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Drill
Mandrillus

SOCIAL ORGANIZATION AND BEHAVIOR

Much of the socio-ecology of Mandrillus is still unclear, especially when it comes to M. leucophaeus, the lesser known species. Also, there is some conflicting information about group structure within the genus. Some researchers suppose a multi-tier organization with subunits (one-male units) aggregating into larger units (hordes) and others observe no suborganization within large aggregations and only a seasonal male presence in groups (Gartlan 1970; Hoshino et al. 1984; Harrison 1988; Forthman et al. 1992; Rogers et al. 1996; Abernethy et al. 2002; Jolly 2007; Astaras et al. 2008). Another option may be daily or temporary fisson-fusion of larger social groups, and further research is required into the organization of smaller groupings of Mandrillus (Astaras et al. 2008).

M. sphinx
M. sphinx
Photo: Joanna Setchell

The most pronounced aspect of M. sphinx social organization, however, is the potential for extremely large stable groups in the wild (Abernethy et al. 2002; Jolly 2007). These stable groups, termed "hordes," often reach into hundreds of members; in one study, they averaged 620 individuals and can be as large as 845 (Sabater Pí 1972; Jouventin 1975; Harrison 1988; Rogers et al. 1996; Tutin et al. 1997b; Abernethy et al. 2002). Data from the wild suggest that adult males only enter hordes during female seasonal sexual cycling (about three months of the year) and leave after, but group size is not correlated with reproduction. Thus, the only annually resident members of M. sphinx groups are adult females and dependent offspring, making the social system female-led (Abernethy et al. 2002). However, social groups can also be quite variable, with smaller groups (less than 50 individuals) also rarely recorded in addition to hordes, as well as solitary males, but never all male (bachelor) groups (Sabater Pí 1972; Jouventin 1975; Hoshino et al. 1984; Harrison 1988; Rogers et al. 1996; Abernethy et al. 2002). Outside of the mating season, males are solitary (Abernethy et al. 2002). Under semi-free-ranging conditions at CIRMF, breeding is moderately seasonal, with 63% of female periovulatory periods occurring between July and September (Setchell & Wickings 2004). There is a corresponding birth peak between January and March, and at least some males appear to remain with the social group year-round, although there is space for them to be solitary in the naturalistic enclosures at CIRMF (Setchell et al. 2002; J. Setchell pers. comm.).

Recorded average group sizes in M. leucophaeus included 93.1, 52.3, and 9.1 individuals, but observations have recorded groups into the hundreds of members and as large as an estimated 400 individuals (Gartlan 1970; Dunn & Okon 2003 cited in Astaras et al. 2008; Wild et al. 2005; Astaras et al. 2008). It is possible that true group sizes are even larger (Wild et al. 2005). On Bioko Island, it appears that M. leucophaeus groups are smaller than on the mainland, usually less than 20 individuals (Gonzalez-Kirchner & de la Maza 1996). Solitary males are sometimes encountered and there are no seasonal patterns of group size (Wild et al. 2005). It is unclear as to the exact social organization of M. leucophaeus, but multimale groups and group fission and fusion have been observed (Astaras et al. 2008).

Male mandrills at CIRMF reach sexual maturity at about 4 years old, and are capable of siring at 4.9 years (Setchell & DIxson 2002; Setchell et al. 2005). They become peripheral to the social group at about 6 years old, and data from the wild suggest that wild males emigrate from their natal group at about this age (Harrison 1988; Abernethy et al. 2002; Setchell et al. 2006). In captivity, M. leucophaeus males also reach maturity around six years old (Böer 1987). Males of both species reach full size at about 9 or 10 years (Setchell et al. 2006; Marty et al. in press). Female mandrills at CIRMF cycle for the first time at an average age of 3.6 years, first give birth at an average of 4.2 years, and reach full size at about 7 years old (Setchell et al. 2001; 2002; Setchell & Wickings 2004).

When by themselves in a captive setting, solitary M. sphinx may groom itself (autogroom), bounce upon surfaces, play, forage, or mark with its sternal gland. Captive social behaviors include allogrooming, solicitation of grooming (usually by presenting the posterior or the neck or armpit), playing, presenting, mounting, threatening, attacking, and "smiling". Threats are commonly conveyed by bobbing the head (Mellen et al. 1981).

