- Conservationists surveying upland forests in central Vietnam have located a new subpopulation of critically endangered gray-shanked douc langurs.
- Fewer than 2,400 individuals are thought to remain in the wild, mostly in Vietnam, where more than half live outside of formally protected areas.
- Forest loss and hunting pressure have driven the species to the brink of extinction, spurring stakeholders to develop an action plan for the species in 2022.
- Experts say the new discovery underscores the need for conservation measures that go beyond traditional area-based approaches to encompass habitat restoration, community-based programs and habitat corridors.
Researchers surveying forested mountains in south-central Vietnam have located a new subpopulation of gray-shanked douc langurs, a critically endangered monkey species. The discovery is a sign that more groups of the rare primate may still be found in unexplored forest areas, the team write in a recently published paper in the journal Oryx.
Fewer than 2,400 gray-shanked douc langurs (Pygathrix cinerea) are thought to remain in the wild, dispersed across six provinces in Vietnam’s central highlands. They typically live in dense canopy in upland forests, which limits their ability to disperse and makes population counts tricky. Although there have been some informal sightings of the species in eastern Cambodia, there’s little evidence of stable populations outside Vietnam.
Deforestation and hunting for meat, the pet trade and body parts that are used in traditional medicine have slashed their numbers by 80% over the past three decades, according to their most recent assessment report for the IUCN Red List, published in 2020.
Conservationists are particularly concerned that more than half of their population inhabits fragmented patches of forest outside of protected areas, where pressures on their numbers are intense and sightings are dwindling.
The new subpopulation was sighted in a 17-hectare (42-acre) area of Quang Nam province called Khe Lim Forest. It came as a surprise for the team comprising researchers from the Frankfurt Zoological Society (FZS), the GreenViet Biodiversity Conservation Centre and local guides, who were initially completing a botanical survey when they chanced upon the group of monkeys in trees during a rest stop.
“Our first encounter with the douc langur group was completely incidental,” said Tay Van Nguyen, an ecologist at the FZS and co-author of the new report. “Following this initial sighting, we organized additional surveys in nearby areas and conducted interviews with local community members living around Khe Lim forest.”
The team learned that the langurs occasionally ventured near people’s homes and were also seen along the routes villagers take to collect rattan and other nontimber forest products. Subsequent surveys led to sightings of adult males and females, subadults and juveniles in several parts of Khe Lim Forest, indicating the presence of a viable, breeding population.
While the discovery is a hopeful sign, the langurs already face threats. Khe Lim Forest lies outside of Vietnam’s formally protected areas, leaving it exposed to significant drivers of forest loss in Quang Nam province, such as road construction and conversion of natural forests into acacia plantations. The researchers also noted more localized pressures from household-level collection of firewood, rattan, mushrooms and other forest resources.
“During our fieldwork, we observed several terrestrial mammals caught in snares, suggesting ongoing trapping and hunting activities in the area,” Tay told Mongabay.
Although Khe Lim Forest itself lacks formal protection, it adjoins a designated Elephant Species and Habitat Conservation Area (SHCA), a protected forest corridor managed by government agencies and patrolled by forest rangers due to its role in sustaining Vietnam’s remaining population of Asian elephants (Elephas maximus). Khe Lim is therefore a vital extension of this “unique ecological corridor that connects various forest patches in the region,” Tay said.
FZS and GreenViet are now seeking funding to do more surveys of forests in Quang Nam province and to set up collaborations with communities in and around Khe Lim Forest to deter hunting and promote habitat protection.
In 2022, conservation organizations, government agencies and community groups developed the first coordinated conservation action plan for gray-shanked douc langur, aiming to achieve a well-connected and protected population by 2050. The plan is centered around addressing four key threats — habitat loss, hunting, degradation, and population fragmentation and isolation — through key actions, such as habitat restoration, community-based programs and habitat corridors.
Lam Van Hoang, director of Fauna & Flora’s Vietnam program, said the species is doing quite well in several neighboring provinces thanks to dedicated conservation efforts, showing the species can survive if given an opportunity.
“The species’ population is stabilizing or even increasing in certain areas like Kon Plong and Ba To where conservation efforts are invested,” Lam, who was not involved in the recent surveys, told Mongabay in an email.
In 2016, surveys led by Fauna & Flora identified three new groups of the species in Kon Plong Forest in Kon Tum province, boosting their known population size at the time by 500 individuals. Sizeable populations have also been found nearby in Ba To Forest in Quang Ngai province and in Kon Ka Kinh National Park in Gia Lai province, where authorities have confirmed 1,000 individuals persist.
Lam said the latest discovery in Khe Lim Forest represents more evidence that gray-shanked douc langurs rely on habitats outside of Vietnam’s network of formally protected areas. Ensuring the species’ long-term survival will therefore call for measures that go beyond traditional area-based management approaches, he noted.
“Including areas like Khe Lim Forest in conservation strategies through OECMs [Other Effective area-based Conservation Measures] can help expand the scope and effectiveness of Vietnam’s biodiversity protection initiatives,” Lam said.
Initiatives focused on community-based habitat protection, sustainable land-use practices and connecting nature reserves in and around Kon Plong and Ba To through habitat corridors will be critical for the species, he added.
The gray-shanked douc langur isn’t the only threatened primate in Vietnam. In fact, the country is home to 11 critically endangered species, including Cao-vit gibbons (Nomascus nasutus) and Cat Ba langurs (Trachypithecus poliocephalus), both of which had the dubious honor of being included on the latest list of the world’s 25 most endangered primates.
“These primates are among the most evolutionarily distinct and globally endangered mammals,” Lam said. “This puts the country on the front line of efforts to prevent global extinctions.”
Banner image: A group of gray-shanked douc langurs. Image © Ryan Deboodt / Fauna & Flora.
Carolyn Cowan is a staff writer for Mongabay.
Citation:
Van, L. N., Nguyen, T. A., Nguyen, T. V., Hoang, C. V., & Thang, L. H. (2025). Discovery of a previously unknown population of the critically endangered grey-shanked douc langur in Quang Nam province, Vietnam. Oryx, 1-1. doi:10.1017/s0030605325000055
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