The grizzled leaf monkey is a folivorous primate, its diet consisting primarily of leaves, but it will also consume fruits, flowers and seeds (5). Like other Colobine monkeys, also known as ‘the leaf eaters’, it is able to digest large volumes of leaves by having a large, multi-chambered stomach, and a forestomach that houses lots of bacteria. Together, these features assist in the breakdown of cellulose, one of the primary components of plants and a substance that is largely indigestible to many animals. However, the specially adapted gut of the grizzled leaf monkey enables it to obtain energy and nutrients from a cellulose-rich diet (7).
Like all leaf monkeys, the grizzled leaf monkey is a tree-dwelling species that is active during the day (5). Group sizes have been documented to range between 2 and 23 individuals (8) (9), with the grizzled leaf monkey also sometimes forming groups with other species such as the Javan langur (Trachypithecus auratus) (10). There is usually only one male of mating age per group, with other males dispersing from the group they were born in before adolescence (11). Juvenile and infant males are known to often engage in social play, an activity which females rarely partake in (11).