Sumatran orang-utan  (Pongo abelii)

Orang-utan means 'person of the forest' (4) and this Asian ape is indeed truly arboreal. Recent genetic evidence has led to the re-classification of Bornean and Sumatran orang-utans as separate species: Pongo pygmaeus and Pongo abelii respectively (5). Orang-utans have distinctive body shapes with very long arms that may stretch as far as two metres. They have a coarse, shaggy reddish coat (6) and grasping hands and feet (2). Orang-utans are highly sexually dimorphic, with adult males being distinguished by their size, throat pouch and flanges either side of the face, known as cheek pads (7).

Evidence from the fossil record suggests that orang-utans were previously widespread throughout South East Asia. Today, however, the Sumatran orang-utan is found only in the north of this island in the Indonesian archipelago (5).

Inhabits lowland tropical rainforests and swamps up to 800 meters above sea level (1) (7).

Sumatran orang-utans are more sociable than their Bornean relatives, due in part to the mast fruiting of the fig trees, where large groups come together to feed (7). Orang-utans are long-lived and females tend to only give birth after they reach 15 years of age (2). The infant spends its first two to three years being carried constantly and will still remain close to the mother for at least another three years (7). The interval between births is the longest for any mammal and may be as long as eight years (4). Orang-utans move slowly through the trees, and will sway trees in order to cross larger gaps (7). Nights are spent in nests built high up in the canopy, constructed from branches and leaves (6).

Because of increased availability, the diet of Sumatran orang-utans has a higher percentage of pulpy fruit and figs compared to that of Bornean orang-utans (7). Orang-utans are highly intelligent and some populations in Sumatra have learnt to use tools, passing this knowledge on through generations. Sticks are used to probe for termites in termite mounds or to extricate seeds from the large Neesia fruit, which has stinging hairs (2).

Orang-utans were hunted relentlessly throughout the majority of their South East Asian range, their large size and slow movements making them easy targets for hunters (8). However, the main threat to orang-utans today is loss of habitat (7). In the past twenty years 80 percent of orang-utan habitat has been lost to illegal logging, gold mining and conversion to permanent agriculture, in particular, palm oil plantations. What is special about these animals is their unique vulnerability to exploitation. Much of this may be attributed to their extremely long inter-birth interval, typically eight years, making them the slowest breeding primates on earth (7).

Forest fires raged through much of Borneo in 1997 and 1998 and it is estimated that around one third of the island's orang-utan population was lost at this time (8). Orang-utans that wander into palm oil plantations and other human-inhabited areas may also be captured for the illegal pet trade, although this is a by-product of shrinking habitat and not a main issue (7). Recent political instability in the region has caused an increase in illegal logging in protected areas, and an increase in the capture of infants for the illegal pet trade. The population of Sumatran orang-utans was reported to have fallen by 46 percent from 1992 to 1999 (1)

The Sumatran orang-utan is fully protected by law in Indonesia and is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), which bans international trade in this species. The key to saving this species is protecting tracts of unexploited forest that are interconnected and contain sufficient habitat (8). A massive national park has been proposed in the north of Sumatra covering 25,000 square kilometres and encompassing the existing Gunung Leuser National Park. The Leuser ecosystem will play a key role in protecting important refuges of the critically endangered Sumatran rhino (Dicerorhinus sumatrensis), elephant (Elephas maximus sumatranus) and tiger (Panthera tigris sumatrae), as well as the orang-utan and numerous lesser-known species (8). Time is running out for the Asian ape however, and there are fears that at current rates of decline both the Sumatran and the Bornean orang-utan could be extinct in the wild by 2010 (8). Due to the large home ranges that these apes require it is the protection of habitat that will ensure that these beautiful and enigmatic 'people of the forest' survive into the next century (7).

For more information on this species see:

• The Orangutan Foundation UK:
  http://www.orangutan.org.uk/
• The Great Apes Survival Project (GRASP):
  http://www.unep.org/grasp

Authenticated (09/01/04) by Martha Lorenz, Orangutan Foundation.
http://www.orangutan.org.uk