Drills live in harem groups. One male can can as many as 20 females in his group. During the dry season several groups may come together to form one large group. As many as 200 individuals together have been observed. Males will emigrate and also can remain solitary.
Mandrills normally form large multimale-multifemale groups with a distinct hierarchy.
However, harem groups are not unheard of, as mandrill competition can be fierce. Dominant male mandrills are more colorful than lower ranked males. Group size can vary from 2 to over 200 individuals. Both drills and mandrills are diurnal quadrupeds and can be arboreal or terrestrial. Adult males tend to be more terrestrial than females than females and juveniles, perhaps because of their larger size.