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. Journal of Wildlife Management, 73, 1077-1081.
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This study is summarised as evidence for the following.

	Action	Category
	Slow rotation of turbine blades at low wind speeds Action Link
	Increase the wind speed at which turbines become operational (‘cut-in speed’) Action Link

Slow rotation of turbine blades at low wind speeds

A replicated, randomized, controlled study in 2006–2007 at a wind farm in an agricultural area of Alberta, Canada (Baerwald et al 2009) found that slowing the rotation of turbine blades at low wind speeds resulted in fewer bat fatalities than at conventional turbines. Average bat fatality estimates were lower at experimental turbines with altered blade angles (8 bats/turbine) than at conventional control turbines (19 bats/turbine). Average bat fatality estimates did not differ significantly between turbines before the experiment (‘experimental’ turbines: 19 bats/turbine; ‘control’ turbines: 24 bats/turbine). Most bats identified during carcass searches were hoary bats Lasiurus cinerus and silver-haired bats Lasionycteris noctivagans (see original paper for data). In 2006, all of 14 turbines were operated using conventional methods (blades rotated freely at low wind speeds). In 2007, six randomly chosen turbines were altered by changing the pitch angle of the rotor blades to slow rotation 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. Carcass counts were corrected to account for searcher efficiency and removal by scavengers.

(Summarised by: Anna Berthinussen)
Increase the wind speed at which turbines become operational (‘cut-in speed’)

A replicated, randomized, controlled 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. Average bat fatality estimates were lower at experimental turbines with increased cut-in speeds (8 bats/turbine) than at conventional control turbines (19 bats/turbine). Average bat fatality estimates did not differ significantly between turbines before the experiment (‘experimental’ turbines: 23 bats/turbine; ‘control’ turbines: 24 bats/turbine). Most bats identified during carcass searches were hoary bats Lasiurus cinerus and silver-haired bats Lasionycteris noctivagans (see original paper for data). In 2006, all of 23 turbines were operated using conventional methods. In 2007, fifteen 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 of 4 m/s). Carcass searches were conducted weekly along spiral transects up to 52 m around each of the 23 turbines in July–September 2006 and 2007. Carcass counts were corrected to account for searcher efficiency and removal by scavengers.

(Summarised by: Anna Berthinussen)