Articulatory and social factors influence the acoustic structure of rhesus monkey vocalizations: a learned mode of production?

This report presents results that show that the acoustic structure of the "coo" vocalization of rhesus macaques (Macaca mulatta) varies between members of different matrilines. In the case examined, members of one matriline produce coos that are acoustically distinctive from all other matrilines and the difference is primarily due to spectral dampening and the presence of energy bands between the primary harmonics of the call. Perceptually, these acoustic modifications lead to what human listeners hear as a "nasal" utterance, suggesting the possibility of supralaryngeal filtering. Moreover, because nasal-sounding coos were only produced by members of one matriline, learning may be the primary cause of such intrafamilial similarities.