proximity (30 km) to a source of water, partially because lactating females constantly need a water source. However, Onagers are able to get required moisture from their food.
Males of this species exhibit different breeding behaviors, but all of them tend to primarily defend resources and only then mates. 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 polygynous mating system. However, this shouldn't be confused with harem-based system. Some females may travel between 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. Gestation period lasts for 11 months, after which one foal is born. Weaning occurs at 1 - 2 years of age, while the age of reproductive maturity is 3 - 4 years old.
Presently, Onager populations a whole is 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 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 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.
Onagers may impact vegetation communities in which they live by grazing.