Three subspecies are recognized. The Bornean Sumatran Rhino (D. s. harrissoni) and the Malaysian Sumatran Rhino (D. s. sumatrensis) survive in tiny populations. However, the Northern Sumatran Rhino (D. s. lasiotis) is regarded as extinct, but for the remote possibility of a remnant population surviving in northern Myanmar.
The current Sumatran Rhino population is estimated at fewer than 80 individuals. (The Asian Rhino Specialist Group (AsRSG) set the range at 40–78 in its briefing document for the CITES Cop 18 held in September 2019.)
The species once occurred widely across southeast Asia, but its precise historical range is uncertain owing to confusion resulting from its overlapping range with the Javan and Indian rhinos. The species is now restricted to four isolated locations on the Indonesian islands of Sumatra and Borneo’s Kalimantan Province). The Sumatran Rhino is now extinct in Malaysia—the only surviving individual died in the country’s Sabah Province at the end of 2019. (See maps)
This shy species favors hilly terrain near water and salt licks in dense primary rain and cloud forests. It will move into higher areas in times of lowland flooding.
Weight: 1,300–2,100 lbs (600–950 kg) Shoulder height: 3 ft 3 in–4 ft 3 in (1–1.3 m) Length nose to tail: 7 ft 10 in–10 ft 4in (2.4–3.2 m) Front horn length: about 10–31 in (25–79 cm) Rear horn length: <4 in (<10 cm)
The Sumatran Rhino is the smallest of all the living rhinos and the only Asian rhino with two horns. Tufted ears and a coat of reddish-brown hair give rise to its alternative common name, the “Hairy Rhino.” Captive Sumatran Rhinos can become particularly hairy due to the lack of wear and tear. Like other Asian rhinos, it has a prehensile upper lip, and the skin is folded. It is also closely related to the extinct Woolly Rhino that survived the previous Ice Age and only died out about 10,000 years ago.
As with the other Asian species, not much is known about the Sumatran Rhino’s biology. It probably lives from 30–40 years in the wild. Sexually mature females are believed to give birth to a single calf every three years or so after a pregnancy of 15–16 months.
The Sumatran Rhino is a browser known to exploit more than 100 different plant species. Salt licks provide essential minerals and are regularly visited, especially by females with young calves.
Though forest confined, the Sumatran Rhino is probably as agile as other Asian rhinos in more open terrain. Like all Asian rhinos, it is a good swimmer.
Unlike the quiet Javan Rhino, the Sumatran Rhino is quite vocal and uses a range of whistles and whines to communicate with neighbors. Some vocalizations have been likened to the songs of humpback whales, and they contain a high level of infrasound which would be effective for communicating in their dense forest habitat. Communal dung heaps are also important communication points.
Sumatran Rhinos are shy, secretive, and solitary, except during mating periods and for nursing females. Male territories are large, overlapping, and well-marked with urine, feces, scrapes, and twisted branches. As with the Javan Rhino, there is no indication that male territories are vigorously defended. Female territories are smaller and only occasionally overlap. Wallowing is also important and takes up much of a Sumatran Rhino’s day. The mud helps maintain a constant body temperature and fend off parasites and other irritating insects.
Human contact is limited, mainly because numbers are so low. The Sumatran Rhino is confined to protected areas where they are under the surveillance of Rhino Protection Units.
Listed as “Critically Endangered” on the IUCN Red Data List. Listed on CITES Appendix I.
Surviving populations of Sumatran Rhinos are small and scattered in relatively inaccessible mountainous terrain. Although poaching remains a threat, the surviving groups are so small and cut off from each other that the species faces a high risk of inbreeding depression. (Inbreeding depression is defined as mating between individuals related by ancestry and is more likely in populations that are, or have been, small.)