Geographic Range
Onagers,
Equus 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.
- Biogeographic Regions
- palearctic
Habitat
The flat regions of the deserts and surrounding foothills are home to
E. onager
. These barren deserts are a harsh environment and receive very little rainfall each
year.
- Habitat Regions
- temperate
- terrestrial
- Terrestrial Biomes
- desert or dune
Physical Description
In comparison with other Asiatic wild asses,
E. 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.
- Other Physical Features
- endothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
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.
- 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.
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- viviparous
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. 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.
- Parental Investment
- precocial
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-independence
-
protecting
- female
-
protecting
- maternal position in the dominance hierarchy affects status of young
Lifespan/Longevity
The maximum lifespan of
E. onager
is reported to be approximately 40 years. However, whether this information is based
on wild or captive animals is not known.
Behavior
Equus 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.
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.
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.
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.
- Key Behaviors
- cursorial
- terricolous
- crepuscular
- motile
- nomadic
- migratory
- solitary
- social
- dominance hierarchies
Home Range
Because of the harsh conditions that the desert presents,
E. onager
must stay within 20 kilometers of a water source.
Communication and Perception
Equus 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.
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.
- Plant Foods
- leaves
- roots and tubers
- wood, bark, or stems
- seeds, grains, and nuts
Predation
Equus 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.
Ecosystem Roles
Grazing by
E. onager
impacts vegetation communities in which they live.
Economic Importance for Humans: Positive
Onagers have been hunted by humans in the past for their flesh and hides. However,
in 1971,
E. onager
became a protected species in Iran and hunting it is prohibited year-round.
- 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.
Conservation Status
IUCN estimates 144 onagers remaining with the rate of decline at 28% over the last
three generations.
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
.
Additional Links
Contributors
Jill Grogan (author), University of Alaska Fairbanks, Link E. Olson (editor, instructor), University of Alaska Fairbanks, Nancy Shefferly (editor), Animal Diversity Web.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- introduced
-
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- 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.
- polygynous
-
having more than one female as a mate at one time
- 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).
- 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
- fertilization
-
union of egg and spermatozoan
- 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
- crepuscular
-
active at dawn and dusk
- motile
-
having the capacity to move from one place to another.
- nomadic
-
generally wanders from place to place, usually within a well-defined range.
- migratory
-
makes seasonal movements between breeding and wintering grounds
- solitary
-
lives alone
- social
-
associates with others of its species; forms social groups.
- dominance hierarchies
-
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- food
-
A substance that provides both nutrients and energy to a living thing.
- herbivore
-
An animal that eats mainly plants or parts of plants.
- folivore
-
an animal that mainly eats leaves.
- 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.
- 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.
References
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.
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 .