Orangutan:
The Man of the Forest

That the Orangutan is an animal of the human form, inside as well as outside: That he has the human intelligence, as much as can be expected in an animal living without civility or arts: That he has a disposition of mind, mild, docile, and humane: That he has the sentiments and affections peculiar to our species, such as the sense of modesty, of honour, and of justice; and likewise an attachment of love and friendship to one individual, so strong in some instances, that the one friend will not survive the other.
Lord Monboddo, 1774 (1)

So what exactly makes us feel so mesmerized with the orangutan, the only great ape living in Asia?

Photo: Leo Reynolds

C O N T E N T S Overview Man of the Forest       Physical Appearance       Habitat       Food       Everyday Life       Reproduction & Lifespan As Part of Rainforest Ecosystem As a Semi-Social Animal       Social Interactions with Humans  As an Intelligent Animal       Self-Awareness       Planning Ability       Tool Use       Language As an Endangered Animal       Habitat Loss & Fragmentation       Fires       Hunting & Pet Trade Conclusion

Like Scottish Lord Monboddo had said back in 1774, this highly intelligent animal is very similar to our own species, in so many different ways which until today we may not even have fully grasped.

Famous Swedish zoologist of the 18th century Carl Linnaeus admitted that he “could not discover the difference between man and the orangutan ...”. (2)

German philosopher Immanuel Kant even went as far as to suggest that:

It is possible for a chimpanzee or an orangutan, by perfecting its organs, to change at some future date into a human being. Radical alterations in natural conditions may force the ape to walk upright, accustom its hands to the use of tools, and learn to talk. (3)

When we look into the orangutan’s eyes, what is it that we see?

Can we see ourselves with all the complexity of our own feelings and emotions?

Or is it our often ignored relationship with the Earth, the planet that we so depend upon for our own survival?

Or perhaps the history of human origins that is being related to us through the contact with these beautiful rainforest animals?

Whatever your answers to these questions may be, one thing is clear – inescapably, we feel very close to them.

In fact, this similarity to the human race gave rise to this animal’s name –  in Malay, orang utan means “the man of the forest”.

The Man of the Forest

Orangutans are the only Asian great apes. All other great apes – gorillas, chimpanzees and bonobos – live in Africa.

Orangutans are arboreal animals, i.e. they live in trees.

They are divided into two species – Bornean species and Sumatran species.

They live respectively in the tropical islands of Borneo (shared by Malaysia, Indonesia and Brunei) and Sumatra (Indonesia) which provide them with their vital rainforest habitats.

Physical Appearance

The most striking feature of the orangutan’s physical appearance is perhaps its characteristic orange red brownish hair which distinguishes it from other black- and brown- haired great apes.

That is why he is sometimes called the red ape.

Adult males and older adult females may have bare backs but the hair on a male can be very long and look like a cape. (4)

Next to gorillas, orangutans are the largest of the great apes. (5)

Adult males are normally twice the size of females (6) and may be as tall as 175 centimeters and weigh over 118 kg, while adult females may reach a height of 127 centimeters and weigh around 45 kg. (7)

Their arms are twice as long as their legs. (8)

In fact, their arms are proportionately the longest of those of all the great apes. (9)

Their feet look and function like hands; and fingers and toes are curved which allows them to grip firmer onto the trees’ branches. (10)

Also, thanks to the unique structure of their hip joints, these animals have much less restriction in the movement of their legs than other primates. (11)

This flexibility in the movement of legs and arms is the orang utans’ adaptation to tree-dwelling.

They are not true knuckle-walkers like gorillas but instead “walk” on the ground on all four limbs, by leaning on the backs of their palms with their fingers curved inwards (12); this type of walk is also called fist-walking.

Among other features, sexually mature adult males have prominent cheek pads (“flanges” that can be very impressive indeed!), throat pouch and long fur which are absent from sexually immature subadult males and adult females. (13)

In general, these animals are incredibly strong creatures – they are about four times as strong as human beings. (14)

A curious episode took place some time ago in Malaysia when an orangutan grabbed a French tourist and stripped him of all his possessions, including clothes, before finally letting him go! (15)

Habitat

Like we mentioned above, the orangutan lives exclusively in two islands in Asia – Borneo and Sumatra which are endowed with rainforests.

Bornean orangutans occupy almost all forested habitat of Borneo (16), and Sumatran orangutans live in the northern part of Sumatra.

