Species Fact Profile: Bornean Orangutan (Pongo pygmaeus)

                                                                 Bornean Orangutan

Pongo pygmaeus (Linnaeus, 1760)

Range: Borneo (including both the Malayan and Indonesian sections, though it is absent from the southeastern portion of the island).  Fossil evidence suggests that the species was once present across much of Southeast Asia

Habitat: Old-Growth Lowland Rainforest (Primary and Secondary)

Diet: Fruit (about 60% of diet), Leaves, Shoots, Flowers, Bark

Social Grouping: Males solitary and territorial.  Females also largely solitary, but may congregate around food sources

Reproduction:  No set breeding season, but females tend to be more fertile during periods of plentiful food. Gestation period is 9 months.  Almost always a single offspring is born, though twins have been reported.  For the first four months or so, the infant is carried by the female everywhere.  Females typically nurse for up to 6 years and breed every 6-8 years, the longest inter-birth interval of any mammal, with young remaining with their mother until the next birth.  Sexually mature at 10-15 years old.  

Lifespan: 35 Years (Average, Wild), 55 Years (Maximum, Zoo)

Conservation Status: IUCN Critically Endangered, CITES Appendix I, USFWS Endangered 

• Males have an average height of 97 centimeters and weight of 87 kilograms (extreme record is over 200 kilograms); females are 78 centimeters tall on average and weigh 37 kilograms.  Both sexes have long arms (up to 1.5 meters long), prehensile feet, and throat pouches, though those of the male are larger than those of the females 
•  The skin is grey, covered with coarse, shaggy red fur.  The face is not furred, though some individuals have a beard or mustache
• Males have two different adult forms.  Some males are flanged – much larger than females (about twice the size) and possessing large, flat cheek pads and larger throat sacs, as well as a crest where the muscles are anchored.  Unflanged males more closely resemble adult females.  Flange status may have to do with dominance and social status, as unflanged males may develop flanges as they get older and stronger, though either may breed
• Diurnal and arboreal (the largest arboreal animal in the world), rarely coming down to the ground.  Generally solitary, but small groups of females may travel together or congregate around plentiful food sources.  Spend the nights sleeping in platforms of vegetation made 15-20 meters off the ground
• Juveniles swing like gibbons, while adults move more slowly and cautiously.  On the ground they walk quadrupedally, on their fists instead of their knuckles.  Sometimes walk bipedally.  They cannot swim, and as such rivers form boundaries to their distribution
• Males can make a loud, 1-2 minute call to announce their presence to both rivals and potential mates; it can be heard several kilometers away.  Other sounds include a lip-smacking sound when in small groups, a fast-call during conflict, and screams when frightened
• Predation of small mammals, including other primates, such as slow lorises, has been observed
• Some orangutans have been observed eating soil, either to obtain essential minerals or to detoxify poisons in their food
• Adults have no significant predators.  Young may be taken by clouded leopards.  Bornean orangutans are seen on the ground more often than Sumatran orangutans, possibly due to fewer predators on Borneo
• Translated from Malay, orangutan means “Person of the Forest,” but is not the name that is used locally for the species – “Maias” or “Mawas” is used instead.  The genus name “Pongo” is from the Bantu for “large primate,” historically used for chimpanzees.  The species name means “pygmy” or “dwarf,” essentially translating as “dwarf chimpanzee”
• Tool use has been observed in the wild, including sticks to (unsuccessfully) spear fish, leaves to wipe feces, leaves as “gloves” for handling spiny durians, and branches as umbrellas
• First captive specimens outside of the native range was sent to a Dutch prince in 1640.  The first in England arrived in 1830 (surviving only two days), and Charles Darwin studied orangutans in the London Zoo (notably “Jenny”) prior to writing this On the Origin of Species The vast majority of the original habitat on Borneo had been lost to deforestation, originally for timber extraction, then for agriculture, especially palm oil plantations.  Habitat fragmentation makes it difficult for animals to move across the forest, decreases dispersal, and increases competition within forest fragments.  Habitat is also lost to fires
• Additional threats include harvesting for meat and capture for the illegal pet trade (rehab centers have been established to help restore rescued infants to at least some semblance of semi-wild status).  They are also sometimes killed as agricultural pests, with some plantation managers putting bounties on them

Zookeeper's Journal: Often overshadowed by the African greats apes – the gorillas and chimpanzees – the Bornean orangutan has always fascinated me.  I attribute this in part to how different it is from them.  Whereas chimpanzees are loud and boisterous and social, orangutans are mostly silent and solitary, moving deliberately through the trees.  Interestingly enough, much of what I thought that I knew about orangutans growing up ended up being false.  For one thing, they aren’t as solitary as was originally believed.  Zoos have long known that orangutans will live happily in group settings, similar to other apes, but observations by Birute Galdikas helped shed light on the surprisingly social nature of these apes in the wild.  From a zoo perspective, my fondest memories of this species date back to the opening of the “O-Line” at the Smithsonian National Zoo.  This innovative exhibit opened in the 1990’s, allowing apes to swing directly over the heads of zoo visitors as they traversed the distance from the Great Ape House to the Think Tank building.  When it opened, there were lots of doubts voiced about how it would work.  At worst case scenario, an orangutan would escape (or, slightly better, bomb visitors below with explosive feces).  At best, many thought that the apes wouldn’t use it.  To be honest, in the many times that I’ve visited National Zoo, I’ve only seen apes on the O-Line towers on a few occasions, and only seen them actually swinging and climbing a handful of times, perhaps less than a dozen.  Still, when I have seen orangutans in motion, it’s been incredible.  They seem so graceful and powerful that they show little resemblance to the sleeping red throw rugs that I usually saw heaped in an exhibit corner.