Borneo Has Lost Half of Its Orangutans in Recent Years—But There’s Still Hope

The author of a new study says the island’s primates could rebound if deforestation and hunting can be contained.

February 20, 2018
A five-month-old female Bornean orangutan with her mother

Jon Nazca/Reuters

Just three months after scientists discovered a new species of orangutan on Sumatra, a new study estimates that the nearby island of Borneo has lost around half of its native orangutans in 16 years.

This is particularly bleak news considering that the Bornean orangutan is already considered critically endangered by the International Union for Conservation of Nature. Experts estimate that only around 100,000 of the frizzy orange primates remain.

Now, that might sound like a decent number of orangutans, but according to Maria Voigt, an environmental biologist with the German Centre for Integrative Biodiversity Research, it’s misleading to look at the population figures out of context.

In reality, Bornean orangutans are broken up into 68 different “metapopulations.” That means they are separated from other orangutans by things like rivers (which they can’t cross), wide roads, and areas without trees. Out of those 64 metapopulations, only 38 are what the scientists deem viable, meaning they have 100 or more animals. “We shouldn’t be thinking, ‘Oh, everything’s good, we still have that many left,’” says Voigt, lead author of the new report, published last week in the journal Current Biology.

In addition to deforestation for palm oil cultivation, Voigt and her coauthors learned that one of the biggest threats to the island’s orangutans over the past decade and a half has been hunting. In fact, of the 100,000 orangutans lost in the past 16 years, the majority died that way.

A large, male Bornean orangutan can stand nearly 4.5 feet tall and weigh up to 220 pounds. That’s a heckuva lot of protein. In addition to being killed for their meat, orangutans can run into trouble when they raid village orchards and gardens. In these instances, people may shoot them or cut down the trees in which they’re hiding.

These sorts of killings add up, says Voigt, who also works with the Max Planck Institute for Evolutionary Anthropology. Orangutans require up to seven years to raise one offspring. So if you have a thousand villages and each kills just one orangutan a year, that’s enough to trigger a population collapse. The animals can’t physically replace the numbers being lost fast enough, she says.

There are also reports of young orangutans being sold into the pet trade. And while Voigt says there aren’t really any good numbers to say how prevalent the practice is, it can be doubly damaging when it does occur since the mother orangs are usually killed to get to their young. Mature females are the most important demographic for rebuilding populations.

To be clear, deforestation is still an enormous problem in this part of the world. And Voigt says it isn’t so much that deforestation has stopped causing orangutan deaths in Borneo, just that a lot of that damage had already been done by the time of the current study.

While the outlook is certainly grim for this charismatic cousin to humans, with whom we share 97 percent of our DNA, the researchers recommend that conservationists continue to develop partnerships with the logging companies that own much of the remaining orangutan habitat in Borneo. There’s some evidence that orangutans can persist even when their forests are encroached upon—so if the loggers can be persuaded to leave enough habitat intact, there’s a chance the species will be able to hold on.

One thing is certain, says Voigt. If Borneo turns into shore-to-shore palm plantations, the orangutans will not survive. But if the killing and deforesting were to stop today, the 38 largest metapopulations of Bornean orangutans would have a good shot at increasing their numbers. What’s more, there are other stretches of forest on the island that probably used to support orangs, and still could, if there were ever enough to colonize new areas.

In other words, as long as there’s habitat, there will be hope. 


onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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