Mandrill

The mandrill is a large Old World monkey native to west central Africa, and the largest monkey. It is one of the most colourful mammals, with red and blue skin on its face and rump, a red line down the middle of the face and a yellow-orange beard. Males weigh 19–30 kg and females 10–15 kg. Mandrills mainly live in tropical rainforest but also travel across savannas, and they are active by day and spend most of their time on the ground. They prefer fruit and seeds but also eat leaves, mushrooms and animals from insects to juvenile bay duiker. They live in large hordes with females at the core, while adult males are solitary outside the breeding season.

About the mandrill

The mandrill is a large Old World monkey native to the rainforests of west-central Africa, famous for the red and blue skin on its face and rump. Its closest living relative is the drill, which shares the genus Mandrillus. Both were long grouped with baboons, but they are more closely related to white-eyelid mangabeys.

The mandrill, Mandrillus sphinx, is the largest monkey and the most sexually dimorphic primate. Males are about twice the weight of females, with longer canines and far brighter color. A male's canine teeth can reach 4.5 cm (1.8 in), against about 1 cm (0.4 in) in females. Both sexes have a short, stumpy tail just 7–10 cm (2.8–3.9 in) long.

The body is stocky, with a large head and long muzzle. The coat is grizzled olive-brown, with a yellow-orange beard, stiff white whiskers around the lips and patches of bare white skin behind the ears. Males carry a crest of long hair on the head and neck. Compared with baboons, mandrills have longer fingers and toes and a more opposable big toe.

The face is the showpiece. A red stripe runs down the middle of the muzzle to a red nose, flanked by grooved blue skin that, in males, sits over ridged swellings of bone. The red comes from blood vessels close to the surface, while the blue is structural color made by parallel bundles of collagen fibers. The male's rump is a mix of red, pink, blue and purple. Females have duller faces, darkened by melanin. Charles Darwin wrote that no other mammal is colored in so extraordinary a manner as the adult male mandrill.

Behavior and diet

Mandrills are diurnal, active about 10 hours a day from morning to dusk, and they often choose a new tree to sleep in every night. They spend most of their time on the ground but will feed as high as the forest canopy.

They are omnivores that eat more than a hundred plant species. In Gabon's Lopé National Park, their diet was about 51% fruit, 26% seeds, 8% leaves, 7% pith, 3% flowers and 4% animal matter. Mandrills eat more seeds than many primates, and adult males are among the few primates that can bite through the hard shell of Detarium microcarpum seeds. Animal food includes ants, termites, crickets, spiders, snails, scorpions, birds and eggs, frogs and rodents. They have even been recorded killing young bay duikers, sometimes hunting cooperatively and sharing the kill.

Mandrills live in huge, stable groups called hordes. In Lopé, hordes averaged 620 animals and reached 845, possibly the largest cohesive groups of wild primates. Hordes are built around related females, and dominant females sit at the center of the social network. Adult males are not permanent members. They join when females become receptive and leave afterward, and outside the breeding season they are believed to live alone.

Rank shows on the body. When a male becomes dominant, his face and rump grow redder, his testes get larger, his chest glands secrete more scent and he puts on fat along his flanks and rump. These "fatted" males sire most of the young. If he loses rank, the changes partly reverse. Males usually settle disputes with calls and facial displays rather than fights.

Mandrills communicate with a rich set of faces and sounds. Threats involve an open-mouth stare, head bobbing and ground slapping. A relaxed open mouth signals play, and males approaching females grin and smack their lips. During group travel, adult males give two-phase grunts and roars, and other members give long "crowing" calls. Mandrills mark trees with secretions from chest glands that signal sex, age and rank, and captive mandrills have been seen using sticks to clean themselves.

Most births happen between January and March, in the wet season, after a gestation of about 175 days. Newborns weigh about 640 g (23 oz) and ride on their mother's belly, and they are weaned at around 230 days.

Range and habitat

The mandrill lives in west-central Africa: southern Cameroon, mainland Equatorial Guinea (Río Muni), Gabon and parts of the Republic of the Congo. Its range is bounded by the Sanaga River to the north and the Ogooué and Ivindo rivers to the east. The Sanaga separates it from the drill, so the two species do not appear to share habitat.

Mandrills prefer primary tropical rainforest over secondary forest, especially thick undergrowth of gingers and other perennial plants. They also use strips of gallery forest surrounded by savanna and cross grassy areas, and have been recorded in mountains, near rivers and in cultivated fields. In the wet season they forage in continuous forest when fruit is plentiful; in the dry season they move to gallery forests and forest-savanna edges.

They share these forests with other primates, including talapoins, guenons, mangabeys, colobus monkeys, chimpanzees and gorillas. A horde of about 700 animals in northern Lopé used a home range of 182 km² (70 sq mi).

Mandrill vs baboon

Mandrills are often called baboons, and for a long time scientists placed them in the baboon genus Papio. Genetic studies have since shown that mandrills and drills form their own genus, Mandrillus, which is a sister lineage to the white-eyelid mangabeys.

Conservation status

The mandrill is listed as Vulnerable on the IUCN Red List in a 2019 assessment. The total population is unknown but is suspected to have fallen by more than 30% over 24 years. It is also listed in CITES Appendix I, which bans commercial trade in wild-caught animals.

The main threats are habitat destruction and hunting for bushmeat. Mandrills appear to have lost a great deal of habitat in Equatorial Guinea and southern Cameroon, and hunting there seems to have shrunk group sizes. Their status in the Republic of the Congo is unknown.

Gabon is considered the species' stronghold, with low human population density and vast rainforests. Most of its forests are leased to timber companies, but about 10% lies within a national park system, 13 parks of which were created in 2002. Each country in the mandrill's range has at least one protected area for the species. Leopards prey on mandrills of all ages, while crowned eagles threaten only the young.