SOCIAL ORGANIZATION AND BEHAVIOR
The sooty mangabey social organization is characterized by large groups which are
(Bergmüller et al., unpublished results cited in Range & Noë 2002; Range &
Fischer 2004). These large groups can contain from around 100 to as many as 120 individuals in the
wild but can be somewhat smaller having been observed in a different study to range from 20-48
individuals (Galat & Galat-Luong 1985; McGraw & Bshary 2002; Range & Noë 2005).
Photo: Irwin S. Bernstein
There are two categories of males within a sooty mangabey group. Some males are full-time
residents of the group while others are more transient, alternating between several weeks of
residence within the group and several weeks of absence (Range et al., in press cited in Range
2005). Males disperse from their natal group while females tend to stay in the same place
(Range 2006). Among males, there is a linear dominance hierarchy which provides the
with preferential breeding opportunities but not one which completely precludes
(unpublished data cited in Range 2005).
Within wild sooty mangabey groups there is a stable
linear dominance hierarchy
of females (Range & Noë 2002; Range 2006). Evidence hints that this hierarchy affects a
female's food intake, with higher-ranking individuals foraging more efficiently as they are
centrally placed in the group and do not need to be as aware of predators as those on the periphery
(Range & Noë 2002). In captivity, the dominance hierarchy of the sooty mangabey is not
kin-based. Starting at 1.5 to 2 years of age, infants approximate their mother's rank until an age
of 3 years, although remaining slightly below them in rank until that point (Gust & Gordon 1994;
Gust 1995a; Range & Noë 2005). Starting at three years old, young sooty mangabeys exhibit a
drive to move up in the dominance rankings and start to do so (Gust 1995b). Also at this time,
the rank of the infants of both sexes surpasses their mothers' and by five to six years of age,
males outrank all of the females (Gust & Gordon 1994; Gust 1995a). Wild juvenile females show some
stability with respect to the ranking of their mothers while males do so initially, but over time
this correlation declines (Range 2006). Female rank does not depend on age or size of an
individual and there is no correlation between the ranks of sisters (Gust & Gordon 1994; Stahl
& Kaumanns 1999). However, in wild populations, adult females show affiliation with those
similar to them in rank (Range 2006). Captive adult females do not often interact with immature
individuals, preferring to interact instead with adults of both sexes (Ehardt 1988). In addition,
there is some inconclusive evidence that older individuals are preferentially groomed by the other
sooty mangabeys in the group (Ehardt 1988). There is also evidence that allogrooming in captivity
serves both hygienic purposes as well as other purposes which may include tactile communication
(Pèrez & Veà Beró 1999).
In captivity, there are four ways that juvenile sooty mangabeys move up the dominance hierarchy and
they do so without the assistance of relatives from the same matriline. Hierarchical mobility
occurs by directly confronting higher-ranking individuals, joining an aggressor against a
higher-ranking individual, challenging a higher-ranking individual and enlisting the help of another
high-ranking individual, or challenging a higher-ranking mangabey and enlisting the support of an
adult male to help in the challenge (Gust 1995a). Outsiders to a conflict are more likely to
assist one side when they outrank both of the other mangabeys involved (Range & Noë 2005).
Aggression between sooty mangabeys is typically not severe and normally does not result in serious
injury, although rare wounding and even death has been known to occur (Gust 1995a). In captivity,
submissive behavior is most often signaled by avoidance (Bernstein et al. 1983). In addition,
captive males were observed to almost never be the target of aggression from other group members
(Bernstein et al. 1983). Post-aggression behavior is typified by a victim approaching an aggressor
and presenting its hindquarters, soothing the aggressor (Gust & Gordon 1993).
The female sooty mangabey sexual cycles are characterized by swellings of the
sex skin synchronized
with ovulation. During
this swelling, the anogenital
region of the female will be bright pink and swell, attracting males (Gust 1995b). In captivity,
perineal swelling starts at an average age of 36.4 months (3 years) of age and the first births
usually occur when the mother is around 56.5 months (4.7 years) of age (Gust et al. 1990). As
first perineal swellings start at around 36 months (3 years) and first conceptions occur at 51
months (4.3 years) of age, a period of sterility likely exists after the onset of sexual swelling
but the reasons for such a period remain unexplained (Gust et al. 1990). Swelling of the sexual
skin typically lasts under two weeks with maximum swelling around two weeks prior to menstruation
(Stevenson 1973). The reproductive status of females is influenced by the seasons with captive
females showing more conceptions between October and March than in the rest of the year (Gust et al.
1990). In the wild, sooty mangabeys have a discrete and distinct mating season (Range & Fischer
Photo: Kathelijne Koops
Captive female sooty mangabeys show postconception perineal swelling which peaks 49 days after
conception and is quite consistent in duration and timing between individuals. This sexual
swelling is indistinguishable from normal fertile swelling associated with ovulation and occurs
near the end of the first trimester of pregnancy (Gordon et al. 1991; Gust 1994b). During this
post-conception swelling, group males will mount and attempt to copulate with the female. The
alpha male however, will not. Through some mechanism, the alpha male is able to differentiate
between fertile and non-fertile post-conception swelling and will not mount a pregnant female
regardless of post-conception swelling (Gust 1994b).
An idiosyncratic aspect of captive male sooty mangabey development is the early onset of sexual
behavior. Between one and four years of age, males exhibit mounting behavior and will start
non-functionally mounting at a rate much higher than mature males, around three times as often.
In addition, mounting behavior at this early age is usually directed at mature females, not females
similar in age to the young males (Gust & Gordon 1991b). Mounting behavior has started as early
as 9 months old and is extremely early for sexual behavior in a primate (Gust & Gordon 1991b).
