A Sumatran rhinoceros is the smallest amongst the living rhinos and the only one of Asian rhinos with two horns. Its shaggy appearance is its best known feature, due to the long, coarse hair covering much of its body. As it grows older, this hair falls out, meaning that its age can, to a certain extent, be determined by how hairy it is. Underneath, its hide has a red undertone, making this rhino unique in appearance. Its hairiness suggests to many scientists that it may be a direct descendant of the woolly rhinoceros, extinct for about 10,000 years. Sumatran rhinos, along with the Javan rhino, are the most threatened rhino species. Sumatran rhinos outnumber Javan rhinos, but are more under threat by poaching. They were declared extinct in Malaysia in the wild in 2015.
The Sumatran rhinoceros once enjoyed a continuous range north to Burma, Bangladesh and eastern India. It may also have lived in Cambodia, Vietnam and Laos. It is now only reported to occur in Peninsular Malaysia, Sabah, Borneo and the island of Sumatra. Some conservationists hope they still survive in Burma, though this is considered unlikely. It lives in lowland and highland secondary rainforest, cloud forests and swamps, in hilly areas with water nearby, particularly steep upper valleys that have copious undergrowth.
Sumatran rhinos are solitary animals. Males and females both maintain home ranges, which overlap. Males have larger territories than females. When rhinos do meet on occasion, they do not remain together for very long. These animals are well-known for their marking behavior, marking their trails with urine, feces and soil scraps, which act as olfactory and visual signals for passing rhinos. These animals are inexhaustible walkers. They eat before dawn and again before sunset, moving mostly by night. In the daytime they are often found in ponds of rainwater or wallows dug out near streams. They also make patterned seasonal movements, traveling along hills at the time when the lowlands are flooded, and descending during times of cool and relatively dry weather, returning to the high ground to avoid summer insects, in particular horse flies.
Sumatran rhinos are polygynous, each male breeding with multiple females during a single year. The mating period is not known. However, most births take place between October and May, which is when the heaviest rainfall occurs. Gestation is thought to be between 12 to 16 months, with the interval between births being at least 3-4 years. A single calf is born, and during the first few days is hidden amongst dense vegetation near a salt lick while its mother browses. When it is about two months old, it wanders near its mother. During the first stages of development, calves may associate with each other, but later they become solitary. Weaning occurs at 16-17 months old and calves stay with their mother until they are 2 or 3 years old. They reach maturity by the age of 7-8.
Hunting has been a primary factor for the decline of this species. Rhino horn and other body parts have been used for centuries in traditional Asian medicine to treat fevers, strokes and other ailments. Hunting is now illegal, but poaching continues, with these animals still being killed for their horns. The other main threat is the loss of habitat due to logging and the conversion of land for other uses. As suitable habitats become fewer, rhino populations are forced into small, fragmented subpopulations, possibly too small to form a viable group. Left in remaining pockets of forest, these animals become even more vulnerable to disease, poaching and environmental disasters.
According to the WWF Panda resource, the total population size of the Sumatran rhino is fewer than 100 individuals. According to the IUCN Red List, the total Sumatran rhino population size is 220-270 individuals. Currently the species is classified as Critically Endangered (CR) and its numbers today continue to decrease.