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Individual study: A synthesis of operational mitigation studies to reduce bat fatalities at wind energy facilities in North America. A report submitted to the National Renewable Energy Laboratory

Published source details

Arnett E.B., Johnson G.D., Erickson W.P. & Hein C.D. (2013) A synthesis of operational mitigation studies to reduce bat fatalities at wind energy facilities in North America. A report submitted to the National Renewable Energy Laboratory. Bat Conservation International report.


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Increase the wind speed at which turbines become operational (‘cut-in speed’) to reduce bat fatalities Bat Conservation

A review of 10 studies in 2006–2012 at wind energy facilities in Canada and the USA (Arnett et al 2013) found that increasing the speed at which wind turbines become operational (‘cut-in speed’), or increasing the cut-in speed along with preventing rotor blades from turning at low wind speeds, resulted in fewer bat fatalities in all 10 studies. In eight studies, average bat fatalities were reduced by 47–82% when cut-in speeds were increased, and by 57–89% when rotor blades were also prevented from turning at low wind speeds, compared to conventionally operated turbines (see original reference for more detailed results). Two studies found that bat fatalities were reduced by 20–38% at wind turbines when cut-in speeds were increased, but sample sizes were small and differences were either not statistically signficant or were not tested. In seven of ten studies, cut-in speeds were increased to 4–6.9 m/s compared to the standard manufacturer’s cut-in speed (3–4 m/s). In three of ten studies, turbine blades were also prevented from turning at low wind speeds by changing the angle of the blade parallel to the wind or turning the turbine out of the wind. Two of 10 studies reported estimated losses in power generation to be <1% of the total annual output. Three studies in this review have been summarised individually (Baerwald et al 2009, Arnett et al 2010, Martin et al 2017).

(Summarised by Anna Berthinussen)

Prevent turbine blades from turning at low wind speeds to reduce bat fatalities Bat Conservation

A review of six studies in 2006–2011 at wind energy facilities in Canada and the USA (Arnett et al 2013) found that preventing turbine blades from turning at low wind speeds, or preventing turbines blades from turning at low wind speeds along with increasing the wind speed at which turbines became operational (‘cut-in speed’) resulted in fewer bat fatalities in all six studies. Average bat fatalities were reduced by 23–57% when turbine blades were prevented from turning at low wind speeds, and by 57–89% when cut-in speeds were also increased, compared to conventionally operated turbines (see original reference for more detailed results). In all six studies, turbine blades were prevented from turning at low wind speeds by changing the angle of turbine blades to be parallel to the wind. In three of the six studies, cut-in speeds were also increased (4–6.5 m/s) compared to the standard manufacturer’s cut-in speed (3–4 m/s). One study in this review has been summarised individually (Baerwald et al 2009).

(Summarised by Anna Berthinussen)