As the name suggests, the Bornean orangutan lives only on the island of Borneo in the Malay Archipelago.
Within the island, the species is divided into three genetically distinct subspecies: Pongo pygmaeus morio in East Kalimantan, Indonesia and Sabah, Malaysia; Pongo pygmaeus pygmaeus in West Kalimantan, Indonesia and Sarawak, Malaysia; and Pongo pygmaeus wurmbii in Central and West Kalimantan, Indonesia. While the orangutan used to be widespread on the island, today, the species is limited in range and fragmented into an estimated 42 populations.
Their range is naturally limited by altitude, as orangutans are typically found beneath 500 m above sea level (asl). The highest they have ever been recorded is 1,500 m asl, but this is the exception to the ‘rule’. The fragmentation of orangutan populations today is not due to the normal altitude restrictions, but rather the action of man. Human activity and development has encroached on many of the natural habitats of orangutans, clearing them completely or degrading them, compromising the health of the ecosystems as a whole.
Orangutans can be found in a large variety of habitat types from brackish mangrove forests to limestone karst forests, but most commonly, orangutans inhabit what is called tropical lowland forests. Within this term, however, it includes a large variety of different forest types, with the two most important for orangutans being dry dipterocarp forests and swamp forests.
Despite the long, unfamiliar name, dipterocarp forests are the ones that people usually imagine when they think of the ‘jungles of Borneo’. The name comes from the fact that the dominant tree type in the forest is from the family Dipterocarpaceae. This family of trees, composed of hundreds of species, includes many famed species of giants such as meranti and kapur trees. While these trees may be at the core of the ecosystem, these forests are full of other life, like unrivalled ironwood trees, plentiful fruit trees, exotic carnivorous flowers, literally more bugs than we know, fish that can be larger than humans, Borneo’s most iconic birds, and thousands of other animal species, ranging from huge leopards and pythons to discrete pangolins and pit vipers.
The orangutans of Borneo can also reside in flooded or swamp forests. While these come in several subtypes, they are all characterised by continuous or seasonal flooding across the forest floor. This flooding can leave the biotic components waterlogged, impacting the decomposition, and in some cases, thousands of years later, creating peatlands. Today, Borneo is home to half of the world’s tropical peatlands and while these peat swamp forests are not as rich in biodiversity as the dipterocarp forests, they are still critical habitats for the Bornean orangutan. These unique peat swamp forest ecosystems are also home to countless specialised, threatened plant and animal species; provide important ecosystem services to humans; and play an key role in the global carbon and water cycles.
Every one of the orangutan’s forest homes is teeming with life that may not be as 'charismatic' as orangutans but is just as important to our global ecosystem. So, we must protect orangutans, and in their name, protect their forest homes and all their living neighbours.