Members of the rhinoceros family are characterized by their large size (they are some of the largest remaining megafauna, with all of the species able to reach one tonne or more in weight); as well as by an herbivorous diet; a thick protective skin, 1.5–5 cm thick, formed from layers of collagen positioned in a lattice structure; relatively small brains for mammals this size (400–600 g); and a large horn. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter, if necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths, relying instead on their lips to pluck food.
Rhinoceros are killed by humans for their horns, which are bought and sold on the black market, and which are used by some cultures for ornamental or traditional medicinal purposes. East Asia, specifically Vietnam, is the largest market for rhino horns. By weight, rhino horns cost as much as gold on the black market. People grind up the horns and then consume them believing the dust has therapeutic properties. The horns are made of keratin, the same type of protein that makes up hair and fingernails. Both African species and the Sumatran rhinoceros have two horns, while the Indian and Javan rhinoceros have a single horn.
Cladogram following a phylogenetic study by Tougard et al., 2011.
The word rhinoceros is derived through Latin from the Ancient Greek: ῥῑνόκερως, which is composed of ῥῑνο- (rhino-, "nose") and κέρας (keras, "horn"). The plural in English is rhinoceros or rhinoceroses. The collective noun for a group of rhinoceroses is crash or herd.
The five living species fall into three categories. The two African species, the white rhinoceros and the black rhinoceros, belong to the Dicerotini group, which originated in the middle Miocene, about 14.2 million years ago. The species diverged during the early Pliocene (about 5 million years ago). The main difference between black and white rhinos is the shape of their mouths – white rhinos have broad flat lips for grazing, whereas black rhinos have long pointed lips for eating foliage.
There are two living Rhinocerotini species, the Indian rhinoceros and the Javan rhinoceros, which diverged from one another about 10 million years ago. The Sumatran rhinoceros is the only surviving representative of the most primitive group, the Dicerorhinini, which emerged in the Miocene (about 20 million years ago). The extinct woolly rhinoceros of northern Europe and Asia was also a member of this tribe.
There are two subspecies of white rhino: the southern white rhinoceros (Ceratotherium simum simum) and the northern white rhinoceros (Ceratotherium simum cottoni). In 2007, the southern subspecies had a wild population of 17,480 (IUCN2008) – 16,266 of which were in South Africa – making them the most abundant rhino subspecies in the world. However, the northern subspecies was critically endangered, with as few as four individuals in the wild; the possibility of complete extinction in the wild having been noted since June 2008. Six are known to be held in captivity, two of which reside at the San Diego Zoo Safari Park. Four born in a zoo in the Czech Republic were transferred to a wildlife refuge in Kenya in December 2009, in an effort to have the animals reproduce and save the subspecies.
There is no conclusive explanation of the name white rhinoceros. A popular theory that "white" is a distortion of either the Afrikaans word wyd or the Dutch word wijd (or its other possible spellings whyde, weit, etc.,) meaning wide and referring to the rhino's square lips is not supported by linguistic studies.
The white rhino has an immense body and large head, a short neck and broad chest. This rhino can exceed 3,500 kg (7,700 lb), have a head-and-body length of 3.5–4.6 m (11–15 ft) and a shoulder height of 1.8–2 m (5.9–6.6 ft). The record-sized white rhinoceros was about 4,500 kg (10,000 lb). On its snout it has two horns. The front horn is larger than the other horn and averages 90 cm (35 in) in length and can reach 150 cm (59 in). The white rhinoceros also has a prominent muscular hump that supports its relatively large head. The colour of this animal can range from yellowish brown to slate grey. Most of its body hair is found on the ear fringes and tail bristles, with the rest distributed rather sparsely over the rest of the body. White rhinos have the distinctive flat broad mouth that is used for grazing.
