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BiologyDrills are active during the day and occur in small troops of around 20 individuals, usually composed of a single dominant male, related females and their offspring (3). In times of food abundance, these small groups may congregate, forming large super-groups of over 100 individuals (3). Vocal communication is very important for troop cohesion in the dense forests that they inhabit; two distinct 'grunt' calls have been identified and these may be important in keeping contact between group members (3). The dominant male is in a position to secure access to most of the females in his troop (4). A female will usually give birth to a single infant; whilst daughters remain in their natal group, males will disperse, once they have reached maturity, to join a new troop (4). Drills mainly forage on the ground or in the lower levels of the trees, and are generally frugivorous (fruit eaters), although they will also take a range of plants, seeds and insects (4). They appear to be semi-terrestrial, moving on all fours on the ground (4), but sleeping in the lower canopy of the trees (3).