Title
Pongo pygmaeus (Bornean Orangutan)
Author(s)
Ancrenaz, M.; Gumal, M.; Marshall, A.J.; Meijaard, E.; Wich, S.A.; Husson, S.
Published
2016
Publisher
The IUCN Red List of Threatened Species
Abstract
Bornean Orangutans are lowland forest specialists, rarely found above 500 m asl. In the 1950s, the habitat suitable for orangutans extended across ~255,000 km² of the island of Borneo (see below).The two major reasons why most Bornean Orangutans populations are in sharp decline are (1) destruction, degradation and fragmentation of their habitats, and (2) hunting. Recurrent forest fires, especially in peat forests, cause additional sharp declines about once every decade. Bornean Orangutans decreased by more than 60% between 1950 and 2010, and a further 22% decline is projected to occur between 2010 and 2025 (see below). Combined, this equates to a loss of more than 82% over 75 years, 1950–2025. Given that a Bornean Orangutan's generation length is ~25 years (Wich et al. 2009), this decline will occur in a period of three generations. Each of the Pongo pygmaeus subspecies is roughly equally affected. Only one comprehensive quantitative survey of Bornean Orangutans has been conducted, in 2010, which prohibits quantitative assessment of changes in numbers for most populations. Temporal changes in population status are therefore best assessed via the proxies of habitat loss and hunting rates. A detailed rationale for a population decline of more than 86% between 1950 and 2025 follows.

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PUB16206