Reducing light pollution improves connectivity for bats in urban landscapes

Alexis Laforge

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. We investigated how potential light-reduction scenarios at a conurbation scale can improve landscape connectivity for bats. Through random stratified sampling and species distribution modelling, we assessed the relative importance of light pollution on presence probability and activity of bats. We recorded bats during one entire night on each 305 sampling points in 2015. In 2016, we surveyed 94 supplementary points to evaluate our 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 of two light non-tolerant bat species. We found that light pollution detected from a satellite image was a good predictor of bat presence and activity up to 700 m radius. Our results exhibited three contrasting responses to light intensity: 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. Light-reduction measures should be urgently included in urban planning to provide sustainable conditions for bats in cities. Finally, we advocate for the use of our new methodological approach to further studies to find the best trade-off between conservation needs and social acceptability.