By Deborah Ciszek and Maija K. Schommer
Geographic Range
Bornean orangutans (Pongo pygmaeus) currently inhabit only the island of Borneo, excluding the southeastern portion of Borneo. Fossil evidence indicates that their past distribution included much of Southeast Asia. Pongo pygmaeus was until recently considered the only orangutan species. Sumatran orangutans (Pongo abelii) are now considered a separate species.
Other Geographic Terms:
island endemic 
.
Habitat
Bornean orangutans are only found in forested areas, but can be found in various types of forests, from low-level swamps to mountainous areas 1500 m in elevation. They can be found at various heights in the trees. They may move large distances to find trees bearing fruit.
These animals are found in the following types of habitat:
tropical ; terrestrial .
Terrestrial Biomes:
forest ; rainforest ; mountains .
Physical Description
(66 to 198 lbs)
(4.92 ft)
Bornean orangutans are sexually dimorphic. Females range from 30 to 50 kg, whereas males are from 50 to 90 kg. Head and body length is about 1.5 meters and the arms have a spread of about 2.2 meters. They have a thin, shaggy coat that is reddish brown in color. Males have large cheek pads, which are made up of deposits of subcutaneous fat bound by connective tissue. These cheek pads continue growing for much of an adult male's life. Orangutans have a high, sloping forehead and a bulging snout. They have short, weak legs, but strong hands and arms.
Some key physical features:
endothermic ; homoiothermic; bilateral symmetry .
Sexual dimorphism: male larger.
Reproduction
The interbirth interval is about 4 years
Breeding occurs throughout the year.
Bornean orangutans are polygynous. Although mainly solitary, the home ranges of males overlap those of females. On the rare occasions that the females within their home ranges are sexually receptive, dominant males will mate with them. Younger, smaller males, which are not able to maintain home ranges of their own, often wander alone through the forests. These males may also mate with females, although such copulations are generally forced, and appear to occur as the opportunity arizes, not because the female is sexually receptive or fertile.
Mating systems:
polygynous .
Female Bornean orangutans have an estrous cycle about 30 days in length with ovulation occurring around the 15th day. This species does not have genital swelling during estrous, and females have a light menstrual flow lasting 3 or 4 days. Copulation is usually done with the male and female facing each other, each hanging by the arms from a tree branch. Gestation can take anywhere from 233 to 263 days, and typically one offspring is born, although twinning sometimes occurs. Weaning occurs around 42 months, although the timing of this may be affected by habitat quality. The interbirth interval is about 4 years, but can be much longer if conditions are poor. In females, sexual maturity is reached at 7 years of age, by which time females have attained their adult size. Males, however, continue to grow until they are 10 years old, and do not have the physical and social maturity required for successful mating until about 14 years of age.
Key reproductive features:
iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous .
Newborn infants weigh around 1.5 kg. Babies nurse every 3 to 4 hours, and begin to take soft food from their mothers' lips at age 4 months. A young orangutan clings to its mother's abdomen by entwining its fingers in and gripping her fur until it is a year old, then it begins to ride on her back, which it may continue to do until 2.5 years of age. An infant will scream loudly if separated from its mother. The young are not weaned until they are 3 1/2 years old.
Parental investment:
pre-fertilization (provisioning, protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (provisioning: female, protecting: female); extended period of juvenile learning.
Lifespan/Longevity
All of the great apes live a long time. In captivity, Bornean orangutans may reach the age of 60 years, although the lifespan in the wild is probably shorter.
Behavior
Bornean orangutans do not form large social groups. Individuals usually travel alone or in small groups consisting of 2 females, their dependent young, and occasionally an adult male. Generally males and females come together only to mate, and otherwise do not associate with one another. Males' home ranges are often 2 to 6 sq. km. in size, and overlap the ranges of several females but not usually those of other males, toward whom they are aggressive.
Bornean orangutans are active during the day (diurnal) and are almost exclusively arboreal. They can be found at various levels in the trees. They locomote by walking along and swinging from branches, descending to the ground only if they cannot move between trees via the branches. Each night they construct, using vegetation, a platform-style nest 40 to 60 feet high in a tree on which they sleep. They may descend briefly to the forest floor to obtain branches for building these nests. They cannot swim.
Communication and Perception
Bornean orangutans have a vocal repertoire of about 13 sounds. Within a small social group they communicate with lip smacking. They scream when scared, and males sometimes roar. They seem to grind their teeth when frustrated. Males also emit a long series of loud groans, which can be heard by a human up to 1 kilometer away. This vocalization may serve to space males apart.
In addition to vocal communication, tactile communication is used by these animals. Social grooming is an important activity in all primates. Facial expressions, gestures, and body postures are also used to communicate.
Food Habits
The diet consists mainly of fruit, especially figs. Various species of figs ripen at different times in the year, and the movement pattern of the animals can largely be explained by their following this process. Bornean orangutans will also eat other kinds of vegetation, such as leaves, bark, buds, and flowers. They will also occasionally eat mineral-rich soil, insects, and possibly eggs and small vertebrates. They drink by reaching into tree holes and lapping water from their hands.
Animal Foods:
eggs; insects.
Plant Foods:
leaves; wood, bark, or stems; fruit; flowers.
Predation
Bornean orangutans fall prey to humans. Large snakes and raptors may take young orangutans.
Ecosystem Roles
Becuase they are frugivorous, these animals play some role in seed dispersal.
Key ways these animals impact their ecosystem:
disperses seeds.
Economic Importance for Humans: Negative
Bornean orangutans prefer many of the same types of fruit that people do, but their numbers are so small now that this is normally not a significant problem for human food production. Attacks on humans occasionally occur.
Ways that these animals might be a problem for humans:
injures humans (bites or stings).
Economic Importance for Humans: Positive
Bornean orangutans provide increasing economic benefits on Borneo by attracting "eco-tourism."
Ways that people benefit from these animals:
ecotourism .
Conservation Status
Bornean orangutans populations have been declining in both range and numbers for many years. The species is now in danger of becoming extinct. Humans have a long history of hunting this particular primate for various reasons, more recently for exhibition in zoos. It is estimated that at least 3 orangutans die for each one that is successfully captured and transported. They are now protected by law, but poaching still occurs. The population is currently being further devastated by the destruction of their habitat through deforestation, mainly for logging purposes.
For More Information
Find Pongo pygmaeus information at
Contributors
Deborah Ciszek (author), University of Michigan. Maija K. Schommer (author), University of Michigan.
Nancy Shefferly (editor), Animal Diversity Web Staff.
