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.
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.
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.
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.
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.
The maximum reported lifespan for this genus is 46 years of age.
Little is known about the wild behavior of drills. In captivity, these monkeys form either one-male or multi-male groups consisting of between 20 to 25 individuals. They have also been known to form larger aggregations of these male dominated subgroups, totalling up to 200 individuals. Locomotion is quadrupedal.
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.
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.
Predation on these animals probably occurs. Likely predators include leopards as well as other large carnivores.
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.
These primates are hunted for meat.
Drills are viewed as crop pests and are often shot and killed by farmers.
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
Nancy Shefferly (editor), Animal Diversity Web.
Ken Briercheck (author), University of Michigan-Ann Arbor.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
Lee, Phyliss C. (1988). Threatened Primates of Africa: The ICUN Red Data Book. IUCN Gland, Switzerland.
Napier J.R., Napier P.H. (1985). The Natural History of the Primates. The MIT Press, Cambridge, Massachutsetts.
Kavanagh, Micheal (1983). The Complete Guide to Monkeys, Apes and Other Primates. Jonathan Cape, London.
Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.