Extreme Rain in Sumatra Claims 7% of Tapanuli Orangutans, Study Finds

A recent study released by wildlife researchers indicates that four days of extreme rainfall and landslides across Indonesia’s Sumatra Island killed an estimated 58 Tapanuli orangutans, roughly 7% of the world’s rarest great ape population.

The authors note that the figure is conservative, as it does not account for canopy damage or reduced food supplies caused by the storm. The study, published in Current Biology, claims that extreme rainfall events can directly threaten the survival of critically endangered species.

Cyclone Senyar, which struck Sumatra in late November, has already caused over 1,000 deaths and triggered widespread flooding, making the loss of the orangutans a tragic overlay to the human tragedy.

Field workers reported finding a semi‑buried Tapanuli orangutan carcass in the debris of a village in central Tapanuli, indicating the level of destruction caused by the landslides. “If several hectares of forest collapse in a massive landslide, even powerful orangutans are helpless and get mangled,” an observer explained.

The study’s authors highlight that Cyclone Senyar was an anomalous event, but that climate‑induced changes are increasing the frequency and intensity of such extreme rainfall. They warn that future storms could pose a continuing threat to the species’ survival.

Research indicates that the species, identified only in 2017, will likely go extinct if it loses more than 1% of its population annually. The finding has prompted Indonesian authorities to temporarily halt major development projects in the Batang Toru protected forest area, offering a chance to reassess ecological risks.

"The crisis illustrates the convergence of climate instability, biodiversity loss, and vulnerability," the authors write, calling for a coordinated response that matches the scale of the threat. They stress that sustained international support is needed to strengthen domestic protection, climate‑responsive planning, and global financial and technical assistance to prevent the first modern extinction of a great ape species.