Despite being widespread, De Brazza’s monkey is generally shy and inconspicuous, only rarely announcing its presence with deep, booming group calls (1) (5). This species is mostly arboreal, but unlike other guenons, which usually stay in the tree canopy, it is often found moving through the forest understory or along the ground (6). The diet consists mainly of fruits and seeds, although leaves, mushrooms and small reptiles and insects may also be consumed (4) (5). As foraging usually takes place in exposed areas, food is stored in cheek pouches, and only eaten when the monkeys return to a safe location (4).
Throughout much of its range, this species lives in polygynous groups of between eight and ten individuals, but in certain regions, such as Gabon, De Brazza’s monkeys can be found in small, monogamous family groups, comprising a male-female pair and their offspring (2) (6). Interestingly, De Brazza’s monkey is the only guenon species that forms these strong breeding pair bonds (5). Although groups maintain small territories that they mark out with saliva and scent, they do not appear to show any aggression towards other groups of De Brazza’s monkey that enter these areas (4) (5). In contrast, when encroachment is made by a different species of monkey, De Brazza’s monkeys may become extremely hostile, with the entire group becoming involved in forcibly ejecting the intruder (4).
De Brazza’s monkey breeds throughout the year, with the female usually giving birth to a single infant after a gestation period of around 168 to 187 days. In order to reduce the risk of predation, the vulnerable infant clings tightly to the mother's stomach. Weaning takes place after around one year, but the young begin to try solid food after about two months of age. De Brazza’s monkeys become sexually mature at around age five or six, and may live for up to 22 years in the wild (4).
De Brazza’s monkey is preyed upon by numerous animals, such as large African eagles, leopards, and other primates—including humans (7). When a group is threatened, the females and the young generally hide in the undergrowth, while the male climbs a tree and makes loud calls in an attempt to distract the predator (6).