Sumatran Orangutan

Sumatran Orangutan

Pongo abelii Lesson, 1827


(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, , 2005)

1. Interactive CD “Primata Indonesia” published by CI Indonesia,2003


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