Thursday, March 7, 2013

black rhino


The black rhinoceros or hook-lipped rhinoceros (Diceros bicornis) is a species of rhinoceros, native to eastern and central Africa including KenyaTanzaniaCameroonSouth Africa,NamibiaZimbabwe, and Angola. Although the rhinoceros is referred to as black, its colors vary from brown to gray.
The other African rhinoceros is the white rhinoceros (Ceratotherium simum). The word "white" in the name "white rhinoceros" is a misinterpretation of the Afrikaans word wyd, itself derived from the Dutch word wijd for wide, referring to its square upper lip, as opposed to the pointed or hooked lip of the black rhinoceros. These species are now sometimes referred to as the square-lipped (for white) or hook-lipped (for black) rhinoceros.[5]
The species overall is classified as critically endangered, and one subspecies, the western black rhinoceros, was declared extinct by the IUCN in 2011.[6]

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[edit]Taxonomy

The species was first named Rhinoceros bicornis by Carolus Linnaeus in the 10th edition of his Systema naturae in 1758. The name means "double-horned rhinoceros". There is some confusion about what exactly Linnaeus conceived under this name as his species was probably based upon the skull of a single-horned Indian rhinoceros (Rhinoceros unicornis), with a second horn artificially added by the collector. Such a skull is known to have existed and Linnaeus even mentioned India as origin of this species. However he also referred to reports of early travelers about a double-horned rhino in Africa and when it emerged that there is only one, single-horned species of rhino in India, "Rhinoceros" bicornis was used to refer to the African rhinos (the white rhinoonly became recognised in 1812).[7] In 1911 this was formally fixed and the Cape of Good Hope officially declared the type locality of the species.[8]

[edit]Subspecies The intraspecific variation in the black rhinoceros was discussed by various authors and is not finally settled.[9] The most accepted scheme considers seven or eight subspecies,[3][10][11] of which three became extinct in historical times and one is on the very brink of extinction:

  • Southern black rhinoceros or Cape rhinoceros (Diceros bicornis bicornis) – Extinct. Once abundant from the Cape of Good Hope to TransvaalSouth Africa and probably into the south of Namibia, this was the largest subspecies. It became extinct by excessive hunting and habitat destruction around 1850.[12]
  • North-eastern black rhinoceros (Diceros bicornis brucii) – Extinct. Formerly central SudanEritrea, northern and southeastern EthiopiaDjibouti and northern and southeastern Somalia. Relict populations in northern Somalia vanished during the early 20th century.
  • Chobe black rhinoceros (Diceros bicornis chobiensis) – A local subspecies restricted to the Chobe Valley in southeastern Angola, Namibia (Caprivi Strip) and northern Botswana. Nearly extinct, possibly only one surviving specimen in Botswana.[11]
  • Uganda black rhinoceros (Diceros bicornis ladoensis) – Former distribution from South Sudan, across Uganda into western Kenya and southwesternmost Ethiopia. Black rhinos are considered extinct across most of this area and its conservational status is unclear. Probably surviving in Kenyan reserves.
  • Western black rhinoceros (Diceros bicornis longipes) – Extinct. Once lived in South Sudan, northern Central African Republic, southern Chad, northern Cameroon, northeastern Nigeriaand south-eastern Niger. The range possibly streched west to the Niger River in western Niger, though this is unconfirmed. A far greater former range in West Africa as proposed earlier[13] is doubted by a 2004 study.[4] The last known wild specimens lived in northern Cameroon. In 2006 an intensive survey across its putative range in Cameroon failed to locate any, leading to fears that it was extinct in the wild.[6][14] On November 10, 2011 the IUCN declared the western black rhinoceros extinct.[6]
  • Eastern black rhinoceros (Diceros bicornis michaeli) – Had a historical distribution from South SudanEthiopia, down through Kenya into north-central Tanzania. Today, its range is limited primarily to Tanzania.
  • South-central black rhinoceros (Diceros bicornis minor) – Most widely distributed subspecies, characterised by a compact body, proportionally large head and prominent skin-folds. Ranged from north-eastern South Africa (KwaZulu-Natal) to northeastern Tanzania and southeastern Kenya. Preserved in reserves throughout most of its former range but probably extinct in eastern Angola, southern Democratic Republic of Congo and possibly Moçambique. Extinct but reintroduced in MalawiBotswana, and Zambia.
  • South-western black rhinoceros (Diceros bicornis occidentalis) – A small subspecies, adapted to survival in desertic and semi-desertic conditions. Originally distributed in north-western Namibia and southwestern Angola, today restricted to wildlife reserves in Namibia with sporadic sightings in Angola. These populations are often erroneously referred to D. b. bicornis or D. b. minor but represent a subspecies to their own.[11]
The most widely adopted alternative scheme only recognizes five subspecies or "eco-types", D. bicornis bicornisD. bicornis bruciiD. bicornis longipesD. bicornis michaeli, and D. bicornis minor.[15] This concept is also used by the IUCN, listing three surviving subspecies and recognizing D. bicornis brucii and D. bicornis longipes as extinct. The most important difference to the above scheme is the inclusion of the extant southwestern subspecies from Namibia in D. bicornis bicornis instead in its own subspecies, whereupon the nominal subspecies is not considered extinct.[2]

Evolution

The black and the white rhinoceros are currently considered to have evolved from the common ancestral species Ceratotherium neumayri during the Late Miocene. The clade comprising thegenus Diceros is characterised by an increased adaptation to browsing. After this split, the direct ancestor of Diceros bicornisDiceros praecox was present in the Pliocene of East Africa (Ethiopia, Kenya, Tanzania). D. bicornis evolved from this species during the Late Pliocene – Early Pleistocene.[16]

