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Providing evidence to improve practice

Individual study: A large-scale mitigation experiment to reduce bat fatalities at wind energy facilities

Published source details

Baerwald E.F., Edworthy J., Holder M. & Barclay R.M.R. (2009) A large-scale mitigation experiment to reduce bat fatalities at wind energy facilities. The Journal of Wildlife Management, 73, 1077-1081


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 randomized, replicated, controlled before-and-after study in 2006–2007 at a wind farm in an agricultural area of Alberta, Canada (Baerwald et al 2009) found that increasing the wind speed at which turbines become operational (‘cut-in speed’) resulted in fewer bat fatalities than at conventional turbines. Bat fatality rates were significantly lower at experimental turbines with increased cut-in speeds (average 8 bats/turbine) than at conventional control turbines (average 19 bats/turbine). Bat fatality rates did not differ significantly between turbines before the experiment (‘experimental’ turbines: average 23 bats/turbine; ‘control’ turbines: average 24 bats/turbine). In 2006, all turbines were operated using conventional methods. In 2007, 15 randomly chosen turbines were altered by increasing the cut-in wind speed to 5.5 m/s. Eight control turbines were left unaltered (cut-in speed 4 m/s). Carcass searches were conducted weekly along spiral transects up to 52 m around each of the 29 turbines in July–September 2006 and 2007.

(Summarised by Anna Berthinussen)

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

A randomized, replicated, controlled before-and-after study in 2006–2007 at a wind farm in an agricultural area of Alberta, Canada (Baerwald et al 2009) found that preventing turbine blades from rotating at low wind speeds resulted in fewer bat fatalities than at conventional turbines. Bat fatality rates were significantly lower at experimental turbines with altered blade angles (average 8 bats/turbine) than at conventional control turbines (average 19 bats/turbine). Bat fatality rates did not differ significantly between turbines before the experiment (‘experimental’ turbines: average 19 bats/turbine; ‘control’ turbines: average 24 bats/turbine). In 2006, all of 14 turbines were operated using conventional methods. In 2007, six randomly chosen turbines were altered by changing the pitch angle of the rotor blades to prevent them from turning at low wind speeds (<4 m/s). Eight control turbines were left unaltered. Carcass searches were conducted weekly along spiral transects up to 52 m around each of the 14 turbines in July–September 2006 and 2007.

(Summarised by Anna Berthinussen)