Indian rhinoceros

The Indian rhinoceros (Rhinoceros unicornis), also called the Indian rhino, greater one-horned rhinoceros or great Indian rhinoceros, is a rhinoceros species native to the Indian subcontinent. It is listed as Vulnerable on the IUCN Red List, as populations are fragmented and restricted to less than 20,000 km² (7,700 sq mi). Moreover, the extent and quality of the rhino’s most important habitat, the alluvial Terai-Duar savanna and grasslands and riverine forest, is considered to be in decline due to human and livestock encroachment. As of August 2018, the global population was estimated to comprise 3,588 individuals, including 2,939 individuals in India and 649 in Nepal. Kaziranga National Park alone had an estimated population of 2,048 rhinos in 2009. Pobitora Wildlife Sanctuary in Assam has the highest density of Indian rhinos in the world with 84 individuals in an area of 38.80 km² (14.98 sq mi) in 2009.

Indian rhinos once ranged throughout the entire stretch of the Indo-Gangetic Plain, but excessive hunting and agricultural development reduced its range drastically to 11 sites in northern India and southern Nepal. In the early 1990s, between 1,870 and 1,895 Indian rhinos were estimated to have been alive. Since then, numbers have increased due to conservation measures taken by the government. However, poaching remains a continuous threat, as more than 150 Indian rhinos were killed in Assam by poachers between 2000 and 2006.

Nearly 85% of the global Indian rhinoceros population is concentrated in Assam, where Kaziranga National Park contains 70% of rhino population.

Etymology

The generic name Rhinoceros is a combination of the ancient Greek words ῥίς (ris) meaning “nose” and κέρας (keras) meaning “horn of an animal”. The Latin word ūnicornis means “one-horned”.

Taxonomy

Rhinoceros unicornis was the scientific name used by Carl Linnaeus in 1758 who described a rhinoceros with one horn. As type locality, he indicated Africa and India.

The Indian rhinoceros is monotypic. Several specimens were described since the end of the 18th century under different scientific names, which are all considered synonyms of Rhinoceros unicornis today:

• R. indicus by Cuvier, 1817
• R. asiaticus by Blumenbach, 1830
• R. stenocephalus by Gray, 1867
• R. jamrachi by Sclater, 1876
• R. bengalensis by Kourist, 1970

Evolution

Ancestral rhinoceroses first diverged from other perissodactyls in the Early Eocene. Mitochondrial DNA comparison suggests the ancestors of modern rhinos split from the ancestors of Equidae around 50 million years ago. The extant family, the Rhinocerotidae, first appeared in the Late Eocene in Eurasia, and the ancestors of the extant rhino species dispersed from Asia beginning in the Miocene.

Fossils of R. unicornis appear in the Middle Pleistocene. In the Pleistocene, the genus Rhinoceros ranged throughout South and Southeast Asia, with specimens located on Sri Lanka. Into the Holocene, some rhinoceros lived as far west as Gujarat and Pakistan until as recently as 3,200 years ago.

The Indian and Javan rhinoceroses, the only members of the genus Rhinoceros, first appear in the fossil record in Asia during the Early Pleistocene. The Indian rhinoceros is known from Early Pleistocene localities in Java, South China, India and Pakistan. Molecular estimates suggest the species may have diverged much earlier, around 11.7 million years ago. Although belonging to the type genus, the Indian and Javan rhinoceroses are not believed to be closely related to other rhino species. Different studies have hypothesised that they may be closely related to the extinct Gaindatherium or Punjabitherium. A detailed cladistic analysis of the Rhinocerotidae placed Rhinoceros and the extinct Punjabitherium in a clade with Dicerorhinus, the Sumatran rhinoceros. Other studies have suggested the Sumatran rhinoceros is more closely related to the two African species. The Sumatran rhino may have diverged from the other Asian rhinos as long as 15 million years ago.

Characteristics

Indian rhinos have a thick grey-brown skin with pinkish skin folds and one horn on their snout. Their upper legs and shoulders are covered in wart-like bumps. They have very little body hair, aside from eyelashes, ear fringes and tail brush. Bulls have huge neck folds. The skull is heavy with a basal length above 60 cm (24 in) and an occiput above 19 cm (7.5 in). The nasal horn is slightly back-curved with a base of about 18.5 cm (7.3 in) by 12 cm (4.7 in) that rapidly narrows until a smooth, even stem part begins about 55 mm (2.2 in) above base. In captive animals, the horn is frequently worn down to a thick knob.

