The islands of Borneo and Sumatra are two of the most biodiverse areas on earth, known for their extraordinarily rich flora and fauna. Although much of the recent international attention has focused on the islands’ wild orangutans, the forests of Indonesia in fact contain over 10% of the world’s flowering plants, 16% of the world’s reptiles and amphibians, 17% of the world’s birds and 12% of the world’s mammal species (Wakker, 2004).  Among these are over 20 species of primate.

OURF has always believed that the key to protecting orangutans is protecting their rainforest home, and ensuring that the remaining rainforests of Borneo and Sumatra remain as intact and inviolate as possible. But protecting orangutans is also important for the very future of that rainforest. Due to their ecological role as seed dispersers and the part they play in breaking up the dense rainforest canopy, studies have shown that rainforests with orangutans present, at their normal densities, can expect the presence of at least 5 other species of primate and hornbill, 50 different species of fruiting tree, and 15 species of liana (Rijksen & Meijaard, 1999). Some of the primate species found are some of the most extraordinary on earth.



White-handed gibbon Like orangutans, gibbons are apes, but, unlike orangutans, they are considered lesser apes, on account of their smaller body size. There are two species found in Sumatra, the white-handed gibbon (Hylobates lar vestitus) and the agile gibbon (Hylobates agilis), and two species found in Borneo, Muller’s Bornean gibbon (Hylobates muelleri) and the Borean white-bearded gibbon (Hylobates albibarbis), although it must be noted that some scientists consider the latter gibbon merely a sub-species of the agile gibbon.

Gibbons are the least known about and least studied of all the apes, and long-term field studies have been hampered by the gibbons’ almost wholly arboreal lifestyle. Unlike orangutans, gibbons are incredibly fast movers and swing through the canopy using only their arms, a form of locomotion known as brachiation. Living in tropical rainforests, they feed chiefly on ripe fruit, which makes up at least 58% of their diet (Bartlett, 2007), which they supplement with leaves, flowers, and insects. Their small body size, a head and body length of between 18-22 inches and a weight of 4.5-7kg, means gibbons can reach the ends of branches, exploiting food sources more large-bodied arboreal animals cannot (Redmond, 2008).

The fur color and physical appearance of gibbons varies from species to species, and there is also often variation between members of the same species and between sexes. However, gibbons are unusual amongst apes for the low level of sexual dimorphism shown, with males and females being around the same size, and often hard to distinguish.

Gibbons are born after a gestation period of 7 months, and reach sexual maturity between the ages of 6-9 years, when they form monogamous pairings with a member of the opposite sex, which lasts for the remainder of their lives, occupying a home range of around 40 hectares (Redmond, 2008), although this varies depending on species and the presence of other species of primate (Bartlett, 2007). Territories are defended aggressively.

The interval between births is usually two to four years, so most gibbon groups will consist of no more than two adults and two or three young, adolescents leaving the family group upon maturity. Unlike other apes, gibbons do not make nests, either for day or night rest, instead sleeping while sitting on bare branches. To aid this adaptation, have thick, hard pads on their lower back, called ischial tuberosities (Bartlett, 2007).

Gibbons are also known for their distinctive vocalizations, which are believed to be used as a spacing mechanism, to defend territories and to attract mates, and their haunting melodies, usually sung in unison, are one of the most beautiful sounds in South East Asian rainforests.



Siamang  The Siamang is a type of gibbon, but is classified in its own genus, as Symphalangus syndactylus. Found in Sumatra, siamangs are around twice the size of other gibbons, reaching around 40 inches in height and weighing up to 15kg, and are distinguishable by their long, shaggy black fur, and the large air sac, known as a gular sac, which sits under the throat of both males and females, and can be inflated to the size of their head, allowing them to make loud, resonating calls and songs.

The life history and adaptation of the siamang is similar to those of other gibbons, but these primates generally have smaller day ranges, and, unusually, male siamangs play a much more active role in the raising of the young than do members of the other gibbon species. Like all apes, they are long-lived, and wild gibbons and siamangs may live until they are 30-40 years old.

Like orangutans, siamangs and gibbons are threatened by habitat loss and the pet trade, particularly for use as tourist attractions on the Asian mainland.


Proboscis Monkey

Proboscis monkey  It would be hard to find a more unusually primate than the proboscis monkey, or the Dutch monkey, as it is known throughout Indonesia, on account of its alleged resemblance to the Dutch officials widespread throughout the country during the period of colonization. The proboscis monkey (Nasalis larvatus) is endemic to the island of Borneo, and lives in waterside forests, either coastal nipa palm, mangrove swamp, lowland riverine or peat swamp forests, and never at elevations higher than 800 ft (Redmond, 2008).

The body of the proboscis monkey is a reddish brown, with white-grey legs, belly, tail, and rump. Juveniles are born with a blue face, which becomes pink at the age of three. Males of this species have a large, protruding nose, which can reach up to 7 inches long, and is believed to be used to attract females and to act as a resonating chamber to enhance vocalizations. Females also have large noses, although these are generally smaller than males, and are upturned. They have a head and body length of between 24-30 inches, and males can weigh up to 20kg (Redmond, 2008). Unusually, males of this species have permanently erect penises, a peculiar trait that still baffles scientists.

