Nonhuman primate vocal repertoires typically contain a relatively small number of different call types and little evidence of syntax. (a) The right-hand panel shows a spectrogram of a long sequence of 'grunt’ vocalizations produced by an adult male baboon while approaching and attempting to handle a young infant. Although this is a long sequence of vocalizations, there is no variation in the calls produced throughout the bout. Rather, the same call is simply repeated over and over many times. (b) A spectrogram of a long bout of distress calls produced by a juvenile baboon that has been forcibly ejected from a feeding site. In this case, the young baboon produces a long stream of broad-band, noisy vocalizations with some more harmonically structured vocalizations interspersed towards the end of the bout. The vocalizations in this bout exhibit tremendous structural variety, they are not simply a single type of call repeated over and over. However, the sequence is notable for being completely unpatterned, or chaotic, and thus evincing no evidence of syntax, which nevertheless may be functional in the contexts in which these calls are produced [9,10].
Rendall BMC Biology 2013 11:108 doi:10.1186/1741-7007-11-108