ORANGUTANS: CHARACTERISTICS, HISTORY, FOOD

ORANGUTANS

orangutan

Orangutans (Scientific Name: Pongo) Orangutans are the largest arboreal animal species (animals that live mainly in trees) and a member of the Great Apes along with humans (homo sapiens), chimpanzees and gorillas. Among the rarest of all apes, wild orangutans can only be found on the islands of Sumatra and Borneo in Indonesia and Malaysia. Highly intelligent, their close-set eyes and facial expressions make them look eerily human. The Dyaks consider orangutans to be the equals of humans, and they are treated with the same respect as neighboring tribes. Orangutans are still respected in Indonesia and Malaysia, where they pictured on some paper money and coins. Orangutan is Malay for "person of the forest." [Sources: Biruté Galdikas, National Geographic, October 1975; June 1980; October 1985; Eugene Linden, National Geographic, March 1992; Cherly Knott, National Geographic, August 1998; “Reflections of Eden” Biruté Galdikas;

Orangutans are apes rather than monkeys. Gorillas are larger than orangutans but they generally don’t live in trees and that is why orangutans are considered the the largest creatures found in the canopy of the rain forest or far that matter are the largest animal period that lives in trees . Although they have human-like expressions and sometimes display human like-behavior they are regarded as less closely related to humans than gorillas or chimpanzees.

Orangutan researcher Biruté Galdikas told Smithsonian magazine “orangutans are tough. They're flexible. They're intelligent. They're adaptable. They can be on the ground. They can be in the canopy. I mean, they are basically big enough to not really have to worry about predators with the possible exception of tigers, maybe snow leopards. So if there were no people around, orangutans would be doing extremely well." [Source: Bill Brubaker, Smithsonian magazine, December 2010]

Orangutans hold the longevity record for non-human primates. The oldest captive orangutan is thought to have been 61 when she died. A pair of orangutan that died in 1976 and 1977 after 48 and 49 years in captivity were believed to be 58 and 59 when they died. In 2008, the oldest orangutan at that time—a Sumatran orangutan named Nonja—choked to death on her own vomit at the age of 55 at the Miami Metro Zoo after suffering a brain hemorrhage. Both sexes of orangutans can live a long time in wild too — up to 58 years for males and up to 53 years for females. Orangutans most commonly die of old age or natural causes in the wild. Human-induced threats include starvation, hunting by humans as pests, capturing babies to be sold on the black market as pets, and wildfires. [Source: Alexander Hey, Animal Diversity Web (ADW)]

Websites and Resources: Animal Diversity Web animaldiversity.org ; BBC Earth bbcearth.com; A-Z-Animals.com a-z-animals.com; Live Science Animals livescience.com; Animal Info animalinfo.org ; World Wildlife Fund (WWF) worldwildlife.org the world’s largest independent conservation body; National Geographic National Geographic ; Endangered Animals (IUCN Red List of Threatened Species) iucnredlist.org

Orangutan Species

Classified in the genus Pongo, orangutans were originally considered to be one species. In 1996, they were divided into two species: 1) the Bornean orangutan (P. pygmaeus, with three subspecies) and 2) the Sumatran orangutan (P. abelii). A third species, the Tapanuli orangutan (P. tapanuliensis), was identified definitively in 2017. [Source: Wikipedia]

Sumatran orangutans and Bornean orangutans were officially recognized as distinct species in 2001 based on mitochondrial DNA analysis. Tapanuli orangutan (P. tapanuliensis), a small group that lives in southern Sumatra, was previously regarded as Sumatran orangutans. There were declared a unique species based on a combination of small morphological differences like skull size, first molar size, hair texture and genomic diversity. The morphological and behavorial differences between Sumatran orangutans and Bornean orangutans are more apparent, with Bornean orangutans (Bornean orangutans) coming to the ground less frequently than Sumatran orangutans and having more fatty flanges in the adult males.[Source: Alexander Hey, Animal Diversity Web (ADW)]

It is not easy to tell the species apart. The most pronounced difference is between adult males. Bornean males tend to have larger cheek pads, rounder faces and darker fur while Sumatran males have more whiskers around their cheeks and chins and curlier, more matted hair on their body. The Bornean orangutans are slightly larger than the Sumatran variety. There is also significant genetic differences between the species. Part of the second chromosome on one species is flipped in relationship to the second chromosome of the other. The population in southwestern Borneo, some scientists say, is different enough from others found elsewhere on the island to warrant classifications into a fourth species.

