The acoustic features of vervet monkey grunts

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Abstract
East African vervet monkeys give short (125 ms), harsh-sounding grunts to one another in a variety of social situations: when approaching a dominant or subordinate member of their group; when moving into a new area of their range; or upon seeing another group. Although all these vocalizations sound similar to humans, field playback experiments have shown that the monkeys distinguish at least 4 different calls. Acoustic analysis reveals that grunts have an aperiodic FO [fundamental frequency], at roughly 240 Hz. Most grunts exhibit a spectral peak close to this irregular FO. Grunts may also contain a 2nd, rising or falling frequency peak, between 550-900 Hz. The location and changes in these 2 frequency peaks are the cues most likely to be used by vervets when distinguishing different grunt types.