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Fast Facts:

Sumatran Orangutan

Conservation

Threats to young orangutans: tigers, red dogs (found in Sumatra), clouded leopards, and large pythons.

Humans threaten the orangutans survival due to habitat loss and the pet trade. An estimated 20,000 orangutans are kept as pets in Asia. Orangutans are used in the entertainment industry for commercials, movies, and greeting cards.

Many projects are working to save orangutans. The American Zoo and Aquarium Association's SSPs (Species Survival Plans) are special programs designed by a team of zoo and wildlife professionals to help orangutans, and many other endangered species. The SSPs outline breeding plans, work to increase public awareness and education, help conduct research, and in some cases, organize programs to reintroduce captive-bred wildlife into secure habitats.

A handful of rehabilitation sites, such as Tanjung Puting National Park, in Borneo, help return orangutans to the wild after confiscation from smugglers or private owners. National parks and reserves on the islands of Sumatra and Borneo work to save orangutans and many other species. Field studies, such as the work conducted by Birute Galdikas in Borneo, help to increase our knowledge about these fascinating creatures and help insure their survival.

Special Features

• Adult female and male orangutans differ greatly in appearance. Female orangutans are about half the size of adult males. Dominant male orangutans develop large cheek pads or flanges. The cheek pads are composed primarily of deposits of subcutaneous fat.
• The word orangutan means "forest man" in the Malay language.
• Orangutans have large throat (laryngeal) sacs. The sac is most well developed in males and gives resonance to their long calls.
• The hands and feet of orangutans are well adapted for hanging from tree limbs. Their big toes, as well as their thumbs, are opposable. Their arms are 11/2 times longer than their legs and are very powerful.
• Orangutans are the largest truly arboreal animals.
• In spite of their bright orange-red coat, orangutans can be quite difficult to see in the dense rain forests.
•  Scientists have documented the use of tools in orangutans. The orangutans modified and used sticks to remove honey and insects from tree holes.
• Orangutans have 32 teeth, the same number as humans.
• Orangutans have been taught American Sign Language. One orangutan learned 150 signs.

Social Structure & Behavior

Orangutans are considered solitary or semisolitary. Mature males are primarily solitary. Females travel with their offspring. Subadult animals may associate with each other.

The lifestyle of orangutans differs from other great apes which usually live in large social groups. The large size and arboreal lifestyle of orangutans prohibit them from forming such groups; the treetops will only bear so much weight. Secondly, fruit is surprisingly scarce in the rain forest and therefore each individual orangutan must have a large area over which to forage. The territory of an individual adult male may overlap with the territories of several females. .

Orangutans have at least 18 vocalizations. Males give "long call' vocalizations. The exact function of these calls is unknown. They may serve to attract mates, announce the presence and location of a high-ranking male, or may express discontent on the part of the utterer (MacKinnon 416).

When males do occasionally meet they will exhibit aggressive displays--stare, inflate pouches, shake branches. If one male does not back down, they may grab and bite each other. (MacKinnon 415)

Orangutans sleep in the forks of trees where they pull in other branches to form a nest. Chimpanzees build similar nests, but orangutans differ in that they often build a roof out of branches to provide shelter from heavy downpours. They will usually find a new place to sleep and make a new nest each night. Orangutans will occasionally build daytime nests (MacKinnon 404).

Breeding & Caring for Young:
Females are sexually mature at 8-10 years of age, but may not give birth until they are 12 years of age or older. They give birth every 6-7 years and may be fertile until they are 30 years old. Males are sexually mature at 9-10 years of age.

The female estrous cycle is 30 days in length on average. Females are willing to mate throughout the entire month. They show no obvious external signs of estrus, as chimpanzees do with their swellings. When a female is ready to mate she will often seek out the male, listening for his long calls to help locate him.

Young males (8-10 years of age) often maintain relationships with females and mate with them. However, it is usually the older males who impregnate the females by associating with them for the few days when the female's willingness to mate is at its peak (MacKinnon 415).

Typically 1 offspring is born after a gestation period of 230-260 days. A newborn baby orangutan weighs 3.5-4.5 pounds on average. A young orangutan maintains constant physical contact with its mother for the first year of its life. It may occasionally encounter another young orangutan or may play with an older sibling, but usually its mother is its sole companion.

Young orangutans have few instinctive behaviors. (Many other infant animals have several instinctive behaviors.) Most of what orangutans need to know to survive, they learn by watching their mothers. At 2 years of age, a young orangutan will begin to leave its mother for short periods of time. However, it never ventures too far and still shares a sleeping nest with her.

Young orangutans are usually weaned at 3-4 years of age, however, some may nurse longer. Young orangutans typically spend 5-6 years with their mothers. When a male orangutan finally leaves his mother, he usually emigrates from his mother's home range. A young female orangutan will also establish her own home range, but it typically overlaps with her mother's range