Scientific results of Vigie-Chiro

Light pollution and bats

Light pollution is generated by artificial lighting in a night environment. Streetlights cause disturbance to fauna (insects, bats, humans, etc.) and flora. This form of pollution affects a total of 20% of the world's land surface (with an increase of 6% per year) and affects terrestrial, aquatic and marine environments!

In terms of consequences for biodiversity, studies have shown that light pollution disrupts the daily and seasonal rhythms of several species. This form of pollution modifies the movement of species because light fragments the night-time landscape.

As everyone knows, bats live at night; however, their response to lighting varies according to species. The so-called aerial species are fast flying and hunt airborne insects. They are often detected hunting in the vicinity of street lights. On a local scale, there is therefore a positive effect of the streetlight attracting a considerable number of insects. On the other hand, another group of species, called gleaners, hunts more in crowded and closed environments (e.g. forests). These species gather insects that are lying on leaves or branches. As they fly more slowly, they are subject to a higher risk of predation and therefore seem to avoid lit areas.

Is night-time switching off (midnight to 5 a.m.) an effective measure to limit the impact of artificial lighting on chiropterans?

First of all, in her study, Clémentine was able to show that for the Common Pipistrelle, lighting seems to favour its presence: it is twice as frequent as in unlit areas that are turned off for part of the night.

Murins, on the other hand, seem to avoid even partially lit areas (according to the error bars, the difference is not significant between lighting all night or partially).

Earwigs seem to be the only ones to benefit from streetlighting measures. They hunt more significantly where lights are turned off. They would take advantage of the "groggy" insects, immobile on the ground or on the walls of houses, recovering from the "too much" light. Easy prey in short.
 
The period between midnight and 5 a.m. when streetlights are switched off is of little interest to most bat species. Other studies seem to show that it would be more effective to switch them off from 11 pm onwards. 

Finally, as these graphs show, the light produced by street lamps impacts bats at a maximum distance of between 10 and 25 metres.

This result raises the question of how to create sufficiently wide ecological corridors for nocturnal species in an urban environment while respecting the feeling of safety of the inhabitants... And Clémentine does not have the answer to this question!