Sumatran Orangutan
Pongo abelii Lesson, 1827
Indonesia
(2000, 2002, 2004)
The Sumatran orangutan is one of two species of the genus Pongo. While the viability of both is
in question, the Sumatran orangutan faces a more immediate extinction risk than the Bornean,
Pongo pygmaeus (Linnaeus, 1760), and is considered Critically Endangered The species is
endemic to the Indonesian island of Sumatra, and is now restricted almost entirely to forests in
the lowlands of Nangroe Aceh Darussalam (NAD) and provinces in North Sumatra. More than
1,500 orangutans remain in the Singkil swamp. Sumatran orangutans are estimated to total about
7,500 individuals (based largely on 2002 satellite images), living in 13 fragmented habitat units
stretching from northern NAD south to the Sibolga-Tarutung-Padangsidempuan area. It has been
suggested that the southernmost population may be genetically distinct from its northern relatives.
The largest populations live within NAD province, where recent political turmoil has made
monitoring and conservation work difficult. A large population is found in the Leuser
Ecosystem, but less than half of these orangutans live within the Gunung Leuser National Park
boundaries. Throughout its range, the primary threat to Sumatran orangutans is logging. Old-
growth forests in Indonesia have declined by more than 80% in the last 25 years, and broad
surveys throughout the species’ range have demonstrated that orangutan populations have
plummeted in the region’s severely logged areas. Of the 13 identified orangutan populations on
Sumatra, only seven are estimated at 250 or more individuals. Six of these relatively large
populations have experienced between 10 and 15% annual habitat loss due to logging. Villagers
and immigrants from nearby areas such as Nias Island and refugees from NAD accelerate habitat
loss through encroachment and conversion of land for agriculture. Hunting often occurs when
orangutans steal fruit from gardens at the forest edge and are shot by farmers. Some refugees
hunt orangutans for meat, but this generally only occurs in the far south of their range (Sibolga).
Key conservation interventions necessary for Sumatran orangutan survival include expanding the
moratorium on logging concessions beyond NAD, improving patrols and law enforcement,
stopping illegal logging, promoting forest restoration, halting road construction, addressing
human-orangutan conflict, and providing connectivity in the landscape to allow for genetic
exchange. At current rates of habitat destruction from logging, a further 50% of Sumatran
orangutans will vanish in a decade. However, there is as much reason to believe the rate of
decline will increase as there is for mitigation of this threat; solutions to conserve the remaining
lowland primary habitats are urgently needed.
Susie Ellis, Mark Leighton & Ian Singleton
Cited from: Primates in Peril, the World’s 25 Most Endangered Primates 2004–2006, (Mittermeier, et.al , 2005)
Ilustration:
1. Interactive CD “Primata Indonesia” published by CI Indonesia,2003
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