Orang-utan (Pongo pygmaeus)

Orang-utans inhabit rainforests in the lowlands of Borneo and Sumatra in the national territories of Malaysia and Indonesia. Two subspecies are known, the Borneo-orang-utan and the Sumatra-orang-utan, which differ in facial characteristics and colour of their fur. Orang-utans also inhabited Java but have been exterminated on that island because they were hunted by early humans. Orang-utans are the largest animals living on trees more or less all the time. Only adult males need to climb down sometimes when they are not able to change from one tree to another, because the branches are not strong enough to carry their weight. Living on trees protects Orang-utans from getting killed by their natural enemies, first of all the Tiger. Orang-utans spend also the nights on trees. They construct sleep nests - mostly a new one each evening -, which they roof over with branches to protect themselves against heavy rain. Orang-utans find their food on trees too. It's consisting of fruits and leaves for the larger part. But the Great apes don't refuse small animals either. So they also take ants and termites or eggs and young birds as well as squirrel nestlings. But their major food - fruits - have a dispersed distribution in the forest habitat, which forces Orang-utans to wander about in order to find enough to eat. Although the territories of adult males might reach an extension of about 10 sqarekilometres, the apes do only short distances each day. Wandering about is very energy consuming and exhausting for apes of that size. The much smaller Gibbons, inhabiting the same area, do much longer distances each day to find their food. How do the Orang-utans, in spite of investing not so much effort in searching for food, manage to find enough to eat? The most important reason is their great deal of intelligence. The few present sources of food are exploited very efficiently by Orang-utans. So they wander to the trees, where they expect food, using the most direct way. Intelligence tests revealed that young Orang-utans are partly more intelligent than Chimpanzees and Gorillas of the same age.

Orang-utans lead a solitary life. Adult males have a large territory, which normally includes smaller territories of several females. To mark their territory and show their position adult high ranking male Orang-utans give loud calls and sometimes emphasize them by breaking branches. Other males that entered the territory of a calling male mostly retire very quietly when confronted with such a spectacle. But the intrusion of a male Orang-utan into another male's territory may also lead to serious conflicts; many Orang-utan males have scars from bites or suffer from broken fingers. The calls of an adult male have another function too: They are attracting females that are willing to mate. They join the males and stay with them for several months sometimes. When they get pregnant, they leave the male Orang-utans and go on their ways. Like in humans, pregnancy lasts for about nine months. The baby stays close to its mother for about one year. During this time it is most of the time carried by the female. After that time the young Orang-utan becomes more and more independent and starts exploring its surroundings. But the child never goes far away from its mother. It is weaned at the age of three years or even later, in case no new young is born. The average interval between two births is six years in free living Orang-utans. Whenever young Orang-utans meet each other, they take the opportunity to play. Even the mothers join on such an occasion, but seldomly get into direct contact to each other. Such communities may stay together for some weeks before they split up and each small family goes on going its way again.

The Orang-utan is probably the most endangered Great ape at the moment. It's estimated that there are only 30,000 to 50,000 free living Orang-utans left. Nowadays the major reason for their disappearance is the destruction of their habitat. Large areas of rainforest are systematically converted to fields and plantations. The ways this is accomplished are not at all soft. An often used means is burning down parts of the forest. The devastating forest fires raging in 1997 and 1998 in Indonesia were caused by man. They had a fatal influence on the stocks of Orang-utans living in that area. A lot of Orang-utans were killed during the fires. Apes, which managed to escape the fires, had to migrate to areas, that were inhabited by other Orang-utans. This increased the population density and the social stress for the single Orang-utans. Although Orang-utans have been protected for decades their survival seems to be possible just in reserves and zoos. According to the current 25-years-plan the Indonesian government plans the conversion of 20 million hectares of rainforest to plantations and fields. Facing such a scenario, efforts to reintroduce Orang-utans, which were raised in zoos, seem to be hopeless. But these efforts, first of all forced by the biologist Biruté Galdikas, at least have the effect, that the Indonesian government establishes new reserves, in which the survival of the remaining Orang-utans seems to be secure.