Rhinoceros

About the rhinoceros

Rhinoceros, commonly shortened to rhino, is the name for any of the five living species of odd-toed ungulate in the family Rhinocerotidae. Two of those species, the black rhinoceros and the white rhinoceros, are native to Africa; the other three, the Javan, Indian, and Sumatran rhinoceros, are native to South and Southeast Asia. All five are among the largest living land animals, weighing over half a tonne as adults, with average weights ranging from about 775 kilograms (1,709 pounds) in the Sumatran rhinoceros up to 2,300 kilograms (5,100 pounds) in the white rhinoceros.

Every living rhinoceros carries one or two horns made of keratin — the same material as hair and fingernails — attached to a roughened patch of bone on the skull, and grown in a way that resembles how human nails develop. Their skin is thick, from 1.5 to 5 centimeters (0.6 to 2 inches), built from densely layered, crosslinked collagen fibers arranged in a lattice that is notably stronger and stiffer than the skin of other mammals; it typically folds prominently. Despite their bulk, rhinoceroses have relatively small brains for their body size — around 531 grams (18.7 ounces) in an adult black rhinoceros. Most rhinoceroses, living and extinct, have three toes on each foot. Skin color runs from gray to brown, and adults are sparsely haired or hairless except for the eyelashes, ears, and tail-brush — the Sumatran rhinoceros is the exception, often carrying a considerable coat of hair.

The name rhinoceros comes from the Ancient Greek for "nose-horned," and has been in English use since the 14th century; the plural can be either "rhinoceros" or "rhinoceroses." Carl Linnaeus named the first two rhinoceros species, the Indian and black rhinoceros, in 1758, and in doing so coined the genus Rhinoceros — though he mistakenly placed them near rodents because Indian rhinoceroses have incisor teeth. The family name Rhinocerotidae was first proposed in 1821.

Behavior and diet

Rhinoceroses are herbivores whose diets range from strict grazing, as in the white rhinoceros, to largely browsing, as in the black rhinoceros, with the Sumatran and Javan rhinoceros falling somewhere in between. As bulk feeders on relatively low-quality vegetation, they spend much of their time foraging, and their hindgut fermentation lets them digest fibrous plant matter that would be difficult for many other mammals to process. The two African species lack front teeth altogether and instead use their lips to pluck food.

Sociability varies by species. Adult males tend to be solitary, and so do female Asian rhinoceroses, though females of the African species — especially white rhinoceroses more than black — sometimes form groups. All living rhinoceroses have a mating system in which both sexes seek multiple partners. Males guard females that are near estrus and taste their urine, performing a curled-lip flehmen response to judge reproductive status; confrontations between rival males near a receptive female range from ritual display to serious, injurious fighting. Copulation itself can last several hours, and pregnancy runs long — around 460 days in the black rhinoceros and 504 days in the white rhinoceros.

Calves typically stand within 30 minutes of birth and nurse within two hours. Mothers form strong bonds with their most recent calf and are fiercely protective against predators, though juveniles remain vulnerable to predation until about three years old. Among one-horned Asian species, a mother generally drives off her older calf around the time her next one is born. Rhinoceroses reach sexual maturity around five to eight years old; males mature roughly a year later than females in the black and Sumatran species, while male white rhinoceroses do not reach socio-sexual maturity until about 12 years old, four years after females begin giving birth.

Range and habitat

Rhinoceroses occupy two separate native ranges today. The white and black rhinoceros are found across parts of Africa: the white rhinoceros in southern Africa, where the southern subspecies numbered roughly 20,405 animals as of 2013, making it the most abundant rhino subspecies in the world, while a critically endangered northern subspecies survives only as two captive females; the black rhinoceros historically ranged across central, southern, and eastern Africa, though its subspecies now occupy fragmented pockets from Tanzania and Zambia to Namibia and South Africa. The three Asian species are far more restricted. The Indian rhinoceros, once found from Pakistan to Myanmar, now survives mainly in protected grasslands and forests in the Himalayan foothills of Assam, West Bengal, and Nepal, with two-thirds of the world's population concentrated in India's Kaziranga National Park. The Javan rhinoceros, among the most endangered large mammals anywhere, is now confined to the island of Java, Indonesia, with an estimated 60 individuals remaining as of 2015. The Sumatran rhinoceros is the smallest living species by weight.

Conservation status

There is no single IUCN Red List status for rhinoceroses, because the IUCN assesses each species separately, and the picture differs sharply between them. The northern white rhinoceros subspecies is critically endangered with only two known captive individuals left, while the Javan rhinoceros survives as an estimated 60 wild animals.

Across the group, the central threat is poaching for rhino horn, sold on the black market at high prices for use in traditional Chinese medicine and other purposes in China and Vietnam, despite horn being made of keratin with no demonstrated health benefit. A market for rhino horn dagger handles in Yemen was the main driver of demand during the 1970s and 1980s.

Black rhinoceros numbers illustrate the scale of the decline and the later recovery. From about 70,000 in the late 1960s, the population fell to a record low of 2,410 by 1995, then roughly doubled to 4,880 by the end of 2010. Even so, as of 2008 the population remained an estimated 90 percent below its level three generations earlier.