Indian rhinoceros

Name and taxonomy

Carl Linnaeus gave the species its scientific name in 1758. The genus name Rhinoceros comes from two Greek words that mean nose and horn. The species name unicornis is Latin for one-horned. English speakers first used the word rhinoceros in the fourteenth century. Common English names include greater one-horned rhinoceros, great Indian rhinoceros and Indian rhino.

Zoologists later described the same animal under other names, such as R. indicus in 1817 and R. bengalensis in 1970. All of those names are now treated as synonyms, and the species has no subspecies. Its closest living relative is the Javan rhinoceros, which shares the genus Rhinoceros. The family Rhinocerotidae sits in the order Perissodactyla, the odd-toed hoofed mammals.

Evolution and relatives

Rhinos share the order Perissodactyla with horses and tapirs. DNA studies suggest that the rhino line split from the horse line about 50 million years ago. The rhino family appeared in Eurasia in the Late Eocene. The ancestors of the genus Rhinoceros branched off from the other living rhinos about 15 million years ago. Genome work shows that the Asian one-horned rhinos sit slightly closer to the Sumatran rhino than to the African rhinos. They are also close to the extinct woolly rhinoceros.

The Indian and Javan rhinos separated from each other about 4.3 million years ago. The earliest fossils of the modern species date from the Early Pleistocene. Pleistocene fossils show that it once lived far to the east, in mainland Southeast Asia, southern China and Java. A partial skeleton found in Thailand was described in 2018.

Appearance

The skin is thick and grey-brown, with a pink tint inside the folds where blood vessels lie close to the surface. Deep folds cross the neck, the shoulders and the tops of the legs. Rounded bumps that look like rivets cover the shoulders and upper legs. Apart from eyelashes, ear fringes and a brush on the tail, the body is almost hairless. The horn is made of keratin, the same material as fingernails, and both sexes grow one. In most adults it is about 25 centimetres long, but the record is 61.6 cm.

The head and body of an adult measure 3.1 to 4.1 metres, and the tail adds 70 to 80 centimetres. Shoulder height runs from 147 centimetres in a small cow to 193 cm in a big bull. Bulls average about 2,070 to 2,200 kilograms, and cows about 1,600 kg. Bulls also carry huge neck folds that cows lack or show only faintly. The largest bulls on record reached 436 cm in body length and 4,000 kg. Calves are born without folds, and the horn appears only after about six years.

Habitat and range

The species once lived along the Indus, Ganges and Brahmaputra rivers, from Pakistan east to the border of Myanmar. By the nineteenth century it survived only in the Terai lowlands of Nepal and northern India, and in the Brahmaputra valley of Assam. Today it occupies about 12 protected areas in the same region. Kaziranga National Park in Assam holds more than 2,000 animals, the largest single population. Chitwan National Park is the main site in Nepal.

The preferred habitat is tall wet grassland on a river floodplain, with pools and channels for wallowing. Rhinos also use dry savanna grassland, swamp forest in the rainy season and deciduous forest at the foot of the Himalayas. The best sites lie below 50 metres above sea level and within 500 m of water. Farms, pastures and villages now surround most rhino areas, so animals often graze in crops and secondary forest. GBIF holds occurrence records from 13 countries, but many of those records come from zoos.

Diet and feeding

The Indian rhino is a grazer, and grass makes up almost all of its diet. It also takes leaves, twigs, shrubs, flowers, fruit and water plants. Cultivated rice and Bermuda grass are among the grasses it eats. Animal Diversity Web estimates that an adult needs 150 to 200 kilograms of food a day.

The upper lip is semi-prehensile, and the rhino uses it to hook a grass stem, bend it and bite off the top. To reach a very tall plant, it walks over the stem and pushes it down with its body weight. Mothers use the same trick to bring food within reach of a calf. During the monsoon the grass floods, so rhinos turn to taller bamboo, reeds and tree leaves. They can also put the head under water to crop submerged plants. Flat, grooved molars grind the tough plant material.

Behaviour and social life

Adult bulls live alone for most of the year. Cows travel with their calves and stay with a calf for up to four years, sometimes longer. Young animals form small groups, and two or three young bulls often keep together at the edge of a dominant bull's range. Up to 10 rhinos can share a wallow, especially in the monsoon. In these gatherings the animals are usually calm and greet each other by bobbing the head, touching noses or licking.

The species is most active in the early morning, the late afternoon and at night. In the heat of the day it rests in shade or lies in water or mud. Wallowing cools the body, keeps the skin from drying and helps to shed biting insects. The skin folds hold water for a while after the animal climbs out. Rhinos swim well, and a charging animal can reach 55 kilometres per hour for a short distance.

A bull holds a home range of about 2 to 8 square kilometres, which overlaps the ranges of other bulls. Outside the mating season a dominant bull lets other bulls pass through. When a cow is in heat, bulls fight, and these fights are the most common cause of adult death. Rhinos usually strike with the long lower incisors rather than the horn. A disturbed rhino more often runs away than attacks.

