Orangutans are born with an ability to reason and think. This large, gentle red ape is one of humankind’s closest relatives, sharing nearly 97% of the same DNA. Indigenous peoples of Indonesia and Malaysia call this ape “orang-hutan” literally translating into English as “person of the forest.”

Great Apes

Orangutans are unique in the ape world. Of the four kinds of nonhuman great apes (pictured above left to right) – gorillas, orangutans, bonobos, and chimpanzees – only the orangutan comes from Asia; the rest come from Africa. Read more about the great apes >>

Orangutans

There are three separate species of orangutan – the Sumatran orangutan (Pongo abelii), the Bornean orangutan (Pongo pygmaeus), and the Tapanuli orangutan (Pongo tapanuliensis). Unfortunately, as soon as it was re-discovered in 2017, the Tapanuli orangutan was classified as the most endangered great ape species.

(Left to Right) Male Bornean, Sumatran, and Tapanuli orangutans. Credit: Eric Kilby Aiwok, Tim Laman

Orangutans are sexually dimorphic, which means that there are significant differences in size and shape between males and females. The most notable difference is seen in their body size and face morphology. Males can often weigh over 200 pounds (90 kg), whereas females are 1/3-1/2 of their size.

Arguably, a more distinct difference between fully mature males and females is that males possess large cheek pads or flanges. Male orangutans have two developmental stages (1) sub adult males and (2) fully adult males. Sub adult males are usually thinner, lack the long hair that mature males possess, do not have cheek pads or flanges (they are unflanged), and they do not have overly large throat sacs. These secondary sexual characteristics are attractive to adult females and aid males in obtaining mates.

Other unique features of male orangutans: Long, thick hair to make them appear even larger and their throat sac, which they use to vocalize. The throat sac is used to make a very notable and recognizable call that echoes through the forest. This is called the “Long Call” and is used to locate and advertise their presence to females or warn other males away.

The males generally remain solitary until they encounter a female who is receptive to mating. They will stay with the female for several days to ensure a successful mating but will soon resume their solitary life. Due to their large size, males will more often travel on the ground than females. The orangutan’s hair color, ranging from orange to reddish brown, is also unique in the ape world.

Orangutans are the only primarily arboreal great ape and are the largest tree living mammal in the world. The other great apes do climb, travel and build sleeping nests in trees, but they are considered semi-terrestrial, spending a considerable portion of their lives on the ground. Orangutans spend about 80% of their time in the trees. Orangutans have remarkable abilities for traveling through the forest canopy. They possess extremely flexible hip joints that allow for great mobility, and their big toes are able to grasp just like a hand.

They make their homes in these trees foraging for food, sometimes building day nests for resting, and building night nests out of leaves and branches. This is where they live and sleep – sometimes as much as 120 feet above the ground. Orangutans usually have little need to come down from the trees, as they are uniquely and very well adapted for their arboreal lifestyle. Orangutans have unique adaptations to their life in the treetops: feet designed much like hands for climbing, flexible hips for holding on in any direction, long arms for reaching and long, strong hands and feet

While almost all the food they eat grows in the treetops they also make use of alternate resources as “fallback” foods, for example the Tapanuli orangutan has been observed harvesting caterpillars for consumption. The frequent rains fill the leaves thus supplying their drinking water. When water is difficult to get, they chew leaves to make a sponge to soak up water in tree cavities. When it rains very hard the orangutan makes an umbrella for themselves out of big leaves. Many people are familiar with the studies that have shown chimpanzees using tools, such as termite-fishing sticks. Recent studies show that some populations of orangutans also fashion tools to aid in the difficult task of foraging for food.

Some might say orangutans have four hands instead of two hands and two feet. This makes them graceful and agile while climbing through the trees but it makes walking on the ground somewhat slow and awkward, although this does not mean they are at a disadvantage on the ground. It is simply not sustainable for them to be strictly arboreal. Orangutans, specifically Bornean, have been observed coming down to the forest floors.

Food is often scarce in the rain forest and that is why the orangutan is very independent unlike most primates. In times of great abundance of food, orangutans may use the opportunity to socialize and gather in small groups.

Their diet is made up of bark, leaves, flowers, a variety of insects, and most importantly, over 300 kinds of fruit. The mothers must teach the babies what food to eat, where to find that food, in which trees and during which seasons. Orangutans must have a very detailed map of the forest in her mind, and knowledge of the fruiting cycles of many species of trees. (This prevents wasting valuable energy searching for fruit trees randomly and traveling to a certain fruiting tree whose fruits will not ripen for some time). The babies must eventually know hundreds of species of plants and trees, which ones are edible, and how to process them; some are very difficult to eat because they are protected by sharp spines and shells.

Putri and her baby. Photo courtesy of the Orangutan Kutai Project.

An orangutan’s lifespan is about 35-40 years in the wild, and sometimes into their late 50’s in captivity. Wild female orangutans reach puberty at about 8 years of age, but a female isn’t ready for her own baby until she’s in her teens. Although in captivity orangutans have been known to be able to produce offspring as early as 6 years of age.

The orangutan has one of the longest childhood dependence on the mother of any animal in the world, because there is so much for a young orangutan to learn in order to survive. The babies nurse until they are about six years of age. The young males may stay close by their mothers for a few more years but the females may stay until they are into their teens, allowing them to observe mothering skills as they watch their younger sibling being raised by the mother. Orangutan females only give birth about once every 8 years – the longest time between births of any mammal on earth. (This results in only 4 to 5 babies in her lifetime.) Therefore, orangutan populations are very slow to recover from disturbance.

Orangutans are one of the most critically endangered of the great apes, due to poaching and habitat loss from deforestation and the palm oil plantations that are devastating Indonesia. This is a crucial time for orangutans. While exact population counts are difficult, the Orangutan Conservancy believes there are only about 50,000-65,000 orangutans remaining in Borneo and Sumatra. Find out what threats orangutans face >>