Once found throughout much of Southeast Asia, the orangutan is today restricted to just two islands in the Indo-Malay archipelago, Borneo and Sumatra.

The only great ape found in Asia, there are two species of orangutan recognised: the Sumatran orangutan (Pongo abelii) and the Bornean orangutan (Pongo pygmaeus). 

The two species vary in both physical characteristics and behaviour. The Bornean species is a slightly darker colour than the Sumatran species, is larger and more robust in appearance, and adult males have wider cheek pads, which tend to protrude forward. Sumatran oranguans are lighter in colour, often appearing more of a yellow colour than their Bornean cousins, have longer fur, narrower faces and distinct beards.

Although both species of orangutan are known for their solitary nature, Sumatran orangutans tend to be more social, are more frugivorous (fruit-eating) and exhibit more evidence of complex tool use than Borneans.

Under the IUCN (International Union for Conservation of Nature) Red List, both the Sumatran and Bornean orangutan are classified as critically endangered. 

Bornean Male Orangutan

Sumatran Male Orangutan

Behavior

Orangutans are the largest arboreal primate in the world, spending almost all of their time in the trees, and are unique amongst primates in leading lives that are best described as semi-solitary. Unlike the complex social groupings of gorillas, chimpanzees, bonobos and gibbons, the lesser apes, the largest orangutan group is a mother and her two offspring. While females are less solitary, and may spend up to 25% of their time in association with another orangutan, males are almost totally solitary, with just 9% of their time being in association. It is thought that this solitary lifestyle evolved due to the erratic fruiting patterns of Bornean and Sumatran forests, leading to intense competition for food. With a predominately frugivorous diet, containing relatively few calories for such a large body size, the orangutan needs to forage for 60% of the day, with the other 40% spent sleeping and resting.

Orangutans are the slowest breeding of all primates, and at 6-9 years, have the longest birth interval of any land mammal. Born after a gestation period of 8-9 months, orangutans spend the first few years of their life in constant contact with their mothers. Females reach sexual maturity at 10, but will only have their first offspring between the ages of 12-15. Puberty ages for male orangutans are similar, but orangutans are unusual in having two types of sexually mature male, those with the physical characteristics of sexual maturity, flanged males, and those without. Females conceive after a courtship of between 3-10 days, which are usually ended by the female, and males play no part in the upbringing of their offspring. Females will usually have no more than 3 offspring in their lifetime, which is estimated at 45 years in the wild.

With these factors combined, orangutan populations, especially small fragmented ones, are at a considerable risk of extinction. With such a low birth rate, they don't have the capacity to recover from population losses, and even a slight rise in the adult female mortality rate, by just 1-2%, can drive a local population to extinction.

Diet

Orangutans are primarily frugivorous, meaning their diet is made up mostly of fruit, but they will also supplement their diets with leaves, bark, insects and, occasionally, meat, especially in periods of low fruit availaibility. In all, over 400 food types have been identified.

By consuming large quantities of ripe fruit, orangutans are one of the most important seed dispersers in the tropical rainforest. Selectively choosing fruit whose seeds are adapted to withstand passage through the gut, the seeds are then excreted at various different positions throughout the forest, and fertilized in the orangutans faeces.

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A larger map of the distribution of orangutans can be found here

Species Information- extracted from the Orangutan Foundation UK website with permission

 

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