Tapanuli orangutans are the oldest species of orangutan, diverging about 3.38 million years ago. About 674,000 years ago, genetic modeling indicates, Sumatran and Bornean populations split.

Orangutan Numbers

Ranges of the three orangutans species: 1) the Bornean orangutan (blue); the 2) the Sumatran orangutan (green); and the Tapanuli orangutan (red)

About 120,000 orangutans are left in the wild, with about 85 to 90 percent of them on Borneo and most of them in Indonesia. About half the orangutans that live on Borneo live in peat-swamp forests in Central Kalimantan and the forest in East Kalimantan and Sabah. In the old days orangutans ranged across the entire island of Borneo but today most live in small, scattered populations. There are about 1,000 orangutans in captivity. [Source: Wikipedia]

Estimates in the 2000s counted around 6,500 Sumatran orangutans and around 54,000 Bornean orangutans in the wild. A 2016 study estimated the population of Sumatran orangutans in the wild was 14,613, twice the previous estimates, and estimated that 104,700 Bornean orangutans lived the in the wild. Only 800 Tapanuli orangutans are estimated to exist, making them the most endangered of the great apes.

There are 30 percent less orangutans than there were in the 1980s. A 2018 study found that Bornean orangutans declined by 148,500 individuals from 1999 to 2015. As recently as 1900, more than 300,000 orangutans roamed freely across the jungles of Southeast Asia and southern China A few decades ago there were still hundreds of thousands of them. In the early 2000s it was said there were around 15,000 to 24,000 orangutans are left in the wild. The number was upped to around 40,000 after studies in 2004. A new population with several thousand members was discovered in Kalimantan.

Orangutan Habitat and Where They Are Found

All three species of orangutans are found in Indonesia. Sumatran orangutans and Tapanuli orangutans are found in Northern Sumatra. Bornean orangutans are found exclusively in Borneo, mainly in the northeastern Malaysia province of Sabah and Kalimantan in Indonesia. Kalimantan makes up 73 percent of the island of Borneo. [Source: Alexander Hey, Animal Diversity Web (ADW) /=]

Orangutans reside mainly in tropical evergreen forests, with the highest population densities occurring in swamps, fertile valleys, and lowland areas. Orangutans prefer places with fertile soil, as they yield the most fruit. Fruit trees in the Meliacedae (mahogany) family are a common feature in orangutan habitats. Generally, it is assumed that Bornean orangutans have smaller ranges than Sumatran ones, but that is not the case. Males typically have larger ranges than females, and both male and female ranges overlap with ranges of other orangutans. Range size is debated and varies from 850 hectares to 2500 hectares, and perhaps even more. /=\

Orangutans prefer areas of increased canopy closure, vertical stability, and uniform height but they have been able to utilize disturbed and fragmented forests, even palm-oil plantations — a valuable adaption as their original old-growth habitat has been chopped down and degraded. Canopy layering and shape is not import to these animals when selecting a place to reside. Orangutan residency in highly fragmented areas has led to increased connectivity of metapopulations that can persist.

In 2009, scientists announced the discovery of a previously unknown orangutan population with more than 1,000 members in a remote area of Borneo. Associated Press reported: A team surveying mountainous forests in eastern Borneo counted 219 orangutan nests, indicating a "substantial" number of the animals, said Erik Meijaard, of the US-based charity The Nature Conservancy. "We can't say for sure how many," he said, but even the most cautious estimate would indicate "several hundred at least, maybe 1,000 or 2,000 even". That a significant orangutan population exists in eastern Borneo appears to be due to the steep topography, poor soil and general inaccessibility of the rugged limestone mountains shielding the area from development, said Meijaard.[Source: Associated Press, April 13, 2009]

Hominidae (Hominids) — the Great Apes and Humans

Primates is the name of an order. Primates are sometimes conveniently divided into the following major groups (which are either suborders of families) : 1) strepsirrhines (lemurs, galagos, and lorisids); 2) Tarsiiformes (tarsiers); 3) Catarrhini (Old World monkeys); 4) Simiiformes (New World monkeys); 5) Hominoidea (gibbons); 6) Hominidae (great apes and humans). [Source: Wikipedia]

Hominidae (Hominids) is a taxonomic family of primates that includes eight extant species in four genera: 1) Pongo (Bornean, Sumatran and Tapanuli orangutans); 2) Gorilla (the eastern and western gorillas); 3) Pan (chimpanzees and bonobos); and 4) Homo, of which only modern humans (Homo sapiens) remain.

