Geographical Range Sumatra (in the South Pacific)
Habitat Tropical forests
Scientific Name Pongo abelii
Conservation Status Critically endangered

Confined to the Trees

The highly-intelligent, gentle orangutan is the largest tree-living mammal in the world. This ape is so well adapted (both behaviorally and physically) to a tree-dwelling lifestyle that it rarely has to descend to the ground. However, this extreme specialization may also spell the orangutan’s doom, since it restricts the other habitats that the species can occupy.

Note: There are two distinct species of orangutans: the Bornean orangutan, Pongo pygmaeus, and the Sumatran orangutan, Pongo abelii. The latter is the one you can see at the Saint Louis Zoo. Although their habits are almost identical, the two species live on separate islands in the South Pacific.

Big Red

Orangutans’ unique bright red hair makes these large apes easy to recognize. But the two sexes are also easy to distinguish from one another. Male orangutans are about twice the size of females, weighing up to 300 pounds and reaching a height of five feet. Not only are the males much larger, but they also develop a throat pouch and prominent cheek pads when sexually mature, about 15 years old.

Thanks to some pretty distinctive physical adaptations, orangutans are the only apes that live primarily in trees. (While chimpanzees, bonobos and western lowland gorillas can climb and nest in trees, they spend most of their lives on the ground.) orangutans’ feet are so well adapted for grasping tree branches, for instance, that they cannot place them flat on the ground. Instead, they have to walk on the outside of the curved foot (called "fist-walking").

In addition, they have extremely long arms for reaching, slender hands with short thumbs and long fingers for hooking over branches, and flexible hips for holding on in any direction. Plus, orangutans have tremendous strength. This enables them to swing from branch to branch and to hang upside-down for long periods of time to retrieve food.

These traits make it possible for orangutans to perform almost all of their necessary behaviors while suspended in the trees – including feeding, traveling, mating, nesting and child rearing. However, these apes move so awkwardly on the ground that they’re essentially unable to live anywhere else but in the forest canopy.

A Passion for Fruit

By far the favorite food of wild orangutans is fruit. They have been observed eating more than 300 kinds of fruit, the two most common of which are figs and durian. When fruit is unavailable, they also eat honey, leaves, flowers, seeds, bark and insects.

Knowing what kinds of food to eat and not to eat is not a simple matter in tropical forests. orangutans need to know hundreds of species of plants and trees, which fruits are edible, and how to get at tasty food that’s covered by sharp spines or shells. Babies rely on their mothers to teach them these skills, as well as where to find food, in which trees, and during which seasons. A successful orangutan is thought to have a very detailed mental “map” of the forest in his or her mind, including knowledge of the fruiting cycles of many species of trees.

Because trees produce fruit only seasonally, this food source tends to be irregular and widely distributed. Although orangutans have an uncanny ability to remember from year to year which trees fruit and when, they’re still limited by the patchy supply (and their slow speed). That means foraging is highly competitive, and any one area can’t support many orangutans. Hence the reason these apes are solitary.

Stocking the Toolbox

Many wild orangutans have developed an amazing ability to use tools to help them exploit what food they can find. They’ve been observed using probes like twigs to extract insects and honey from tree trunks (held in their hands or their teeth), as well as blunt tools to scrape seeds from spiny fruit cases.

In addition to food-gathering tools, wild orangutans have been observed making tools to scratch themselves, fashioning leafy branches into “umbrellas” to shelter themselves from sun and rain, and using branches as swatters to repel bees or wasps that are attacking. Many have also been seen using “leaf gloves” to handle prickly fruits or branches, or creating “seat cushions” to sit comfortably in thorny trees.

Tool use hasn’t been observed in all orangutan populations, and it shows great variations even when it exists. This suggests to scientists that tool use is the result of innovation and learning that’s passed on from one generation to the next – one of the hallmarks of culture.

In fact, there seems to be more and more evidence of orangutan culture coming in all the time. Scientists have recently found variations in orangutan behaviors from population to population. Among the behaviors that differ from region to region: feeding techniques (including tool use), nest building, and “good night” calls.

A Long Childhood

Except for humans, orangutans have the longest childhood of any animal in the world. This is partly because they have to learn so much just to survive, just as juveniles in other ape species must do. But whereas babies of more social ape species can learn from multiple adults, orangutan babies depend on just one adult -- their mother. So an extra-long childhood allows time for the mother to teach her offspring everything it needs to know.

