BLACK GRID in the Lille metropolitan area

Working together with the CESCO laboratory at the National Museum for Natural History in Paris, the Centre for Functional and Evolutionary Ecology (the “CEFE”) in Montpellier and the TVES laboratory at the University of Lille, Biotope has studied the effect of the reduction of light on landscape connectivity for bats across the Lille European Metropolis.  This project has been financed by the Hauts de France Region in partnership with the Foundation for Research on Biodiversity.

Light reduction for landscape connectivity for bats

In Europe, all bat species are nocturnal.  They are particularly sensitive to disturbance related to light pollution.  To alleviate that, they adapt by changing or extending their movements.  They are also deprived of many hunting-grounds that are over-lit.  The dark areas are in turn depleted of insects, which are attracted by the artificial light sources.  In some cases, the individuals’ survival and reproductive success are at risk.

The BLACK GRID project to address these issues

In order to address the issue of light pollution and its impact on bats, Biotope was asked to carry out a study on the BLACK GRID. The objectives of that study were to determine (1) if it were possible to use the existing network of corridors to develop a local black grid, (2) to determine the current state of nocturnal ecological connectivity across the Lille European Metropolis and finally (3) to discover if it were possible to improve that connectivity by reducing the luminous intensity.

The ecological issues for the project

The first step in that project was to draw up ecological inventories and thus to determine the varieties of bat species found in the study area.

399 sites were selected.  The inventories were carried out during complete nights in the most contrasted sectors in the study area.  The sampling effort implemented for this project, given its intensity, is the only one of its kind in the world for urban and peri-urban environments.

In total, 9 bat species, all protected, were identified in the area of the Lille European Metropolis.

Modelling the black grid

The modelling made it possible to predict and map the probability of the presence, as well as the abundance, of several bat species

Social acceptability

An analysis carried out in several towns shows that the Black Grid concept in France is still very new and poorly defined.  Survey results have shown that in principle, the implementation of the concept would be acceptable local population.  The town residents say that they would be willing to go without the comfort of public lighting in order to protect species from the impacts of artificial light. The survey results also highlight the importance of involving the residents from the outset of the projects to implement a black grid.

Study results

• The results from this study demonstrate that the various bat species show mixed responses to light pollution (negative, positive or intermediate with a threshold effect).
• The effect of the light on the presence and activity of the bats is significant and preponderant in a perimeter of up to 700m from the light sources.
• A reduction in the luminous intensity makes it possible to improve landscape connectivity for the species studied in urban areas.

This study shows the importance of including recommendations about lighting (positioning, power, spectrum and duration) in urban planning documents in order to improve conditions for bats in urban areas and makes it possible to envisage vectors for action that would take account of the conflicts of interest between environmental, economic and social issues.

You can find the full article written by the team of scientists who took part in that study on: https://link.springer.com/article/10.1007%2Fs10980-019-00803-0