In early May, during a drone survey by a team of experts in the limestone mountain region bordering Ninh Binh and the former Hoa Binh area, images on the screen showed a group of white-rumped langurs navigating a cliff face before stopping at national highway 21, a route running between Kim Bang forest and the Huong Son - Lac Thuy limestone mountain range.

Below, a continuous stream of vehicles traveled along the national highway, which is about 20 m wide. Just dozens of meters across the road were limestone cliffs that once connected seamlessly with the forest where the langurs live. Instead of crossing the open space below, the entire group of langurs turned back to the original cliff face, continuing their movement within their increasingly shrinking habitat.

Not far from this area are stone quarries, some active and some previously exploited. The noise of stone trucks, deeply cut mountain faces, and newly opened roads have gradually fragmented the once continuous limestone forest range into many smaller patches.

A pair of white-rumped langurs in Ninh Binh. *Xuan Hoa*.

The white-rumped langur is an endemic primate species found only in Vietnam, currently classified as "critically endangered" in the Vietnam Red Book and the IUCN Red List. This species once had a relatively wide distribution in the Northern and North Central regions, but decades of hunting, road construction, and stone quarrying have led to the shrinking of its habitat.

Currently, white-rumped langurs are concentrated in two large populations: Van Long Nature Reserve - Dong Tam forest (Lac Thuy) with about 304-336 individuals, and Kim Bang forest with 175 individuals. Additionally, the species is present in Yen Mo - Tam Diep - Bim Son forest and Huong Son Special-Use Forest (Ha Tinh) in small numbers but still capable of reproduction. Pu Luong Nature Reserve (Thanh Hoa) currently has only about 5-7 individuals, placing it among the most endangered groups.

Trinh Dinh Hoang of the Save Vietnam's Wildlife (SVW) stated that the greatest risk to white-rumped langurs is not just their small population size, but their habitat being fragmented into "islands" by national highways, tourist roads, residential areas, power lines, and stone quarries. Unlike many primate species, white-rumped langurs rarely move on the ground, primarily clinging to cliffs and tree canopies. When mountain ranges are cut by roads or quarrying areas, langur groups almost lose the ability to interact with each other, leading to a risk of gene pool reduction and long-term reproductive decline.

One of the most severe fragmentation points is the national highway 21 area, where the road, about 20 m wide, cuts across between Kim Bang forest and the Huong Son - Lac Thuy forest range. Just 200 m from this habitat connection point is a quarrying area, further shrinking the langurs' living space.

What can be done to save the langurs?

To address the fragmentation, scientists propose building concrete ecological bridges with green coverings to create corridors for langurs to move between the two forest areas without descending to the ground. This is not merely an infrastructure project but a "living corridor" that would help the remaining langur populations continue to exchange gene and expand their survival space.

Besides national highway 21, many other fragmentation points have been identified as needing habitat connectivity restoration, such as the dam area connecting Dong Quyen - Hang Tranh in Van Long, the tourist road linking Huong Pagoda with Bai Dinh, the newly opened road into Dai Dong valley, or former quarrying areas in Kim Bang forest. The proposed solution involves constructing overpasses and underpasses combined with tree planting to create green corridors, reconnecting the fragmented limestone mountain ranges.

6 proposed locations for bridge construction and tree planting for connectivity.

Beyond transportation, stone quarrying continues to be considered the greatest pressure on the white-rumped langur's habitat. These limestone mountains are not only shelters but also "natural fortresses" that have helped this primate species survive for decades.

Tang Xuan Hoa, Deputy Head of the Ninh Binh Forest Protection Department, stated that the province has integrated white-rumped langur conservation into its development planning adjustments. Additionally, directives have been issued to complete the dossier for establishing the Kim Bang white-rumped langur species-habitat reserve before 30/6/2026. According to Hoa, forest rangers, in collaboration with conservation organizations such as Fauna & Flora International and CCD, have recently surveyed, patrolled, and protected many limestone mountain areas with high biological value, preventing them from being exploited despite significant pressure from construction material demands. "We are determined to protect areas directly related to white-rumped langur habitat, special-use forests, and limestone forests," Hoa said.

Model of a habitat connectivity bridge over a road in Canada.

Experts believe that if the Kim Bang white-rumped langur reserve is established, along with a system of overpasses and ecological corridors connecting the limestone mountain ranges, it will mark a significant turning point in the conservation efforts for one of the world's most critically endangered primate species. Amidst the limestone mountain ranges fragmented by national highways and stone quarries, groups of white-rumped langurs continue to cling to the remaining cliff faces. For conservationists, securing pathways for the langurs today also means preserving the last chance for survival for a primate species found only in Vietnam.

Gia Chinh