The digestive system of the proboscis monkey is divided into compartments, with bacteria that neutralize the toxins of certain leaves, and, as such, leaves make up the majority of their diet, with fruit and seeds also consumed (Nowak, 1999). Their diet has left them with a large pot belly, which weighs about a quarter of their whole body weight.

These monkeys live in a harem of one adult male, several females and their offspring, groups that can be as large as 23 animals. Proboscis monkeys are not territorial and may meet up with other groups, to feed or travel together, and they often sleep in neighboring trees. They are extremely proficient swimmers, and will often swim across rivers to reach the opposite bank, one member of the group jumping in first to test the water. Young are born after a gestation period of 5 months, and sexual maturity for females is reached at 3-5 years, with males reaching maturity at 5-7 years.

Widespread forest conversion has seen these primates placed on the IUCN endangered list, but it is hoped their increasing popularity with tourists, and the ease with which they can be spotted from boats, could lead to more concerted conservation efforts.




long-tailed macaque Of all the primates, macaques almost certainly have the worst reputation, being considered a pest throughout much of their range, which is the widest of any non-human primate. But their pest-like status is simply a result of their extraordinary resilience and adaptability, and their ability to thrive in almost any environment.

There are two species of macaque found in both Borneo and Sumatra, the pigtailed macaque (Macaca nemestrina) and the long-tailed macaque (Macaca fascicularis), which are found throughout primary and secondary forest, coastal mangroves, swamp, and riverine forest, and even some urban situations (Nowak, 1999).

Pigtailed macaque  Pigtailed macaques have olive-brown fur over their bodies, with white undersides and a black patch on top of their heads, with males of this sexually dimorphic species having a head and body length of 19.4 to 22.2 inches, and weighing 6.2-14.5kg. Females are considerably smaller, weighing between 4.7 & 10.9kg. Long-tailed macaques are the smaller species, with males weighing between 4.7-8.3kg. They are grayish in color, and have hair that sweeps back over their forehead, creating a rather cute looking crest of hair above their heads. Both species of primates are named after their distinctive tails.

Both species of macaque are largely frugivorous, and also eat insects, seeds, young leaves, leaf stems, dirt, and fungus, with long-tailed macaques known to feed on crabs, frogs, shrimp and octopus when foraging in coastal mangroves. Like all other species of macaque, they live in large social groups, sometimes as strong as 100 individuals, which break into smaller groups for foraging, and social groups for both of these species are multi-male but female dominated.

Although not considered endangered, macaques are the focus of increasing animal welfare efforts, as they are the most common primates used for invasive medical research.


Leaf monkeys, Langurs and Surilis

Thomas leaf-eating monkey  Langur means ‘having a long tail’ in Hindi, and almost all species of langur monkey, and their relatives the leaf monkeys and surilis, live up to this name, having long, slender tails often longer than their bodies. The langurs, leaf monkeys and surilis are divided into three separate genus groups, and there are up to 9 separate species on both Borneo and Sumatra.

red leaf-eating monkey  The life histories and appearance of leaf monkeys, langurs, and surilis differ from genus to genus and species to species, but the species found in Borneo and Sumatra are diurnal, arboreal tropical rainforest dwellers, and feed on leaves, seeds, fruit, shoots, flowers, bark, stems and fungi. Two species of monkey in Borneo, Hose’s langur (Presbytis hosei) and the red leaf monkey (Presbytis rubicunda), have been seen occasionally descending to the forest floor to visit natural mineral sources, and have a daily foraging range of around 500-800 meters (Nowak, 1999). In Sumatra, Thomas’s langur also descends to the floor to feed on mature rubber seeds and durian fruits.

Sumatran surili The head and body length of these monkeys is between 16-33 inches, and they weigh between 5-8.1kg (Redmond, 2008; Nowak, 1999). They have a gestation period of around 6 months and are believed to reach sexual maturity after a few years. The species found on Borneo and Sumatra usually live in groups consisting a single male and one or two adult females, although, in some species, such as Thomas’s langur, groups with two adult males have been observed. Lone males and small all-male units have been observed, as juvenile males disperse from their natal group on sexual maturity (Nowak, 1999), as have monogamous pairings (Kirkpatrick, 2007).

Although relatively little is known about the various species of langur monkeys, leaf monkeys and surilis in Borneo and Sumatra, all are threatened by deforestation, forest conversion, and hunting, and there is a danger they may become extinct before the full complexity of their social systems is known.


Slow loris

greater slow loris With their large, forward-facing eyes, small wooly bodies and tightly clinging hands and feet, with their human-like nails, slow lorises are among the most unusual looking primates. In fact, so beguiling were these creatures to Dutch officials, their popular western name derives from the Dutch word for clown, ‘loerus’. Highly prized as pets throughout their range, slow lorises are, along with the tarsier, the oldest and most primitive primates found in Borneo and Sumatra.

