Gelada baboon
Theropithecus gelada

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).

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).

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 1979c).

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).

REPRODUCTION

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 (McCann 1995).

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).

PARENTAL CARE

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).

COMMUNICATION

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 & Dunbar 1979c).

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 2013 May 23.