Zebra - biology.

« C Life Span Captive zebras have lived into their late 30s.

Life expectancy in the wild, where predators abound, is probably not much more than 12 years. IV SOCIAL BEHAVIOR Like horses, zebras have large brains and a wide variety of social behaviors.

Although they cannot match the overall intelligence of mammals that hunt, zebras interactwith each other in complex ways. Zebras usually live in groups known as herds, but the social structure of these groups depends on the species.

The plains zebra and mountain zebra form small familyunits, consisting of up to six mares (adult females) and their foals (young), under the leadership of a stallion (adult male). Once a stallion has assembled a group of mares, it faces the constant threat of being displaced by a more powerful rival.

When an intruder does appear, the residentstallion issues a challenge by touching noses or rubbing shoulders with the rival.

If the rival male does not give way, a fight breaks out, with the two stallions biting eachother’s neck or legs, and as a last resort, kicking with their back legs.

Unlike some courtship contests in the animal world, these fights are as dangerous as they look,and severe injuries can result. The family units of the plains and mountain zebra are very stable, and although a younger rival may eventually oust the stallion, the mares often remain in the groupfor life.

Within the group, there is a strict order of seniority by age, which shows itself when the animals are on the move.

The oldest mare is first in line, followed by herfoals, and then by the other mares and foals, with the youngest coming last.

Finally, the stallion brings up the rear. By contrast, among Grévy’s zebras, there are no permanent bonds between the adult animals.

The chief social unit is a nursing mare and one or two of her foals.Although the mare will often associate with other adults, there is no order of rank, and each mare comes and goes as she pleases.

However, as with the other twospecies, the behavior of Grévy’s zebras is affected by their food supply.

If food is scarce, the animals spread out, but if it is abundant in one particular place, hundredsof Grévy’s zebras may converge to feed, giving the impression of a single herd. For all zebras, physical contact plays an important part in daily life.

Pairs of adults, as well as mothers and foals, often groom each other.

They stand side by side, withthe head of one zebra adjacent to the tail of its partner in order to nibble each other’s fur.

Zebras also rest in this position, because it enables them to use their tails tokeep flies away from each other’s faces.

This stance has another advantage: Together, the two animals have a complete 360° view of their surroundings.

Zebras alsosignal to each other with body language and sounds.

Lowered ears, for example, show that a zebra is likely to kick, while a snort shows that it is alarmed.

Domesticatedhorses behave in exactly the same way. Zebras adapt well to life in captivity, and make popular zoo animals.

Although they are less cooperative than horses, they can be tamed and trained to pull carriages,but they are very difficult to ride. V FEEDING, SLEEPING, AND MIGRATION Like many other plant-eating mammals, zebras do most of their feeding early and late in the day, resting during the midday heat.

During the day zebras sometimessleep on their feet, as horses do, but at night they often lie down.

For any animal, sleeping is potentially hazardous because it offers predators an opportunity to attack.For this reason, a zebra will only sleep if one or more of its neighbors is fully awake to act as a sentry.

Zebras use a similar system when they feed—while some animalshave their heads down munching on grass, others are on the lookout for danger. During the course of a day, a zebra herd may wander 20 km (12 mi) or more in search of food, usually returning to the same resting place each evening.

But in someparts of Africa, such as Tanzania, the dry season prompts a much longer annual migration in the company of thousands of gnus and gazelles, creating one of thegreatest wildlife spectacles in the world. VI REPRODUCTION Female zebras can give birth to their first foal when they are just three years old, and from then onward they produce young at intervals of between 18 months andthree years.

For males, breeding often does not begin until age five or six. After a gestation period of about 12 months, female zebras typically give birth to a single foal.

The newborn foal feeds on its mother’s milk for up to a year.

This 12-month period is by far the most dangerous in a zebra’s life, because although foals can run soon after birth, they lack the speed and endurance to escape lions andother predators. Grévy’s zebra mares look after their foals without the help of stallions.

In plains zebras and mountain zebras the stallion helps to protect all the foals in its family unit,and also their mothers.

If a foal wanders too far from the rest of the group, the stallion will round it up and shepherd it back to safety.

Despite the constant vigilance oftheir parents, only about 50 percent of zebra foals manage to survive their first year. VII CONSERVATION STATUS Zebras have been hunted for thousands of years, both for their meat and for their hides.

Primitive hunting techniques probably had only a minor impact on zebrapopulations, but the introduction of firearms by European settlers made zebras much more vulnerable.

During the 19th century the quagga, a species of zebra thatlived in South Africa, was hunted to extinction.

The last captive specimen, held in the Amsterdam Zoo, died in 1883, several years after the species had vanished in thewild. Both the Grévy’s zebra and the mountain zebra are listed as endangered on the Red List of Threatened Species, prepared by the World Conservation Union (IUCN), anongovernmental organization that compiles global information on endangered species.

With a total population of less than 10,000, the Grévy’s zebra is threatened bothby hunting and by livestock that compete with it for water and food.

Its range has shrunk dramatically, and it is now so small that environmental hazards, such asdrought, can easily affect the entire species. A distinctive subspecies of the mountain zebra that lives in South Africa, commonly known as the cape mountain zebra, has come perilously close to extinction in the20th century.

During the 1930s, the population of cape mountain zebras fell to less than 100 animals.

Several decades of conservation work, including theestablishment of the Mountain Zebra National Park in South Africa for the preservation of the mountain zebra, has helped the population rise to about 700 animals.Further north, in Namibia and Angola, mountain zebras are more numerous, with an estimated 25,000 animals, although these populations are also threatened byhunting and loss of habitat.. »