ZooNooz Article - September 2003

Three of a kind

Aren't all rhinoceroses big, grey, prehistoric-looking animals with horns on their noses? Well, yes and no, reports JUDY GIBSON. Each species has its own distinct characteristics and behaviours and all are highly endangered.

Photographs Leonie Saville

Rhinoceroses first evolved over 40 million years ago from animals that looked something like tapirs - giant, hornless animals that may have weighed over 20 tonnes. Two of the five living rhino species now live on the savannas of Africa, while the other three come from the tropical forests and swampy grasslands of Asia.

HIGHLY ENDANGERED

• Black Rhinoceros and calf

  Black Rhinoceros (sometimes known as the Hook-lipped Rhino) Diceros bicornis. In 1970 it was estimated that there were 65,000 Black Rhinos in Africa but during the '90s this dropped massively to 2,300. Numbers have recovered slightly to about 3,100.

• White Rhinoceros

  White Rhinoceros (or Squarelipped Rhino) Ceretotherium simum. After being critically endangered earlier in the 20th Century, numbers of the Southern White Rhino sub-species have increased to about 11,670 animals in the wild. Northern White Rhino numbers may be as low as 30.
• Greater One-horned Rhinoceros (or Indian Rhino) Rhinoceros unicornis. Now only found in a few locations in Assam, Nepal and Bhutan, in the early 20th Century there were only about 200 left in the wild. Through strict protection this has now increased to about 2,400.
• Javan Rhinoceros (or Lesser One-horned Rhino) Rhinoceros sundaicus. Once found throughout Asia, they are now only found in Indonesia and Vietnam and are thought to number about 60 in the wild.
• Sumatran Rhinoceros (sometimes known as the Asian Two-horned or Hairy Rhino) Dicerorhinus sumatrensis. Fewer than 400 are thought to survive in the remote forests of Sumatra, the Malay Peninsula and Borneo.

KNOW YOUR RHINO

How can you tell one species of rhino from another?

Greater One-horned Rhinoceros

The first feature is probably the most obvious one. The word rhinoceros is derived from the Greek words rhino meaning "nose" and keras meaning "horn", the unique feature for which all members of the rhino family are famous. Some rhino horns are little more than bumps while others can be enormous. The largest one recorded was from a female White Rhino in South Africa that measured nearly 1.6m from tip to base - longer than the total height of a Sumatran Rhino.

Rhino horn is made from a dense mass of keratin fibres, the same substance found in our hair and fingernails, which is perched on a roughened area of the skull and embedded in the skin. It has no bony core like the true horns of cattle, sheep or antelopes. Black, White and Sumatran Rhinos all have two horns, with the one closest to the tip of the nose (the anterior) usually larger and longer than the other. The Greater One-horned and the Javan Rhinos only have a single horn.

Rhinos may occasionally use their horns for digging for food, but their main function is for defence. Male rhinos in Africa have been observed attacking rivals with their horns, first using the front horn like a club and then jabbing upwards with the tip. The Asian rhinos, which usually have smaller horns, also use their mouths and tusk-like canine teeth when fighting. Female rhinos will use their horns to defend their calves from attacking predators.

It is ironic that rhinos' main means of attack and defence is also one of the primary reasons for them becoming so critically endangered. They have been poached for their horn (literally worth more than its weight in gold) which is used for dagger and sword handles in the Middle East, as an ingredient in Asian medicines and as an aphrodisiac.

Rhinoceros skin is also a distinctive feature. The African rhinos have fairly smooth skins but their names are misleading - both White and Black Rhinos are basically grey but can be tinted by the local soil colour. One theory is that the name White Rhino is a corruption of the Cape Dutch (Boer) name widj mond (or Afrikaans word weit) meaning "wide mouth" - a reference to the shape of its mouth. Another theory is that the first White Rhinos encountered by Europeans in the northern Cape had been wallowing in the pale, calciumrich soil which made them appear white.

Greater One-horned Rhinos have extremely thick skin arranged in heavy folds which give them the appearance of wearing a jointed suit of armour. This impression is enhanced by wart-like bumps called "tubercles" on their shoulders and upper legs that look like rivets. The hide of a Greater One-horned Rhino is mostly greyish-brown but becomes pink in the skin folds.

The mouths are also distinctly different. Black Rhinos have a pointy, prehensile upper lip that allows them to grasp long grasses and shrubs. They are browsers, while the White Rhino has a lengthened skull and broad lips suited for grazing on short grasses. The Greater One-horned Rhino has the best of both, as they can use their prehensile upper lip to browse on taller plants and fold it away when grazing on short grass.

In body profile, White Rhinos are easy to distinguish from Black Rhinos as they have a prominent hump on the back of their neck, called the "nuchal crest". The crest is formed by bones, muscles and ligaments that are used to support their massive head, and this makes their head carriage much lower than other rhinos. In contrast, Black Rhinos need to be able to reach into shrubs and low trees so their heads are set much higher on the neck and shoulders.

The milder natured White Rhino is the heaviest of the rhino family with an average weight of 2,500kg. Second is the greater One-horned Rhino at 2,200kg. The males in both these species are noticeably larger than the females, standing approximately 2m at the shoulder. The Black Rhino comes in third and, although they are not much shorter, they are considerably lighter in weight at only 1,400kg, with the males only slightly larger than the females. In spite of their bulk, rhinos can be surprising light on their feet, charging at speeds of 48km per hour.

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