header: Orang-utan
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line Pongo pygmaeus (Hoppius, 1763)


POPULATION

The total number of wild orang-utans in Borneo and Sumatra is currently estimated to be less than 30,000 individuals - a figure which represents a decline of 30% to 50% in the last decade. However, there is a need for more precise data based on much-neede d surveys.24

Orang-utan population sizes are difficult to estimate with precision. The dense structure of the species' forest habitat makes survey work difficult. In 1987, one author tentatively estimated a world population of 179,000, by multiplying the remaining are a of habitat by an estimate of the species' density.9 At the 65th meeting of the IUCN/Species Survival Commission (SSC) in 1990, the Primate Specialist Group estimated that there were approximately 30,000 to 50,000 orang-uta ns remaining in the wild, but cautioned that these figures were probably inflated.1 A count of nests from helicopters has resulted in a population figure of 9,800 to 21,000 in Sabah.22

In 1993, at the Orang-utan Population and Habitat Viability Analysis (PHVA) Workshop held in Medan, Sumatra, subspecies population estimates were determined. In Sumatra, the exact boundaries of distribution are not known. The Greater Leuser orang-utan po pulation is thought to cover 11,710 km2 with a total population of about 9,200 animals; the Gunung Leuser National Park has two separate populations, a western population of 3,450 in an area of 5,570 km2, and an eastern population of 2,400 covering 2,957 km2. The available area of orang-utan habitat in Borneo was calculated at 22,360 km2, with total population estimates ranging from a minimum of 10,282 to a maximum of 15,546. These estimates suggest a more serious decline in the Bornean population than was previously thought.16

Major population: Most orang-utans in Sumatra occur in Gunung Leuser National Park (9,460 km2). This park is very mountainous and is not uniformly suitable as orang-utan habitat. It is currently under pressure from a gricultural and human settlement in the Atlas Valley, which divides the Park into two separate regions.15 The Bornean subspecies of orang-utan has a wider range; although most individuals occur in Kalimantan, no particular a rea is known to be of special importance.6


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