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).
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.
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.
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).
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).
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
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).
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).
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).
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
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 September 14.