Artificial light at night (ALAN) pollution alters bat lunar chronobiology: Insights from broad-scale long-term acoustic monitoring

Abstract

Background The timing of behavior and habitat associations of nocturnal animals can be influenced by the lunar cycle in nature. The prevalence of artificial light at night (ALAN) has been recognized as a source of environmental pollution. The interaction between ALAN pollution and the lunar cycle on bat behavior is important for understanding anthropogenic effects on bats. We utilized a decade (2012–2022) of acoustic monitoring data collected in North Carolina, United States, to investigate the relationship between bat activity, lunar cycle, and ALAN pollution in temperate insectivorous bats. We examined whether the amount of lunar illumination affected species-specific nightly activity and whether hourly bat activity patterns varied between nights with different moon phases. We further investigated if the relationship between bat activity and the lunar cycle might be altered by ALAN pollution. Results We found that seven bat species showed activity variation across nights in relation to the amount of moon illumination when ALAN pollution was absent. Generally, bats were less active on full moon nights compared to new moon nights. ALAN pollution interacted with the bat-lunar relationship in five of the seven species, masking the effect of the lunar cycle. We identified delayed bat activity patterns on nights with a full or waxing moon in seven species, and ALAN pollution altered that pattern in four species. Overall, ALAN pollution was associated with decreased bat activity independent of lunar cycle effects. Conclusions Our study demonstrated that at a broad spatial scale, ALAN pollution negatively affected many North American temperate bat species and altered their lunar chronobiology. As the cost of illumination declines and the economic benefits of nighttime farming and other activities increase, ALAN pollution is spreading to historically dark areas and habitats. ALAN pollution might couple with other threats, such as the white-nose syndrome or climate change, to cause cascading damage in the environment that depends on ecosystem services provided by bats. We argue that further research and conservation actions are needed to mitigate the impact of ALAN pollution.