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Sumatran orangutan

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Sumatran orangutan

Sumatran orangutan[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Subfamily: Ponginae
Genus: Pongo
Species: P. abelii
Binomial name
Pongo abelii
Lesson, 1827
Distribution in Indonesia

The Sumatran orangutan (Pongo abelii) is one of the two species of orangutans. Found only on the island of Sumatra, in Indonesia, it is rarer than the Bornean orangutan. The word orangutan is made up of two separate words. In the local languages of Malay and Indonesia, "Orang" means "people" or "person". "Hutan" means "forest". So "Orang Hutan" becomes orangutan. Orangutan means 'man of the forest'.


Male Sumatran orangutans grow to about 1.4 m (4.6 ft) tall and 90 kg (200 lb). Females are smaller, averaging 90 cm (3.0 ft) and 45 kg (99 lb). Compared to the Bornean species, Sumatran orangutans are thinner and have longer faces; their hair is longer with a paler red color.[3]

Behaviour and ecology

Sumatran orangutan

Compared with the Bornean orangutan, the Sumatran orangutan tends to be more frugivorous and especially insectivorous.[4] Preferred fruits include figs and jackfruits. It will also eat bird eggs and small vertebrates.[5] Sumatran orangutans spend far less time feeding on the inner bark of trees.

Wild Sumatran orangutans in the Suaq Balimbing swamp have been observed using tools.[6] An orangutan will break off a tree branch that is about a foot long, snap off the twigs and fray one end. With its teeth,[7] the orangutan will use the stick to dig in tree holes for termites. They will also use the stick to poke a bee's nest wall, move it around and catch the honey. In addition, orangutans use tools to eat fruit. When the fruit of the Neesia tree ripens, its hard, ridged husk softens until it falls open. Inside are seeds that the orangutans enjoy eating, but they are surrounded by fiberglass-like hairs that are painful if eaten. Tools are created differently for different uses. Sticks are often made longer or shorter depending on whether they will be used for insects or fruits.[7] If a particular tool proves useful, the orangutan will often save it. Over time they will collect entire "toolboxes".[7] A Neesia-eating orangutan will select a five-inch stick, strip off its bark, and then carefully collect the hairs with it. Once the fruit is safe, the ape will eat the seeds using the stick or its fingers. Although similar swamps can be found in Borneo, wild Bornean orangutans have not been seen using these types of tools.

NHNZ filmed the Sumatran orangutan for its show Wild Asia: In the Realm of the Red Ape; it showed one of them using a simple tool, a twig, to pry food from difficult places. There is also a sequence of an animal using a large leaf as an umbrella in a tropical rainstorm.

As well as using tree branches as tools, tree branches are a means of transportation for the Sumatran orangutan. The orangutan's are the largest mammals to travel by tree, having a body mass of around 40 kg for females and around 80 kg for males. This makes them particularly susceptible to the changes in arboreal compliance. To deal with this their locomotion is characterized by the slow movement, long contact times, and an impressively large array of locomotors postures. Orangutans have even been shown to utilize the compliance in vertical supports to lower the cost of locomotion by swaying trees back and forth and they possess unique strategies of locomotion moving slowly and using multiple supports to limit oscillations in complaint branches, particularly at their tips.

The Sumatran orangutan is also more arboreal than its Bornean cousin; this could be because of the presence of large predators like the Sumatran Tiger. It moves through the trees by quadrumanous locomotion and semibrachiation.

As of 2015, the Sumatran Orangutans species has approximately seven thousand remaining members in its population. Thus, being label "critically endangered" by the world wildlife (WWF) organization. The Orangutan’s low population has forced the WWF to protect the species by allowing them to reproduce in the safe environment of captivity. However, this comes at a risk to the Sumatran Orangutan’s native behaviors in the wild. While in captivity, the Orangutans are at risk to the "Captivity Effect," which states that overtime animals held in captivity will no longer know how to naturally behave in the wild. During captivity, Orangutans are given water, food, and shelter and lack all the challenges of living in the wild.[8] Therefore, will all these essential goals already fulfilled for Orangutans in captivity, their behaviors will be modified and become exploratory in nature, simply do to the lack of tasks at hand.