The earliest recorded captive age at which a male successfully impregnated a female counterpart is
3 years and 8 months of age but sexual maturity usually arrives later at around 7 years (Gust &
Gordon 1991b; Gust et al. 1998). By the time that males reach reproductive maturity, the frequency
of mounting behavior and copulation decreases from the rates seen in adolescents (Gust & Gordon 1991b).
The copulation posture
of the captive sooty mangabey consists of a male holding onto the female by the ankles and hips with
the female in some instances looking back toward the male (Gust & Gordon 1991b). After
copulation, the female will quickly move away from the male and continue vocalizations which
started during copulation or immediately after (unpubl. observ. cited in Gust 1994a). In the wild,
copulation vocalizations are uttered during intercourse by females but not by males (Range &
Fischer 2004). Copulation vocalizations are also occasionally uttered by females in non-copulation
contexts such as during defecation and in the absence of males although the meaning of this behavior
is not understood (unpubl. observ. cited in Gust 1994a; Range & Fischer 2004). More than one
mount by a male is common before ejaculation occurs. Over half of mounts by adult males in a group
are performed by the alpha male of the group (Gust & Gordon 1991b).
In the wild, the alpha male
attempts to monopolize sexual partners but
are common (Range 2005). Group encounters with non-resident males as well as solitary non-group
males are common in the wild, and these encounters sometimes result in copulations with receptive
females (Range 2005). It appears nevertheless, that the dominant male has the best opportunities
to reproduce and rank can be an indicator of potential reproductive success (Gust et al. 1998;
Benneton & Noë 2004). Mates change in captivity however, as female offspring from year to
year are not typically sired by only one single male (Gust et al. 1998). Contrary to this,
consistent preference for a specific sexual partner has been seen in captive populations
Gestation in the captive
sooty mangabey averages 167 days (5.5 months) with over 83% of infants surving past 30 days
(Gust et al. 1990; Gordon et al. 1991).
The interbirth interval
in sooty mangabey females averages
16.6 months (1.4 years) (Gust et al. 1990).
All of the information on parental care and infant development in sooty mangabeys comes from captive
animals. The developmental data comes from a single mother-infant pair of the white-naped mangabey
(C. a. lunulatus), which is now generally considered to be a subspecies of C. atys. The other
data are from captive C. atys elsewhere.
Photo: Irwin S. Bernstein
In C. a. lunulatus, at about two weeks of age, some infants start eating solid fruit.
From around four to six weeks of age, a common carrying posture is the infant clinging ventrally to
its mother. Also during this period, the mother will groom her offspring's back while nursing and
by the fifth week, grooming extends to the infant's hands and feet. Also between four and six weeks
of age, infants start playing and starts grasping and mouthing and by six weeks of age, the infant
will leave its mother's arms for the first time, but remaining quite close to its mother. Between
six and fourteen weeks of age, exploration of the infant's immediate surroundings starts, but
remains confined to an area quite close to its mother. Movement during this time also becomes more
independent and includes running, walking and jumping. However, when high branch movement or
troop movement is required, the infant will still cling to its mother ventrally. Social play starts
at 16 weeks old and in the 18th week, a mother starts refusing its infant's attempts to nurse. The
father of the infant does not interact with his offspring and its mother actively discourages any
such interaction (Schlee & Labejof 1994).
Captive male sooty mangabeys carry infants in certain circumstances, particularly when deposed
alpha males carry infants
in the presence of the new alpha male. This behavior is likely to protect the infant from
aggression (Busse & Gordon 1984). Attacks on infants and
infanticide by newly
ascended alpha males are known, with some attacks even proving fatal for the infant (Busse &
Gordon 1983). The reason for such attacks is consistent with male behavior aimed at increasing his
chances of passing his genes by killing the offspring of a female and subsequently mating with that
female (Busse & Gordon 1983).
Captive female sooty mangabeys groom the eyelid region of their infants with carefully selected
stones. However, the purpose of this grooming has not yet been ascertained (Kyes 1988). Also in
captivity, 1.3% of infants are neglected by their mothers and 5.8% are physically abused
(Maestripieri et al. 1997).
The wild sooty mangabey emits 19 different vocalizations. The most common vocalization is the
"grunt," which is uttered in many different contexts by both sexes including while foraging,
during social interactions and in dominance relations. Males often "grunt" several times in
a row while females vary in the spacing of their "grunts." "Twitters" are uttered in
similar contexts to "grunts" but mostly in foraging contexts and only by adult females and
both sexes of juveniles. "Screams" are uttered in contexts of conflict by adult females and
juveniles but only rarely by adult males. Other agonistic calls include the "growl," the
"grumble," the "hoo," the "intense threat," and the "wau" (Range & Fischer
2004). Copulatory calls are given by females during copulation and immediately afterward but males
do not utter specific copulation calls (unpubl. observ. cited in Gust 1994a; Range & Fischer
2004). Only adult males emit "whoop gobbles," usually in contexts involving contact with
other sooty mangabey groups or predators (Range & Fischer 2004). Alarm calls are given in the
presence of predators and are responded to by other group members climbing into trees and scanning
for the predator (Range & Fischer 2004).
Sooty mangabeys observe one another and follow the gaze of others. In a captive study, sooty
mangabeys would recognize where a conspecific was looking and would redirect their gaze in the same
direction (Tomasello et al. 1998).
Content last modified: December 2, 2008
Written by Kurt Gron. Reviewed by W. Scott McGraw.
Cite this page as:
Gron KJ. 2008 December 2. Primate Factsheets: Sooty mangabey (Cercocebus atys) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/sooty_mangabey/behav>. Accessed 2015 March 5.