Abstract
Context
Collisions with wind turbines threaten bat populations worldwide. Previous studies tried to assess the effects of landscape on mortalities. Yet, the count of carcasses found per species is low, leading to a low statistical power. Acoustic surveys collect large datasets (proxy for bat density); however, if bat vertical distribution is not accounted for, a key mechanism in collisions is missed.
Objectives
Our goal was to disentangle the effects of landscape on bat density and vertical distribution to produce recommendations for wind farm siting.
Methods
With a vertical array of two microphones, we monitored the acoustic activity and located the vertical distribution of more than 16 bat species on 48 wind masts in France and Belgium (> 8000 nights). We modelled bat density and vertical distribution for six species in function of distance to water, woodland and buildings, and in function of the topography at three different scales (200 m, 1000 m and 5000 m).
Results
The proportion of flights at heights with collision risk was maximum in spring and autumn and minimum in summer for three species. This effect was often antagonistic to the effect of bat density. The landscape had a stronger effect on bat density than on bat vertical distribution.
Conclusions
Positioning wind farms away from woodland should reduce the density and therefore the collision risks of low-flying species but should be inefficient for high-flying species. The effect of topography was stronger at large scales and complex, thus studying situations such as coastlines or mountain passes would provide more insight.