Female–female competition for male ‘friends’ in wild chacma baboons (Papio cynocephalus ursinus)

Abstract

Lactating female chacma baboons, Papio cynocephalus ursinus, maintain close associations, or ‘friendships’, with particular males that may protect infants from sexually selected infanticide by a newly immigrated alpha male. In a 2-year study, we sought evidence of female–female competition for male friends in cases where two mothers maintained friendships with the same male simultaneously. In this context, relative competitive abilities of the rival females influenced social access to the shared male friend: dominant females 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 friend. This pattern resulted from social displacement: subordinate females experienced a significant decrease in time spent near the male friend immediately 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 compete for friends based on male rank and probability of paternity of their current 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 changes in their relationships with the potentially infanticidal alpha male: spatial proximity and the rate of contact with him fell significantly in the period immediately following displacement. Second, across the entire sample of friendships, female social behaviour and age were significantly correlated. Compared to younger mothers, older females showed: (1) a smaller relative contribution to maintaining close proximity to the male friend; (2) less close proximity to the male friend; and (3) greater proximity to relatives (this association applied to higher-ranking females). Thus, avoidance of infanticidal threat and protective association with maternal kin may constitute two alternative counterstrategies for some lactating females.