Primate Habitat Acoustics

Natural habitats are not recording studios. Calls emitted in nature encounter an irregular assortment of hard surfaces that reflect and scatter the wave front, producing complicated patterns of constructive and destructive interference. The propagated wave front is subsequently disturbed by wind, thermal gradients, and atmospheric absorption. Collectively, these phenomena result in an unpredictable and untidy acoustic environment. Furthermore, thunder, rain, crashing waves, or the relentless chatter of biotic sources can result in high ambient-noise levels that may mask the signal, overwhelm the recipient, and obliterate significant nuances and embellishments. Thus, vocal communication is hampered by attenuation, reverberation, distortion, and acoustic disturbances. Accordingly, the twin components of vocal communication, sound production and acoustic perception, may have undergone persistent selection to counter the most prominent impediments to both hearing and being heard. Primates have radiated from rain forest to grassland and other habitats, and each habitat differs acoustically. Hence, there is reason to believe that the duration, amplitude, pitch, and composition of primate vocal repertoires, the timing of emissions, and the placement and orientation of vocalizers is not haphazard, but each has become tuned to the acoustic parameters of the natal habitat to heighten the clarity of vocal exchanges. This chapter begins with an overview of the acoustic properties of rain forest, riverine forest, and savanna habitats occupied by East African primates, which is followed by reviews of how primate calls become distorted when propagated in natural habitats and how distortion scores have been used to explore the acoustic adaptation hypothesis. Finally, significant opportunities for additional research are highlighted.