The taxonomic status of the slow lorises has long been a source of confusion, hampered by the scarcity of wild loris studies, but there are now believed to be two separate species inhabiting the forests of Borneo and Sumatra. The Bornean slow loris (Nycticebus menagensis) is found on the island of Borneo, and the greater slow loris (Nycticebus coucang) is found on the island of Sumatra, with both species inhabiting primary and secondary forest, wooded savannas and even plantations (Redmond, 2008). It was originally thought that there were just two species of loris found on these islands, but in late 2012, authors discovered that Bornean slow lorises had different facemask patterns depending on their geographical location and that these face masks, particularly the amount of white on the face, are sufficiently different to indicate different species; hence, as well as N. managensis, N. bancanus, N. borneanus and N. kayan are now recognized as different species of Bornean slow lorises (Munds et al, 2013). 

The Bornean slow loris is one of the smallest loris species, weighing 0.26-0.3kg, and is covered in pale golden to red fur. It is distinguishable by the relative lack of markings on the back of its head, having instead a soft brown crown. In comparison, the greater slow loris weighs 0.59-0.68kg, has a darker, deep red fur, and dark rings around the eyes, which meet a dark dorsal stripe on the back of the head.

Slow lorises are slow-moving, arboreal and nocturnal, and feed on a diet of fruit, seeds, leaves, bark, fungi, gums, shoots, flowers, birds’ eggs insects, small vertebrates and invertebrates (Redmond, 2008). During the day they sleep curled up in branches.

Little is known of the slow loris social systems, although they are thought to be largely solitary creatures, although groups have been observed when home ranges overlap, and relations between males are thought to be highly antagonistic. Slow lorises are born after a gestation period of around 6 months, and sexual maturity is reached between 17 and 24 months, at which time they disperse from their mothers. The lifespan of wild slow lorises has not been determined, but it is believed to be between 20-30 years.

Incredibly popular as pets, slow lorises are the only primate known to be poisonous, having glands on their arms that secrete a substance that contains toxins to paralyze prey. Their status in the wild is believed to be endangered, although the lack of concrete data means exact figures and population estimates are difficult to determine.



Horsfield's tarsier Tarsiers are small nocturnal primates found throughout Southeast Asia and known for their huge round eyes, which are larger, relative to the size of the head, than in any other species (Redmond, 2008). Just one species of tarsier is found in Borneo and Sumatra, the Horsfield’s tarsier (Tarsius bancanus), and it is found in both primary and secondary rainforest, as well as coastal forest and mangrove associations.

Like lorises, tarsiers are small, unusual looking primates, with a head and body length of between 34-63 inches. Unlike lorises, however, they are agile and fast moving, known for being able to jump extraordinary distances between trees. Their leaping ability stems from their powerful legs, which are one and a half times the length of the head and body combined (Redmond, 2008). Entirely carnivorous, tarsiers cling vertically to branches, catching and eating large insects such as beetles, grasshoppers, cockroaches, butterflies, moths, praying mantis, ants, phasmids and cicadas, as well as bats, frogs, and snakes.

Tarsiers are born after a gestation period of 6 months and reach sexual maturity around 1. Surprisingly, the social system of the Horsfield tarsier is similar to that of an orangutan, with the female raising the young until it leaves the natal home range upon sexual maturity, establishing its own territory. Male home ranges, of between 2-8-11 hectares, overlap those of several females, and it is likely that the male will mate with all females in his home range, although he will play no active part in the raising of any young. Territories are defined and enforced by a series of vocalizations and scent markings (Redmond, 2008).

Unlike most nocturnal primates, tarsiers do not possess a tapetum lucidum, the reflective layer in the back of the eye the produces the ‘cat’s eye’ reflections, which makes them difficult to see at night (Redmond, 2008). This adaptation has likely spared tarsiers from higher levels of poaching but has made studying them in the wild difficult.



Bartlett, T.Q. (2007). The Hylobatidae: Small apes of Asia. In Campbell, C.J., Fuentes, A., Mackinnon, K.C., Panger, M. & Bearder, S.K, editors, Primates in Perspective. Oxford University Press, UK

Kirkpatrick, R.C. (2007). The Asian colobines: Diversity among leaf-eating monkeys. In Campbell, C.J., Fuentes, A., Mackinnon, K.C., Panger, M. & Bearder, S.K, editors, Primates in Perspective. Oxford University Press, UK

Munds, R.A., Nekaris, K.A.I. & Ford, S.M. (2013). Taxonomy of the Bornean slow loris, with new species Nycticebus kayan (Primates, Lorisidae). American Journal of Primatology, 75, pp. 46-56

Nowak, R. M (1999). Primates of the world. Johns Hopkins University Press, USA

Primate Info Net- Library and Information Service of the National Primate Research Center, University of Wisconsin.

Redmond, I. (2008). The Primate Family Tree. Firefly, UK

Rijksen, H.D. & Meijaard, E. (1999). Our vanishing relative: The status of wild orangutans at the close of the 20th century. Kluwer Academic Publishers, Dordrecht, Netherlands

While the islands of Borneo and Sumatra are perhaps best known for their extraordinary array of primate species, they are by no means the only fascinating mammals founds on the islands, and Borneo and Sumatra’s rainforests provide refuge to some of the most iconic species alive. Although increasing rates of deforestation, agricultural expansion and the illegal pet trade has forced many of these species to the brink of extinction, the following are just some of the species found.

