Far-reaching displacement effects of artificial light at night in a North American bat community

Artificial light at night (ALAN) is a global pollutant that disrupts circadian rhythmicity and a broad range of physiological processes and behaviors in animals. However, ALAN sensitivity can vary greatly even among closely related species and urgently needs study for much of the world’s nocturnal wildlife, including bats. While an increasing number of bat species have recently been assessed for light tolerance, the spatial extent of ALAN’s influence on bats has received little attention. This information need is a barrier to the protection of bats from ALAN in land-use planning and policy, and the development of best practices that effectively buffer bat habitat from light trespass. To help address this information gap for North America, we experimentally tested the distances up to which ALAN affects presence and activity of light-averse little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus), and the composition of a foraging bat assemblage in Connecticut, USA. We used three residential-scale, white, LED floodlights to expose bat foraging habitat to ALAN and compared acoustic activity of bats at distances of 0, 25, 50, and 75 m from the lights between nights when the lights were on versus off. Little brown bats were present on significantly fewer light than dark nights at every distance. Lighting significantly reduced little brown bat activity overall and at the farthest location from the lights (75 m), where it was only 43% of dark-night activity despite