Overview

Brief Summary

Description

Grevy's zebra is the largest of the equids (a group that includes horses, asses and zebras) (4). It possesses the same body shape as other equids with a long head and neck and slender legs resting on a single digit in the form of a hoof (5). The sleek coat is patterned with black and white vertical stripes that are much narrower than those of the plains zebra (Equs burchelli) and persist until above the hind legs where a chevron pattern occurs (6). The horizontal stripes on the legs remain distinct all the way down to the hooves, and the tall, upright mane is also striped in a pattern that continues on from the neck. A wide black stripe along the back is bordered by white and is very distinctive (2). The muzzle is a tan colour with white edges, and the large, rounded ears are striped on the back (2).
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Biology

Grevy's zebra has a much more open society than those of other equid species and associations between individuals, other than between a mother and her foal, rarely last for more than a few months (4). Within a single population around ten percent of the mature stallions will occupy territories from which they have sole access to receptive females, although other males are still tolerated within the area (2). These territories are patrolled and marked with dung and are the largest of any living herbivore, at up to 10km2 (2). Temporary groups of between six to twenty zebras also form and may be either single sex or mixed. Mares become sexually mature at three to four years and give birth to a single foal after a gestation period of 13 months every couple of years (2). Foals are able to stand after a mere six minutes and can run after 45 minutes (6), they remain dependent on their mother's milk until six to eight months of age (2). Grevy's zebras are predominately grazers, feeding on a variety of grasses, although they will also browse on trees and scrubs (4). Several theories exist as to the function of zebra stripes, from camouflage to the dazzling of predators. Recent research has suggested however, that they may serve a social function and may stimulate grooming (5). It is believed that the equine ancestor of horses, asses and zebras was striped, but these have subsequently been lost during the evolution of the other two groups (5).
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Distribution

Range Description

Grevy's Zebra is confined to the Horn of Africa, specifically Ethiopia and Kenya. They may persist in South Sudan. Grevy's have undergone one of the most substantial reductions of range of any African mammal. Historically, they ranged east of the Rift Valley in Kenya to western Somalia, and in northern Ethiopia from the Alledeghi Plain through the Awash Valley, the Ogaden, and north-east of Lake Turkana in Ethiopia to north of Mt. Kenya and south-east down the Tana River in Kenya (Bauer et al. 1994). Currently, Grevys’ Zebra have a discontinuous range, and are found from the eastern side of the Rift Valley in Kenya to the Tana River. There is a small, isolated population in the Alledeghi Plains northeast of Awash N.P. in Ethiopia. From Lake Ch’ew Bahir in southern Ethiopia, the population extends to just north of Mt. Kenya although a few animals are found further southeast along the Tana River. A small introduced population survives in and around Tsavo East N.P. in Kenya. They are considered to be extirpated from Somalia, where the last confirmed sightings date to 1973. There are no confirmed records that the species ever occurred in Eritrea or Djibouti (Bauer et al. 1994, Yalden et al. 1986). Sightings from South Sudan require verification (Williams 2002, 2013).
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Geographic Range

Grevy's zebras live in northern Kenya and a few small areas of southern Ethiopia. Historically, Grevy's zebras inhabited Somalia, Ethiopia, Eritrea, Djibouti, and Kenya in East Africa. The last survey in Kenya in 2000 resulted in an estimated population of 2,571. Current estimates place the number of Grevy's zebras in Kenya between 1,838 and 2,319. In Ethiopia, the current population estimate is 126, over a 90% decrease from the estimated 1,900 in 1980. The eastern distribution is north of the Tana River east of Garissa and the Lorian Swamp. In the west, they are found east and north of a line from Mount Kenya to Donyo Nyiro, and east of Lake Turkana to Ethiopia. In Ethiopia, they are found east of the Omo River north to Lake Zwai, southeast to Lake Stephanie and to Marsabit in Kenya.

Biogeographic Regions: ethiopian (Native )

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Historic Range:
Kenya, Ethiopia, Somalia

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Range

Previously found in central Ethiopia, Somalia and northern Kenya, but currently restricted to northeastern Ethiopia and Kenya (1) (4). The species has not been sighted in Somalia since 1973 and is therefore presumed extinct in this country (4).
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Physical Description