Sumatran tiger

Sumatran tiger The Sumatran tiger (Panthera tigris sumatrae) is, following the extinction of the Bali and Javan tigers, the only tiger found in Indonesia, and lives in lowland forest, sub-mountain forest, mountain forest, and peat moss forests, on the island of Sumatra. The smallest of all the tiger species, male Sumatran tigers have a head to tail length of around 2.20-2.55 meters, and weigh around 100-160 kg, while females have a head and body length of 2.15-2.30 meters and weigh around 75-110 kg (Sumatran Tiger Trust). The coloring and patterns of tigers are instantly recognizable, but Sumatran tigers are the darkest of the subspecies’, ranging from reddish yellow to deep orange, and it’s black stripes are often broad and close together, an adaptation that helps it camouflage in the dense jungle.  It’s undersides, and underneath its chin, are white, while the chin has a short mane, and it has striped forelegs.

Tigers are largely solitary animals, although they are not anti-social; males are occasionally seen resting with females and cubs, and they may also travel in groups (Burnie, 2001). Active at night, tigers are nocturnal animals, but will hunt during the day during cooler periods, and range over territories of 10-30 or more square miles, which they mark out by spraying their urine or a glandular secretion, by leaving fecal droppings, or by scratching marks in to trees (Sumatran Tiger Trust). The ranges of males overlap with those of several females.

Tigers are born after a gestation period of 16 weeks, and the litter usually consists of around 3-4 cubs, which are born blind and helpless, and raised entirely by their mother. Tiger cubs have a high mortality rate, due to high instances of predation, often by male tigers, who will kill cubs to make the mother sexually receptive. Tiger cubs become independent at around 18 months and will leave their mother's side at around 2-2.5 years of age. Females reach sexual maturity at 3-4 years of age, and males reach sexual maturity at 4-5 years. They have a life expectancy of around 15 years in the wild (Burnie, 2001).

Tigers are carnivorous meat eaters, and Sumatran tigers feed chiefly on different members of the deer family, pigs, rhino’s, snakes, tapirs, and other large mammals, which are usually killed in an ambush from behind, with a bite to its neck breaking the prey’s spinal cord (Sumatran Tiger Trust).

Once widespread throughout the island, deforestation and forest conversion has seen the population plummet, and there are now believed to be around 350 tigers surviving in the wild.


Bornean pygmy elephantElephants are the largest land mammals in the world and are distributed throughout much of Africa and Asia. There are two subspecies of the Asian elephant found in Indonesia; the Bornean pygmy elephant (Elephas maximus borneensis) and the Sumatran elephant (Elephas maximus sumatranus). Bornean pygmy elephants are restricted to the rainforests in the north and east of the island, while the Sumatran elephant is found in tropical and subtropical moist broadleaf forests throughout Sumatra (WWF, 2011)

Sumatran elephants reach a shoulder height of between 2 and 3.2 meters and can weigh between 2,000 and 4,000 kg. Unlike other elephants, males of this subspecies rarely develop long tusks, while those of adult females may be so short they are hidden by the upper lip, and they are also much lighter in color than other elephants. Bornean pygmy elephants are, hence their name, the smallest of all elephants, with males growing to less than 2.5 meters, and are identifiable by their large ears, younger looking faces, longer tails and more rotund shape (WWF, 2011).

All elephants are herbivores, and a single Bornean elephant can eat up to 150 kg’s of vegetation every day, feasting on various species of palms, grasses and wild bananas. They also acquire minerals found in salt licks or from the mineral concentrations in limestone outcrops. Sumatran elephants will usually consume more, around 200 kg’s of vegetation a day, and will feed chiefly on bananas, ginger, young bamboo and leaves of a variety of vine (WWF, 2011).

Sumatran elephant In comparison to African savannah elephants, Asian elephants live in small family groups, which consist of a female matriarch and other related females of varying ages. Males only join such groups when females are sexually receptive and are otherwise either solitary older bulls or, when young, part of bachelor groups. Adult males have little to do with their young, which are born after a gestation period of 22 months, weaned at around 4 years old and reach sexual maturity at 9-15 years, if it is female, and 12-15 if it is male (Burnie, 2001).

While African elephants have suffered from a long history of hunting, Asian elephants have a long association with humans (Bornean pygmy elephants are particularly docile), and are endangered largely due to the intense competition with people for land. Both the Sumatran and Bornean pygmy elephants are listed on Appendix I of CITES, and both face the threat of extinction, due to habit lass, fragmentation and persecution as crop raiders (Burnie, 2001).

Clouded Leopard

Clouded leopard There was once thought to be just one species of clouded leopard found throughout Asia, but studies in 2006 confirmed that the species found in Borneo and Sumatra, the Sunda clouded leopard (Neofelis diardi), is distinct from the species found on the Asian mainland.

Clouded leopards inhabit tropical rainforests, with populations in Borneo inhabiting lowland forests, and populations in Sumatra largely inhabiting forests at higher elevations, in hilly, montane areas, possibly because they share their habitat with Sumatran tigers on this island (Hearn et al, 2008).

