Animals of the night in the glow of lanterns and the like: Of the numerous European bat species, ultimately all of them suffer from light pollution – but there are considerable differences between the species and groups, according to researchers. According to this, species that are adapted to hunting in dense vegetation are particularly sensitive. Bats that hunt on the edge of the forest or in open areas, on the other hand, tend to tolerate artificial light and sometimes even hunt deliberately using its glow. In the area of day quarters or drinking places, however, lighting interferes with all bat species, say the researchers.
Where once only the moon and stars shimmered, street lamps, spotlights and other light sources turn night into day. It is already known from numerous studies that this unnatural brightness has a negative effect on many animals: They are attracted or repelled by the nocturnal light sources and the lighting can disrupt their rhythm of life. Light pollution is particularly problematic for insects – it is therefore also a factor in the sometimes drastic decline in populations.
Because of blind
It may seem surprising that bats are also affected by light pollution, as they are known for their orientation by echo sounder. However, their small eyes are not insignificant: they provide the bats with important additional information from the environment and are particularly sensitive to light. As studies in recent years have shown, artificial light can therefore also significantly disturb bats. However, it already became apparent that there are clear differences between the representatives of this species-rich group of animals. In order to get an overview and to show patterns of sensitivity, the researchers led by Christian Voigt from the Leibniz Institute for Zoo and Wildlife Research in Berlin (IZW) have now systematically evaluated studies on European bat species: They looked in the data for clues about the reactions to it artificial light at night.
In the evaluation, they followed the usual division of around 50 European species into three groups with a similar way of life: One section is adapted to the insect hunt in dense vegetation. Another group, on the other hand, is typically on the move at structural transitions – for example on buildings or at the edges of forests. A third group catches their prey in the open air above fields, bodies of water or above the treetops. The bats in these three categories have developed similar characteristics and behaviors for their respective hunting behavior, the researchers explain.
Sensitivities in view
As they report, basic and special patterns of reactions to artificial light emerged in the evaluations: “In principle, it becomes clear that all European bat species can react very sensitively to artificial light, especially in the vicinity of day roosts and drinking places,” says Voigt. As he explains, this can be explained by the fact that bats are not only hunters but also hunted: “The presence of bats in these places is predictable for predators such as owls and the bats are therefore particularly careful there,” says the scientist. Therefore, artificial light apparently fundamentally unsettles the animals in these areas.
In flight corridors that connect day quarters and hunting areas, on the other hand, the reaction between the species and groups is significantly more variable: It has been shown that especially those species that hunt in dense vegetation are generally very light-shy: They avoid illuminated areas and give way to theirs Flight routes based on dark corridors. In the case of the representatives of the other two groups, on the other hand, there are many species that react only little to artificial light on their excursions.
Lights out for bat protection
“Two different reaction patterns then become apparent in the hunting areas,” says co-author Daniel Lewanzik from the IZW. “Some species that hunt in open air or on the edges of structures are attracted by the abundance of insects in light sources. In summer you can sometimes watch them fly from one street lamp to the next, hunting insects there. Forest-dwelling species, on the other hand, generally avoid light sources, even when hunting insects. ”For all species, it is the case that with artificial light the risk of becoming a victim of a predator is weighed against the possible advantages. This apparently leads to different results for the different bat groups, the researchers sum up.
According to them, the variance in reactions to artificial light should now be given greater consideration in bat protection. This means, for example, that potential day quarters and drinking places should generally be protected from artificial light. The overview study now also shows which species are particularly sensitive to interference from light and which are less. Ultimately, however, all species would benefit if light pollution were reduced and dark corridors – such as urban parks – remained consistently unlit and new dark islands were established in the urban landscape, say the researchers.
Concerning the supposed use of lighting for hunting behavior of some species, they conclude: “In view of the harmful effects of artificial light on insect populations, we come to the conclusion that nighttime lighting ultimately has a negative effect on all bat species – including those that go looking for food at street lights ”.