Abstract
Progressive illumination at night poses an increasing threat to species worldwide. Light at night is particularly problematic for bats as most species are nocturnal and often cross relatively large distances when commuting between roosts and foraging grounds. Earlier studies have shown that illumination of linear structures in the landscape disturbs commuting bats, and that the response of bats to light may strongly depend on the light spectrum. Here, we studied the impact of white, green, and red light on commuting Daubenton's bats (Myotis daubentonii). We used a unique location where commuting bats cross a road by flying through two identical, parallel culverts underneath. We illuminated the culverts with white, red, and green light, with an intensity of 5 lux at the water surface. Bats had to choose between the two culverts, each with a different lighting condition every night. We presented all paired combinations of white, green, and red light and dark control in a factorial design. Contrary to our expectations, the number of bat passes through a culvert was unaffected by the presence of light. Furthermore, bats did not show any preference for light color. These results show that the response of commuting Daubenton's bats to different colors of light at night with a realistic intensity may be limited when passing through culverts.
Highlights
Artificial light has increased dramatically over the last decades and is ubiquitous in virtually all populated areas worldwide (Falchi et al, 2016; Kyba et al, 2017)
In order to have an impression of the number of individual bats passing, and the dominant flight direction, we manually counted the number of bats during five different nights throughout the experiment, using a handheld bat detector (Pettersson D100× and D240×; Pettersson, Uppsala, Sweden) and an infrared sensitive camera (Sony DCR-SR85) with a LED infrared light (IRlamp6, David Dalton, Tucson, Arizona)
With handheld detectors and the infrared camera, we counted between 17 and 41 Daubenton's bats flying into the Southern entrances of the culverts during five evenings throughout the experiment
Summary
Artificial light has increased dramatically over the last decades and is ubiquitous in virtually all populated areas worldwide (Falchi et al, 2016; Kyba et al, 2017). Bats are strongly affected by light at night, and the indirect attraction of bats by accumulated insects around illumination has been known for a long time (Rydell, 1992; Rydell & Racey, 1995) This effect has more recently been shown in experimental setups (Cravens, Brown, Divoll, & Boyles, 2018; Minnaar, Boyles, Minnaar, Sole, & McKechnie, 2014; Spoelstra et al, 2017; Wakefield, Stone, Jones, & Harris, 2015). In a recent experimental study, free ranging, slow-flying Myotis, and Plecotus bat species were shown to avoid white and green light, but to be active in red light compared to dark control (Spoelstra et al, 2017). We expected a clear effect of light spectrum on the number of bats passing through each culvert, with bats avoiding white and green light
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