New population of Sumatran orangutans found living in highlands

An international team of researchers has discovered 8,000 Sumatran orangutans which were as yet uncounted. The huge number of this critically endangered species of large apes was found living in mountains, as well as in areas west of Lake Toba. With this discovery, the population of the Sumatran orangutan is now estimated at about 14,600.

Sumatran orangutans, one of the two existing species of orangutans, live exclusively in the North of the Indonesian island Sumatra. Their population has been decimated by poaching and forest loss, as its habitat is being converted for agricultural purposes. The second orangutan species lives on the Malaysian island of Borneo. Their numbers are estimated at about 55,000 and it is classified as endangered by the IUCN.
The scientists who found the new populations warned that should the deforestation of the orangs' habitat go ahead as planned, as many as 4,500 individuals could vanish by 2030. The researchers thus urge Sumatran national and provincial legislation to implement measures to avoid negative impacts on forests where orangutans occur.


"It was very exciting to find out that there are more Sumatran orangutans than we thought, but this does not mean that we can be complacent," says Serge Wich of Liverpool John Moores University. "Numerous development projects are planned in the area that - if they are not stopped - could sharply reduce the number of orangutans over the coming years."

Researchers from Europe and Indonesia conducted surveys during which they counted more than 3,000 orangutan nests on more than 200 line transects covering more than 300 kilometers, equaling approximately to 14,600 Sumatran orangutans.

The researchers then examined several future deforestation scenarios based on actual land-use plans in the area using computer simulation. Their analyses show that as many as 4,500 orangutans could disappear by 2030 should these plans be implemented. Therefore, even though the higher population estimate is good news, orangutan numbers are expected to increasingly decline in the long run if deforestation continues at its current pace.

"Given the rapid development in field and analytical methods, we will likely see upwards or downwards corrections of the estimated population sizes for several of the other 12 ape taxa in the years to come. This will help us to better inform conservation policy and management and provide guidance for the improved protection of great apes," said project leader Hjalmar Kuehl of the Max Planck Institute for Evolutionary Anthropology and the German Centre for Integrative Biodiversity Research.