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Equus grevyiGrevy's zebra

By Alexis J. Hollingshead

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. ("Grevy's Zebra", 2004; "Grevy's Zebra Trust: Endangered Species", 2007; "Grevy's Zebra", 2004; Churcher, 1993; "Grevy's Zebra", 1999; "Equus Grevyi", 2003)

Habitat

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. ("Grevy's Zebra Trust: Endangered Species", 2007; "Grevy's Zebra", 2004; Cordingley, et al., 2009; "Grevy's Zebra", 1999; Sundaresan, et al., 2008)

  • Range elevation
    300 to 600 m
    984.25 to 1968.50 ft
  • Average elevation
    500 m
    1640.42 ft

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. ("Grevy's Zebra Trust: Endangered Species", 2007; "Grevy's Zebra", 2004; Churcher, 1993; "Grevy's Zebra", 1999)

  • Sexual Dimorphism
  • male larger
  • Range mass
    349 to 451 kg
    768.72 to 993.39 lb
  • Range length
    125 to 150 cm
    49.21 to 59.06 in
  • Average length
    135 cm
    53.15 in

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. (Churcher, 1993; Ginsberg and Rubenstein, 1990)

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. ("Grevy's Zebra Trust: Endangered Species", 2007; "Grevy's Zebra", 2004; Churcher, 1993; "Grevy's Zebra", 1999)

  • 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
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    358 to 438 days
  • Average gestation period
    390 days
  • 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

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

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. (Churcher, 1993)

  • 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

Behavior

Grevy's zebras are different from most other members of the genus Equus in that they do not have concrete social structure. They are loosely social animals; herd composition can vary on a daily basis as new members enter a dominant male's territory and old members leave. The two most stable relationships that Grevy's zebras have are a stallion's attachment to his territory and a mare's attachment to her young. There is not a rigorously observed hierarchy of dominance within a group of Grevy's zebras, although a dominance structure is present. A territorial male has the right to breeding females in that territory. In the absence of females, males will associate in bachelor herds with a loose dominance structure. Males are territorial and claim prime watering and grazing areas. These territories can get up to 6 square kilometers in size. Males mark their territories with piles of dung, called "middens," and emit loud vocalizations that let other zebras know they're present. A territorial male may retain his territory for a period of 7 years before a younger, stronger male challenges him for it. Grevy's zebra males are solitary in their territories, except when females arrive in breeding season. Bachelor males, or non-territorial males, travel together in groups of 2 to 6. This social system is different from other zebras, which form female harems in a single male's territory all year. During droughts, some Grevy's zebras migrate to mountain pastures where food sources are more abundant, but territorial males often remain on their territories year-round.

Lactating females have different resource requirements than non-lactating females. When females are lactating, they need water at least every other day, so male zebras in territories with large, safe bodies of water in them usually get the opportunity to mate with more females. Lactating females have more restricted movements and fewer male associates than non-lactating females. It is possible that male harassment also influences female distribution and associations with males. Lactating females experience higher harassment rates from males than non-lactating females and tend to move faster during harassment periods ("Grevy's Zebra Trust: Endangered Species", 2007; "Grevy's Zebra", 2004; "Grevy's Zebra", 1999; Sundaresan, et al., 2007)

  • Range territory size
    2 to 12 km^2
  • Average territory size
    6 km^2

Home Range

Territorial males have territories of as little as 2 square kilometers and as much as 12 square kilometers, although the average territory is 6 square kilometers. The home range size of non-territorial zebras is sometimes as great as 10,000 square kilometers. Grevy's zebras are extremely mobile and some individuals have been known to move distances of greater than 80 kilometers. ("Grevy's Zebra", 2004; Sundaresan, et al., 2007)

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. ("Grevy's Zebra Trust: Endangered Species", 2007; "Grevy's Zebra", 2004; Churcher, 1993)

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. ("Grevy's Zebra Trust: Endangered Species", 2007; "Grevy's Zebra", 1999)

  • Plant Foods
  • leaves

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. ("Grevy's Zebra Trust: Endangered Species", 2007; Churcher, 1993)

  • Anti-predator Adaptations
  • cryptic

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. ("Grevy's Zebra", 2004; Churcher, 1993)

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

Economic Importance for Humans: Negative

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

Conservation Status

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. (Low, et al., 2009; Moehlman, et al., 2009; Muoria, et al., 2009)

Other Comments

Equus grevyi individuals can run at speeds of up to 40 mph (64 kph). ("Grevy's Zebra", 2004)

Contributors

Alexis J. Hollingshead (author), Case Western Reserve University, Darin Croft (editor, instructor), Case Western Reserve University, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

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

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

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.

folivore

an animal that mainly eats leaves.

herbivore

An animal that eats mainly plants or parts of plants.

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).

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

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

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

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

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.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

The Wild Classroom. 2003. "Equus Grevyi" (On-line). Biomes of the World. Accessed November 15, 2009 at http://www.thewildclassroom.com/biomes/speciesprofile/savanna/grevyszebra.html.

2007. "Grevy's Zebra Trust: Endangered Species" (On-line). Grevy's Zebra Trust. Accessed November 15, 2009 at http://www.grevyszebratrust.org/.

American Wildlife Foundation. 2004. "Grevy's Zebra" (On-line). American Wildlife Foundation. Accessed November 15, 2009 at http://www.awf.org/content/wildlife/detail/grevyszebra.

Friends of the National Zoo. 1999. "Grevy's Zebra" (On-line). Smithsonian National Zoological Park. Accessed November 15, 2009 at http://nationalzoo.si.edu/Animals/AfricanSavanna/fact-gzebra.cfm.

Churcher, C. 1993. Mammalian Species. American Society of Mammalogists, 453: 1-9. Accessed November 10, 2009 at http://www.jstor.org/stable/3504222.

Cordingley, J., S. Sundaresan, I. Fischhoff, B. Shapiro, J. Ruskey. 2009. Is the endangered Grevy's zebra threatened by hybridization?. Animal Conservation, Vol. 12 Issue 6: 505-513. Accessed December 01, 2009 at http://search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=45231153&site=ehost-live.

Ginsberg, J., D. Rubenstein. 1990. Sperm Competition and Variation in Zebra Mating Behavior. Behavioral Ecology and Sociobiology, Vol. 26: 427-434. Accessed November 10, 2009 at http://www.jstor.org/stable/4600432.

Low, B., S. Sundaresan, I. Fischhoff, D. Rubenstein. 2009. Partnering with local communities to identify conservation priorities for endangered Grevy’s zebra. Biological Conservation, Vol. 142 Issue 7: 1548-1555. Accessed November 10, 2009 at http://search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=38806267&site=ehost-live.

Moehlman, P., D. Rubenstein, F. Kebede. 2009. "IUCN Redlist of Threatened Species" (On-line). IUCN Redlist. Accessed November 23, 2009 at www.iucnredlist.org.

Muoria, P., P. Muruthi, P. Omondi, C. Mutua, J. Bernard, N. Oguge, J. King. 2009. Kenya launches national strategy to conserve Grevy's zebra.. Oryx, Vol. 43 Issue 2: 271-272. Accessed November 10, 2009 at http://search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=39795368&site=ehost-live.

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, Vol. 46 Issue 3: 359-364. Accessed November 10, 2009 at http://search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=34038297&site=ehost-live.

Sundaresan, S., I. Fischhoff, D. Rubenstein. 2007. Male harassment influences female movements and associations in Grevys zebra (Equus grevyi).. Behavioral Ecology, Vol. 18 Issue 5: 860. Accessed November 10, 2009 at http://search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=26420265&site=ehost-live.

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