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Pongo pygmaeus; the "person of the forest"
This distinctive-looking ape has long, coarse, shaggy orange-red hair. It weighs between 66 and 220 pounds, is 3-4.5 feet tall, and has an armspan of up to 8 feet, making it the largest tree-dwelling mammal in the world; males are significantly larger than females. The Bornean orangutan differs from the Sumatran orangutan, which was once thought to belong to the same species, by being slightly darker in color and having a broader face and shorter beard.
Both sexes have a throat pouch for calling, but those of males are larger. Males also have cheek pads known as flanges that get larger as the male ages; males that are higher up in the social hierarchy tend to have larger flanges, and those with the largest flanges are more likely to find willing mating partners.
Distribution and Habitat
The Bornean orangutan is only found on the Indonesia island of Borneo, where it inhabits some of the oldest forests in the world.
Three subspecies are recognized, each localized to different parts of the island -- Northwest Bornean orangutans (P. p. pygmaeus) are the most threatened subspecies, with a mere 1,500 or so individuals remaining; Northeast Bornean orangutans (P. p. morio) are the smallest in size; Central Bornean orangutans (P. p. wurmbii) are the subspecies with the most animals, with at least 35,000 individuals.
All three Bornean orangutan subspecies are currently listed as endangered, with the prime threat being habitat destruction.
Dominant flanged males often have an established territory that will encompass multiple females' territories, and those females will usually willingly mate with him and produce his offspring. Younger unflanged males often cannot sustain a home range of their own and usually have to force females to mate with them.
There is no established breeding season, but females tend to be more fertile durng periods of food abundance.
The gestation period is approximately nine months. While single births are by far the most common, twin births are not unheard of. From birth, the offspring will be in constant contact with the mother for four months and will be carried everywhere the mother goes. It remains completely dependent upon the mother for the first two years of life, is weaned by its fourth year, and will begin making short trips on its own, still staying within sight of its mother, at about five years of age. The offspring will generally stay around the mother until the next offspring are born. After this, the young females establish their own territory and the young males travel the forest until they can establish their own home territory. Since Bornean orangutans are semi-solitary in nature, the males have very little contact and no investment in their young.
Both male and female orangutans reach sexual maturity at about six or seven years of age, but females generally do not have their first baby until they are at least 15 years old. In addition, a mother orangutan will not willingly mate again until her offspring reaches adolescence, making orangutans the slowest breeding of all mammals. Female Bornean orangutans reach menopause around the age of 48 years, and can live for over 50 years in the wild.
Bornean orangutans have been documented eating more than 500 plant species as part of their diet. Fruits make up more than 60% of their total dietary intake and they will migrate depending on fruit availability. The remainder of their diet consists of leaves and shoots, insects, sap, vines, spider webs, bird eggs, fungi, flowers, barks, and, occasionally, nutrient rich soils. They drink water captured in leaves when available, and, in drier times, soak up moisture from tree hollows using chewed leaf sponges. Food is plucked with the fingers and the palm due to their inability to use their thumbs.
Other Habits and Behaviors
Small groups of females may travel with their infants in search of food, but adult males are usually solitary. Groups of six or more Bornean orangutans are rare but can be found when a group of trees suddenly fruit at the same time.
Because they are generally solitary, Bornean orangutans have little need for social vocalizations. The most prominent form of communication is the long-call, a one- to two-minute call performed only by flanged males taht can be heard from several miles away in the right conditions. The main purposes of long-calls are to inform other males of the caller's presence (when unflanged males hear long-calls they flee the area) and to call out to sexually responsive females. Long-calls are spontaneous and do not follow any specific pattern. The other type of calling is a fast-call, which is most often made after male-to-male conflict. In addition to the long and fast calls, Bornean orangutans smack their lips to produce sounds when in small social groups. When scared, Bornean orangutans will funnel their lips and scream. And, similar to humans, baby orangutans cry, whimper, and smile at their mothers.
Bornean orangutans rarely come down from the trees, not even for mating. While young orangutans will swing from branch to branch and tree to tree, older orangutans walk along tree branches on all fours, or, occasionally, on their hind legs. When they do come to the forest floor they almost always walk quadrupedally. When walking quadrupedally, they walk on their fists rather than their knuckles, unlike other great apes. Bornean orangutans sleep in nest platforms made of vegetation 40 to 60 feet off the ground.
Bornean orangutans cannot swim, which make rivers and other water sources impassable boundaries, limiting their range.
Bornean orangutans are diurnal, with most feeding done in the morning and late afternoon.
Bornean orangutans are known to use tools in daily activities. They employ branches to test water depth or poke termite holes, and they utilize leaves as umbrellas, sponges, or napkins. Furthermore, research from the National Zoo in Washington, D.C. has demonstrated their great capacity to reason, solve problems, and even use computers.
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This page was last updated on June 20, 2018.