Mandrill

Mandrill eating a flower

The mandrill is an omnivore. It usually consumes plants, of which it eats over a hundred species. Fruits, including the seeds, are the most important food item in the species diet.[36] Fruits taken include those of the cashew species Pseudospondias microcarpa, the coffee species Nauclea diderrichii and the wort species Psorospermum febrifugum.[37] Consumption of seeds is higher in mandrills than many other primate species and crushed seeds are commonly found in their feces.[36] Adult male mandrills are one of the few primates capable of biting through the hard shell of Detarium microcarpum seeds.[38] For vegetation, they mostly eat young leaves, shoots and piths of monocot plants.[36] These include the young leaves of the arrowroots Haumania liebrechtsiana and Trachyphrynium braunianum and the piths of the gingers Renealmia macrocolea and Aframomum species.[37] Mushrooms are also eaten.[36] During the wet season, mandrills forage in continous forest, when fruit is most available, while during the dry season they feed in gallery forests and on the savanna-forest edge.[37]

Invertebrates make up most of the animals consumed, particularly ants, termites, crickets, spiders, snails, and scorpions. Other animal matter eaten include birds and their eggs, frogs and rodents.[36][39] Mandrills have been recorded taking larger vertebrates such as juvenile bay duikers. Such prey is killed with a bite to the head followed by pulling the hind limbs and skinning the belly. Individuals may cooperative during hunting and share kills.[39] 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 foods (4.1%), with other foods making up the remaining (1.4%).[38]

Mandrill traces have been found in the feces of leopards.[40] Other potential predators include African rock pythons, crowned eagles and chimpanzees.[34][41] Leopards are threats to all ages while eagles are only threats to infants and juveniles.[42] Adult male mandrills, with their size and long canine teeth, would be formidable even for leopards.[41] 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 into 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 back and forth while looking in their direction. Alarm calls were more commonly heard in response to leopards than eagles.[42]

Mandrills may contain gastrointestinal nematode worms and protozoa. Blood parasites include the malaria-causing Plasmodium and the nematode loa loa, which is transmitted by bites from deer flies. Tumbu fly larve may burrow into the skin. Mandrills that walk though grassland can get infested with ticks.[43] In addition to SIV,[16] wild mandrills have tested positive for enteroviruses of the species EV-J and astroviruses, including a human variant.[44]

Mandrills live in large "supergroups" or "hordes" which number in the hundreds.[48] These groups are fairly stable are do not appear to be gatherings of smaller units. At Lopé National Park, Gabon, the mean size of mandrill hordes was found to be 620 individuals and some groups were as large as 845, possibly the largest stable groups of unaided wild primates.[49] 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.[37] A mandrill horde of around 700 individuals in northern Lopé used a total home range of 182 km² (70 sq mi) over a period of six years, 89 km² (34 sq mi) of which was suitable habitat. They spent less than half their time in 10 percent of their total range. The supergroup would occasionally diverge into two to four subgroups that would reunite after certain periods.[50] Another 15 month long study of a 120 member group found that the mandrills had a home range of 8.6 km² (3.3 sq mi) and traveled an average of 2.42 km (1.50 mi) per day.[45]

Mandrills grooming at Natura Artis Magistra

Females in a group belong to matrilineal families and are important for maintaining social cohesion. Having strong relationships with their relatives may give females advantages such as support during conflicts, higher survival of offspring and a higher lifespan. Dominant females are at the center of the group network and their removal leads to less social connections between individuals.[51] The social rank of a mother mandrill can contribute to the social rank of both her female and male offspring.[52]

Mature males are not permanent members of groups but join as females become sexually receptive and leave as their sexual cycle ends. The prominent coloration and large size of males thus may have evolved as important competitive signals in a social organization where long-term social bonds between mates are non-existent.[49] Higher ranking males are found in the center of a social group while lower ranking males are more on the periphery.[53] Females have some control over male membership and coalitions can expel an unwanted male from a group.[54] When outside the hordes, males live a seemingly solitary life and all-male bachelor groups are not known to exist.[49]

