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Equus hemionus onageronager

By Jill Grogan

Geographic Range

Onagers, Equus hemionus onager, are found from Mongolia to Saudi Arabia and as far north as southern Russia and Kazakhstan. Some also inhabit northwestern India and Tibet. They have been reintroduced in Mongolia and Iran. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; Wilson and Reeder, 1993)

Habitat

The flat regions of the deserts and surrounding foothills are home to E. hemionus onager. These barren deserts are a harsh environment and receive very little rainfall each year. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; Moehlman and Feh, 2004; Wilson and Reeder, 1993)

Physical Description

In comparison with other Asiatic wild asses, E. hemionus onager is slightly smaller with a paler coat. Onagers have a pale sandy-red colored coat with a light brown dorsal stripe. The dorsal stripe has two surrounding white strips that blend into the lighter colored hind quarters. In addition to the dorsal stripe, onagers also have a shoulder stripe. The flanks, back and underside of onagers are white. In the winter, the coat grows longer and turns grayer and the white parts become more defined. Males and females differ only slightly outwardly, with males being only slightly larger. Males stand 1.5 meters at the shoulder and are about 2 meters in length, weighing about 250 kilograms. ("Iran Nature and Wildlife Magazine", 2004)

  • Sexual Dimorphism
  • male larger
  • Average mass
    males: 250 kg
    lb
  • Average length
    males: 2 m
    ft

Reproduction

A dominant stallion mates with females in the herd. In order to assure breeding status, stallions defend the territories that females move through, with dominant stallions defending the best territories. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; "Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; "Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; "Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003)

During mating season in mid-June, stallions fight each other for mating rights. Females have a short estrus period of 3 to 5 days. After a year-long gestation, mares leave the herd to give birth in a safe place. A single foal is born that stays with its mother for two years. After giving birth, both mare and foal rejoin the herd, where the mother protects her foal from danger. ("Iran Nature and Wildlife Magazine", 2004; Nowak, 1999)

Pregnancy in onagers lasts 365 to 368 days. Nowak (1999) reports that lactation in female Equus hemionus (a species of wild ass in which some authorities include onagers) nurse their young for between 1 and 1.5 years. It is reasonable to assume that onagers fall within this range. Young onagers become independent around two years of age. Females are sexually mature around the age of 2, but males, at least in E. hemionus, mature about a year later. ("Iran Nature and Wildlife Magazine", 2004; Nowak, 1999)

  • Breeding interval
    Onager mares breed every other year.
  • Breeding season
    Onagers usually mate in mid-June.
  • Range number of offspring
    1 to 1
  • Range gestation period
    365 to 368 days
  • Range weaning age
    18 to 24 months
  • Average time to independence
    2 years
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Range age at sexual or reproductive maturity (male)
    2 to 4 years

All members of the genus Equus are fairly precocial at birth, and are able to run shortly after birth. During the first two years of a foal's life, it stays with its mother. Mares protect their foals against all dangers. Nursing lasts between 1.5 and 2 years. Although specific details on the relationship between maternal dominance status and status of offsping, it is reasonable to assume that this species is like other members of the genus. If E. hemionus onager is like other horses, maternal dominance status affects status of the young within the herd. The role of males in care of offspring has not been reported. ("Iran Nature and Wildlife Magazine", 2004; "Iran Nature and Wildlife Magazine", 2004; "Iran Nature and Wildlife Magazine", 2004; "Iran Nature and Wildlife Magazine", 2004; "Iran Nature and Wildlife Magazine", 2004; Nowak, 1999)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female
  • maternal position in the dominance hierarchy affects status of young

Lifespan/Longevity

The maximum lifespan of E. hemionus onager is reported to be approximately 40 years. However, whether this information is based on wild or captive animals is not known. ("Iran Nature and Wildlife Magazine", 2004)

Behavior

Equus hemionus onager usually lives in herds, with the exception of older stallions, who can be found living alone. Mares live with their foals in herds made up entirely of other females and young. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003)

Data specific to onagers is difficult to find, because of their debated taxonomic status. However, it is reasonable to assume that these animals are similar to E. hemionus, since they are sometimes placed in the same species. With that in mind, the following information on E. hemionus is provided.

