What’s in a name?
Orangutan (sometimes spelled Orang-utan) is a Malay or Indonesian word meaning “person of the forest”. Local peoples use many different names, like mawas, maias or kahiyu.
Orangutans are Asia’s only great apes, close relatives of Africa’s chimpanzees, bonobos, and gorillas. Orangutans survive only on the islands of Borneo and Sumatra. Based on recent genetic findings, many scientists now classify Bornean and Sumatran orangutans as separate species, Pongo abelii and Pongo pygmaeus. By 2005, scientists estimated only 55,000 remain on Borneo and 7,300 on Sumatra.
On IUCN’s Red List of Threatened Species Borneans are endangered, at very high risk of extinction in the near future. Sumatrans are critically endangered, among the world’s 25 most endangered primates. Humans cause their greatest threats: habitat loss, hunting and disease. Clearing forests is often the first phase of development. It destroys orangutan habitat because the forests humans want are often those orangutans need. Logging, oil palm plantations and natural resource industries have cleared vast tracts of Bornean and Sumatran forest. Development is also at the root of fires that have eradicated much forest, even if natural droughts set the stage. Humans hunt orangutans for food, as pests, and to sell to the illegal wildlife trade. Development enables hunting by making forest foods scarce. Orangutans leave the forest seeking food, often raid farms or plantations, and become easy targets. Development also increases disease threats. Orangutans are susceptible to many human diseases, even tuberculosis, polio, and hepatitis.
What they look like (Morphology)
Orangutans share many features with African great apes, including large body, no tail, building nests for sleeping, and long, slow lives. Their most distinctive feature is their red-orange color—other great apes are black.
Adult male and female orangutans are physically very different (sexual dimorphism). Males are almost twice as large; they also have flanges on the sides of their face (cheekpads), long shaggy hair that can resemble dreadlocks, drooping throat pouches, and a unique long call. Borneans and Sumatrans also differ. Borneans have stocky bodies, broad faces, coarse hair ranging from orange to brown or maroon, and dark skin. Sumatrans are more gracile. They have more slender bodies, narrower faces, redder, lighter, longer, denser hair, and very light hair around eyes, mouth, and flanges. Bornean adult males have larger throat pouches and flanges. Sumatran males and females both grow long beards and the males may have mustaches. Origins cannot by identified by looks alone. On Sumatra, hair grades from bright red to rather dark brown and individuals with very long, gracile fingers are found along with those with much stubbier fingers. Variation is even greater in Borneo, much of it following the geographic lines that divide its three subspecies.
Life History and Development
Orangutans live life in the slow lane. They grow and breed slower than any other land mammal, even elephants and whales.
- Life span: 45-55 yr (over 60 in captivity)
- Weight: adult M/F 87/37 kg; newborn 1-2 kg
- First Birth: 11-15 yr (females)
- Gestation: 8.6 mo (260 days)
- Inter-birth: 6-9 yr (longer on Sumatra)
- Weaning age: 5-6 yr (Borneo), 6-7 yr (Sumatra)
- Dependency: 7-10 yr
- Dispersal: males and females leave mother’s range
Orangutans are frugivores, or fruit eaters. 50-60% of their food is fruit. Fruit is poor in proteins and fats, so they eat many other items too: leaves, flowers, honey, shoots, stems, seeds, fungus, pith, bark, soil, insects, eggs, and small mammals. They eat lower quality items when fruit is scarce. Some of their foods are medicinal: they protect against malaria, control parasites, or treat diarrhea. Orangutans also use leaves as topical medicines; they rub special leaves on their skin to soothe sore muscles and joints.
Distribution and Habitat
Orangutans are only found in Indonesia on the islands of Sumatra and Borneo. In Sumatra, orangutans remain only in the northern tip. They are found in many areas of Borneo, but many populations are isolated from each other. Orangutans live in tropical rainforests, mostly lowland and swamp forests rich in biodiversity.
A typical orangutan day starts at dawn around 6:00 am, waking in the nest where they slept the night. Then they eat, rest, travel, and (rarely) socialize.
Foraging. Orangutans spend 50%-60% of their day foraging. Basically, they follow their foods. They seek out fruits (their favorite) but are also rather opportunistic, eating whatever they find along the way. They seem to remember the location of important foods because they travel directly to them.
Travel. Each day orangutans travel at around 0.3 km/hr, mostly looking for food within their home range. They may travel only as far as needed to eat, as little as 90 m or as much as 3 km in a day. They are rather nomadic, traveling and nesting in different places each day. They travel mainly in the trees but adult males may travel on the ground—perhaps where they are too heavy to move safely in the canopy. Unlike other apes, orangutans rarely jump, drop, or brachiate (swing branch to branch by their arms). Instead they climb, clamber, or sway slender trees to cross forest gaps.
Resting. Orangutans rest a lot. Each night, they build an intricately woven nest of leafy branches in the trees. They often nest near a food tree that can provide the evening’s dinner and tomorrow’s breakfast. They also spend up to 40% of the day resting, napping on a quickly made day nest or a comfortable branch or liana.
Orangutans are known as quiet, but they communicate desires, needs, and intentions by vocalizations, gestures, postures, and facial expressions. Like chimpanzees and humans, orangutans peer at items that interest them and beg for ones they want. They make play faces and breathy laughter when playful; whimper, pout and throw tantrums when unhappy, and scream in fear, frustration, or rage.
Orangutans are semi-solitary—or semi-social. It is adults who prefer solitude, especially adult males. Adult males range alone and are so intolerant of one another that they may fight to the death if they meet. Adult females are semi-social, usually living with one or more offspring. Offspring leave their mother at adolescence but females stay near their mother’s range while males move farther away. Immatures are more sociable, traveling and playing with family or friends for days on end.
Orangutans, like other great apes, are among the most intelligent animals and one of the species most similar, mentally, to humans.
Orangutans show high social intelligence despite their solitary side. They can purposefully deceive their peers, just like chimpanzees. They intervene in quarrels to support friends, console victims of attacks, reconcile after conflicts, and share food with friends. They are astute social learners, learning new skills by imitation and close watching. They rarely teach but show others what they want by miming. They may mime their partner’s role as well as their own role – especially if the partner doesn’t respond as they desire. Perhaps the most stunning finding is that they create complex cultures.