There are five species of rhino alive today, four of which are endangered or critically endangered. Rhinos have poor eyesight but a very keen sense of smell and hearing. Their horns, for which they have been extensively hunted, are made up of keratin, the same substance that forms human fingernails and hair. Rhinos are vegetarian and related to horses and tapirs.
Rhinos are large, squat mammals with thick but loose, grayish skin and square heads. They are famous for their horns, which protrude forward from their noses, although the females of some species do not have visible horns. Rhinos have one or two horns and three toes on each foot. All species can weigh over a ton and can run as fast as 40 miles per hour.
The white rhinoceros (Ceratotherium simum) is actually gray and is also known as the square-lipped rhino. It is the most abundant living species with a population of about 17,500 ranging across game parks and nature reserves in South Africa, Namibia, Botswana, Zimbabwe and Swaziland. The white rhino can weigh 7,700 lbs. and stand over 6 feet high at the shoulder. It feeds mainly on grass.
The black rhinoceros (Diceros bicornis) is sometimes called the hook-lipped rhinoceros because of its long, almost prehensile upper lip. Both sexes have two horns, the larger of which can be up to 5 feet long. The black rhino lived across sub-Saharan Africa but is now limited to parks and game reserves. It feeds on grass and other vegetation.
The Indian or great one-horned rhinoceros (Rhinoceros unicornis) once ranged across much of northern and eastern India on the Indus and Ganges River plains but is now found only in nature reserves in Northern India and Nepal. It is the largest of the rhino species and large adult males can weigh up to 7,700 lbs. Indian rhinos have a single horn up to 20 inches long.
The Javan rhinoceros (Rhinoceros sondaicus) grows to 6 feet at the shoulder and can weigh 5,500 lbs. Like the Indian rhino, it has heavily folded skin and a single horn. Javan rhinos are the rarest of the rhinos, with perhaps 50 living in Java and less than 10 in Vietnam.
The two-horned Sumatran rhinoceros (Dicerorhinus sumatrensis) is the smallest rhino species, being less than 5 feet high and weighing no more than 1,750 lbs. It is covered in coarse red hair. There are thought to be less than 300 wild Sumatran rhinos living in the tropical forests of Malaysia, Sumatra and Borneo. It was once found in forests all across South Asia from Bhutan to Laos and China.
African rhinos and the Indian rhino live in open grassland and savannah, while the Javan and Sumatran species prefer thick tropical forest. All species are vegetarian, with the white and Indian species eating mainly grass and the others a wide range of vegetation. Due to their size, rhinos have few natural predators, although young ones may be eaten by big cats and crocodiles. Females give birth to a single calf after a gestation period of about 15 months.
All species are solitary except for the white rhino, which lives in groups, called crashes, of up to 15 animals. Rhinos spend a lot of time in wallows and will even enlarge existing mud pits with their horns. They use urine and feces to mark their territory. Black rhinos in particular are known to be very aggressive and up to 50 percent of male black rhinos die in combat with other males.
Of all the large mammals, the rhino species have suffered most from human hunting. Their horns are considered a powerful aphrodisiac in traditional Chinese medicine and also said to cure fevers and convulsions. The northern subspecies of the white rhino is now extinct in the wild. There are no more than 24,500 rhinos left, of which 17,500 are white rhinos. Between 1970 and 1992 the black rhino population crashed by 96 percent due to poaching.