White / Square-lipped Rhinoceros

Ceratotherium simum (Burchell 1817)

Photo: Doug Lee

IUCN Conservation Status:

• The Southern white rhino is NT = Near Threatened
• The Northern white rhino is CE = Critically Endangered

After the elephant the white rhino is the largest land mammal on earth today. It evolved from the black rhino in relatively recent historical times and spread in large numbers over Africa, Eurasia and North America. However mans greed took its toll on the populations, and by 1904 only 10 southern white rhinos still survived, and by 1988 only 17 northern white rhinos. Conservation initiatives have restored the numbers of the southern white subspecies and the total population now exceeds 13 000 animals. Although the white rhino may have earned its name by rolling in white mud it is also possible that the name was an early mistranslation of the Dutch word “wijd” which refers to its wide mouth. The generic name “Ceratotherium” is derived from the Greek terms keras "horn" and therion "beast".

Taxonomy

Classification

Four genera with five extant species and six subspecies are recognized:

• Rhinoceros the single-horned rhinoceros with two species
• R. unicornis the Indian rhinoceros
• R. sondaicus the Javan rhinoceros
• Dicerohinus the two or double-horned Sumatran rhinoceros Dicerohinus sumatrensis
• Ceratotherium the white or square-lipped rhinoceros with two subspecies
• C. simum simum the southern white rhinoceros
• C.s. cottoni the northern white rhinoceros
• Diceros the hook-lipped or black rhinoceros with six subspecies
• D. bicornis longipes the West African black rhinoceros
• D.b. brucii the north-eastern black rhinoceros
• D.b. michaeli the East African black rhinoceros
• D.b. bicornis the Cape or black rhinoceros
• D.b. minor the southern black rhinoceros
• D.b. chobiensis the south-western black rhinoceros

Diceros praecox, from which the black rhino originated, evolved 14 million years BP in Europe and arrived in Africa between 11and 8 million years BP. The ancestors of the white rhinoceros diverged from a black rhinoceros ancestor in Africa during the early Pliocene about 5-4 million years BP. The black and white rhinos remain so closely related that inter-specific hybridization has been confirmed by Robinson et al (2005). A reproductive hybrid of the northern and southern white rhinoceros subspecies was bred in the Dvur Kralové Zoo in the Czech Republic in 1977. The most southern record of white rhino is a skeleton exposed by workers digging the foundations for the Grassridge Dam between Hofmeyr and Middelburg in the Eastern Cape. At present the distribution of rhino in Africa is limited to protected parks and private game farms.

Image gallery

Click here to view more photographs.

Description

As the white rhino evolved from the black rhino they are similar in appearance. The main differences between white and black rhino lie in the neck and the shape of the mouth. White rhinos have broad, flat lips 20 cm wide for grazing and the head cannot be lifted above the back. Bulls are 30% larger than cows. The body colour bears no relation to the names “white” and “black” as rhinos are fond of rolling in mud baths and the body takes on the colour of the soil. The skin is up to 20 mm thick on the back and thighs and up to 50 mm on the forehead. There are minor differences between the southern and northern white rhino subspecies. The latter has a shorter body and legs. The skin of the southern form contains hard, pin-like, sparsely scattered hairs that are absent in the northern form. The dorsal side of the skull of the northern sub-species is flatter than that of the southern and the molars have smaller crowns.

Comparison To Man

Trophy

Both sexes have two asymmetrical horns, the larger horn is situated on the end of the muzzle just behind the nostrils and the second, smaller horn halfway up the nose between the first horn and the forehead. The horns do not have a bone core and consist of a compact mass of tubular keratin fibres growing directly from the skin. Cow horns, although thinner, are generally longer than those of a bull. The mean, accumulative mass of both horns of adult white rhinos ranges from 5.8-14.0 kg. The mass of the anterior horn ranges from 0.29-11.04 kg, and the posterior horn from 0.01-4.0 kg. The mean horn growth rate of calves is 15 cm during the first year, declining to 5.6-6.4 cm per annum in young adults aged 8-25 years and 2.7-4.5 cm in adults of 25 years and older (Pienaar et al 1991). The anterior horn becomes visible at five weeks and measures approximately 4 cm at 3 months and 10 cm at 7 months. Rhinos, especially bulls, frequently rub their horns against tree trunks and rocks causing the horn tip to wear away. This rapidly reduces the growth to a maximum trophy length of about 120 cm at a prime age of 28-30 years, after which it is further reduced to a maximum of 100 cm at 40 years age.

Habitat requirement

Moderate to dry savannahs are the most suitable habitat and should meet the following basic parameters

• a herbaceous layer of sweet, short, grass species 5-25 cm high
• surface drinking water
• mud holes for baths
• patches of dense thicket vegetation for refuge
• scattered tree foliage for shade and resting
• relatively flat terrain with slopes <20°.

Temperate grasslands, the moist, sour grasslands of the highveld and montane regions, or moist forest-like environments, are totally avoided. Veld on a substrate of dolerite and shale is preferred, on a granite substrate is marginal and on sandstone is unsuitable and avoided. A habitat of mixed sweet and sour grasses is marginal while pure sour veld is unsuitable. White rhinos are highly attracted by the new grass growth on burnt veld and are usually the first animals to move onto it.

Distribution

Feeding & Nutrition

White rhino are partly selective, roughage grazers. They feed predominantly on short, sweet, palatable grasses and do not ruminate as they are monogastric. Care should be taken when supplying supplementary food concentrates as rhino, together with zebra, cannot tolerate the high levels of urea found in some brands. When grazing is poor, rhino do well on supplementary dry lucerne and horse cubes but these supplements should not exceed 10% of the daily dietary intake. White rhinos are dependant on water and drink up to 50 litres at a time with an average water consumption of 12 litres per day. The bulk of their feeding usually takes place during the morning and from late afternoon into the evening. The daily food intake for an adult is 50-65 kg and when confined to a boma, 35-40 kg.

Social structure

White rhino are semi-social and stay in small breeding groups of one adult cow older than 5 years, her calf of younger than 2.5 years and 1-3 sub-adult cows of 3-5 years. An adult bull often accompanies the group for mating purposes, an association that rarely lasts more than 7-8 days. Sub-adults of both sexes form mixed groups of 3-5 individuals, while adult bulls are mostly solitary and territorial. Bull calves leave the breeding group at 2.5-3.5 years after the birth of the next calf and join sub-adult groups until they reach social maturity. Temporary aggregations of 2-3 groups are often found at water holes, at centralized feeding grounds during drought and in bad seasons. The natural population structure is 19% adult bulls, 26% adult cows, 32% sub-adults and 23% calves. Due to the long calving interval, a maximum of 40% of the adult cows, or 10.4% of the population calve per annum.

Information Table

Bibliography