These rainforest animals depend on trees like no other great apes, where they spend nearly all of their time.

They are currently the largest living arboreal animals in the world. (17)

The historical reason for their tree-dwelling may have been their need to escape their natural predators – tigers and leopards – living on the ground. (18)

But now since tigers are extinct in Borneo, Bornean orangutans may occasionally venture down, presumably to move from one stand of trees to another. (19)

However, this problem persists in Sumatra where Sumatran orangutans are still actively threatened by tigers as well as clouded leopards, hunting dogs and crocodiles.

This is probably the reason why Sumatran orangutans are seen on the ground a lot less often that their Bornean relatives. (20)
 

Orangutans live in the tropical rainforest canopy, as high as 7 to 30 meters above the ground. (21)

Bornean orangutans prefer peat swamp forests and lowland dipterocarp forests (22) which are biodiversity rich and provide these animals with all their dietary needs. 

They are normally not found in forests at elevations above 1.000 m. (23)

Just like the Bornean species, Sumatran orangutans’ primary habitats are peat swamp forests and dipterocarp forests. (24)

Unlike the Bornean species though, Sumatran orangutans can be found at elevations up to 1.500 m. (25)

Though there is plenty of water in their habitats, orangutans cannot swim but can be taught to do so. (26)

Tropical rainforests are, of course, fantastic habitats for orang utans.

Warm climate with lots of moisture throughout the year produce plentiful (albeit irregular) supplies of food for tropical wildlife. You can learn more about the tropical climate here.

Food

Orangutans’ main diet is ripe fruit.

They consume more than 400 different types of foods (27) as well as buds, flowers, young leaves, bark, vines, orchids, bird eggs, spider webs, ants etc. (28)

That said, foods such as bark are only consumed as a last resort in case of seasonal unavailability of fruits. (29)

Among some of the fruits that orangutans eat are rambutans, jackfruits, mangosteens, mangoes, figs.

Out of all fruits though, it is the durian fruit which they absolutely love. (30)

This fruit is supposed to have a very strange taste and a very strong odor. Apparently, it is even prohibited in some public transport systems in Southeast Asia! 

In the wild, orangutans are known to engorge themselves on fruit when it is available; this allows them to put on additional fat stores to be used in less abundant times. (31)

Quite interestingly, they were even observed to eat soil or rock, mainly for 3 reasons: to get additional minerals to their diet, to get the clay minerals which can absorb toxic substances, and to treat a disorder such as diarrhea. (32)

Everyday Life (33)  

Obviously, orangutans spend most of their time up in the trees where they feel most comfortable.

If you watch orangutans swing from one branch to another, you'll be totally amazed at the beauty and grace of their movements!

However, male orangutans may often be too heavy to travel in the higher, thinner branches. That may be why they travel on the ground more often than their female counterparts. 

Orangutans' main activities during the day are feeding and resting as well as moving between feeding and resting sites.

After waking up in the morning, orangutans spend several hours feeding, then build their sleeping nests for a midday nap and rest.

They travel more during the afternoon hours and prepare their nests again – this time for their night sleep.

Young orangutans will normally sleep in their mothers' nest until they become more independent.

Sometimes orangutans will sleep in their old nests.

Reproduction & Lifespan (34)

The reproduction process of orangutans is similar to that of humans in many ways.

The process of sexual maturity in wild female orangutans may start between the age of 6 and 11 years, but they become fully mature by the age of 14 and 15 when, after the gestation period of around 9 months, they will usually give birth to their first child.

Sexual maturity in males occurs between 8 and 15 years of age.

Intervals between each  birth for female orangutans are around 8 years, which is the longest period among all great apes.

When they are born, infants weigh less than 1.5 kg and have prominent white / pink patches around their eyes and mouths as well as in other areas of their bodies; as they age, their skin will become dark brown or almost black. 

Mortality rates in the wild are very low; it may be because mothers take extremely good care of their infants.

Mothers carry their infants constantly for the first year, and then during travel until the of age 4.

Young orangutans stay with their mothers until they are 8 – 10 years old, when they become fully independent.

Orangutans live between 50 and 60 years in the wild. 

Orangutan as Part of Rainforest Ecosystem

Indeed, we should never underestimate the importance of orang utans within the rainforest ecosystem that they call home.

These animals are so valuable to the well-being of many other rainforest plant and animal species that they are considered to be a keystone species: a species which has a disproportionately large effect on other living beings that it co-exists with.