Hominidae taxonomy: After an initial separation from the main line by the Hylobatidae (gibbons) some 18 million years ago, the line of Ponginae broke away, leading to the orangutan; later, the Homininae split into the tribes Hominini (led to humans and chimpanzees) and Gorillini (led to gorillas)

Phil Myers wrote in Animal Diversity Web: Until recently, most classifications included only humans in this family; other apes were put in the family Pongidae (from which the gibbons were sometimes separated as the Hylobatidae). The evidence linking humans to gorillas and chimps has grown dramatically in past decades, especially with increased use of molecular techniques. It now appears that chimps, gorillas, and humans form a clade of closely related species; orangutans are slightly less close phylogenetically, and gibbons are a more distant branch. [Source: Phil Myers, Animal Diversity Web (ADW) /=]

Hominids range in weight from 48 kilograms to 270 kilograms. Males are larger than females. Hominids are the largest primates, with robust bodies and well-developed forearms. Their thumb and big toe are opposable except in humans, who have lost opposability of the big toe. All digits have flattened nails. No hominid has a tail, and none has ischial callosities. Numerous skeletal differences between hominids and other primates are related to their upright or semi-upright stance. /=\

All members of this family have large braincase. Most have a prominent face and prognathous jaw; again, humans are exceptional. All are catarrhine, with nostrils close together and facing forward and downward. The dental formula is the same for all members of the group: 2/2, 1/1, 2/2, 3/3 = 32. Hominids have broad incisors and their canines are never developed into tusks. The upper molars are quadrate and bunodont; the lowers are bunodont and possess a hypoconulid. The uppers lack lophs connecting labial and lingual cusps and thus, in contrast to cercopithecid (Old World monkey)s (Old World monkeys), are not bilophodont. /=\

Hominids are omnivorous (eating a mixed and varied diet), primarily frugivorous (fruit eating) or folivorous (leaf-eating). All but humans are good climbers, but only the orangutan is really arboreal. Members of this family are well-known for the complexity of their social behavior. Facial expression and complex vocalizations play an important role in the behavior of hominids. All make and use nests. Hominids generally give birth to a single young, and the period of parental care is extended.

History of Orangutans

The orangutans are the only surviving species of the subfamily Ponginae, which diverged genetically from the other hominids (gorillas, chimpanzees, and humans) between 19.3 and 15.7 million years ago. The ape-like primate so far discovered is a 33 million year old arboreal animal nicknamed the "dawn ape" found in the Egypt's Faiyum Depression.. This fruit-eating creature — Aegyptopithecus zeuxis — weighed about eight pounds (three kilograms) and had a lemur-like nose, monkey-like limbs and the same number of teeth (32) as apes and modern man. About 25 million years ago the line that would eventually lead to apes split from the old world monkeys. Between 14 million and 5 million years ago numerous species of early apes spread across Asia, Europe and Africa.

In a June 2007 article in the journal Science, Susannah Thorpe and Roger Holder of the University of Birmingham and Robin Crompton of the University of Liverpool suggested that bipedalism arose much earlier than previously thought among arboreal apes—perhaps as early as between 17 million and 24 million years ago— based on the way wild orangutans navigate their way along fragile tree branches. Thorpe spent a year observing wild orangutans in the forest of Sumatra and saw them walk on two legs on fragile branches to reach fruit, using their arms to keep balance or grasp for fruit while using all four limbs on bigger branches. The finding is significant in that it shows bipedalism might have first evolved as a way to move around in the trees rather than on the ground.

Thorpe spent a year in Indonesia's Sumatran rain forest painstakingly recording the movements of the orangutans. "I followed them from when they woke up in the morning to when they made their night nest in the evening," Thorpe told Reuters. "Our results are important because we have shown how bipedalism could have evolved in the original ape habitat, to navigate the very smallest branches where the tasty fruits are, and the smallest gaps between tree crowns.” [Source: Will Dunham, Reuters, May 31, 2007]

"As the only great ape which remains in the ancestral ape niche (arboreal fruit eaters), orangutans are therefore a vital model for the understanding of the evolution of limb adaptation in apes," Crompton said. The researchers said as the rain forest in eastern and central Africa receded due to climate changes near the close of the Miocene epoch, which ended 5 million years ago, arboreal apes that already had acquired the ability to walk on two legs were forced to spend more time on the ground. They proposed that apes in the evolutionary line that led to people descended to the ground, remaining bipedal. [Ibid]

On seeing an orangutan named Jenny at the London Zoo in 1842, Queen Victoria, declared the beast "frightful and painfully and disagreeably human."

