Factfile: Sumatran rhino
- Common name: Sumatran rhino.
- Synonyms: Asian two-horned rhino or the Hairy rhino.
- Scientific name: Dicerorhinus sumatrensis, from the Greek “di”, meaning "two", “cero”, meaning "horn" and “rhinos”, meaning "nose"; “sumatrensis”, from Sumatra.
- Size: Sumatran rhino are by far the smallest species of rhino.
- Weight: they weigh between 500-800 kg.
- Shoulder height: they usually stand at 1.20-1.45 metres and are about 2.50 metres long.
- Skin colour:Sumatran rhinos have a reddish-brown skin, in the wild variably covered with short bristly hair.
- Hair: these are the hairiest species of rhino. This can vary from a short, bristly coat, to a shaggy fur for those in captivity because of less abrasion from vegetation. The ears have a fringe of longer hairs, and the tail end has a tuft of thicker hairs.
- The horn: Sumatran rhinos have two horns that are dark grey to black in colour. In the wild they are usually very smooth and form a slender cone that is curved backwards. The larger front (anterior) horn is typically 15-25 cm long, and the smaller second (posterior) horn is normally much smaller, seldom more than a few cm in length, and often not more than an irregular knob on the tip of the nose. Rhino horn is made of keratin (the same as fingernails and hair fibres) and will re-grow if broken off. It is not used for fighting, but for scraping mud from the sides of wallows, pulling down food plants, and aids protection of the head and nose when breaking through dense forest vegetation.
- Distinctive characteristics: Aside from their smaller size and hairy bodies as distinguishable features of the Sumatran rhinos from other rhino species, they also have unique skin folds. There are two prominent folds in the skin that circle the body behind the front legs and before the hind legs, and lesser folds on the neck and at the base of the legs. The skin is fairly thin: about 10-16 mm, and is soft and pliable. Sumatran rhinos also have a prehensile upper lip, which assists in grasping their food.
- Sumatran rhinos can run fast and are very agile. They climb mountains easily and can negotiate very steep slopes and riverbanks. With the protection provided by the horns and rims of hard skin and cartilage on nose and head, they can easily break through the densest vegetation, leaving round tunnels
Location and habitat
- Location: across parts of Southeast Asia, including: Sumatra, Indonesia, the foothills of Bhutan and northeast India, southern China, Cambodia and Borneo.
- Habitat: the Sumatran rhino lives in dense tropical forest, in both the lowlands and highlands. Sumatran rhinos are very well adapted to life in very dense tropical forests. They are primarily attracted to areas with plentiful food resources (shrubs, fruits, shoots, leaves and roots etc.)
Social behaviour and territory
- Sociability: Sumatran rhinos are usually solitary, except for females with small calves, and during a short period of courtship around the time a female is in oestrous.
- Male territory: males have large territories (can range up to 50 km2), which overlap with other males’ territories. There is no indication that these territories are actually defended by territorial fights as happens in other rhino species, but they are marked along the main trails by urine, faeces, scrapes and twisted saplings.
- Female territory: females have much smaller ranges (around 10-15 km2), and appear to be quite well spaced but will sometimes overlap with male territories.
- Communicating and sounds: The Sumatran rhino is surprisingly vocal and communicates with many different sounds, mostly whistling or whining noises. Dung heaps (middens) also serve as a communication point, though the large latrines common in territories of the Greater one-horned rhino do not occur, probably because of the much lower natural density of these animals. However when a Sumatran rhino meets a heap of dung, it usually deposits a fresh pile nearby. After defecating, Sumatran rhinos scratch their hind feet in the dung and kick it around in the bushes. This probably serves to mark the feet and surrounding tracks with the scent of the faeces. Foot glands, as for the Javan rhino, are most likely absent in the Sumatran rhino.
- Tracks and trails: Sumatran rhinos tend to use a network of game trails that occur on all major ridges and along all major rivers. The trails are well defined and are kept open by the regular passage of the larger animals, especially rhinos and elephants. They are also marked by the depositing of urine, dung, scrapes and twisted saplings. The rhinos use the trails to travel between feeding areas, salt-licks or seasonal movements where they occur.
Breeding and Birth
- Sexual maturity: females reach sexual maturity at around 4 years of age, and males are sexually active by around 7 years old.
- Gestation period: approximately 15-16 months. Sumatran rhinos will have a single calf every 4-5 years.
