Orangutan
- CLASS: Mammalia (Mammals)
- ORDER: Primates
- FAMILY: Pongidae
- GENUS: Pongo
- SPECIES: abelli (Sumatran orangutan); pygmaeus (Bornean orangutan); tapanuliensis (Tapanuli orangutan)
ABOUT
Red apes of the forest: Orangutans live in tropical and swamp forests on the Southeast Asian islands of Borneo and Sumatra. These shaggy red apes are the largest arboreal mammal and the only great apes found in Asia. The other great apes—gorillas, chimpanzees, and bonobos—are all native to Africa.
Long, flowing, reddish hair covers most of an orangutan’s gray skin. Its stocky body has a flexible pelvis, a thick neck, and bowed legs. An orangutan's arms are longer than its legs, reaching nearly to its ankles when standing. Like other apes, orangutans don't have a tail.
Orangutans spend most of their life in the trees, swinging confidently from branch to branch. Their long fingers and toes can easily grasp branches and vines. With arms longer than their body and long, strong fingers and prehensile feet, life in the trees works well for them. In fact, orangutans look a bit awkward on the ground, using their arms as we might use a pair of crutches or lifting them high above their head when they walk. Adult male orangutans are much larger than adult females.
There are some differences between the three orangutan species:
Sumatran orangutan: These orangutans live on the island of Sumatra. Their hair is longer and lighter-colored than Bornean orangutans. An adult male’s cheek pads, called flanges, form rigid half circles on the sides of his face, and both males and females usually develop beards as they age.
Bornean orangutan: Native to the island of Borneo, these adult males have much larger flanges and a large throat pouch. Their hair is shinier, and females rarely have any beard at all. Bornean orangutans are more heavy-set than Sumatran orangutans.
Tapanuli orangutan: These are the southernmost population of orangutans native to Sumatra. This species, described in 2017, differs from the other two species in subtle—but consistent—ways: they have a slightly smaller skull, a shallower face, and various skull, jaw, and tooth measurements that differ. In comparison to the other species on Sumatra, Tapanuli orangutans have shorter, frizzier, cinnamon-colored hair.
Within all three species, there are two morphs of mature male orangutans, and it’s easy to tell them apart. A cheek-padded, or flanged, male has big, fleshy cheek pads on the sides of his face and a large throat sac under his chin. He’s more likely to have facial hair, and the hair on his back grows long.
Non-cheek-padded, or unflanged, males don’t have these traits. They are usually smaller than cheek-padded males. Both flanged and unflanged males can father offspring.
Orangutans are naturally more solitary than other great apes. While other great apes are usually found in groups socializing, foraging, or playing, orangutans tend to choose solitude and seem to have a more internal approach to everything. While other great apes might go from tree to tree searching for fruit, an orangutan just sits in the forest canopy for hours on end until the location of hidden fruit seems to mysteriously reveal itself and they swing over for a meal.
Scientists like to explain an orangutan’s unique approach to problem-solving with this example: If a chimpanzee is given an oddly shaped peg and several different holes to try to put it in, the chimpanzee immediately tries shoving the peg in various holes until it finds the correct hole. But an orangutan approaches the challenge quite differently. It may stare off into space or even scratch itself with the peg. Then, after a while, it offhandedly sticks the peg into the correct hole while looking at something else that has caught its interest!
HABITAT AND DIET
Orangutans spend most of their lives in trees and travel by swinging from branch to branch with their long arms. They usually build a new nest every night, but may occasionally reuse one. Orangutans also use leafy branches to shelter themselves from rain and sun, and sometimes they drape large leaves over themselves like a poncho!
Orangutans on Sumatra, especially younger ones, must beware of tigers, as well as other predators such as clouded leopards, large pythons, and crocodiles. To stay safe, they tend to spend more time in the trees than Bornean orangutans, which don’t have those predators on their island.
Orangutans eat lots of ripe fruits—up to 100 kinds. Figs, along with fruit of the durian tree, are most common. When fruits are scarce, they eat leaves, flowers, bark, honey, termites, ants and other insects, and even bird eggs. They spend their mornings and afternoons foraging for these food items, with nap time during the midday’s heat. Sometimes several mothers and their young encounter each other by a fruit tree within their overlapping ranges. They peacefully feed together and watch their youngsters play. Adult males, however, generally don’t care for company—especially with other males.
Although orangutans get lots of water from the fruits and other vegetation they eat, they drink water, too. They lick water from tree hollows, wet plants, and even from the hair on their arms.
FAMILY LIFE
Orangutans have large home ranges, which may overlap. Each adult female usually lives in a stable home range of about 3.5 square miles (9 square kilometers). An adult male’s territory may be up to 15 square miles (39 square kilometers). A male’s range may overlap with the home ranges of several females. Males tend to be more nomadic, visiting female ranges as needed. If a male accidentally swings into a territory occupied by a more dominant male, the dominant male gives a booming roar called a “long call” to scare off the intruder.
