About Orangutans

People Of The Forest

Orangutans are the only Asian great ape and share around 96.4% of their DNA with humans. Once widespread across southern Asia, they now only survive on the islands of Sumatra and Borneo.

There are three recognised species – the Bornean orangutan (Pongo pygmeaus), the Sumatran orangutan (Pongo abelii) and the recently described Tapanuli orangutan (Pongo tapanuliensis). The Tapanuli orangutan lives south of the Sumatran orangutan’s range, with their closest populations only 100km apart.

•  Although mostly solitary, orangutans typically have large home ranges with extensive overlaps.
•  Orangutans communicate using several vocalisations including the male ‘long call’ which can be heard from nearly a mile away.
• Orangutans are highly intelligent, and in captivity have been shown to recognise themselves in a mirror.
•  Wild orangutans use medicinal plants to treat wounds; different populations have their own traditions of tool use, showing they have unique cultures.

The orangutans on Sumatra are almost entirely arboreal (so they can stay safe from the tigers – Sumatra is the only place on the planet where orangutans and tigers co-exist), A total of 90% of their food comes from the forest canopy: they feed on hundreds of different plants – figs and durian fruit are among their favourites. They help to spread seeds in their dung which promotes forest regeneration. 

Every night orangutans build a new nest to sleep in, creating gaps in the canopy which allow light through and stimulate plant growth in lower forest layers. They are known as ‘gardeners of the forest’ because of the vital roles they play in supporting and maintaining the ecosystem.

Why Protect Orangutans?

The key to saving orangutans is preserving their forest home. Without this they cannot survive, and without them the forest would lose a key ‘gardener’ which helps to maintain the health and resilience of the ecosystem. This is also crucial habitat for many unique and threatened animals such as the Sumatran tiger, rhino and elephant, as well as countless birds, insects and other creatures. So, by protecting orangutans we are also protecting thousands of other species – the entire biodiversity of the tropical rainforest.

The forests also perform vital ecosystem services for communities around them and further afield. They act as crucial watersheds, absorbing huge amounts of rainfall and releasing it steadily to ensure a regular water supply downstream whilst reducing the risks of floods, landslides and soil erosion. They also support agriculture by regulating the local climate and provide many resources which can be harvested sustainably by forest-edge communities.

At a global level, Sumatra’s intact rainforests and the soil below them are huge carbon sinks. Protecting orangutan habitat is a vital natural climate solution that will help to achieve Indonesia’s goal to cut emissions and adapt to climate impacts, as part of the country’s 2030 climate targets. 

Orangutan Behaviour

Social Interaction 

Orangutans are a semi-solitary species, which may have evolved as a result of the unpredictability and scattered nature of available ripe fruit – their staple diet. Orangutans spend 60% of their time foraging and eating. 

The relationship between a mother and her child lasts for many years, but the time spent with other orangutans is limited. Once adolescent orangutans become independent, they will live alone or just spend time in the company of other immature orangutans. In the case of females, they frequently return to their mothers to ‘visit’ until they are about 15-16 years old.

Males who are not yet fully mature tend to associate with other females, particularly adolescents. Flanged adult male orangutans are the most solitary of all, their social interaction is usually limited to mating encounters with receptive females. 

There are two types of mature male orangutans – flanged and unflanged. A flanged male has the big flat cheek pads and a large throat sack under his chin. Unflanged males have neither of these and are typically are slightly smaller in the body. Both mature male orangutans are able to mate and successfully father children – however female orangutans seem to prefer flanged males. 

Male on male competition for access to females is a major factor in orangutan society. Flanged males have the ability to use their pendulous throat sacs as a resonating chamber for the unmistakable ‘Long Call’ – a truly remarkable sound which can be heard up to a mile away and signifies their flanged status to attract females. 

We still don’t really know when and why a male oragutan undergoes the transformation from unflanged to flanged, or even if every male undergoes this transformation.

Life Cycle and Maternal Care

Orangutans have the slowest known life histories of any mammal. They take the longest time to grow up and they are the slowest to reproduce. 

Orangutans breed more slowly than any other primate, with the female having a baby on average only once every 7-8 years. The gestation period of a baby orangutan is approximately eight and a half months. Single births are most common and babies tend to weigh about 3 ½ pounds. Infants are dependent on their mothers for at least five years, learning about survival in the forest.

For the first two years of a young orangutan’s life, the baby is completely dependent on its mother for food and transportation. A baby orangutan clings to its mother’s stomach, side, or back while she moves through the trees, and feeds on her breast milk. 

Orangutan offspring will sometimes be carried until they are 5 years old and be breast-fed until they are 8 years old. Even when young orangutans are too old to be carried and fed by their mother, they may still remain close to her, travelling with her, eating, and resting in the same trees, until they are about 10 years old.

Wild female orangutans usually become sexually active at approximately 12 years, but they will often have their first offspring only at 15-16 years of age.

Orangutans live for around 45 years in the wild, and a female will usually have no more than 3 offspring in her lifetime. This means that orangutan populations increase very slowly, and take a long time to recover from habitat disturbance and hunting.

Such a long association between mother and offspring is rare among mammals. Probably only humans have a more intensive relationship with their mothers. Primatologists believe that orangutans have such long childhoods because there is so much that they need to learn before they can live alone successfully. Young orangutans learn almost everything from their mothers, including where to find food, what to eat and how to eat it, and how to build a proper sleeping nest.

Tool Use

Orangutans have significant cognitive abilities in comparison to the other great apes. This high level of intelligence manifests itself in tool-use and even the making of simple tools in the wild. Some tool use is unique, but other kinds of tool use represent cultural traditions in orangutan populations.

For example, orangutans have been observed making simple tools to scratch themselves. They also use leafy branches to shelter themselves from rain and sun, and sometimes even drape large leaves over themselves. They have also been observed using branches as tools during insect foraging, honey collection, and protection against stinging insects. 

In Sumatra, wild orangutans use tools to extract seeds from hard shelled species of fruit.

In parts of Borneo, orangutans use handfuls of leaves as napkins to wipe their chins while orangutans in parts of Sumatra use leaves as gloves, helping them handle spiny fruits and branches, or as seat cushions in spiny trees.