Black rhinoceros

Appearance

An adult black rhinoceros stands 132–180 cm high at the shoulder and is 2.8–3.8 m in length, plus a tail of about 60 cm in length. An adult typically weighs from 800 to 1,400 kg, however unusually large male specimens have been reported at up to 2,199–2,896 kg. The females are smaller than the males. Two horns on the skull are made of keratin with the larger front horn typically 50 cm long, exceptionally up to 140 cm.

The longest known Black rhinoceros horn measured nearly 1.5 m 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. Skin color depends more on local soil conditions and the rhinoceros's wallowing behavior than anything else, so many black rhinos are typically not truly black in color.

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. 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 : 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 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. 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 of predators.

Naming

There are four recognized subspecies of the black rhinoceros:
⤷  South-central which are the most numerous, and once ranged from central Tanzania south through Zambia, Zimbabwe, and Mozambique to northern and eastern South Africa.
⤷  South-western are better adapted to the arid and semi-arid savannas of Namibia, southern Angola, western Botswana, and western South Africa.
⤷  East African which had a historic distribution from south Sudan, Ethiopia, down through Kenya into north-central Tanzania. Today, its range is limited primarily to Tanzania.
⤷  West African once lived across the savanna belt in western Africa. 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. On November 10, 2011 the IUCN declared the Western Black Rhinoceros extinct.

Distribution

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. According to the International Rhino Foundation, the total African population had recovered to 4,240 by 2008. 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. In 2011 the IUCN declared the Western black rhino extinct.

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.

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. 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 occurred at a traditional Chinese medicine supply store in Portland, Oregon's Chinatown.

Behavior

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 , while in the Ngorongoro it is between 2.6 to 44 km2. 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.

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 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. Adult rhinos normally have no natural predators, but they may fall prey to crocodiles in exceptional circumstances.

Black rhinoceros follow the same trails as 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 running on their toes. 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.

Different types of vocalizations have also been observed. Growls and trumpets may be used during a fight. A long snort indicates anger, while sneeze-like calls are used as an alarm to danger. Short snorts with pricked ears and wrinkled nostrils are a startle reaction to a newcomer. A high-pitched "wonk" has been described for when they are fearful. A high-pitched scream has been observed in times of terror. "Mmwonk", a deep, resonant sound is a sign of contentment. Squeak, done with different tones and intonations may mean "I'm lost", "Where are you?", "I'm over here", or other signals that are not yet understood. Breathing speeds can be used to communicate greetings, anxiety, and reassurance. A puffing snort is a common greeting when males and females encounter one another.

Body language also a form of black rhinoceros communications. A bull will sometimes display an aggressive ritual towards a potential rival. They will smell, spray repeatedly, scrape, trample, and bash with their heads in bushes. They may also snort in an attack posture. When their tail is up, it may indicate one of several things: curiosity, alarm, or sexual receptivity. Erect ears also indicate curiosity, and flat ears express anger.

Reproduction

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 following females that are in season will follow her; when she defecates he will scrape and spread the dung, making it more difficult for any other 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 an hour.

The gestation period is 15 to 16 months. The single calf weighs about 35–50 kg 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 5–7 years old for females, and 7–8 years for males. The life expectancy in natural conditions is from 35–50 years.

Food

The black rhinoceros is a herbivorous browser that eats leafy plants, branches, shoots, thorny wood bushes, and fruit. Their diet can reduce the amount of woody plants, which may benefit grazers, 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 grasslands, savannas, 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 the mud. Wallowing helps cool down body temperature during the day and protects against parasites. If mud is not available rhinos will wallow in dust. Drinking water is most common in the afternoon. When black rhinos browse they use their lips to strip the branches of their leaves.