[edit]Description

Black rhino in Ngorongoro crater, Tanzania
Diceros bicornis skull
An adult black rhinoceros stands 132–180 cm (52–71 in) high at the shoulder and is 2.8–3.8 m (9.2–12 ft) in length, plus a tail of about 60 cm (24 in) in length.[17] An adult typically weighs from 800 to 1,400 kg (1,800 to 3,100 lb), however unusually large male specimens have been reported at up to 2,199–2,896 kg (4,850–6,380 lb).[3] 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.[18] 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 has a pointed and prehensile upper lip, which it uses to grasp leaves and twigs when feeding.[18] 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.[citation needed]
Their thick-layered skin protects the rhino from thorns and sharp grasses. Their skin harbors external parasites, such as mites and ticks, which are eaten by oxpeckers and egrets that live with the rhino. 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.[19] Black rhinos have poor eyesight, relying more on hearing and smell. Their ears possess a relatively wide rotational range to detect sounds. An excellent sense of smell alerts rhinos to the presence ofpredators.

[edit]Distribution

Black rhinos in Ngorongoro crater, Tanzania

[edit]Prehistorical range

As 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.[20]

[edit]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.[3] Its former native occurrence in the extreme dry parts of the Kalahari desert of southwestern Botswana and northwestern South Africa is uncertain.[21] In western Africa it was abundant in an area stretching east to west from Eritrea and Sudan through South Sudan to northeastern Nigeria, and especially around Lake Chad. Its occurrence further to the west is questionable, though often purported in the literature.[4] 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.[2] The black rhino has been successfully reintroduced toMalawi since 1993, where it went extinct in 1990.[22] Similarly it was reintroduced to Zambia (North Luangwa National Park) in 2008, where it became extinct in 1998,[23] and to Botswana (extirpation in 1992, reintroduction in 2003).[24]

[edit]Conservation

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[2] living in Africa. During the latter half of the 20th century their numbers were severely reduced from an estimated 70,000[25] 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. According to the International Rhino Foundation, the total African population had recovered to 4,240 by 2008 (which suggests that the 2004 number was low).[26] In 2002 only 10 West African rhinos remained in Cameroon, and in 2006 intensive surveys across its putative range failed to locate any, leading to fears that this subspecies was extinct.[14] In 2011 the IUCN declared the Western black rhino extinct.[27]
The only rhino that has recovered somewhat from the brink of extinction is the southern white whose numbers now are estimated around 14,500, up from fewer than 50 in the first decade of the 20th century.[28]
The black rhinoceros had been pushed to the brink of extinction by illegal poaching for their horn, and to a lesser extent by loss of habitat. A major market for rhino horn has historically been in the Arab nations to make ornately carved handles for ceremonial daggers called jambiyas. Demand for these exploded in the 1970s causing the black rhinoceros population to decline 96% between 1970 and 1992. The horn is also used in traditional Chinese medicine, and is said by herbalists to be able to revive comatose patients, cure fevers, and aid male sexual stamina and fertility.[29] The purported effectiveness of the use of rhino horn in treating any illness has not been confirmed by medical science. In June 2007, the first-ever documented case of the medicinal sale of black rhino horn in the United States (confirmed by genetic testing of the confiscated horn) occurred at a traditional Chinese medicine supply store in Portland, Oregon'sChinatown.[29]

[edit]Behavior

Black rhinoceros at Lincoln Park Zoo
Although they are typically solitary animals, with the exception of coming together to mate, mothers and calves will sometimes congregate in small groups for short periods of time. Males are not as sociable as females, although they will sometimes allow the presence of other rhinos. They are not very territorial and often intersect other rhino territories. Home ranges vary depending on season and the availability of food and water. Generally they have smaller home ranges and larger density in habitats that have plenty of food and water available, and vice versa if resources are not readily available. In the Serengeti home ranges are around 43 to 133 km2 (17 to 51 sq mi), while in the Ngorongoro it is between 2.6 to 44 km2 (1.0 to 17 sq mi). 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.[citation needed]
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.[citation needed] Black rhinos will fight each other, and they have the highest rates of mortal combat recorded for any mammal: about 50% of males and 30% of females die from combat-related injuries.[30] Adult rhinos normally have no natural predators, thanks to their imposing size as well as their thick skin and deadly horns.[31] However, adult black rhinos have fallen prey tocrocodiles in exceptional circumstances.[32] Calves and, very seldom, small sub-adults may be preyed upon by lions as well.[3]
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 56 kilometres per hour (35 mph) running on their toes.

[edit]Diet

Chewing on plants
The black rhinoceros is a herbivorous browser that eats leafy plants, branches, shoots, thorny wood bushes, and fruit.[33] Their diet can reduce the amount of woody plants, which may benefit grazers (who eat grass), but not competing browsers. It has been known to eat up to 220 species of plants. It can live up to 5 days without water during drought. Black rhinos live in primarily grasslandssavannas, and tropical bushland habitats.
They browse for food in the morning and evening. 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. If mud is not available rhinos will take dust baths. Drinking water is most common in the afternoon. When black rhinos browse they use their lips to strip the branches of their leaves.

[edit]Communication

Black rhino in Ngorongoro crater, Tanzania
Rhinos use several forms of communication. Due to their bad eyesight and 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. Less commonly they will rub their heads or horns against tree trunks to scent-mark.

[edit]Reproduction

Mother and calf in Lewa, central Kenya
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 is 15 to 16 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.[17]

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