Herd size may vary. In E. hemionus, average herds contain between 10 and 20 animals, with one male and many females. However, in some ecological conditions, pressure from predators causes small single male groups to come together. (Nowak, 1999; Nowak, 1999)

Onagers are reported to be crepuscular. However, E. hemionus is reported to be primarily diurnal, feeding during the day and bedding down at night, with some populations feeding at night. (Nowak, 1999)

Equus hemionus is able to reach top speeds of about 70 km/hour, and can run at a sustained speed of 50 km/hour. It is likely that onagers are similar in their ability to attain such speeds. (Nowak, 1999; Nowak, 1999)

Home Range

Because of the harsh conditions that the desert presents, E. hemionus onager must stay within 20 kilometers of a water source. ("Iran Nature and Wildlife Magazine", 2004; "Iran Nature and Wildlife Magazine", 2004; Nowak, 1999)

Communication and Perception

Equus hemionus onager has strong senses with an extremely keen sense of smell. Like other members of the genus Equus, onagers have vocal, tactile and chemical communication. In addition, visual signals may be important. ("Iran Nature and Wildlife Magazine", 2004; Nowak, 1999)

Food Habits

Onagers are herbivores that feed on the scarce plant life in the desert. Foods of these animals include grasses, bushes, herbs and foliage. Onagers receive most of their water from their food, but must remain close to a site of open water. Grazing time for onager sis usually during the cooler part of the day such as morning and evening. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; Moehlman and Feh, 2004; Wilson and Reeder, 1993)

  • Plant Foods
  • leaves
  • roots and tubers
  • wood, bark, or stems
  • seeds, grains, and nuts

Predation

Equus hemionus onager has no natural predators other than humans. This species is being driven to extinction due to hunting, competition for food and water with livestock, and loss of natural habitat. Onagers have a well developed sense of smell and can detect potential predators, such as humans, from a far distance. Onagers are also very fast, with the ability to run 60 to 70 kilometers per hour over short distances, and 40 to 50 kilometers per hour for several hours at a time. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; "UNEP-WCMC Species Database: CITES-Listed Species", 2004; Bennett, 1980; Moehlman and Feh, 2004; Wilson and Reeder, 1993; "Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; "UNEP-WCMC Species Database: CITES-Listed Species", 2004; Bennett, 1980; Moehlman and Feh, 2004; Wilson and Reeder, 1993)

Ecosystem Roles

Grazing by E. hemionus onager impacts vegetation communities in which they live. ("Iran Nature and Wildlife Magazine", 2004)

Economic Importance for Humans: Positive

Onagers have been hunted by humans in the past for their flesh and hides. However, in 1971, E. hemionus onager became a protected species in Iran and hunting it is prohibited year-round. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003; Moehlman and Feh, 2004)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

Although there is no apparent direct negative economic impact that this species has on humans, it is possible that these wild asses compete with livestock for water and scarce food resources. ("Iran Nature and Wildlife Magazine", 2004; "IUCN SSC Equid Specialist Group", 2003)

Conservation Status

IUCN estimates 144 onagers remaining with the rate of decline at 28% over the last three generations. ("IUCN SSC Equid Specialist Group", 2003; "UNEP-WCMC Species Database: CITES-Listed Species", 2004; Moehlman and Feh, 2004)

Other Comments

Onagers are reported to have a bad temperment, which makes them unsuitable as work-a-day domestic animals. However, the ancient Roman Legions are thought to have used these animals to pull their war machines. Onagers were previously considered a species, Equus onager, but have since been included as a subspecies of kulans, Equus hemionus. (AZA Taxon Advisory Group, unknown)

Contributors

Jill Grogan (author), University of Alaska Fairbanks, Link E. Olson (editor, instructor), University of Alaska Fairbanks, Nancy Shefferly (editor), Animal Diversity Web.

Glossary

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

herbivore

An animal that eats mainly plants or parts of plants.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

References

2003. "IUCN SSC Equid Specialist Group" (On-line). Accessed October 31, 2004 at http://www.iucn.org/themes/ssc/sgs/equid/ASWAss.html.

2004. "Iran Nature and Wildlife Magazine" (On-line). Species Fauna and Flowers. Accessed November 18, 2004 at http://www.hamshahri.org/musiems/daarabad/inwm/no.2/english/fau_flow/ir_mammalia01.html.

2004. "UNEP-WCMC Species Database: CITES-Listed Species" (On-line). Accessed October 31, 2004 at http://www.cites.org/eng/resources/species.html.

AZA Taxon Advisory Group, unknown. "Information for the Upper Level Scientist, Onager (Equus hemionus onager)" (On-line). WILD HORSE RESOURCE. Accessed March 04, 2005 at http://equid.topcities.com/onager.html.

Bennett, D. 1980. Stripes Do Not a Zebra Make, Part I: A Cladistic Analysis of Equus. Systematic Zoology, 29/3: 272-287.

Moehlman, P., C. Feh. 2004. "IUCN Red List of Threatened Species" (On-line). Accessed October 24, 2004 at http://www.redlist.org/search/details.php?species=7966.

Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.

Wilson, D., D. Reeder. 1993. Mammal Species of the World. Washington, DC: Smithsonian Institution Press.

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