All About Orangutans!


Along with the bonobo, the chimpanzee, and the gorilla, the orangutan is remarkably similar to humans, in terms of anatomy, physiology, and behavior. Like the other great apes, orangutans are highly intelligent, as seen in their advanced tool use and distinct cultural patterns. Their native intelligence is often used to solve problems related to arboreal travel and food processing. However, their rainforest habitat is continuously being destroyed by illegal logging, mining, farming, and palm oil plantations. Despite formally protected status, the wild orangutan continues to be a critically endangered species and could soon become extinct in the wild. Experts predict wild orangutans could become extinct as natural populations in ten to twenty years.


Ten thousand years ago, orangutans were found throughout Southeast Asia ranging all the way into southern China. Their populations probably numbered in the hundreds of thousands. Today, however, the few orangutans left live in the tropical rainforests of Borneo and Sumatra.

Indonesia’s forests represent 10% of the world’s remaining tropical forests with an area of 260 million acres. According to the European League, by 2001 Indonesia has lost 99 million acres of forest in the last 32 years, which is equivalent to the combined size of Germany and the Netherlands. In total, Indonesia has lost 80% of its original forest habitat and continues to lose 6.2 million acres a year.

Indonesia is one of the five most species-diverse countries in the world, with 12% of all mammal species, 16% of reptile and amphibian species, and 17% of bird species. Of these, 772 are threatened, giving Indonesia the third highest number of threatened species, falling behind Malaysia and the United States. Of Indonesia’s approximately 40 primate species, 20 were found to have lost more than half their original habitat in the last 10 years.


Females become sexually mature when fully grown, although they will not have their first offspring until 13 to 16 years of age in the wild. Males may attain sexual maturity in their teens, but their cheek pads may not become fully-developed until they are in their twenties since the presence of a dominant cheek-padded male within the sensory range of a younger adult male may inhibit the younger orangutan’s development. Generally, males are not successful in attracting sexually receptive females until they get their cheek pads. Thus, as sub-adults, the males frequently resort to "forceful copulation."

The female orangutan’s menstrual cycle is 29 to 32 days, with menstruation lasting three to four days. The gestation period is approximately eight months. Usually a single offspring is born, weighing about 3 ½ pounds. The young stay close to their mothers until they reach adolescence. Orangutans have the longest "childhood" of the great apes.


Orangutans primarily eat fruit, along with young leaves, bark, flowers, honey, insects, and vines. One of their preferred foods is the fruit of the durian tree, which tastes somewhat like sweet, cheesy, garlic custard. They discard the skin, eat the flesh, and spit out the seeds. In some regions, orangutans also occasionally eat soil, thus ingesting minerals that perhaps neutralize the high quantities of toxic tannins and acids in their vegetarian diet.


Orangutans are diurnal animals, spending a large portion of daylight hours searching for and consuming food. Most of their lives are spent in trees where they travel from branch to branch by climbing, clambering, and brachiating. Usually each night, a new nest for sleeping is constructed from branches and built 15 to 100 feet up in a tree. Although mostly arboreal, males will occasionally come to the ground to move between stands of trees. While females stay near their mothers’ home ranges, males emigrate long distances. This helps minimize inbreeding within populations.

In the wild, 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 like a poncho. They have also been observed using branches as tools during insect foraging, honey collection, and protection against bees, and to fish for branches or fruit that is out of reach.

Adult male orangutans usually keep a considerable distance between one another; their participation in social groups is usually limited to temporary sexual "consortships" with adult and adolescent females. Adult females may be seen with their young, with adult females, and with adolescents who are not necessarily their own. The mother-young relationship lasts for many years, whereas the time spent with non-related orangutans is relatively short. Sub-adult males usually associate with females. Adolescent females travel together when age differences are minimal. This semi-solitary social system may have evolved as a result of the scattered food distribution and a lack of large predators.

Whereas the female orangutan can often remain sexually passive, a male must pursue his reproductive interest, using his pendulous laryngeal sac for the "long call," parts of which sound like a loud roar. The male orangutan’s call plays an important role in repelling male rivals and advertising his availability to sexually receptive females, helping him to compete aggressively with other adult males. Thus, mature male orangutans appear to be intolerant of each other, and the meeting of two mature males usually results in either aggression or avoidance.