An adult black rhinoceros stands 1.50–1.75 m (59–69 in) high at the shoulder and is 3.5–3.9 m (11–13 ft) in length. An adult weighs from 850 to 1,600 kg (1,870 to 3,530 lb), exceptionally to 1,800 kg (4,000 lb), with the females being smaller than the males. Two horns on the skull are made of keratin with the larger front horn typically 50 cm long, exceptionally up to 140 cm. Sometimes, a third smaller horn may develop. The black rhino is much smaller than the white rhino, and has a pointed mouth, which it uses to grasp leaves and twigs when feeding.
During the latter half of the 20th century, their numbers were severely reduced from an estimated 70,000 in the late 1960s to a record low of 2,410 in 1995. Since then, numbers have been steadily increasing at a continental level with numbers doubling to 4,880 by the end of 2010. Current numbers are however still 90% lower than three generations ago.
The Indian rhinoceros, or greater one-horned rhinoceros, (Rhinoceros unicornis) has a single horn 20 to 100 cm long. It is nearly as large as the African white rhino. Its thick, silver-brown skin forms huge folds all over its body. Its upper legs and shoulders are covered in wart-like bumps, and it has very little body hair. Grown males are larger than females in the wild, weighing from 2,500–3,200 kg (5,500–7,100 lb). Shoulder height is 1.75–2.0 m (5.75–6.5 ft). Females weigh about 1,900 kg and are 3–4 m long. The record-sized specimen was approximately 3,800 kg.
The Javan rhinoceros (Rhinoceros sondaicus) is one of the most endangered large mammals in the world. According to 2002 estimates, only about 60 remain, in Java (Indonesia) and Vietnam. It is also the least known rhino species. Like the closely related, and larger, Indian rhinoceros, the Javan rhino has a single horn. Its hairless, hazy gray skin falls into folds into the shoulder, back, and rump, giving it an armored appearance. Its length reaches 3.1–3.2 m (10–10 ft) including the head, and its height 1.5–1.7 m (4 ft 11 in–5 ft 7 in). Adults are variously reported to weigh 900–1,400 kg or 1,360–2,000 kg. Male horns can reach 26 cm in length, while in females they are knobs or altogether absent. These animals prefer dense lowland rain forest, tall grass and reed beds that are plentiful with large floodplains and mud wallows.
Though once widespread throughout Asia, by the 1930s they were nearly hunted to extinction in Nepal, India, Burma, Peninsular Malaysia, and Sumatra for the supposed medical powers of their horns and blood. As of 2009, only 40 remain in Ujung Kulon Conservation, Java, Indonesia. The last rhino in Vietnam was reportedly killed in 2010.
The Sumatran rhinoceros (Dicerorhinus sumatrensis) is the smallest extant rhinoceros species, as well as the one with the most hair. It can be found at very high altitudes in Borneo and Sumatra. Due to habitat loss and poaching, their numbers have declined and it has become the most threatened rhinoceros. About 275 Sumatran rhinos are believed to remain.
A mature rhino typically stands about 1.3 m (4 ft 3 in) high at the shoulder, has a length of 2.4–3.2 m (7 ft 10 in–10 ft 6 in) and weighs around 700 kg (1,500 lb), though the largest individuals have been known to weigh as much as 1,000 kilograms. Like the African species, it has two horns; the larger is the front (25–79 cm), with the smaller usually less than 10 cm long. Males have much larger horns than the females. Hair can range from dense (the densest hair in young calves) to sparse. The color of these rhinos is reddish brown. The body is short and has stubby legs. The lip is prehensile.
Sumatran rhinoceros are on the verge of extinction due to loss of habitat and illegal hunting. Once they were spread across South-east Asia, but now they are confined to several parts of Indonesia and Malaysia due to reproductive isolation. There were 320 of D. sumatrensis in 1995, which by 2011 have dwindled to 216. It has been found through DNA comparison that the Sumatran rhinoceros is the most ancient extant rhinoceros, and related to the extinct Woolly Rhinoceros, Coelodonta. In 1994 Alan Rabinowitz publicly denounced that governments, NGOs and other institutions were lacking in attempts to conserve the Sumatran rhinoceros. In order to conserve it, they would have to be relocated from small forests to breeding programs where their breeding success could be monitored. In order to boost reproduction, the Malaysian and Indonesian governments could also agree on exchanging the gametes of the Sumatran and (smaller) Bornean subspecies. There has also been a proposal by the Indonesian and Malaysian governments for a single management unit for these two ancient subspecies.