Morphology

Physical Description

Grevy's zebras have large heads, large and rounded ears, and thick, erect manes. The muzzle is brown. The neck is thicker and more robust than in other zebra species. These qualities make it appear more mule-like than other zebras. The coat has black and white narrow stripes, shaped like chevrons, that wrap around each other in a concentric pattern and are bisected by a black dorsal stripe. The chevron pattern is especially distinct on the limbs, where the point of the chevron points dorsally, becoming more acute the further up the limb they climb; they reach a final peak at the shoulders and the withers. On the cranium, chevrons extend dorsally to the cheek, where the pattern becomes more linear. The belly of this zebra is completely white, unlike other zebras. Grevy's zebras are also the largest of all the wild equids and only domestic horses are larger. Grevy's zebras exhibit slight sexual dimorphism; males are usually about 10 percent larger than females. Grevy's zebra foals are born with a coat that has reddish-brown or russet stripes instead of the black of adults. This gradually darkens to black as the zebra ages. A dorsal mane that extends from the top of the head to the base of the tail is present in all young zebras. This mane is erect when an animal is excited and flat when it is relaxed. Adult dental formula is 3/3, 1/1, 4/4, 3/3.

Range mass: 349 to 451 kg.

Range length: 125 to 150 cm.

Average length: 135 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Grevy’s Zebras live in arid and semi-arid grass/shrubland where there is permanent water (Klingel 1974; Rubenstein 1986; Rowen and Ginsberg 1992; Williams 2002, 2013). They are predominantly grazers, although browse can comprise up to 30% of their diet during times of drought or in those areas which have been highly transformed through overgrazing. Breeding males defend resource territories (water and food being the key resources) of 2–12 km²; the home range size of non-territorial individuals is up to 10,000 km². They are extremely mobile and individuals have been recorded to move distances of greater than 80 km, with movements determined by the availability of resources; lactating females, for example, can only tolerate one or two days away from water (Klingel 1974; Rubenstein 1986; Rowen and Ginsberg 1992; Williams 2002, 2013).

Systems
  • Terrestrial
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Grevy's zebras inhabit semi-arid grasslands, filling a niche distinct from that of other members of the genus Equus that live within the same geographical range, such as wild asses (which prefer arid habitats) and plains zebras (which are more dependent on water than Grevy's zebras). They usually prefer arid grasslands or acacia savannas. The most suitable areas have a permanent water source. In recent years, Grevy's zebras have become increasingly concentrated in the south of their range due to habitat loss in the north. During the dry season, when location near a permanent water source is especially important, zebras tend to become more concentrated in territories with permanent water sources. In rainy seasons, they are more dispersed. Areas with green, short grass and medium-dense bush are used by lactating females and bachelors more frequently than non-lactating females or territorial males. Lactating females may trade off forage quantity and safety to access nutrients in growing grass.

Range elevation: 300 to 600 m.

Average elevation: 500 m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: savanna or grassland

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Inhabits dry, semi-desert grasslands of Africa (2).
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Trophic Strategy

Food Habits

Grevy's zebras are herbivores and grazers with occasional browsing tendencies. They primarily eat tough grasses and forbs but, in the dry season when grasses are not as abundant, leaves can constitute up to 30 percent of their diet. Grevy's zebras can digest many different types and parts of plants that cattle cannot. Grevy's zebras are water dependent and will often migrate to grasslands within daily reach of water. Most Grevy's zebras can survive without water for up to five days, but lactating females must drink at least every other day in order to maintain healthy milk production.

Plant Foods: leaves

Primary Diet: herbivore (Folivore )

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Associations

Ecosystem Roles

Grevy's zebras are large, grazing ungulates that feed on grasses and serve as prey for a number of large predators. They fill a niche left open between arid-habitat loving wild asses and water-dependent plains zebras.

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Predation

The stripes of Grevy's zebras may act as camouflauge, especially at night. Zebras are often hard to spot from large distances at night. The stripes also help to break up the outline of the animal to predators and may help to camouflage them in tall grass. When in the same territory, Grevy's zebras band together in temporary social groups to provide protection from predators.

Known Predators:

Anti-predator Adaptations: cryptic

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Life History and Behavior

Behavior

Communication and Perception

No two zebras have the same stripe pattern. Each individual zebra's stripe pattern acts as a type of fingerprint that allows it to be identified accurately by human researchers up to 90% of the time. This, along with scent and individual vocalizations, allow individuals to be recognized by conspecifics.

Scent marking, especially by females, plays a significant role in breeding. Males often sniff the leavings of a female in order to determine if she is in estrous. Males use dung and urine in order to mark their territory.

Males use sounds and visual cues to assert their dominance. They may do this by baring their teeth, flattening their ears, kicking, or biting other males. Territorial males often harass females into breeding with them using these same techniques.

Grevy's zebras are very vocal, though not quite as vocal as plains zebras. Their vocabulary includes several distinct pitches. Individuals often emit these pitches when they are escaping predators or when they are fighting.