Sumatran orangutans have 64 gestures that have been identified for the orangutans. It has been concluded that 29 of these gestures have a specific meaning that can be interpreted by other orangutans the majority of the time. Six intentional meanings were identified by scientists, those actions were: Affiliate/Play, Stop action, Look at/Take object, Share food/object, Co-locomote and Move away. These show that there is some form of communication between the Sumatran orangutans. While their communication is nothing like human language it is something to take note. Sumatran Orangutans do not elect to use sounds as part of their communication. Many other animals decide to make noises that signify danger or where they are located. However, these orangutans mostly base their communication of gestures alone.[9]

Life cycle

The Sumatran orangutan has five stages of life that are characterized by different physical and behavioral features. The first of these stages is infancy which last from birth to around 2.5 years-old. The orangutan weighs between 2 and 6 kilograms. An infant is identified by light pigmented zones around the eyes and muzzle in contrast to darker pigmentation on the rest of the face as well as long hairs that protrude outward around the face. During this time the infant is always carried by the mother during travel, s/he is highly dependent on the mother for food, and also sleeps in the mother's nest. The next stage is called juvenile-hood and takes place between 2.5 and 5 years-old. The orangutan weighs between 6 and 15 kilograms and does not look dramatically different from an infant. Although s/he is still mainly carried by the mother, a juvenile will often play with peers and make small exploratory trips within the vision of the mother. Toward the end of this stage, the orangutan will stop sleeping in the mother's nest and will build its own nest nearby. From the ages of 5 to 8 years-old, the orangutan is in an adolescent stage of life. S/he weighs around 15-30 kilograms. The light patches on the face start to disappear and eventually the face becomes completely dark. During this time orangutans still have constant contact with their mothers, yet they develop a stronger relationship with peers while playing in groups. They are still young and act with caution around unfamiliar adults, especially males. At 8 years-old, female orangutans are considered fully developed and begin to have offspring of their own. Males, however, enter a stage called sub-adulthood. This stage lasts from 8 to around 13 or 15 years-old and the orangutans weigh around 30 to 50 kilograms. Their faces are completely dark and they begin to develop cheek flanges. Their beard starts to emerge while the hair around their face shortens and instead of pointing outwards it flattens along the skull. This stage marks sexual maturity in males, yet these orangutans are still socially undeveloped and will still avoid contact with adult males. Finally, male Sumatrans orangutans reach adulthood at 13 to 15 years of age. They are extremely large animals weighing between 50 and 90 kilograms, roughly the weight of a fully grown human. They have a fully grown beard, fully developed cheek callosities, and long hair. These orangutans have reached full sexual and social maturity and now only travel alone.[10]

The Sumatran orangutan is more social than its Bornean counterpart; groups gather to feed on the mass amounts of fruit on fig trees. The Sumatran Orangutan community is best described as loose, not showing social or spatial exclusivity. Groups generally consist of female clusters and a preferable male mate.[11] However, adult males generally avoid contact with other adult males. Subadult males will try to mate with any female, though they probably mostly fail, since mature females are easily capable of fending them off. Mature females prefer to mate with mature males. Usually, there is a specific male in a group of Sumatran Orangutans that mature females will exhibit preference for.[11] Male Sumatran orangutans sometimes have a delay of many years in the development of secondary sexual characteristics, such as cheek flanges and muscle mass.[12]

Males exhibit bimaturism, whereby fully flanged adult males and the smaller unflanged males are both capable of reproducing, but employ differing mating strategies to do so.[13]