The thick dermal armour of the rhinoceros evolved at the same time as shearing tusks
Rhinocerotoids diverged from other perissodactyls by the early Eocene. Fossils of Hyrachyus eximus found in North America date to this period. This small hornless ancestor resembled a tapir or small horse more than a rhino. Three families, sometimes grouped together as the superfamily Rhinocerotoidea, evolved in the late Eocene, namely the Hyracodontidae, Amynodontidae and Rhinocerotidae.
Hyracodontidae, also known as 'running rhinos', showed adaptations for speed, and would have looked more like horses than modern rhinos. The smallest hyracodontids were dog-sized; the largest was Indricotherium, believed to be one of the largest land mammals that ever existed. The hornless Indricotherium was almost seven metres high, ten metres long, and weighed as much as 15 tons. Like a giraffe, it ate leaves from trees. The hyracodontids spread across Eurasia from the mid-Eocene to early Miocene.
The Amynodontidae, also known as "aquatic rhinos", dispersed across North America and Eurasia, from the late Eocene to early Oligocene. The amynodontids were hippopotamus-like in their ecology and appearance, inhabiting rivers and lakes, and sharing many of the same adaptations to aquatic life as hippos.
The family of all modern rhinoceros, the Rhinocerotidae, first appeared in the Late Eocene in Eurasia. The earliest members of Rhinocerotidae were small and numerous; at least 26 genera lived in Eurasia and North America until a wave of extinctions in the middle Oligocene wiped out most of the smaller species. However, several independent lineages survived. Menoceras, a pig-sized rhinoceros, had two horns side-by-side. The North American Teleoceras had short legs, a barrel chest and lived until about 5 million years ago. The last rhinos in the Americas became extinct during the Pliocene.
Modern rhinos are thought to have begun dispersal from Asia during the Miocene. Two species survived the most recent period of glaciation and inhabited Europe as recently as 10,000 years ago: the woolly rhinoceros and Elasmotherium. The woolly rhinoceros appeared in China around 1 million years ago and first arrived in Europe around 600,000 years ago. It reappeared 200,000 years ago, alongside the woolly mammoth, and became numerous. Eventually it was hunted to extinction by early humans. Elasmotherium, also known as the giant rhinoceros, survived through the middle Pleistocene: it was two meters tall, five meters long and weighed around five tons, with a single enormous horn, hypsodont teeth and long legs for running.
Of the extant rhinoceros species, the Sumatran rhino is the most archaic, first emerging more than 15 million years ago. The Sumatran rhino was closely related to the woolly rhinoceros, but not to the other modern species. The Indian rhino and Javan rhino are closely related and form a more recent lineage of Asian rhino. The ancestors of early Indian and Javan rhino diverged 2–4 million years ago.
The origin of the two living African rhinos can be traced to the late Miocene (6 mya) species Ceratotherium neumayri. The lineages containing the living species diverged by the early Pliocene (1.5 mya), when Diceros praecox, the likely ancestor of the black rhinoceros, appears in the fossil record. The black and white rhinoceros remain so closely related that they can still mate and successfully produce offspring.
