Landscape-scale effects of single- and multiple small wind turbines on bat activity

While the effects of wind farms on bats are widely studied, effects of small wind turbines (SWTs, here <25m hub height) remain understudied. SWTs are installed in a wider range of habitats compared to wind farms and their effect on wildlife can therefore be different. While single SWTs can adversely affect bat activity in their immediate vicinity, they are often installed in clusters, and to date no data are available on whether installation of more than one turbine increases the likelihood of adverse effects on bats. 
Here, we test whether (1) SWT installations affect the activity of two species of bat (the common pipistrelle Pipistrellus pipistrellus and soprano pipistrelle P. pygmaeus) on a landscape scale (here defined as up to 500m from SWTs) and (2) such an effect is stronger when multiple (2-4) SWTs are installed. We show that, after accounting for potentially confounding effects (e.g. variation in habitat and weather), (1) mean P. pipistrellus activity is lower at 0-100m compared to 200-500m from SWTs, and (2) the effect on P. pygmaeus activity tends to be similar and stronger in multiple SWT sites, although evidence for the latter is limited.
We conclude that in some cases, adverse effects of SWTs on bat activity may be measurable over longer spatial scales (within 100m) than previously thought. However, combined with earlier findings, it is likely that the bulk of such effects operate within relative close proximity of SWTs (<25m). Moreover, although these effects may be species-specific, with e.g. P. pygmaeus potentially more strongly affected by multiple SWT sites, this requires further data. These findings are highly relevant to decision-making aimed at minimizing any adverse effects of wind turbines, specifically single- vs. multiple SWT developments, on wildlife.