The western red colobus forms large polyandrous groups of between 12 and 80 individuals (6). A diurnal species, it spends the day moving through the top of the canopy looking for leaves, shoots, fruits, and fungi. It has a complex stomach divided into sacs, as an adaptation to its diet. In the upper chamber of the stomach, foliage is fermented by bacteria, and once in the lower chamber it can be digested by acid. The stomach is particularly large so that it can take the large quantities of this low value food that are needed to provide the western red colobus with the necessary energy and nutrients to survive. More than a quarter of the body weight of an adult red colobus can be attributed to the food in its stomach (5).
Although not territorial, larger groups of western red colobus tend to have dominance over smaller groups when interactions occur. Mixed-sex groups contain more females than males, leaving bachelor groups of between 8 and 40 males. When ready to mate, females develop swollen genitals and will present to males to encourage mating. Each female may mate with many males, producing just one offspring every two years. Infanticide (the killing of infants) can occur, but the reasons for this are not fully understood. Once weaned, both male and female western red colobus will leave the group, but females will join another mixed-sex group, whereas males may join a bachelor group. A social monkey, the western red colobus conforms to a hierarchy, crouching to communicate submission, which may lead to ‘social’ mounting, not to mate, but as a prelude to social grooming (4).