Even indirect light disturbs bats: they are sensitive to the low-intensity halo that diffusely surrounds cities. It is a great operation of participative science which makes it possible to affirm it. For seven years, citizens have observed the activity of serotines, common bats, on more than a thousand sites in France and the result: not only are these bats less numerous in the luminous halo of cities but in the later they leave to hunt. Near medium-sized towns, they take off six to ten minutes late. Even low levels of light pollution affect the spatial distribution and timing of activity of a “light-tolerant” bat species.
This jet lag is really a problem for bats. In any case
much more than you think, because by leaving to hunt later, they find themselves out of step with the insects on which they feed, explain the authors of this study. However, the hunting window is narrow, the peak of activity should normally be at dusk so that the bats can feed properly.
Moreover, when these bats cross luminous points on the hunting path, they avoid them. They therefore make detours, which takes more energy from them and in the end all this can affect the survival of these populations, indicates this study. A finding that worries all the more that a third of common bats have disappeared in 15 years in France. And that at the same time the quantity of light emitted by public lighting has increased by 90% in 30 years.
This decline of bats is not only due to light pollution, it is also due to the destruction of their habitat, and the impact of global warming. But the researchers insist on the urgency of lowering the light intensity at night, which also disturbs other species, in particular insects or pollinating butterflies. They offer different solutions ranging from completely switching off streetlights and shop windows at night to changing their intensity through a different orientation of the lighting, towards the ground rather than towards the sky.
In France, 12,000 municipalities have already adopted partial or complete extinction at night, indicates the association for the protection of the sky and the nocturnal environment. It is a win-win solution, both to preserve biodiversity and to save money thanks to energy sobriety.