May 22, 2008

All About Orang Utan

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 � 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. Birut 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.