Comparison of sizes between extant and extinct rhinos
Although rhinos are large and have a reputation for being tough, they are very easily poached; they visit water holes daily and can be easily killed while they drink. As of December 2009, poaching increased globally while efforts to protect the rhino are considered increasingly ineffective. The worst estimate, that only 3% of poachers are successfully countered, is reported of Zimbabwe, while Nepal has largely avoided the crisis. Poachers have become more sophisticated. About 69% of Rhino in the world are inhabituated in Nepal. South African officials have called for urgent action against poaching after poachers killed the last female rhino in the Krugersdorp Game Reserve near Johannesburg. Statistics from South African National Parks show that 333 rhinoceros were killed in South Africa in 2010, increasing to 668 by 2012, and over 1,004 in 2013. In some cases rhinos are drugged and their horns removed, while in other instances more than the horn is taken.
The Namibian government and Save the Rhino International have been positive about the benefits that rhino trophy hunting may hold for conservation. Hunting licenses for five Namibian Black rhinos are auctioned annually. Additionally, support for a legal trade of rhino horn to combat poaching has been growing. Some conservationists and members of the public however oppose or question this practice.
It is a pervasive misconception that rhinoceros horn in powdered form is used as an aphrodisiac in Traditional Chinese Medicine (TCM) as Cornu Rhinoceri Asiatici (犀角, xījiǎo, "rhinoceros horn"). It is in fact prescribed for fevers and convulsions, a treatment not supported by evidence-based medicine. Discussions with TCM practitioners to reduce its use have met with mixed results because some TCM doctors consider rhino horn a life-saving medicine of better quality than its substitutes. China has signed the CITES treaty and removed rhinoceros horn from the Chinese medicine pharmacopeia, administered by the Ministry of Health, in 1993. In 2011, in the United Kingdom, the Register of Chinese Herbal Medicine issued a formal statement condemning the use of rhinoceros horn. A growing number of TCM educators have also spoken out against the practice. Rhino-horn shavings boiled in water are said to cool and cure headaches in traditional Chinese medicine; however, the brew has instead been compared to consuming fingernail clippings in water.
To prevent poaching, in certain areas, rhinos have been tranquilized and their horns removed. Armed park rangers, particularly in South Africa, are also working on the front lines to combat poaching, sometimes killing poachers who are caught in the act. A recent spike in rhino killings has made conservationists concerned about the future of the species. An average sized horn can bring in as much as a quarter of a million dollars in Vietnam and many rhino range states have stockpiles of rhino horn.
In 2011 the Rhino Rescue Project, organized by Ed and Lorinda Hern of the Rhino & Lion Nature Reserve in Krugersdorp South Africa, began a horn-trade control method consisting of infusing the horns (while on the animal) with a mixture of a pink dye and an acaricide (to kill ticks) which is safe for rhinos but toxic to humans. After sedating the animal, holes are drilled into the horns, fittings added, and the cavity connected with rubber hoses to a 2-foot-by-4-inch diameter metal container of the liquid mixture which is then pressurized. The infusion takes less than 20 minutes of the 45 minutes of anesthesia; because of the effect of the mass of the animals on their internal organs, they are rolled every 7 minutes while sedated. The procedure also includes inserting three RFID identification chips and taking DNA samples.
Because of the fibrous nature of rhino horn, the pressurized dye infuses the interior of the horn but does not color the surface or affect rhino behavior. The acaricide is expected to cause nausea, stomach-ache and diarrhea, or convulsions for anyone consuming the horn in Traditional Chinese Medicine, depending on the quantity, but would not be fatal; the primary deterrent being the knowledge that the treatment has been applied, communicated by signs posted at the refuges. The original idea grew out of research looking into using the horn as a reservoir for one-time tick treatments, and the acaricide is selected to be safe for the rhino, oxpeckers, vultures, and other animals in the preserve's ecosystem. It was claimed that the dye can not be successfully removed from horns, and would remain visible on x-ray scanners even when the horn is ground to a fine powder.
