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Zebras

Zebras

The common zebra

Mountain zebras

Grevys zebra

Resources

Zebras are members of the horse family (Equidae) that inhabit tropical grasslands (savannas) in much of sub Saharan Africa. Three of the seven species of equids are zebras. Zebras are herd-living, social ungulates (hoofed mammals) recognized by a black-and-white (or cream or yellowish) striped coat, short erect mane, and a tail averaging about 18 in (0.5 m) long. The body length of a zebra is about 6-8.5 ft (2-2.6 m) long, and body weight can reach 770 lb (350 kg), with males slightly bigger than females.

There are three species and several subspecies of zebra. The common, Burchells, or plains zebra (E. burchelli) lives throughout much of eastern and southern Africa, and is the best-studied species. Grevys zebra (Equus grevyi) is found in Somalia, Kenya, and Ethiopia, and is the largest of the wild horses, characterized by large ears, narrow stripes, and a thick neck. The third species is the mountain zebra (E. zebra) found in the hill country of Angola, Namibia, and western South Africa.

The stripes of the zebra camouflage the animal in the waving grasses of the African grasslands, especially at dusk and dawn. Zebras rest in herds in open ground where they can see predators approaching, rather than lying down in the grass. When a herd of zebras is being chased by predators such as lions or hyenas, their stripes make it difficult for predators to visually latch on to a specific animal to attack. Other suggestions are that the stripes identify individual zebras as part of a group and also initiates mating behavior.

The common zebra

The common or Burchells zebra stands about 50-52 in (1.3 m) tall at the shoulder. It has the widest stripes of all zebras, and the stripes continue down to the belly of the animal. The stripes of Burchells zebra become fainter and almost disappear in southern populations.

There are several subspecies of the common zebra, distinguishable by the pattern of stripes on the rump. Grants zebra (E. burchelli granti) has wide rump stripes, the Chapmanns or Damaraland zebra has tan shadow stripes between the black stripes, and Selouss zebra has only faint shadow stripes between the black stripes. A subspecies known as the true Burchellis zebra had reddish brown stripes, and became extinct in the early 1900s.

Herds of common plains zebras are actually a collection of family groups. Each family group is headed by a dominant male stallion, and one female is dominant over the other seven or eight females and their young. When the group is feeding or drinking, one animal stands guard. If a predator approaches, such as a troop of wild dogs or lions, the stallion zebra moves to the back of the fleeing herd and ensures that no single animal falls behind or gets separated and becomes vulnerable to attack. Zebras that become isolated call attention to their plight by making a harsh sound like a combination bark and bray, which draws the other zebras back to protect it.

The zebras large, rounded ears turn in every direction and are able to pick up the slightest sound. The zebras primary defense is running, which it can do at speeds approaching 40 mph (64 kph), though for only a short time. Given the chance, a zebra fights primarily by kicking with its hind hooves. However, an attacking predator is likely to grasp the animals neck with one quick leap that prevents the zebra from acting.

After a young mare mates for the first time, she will stay with the same family group for the rest of her life. Males that have not yet developed herdsor that have been ousted from their herds by other males live in male-only bands (bachelor herds), which they leave to find mates at about six years old. If stallions try to take mares from an existing family group, they will have to fight that groups stallion.

Gestation lasts approximately one year, with only one off spring produced. The young are born with disproportionately long legs and are ready to run with the herd within a few minutes. The brown-striped coat of a new foal gradually changes to the familiar black and white.

Mountain zebras

There are two subspecies of mountain zebras in South Africa which live on rough, rocky highlands, but once also occurred in large numbers in the grassy lowland plains. The Cape mountain zebra of South Africa is the smallest zebra, standing about 4 ft (1.2 m) at the shoulder and weighing about 600 lb (272 kg). The stripes of the Cape mountain zebra are slightly wider and shorter than those of the other subspecies, Hartmanns mountain zebra of Namibia. The Cape mountain zebra has a dewlap under the lower jaw, which other zebras do not have.

Herds of the common zebra readily mix with herds of wildebeest, but Cape mountain zebras tend to keep apart from other animals. Hartmanns zebras have the ability to locate water in apparently dry valleys.

Grevys zebra

Grevys zebra is quite different in both appearance and behavior from the common zebra. It stands about 5 ft (1.5 m) tall at the shoulder and weighs about 990 lb (450 kg). Its stripes are very narrow, do not cross over the lower back as they do in the Cape mountain zebra.

Grevys zebras live in semidesert country and do not form herds. Instead, only the mother and foals remain together, while the males and the young females drift off. Individual stallions have remarkably large breeding territories, and any female found within the territory belongs to the male. A stallion will tolerate other males in his territory only if they do not try to mate with the mares. The gestation period of the Grevys zebra is about 13 months, one month longer than other species of zebra.

The recently extinct zebra-like quagga (E. quagga) looked like a combination of wild ass and zebra and had a reddish coat and stripes only on the head, neck, and shoulders. The name quagga is derived from the odd bray of this species, which was described as kwa-ha. The quagga lived throughout South Africa but was killed by nineteenth-century settlers for its meat and hides. The last quagga died in an Amsterdam zoo in 1883.

KEY TERMS

Dewlap A loose fold of skin that hangs from the neck.

