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The black rhinoceros

25 August 2015

 

www.leopard.tvBlack rhinoceroses once occurred on the slopes of Table Mountain and were common on the Cape Flats. There are five types of living rhinoceros in the world but only the white rhinoceros Ceratotherium simum and the black rhinoceros Diceros bicornis occur in Africa. They all have single stomachs and do not chew the cud. The black rhinoceros was first described scientifically as Rhinoceros bicornis by Linnaeus in 1758 but the genus Diceros was coined by Gray in 1821 because the genus Rhinoceros only occurs outside Africa. The first black rhinoceroses in South Africa were seen by the explorers Kolb, Jacobaeus and Schroekius in the Western Cape. There are six subspecies of black rhinoceros in Africa, with Diceros bicornis bicornis in the south-western semi-deserts, Diceros bicornis minor in the savannas from South Africa northward to the south of Tanzania and Diceros bicornis chobiensis from the Northern Cape to south-eastern Angola in southern Africa. They are all either vulnerable or are being threatened with extinction. A fossil ancestor lived in Europe and its descendants later split into one group in Africa and another one in Asia. Fossil black rhinoceroses that are some 7 to 2.5 million years old are found in Africa.

The skin of a black rhinoceros of some 32 mm thick is in fact dark grey in colour but the mud in which it rolls at times gives it a black colour. In opposition to the white rhinoceros, the black rhinoceros has a prehensile upper lip which allows it to strip leaves from woody plants. The head is some 55 cm long as opposed to 76 cm in a white rhinoceros, but the black rhinoceros has a longer neck to enable it to feed higher than a white rhinoceros. The ears are small and round and have a fringe of hair on the upper edge. A black rhinoceros does not have the characteristic hump on the neck that is found on a white rhinoceros. There are eyelashes and the horns consist of hair without contact with the skull. The front horn usually is usually longer than the hind one, but the horns may at times be equal in length. In an adult black rhinoceros the front horns grows at a mean rate of 6 cm per year and the hind one at 2.7 cm per year, but growth is more rapid in young animals.

The shoulder height in adult bulls and cows is some 1.6 m, and the bull usually weighs 700 to 1000 kg as opposed to 720 to 1150 in a cow, but at times even heavier. The skin is covered sparsely with hair and each foot has three, flat nails. Both sight and hearing are acute. A black rhinoceros seldom charges uphill but can reach a speed of 50 km per hour when charging. The ideal habitat consists of shrub- or woodland with numerous shrubs and young trees lower than 4 m, and natural waterholes within 15 km in which to cool off. At times, the black rhinoceros occurs in forests and riverine woodlands too.

Depending on the region a black rhinoceros will eat up to 30 per cent grass. In most habitats, however, the diet consists of 96 per cent leaves, twigs and wild fruits, and 4 per cent grass. Black rhinoceroses eat less than 10 per cent of the available leaves, can handle thorns with ease and also eat the tamboti tree and several types of Euphorbia despite the toxic, milky sap. Some plants are eaten for their moisture content. Digestion occurs in the hindgut and as a result of utilisation some shrubs may be trimmed to a round shape. A black rhinoceros drinks some 35 litres of water every night during the hot season, but does so every second night in the cool season. When water is not freely available black rhinoceroses will dig for water in sandy riverbeds by using their forefeet. Feeding is being done mainly at night, the dung is dark brown in colour and it contains twigs that have been bitten off at a characteristic 45 degree angle.

Black rhinoceroses are single animals but up to 16 animals have been seen together in a loose association. There is no strict territoriality bur there are specific ranges which overlap. In dense woodlands, the range size is some 3 km2 for an adult cow and 4.3 km2 for an adult bull. However, in arid regions a range can be as large as 500 km2. The bulls use latrines in which to defecate, scrape through the dung with their hind feet to serve as scent marks, and they scent-mark the boundaries of their ranges by spraying urine on tufts of grass, shrubs, tree stumps or rocks. Nursery herds are not formed and activity mostly occurs at night but also at sunset and sunrise. They rest in cover under bushes by day.

Mating occurs throughout the year, with peaks in October and November and again from April to June. Bull calves are born more often when mating occurs in the wet season and heifers when it happens in the dry season. The calf is paler grey in colour at birth and weighs some 40 kg at birth. It is not hidden and starts to nibble at plants a few weeks after birth. However, it only owever, it only However, it only weans when it is a year or older and leaves its mother when it is two to four years old and the next calf has been born. Bulls occupy adjacent ranges which become vacant slowly because it disturbs the natural mating relationships.

A population grows at 5 to 10 per cent per year because a cow only becomes sexually mature when she is six to seven years old, and a bull when he is eight to nine years old. However, sometimes cows can be younger when first mating. Gestation lasts for 15 months and there is a low natural mortality. The life expectancy is 35 to 40 years. Adult black rhinoceroses are attacked by lions and spotted hyaenas, and are susceptible to extended droughts. Up to 16 per cent of the calves can die in their first year of life. In the wild there are 1 to 1.5 adult cows per adult bull. The black rhinoceros is not susceptible to rinderpest and is resistant to anthrax. The intensive production of black rhinoceroses is discussed elsewhere.

An electrified wire some 750 mm above the ground and 225 mm away from a wire fence is required when fencing. The best forage is fresh lucerne, but antelope pellets are not advised because they can contain gossypol which is toxic to a black rhinoceros. Vitamin B syrup can be mixed with the water.

When capturing a black rhinoceros it should preferably occur early in the morning in early autumn by using M-99 mixed with azaperone as a tranquillizer. Capture should occur when the ambient temperature is less than 25°C and the moisture content of the air is low. Following immobilisation, a black rhinoceros must lie on its brisket. As an alternative, A3080 can also be used in combination with azaperone as a tranquillizer. Short-term tranquillization can be done with azaperone, and long-term tranquillization with perphenazine enanthate. Transport a black rhinoceros directly after capture in a strong single crate which has been designed especially for rhinoceroses or allow them to acclimatize in special bomas. During transportation, a black rhinoceros will eat lucerne.

On the basis of its weight and diet a black rhinoceros is equivalent to 3.11 Grazing Units (0.32 black rhinoceroses per Grazing Unit) and 3.76 Browsing Units (0.27 black rhinoceroses per Browsing Unit). A limited number of rhinoceros hunts are being regulated carefully. The best known trophy based on the Rowland Ward System had a horn that measured 135.890 cm. It was collected by K V Painter in Kenya in 1902.


References:

Berkeley E V and L W Linklater 2010. Annual and seasonal rainfall may influence progeny sex ratio in the black rhinoceros. South African Journal of Wildlife Research 40(1): 53 - 57.

Bothma, J du P and J G du Toit (Eds) 2015.Game ranch management, sixth edition. Pretoria: Van Schaik. In press.

Grubb, P 2005. Order Perissodactyla. In D E Wilson and D M Reeder (Eds), Mammal species of the world – a taxonomic and geographic reference, third edition. Baltimore: Johns Hopkins University Press, p 629 - 636.

Skinner, J D and C T Chimimba (Eds) 2005.The mammals of the southern African subregion, third edition. Cambridge: Cambridge University Press, pp 531 - 537.

 

article by Prof J du P Bothma

 

 

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