The Drill is a large baboon with a short tail and a dark grey-brown body. This animal is among the most endangered primates in Africa. Drills exhibit well-defined sexual dimorphism with males, being up to twice as large as females. These forest baboons have pink, mauve and blue rumps. Adult males are distinguished by pink lower lip as well as dark grey to black face with a white chin and raised grooves on the nose. Meanwhile, females are identified by lacking the pink chin.
The natural range of this species is restricted to Cameroon, where these animals occur north of the Sanaga river and on the south-western edge of the coastal island of Fernando Poo (Bioko). The Korup National Park in the north of Cameroon holds the largest protected population of Drills. The preferred habitat of these primates is mature lowland, coastal and riverine forest. However, they are also known to frequent young secondary forests of their range. They generally look for sheltered areas and avoid open terrains.
Drills are diurnal and social animals. They typically form small groups of an average of 20 individuals. These troops consist of one dominant male and multiple related females with their young. During periods of abundant food, Drills occasionally occur in large concentrations or super-groups of more than 100 animals. They are semi-terrestrial creatures, sleeping in the lower canopy of the trees. When moving along the ground, they use of all their four limbs. Drills are highly territorial animals. In order to mark their territory, these primates rub their chests on trees. Living in dense forest habitat, Drills mainly rely on vocalization to keep contact between members of a troop. The most commonly used vocalizations are two grunting calls.
As omnivorous animals, Drills feed upon a wide variety of food, particularly favoring fruits, leaves as well as invertebrates, generally termites. They supplement this diet by raiding manioc and palm oil plantations.
There is no information on reproductive system of this species, although the defined sexual dimorphism suggests that Drills may be polygynous with each male having numerous partners. Gestation period lasts for about 179 - 182 days and young are born in December-April. During the breeding season, each female yields a single baby. The newborn Drill remains close to its mother until reaching 15 - 16 weeks old, when it's completely weaned. Then, males will leave to find another group, whereas females will continue living with their natal group. The age of sexual maturity is 3 years old in females and 6 years old in males.
During the last 20 years, these primates have largely suffered from destruction of their mature forest habitat, which has led to notable population decline of the Drills in Cameroon. On the other, reforestation of the area is mainly associated to planting of exotic, non-palatable species. The Drills also attract hunters for their meat, which occasionally come across large concentrations of this species, killing up to 20 animals in a single expedition.
The IUCN Red List doesn’t provide the exact number of the Drills’ total population. However, population on the Bioko Island is estimated to remain under 5,000 individuals. Overall, Drills are currently classified as Endangered (EN) on the IUCN Red List.
The Drills may play some role in seed dispersal, due to their diet. They may also affect predator populations, as items of prey.