The bornean orangutan or pongo pygmaeus is a species of orangutan that is critically endangered. It lives in lowland rainforests and tropical, swamp and mountain forests. Orangutans play a critical role in seed dispersal, keeping forests healthy. Over 500 plant species have been recorded in their diet. Their population is about 104,700. WWF states that the population of the bornean orangutan has decreased over 50% over the past 60 years.
Northwest Bornean orangutans are the most threatened subspecies. Its habitat has been seriously affected and a mere 1,500 individuals or so remain. Many habitat patches in the area are small and fragmented. Northeast Bornean orangutans are the smallest in size and found in Sabah and eastern Kalimantan as far as the Mahakam River. Central Bornean orangutans are the subspecies with the most animals, with at least 35,000 individuals.
Orangutan numbers and distribution have declined rapidly since the middle of the 20th century, due to human activities. These include hunting, unsustainable and often illegal logging, mining, and conversion of forests to agriculture. One particularly catastrophic event was the 1997-98 forest fires in Kalimantan, which killed up to 8,000 individual orangutans.