Sumatra: A new study has found that extreme weather has had a devastating impact on orangutans living in Indonesia’s Sumatra island. The research has estimated that 58 Tapanuli orangutans died during a severe rainfall event last November, bringing the species closer to extinction.
The findings suggest that around seven percent of the total species population was lost due to the disaster. Researchers have described the figures as conservative because the assessment did not include the effects of canopy destruction or reduced food availability caused by the storm.
Cyclone Senyar ravaged Sumatra in late November and became Southeast Asia’s deadliest natural disaster of 2025, claiming more than 1,000 lives. According to the study, the event has demonstrated how extreme rainfall can directly threaten the survival of great ape populations.
Following the cyclone, wildlife experts and conservationists reported a sharp decline in sightings of Tapanuli orangutans, raising concerns that many had been swept away by floods and landslides. Earlier estimates suggested around 35 orangutans may have died, but the latest research has indicated that the actual losses were nearly double.
Researchers have also highlighted the role of climate change in intensifying extreme weather conditions. The study noted that the frequency and severity of heavy rainfall events in the region are likely to continue increasing, creating additional risks for both the species and its habitat.
Scientific assessments have shown that the species, first identified in 2017, could face extinction if annual population losses exceed one percent. The deaths recorded during the cyclone have far surpassed that threshold, with researchers warning that the mortality level is beyond what the population can sustain.
The Indonesian government has temporarily suspended major development projects in the Batang Toru protected forest area, including mining, oil palm and hydropower expansion. This pause has provided researchers with an opportunity to further evaluate environmental threats facing Tapanuli orangutans.
The study’s authors have called for stronger domestic protections, climate-responsive planning and continued international support to help prevent the extinction of the world’s rarest great ape species.
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