Mandrill (Mandrillus sphinx): Facts, Colors and Habitat

Appearance

The mandrill has a stocky body, a big head with a long muzzle, strong limbs of similar length and a very short, stumpy tail. The fur is olive-brown to dark gray, finely banded, with a yellow-orange beard and paler underparts. Stiff white whiskers surround the lips.

The face is what makes the mandrill unmistakable. A bright red stripe runs down the center of the muzzle to a red nose, and on each side the bare skin is blue and deeply grooved. In adult males, bony swellings support these blue ridges. The rump and genital area of males are a mix of red, pink, blue and purple skin. Females have the same pattern but in duller tones, and some have dark, almost black faces.

The red comes from blood vessels close to the skin’s surface, while the blue is a structural color produced by orderly layers of collagen fibers that scatter light, not by blue pigment. Read more in Why do mandrills have colorful faces?.

Size: the largest monkey

The mandrill is generally regarded as the largest monkey and is the most sexually dimorphic primate, meaning males and females differ more in size than in any other primate. Wild adult males weigh about 19–30 kg (42–66 lb), around twice as much as females at 10–15 kg (22–33 lb). Some captive males have weighed considerably more.

Large baboons such as the chacma baboon can match or exceed mandrills in length and occasionally in weight, so the title is close. Compare them in What is the largest monkey in the world?.

Mandrill vs drill

The mandrill has only one close relative, the drill (Mandrillus leucophaeus). Together they form the genus Mandrillus. For a long time both were classed as baboons, because they share a long muzzle, a powerful build and a life spent mostly on the ground. Studies of anatomy and DNA since the late 20th century showed that they are closer to the white-eyelid mangabeys, and the two lineages split from each other several million years ago.

The easiest difference is the face. A drill has a black face framed by pale fur and a red lower lip, without the mandrill’s red stripe and blue ridges. Drills live north of the Sanaga River, in western Cameroon, southeastern Nigeria and on Bioko Island, so the two species do not overlap. The drill has a much smaller range and is listed as Endangered.

Habitat and range

Mandrills live only in west-central Africa: in southern Cameroon south of the Sanaga River, in mainland Equatorial Guinea (Río Muni), across Gabon and in the southwest of the Republic of the Congo. The Sanaga River separates them from the closely related drill to the north.

They prefer dense, mature tropical rainforest but also use secondary forest, gallery forests along rivers within savanna, and the edges between forest and grassland. They spend most of their time on the ground, moving on all fours, but climb trees to feed and to sleep at night, often choosing a new sleeping tree each evening. For other animals of these forests, see rainforest animals.

Diet

The mandrill is an omnivore with a mostly plant-based diet. A study in Lopé National Park, Gabon, found that fruit made up about half of the diet and seeds about a quarter, with leaves, pith, flowers and mushrooms making up much of the rest. Mandrills eat more than 100 plant species and have powerful jaws: adult males can crack some very hard seeds that few other primates can open.

About 4–5% of the diet is animal food. Mandrills turn over stones and logs and dig through leaf litter for ants, termites, crickets, spiders, snails and scorpions. They also take eggs, frogs, rodents and occasionally larger prey such as young duikers, small forest antelopes. In the wet season they forage in continuous forest, and in the dry season they use gallery forests and forest edges more.

Hordes: giant groups

Mandrills live in some of the largest stable groups of any wild primate. At Lopé, hordes averaged about 620 animals, and one was counted at about 845. One horde of around 700 mandrills ranged over about 182 square kilometers (70 square miles).

Hordes are built around related females and their young, who stay together for life. Adult males are different: they spend much of the year alone and join the horde mainly during the breeding season, when females are fertile. Large all-male groups are not known.

Mandrills communicate with facial expressions, such as an open-mouth threat stare, a silent bared-teeth grin and lip-smacking, and with calls including deep two-phase grunts from males that help keep the horde together as it moves through thick forest. Both sexes rub scent from a chest gland onto trees.

Rank, color and fatted males

Adult males compete for rank, and their bodies change with it. When a male becomes dominant, his face and rump turn a more intense red, his testes grow larger, his chest gland produces more scent and he puts on fat along the flanks and rump. Researchers call these high-ranking males “fatted” males. Lower-ranking “non-fatted” males are slimmer and duller, and many spend more time on the edges of the horde or alone.

These changes are reversible. Studies of a semi-free-ranging colony in Gabon found that a male who lost his top position also lost some of his red coloring. Long canines matter too: males with short canines rarely father young. Most contests are settled by displays, such as head-bobbing, ground-slapping and open-mouthed threats, rather than serious fights.

Reproduction and life cycle

Most mating happens in the dry season, from about June to September, and most births follow in the wet season, from about January to March. Pregnancy lasts around 175 days, and a female usually gives birth to a single infant weighing about 640 g (1.4 lb).

Infants have pale skin and dark hair on the head and back and cling to their mother’s belly. They are weaned at around seven to eight months. Females usually give birth for the first time at about four to eight years old, while males take much longer to mature and reach full size at around nine to ten years. Dominant males with the brightest colors father most of the infants.

Wild lifespans are poorly known, because few mandrills have been followed for their whole lives; estimates are around 12–14 years or somewhat more. In zoos, mandrills often live 30 years or longer.

Predators and threats

Leopards are the main natural predator of adult mandrills. Crowned eagles may take young ones, and African rock pythons and chimpanzees are other possible predators. When threatened, the horde scatters into trees or dense cover, while dominant males may stay to face the danger.

The biggest threats come from people. Mandrills are hunted for bushmeat, and their large, noisy groups make them easy to find and to trap or shoot in numbers. Logging roads open up remote forest to hunters, and farming and development have cleared habitat, especially in Cameroon and Equatorial Guinea. Hunting has also reduced group sizes in some areas.

Conservation status

The mandrill is listed as Vulnerable on the IUCN Red List (2019 assessment), with a decreasing population. Its total numbers are unknown, but the IUCN suspects a decline of more than 30% over about 24 years. It is listed on Appendix I of CITES, which bans international commercial trade in wild-caught animals.

Gabon is the stronghold of the species. It still has vast forests and a low human population, and a national park system created in 2002 protects key mandrill areas such as Lopé. Each country in the mandrill’s range has at least one protected area where it lives.

Mandrills and people

The mandrill’s name dates to the 1700s and combines “man” with “drill,” an old West African-derived word for a large monkey or ape. Charles Darwin described the adult male mandrill as the most extraordinarily colored of all mammals in The Descent of Man (1871), and the species remains a classic example of sexual selection.

Mandrills are popular in zoos in Europe and North America, where breeding programs help maintain healthy captive populations. The famous animated character Rafiki in The Lion King is often called a baboon, but his colorful face was inspired by the mandrill. A common myth is that mandrills are apes because they are large and have short tails, but they are true monkeys, members of the Old World monkey family. To understand the difference between monkeys and apes, read Are chimpanzees monkeys?.