Orangutan Characteristics

orangutan in Sumatra

Large males in the wild weigh up to 136 kilograms (300 pounds), reach a height of 1.67 meters (5½ feet), and have an arm span of 2.13 meters (seven feet). The largest on record was almost 1.82 meters (six feet) tall. Females weigh about half as much. In captivity they can get quite fat. Some males in zoos have tipped the scales at over 200 kilograms (441 pounds). [Source: National Geographic

Orangutan arms and hands are almost twice as long as their legs and feet and reach down to their ankles when the animal stands erect. The legs are short and weak. Although they have a body weight comparable to that of humans, orangutans can be four times stronger. German zoologist Peter Pratje, who was once attacked by a slightly smaller orangutan, told the Los Angeles Times he has calculated that a 63.5-kilogram (140-pound) orangutan is twice as strong as Arnold Schwarzenegger when he was in his prime.

Orangutans adults have cheek pads and they are especially pronounced in older males 12 years old and older. The cheeks are comprised of fat covered by skin with only a minimal amount of hair. Older males acquire bulging, fatty cheek pads and throat sacs. Healthy males have tight extended face pads. Shriveled cheek pads indicate poor health.

Orangutans are characterized by their distinctive orange-red, shaggy hair that covers almost their entire body, with males and some female possessing a beard of the same color. They have white around the irises in their eyes like humans. Unlike chimpanzees and gorillas they have don’t have pronounced brow ridges. Their powerful jaws and spadelike incisors can rip apart and tear through tough fruit skins and nuts. The grip of their powerful hands is strong enough to crush the bones in your hands. Their unusually flexible mouths are capable of making a wide range of expressions and noises.

Differences Between Different Orangutan Groups

Sexual Dimorphism (differences between males and females) is present: Males are larger than females and have different shapes and facial features. Males weigh around 72 kilograms (160 pounds) on average while females weigh about half that. [Source: Alexander Hey, Animal Diversity Web (ADW) /=]

Orangutan males exhibit bimaturism (two different forms of mature animals): 1) flanged and 2) unflanged. Flanged males are twice the size of females, have a large facial disk with flanges, and a large throat patch. Unflanged males look much more like the females and are about the same size and do not display the same calling behavior as flanged males. Both types of adult male orangutans reproduce. Unflanged males may become flanged at any time, as it is a reflection of social hierarchy as well as age. Males between eight and 15 years of age are generally unflanged and become flanged between 15 and 20. [Source: Benjamin Strobel, Animal Diversity Web (ADW) /=]

Orangutan Adaptions for Life in the Trees

Orangutan adaptions for life in the trees includes: 1) long arms; 2) extremely flexible joints; 3) and full rotation of their hips. Both their long arms and flexible hips aid in their quadrumanous (four-limbed) scrambling, which differs from swinging from branches, and features individuals shifting their weight to force branches to bend over to the next branch. Orangutans climb, clamor and brachiate (use their arms to swing from branch to branch) to make their way through the canopy, getting over 90 percent of their food in the trees. [Source: Alexander Hey, Animal Diversity Web (ADW) /=\

The long orangutan arms are advantageous for traveling through the canopy. Orangutans grasp with both their feet and hands. Their powerful arms are used for climbing and swinging. Their hook-like hands allow them to move through high canopy by keeping contact with the limbs at all times and also allow them to hang freely and comfortably from trees and even sleep in this position. The use their weight to sway saplings back and forth to reach their next destination. Even their legs are adapted to walking on branches rather on the ground. When they walk on the ground they do so on all fours with clenched fists (not knuckles like gorillas and chimpanzees).

orangutan with a coconut at Semenggok Forest Reserve, Sarawak, Borneo, Malaysia

Orangutan spend almost all their time in the trees and are the only true tree-dwelling ape. The only time that they walk on the ground is to get from one tree to another and occasionally to forage. Because they are so big they have difficulty moving from one tree to another and often descend down one tree to the ground and ascend another using a liana, climbing hand over hand. One reason that orangutans survive better in primary forests rather than secondary ones is that they can move round better on big trees.

The thin and shaggy, dark rufous to reddish brown fur serves as camouflage. Biruté Galdikas wrote in “Reflections of Eden” At first I simply could not understand how a large, lumbering, two- to three-hundred pound male orangutan covered with bright red hair could virtually melt into the dark shadows of the canopy. I finally deduced that in the shade, the sparse hair of the orangutan almost disappeared from view because no light caught its tips. All one could see was the orange dark skin. Only in the sunlight would the hair catch the light, causing it to blaze as the orangutan were on fire." [Source: “Reflections of Eden" by Biruté Galdikas]

"Hidden high in the crowns of the trees, amid heavy foliage, an orangutan becomes a shapeless black shadow,” Galdikas wrote. “To perfect my spotting technique, I had to learn the search images. I needed to look for shadows that were black and amorphous, and not the shape and color of large, bright orange orangutans."