These leopards have a stocky build and weigh between 12 to 25kg, with a head to body length of 50 to 110cm and a tail length of 55-91 cm. It has a dark coat covered in black-edged, darker-centered ovals, which look like clouds and gives the leopard its common name. They also have extremely long canine teeth in proportion to their skull size, and they are extremely proficient carnivores, feeding chiefly on different species of deer, bearded pigs, civet cats, monkeys, gibbons, porcupines and fish.

The leopard is nocturnal and feeds predominantly in tree tops, but will descend to the forest floor to hunt. Unfortunately, due to their shy nature, virtually nothing is known about the social structure and mating systems of the clouded leopard (Burnie, 2001; Hearn et al, 2008).

Sumatran rhinoceros

Sumatran rhino One of the most iconic animals alive, there are five species of rhinoceros found throughout Africa and Asia, with the Sumatran rhinoceros (Dicerohinus sumatrensis) divided in to three further subspecies. The Western Sumatran rhino (Dicerohinus sumatrensissumatrensis) is found in Sumatra and peninsular Malaysia, and numbers just 170-230 individuals. The eastern Sumatran rhino (Dicerohinus sumatrensisharrissoni) survives with a population of just 50 individuals, and lives in fragmented forest in the Malaysian state of Sabah on Borneo, while the Northern Sumatran rhino (Dicerohinus sumatrensislasiotis), which once roamed throughout India and Bangladesh, is now only found in Burma, and may even be extinct there, the political situation in that country making surveys and verification difficult. Sumatran rhinoceroses live in dense tropical forest, lowland and highland, primary and secondary, and often hilly areas close to water, and steep upper valleys with dense undergrowth (van Strien et al, 2008).

Rhinoceroses are large, heavy built animals, but the Sumatran rhinoceros is the smallest species, with a weight of around 600-950kg, a height of 3-5 feet and a length of 6.5 to 9.5 feet (International Rhino Foundation). Often called the ‘hairy rhino’ due to the reddish brown fur that covers its body, the Sumatran rhino has two horns, a large nasal horn of around 5.9 to 9.8 inches and a much smaller posterior horn of around 3.9 inches long. Rhinoceroses have a strong sense of smell, and mobile, tubular ears provide good hearing. Their eyes, however, are small, and rhinoceroses have poor vision (Burnie, 2001).

Relatively little is known about the behavior of Sumatran rhinoceroses, but they are believed to be largely solitary. Males have home ranges of around 50 km2, which seem to overlap with those of other males, while females have ranges of 10-15 km2, which appear to be spaced out. Rhino’s spend most of their day wallowing in mud to call down, and is most active when eating, at dawn and after dark, when it feeds on a diet of young saplings, leaves, fruits, shoots and twigs. It will usually consume up to 50 kg of food a day.

Young are conceived after a consortship between a male and a female, and are born after a gestation period of 15-16 months, at which time the female raises the young independently. Young are weaned at around 15 months and will stay with their mother for the first 2-3 years of their life. Females have an inter-birth interval of 4-5 years. Males reach sexual maturity at 10 years of age, with females reaching it at between 6-7 (Burnie, 2001; International Rhino Foundation).

Malayan Sun Bear

 Malayan Sun Bear Bears are among the most charismatic animals on earth, but while the brown, black, grizzly, polar and panda bears are internationally known and icons of the conservation movement, many people don’t realize that bears can also be found in Borneo, Sumatra and mainland south east Asia.

Sun bears (Ursus malayanus) are the only truly tropical bear, and are found in tropical evergreen rainforests, which include areas of peat swamp, lowland dipterocarp, freshwater swamp, limestone hills, lower montane forest and mangroves, and live anywhere up to 2,100 meters above sea level (Fredriksson et al, 2008) .

Shy and elusive, little is known about the sun bear’s social structure, but they are believed to be solitary, with the largest social group consisting of a mother and her dependent offspring. Sun bears do not hibernate, and can produce young all year round, with young being born after a gestation period of 96 days. Born blind and hairless, sun bears are completely dependent on their mothers for the first 18 months of their lives, and reach sexual maturity at around 3 years, by which time males will weigh between 30 to 70kg and females between 20 to 40 kg.

A nocturnal animal, sun bears are omnivores and feed chiefly on termites, ants, beetle larvae, bee larvae and a large variety of fruit species. Their propensity for eating honey has given rise to their alternative name, and the sun bear is referred to throughout Indonesia and Malaysia as the honey bear.

Sun bears have extremely long, curved claws, an adaptation for tree climbing and used to dig for worms and insects, and to tear up logs and old bark to expose and extract termites, and remove honey from wild bees’ nests. It also has a tongue that can protrude 10 inches and is used to extract honey, grubs and similar foods from holes & crevices (Burnie, 2001; Fredriksson et al, 2008).

Malayan Tapir

Malayan Tapir The Malayan tapir (Tapirus indicus) is the only found tapir found in Asia and is found in Sumatra, where it lives in heavily fragmented populations in tropical moist forests.

Tapirs are large, ground-dwelling mammals, weighing around 250-540kg, with a length of between 1.8 and 2.5 meters, and are easily identifiable by their two tone coloring; they are black with a white saddle that extends from its shoulder to its rear and has white rimmed ears. They have short stubby tails and long flexible noses.

