In a remote forest along the border between Vietnam and China, conservationists are engaged in a critical effort to protect the world’s second-most endangered ape, the cao vit gibbon (Nomascus nasutus). This species, known for its distinctive “cowww-vit” call, survives in a fragile population of just 74 individuals confined to a 1,600-hectare limestone karst forest—the only place on Earth where the gibbons are found.
The cao vit gibbon was believed extinct around the year 2000 following decades of hunting and habitat destruction caused by local farming and charcoal production. Its rediscovery in 2002 triggered renewed conservation efforts led by Fauna & Flora, a British-based international wildlife charity. Despite these initiatives, the species remains critically endangered, with its survival precariously dependent on the difficult-to-access, rugged terrain that has provided a natural refuge.
A census conducted in mid-September was the sixth since the gibbons’ rediscovery, a labor-intensive survey requiring surveyors to scale steep karst mountains to reach 35 listening posts scattered across the gibbons’ range—26 of which are on the Vietnamese side. The apes’ vocalizations, occurring predominantly between dawn and mid-morning, help researchers estimate population size. However, counting the gibbons is challenging due to their fast movements and acoustic complexity caused by the limestone landscape, which can amplify and distort their calls.
Earlier population estimates as high as 120 individuals were later revised downward to 74, following improvements in census methodology. Researchers incorporated automated audio recorders and identified that each adult male possesses a unique call, enabling more accurate triangulation of their positions and avoiding double counts caused by echoing on the karst peaks. This technological refinement has provided a clearer but sobering picture of the species’ status.
The cao vit gibbons live in small family groups and reproduce slowly, with females birthing infants approximately every four years. Their unique coloration also aids identification: adult males are black, females have orange fur, and all infants appear black regardless of sex. Ecologists emphasize that the gibbons' restricted range and limited habitat use—primarily about 1,000 hectares of the available forest—increase their vulnerability. A localized disaster such as disease, fire, or flooding could have devastating effects.
Security concerns in the border region hindered the use of drones equipped with thermal cameras during the latest survey, tools previously employed to improve population counts. Instead, survey teams used thermal monoculars under difficult field conditions exacerbated by heavy rains and treacherous terrain.
Conservationists stress that protecting the gibbons depends not only on biological research but also on fostering local community engagement. Programs aimed at providing alternative livelihoods aim to reduce reliance on forest resources. These initiatives include promoting sticky rice cultivation, ecotourism activities such as birdwatching, and developing homestays for visitors. Though nascent, these efforts are seen as crucial for long-term sustainability, especially as direct conservation funding cannot be expected to continue indefinitely.
Local attitudes toward the gibbons appear to be shifting. Nong Ngoc But, an 80-year-old elder from Gioc Sau village who once hunted the apes for food, expressed hope that their distinctive song will continue to echo through the forest. “If it were lost now, I would feel great regret,” he said. The future of the cao vit gibbon depends on balancing the protection of its unique habitat with the needs and cooperation of the human communities sharing this remote landscape.