Aggressive Competition in Multi-Male Groups. Within the multi-male multi-female groups of most baboons, males compete aggressively for females when they come into reproductive condition or estrus. Aggression among males increases in frequency and intensity during the mating season in general and/or specifically when estrous females are present (Hall 1962b; Hall and DeVore 1965, Chalmers 1968b; Hausfater 1975b; Packer 1979b, Berenstain and Wade 1983, Bulger 1993). This competition is usually mediated by a linear dominance hierarchy among males in which high rank often, but not always, correlates with priority of access to females (DeVore 1965; Hausfater 1975a; Packer 1979b; Berenstain and Wade 1983; Bercovitch 1986; Cowlishaw and Dunbar 1991; Bulger 1993) and resultant mating and reproductive success (Dixson et al 1993; Wickings et al 1993; Altmann et al 1996). Males may maintain sexual access to females via sexual consortships (see Baboon Reproduction and Life History) in which males ‘mate guard’ females for several hours to several days (Hausfater 1975a; Bercovitch 1987b; Alberts et al 1996). Efforts by high-ranking males to monopolize matings are constrained, however, by female mate preferences, surreptitious copulations, and male coalitions that may overturn consortships (Packer 1977; Bercovitch 1986, 1988; Cowlishaw and Dunbar 1991; Bulger 1993). In olive and yellow baboon males, for example, consortship duration is relatively short, largely due to coalitions formed by lower-ranking males (Hall and DeVore 1965; Smuts 1985; Bercovitch 1988; Noë and Sluijter 1990). Chacma baboon males, by contrast, do not form coalitions and alpha males are able to monopolize estrous females for most of peak estrus, resulting in a higher reproductive skew in chacmas compared to olive and yellow baboons (Bulger 1993; Weingrill et al 2000). Males may also forge friendships with females as an alternate means to increase mating success, effectively ‘opting out’ of the power struggle (Smuts 1983a, 1985).
Exclusion Strategies. In hamadryas baboons and possibly in Guinea baboons as well, males adopt an exclusion strategy whereby they defend a small group of females from other males at all times. In this way, a male maintains (nearly) exclusive reproductive access to a set of females, with reproductive success largely determined by the length of his tenure as leader male (see Baboon Social Organization). In hamadryas, males ‘respect’ the ‘possession’ of females in that they are inhibited from challenging a leader male for his females or openly attempting to mate with females that are part of an OMU (Kummer et al 1974; Sigg and Falett 1985). Males may acquire females via three general routes: via aggressive takeovers; via assuming a follower male role and waiting to inherit females; or via ‘adopting’ a young pre-reproductive female and forming an ‘initial unit’ with her that will eventually develop into a reproductive unit (Kummer 1968a; Sigg et al 1982; Pines et al 2011; Pines and Swedell 2011).
While one-male groups are relatively common in chacma baboons, they do not appear to be an exclusion strategy but simply the outcome of males mapping themselves onto females found at a lower density than normal due to low habitat quality and reduced predator pressure (see Baboon Social Organization). When this occurs, patterns of bonding often change as well, with stronger cross-sex social bonds than in multi-male groups, likely a result of increased paternity certainty and reproductive investment by males (Byrne et al 1989; Anderson 1992; Barton et al 1996; Henzi et al 1997b, 2000).
Herding and Coercion. Baboon males are often aggressive towards females who consort or attempt to copulate with other (usually lower-ranking or extra-group) males (Kummer 1968a; Berenstain and Wade 1983; Kitchen et al 2009). Herding behavior, in which males use visual threats, chasing, and aggression to control female movements, is most prevalent and stereotyped in hamadryas baboons, in which leader males routinely herd females - via threats and bites on the nape of the neck or neckbites - to establish and maintain cohesion of OMUs (Swedell and Schreier 2009). Herding also sometimes occurs in chacma and olive baboons, especially during intergroup encounters (Saayman 1971, Packer 1979a; Byrne et al 1987, Henzi et al 1998; Kitchen et al 2004), at the initiation of troop movement (Stoltz and Saayman 1970; Buskirk et al 1974), and during consortships (Bercovitch 1995). In chacmas, herding occurs more in one-male than multi-male groups (Byrne et al 1987; Hamilton and Bulger 1992; Barton et al 1996).
Content contributed by:
Dr Larissa Swedell
|Thanks to the following reviewers:
Dr Susan Alberts
Dr Cliff Jolly
photograph by M. Pines
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.
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