Zebra

For other uses, see Zebra (disambiguation).

Zebras
Plains zebra (Equus quagga)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Equidae
Genus:	Equus
Subgenus:	Hippotigris and Dolichohippus
Species
Equus zebra Equus quagga Equus grevyi See here for subspecies.

Zebras (/ˈzɛbrə/ ZEB-rə or /ˈziːbrə/ ZEE-brə) are several species of African equids (horse family) united by their distinctive black and white stripes. Their stripes come in different patterns, unique to each individual. They are generally social animals that live in small harems to large herds. Unlike their closest relatives, horses and asses, zebras have never been truly domesticated.

There are three species of zebras: the plains zebra, the Grévy's zebra and the mountain zebra. The plains zebra and the mountain zebra belong to the subgenus Hippotigris, but Grévy's zebra is the sole species of subgenus Dolichohippus. The latter resembles an ass, to which it is closely related, while the former two are more horse-like. All three belong to the genus Equus, along with other living equids.

The unique stripes of zebras make them one of the animals most familiar to people. They occur in a variety of habitats, such as grasslands, savannas, woodlands, thorny scrublands, mountains, and coastal hills. However, various anthropogenic factors have had a severe impact on zebra populations, in particular hunting for skins and habitat destruction. Grévy's zebra and the mountain zebra are endangered. While plains zebras are much more plentiful, one subspecies, the quagga, became extinct in the late 19th century – though there is currently a plan, called the Quagga Project, that aims to breed zebras that are phenotypically similar to the quagga in a process called breeding back.

Etymology

Zebra in English dates back to c.1600, from Italian Zebra, perhaps from Portuguese, which in turn is said to be Congolese (as stated in the Oxford English Dictionary). The Encarta Dictionary says its ultimate origin is uncertain, but perhaps it may come from Latin Equiferus meaning "Wild horse," from equus "horse" and ferus "wild, untamed".

Taxonomy and evolution

See also: Horse evolution

Zebras in Mikumi, Tanzania

Zebras evolved among the Old World horses within the last 4 million years. Grévy's zebras (and perhaps also Mountain Zebras) are, together with asses and donkeys, in a separate lineage from other zebra lineages. This means either that striped equids evolved more than once, or that common ancestors of zebras and asses were striped and only zebras retained the stripes. Extensive stripes are posited to have been of little use to equids that live in low densities in deserts (like asses and some horses) or ones that live in colder climates with shaggy coats and annual shading (like some horses).

Fossils of an ancient equid were discovered in the Hagerman Fossil Beds National Monument in Hagerman, Idaho. It was named the Hagerman horse with a scientific name of Equus simplicidens. It is believed to have been similar to the Grévy's zebra. The animals had stocky zebra-like bodies and short, narrow, donkey-like skulls. Grévy's zebra also has a donkeylike skull. The Hagerman horse is also called the American zebra or Hagerman zebra.

Classification

Zebras in Botswana

There are three extant species. Collectively, two of the species have eight subspecies (seven extant). Zebra populations are diverse, and the relationships between, and the taxonomic status of, several of the subspecies are not well known.

• Genus: Equus
  • Subgenus: Hippotigris
    • Plains zebra, Equus quagga
      • Quagga, Equus quagga quagga (extinct)
      • Burchell's zebra, Equus quagga burchellii (includes Damara Zebra)
      • Grant's zebra, Equus quagga boehmi
      • Selous' zebra, Equus quagga borensis
      • Chapman's zebra, Equus quagga chapmani
      • Crawshay's zebra, Equus quagga crawshayi
    • Mountain zebra, Equus zebra
      • Cape mountain zebra, Equus zebra zebra
      • Hartmann's mountain zebra, Equus zebra hartmannae
  • Subgenus: Dolichohippus
    • Grévy's zebra, Equus grevyi

An albino zebra in captivity

The plains zebra (Equus quagga, formerly Equus burchelli) is the most common, and has or had about six subspecies distributed across much of southern and eastern Africa. It, or particular subspecies of it, have also been known as the common zebra, the dauw, Burchell's zebra (actually the subspecies Equus quagga burchellii), Chapman's zebra, Wahlberg's zebra, Selous' zebra, Grant's zebra, Boehm's zebra and the quagga (another extinct subspecies, Equus quagga quagga).

The mountain zebra (Equus zebra) of southwest Africa tends to have a sleek coat with a white belly and narrower stripes than the plains Zebra. It has two subspecies and is classified as vulnerable.

Grévy's zebra (Equus grevyi) is the largest type, with a long, narrow head, making it appear rather mule-like. It is an inhabitant of the semi-arid grasslands of Ethiopia and northern Kenya. Grévy's zebra is the rarest species, and is classified as endangered.

Although zebra species may have overlapping ranges, they do not interbreed. In captivity, plains zebras have been crossed with mountain zebras. The hybrid foals lacked a dewlap and resembled the plains zebra apart from their larger ears and their hindquarters pattern. Attempts to breed a Grévy's zebra stallion to mountain zebra mares resulted in a high rate of miscarriage. In captivity, crosses between zebras and other (non-zebra) equines have produced several distinct hybrids, including the zebroid, zeedonk, zony, and zorse. In certain regions of Kenya, plains zebras and Grévy's Zebra coexist, and fertile hybrids occur.