The calls male orangutans make also serve as an invitation to any available females within hearing distance. Females seem to be impressed by a male orangutan’s cheek pads, but the pads have another purpose. When males fight, they charge at each other and break branches. If that doesn’t scare one of them away, they grab and bite each other on the cheek pads or ears until one of them gives up and runs away!
All other apes and monkeys live in social groups, but orangutans are a little different. Experts used to think they were solitary, but recent studies tell us more. On Sumatra, small groups or pairs of adolescents, a few adult females, or even a small group of non-cheek-padded males may travel together for a few days at a time. Sometimes several mothers and their young feed peacefully together while their youngsters play.
On both islands, cheek-padded males don’t care for company. They compete for mates and territory, and they don’t tolerate each other. They choose to remain alone unless breeding with a female or fighting with another male.
Orangutans have the slowest breeding rate of all mammals. They reproduce only once every seven or eight years. Orangutan females usually have their first baby at age 12 to 15, which is late compared to other mammals.
Newborns have pink faces that change to dark brown or black as they age, with tufts of hair that stand straight up. For the first few weeks of life, a baby holds tight to its mother’s belly as she swings through the forest in search of fruit. When a baby is older and better at balancing, they ride on the side of her torso, facing forward, so they can see what’s going on. Like most mammal offspring, young orangutans are much more active than their parents. They are also more social and enjoy interacting and playing with other orangutan youngsters.
A four- to five-year-old orangutan moves around independently but doesn’t go far, because it’s still nursing. Young orangutans may stay with their mothers to nurse for up to seven years—the longest childhood of the great apes. Their mother teaches them how to find fruit, build night nests, and other survival techniques before they set off on their own. Fruit trees are spread out over the rainforests where orangutans live, flowering and fruiting at different times. Young orangutans learn to make a mental map of the forest, including where they're likely to find ripe fruit.
Orangutans make at least 32 different vocalizations. A “kiss-squeak” expresses excitement or fear. A “grumph” sounds like a belch and can signal disturbance or annoyance. Mothers warn their babies to stay close by making a soft, scraping sound.
Orangutans communicate play, submission, aggression, fear, and worry through touch, facial expressions, and gestures.
AT THE ZOO
We've had the honor of caring for orangutans since 1928. Over the years, we've cared for both Bornean and Sumatran orangutans and have celebrated many births at the Zoo.
Orangutans are known for their intelligence, observational skills, physical strength, and agility. Ken Allen, a Bornean orangutan who lived at the San Diego Zoo, became well known for his creativity and ability to solve puzzles. Each time wildlife care specialists offered him a new challenge, he soon found a way to solve it. He quickly became a legend in San Diego and beloved by visitors from around the world.
Today, orangutans at the San Diego Zoo share their habitat with playful siamangs, the largest species of gibbons, which inhabit the same forest of Indonesia and Malaysia as orangutans. Their habitat includes climbing structures that are joined by ropes and nets, a “termite mound” that is often filled with tasty morsels for the orangutans to retrieve, rocky caves, and vertical “sway poles,” which are sturdy poles that gently bend like tree branches and create aerial pathways through the habitat.
CONSERVATION
Most of the forest habitat orangutans occupy has been destroyed to make palm oil plantations; and unfortunately, these highly intelligent red apes are now extinct in much of their range. Those that remain are Critically Endangered. On top of that, people often poach orangutan mothers and sell their young for the illegal pet trade. Fortunately, there are some organizations that rescue orphaned orangutans. Many of these organizations have programs to educate loggers and local people about the need to protect their orangutan neighbors and to help enforce the laws against poaching.
Indonesia is the top supplier of wood products and paper pulp in the world, and at least 70 percent is illegally logged. The world operates on the law of supply and demand, so we need to lessen the demand and carefully manage the supply. Conserve and recycle: we hear this often, but it really is an important part of the answer for helping orangutans.
Studies identifying levels of genetic variation between the three orangutan species have provided information that can help with habitat conservation efforts. Comparing the genomes of five Bornean and five Sumatran orangutans with DNA provided from our Wildlife Biodiversity Bank, we identified that both species have high levels of genetic diversity but contrasting histories of population growth and decline. Previous studies conducted by our geneticists identified chromosomal differences between Bornean and Sumatran orangutans. This information helps build the Association of Zoos and Aquarium’s Species Survival Plan programs for orangutans.
San Diego Zoo Wildlife Alliance supports the Association of Zoos and Aquariums’ (AZA) Saving Animals From Extinction (SAFE) Orangutan Program. The goal is to protect and restore wild orangutan populations and their habitats through public engagement, funding, and fieldwork that focuses on habitat protection, rescue and rehabilitation, and capacity enhancing. Together, we are working to keep healthy populations of these beloved, shaggy, red apes thriving, high in the trees on Borneo and Sumatra.
San Diego Zoo Wildlife Alliance is also a member of the Roundtable on Sustainable Palm Oil (RSPO), which was started to promote a sustainable palm oil industry to limit the destruction of rainforests. Look for products that are RSPO-designated as containing certified sustainable palm oil.
By joining San Diego Zoo Wildlife Alliance as an ally for wildlife, you help save species worldwide.
