Sumatran orangutan numbers double but fires destroy habitat

Researchers find Sumatran orangutans living at higher altitudes but critically endangered status unlikely to change

There are twice as many Sumatran orangutans alive than previously thought but the critically endangered great ape is far from out of the woods, say researchers who conducted the landmark survey.

Loss of forest habitat is the biggest threat facing Sumatran orangutans, followed by the illegal pet trade and poaching. Fires lit to illegally clear land for conversion to palm oil plantations continue to burn throughout Indonesia, destroying some of the orangutans’ remaining habitat.

“The chance that there will be zero [Sumatran orangutans] in the near future is certainly less now,” said the lead author of the survey, Serge Wich, of Liverpool John Moores University in the UK.

Wich and his colleagues estimated there were about 14,600 living in the wild, compared with the 6,600 Wich and colleagues estimated in 2008.

Earlier estimates suggested the population had dropped by 80% in the past 75 years and Wich said the new findings would not significantly change that figure.

“There has been so much forest loss in Sumatra during the past decades that the population will still have declined [about] that much, albeit a bit less.”

He said it was vital to realise this did not meant the population was growing. Rather, the new survey looked more closely at places where it was previously thought no orangutans lived.

They surveyed regions in Sumatra 1,500m above sea level, whereas previous surveys assumed no orangutans would live above 900m. They also looked at areas that had previously been logged and were surprised to find some orangutans repopulating the areas. Finally, they surveyed areas further west, where orangutan populations were only recently discovered.

Map of Indonesia
Map of Indonesia

The authors concluded that previous estimates “drastically underestimated” the animals’ range, now estimated as 2.56 times as big as previously thought.

But with more orangutans, there were also more to be lost. Modelling the impact of future deforestation, the researchers found as many as 4,500 individuals could be lost by 2030.

But Wich warned that protecting Sumatran orangutans was not just a matter of avoiding extinction of the whole species.

“Not all orangutans are the same,” he said. “What we have discovered in orangutans, similarly as in chimpanzees and other great apes, is there are these differences between populations: different rich cultures of different vocalisations, different tool use and other behaviours. If we lose the orangutans in the peat swamp areas, say, then we lose most of the tool use cultures in orangutans in Sumatra.”

The discovery that Sumatran orangutans lived at higher altitudes opened up the promise of exciting new findings, he said. Initial observations suggested those orangutans had a different diet, eating trees not consumed by orangutans in lower-lying areas. And they used tools differently too, Wich said. “There’s some unique cultural behaviours.”

The discovery that orangutans seem to live in forests that have been affected by logging suggested they might be more resilient to human impacts than previously thought.

Wich said the new population estimate was unlikely to change the animals’ conservation status, which the International Union for Conservation of Nature lists as “critically endangered”.

“If we look at forests that have been logged, the reduction in numbers is still big enough for them to remain critically endangered,” he said.

Wich said it was urgent that Indonesia enforced its anti-deforestation regulations.

“There are regulations that there shouldn’t be any forest clearance when peatland areas are deeper than 3m, but it still happens,” he said. “And there shouldn’t be deforestation on slopes more than a certain steepness but it still happens. And deforestation happens in protected areas too.”

He said roads through orangutan habitats should be stopped where possible, since illegal clearing often happened around roads.

But he agreed the research finding was definitely good news. “It does give us, in a way, some more time to try to put conservation strategies in place.”

Sumatran orangutans are one of two distinct species of orangutans. Bornean orangutans number about 50,000 or 60,000. Sumatran orangutans have longer, paler fur and slightly longer faces. Orangutans are the only great apes that live in Asia, besides humans.

Orangutans spend most of their time in trees, moving through forests by swinging between them. They are the largest arboreal animal in the world.


Michael Slezak

The GuardianTramp

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