Antelope

I

Introduction

Antelope, common name applied to a diverse group of hollow-horned mammals that belong to the same family as cattle, goats, and sheep. About 100 species of antelopes live in Africa and Asia, including some of the world's fastest and most elegant hoofed mammals, as well as some of the most endangered. In size, antelopes range from the tiny royal antelope, which stands about 25 cm (10 in) high at the shoulder, to the massively built common eland, which can weigh as much as 900 kg (nearly 2,000 lb)—more than an average car. Some better-known antelopes include impalas, gazelles, and gnus.

Antelopes vary widely in their physical appearance and the way they live. Some antelopes, including many of the smallest species, stay close to vegetative cover and disappear into the undergrowth if disturbed, but most live in more open habitats where they rely on speed and alertness to escape attack. The species that flee also use their superb jumping skills to escape from predators: impalas, for example, can leap over fences 3 m (10 ft) high, and cover 10 m (33 ft) in a single bound.

Unlike deer, which have branched antlers that they shed annually, antelopes have pointed horns that they keep throughout life. Antelope horns can grow up to 1.5 m (about 5 ft) long; they look formidable but their value as weapons is limited. There are records of antelopes impaling (spearing) and even killing predators as large as lions, but when faced with danger antelopes are far more likely to run away.

Some antelopes are solitary but most live in herds. In the late 1800s, herds of springbok in southern Africa sometimes included over 10 million animals that spread over a distance of 160 km (100 mi). Although herds no longer reach this astounding size today, antelopes still dominate life in African plains. They help grass thrive by nibbling away competing plants, and they provide food for predators and also for people.

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II

Range and Habitat

About 5 million years ago at the beginning of the Pliocene Epoch, antelopes were widespread throughout Europe, Asia, and Africa. Today they live only in Africa and in central and southern Asia, with Africa having the greatest number of species. Antelopes have never lived in the Americas, although one North American mammal, the pronghorn, looks very much like an antelope and shares a similar way of life.

Although antelopes all eat plants, some are grazers, preferring to feed on grasses on the ground, while others browse vegetation from low-lying branches on trees and bushes. These feeding preferences determine their habitat. Some species, such as Thomson's gazelles, live almost entirely on grass and rarely turn to any other kind of plant food. Thomson's gazelles feed where the grass is short, a preference that restricts them to dry, open plains. By contrast, the common reedbuck feeds in swampy ground. It specializes in eating coarse grasses that other grazing antelopes find difficult to digest.

Browsing antelopes, unlike grazers, live in a wider variety of habitats, from tree-studded savannas to dense rain forests. Some of them feed exclusively on leaves, but most eat other kinds of food as well. This additional food usually includes flowers and fruit, but in the case of small forest antelopes called duikers, it also includes birds and animal remains.

Water also plays an important part in determining where antelopes live. For example, gnus need to drink every day, so they cannot wander more than about 15 km (9 mi) from the nearest river or waterhole. Other species can get all the water they need from their food. The addax, a critically endangered antelope that was once widespread along the southern fringes of the Sahara Desert, needs at least 3 litres (5 pints) of water a day. However, the addax can absorb all the water it needs from roots, bulbs, and fruit, enabling it to survive indefinitely without drinking from a waterhole.

III

Physical Description

Antelopes differ from one another almost as much as they differ from other members of the cattle, goat, and sheep family. Size is one of the most striking and variable features of antelopes: The common eland towers over most breeds of domestic cattle and can be 300 times heavier than the royal antelope. In many species, including the eland, males are considerably larger than females. In a few species, such as the Asian black buck, males and females also differ in color.

Antelopes have a dense coat with short fur. Most antelopes have fawn or brown fur that helps camouflage them as they feed. But there are some exceptions to this rule. The rare zebra duiker has dark vertical stripes, while the gemsbok has gray and black fur and a vivid black-and-white face. A common feature of gazelles is a white rump, which flashes a warning signal to others when they run from danger. One gazelle, the springbok, also has a pouch of white brushlike hairs running along its back. When a springbok is alarmed, its pouch opens up, and the hairs stand on end.

All antelopes have long slender legs. Powerful muscles where the upper legs meet the antelope’s body provide leverage, increasing leg stride and speed. Although antelopes are good jumpers they are not great climbers, particularly when compared with sheep and goats. But a few do exhibit good balance—most notably the klipspringer, which stands on the tips of its hooves. Another African species, the gerenuk, is one of the few antelopes that habitually stands on its back legs. It does this to reach leaves in trees: As it stretches upward, the gerenuk uses its front legs to hold itself steady against the tree.