Communication Channels: visual ; tactile ; acoustic

Other Communication Modes: scent marks

Perception Channels: visual ; acoustic

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Life Expectancy

Lifespan/Longevity

Like most other species the lifespan of Equus grevyi is longer in captivity than in the wild. In captivity, Equus grevyi usually lives between 22 and 30 years. In the wild, the median age is closer to 12 or 13, although an 18 year old animal has been reported.

Range lifespan

Status: wild:
18 (high) years.

Range lifespan

Status: captivity:
30 (high) years.

Typical lifespan

Status: wild:
18 (high) years.

Average lifespan

Status: wild:
12-13 years.

Typical lifespan

Status: captivity:
22 to 30 years.

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Lifespan, longevity, and ageing

Maximum longevity: 31 years (captivity) Observations: One wild born specimen was about 31 years old when it died in captivity (Richard Weigl 2005).
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Reproduction

A male mates with any females that come into his territory if they are in estrous. Mares are usually polyandrous and mate with one male before switching territories and mating with another, although sometimes mares become monandrous. When a mare stays in a single territory, usually because she desires the resources that are present in that territory, she will stay with a single male and mate only with him.

Mating System: polygynous

Grevy's zebras can mate year round, but the majority of breeding occurs from July to August and September to October. Foals are born after a 13 month gestation period, usually within the rainy months of the year. Peaks usually occur in May and June, the period of long rains, and in November and December, the period of short rains. As birth approaches, females isolate themselves from the herd. Birth normally takes place lying down, with the young's hoofs appearing first, and full emergence in 7 to 8 minutes. If birth begins with the mother standing, it is completed lying down. The newborn frees itself from the amniotic membranes and crawls towards its mother's head. The mother licks it clean and ingests the membranes and some amniotic fluid, which may be important in initiating lactation or the maternal bond. Zebras take an average of 275 days to be weaned. Once weaned, they continue to stay with their mother. Females disperse sooner than males, females disperse at 13 to 18 months and males often stay with their mother for up to 3 years. A newborn Grevy's zebra foal is russet-colored with a long hair crest down its back and belly. At this stage, imprinting occurs. Female zebras keep other zebras at a distance so that the foal can bond with its mother. Newborn foals can walk just 20 minutes after being born and run after an hour, which is a very important survival adaptation for this cursorial, migrating species. Foals nurse heavily for half a year and may take as long as three years to be completely weaned. Females achieve sexual maturity around 3 years of age and males achieve sexual maturity around 6 years of age. Females tend to conceive once every two years.

Breeding interval: Female Grevy's zebras breed about once every two years.

Breeding season: Grevy's zebras can mate year round, but most breeding occurs July through August and October through November.

Range number of offspring: 1 to 1.

Range gestation period: 358 to 438 days.

Average gestation period: 390 days.

Average birth mass: 40 kg.

Average weaning age: 275 days.

Range time to independence: 1 to 3 years.

Range age at sexual or reproductive maturity (female): 3 to 4 years.

Average age at sexual or reproductive maturity (female): 3 years.

Range age at sexual or reproductive maturity (male): 1 to 7 years.

Average age at sexual or reproductive maturity (male): 6 years.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average birth mass: 40000 g.

Average number of offspring: 1.

Males play little to no role in caring for the young, females are solely responsible for caring for the young. Immediately after childbirth, the foal imprints on the mother and can recognize her distinct scent, appearance, and vocalizations. An imprinted foal will directly follow its mother and can recognize the shape of the stripes on its mother's backside. Until it is weaned, a foal will follow its mother and learn to mimic all of her behavior. Female foals become independent from their mothers sooner than male foals, even though both genders are weaned at around the same time. Males often remain with their birth herd until they reach three years of age and females have been known to separate at just 13 months of age.

Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Equus grevyi

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A2ac; C2a(i)

Version
3.1

Year Assessed
2013

Assessor/s
Moehlman, P.D., Rubenstein, D.I. & Kebede, F.

Reviewer/s
Low, B. & Flander, M.

Contributor/s

Justification
Listed as Endangered as Grevy's Zebra is estimated to have declined by more than 50% over the past 18 years based on direct observation and potential/actual levels of exploitation. In addition, the current total population is estimated at 750 mature individuals, with the largest subpopulation estimated at 255 mature individuals.

