Sumatran orangutans, one of the two existing species of orangutans, live exclusively in the North of the Indonesian island Sumatra and are critically endangered. This great ape is threatened by poaching and forest loss, as its habitat is being converted for agricultural purposes. An international team of researchers has now conducted an extensive series of surveys to estimate the number of Sumatran orangutans. They discovered that about 14,600 of these animals still live in the wild today - 8,000 more than previously¹ thought. Good news, however, the increase in numbers is due to a more wide-ranging survey effort and not to an increase in the orangutan population. Moreover, 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 provincial² legislation to implement³ measures to avoid negative impacts on forests where orangutans occur. An accurate estimation of population size is crucial for planning future conservation activities effectively. Therefore, to cover the species' complete range, researchers from Europe and Indonesia have conducted surveys during which they counted more than 3,000 orangutan nests on more than 200 line transects covering more than 300 kilometres, equalling approximately to 14,600 Sumatran orangutans. A previous estimate found that 6,600 Sumatran orangutans lived in Northern Sumatra, a number that did not include orangs living at higher elevations⁴, in logged forests and in areas west of Lake Toba.

 

The researchers then examined several future deforestation scenarios⁵ 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 implemented⁶. 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.

 

"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."

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