Rhinos are heavily built, thick-skinned, herbivorous mammals with one or two horns, and three toes on each foot. The family Rhinocerotidae includes five species found in Asia or Africa, all of which are threatened by extinction.
The two-ton, one-horned Great Indian rhinoceroses (Rhinoceros unicornis) is a shy and inoffensive animal that seldom acts aggressively. This rhino was once abundant in Pakistan, northern India, Nepal, Bangladesh, and Bhutan. Today there are about 2,000 Great Indian rhinos left in two reserves, located in Assam, India, and in southern Nepal.
The smaller, one-horned Javan rhinoceros (Rhinoceros sondaicus) is the only species in which the females are hornless. Javan rhinos once ranged throughout southeast Asia, but are now on the edge of extinction, with only about 65 individuals remaining in reserves in Java and Vietnam.
The Sumatran rhinoceros (Didermocerus sumatrensis) is the smallest species of rhino. It has two horns and a hairy hide. There are two subspecies: D. s. sumatrensis of Sumatra and Borneo, and D. s. lasiotis of Thailand, Malaysia, and Burma. Sumatran rhinos are found in hilly jungle and once coexisted in southeast Asia with Javan rhinos. Only about 700 Sumatran rhinos still exist.
The two-horned white, or square-lipped, rhinoceros (Ceratotherium simum) of the African savanna is the second-largest land mammal (after the African elephant). It stands 7 ft (2 m) at the shoulder, and weighs more than 3 tons (2,700 kg). White rhinos have a wide upper lip, useful for grazing. There are two subspecies: the northern white rhino (C. s. cottoni) and the southern white rhino (C. s. simum). Once common in Sudan, Uganda, and Zaire, northern white rhinos are now extremely rare, with only 40 individuals left (28 in Zaire, the rest in zoos). Southern white rhinos are doing somewhat better, with 4,800 individuals left in the wild, and are the world's most abundant rhino.
The smaller, two-horned black rhinoceros (Diceros bicornis) has a pointed upper lip for browsing on leaves and twigs. Black rhinos (which are actually dark brown) can be aggressive but their poor eyesight makes for blundering charges. Black rhinos were once common throughout sub-Saharan Africa, but now are found only in Kenya, Zimbabwe, Namibia, and South Africa. In the late 1990s there were fewer than 1,000 black rhinos left in the wild, compared to 100,000 only 35 years previously.
Widespread poaching has caused crashes in the populations of all species of rhinos. These animals are slaughtered for their horn, which is made of hardened, compressed, hair-like fibers. The horn sells for extremely high prices. In Asia, rhino horn is prized for its supposed medicinal properties, and powdered horn can fetch $12,700 per lb ($28,000 per kg). Rhino horn is also valuable for sale in Yemen, where it is used to make traditional dagger-handles. Because their horns are so valuable, rhinos have been over-hunted throughout their range. They now survive only where there is strict protection from poachers.
Captive-breeding programs for endangered rhinos are hindered by the general lack of breeding success for these animals in zoos, and a slow reproduction rate of only one calf every 3-5 years. The present world rhino population of less than 10,000 is much smaller than half the estimated "safe" long-term survival number of 22,500.
Cunningham, C., and J. Berger. Horn of Darkness: Rhinos on the Edge. New York: Oxford University Press, 1997
Watt, E.M. Black Rhinoceros. Orlando, FL: Raintree Steck-Vaughan, 1998.
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