Bioko Drill Monkey

Vital Stats

  • Latin Name: Mandrillus leucophaeus
  • Bioko's Endemic Subspecies: Mandrillus leucophaeus poensis
  • IUCN Status: Endangered
  • Captive Population: ≈280 animals, including 200 at the Drill Rehabilitation and Breeding Center in Nigeria, according to ISIS.


The drill resembles a stocky, olive-brown baboon with a large head, a white ruff around its face and, in males, a bright red chin and an impressive pink and blue rump. Drills are omnivores eating fruits, leaves, roots, mushrooms, giant land snails, sea turtle eggs, insects and small vertebrates. On Bioko, they have also been known to eat injured duikers or the stranded young of other monkey species.

On Bioko Island, drills live in diffuse groups consisting of a single dominant male and multiple females and young. They travel on the ground but feed and sleep in the trees. Drills have a variety of vocalizations including a soft grunt while feeding and a louder bark when alarmed. Females use "crows" (sounds like a chichen being strangled) to maintain contact with each other. Adult males express aggression and alarm with loud "huff-grunts." Like mandrills, drills have been known to gather in large multigroup hordes numbering in the hundreds, but Bioko Island hordes have become rare. The only horde recorded by BBPP occurred in the late 1990's and numbered about 60 animals.

On Bioko Island drills were once found throughout the forests up to the maximum elevation of 3000 m (10,000 ft) above sea level. Now they are restricted to the island's two protected areas, especially those areas that are relatively far from villages and roads. On the mainland, drills can be found in the moist evergreen forests between the Cross River in Nigeria and the Sanaga River in Cameroon. In Cameroon drills have been seen as high as 1000 m above sea level, and they are also found in drier, more savannah-like habitats. However, on the mainland, their range has been devastated by the clear cutting of forests and human settlement. They are hunted everywhere as bushmeat and it is not uncommon for hunters to use dogs to tree an entire group and then shoot all the group members. Although drills are hunted by shotgun on Bioko Island, and then sold as bushmeat in the market in the capital city of Malabo (the carcass of an adult male drill sells for about $180.00), there are still places on Bioko where they are protected by BBPP's local wildlife patrols and they continue to live relatively undisturbed.

To learn more about BBPP's efforts to protect Bioko's drills, consult our section on the Bioko Drill Ecology Project.

Cronin, D. T., D. Bocuma Meñe, T. B. Butynski, J. M. E. Echube, G. W. Hearn, S. Honarvar, J. R. Owens, and C. P. Bohome. 2010. Opportunities Lost: The Rapidly Deteriorating Conservation Status of the Monkeys on Bioko Island, Equatorial Guinea (2010). A Report to the Government of Equatorial Guinea by the Bioko Biodiversity Protection Program, Drexel University, Philadelphia, PA. 40pp.