Relation between the level of acoustic variability and the call social function in red-capped mangabeys

Abstract

International audienceDespite a strong influence of genetic factors on the structuring of nonhuman primate vocalrepertoires, the last decade evidenced to some extent abilities in vocal plasticity. Snowdon etal. (1997) suggested a relation between the level of acoustic variability and the call function.The highest variability is expected in calls with an affiliative social value. But this hypothesishas rarely been tested. Here, we conducted a quantitative analysis of acoustic structures’variability and associated contexts of emission by studying the, still unknown, vocalrepertoire of red-capped mangabeys (Cercocebus torquatus torquatus). Seven adult males andseven adult females were studied in captivity. We found 13 structurally-different sound units(4 peculiar to females, 3 to males and 6 shared). These units were combined to form 12 calltypes (including 6 sex-specific) that were also contextually differentiable. Interestingly,females, who are more socially integrated than males, produced a higher number of call typesand unclassifiable graded acoustic structures. The highest level of inter- and intra-individualacoustic variability was found in the intra-group socially affiliative grunts and the lowest innon-affiliative calls like Wahoo alarm calls and inter-group Whoop-gobble loud calls. Anintermediate pattern of variability was found in food calls for instance. Thus, our data supportSnowdon et al.’s hypothesis