Like we've seen above, orangutans consume an enormous amount of fruits whose seeds they subsequently disperse throughout the forest.

Many of these fruits and other plants – which are also crucial components of the rainforest – depend on orangutans for the dispersal of their seeds.

This is especially true for the large seeds that are not dispersed by smaller animals. (35)

For some species, such as Strychnos ignatia which contains some toxic elements, orangutans are the only dispersers. (36)

Because orangutans are such efficient dispersers of seeds, they are sometimes called “gardeners of the forest”.

Orangutan as a Semi-Social Animal (37)

Though orangutans are considered to be more solitary than any other ape species (38), there are still many ways in which they can express and realize their social needs.

These animals have a very interesting social structure which is certainly worth a look at. 

Their society seems to be working as follows.

 

Young, subadult males and females may travel together in small groups until their adulthood. At this stage, they don't have their own home ranges.

Resident (or adult) females and their infants and juveniles do have their own home ranges. 

The ranges of adult females (that may actually be relatives) overlap each other. 

When they meet, adult females can be both aggressive or friendly.

Home ranges of females usually fall within the home range of an adult male with whom these females mate.

A resident male is the one that has his own home range which may overlap the ranges of several adult females.

Home ranges of adult males may also overlap, and when they meet, their behavior is aggressive towards one another. 

Because the home ranges of resident adult males and adult females overlap, they have frequent general encounters and brief social interactions.

There are also non-resident males (both subadult and adult) and females that may range either alone or in small groups.

 

In general, there are several situations in which orang utans' socialization can take place.

 
The first situation is socialization for mating purposes.

For these purposes, the animals form a consortship group of several individuals that stay together for several days or weeks. This group normally consists of the breeding pair and the female's infant or juvenile.

An adult male makes a long call to attract females and discourage other males.

Interested females then use it as a tool to track this adult male and make their way to his location.

The second situation is mothers taking care of their infants and guiding them until they become fully independent. 

Since males do not contribute anything to bringing up their offspring, this burden lies fully on mothers' shoulders.

The mother and her infant share the strongest social bond possible in orangutans' society, with the infant totally depending on his mother for all his needs in the first several years of life. 

There is an amazing amount of physical contact between these two, especially during the child's first year from birth when the mother almost constantly carries him and sleeps with him in her own nest.

By the age of two, the child acquires climbing and swinging skills, and the mother can now walk with him by holding his hand.

As the child grows, the mother allows him to take exploratory trips on his own, and teaches him to build his own nests and choose the right types of foods.

The mother will usually have more than one offspring with her – this will also allow the growing child to socialize with his older siblings.   

After about the age of five, the newly developed adolescent will seek more communication and travel with his peer groups, and will ultimately become independent by the age of 8.

 

The third situation is so called feeding aggregations.

Feeding aggregations take place when orangutans get together and consume fruits on large trees.

This form of socialization becomes possible when there is an abundant supply of fruits and there is no competition for resources.

One of the reasons why Sumatran orangutans are more social than their Bornean counterparts is because of the higher productivity of Sumatran habitats; so they don't have to compete with each other, and instead they socialize.

 

The fourth situation is travel bands which are formed by individuals feeding and traveling together between food sources during the times of fruit abundance.

These are usually consortship groups consisting of a male and a female as well as the female's offspring.

Social Interactions of Orangutans and Humans 

Orangutans have of course generated an incredible amount of interest around the world, and now there is a lot more social contact between these animals and humans who are eager to come and visit them in the wild.

They are known as placid and unaggressive animals that are rarely dangerous to humans with whom they normally avoid contact in the wild. (40)

Here is how actress Julia Roberts describes her own meeting with a male orangutan in Borneo: (41)

We have also heard of some truly fascinating twists in the human – orangutan relationship.

Birute Galdikas, the world's most respected authority on orangutans, describes the following situation: (42)

I had a student in 1978, Gary Shapiro, who came to Camp Leakey and he taught an adult female, Rinnie, sign language. He could not believe how fast she learned it. Rinnie took the tutoring personally. One day, Rinnie took Gary by the hand and tried to seduce him. Gary pushed her away. She thereafter lost all interest in signing.

See, we are not the only ones to think that orangutans are like us.

It looks like orangutans think that we are very much like them as well!

Orangutan as an Intelligent Animal

Orangutans look and behave so much like us that, naturally, we want to learn as much as possible about these beautiful creatures.

