Rhinoceros

III

Physical Description

The word rhinoceros is derived from the Greek words rhino, meaning “nose,” and keras, meaning “horn,” a reference to the most eye-catching feature of these huge and often awkward-looking animals. Rhino horns are made of a mass of thousands of fibers of keratin, the same substance found in hair. Unlike the true horns found in, for instance, cows and deer, rhinoceros horns do not have a bony core, and they are embedded in skin rather than in the animal’s skeleton. However, as with true horns, rhino horns are permanent and grow steadily throughout their owner’s lifetime.

Some rhinoceros horns are little more than bumps, but in the white rhinoceros particularly, they can reach an impressive size. The largest one on record, from a female white rhino in South Africa, measured nearly 1.6 m (5 ft) from tip to base. Rhinos sometimes use horns to get at food, but a horn’s main function is for defense: With so much muscle-power behind them, horns make formidable weapons. Unfortunately, horns are also the main reason for the rhino family’s endangered plight. On the black market, rhinoceros horns command astronomical prices for use as dagger and sword handles in the Middle East and as an ingredient for traditional Chinese medicine.

Rhinoceros skin is remarkable, both for its thickness and its texture. African rhinos have fairly smooth skin, but in the Asian species skin hangs down in heavy folds. The skin of the Indian rhinoceros forms platelike folds that give the appearance of armor plating. It is covered with tubercles, hard lumps that look like rivets holding the animal’s armor together. Four out of the five rhino species are almost hairless, but the Sumatran rhino is born with a thick coat of hair, which becomes more straggly and bristly as it ages.

Rhinos have elongated heads, with small, puffy-looking eyes. Because their eyes face sideways, they have to turn their heads one way and then the other to look at anything in front. This impediment coupled with their weak eyesight means that rhinos often fail to spot danger—a motionless person 30 m (100 ft) ahead is more or less invisible to a rhinoceros. However, rhinos quickly scent anything that is upwind, and their ears flick in different directions to pick up the faintest sounds.

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Rhinos have few or no front teeth, but their cheek teeth, or molars, are well developed for grinding up food. A rhino’s lips also play an important part in feeding, and their shape helps to show what it eats. In most species the upper lip is pointed and prehensile (able to grasp), and is used for collecting twigs and leaves. But in the white rhino, the upper lip is wide, enabling this species to pull up mouthfuls of low-growing grass.

Because rhinos are such heavy animals, their legs are shaped primarily for bearing weight. As in other heavyweight mammals, such as hippos and elephants, rhinoceros legs are almost straight—a kind of anatomy that prevents buckling when the animal stands. Rhino feet are large, which helps to spread the load they carry, and they leave characteristic three-lobed tracks that look like an ace of clubs. Rhinos normally move with a ponderous walk, but when they are alarmed they break into a rapid canter. As they pick up speed, they develop a huge amount of momentum, making them potentially lethal to anything standing in their way.

Male and female rhinos have a similar physical appearance, although male rhinos are usually larger than females, with the size difference varying between species. In the wild, some rhinos probably live into their late 40s, and they have survived into their 30s in captivity.

IV

Types of Rhinoceroses

Until recently, mammalogists divided the rhinoceros family into three subfamilies, each with different characteristics. Scientists now believe that living rhinos belong to a single subfamily, although some of the species are clearly more closely related than others.

A

Asian Rhinos

With its unique gray or reddish-brown coat, the Sumatran rhinoceros is the smallest rhino species, and also the most distinctive. It is believed to be the only survivor of the lineage that included the woolly rhinoceros. Sumatran rhinos stand up to 1.4 m (4.6 ft) at the shoulder and weigh up to 1,000 kg (2,200 lb). They have folded skin, like the other Asian rhinos, except that it is covered with coarse, bristly hair. The Sumatran is the only rhino in Asia with two horns. The front horn is usually the longest, reaching a length of 90 cm (36 in), and the rear one is sometimes so small that the animal looks as if it is single-horned.

Sumatran rhinos live mainly in forest-covered hills near water and are known to be good at climbing slopes and swimming. They move mainly at night, and spend most of the day wallowing in mud-holes and pools.

