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The orangutan

The «woodman», or the orangutan as we know him, belongs to the genus of great apes that consists of three different species and only occurs in Asia. These large tree inhabitants mainly feed on fruits and have to travel long distances, roaming the rainforest in order to find food. They spend most of the time on their own, except for mothers and their young who remain together for a longer period of time. Loss of habitat and poaching are big threats to them, especially since all three species of orangutan are seriously threatened by extinction.

Distribution

Once, the orangutan was widely distributed, from the foot of the Himalayas all the way down to the islands of Sumatra, Java and Borneo. Climate change, agriculture and hunting heavily depleted its distribution. Ever since the 17th century, they can merely be found on Borneo and Sumatra. They especially live in the swamp rainforests and in the surroundings of rivers up to 1500 Meters above sea level. The numbers of orangutans in one certain area can change significantly over one year – depending on food supplies.

 

Appearance

Orangutans are easily distinguishable from other great apes by their scraggy-looking, red-brown coat. They are around 1.25 to 1.5 Meters tall. Males weigh between 50 and 90 kilogrammes, females are about half as heavy with 30 to 50 kilogrammes. Generally speaking, the orangutans of Sumatra are somewhat lighter than the orangutans of Borneo. They are very well adapted to climbing the treetops: Their arms are very long with a total arm span of 2.25 Meters, but their legs are relatively short, but very flexible. Their feet look like hands since their toes are quite long and their big toe is affixed to the tarsus.

Dominant males are clearly identifiable by distinctive cheek pads and a throat pouch that allows them to enhance their calls and make them audible over wide ranges. Female and non-dominant males have no cheek pads. The bulges above the eyes are quite small in comparison to other great ape species. Both sexes have a prominent bearded snout.

Lifestyle

Orangutan live high up in the treetops of the rainforest and hardly come down to the forest ground. While searching for food, they roam the forest for fruits and travel long distances. They spend the night in self-made nests. Orangutans are rarely seen in groups, only mothers and their young remain together over a longer period of time. However, they are no strict “loners”: Groups of orangutans are sometimes observed sharing a tree full of fruits and moving on to the next tree together. Neither males nor females are territorial, but travel long distances while foraging. If females settle down, they look for a territory which overlaps the maternal district. Males only settle down as soon as they can assert themselves against the dominant male that already lives there. They are easily recognisable by their cheek pads.

Orangutans reproduce quite slowly; even slower than most animals. Females go into heat for the first time when they are about seven to ten years old and give birth to a young once in eight years. A new-born orangutan clings to its mother for the first four months of its life. They accompany their mother until they are about four years old and learn everything from her to survive in the rainforest. Little by little, it distances itself from its mother until they go their separate ways at last.

 

Species of orangutan

In total, there are three species of orangutan: The Sumatran orangutan (Pongo abelii) and the Tapanuli orangutan (Pongo tapanuliensis) on Sumatra and the Bornean orangutan (Pongo pygmaeus) on Borneo. Being originally one species, 3.4 million years ago, the Sumatran orangutan split from the common ancestor of the Bornean orangutan and the Tapanuli orangutan. Subsequently the orangutan populations of Borneo and Sumatra split into two separate species: the Tapanuli orangutan and the Bornean orangutan.

All three species of orangutan look very similar. The Tapanuli and Sumatran orangutans are slender and have brighter hair than their relatives on Borneo. Apart from their appearances, they show differences in their behaviour as well: The orangutans on Sumatra spend less time on the ground than the Bornean orangutans. It is assumed this results from the fact that there are no tigers living on Borneo. The Sumatran orangutan is described as generally more social and the use of tools has been observed more often than with Bornean orangutans.

 

Threats

All species of orangutan are endangered. The biggest threat to them is the loss of habitat. On both islands, rainforest were cleared make room for agriculture: Every year, palm oil plantations and timber industry cause the destruction of great areas of rainforest as well as their inhabitants. In 2012, 840’000 hectares of rainforest were cleared in Indonesia alone, a district bigger than the canton Grisons. Not only the habitats of orangutan disappear entirely, but the remaining rainforest is being divided into small fragments where orangutans and other animals cannot thrive anymore.

In addition to the disappearing habitats, poaching is a big problem for the orangutans. The animals wander into the plantations as their habitats shrink. The farmers fear for their crops and hunt the orangutans down. Young orangutans are valuable assets to be sold at high prices as «pets» on the black market. In order to get hold of an orangutan-baby, in most cases the mothers are are to be killed. Most young orangutans die from stress during the transport or illnesses and malnutrition while being held in captivity. Due to the fact that orangutans have a long reproductive cycle, every killed orangutan increases the risk of extinction of these great apes.

The threats are shown in the figures as well: It is assumed that the numbers of Sumatran orangutan have gone down by 80% in the last 75 years. Today, the remaining populations are estimated to consist of 14’000 individuals. The worst case concerns the Tapanuli orangutan: When the species was defined in November of 2017, their populations were estimated to consist from only 800 specimens. Therefore, the Tapanuli-orangutan is the most endangered species of great ape in the world. If nothing is done against the clearings of the rainforest and poaching on Sumatra and Borneo, we assume that orangutans will be extinct by 2030.

 

WHY PROTECT THE ORANGUTAN?

The orangutan is a so-called «umbrella species» or «patron species». Orangutans require high standards in terms of the size and quality of their habitat. Therefore, lots of other species of animals and plants that share the great apes’ habitat profit from protecting the rainforest.

In return, the orangutan is as important to the rainforest as the rainforest is to the orangutan. He is not called «the rainforest’s gardener» for no reason: By swinging through the treetops he breaks off dead branches from the leafy canopy and therefore allows the sunlight to reach the ground, which then helps many rare plants to grow. Furthermore, they devour a lot of fruit and along with it, the seeds. These seeds are being defecated during the orangutan’s patrols and therefore widely spread throughout the rainforest. Especially plants with large seeds, like stone fruits, depend on the orangutan because without him, they cannot spread. And so the orangutan is of great importance for the preservation of the biodiversity in the rainforest.