Equid Any member of family Equidae, including horses, zebras, and asses.

Gestation The period of carrying developing off spring in the uterus after conception; pregnancy.

The populations of the common zebra are high, especially in the Serengeti Plains of Tanzania and Kenya, where zebras run with the huge wildebeest herds on their annual migrations.

Grevys zebra and the Cape mountain zebra are both endangered. As of 2003, there were from 3,000 to 3,500 Grevys zebras in Ethiopia, Somalia, and Kenya, in three separate populations. A major herd of Grevys zebra is protected in a game reserve in Kenya. There are about 1,200 Cape mountain zebras, most of which live in Mountain Zebra National Park in South Africa.

Resources

BOOKS

MacDonald, David, and Sasha Norris, eds. Encyclopedia of Mammals. New York: Facts on File, 2001.

Moehlman, P.D., ed. Equids: Zebras, Asses and Horses. Status Survey and Conservation Action Plan. Gland, Switzerland: IUCN, 2002.

Nowak, Ronald M. Walkers Mammals of the World. 6th ed. Baltimore: The Johns Hopkins University Press, 1999.

Wilson, D.E., and D. Reeder. Mammal Species of the World. 3rd ed. Baltimore: Johns Hopkins University Press, 2005.

OTHER

IUCN/SSC Equid Specialist Group. Species Profiles. <http://www.iucn.org/themes/ssc/sgs/equid/Spp.html> (accessed October 5, 2006).

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Zebras

Zebras


Zebras are striped members of the horse family (Equidae ) native to Africa. These grazing animals stand 45 ft (1.21.5 m) high at the shoulders and are distinctive because of their striking white and black or dark brown stripes running alternately throughout their bodies. These stripes actually have important survival value for zebras, for when they are in a herd, the stripes tend to blend together in the bright African sunlight, making it hard for a lion or other predator to concentrate on a single individual and bring it down.

The zebra's best defense is flight, and it can outrun most of its enemies. It is thus most comfortable grazing and browsing in groups on the flat open plains and grasslands . Zebras are often seen standing in circles, their tails swishing away flies, each one facing in a different direction, alert for lions or other predators hiding in the tall grass.

Most zebras live on the grassy plains of East Africa, but some are found in mountainous areas. They live in small groups led by a stallion, and mares normally give birth to a colt every spring. Zebras are fierce fighters, and a kick can kill or cripple predators (lions, leopards, cheetahs, jackals, hyenas, and wild dogs). These predators usually pursue newborn zebras, or those that are weak, sick, injured, crippled, or very old, as those are the easiest and safest to catch and kill. Such predation helps keep the gene pool strong and healthy by eliminating the weak and diseased and ensuring the "survival of the fittest."

Zebras are extremely difficult to domesticate, and most attempts to do so have failed. They are often found grazing with wildebeest, hartebeest, and gazelle, since they all have separate nutritional requirements and do not compete with each other. Zebras prefer the coarse, flowering top layer of grasses, which are high in cellulose. Their trampling and grazing are helpful to the smaller wildebeest, who eat the leafy middle layer of grass that is higher in protein. And the small gazelles feed on the protein-rich young grass, shoots, and herb blossoms found closest to the ground.

One of the most famous African wildlife events is the seasonal 800-mi (1,287-km) migration in May and November of over a million zebras, wildebeest, and gazelles, sweeping across the Serengeti plains, as they have done for centuries, "in tides that flow as far as the eye can see." But it is now questionable how much longer such scenes will continue to take place.

Zebras were once widespread throughout southern and east Africa, from southern Egypt to Capetown. But hunting for sport, meat, and hides has greatly reduced the zebra's range and numbers, though it is still relatively numerous in the parks of East Africa. One species , once found in South Africa, the quagga (Equus quagga quagga ) is already extinct, wiped out by colonists in search of hides to make grain sacks.

Several other species of zebra are threatened or endangered, such as Grevy's zebra (Equus grevyi ) in Kenya, Ethiopia, and Somalia; Hartmann's mountain zebra (Equus zebra hartmannae ) in Angola and Namibia; and the mountain zebra (Equus zebra zebra ) in South Africa. The Cape mountain zebra has adapted to life on sheer mountain slopes and ravines where usually only wild goats and sheep can survive. In 1964, only about 25 mountain zebra could be found in the area, but after two decades of protection, the population had increased to several hundred in Cradock National Park in the Cape Province's Great Karroo area.

Probably the biggest long-term threat to the survival of the zebra is the exploding human population of Africa, which is growing so rapidly that it is crowding out the wildlife and intruding on the continent's parks and refuges. Political instability and the proliferation of high powered rifles in many countries also represent a threat to the survival of Africa's wildlife.

[Lewis G. Regenstein ]


RESOURCES

PERIODICALS


D'Alessio, V. "Born-Again Quagga Defies Extinction." New Scientist 132 (November 30, 1991): 14.

Grubb, P. "Equus burchelli." Mammalian Species no. 157, 1981.

Miller, J. A. "Telling a Quagga By Its Stripes." Science News 128 (August 3, 1985): 70.

Penzhorn, B. L. "Equus zebra." Mammalian Species no. 314, 1988.

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