Social bonds and the coherence of mountain baboon troops

Female chacma baboons (Papio cynocephalus ursinus) in the Drakensberg mount ains, experiencing neither predation nor within-group competition, structur e their social relationships with other females in order to sustain recipro cated grooming (Henzi et al., 1997b). To do so, they cap, where time constr aints demand, the size of their grooming cliques. From this we have assumed that the social orientation of mountain baboon females is primarily toward s other females and that fission is a consequence of the increasing differe ntiation of cliques, leading to one or a few females following a male 'frie nd' when he departs. An alternative argument (Barton et nl., 1996) is that, where predation or within-group competition do not occur, neither should f emale-bonded groups. In this view, females under such conditions should be 'cross-bonded' to males, each group male associating with a few females in the manner of hamadryas baboons (P. c. hamadryas). We test this prediction of 'cross-bonding' at both troop and individual level and find no evidence to support it. We then present data on fission events which argue for fissi on in the Drakensberg being due to the departure of small one-male units. H owever, the data do not support, unequivocally, the proposal that females l eave with male 'friends'. They do, however, always leave with a male who ha s fathered at least one of their non-adult offspring.