Baboons are among the most social and affiliative animals and strong social bonds are fundamental to their lives.  As described below, strong social bonds characterized by close proximity and grooming are exceptionally important to female olive, yellow, and chacma baboons.  In hamadryas baboons, close social relationships are more important for males - and this pattern apparently characterizes Guinea baboons as well.  These patterns of social bonding are closely tied to patterns of dispersal and philopatry that characterize each species, i.e., which sex typically stays in their natal group and which sex leaves to seek reproductive opportunities elsewhere.

Olive baboons, yellow baboons, and chacma baboons live in large social groups or troops, which can be as small as 10-15 individuals and as large as 200 or more.  These groups contain both males and females of all ages.  The females in these groups are usually philopatric, i.e., they remain in the troop in which they were born and maintain strong social bonds with their female kin.  It is these bonds that form the core of a baboon social group: they are the glue holding the troop together and are in fact adaptively beneficial to females (Silk 2007).  Males, by contrast, do not typically form strong bonds with other males; rather, they leave their natal troops around puberty and immigrate into a new troop to reproduce, i.e., they disperse.  In all but hamadryas baboons, troops generally function as cohesive social units.  Troops do, however, sometimes spread out and break up into smaller groups during foraging.

Unlike most other baboons, hamadryas baboons (found in the Horn of Africa and the southwestern Arabian peninsula) have a multi-level social system with four layers of social structure (Kummer 1968a,b, 1984, 1990; Abegglen 1984; Schreier and Swedell 2009).  The smallest and most stable social grouping is the one-male unit (OMU), comprising a ‘leader male’, several females, dependent offspring, and sometimes one or more ‘follower’ males that socialize with but do not typically mate with the females (Kummer 1968a,b).  OMUs comprise 1-9 females, averaging 2-3 females per OMU (Kummer 1968a; Nagel 1973; Swedell 2006).  Several OMUs and additional ‘solitary’ (unaffiliated) males may together form a clan, a spatial and social association within which the male may be close relatives (Abegglen 1984; Colmenares 1992; Schreier and Swedell 2009).  The hamadryas social unit analogous to the troops of other (non-hamadryas) baboons described above is the band, which consists of multiple clans that share a common home range, travel pattern, and sleeping site (Kummer 1968a; Abegglen 1984).  Finally, the largest social grouping in hamadryas baboons, a temporary aggregation of bands at a sleeping site or foraging area that can number up to 800 individuals, is called a troop (Kummer 1968a).

Less is known about Guinea baboons compared to other baboon species, but they may also be characterized by a multi-level social system.  The largest social unit in Guinea baboons is an aggregation at a sleeping site, which consists of several hundred baboons (Sharman, 1981; Anderson and McGrew, 1984).  These aggregations subdivide into smaller groupings that appear similar to the clans and OMUs of hamadryas (Dunbar and Nathan 1972; Sharman 1981; Boese 1973, 1975; Galat-Luong et al 2006).  Current evidence for Guinea baboons suggests an intermediate social organization between the unstructured multi-male groups of most baboons and the more rigid multi-level societies of hamadryas, with greater flexibility in female behavior compared to hamadryas baboons (Jolly and Phillips-Conroy 2006; Galat-Luong et al 2006).

 


Bonds Among Females.   In most baboons, strong social relationships, or bonds, among female kin form the core of a social group (Seyfarth 1976; Altmann 1980; Strum 1987; Barton et al 1996; Silk et al 1999, 2003, Henzi et al 2000). Females maintain social bonds of varying strengths with different individuals; these bonds are expressed mainly via grooming (whereby the hair is parted and the skin is examined, then debris, insects, or scabs are removed) and they occur preferentially with close relatives (Boese 1975; Seyfarth 1977; Smuts 1985; Barrett et al 1999, 2000, 2002; Bentley-Condit and Smith 1999, 2006a,b; Leinfelder et al 2001; Smith et al 2003).  These species are thus characterized as female-bonded, i.e., females remain in their natal groups and form strong social relationships with female kin. These relationships have been shown to be beneficial to females: both yellow and chacma baboon females with stronger social networks experience greater infant survival and even greater longevity (Silk et al. 2003, 2009, 2010). 

While less is known about individual social interactions in Guinea baboons, current evidence supports a female bonded social organization for these species as well (Boese 1973).  The one exception to the above pattern lies with hamadryas baboons, in which female bonding is reduced due to coercive transfer of females among social units by males (Swedell and Schreier 2009; Swedell et al. in press). Leader males aggressively herd females among OMUs, breaking up female kin groups in the process.  Related females, however, do often end up in the same OMU (Sigg et al 1982; Chalyan et al 1994), and the highly variable level of social interaction among female dyads likely reflects variation in kinship among them (Swedell 2002a, 2006).