History
  • 2008
    Endangered
  • 1996
    Endangered
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Endangered
    (IUCN 1990)
  • 1988
    Endangered
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Endangered
    (IUCN Conservation Monitoring Centre 1986)
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Current Listing Status Summary

Status: Threatened
Date Listed: 09/20/1979
Lead Region: Foreign (Region 10) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: T

For most current information and documents related to the conservation status and management of Equus grevyi , see its USFWS Species Profile

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A 5-year conservation plan of the Kenya Wildlife Services (KWS) was launched on June 25, 2008. This conservation plan aims to recover the population of Grevy's zebras, which declined from 15,000 in the 1970s to just over 2,500 in 2009. The plan suggests the need for a monitoring system to estimate the population size of Equus grevyi, to assess its condition, to track movements, and to determine the causes of mortality. In addition to this, local communities in Kenya are getting more involved in the conservation of Equus grevyi and Ethiopa has held two workshops regarding status and conservation. Equus grevyi was previously listed as a game animal in Kenya and is now being upgraded to a protected animal. It is also listed as protected in Ethiopia, although official protection has been limited.

US Federal List: threatened

CITES: appendix i

State of Michigan List: no special status

IUCN Red List of Threatened Species: endangered

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Status

Classified as Endangered (EN) on the IUCN Red List 2007 (1) and listed on Appendix I of CITES (3).
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Population

Population
Current estimates put the total population of Grevy's Zebra remaining in the wild in Kenya and Ethiopia at approximately 1,966 to 2,447 (B. Lowe pers. comm. 2008; F. Kebede pers. comm. 2008). From 1988 to 2007, the global population of Grevy’s Zebra declined approximately 55%. The worse case scenario is a decline from 1980 to 2007 of 68%. The number of mature individuals is approximately 750, and the largest subpopulation is approximately 255 mature individuals.

In Kenya, the Grevy’s Zebra population declined from an estimated 4,276 in 1988 (KREMU 1989) to 2435-2707 in 2000 (Nelson and Williams 2003) to 1567-1976 in 2004 (B. Low pers.comm.) to an estimated population size of 1468-2135 in 2006 (B. Low pers. comm. 2007). In 2007, the population estimate of 1838-2319 indicates that either more individuals were being accurately observed or that the population is stabilizing and increasing (Mwasi and Mwangi 2007). The trend from 1988 to 2006 (18 years) is a decline of 50 to 66%. The data for 2007 indicates a potential increase in the population in Kenya.

In Ethiopia, Grevy’s Zebra declined from an estimated 1,900 in 1980 to 577 in 1995 (Rowen and Ginsberg 1992, F. Kebede pers. comm. 2007), to 106 in 2003 (Williams et al. 2003). In 2006, the population in Ethiopia was estimated to be 128 (F. Kebede pers. comm. 2007). The trend from 1980 to 2003 (23 years) is a decline of roughly 94%. The data for 2006 indicates a potential increase in the population in Ethiopia.

The density and area of occupancy of Grevy’s Zebras fluctuates seasonally as animals move in their search for resources. During the dry season, when they are dependent on permanent water, animals tend to be more concentrated. However, given that they can move up to 35 km from water even during the dry season, their densities are never high. They are most abundant and most easily observed in the southern portion of their range in southern Samburu and the Laikipia Plateau.

Population Trend
Stable
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Threats

Major Threats
The major threats to Grevy's Zebra include: reduction of available water sources; habitat degradation and loss due to overgrazing; competition for resources; hunting; and disease (Rowen and Ginsberg 1992; Williams 2002, 2013).

In Kenya, hunting for skins in the late 1970s may have contributed to the observed decline, although recent data suggest that the continuing decline in this country is attributable to low recruitment due to low juvenile survival. This is a result of competition for resources – both food and access to water – with pastoral people and domestic livestock (Williams 1998). However, a low level of hunting of Grevy’s Zebra for food and, in some areas, medicinal uses continues (Williams 2002, in press). Furthermore, the water supply in critical perennial rivers has declined, most notably in the Ewaso Ng’iro River where over-abstraction of water for irrigation schemes has reduced dry season river flow by 90% over the past three decades (Williams 2002, in press).

In Ethiopia, killing of Grevy’s Zebra is the primary cause of the decline (F. Kebede pers. comm. 2007).

