Acoustic features of female chacma baboon barks

We studied variation in the loud barks of free-ranging female chacma baboon s (Papio cynocephalus ursinus) with respect to context, predator type, and individuality over an 18-month period in the Moremi Game Reserve, Botswana. To examine acoustic differences in relation to these variables, we extract ed a suite of acoustic parameters from digitized calls and applied discrimi nant function analyses. The barks constitute a graded continuum, ranging fr om a tonal, harmonically rich call into a call with a more noisy, harsh str ucture. Tonal barks are typically given when the signaler is at risk of los ing contact with the group or when a mother and infant have become separate d (contact barks). The harsher variants are given in response to large pred ators (alarm barks). However, there are also intermediate forms between the two subtypes which may occur in both situations. This finding is not due t o an overlap of individuals' distinct distributions but can be replicated w ithin individuals. Within the alarm bark category, there are significant di fferences between calls given in response to mammalian carnivores and those given in response to crocodiles. Again, there are intermediate variants. B oth alarm call types are equally different from contact barks, indicating t hat the calls vary along different dimensions. Finally, there are consisten t, significant differences among different individuals' calls. However, ind ividual identity in one call type cannot directly be inferred from knowledg e of the individuals' call characteristics in the other. In sum, the barks of female baboons potentially provide rich information to the recipients of these signals. The extent to which baboons discriminate between alarm and contact barks, and classify calls according to context and/or acoustic simi larity will be described in a subsequent paper.