Bonds Among Males. Bonds among males also vary among baboon populations and species. Unlike in some other monkeys in which males avoid one another, baboon males do remain together in social groups year-round and are tolerant of one another.  Most baboon males are less social than females, however, especially with members of their own sex (Aldrich-Blake et al 1971; Saayman 1971; Davidge 1978a; Smuts 1985), and interactions among males in these species are more likely to be agonistic (involving aggression and submission) than affiliative (involving friendly interactions such as grooming) (Hausfater 1975a).  Conflict among males is reduced by formalized dominance relationships, which are essentially power relationships among pairs of males, and males compete over the highest positions in the troop's dominance hierarchy, with the alpha male being able to secure first access to ovulating females. 

In hamadryas baboons, by contrast, males groom more with other males, maintain differentiated affiliative relationships, and engage in ritualized greetings called notifications that, for leader males, replace grooming relationships (as males are less tolerant of other males once they acquire females; Abegglen 1984; Colmenares 1990, 1991). 


Cross-Sex Bonds in One-Male Groups. Strong affiliative relationships between the sexes, or cross-sex bonds, are usually limited to sexual consortships, exclusive sexual associations between a male and a female (see Reproduction page).  However, strong cross-sex bonds occur outside of this context as well, particularly in one-male groups (Byrne et al 1989; Barton et al 1996).  Compared to lowland chacma baboons, for example, mountain chacmas are more commonly found in one-male groups, cross-sex bonds are stronger, female-female bonds are weaker, and herding behavior by males (see Male Strategies page) occurs more frequently (Anderson 1981a, 1990; Byrne et al 1987, 1989; Whiten et al 1987; Henzi et al 1990, 1999; Hamilton and Bulger 1992).  This suggests a relationship between the one-male group structure and (a) a male’s motivation to invest in and defend his females and infants, probably due to increased certainty of paternity of their offspring, and (b) a female’s motivation to invest in relationships with the resident male, possibly due to the increased importance of protection against predation and infanticide in a one-male group.


Cross-Sex Bonds in Multi-Male Groups. Affiliative relationships between the sexes occur in multi-male groups as well. In olive, yellow, and chacma baboons, some male-female dyads form grooming relationships, sometimes called friendships, outside of a female's period of estrus or sexual receptivity (see Reproduction page) (Seyfarth 1978b; Altmann 1980; Smuts 1983a, 1985; Byrne et al 1989; Henzi et al 2000).  These friendships likely benefit a female via protection for herself and her offspring (Smuts 1983b, 1985; Nguyen et al 2009). The effort devoted by males to maintaining these relationships has been alternately interpreted as mate investment or parental investment, with the relative importance of each factor possibly reflecting differing infanticide risk – and hence cross-sex bonding to counteract this risk – among baboon populations (see Infanticide page) (Smuts 1983b, 1985; Anderson 1992; Palombit et al 1997; Weingrill 2000; Henzi and Barrett 2003).

In hamadryas baboons, bonds between the sexes last year-round.  Hamadryas leader males use physical coercion, or the threat thereof, to maintain proximity to females, who are essentially conditioned to remain within the spatial and social sphere of their own OMU (Swedell and Schreier 2009).  In Guinea baboons, the degree of male aggression towards females appears to be lower, but the basis for the OMU social structure appears to be similar to hamadryas in that it is centered on the bonds between the leader male and each of his females (Boese 1975; Maestripieri et al 2007).

 


Content contributed by:

Dr Larissa Swedell

Thanks to the following reviewers:
Dr Susan Alberts
Dr Cliff Jolly

 

photographs by L. Swedell (3 photos of baboons grooming) and M. Pines (family looking at infant and hamadryas males hugging)

For a more scholarly version of the information on these pages, see:
Swedell, L (2011) African Papionins: Diversity of Social Organization and Ecological Flexibility. IN Primates in Perspective, Second Edition (Campbell CJ, Fuentes A, MacKinnon KC, Bearder SK, Stumpf, RM, eds). New York: Oxford University Press, pp. 241-277.

When using information on these pages, please cite the URL of the specific page from which you acquired the information. For scholarly citations of this material, please cite the above chapter by L. Swedell, available as a pdf by emailing the author.  Please credit either this website or the above chapter for any and all use of this material.