The Sumatran rhinoceros (Dicerorhinus sumatrensis), also called the hairy rhinoceros or Asian two-horned rhinoceros, is a rare member of the rhinoceros family. It is one of five living rhinoceros species and the only species in its genus, Dicerorhinus. It is the smallest rhinoceros, but it is still a large animal. It stands 112–145 cm (44–57 in) tall at the shoulder, has a body length of 2.36–3.18 m (7 ft 9 in – 10 ft 5 in), and a tail of 35–70 cm (14–28 in). Its weight ranges from 500–1,000 kg (1,100–2,200 lb), with an average of 700–800 kg (1,540–1,760 lb). It has two horns, with the larger one on its nose, usually 15–25 cm (5.9–9.8 in) long, and a smaller horn that is often a stub. Its body is covered in reddish-brown hair.

The Sumatran rhinoceros once lived in rainforests, swamps, and cloud forests in India, Bhutan, Bangladesh, Myanmar, Laos, Thailand, Malaysia, Indonesia, and southwestern China, especially in Sichuan. It is now critically endangered, with only five small groups remaining in the wild: four in Sumatra and one in Borneo. Fewer than 80 adult rhinos are estimated to survive. The species was lost in Malaysia in 2019, and one group in Sumatra may already be extinct. In 2015, scientists confirmed that the Bornean rhino had disappeared from northern Borneo in Sabah, Malaysia. A small group was found in East Kalimantan in 2016.

The Sumatran rhino is mostly solitary, except during mating or when raising young. It is the most vocal rhino species and communicates by marking soil with its feet, bending saplings into patterns, and leaving droppings. It is better studied than the similarly secretive Javan rhino, partly because 40 rhinos were moved to captivity to help save the species. At first, few rhinos survived in their new homes, and no babies were born for nearly 20 years. In March 2016, a Bornean rhino was seen in Indonesian Borneo.

In February 2019, Indonesia’s environment ministry began a three-year effort to count all remaining Sumatran rhinos. Malaysia’s last known male and female rhinos died in May and November 2019, making the species extinct in that country. Today, the Sumatran rhino survives only in Indonesia, with fewer than 80 individuals left.

Taxonomy and naming

The first recorded Sumatran rhinoceros was shot 16 km (9.9 mi) outside Fort Marlborough, near the west coast of Sumatra, in 1793. Drawings of the animal and a written description were sent to Joseph Banks, a naturalist and president of the Royal Society of London, who published a paper about the specimen that year. In 1814, the species was given a scientific name by Johann Fischer von Waldheim.

The specific name "sumatrensis" means "of Sumatra," the Indonesian island where the rhinos were first discovered. Carl Linnaeus first grouped all rhinos into the genus Rhinoceros, so the species was originally called Rhinoceros sumatrensis or sumatranus. Joshua Brookes later classified the Sumatran rhinoceros as a separate genus because it has two horns, naming it Didermocerus in 1828. Constantin Wilhelm Lambert Gloger proposed the name Dicerorhinus in 1841. In 1868, John Edward Gray suggested the name Ceratorhinus. Normally, the oldest name would be used, but a 1977 decision by the International Commission on Zoological Nomenclature set Dicerorhinus as the correct genus name. Dicerorhinus comes from the Greek words di (meaning "two"), cero (meaning "horn"), and rhinos (meaning "nose").

The three subspecies are:

• D. s. sumatrensis, known as the western Sumatran rhinoceros, which has 75 to 85 rhinos remaining, mostly in national parks in Sumatra, such as Bukit Barisan Selatan, Kerinci Seblat, and Gunung Leuser, and in small numbers in Way Kambas National Park. This subspecies became extinct in Malaysia in 2019. The main threats are habitat loss and poaching. A slight genetic difference exists between western Sumatran and Bornean rhinos. Rhinos in Peninsular Malaysia were once called D. s. niger but are now considered the same as D. s. sumatrensis. Three males and five females live in captivity at the Sumatran Rhino Sanctuary in Way Kambas. The youngest male was born there in 2012. A female calf was born in May 2016. The sanctuary’s two males were born at the Cincinnati Zoo. A third female calf was born in March 2022.

• D. s. harrissoni, known as the Bornean rhinoceros or eastern Sumatran rhinoceros, which was once common in Borneo but now has about 15 individuals left. The population lives in East Kalimantan, with recent extinctions in Sabah. Reports of rhinos in Sarawak are unconfirmed. This subspecies is named after Tom Harrisson, who studied Bornean wildlife in the 1960s. The Bornean subspecies is smaller than the other two. A captive population of one male and two females lived at the Borneo Rhinoceros Sanctuary in Sabah, but the male died in 2019, and the females died in 2017 and 2019.