Both male and female mandrills rub and mark trees and branches with secretions from their chest glands, though males mark more than females with dominant males marking most of all. The chemicals in the secretions contain information on the individual's sex, age and rank. Scent-marking may also serve a territorial function, captive alpha males mark enclosure boundaries more frequently.[55] Mandrills groom one another, even when there is no ulterior benefit to be gained from doing so.[56] During grooming, subordinate individuals prefer to pick the back and rump, as it allows them to avoid eye contact and gives them more time to flee if the groomee turns to attack. The recipients of grooming will try to maneuver the groomer to pick at more "risky" areas.[57]

"Fattened" male mandrill

Dominant or alpha male mandrills have the most mating success. Upon gaining alpha status, males develop larger testicles, redder skin on the face and genitals, heightened secretion of the chest glands and fatter flanks and rumps. When a males loses dominance, the reverse happens though not to the extreme as when they gain dominance.[30] The blue facial skin is more consistant in brightness while the blue posterior does get brighter with age.[30][58] Blue skin may also signal dominance; and higher ranking males tend to have more contrast between red and blue facial coloring.[32] Due to their distribution of fat, dominant males are also known as "fattened" males while subordinate males are known as "non-fatted" males.[59] Long canines are also a sign of dominance and males are unable to sire offsping until their canines are 30 mm (1.2 in).[21] The intense competition that exists between males suppresses the development of secondary sexual characteristics in some individuals.[53]

Mating occurs mostly during the dry season, with female ovulation peaking between June and September. Receptive females develop sexual swellings,[60] and the red facial coloration can signal their reproductive quality.[61] Dominant males try to monopolize access to respective females by mate guarding, which involves the male following and copulating with a female for some days.[62] While dominant males tend to sire most the offspring, as more females reach estrus at the same time their paternity decreases as they are less able to monopolize access to the females. A subordinate male is also more likely to have reproductive success if they are closely related to an alpha male.[63] Ovulating females are more likely to allow the brightest colored males near them and inspect their perineum, and are more likely to groom and solicit them.[64] The female invites the male to copulate by presenting her posterior to him. Intermission usually lasts for 60 seconds, with the male mounting the female and making pelvic thrusts.[65]

Sleeping mother with young in Hagenbecks Tierpark

Gestation in the species lasts an average of 175 days with most births taking place between January and March, during the wet season. Interbirth periods last an average of 405 days,[66] and tend to be shorter in higher ranking females.[67] Infants are born around 640 g (23 oz), and covered in sparse white hair with blackish hair along the spine, a black cap on the scalp and a hairless flesh-colored face. Over the next two or three months, they develop more brownish hair on the body, limbs and head while the face and snout darken.[28] Dependent infants are carried on their mothers' bellies.[68][49] Young are typically weaned at around 230 days old. During the post-weaning period, males develop more sexually dimorphic characteristics. They experience a subadult growth spurt between four and eight years old at which point females are already beginning to give birth.[52] Males start leaving their horde around the age of six years.[49] Females may reach their adult size around seven years while males do so at ten years.[52]

Mandrills communicate with various facial expressions and postures. Threat displays involve open mouth staring, usually accompanied by head bobbing, ground slapping and raised hair. This is performed by dominant individuals towards subordinates, who response with bared teeth grimaces, signaling fear and aggression. Both young and low-ranking individuals show submission and anxiety with a pouting "duck face". Playful intentions are communicated with a relaxed open-mouth face. Males will signal non-aggressive intent towards mates with a "grin" or silent bared-teeth face and lip-smacking which permits them to approach and make contact with the females. This display many also occur with teeth-chattering.[69] Mandrills can learn and pass on new gestures culturally, captive individuals at the Colchester Zoo learned to facepalm.[70]

Mandrills also produce several vocalizations, both for long and short distances. During group movements, adult males produce two-phase grunts and roars, the latter being one-syllable. Both sounds are acoustically similar to the "wahoo" bark of baboons. Other group members produce "crowings", which begin as a vibration followed by a continuous harmonic sound that lasts 1.8 seconds or more. Short distance vocals include the "yak", a sharp pulse-like call produced by all age or sex classes expect for adult males and made in tense situations. All age or sex classes may grunt during aggressive encounters. Growls are made as mild alarms 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 moaning and purring sound, is made as a form of appeasement or frustration among females and young.[71] Individual voices are similar among related animals but social factors can also be an influence and unrelated mandrills can have similar voices if they have a certain degree of familiarity.[72]

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