François' langurs are medium-sized primates with black, silky hair. They have very distinct white sideburns that grow down from their ears to the corners of their cheeks. Their tails are long and black in color with a white area on the tip. Males are larger and havier than females and have longer tails.
François' langurs are distributed from Southwestern China to northeastern Vietnam. They live in dry and moist forests. Their preferred habitat are limestone cliffs and caves of tropical and subtropical zones.
François' langurs are diurnal and social creatures that spend most of the day resting and foraging. The average group size ranges from 4 to 27. These monkeys live in a matriarchal society where the females lead the group. Within the society, the females share parenting responsibilities with one another and stay in their natal group forever. Males within the group take no part in the raising of the young, and the young males leave the group before reaching sexual maturity. François' langurs are very agile and when on trees move jumping from one tree to another. When it comes to sleeping sites these animals prefer limestone cliffs. They sleep either on ledges or in caves. By living and sleeping in these limestone caves and cliffs, far from flat land, they greatly avoid predation. In addition, these monkeys produce a loud call to declare their territorial spacing. François' langurs choose the sleeping sites that are close to potential foraging sites. This way they conserve energy and reduce travel costs. When they don't go to forage, individuals usually travel along the same route and return to the same sleeping site.
François' langurs live primarily in one-male groups, in which one male mates with multiple females. This means that these animals have a polygynous mating system. The breeding season takes place year-round with the peak in autumn and winter. Females give birth to a single infant after the gestation period that lasts around 6-7 months. Infants are born fully furred with their eyes open and are fairly active. Young are nursed up to two years before being weaned. By that time the mother and other females in the group nurse, groom and take all the care about the infant. Young François' langurs become reproductively mature after 4-5 years of age.
Of the many factors threatening François' langurs' survival today is hunting that has had one of the largest impacts. In Nonggang Nature Reserve (China), where it is most prevalent, the natives believe that the langur has medicinal values, and have hunted them to make wine out of their bones, which they believe could cure fatigue and rheumatism. Another threat to François' langurs is the destruction of their habitat. These animals live on limestone cliffs, and when farmers look to cultivate their land, they light fires on the lower slopes. Limestone is particularly susceptible to fire; therefore, this practice not only destroys their habitats but also causes major food shortages for these langurs because their diet is primarily foliage.
According to the IUCN Red List, the total population size of the François' langur is unknown. However, there are estimated populations of the species in the following areas: Viet Nam - less than 500 individuals; Nonggang Nature Reserve (China) - 75 individuals; Mayanghe Nature Reserve (China) - around 700 individuals. In 2003 in China the total population size of François' langurs was 1,400-1,650 individuals. Currently, this species is classified as Endangered (EN) on the IUCN Red List and its numbers today are decreasing.