The Indian rhino’s single horn is present in both bulls and cows, but not on newborn calves. The horn is pure keratin, like human fingernails, and starts to show after about six years. In most adults, the horn reaches a length of about 25 cm (9.8 in), but has been recorded up to 36 cm (14 in) in length and 3.051 kg (6.73 lb) in weight.

Among terrestrial land mammals native to Asia, Indian rhinos are second in size only to the Asian elephant. They are also the second-largest living rhinoceros, behind only the white rhinoceros. Bulls have a head and body length of 368–380 cm (12.07–12.47 ft) with a shoulder height of 170–186 cm (5.58–6.10 ft), while cows have a head and body length of 310–340 cm (10.2–11.2 ft) and a shoulder height of 148–173 cm (4.86–5.68 ft). The bull, averaging about 2,200 kg (4,850 lb) is heavier than the cow, at an average of about 1,600 kg (3,530 lb).

The rich presence of blood vessels underneath the tissues in folds gives them the pinkish colour. The folds in the skin increase the surface area and help in regulating the body temperature. The thick skin does not protect against bloodsucking Tabanus flies, leeches and ticks.

The largest individuals reportedly weighed up to 4,000 kg (8,820 lb).

Distribution and habitat

Indian rhinos once ranged across the entire northern part of the Indian Subcontinent, along the Indus, Ganges and Brahmaputra River basins, from Pakistan to the Indian-Myanmar border, including Bangladesh and the southern parts of Nepal and Bhutan. They may have also occurred in Myanmar, southern China and Indochina. They inhabit the alluvial grasslands of the Terai and the Brahmaputra basin. As a result of habitat destruction and climatic changes its range has gradually been reduced so that by the 19th century, it only survived in the Terai grasslands of southern Nepal, northern Uttar Pradesh, northern Bihar, northern West Bengal, and in the Brahmaputra Valley of Assam.

The species was present in northern Bihar and Oudh at least until 1770 as indicated in maps produced by Colonel Gentil. On the former abundance of the species, Thomas C. Jerdon wrote in 1867:

This huge rhinoceros is found in the Terai at the foot of the Himalayas, from Bhutan to Nepal. It is more common in the eastern portion of the Terai than the west, and is most abundant in Assam and the Bhutan Dooars. I have heard from sportsmen of its occurrence as far west as Rohilcund, but it is certainly rare there now, and indeed along the greater part of the Nepal Terai; … Jelpigoree, a small military station near the Teesta River, was a favourite locality whence to hunt the Rhinoceros and it was from that station Captain Fortescue … got his skulls, which were … the first that Mr. Blyth had seen of this species, …

Today, its range has further shrunk to a few pockets in southern Nepal, northern West Bengal, and the Brahmaputra Valley. Its habitat is surrounded by human-dominated landscapes, so that in many areas, it occurs in cultivated areas, pastures, and secondary forests. In the 1980s, Indian rhinos were frequently seen in the narrow plain area of Manas River and Royal Manas National Park in Bhutan.

Populations

In 2006, the total Indian rhinoceros population was estimated to comprise 2,577 individuals, of which 2,165 lived in India:

• 23 individuals in Uttar Pradesh, including 21 in Dudhwa National Park and 2 in Katarniaghat Wildlife Sanctuary
• 135 individuals in West Bengal, including 108 in Jaldapara National Park and 27 in Gorumara National Park
• 2,007 individuals in Assam, including 1,855 in Kaziranga National Park, 81 in Pobitora Wildlife Sanctuary, 68 in Orang National Park and 3 in Manas National Park.

By 2014, the population in Assam increased to 2,544 Indian rhinos, an increase of 27% since 2006, although more than 150 individuals were killed by poachers during these years. The population in Kaziranga National Park was estimated at 2,048 individuals in 2009. By 2009, the population in Pobitora Wildlife Sanctuary had increased to 84 individuals in an area of 38.80 km² (14.98 sq mi).

