Populations of the critically endangered Indochinese tigers in eastern Thailand’s forest reserves remained stable between 2018 and 2021, but a shortage of prey and the presence of highways prevented their expansion to promising habitat, a recent study has found.

Scientists have been monitoring Indochinese tiger (Panthera tigris corbetti) populations across the Dong Phayayen-Khao Yai (DPKY) forest complex since 2008. They’ve even found evidence of the tigers breeding. However, studies have found little evidence of the big cats spreading out to newer areas, despite an abundance of suitable habitat across the forest complex, which encompasses five protected areas.

To investigate what might be limiting the tigers’ dispersal, researchers in the recent study analyzed camera-trap data of tigers and seven of their prey species collected at 187 locations in 2021. They also looked at tiger population trends from 2018-2021.

They found that during this period, tiger numbers remained steady, although at relatively low density, with evidence of breeding and high survivorship. However, the tigers remained confined to the eastern section of DPKY, representing just 55% of the landscape’s suitable tiger habitat.

One possible reason for this is Highway 304, the authors write. It fully bisects the forest complex, separating the lush forests of Khao Yai National Park to the west from the eastern part, where the tigers live. While several large-scale wildlife crossings along Highway 304 have been built, there’s no evidence yet that tigers use them.

The study found the strongest factor influencing the presence of tigers was prey availability: Relatively few records of sambar deer (Rusa unicolor) and other large prey were found in Khao Yai National Park, suggesting that even if tigers crossed Highway 304, there might not be enough food for them.

Eric Ash, a conservation biologist who has conducted research on tigers in DPKY with the University of Oxford, U.K., but wasn’t involved in the recent study, said the findings enhance the understanding of an important tiger population in a region rapidly losing its big cats to habitat loss and poaching.

“The trajectory of tiger populations throughout Southeast Asia in recent decades has been cataclysmic,” Ash told Mongabay by email. “A potentially stable breeding population of tigers in DPKY is a rare and encouraging departure from this trend.”

The persistence of the tigers in DPKY, even at a low population density, indicates that efforts to protect the big cats and their prey are paying off, Ash said. Besides monitoring studies like this one, Ash attributed the success to NGO efforts and Thailand’s investment in SMART (Spatial Monitoring And Reporting Tool) patrol-based monitoring, ranger training, and community outreach programs.

Ash agreed with the study’s authors that policy solutions around reconnecting habitats using wildlife corridors and boosting prey populations will be key for Thailand’s tigers. “Continued investments in protection and monitoring can serve as a foundation upon which tiger recovery can occur,” he said.

Banner image of an Indochinese tiger by Rhett A. Butler/Mongabay.