When scientists identified the Tapanuli orangutan as its own species in 2017, it immediately became the world’s rarest great ape. A survey suggested there were fewer than 800 remaining. The animals had already been pushed into a forbidding mountainous territory about the size of Los Angeles in northern Sumatra, and were hemmed in by human settlements, a gold mine and a hydroelectric dam that had just begun construction. The outlook was not good.

Now, a pair of new studies indicate there were even fewer of the arboreal apes remaining than previously thought and that its population was decimated by a rare equatorial cyclone that tore through Sumatra in November.

In July, scientists published a survey estimating the total population of Tapanuli orangutans in the low 700s. While the previous estimate placed the number in the high 700s, the difference may reflect better survey techniques rather than an actual decline in population.

But the new survey was conducted from 2021-2023, before the cyclone caused widespread flooding and landslides that devastated the Batang Toru ecosystem, the orangutan’s home. A peer-reviewed paper that was published in June determined that landslides wiped away some 32 square miles of forest within the orangutan’s prime habitat, killing an estimated 58 individuals.

Taken together, the studies suggest there are likely about 650 Tapanuli orangutans left.

“It looks bleak,” said Serge Wich, a professor in primate biology at Liverpool John Moores University in the United Kingdom and a co-author on both studies. The animals that remain, he added, live across a fragmented forest that is still being cut down as roads, farms and the dam and mine continue to encroach. “All these things combined made a real alarm bell go off in my head.”

Scientists and environmental advocates had fought hard to block construction of the dam, which is owned, financed and being built by Chinese state-owned enterprises. Some of those who opposed the dam lost their jobs or, like Wich, were barred from working in Indonesia’s national parks. One person died under suspicious circumstances. But the construction continued.

Read the full article about Tapanuli orangutans by Nicholas Kusnetz at Inside Climate News.