Four Days Of Rain Tragically Kills 7% Of World's Rarest Orangutan In Indonesia

Nearly seven per cent of the world's rarest great apes have been tragically wiped out by four days of extreme rain and landslides in the Indonesian island of Sumatra. 58 of less than 800 critically endangered Tapanuli orangutans were killed last November as a result of an extreme weather event when the North Sumatra province witnessed more than 1,000mm of rain, according to a new study. The rare Tapanuli orangutan was only discovered in 2017, but researchers fear it could be headed for extinction.

By combining population density estimates with satellite analysis, researchers mapped the exact toll of Cyclone Senyar on the population of Tapanuli orangutans. This combined data revealed exactly where and by how much the storm's landslides and flooding devastated the apes' primary West Block habitat.

"In November 2025, an extreme, multi-day rainfall event triggered widespread landslides in the West Block of the Batang Toru ecosystem, the orangutan's largest remaining habitat area," the study published in Current Biology highlighted.

The researchers highlighted that the current death numbers are conservative, as they do not take into account rain-induced canopy damage or reduced food availability

"The loss of these estimated 58 individuals represents a major shock to the viability of this Tapanuli orangutan population. Potential mortality caused by other effects, such as rainfall-induced canopy breakage and reduced food availability, has not been included and makes the estimate conservative."

Even a marginal increase in mortality or decline in habitat quality can trigger a population-level decline among Tapanuli orangutans, the researchers explained.

"Because the species' persistence hinges on near-zero mortality and the maintenance of stable, high-quality forest, the scale of habitat destruction documented here indicates that current conservation safeguards are insufficient to ensure long-term viability."

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The Indonesian government has temporarily paused all major industrial activity in the Batang Toru area to allow scientists to investigate how best to secure the long-term survival of the Tapanuli. However, scientists believe it would require something more solid and permanent to ensure the species' survival.

“It is tragic to lose so many apes in this way. In landscapes where populations are small and fragmented, this type of weather or climate event can have population-level consequences. It is extremely worrying for the future of this ape,” Professor Serge Wich of Liverpool John Moores University and a co-author of the study told The Guardian.

Apart from efforts at the government level, the scientists said sustained international support will be required to protect these wonderful creatures.