A new survey indicate that about 150,000 Bornean Orangutans (Pongo pygmaeus) have been killed in the last 16 years

The Bornean orangutan (Pongo pygmaeus) is a critically endangered orangutan that is native to the (mostly) Indonesian island Borneo. These great apes are considered highly intelligent, and have displayed the use of tools both in the wild and in captivity. By sequencing their genome, researchers have discovered that they share about 97 % of the DNA with us humans, so they are a lot like us!

A male Bornean orangutan (Pongo pygmaeus). Image by Wikimedia user Eleifert, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

I have written about the Bornean orangutans in the past, so click here to check out my previous post about them.

As you might have guesses, these intelligent apes are threatened with extinction because of human activity, and a recently published paper has taken a closer look at this. For this research, a group of scientists led by lead author Maria Voigt decided to gather and make sense of all the knowledge we have about the Bornean orangutans. The basis of the study was applying previous knowledge with a big survey of orangutan nests to find out how many there are, how many get killed, and where they live.

You might have noticed that I said orangutan nests, and this is in fact not a typo. When orangutans sleep at night they bend long branches into a structure that looks like leafy baskets. A single nest will typically house either a lone orangutan, or a mother with offspring. These nests are really big, so the researchers have been able to identify them from helicopter rides, making it possible to sample big regions at a time.

This is an orangutan nest. Image by Rob and Stephanie Levy, posted with the Creative Commons Attribution 2.0 Generic license.

Since the start of the survey in 1999, the researchers have covered over 500 square miles in the Bornean forest to look for these nests. At the beginning of the study the scientists found on average 22 nests per kilometer they travelled. After 16 years, in 2015, the found only 10 nests in the same distance, and a clear trend of a population decline can be extrapolated from these data.

Why look for orangutan nests?

Some of you might wonder why they are looking for orangutan nests, and not just going into the jungle to count the orangutans themselves. Well, finding orangutans is extremely difficult. Despite their large size, these primates are very well-adapted to hide high up in the trees, and scientists could easily walk right below them without ever knowing. This method would be highly inaccurate, so therefore it is much better to count the nests they are using.

Image by Natalie S, posted with the Creative Commons Attribution 2.0 Generic license.

The results of the study

As mentioned, the number of nests have more than halved during the 16 year study period, and these data can be further extrapolated to give us a rough idea of how well the Bornean orangutan population is doing. By bundling the decreasing number of nests together with human population density, deforestation and rate of which orangutans are hunted and killed, the got some estimates for the population as a while.

Their estimates suggest that there were 148,500 more orangutans back in 1999 than it was in 2015. Some people were surprised by this result, because that is a much faster population decline than anyone had expected. However, it seems to match the rate of decline in both Grauer’s gorillas and western chimpanzee, so it is not unheard of.

The exact amount of wild Bornean orangutans left in the wild is uncertain, but the researchers believe it to be between 17,000 and 100,000. More research is needed, but as mentioned above, finding the exact numbers of orangutans that are alive can be really difficult.

Image by Thomas Quine, posted with the Creative Commons Attribution 2.0 Generic license.

Why are the Bornean orangutan population decline so fast?

The research is pretty conclusive about a huge population decline, so what do they think is the reason for this? One of the biggest problems for the Bornean forests have been the demand for palm oil, wood and other natural resources. Areas have been stripped down, and this has not only destroyed the affected areas, it has also created a phenomenon called habitat fragmentation where the habitat is divided into many smaller “islands” instead of a huge, continuous forest.

One of the biggest perpetrators for the decline is the palm oil plantations, but the researchers also believe that this is just a stepping-stone for the decline. They believe that this had led to easier access to the forest for humans, where they have hunted and killed orangutans, either to protect their crops, or to sell as bush meat. Either way, the researchers are pretty confident that we have been underestimating the amount of orangutans that are being killed directly by humans.

A palm oil plantation in Cigudeg, Bogor. I can totally understand why the orangutans don't want to cross these fields. Image by Achmad Rabin Taim, posted with the Creative Commons Attribution 2.0 Generic license.

Orangutans are slow to reproduce

One of the biggest problems with killing orangutans is that they are very slow to reproduce, and a single pair can go as long as 6 years between each time they give birth. This slow reproduction rate means that even killing just a few orangutans every year can have a big effect on the entire population, and we really need to stop killing any of them if we want to keep the species alive.

A mother with her offspring. Image by Bernard DUPONT, posted with the Creative Commons Attribution-Share Alike 2.0 Generic license.

There’s also a bit good news!

There has been lots of grim news so far, so let us end the post with a bit of good news. The orangutan populations that are living inside national parks on Borneo is doing very well, and have a stable population. This means that there is hope for humans to coexist with the amazing primate, and hopefully we will learn how to do so before it is too late.

More posts about orangutans

I’ve written a few posts about orangutans in the past, so click on these if you want more knowledge:

• Sumatran orangutans (Pongo abelii) have been found to plan their travel route ahead of time, and then share it with other apes to let them know.
• A new species of orangutan has been recognized, and it is already threatened by extinction.
• On the Brink of Extinction: The Bornean orangutan (Pongo pygmaeus); estimated 54,500 individuals left in the wild.

Thanks for reading

As always, thanks for reading, and make sure to follow the links in the post if you want to learn more about Bornean orangutans.

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