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


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Switch off turbines at low wind speeds to reduce bat fatalities Bat Conservation

A replicated, randomized, controlled study in 2006 and 2007 in an agricultural area of Alberta, Canada (Baerwald et al 2009) found that fatalities of hoary bats Lasiurus cinereus and silver-haired bats Lasionycteris noctivagans were reduced when two different operational changes were made to wind turbines to reduce rotor rotation at low wind speeds. Bat fatality rates were significantly lower at experimental turbines with increased cut-in speed or altered blade angle (both average 8 bats/turbine) than control turbines (average 19 bats/turbine). In both years, from August to September, carcass searches were conducted weekly along spiral transects up to 52 m around each of the 39 turbines. Bat fatality rates were corrected for searcher efficiency and scavenger removal. In 2006, no operational changes were made and fatality rates were not found to differ between turbines. In 2007, 15 randomly chosen turbines were altered by increasing the cut-in wind speed to 5.5 m/s, and six randomly chosen turbines were altered by changing the pitch angle of the rotor blades. The remaining control turbines were left unaltered. Both operational changes caused turbines to remain motionless at low wind speeds and bat fatality rates did not differ significantly between them. Turbines with increased cut-in speed caused a greater reduction in electricity generation than those with altered blade angles.