In 2015, Nepal had 645 Indian rhinos living in Parsa National Park, Chitwan National Park, Bardia National Park, Shuklaphanta Wildlife Reserve and respective buffer zones in the Terai Arc Landscape as recorded in a survey conducted from 11 April to 2 May 2015. The survey showed that the population of rhinos in Nepal from 2011 to 2015 increased 21% or 111 individuals.

The Indian rhino population, which once numbered as low as 100 individuals in the early 1900s, has increased to more than 3,700 in year 2021 as per The International Rhino Foundation (IRF) signature 2021 report, State of the Rhino.

Ecology and behaviour

Bulls are usually solitary. Groups consist of cows with calves, or of up to six subadults. Such groups congregate at wallows and grazing areas. They are foremost active in early mornings, late afternoons and at night, but rest during hot days. They bathe regularly. The folds in their skin trap water and hold it even when they exit wallows.

They are excellent swimmers and can run at speeds of up to 55 km/h (34 mph) for short periods. They have excellent senses of hearing and smell, but relatively poor eyesight. Over 10 distinct vocalisations have been recorded. Males have home ranges of around 2 to 8 km² (0.77 to 3.09 sq mi) that overlap each other. Dominant males tolerate other males passing through their territories except when they are in mating season, when dangerous fights break out. Indian rhinos have few natural enemies, except for tigers, which sometimes kill unguarded calves, but adult rhinos are less vulnerable due to their size. Mynahs and egrets both eat invertebrates from the rhino’s skin and around its feet. Tabanus flies, a type of horse-fly, are known to bite rhinos. The rhinos are also vulnerable to diseases spread by parasites such as leeches, ticks, and nematodes. Anthrax and the blood-disease sepsis are known to occur. In March 2017, a group of four tigers consisting of an adult male, tigress and two cubs killed a 20-year-old male Indian rhinoceros in Dudhwa Tiger Reserve.

Diet

Indian rhinos are grazers. Their diet consists almost entirely of grasses, but they also eat leaves, branches of shrubs and trees, fruits, and submerged and floating aquatic plants. They feed in the mornings and evenings. They use their semi-prehensile lips to grasp grass stems, bend the stem down, bite off the top, and then eat the grass. They tackle very tall grasses or saplings by walking over the plant, with legs on both sides and using the weight of their bodies to push the end of the plant down to the level of the mouth. Mothers also use this technique to make food edible for their calves. They drink for a minute or two at a time, often imbibing water filled with rhinoceros urine.

Social life

Indian rhinos form a variety of social groupings. Bulls are generally solitary, except for mating and fighting. Cows are largely solitary when they are without calves. Mothers will stay close to their calves for up to four years after their birth, sometimes allowing an older calf to continue to accompany her once a newborn calf arrives. Subadult bulls and cows form consistent groupings, as well. Groups of two or three young bulls will often form on the edge of the home ranges of dominant bulls, presumably for protection in numbers. Young cows are slightly less social than the bulls. Indian rhinos also form short-term groupings, particularly at forest wallows during the monsoon season and in grasslands during March and April. Groups of up to 10 rhinos may gather in wallows—typically a dominant male with females and calves, but no subadult males.

Indian rhinos make a wide variety of vocalisations. At least ten distinct vocalisations have been identified: snorting, honking, bleating, roaring, squeak-panting, moo-grunting, shrieking, groaning, rumbling and humphing. In addition to noises, the Indian rhino uses olfactory communication. Adult bulls urinate backwards, as far as 3–4 metres (9.8–13.1 ft) behind them, often in response to being disturbed by observers. Like all rhinos, the Indian rhinoceros often defecates near other large dung piles. The Indian rhino has pedal scent glands which are used to mark their presence at these rhino latrines. Bulls have been observed walking with their heads to the ground as if sniffing, presumably following the scent of cows.

In aggregations, Indian rhinos are often friendly. They will often greet each other by waving or bobbing their heads, mounting flanks, nuzzling noses, or licking. Indian rhinos will playfully spar, run around, and play with twigs in their mouths. Adult bulls are the primary instigators in fights. Fights between dominant bulls are the most common cause of rhino mortality, and bulls are also very aggressive toward cows during courtship. Bulls will chase cows over long distances and even attack them face-to-face. Unlike African rhinos, Indian rhinos fight with their incisors, rather their horn.

