SOCIAL ORGANIZATION AND BEHAVIOR
The dynamic and complex social system of the gelada baboon is a nested,
multi-level hierarchy of social units consisting, in increasing order of size;
reproductive units (1-12 adult females, young, 1-4 males) and all-male groups
(2-15 males), bands (2-27 reproducive units and several all-male groups), herds
(ephemeral accumulations of 2-60 reproductive units, sometimes from different
bands), and communities (1-4 bands that overlap extensively) (Crook 1966; Ohsawa
1979; Kawai et al. 1983; Dunbar 1986; 1993; Grüter & Zinner 2004).
Herds can be up to around 350 individuals and perhaps as large as 400, but do
not last long, are unstable and usually average lower numbers of individuals
(Crook 1966; Ohsawa & Kawai 1975; Dunbar 1986; 1993).
Photo: Peter Fashing
The two main levels of organization that comprise the social system are the
reproductive unit and the bands that consist of multiple reproductive units
(Dunbar 1984b). A result of this is that reproduction occurs at a different
level of social complexity (the reproductive unit) than the ecological
activities of the species (the band). However, foraging can be coordinated at
various levels of gelada social organization (Kawai et al. 1983).
Females are the focus of social relations and interactions in geladas (Dunbar
1986). In reproductive units, if more than one adult male is present, only one
is reproductively active to the exclusion of extra-group males as well as other
males in the group and thus the reproductive unit is effectively a single-male
unit (Dunbar & Dunbar 1975; Ohsawa 1979; Mori et al. 1997). Reproductive
units are often stable in composition for longer than six months and are able to
withstand disruptions which otherwise might cause social reorganization in other
species (Dunbar 1979). Males are usually resident in a reproductive unit for
4-5 years (Dunbar 1986).
Little aggression within a reproductive unit is recorded, with the majority
of aggression being directed outward towards non-unit individuals (Dunbar &
Dunbar 1975). When it does happen, it is females who initiate agonism with other groups
and as the conflict escalates, both males and sometimes many females of the opposing sides get
involved. (Dunbar & Dunbar 1975; R.I.M. Dunbar pers. comm). Similarly, in the rare instances where it
is seen within a reproductive unit, most aggression is between females (Dunbar & Dunbar 1975).
Further, grooming and other social interactions between females
usually occurs between pairs which are kin-related and females do not usually
interact at all with more than two or three kin females within the reproductive
group (Dunbar 1979; 1983; 1986). The restriction in number of individuals with
which any individual female socially interacts may be explainable in light of
time constraints enforced by large proportions of time spent feeding (Dunbar
1983a). Reproductive units are limited in size however, with periodic fission
occurring when they grow too large (Dunbar 1993). Within the reproductive unit,
there exists a hierarchy of females, with lower-ranking females attaining less
reproductive success and having fewer offspring than higher-ranking individuals
(Dunbar 1980b; 1993). Closely related females have similar social status within
the hierarchy (Dunbar 1980b). The relationships between females develop and are
acted out independently of reproductive interactions with the male (Dunbar
1986). In fact, males are not socially integral to the cohesion of the
reproductive unit as a whole (Dunbar 1993).
Females stay in their natal units for life and emigrate only on exceedingly
rare occasions (Ohsawa 1979; Dunbar 1993). True transfer between bands is
limited to males seeking mating success in a new reproductive unit of their own
(Dunbar 1980a). There are two main ways in which the breeding male can change
within a reproductive unit; the takeover of a reproductive unit intact or
through joining as a subordinate and eventually breaking off with some females
as a new reproductive unit (Dunbar 1986). During aggression, a male may use
infants (grooming, mounting, handling, carrying, etc.) to his advantage,
possibly to enlist help from the mother of the infant in question (Dunbar
1984a). After a takeover by a new male, the former reproductive male can remain
in the unit as a non-reproducing subordinate. Further, soon after a takeover,
group females acknowledge the new reproductive male by presenting to him (Mori
& Dunbar 1985).
