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A new survey of orangutan nests in Sumatra has yielded a surprising discovery: There are more apes living on the island than we previously thought.

Sumatran Orangutan

Sumatran orangutan in a tree (Source: Creative Commons)

“Positive news about Sumatran orangutans is rare,” researchers write in the peer-reviewed journal Science Advances. Once found across southeast Asia, the great ape now lives only on the islands of Sumatra and Borneo. The orangutan’s population has been critically endangered over the last century, the trees that it relies on for shelter torn down to feed the region’s rapacious logging industry.

The last survey of Sumatra’s orangutans was made in 2004 and put the remaining apes at about 6,600. In 2015, a new survey was conducted and found that the orangutan population is more than twice that size.

In their article in Science Advances, researchers explain the jump in population is due to more complete data. In other words, these apes were living where no one had looked for them before. Orangutans were found at higher elevations than their estimated range (in regions not previously surveyed); they were found more widely distributed in logged forests; and in areas west of Toba Lake (also previously unsurveyed). The new population count for Sumatran orangutans is estimated at 14,613.

Chomel, a Sumatran orangutan, at Singapore Zoo, 2009. (Photo Credit: Lionel Leo via WikiMedia Commons)

Chomel, a Sumatran orangutan, at Singapore Zoo, 2009. (Photo Credit: Lionel Leo via WikiMedia Commons)

Good News, but No Cause for Celebration

Don’t mistake this good news for proof that orangutans are thriving. In their report, ecologists emphasize that this new estimate is due to improved survey methods, which do not render the apes any safer from poaching and habitat destruction.

“Since 2004, Sumatran orangutan numbers have undoubtedly declined, and they continue to do so at an alarming rate because of ongoing deforestation and poaching/persecution,” researchers write in Science Advances.

“The threats to the forest are as real as ever and the predictions we make in the paper for the future indicate that in all the scenarios we considered there will be continuing decreases in orangutan numbers over the coming years,” said Serge Wich, professor of primate biology at Liverpool John Moores University and lead author of the study.

The researchers calculate that current scenarios for future forest loss will see as many as 4,500 orangutans killed in the next 14 years. In their paper, they urge developers to draw up environmental impact assessments that conform with current national and provincial legislations to reduce or avoid further endangerment of orangutans.

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