Some guenons, such as C. aethiops, often run about on the ground. This species is also a good swimmer. All guenons take shelter in trees when alarmed, however, and C. aethiops may even gather and hold well-leaved branches around itself. They sleep in trees, probably in a sitting position while holding onto branches or to each other. The diet is varied but consists mainly of fruits, leaves, grain, and roots and also includes, at least on occasion, young birds, birds' eggs, small reptiles, and insects.
Home range varies greatly in size.
The same species, however, has been reported to have a home range of up to 130 ha. In Uganda a group of C. mitis used a 72.5-ha. The group often split into subgroups composed of either adult pairs and their young, females, or juveniles. Apparently, most males dispersed from the groups upon reaching maturity and then lived alone. Although there was a dominant male, most of the others participated in mating with the group's females.