Renewed Fears of Tiger Extinction

A research expedition to Sumatra has found that well-protected forests on the island are disappearing and becoming increasingly fragmented, leading to renewed fears of the extinction of the Sumatran tiger.

Panthera Tigris Altaica Image: U.S. Fish and Wildlife Service - Public Domain

A research expedition funded by the National Geographic Society which tracked endangered tigers through the Sumatran jungle for a year has found that tigers are clinging to survival in low density populations.

The study, published last month in Nature Communications, reports that well-protected forests are disappearing and are increasingly fragmented. Of the habitat relied on by tigers in Sumatra, 17% was deforested between 2000 and 2012 alone. The findings have renewed fears about the possible extinction of these elusive predators.

Tigers on the neighbouring islands of Bali, Java and Singapore went extinct in the 20th Century. This prompted new anti-poaching efforts to prevent the same fate befalling the subspecies on Sumatra, efforts which have largely been successful. The density of tigers has increased over the last two decades and their numbers are twice as high in unlogged forests.

But the study also found that these well-protected forests are disappearing and becoming increasingly fragmented, erasing any gains to the tigers’ chance of survival, the authors wrote. The leading culprit for habitat destruction is to make way for palm oil plantations.

“Our results are a mixed bag,” said lead author Matthew Luskin. “The loss of key habitat is causing significant conservation challenges for Sumatra – and in particular for this critically endangered species.”

Obtaining information on rare, stealthy predators is not easy, especially in jungles. The researchers spent a year trekking through remote Sumatran forests, setting hundreds of camera traps. Individual tigers can be identified by their unique pattern of stripes, allowing their movements to be tracked.

With data from the cameras, a Sumatran tiger home range was calculated to be roughly 150 square miles. This is much larger than tiger home ranges in other regions such as India, indicating that they need larger protected areas to survive.

The study discovered that tiger densities are 47% higher in primary versus degraded i.e. logged forests, and that extensive clearing of pristine lowland forest (37% of primary forest was lost between 1990 and 2010) has reduced tiger numbers. As a result, tiger subpopulations became significantly more fragmented, greatly increasing their chance of extinction.

The research team combined their results with data from other scientists and estimated the number of tigers in each remaining forest in Sumatra. An indicator of viable tiger populations over the long term is more than 30 breeding females, but currently just two habitats on the island are large enough to support this number.

“The erosion of large wilderness areas pushes Sumatran tigers one step closer to extinction,” Luskin said. “We hope this serves as a wakeup call.” Co-author Mathias Tobler of San Diego Zoo Global added: “Safeguarding the remaining expanses of primary forests is now absolutely critical to ensuring tigers can persist indefinitely on Sumatra.”

The most famous of these expanses is Gunung Leuser National Park in northern Sumatra, where organisations like the Leonardo DiCaprio Foundation work to prevent deforestation and poaching. “Largescale reforestation is unlikely,” Tobler said. “If we are going to save Sumatran tigers in the wild, the time to act is now.”


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