Manipulating spectra of artificial light affects movement patterns of bats along ecological corridors

Abstract

AbstractAnimal movement throughout the landscape is a key concept for population viability. Human footprint can reduce animal movement through barrier effects such as habitat change and fragmentation, or through enhanced resources. Artificial light at night (ALAN) can affect the movement of nocturnal animals such as bats that are highly mobile in the landscape. Very few studies have explicitly quantified the choices that moving bats make when they encounter a light source on their flight routes. We assessed whether ALAN of different colours (green, red and white) compared to control conditions affected the use of ecological corridors, considering (i) activity and (ii) movement along the corridor, for open, edge (i.e. light‐opportunistic) and narrow‐space (i.e. light‐averse) foraging bats. We modelled the effects of 28 independent lampposts at four experimental sites on bat activity and movement (i.e. the number of trajectories towards the lamppost and the probability of lamppost crossing). Each lamppost was sampled two to three times over eight complete nights using paired passive acoustic stereo recorders to record bat activity and reconstruct bat trajectories. Narrow‐space foragers were much less active in presence of any light source, and fewer flew towards any lit lampposts. Open and edge‐space foragers were more active close to white and green lights, and to a lesser extent red light, compared to unlit control sites. Edge‐space foragers overall flew more towards white and green lampposts, but had a lower probability of fully crossing a white and red‐lighted site. The study shows that ALAN can strongly alter bat movements along landscape structures, for light‐averse but also light‐opportunistic species. Such changes in flight behaviour may involve bypasses or detours, which may force bats to fly longer distances at night which could ultimately affect fitness. Our findings suggest that avoiding artificial lighting close to flight routes will benefit bats.