Camera traps installed in a jungle in northern Sumatra have recorded nearly three times more images of critically endangered Sumatran tigers than previous surveys.
The work, which took place in the Leuser Ecosystem – a huge area of forest located in the provinces of Aceh and North Sumatra – shows that sustained conservation on the Indonesian island is helping one of the world’s most threatened big cats survive.
“We documented a robust tiger population, apparently among the healthiest on the island,” says conservation biologist Dr Joe Figel, who co-authored the study, published recently in Frontiers in Conservation Science. “For those on the ground, the onus now falls on us to double down and adequately protect them.”
Sumatran tigers have lost most of their historical range due to habitat destruction, poaching and declining prey. But Leuser’s mix of lowland, hill and montane forests continues to provide refuge, and it is the largest remaining block of tiger habitat in Sumatra.
Almost half of the area is classified as intact forest landscape and, crucially, “it’s also more thoroughly patrolled by rangers than nearly any other place on the island,” says Figel.
Working with local communities, the team’s goal was to estimate sex-specific tiger population densities and to learn more about their movements. They set up dozens of infrared cameras during three survey periods between 2023 and 2024.
Across these periods, they captured 282 clear tiger images, enabling them to identify 27 individuals. This included 14 females and 12 males, as well as one tiger whose sex could not be confirmed.
“Multi-year camera trap monitoring is critically important for estimating key tiger demographic parameters such as survival, recruitment, tenure and population growth rate,” explains Figel.
The repeated sightings of female tigers in high-quality habitat are particularly encouraging, say the researchers, because it suggests a healthy social system that supports higher cub birth rates. During one of the 2023 surveys, three different sets of cubs were documented.
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The number of images captured far exceeds earlier 90-day surveys elsewhere in Sumatra, even those inside nationally protected areas, and only a handful of previous studies have documented more than 10 tigers in a single survey.
For Figel, the results underline how pockets of provincially protected forest, when properly supported, can rival national parks in conservation value.
“Thanks to the work, activities and support of government agencies, local Acehnese and Gayo communities, donors and other researchers, Leuser has maintained important patches of lowland and hill forests where, in Sumatra, tiger prey densities reach their highest levels,” he says. “The persistence of these habitats and prey populations are the main reasons for our findings.”
Top image: Camera trap snapshot of tiger in the Leuser Ecosystem. Credit: Figel et al. 2025, BKSDA-Aceh, DLHK
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