• D. s. lasiotis, known as the northern Sumatran rhinoceros or Chittagong rhinoceros, which once lived in India and Bangladesh but is now extinct in those countries. Unconfirmed reports suggest a small population may still exist in Myanmar, but political issues have prevented verification. The name lasiotis comes from Greek for "hairy-ears." Later studies showed their ears were not longer than other Sumatran rhinos, but D. s. lasiotis remained a subspecies because it was larger than the others.

Ancestral rhinoceroses first split from other perissodactyls in the Early Eocene. Comparing mitochondrial DNA suggests modern rhino ancestors split from horse ancestors around 50 million years ago. The Rhinocerotidae family, which includes living rhinos, first appeared in the Late Eocene in Eurasia, and their ancestors spread from Asia during the Miocene.

Modern genetic evidence shows the Sumatran rhinoceros is more closely related to Asian one-horned rhinos (Indian and Javan rhinos) in the genus Rhinoceros than to African rhinos. The split between Rhinoceros and Dicerorhinus is estimated to have occurred around 14.8 million years ago, shortly after the split between Dicerorhinus and African rhinos, which happened around 15.6 million years ago.

Based on physical and genetic evidence, the Sumatran rhinoceros is closely related to the extinct woolly rhinoceros (Coelodonta antiquitatis) and Stephanorhinus. Their last common ancestor is estimated to have split around 9.5 million years ago. The woolly rhinoceros, named for its hairy coat like the Sumatran rhino, first appeared in China and lived across Eurasia until it went extinct around 14,000 years ago. Stephanorhinus species were common in Europe and China during the Pliocene and Pleistocene, with two species surviving into the last glacial period until at least 40,000 years ago.

Today, only two fossil species are confidently placed in the genus Dicerorhinus: Dicerorhinus fusuiensis from the Early Pleistocene of South China and Dicerorhinus gwebinensis from the Pliocene–Early Pleistocene of Myanmar. Fossils of modern Sumatran rhinos are known from the Early Pleistocene onward.

A study using a complete nuclear genome of a Sumatran rhino showed population size changes over time, with a peak of 57,800 individuals 950,000 years ago and a decline to 500–1,300 individuals at the start of the Holocene. A slight increase occurred during the Eemian Interglacial. This decline may have been caused by climate change, habitat loss, and human activity. Later criticism noted the study did not include DNA from extinct mainland populations. A different study using mitochondrial DNA suggested a stable population of 40,000 individuals over 400,00

Description

A grown Sumatran rhino is about 112 to 145 centimeters (3.67 to 4.76 feet) tall at the shoulder, has a body length of around 236 to 318 centimeters (7.74 to 10.43 feet), and weighs 500 to 800 kilograms (1,100 to 1,760 pounds). Some rhinos in zoos have been known to weigh as much as 2,000 kilograms (4,410 pounds). Like the two African rhino species, the Sumatran rhino has two horns. The larger horn is called the nasal horn, usually measuring 15 to 25 centimeters (5.9 to 9.8 inches). The longest recorded nasal horn was 81 centimeters (32 inches). The smaller horn, called the posterior horn, is usually less than 10 centimeters (3.9 inches) long and often appears as a small bump. The nasal horn is also known as the anterior horn, and the smaller posterior horn is called the frontal horn. Both horns are dark grey or black in color. Male rhinos have larger horns than females, but the species does not show other differences between males and females. In the wild, Sumatran rhinos live about 30 to 45 years. The longest recorded lifespan in captivity was 32 years and 8 months, belonging to a female D. lasiotis at the London Zoo in 1900.

Two thick folds of skin wrap around the body behind the front legs and before the hind legs. A smaller fold of skin surrounds the rhino’s neck. The skin is thin, measuring 10 to 16 millimeters (0.39 to 0.63 inches), and wild rhinos appear to have no fat under the skin. The rhino’s hair can range from very thick (as seen in young calves) to very sparse, and is usually reddish brown. In the wild, this hair is hard to see because rhinos are often covered in mud. In captivity, the hair grows longer and becomes shaggier, possibly because they walk less through plants, which usually wears down the hair. The rhino has a patch of long hair around its ears and a thick clump of hair at the end of its tail. Like all rhinos, the Sumatran rhinoceros has very poor vision. It is fast and agile, able to climb mountains easily and move comfortably on steep slopes and riverbanks.