Malayan tapirs are solitary creatures and live in large territories, which often overlap with those of others and which they mark by spraying urine on plants. Exclusively vegetarian, tapirs feed on the tender shoots and leaves of more than 115 species of plant and tend to eat soon after sunset or before sunrise, being mainly active at night. They have extremely poor eyesight and rely on their strong sense of smell and hearing.

The gestation period for Malayan tapirs is approximately 390-395 days, and single young are born weighing around 6.8kg. They are weaned at around 6 to 8 months, at which time they are fully grown, and sexual maturity is reached at the age of three. They have a life expectancy of 30 years (Burnie, 2001; Lynam et al, 2008).

Due to their size, tapirs have few natural predators and are endangered purely as a result of human activities. Although local traditions in Sumatra mean they are not usually hunted for food, they are prized highly on the international illegal wildlife trade, and forest conversion has forced remaining populations into heavily fragmented areas.

Flying lemur

Flying lemur The Malayan flying lemur (Galeopterus variegatus) is one of the most unusual animals in the world, and not just because of its name. Found in both Borneo and Sumatra, the flying lemur, or Colugo, is not actually a lemur, and cannot fly. Instead, by extending a strong membrane that surrounds its body, these lemurs are able to glide between trees for distances up 100 meters, with very little loss of height, giving the impression they can fly (Burnie, 2001).

Active in twilight and at night, flying lemurs are found in tropical rainforests and feed on soft plant parts such as flowers, fruits, buds, and young leaves, and scrape up nectar and sap with their comb-like incisor teeth.

At between 33-42 cm in length, with a tail of 17.5-27 cm and a weight of 0.9-2kg, these lemurs are small animals, around the size of a domestic cat, and are covered in short, fine fur of a grey, red color, often with lighter flecks that mimic lichen covered branches. It has a paler underbelly.

Like so many animals in Borneo and Sumatra, lemurs are little studied and there is a scarcity of information about their social lives, but they are known to be born after a gestation period of 2 months and are weaned at 6 months, and adults of this species are either solitary, or live in small, loose groups (Burnie, 2001).


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Fredriksson G. et al (2008). Helarctos malayanus. IUCN

Hearn A. et al. (2008). Neofelis diardi. IUCN

Lynam A. et al. (2008). Tapirus indicus. IUCN

Van Strien N. J. et al (2008). Dicerorhinus sumatrensis. IUCN

WWF (2011). Sumatran elephants. World Wildlife Foundation

Rainforest Ecology

Tropical rainforests are the most biologically diverse ecosystems on earth, and, despite covering just a small portion of the world’s service, are home to around 80% of its biodiversity. Indonesia’s 88,496,000 hectares of forest represents 10% of the world’s remaining tropical forest, and are, despite massive levels of deforestation, the largest contiguous area of forest in Asia (FAO, 2009).

Tropical rainforests are found within 28 degrees north and south of the equator, and are characterized by constant warm temperatures and high levels of humidity and rainfall, usually between 80 to 430 inches a year (Mongabay, 2010). As with all ecosystems, tropical rainforests are defined by the amount of sunlight they have access to, and as every month in the tropics features strong sunlight, intense competition to break through the dense forest canopy means tropical rainforests are usually characterized by tall, straight, branchless trees, which spread in to a large crown towards the top. The large amounts of annual rainfall mean rainforest soils experience a large amount of runoff, and are, as a result, nutrient poor. To compensate, the trees have shallow roots which allow them to absorb the nutrients from the layer of compost that builds up on the forest floor from decomposing trees and leaves (Brend, 2007).

Although the types of rainforest vary throughout Indonesia, Malaysia and the wider tropics, almost all rainforests have the same characteristics and structure, which can be divided in to four different layers; the forest floor, the understory, the canopy and the emergent layer. The emergent layer is the highest level of the rainforest, and grows beyond all other trees, to heights of around 130 feet or higher, where most of the foliage is exposed to sunlight (Mongabay, 2010). The canopy is the next layer down, usually at around 100 feet (Mongabay, 2010), where rain and sun drenched interlocking leaves and branches support large amounts of fruit, and, correspondingly, most of the life in the forest, including primates. The layer between the canopy and the forest floor is known as the understory, and contains many of the smaller trees, climbing plants, lianas and large-leafed shrubs that thrive in this sun starved environment (Brend, 2007). The ground floor is the darkest layer of the rainforest, with as little one percent of the sunlight reaching the floor, and the ground is covered with a thick layer of leaves, ferns, herbaceous plants, herbs and tree saplings (Brend, 2007).

The unique climate and geology of Borneo and Sumatra has encouraged the development of an incredible array of biodiversity. Due to its location further from the Asian mainland, Borneo’s fauna is less diverse than Sumatra, although it does contain a higher number of endemic mammals than its neighbor, and most species found inhabit the islands’ tropical rainforests. Although the types of rainforests found vary, there are a few forests that dominate.

Dipterocarp forests

The major tropical forest type found throughout Indonesia and Malaysia is evergreen dipterocarp forest, which is found in both lowland and hill areas, and provides suitable habitat for the islands’ wild orangutans, tigers, rhinos, elephants, leopards and proboscis monkeys, as well as numerous other species (WWF, 2010). Dipterocarp forests are tropical forests dominated by trees of the Dipterocarpaceae family, trees known for their incredible size and durability, and are the most luxuriant and diverse of all plant communities found on the islands.

