The drill (Mandrillus leucophaeus) is one of the most endangered of all African primates. It is a large short-tailed forest baboon, which displays pronounced sexual dimorphism. The males can grow up to twice the size of females!
Drills 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. In times of food abundance, these small groups may congregate, forming large groups of over 100 individuals.
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.
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.
Drills mainly forage on the ground or in the lower levels of the trees, and are generally fruit eaters, although they will also take a range of plants, seeds and insects.
This species has an extremely restricted range; the mainland subspecies is known only from the Cross River in Nigeria to the Sanaga River in Cameroon. The Bioko drill is found on the southern tip of the island of Bioko, Equatorial Guinea.
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