Great Apes and Humans: Hominidae

Physical characteristics: Bornean orangutans have long, shaggy, reddish brown hair. Facial skin color ranges from pink to red to black. Arms, which are longer than the orangutan is tall, are useful for reaching fruits and brachiating. Scooplike hands and feet have powerful grips for grasping branches. Cheek pads in adult males make the face look larger. A throat pouch is inflated to produce loud, long calls to advertise their whereabouts. Males may reach 200 pounds (90.7 kilograms), with a standing height of about 5 feet (1.5 meters). Females are about 100 pounds (45.4 kilograms), standing 3 feet (1 meter) tall.

Geographic range: Bornean orangutans are found in Indonesia and Malaysia.

Habitat: Bornean orangutans prefer mature forests with fruiting trees. They also inhabit mangroves, swamps, mountain forests, and deciduous forests.

Bornean orangutans spend most of their time in the trees, and they feed on fruits there. Males sometimes travel on the ground, and they sleep in nests on the ground. (© B. G. Thomson/Photo Researchers, Inc. Reproduced by permission.)

Diet: Orangutans feed mainly on fruits, supplemented with leaves, flowers, buds, barks, honey, insects, and bird eggs. They use tools, such as sticks, to get honey out of beehives.

Behavior and reproduction: Orangutans are mostly arboreal, although heavy adult males travel on the ground, walking on their clenched fists and feet. They ascend trees to feed. Females and juveniles build sleeping nests in trees, while adult males sleep on ground nests. Orangutans use big leaves as umbrellas for protection from the hot sun and rain.

Orangutans do not form social groups. Adult males avoid one another, using long calls to warn neighbors to stay away. When encounters are unavoidable, fights may end fatally. Females with offspring congregate briefly at abundant feeding sites. Females ready to breed pursue males, who leave soon after mating. Both sexes may have several partners. Some males force themselves on unwilling females. Females have single births every four to eight years, the longest interval between births of any mammal. Orangutan young also have the longest childhood of all animals. After nursing for about four years, they stay close to their mothers for another three (males) to five (females) years.

Bornean orangutans and people: Orangutans are hunted for meat and infants are sold as pets.

Conservation status: The IUCN lists the Bornean orangutan as Endangered due to hunting for food and capture of young for the pet trade. Habitat is lost to agriculture, logging, and human settlements. ∎