Three subspecies are recognized—the Northern Sumatran Rhino (D. s. lasiotis), regarded as extinct but for a remote possibility that a remnant population survives in northern Myanmar, the Bornean Sumatran Rhino (D. s. harrissoni) and the Malaysian Sumatran Rhino (D. s. sumatrensis).
The current population of Sumatran Rhinos is estimated at fewer than 80 individuals. The Asian Rhino Specialist Group (AsRSG) places the population in the range 40–78 in its briefing document for the CITES Cop 18 meeting set for 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 in Indonesia (on the island of Sumatra and Kalimantan Province on the island of Borneo). Only one infertile female lives in captivity in Sabah Province (the Malaysian part of Borneo). (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 of 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 regarded as closely related to the Woolly Rhino that, although now extinct, survived the previous Ice Age, only dying 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 gestation period of 15–16 months.
The Sumatran Rhino is a browser known to exploit more than 100 different plant species. Salt licks are important sources of 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 mostly 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 dense forest. Communal dung heaps are also important communication points.
Sumatran Rhinos are shy, secretive and solitary, but for mating periods and females nursing calves. 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 helping to maintain a constant body temperature and to 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, a population bottleneck that would compromise breeding potential.