|Historical black rhinoceros range (c 1700 AD)|
The black rhinocerous (Diceros bicornis), is a species of rhinoceros. It lives in eastern and central Africa including Kenya, Tanzania, Cameroon, South Africa, Namibia, Zimbabwe, and Angola. The black rhinoceros is not actually black, but dark. It is a browser, with lips that help eating from low branches.
The other African rhinoceros is the white rhinoceros (Ceratotherium simum). The white rhinoceros is not white, but lighter coloured.
The rhinoceros originated in the Eocene about fifty million years ago alongside other ungulates (hooved animals). Ancestors of the black and the white rhinoceros were present in Africa by the end of the Late Miocene about ten million years ago. The two species evolved from the common ancestral species Ceratotherium neumayri during this time. The clade comprising the genus Diceros is characterised by an increased adaptation to browsing. Between four and five million years ago, the black rhinoceros diverged from the white rhinoceros. After this split, the direct ancestor of Diceros bicornis, Diceros praecox was present in the Pliocene of East Africa (Ethiopia, Kenya, Tanzania). D. bicornis evolved from this species during the Late Pliocene – Early Pleistocene.
An adult black rhinoceros stands 140–180 cm (55–71 in) high at the shoulder and is 3–3.75 m (9.8–12.3 ft) in length. An adult typically weighs from 800 to 1,400 kg (1,760 to 3,090 lb), however unusually large male specimens have been reported at up to 2,199–2,896 kg (4,848–6,385 lb). The females are smaller than the males. Two horns on the skull are made of keratin with the larger front horn typically 50 cm (20 in) long, exceptionally up to 140 cm (55 in).
The longest known black rhinoceros horn measured nearly 1.5 m (4.9 ft) in length. Sometimes, a third, smaller horn may develop. These horns are used for defense, intimidation, and digging up roots and breaking branches during feeding. The black rhino is smaller than the white rhino, and is close in size to the Javan Rhino of Indonesia. It has a pointed and prehensile upper lip, which it uses to grasp leaves and twigs when feeding. The white rhinoceros has square lips used for eating grass. The black rhinoceros can also be distinguished from the white rhinoceros by its size, smaller skull, and ears; and by the position of the head, which is held higher than the white rhinoceros, since the black rhinoceros is a browser and not a grazer. This key differentiation is further illustrated by the shape of the two species mouths (lips): the "square" lip of the white rhinoceros is an adaptation for grazing, and the "hooked" lip of the black rhinoceros is an adaptation to help browsing.
Their thick-layered skin helps to protect the rhino from thorns and sharp grasses. Their skin harbors external parasites, such as mites and ticks, which may be eaten by oxpeckers and egrets. Such behaviour was originally thought to be an example of mutualism, but recent evidence suggests that oxpeckers may be parasites instead, feeding on rhino blood. It is commonly assumed that black rhinos have poor eyesight, relying more on hearing and smell. However, studies have shown that their eyesight is comparatively good, at about the level of a rabbit. Their ears have a relatively wide rotational range to detect sounds. An excellent sense of smell alerts rhinos to the presence of predators.
As with many other components of the African large mammal fauna, black rhinos probably had a wider range in the northern part of the continent in prehistoric times than today. However this seems to have not been as extensive as that of the white rhino. Unquestionable fossil remains have not yet been found in this area and the abundant petroglyphs found across the Sahara desert are often too schematic to unambiguously decide whether they depict black or white rhinos. Petroglyphs from the Eastern Desert of southeastern Egypt relatively convincingly show the occurrence of black rhinos in these areas in prehistoric times.
Historical and extant range
The natural range of the black rhino included most of southern and eastern Africa, but it did not occur in the Congo Basin, the tropical rainforest areas along the Bight of Benin, the Ethiopian Highlands, and the Horn of Africa. Its former native occurrence in the extremely dry parts of the Kalahari desert of southwestern Botswana and northwestern South Africa is uncertain. In western Africa it was abundant in an area stretching east to west from Eritrea and Sudan through South Sudan to southeastern Niger, and especially around Lake Chad. Its occurrence further to the west is questionable, though often purported to in literature. Today it is totally restricted to protected nature reserves and has vanished from many countries in which it once thrived, especially in the west and north of its former range. The remaining populations are highly scattered. Some specimens have been relocated from their habitat to better protected locations, sometimes across national frontiers. The black rhino has been successfully reintroduced to Malawi since 1993, where it became extinct in 1990. Similarly it was reintroduced to Zambia (North Luangwa National Park) in 2008, where it had become extinct in 1998, and to Botswana (extinct in 1992, reintroduced in 2003).
Black rhinoceros are generally thought to be solitary, with the only strong bond between a mother and her calf.