Recently, Muoria et al. (2007) recorded an outbreak of anthrax in the Wamba area of southern Samburu, Kenya, during which more than 50 animals succumbed to the disease.
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Numbers of Grevy's zebra underwent a dramatic decline in the 1970s when the coat became prized on the international fashion circuit (4). Poaching has since declined due to effective protection measures and a lack of demand. Habitat loss is the most potent threat to the survival of the species today; grasslands are cleared to make way for agriculture and zebras also compete with domestic stock for grazing areas and water (4).
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Management

Conservation Actions

Conservation Actions
Listed on CITES Appendix I. Grevy's Zebra are legally protected in Ethiopia, although official protection has been limited. Community-based conservation has been more effective. In Kenya, they have been protected by a hunting ban since 1977. While under the Wildlife Conservation and Management Act No 376 of 1976 (Part II of the First Schedule), Grévy’s Zebra was listed as a ‘Game Animal’ (Williams 2002); they are currently being uplisted to a legally ‘Protected Animal’ in Kenya.

At present, protected areas form less than 0.5% of the range of Grevy’s Zebra. In Ethiopia, the protected areas are nominal (Alledeghi Wildlife Reserve, Yabello Sanctuary, Borana Controlled Hunting Area and Chalbi Sanctuary). In Kenya, the Buffalo Springs, Samburu, Shaba N.R. complex and the private and community land wildlife conservancies in Isiolo, Samburu and the Laikipia Plateau provide a core and crucial protection of Kenya’s southern population of Grevy’s Zebra (Williams 2002). On the Laikipia Plateau, protection and reduced competition with domestic livestock, have seen Grevy's Zebra numbers increasing since they first expanded into this area in the early 1970s (Williams 2002, 2013).

Kenya has recently taken steps to develop a national conservation strategy for Grevy’s Zebras. Ethiopia has held two workshops on the status and conservation of the Grevy’s Zebra. Research and community-based conservation is on-going in the three known population areas.

Williams (2002) highlights several other conservation actions focused on wild populations, involving: 1. Protection of water supplies; 2. Management of protected areas; 3. Community conservation; and 4. Monitoring of numbers in the wild.
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Conservation

Grevy's zebra is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), effectively banning international trade in this species (4). It is protected by law in Ethiopia and by a hunting ban in Kenya (7). This rare species also occurs in protected reserves throughout much of its current range (7), such as in Lewa Wildlife Conservancy in Kenya, which currently holds 425 individuals, representing 20 percent of the world's total population (8).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Equus grevyi may sometimes compete with domesticated cattle for resources on grazing lands.

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Economic Importance for Humans: Positive

Grevy's zebras have a distinct appearance and are a source of ecotourism interest. Grevy's zebras have been used as food and a source of pelts in the past.

Positive Impacts: body parts are source of valuable material; ecotourism

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Wikipedia

Grévy's zebra

The Grévy's zebra (Equus grevyi), also known as the imperial zebra, is the largest extant wild equid and the largest and most endangered of the three species of zebra, the other two being the plains zebra and the mountain zebra. Named after Jules Grévy, it is the sole extant member of the subgenus Dolichohippus. The Grévy's zebra is found in Kenya and Ethiopia. Compared with other zebras, it is tall, has large ears, and its stripes are narrower.

The Grévy's zebra lives in semi-arid grasslands where it feeds on grasses, legumes, and browse; it can survive up to five days without water. It differs from the other zebra species in that it does not live in harems and has few long-lasting social bonds. Male territoriality and mother–foal relationships form the basis of the social system of the Grévy's zebra. This zebra is considered to be endangered. Its population has declined from 15,000 to 3,000 since the 1970s. However, as of 2008 the population is stable.

Taxonomy and naming[edit]

The Grévy's zebra was first described by English naturalist Émile Oustalet in 1882. He named it after Jules Grévy, then president of France, who, in the 1880s, was given one by the government of Abyssinia. It is the only extant species of the subgenus Dolichohippus. The plains zebra and mountain zebra belong to Hippotigris. Fossils of Dolichohippus zebras have been found throughout Africa and Asia in the Pliocene and Pleistocene deposits.[3] Notable examples include E. sanmeniensis from China, E. cautleyi from India, E. valeriani from central Asia and E. oldowayensis from East Africa.[3] The latter, in particular is very similar to the Grévy's zebra and may have been its ancestor.[3]

The modern Grévy's zebra arose in the early Pleistocene.[3] A 2009 phylogenetic study suggests that Grevy's zebras are with asses and donkeys in a lineage separate from plains zebras, but perhaps not from mountain zebras.[4] In areas where Grévy's zebras are sympatric with plains zebras, the two may gather in same herds[5] and fertile hybrids do occur.[6]

Description[edit]

Detail of head
From left to right: a cranium, a complete skeleton, a left forefoot frontal, and a left forefoot lateral from a Grévy's zebra.