Distribution and habitat

Remains of the Sumatran rhinoceros have been found in Neolithic sites in Zhejiang, Henan, Fujian, and the northeastern Tibetan Plateau in China. A review of Rhinoceros sinensis fossils in Chongqing showed that some remains previously thought to be from another species were actually from Sumatran rhinoceroses. This proves that the species lived in southern China during the Pleistocene era. The Sumatran rhinoceros was the most common rhino species in ancient and medieval China, where it lived alongside the less common Javan rhinoceros.

In Southeast Asia, the Sumatran rhinoceros lives in lowland and highland rainforests, swamps, and cloud forests. It prefers hilly areas near water, especially steep valleys with thick vegetation. The species once lived as far north as Myanmar, eastern India, and Bangladesh. Some unconfirmed reports suggest it also lived in Cambodia, Laos, and Vietnam. Today, all known living Sumatran rhinoceroses are found only on the island of Sumatra. Some experts believe the species might still survive in Burma, but this is unlikely due to political instability there. The last confirmed sightings of stray rhinos in India were in the 1990s.

The Sumatran rhinoceros is spread out across its habitat more than other Asian rhino species, making it harder for conservationists to protect them. Only four areas are known to have Sumatran rhinoceroses: Bukit Barisan Selatan National Park, Gunung Leuser National Park, and Way Kambas National Park on Sumatra; and a region on Indonesian Borneo west of Samarindah.

Kerinci Seblat National Park, the largest in Sumatra, was estimated to have about 500 rhinos in the 1980s. However, due to poaching, this population is now considered extinct. It is unlikely that any rhinos survive in Peninsular Malaysia.

Genetic studies show three distinct groups of Sumatran rhinoceroses. The sea between Sumatra and Malaysia was not a major barrier for rhinos, as rhinos in eastern Sumatra and Peninsular Malaysia are genetically similar. This suggests they may have lived together during the Pleistocene when sea levels were lower and Sumatra was connected to the mainland. Rhinos in Borneo, however, are genetically different enough that experts advise against mixing them with other populations. Scientists are studying genetic diversity within these groups using specific DNA markers. Early results show Sumatran rhinos have genetic diversity similar to less endangered African rhinos, though research on this topic continues.

Although Sumatran rhinos were thought to be extinct in Kalimantan since the 1990s, in March 2013, the World Wildlife Fund (WWF) reported finding signs of rhinos, including footprints, mud holes, and plant remains, in West Kutai Regency, East Kalimantan. In October 2013, camera traps captured images of rhinos in Kutai Barat, Kalimantan. Experts believe the videos show two different rhinos, but they are not certain. Indonesia’s Minister of Forestry called the video evidence “very important” and mentioned a goal to increase rhino populations by 3% each year. In March 2016, the WWF announced the discovery of a live Sumatran rhino in Kalimantan, the first confirmed sighting in over 40 years. The female rhino was moved to a sanctuary for safety.

In November 2019, Iman, the last known Sumatran rhino in Malaysia, died. Scientists are using stem cell technology to help restore the species in the country. As of 2023, two baby rhinos have been born at the Sumatran Rhino Sanctuary in Way Kambas National Park, Indonesia.

Behavior and ecology

Sumatran rhinos usually live alone, except when they pair up to mate or care for their young. Each rhino has a home area; male rhinos have territories as large as 50 km (19 mi), while female rhinos have smaller areas of 10–15 km (3.9–5.8 mi). Female rhinos seem to keep their areas separate, but male rhinos often share territory. There is no evidence that Sumatran rhinos fight to defend their space. They mark their territory by scraping soil with their feet, bending small trees into special shapes, and leaving behind waste. These rhinos are most active when eating, at sunrise, and just after sunset. During the day, they roll in mud baths to stay cool and rest. In the rainy season, they move to higher ground; in cooler months, they return to lower areas. If mud holes are not available, rhinos use their feet and horns to dig in puddles. Wallowing helps them regulate body temperature and protect their skin from insects. In captivity, rhinos without enough wallowing have developed skin injuries, eye problems, and eventually died. A study found that rhinos use no more than three wallows at a time. After 2–12 weeks, they leave a wallow. They typically wallow for 2–3 hours around midday before searching for food. In zoos, rhinos wallow less than 45 minutes a day, but wild rhinos spend 80–300 minutes (about 166 minutes) daily in wallows.

Little is known about the health of Sumatran rhinos. In the 1800s, ticks and a disease called gyrostigma caused deaths in captive rhinos. They are also vulnerable to surra, a blood disease spread by horse-flies carrying parasites. In 2004, all five rhinos at a conservation center died from surra within 18 days. Humans are the only known predators of Sumatran rhinos. Tigers and wild dogs might kill young calves, but calves usually stay close to their mothers. The frequency of such attacks is unknown. Although rhinos share space with elephants and tapirs, they do not compete for food or habitat. Elephants and rhinos often use the same trails, and smaller animals like deer and wild dogs also use these paths.

