Reducing light pollution improves connectivity for bats in urban landscapes

Context Light pollution can alter animal movements and landscape connectivity. This is particularly true in urban landscapes where a need to incorporate conservation issues in urban planning is urgent. Objectives We investigated how potential light-reduction scenarios at conurbation scale change landscape connectivity for bats. Methods Through random stratified sampling and species distribution modelling, we assessed the relative importance of light pollution on bat presence probability and activity. We recorded bats during one entire night on each 305 sampling points in 2015. In 2016, we surveyed 94 supplementary points to evaluate models performance. We used our spatial predictions to characterize landscape resistance to bat movements. Then we applied a least-cost modelling approach to identify nocturnal corridors and estimated the impact of five light-reduction scenarios on landscape connectivity for two light non-tolerant bat species. Results We found that light pollution detected from satellite images was a good predictor of bat presence and activity up to 700 m radius. Our results exhibited contrasting responses to average radiance: M. daubentonii responded negatively, P. nathusii had a positive response for low values then a negative response after a threshold radiance value of 20 W.m −2 .sr −1 and E. serotinus responded positively. Five and four light-reduction scenarios significantly improved landscape connectivity for M. daubentonii and P. nathusii respectively. Conclusions Light-reduction measures should be included in urban planning to provide sustainable conditions for bats in cities. We advocate for the use of our methodological approach to further studies to find the best trade-off between conservation needs and social acceptability.