The Indian and Javan rhinos are similar to each other in many ways, the most conspicuous being that they are both single-horned. The Indian rhino’s horn reaches a length of up to 50 cm (20 in), but the Javan’s horn is only half this size, and in females is often absent altogether. Both species have gray-brown skin thrown into thick folds—a feature particularly prominent in male Indian rhinos, which develop extra folds around their necks as they age. Unlike the Sumatran rhino, both these species are practically hairless, except for a fringe around their ears and a tassel of hair on their tails.

Indian rhinos are the biggest Asian species, standing up to 1.8 m (6 ft) at the shoulder. Mature males weigh up to 2,200 kg (4,900 lb), which makes them Asia’s second heaviest land animal (after the Asian elephant). The Javan rhinoceros has a maximum weight of about 2,000 kg (4,400 lb), and unusually, the females are bigger than the males. Both these animals need surroundings with plenty of water, but the Indian rhino is the only one that spends much of its time in open grassland, instead of remaining concealed in thick forest.

B

African Rhinos

In Africa the white and the black rhinos evolved from a shared ancestor about 3 million years ago. They have misleading names, because the white rhinoceros is usually light gray, while the black rhinoceros is often dark brown. The white rhino got its name from the Afrikaans word weit, meaning “wide”—a reference to the shape of its mouth—while the black rhino may have been named because the animal wallowed in dark soil. African rhinos have two large horns and some black rhinos even have the beginnings of a third horn.

The white rhino is the biggest member of the rhinoceros family, with a combined head and body length of nearly 4 m (13 ft). Adult males have an average weight of about 2,500 kg (5,500 lb), but exceptionally heavy specimens can reach 3,500 kg (7,700 lb). Their barrel-shaped bodies are almost hairless, and from a distance their skin looks smooth. The front horn is often twice as big as the rear one, with a leading edge that comes almost as far forward as the broad top lip. The black rhino is slightly smaller, but considerably lighter, with a maximum weight of up to 1,400 kg (3,100 lb). Its forehead is steeper, and its front horn is set slightly further back, leaving room for its prehensile top lip to reach out and collect food.

In the wild, white and black rhinos can be distinguished not only by their color, size, and the shape of the heads, but also by their stance. Like other grazers, white rhinos spend much of their time with their heads down, using their tough lips to tear up mouthfuls of grass. Despite their huge proportions, they are relatively placid animals and will often allow humans to approach them. Black rhinos are more often seen with their heads up, reaching into shrubs and small trees. They are much more wary of human intrusion and will charge if disturbed, making it hazardous for anyone to get too close.

African rhinos often wallow in mud, a habit that probably helps to protect their bare skin from biting flies. These rhinos also play host to oxpeckers, sharp-clawed birds that scamper over rhino bodies in search of ticks. Oxpeckers rid the rhinos of these troublesome parasites while gaining themselves a meal.

V

Behavior

Rhinos are often portrayed as aggressive and unintelligent, but neither of these labels is completely true. The Indian rhino and black rhino have been known to attack people without warning, but the white rhinoceros is a more docile animal, despite its immense size. The Javan and Sumatran rhinos are now so rare that, as far as humans are concerned, they present very little danger at all. In intelligence, probably rhinos rank as high as other hoofed mammals, but their poor eyesight can sometimes make their behavior seem hesitant and slow-witted.

Rhinos are predominantly solitary animals. The only stable rhino social unit consists of a nursing mother and her calf. Female white rhinos sometimes gather in small herds, and males will also socialize when they are young. But in all five species, adult males are strongly territorial and do not tolerate the presence of any rivals. Males mark their territories by leaving piles of dung, and by spraying urine on the ground in a powerful backward jet. Rhinos also communicate with their neighbors by sound, and their calls range from deep grunts to a loud puffing that indicates alarm.

When neighboring males meet, one animal may show signs of subordination, for example by turning back its ears. If subordination does not occur, the stage is set for a contest that can quickly turn violent. The African rhino attacks rivals with its horns, first using its front horn like a club, and then, if this does not deter the intruder, jabbing with the tip. Their Asian counterparts, which have smaller horns, tend to use their mouths and their teeth when fighting. In both African and Asian rhinos, fights can result in serious injury.

With the exception of these territorial clashes, a rhino’s life is normally one of quiet routine. Most rhinos feed by day or by night, but they are least active during the midday heat. They rarely stray far from water, and the Indian rhinoceros spends much of its time lying in pools. Rhinos can travel up to 25 km (16 mi) every day in search of water and food.

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