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 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).

The distribution on the Drill is uncertain, but it appears to have a very restricted distribution in western and south-western Cameroon (including Korup National Park) and south-eastern Nigeria, between the Cross River and Sanaga River. There is one record from just south of the lower Sanaga at Ongue Creek (Grubb 1973). It is also present in the south-western corner of Bioko Island.

There are two subspecies: M. l. leucophaeus occurs on the mainland, between the Cross River and Sanaga River valleys; M. l. poensis occurs only on Bioko Island.

Drills are found only in Cameroon, north of the Sanaga river and on the coastal island of Fernando Poo. The largest protected population is found in the Korup National Park in the northern part of Cameroon.

Biogeographic Regions: ethiopian (Native )

Historic Range:
Equatorial West Africa

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).

Members of the genus Mandrillus meaure 610 to 764 mm in length, with the tail adding an additional 52 to 76 mm. Males are nearly twice the size of females, weighing in at an average 25 kg, compared to the diminuative females, which weigh only 11.5 kg on average.

Drills have distinct ridges on the side of their nasal bones, which are caused by outgrowth of the ridged and grooved bone. Male drills are easily distinguished from male mandrills by the absence of brightly colored facial skin, and the absence of prominent grooves in the facial ridges. The facial coloration of drills is jet black, except for the lower lip, which is bright red.

This genus is characterized by beards, crests, and manes. The pelage of drills is brown with a yellow tinge.

The skin on the rump of these animals is bright red, due to increased density of blood vessels in the region. The genitals of males may also be blue or violet. The rump coloration in females and juveniles is less pronounced.

Average mass: females, 11.5 kg; males 25 kg.

Range length: 610 to 764 mm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger; sexes colored or patterned differently; male more colorful; ornamentation

Average mass: 18250 g.

Habitat and Ecology

Systems

• Terrestrial

Drills are found in the lowland forests, coastal, and riverine forests of western Africa. They prefer the habitat of mature forests, but have been seen on occasion in young secondary forests. Drills avoid open country away from the shelter of the forests. Males are mostly terrestrial, with smaller females and young ascending into the lower canopy to obtain both food and shelter.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: rainforest

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

Drills are omnivorous creatures that rely on fruit, leaves and invertebrates (mainly termites) as food sources. They have been known to raid the manioc and palm oil plantations in search of food.

Animal Foods: insects

Plant Foods: leaves; fruit

Primary Diet: omnivore

To the extent that these animals serve as prey for carnivores, they may impact carnivore populations. It is likley that through their frugivory they play some role in seed dispersal.

Ecosystem Impact: disperses seeds

Predation on these animals probably occurs. Likely predators include leopards as well as other large carnivores.

Much of the communication among drills is visual, with displays of brightly colored posteriors and markings bordering their nasal passages. Drills are noisy creatures, regularly emitting grunts and screams, but the purpose of these sounds is not yet known.

In addition to these forms of communication, it is likely that tactile communication is important, both between mothers and their offspring, and between mates. Most primates spend significant amounts of time grooming their allys, and grooming can be used to maintain social bonding.

Both drills and mandrills possess scent glands on the chest which are used for marking branches. This scent marking is a form of chemical communication.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: scent marks

Perception Channels: visual ; acoustic

The maximum reported lifespan for this genus is 46 years of age.

Average lifespan

Sex: female

Status: captivity: 33.4 years.

Average lifespan

Status: captivity: 28.6 years.

Average lifespan

Status: captivity: 28.4 years.

Maximum longevity: 39 years (captivity) Observations: There have been claims of animals living up to 46 years (Ronald Nowak 1999), which is not impossible but has not been verified either. In captivity, the record longevity of this species belongs to one wild born female that was about 39 years old when she died (Richard Weigl 2005).

The mating system of M. leucophaeus has not been described in detail. However, given the sexual dimorphism present in this species, it is likely that these monkeys mate polygynously. The other member of the genus Mandrillus, M. sphinx is known to form single male harems with 5 to 10 adult females and their dependent offspring. It is likely that M. leucophaeus is similar in this regard.

Breeding status of drills is conveyed through coloration differences exhibited in the genital region, which ranges in color from deep scarlet to pink and blue. The ovulatory cycle of female drills typically lasts about 33 days. The birth season of these primates is thought to be between December and April. Gestation length has not been reported for this species, but is known to be 168 to 176 days in M. sphinx, and is probably similar for M. leucophaeus.

Mandrillus sphinx reaches sexual maturity around the age of 3.5 years. This species also has an interbirth interval for multiparous females if 13 to 14 months, indicating that these primates give birth approximately annually. It is likley that M. leucophaeus is similar in these features.

Breeding interval: Females of this species probably breed annually.

Breeding season: Breeding is seasonal, although breeding season is not reported. Births peak between December and April.

Average number of offspring: 1.

Range gestation period: 168 to 179 days.

Average age at sexual or reproductive maturity (female): 3.5 years.

Average age at sexual or reproductive maturity (male): 3.5 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous

Average birth mass: 772 g.

Average number of offspring: 1.

Average age at sexual or reproductive maturity (female)

Sex: female: 1277 days.

Parental investment in these animals has not been fully described, although it is likely to be similar to that seen in other polygynous primate species.

Mothers provide the bulk of the care and protection for their offspring. Maternal kin, brothers and sisters, may also help in carrying, grooming, and playing with young. Males in some species care for the young on occasion, and may do so in M. leucophaeus.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); extended period of juvenile learning

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There is 1 barcode sequence available from BOLD and GenBank.   Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen.  Other sequences that do not yet meet barcode criteria may also be available.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Species: 2
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Justification

History

• 2000
  Endangered
• 1996
  Endangered
• 1994
  Endangered
  (Groombridge 1994)
• 1990
  Endangered
  (IUCN 1990)
• 1988
  Endangered
  (IUCN Conservation Monitoring Centre 1988)
• 1988
  Endangered
• 1986
  Endangered
  (IUCN Conservation Monitoring Centre 1986)

Destruction of the mature forest in Cameroon is the primary factor in the decline of drills over the last twenty years. Unfortunately, the reforestation in these areas has concentrated on the planting of exotic, non-palatable species. Drills are also hunted extensively for their meat, which is considered sweet. Unfortunately, since drills form huge aggregations, hunters easily slaughter up to twenty individuals in one expedition.

It is essential that hunting and logging restrictions be placed in the areas where the drill lives or the species wil surely not survive. Cites Appendix I, Endangered

US Federal List: endangered

CITES: appendix i

IUCN Red List of Threatened Species: endangered

Current Listing Status Summary

Status: Endangered
Date Listed: 10/19/1976
Lead Region: Foreign (Region 10) 
Where Listed:


Population detail:

Population location: entire
Listing status: E

For most current information and documents related to the conservation status and management of Mandrillus leucophaeus, see its USFWS Species Profile

Classified as Endangered (EN) on the IUCN Red List 2007 (1) and listed on Appendix I of CITES (2). Subspecies: Mainland drill (Mandrillus leucophaeus leucophaeus) classified as Endangered (EN); Bioko drill (M. l. poensis) classified as Endangered (EN) on the IUCN Red List 2007 (1).

Population

Population Trend

Major Threats

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).

Conservation Actions

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.

Drills are viewed as crop pests and are often shot and killed by farmers.

Negative Impacts: crop pest

These primates are hunted for meat.

Positive Impacts: food