Female-female competition for male 'friends' in wild chacma baboons, Papiocynocephalus ursinus

Lactating female chacma baboons, Papio cynocephalus ursinus, maintain close associations, or 'friendships', with particular males that may protect inf ants from sexually selected infanticide by a newly immigrated alpha male. I n a a-year study, we sought evidence of female-female competition for male friends in cases where two mothers maintained friendships with the same mal e simultaneously. In this context, relative competitive abilities of the ri val females influenced social access to the shared male friend: dominant fe males maintained higher levels of close proximity and allogrooming with the male than their subordinate counterparts. This disparity was greatest when younger dominant females and older subordinate females shared a male frien d. This pattern resulted from social displacement: subordinate females expe rienced a significant decrease in time spent near the male friend immediate ly after a dominant female began associating with him (but the converse was not true). Changes in time male-female friends spent near one another were due primarily to changes in the behaviour of the females. Females may comp ete for friends based on male rank and probability of paternity of their cu rrent infants. Evidence that lactating females may pursue alternative anti- infanticide strategies besides friendship formation came from two sources. First, subordinate females displaced from a friendship made compensatory ch anges in their relationships with the potentially infanticidal alpha male: spatial proximity and the rate of contact with him fell significantly in th e period immediately following displacement. Second, across the entire samp le of friendships, female social behaviour and age were significantly corre lated. Compared to younger mothers, older females showed: (1) a smaller rel ative contribution to maintaining close proximity to the male friend; (2) l ess close proximity to the male friend; and (3) greater proximity to relati ves (this association applied to higher-ranking females). Thus, avoidance o f infanticidal threat and protective association with maternal kin may cons titute two alternative counterstrategies for some lactating females. (C) 20 01 The Association for the Study of Animal Behaviour.