The cyclone-induced floods and landslides killed at least 1,200 people and damaged around 300,000 homes, with environmental groups blaming the scale of the destruction on the rapid deforestation of Sumatra island.
At least 58 Tapanuli orangutans, which are endemic to an area around North Sumatra’s Batang Toru forest, were killed in the floods, the report said. It cited a survey of the western block of the forest, which is home to the majority of the species’ total population of about 800 primates.
The report, a joint study by Brunei-based Borneo Futures, World Weather Attribution and Liverpool John Moores University, did not survey other parts of the forest, meaning the death toll could have been higher.
The findings were based on an analysis of satellite images showing the damage in the West Block of Batang Toru and historical records of the orangutan population in the area.
Human-induced climate change has likely increased the intensity and frequency of extreme rainfall around Malacca Strait, putting Tapanuli orangutan’s habitat at greater risk, the study said.
Erik Meijaard of Borneo Futures, the lead author of the study, said heavy rain saturated the soil to such an extent that large sections of hillsides in the primary forests collapsed in fast-moving landslides.
“If you get caught as an orangutan… if anything comes down at great speeds, survival chances are going to be very minimal, so it became a real concern,” he said.
“This level of loss is substantial for a species with such a small total population. When combined with ongoing pressures such as habitat degradation and human-wildlife conflict, it further increases the urgency of implementing and adequately resourcing a coordinated species action plan,” Meijaard added.
Panut Hadisiswoyo, another researcher involved in the study, urged the Indonesian government to work with NGOs and researchers to prevent a further decline in the orangutan population.
“We can minimise poaching and hunting, and the population can probably be stabilised,” he said, adding that poor land-use practices have also contributed to the decline.