The average interbirth rates for the Sumatran orangutan is 9.3 years, the longest reported among the great apes, including the Bornean orangutan. Infant orangutans will stay close to their mothers for up to three years. Even after that, the young will still associate with their mothers. Both orangutan species are likely to live several decades; estimated longevity is more than 50 years. The average of the first reproduction of P. abelii is around 15.4 years old. There is no indication of menopause.[4]

Nonja, thought to be the world's oldest in captivity or the wild at the time of her death, died at the Miami MetroZoo at the age of 55.[14]


Sumatran Orangutans are primarily frugivores, favoring fruits consisting of a large seed and surrounded by a fleshy substance, such as fig fruits.[15][16] Insects are also a huge part of the Orangutan's diet; the most consumed of the insects are ants, predominantly of the genus Camponotus (at least four species indet.) [16] The main diets can be broken up into five categories: fruits, insects, leaf material, bark and other miscellaneous food items. Studies recorded showed that Orangutans in the Ketambe area in Indonesia ate over 92 different kinds of fruit, 13 different kinds of leaves, 22 sorts of other vegetable material such as top-sprouts, and pseudo-bulbs of orchids.[17] Insects included in the diet are numbered at least 17 different types. Occasionally soil from termite mounds were ingested in small quantities.[18] When there is low ripe fruit availability, Sumatran orangutans will eat the meat of the slow loris, a nocternal primate.[19] Water consumption for the Orangutans was ingested from natural bowls created in the trees they lived around. They even drank water from the hair on their arms when rainfall was heavy.


Meat-eating happens rarely in Sumatran orangutan, and orangutans do not show a male bias in meat-eating. A research in Ketambe area reported cases of meat-eating in wild Sumatran orangutans, of which 9 cases of orangutans eating slow lorises. The research shows, in the recent 3 cases of slow lorises eaten by Sumatran orangutan, a maximum mean feeding rate of the adult orangutan for an entire adult male slow loris is 160.9 g/h and, of the infant, 142.4 g/h .There is no case reported during mast year, which suggests orangutans take meat as a fallback for the seasonal shortage of fruits. Slow loris eaten by Sumatran orangutans occurs more often in periods of low fruit availability. From the observations so far, similar to most primate species, orangutans only share meet between mother and infants.[20]


Sumatrans encounter threats such as logging (both legal and illegal), wholesale conversion of forest to agricultural land and oil palm plantations, and fragmentation by roads.[13] Oil companies use a method of deforestation to utilize palm oil. This palm oil is taken from the trees in which Sumatran Orangutans live and swing from. An assessment of forest loss in the 1990s concluded that forests supporting at least 1,000 orangutans were lost each year within the Leuser Ecosystem alone.[13] It was also that concluded in 1995 that the forest declined 54%, and 18% in 2009, while palm oil productions increased from 4-39% that year.

While poaching generally is not a huge problem for the Sumatrans, occasional local hunting does decrease the population size. They have been hunted in the Northen Sumatra in the past as targets for food; although deliberate attempts to hunt the Sumatrans are rare nowadays, locals such as the Batak people are known to eat almost all vertebrates in their area. Additionally, the Sumatrans are treated as pests by Sumatran farmers, becoming targets of elimination if they are seen damaging or stealing crops. For commercial aspects, hunts for both dead or alive specimens have also been recorded as an effect of the demand by European and North American zoos and institutions throughout the 20th century.[16]

Sumatran Orangutans have developed a highly functioning cardiovascular system. However, with this development air sacculitis has become more prevalent among Orangutans in this species, due to the new hugely improved air sacs in their lungs. Air sacculitis is similar to Streptococcus i.e. strep throat in Homo sapiens. The bacterial infection is becoming increasing common in captive Orangutans, due to the fact that captive Orangutans are exposed to the human strain of Streptococcus in captivity. At first, both strains are treated and cured with antibiotics along with rest. Yet, in 2014 a Sumatran Orangutan, ten years in captivity was the first of its species to die from Streptococcus anginosus.[21] Since, the number only remains at one, it does not warrant a crisis; however, it does raise the question of why a relatively simple infection could not be treated with its own cure.

