Bats seek refuge in cluttered environment when exposed to white and red lights at night

Abstract

Background Artificial light at night is recognized as an increasing threat to biodiversity. However, information on the way highly mobile taxa such as bats spatially respond to light is limited. Following the hypothesis of a behavioural adaptation to the perceived risks of predation, we hypothesised that bats should avoid lit areas by shifting their flight route to less exposed conditions. Methods Using 3D acoustic localization at four experimentally illuminated sites, we studied how the distance to streetlights emitting white and red light affected the Probability of bats Flying Inside the Forest (PFIF) versus along the forest edge. Results We show that open-, edge-, and narrow-space foraging bats strongly change flight patterns by increasing PFIF when getting closer to white and red streetlights placed in the forest edge. These behavioural changes occurred mainly on the streetlight side where light was directed. Conclusions The results show that bats cope with light exposure by actively seeking refuge in cluttered environment, potentially due to involved predation risks. This is a clear indication that bats make use of landscape structures when reacting to light, and shows the potential of vegetation and streetlight orientation in mitigating effects of light. The study nevertheless calls for preserving darkness as the most efficient way.

Influencing Activity of Bats by Dimly Lighting Wind Turbine Surfaces with Ultraviolet Light

“…Among bats, species composing regional communities often respond in different ways, with both spectral composition and intensity influencing response; few patterns of bat response to ALAN apply to all species [ 80 , 81 ]. In general, experiments consistently demonstrate certain species of bats avoiding experimentally lit areas of landscapes, whereas other species in a local bat community might forage opportunistically on insects at the lights [ 82 , 83 ]. For example, experimental treatment with ALAN reduced drinking by forest bats in Italy [ 84 ], and in an urban area of Germany, greater noctule bats ( Nyctalus noctula ) tended to avoid lit areas but opportunistically foraged in some situations [ 85 ].…”

Assessing the extent of land-use change around important bat-inhabited caves

“…Notably, human populations in major cities in South Africa are projected to increase by as much as 23% by 2030 [ 62 ]. Urbanisation generally impacts bat populations negatively through habitat loss, artificial lights (through insect prey loss and commuting disruption) and vehicle collisions on major roads [ 10 , 49 , 72 ]. Both M. natalensis and R. aegyptiacus appear to be adaptable foragers in urban settings [ 8 , 79 ], yet little evidence is available as to how these species respond to areas that have recently undergone land-use transformation .…”

Even low light pollution levels affect the spatial distribution and timing of activity of a “light tolerant” bat species

“…Gaston et al, (2012) suggested five levers to reduce light pollution: prevent dark areas from being lit, limit the duration of artificial lighting, reduce light trespass, reduce light intensity and change ALAN spectral composition. Bats are known to present different responses to light with different spectra (Barré et al, 2021;Lewanzik & Voigt, 2017;Spoelstra et al, 2017;Straka et al, 2020). However, in this study, we could not assess how different spectral compositions would have affected our results, as the light pollution data available at landscape scale were not made of multiple spectral bands.…”