Infanticide and attempted infanticide by males – either directly observed or strongly inferred – has been reported for many baboons, most notably chacma baboons in southern Africa and hamadryas baboons in Ethiopia (Palombit 2003; Swedell and Saunders 2006). The occurrence of infanticide varies widely across baboon populations and subspecies, but its prevalence across baboons as a whole suggests that it is a behavioral predisposition of baboon males that is variably expressed depending on ecological and social conditions (Palombit 2003).
For example, in the chacma baboons of the Okavango Delta in Botswana (e.g., Palombit et al 1997; 2000) where adult males are commonly in the same groups with infants of which they are not the father, the risk of infanticide is chronic and infanticide is the primary cause of infant mortality (Cheney et al 2006). Females are in fact highly attuned to this risk, as stress hormone levels rise in females with infants following immigration of new males (Engh et al 2006). In hamadryas baboons, by contrast, the chronic risk of infanticide is low but the acute risk after takeovers is high; i.e., after a hamadryas one-male unit (OMU) is taken over by a new male, infants often die or disappear. In fact, the normally high rate of infant survival in hamadryas compared to other baboons (Sigg et al 1982; Swedell 2006) coupled with the observed and inferred infant mortality after takeovers (Swedell 2000; Swedell and Tesfaye 2003) suggests that infanticide is the primary cause of infant mortality in hamadryas baboons as well (Swedell and Saunders 2006).
Infanticide is viewed as an adaptive behavior by male baboons for several reasons. First, the infants that die are almost always very unlikely to have been fathered by the infanticidal (or suspected infanticidal) males, so males are not killing their own infants but rather the infants of other males. Second, female baboons undergo a period of lactational amenorrhea whereby they do not ovulate while an infant is nursing at a high rate, thus the death of a young infant will terminate this amenorrhea and hasten a female's return to ovulatory cycling. Third, these males are usually observed mating with the mothers of these infants shortly after infant death, thus their likelihood of fathering an infant by that female is higher than if the infant had not died.
Some female baboons appear to have evolved adaptive responses to male infanticide. These may include minimizing losses via an earlier return to reproductive condition following immigration or takeovers (Pereira 1983; Dunbar 1984; Colmenares and Gomendio 1988; Alberts et al 1992; Swedell, 2000, 2006); the manipulation of paternity assessment through “pseudo-estrus” (Zinner and Deschner, 2000; Swedell 2006) or mating with multiple males (Hausfater 1975a; Smuts 1985; Bercovitch 1987b; Swedell 2006); and social bonding with a protective male for infant defense (Smuts 1985; Palombit et al 1997; Weingrill 2000; Swedell and Saunders 2006). Within the paternity confusion-concentration dichotomy proposed by van Schaik et al (1999), most baboons use a predominant anti-infanticide strategy of paternity confusion, characterized by behavioral elements such as presentations to multiple males, copulation with multiple males, post-copulatory darts, and copulation calls, all of which elicit contest and/or sperm competition and promote mating with multiple partners (Hall and DeVore 1965; Hausfater 1975a; Cox and LeBoeuf 1977; Bercovitch 1991, 1995; O’Connell and Cowlishaw 1994, 1995; Dixson 1998; Soltis 2002; Swedell and Saunders 2006). Even in chacma baboons, in which alpha males monopolize females during peak estrus (see above), females solicit and copulate with other males during early and late estrus (Saayman 1970; Bulger 1993; Weingrill et al 2000, 2003).
In hamadryas baboons, by contrast, females use a predominant anti-infanticide strategy of paternity concentration, with both males and females focusing their reproductive effort more narrowly than in other baboons (Swedell and Saunders 2006). This strategy involves close association with a single protective male; the male's paternity certainty is very high and, as a result, he is very likely to protect and defend infants from any potential threats, such as predators or potentially infanticidal males.
Among baboons, such a system whereby males and females engage in mutualistic strategies of close association, protection, and (relatively) exclusive mating has evolved to an extreme only in hamadryas, but it appears to exist to varying degrees in other baboon species (Boese 1973; Smuts 1985; Anderson 1989, 1990; Palombit et al 1997). For example, as described above, strong social bonds or ‘friendships’ characterize some baboon females and specific adult males; these relationships may benefit females via protection from infanticide or aggression by males (Smuts 1985; Palombit et al 1997; Weingrill 2000). In some cases, males that pursue a ‘friendship’ strategy have greater access to those females as mates. In chacma baboons in particular, females may be in effect ‘concentrating’ paternity by focusing their peri-ovulatory mating on the alpha male (or the resident male in a one-male group) while simultaneously ‘confusing’ paternity by mating with other males at other times (Swedell and Saunders 2006).
Content contributed by:
Dr Larissa Swedell
|Thanks to the following reviewers:
Dr Susan Alberts
Dr Cliff Jolly
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.