Physical attributes

Size and weight

The common plains zebra is about 50–52 inches (12.2–13 hands, 1.3 m) at the shoulder with a body ranging from 6–8.5 feet (2–2.6 m) long with an 18-inch (0.5 m) tail. It can weigh up to 770 pounds (350 kg), males being slightly bigger than females. Grévy's Zebra is considerably larger, while the mountain zebra is somewhat smaller.

Stripes

It was previously believed that zebras were white animals with black stripes, since some zebras have white underbellies. Embryological evidence, however, shows that the animal's background color is black and the white stripes and bellies are additions. It is likely that the stripes are caused by a combination of factors.

The stripes are typically vertical on the head, neck, forequarters, and main body, with horizontal stripes at the rear and on the legs of the animal. The "zebra crossing" is named after the zebra's black and white stripes.

A wide variety of hypotheses have been proposed to account for the evolution of the striking stripes of zebras. The more traditional of these (1 & 2, below) relate to camouflage.

1. The vertical striping may help the zebra hide in grass by disrupting its outline. In addition, even at moderate distances, the striking striping merges to an apparent grey.

2. The stripes may help to confuse predators by motion dazzle—a group of zebras standing or moving close together may appear as one large mass of flickering stripes, making it more difficult for the lion to pick out a target.

3. The stripes may serve as visual cues and identification. Although the striping pattern is unique to each individual, it is not known whether zebras can recognize one another by their stripes.

Zebra in Ngorongoro: its pattern may reduce its attractiveness to large biting flies.

4. Experiments by different researchers indicate that the stripes are effective in attracting fewer flies, including blood-sucking tsetse flies and tabanid horseflies. A 2012 experiment in Hungary showed that zebra-striped models were nearly minimally attractive to tabanid horseflies. These flies are attracted to linearly polarized light, and the study showed that black and white stripes disrupt the attractive pattern. Further, attractiveness increases with stripe width, so the relatively narrow stripes of the three living species of zebras should be unattractive to horseflies.

5. Some biologists are uncomfortable with the idea that the zebra’s stripes serve as camouflage. The black and white pattern is highly contrasted and unlike color variability in camouflage, its visibility is unaffected by the wide range of color sensitivity found of predators. In 2013 a novel theory of the zebra’s stripes was presented to scientists at the National Institute of Standards and Technology in Maryland by author/researcher Roy Feinson. Feinson’s hypothesis proposed that the zebra’s stripes cannot be explained without a wholly new theory of animal vision based on the concept that animals only see objects that change from “frame to frame”. When a video of a zebra herd being stalked by a lion is examined through a delta-vision filter (a system that only shows changes in the visual field), it becomes clear that the stripes are actually serving to separate individual animals from the herd. This allows the predator to maintain a visual lock on the pre-selected individual even with the visual chaos created by a stampeding herd, clouds of dust and visual instability caused by the predator’s own movements. The specific orientations of the stripes -- vertical on the midsection, horizontal on the legs and 45 degrees on the rump – help to precisely delineate the individual throughout its range of motion. Exactly how this visual aid serves the interest of the zebra is detailed in the talk. The hypothesis addresses many other puzzling aspects of animal behavior including head-cocking, serpentine movement, and freezing behavior, and proposes an answer to perhaps the most vexing aspect of vision: how is it that humans use approximately 40% of their massive brains to process vision, while mice, cats and flies (with a tiny fraction of this processing power) can see the world well enough to navigate, hunt and evade capture?

Gaits

Like horses, zebras walk, trot, canter and gallop. They are generally slower than horses, but their great stamina helps them outpace predators. When chased, a zebra will zig-zag from side to side, making it more difficult for the predator. When cornered, the zebra will rear up and kick or bite its attacker.

Senses

Zebras have excellent eyesight. It is believed that they can see in color. Like most ungulates, the zebra has its eyes on the sides of its head, giving it a wide field of view. Zebras also have night vision, although not as advanced as that of most of their predators.

Zebras have excellent hearing, and tend to have larger, rounder ears than horses. Like horses and other ungulates, zebras can turn their ears in almost any direction. In addition to eyesight and hearing, zebras have an acute sense of smell and taste.

Ecology and behavior

Harems

Zebras in Tanzania

Like most members of the horse family, zebras are highly social. Their social structure, however, depends on the species. Mountain zebras and plains zebras live in groups, known as 'harems', consisting of one stallion with up to six mares and their foals. Bachelor males either live alone or with groups of other bachelors until they are old enough to challenge a breeding stallion. When attacked by packs of hyenas or wild dogs a zebra group will huddle together with the foals in the middle while the stallion tries to ward them off.

Unlike the other zebra species, Grévy's zebras do not have permanent social bonds. A group of these zebras rarely stays together for more than a few months. The foals stay with their mothers, while adult males live alone. Like the other two zebra species, bachelor male zebras will organize in groups.

Like horses, zebras sleep standing up, and only sleep when neighbors are around to warn them of predators.

