The species crashed through the twentieth century, from perhaps two thousand animals in the 1950s to a low of around seven to ten individuals in the late 1970s, when hunting and the clearance of lowland forest for rubber had reduced it to a single valley in Bawangling.
Since then the count has climbed slowly, reaching the mid to high thirties across a handful of family groups by the early 2020s. Because the groups sing at dawn from known territories, monitoring teams positioned on ridges can locate every group in a single coordinated morning, then follow individuals to record births and dispersals.
The risk is concentration rather than trend. A population confined to one small block of hill forest is exposed to a single typhoon or landslide, and one such landslide in 2014 cut a gap that gibbons were later filmed crossing on a rope bridge installed by researchers.