The mandrill (Mandrillus sphinx) is the world’s largest monkey species, native to the tropical forests of west-central Africa. Despite its formidable size, it is scientifically classified as an Old World monkey, distinct from the baboons it superficially resembles. Mandrills are semi-terrestrial, spending their day foraging on the forest floor before retreating to the trees to sleep at night.
Defining Physical Characteristics
The mandrill’s appearance is marked by extreme sexual dimorphism, meaning males and females differ significantly in size and coloration. Adult males are substantially larger than females, often weighing between 42 and 66 pounds, while females typically weigh only 22 to 33 pounds. Males also possess canine teeth, which can reach up to 1.8 inches, and have a more prominent, elongated snout.
The most distinguishing feature is the vibrant coloration displayed by the males, which serves as a visual signal of dominance and health. The face is adorned with a bright red stripe running down the center of the muzzle, flanked by thick, grooved ridges of bright blue skin. This striking pattern is mirrored on the rump and posterior, which features bare skin in shades of red, blue, and purple. These colors are directly linked to testosterone levels; dominant males display the most intense hues, which can fade if their social status declines.
Life in the Wild
Mandrills are found in the equatorial rainforests of west-central Africa, including Gabon, Cameroon, Equatorial Guinea, and the Republic of the Congo. The largest population is believed to reside in Gabon, considered a stronghold for the species. Their distribution is largely bound by the Sanaga River to the north and the Ogooué and Ivindo Rivers to the east, which helps define their specific ecological niche.
While they prefer the dense, humid environment of primary rainforests, mandrills also traverse forested savannas for foraging. As flexible omnivores, their diet is diverse, consisting mainly of fruits and seeds, which are particularly abundant during the wet season. They also supplement their diet with leaves, roots, fungi, and a variety of animal matter, including insects, snails, bird eggs, and small vertebrates.
Complex Social Structure
Mandrills exhibit a complex social organization, living in massive, multi-male and multi-female groups known as “hordes” or “troops.” These aggregations can be exceptionally large, sometimes numbering in the hundreds of individuals, with some recorded reaching up to 845 members. Females form the stable, core unit of these groups, often remaining within their birth group throughout their lives, while males typically disperse once they reach maturity.
The group structure is hierarchical, with a single, dominant male typically leading the horde. This leader is identified by his larger size and the brighter coloration of his face and rump, which signals his status and reproductive success. Communication relies on a combination of visual, vocal, and olfactory signals, crucial for maintaining cohesion across large numbers and dense habitat. Vocalizations include grunts, screams, and a distinctive low-frequency “two-phase grunt” used by adult males for long-distance coordination.
Survival Status
The mandrill is currently classified as Vulnerable on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The overall population trend is decreasing, with estimates suggesting a decline of more than 30 percent over the past 24 years. This decline is driven by two primary threats: habitat loss and relentless hunting pressure.
Extensive deforestation fragments the mandrill’s dense rainforest habitat, making it difficult for groups to find food and mates. This habitat loss results from commercial logging, agriculture, and human settlements. Additionally, the species is heavily targeted by the bushmeat trade, where their meat commands high prices in Central African markets. Conservation efforts are focused on establishing protected areas, with Gabon’s national parks serving as important refuges.