Orangutan Facts

Bornean Orangutan (Pongo pygmaeus)

Orangutan is a Malay name meaning "People of the Forest," (Orang : People and Utan : Forest or Jungle). Orangutans share 97% of the same DNA as humans. Not surprisingly, they possess great intelligence as well as other human-like qualities.

Bornean Orangutans for example, use tools in daily activities. They employ branches to test water depth or poke termite holes, and they utilize leaves as umbrellas, sponges, or napkins. Research from the National Zoo in Washington, DC has demonstrated their great capacity to reason, solve problems, and even use computers. And similar to humans, baby Orangutans cry, whimper, and smile at their mothers.

The Orangutan, with its distinctive red-orange hair, is the only ape that inhabits Asia. Weighing up to 90 kg (200 lb.), the male Bornean Orangutan is about 1-1.5 m tall (3.5-4.5 ft.) with an arm span as long as 2.5 m (8 ft.). The Sumatran Orangutan is smaller than the Bornean.

Orangutans are the largest arboreal mammals found on earth today. That means that they predominantly live above the ground within the rainforest canopy 95% of the time. Their bodies are adapted to their unique method of arboreal locomotion – called quadrumanous scrambling.” The Orangutans’ long, narrow hands and feet are especially useful for grasping branches. Their opposable thumbs and big toes are short to facilitate the hook-like function of hands and feet, particularly in brachiation and hanging on to tree branches. They have highly mobile hip and shoulder joints that allow them to easily move from branch to branch and tree to tree. In Orangutans the ligament, ligamentum teres, that binds the top of the femur to the pelvis in humans is much modified. Thus, Orangutans can easily do yoga-like poses – like putting their legs behind their heads – that in humans are restricted to the most accomplished yoga practitioners or professional acrobats and circus performers.

While they live on their own they do form complex social networks of loose relationships with other members of a local Orangutan community. At maturity, male Orangutan tend to wander further through the jungle than females.

The Orangutans diet is made of fruits (approx. 60%) with the remainder being leaves, flowers, barks and even insects such as ants. Overall, over 500 species of plant are part of the Orangutan diet.

The Orangutan plays a vital role in seed dispersal especially for larger seeds that cannot be consumed by smaller mammals. One of their preferred foods is the fruit of the durian tree, which has a very strong smell and tastes somewhat like sweet, cheesy, garlic custard. Cultivated durian is known as the “king of fruits”, possibly for its large size, strong smell, and unusual taste. Orangutans eat wild durians in the forest but also enter cultivated durian trees in people’s gardens. Orangutans discard the skin, eat the flesh, and spit out the seeds, acting as major seed dispersers for this fruit as well as for many others.

They drink water captured in leaves when available, and in drier times, they soak up moisture from tree hollows using chewed leaf "sponges."

Male Orangutans

The Orangutan is the only primate species with two different forms of mature males (bimaturism). The first is known as a Flanged (jipek) male. These members are on average twice the size of the female. They possess a long coat of dark hair on the back, a facial disk, flanges and a throat sac used for “long calls”. The “long call” is sometimes used during mating and can be heard up to 3km away. These males are rather intolerant and aggressive towards other adult males. Combats almost always take place when two cheekpadded males are in the presence of a sexually receptive female. These combats may last for a few minutes (especially if the two males have fought before) or an hour or more. Males may be severely wounded during these combats. Almost all flanged males exhibit injuries as a result, whether it is missing and/or stiff fingers or toes, healed scars on their faces or heads, missing eyes or the like. Orangutan females rarely exhibit violent aggression of the sort seen in combat, and hence do not sustain such injuries.

“Unflanged” (jipek) males do not possess these sexual characteristics. They are the size of an adult female, they do not emit long calls nor do they show mutual intolerance. Both male types sire offspring and contribute to the reproduction of a given population. However the “flanged” male dominates reproduction in Orangutan populations. Thus, subadult males (such as the ones studied at Tanjung Puting) frequently resort to “forcible copulation”. The transition from the unflanged to the flanged (jipek ) form can happen anytime depending mostly on complex social cues that are not yet fully understood.

Female Orangutans

The female Orangutan’s menstrual cycle is 29 to 32 days, with menstruation lasting three to four days. Females generally give birth to a single infant (weighing approx 1.5kg or 3.5 pounds) after a gestation period of approximately 8 months. Female Bornean Orangutans reach maturity between 10 and 15 years old and reproduce every six to eight years on average, that is approximately 4 – 6 offspring in a lifetime. This is one of the reasons why regenerating Orangutan populations is difficult.

A mother Orangutan will nurse her offspring for 6-7 years. Although Orangutans reach maturity at 8 years old, females will stay with their mothers up until their teen years to learn essential parenting skills, observing their mothers care for their younger sibling. Only then are they capable of rearing their own young. As female Orangutans only give birth every 8 years, their rate of reproduction is very slow. At Tanjung Puting females typically carry young up to the age of five years when crossing the canopy from tree to tree. In the case of females, they frequently return to their mothers to “visit” until they are about 15-16 years old. Studies indicate that Bornean Orangutans may“grow up” faster than Sumatran Orangutans and may become independent from their mothers at an earlier age.

Each night, they build nests in the treetops with leaves and branches. In this way, they have little need to venture to the ground, where their hand-like feet and elongated arms make walking very awkward.