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.

Actions

This study is summarised as evidence for the following.

Action Category

Increase the wind speed at which turbines become operational (‘cut-in speed’)

Action Link
Bat Conservation

Increase the wind speed at which turbines become operational (‘cut-in speed’)

Action Link
Bat Conservation
  1. Increase the wind speed at which turbines become operational (‘cut-in speed’)

    A replicated, randomized, controlled study in 2010 at a wind energy facility in an agricultural area in the Midwest region, USA (Arnett et al 2013) found that increasing the wind speed at which turbines become operational (‘cut-in speed’) resulted in fewer bat fatalities than at conventional turbines. Bat fatalities were estimated to be 47% and 72% lower at turbines with cut-in speeds increased to 4.5 and 5.5 m/s respectively compared to control turbines with conventional cut-in speeds (data reported as statistical model results). A total of 25 and 14 bat carcasses were found at turbines with cut-in speeds of 4.5 and 5.5 m/s respectively, whereas 53 carcasses were found at control turbines. Two treatments (cut-in speed increased to 4.5 and 5.5 m/s from 1 h before sunset to 1 h after sunrise) and a control (conventional cut-in speed of 3.5 m/s) were each randomly assigned to four turbines. Treatments were rotated weekly between turbines over nine weeks in August–October 2010. Daily carcass searches were conducted in plots (80 x 80 m) centred on each of the 12 turbines.

    (Summarised by: Anna Berthinussen)

  2. Increase the wind speed at which turbines become operational (‘cut-in speed’)

    A replicated, randomized, controlled study in 2012 at a wind energy facility in a desert scrub area in the Pacific Southwest region, USA (Arnett et al 2013) found that increasing the wind speed at which turbines become operational (‘cut-in speed’) did not result in fewer bat fatalities compared to conventional turbines. Total numbers of bat fatalities were reported to be 20–38% lower for four different treatments with increased cut-in speeds than at conventional turbines, but none of the differences were significant. The authors report that sample sizes were small (numbers not reported). Three bat species were found, although 74% of bat carcasses were Brazilian free-tailed bats Tadarida brasiliensis (see original paper for details). Four treatments (cut-in speed increased to 4, 5 or 6 m/s for 4 h after sunset, or cut-in speed increased to 5 m/s all night) and a control (conventional cut-in speed of 3 m/s) were randomly rotated each night between four groups of 10 turbines in August–September 2012. Daily carcass searches were conducted along transects in plots (126 x 126 m) centred on each of the 40 turbines.

    (Summarised by: Anna Berthinussen)

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