In semi-captive M. sphinx, affiliative relationships between adult males are extremely infrequent and males form linear dominance hierarchies, with a single alpha male at the top (Setchell & Wickings 2005; Setchell et al. 2005a). The top-ranking male can be often identified as the male individual with the brightest red coloration with roughly less and less red coloration in decreasingly ranked males (Setchell & Wickings 2005; Setchell et al. 2008). Early studies, based on six males, suggested that there are two phases of M. sphinx adult male; "fatted" (with brighter and more pronounced coloration as well as higher cutaneous gland secretion and an increase in "fattedness" of the rump) and "non-fatted" (with less pronounced coloration and "fattedness" of the rump) (Dixson et al. 1993). "Fatted" and "non-fatted" males did not differ in body mass, merely in the distribution of weight in the body (Wickings & Dixon 1992). However, subsequent studies suggest that there is a continuum between paler and brighter males, and that color is not necessarily associated with "fattedness" (Setchell & Dixson 2001b). When alpha-male status is attained, a male undergoes physical changes and becomes more brightly colored with higher testosterone, and becomes more social (Setchell & Dixson 2001b). With a loss of status, the reverse changes occur (Setchell & Dixson 2001b; Setchell et al. 2008).

When semi-captive adult males encounter one another, they may enter a "stand-off" in which they remain near each other while anxious or stressed, and may threaten each other (Setchell & Wickings 2005). Such "stand-offs" can end either without resolution, with one individual leaving, or with physical contact, and are more likely to occur between closely-ranked, physically similar males (Setchell & Wickings 2005). Males show submission by avoidance, fleeing, presentation of the hindquarters, or screaming. Threats are conveyed through "stares," "head-bobs," "ground-slaps," "threat-grunts," lunges and chases. Confrontations between males can become violent and can even result in the death of individuals (Setchell & Wickings 2005). The M. sphinx "grin" appears to have a non-agonistic function, much as the captive M. leucophaeus "smile" indicates a friendly approach or benign intentions (Hearn et al. 1988; Setchell & Wickings 2005; Otovic 2007).

M. sphinx
M. sphinx
Photo: Verena Behringer

In semi-captivity, several female mandrills were observed to attack a wounded adult male, possibly to exclude it from group membership and indicating some female control over group membership (Setchell et al. 2006b).

REPRODUCTION

Most data on reproduction in the genus Mandrillus come from a long-term semi-captive population of M. sphinx in Gabon. There is little data on reproduction in wild, free-ranging groups. In semi-captivity, M. sphinx have a polygyandrous mating system (Setchell et al. 2002).

In wild M. sphinx in Gabon, there is a discrete mating season during which females exhibit sexual swellings, usually between June and November with a corresponding birth season between January and April (Jouventin 1975; Abernethy et al. 2002). Outside of the mating system, adult males leave M. sphinx groups, only returning at the onset of the subsequent mating season (Abernethy et al. 2002). In semi-captivity at CIRMF, a mating peak is also observed between July and September with a corresponding birth peak from January to March, and males do not necessarily leave the social group outside the mating season (Setchell et al. 2002; Setchell & Wickings 2004).

In captivity, female M. sphinx present by aiming their bodies away from the male and looking back towards the male over their shoulders (Mellen et al. 1981). The copulatory posture is dorsal-ventral, with the male behind the female (she may be straight-legged, with the ventrum on the ground or somewhere in-between), forearms holding in front of the pelvis and feet on the ground (Mellen et al. 1981). Copulatory sperm-plugs are formed (Wickings & Dixson 1992).

M. sphinx females in a semi-captive group first give birth at an average age of 4.2 years old with higher-ranking females reproducing earlier than lower-ranking females (Setchell & Wickings 2004; Setchell et al. 2005b). Males start to reproduce significantly later, starting at an average of 11.6 years old, although they are capable of reproducing from 4 years old (Setchell et al. 2005b). In a long-term study of a semi-captive population at CIRMF, all females reproduced while only a third of the males were successful (Setchell et al. 2005b).

