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.