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Learn to recycle, reduce, reuse and revere with Environmental Resources from Gale

Sumatran Orangutan

Orangutan photo courtesy of the San Fransisco ZooPongo abelii

Status: Endangered
Listed: June 2, 1970
Family: Pongidae (Primates)
Description: Large primate with long, shaggy hair, colored orange, brown-orange, or black. Face is pale when young, darkening as the orangutan ages.
Habitat: Tropical forests.
Food: 375 varieties of foods, including fruit, vegetation, insects, and small animals.
Reproduction: Gestation is one of the longest among primates, 260 to 270 days, usually resulting in a single birth.
Threats: Loss of habitat to logging and agriculture; hunting; collecting for zoos.
Range: Indonesia: Sumatra


The orangutan formerly included two subspecies, but Pongo abelii has been elevated to a full species. Pongo abelii lives on Sumatra, and Pongo pygmaeus lives on Borneo. The Sumatran species has fairer hair color than the Bornean species, with black-haired orangutans seemingly rarer than on Borneo; the black hair is often reddish. In addition, the Sumatran species has longer hair than its Bornean relative. It has a longer face and a thinner, lighter build than the Bornean species. Like that of the Bornean orangutan, the face of the Sumatran darkens to black as it ages, although it seems to remain somewhat paler than the darkest faces among the Bornean species. Most orangutans have orange hair, which has led to their common nickname, "the red ape." Their hair color varies from one orangutan to another, and the hair can be brownish and is sometimes black.


The Sumatran orangutan is a solitary animal requiring large tracts of land with sparse populations. The center of the Sumatran orangutan's society is the dominant male, a large, mature male over ten years old. It probably takes over the territory of its father. Once it has secured its territory of several square miles, it makes great, booming calls, using its throat sack to give the calls resonance. Explorers have reported that the call can be startling and even frightening; still, all the territorial male is doing is letting other males know that it lays claim to a certain area and letting them know where it is-helping them avoid direct confrontations. Within the dominant male's territory are several female territories; these belong to mature females over seven years old. These are the females with whom the dominant male mates, probably because mature females have the best chance of successfully bearing and raising their young. Adolescent and younger females are usually left alone by the dominant male. The mature females prefer to mate with the dominant male and will try to fight off the advances of other males; this is probably because the dominant male offers the best protection for their young. The dominant male will protect both mother and child from other orangutans and predators. The fully mature male is both very strong and very protective. Sexual unions involving dominant males are entirely consensual; the dominant males do not commit rape. The dominant males prefer to mate infrequently and only with fully mature females. This behavior puzzled observers for decades; young males mated far more than old males, which would make it seem that the young males were likelier to sire young than the supposedly dominant males. Some naturalists thought that the old territorial males did little other than bellow at each other, without producing young of their own. More recent work shows these ideas to be mistaken. For one thing, the rapes hardly ever result in pregnancy; for another, the young males tend to mate with immature females that are unlikely to become pregnant. In the unions between mature orangutans, the female is an active, willing participant; this enhances the chances that she will become pregnant.

The mothers are the primary caregivers for their young. For the first year of its life, the youngster holds tight to its mother, never leaving her physical touch. As it matures, the youngster leaves its mother to find food and eat on its own or to find playmates near its own age. Adolescence arrives at about seven years of age for males and somewhat earlier for females. Adolescent males are rambunctious and eager for sexual activity. Females prefer to mate with older males and tend to resist the advances of adolescent males; this can result in rape, with the female struggling against the violent sexual union with the young male. Females usually do not become mothers until they are over ten years old; in their teens, males begin to settle down.


Orangutans of Sumatra once lived in large tropical forests. They are now restricted to remote mountainous regions and a few swampy areas.


The Sumatran orangutan has long lived in the highland forests of Sumatra. In the last thirty years, logging and especially agriculture have destroyed most of its habitat, and its range is now restricted to a few wildlife reserves and patches of highland forest.


Slash-and-burn agriculture is responsible for most of the destruction of the Sumatran orangutan's forest. This old practice has been forcing the forests into retreat for centuries, but, like much of the rest of the world, Sumatra has had a boom in its human population, accelerating the process of deforestation to the point that most of the forest has been eliminated in only a few decades. The Indonesian government has met with a great deal of frustration in its efforts to save what is left of its natural heritage. It made it illegal to sell timber from the forests, so local people chopped down the trees and burned the timber, stubbornly continuing to clear the land for farming. Elsewhere, the slash-and-burn mode of agriculture continues, with people setting fire to the forests. In any case, the farming is primitive, with no thought to preserving the land; after a few years, a cleared plot of forestland has been depleted of its nutrients and eroded so badly that it cannot support most plant life. Observers say these areas in what was once the forestlands of orangutans look like desolate, blasted heaths.

Logging is also a significant factor in the decline of the Sumatran orangutan. The animal is sometimes treated as a pest by loggers; where the orangutans live naturalists press for restrictions on logging, and some logging companies, therefore, kill the orangutans, eliminating one of the important reasons for halting their work.

Between agriculture and logging, the Sumatran orangutan has lost nearly all of its range. This has resulted in the isolation of individual orangutans from other ones because their forests have been broken up into small patches, and it has resulted in a decline in the fertility of the orangutans. Apparently, the orangutans have a mechanism for regulating the size of their population according to how much range is available to them; as the range has shrunk, so have the number of births as a percentage of the remaining population.

The Sumatran orangutan is also severely threatened by hunting. Mothers are killed and their babies sold to exporters who sell them as pets in America, Canada, Europe, and other industrialized regions, and orangutans of all ages are sold to medical researchers. Orangutans are also purchased for use in zoos, circuses, motion pictures, and television. Penalties for poaching orangutans are high in Indonesia, but just one orangutan can earn a poacher the equivalent of a year's wages for most of his neighbors, and the animals earn importers several tens of thousands of dollars in Canada, Europe, the United States, and elsewhere. In the United States, the penalties for importing orangutans are high, increasing the price of illicitly imported orangutans greatly.

Conservation and Recovery

Indonesia has established wildlife reserves on Sumatra, but maintaining these reserves has proven to be a daunting task. Some reserved areas are open to tourists and have proven to be a significant attraction for foreigners and their international currency, which helps pay for the maintenance of Sumatra's reserves. If the Sumatran orangutan is to survive, the destruction of its forests must stop altogether. This is a matter of urgency; not all areas are well patrolled, and thus, even the reserves are disappearing to logging and agriculture. Soon, there will not be enough forest remaining to support a viable breeding population of orangutans.

The orangutan breeds well in captivity, and zoos and wildlife parks have had good success in maintaining their orangutan populations. The problem for the Sumatran species is that it has been crossbred with the Bornean orangutans; therefore, it is not a distinct species as it is in the wild. If the wild population disappears, as seems likely, then the Sumatran species will probably cease to exist.

Source: Beacham's Guide to International Endangered Species, Gale Group. 1998.

Orangutan photo courtesy of the San Fransisco Zoo.

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