Activity of forest specialist bats decreases towards wind turbines at forest sites

Worldwide, wind turbines are increasingly being built at forest sites to
meet the goals of national climate strategies. Yet, the impact on forest
ecosystems and biodiversity is barely understood. Bats may be heavily
affected by wind turbines in forests, because many species depend on
forest ecosystems for roosting and hunting and can experience high
fatality rates at wind turbines. We performed acoustic surveys in 24
temperate forests in the low mountain ranges of Central Germany to monitor
changes in the acoustic activity of bats in relation to wind turbine
proximity, rotor size, vegetation structure and season. Call sequences
were identified and assigned to one of three functional guilds:
open-space, edge-space and narrow-space foragers, the latter being mainly
forest specialists. Based on the response behaviour of bats towards wind
turbines in open landscapes, we predicted decreasing bat activity towards
wind turbines at forest sites, especially for narrow-space foragers.
Vertical vegetation heterogeneity had a strong positive effect on all
bats, yet responses to wind turbines in forests varied across foraging
guilds. Activity of narrow-space foragers decreased towards turbines over
distances of several hundred meters, especially towards turbines with
large rotors and during midsummer months. The activity of edge-space
foragers did not change with distance to turbines or season, whereas the
activity of open-space foragers increased close to turbines only in late
summer. Synthesis and applications: We show that narrow-space foragers
avoid wind turbines in forests over a spatial scale of several hundred
meters. This response was most apparent towards turbines with large
rotors. Since forests are an important habitat for this guild, we advise
to exclude forests with diverse vegetation structure as potential wind
turbine sites and to consider compensation measures to account for habitat
degradation associated with the operation of wind turbines in forests.