Sumatran rhinos create two types of trails. Main trails are used by many rhinos over time to move between important areas, like salt licks or through difficult terrain. In feeding areas, they make smaller trails through vegetation to reach food. Some rhino trails cross rivers over 1.5 m (4.9 ft) deep and 50 m (160 ft) wide. These rivers have strong currents, but rhinos are strong swimmers. Few wallows are near rivers, suggesting rhinos may sometimes bathe in rivers instead of wallows.

Most eating happens just before nightfall and in the morning. Sumatran rhinos eat mostly young leaves, twigs, and saplings. They consume up to 50 kg (110 lb) of food daily. Researchers have identified over 100 plant species in their diet, with tree saplings (1–6 cm in trunk diameter) making up the largest part. Rhinos often push saplings over with their bodies to eat the leaves. Many of the plants they eat are rare, showing they change feeding areas often. Common plants include species from the Euphorbiaceae, Rubiaceae, and Melastomataceae families, with Eugenia being the most frequently eaten.

The rhino’s diet is high in fiber and has moderate protein. Salt licks are important for their nutrition. These licks can be hot springs, salty water seepages, or mud volcanoes. Salt licks also help rhinos find mates, as males sniff females in heat. Some rhinos live where salt licks are not available and get minerals from plants.

Sumatran rhinos are the most vocal of all rhino species. In zoos, they make sounds constantly, and they do so in the wild as well. They produce three types of noises: eeps, whales, and whistle-blows. Eeps are short yelps lasting one second and are the most common. Whales sound like humpback whale songs and last 4–7 seconds. Whistle-blows are loud, two-second whistles followed by a burst of air. These sounds can vibrate iron bars in zoo enclosures. The purpose of these sounds is unknown, but they may signal danger, mating readiness, or location. Whistle-blows can be heard far away, even in dense forests. Rhinos also twist saplings they do not eat, which may be a way to communicate or mark trail intersections.

Female rhinos reach sexual maturity at 6–7 years old, while males mature at about 10 years. Pregnancy lasts 15–16 months. Calves weigh 40–60 kg (88–132 lb) and are weaned after 15 months, staying with their mothers for 2–3 years. In the wild, females give birth every 4–5 years, but little is known about their parenting habits.

In captivity, mating begins with courtship, including vocalizing, tail raising, and physical contact. Both males and females bump each other’s heads and genitals. This behavior is similar to black rhinos. Young male rhinos in captivity are sometimes too aggressive, injuring or killing females during courtship. In the wild, females could escape aggressive males, but in small enclosures, they cannot. This may explain the low success of captive breeding programs.

The female’s fertile period lasts about 24 hours and repeats every 21–25 days. In zoos, mating lasts 30–50 minutes, similar to other rhinos. At a conservation center in Malaysia, mating periods were shorter. Observations in Cincinnati Zoo showed similar durations.

Population trends

Sumatran rhinos were once common throughout Southeast Asia. Today, fewer than 100 are believed to remain. This species is classified as critically endangered, mainly because of illegal hunting. A survey in 2008 estimated about 250 rhinos survived. From the early 1990s, their population dropped by more than 50% each decade. Now, small and scattered groups face risks from health problems caused by not having enough genetic diversity. Most of their remaining habitat is in hard-to-reach mountain areas of Indonesia.

Poaching is a major threat because rhino horns are valuable on the black market. This species has been hunted for centuries, leading to its current low numbers. Rhinos are hard to find and hunt directly, so poachers use traps like spear traps and pit traps. In the 1970s, local people in Sumatra used rhino horns in amulets and believed they protected against poison. Dried rhino meat was used to treat illnesses like diarrhea, leprosy, and tuberculosis. A mixture made from a rhino’s skull in coconut oil, called "rhino oil," was used for skin diseases. However, the extent of these practices is unknown. Rhinoceros horn was once thought to be used as an aphrodisiac, but traditional Chinese medicine never used it for this purpose. Hunting has mainly been driven by demand for rhino horns, which are claimed to have unproven medicinal benefits.

The rainforests of Indonesia and Malaysia, where Sumatran rhinos live, are also targeted for logging because of valuable hardwoods like merbau, meranti, and semaram. These woods can cost up to $1,800 per cubic meter on international markets. Enforcing laws against illegal logging is difficult because people live near or within these forests. The 2004 Indian Ocean earthquake led to increased logging permits, even though the wood is mostly exported, not used domestically. While habitat changes affect rhinos, hunting remains the main cause of their decline, likely due to the Allee effect, which occurs when small populations struggle to survive.

