Mandrill

The mandrill is an omnivore. The core of its diet consists of plants, of which it eats over a hundred species.[38] One study found the mandrill's diet was composed of fruit (50.7%), seeds (26.0%), leaves (8.2%), pith (6.8%), flowers (2.7%), and animal matter (4.1%), with other foods making up the remaining 1.4%.[39] During the wet season, mandrills forage in continuous forest, when fruit is most available, while during the dry season they feed in gallery forests and at the borders of savannas and forests.[40]

Mandrills eating fruit

The mandrill's preferred fruits include those of the cashew species Pseudospondias microcarpa, the coffee species Nauclea diderrichii and the wort species Psorospermum febrifugum.[40] Mandrills consume more seeds than many other primate species.[38] Adult male mandrills are one of the few primates capable of biting through the hard shell of Detarium microcarpum seeds.[39] For vegetation, they mostly eat the young leaves, shoots and piths of monocot plants.[38] In particular, mandrills consume leaves from the arrowroots Haumania liebrechtsiana and Trachyphrynium braunianum, as well as the piths of ginger plants like Renealmia macrocolia and species in the genus Aframomum.[40] They are also known to consume mushrooms.[38]

The rest of a mandrill's diet is largely made up of invertebrates, particularly ants, termites, crickets, spiders, snails, and scorpions. They also eat birds and their eggs, frogs and rodents.[38][41] Mandrills have been recorded preying on larger vertebrates such as juvenile bay duikers. Such prey is killed with a bite to the head followed by pulling off the hind limbs and tearing open the belly. Individuals may cooperate during hunting and share kills.[41]

Leopards may prey on mandrills, as traces of mandrill have been found in their feces.[42] Other potential predators include African rock pythons, crowned eagles and chimpanzees.[36][43] Leopards are a threat to all individuals, while eagles are only threats to the young.[44][43] In a study where a mandrill group was exposed to models of leopards and crown eagles, the leopard models tended to cause the mandrills to flee up trees while the eagles were more likely to drive them to take cover. The dominant male did not flee from either model types; in the case of the leopards, he paced around while looking in their direction. Alarm calls were more commonly heard in response to leopards than eagles.[44]

Mandrills can become infected with gastrointestinal parasites, such as nematodes and protozoa. Tumbu fly larvae may live under the skin and individuals that walk though grassland can get infested with ticks. Blood parasites include the malaria-causing Plasmodium and the nematode Loa loa, which is transmitted by bites from deer flies.[45] Wild mandrills have tested positive for SIV, enteroviruses of the species EV-J and astroviruses, including a human variant.[17][46]

Mandrills live in large "supergroups" or "hordes" that can contain hundreds of individuals.[40][50][51] These large groups are fairly stable and do not appear to be gatherings of smaller ones. At Lopé National Park, Gabon, mandrill hordes were found to have an average of 620 individuals, and some groups were as large as 845, making them possibly the largest cohesive groups of wild primates.[51] Another study in Lopé found that a horde of 625 mandrills consisted of 21 dominant males, 71 less dominant and subadult males, 247 adult and adolescent females, 200 juveniles, and 86 dependent infants.[40] A mandrill horde of around 700 individuals in northern Lopé had a total home range of 182 km² (70 sq mi), 89 km² (34 sq mi) of which was suitable habitat. The supergroup would occasionally diverge into two to four subgroups before reuniting.[52] Another 15-month long study of a 120 member group found a home range of 8.6 km² (3.3 sq mi) with an average traveling distance of 2.42 km (1.50 mi) per day.[47]

Mandrills grooming at Natura Artis Magistra

Hordes consist of matrilineal family groups, and females are important for maintaining social cohesion. Strong connections with their relatives may lead to support during conflicts, higher survival rate of offspring and a longer lifespan for females. Dominant females are at the center of the group network and their removal leads to fewer social connections in the group.[53] The social rank of a mother mandrill can contribute to the social rank of both her female and male offspring.[54] Mature males are not permanent members of hordes but join as females become sexually receptive and leave as their sexual cycle ends. As a result, the coloration of the male mandrill may be intended to attract attention in a social structure with no long-term relationships between mates.[51] Higher ranking males are found in the center of a social group while lower ranking males are more likely to occupy the periphery.[55] Females have some control over the males and coalitions can expel an unwanted male from a group.[56] Outside the breeding season, males are believed to lead a solitary life and all-male bachelor groups are not known to exist.[51]