Conservation status

A Sumatran orangutan and a man

The Sumatran orangutan is endemic to Sumatra island and is particularly restricted to the north of the isla nd. In the wild, Sumatran orangutans survive in the province of Nanggroe Aceh Darussalam (NAD), the northernmost tip of Sumatra.[15] The primate was once more widespread, as they were found more to the south in the 19th century such as in Jambi and Padang.[22] There are small populations in the North Sumatra province along the border with NAD, particularly in the Lake Toba forests. A survey in the Lake Toba region found only two inhabited areas, Bukit Lawang (defined as the animal sanctuary) and Gunung Leuser National Park.[23] The species has been assessed as critically endangered on the IUCN Red List since 2000.[2] It is considered one of "The World's 25 Most Endangered Primates."[24]

A survey in 2004 estimated that around 7,300 Sumatran orangutans still live in the wild. The same study estimates a 20,552 km² occupied area for the Sumatran orangutans, of which only an approximate area range of 8,992 km² harbors permanent populations.[15] Some of them are being protected in five areas in Gunung Leuser National Park; others live in unprotected areas: northwest and northeast Aceh block, West Batang Toru river, East Sarulla and Sidiangkat. A successful breeding program has been established in Bukit Tiga Puluh National Park in Jambi and Riau provinces. The main reason for the endangerment of these orangutans is because of palm oil companies destroying the native rain forests.

Two strategies that are recently being considered to conserve this species are 1) rehabilitation and reintroduction of ex-captive or displaced individuals and 2) the protection of their forest habitat by preventing threats such as deforestation and hunting. By analyzing both options it was determined that one is more cost efficient for maintaining the wild orangutan populations but has a longer time scale of 10–20 years.[25]

In addition to the above, original wild populations, a new population is being established in the Bukit Tigapuluh National Park (Jambi and Riau Provinces) via the re-introduction of confiscated illegal pets. This population currently numbers around 70 individuals and is reproducing.[13] However it has been concluded that forest conservation costs twelve times less than reintroducing orangutans into the wild, and conserves more biological diversity.[26]

To summarize and add to the above information, there are two main efforts in regards to conserving the Sumatran Orangutan currently being put to action. The first one being the reintroduction of older orangutans formerly kept in captivity and just other orangutans which are out of place, to their environments. The second effort is just the protection and guard of their natural habitats in the forest against deforestation and hunting of the orangutans. These are similar to methods used to save other endangered species from extinction. The first method comes to be very expensive compared to just protecting the forest. The best plan for long-term productivity would be investing in the protection of the forest habitat over reintroducing the orangutans to the environment.[25] An example of an effort would be from WWF, or World Wildlife, who joined forces with many other organizations to stop the clearing of the biggest part of remaining natural forest, which is by the Bukit Tigapuluh National Park. This area of forest is home to the Sumatran orangutan, and also to many other species of animals. WWF has helped make a plan that supports the ecosystem of the orangutans to help keep the forests on the island safe.[27]

The Sumatran Orangutan is critically endangered today mostly because of hunting by humans and habitat destruction. These causes mixed with the fact that these orangutans are more likely to become extinction cause a large issue. The fact that these animals require large areas and act as individuals, thus making their population densities low makes them more susceptible to extinction. The home ranges of the orangutans make their situation even worse. The population densities of Sumatran orangutan depends on the abundance of fruits with soft pulp. Seasonally, Sumatran orangutan commutes between lowland, intermediate, and highland region in different months, depending on which region produces the fruit most. In a year, Sumatran orangutan moves from lowland region to intermedia region, then to highland region. Therefore, undisturbed forests with broader altitudinal range can harbor more orangutan than narrower one. The extensive forest clearance of agriculture and commercial use is cutting down the lowland rainforest that disturbs Sumatran orangutan’s seasonal movement. The issue here is that Sumatra has one of the highest deforestation rates in the world. Orangutans need a large area that scales through multiple types of forests to survive. With the orangutans food source being in high and low lands throughout the forests of Sumatra. The destruction of the lowland forests will create the orangutans range to shrink and their food source to shrink, which in turn could create the Sumatran orangutans to go extinct all together.[28]