Photo: Kalle Stolt
All-male groups are led by a single male individual and normally contain one
young adult and several sub-adult males, with individuals usually spending 2-4
years after emigration in an all-male group before joining or attempting to join
a reproductive unit. In general, interactions between all male groups, other
all-male groups, and reproductive units are usually agonistic (Dunbar &
Dunbar 1975). There is some indication that all-male groups may function as
buffer groups in which males who are not members of a reproductive unit may
reside (Mori et al. 2003). Similar to the case of the reproductive unit, the
all-male group is also aggressive to non-group individuals but not often amongst
itself (Dunbar & Dunbar 1975).
The band and its constituent reproductive units exist within a common home
range (Dunbar 1984b). Bands typically break apart every eight or nine years
with a new band being formed in a new home range (Dunbar 1980a; 1993). Members
of a band are probably highly related to each other (Dunbar 1993). Between
units or their leaders comprising a band, there are no status hierarchies (Mori
Play among juveniles is curtailed in periods of environmental impoverishment,
as is the case during the dry season (Barrett et al. 1992).
In captivity, post-conflict geladas will amicably rejoin the individual
toward whom aggression was directed (Swedell 1997).
Most copulations occur during the morning before midday, and when in estrus,
a female usually copulates 2-5 times per day (Mori 1979d).
Only the male unit leader copulates with unit females (Mori 1979d). Prior to
copulation, the male usually approaches the female, inspects her ano-genital
region and chest, and then copulates with her while the female usually solicits
copulation, receives or accepts the genital inspection of the male, and then
copulates with him (Dunbar 1974c; Bernstein 1975; Mori 1979d). Females usually
solicit the majority of copulations, but aside from solicitation, social
interest between males and females is generally unchanged during estrus, and
similarly, social relations within the reproductive unit remain stable and
unchanged during estrus (Dunbar 1978b). The usual female solicitation posture
involves the female pointing and raising her posterior towards a male and moving
her tail to one side (Bernstein 1975; Dunbar 1978b). Copulations are short in
duration, usually lasting only around ten seconds and are normally accompanied
by vocalizations. Post-copulation, grooming often occurs (Mori 1979d).
Estrus and hormonal changes in gelada baboon females are externally visible
in changes in the physical appearance of the pink-red patches of skin on their
chests and abdomen as well as ano-genital regions. The main change is beading,
the appearance of so-called beads of skin (fluid filled vesicles) along the
periphery of each of the patches of skin which may emit some sort of olfactory
signal (Dunbar & Dunbar 1974c; Dunbar 1977a; 1978b; McCann 1995). Changes
in color of the patches themselves however, do not correspond with the estrus
condition (Dunbar & Dunbar 1974c). However, the color of the chest patches
does correspond with age, with younger females having purplish patches which
fade to pink in older females (Dunbar 1977a). Also, females emit a specific
type of estrus call to inform males of their condition (Moos-Heilen
& Sossinka 1990). Mating can occur at any time in the estrus cycle; however
copulation frequency increases around ovulation (Dunbar 1984b; McCann 1995). In
captivity, the length of the estrus cycle varies greatly, but averages 37.3 days
Photo: Kalle Stolt
Reproduction occurs throughout the year and the species does not display a
discrete reproductive season, however at some study sites there are birth peaks
(Mori 1979a; 1979c; Dunbar et al. 2002; Jolly 2007). Females reach puberty at 3
years old, but usually first give birth at around 4 years old and the interbirth
interval averages 2.1 years (Dunbar & Dunbar 1975; Dunbar 1984b). Males are
capable of reproduction between 4-5 years old, but do not usually father
offspring before 8-10 years of age due to social factors (Jolly 2007). The
usual pattern for males is to emigrate from the natal group at puberty, spend several
years in an all male-group, and then attempt to monopolize a reproductive unit
(Dunbar 1993). The gestation length is estimated at around 6 months (Hill 1970;
Klecha et al. 1998; Jolly 2007).