- Birth: the birth weight is 40-50 kg. A calf drinks and grows 1- 2kg daily. They start nibbling from the food hanging from the mother’s mouth at an early age to learn which plants are good to eat, but may continue to suckle up to the age of 13-15 months.
- Maternal calves: calves may occasionally be predated by tigers or wild dogs, but when young they stay very close to the mother at all times, and natural predation is largely insignificant to the mortality rates of the species.
Other interesting facts
- Food: the Sumatran rhino is a browser, and its diet consists of a divers range of tropical forest plant life. They eat the tips of plants growing on the forest floor, browse the leaves from sapling trees that they break to reach the crown and pull climbers from trees. They feed mostly in small patches of juicy secondary vegetation created by landslides, tree falls and along river banks. They are also fond of fruits that have fallen from the forest trees.Sumatran rhinos eat on average 50-60 kg (almost 1% of their body weight) of plant matter per day.
- Historical legend: the Sumatran rhino is considered the most “primitive” rhino species, because of its hairy skin and other prehistoric characteristics. It is the closest living relative to the famous woolly rhinoceros that lived in the frigid lands of Europe and Asia during the ice-age.
- Horn record: the longest horn ever found was 81 cm long and is now in the British Museum, London.
- Teeth: To masticate the large quantities of coarse food, rhinos have two rows of six strong broad and low-crowned molars on each side. The teeth are fitted with strong ridges of enamel, which cut the woody parts in characteristic 1-2 cm long bits. Over the years the teeth wear down by several centimetres to become shallow dish-like structures, and old animals will have problems masticating their food, will lose condition, and may eventually die of undernourishment. Sumatran rhinos, like all Asian rhinos, have long dagger-shaped lower incisor teeth. They are very sharp and are used in fighting and can inflict deep wounds. These teeth are lacking in the African rhino species.
- Digestion: Sumatran rhinos are hind-gut fermenters (they use micro-organisms in the last part of the intestine to break down indigestible parts of the food) and have a large cavernous caecum and colon.
- Longevity: Sumatran rhinos are estimated to live an average of 30-45 years in the wild; while the longevity record for those in captivity is almost 33 years.
- Senses: Sumatran rhinos have a good sense of smelling and hear very well, but are rather short sighted. When encountered in the forest, they usually run away and attacks on humans are very rare and probably mainly accidental because of the animal’s limited eyesight.
- Salt licks: these are an important asset within a Sumatran rhinos' territory. They usually materialise in the form of small hot springs, seepages of mineral water or so-called “mud volcanoes”. Each rhino has a favourite salt-lick that is visited once every one or two months, but much more often when a female is with a calf. These are important for the extraction of important minerals for the rhino's health. Wildlife trails lead from all directions to these places, and other animals like elephants, tigers, orangutans and deer, etc. visit these places also to get a supplement of scarce minerals. Salt-licks also appear to be important social focal points, where males can pick up scent marks from oestrous females. Unfortunately the big trails leading to the salt-licks also attracts poachers, who place their traps and snares around the licks.
- Wallowing: Sumatran rhinos spend a large part of the day wallowing in mud holes. They may use temporary pools and puddles which they deepen with the feet and horn. In mountain areas good places for wallows are scarce and some are used repeatedly for a very long term, and eventually become characteristic holes dug in several meters into a slope. The access to mud wallows is essential for thermo-regulation, skin condition and to get rid of ectoparasites and biting insects.
- Poaching: The biggest threats for Sumatran rhinos is poaching. Sumatran rhinos are poached for their horn, and the loss of their habitat occurs for human agricultural development. The horn is used in Asia as a medicine for fever and pain, and trade in rhino horn between Borneo and other source areas in SE Asia and China has been reported since before more than 2,000 years ago. Over the centuries, the Sumatran rhino had been exterminated over most of its range, though in many places suitable habitat remains. This continued until 1995, when there were only about 2-300 left worldwide: largely in the places where they are still found today, and only in National Parks or Wildlife Reserves. Since then, the decline has stopped thanks to the concentrated efforts of dedicated anti-poaching teams called Rhino Protection Units (RPUs) in all major rhino areas.
- Protection: With continued strict protection of both the remaining rhinos and their habitat, over the next century the populations will hopefully eventually be able to recover to at least 2,000 to 2,500 individuals, as this number is estimated by population biologists as a minimum requirement for long-term survival of the species such as the Sumatran rhino.
Nico van Strien