The Grévy's zebra is the largest of all wild equines. It is 2.5–3 m (8–9.8 ft) from head to tail with a 38–75 cm (15–30 in) tail, and stands 1.45–1.60 m (4'7"–5'3"; 13 to 16 hands) high at the shoulder. These zebras weigh 350–450 kg (770–990 lb).[5][7] Grévy's zebra differs from the other two zebras in its more primitive characteristics.[8]:147 It is particularly mule-like in appearance; the head is large, long, and narrow with elongated nostril openings;[8]:147 the ears are very large, rounded, and conical and the neck is short but thick.[9] The zebra's muzzle is ash-grey to black in color with the lips having whiskers. The mane is tall and erect; juveniles have a mane that extends to the length of the back and shortens as they reach adulthood.[9]

As with all zebra species, the Grevy's zebra's pelage has a black and white striping pattern. The stripes are narrow and close-set, being broader on the neck, and they extend to the hooves.[9] The belly and the area around the base of the tail lack stripes which is unique to the Grevy's zebra. Foals are born with brown and white striping, with the brown stripes darkening as they grow older.[9] Embryological evidence has shown that the zebra's background color is dark and the white is an addition.[3] The stripes of the zebra may serve to make it look bigger than it actually is or disrupt its outline. It appears that a stationary zebra can be inconspicuous at night or in shade.[9] Experiments have suggested that the stripes polarize light in such a way that it discourages biting horse-flies in a manner not shown with other coat patterns.[10] Other studies suggest that when moving the stripes may confuse observers, such as mammalian predators and biting insects, via two visual illusions, the wagon wheel effect, where the perceived motion is inverted, and the barber pole illusion, where the perceived motion is in a wrong direction.[11]

Ecology and behavior[edit]

Zebra in dense brush

The Grévy’s zebra largely inhabits northern Kenya, with some isolated populations in Ethiopia.[8]:147[9] It was extirpated from Somalia and Djibouti and its status in South Sudan is uncertain.[2] It lives in Acacia-Commiphora bushlands and barren plains.[5] Ecologically, this species is intermediate between the arid-living African wild ass and the water-dependent plains zebra.[8]:147[5] Lactating females and non-territorial males use areas with green, short grass and medium, dense bush more often than non-lactating females and territorial males.[12]

Grévy's zebras rely on grasses, legumes, and browse for nutrition.[9] They commonly browse when grasses are not plentiful.[5][13] Their hindgut fermentation digestive system allows them to subsist on diets of lower nutritional quality than that necessary for ruminant herbivores. Grevy's zebras can survive up to five days without water, but will drink daily when it is plentiful.[14] They often migrate to better watered highlands during the dry season.[5] Females require significantly more water when they are lactating.[15] During droughts, the zebras will dig water holes and defend them.[5] Grévy's zebras are preyed on by lions, hyenas, wild dogs, cheetahs and leopards.[9] In addition, they are susceptible to various gastro-intestinal parasites, notably of the Trichostrongylus genus.[16]

Herd of zebras

Adult males mostly live in territories during the wet seasons but some may stay in them year round if there's enough water left.[5] Stallions that are unable to establish territories are free-ranging[8]:151 and are known as bachelors. Females, young and non-territorial males wander through large home ranges. The females will wander from territory to territory preferring the ones with the highest-quality food and water sources.[17] Up to nine males may compete for a female outside of a territory.[9]

Territorial stallions will tolerate other stallions who wander in their territory, however when an estrous female is present the territorial stallion keeps other males at bay.[5][8]:151 Non-territorial males may avoid territorial ones because of harassment.[12] When females are not around, a territorial stallion will seek the company of other stallions. The stallion shows his dominance with an arched neck and a high-stepping gait and the least dominant stallions submit by extending their tail, lowering their heads and nuzzling their superior's chest or groin.[8]:151 The call of the Grévy's zebra has been described as "something like a hippo's grunt combined with a donkey's wheeze".[5] To get rid of flies or parasites, they roll in dust, water or mud or, in the case of flies, twitch their skin. They also rub against trees, rocks and other objects to get rid of irritations like itchy skin, hair or parasites.[9] Although Grévy's zebras do not perform mutual grooming, they do sometimes rub against a conspecific.[9]

Reproduction[edit]

Zebra foal resting

Grévy's zebras can mate and give birth year-round, but most mating takes place in the early rainy seasons and births mostly take place in August or September after the long rains.[9] An estrous mare may visit though as many as four territories a day[17] and will mate with the stallions in them. Among territorial stallions, the most dominant ones control territories near water sources, which mostly attract mares with dependant foals,[18] while more subordinate stallions control territories away from water with greater amounts of vegetation, which mostly attract mares without dependant foals.[18]