The Bornean rhino in Sabah was declared extinct in the wild in April 2015, with only three left in captivity. The mainland Sumatran rhino in Malaysia was also declared extinct in the wild in August 2015. In March 2016, a Sumatran rhino was sighted in East Kalimantan, Indonesia, but the same rhino, named Najaq, was later found dead from an infection caused by a snare.

Sumatran rhinos do not survive well outside their natural habitat. In 1872, London Zoo acquired a bull and cow captured in Chittagong in 1868. The female, named "Begum," lived until 1900, the longest recorded lifespan for a captive rhino. She was one of several rhinos from an extinct subspecies held in zoos and circuses. In 1972, Subur, the last Sumatran rhino in captivity, died at the Copenhagen Zoo.

In the early 1980s, conservation groups started a captive-breeding program to help the species. Between 1984 and 1996, 40 rhinos were moved to zoos and reserves worldwide. However, by the late 1990s, no rhinos had been born in the program, and most participants agreed it had failed. In 1997, the IUCN’s Asian rhino specialist group noted that 20 of the captured rhinos had died, and the program could not maintain the species safely. A disease outbreak in 2004 killed all captive rhinos in Peninsular Malaysia, leaving only eight.

Seven of these rhinos were sent to the United States, and three to the UK, but by 1997, only three remained: a cow in Los Angeles, a bull in Cincinnati, and a cow in the Bronx. In 2001, a cow named Emi gave birth to a male calf named Andalas, the first successful captive birth in 112 years. A female calf, Suci, was born in 2004, and a second male, Harapan, in 2007. In 2012, Andalas sired a calf named Andatu in Sumatra.

Despite these successes, the captive-breeding program remains controversial. Supporters say zoos help conservation by studying rhinos, raising awareness, and funding efforts in Sumatra. Opponents argue the program is too costly, causes harm by removing rhinos from their habitat, and cannot match recovery rates in protected wild areas. In 2015, Harapan, the last rhino in the Western Hemisphere, was sent to Indonesia.

In 2016, only three Sumatran rhinos remained in Malaysia, all in captivity in Sabah. A bull named Tam and two cows, Puntung and Iman, died between 2017 and 2019, making the species extinct in Malaysia.

In Indonesia, the Sumatran Rhino Sanctuary in Way Kambas National Park now has seven rhinos. A female named Delilah was born in 2016, and two more females, Sedah Mirah and another, were born in 2022 and 2023. A male calf was born in 2023, the son of Delilah and Harapan.

In Indonesian East Kalimantan, only one old rhino, estimated to be 35 to 40 years old, remains.

Cultural depictions

The Sumatran rhinoceros has not been well known to most people, except for those seen in zoos or in books. It has been less famous than other rhino types, like the Indian, black, and white rhinos. Recently, videos of the Sumatran rhinoceros in its natural home and in breeding centers have appeared in several nature documentaries. A lot of footage is included in an Asia Geographic documentary titled The Littlest Rhino. Another documentary, Forgotten Rhino, by Natural History New Zealand, showed a Sumatran rhino. This footage was taken by an Indonesian cameraman named Alain Compost in 2001. The documentary mainly focused on Javan and Indian rhinos.

The Bornean rhinoceros was first recorded by looking at its droppings and tracks. However, pictures of this rhino were first widely shared in April 2006, when camera traps captured images of a healthy adult in the jungles of Sabah, Malaysian Borneo. On April 24, 2007, it was announced that cameras had recorded the first video of a wild Bornean rhino. The nighttime footage showed the rhino eating, looking around through jungle plants, and sniffing the camera equipment. The World Wildlife Fund, which made the video, has used it to help local governments create a rhino conservation area. Monitoring has continued, with 50 new cameras placed in the area. In February 2010, a video showed what looked like a pregnant rhino.

From the mid-1800s to the early 1900s, colonial naturalists and hunters collected many stories about the Sumatran rhino. In Burma, people once believed the rhino could eat fire. Stories said the rhino followed smoke to its source, such as campfires, and then attacked the camp. In Burma, it was also believed that the best time to hunt rhinos was in July, when they gathered under the full moon. In Malaya, it was thought that the rhino’s horns were hollow and could be used like a hose for breathing air or spraying water. In Malaya and Sumatra, people once believed the rhino shed its horns each year and buried them underground. In Borneo, it was said the rhino ate fish that had been stunned by its own waste after defecating in a stream.