This article is about the Greater one horned rhinoceros. For the lesser one-horned rhinoceros, which has an extinct subspecies known as the lesser Indian rhinoceros, seeJavan rhinoceros.
TheIndian rhinoceros (Rhinoceros unicornis), also known as thegreater one-horned rhinoceros,great Indian rhinoceros orIndian rhino, is a species of rhinoceros found in theIndian subcontinent. It is the second largest livingrhinoceros species, with adult males weighing 2.07–2.2 t (2.04–2.17 long tons; 2.28–2.43 short tons) and adult females 1.6 t (1.6 long tons; 1.8 short tons). Its thick skin is grey-brown with pinkish skin folds. It has a single horn on its snout that grows up to 57.2 cm (22.5 in) long. Its upper legs and shoulders are covered in wart-like bumps, and it is nearly hairless aside from the eyelashes, ear fringes and tail brush.
The Indian rhinoceros is native to theIndo-Gangetic Plain and occurs in 12protected areas in northernIndia and southernNepal. It is agrazer, eating mainly grass, but also twigs, leaves, branches, shrubs, flowers, fruits and aquatic plants. It is a largelysolitary animal, only associating in thebreeding season and when rearing calves. Females give birth to a single calf after agestation of 15.7 months. The birth interval is 34–51 months. Captive individuals can live up to 47 years. It is susceptible to diseases such asanthrax, and those caused by parasites such asleeches, ticks andnematodes.
The Indian rhinoceros is listed asVulnerable on theIUCN Red List, as the population is fragmented and restricted to less than 20,000 km2 (7,700 sq mi). Excessive hunting and agricultural development reduced its range drastically. In the early 1990s, the global population was estimated at between 1,870 and 1,895 individuals. Since then, the population increased due to conservation measures taken by the governments. As of August 2018, it was estimated to comprise 3,588 individuals. However, poaching remains a continuous threat.
Rhinoceros unicornis was thescientific name used byCarl Linnaeus in 1758 whodescribed a rhinoceros with one horn. Astype locality, he indicated Africa and India. He described two species in India, the other beingRhinoceros bicornis, and stated that the Indian species had two horns, while the African species had only one.[2]
The Indian rhinoceros is a singlespecies. Several specimens were described since the end of the 18th century under differentscientific names, which are all consideredsynonyms ofRhinoceros unicornis today:[3]
Thegeneric namerhinoceros is derived through Latin from theAncient Greek:ῥινόκερως, which is composed ofῥινο- (rhino-, "of the nose") andκέρας (keras, "horn") with a horn on the nose.[5] The name has been in use since the 14th century.[6][7] TheLatin wordūnicornis means "one-horned".[8]
Ancestral rhinoceroses first diverged from otherperissodactyls in theEarly Eocene. Mitochondrial DNA comparison suggests the ancestors of modern rhinos split from the ancestors ofEquidae around 50 million years ago.[9] The extant family, the Rhinocerotidae, first appeared in theLate Eocene inEurasia, and the ancestors of the extant rhino species dispersed from Asia beginning in theMiocene.[10] The last common ancestor of living rhinoceroses belonging to the subfamily Rhinocerotinae is suggested to have lived around 16 million years ago, with the ancestors of the genusRhinoceros diverging from the ancestors of other living rhinoceroses around 15 million years ago. The genusRhinoceros has been found to be overall slightly more closely related to theSumatran rhinoceros (as well as to the extinctwoolly rhinoceros and the extinct Eurasian genusStephanorhinus) than to living African rhinoceroses, though there appears to have beengene flow between the ancestors of living African rhinoceroses and the genusRhinoceros, as well as between the ancestors of the genusRhinoceros and the ancestors of the woolly rhinoceros andStephanorhinus.[11]
Acladogram showing the relationships of recent and Late Pleistocene rhinoceros species (minusStephanorhinus hemitoechus) based on whole nuclear genomes, after Liu et al., 2021:[11]
The earliest fossils of the genusRhinoceros date to the Late Miocene, around 8–9 million years ago.[12] The divergence between the Indian andJavan rhinoceros is estimated to have occurred around 4.3 million years ago.[11] The earliest representatives of the modern Indian rhinoceros appeared during the Early Pleistocene (2.6-0.8 million years ago). Fossils indicate that the Indian rhinoceros during the Pleistocene also inhabited areas considerably further east of its current distribution, including mainland Southeast Asia, South China and the island of Java, Indonesia.[13]
Indian rhinos have a thick grey-brown skin with pinkish skin folds and onehorn 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. Theskull is heavy with a basal length above 60 cm (24 in) and anocciput 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.[14] The Indian rhino's single horn is present in both bulls and cows, but not on newborn calves. The horn is purekeratin, 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 57.2 cm (22.5 in) in length and 3.051 kg (6.73 lb) in weight.[15][14]
