Orangutans and other primates

The primates of Bukit Lawang…..and beyond!

Humans are primates. You are a primate! There are an unbelieveable eight species of primate in and around Bukit Lawang which is actually one of the highest densitys of primate anywhere in the world! Unfortunately most of them are endangered! Look out for them when you are trekking or even just chilling out at Green Hill. Each species is fascinating and you can use this opportunity to compare and contrast several different species. You can not go anywhere else in the world and see this number of different primates..and Thomas Leaf Monkeys are ONLY found in North Sumatra!! click here to read an article on exactly what is a primate.

Actually…..there are NINE! A few years ago we spotted an unusual looking species of leaf monkey close to the Simolap Hot Springs which has been identified as a Black Sumatran Langur (Presbytis sumatrana). It was a rare sighting as it was at the top of its suspected range and our photos have since been published in two field guide books and on a well respected identification website.

ORANGUTANS

Orangutans are the only great ape found in Asia. They are now only found in isolated fragments of forest on the islands of Borneo and Sumatra. Orangutans found on these two islands look and behave differently and are different species:

Sumatran orangutan, Pongo abelii
Bornean orangutan, Pongo pygmaeus.
Tapanuli orangutan, Pongo tapanulensis

Orangutans have many characteristics which make them unusual :

relatively solitary lifestyle

rarely observed in groups bigger than two or three individuals.
Usually you will see orangutans in group of a mother and one or two offspring or a male and female orangutan engaged in consort ship.
Bornean orangutans spend approx 5% of their time with others
Sumatran orangutan form feeding groups and may even co-ordinate movements between food sources = travel parties.

Orangutans spend 95% of their time high in the forest canopy and have many adaptations for this lifestyle.

hands and feet are hook like with curved phalanges
short but highly opposable thumbs / big toes.
rotatory joints and an extremely mobile hip joint
they move by “quadrumanous scrambling” (on all four limbs) and tree swaying

Look out for these things when you see them in the forest!

Male and female orangutans look different.

A fully adult male (80-100kg) is almost twice the size of a female.

There are two distinct types of sexually mature adult male (bimaturism). The most impressive is large (80kg) and has big fatty cheek pads, a long coat of hair and a pendulous throat pouch to amplify their “long calls”.

The second type of male is smaller and does not have these secondary sexual characteristics. They are often called sub-adult but this is misleading: they are fully adult and perfectly capable of siring offspring and a particularly distinguishing characteristic has been their propensity for engaging in forced copulations.

Female orangutans

• Weigh approx 40 kg
• Sexually mature at around 8 years; first birth approx at 15 years.
• Give birth to a single offspring with an inter-birth interval of 8 years, which is the longest interbirth interval for non-human primates.
• Offspring stay with mother for up to 8 years to learn how to find food and survive in the forest.

Diet

Orangutans can have an extremely varied diet and have been documented to eat up to 300 different plant species and more than 150 different fruits. Because of their large body size, they require a lot of calories which they can get from high energy ripe fruits.

They can spend 100% their time eating fruit when it is available but when it isn’t they eat lower quality food e.g. bark, flowers, leaves, shoots, insects.

** the following section is currently being updated to reflect changes on the last ten years **

Why the orangutan and its habitat are important
Orangutans eat a lot of fruit = disperse seeds in the forest = effect pattern of forest regeneration and plant species diversity.

Tropical rainforests are an extremely important resource for local communities and they provide services such as a regular supply of fresh water and erosion and flood control. On a global scale they are crucial for the regulation if climate control. Tropical peat swamp forests are one of the largest global carbon stores. Forest destruction and drainage of the land releases massive amounts for carbon dioxide.

Threats
The biggest threat to the continued survival of orangutans is the destruction of their forest habitat by humans!

The main cause of habitat destruction has been illegal logging both legal and illegal but now the biggest cause of habitat loss is the conversion of the forest for the unsustainable development of palm oil plantations. Palm oil is not necessarily 'evil' it is more so the fact that rainforest is destroyed in order to make plantations...when they could be developed on different land.

The capture of young orangutans for the pet trade is fuelled mostly by orangutans found on landthat is cleared for conversion to palm oil plantations. A mother orangutan has to be killed in order to get her baby as she will never willingly give it up, even to protect herself. Although it is an offence under Indonesian law to possess an orangutan they are often kept as pets by local politicians and military/police personnel illegal trade.

Illegal mining: (alluvial gold, silica, quartz) is now a major threat to Indonesia’s national parks. ‘Legal’ mining also presents a major problem because large international mining corporatins lobby the government for concessions in national parks.

Forest fires (to clear land for palm oil plantations) have had a devastating effect on orangutan habitat. During the terrible fires of 1997-98 the orangutan population of Borneo decreased by 33% in one year! forest fires Human induced, uncontrolled.

In an attempt to combat global warming and climate change it has been suggested that palm oil can be used as a biofuel BUT the amount of carbon dioxide released by converting forest to industrial plantations is 10 times that released by burning fossil fuels.

Scientists estimate that 98% of Indonesia's forests will be destroyed by 2022 and Greenpeace estimated that Indonesia destroys about 51 square kilometres of forests every day, equivalent to 300 football fields every hour.