Baby orangutans nurse until they are about six years of age, slowly learning how to eat fruit and other solid food as they travel through the forest with their mother. Even after weaning, a young male often stays close by his mother for a few more years. Eventually, males become usually nomadic, often traveling great distances from their home region. "Long-calls" and loud roars enable them to maintain their distance from one another in the forest.

Young females, however, may stay near their mother until they are into their teens. This allows them to observe parenting skills as they watch their mother care for a younger sibling. Females usually don’t have their first offspring until 13 to 16 years of age, and males are not successful in attracting sexually receptive females until they get their cheek pads, also as teenagers.

Orangutan females only give birth about once every eight years -- the longest time between births of any mammal on earth. This means they normally have only four to five babies in their lifetime. (This low reproductive rate is why orangutan populations are very slow to recover from disturbances.)

orangutans normally live about 35 to 40 years in the wild; in captivity they’ve been known to live into their 50s.

A Solitary Life

Wild orangutans generally live alone (see A Passion for Fruit above), a byproduct of their food preferences. The only long-term bond they have is between a female and her young. When orangutans do encounter one another, they are normally very tolerant and non-aggressive, unless the encounter is between two mature males.

A male in control of a home range that includes several females often won't tolerate the intrusion of other males. Fights occasionally break out. One male usually charges another, breaking branches and threatening his rival. If that doesn’t scare him off, the two might grapple and bite each other until one backs down.

A Species on the Brink

About 10,000 years ago, orangutans were found throughout Southeast Asia, even in southern China. Scientists estimate there were probably hundreds of thousands of orangutans. Today, however, only 10,000-25,000 still survive in the tropical forests of Borneo and Sumatra.

Both Bornean and Sumatran orangutans have been in dire trouble for some time. The primary reasons are habitat loss and degradation from logging, forest fires, and timber clearing for farming (including palm oil plantations) and human settlements. orangutans are also hunted and killed for their meat (bushmeat), and young apes are captured for sale in the illegal pet trade.

Although orangutans are protected by law in Indonesia and Malaysia, enforcement is spotty. The animals aren’t even safe in national parks, where illegal logging is rampant. Most Sumatran orangutans, for example, live in Gunung Leuser National Park. By 2000, their numbers there totaled about 6,000 animals. But scientists believe they are falling at 1,000 per year.

If this trend continues, Sumatran orangutans could be extinct in the wild in as little as five years.

To the Rescue

So what can be done to help Sumatran orangutans? Though the situation is dire, there are organizations and individuals in many countries trying to reverse their severe decline. They are working to stop illegal logging, to increase sustainable economic alternatives for communities surrounding orangutan habitat, helping instill national pride in orangutans and their environment, and rehabilitating ex-captive orangutans into protected habitat. To find out about one such group -- the Balikpapan Orangutan Society -- click on www.orangutan.com.

You can help too. You can donate money to conservation organizations working to help orangutans or to save their habitat. You can also help in the effort to protect orangutan habitat by choosing wisely when you shop for certain products. Avoid buying wood or wood products that originate in fragile tropical forest areas:

  • Ramin is one of the most frequently logged types of wood from Borneo – used to make broom and brush handles and other common consumer items. To avoid ramin, instead choose items with plastic or metal handles.
  • Teak, ironwood, ebony and sandalwood are all logged in Indonesia. Avoid these.
  • The unsustainable harvest of lauan, a tropical plywood, is taking a huge toll on tropical forest habitat in Asia and the South Pacific. Make sure any plywood you buy (including plywood used in flooring and furniture construction) is harvested sustainably. Certain retailers, including Lowe’s and Home Depot, are taking steps to discontinue sale of lumber products from environmentally sensitive areas. Ask your retailer where your wood products come from.
  • The production of rayon, made from wood pulp, is a huge consumer of rainforest resources. Avoid buying clothes made with rayon viscose.
  • Palm oil plantations have been responsible for the clearing of hundreds of thousands of acres of orangutan habitat. Avoid foods that contain palm oil, palm kernel, palmitate or any derivative with the word “palm”.

Fun Facts:

  • In the Malay language, the name "orangutan hutan" means "person of the forest.”
  • Early indigenous people of Indonesia and Malaysia wouldn’t kill an orangutan because they felt it was simply a person hiding in the trees, avoiding work.
  • Although orangutans don’t use a lot of vocalizations, one sound they do make is a “kiss squeak,” often used when they’re alarmed or displeased.

Class: Mammalia
Order: Primates
Family: Pongidae