The evolution of communication in a complex acoustic environment


Animals use communicatory signals for species recognition, mate choice, and territory defense. In many cases, communication occurs in the presence of other species with similar signals, which can make it difficult to discriminate conspecific from heterospecific signals. To avoid interference from syntopic signals, species should partition communication space. I studied partitioning of acoustic space in the dawn chorus of birds in the Amazon basin, an example of communication in high levels of heterospecific background noise. My research analyzed bird songs to determine whether the timing of signal transmission, the structure of signals, or both, serve to partition the acoustic space among different species. I used a combination of acoustic censuses and field experiments to investigate acoustic partitioning. With the censuses, I documented the times and places at which species sing, and I measured the features of each species’ song to determine their locations in acoustic space. Playback experiments in the field enabled me to test predictions about partitioning of both acoustic signal space and acoustic perceptual space. The analyses of the acoustic censuses revealed that songs of species that used the same forest stratum and sang during the same 30-min intervals had more dispersed signals than other species. The first experiment indicated that signalers and receivers coordinate the timing of production and reception of signals within the dawn chorus. The second experiment revealed that, although the partitioning of acoustic signal space was disjunct, with gaps between nearest species’ signals, the partitioning of acoustic perceptual space was saturated. Since signals are degraded as they travel through the environment, receivers must respond to degraded signals mixed with background noise. As a consequence, receivers should allow for more variation in signals than signalers include at the source. The results of these censuses and experiments allowed me to examine the influence of background noise from heterospecific species on the evolution of acoustic communication. It is the first study to investigate acoustic perceptual space in a multispecies community. The results indicate that signalers and receivers have evolved distinct strategies to reduce errors in recognizing conspecific signals

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