Mother zebra with foals

The resident stallions of territories will try to subdue the entering mares with dominance rituals and then continue with courtship and copulation.[5] Grévy's zebra stallions have large testicles and can ejaculate a large amount of semen to replace the sperm of other males.[17] This is a useful adaptation for a species whose females mate polyandrously. Bachelors or outside territorial stallions sometimes "sneak" copulation of mares in another stallion’s territory.[17] While female associations with individual males are brief and mating is promiscuous, females who have just given birth will reside with one male for long periods and mate exclusively with that male.[17] Lactating females are harassed by males more often than non-lactating ones and thus associating with one male and his territory provides an advantage as he will guard against other males.[19]

Gestation of the Grévy's zebra normally lasts 390 days,[9] with a single foal being born. A newborn zebra will follow anything that moves, so new mothers prevent other mares from approaching their foals while imprinting their own striping pattern, scent and vocalization on them.[9] Females with young foals may gather into small groups.[15] Mares may leave their foals in "kindergartens" while searching for water.[15] The foals will not hide, so they can be vulnerable to predators.[5] However, kindergartens tend to be protected by an adult, usually a territorial male.[15] A female with a foal stays with one dominant territorial male who has exclusive mating rights to her. While the foal will not likely be his, the stallion will look after it to ensure that the female stays in his territory.[20] To adapt to a semi-arid environment, Grévy's zebra foals have longer nursing intervals and wait until they are 3 months of age before they start drinking water.[15] Although foals became less dependant on their mothers after half a year, associations with them continue for up to three years.[5]

Relationship with humans[edit]

Drawing of the zebra given to Jules Grévy and kept at the Ménagerie du Jardin des Plantes in 1882

The Grévy's zebra was known to the Europeans in antiquity and was used by the Romans in circuses.[3] It was subsequently forgotten in the Western world for a thousand years.[3] In the seventeenth century, the king of Shoa (now central Ethiopia) exported two zebras; one to the Sultan of Turkey and another to the Dutch governor of Jakarta.[3] A century later in 1882, the government of Abyssinia sent one to French president Jules Grévy. It was at that time that the animal was recognized as its own species and named in Grévy’s honor.[3]

Status and conservation[edit]

Grevy's zebras in Samburu National Reserve

The Grévy's zebra is considered endangered.[2] Its population was estimated to be 15,000 in the 1970s and by the early 21st century the population was lower than 3,500, a 75% decline.[21]:11 It is estimated that there are less than 2,500 Grévy's zebras still living in the wild.[2] There are also an estimated 600 Grévy's zebras in captivity.[21]:20 Captive herds have been known to thrive, like at White Oak Conservation in Yulee, Florida, United States, where more than 70 foals have been born. There, research is underway in partnership with the Conservation Centers for Species Survival on semen collection and freezing and on artificial insemination.[22] The Grévy's zebra population trend is considered stable as of 2008.[2]

The Grévy's zebra is legally protected in Ethiopia. In Kenya it is protected by the hunting ban of 1977. In the past, Grévy's zebras were threatened mainly by hunting for their skins which fetched a high price on the world market. However hunting has declined and the main threat to the zebra is habitat loss and competition with livestock. Cattle gather around watering holes and the Grévy's zebras are fenced from those areas.[21]:17 Community-based conservation efforts have shown to the most effective in preserving Grévy's zebras and their habitat. Less than 0.5% of the range of the Grévy's zebra is in protected areas. In Ethiopia, the protected areas include Alledeghi Wildlife Reserve, Yabelo Wildlife Sanctuary, Borana Controlled Hunting Area and Chalbi Sanctuary. In Kenya, important protected areas include the Buffalo Springs, Samburu and Shaba National Reserves and the private and community land wildlife conservancies in Isiolo, Samburu and the Laikipia Plateau.[2]

References[edit]

