Adapting street lighting to limit light pollution’s impacts on bats

Artificial light at night (ALAN) affects biodiversity conservation through its impacts on spatio-temporal distribution patterns of species, in particular bat species. The development of this threat underlines the urgency to adopt lighting practices (characteristics) that have the least impact on species, in particular the most vulnerable species still present in semi-natural areas. It is therefore crucial to better assess the relative effects of the different light parameters for a wide variety of species. Our study investigates the relative effects of streetlights characteristics, i.e. height, lamps type (HPS, LED), illuminance, and the distance to a streetlight on the activity of a variety of species (15) according to their flight traits. We compared bat species activity in lit and dark conditions along streets and in hedges at less than 200 m away from streetlights of various characteristics, in a Mediterranean protected area.Lighting had contrasting effects on the activity of clutter and aerial bat species, with a strong negative effect on clutter species (90% reduction of bat activity), half of which are strictly protected. Illuminance particularly affected their activity.Among the possible management options to reduce the effect of light pollution at night (reduction of light intrusion by modifying the height of street lamps, lighting intensity, spectral composition), the removal of light sources, or at least the reduction of illuminance, seems to be the most effective option. Due to its strong impact on highly protected species, we urge the need to manage lighting, in particular in protected areas.Artificial light at night had a negative effect on clutter bats activity (90% reduction of bat activity) and among streetlight characteristics illuminance was the most relevant.Data used for statistical analysis are include in Appendix C. Acoustic row data was delivered to the citizen science program “VigieChiro” (https://vigiechiro.herokuapp.com/).