Population Status and Conservation of the Largest Population of the Endangered François' Langur (Trachypithecus francoisi) in Vietnam.

François' langur is an Endangered colobine inhabiting limestone habitats in southern China and northern Vietnam. Its global population has been estimated to be just more than 2000 mature individuals. Populations in Vietnam are highly fragmented with reportedly fewer than 200 adults in total and 50 in a single location. Although the François' langur in Vietnam is highly imperiled as remnant populations persist in only three to four sites, little research has been carried out to provide a reliable estimate of its remaining population. In this study, we conducted field surveys in Lam Binh District, Tuyen Quang Province, northeastern Vietnam. In total, we recorded at least 16 groups of François' langurs, with 156 individuals, raising the total number of individuals by approximately 10% compared to a previous study. The group structure, group size, activity budget, and density of the Lam Binh population resemble those reported in François' langurs in China and other limestone langur species. The results show that the behavior ecology of limestone langurs significantly differs from that of forest langurs probably because they occupy separate habitats with distinctly different environmental variables. During our surveys, we detected a number of direct threats to this population, namely illegal logging, hunting, firewood collecting, hydropower development, grazing, and mining. It is recommended that the protection forest be elevated to the nature reserve status to better protect the most important population of the François' langur in Vietnam. [ABSTRACT FROM AUTHOR]