Gestation averages 175 days in M. sphinx with an inter-birth interval in semi-captivity of 405 days on average, although values vary slightly between specific captive populations (Setchell et al. 2002; but see also Bettinger et al. 1995). M. leucophaeus have a gestation period between 179-182 days and an inter-birth interval of 17-19 months (Böer 1987). The estrous cycle in M. leucophaeus is 33 days, while in M. sphinx it is 35 or 38 days (Harvey & Clutton-Brock 1985; Setchell & Wickings 2004).

In a semi-captive group, roughly two-thirds of offspring were sired by dominant males (Setchell et al. 2005a). Males mate-guard higher ranking females more than lower ranking females (Setchell & Wickings 2006). The larger the canine teeth of an M. sphinx, the higher reproductive success the animal is likely to have (Leigh et al. 2008).

PARENTAL CARE

As expected in populations with a mating season, wild M. sphinx in Gabon has a birth season between January and April (Jouventin 1975). In semi-captivity, M. sphinx have a birth season from January to March and give birth at night only (Feistner 1992; Setchell et al. 2002). At birth female M. leucophaeus weigh 722 g (25.5 oz) while female M. sphinx weigh 890 g (31.4 oz) and M. sphinx males 906g (32.0 oz) (Smith & Leigh 1998). In general, there is little difference between the birth weights of the sexes (Wickings & Dixson 1992). The face of the infant M. leucophaeus is light in color, fading to black by 8 months old (Böer 1987). M. sphinx infants are born either gray or white with a dark stripe down the back. The top of the head is black with a pink face and the torso and limbs have bluish skin (Feistner 1992).

M. leucophaeus
M. leucophaeus
Photo: Irwin Bernstein

One M. sphinx infant was first seen away from its mother at 20 days of age, and started trying solid foods at around 35 days old. By four months old, the infant left its mother often and for long periods. The infant was weaned at 8 months old (Carman 1979). M. leucophaeus are weaned by 15-16 months of age (Böer 1987).

COMMUNICATION

One of the most conspicuous of displays in M. sphinx is the "silent bared-teeth face" (also called "smiling" and "grinning"), in which the animal exposes its teeth by curling back the lips, erects the crest of the head, while shaking the head. While multiple interpretations have been offered for this display, it most likely has a conciliatory, non-aggressive or peaceful function (Bout & Thierry 2005; Laidre & Yorzinski 2005; Setchell & Wickings 2005). The "crest-raise" signal (erection of the sagittal crest) may be related to the "silent bared-teeth face" signal in function and may grade into it (Laidre & Yorzinski 2005). Submission is signaled by a presentation of the rump. Aggression is signaled by staring, head-bobbing, and ground-slapping (Setchell & Wickings 2005).

Facial color in M. sphinx females may communicate reproductive information to others - color is brighter during the follicular phase than during the luteal phase, varies across gestation, and peaks at four and eight weeks post-parturition (Setchell et al. 2006a). In addition, facial redness in male M. sphinx communicates competitive information to other males and information about male fitness to females (Setchell et al. 2008).

Wild M. sphinx vocalizations can be divided into roughly 11 categories, divided between long distance calls and short distance calls (Kudo 1987). Long distance calls include the "2-phase grunt," "roar," and "crowing". Short distance calls include the "yak," "grunt," "k-alarm," "k-sound," "scream," "girney," and "grind" (Kudo 1987). The "2-phase grunt" is the most commonly emitted vocalization, even though it is only emitted by adult males, and may indicate the adult male's role in group cohesion. Both "crowing" and the "2-phase grunt" may function as long-distance contact calls and serve to communicate information about the locations of group members (Kudo 1987; Harrison 1988). When with sexually receptive females, wild M. sphinx males may emit "grunt" vocalizations continuously, but never when alone (Abernethy et al. 2002). Males also emit "threat-grunts" to other males to indicate aggression (Setchell & Wickings 2005).

Both members of the genus Mandrillus possess a sternal gland (Hill 1970; Feistner 1991). Both female and male M. sphinx use this gland to scent mark by grasping a substrate or object and rubbing their chest upon it (Mellen et al. 1981; Feistner 1991). Scent marking may help reinforce dominance status or help a M. sphinx orient itself within its home range (Feistner 1991).

Content last modified: October 14, 2009

Written by Kurt Gron. Reviewed by Joanna Setchell.

Cite this page as:
Gron KJ. 2009 October 14. Primate Factsheets: Drill (Mandrillus) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/drill/behav>. Accessed 2014 November 23.