The Orangutan was a common species throughout Southeast Asia two million years ago, spreading from the foothills of the Himalaya mountain range to the Sunda island of Sumatra, Borneo and Java, covering an area greater than 1.5 million km2 (an area the size of Germany, France and Spain combined).
The orangutans spread to Sumatra and Borneo during the ice age where a lower global sea-level exposed the ocean floor between the two islands and peninsular Malaysia. Orangutans are believed to first have entered Sumatra, before moving on to southern Borneo, where they probably have dispersed along Borneo's central mountain chain. The great rivers of Borneo made the population spread in various direction (as orangutans cannot pass great rivers) creating three separate subspecies on Borneo; Pongo pygmaeus pygmaeus in the western part, P. p. morio to the east and P. p. Wurmbii in southern Borneo.
Past and present distribution
The distribution of orangutans decreases as their rainforest home shrinks. In 1973 around 288.000 thousand individuals lived on Borneo, but today around 104.000 lives on Borneo and it is estimated that this number will shrink to only 47.000 by 2025 as 3.000 orangutans continue to die every year because of deforestation. In the El Nino years of 1997-98 the most rapid reduction took place, as one third of the population was lost due to widespread drought and fires (up to 5 million ha of Indonesian rainforest was lost).
As the orangutans typically confine themselves to dense forest canopy and avoid humans, it has proven tricky to estimate the exact living population. However it is possible to estimate the number of orangutans in a given area, through the distribution of orangutan nests, and by tracking the home range of encountered orangutans. The most recent population estimate is from 2016 where the numbers of orangutans is estimated to be around 104.000 individuals.
The future of orangutans
Even though more than 16 % of Borneo is considered protected, the majority of the remaining orangutans are found outside the location of protected areas, living in forests in high risk of being exploited for timber or converted into agricultural plantations (e.g. oil palm). By 2020 orangutans habitat is estimated to be further reduced, as human alteration of the rainforest continues. Read more about the threats to the orangutans here >>
The Bornean and Sumatran orangutans are due to their great reduction in numbers both considered critically endangered by IUCN.
Read more about the way that the orangutan has adapted to its rainforest environment here >>