Save the Rhino has criticized horn poisoning on moral and practical grounds. Not only does the poison and dye not permeate the dense horn, but even if the poison was effective, it is unlikely that middlemen in a lucrative, illegal trade would care much about the effect it would have on buyers on another continent. Furthermore, poisoned horns could heighten demand for non-poisoned horns among wealthier buyers or could fuel the belief in magical properties of the horn if people survive the poisoning. Additionally, rhino horn is increasingly purchased for decorative use, rather than for use in traditional medicine. And not only would the poisoning of all African rhino horns be an impossible task since it would have to be reapplied every 4 years, it was reported that one out of 150 rhinos treated did not survive the anesthesia.
Still, poaching is hitting record levels due to demands from China and Vietnam. In March 2013, some researchers suggested that the only way to reduce poaching would be to establish a regulated trade based on humane and renewable harvesting from live rhinos. The WWF however opposes legalization of the horn trade, as it may increase demand, while IFAW released a report by EcoLarge, suggesting that more thorough knowledge of economic factors is required in order to justify the pro-trade option. The South African government has supported the establishment of a legal trade of rhino horn stating that at the 17th Meeting of Conference of the Parties to CITES (CoP17) in 2016 they will apply for a legal trade in Rhino Horn in an attempt to reduce poaching and prevent the extinction of this species.
Albrecht Dürer created a famous woodcut of a rhinoceros in 1515, based on a written description and brief sketch by an unknown artist of an Indian rhinoceros that had arrived in Lisbon earlier that year. Dürer never saw the animal itself and, as a result, Dürer's Rhinoceros is a somewhat inaccurate depiction.
There are legends about rhinoceroses stamping out fire in Burma, India, and Malaysia. The mythical rhinoceros has a special name in Malay, badak api, wherin badak means rhinoceros, and api means fire. The animal would come when a fire was lit in the forest and stamp it out. There are no recent confirmations of this phenomenon. However, this legend has been reinforced by the film The Gods Must Be Crazy (1980), wherein an African rhinoceros is shown to be putting out two campfires.
Rhinoceroses in art
A wine vessel in the form of a bronze rhinoceros with silver inlay, from the Western Han (202 BC – 9 AD) period of China, sporting a saddle on its back
^Ahmad Zafir, A. W.; Payne, J., Mohamed, A., Lau, C. F., Sharma, D. S. K., Alfred, R., ... Clements, G. R. (2011). "Now or never: What will it take to save the sumatran rhinoceros dicerorhinus sumatrensis from extinction?". Oryx 45 (2): 225–233. doi:10.1017/S0030605310000864.Cite uses deprecated parameters (help);|accessdate= requires |url= (help)
^Benoît, Goossens; Milena Salgado-Lynn, Jeffrine J. Rovie-Ryan, Abdul H. Ahmad, Junaidi Payne, Zainal Z. Zainuddin, Senthilvel K. S. S. Nathan and Laurentius N. Ambu (2013). "Genetics and the last stand of the Sumatran rhinoceros Dicerorhinus sumatrensis". Oryx 47: 340–344. doi:10.1017/S0030605313000045.Cite uses deprecated parameters (help)
^Geraads, Denis (2010). "Chapter 34: Rhinocerotidae". In Werdelin, L.; Sanders, W.J. Cenozoic Mammals of Africa. University of California Press. pp. 675–689. ISBN978-0-520-25721-4.
^Geraads, Denis; McCrossin, Monte and Benefit, Brenda (2012). "A New Rhinoceros, Victoriaceros kenyensis gen. et sp. nov., and Other Perissodactyla from the Middle Miocene of Maboko, Kenya". Journal of Mammalian Evolution 19: 57. doi:10.1007/s10914-011-9183-9.
The mammal families Rhinocerotidae (rhinoceroses), Equidae (horses), and Tapiridae (tapirs) together comprise the order Perissodactyla (the odd-toed ungulates). Dinerstein (2011) recognized five extant rhinoceros species in two subfamilies, Dicerotinae (including the two African species) and Rhinocerotinae (including the three Asian species) (see also Price and Bininda-Emonds 2001). Rhinoceroses are found in the tropics and subtropics of Africa and Asia in a range of open habitats; both African species sometimes ascend to montane forests.
