Effects of variation in natural and artificial light at night on acoustic communication: a review and prospectus

Acoustic communication is prevalent throughout the animal kingdom, from insects and fish to birds and mammals and has been strongly conserved over evolutionary time. It is influenced by environmental variables, such as light, through direct and indirect mechanisms. Whereas visual perception depends on light for the majority of species, acoustic communication does not, yet nocturnal vocalizations can be affected by natural light at night from the moon. Subtle changes in illumination across the lunar cycle promote population and community level changes in acoustic communication. These are often driven by intra- and interspecific factors, such as social interactions, foraging and predation pressures. We have some understanding of how moonlight affects acoustic communication across a limited number of species. However, given the recent worldwide spread of artificial light at night (ALAN), the lack of knowledge of broader baseline effects of natural light at night is critical to understanding the effect of ALAN on communication behaviours. ALAN has rapidly and drastically changed the night-time light environment resulting in shifts in the timing, duration, rate and structure of acoustic communication. Inconsistencies in research methods and lack of diversity in taxa studied make results hard to compare and generalizations challenging. Further, aspects of light beyond its presence or absence, such as its intensity, colour and scale, have seldom been examined. Here, we review the current evidence for the relationship between acoustic communication and light at night, both natural and artificial. We highlight gaps in our understanding and potential methodological oversights and suggest directions for future research.