Communication

A zebra feeding on grass

Zebras communicate with each other with high pitched barks and whinnying. Grévy's zebras make mulelike brays. A zebra's ears signify its mood. When a zebra is in a calm, tense or friendly mood, its ears stand erect. When it is frightened, its ears are pushed forward. When angry, the ears are pulled backward. When surveying an area for predators, zebras will stand in an alert posture; with ears erect, head held high, and staring. When tense they will also snort. When a predator is spotted or sensed, a zebra will bark (or bray) loudly.

Hartmann's Mountain Zebra with a Barbary sheep behind it, in captivity at Ueno Zoo, in Japan. (video)

Food and foraging

Zebras feed almost entirely on grasses, but may occasionally eat shrubs, herbs, twigs, leaves and bark. Their digestive systems allow them to subsist on diets of lower nutritional quality than that necessary for other herbivores.

Reproduction

Female zebras mature earlier than the males, and a mare may have her first foal by the age of three. Males are not able to breed until the age of five or six. Mares may give birth to one foal every twelve months. She nurses the foal for up to a year. Like horses, zebras are able to stand, walk and suckle shortly after they are born. A zebra foal is brown and white instead of black and white at birth.

Plains and mountain zebra foals are protected by their mothers, as well as the head stallion and the other mares in their group. Grévy's zebra foals have only their mother as a regular protector, since, as noted above, Grévy's zebra groups often disband after a few months.

Interaction with humans

Lord Rothschild with his famed zebra carriage (sp. Equus quagga burchellii), which he frequently drove through London

Domestication

Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. Most of these attempts failed, though, due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between any species of zebra and a horse, pony, donkey or ass) are preferred over purebred zebras.

In England, the zoological collector Walter Rothschild frequently used zebras to draw a carriage. In 1907, Rosendo Ribeiro, the first doctor in Nairobi, Kenya, used a riding zebra for house calls. In the mid-19th century, Governor George Grey imported zebras to New Zealand from his previous posting in South Africa, and used them to pull his carriage on his privately owned Kawau Island.

Jumping an obstacle: riding a zebra in East Africa, about 1900

Captain Horace Hayes, in "Points of the Horse" (circa 1893), compared the usefulness of different zebra species. In 1891, Hayes broke a mature, intact mountain zebra stallion to ride in two days time, and the animal was quiet enough for his wife to ride and be photographed upon. He found the Burchell's zebra easy to break, and considered it ideal for domestication, as it was immune to the bite of the tsetse fly. He considered the quagga (now extinct) well-suited to domestication due to being easy to train to saddle and harness.

Conservation

Modern man has had great impact on the zebra population. Zebras were, and still are, hunted for their skins, and for meat. They also compete with livestock for forage, and are sometimes culled.

The Cape mountain zebra was hunted to near extinction, with less than 100 individuals by the 1930s. The population has since increased to about 700 due to conservation efforts. Both mountain zebra subspecies are currently protected in national parks, but are still endangered.

Zebras on the Botswana coat of arms.

The Grévy's zebra is also endangered. Hunting and competition from livestock have greatly decreased their population. Because of the population's small size, environmental hazards, such as drought, are capable of affecting the entire species. Plains zebras are much more numerous and have a healthy population. Nevertheless, they too have been reduced by hunting and loss of habitat to farming. One subspecies, the quagga, is now extinct.

Cultural depictions

Zebras have been the subject of African folk tales which tell how they got their stripes. According to a Bushmen folk tale of Namibia, the zebra was once all white, but acquired its black stripes after a fight with a baboon over a waterhole. After kicking the baboon so hard, the zebra lost his balance and tripped over a fire, and the fire sticks left scorch marks all over his white coat. In the film Fantasia, two centaurs are depicted being half human and half zebra, instead of the typical half human and half horse.

Illustration of a zebra by Ludolphus

Zebra are a popular subject in art. The fourth Mughal emperor Jahangir (r.1605–24), commissioned a painting of the zebra, which was completed by Ustad Mansur. Zebra stripes are also a popular style for furniture, carpets and fashion.

When depicted in movies and cartoons, zebras are most often miscellaneous characters, but have had some starring roles, notably in Madagascar and Racing Stripes. One of the recurring characters in My Little Pony: Friendship is Magic is a zebra named Zecora. Zebras also serve as mascots and symbols for products and corporations, notably Zebra Technologies and Fruit Stripe gum as well as Investec. Zebras are featured on the coat of arms of Botswana.

See also

• Tijuana Zebra

Further reading

• Churcher, C.S. 1993. Mammalian Species No. 453. American Society of Mammalogists.
• Estes, R. (1991). The Behavior Guide to African Mammals, Including Hoofed Mammals, Carnivores, Primates. Los Angeles, The University of California Press.
• McClintock, Dorcas. "A Natural History Of Zebras" September 1976. Scribner's, New York. ISBN 0-684-14621-5

External links

• PBS Nature: Horse Tigers (Zebras)
• Plains Zebra – Equus Burchelli
• HowStuffWorks article on Zebras
• Out of Africa info on Zebras
• Molecular Mechanism for Stripes in Zebras – and explains the different number of stripes for each type of Zebra.