Abstract
Over recent years, it became widely accepted that alternative, renewable energy may come at some risk for wildlife, for example, when wind turbines cause large numbers of bat fatalities. To better assess likely populations effects of wind turbine related wildlife fatalities, we studied the geographical origin of the most common bat species found dead below German wind turbines, the noctule bat (Nyctalus noctula). We measured stable isotope ratios of non-exchangeable hydrogen in fur keratin to separate migrants from local individuals, used a linear mixed-effects model to identify temporal, spatial and biological factors explaining the variance in measured stable isotope ratios and determined the geographical breeding provenance of killed migrants using isoscape origin models. We found that 72% of noctule bat casualties (n = 136) were of local origin, while 28% were long-distance migrants. These findings highlight that bat fatalities at German wind turbines may affect both local and distant populations. Our results indicated a sex and age-specific vulnerability of bats towards lethal accidents at turbines, i.e. a relatively high proportion of killed females were recorded among migratory individuals, whereas more juveniles than adults were recorded among killed bats of local origin. Migratory noctule bats were found to originate from distant populations in the Northeastern parts of Europe. The large catchment areas of German wind turbines and high vulnerability of female and juvenile noctule bats call for immediate action to reduce the negative cross-boundary effects of bat fatalities at wind turbines on local and distant populations. Further, our study highlights the importance of implementing effective mitigation measures and developing species and scale-specific conservation approaches on both national and international levels to protect source populations of bats. The efficacy of local compensatory measures appears doubtful, at least for migrant noctule bats, considering the large geographical catchment areas of German wind turbines for this species.
Highlights
Over the past two decades, wind energy has continuously been promoted in many European and North American countries and is currently widely recognized as an environmentally friendly alternative to conventional energy production such as those based on nuclear and fossil fuels
Recent bat fatality surveys revealed that the numbers of bats killed annually at European and North American wind turbines is alarming [2,5,6], with estimates of hundreds of thousands of bats killed by wind turbines in the U.S.A. [7]
The majority of bat fatalities in Europe occurs during the migration period [5,6], and is most often affecting species with documented migratory behaviour such as Nyctalus noctula, Pipistrellus nathusii, N. leisleri and Vespertilio murinus (Durr 2009 cited in [5])
Summary
Over the past two decades, wind energy has continuously been promoted in many European and North American countries and is currently widely recognized as an environmentally friendly alternative to conventional energy production such as those based on nuclear and fossil fuels. The majority of bat fatalities in Europe occurs during the migration period [5,6], and is most often affecting species with documented migratory behaviour such as Nyctalus noctula, Pipistrellus nathusii, N. leisleri and Vespertilio murinus (Durr 2009 cited in [5]). It is unknown whether killed bats are of local origin or originate from distant populations. Information on the migratory status of killed bats is a crucial prerequisite to determine their breeding origin and, to assess the geographical catchment area of bat fatalities at wind turbines. Considering the presumed large numbers of killed bats and the low capacity of bat populations for recovering from increased mortality rates [15], an improved understanding of the location of affected source populations is essential to evaluate the impact of wind turbines on breeding populations and to formulate and evaluate effective conservation measures
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