This highly social primate indulges in much play as an infant, and continues to interact extensively as an adult, through well-developed vocal calls and strongly tactile gestures, including grooming and face-to-face hugging. Groups contain between 2 and 15 individuals, and are most commonly made up of one adult male and several females with their young. This unimale system ensures that a dominant male is able to mate with all the females in his group, and must defend them and their young in return. Solitary males and small bachelor groups are formed as well, usually from younger males who have not yet ousted an older dominant male from his group. Some multi-male, multi-female groups are also found, in which the females control the movement and direction, while the males lag behind and are slower to stop eating when the group moves on (3).
When travelling, the capped langur group is relatively quiet and individuals keep close together, unless they encounter a rival group. The home ranges are large and frequently overlap with others, and whilst males do not defend food sources, they will act aggressively to defend their females. Male group leaders are particularly aggressive to solitary males, who may try to capture females in order to start a group of their own. Any females who appear to be defecting risk a bite from their dominant male, who will try to herd them together. Upon encountering another unimale group, the two dominant males may have a visual showdown, running in circles around the crown of a tree whilst breaking branches and making alarm vocalisations (3).
The capped langur group wakes with the dawn, but they remain in their sleeping trees until the sun has fully risen. Even then they may simply move to higher branches with little foliage where they can bask in the sunlight before heading off to forage. Their diet of leaves demands that they have a specialised digestive system to break down the tough fibre. Enlarged salivary glands release hormones that prepare the leaves for the sacculated stomach: an upper neutral chamber contains bacteria able to break down the fibre before it passes into the lower acidic chamber to be fully digested. The diet includes the leaves, as well as the fruit, flowers, seeds and bark of 35 species of plant. During the rainy season, fruit is eaten more frequently due to its abundance, whereas shortly before and after the monsoon, in May and October, flowers feature more in the diet as flowering peaks. Capped langurs will drink from depressions in the forks of trees, but rarely descend to the ground, particularly when young. They feed mainly in the early morning and late afternoon, and will find a suitable sleeping tree at dusk, changing tree every night. Each langur sleeps in a tree alone, except for mothers who sleep with their young (3).
Most mating takes place in the mornings between September and January, but a smaller peak occurs in April and May. Gestation lasts 200 days and births are concentrated between December and April, with the majority occurring in March (6). The single infant will spend the first two months of its life with either its own mother or with another female in the group, known as an allomother, before straying increasingly to play with the other young monkeys. At one year old infants continue to return to their mother when resting during the day, and to be nursed by her in the evening, although they begin to forage alone at 10 or 11 months (3).