Abstract
Wind farm developers have to provide an effective mitigation hierarchy: an avoidance and a reduction of negative impacts of wind farm on biodiversity (bats in our case), and to implement offsetting measures when residual impacts persist. Offsetting consists in implementing measures (e.g. hedgerows) that counteract residual losses of biodiversity and generate gains in order to achieve a no net loss or a net environmental benefit. Indeed, due to the reluctance of local people to install wind turbines near their homes, project developers often attempt to install wind energy facilities on agricultural land, particularly in arable land dominated by open fields or wooded countryside. Research and ecological impact assessments studies are focused for many years on bat mortality impact, without really know if the mitigation hierarchy applied is effective. Mortality is often describe as a significant negative impact on bat population, even though population parameters are poorly known, but what about habitat losses by revulsion? To our knowledge no study attempts to evaluate impact distance of wind turbines on bat activity. To determine the loss of number of bat passes according to distance to wind turbine, we performed a sampling design focused on hedgerows. We simultaneously recorded activity on 10 points per night, at 10 different distances to wind turbine. We studied one wind farm per night, and each record point was chosen in order to minimize differences in local and landscape characteristics with other simultaneous points. Sampled distances were between 0 and 1000 meters to wind turbines, thus, we did not use controls. A total of 36 wind farms were studied using 280 record points in north-west France. Results show for all species/species groups, for which statistical analysis were possible, a significant negative impact of wind farms on bat activity. We found quadratic or linear positive relationship between bat activity and distance to wind farm, without threshold effects, except for Plecotus sp (around 750 meters). Predicted number of bat passes from models reveals a loss of a minimum of 50% within a range from 1000 to 0 meters. Amongst these species, some are known to be less sensitive to wind turbines in literature (i.e. mortality) are affected by long distances. Results indicates that loss of foraging and moving habitat is very important and could play an important role on population dynamics. This concern should therefore be taken into account in mitigation reflections and implementation ways, especially in wooded countryside regions.