Phantom oceans restructure bat communities

Abstract

Breaking waves are a widespread and often intense source of background sounds in coastal areas. Yet, the influence that natural sounds like crashing surf have on the distribution and behavior of animals, and the structure of communities, has been largely overlooked. Here, we examined how ocean sounds impact the activity and distribution of bats. For three seasons, we quantified the activity of 11 species across 19 sites that varied in their exposure to surf sounds. In the latter two years, we performed a large-scale playback experiment to create realistic coastal soundscapes at five sites where surf sounds are naturally faint or absent. We also broadcast spectrally shifted higher frequency surf sounds at five additional sites to disentangle the mechanisms driving changes in bat activity. We detected divergent responses across species to variation in the acoustic environment that were linked to their acoustic foraging niche. Bats that passively listen to prey exhibited lower activity in high sound levels but were more active in high frequency soundscapes. In contrast, aerial hawking bats that hunt using echolocation exhibited greater activity in high sound levels and avoided high frequency environments. By comparing the community before and during the playbacks, we found that the shifted ocean sounds caused turnover such that passive listening species replaced hawking species, while unaltered ocean sounds led to lower species richness due to passive listening bats avoiding these sites. These findings provide compelling evidence that natural sounds are an underappreciated habitat feature that shape species distributions and non-randomly filter communities.