  1. ^ Grubb, P. (2005). "Order Perissodactyla". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 631–632. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  2. ^ a b c d e f Moehlman, P.D., Rubenstein, D.I. & Kebede, F. (2008). Equus grevyi. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 10 April 2009. Database entry includes a brief justification of why this species is endangered.
  3. ^ a b c d e f g h i Prothero D.R, Schoch R. M (2003). Horns, Tusks, and Flippers: The Evolution of Hoofed Mammals'. Johns Hopkins University Press. pp. 216–18. ISBN 0-801-87135-2. 
  4. ^ Orlando, Ludovic; et al. (2009). "Revising the recent evolutionary history of equids using ancient DNA". PNAS 106: 21754–21759. doi:10.1073/pnas.0903672106. PMC 2799835. PMID 20007379. 
  5. ^ a b c d e f g h i j k l m Estes, R. (1991). The Behavior Guide to African Mammals. University of California Press. pp. 240–242. ISBN 0-520-08085-8. 
  6. ^ J. E. Cordingley, S. R. Sundaresan, I. R. Fischhoff, B. Shapiro, J. Ruskey, D. I. Rubenstein (2009). "Is the endangered Grevy's zebra threatened by hybridization?". Animal Conservation 12 (6): 505–13. doi:10.1111/j.1469-1795.2009.00294.x. 
  7. ^ Burnie, D.; Wilson, D., eds. (October 2005). Animal: The Definitive Visual Guide to the World's Wildlife. Dorling Kindersley. p. 227. ISBN 978-0-7566-1634-2. 
  8. ^ a b c d e f g Kingdon, J. (1988). East African Mammals: An Atlas of Evolution in Africa, Volume 3, Part B: Large Mammals. University of Chicago Press. pp. 147–61. ISBN 9780226437224. 
  9. ^ a b c d e f g h i j k l m n Churcher C.S. (1993). "Equus grevyi". Mammalian Species 453: 1–9. doi:10.2307/3504222. 
  10. ^ Egri, Ádám; Blahó, Miklós; Kriska, György; Farkas, Róbert; Gyurkovszky, Mónika; Åkesson, Susanne; Horváth, Gábor (2012). "Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes". J Exp Biol 215: 736–745. doi:10.1242/jeb.065540. 
  11. ^ How, Martin J.; Zanker, Johannes M. (2014). "Motion camouflage induced by zebra stripes". Zoology: TBA. doi:10.1016/j.zool.2013.10.004. 
  12. ^ a b Sundaresan, S.; I. Fischhoff, H. Hartung, P. Akilong, D. Rubenstein. (2008). "Habitat choice of Grevy’s zebras (Equus grevyi) in Laikipia, Kenya". African Journal of Ecology 46 (3): 359–64. doi:10.1111/j.1365-2028.2007.00848.x. 
  13. ^ Bauer, I. E., McMorrow, J. and Yalden, D. W. (1994). "The Historic Ranges of Three Equid Species in North-East Africa: A Quantitative Comparison of Environmental Tolerances". Journal of Biogeography 21 (2): 169–182. JSTOR 2845470. 
  14. ^ Youth H (2004). "Thin Stripes on a Thin Line". ZooGoer. 33: 6. 
  15. ^ a b c d e Becker, C. D.; Ginsberg, J. R. (1990). "Mother-infant Behaviour of Wild Grevy's Zebra". Animal Behavior 40 (6): 1111–1118. doi:10.1016/S0003-3472(05)80177-0. 
  16. ^ Muoria. P. K., Muruthi. P, Rubenstein. D, Oguge N. O, Munene E. (2005). "Cross-sectional survey of gastro-intestinal parasites of Grevy's zebras in southern Samburu, Kenya". African Journal of Ecology 43 (4): 392–95. doi:10.1111/j.1365-2028.2005.00588.x. 
  17. ^ a b c d e Ginsberg, R., D. I. Rubenstein (1990). "Sperm competition and variation in zebra mating behavior". Behavioral Ecology and Sociobiology 26 (6): 427–34. doi:10.1007/BF00170901. 
  18. ^ a b Rubenstein, D. I. (2010) "Ecology, social behavior, and conservation in zebras". Pp. 231-58. In: Advances in the Study Behavior: Behavioral Ecology of Tropical Animals, Vol. 42. R. Macedo, ed. Elsevier Press. ISBN 0123808944
  19. ^ Sundaresan, S., I. Fischhoff, D. Rubenstein. (2007). "Male harassment influences female movements and associations in Grevys zebra (Equus grevyi)". Behavioral Ecology 18 (5): 860–65. doi:10.1093/beheco/arm055. 
  20. ^ Rubenstein, D. I. (1986) "Ecology and sociality in horses and zebras". Pp. 282-302. In: Ecological Aspects of Social Evolution. D. I. Rubenstein & R. W. Wrangham, (eds.). Princeton University Press, ISBN 0691084394
  21. ^ a b c Moelman, P.D (2002). "Status and Action Plan for the Grévy's Zebra (Equus grevyi) by Stuart D. Williams". Equids. Zebras, Assess and Horses. Status Survey and Conservation Action Plan'. IUCN/SSC Equid Specialist Group. pp. 11–27. ISBN 2-831-70647-5. 
  22. ^ "Grevy's Zebra". Retrieved 21 June 2013. 
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