Distance to hedgerows drives local repulsion and attraction of wind turbines on bats: implications for spatial siting.
Abstract
The exponential development of wind energy raises concerns regarding its impacts on airborne biodiversity. Evidence of wind turbine attraction and repulsion on bats, and underlying collision risks and habitats losses, are increasingly reported. Since bat activity strongly decreases with distance to optimal habitats such as woody edges, we hypothesize that the distance to these habitats could drive attraction and repulsion in the immediate vicinity of wind turbine. Although several studies have demonstrated wind turbine attraction and repulsion on bats separately, none have so far investigated the co-existence of both in the same landscape context and evaluated the underlying safe siting distance of wind turbines to bat habitats. We assessed how wind turbines alter bat activity in their immediate vicinity when located at different distances from hedgerows. We acoustically quantified bat activity for two guilds (short-and long-range echolocators) and two species/species group (Pipistrellus pipistrellus and Pipistrellus kuhlii/nathusii from the mid-range echolocators guild) in open areas from 10 to 283 m from hedgerows using a paired sampling design (i.e. recordings conducted simultaneously in areas with and without wind turbines). Sixty-five pairs were sampled over 23 nights during the migration period (i.e. from late summer to late fall) in France. Overall, in the absence of wind turbine, we found that bat activity decreased with increasing distance to hedgerows for all guilds, as widely reported in the literature. Yet, this pattern was no longer observed under wind turbine. When looking at specific distances to hedgerows, we found the activity of all bat groups and species (except for Pipistrellus kuhlii/nathusii) near hedgerows (10-43 m) to be drastically lower under wind turbines than without wind turbine. In contrast, the activity of short-range echolocators was higher under wind turbines when located at 43-100 m from hedgerows, and it tended to be higher for long-range echolocators. Lastly, no effect was detected under wind turbines located at 100-283 m from hedgerows for any guild. Synthesis and applications. This study provides empirical evidence that wind turbines close to optimal habitats such as hedgerows strongly repel bats, while wind turbines located farther away in open areas could attract them. Increased risks of collisions and habitat losses near edges strengthen the importance of keeping wind turbines at a sufficient distance from woody edges (e.g. 200 m as recommended by EUROBATS guidelines).