Male orangutans are approximately twice the size of females, weighing up to 300 pounds and reaching a height of 5 feet. The male’s larger size may be an adaptation for mating, as strong competition among males for females tends to promote this type of sexual dimorphism. The orangutans’ long, narrow hands and feet are especially useful for grasping branches. Their opposable thumbs and big toes are short to facilitate the hook-like function of their hands and feet.


Not long ago, many people thought culture was unique to the human species, but in recent years, scientists are finding increasing evidence of socially learned traditions elsewhere in the animal kingdom. In January 2003, a group of researchers, including primatologist Dr. Carel van Schaick of Duke University and OFI’s president, Dr. Biruté Mary Galdikas, described two dozen behaviors that are present in some orangutan groups and absent in others. According to the report, these practices are learned from other group members and passed down through the generations. In parts of Borneo, for example, orangutans use handfuls of leaves as napkins, wiping leftover food from their chins. Orangutans in parts of Sumatra, conversely, use leaves as gloves, helping them handle spiny fruits and branches, or as seat cushions in spiny trees.


Prehistorically, the number of orangutans was probably in the hundreds of thousands, their range extending from Southern China through Southeast Asia. Today, their total numbers range from 50,000 to 60,000 in the wild. On northern Sumatra, their numbers are critically low at 7,500 individuals. They are now endangered in the wild, primarily because illegal logging, mining, farming, the spread of palm oil plantations, and forest fires have altered or destroyed more than three-fourths of their rainforest habitat. Additionally, poachers often kill orangutan mothers to secure an infant for the live animal trade - about six to 10 orangutans die for every one that survives. The orangutans’ reproductive rate is also very slow; in the wild, they have only one infant every seven or eight years.

Under ideal conditions, these solitary animals roam the forests in search of widely distributed food sources. The reduction of suitable habitat is forcing orangutan populations into smaller areas that cannot support them. Though protected by law in Indonesia, Malaysia, and internationally, enforcement of these laws is extremely difficult in many areas. If the alarming rate of forest destruction continues at today’s pace, the orangutan species as we know it could be completely gone in as little as five years.

Quick Facts!

  • Class: Mammalia
  • Order: Primates
  • Super family: Hominoidea
  • Family: Pongidae
  • Genus: Pongo
  • Species: abelii (Sumatran) and pygmaeus (Bornean)
  • Length: males - about 40 inches from top of head to rump; females - about 30 inches
  • Weight: males - 110 to 300 pounds; females - 66 to 110 pounds
  • Life Span: 60 years or more
  • Gestation: about 8.5 months
  • Number of Young at Birth: usually 1, very rarely 2 (in captivity)
  • Size at Birth: 3.3 to 4.5 pounds
  • Age of Maturity: males - about 15 years; females - about 12 (in captivity)
  • Conservation Status: Pongo pygmaeus (Bornean) is endangered; Pongo abelii (Sumatran) is critically endangered

Fun Facts!

  • In Malay orang means "person" and utan is derived from hutan, which means "forest." Thus, orangutan literally means "person of the forest."
  • Orangutans’ arms stretch out longer than their bodies - over 7 ft. from fingertip to fingertip - and are used to employ a "hookgrip." When on the ground, they walk on all fours, using their palms or their fists.
  • When male orangutans are about 15 years old, they develop large cheek pads, which female orangutans apparently find attractive.
  • When males are fighting, they charge at each other and break branches. If that doesn’t scare one of them away, they grapple and bite each other.
  • For the first few years of his/her life, a young orangutan holds tight to his/her mother’s body as she moves through the forest in search of fruit. Later, he/she will follow the mother as she moves through the trees.
  • Like humans, orangutans have opposable thumbs. Their big toes are also opposable.
  • Orangutans have tremendous strength, which enables them to brachiate (swing from branch to branch) and hang upside-down from branches for long periods of time to retrieve fruit and eat young leaves.