OLL LEWIS: The Sumatran Orang-utan

Whilst there is still no news from Sumatra, Oll is hard at work looking at the forteana of that strange island...
Although the CFZ Sumatra expeditions focus mainly on Sumatra’s cryptid ape, the Orang-pendek, Sumatra’s better known ape, the orang-utan, is in many ways just as fascinating.

The Sumatran orang-utan, Pongo abelii, is critically endangered and although once widespread is now thought to be only found in two locations in the North of the island. However, In the last CFZ expedition to Sumatra the team found hairs, which were found to be orang-utans by DNA testing, much further south, which may mean that there are still some small pockets of Sumatran orang-utan populations that, like the Orang-pendek are undocumented by science. In the two known population centres a survey was conducted in 2004 which estimated that there were around 7,300 individuals left in the wild. Because of habitat destruction and illegal hunting it is highly likely that the numbers of orang-utan left in the wild have decreased in the seven years since the survey was taken. Sumatran orang-utan populations do not cope well with changes to their environment or ‘predation’ by humans because they do not have a very high birth rate. Female orang-utan become fertile at around 15 years of age and the average period between births for the Sumatran Orang-utan is 9.3 years, which is the longest of all the great apes. This is likely to be one of the main reasons why orang-utans show a great deal of parental care, a baby will stay close to its mother for about three years, which is a comparatively long time even among primates, and is thought to recognise its mother, children and other close family members for its whole life, making orang-utan groups fairly close knit communities.

Sumatran orang-utans have, unlike the Borneo species, been observed using tools. In the Suaq Balimbing swamp orang-utans have been seen fashioning devices to get termites out of termite mounds and honey from hives. The device is made by snapping off a tree branch about 30cm in length and striping any smaller branches and leaves from it. The orang-utan will then fray one end of the branch to stick into the mound or hive to collect their delicious meal. This shows a great deal of ingenuity and intelligence on the orang-utans part to actually make a tool by manipulating their environment rather than just picking up any old twig from the ground to prod into a termite mound as some tool users do. In another instance of tool use the orang-utans have been observed using a stick to remove the sharp hard fibres that surround fruit from neesia trees, making it safe to eat. Most animals that use tools will also only use tools in the pursuit of food, and it is perhaps a further sign of the intelligence of orang-utans that they will also use tools in order to make their life more comfortable. One example of this is that Sumatran orang-utans have been observed, and filmed, breaking off large waxy leaves from plants to use as umbrellas in rainstorms. It would be a real tragedy if we were to loose such a fascinating and amazing creature.