This study aims to analyse the potential impacts of wind farm development on populations of the greater mouse-eared bat (Myotis myotis). At the moment, direct mortality linked to wind turbines, whether through collision or barotrauma, appears to be extremely low, or even negligible, for this species. However, the question of indirect effects, particularly through disturbance and avoidance phenomena that may lead to a loss of hunting habitats, remains open. Our approach to this issue is to determine whether such presumed effects can influence population dynamics by affecting their health, reproduction or survival. To address this, the study is structured around five research questions grouped into three complementary sections.

The first section consists of a benchmarking study on the conservation status of the greater mouse-eared bat in Europe, its sensitivity to wind power, and the threats facing the species. It shows that the greater mouse-eared bat has a variable but generally unfavourable conservation status across the regions studied. In most countries, the species is not considered a particularly limiting factor for wind energy development. The environmental assessment guidelines analysed indicate that the greater mouse-eared bat is not highly sensitive to the risk of mortality. The German guidelines also highlight a potential impact through disturbance at roosting sites, breeding sites and hunting habitats. It is in Wallonia that the challenge for this species is most pronounced.

The second section analyses the population dynamics of the greater mouse-eared bat in relation to local wind farm development, based on time series of breeding colonies in six European countries combined with spatial data on wind turbines. The results from statistical models highlight a significant increase in population numbers over time, regardless of the number of wind turbines in the vicinity. The interaction between time and turbine density is not significant, indicating that wind turbines have no measurable effect on population trends. Analyses comparing situations before and after the installation of wind turbines confirm these results: no significant change in trends is observed, and the variations detected remain small and uncorrelated with the number of turbines.

The third section explores the influence of land-use changes on population dynamics. It highlights a significant effect of landscape transformations, with a delayed negative impact from urbanisation and, conversely, a delayed positive effect associated with agricultural and grazed areas on the probability of colony growth. These two effects reflect a single process: the gradual conversion of agricultural land into urbanised areas.

Overall, the results indicate that wind farm development is not a major factor explaining variations in the populations of the greater mouse-eared bat at the European level. The global positive trend can be explained by the species’ gradual recovery following its massive historical decline in the mid-20th century. The differences in trends observed between colonies appear to be influenced more by factors other than the presence of wind turbines, such as land use, highlighting the importance of issues relating to habitat quality and availability in the conservation of the species.