How do orang utans think?

What is on their minds?

Can they copy each other's actions?

Can they plan ahead?

Can they use tools to achieve better results?
 
Are they able to learn and use language to communicate with each other, and with humans?

Are they able to teach their children different skills for their future lives?

Self-awareness

Guided by the fact that self-awareness is an indicator of a certain level of intelligence, researchers usually use a mirror test as an instrument to understand whether animals are aware of themselves.

Orangutans have passed this test.

First, they are given a chance to get used to mirrors and seeing their own reflections in them. 

Their faces are then marked with paint and they are given mirrors again to see if they find something unusual on their faces, which they do.

Right after noticing paint spots on their faces, they immediately reach and touch them, just like we do. (43)

This means that they are aware of their own presence.

So why do we use self-awareness as a measure of intelligence?

We do so because we assume that animals that are aware of themselves may also have a better, more conscious understanding of the world around them.

Planning Ability 

Orangutans use their mental abilities to map their tree-swinging routes.

Because their bodies are so heavy, any miscalculation can result in a fall if they land on a wrong tree with thin branches.

This points to their computational ability, ability to plan ahead. (44)

Tool Use (45)

Orangutans can certainly use tools to achieve desired results.

For instance, they use vegetation to protect themselves from the rain.

They can also manufacture tools.

As an example, they can modify sticks to collect insects or to open large fruit and seed pods. They can also use stacks of leaves for holding spiny fruit while opening it. 

It is mostly Sumatran orangutans that use tools; this behavior is rarely seen among Bornean populations. (46)

Language

Language is probably one of the strongest indicators of intelligence – one's ability to understand and respond to the outside world in a meaningful way.

It has been shown that orangutans can effectively learn to use the sign language.
 
Famous male orangutan Chantek, who was raised in captivity in the US, has a vocabulary of several hundred signs and understands spoken English as well as American Sign Language. He can even invent signs of his own. (47)

It is obvious that orangutans are capable learners.

Birute Galdikas says that they can learn how to use language at the level of a 3-year-old child. (48)

We discuss orang utans' intelligence in further detail here.

Orangutan as an Endangered Animal

There is no doubt about it, orangutans have recently become real victims of hostile human actions.

While they had been living safely in their rainforest homes for thousands of years before, the unforgiving force of economic development of the last several decades brought about a huge negative impact on the well-being of these animals and their natural habitats.

Their populations have been in steady decline for many years now.

The IUCN now classifies the Bornean orangutans as endangered, and Sumatran orangutans as critically endangered species. (49)

There are several major causes why these animals are now endangered: (50)

Habitat Loss & Fragmentation

International demand for palm oil (as well as some other “cash crops” such as rice, cocoa etc) is a major cause of deforestation in South East Asia.

As rainforests are cleared, more and more palm tree plantations are replacing the ancient ecosystems which used to maintain complex webs of life. Precious biodiversiy is lost for ever …

Just  like palm tree plantations, illegal logging by timber business is another cause of habitat loss. It is a very difficult issue to tackle; governmental corruption of host countries does not help either.

Once orangutans lose their habitats, they have no available food. So they can start raiding local crop plantations and may be killed by plantation owners.

Habitat loss is certainly one of the main driving forces behind the recent decline in populations of these endangered animals.

But habitat fragmentation should not be underestimated either.

Orangutans need vast areas of forest to range, feed and reproduce, and forest fragmentation reduces their chances for such everyday activities.

Fires

The island of Borneo has been recently hit by a number of severe forest fires that have killed thousands of orangutans. And when they tried to flee flames and smoke, they were killed by people who see them as competition for scarce resources.

Hunting & Pet Trade

Hunting may present a real threat to the survival of these endangered animals.

It has been estimated that a 2% hunting rate is not sustainable for orangutans, especially that that their reproduction rates are so low.

People hunt them for bushmeat trade, use of their body parts for traditional medicine, for pet trade.

As for pet trade, mothers are killed in the wild for their infants which are then exported to other countries, one of them being Thailand. This also leads to a decrease in population numbers.

We discuss orang utan conservation in more detail here.

Conclusion

Experts are sounding an alarm that if nothing is done to help these animals now, they may be totally gone in 10 years' time. (51)

In other words, they may well be on the brink of extinction.

We know the root causes of their endangerment; we now need to find the ways to eliminate them and save these beautiful animals from extinction.

Last update: January 2009