Sumatra, Indonesia: A study found that four days of extreme rain and landslides killed an estimated 58 Tapanuli orangutans, about 7% of the world’s rarest great ape species.
The study, published in Current Biology, said the loss was conservative because it did not include canopy damage or reduced food availability after Cyclone Senyar.
Researchers said the storm pushed the critically endangered species closer to extinction. Fewer than 800 Tapanuli orangutans remain, and the species was identified only in 2017.
Professor Erik Meijaard, managing director of Borneo Futures in Brunei, said he had earlier estimated that the storm likely killed about 35 orangutans. The new study found the loss was nearly double that estimate.
Professor Serge Wich, a primatologist at Liverpool John Moores University, said the mortality was beyond the animals’ capacity to withstand. The study warned that even repeated annual losses of 1% could push the species toward extinction.
Researchers said human-induced climate change played a significant role in the extreme rainfall event. The Guardian reported that the storm destroyed about 11.7% of the primary habitat, or roughly 8,300 hectares, in the Batang Toru ecosystem.
Cyclone Senyar hit Sumatra in late November 2025 and killed more than 1,000 people across Southeast Asia. Mongabay reported that Indonesian government figures put the death toll at at least 1,178 people.
The Indonesian government has temporarily halted major development in Batang Toru, including mining, oil palm and hydropower expansion. The study’s authors said stronger domestic protection and international support are needed to prevent the first modern extinction of a great ape species.
