Acoustic communication in noisy environments:Signal recognition in fluctuating backgrounds.

Abstract

Following one conversation in multi-talker environments is a difficult perceptual task that we encounter frequently. How the human auditory system solves this problem has been the focus of research for decades. While many nonhuman animals also communicate in noisy social aggregations, we know very little about how they solve analogous problems. Dip listening, an ability to catch `acoustic glimpses' of target signals when the level of fluctuating backgrounds momentarily drops, represents one way by which receivers may recognize signals in noise. It has even been suggested that animals may be adapted to exploit level fluctuations of the natural soundscape (i.e., the mixture of sounds in the environment) to recognize communication signals. This hypothesis, however, is not yet supported by empirical evidence because (i) we know little about the characteristics of level fluctuations in natural soundscapes, (ii) very few studies have investigated the ability of nonhuman animals to recognize communication signals in fluctuating backgrounds, and (iii) no study has investigated signal recognition in the presence of noises with level fluctuations of natural soundscapes. I addressed these gaps in knowledge using gray treefrogs (Hyla chrysoscelis) and green treefrogs (Hyla cinerea) as model systems. I found that level fluctuations of the noise generated in social aggregations vary across species. I also show that gray treefrogs, but not green treefrogs, have an ability to listen in the dips of fluctuating backgrounds when recognizing communication signals. This ability, however, is not specifically `tuned' to exploit level fluctuations of natural soundscapes. Together, my findings offer little support for the hypothesis that receivers are adapted to exploit level fluctuations of the natural soundscape to recognize communication signals.