Zebra

I

Introduction

Zebra, member of the horse family with an eye-catching coat of black and white stripes. Zebras are found only in Africa, but their remarkable markings make them among the most familiar mammals in the world. There are three species of zebras, each with a distinctive stripe pattern: Grévy’s zebra, the mountain zebra, and the plains zebra (also known as Burchell’s zebra).

Zebras are members of the family Equidae, which also includes horses and asses. The earliest known ancestor of the animals in this family was a small animal called Hyracotherium, or more commonly, Eohippus, which lived 60 million years ago during the Pleistocene Epoch. Animals known to be the direct ancestors of the modern horse, ass, and zebra appeared in Europe, Africa, and Asia about 4 million years ago during the Pliocene Epoch.

Like other members of the horse family, zebras are primarily grazing animals. They feed on coarse grass, leaves, and shoots. Zebras face many predators, particularly lions and hyenas, but over the last 200 years humans have posed a greater threat to their survival. The quagga, a zebra with stripes on its head and neck, but often none on its sides and hindquarters, lived in southern Africa until the 1870s, when it was hunted to extinction. Today, both Grévy’s zebra and the mountain zebra are endangered due to hunting and habitat loss.

II

Range and Habitat of Zebras

The water needs of each zebra species vary, and this factor helps to explain differences in where they live.

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Grévy’s zebra is the best at coping with drought conditions. It lives in grasslands and thorny scrublands on the borders of northern Kenya, Somalia, and Ethiopia, a harsh region scorched by high temperatures. During the dry season when rivers, streams, and other surface waters often dry up, Grévy’s zebras survive by using their hooves to dig waterholes in riverbed sand.

The mountain zebra lives in the high ground of South Africa, and in the coastal hills of Namibia and Angola. Like Grévy’s zebra, it is also drought-adapted and will dig for water when supplies become scarce. However, the mountain zebra survives the dry season largely by migrating to higher ground, where moisture condenses in the cooler air to form rain or snow.

Compared to the Grévy’s zebra and the mountain zebra, the plains zebra has a much broader range. It lives throughout the grasslands, savanna, and scrub of East Africa, reaching as far as Angola in the west. Unlike its two relatives, the plains zebra needs access to surface water every day, and in some places it must migrate in step with the seasons to find places with enough water to drink.

III

Physical Description of Zebras

Although zebras are similar in shape to horses, they are generally smaller, with upright manes and shorter tails. The mountain zebra is the smallest species of zebras. Adults average about 1.2 m (4 ft) high at the shoulders. Adult plains zebras are only slightly larger, averaging about 1.4 m (4.6 ft) at the shoulder. Grévy’s zebra is the largest species, with adults standing about 1.5 m (5 ft) high at the shoulder. The plains and mountain zebras weigh 290 to 340 kg (640 to 750 lb) and the Grévy’s zebra weighs up to 450 kg (990 lb), which is about the same weight as a typical riding horse. In plains and mountain zebras, the males are slightly larger than the females, but in Grévy’s zebras the sexes weigh about the same.

Like horses, zebras have keen hearing. They turn their ears and large eyes toward the source of a sound to quickly pick up any movements or noises that might indicate danger. The position of their ears also helps to show their mood, another characteristic that zebras and horses share. For instance, ears that flick back and forth indicate the zebra is distressed. Their sense of smell is not particularly well developed, but like most grassland mammals, zebras are very sensitive to smoke, a useful feature in habitats where lightning strikes sometimes start grassfires.

Zebras have chisel-shaped incisor teeth at the front of both jaws, and large molars or cheek teeth that grind up food before it is swallowed. Compared to digestion in ruminants (animals that regurgitate partially digested food and chew it again, such as buffaloes and antelope), zebra digestion is relatively inefficient in breaking down food and absorbing nutrients. To make up for their inefficient digestion, zebras spend over half their time eating.

A

Stripes

Each zebra species has a different stripe pattern, and no two individuals within a species have exactly the same markings. The Grévy’s zebra has narrow stripes set closely together. Horizontal stripes on the haunches, shoulders, and legs are short and fine and extend all the way down the legs to the hooves. The mountain zebra has wider stripes than the Grévy’s zebra, particularly on its rump, while the plains zebra has the widest stripes of all. Of the three species, the plains zebra is the only one with stripes that wrap around from the back to the belly; in the other two species, the underside is completely or mainly white. The plains zebra is also the only species that sometimes has faint gray markings called shadow stripes between the main black stripes on its sides.

Because zebras spend so much time eating, they are an easy target for predators, and some zoologists have suggested that zebra stripes act as a protective camouflage. According to this theory, their bold markings break up their body outline, making them difficult to see from far away. Another explanation for zebra markings is that in a herd, zebra stripes confuse would-be attackers by making it hard for them to single out an individual animal from a backdrop of constantly shifting stripes.

To many experts, a more convincing explanation for zebra stripes lies in their social life. Like most members of the horse family, zebras are highly gregarious, and they constantly seek out each other’s company. Their stripes may act like an identity badge, helping individual animals stay in contact with one another. Very occasionally, unstriped zebras do occur, and these animals tend to stay isolated from their own kind—suggesting to some scientists that zebra stripes act more as a way to develop social relationships than as a form of camouflage.

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