Animal Diversity Web

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)

• Biogeographic Regions
• palearctic
  • introduced
  • native

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)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• desert or dune

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)

• Other Physical Features
• endothermic
• bilateral symmetry

• 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)

• Mating System
• polygynous

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)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• viviparous

• 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)

• Key Behaviors
• cursorial
• terricolous
• crepuscular
• motile
• nomadic
• migratory
• solitary
• social
• dominance hierarchies

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)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical

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)

• Primary Diet
• herbivore
  • folivore

• 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)

• Known Predators

  • Homo sapiens

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)

• IUCN Red List

  Critically Endangered

• US Federal List

  Endangered

• CITES

  Appendix II

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.

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.