Thierry Aubin, Université Paris-Sud: Coding strategies in vocal communications of song birds

Constraining environments constitute a strong selective pressure potentially driving strategies to optimize the reliability of communication processes. In this perspective, the “Signal Structure Hypothesis” predicts that the structure of animal signals will differ depending on features of the habitat. For example and for vocal communications, the so-called “Acoustic Adaptation Hypothesis” predicts that bird songs optimized for long-range propagation in a forest should be slowly modulated in frequency and as low in frequency as the sender can produce. Since the susceptibility to propagation-induced modifications of emitted signals depends on their acoustic characteristics, the emitter also could enhance or on the contrary reduce its active space of communication by coding the information in more or less propagation-resistant parameters. I will show that this adjustment of the coding strategies according to the habitat can be experimentally demonstrated for the vocalizations of songbirds living in different habitats. Due to the variable spacing of territorial individuals, some information may be coded to degrade over short distance and some might be coded such that it transmits over long distance without much degradation. Thus, species-specific identity is encoded in propagation resistant acoustic features allowing individual to reach a wide audience and constitutes public information. Conversely, group identity, individual identity and motivation state are encoded by song features susceptible to propagation, a private information reserved for close neighbors or for the partner.