Although the appearance and structure of dipterocarp forests varies depending on the altitude, which can be as high as 1000 meters above sea level (Rautner et al, 2005), they are characterized by the height of their trees, which can reach heights of up to 60 meters (WWF, 2010). There are believed to be around 385 species of diperocarp tree found throughout the world (Mongabay, 2005), and Borneo alone contains 270 species, 155 of which are endemic to the island (WWF, 2010), and which thrive in well-drained soil.  

Dipterocarp forests are highly unusual in that their plants flower so rarely, usually only once or twice in a 10 year period, a process known as mast fruiting, which is linked to the arrival of the El Nino weather phenomenon. The climatic conditions of El Nino years stimulate synchronous fruiting, and the canopy of diperocarp forests bust in to color simultaneously. At this time, individual trees may carry up to 120 fruits, and trees have been known to synchronize over a scale of 370 million acres (Mongabay, 2005). Although the exact reason for this masting is unknown, it is believed that it may be a strategy to intermittently starve and swamp seed predators, to allow seeds survive and germinate. Dipterocarps are principally pollinated by small insects called thirps, which have adapted short lifestyles to coincide with the irregular masting periods, and studies have shown thorp populations increase exponentially at times of high fruit abundance (Mongabay, 2005).

Fossil pollen from dipterocarp trees found in Sarawak has been dated as far back as 30 million years (Rautner et al, 2005), but despite once covering much of the region, huge rates of land clearance, particularly for the Borneo ironwood tree (Eusyderoxylonzwageri), has seen a dramatic decrease in the amount of dipterocarp forest in Borneo.

 Peat Swamps

Some of the largest populations of orangutans are found in Borneo and Sumatra’s peat swamp forests, with these forests providing home for five out of the world’s most viable wild populations, and comprising about a third of the total population of Bornean orangutans (Singelton et al, 2004).

Peats swamp forests are lowland forests that have formed over thousands of years, in areas where waterlogged soils prevent dead leaves and wood from fully decomposing, and where decomposition rates are exceeded by the addition of further dead materials from the forest, leading to an accumulation of peat (Harrison, 2009). Peat swamps are usually found close to the coastline or near the shores of lakes, and form extensive, gently domed deposits, which can extend up to 200 km inland, and reach thicknesses of up to 20 meters (Page et al, 2004). Unlike freshwater swamps, which cover large areas of Borneo and Sumatra and receive water from mineral rich river floodwaters, the spongy and unstable beds of peat swamp forests receive the vast majority of their nutrient influx from rain, with the exception of peripheral, shallow peats, which are subject to tidal or riverine inundations (Harrison, 2009). As such, these forests are generally nutrient poor (Rautner et al, 2005), and, in order to cope, plants of peat swamp forests have developed strong toxic and physical defenses. It is these defenses that prevent leaves from decaying when they fall to the forest floor, and they build up as peat.

Despite their lack of nutrients and the fact that they contain a lower density and diversity of flora and fauna than dryland dipterocarp forests, peat swamp forests contain a large number of endemic species, and are considered important reservoirs of biodiversity (Harrison, 2009), with Borneo’s peat swamp forests home to at least 927 species of flowering plant and ferns (Anderson, 1963).

Tropical peat swamps form over thousands of years, with the oldest peat formation in South East Asia, which began forming around 26,000 years ago, found in the Sebangau area of central Kalimantan, and are incredibly important carbon sinks, with between one-fifth and one-third of global soil carbon locked up in their soils (Harrison, 2009).  Despite this, and the implications these massive storage sinks have for the global climate, peat swamp forests in Borneo and Sumatra have suffered from a history of degradation, drainage, fires, logging and conversion for agriculture, and it is believed that, of the 9 million hectares of land in Kalimantan that was damaged by Indonesia’s 1997-1998 forest fires, 40% were peat swamp forests (Rieley, 2002).


Mangroves are among the most unique ecosystems on earth. Found in around 117 countries and covering an area of up to 24 million hectares, mangroves have the highest level of productivity of all natural ecosystems (Rautner et al, 2005), and are comprised of salt tolerant trees that are found along tidal mudflats, shallow water coastal areas and along rivers, streams and their tributaries (Brown, 2007). Lying in these areas, mangrove forests are prone to inundation by heavily salty, nutrient poor water, and have therefore developed a series of adaptations to cope (Rautner et al, 2005).

Mangrove trees are distinguishable by their long, gnarled, twisted roots, which act as stilts, holding the mangrove tree trunks and leaves above the water. These roots not only act as supports and allow trees and plants to grow in the unstable mud flats, they are also equipped with breathing mechanisms that allow them to absorb air through their bark. These impenetrable roots also have a mechanism that limits the amount of salt that can be absorbed from the water, as well as an adaptation on their leaves that limits the amount of fresh water that can be lost (MAP, 2011; Rautner at al 2005). Mangrove tree seeds are buoyant and adapted to disperse in water. However, unlike most seeds, which germinate in soil, many mangrove seeds germinate while still attached to the parent tree, a process known as vivipary, which helps offspring to survive (MAP, 2011).

