Female Bornean orangutan with offspring. Photo credit: Marc Ancrenaz

Orangutans are dying. We’ve known this fact for a while now, but the rate of their decline is shocking. A study published in Current Biology estimates that more than 100,000 orangutans were lost on the island of Borneo from 1999 to 2015; that comes out to about 50% of all the Bornean orangutans in the world, lost in the past 16 years. Historically the main factor driving their decline has been habitat loss (jungles reduced to timber or farmland), but researchers found that in recent years, orangutans have come under fire from a far more sinister threat: the straight-up slaughter of orangutans, either for meat or because of conflict with villages and farmers.

“If you look at the overall loss of more than 100,000…about 70% is due to orangutans disappearing from primary and logged forests, which we think is mainly due to hunting and killing in human-orangutan conflict,” explained Serge Wich, professor at John Moores University and one of the paper’s co-authors.

Bornean orangutan. Photo credit: Marc Ancrenaz

“From previous studies, we know that hunting and killing has been a driver, and the declines we saw in our study supports the thesis that killing is one of the major drivers of orangutan loss,” said Maria Voigt, the lead author of the study and PhD candidate at the German Centre for Integrative Biodiversity Research and Max Planck Institute for Evolutionary Anthropology. Voigt went on to explain that one of the most troubling takeaways from the study is that many orangutan populations will likely cease to be viable in the coming decades. Bornean orangutans are spread across the entire island, which at about 290,00 square miles is roughly the size of Texas; so, while there are about 100,000 orangutans left alive, many are in isolated populations that aren’t able to interact with each other and therefore far less likely to survive under the continued pressures.

By projecting out current rates of deforestation and making assumptions based on population viability, Voigt and her colleagues estimate that 45,000 more orangutans will be lost over the next 35 years. “We found that of the 64 metapopulations that we considered, only 38 had above 100 individuals, and so were actually viable,” she explained. “Below that number, the natural mortality and inbreeding would cause the populations to decline.”


Graphic credit: Voigt et al

All of the world’s wild orangutans are found on just two islands in Southeast Asia: Borneo (with less than 100,000 orangutans) and Sumatra (with less than 15,000). For the past few decades, both islands have been under intense pressure from extraction industries, particularly industrial logging and palm oil production; about 40% of Bornean forests have been ripped up since the 1970's, and in Sumatra, about half of all rainforests have been lost in the past 20 years. Not surprisingly, the decline in suitable habitat have led to equally devastating declines in orangutan populations, leading all three species of orangutan to be listed as critically endangered.

Intersection of forest and palm oil plantation. Photo credit: Marc Ancrenaz


The plight of the orangutan has garnered international attention over the years, with public awareness campaigns increasingly directed against the use of palm oil (a product which is found in a wide range of items, from lipstick, to ice cream to instant needles). And while habitat loss remains an urgent threat to both species, conservation pressures have yielded some positive results. Much needed protections have been granted inside large national parks, and there are a variety of ongoing efforts to construct wildlife corridors to reconnect isolated orangutan populations.

But decreasing habitat loss will hardly yield positive results if the rate of orangutan hunting doesn’t decrease. The trickiest part about halting the killings is that they’re primarily driven by a desire for food; the indigenous people of Borneo have long hunted orangutan for meat, and a 2013 study found that hunting was the driving factor in over half of all orangutan killings. Wich believes that critical in saving the species will be persuading the people of Borneo to change their traditions. “Indigenious tribes might say they’ve been eating orangutans for thousands of years and so it’s a traditional right that they have; it can be difficult to argue with that, but traditions must sometimes change over time,” he said.

Of the orangutans not targeted for meat, the most common reason for killing was fear of orangutans or in self-defense. “Part of the effort to decrease the killing has to be to make people aware that it’s illegal to kill orangutans,” said Wich. “And part of it has to be to make people aware that orangutans are not actually dangerous animals; they’re big, and can look intimidating, but they don’t generally attack people.”


Bornean orangutan. Photo credit: Marc Ancrenaz

Despite the dire figures found in the paper (a 50% decline in the past 16 years, with projections showing another 45,000 orangutans disappearing in the coming decades), there are some hopeful signs of local conservation efforts that can bring about the change that’s needed. Voigt brought up the work of an NGO called HUTAN that works in Kinabatangan in Borneo, that has slowed the decline in orangutans by having teams monitor the region’s forest. “We’re finding that simply by having people interested nearby, whether researchers or conservationists, that can help conserve species,” she said.

Wich admitted that there likely isn’t a one-size-fits-all solution here, and yet he’s hopeful that through continued research, education and conservation pressure, the downward trend can be halted. “What we can do, perhaps not as individuals but as a society, is fund research and conservation efforts that try to tackle this hunting issue, and come up with expertise that might help to solve this issue,” he said.