Concerns are growing that the world’s rarest apes were swept away in Sumatra floods

An unusual silence in the forests of North Sumatra, Indonesia, is worrying wildlife experts and conservationists.

Here, in the mountain forests of Batang Toru, they often see and hear the Tapanuri orangutan, the rarest ape in the world.

But conservation workers say the critically endangered primate has not been seen in the area since Cyclone Xenya devastated the island of Sumatra on November 25.

Their disappearance has sparked speculation about whether the great apes were swept away by floods and landslides. While some believe the animals may have been moved to safer locations, the discovery of a carcass said to be that of an orangutan in the area has heightened concerns among conservationists.

Conservationists say there are fewer than 800 Tapanuli orangutans left and any loss would have a serious impact on the species.

Humanitarian workers told the BBC they found the animal carcasses half-buried in mud and log debris earlier this week in the village of Pulopakat in central Tapanuri district.

“When I first saw it, I wasn’t sure what it was because it was a bit damaged, maybe because it was buried under sludge and logs,” said Dejichandra, who has been working with humanitarian teams in the area. He previously worked on the conservation of the Tapanuri orangutan.

“I’ve seen a few human corpses over the past few days, but this is the first case of a wild animal dying,” he said. “They used to come to this place to eat fruit, but now it seems like it’s become their graveyard.”

Mr Chandra shared photos of the carcasses he had taken with the BBC, some of which showed him with the dead animals.

Conservationists working in the area believe it is the Tapanuli orangutan, which was only discovered in 2017. The other two species are the Bornean orangutan and the Sumatran orangutan.

Heavy rains, floods and landslides have killed more than 900 people since Cyclone Senyar tore through parts of Indonesia in late November. Hundreds of people are still missing as the storm sweeps across Sumatra, leaving many villages completely destroyed.

Professor Eric Mejad, managing director of Brunei Borneo Futures, is currently studying the impact of the disaster on orangutans with the help of satellite imagery.

He said 4,800 hectares (11,860 acres) of forest on the slopes had been destroyed by landslides, but he extrapolated the damage figure to 7,200 hectares in preliminary observations because part of the satellite image was covered by clouds.

“There were probably about 35 orangutans in the area that was destroyed, and given the violence of the destruction, we wouldn’t be surprised if they were all dead. It would be a major blow to the local population,” he told the BBC.

“These areas show up as bare soil on satellite images, and two weeks ago this was virgin forest. It’s completely destroyed. Many hectares of land have been completely stripped bare. The forest must have been hellish at that time.”

Professor Mejad said he had also seen the photo of the dead orangutan shared by Chandra.

“What shocked me was that all the flesh on the face was torn off,” he said. “If a few hectares of forest collapse due to a massive landslide, even the mighty orangutans will be unable to do anything but be destroyed.”

Panut Hadisiswoyo, founder of the Orangutan Information Center, which works to protect primates in the region, said the carcass means some Tapanuri orangutans likely will not escape as raging floods and landslides sweep through their habitat.

Last week, photos of another critically endangered species, the Sumatran elephant, washed away by floods in Aceh, northern Sumatra, went viral on social media.

The island is home to a range of endangered species such as Sumatran tigers, elephants and rhinos.

But conservation workers say other primates such as orangutans and gibbons are of particular concern as much of the montane forest in the Tapanuri region has suffered massive landslides from Cyclone Senyar’s extreme rainfall.

Some locals said the primates must have escaped before the disaster happened because they could sense danger in advance. But some primate experts say that may not be the case.

“During heavy rains, orangutans either sit in trees or collect branches and leaves to use as umbrellas and wait for the rain to stop,” said Serge Wich, a professor of primate biology at Liverpool John Moores University who has studied Tapanuri orangutans.

“But this time, by the time the rain stopped, it was too late: part of their habitat – the slopes of the valley – had been destroyed by landslides, meaning they must have been affected.”

Recent floods have also damaged a number of orangutan research centers in Sumatra, including Ketambe, the world’s first orangutan research center in Aceh province.

Dr Ian Singleton, scientific director of the Sumatran Orangutan Conservation Programme, said the Ketambe center was now almost completely destroyed.

“It needs to be rebuilt as soon as possible so that it can continue to play its role in protecting the area’s forests and its orangutans.”