Orangutans have 48 chromosomes.[29] The Sumatran orangutan genome was sequenced in January 2011, based on a captive female named Susie.[30] Following humans and chimpanzees, the Sumatran orangutan has become the third extant hominid[31] species to have its genome sequenced.[30][32]

The researchers also published less complete copies from 10 wild orangutans, five from Borneo and five from Sumatra. The genetic diversity was found to be lower in Bornean orangutans (Pongo pygmaeus) than in Sumatran ones (Pongo abelii), despite the fact that Borneo is home to six or seven times as many orangutans as Sumatra. The comparison has shown these two species diverged around 400,000 years ago, more recently than was previously thought. The orangutan genome also has fewer rearrangements than the chimpanzee/human lineage.[30] The full sequence and annotation can be viewed on the Ensembl Genome Browser.

Differences between Pongo Abelii and Pongo Pygmaeus

The Sumatran and Bornean orangutans have a large number of differences which leads the their taxonomy difference. Sumatran Orangutans being Pongo Abelii while Bornean orangutans being Pongo Pygmaeus. One major difference between them is that Bornean orangutans have an abnormal state in development in comparison to the Sumatran orangutans. Also Sumatran orangutans spend less time than Bornean orangutans feeding on the inner bark of trees. This represents the different food sources that both species have. The food availability is lower in Borneo which is shown by the fact that female orangutans in Sumatra spend a lot more time in associations than orangutans in Borneo. Another difference is with their interbirth intervals, Bornean orangutans have an interbirth interval of 6.1 years while Sumatran orangutans have an interbirth interval of 9.3 years.[33]

Differences between Pongo Abelii and hominin

First off hominin species have a life expectancy of 53 for males and 56 for females. Also the interbirth difference between hominin and orangutans is quite large. Orangutans are around 61.-9.3 years while hominin are around 3.2-3.8 years. The life expectancy for orangutans is 46 for males and 40 for females. Also hominin females experienced menopause as where orangutan females did not. That information could be a key reason why the humans evolved the way they did. These changes all represent evolution and represent the favorable traits being passed on. These facts show the evolutionary change between orangutans and hominin.[33]

See also


  1. ^
  2. ^ a b
  3. ^ PongoPrimate Info Net: Orangutan
  4. ^ a b
  5. ^
  6. ^ Zimmer, Carl. "Tooling through the trees - tool use by wild orangutans" Discover Magazine, November 1995.
  7. ^ a b c
  8. ^
  9. ^
  10. ^
  11. ^ a b
  12. ^ Pradhan, Maria A. van Noordwijk1, Carel van Schaik1, 2012 A model for the evolution of developmental arrest in male orangutans
  13. ^ a b c d
  14. ^
  15. ^ a b c
  16. ^ a b c
  17. ^
  18. ^
  19. ^
  20. ^
  21. ^
  22. ^
  23. ^
  24. ^
  25. ^ a b
  26. ^ / last=Wilson/ first=Howard/ title=Conservation Strategies for Orangutans: Reintroduction versus Habitat Preservation and the Benefits of Sustainably Logged Forest/ url= accessdate= 29 October 2015/ article= plos one/ date=2014/ agency=Public Library Science}}
  27. ^
  28. ^
  29. ^
  30. ^ a b c
  31. ^
  32. ^
  33. ^ a b

External links

  • Sumatran Orangutan Society
  • Sumatran Orangutan Conservation Programme
  • Orangutan Foundation Info on project in Aceh
  • The Orangutan Conservancy
  • ARKive – (Pongo abelii)images and movies of the Sumatran orang-utan
  • View the orangutan genome on Ensembl.
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