Acoustic propagation in heterogeneous environments and its implications on the active space of rock ptarmigan

Abstract

Acoustic communication networks among birds are widely studied in homogeneous environment like tropical forest or open field. There is no study in heterogeneous environment to our knowledge. However, the propagation of an acoustic signal is strongly influenced by topography, meteorological and ground effects, especially at long distance. For bird species living in high mountains, these effects can have a prominent impact on how their vocalization spreads. Here we try to redefine the active space notion, using the rock ptarmigan as a model. We develop a sound propagation code dedicated to bioacoustic studies based on the parabolic equation method and taking into account the above mentioned effects. Propagation measurements were carried out at a mountain site to provide information on typical conditions encountered and to test the validity of our model in this context. Using this model, we describe how the mountainous conditions affect active spaces of communication compared to typical homogeneous situations. We further test how singing during display flights can be a good strategy for a transmitter to expand its active space in such a context. A fine modeling of the propagation of acoustic signals is likely to provide important cues for understanding communication networks of mountainous species.