All European bat species are vulnerable to artificial light at night – this varies across habitats and feeding guilds
The artificial illumination of the night by lamps is considered a central achievement of civilisation with countless economic, social and cultural benefits for people. For many animals, however, artificial light poses a considerable challenge. Nocturnal and light-shy species are forced to move to dark areas or adjust their behaviour to the new nocturnal brightness. In a paper published in the journal “BioScience”, an international research team led by the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) provides an evidence-based overview of the effects of artificial light on European bat species. They find that especially those species that hunt insects in narrow spaces such as forests are very sensitive to artificial light. In contrast, bats hunting along forest edges or in open areas are somewhat more tolerant of artificial light. At roosts or drinking sites all species are distinctly light-shy.
For their analysis, the scientists surveyed the literature for the response of European bat species to artificial light at night (ALAN) in different ecological contexts and for different foraging guilds. They followed the classification of European bat species into three foraging guilds – species groups with a similar way of life: Species that hunt in dense spaces such as forests, species that forage for insects at structural edges near objects (for example, along buildings or forest edges), and species that forage in the open airspace above meadows, canopies, water bodies or arable land. Species of these three groups developed special functional characteristics, for example in terms of their echolocation or wing shape, suitable for their hunting habitat and foraging tactics. The scientists assessed how these foraging guilds responded to artificial light in their respective habitats, particularly near roosts, in flight corridors, hunting areas or drinking sites.
The analyses revealed a variable, but consistent picture, says first author Dr Christian Voigt, head of the Leibniz-IZW Department of Evolutionary Ecology. “Generally, all European bat species are very sensitive to artificial light, especially near roosts and drinking sites,” says Voigt. “This can be explained by the fact that the presence of bats in these places is predictable for predators such as owls. Consequently, bats are particularly cautious here.” In flight corridors that connect roosts and foraging areas the picture is more variable. Many species (especially those that hunt in forests or at structural edges) avoid the light here as well and shift their routes to dark corridors when artificial light illuminates the night. Other species, however, are not repelled by artificial light in such a situation – but are not attracted by light either. “When it comes to hunting areas, we identified two responses,” says Dr Daniel Lewanzik, a scientist at Voigt’s department and co-author of the paper. “Some species, those that forage in the open space or at structural edges, are attracted by the abundance of insects at light sources. They can sometimes be seen in summer flying from one streetlight to the next when hunting insects. Forest-dwelling species, on the other hand, generally avoid artificial light sources, even when hunting insects.” For all species, the risk of falling prey to a predator in the spotlight is weighed against the possible foraging benefits – different functional groups obviously come to different conclusions in this risk assessment.
Voigt and his co-authors argue that these findings should be taken into account in bat conservation. This could mean, for example, to protect roosts and drinking sites from artificial light and to target protection measures especially at those species that would not benefit from artificial light even when hunting. And, since the benefit is limited to certain places and activities, all species would benefit if light pollution was reduced, dark corridors (for example urban parks) were consistently kept dark or new dark islands were established in urban landscapes.
Voigt CC, Dekker J, Fritze M, Gazaryan S, Hoelker F, Jones G, Lewanzik D, Limpens HJGA, Mathews F, Rydell J, Spoelstra K, Zagmajster M (2021): The Impact of Light Pollution on Bats Varies According to Foraging Guild and Habitat Context. BioScience, Volume 71, Issue 10, October 2021, Pages 1103–1109, DOI: 10.1093/biosci/biab087
Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) in the Forschungsverbund Berlin e.V.
Alfred-Kowalke-Str. 17, 10315 Berlin, Germany
PD Dr Christian Voigt
Head of the Department of Evolutionary Ecology
phone: +49 30 5168 511
Dr Daniel Lewanzik
Scientist in the Department of Evolutionary Ecology
phone: +49 (0)30 5168121