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Uploaded on Monday 11 Mar 2013
Orangutan range and population estimates
Riccardo Pravettoni, GRID-Arendal
The orangutan is the only great ape found in Asia, and historically is thought to have once ranged across Indochina. Today, two distinct species are found on the islands of Borneo and Sumatra, respectively. The Bornean orangutan is divided into
three further sub-species.
The Sumatran orangutan (Pongo abelli) has been listed as
Critically Endangered since 2000 and its population has decreased by 80 per cent over the last 75 years (Wich et al. 2011). This species is native to the Indonesian island of Sumatra and today mainly inhabits the northern end of the island as a result of habitat loss and human encroachment. An estimated
6,600 wild individuals are left, based on nest density surveys
and models applied to satellite images of forest distribution
(Wich et al. 2008; Mittermeier et al. 2009), although extensive
forest clearance and fires in Tripa in 2012 are likely to
have reduced the overall number.
The Bornean orangutan (Pongo pygmaeus) is found on the island of Borneo, in areas governed by Indonesia and Malaysia. The species is divided into three sub-species: the Southern Bornean orangutan (Pongo pygmaeus wurmbii); the Northeastern Bornean orangutan (Pongo pygmaeus morio); and the Western Bornean orangutan (Pongo pygmaeus pygmaeus). The species has been classified as Endangered on the IUCN Red List since 1986 – with an exception in 1996, when it was briefly listed as Vulnerable. As with its Sumatran relative, the population of Bornean orangutans has declined by 50 per cent over the last 60 years, and an estimated 1,950 to 3,100 individuals have been killed annually over the last few decades in Indonesian Borneo, which is higher than the rate at which the species can reproduce (Meijaard et al. 2011). The Bornean orangutan is endemic to Borneo, where it inhabits patchy areas in the central, north eastern and north western part of the island. The latest population estimates indicate a total population of 54,000 remaining in Borneo (Wich et al. 2008).