Orangutan Food and Feeding Behavior

Orangutans have been labeled as omnivores (eat a variety of things, including plants and animals), herbivores (eat plants or plants parts), folivores (eat leaves), frugivores (eat fruits), granivore (eat seeds and grain), lignivore (eats wood), nectarivores (eat nectar from flowers), carnivores (eat meat or animal parts) and insectivores (eat insects). There are regional differences in what orangutans eat. Food availability often determines was subpopulations of orangutans eat. For example, Sumatra is rich in figs and thus orangutans there have a higher fig density in their diet. [Source: Alexander Hey, Animal Diversity Web (ADW) /=]

Many orangutans are at the mercy of boom and bust cycles of rain forest fruit. They gorge themselves silly on high-calorie fruit when there is a mast fruiting (when a large number of trees bear fruit at the same time). When times are lean the eat food that are plentiful but low in calories such as leaves bark and stems. Travel patterns of orangutans are affected by the cycle: namely they have to move around more when food sources are more limited. The cycle is also believed to have an affect on when males mature and when females decide to have children.

Rather than eating a whole fruit, orangutans often take a bite form the juiciest part and then throw the rest fruit. One of their favorite treats is the “banitan” fruit which contains two large pits that are so hard even a nutcracker won't break them. To get at the coconut-like material inside orangutans spend hours crushing the pits with their teeth. Orangutans have also been observed hang upside down from branches to drink from a river and bending fruit tree branches to reach them.

Bill Brubaker wrote in Smithsonian magazine, “Males usually search for food alone, while females bring along one or two of their offspring. Orangs have a keen sense of where the good stuff can be found. "I was in the forest once, following a wild orangutan female, and I knew we were about two kilometers from a durian tree that was fruiting," Galdikas says on the front porch of her bungalow at Camp Leakey. "Right there, I was able to predict that she was heading for that tree. And she traveled in a straight line, not meandering at all until she reached the tree." [Source: Bill Brubaker, Smithsonian magazine, December 2010]

Foods That Orangutans Eat

Orangutans mostly eat fruit and have a strong preference for wild figs and will travel long distances to seek out fig trees when they are fruiting. They will also eat young leaves and soft material on the inside of tree bark, fungus, wild ginger roots, durians, the red fruit from “baccaurea" trees, “pandanus", most forms of vegetation, grubs, ants and termites and dirt. Altogether they have been observed eating 400 different items found in the tropical rain forest, including fruit, flowers, bark, leaves and insects. Wild orangutans are rarely seen eating meat (one scientist saw an orangutan eating a gibbon carcass) although they been observed eating insects, termites, rats and bird's eggs. Sometimes the seem inappropriate more by curiosity than hunger and desire. In zoos, they readily accept meat.

According to Animal Diversity Web: Orangutans are highly opportunistic foragers, with over 317 food sources noted in 1988 with a complete species list numbering over 1600 different species preyed upon by orangutans. When resources are abundant, they prefer to consume fruits as 60 percent of the orangutan diet is fruit, but this varies month to month. When fruit is available, they consume a plethora of different species like ficus and durian, the bulk of their diet, but they will eat apples, oranges, bananas, berries, lychees, breadfruit, and jackfruit. With decreasing habitat available, many orangutans are raiding farmers fruit crops, with females being more likely to raid than males. In addition, it's been found that the greatest factor to their distribution, which is linked to foraging, is resting time. While much of their time is spent foraging, the periods of rest in between are the main determinant of distribution. [Source: Alexander Hey, Animal Diversity Web (ADW) /=]

When fruit isn't an option, many orangutans will increase from 22 percent of their foraging time for bark to 44 percent. In addition to tree bark, species like Gironniera nervosa are also an important source of leaves and flowers. Most members of pongo prefer younger leaves and flowers, as many adult leaves develop toxins that can be harmful for herbivores. They also consume nectar and honey from trees and plants. /=\

Invertebrate species that orangutans have been observed include four species of ants, four species of termites, two species of caterpillars, leeches, maggots, ticks, and larvae. They poke out many of these invertebrates using a stick in the burrows or crevices where the invertebrates reside. Orangtuans will also eat food related to vertebrates including the eggs of many bird species, tree rats, small lizards, and primates like loras or gibbons. /=\

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated December 2024