Antelopes are ruminants, animals that regurgitate partially digested food, called cud, and chew it again. Like other ruminants, including cattle and sheep, antelopes have well-developed cheek teeth or molars, which grind cud into a pulp. They have no upper incisors, and in order to tear off grass stems or leaves, their lower incisors press against an upper hard gum pad when they bite.

Whether they are eating or resting, antelopes rely on their keen senses to avoid danger. Their eyes face sideways, and their pupils are elongated horizontally, giving them a good view of danger from behind as well as in front. Their hearing and sense of smell are also acute—valuable features for life in the open where many predators are on the prowl after dark.

Whereas in deer only males for the most part grow antlers, in antelopes, both sexes usually have horns, although the horns of males are normally larger. In species where males have only one mate, such as the dik-dik and klipspringer, horns are little more than spikes. In species where the males compete to mate with several females, antelope horns may grow as long as 1.5 m (5 ft). Despite their large size, antelope horns are hollow and lightweight. Antelope horns are always slightly curved, and in some species, such as the black buck, they are shaped like a pair of corkscrews, spiraling in opposite directions.

Antelope life spans in the wild are difficult to determine, and most known figures relate only to captive animals. Captive gnus, for example, have lived to be over 20, while impalas have lived into their late teens. But in the wild, where predators weed out all but the fastest and fittest animals, few antelopes reach their teen years.

IV

Antelope Behavior

Compared to some mammals, such as carnivores (meat-eaters) and primates (apes, monkeys, and humans), antelopes are not noted for high intelligence. This trait is partly explained by their plant-eating lifestyle: Because their food cannot run away, they do not need to be quick-witted or resourceful to track it down. However, antelopes still display complex patterns of behavior, although much of it is instinctive rather than learned.

In open habitats, antelopes run a high risk of predation (being preyed upon). To survive they use several kinds of defensive strategy, including living in herds. Herd living ensures that many pairs of eyes and ears are on the alert for danger. Herd living also gives individuals a better chance of avoiding attack, because predators can choose from many potential targets.

When danger threatens, antelopes behave in characteristic ways. Paradoxically, many species, particularly gazelles, walk toward potential enemies, such as lions or cheetahs, when they first come into view. This behavior is not as reckless as it sounds, because it alerts the herd and allows the antelopes to assess the threat that they face. If the approaching animals do turn out to be predators, gazelles keep them under constant surveillance, always at the ready to run. The decision to start running is based on the type of predator and its distance. Gazelles will permit lions to come within 200 m (650 ft), because they instinctively know that a hunting lion prefers to stay hidden while it stalks its victim and a visible lion is unlikely to launch an attack. Cheetahs, which are superb sprinters, pose more of a threat—gazelles will often start to run when cheetahs are still over 800 m (0.5 mi) away.

Antelopes communicate with one another using a variety of sounds. Dik-diks, for example, whistle when alarmed, a habit that alerts other animals to danger and makes dik-diks unpopular with hunters. But for antelopes generally, sight is a much more important form of communication. They indicate their mood by their posture, and also by the way they move. When they are excited or alarmed, many medium-sized antelopes bounce up and down on all four legs, keeping their legs stretched out straight. This behavior, known as pronking or stotting, acts as an alarm display. Some biologists theorize that stotting also communicates a message to predators, showing that individual antelopes are fit and alert and therefore not worth pursuing.

In addition to visual displays, antelopes use scent signals to communicate. Scent signals have the advantage that they can linger for many days. Antelopes that live in herds have glands in their hooves that leave a scented record of their movements. Antelopes use these scented tracks to find their way back to the herd if they accidentally become separated from it.

Antelopes that live in forests tend to stay in the same area all their lives, but species that live in open habitats often migrate to feed and breed. The most famous of these migrations are carried out by gnus, which live in the plains and open woodlands of eastern and southern Africa. In some places gnus are sedentary, but in others, such as Tanzania's Serengeti National Park, gnus journey between two home ranges—one used during the dry season and the other during the wet season, when rain produces a fresh crop of grass. Migration can be risky, particularly when it involves crossing crocodile-infested rivers, but it does guarantee that the gnus have the best supply of food at different times of the year.