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Tigers cling to survival in Sumatra’s increasingly fragmented forests

06 Dec 2017

A research expedition tracked endangered tigers through the Sumatran jungles for a year and found renewed fears about the possible extinction of the elusive predators.

Tigers on neighboring islands of Java, Bali, and Singapore went extinct in the 20th century, prompting new anti-poaching efforts to prevent the same fate on Sumatra. Those efforts have largely been successful. The number of tigers in well-protected forests are now twice as high as in non-protected habitats, the study found. But the study also found that well-protected forests are disappearing: Of the habitat tigers rely on in Sumatra, 17 percent was deforested from 2000 to 2012 alone, erasing gains to the tigers’ population. Habitat destruction for oil palm plantations was a leading culprit of deforestation.

“Our results are a mixed bag for tigers” said lead author Matthew Luskin, who conducted the research for his graduate studies at UC Berkeley and is now a research fellow at the Nanyang Technological University in Singapore. “The loss of key habitat is causing significant conservation challenges for Sumatra — and in particular for this critically endangered species.”

The study will be published November 2017 in the journal Nature Communications and was funded by the National Geographic Society.

Obtaining information on rare, stealthy predators is not easy, especially in jungles. The researchers spent a year trekking through remote Sumatran forests, mounting hundreds of cameras that take pictures and video whenever an animal passes. Individual tigers are identified by their unique pattern of stripes, allowing the researchers to track their movement.

With data from the cameras, the scientists calculated a Sumatran tiger’s home range to be roughly 150 square miles, about the three times the size of San Francisco. This is much larger than tigers’ home ranges in other regions like India and indicates they need larger parks to survive.

The study also found that tiger densities increased 4.9 percent per year on average from 1996-2014, likely indicating a recovery from earlier poaching, and that tiger densities are 47 percent higher in primary versus degraded (logged) forests. The clearing of pristine lowland forest disproportionately reduced tiger numbers. This is no surprise: between 1990 and 2010, Sumatra lost 37 percent of its primary forest. As a result, tiger subpopulations also became significantly more fragmented, increasing their threat of extinction.

The research team combined their results and with data from other scientists and estimated the number of tigers in each remaining forest in Sumatra. They found there are now only two habitats large enough to host more than 30 breeding females, an indicator of viable tiger populations over the long term.

“The erosion of large wilderness areas pushes Sumatran tigers one step closer to extinction,” Luskin said. “We hope this serves as a wakeup call.”

“Safeguarding the remaining expanses of primary forests is now absolutely critical to ensuring tigers can persist indefinitely on Sumatra,” said co-author Mathias Tobler of the San Diego Zoo Global. The most famous of these is Gunung Leuser National Park where the Leonardo DiCaprio Foundation works. “Largescale reforestation is unlikely. If we are going to save Sumatran tigers in the wild, the time to act is now.”

CONTACTS:
Matthew Luskin, Nanyang Technological University, 54 Nanyang Ave, Singapore, mattluskin@gmail.com, +65 8153 6301
Mathias Tobler, San Diego Zoo Global, mtobler@sandiegozoo.org