Communication and senses

Hearing and smell are sharp, but eyesight is poor. Researchers have recorded more than 10 distinct calls, among them snorts, honks, bleats, roars, grunts and shrieks. A snort is a first contact call, and a calf grunts to find its mother. Rival bulls honk, bleat and roar at each other during a standoff. A scream or a panting sound warns of danger.

Scent carries much of the message. All rhinos in an area add dung to shared heaps, and each animal sniffs a heap before it uses it. Glands on the feet leave a trace at these latrines. A bull can spray urine 3 to 4 metres behind him, and he often does so when observers disturb him. Flattened ears warn other rhinos of a threat.

Reproduction and life cycle

There is no fixed breeding season. A cow in heat urinates often and gives a loud whistle, and a bull usually arrives within 8 to 10 hours. The bull tests the urine, then chases the cow for 1 to 2 kilometres before mating. Both sexes mate with several partners over a lifetime, and pairs do not stay together.

Gestation lasts about 15.7 months, or 425 to 496 days. The cow gives birth to a single calf that weighs 40 to 81 kilograms. A calf doubles its birth weight within a month. It suckles for 12 to 18 months and stays with its mother for years afterwards. The next calf arrives after a gap of 34 to 51 months. About 10% of calves die before they grow up, mostly to tigers.

Wild cows first breed at about six years old. Bulls can breed at five in captivity, but in one field study almost no bull under 15 years old mated. A wild rhino lives up to about 40 years. In captivity four animals passed 40 years, and the record is 47.

Predators and threats

An adult Indian rhino has no regular predator apart from people. Tigers kill unguarded calves, and a calf up to about six months old is at most risk. In 2017 a group of four tigers killed an adult bull in Dudhwa Tiger Reserve, but such an event is rare. Disease is a bigger danger: anthrax and blood poisoning both occur, and leeches, ticks and worms live on and in the rhino. Horseflies bite through the thick skin.

Poaching for the horn is the main human threat, because powdered horn is sold in traditional Chinese medicine. Between 1980 and 1993 poachers killed 692 rhinos in India. Floods, invasive plants and grazing by cattle degrade the grasslands. More than 70% of all Indian rhinos live in one park, so a single epidemic or flood could hit most of the species at once.

Population and conservation

The IUCN lists the Indian rhinoceros as Vulnerable, and the species has been on CITES Appendix I since 1975. Sport hunting in the nineteenth century drove the animal close to extinction. Some British officers each shot more than 200 rhinos in Assam. By 1908 Kaziranga held about 12 rhinos. India banned all rhino hunting in 1910.

In the early 1990s, the world population stood at about 1,870 to 1,895 animals. A count in 2022 found 4,014, and the estimate for March 2025 is 4,075, with 3,323 in India and 752 in Nepal. Nepal set up an armed rhino patrol and made Chitwan a national park in the early 1970s. Since 1986 Nepal has moved rhinos from Chitwan to Bardia and Shuklaphanta as insurance against an epidemic. The Indian Rhino Vision 2020 programme moves animals into parks such as Manas to found new populations. Zoos breed the species well, and Zoo Basel in Switzerland keeps the international studbook.

Relationship with humans

Seals and figurines of the Indus Valley Civilisation show the rhino, so people have known it for thousands of years. Ancient Indian kings reportedly rode rhinos into battle. Tamed rhinos have pulled ploughs, carried loads and performed in circuses. Rhinos graze in fields around the parks, and farmers have long hunted them to protect crops. Every year a few people in India and Nepal die from rhino attacks, and the attacker is most often a cow with a young calf.

Horn prices rose from about 35 dollars a kilogram in 1972 to about 18,000 dollars in 1991. Rhino viewing in Kaziranga and Chitwan is thought to support many local jobs. Zoos hold the species around the world, and most captive animals descend from the Basel line. The first captive birth took place in Kathmandu in 1826. In 2010 a calf was born in Cincinnati from frozen sperm, a first for the species.

In culture and myth

The Rhinoceros Sutra, an early Buddhist text, tells the seeker to wander alone like the rhino. The text praises the animal's solitary life and its calm. In the Rigveda the animal is called khadga, a word that also means sword. In the Mahabharata, rhino hide is the material of Arjuna's great bow, the Gandiva. In Gujarat a folk goddess, Dhavdi Mata, rides a rhinoceros.

The Tharu people of the Terai say that the god Vishwakarma built the rhino from parts of other animals. The Karbi people of Assam treat the rhino as a lucky animal, and a rhino in the paddy is a good sign. Persian and Arabic writers described a one-horned beast, the karkadann, which probably grew from travellers' tales of this rhino. Albrecht Dürer made his famous woodcut in 1515 from a description of a rhino sent to Portugal. Clara, a female rhino, toured Europe for 17 years from 1741, and Pietro Longhi painted her in Venice. For most Europeans of that time, a rhino was probably an animal known only from pictures.