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Well-known and newly discovered mammals

The Heart of Borneo’s tropical forests are home to many well-known mammals, some less known and a steadily growing number of newly discovered ones.

These forests provide food and shelter for mammals ranging from the large armour-plated Sumatran rhino and the pygmy elephant, to up to 13 species of primates including orang-utans and proboscis monkeys.
Sumatran rhino 
© / Mark Carwardine / WWF
Sumatran rhino
© / Mark Carwardine / WWF
With around 90 different species, bats are the most common mammals found in Borneo’s rainforests. Usually making up 40-50% of any tropical mammal community, they play an important role in forest ecology as pollinators and seed dispersers. They have also been recognised as important forest health indicators.

The orang-utan - Asia’s only great ape

The Borneo orangutan is the largest tree-climbing mammal and the only great ape found in Asia. It’s estimated that around1/3 of its population was lost during the 1997/98 forest fires that swept across Indonesia, including Kalimantan (Indonesian Borneo).

Orangutans share Borneo's forests with 12 other primate species, including 2 gibbon species, 5 langurs, 2 macaques, the tarsier (Tarsiusbancanus), the slow loris (Nycticebuscoucang), and the endangered proboscis monkey (Nasalislarvatus).

Critically endangered rhinos and elephants

In the northeast corner of the Heart of Borneo lives the eastern Sumatran rhinoceros (Dicerorhinus sumatrensis harrissoni).The most critically endangered rhino species in the world.

This rhino, a subspecies of the Sumatran rhinoceros, is represented by around 13 individuals in fragmented populations on the Malay Peninsula, Sumatra and Borneo. The Borneo subspecies used to be widespread across the island but now only a population of less than 30 individuals remains, confined to eastern and central Sabah (Malaysia).

The Heart of Borneo is also home to the Borneo pygmy elephant (Elephasmaximusborneensis). The population is restricted to the northeast corner of Borneo, in an area extending from eastern and central Sabah into the Sebuku-Sembakung region of east Kalimantan (Indonesia).

Hiding in the shadows: the small mammals of Borneo

The dense cover of high forests throughout the island of Borneo has led to the evolution of many squirrels, from the tiny pygmy squirrel (Exilisciurus species)—no larger than your average mouse—to the giant squirrel (Ratufaaffinis)—larger than your average house cat.

Even more unusual are the flying squirrels (Pteromyinae sub family), of which there are 12 known species in Borneo. These animals have developed membranes between their fore and hind legs, allowing them to launch themselves off high trees and glide through the air with outstretched limbs.

Borneo’s elusive carnivores

Several small-medium carnivores dominate lowland forests, including the endangered clouded leopard (Neofelisnebulosa), Borneo bay cat (Pardofelis badia), sun bear (Helarctos malayanus), Sunda otter-civet (Cynogale bennettii), and other mustelids.

The Borneo bay cat is considered one of the rarest cats in the world. Endemic to Borneo, it is classified as endangered on the IUCN Red List of Threatened Species.

Other Borneo mammals that occur in high numbers and which play a major role in the rainforest ecosystem are the smaller carnivores (meat-eating species) of the island.

On average, 3 new species are discovered each month in the Heart of Borneo

Between 1995 and 2010 more than 600 species have been discovered - that is 3 species each and every month.


Bornean Pygmy elephant (<i>Elephas maximus borneensis</i>) family, parents with calf. ... 
© WWF / A. Christy WILLIAMS
Bornean Pygmy elephant (Elephas maximus borneensis) family, parents with calf. Danum Valley Conservation Area, Sabah, North Borneo, Malaysia.
© WWF / A. Christy WILLIAMS
Sun bear (<i>Helarctos malayanus</i>), one of Borneo's threatened species. 
© WWF / Terry Domico
Sun bear (Helarctos malayanus), one of Borneo's threatened species.
© WWF / Terry Domico

Mammal discoveries in the Heart of Borneo

  • A new species of small nocturnal primate, a slow loris (Nycticebuskayan) was discovered by scientists in Borneo in 2012.

  • A horsehoe bat was one of a number of new discoveries scientists made during a two-year expedition into Brunei's Sungai Ingei forests. The study discovered 3 new Bruneian species including Rhinolopid taxa (horseshoe bat) - and unique to Sg Ingei - the "spectacular, relatively rare" Rhinolophus philippinensis (Large-eared, horseshoe bat). 
Pygmy slow loris, shown here is a closely related species from Malaysia, are rarely observed in the ... 
© Mikaail Kavanagh / WWF
Pygmy slow loris, shown here is a closely related species from Malaysia, are rarely observed in the wild but often confiscated from wildlife traders in Cambodia's Eastern Plains Landscape.
© Mikaail Kavanagh / WWF