The two African rhino species are the White Rhinoceros (Ceratotherium simum) and Black Rhinoceros (Diceros bicornis) (despite their common names, the White Rhinoceros is not white and the Black Rhinoceros is not black). Both of these species have two horns. The White Rhinoceros has a wide, square upper lip that facilitates grazing, allowing the animal to crop grasses close to the ground with its teeth. The Black Rhinoceros has a prehensile upper lip that facilitates browsing, allowing the animal to pluck leaves and grass stems. A recent genetic and morphometric analysis (Groves et al. 2010) argued that the northern and southern forms of White Rhinoceroses should be recognized as distinct species. Populations of the southern form are relatively stable whereas just a handful of individuals of the northern form are alive today.
Three rhino species occur in Asia. The Greater One-horned Rhinoceros (Rhinoceros unicornis) and Javan (or Lesser One-horned) Rhinoceros (Rhinoceros sondaicus) have just a single horn, but the Sumatran Rhinoceros (Dicerorhinus sumatrensis) has two horns. The horns of the Asian species are smaller than those of the African ones. Rhinoceros horns lack a bony core, containing only tiny keratin tubes dispersed in a keratinous matrix; a dark central core is strengthened by a composite of calcium and melanin. A close examination of rhino dentition reveals that only the three Asian species have tusks (enlarged incisors) in the lower jaw, especially striking in the Greater One-horned Rhinoceros. These tusks, rather than their horns, are used in fighting and defense (African rhinos use their horns).
Rhinoceros Ecology and Behavior
Rhinoceroses are massive animals. At the upper limit, White Rhinos can have a mass of as much as 3500 kg (despite their large size, rhinos can run quickly for brief periods, with most species able to reach a speed of 55 km/h). To obtain enough food to sustain their massive bodies, rhinos must often feed both day and night. Roughly speaking, the White Rhino and Greater One-horned Rhino are grazers (White Rhinos feed only on grass, but Greater One-horned Rhinoceroses eat a wide range of vegetation) whereas the Black, Sumatran, and Javan Rhinos are browsers.
Rhinos spend a substantial fraction of their time wallowing. The primary function of wallowing is presumed to be reducing heat stress, although escaping from biting insects may be another motivation. Rhinos are landscape engineers, with their grazing and browsing and defecation into latrines, and even wallowing, significantly modifying their habitat, shaping both its physical structure and species composition. In Asia, rhinoceroses play an important role in dispersing seeds of woody species into riverine grasslands.
All three Asian rhino species are excellent swimmers, but the African White and Black Rhinos are poor swimmers and can drown if they lose their footing in deep water. Greater One-horned Rhinoceroses are rarely found more than 2 km from water (this is suspected to be true also for Javan and Sumatran Rhinos although this is not actually known). In contrast, White and Black Rhinos can go several days without drinking and are less tied to water.
Rhinoceroses possess acute senses of hearing and smell, but have relatively poor vision. Their ears swivel independently. Diverse vocalizations are produced and at least the White Rhinoceros uses infrasonic communication, like elephants.
Intraspecific combat in Black Rhinos reportedly kills a substantial fraction of both male and female Black Rhinos.
In general, far more is known about Black Rhinos, White Rhinos, and Greater One-horned Rhinos than about the Javan and Sumatran Rhinos, which are rarely even seen.
Rhinoceroses and Humans
Until the last few hundred years, Black Rhinoceroses ranged widely across sub-Saharan Africa. During the colonial era in Africa and Asia, rhinos were hunted and all five species were apparently abundant. Subsequently, conflicts with human agriculture became more common and rhinos persisted mainly in regions unsuitable for farrming for one reason or another. The use of rhino horns in traditional medicine in Asia (especially Vietnam) has led to an illegal trade that has negatively impacted rhino populations. The horns, which are made entirely of densely appressed hairs (with no bony core as seen in the horns of cattle, sheep, and goats) have also been used for dagger handles in the Middle East.
