The Mentawai leaf monkey, however, is monogamous and lives in mated pairs. The thumb is particularly short. Females form the stable core and have a clear stable hierarchy. Males without females live alone or in small bachelor groups. Harems of 1 male with 4-6 females and their young.
Males keep a look out for predators, keeps the group together and patrols the territory.
In good weather, they sleep outside, but during cold winters, they shelter in caves. Other species are in serious danger in some parts of their distribution due to habitat destruction and hunting. Francois' leaf monkey populations in Vietnam also suffered during the Vietnam War. One young, twins are rare. Newborns are bright yellow or orange red with pink faces.