Gelada births tend to occur at night but have been observed in the early
morning (Dunbar & Dunbar 1974a). At birth, the infant's eyes are closed,
the face is red, and the body is covered with black hair until around three months old
(Dunbar & Dunbar 1974a; Mori 1979a; R.I.M. Dunbar pers. comm.). Weight at birth averages 464.0 g
(Leutenegger 1973). For some time after birth, the mother remains on the
periphery of the reproductive group with other group juveniles and young and adult females
showing keen interest in the neonate (Dunbar & Dunbar 1974a; Mori 1979a).
This interest is strong and younger females may even try to take a very young
infant from its mother (Mori 1979a).
From birth, the infant is carried ventrally, however after 5 weeks old the
infant is predominantly carried on the mother's back, sometimes with its tail
entwined with hers (Mori 1979a; Barrett et al. 1995). By 5 months of age,
infants are more likely to be moving independently than being carried and by
this time, ventral carrying is never seen (Barrett et al. 1995).
The infant first starts trying to move away from its mother at two weeks old
(Mori 1979a). Also, sometimes juveniles and infants of neighboring harems in the same herd join into
play groups of up to around ten individuals of both sexes. As they approach
puberty, males may aggregate into unstable groups that may move independently of
reproductive units. Starting around six months old, subordinate group males may
help provide care for a specific infant (Mori 1979a).
Infanticide has been observed in the wild and captivity among gelada baboons,
and is often perpetrated by immigrant or newly dominant males (Moos et al. 1985;
Mori et al. 1997; 2003). Regardless, infant mortality is relatively low, with
over 85% of infants living at least until their 4th birthday. Infant mortality
is higher in the wet season than during the dry season (Dunbar 1980a).
Photo: Peter Fashing
Adult geladas have a diverse repertoire of over thirty discrete
vocalizations, including contact, reassurance, appeasement, solicitation,
ambivalence and aggressive-defensive vocalizations (Kawai 1979; Aich et al.
1990). Vocalizations are often combined together into sequences. Contact
calling may be continuous and the common calling and replying between
individuals may have important social functions. When vocalizations are
directed at the members of a different reproductive unit, they are usually
threatening (Kawai 1979). In captivity, vocalizations can be divided into four
discrete groups, harmonic calls (friendly and positive situations), aspirated
calls (agonistic and threatening situations), kecker calls (submissive
situations) and scream calls (show submission to a superordinate). Calls are to
an extent related to the social status of a gelada, with certain calls
restricted to those of a particular social status. Particular calls are always
uttered towards dominant individuals. In addition, if social status changes,
the qualitative and quantitative aspects of vocalizations change (Aich et al.
1990). In captivity, higher-ranking individuals of both sexes exhibit higher
calling rates (Aich et al. 1987).
In captivity, female geladas have specific estrus calls which inform males of
their condition. Further, captive experiments have shown that unit males are
able to differentiate females from one another exclusively based on their calls
(Moos-Heilen & Sossinka 1990).
Types of threatening or agonistic gestures include lip rolls (in which the
gums and teeth are exposed by flipping the upper lip inside out over the
nostrils) and the raising of the eyelids (by pulling back the scalp to show the
pale eyelids) (Mori 1979b; Napier 1981; Aich et al. 1990). Submission is
indicated by fleeing or presenting (Aich et al. 1990).
It is suggested that the beads of skin (fluid-filled vesicles) which appear
on females during estrus may function in olfactory communication (Dunbar &
Content last modified: September 3, 2008
Written by Kurt Gron. Reviewed by Robin Dunbar.
Cite this page as:
Gron KJ. 2008 September 3. Primate Factsheets: Gelada baboon (Theropithecus gelada) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/gelada_baboon/behav>. Accessed 2014 September 1.