Among terrestrial land mammals native to Asia, Indian rhinos are second in size only to theAsian elephant.[16] They are also the second-largest living rhinoceros, behind only thewhite rhinoceros. Bulls have a head and body length of 368–380 cm (12.07–12.47 ft) with a shoulder height of 163–193 cm (5.35–6.33 ft), while cows have a head and body length of 310–340 cm (10.2–11.2 ft) and a shoulder height of 147–173 cm (4.82–5.68 ft).[17][14] The bull, averaging about 2,070–2,200 kg (4,560–4,850 lb) is heavier than the cow, at an average of about 1,600 kg (3,530 lb).[17][14] The largest individuals reportedly weigh up to 4,000 kg (8,820 lb).[18]
Indian rhinoceros atKaziranga National ParkWart-like bumps on the hind legsThe Indian rhinoceros's single hornThe skull of an Indian rhinoceros
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.[19] The thick skin does not protect against bloodsuckingTabanus flies,leeches andticks.[14]
The species was present in northern Bihar and Oudh at least until 1770 as indicated in maps produced byColonel Gentil.[22] On the former abundance of the species,Thomas C. Jerdon wrote in 1867:[23]
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 ofManas River andRoyal Manas National Park in Bhutan.[21]
In 2022, the total Indian rhinoceros population was estimated to be 4,014 individuals, up from 2,577 in 2006. Among them, 3,262 are in India and the remaining 752 are in Nepal and Bhutan. There is no permanent rhino population in Bhutan, but small rhino populations are occasionally known to cross from theManas National Park orBuxa Tiger Reserve in India.[24]
Indian rhinoceros inManas National Park, AssamRhino at Jaldapara National Park, West BengalRhino in Dudhwa National Park, Uttar Pradesh
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.[27]The population in Kaziranga National Park was estimated at 2,048 individuals in 2009.[28] By 2009, the population in Pobitora Wildlife Sanctuary had increased to 84 individuals in an area of 38.80 km2 (14.98 sq mi).[29]
The Indian rhino population, which once numbered as low as 100 individuals in the early 1900s, has increased to more than 3,700 in the year 2021 as per The International Rhino Foundation.[31]
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.[14]They bathe regularly. The folds in their skin trap water and hold it even when they exit wallows.[19] 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 distinctvocalisations 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.[32]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 andegrets both eat invertebrates from the rhino's skin and around its feet.Tabanus flies, a type ofhorse-fly, are known to bite rhinos. The rhinos are also vulnerable to diseases spread by parasites such asleeches,ticks, andnematodes likeBivitellobilharzia nairi.Anthrax and the blood-diseasesepsis are known to occur.[14]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 inDudhwa Tiger Reserve.[33] Such cases are rare, as Indian rhinoceroses—like mostmegaherbivores—are mostly invulnerable to predation.[34][35]
Indian rhinos aregrazers. Their diet consists almost entirely of grasses (such asArundo donax,Bambusa tulda,Cynodon dactylon, andOryza sativa), but they also eat leaves, twigs and branches of shrubs and trees (such asLagerstroemia indica), flowers, fruits (such asFicus religiosa), and submerged and floatingaquatic plants.[36]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.[14]
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.[37] 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.[38] Groups of two or three young bulls 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 themonsoon season and in grasslands during March and April. Groups of up to 10 rhinos, typically a dominant male with females and calves, gather in wallows.[15]
Indian rhinos make a wide variety of vocalisations. At least 10 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 usesolfactory communication. Adult bulls urinate backwards, as far as 3–4 m (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.[15]
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 chase cows over long distances and even attack them face-to-face. Indian rhinos use their horns for fighting, albeit less frequently than African rhinos, largely using the incisors of the lower jaw to inflict wounds.[15]
Rhino in Kaziranga National ParkIndian rhinoceros showing its sharp lower incisor teeth used for fightingClash for territory between two Rhino
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.[15] Theovarian cycle lasts 5.5 to 9 weeks on average.[39] Theirgestation period is around 15.7 months, and birth interval ranges from 34 to 51 months.[15] An estimated 10% of calves will die before maturity. This is mainly attributed to predatory attacks fromtigers (Panthera tigris).[40] In captivity, four Indian rhinos lived over 40 years, the oldest living to be 47.[14]
Habitat degradation caused by human activities andclimate change as well as the resulting increase in thefloods has caused many Indian rhino deaths and has limited their ranging areas which is shrinking.[1]
Serious declines in quality of habitat have occurred in some areas, due to severe invasion byalien plants into grasslands affecting some populations, and demonstrated reductions in the extent of grasslands and wetland habitats due to woodland encroachment and silting up ofbeels (swampy wetlands). Grazing by domestic livestock is another cause.[1]