Known as ‘rainforests by the sea’, mangrove forests are breeding grounds for many fish, shrimps, prawns, crabs, shellfish and snails, as well as habitat for numerous species of birds, lizards, turtles, crocodiles, and primates including crab eating macaques, proboscis monkeys and, occasionally, orangutans. They also offer a number of vital ecological services, protecting coastal areas from erosion, storm surges, particularly during hurricanes, and tsunamis; after the 2004 Asian tsunami, which killed an estimated 200,000 people in Sumatra, studies showed that intact mangrove forests had provided protection to some coastal communities not far from the epicenter of the earthquake (EJF, 2006). Their roots also dissipate wave energy and collects sediment that would ordinarily be deposited when the tide comes in (MAP, 2011). Despite this, mangrove forests continue to be converted to agriculture. In 2002, just over 1.2 million hectares of mangrove forests could be found in Borneo (Rautner at al, 2005), and in 2000, in the Aceh province of Sumatra, only 30,000 hectares was considered in good condition, with 25,000 hectares considered damaged, and 286,000 hectares considered to be in moderate condition (EJF, 2006).

Heath Forests

Heath forest is commonly known as kerangas forest in Indonesia and Malaysia, which means ‘the land which cannot grow rice’ in the indigenous Iban language, and kerangas forests are the most distinctive and recognizable of all lowland forests throughout the countries (Rautner at al, 2005). Although found throughout many of the regions islands, kerangas forest predominates on the island of Borneo, and grows in both coastal and inland areas, on acidic, sandstone plateaus (Rautner et al, 2005).

Heath forests differ from other lowland forests, including dipterocarps, in species composition, structure, texture and colour, and are much smaller than other rainforests, with a low, uniform single-layered canopy, sometimes as low as 4.5-9 meters, formed by the crowns of large saplings and small poles, with a thick underbrush of moss and epiphytes. Heath forests are also known for having small, very leathery leaves.

Although the nutrient level of heath forests in comparison to other types of lowland forest is debated among ecologists, soils of these forests are inherently poor in bases, highly acidic, commonly coarsely textured and free draining, and are often described as white sand soils, and it is believed that toxic phenols, abundant in the soil through leaves and litter, could be responsible for the lack of nutrient uptake (MacKinnon et al, 1997). As such, heath forests are poorer in species than other lowland forests, with one one hectare research plot recording 123 tree species, in comparison to 214 tree species recorded in a neighboring plot of dipterocarp forest (Rautner et al, 2005),

Although these forests do contain some of the world’s most extraordinary plant species, including pitcher plants that obtain their nutrients through insects, a carnivorous habit developed in response to the scarcity of available nitrogen (MacKinnon et al, 1997), fewer plant species mean these forests are generally low in animal species, with forests in Sarawak containing less than half the number of frog species, lizards and snakes than dipterocarp forests, as well fewer endemic species and no recorded populations of turtles (MacKinnon et al, 1997). They do, however, provide habitat for wild orangutans, with a viable and incredibly important population found in the extensive heath forests of Tanjung Puting national park in Indonesian Borneo.

Despite the unsuitability of these forest soils for agriculture, heath forests have been extensively logged, and of the 6,688,200 hectares of heath forest that originally covered Borneo, just 48% of that was still intact in 1986, and continued deforestation will likely see these forests disappear within a decade (Rautner et al, 2005).

 Montane forests

Orangutans are creatures of the lowlands, inhabiting tropical rainforests up to elevations of 1,000 meters above sea level. Although peat swamp, dipterocarp, heath and other types of lowland forest make up the majority of their habitat, at higher elevations they are found in montane forests, which cover large areas of Borneo and Sumatra and can grow up to 3,300 meters above sea level (Rautner et al, 2005; WWF, 2010).

Occurring at higher elevations, montane forests receive much higher levels of rainfall than lowland rainforests, and are often covered in thick cloud. As such, montane forests are much cooler and moister than lowland forests, and mosses and other epiphytes, including orchids, ferns, lichen and liverworts, abound (WWF, 2010). The canopy in montane forests is low, with upper montane forests, often called elfin forests, having a canopy of less than ten meters in height (Rautner et al, 2005), and lowland dipterocarp trees species are often replaced in these forests by oaks and laurels, while rhododendrons and pitcher plants are observed at higher densities. There is also a decrease in biomass and the leaves of montane forest trees are much smaller (WWF, 2010; Rautner et al, 2005).

Although the harsh climate, lack of shelter and corresponding lack of food make these forests scarcer in plant and animal species than lowland forest, they are still species-rich and contain a high level of biodiversity. As well as orangutans, montane forests provide homes for gibbons, langur monkeys, macaques, Sumatran rhinos, kingfishers, and numerous other species (WWF, 2010). 

Like all forests in Borneo and Sumatra, montane forests are threatened by mining operations, large dams, high altitude timber plantations, conversion to agriculture and shifting cultivation, and animal species inhabiting these forests are increasingly being targeted as specimens for the illegal pet trade (WWF, 2010).



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