Drill  (Mandrillus leucophaeus)

The drill is one of the most endangered of all African primates (6). It is a large short-tailed forest baboon, which displays pronounced sexual dimorphism; males can grow up to twice the size of females (5). In both sexes the coat is olive brown, with a pale underside and the bare black face, which has an unusual extended muzzle featuring prominent ridges along each side (4). There is a white ruff around the head and in mature males this is particularly dense, accentuating the size of his head and chest (6). Males have pink and lilac coloured testicles and a reddish region around the anus; if an individual is excited these colours are brighter (4). When females are in oestrus the area around her sexual organs swells up, and during pregnancy this area becomes deep red (4). Two subspecies of drill are recognised, both are similar in appearance except for the hairs on the sides of the crown which are ringed yellow and black in the mainland drill (M. l. leucophaeus) and are brownish yellow with a black tip in the Bioko drill (M. l. poensis) (4).

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, whilst the Bioko drill is found on the southern tip of the island of Bioko, Equatorial Guinea (6).

Drills inhabit mature lowland, coastal and riverine tropical rainforest (3).

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 (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).

The mature rainforest in this equatorial region of Africa has been destroyed at an alarming rate, causing many species to become endangered. The drill is under additional pressure from hunting as the sweet 'bushmeat' of this species is an important income for many people in the region (3). Large groups of noisy drills, either on the ground or within range amongst the trees, make an easy target for hunters and cleared forests are ever more accessible (3).

In 1995, the drill was identified as an important priority for conservation due to its taxonomic uniqueness; it has only one close relative (3). It is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), thus prohibiting international trade (2). In the wild, only a single population is known to occur within a protected area, the Korup Reserve in Cameroon (7). Fauna and Flora International (FFI) are involved in the Drill Rehabilitation and Breeding Centre, Nigeria, which aims to rehabilitate young orphaned drills, and to raise awareness of the plight of this species in the local area (7). In addition, there are over 40 drills in captivity around the world, some of which have been successfully bred (7). This may provide a last redoubt against the extinction of this magnificent species.

For more information on the drill see:

• The Primate Info Net:
  www.primate.wisc.edu/pin/

Authenticated (10/7/03) by Anna Feistner. Head of Species Conservation, Durrell Wildlife Conservation Trust.
http://www.durrellwildlife.org