The conservation status of rhinos varies considerably among species.
The Southern White Rhinoceros was abundant prior to the colonization of southern Africa, but the population dropped to 100 individuals around 1900. Today, however, there are more than 20,000 individuals, representing a great accomplishment resulting from concerted conservation efforts. The Northern White Rhino (which a 2010 study argued should be recognized as a distinct species rather than a subspecies) has had a very different trajectory. In the late nineteenth century, there may have been more Northern White Rhinos in Sudan, the Central African Republic, northern Uganda, and the DR Congo than there were Southern White Rhinos in South Africa. However, by the mid-1980s civil war had taken its toll; by the first decade of the 21st century, they were apparently extinct in the wild and the handful of remaining captive animals are closely related and likely insufficient for population recovery.
The Black Rhinoceros was once the most abundant of all five living rhino species and occurred across much of sub-Saharan Africa. Estimates of the Black Rhino population at the dawn of the 20th century range between around 300,000 and 1 million individuals. Subsequently, however, core populations were decimated across much of their range. Intensive conservation and translocation efforts, combined with locally based ecotourism efforts, have met with some, but not enough, success. In some areas, desperation in the face of poaching led to de-horning of Black Rhinos to make them unappealing to poachers, but this approach has been abandoned as ineffective, among other problems.
In Asia, rhino populations are severely threatened. The total population of all three Asian species combined is less than 3000, with only two populations having more than 100 individuals. The loss of Asian rhinos has resulted from both poaching and habitat loss. In Africa, extensive habitat still remains, so controlling poaching would allow rhino populations to rapidly increase. In Asia, unfortunately, similar enormous blocks of habitat do not exist and habitat is threatened by deforestation, plantations to produce oil palm and pulp and paper, and human population growth adjacent to protected areas.
Greater One-horned Rhinoceros populations are estimated to have totaled at least 475,000 before the spread of agriculture to the Gangetic and Brahamputra River floodplains of South Asia around 1400 AD. A deadly strain of malaria largely protected their habitats from humans until malaria was controlled in the region in the late 1950s. Two core populations in Chitwan National Park in Nepal and Kaziranga National Park in Assam, India, dropped as low as 60-80 individuals in Nepal in the late 1950s or early 1960s and to less than 100 in Kaziranga National Park around 1900. Many smaller reserves in Assam and West Bengal had numbers in the single digits or less than 20 in the 1970s. Since 1986, however, Nepal and India have undertaken intensive conservation and translocation efforts.
The Javan Rhinoceros is believed to be the most endangered large mammal on Earth, with just a few dozen individuals surviving, all of them possibly restricted to a single population in western Java, although establishment of a second population on Java by translocation was being planned as of 2010. Proposals to try to establish a captive breeding population were rejected, given the dramatic failure of captive breeding efforts for the Sumatran Rhino.
At one time, the Sumatran Rhino was widely distributed across Southeast Asia, but it experienced a dramatic decline and so few individuals remain that today, together with the Javan Rhinoceros, it is considered the most endangered large mammal on Earth. Although common nowhere, very small Sumatran Rhino populations persist in Peninsular Malaysia, Sabah (on Borneo) and Sumatra. The Sumatran Rhino was the focus of an effort to capture individuals from vulnerable sites and use them in a captive breeding program, with the goal of eventual reintroduction. Tragically, the effort was a huge failure, with extremely high mortality in captivity. Many conservation biologists view this episode as an illustration of the fact that captive breeding is no substitute for the often politically and sociologically difficult challenges of in situ conservation efforts.
(Dinerstein 2011 and references therein)
Dinerstein, E. 2011. Family Rhinocerotidae (Rhinoceroses). Pp. 144-181. in: Wilson, D.E. & Mittermeier, R.A., eds. Handbook of the Mammals of the World. Volume 2. Hoofed Mammals. Lynx Edicions, Barcelona.