Reproduction

Captive bulls breed at five years of age, but wild bulls attain dominance much later when they are larger. In one five-year field study, only one Indian rhino estimated to be younger than 15 years mated successfully. Captive cows breed as young as four years of age, but in the wild, they usually start breeding only when six years old, which likely indicates they need to be large enough to avoid being killed by aggressive bulls. Their gestation period is around 15.7 months, and birth interval ranges from 34 to 51 months.

In captivity, four Indian rhinos are known to have lived over 40 years, the oldest living to be 47.

Threats

Habitat degradation and floods

Habitat degradation caused by human activities and climate change as well as the resulting increase in the floods has caused large death of Indian rhinos and has limited their ranging areas which is shrinking.

Serious declines in quality of habitat have occurred in some areas, due to:

• severe invasion by alien plants into grasslands affecting some populations;
• demonstrated reductions in the extent of grasslands and wetland habitats due to woodland encroachment and silting up of beels (swampy wetlands);
• grazing by domestic livestock.

Lack of site diversity

The Indian rhino species is inherently at risk because over 70% of its population occurs at a single site, Kaziranga National Park. Any catastrophic event such as disease, civil disorder, poaching, or habitat loss would have a devastating impact on the Indian rhino’s status. However, small population of rhinos may be prone to inbreeding depression. Expansion of other protective areas and introduction of rhinos in more areas is needed.

Poaching

Sport hunting became common in the late 19th and early 20th centuries and was the main cause for the decline of Indian rhinoceros populations. Indian rhinos were hunted relentlessly and persistently. Reports from the mid-19th century claim that some British military officers shot more than 200 rhinos in Assam alone. By 1908, the population in Kaziranga National Park had decreased to around 12 individuals. In the early 1900s, the Indian rhinoceros was almost extinct. At present, poaching for the use of horn in traditional Chinese Medicine is one of the main threats that has led to decreases in several important populations. Poaching for the Indian rhino’s horn became the single most important reason for the decline of the Indian rhinoceros after conservation measures were put in place from the beginning of the 20th century, when legal hunting ended. From 1980 to 1993, 692 rhinos were poached in India, including 41 rhinos in India’s Laokhowa Wildlife Sanctuary in 1983, almost the entire population of the sanctuary. By the mid-1990s, the Indian rhinoceros had been extirpated in this sanctuary. Between 2000 and 2006, more than 150 rhinos were poached in Assam. Almost 100 rhinos were poached in India between 2013 and 2018.

In 1950, in Nepal the Chitwan’s forest and grasslands extended over more than 2,600 km² (1,000 sq mi) and were home to about 800 rhinos. When poor farmers from the mid-hills moved to the Chitwan Valley in search of arable land, the area was subsequently opened for settlement, and poaching of wildlife became rampant. The Chitwan population has repeatedly been jeopardised by poaching; in 2002 alone, poachers killed 37 animals to saw off and sell their valuable horns.

Six methods of killing Indian rhinos have been recorded:

• Shooting is by far the most common method used; rhino horn traders hire sharpshooters and often supply them with rifles and ammunition.
• Trapping in a pit depends largely on the terrain and availability of grass to cover it; pits are dug out in such a way that a fallen animal has little room to manoeuvre with its head slightly above the pit, so that it is easy to saw off the horn.
• Electrocution is used where high voltage powerlines pass through or near a protected area, to which poachers hook a long, insulated rod connected to a wire, which is suspended above a rhino path.
• Poisoning by smearing zinc phosphide rat poison or pesticides on salt licks frequented by rhinos is sometimes used.
• Spearing has only been recorded in Chitwan National Park.
• A noose, which cuts through the rhino’s skin, kills it by strangulation.

Conservation

Globally, Rhinoceros unicornis has been listed in CITES Appendix I since 1975. The Indian and Nepalese governments have taken major steps towards Indian rhinoceros conservation, especially with the help of the World Wide Fund for Nature (WWF) and other non-governmental organisations. In 1910, all rhino hunting in India became prohibited.