Mandrill Facts

The gap between the sexes is one of the most extreme in any mammal. A full-grown male can reach 37 inches long and 70 to 80 pounds — dominant males up to 119 — while a female is less than half that, 22 to 25 pounds. The male's face carries a bright red stripe down the muzzle flanked by grooved ridges of vivid blue and purple, colors produced by the structure of collagen fibers rather than pigment; his rump is similarly bright, helping the horde follow him through the dark understory. His canines can top 2.5 inches — longer than a lion's — used mostly in gaping threat displays at rivals rather than in fights, and both sexes have cheek pouches for stuffing fallen fruit to chew later in safety. Once grouped with baboons, the mandrill was moved into its own genus, Mandrillus (shared only with the drill), after genetics showed it is closer to the mangabeys; it belongs to the Old World monkey family Cercopithecidae. Its extreme ornamentation is the work of sexual selection in a dim forest where bright signals settle status without fatal combat.

The mandrill is endemic to the tropical rainforests of equatorial West-Central Africa, in a narrow range south of the Sanaga River and north of the Congo — southern Cameroon, Equatorial Guinea, Gabon, and the Republic of the Congo. It favours primary and secondary lowland rainforest, gallery forest reaching into savanna, and rocky montane forest, foraging mostly on the ground by day but climbing into the middle canopy of tall trees each night to sleep safe from ground predators.

Mandrills are opportunistic omnivores, though over 80% of the diet is plant matter — chiefly fruit, worked out of the leaf litter along with nuts and hard seeds that powerful jaws can crack when other primates can't. When fruit is scarce they turn to roots, tubers, leaves, bark, and fungi, and they actively hunt invertebrates, flipping rocks and tearing rotting logs for ants, termites, spiders, snails, and scorpions. Big males occasionally take small vertebrates too — frogs, tortoises, rats, even small duikers.

Mandrill society is unusual for its scale: they live in huge, cohesive hordes that often number in the hundreds, and the largest recorded, in Gabon's Lopé National Park, held about 1,300 animals — matriarchal at the core, built around adult females and young. Adult males are largely solitary, joining the hordes for the breeding season, and their rank is set by size and color: dominant males show the brightest facial ridges (tied to high testosterone), and a male that loses rank literally fades. Grooming holds the horde together, easing aggression and cementing female alliances.

Breeding tracks the dry season, peaking June to October when solitary males rejoin the hordes and dominant males guard estrous females with canines and roaring calls. After about 175 days' gestation the female bears a single infant, dark-furred with pale skin that darkens over its first months; it clings to her belly, then rides her back, with the horde providing collective defense against crowned eagles and leopards. Daughters stay in the natal horde for life, while sons disperse around age six to live alone and eventually fight into a new horde's hierarchy. Wild mandrills live 20 to 25 years.

The mandrill is Vulnerable and steadily declining across its range. The foremost threat is the commercial bushmeat trade: traveling in large, noisy ground hordes makes mandrills conspicuous and easy to hunt with guns and snares, and a big male is a prized target. Logging compounds it — damaging the canopy and, more devastatingly, carving roads deep into once-inaccessible forest that give poachers direct access — while farmland expansion fragments ranges and brings mandrills into conflict as crop pests. Survival depends on protecting large forest tracts, anti-poaching enforcement, and curbing bushmeat demand.

• San Diego Zoo Wildlife Alliance: Mandrill Profile
• IUCN Red List of Threatened Species: Mandrillus sphinx