They are not very territorial and often intersect other rhino territories.
Black rhinos have also been observed to have a certain area they tend to visit and rest frequently called "houses" which are usually on a high ground level. These "home" ranges can vary from 2.6 km2 to 133 km2 with smaller home ranges having more abundant resources than larger home ranges.
Black rhinoceros in captivity and reservations sleep patterns have been recently studied to show that males sleep longer on average than females by nearly double the time.
The black rhino has a reputation for being extremely aggressive, and charges readily at perceived threats. They have even been observed to charge tree trunks and termite mounds.
Black rhinoceros follow the same trails that elephants use to get from foraging areas to water holes. They also use smaller trails when they are browsing. They are very fast and can get up to speeds of 55 kilometres per hour (34 mph) running on their toes.
The black rhinoceros is a herbivorous browser that eats leafy plants, branches, shoots, thorny wood bushes, and fruit. The optimum habitat seems to be one consisting of thick scrub and bushland, often with some woodland, which supports the highest densities. Their diet can reduce the amount of woody plants, which may benefit grazers (who focus on leaves and stems of grass), but not competing browsers (who focus on leaves, stems of trees, shrubs or herbs). It has been known to eat up to 220 species of plants.
They have a significantly restricted diet with a preference for a few key plant species and a tendency to select leafy species in the dry season. The plant species they seem to be most attracted to when not in dry season are the woody plants. Different subspecies live in different bushlands including, Acacia bushlands, Euclea bushlands, mixed bushlands, and dense euclea bushland.
They browse for food in the morning and evening. They are selective browsers but, studies done in Kenya show that they do add the selection material with availability in order to satisfy their nutritional requirements. In the hottest part of the day they are most inactive- resting, sleeping, and wallowing in mud. Wallowing helps cool down body temperature during the day and protects against parasites. When black rhinos browse they use their lips to strip the branches of their leaves. Competition with elephants is causing the black rhinoceros to shift its diet. The black rhinoceros alters its selectivity with the absence of the elephant.
Rhinos use several forms of communication. Due to their solitary nature, scent marking is often used to identify themselves to other black rhinos. Urine spraying occurs on trees and bushes, around water holes and feeding areas. Females urine spray more often when receptive for breeding. Defecation sometimes occurs in the same spot used by different rhinos, such as around feeding stations and watering tracks. Coming upon these spots, rhinos will smell to see who is in the area and add their own marking. When presented with adult feces, male and female rhinoceroses respond differently than when they are presented with subadult feces. The urine and feces of one black rhinoceros helps other black rhinoceroses to determine its age, sex, and identity. Less commonly they will rub their heads or horns against tree trunks to scent-mark.
The black rhino has powerful tube-shaped ears that can freely rotate in all directions. This highly developed sense of hearing allows black rhinos to detect sound over vast distances.
The adults are solitary in nature, coming together only for mating. Mating does not have a seasonal pattern but births tend to be towards the end of the rainy season in more arid environments.
When in season the females will mark dung piles. Males will follow females when they are in season; when she defecates he will scrape and spread the dung, making it more difficult for rival adult males to pick up her scent trail.
Courtship behaviors before mating include snorting and sparring with the horns among males. Another courtship behavior is called bluff and bluster, where the rhino will snort and swing its head from side to side aggressively before running away repeatedly. Breeding pairs stay together for 2–3 days and sometimes even weeks. They mate several times a day over this time and copulation lasts for a half-hour.
The gestation period for a black rhino is 15 months. The single calf weighs about 35–50 kilograms (80–110 lb) at birth, and can follow its mother around after just three days. Weaning occurs at around 2 years of age for the offspring. The mother and calf stay together for 2–3 years until the next calf is born; female calves may stay longer, forming small groups. The young are occasionally taken by hyenas and lions. Sexual maturity is reached from 5 to 7 years old for females, and 7 to 8 years for males. The life expectancy in natural conditions (without poaching pressure) is from 35 to 50 years.
For most of the 20th century the continental black rhino was the most numerous of all rhino species. Around 1900 there were probably several hundred thousand living in Africa. During the latter half of the 20th century their numbers were severely reduced from an estimated 70,000 in the late 1960s to only 10,000 to 15,000 in 1981. In the early 1990s the number dipped below 2,500, and in 2004 it was reported that only 2,410 black rhinos remained.
Today, there are various threats posed to the black rhinoceros including habitat changes, illegal poaching, and competing species. Civil disturbances such as war have made mentionably negative effects on the black rhinoceros populations in since the 1960s in countries including, but not limited to, Chad, Cameroon, Rwanda, Mozambique, and Somalia.
Illegal poaching for the international rhino horn trade is the main and most detrimental threat.
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