The Old World monkeys (family Cercopithecidae) are split into two subfamilies: the Cercopithecinae and the Colobinae, or colobine monkeys. As a colobine, the white-headed langur has large salivary glands and a complex sacculated stomach. This is an adaptation to the highly folivorous lifestyle of the leaf monkey or langur. Leaves are very difficult to process, requiring digestion by bacteria in the neutral upper chamber of the stomach before moving into the lower acid region. As well as consuming a large volume of leaves daily, the white-headed langur also eats fresh shoots, flowers, bark and some fruits. The very high concentration of fibre and tannic acids in this diet would be poisonous to many other species, including humans (3). The white-headed langur lives in groups of about five to nine individuals (2), usually with just one dominant male (3). The group sleeps together in limestone caves, spending one or two nights in each one before moving on to another. There may be up to 12 resting caves in the range of a group, although rock ledges and tall trees are also used as sleeping sites, particularly in good weather. The group leaves the sleeping sites between 5 and 6:30 am according to season, and will spend a short time socialising before moving out to forage. Resting periodically through the day, the group makes its way towards the new sleeping sites as it feeds, settling down at around 5 or 6pm (3). Females, who all mate with the only male of the group, give birth to a single, golden-orange infant. The majority of births appear to occur in April, but very little is known of the reproductive biology of this species. The young are thought to stay with their mother's group for up to two years, before leaving to find or start a group of their own (4).
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