Both male and female mandrills rub and mark trees and branches with secretions from their chest glands, though males (and especially dominant males) mark more than females. The chemicals in the secretions signal the individual's sex, age and rank. Scent-marking may also serve a territorial function, captive alpha males will mark enclosure boundaries.[57] Mandrills will groom one another, even when there is no benefit to be gained from doing so.[58] During grooming, subordinates prefer to pick at other mandrills from behind, in order to minimize eye contact and give them more time to flee if the more dominant individual attacks. The recipients of grooming will try to maneuver the groomer to pick at more "risky" areas.[59]

"Fatted" male mandrill showing colorful posterior

Dominant or alpha male mandrills have the most mating success. Upon gaining alpha status, males develop larger testicles, redder faces and posteriors, more secretion from the chest glands and fatter sides and rumps. When a male loses dominance, these physiological changes are at least partially reversed.[31] The blue facial skin is more consistent in brightness.[31][60] Higher ranking males tend to have more contrast between red and blue facial coloring.[33] Due to their distribution of fat, dominant males are also known as "fatted" males while subordinate males are known as "non-fatted" males.[61] Canine length also correlates with dominance, and males are less likely to sire offspring when their canines are under 30 mm (1.2 in).[22] In some individuals, the development of secondary sexual characteristics is suppressed in response to competition from other males.[55] Male mandrills tend to establish dominance with vocalizations and facial expressions, rather than fighting.[62]

Mating occurs mostly during the dry season, with female ovulation peaking between June and September. Receptive females have sexual swellings on their posteriors,[63] and the red facial coloration can communicate age and fertility.[64] Males also appear to detect a female's reproductive state using the vomeronasal organ (known as the flehmen response).[65] Dominant males try to monopolize access to females by mate guarding, which involves the male tending to and copulating with a female for days.[66] Dominant males tend to sire most of the offspring, but they are less able to monopolize access to the females when many females reach estrus at the same time. A subordinate male is also more likely to have reproductive success if he is closely related to an alpha male.[67] An ovulating female tends to allow the brightest colored males to come near her and touch her perineum, and is more likely to groom and solicit them.[68] The female signals her willingness to mate by positioning her posterior towards the male. Intercourse lasts no more than 60 seconds, with the male mounting the female and making pelvic thrusts.[69]

Mandrill infant perched on mother

Mandrill gestation lasts an average of 175 days with most births taking place between January and March, during the wet season. Gaps in between births range from 184 to 1,159 days with an average of 405 days.[70] and tend to be shorter in higher ranking females.[71] Infants are born at an average weight of 640 g (23 oz), and mostly bare-skinned with some white hair and a tuft of dark hair on the head and along the spine. Over the next two or three months, they develop their adult hair color on the body, limbs and head while the flesh-colored face and snout darken.[72] Dependent infants are carried on their mothers' bellies.[73][51] Young are typically weaned at around 230 days old. Males become more sexually dimorphic between four and eight years old, at which point females are already beginning to give birth.[54] Males start leaving their horde after they reach six years old.[51] Females reach their adult size around seven years while males do so at ten years.[54]

Mandrills communicate with various facial expressions and postures. Threat displays involve open mouth staring, usually in combination with head bobbing, ground slapping and raised hair. These gestures are usually performed by dominant individuals towards subordinates, who respond with bared teeth grimaces, signaling fear and aggression. Both young and low-ranking females show submission and anxiety with a pouting "duck face". Playful intentions are communicated with a relaxed open-mouth face. Males approaching females display a "grin" or silent bared-teeth face and make lip-smacks. This display may also occur with teeth-chattering.[74] Mandrills can develop and pass on new gestures; captive individuals at the Colchester Zoo, England facepalm to discourage being disturbed, particularly while resting.[75]

Mandrills also produce several vocalizations, for both long and short distances. During group movements, adult males produce two-phase grunts and one-syllable roars, both of which are equivalent to the "wahoo" bark of baboons. Other group members produce "crowings", which last almost two seconds and start as a vibration and transition into a longer harmonic sound. Short distance vocals include the "yak", a sharp, repeating, pulse-like call produced by all individuals except for adult males and made in tense situations. Mandrills may also grunt during aggressive encounters. Growls are used to express mild alarm while intense alarms come in the form of a short, two-syllable sharp call known as the "k-alarm". A sharp, loud "K-sound" is produced for unknown reasons. Screaming is a signal of fear and made by individuals fleeing, while the girney, a type of moan or purr, is made as a form of appeasement or frustration among females and young.[76][77] Individual voices are more similar among related animals, but unrelated mandrills can have similar voices if they regularly interact.[78]

• Dixson, Alan F. (2015). The Mandrill: A Case of Extreme Sexual Selection. Cambridge University Press. ISBN 978-1-107-11461-6.