SELECTION FOR ACOUSTIC INDIVIDUALITY WITHIN THE VOCAL REPERTOIRE OF WILD CHIMPANZEES

Individual primates typically produce acoustically distinct calls. To investigate the factors that facilitate the evolution of individual vo cal signatures, we examined two components of the call repertoire of c himpanzees: the pant hoot and pant grunt. Pant hoots are long-distance signals whose recipients can be several hundred meters away, while pa nt grunts are short-range calls given to conspecifics within close vis ual range. Given their markedly different contexts of emission, we pre dicted that natural selection would favor the elaboration of individua lly distinctive acoustic features in pant hoots compared with pant gru nts. Analyses of nine acoustic features revealed that pant hoofs are m ore stereotyped within-individuals and variable between-individuals th an pant grunts. These data are consistent with the hypothesis that sel ection may act to encode varying degrees of individuality in different components of the vocal repertoire of a single species.