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. Additionally, a small population of rhinos may be prone to inbreeding depression.[1]
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.[14] In the early 1900s, the Indian rhinoceros was almost extinct. At present,poaching for the use of horn intraditional Chinese Medicine is one of the main threats that has led to decreases in several important populations.[1] 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'sLaokhowa Wildlife Sanctuary in 1983, almost the entire population of the sanctuary.[41] By the mid-1990s, the Indian rhinoceros had beenextirpated in this sanctuary.[20] Between 2000 and 2006, more than 150 rhinos were poached in Assam.[27][42] Almost 100 rhinos were poached in India between 2013 and 2018.[43]
In 1950, in Nepal theChitwan'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, andpoaching 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.[44]
The Indian rhinoceros is listed asvulnerable by theIUCN Red list, as of 2018.[1] Globally,R. unicornis has been listed inCITES Appendix I since 1975. The Indian and Nepalese governments have taken major steps towards Indian rhinoceros conservation, especially with the help of theWorld Wide Fund for Nature (WWF) and other non-governmental organisations.[1] In 1910, all rhino hunting in India became prohibited.[14]
In 1957, the country's first conservation law ensured the protection of rhinos and theirhabitat. In 1959,Edward Pritchard Gee undertook a survey of theChitwan Valley, and recommended the creation of a protected area north of theRapti River and of a wildlife sanctuary south of the river for a trial period of 10 years.[45] After his subsequent survey of Chitwan in 1963, he recommended extension of the sanctuary to the south.[46] By the end of the 1960s, only 95 rhinos remained in the Chitwan Valley. The dramatic decline of the rhino population and the extent of poaching prompted the government to institute theGaida Gasti – a rhino reconnaissance patrol of 130 armed men and a network of guard posts all over Chitwan. To prevent the extinction of rhinos, theChitwan National Park was gazetted in December 1970, with borders delineated the following year and established in 1973, initially encompassing an area of 544 km2 (210 sq mi). To ensure the survival of rhinos in case of epidemics, animals were translocated annually from Chitwan toBardia National Park andShuklaphanta National Park since 1986.[44]The Indian rhinoceros population living in Chitwan andParsa National Parks was estimated at 608 mature individuals in 2015.[35]
Indian rhinos have been reintroduced to areas where they had previously inhabited but became extinct. These efforts have produced mixed results, mainly due to lack of proper planning and management, sustained effort, and adequate security for the introduced animals.[47]
In 1984, five Indian rhinos were relocated toDudhwa National Park—four from the fields outside thePobitora Wildlife Sanctuary and one from Goalpara.[21] This has born results and the population has increased to 21 rhinos by 2006.[25] In early 1980s, Laokhowa Wildlife Sanctuary in Assam had more than 70 Indian rhinos which were all killed by poachers. In 2016, two Indian rhinos, a mother and her daughter, were reintroduced to the sanctuary from Kaziranga National Park as part of the Indian Rhino Vision 2020 (IRV 2020) program, but both animals died within months due to natural causes.[43]
Indian rhinos were once found as far west as thePeshawar Valley during the reign ofMughal EmperorBabur, but are now extinct in Pakistan. After rhinos became "regionally extinct" in Pakistan,[48] two rhinos from Nepal were introduced in 1983 toLal Suhanra National Park, which have not bred so far.[1][21]
Indian rhinoceroses were initially difficult to breed in captivity. In the second half of the 20th century, zoos became adept at breeding Indian rhinoceros. By 1983, nearly 40 babies had been born in captivity.[14] As of 2012, 33 Indian rhinos were born atSwitzerland'sZoo Basel alone,[49] meaning that most captive animals are related to theBasel population. Due to the success ofZoo Basel's breeding program, the InternationalStudbook for the species has been kept there since 1972. Since 1990, the Indian rhinoEuropean Endangered Species Programme is also being coordinated there, with the goal of maintaining genetic diversity in the global captive Indian rhinoceros population.[50]
The first recorded captive birth of an Indian rhinoceros was inKathmandu in 1826, but another successful birth did not occur for nearly 100 years. In 1925, a rhino was born inKolkata. No rhinoceros was successfully bred in Europe until 1956 when first European breeding took place when baby rhino Rudra was born in Zoo Basel on 14 September 1956.[14] In June 2009, an Indian rhino wasartificially inseminated using sperm collected four years previously andcryopreserved at theCincinnati Zoo's CryoBioBank before being thawed and used. She gave birth to a male calf in October 2010.[51] In June 2014, the first "successful" live-birth from an artificially inseminated rhino took place at theBuffalo Zoo in New York. As in Cincinnati, cryopreserved sperm was used to produce the female calf, Monica.[52]
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