NORTH SUMATRA — Landslides triggered by intense rainfall destroyed 11.7% of the Tapanuli orangutan's key forest habitat in North Sumatra, leading to an estimated 58 deaths.
Researchers utilized satellite imagery analysis and ape density estimates to assess the impact of the rainfall on the orangutan population. The satellite analysis showed that approximately 8,300 hectares of forest habitat were destroyed.
The 58 deaths account for about 11% of the local Tapanuli orangutan population in the Batang Toru area and 7% of the total species population. Previous research indicates that annual population losses of 1% would be sufficient to lead to the eventual extinction of the species.
Primatologist Serge Wich, from Liverpool John Moores University, said, "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."
Conservation biologist Jatna Supriatna, at Universitas Indonesia, said, "The loss of an estimated 58 Tapanuli orangutans to a single climate-induced landslide event is a devastating demographic shock to the world's rarest great ape. To prevent the first modern extinction of a great ape species, Indonesia must permanently protect the Batang Toru ecosystem, but our international partners must also meet their global commitments by providing immediate biodiversity-recovery financing."
The Indonesian government has temporarily paused all major industrial activity in the Batang Toru area. The temporary pause allows researchers to investigate methods for securing the population's long-term survival and assess parallel risks to human lives. Researchers recommended an immediate moratorium on habitat-degrading land-use activities and an expansion of protected areas to stabilize the population.
The Batang Toru ecosystem is home to mining operations, palm oil plantations, and a large hydropower project. Human-induced climate change from fossil fuel combustion increased the rainfall intensity by up to 50%, according to the study authors. The study was published in the journal Current Biology, with participants including researchers from Borneo Futures, World Weather Attribution, and Liverpool John Moores University.