Black / Hook-lipped Rhinoceros

Diceros bicornis (Linnaeus 1758)

Photo: B.J. Oelofsen

IUCN Conservation Status:

CR/en = Critically endangered.

In July 2006, the West African black rhinoceros Diceros bicornis longipes was tentatively declared extinct (EX).

Ancestors of the Rhinocerotidae family were the largest mammals to have lived on earth. Today, the black rhino is one of the world’s most endangered species due to organized poaching for its horn and between 1970-1992, 96% of the African rhinoceros population was eradicated.

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
• 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

The subspecies status of the south-western black rhinoceros D.b. chobiensis is still under debate and some scientists claim it is not significantly different from D.b. minor. The super family Rhinocerotoidea diverged from other perissodactyls in the early Eocene some 40 million years BP. Rhinocerotoidea consisted of three families, Hyracodontidae, Amynodontidae and Rhinocerotidae. The Hyracodontidae or "running rhinos" ranged from dog-sized to the largest mammal ever found on earth, the Indricotherium, 6 m tall, 9 m long and exceeding 20 000 kg. The Amynodontidae or "aquatic rhinos" resembled hippopotamuses and dispersed in rivers and lakes across North America and into Eurasia from the late Eocene to the early Oligocene. The Rhinocerotidae which evolved in Eurasia in the late Eocene and crossed into North America, had 26 known genera. An ancestor of the African black rhinoceros, Diceros praecox, arrived in Africa from Eurasia in the late Miocene 11-8 million years BP. The white rhinoceros diverged from the black rhinoceros in Africa during the early Pliocene about 5-4 million years BP.

Description

Black rhinos have long, pointed, hooked, upper lips for browsing foliage and the head can be lifted far above the height of the back and shoulders to reach browse in trees. The ears are round compared to the pointed ears of the white rhino. The West African subspecies is the smallest and the Cape or desert subspecies, the largest. Adult cows are 4-8% larger than bulls. The skin contains numerous subcutaneous glands that secrete a pale red substance when the animal is under extreme stress. Warts are common, especially in the southern and East African subspecies, and are normally found behind the shoulders and on the breast and front legs.

Comparison To Man

Trophy

Both sexes bear two asymmetrical horns, the larger horn 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. The horns of adult black rhino bulls are thicker round the base and have a larger circumference than those of the cows. Cow horns, although thinner, are generally longer than those of the bulls.

The mass of the anterior horn ranges from 0.18-3.8 kg, and that of the posterior, 0.02-2.38 kg. 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.

Habitat Requirement

The black rhinos’ distribution is dictated by the abundance of sufficient browse forage within its reach, which is a height of 0-200 cm above ground level. The habitat requirement is well-developed, closed woodland and/or bush thickets for feeding and refuge, constant surface drinking water and mud baths. Even though black rhinos are not generally associated with grass plains and open savannah, they inhabit a wide range of environments with an annual rainfall of more than 150 to less than 1 000 mm including succulent and karroid shrubland, savannah, bush, closed woodland and the ecotones of open woodland and semi-forests.

Distribution

Feeding & Nutrition

A bulk or partly selective, roughage browsers of tree foliage, shrubs and woody forbs of mainly sweetveld. When the preferred food becomes scarce, the black rhino will consume leaves, branches, shoots, berries, pods, succulents and, to a limited extent, taller grasses that form 1-4% of the total diet. Sourveld and cold winter environments are not suitable, while mixed-veld is moderately marginal. When feeding on succulents containing a high moisture content, black rhino can go without drinking for up to 5 days and can move up to 30 km away from the nearest surface water. The daily food intake for an adult is 40-45 kg fresh browse and 28-30 kg when confined to a boma. Free-roaming sub-adults consume approximately 20 kg per day. Most activity takes place during the daylight hours. On moonlight nights they forage far into the night hours.

Social structure

Black rhino are solitary except for cows with calves. The calf leaves its mother at an age of 2.2-3.3 years when the next calf is born. It then becomes a solitary nomad until it reaches social maturity and establishes its own home range. Temporary aggregations of 4-7 females of different ages are often found at water holes, at centralized feeding grounds during drought and in bad seasons. Bulls become territorial at an age of 9 years and defend their territories aggressively. They are also aggressive towards calves. A single dominant bull associates with an adult cow and her calf for mating purposes only and the association rarely lasts more than 6-7 days.

Diseases

In cold areas such as the Free State, frost-bite is common on the skin of the belly, the ear tips and the end of the tail. Mortalities due to freezing and pneumonia have been reported. Warts are caused by the parasite “filaria” that is dispersed by biting flies. Malnutrition during droughts and in captivity causes females to abort. Diarrhoea caused by the Salmonella sp, anthrax and tuberculosis cause mortalities, as do babesiosis and theileriosis carried by ticks and trypanosomiasis by tsetse flies.

Information Table

Bibliography