THE ADAPTIVE VALUE OF FRIENDSHIPS TO FEMALE BABOONS - EXPERIMENTAL AND OBSERVATIONAL EVIDENCE

Lactating female baboons, Papio cynocephalus, often maintain close ass ociations with particular males. There are at least three proposed ben efits of 'friendships' to females: (1) male protection against potenti ally infanticidal males; (2) male protection against harassment by dom inant females; (3) male attachment to an infant that develops into fut ure care of juveniles. These hypotheses were examined in a population of chacma baboons, P. c. ursinus, in which male infanticide accounted for at least 38% of infant mortality. Almost all mothers of young infa nts formed strong bonds with one or two males with whom they had copul ated during the cycle in which they conceived their infants. Females w ere primarily responsible for maintaining friendships during lactation , but they terminated these relationships if their infants died. In pl aybacks of females' screams, male friends responded more strongly than control males. They also responded more strongly to the screams of fe male friends than to the screams of control females. Following an infa nt's death, however, male friends responded less strongly than control males to the same females' screams. Finally, male friends responded m ore strongly than control males to playback sequences in which female screams were combined with the threat vocalizations of a potentially i nfanticidal alpha male, but not when female screams were combined with the threat calls of a non-infanticidal male or the alpha female. Both observations and experiments suggest that the benefits of friendships to females derive from the protection of their infants against infant icide. (C) 1997 The Association for the Study of Animal Behaviour.