Mandrillus is a genus of large Old World monkeys distributed throughout central and southern Africa, consisting of two species: M. sphinx and M. leucophaeus, the mandrill and drill, respectively. Mandrillus, originally placed under the genus Papio as a type of baboon, is closely related to the genus Cercocebus. They are characterised by their large builds, elongated snouts with furrows on each side, and stub tails. Both species occupy the west central region of Africa and live primarily on the ground. They are frugivores, consuming both meat and plants, with a preference for plants.

Originally, both species were considered part of the Papio genus, as forest baboons, due to superficial similarities such as size and appearance, particularly in facial features. However, studies conducted analysing anatomical and genetic differences between the current Mandrillus and Papio genera showed more differences than similarities resulting in the current taxonomic ranking. Furthermore, the studies showed Mandrillus are more closely related to the white eyed mangabeys, and diverged relatively recently (4 million years ago) from this genus. Mandrillus teeth consist of two incisors, two premolars, one canine and three molars in each half of the upper and lower jaw, totalling 32 teeth.

left|thumb|Mandrillus sphinx skull and shoulder blade

Within the shoulder and upper arm structures of the Mandrillus monkeys a deep scapular, broad deltoid plane, narrow stable elbow region and other skeletal features indicate the use of the forelimbs for climbing and foraging. This is used by the monkeys to climb trees when searching for ripe fruit and in the aggressive foraging of the forest floor in search of food. Similarly, drills are one of the most sexually dimorphic primates for body weight, with a male growing up to 32 kg while a female grows to 12 kg. Sexual dimorphism is also displayed in the growth of the craniofacial bones of both species. The males of each species have longer muzzles, much larger paranasal swellings and longer canines than their female counterparts. In a study of wild drills, female muzzles only grew up to 70% the length of the male muzzles. In a study conducted in Cameroon, approximately 84% of the faecal matter of mandrills consisted of fruit. Seasonal changes can be seen within Mandrillus diet, during peak fruit season (September to March) their diet consisted mostly of fruit, pulp and seeds whilst during the fruit scarce season (June to August) there was a great increase in the consumption of insects, woody tissue and especially nuts. Important fruit include but are not limited to, the fruit of the bush mango (Irvingia gabonensis), African Corkwood tree (Musanga cecropioides), Grewia coriacea, Sacoglottis gabonensis and Xylopia aethiopica. Invertebrates consumed include crickets, ants, caterpillars and termites. Rarely, Mandrillus monkeys will eat larger animals, such as rats and gazelles when presented with the opportunity. A study of mandrills done at Campo reserve in Cameroon found small groups contain 14 - 95 individuals. Mandrillus leucophaeus social structures are unknown, due to low populations, and secluded habitats with dense forestry. This aligned with the social structures reported in other research papers done on wild mandrills, where stable multi-male and multi-female groups were found. Roars are single low, single syllable sounds used exclusively by males in the same context as two-phase grunts. Crowling is used by infants and females during group movement or foraging to call together the dispersed group.

They also use numerous short-range vocal sounds for various purposes. The "yak" and grinding of teeth are used during tense situations. The grunt is used in aggressive situations and screams are used to escape or while experiencing fear. The growl is used to convey mild alarm, the K-alarm is used to convey intense alarm and the "girney" is used for appeasement. Staring open-mouthed is a display of aggression, frowning with bare teeth is used to encourage submission, staring with bare teeth can communicate aggression or fear, pouting signals submission and a relaxed open mouth encourages playing. The loss of habitat is an ongoing threat that can be attributed to the expansion of human settlements as well as the clearing of forests for chipping factories and agriculture. Hunting and poaching of Mandrillus monkeys for meat or to protect crops is also major, ongoing threat to the population despite the implementation of hunting restrictions and sanctuaries.

Sources

  • Primate Info Net Mandrillus Factsheets