Action

Action Synopsis: Bat Conservation About Actions

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

How is the evidence assessed?
  • Effectiveness
    80%
  • Certainty
    72%
  • Harms
    0%

Source countries

Key messages

  • Twelve studies evaluated the effects of increasing the wind speed at which turbines become operational (‘cut-in speed’) on bat populations. Ten studies were in the USA and two were in Canada.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (12 STUDIES)

  • Survival (12 studies): Ten of 12 studies (including 10 replicated, randomized, controlled studies and one before-and-after study) in the USA and Canada found that increasing the wind speed at which turbines become operational (‘cut-in speed’), or increasing the cut-in speed along with preventing turbine blades from turning at low wind speeds (‘feathering’) resulted in fewer bat fatalities than at conventionally operated turbines. The other two studies found that increasing cut-in speeds did not reduce bat fatalities, but sample sizes were small or treatments were applied for short periods only.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. 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.

    Study and other actions tested
  2. A replicated, randomized, controlled study in 2008–2009 at a wind farm in a forested area of Pennsylvania, USA (Arnett et al 2010) 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 turbines with cut-in speeds increased to 5 m/s (0.3–0.7 bats/turbine) and 6.5 m/s (0.5–0.6 bats/turbine) than at turbines with conventional cut-in speeds (3.5 m/s: 2.0–2.3 bats/turbine). Fatality estimates did not differ significantly between the two treatments. In July–October 2008 and 2009, two treatments (cut-in speed increased to 5 or 6 m/s) and one control (cut-in speed of 3.5 m/s) were each randomly assigned to three groups of four turbines for 25 nights/treatment. All 12 turbines were prevented from turning (‘feathered’) below cut-in wind speeds. Daily carcass searches were conducted along transects in plots (126 x 120 m) centred on each of the 12 turbines. Carcass counts were corrected to account for unsearchable areas within plots. If applied to the entire wind farm (23 turbines), annual power output losses were projected to be 0.3% with cut-in speeds increased to 5 m/s, and 1% with cut-in speeds increased to 6.5 m/s.

    Study and other actions tested
  3. 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.

    Study and other actions tested
  4. 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.

    Study and other actions tested
  5. A replicated, randomized, controlled study in 2010 at a wind farm in an agricultural area of Indiana, USA (Good et al 2011; same site as Good et al 2012) 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 50% and 78% lower when cut-in speeds were increased to 5 and 6.5 m/s respectively (7 and 3 bats/turbine) compared to conventional control turbines (14 bats/turbine). Six bat species were found, although 72% of bat carcasses were eastern red bats Lasiurus borealis (see original report for data). Two treatments (cut-in speed increased to 5 or 6 m/s) and a control (conventional cut-in speed of 3.5 m/s) were each randomly assigned to a group of nine turbines. Treatments were rotated between the three turbine groups weekly in August–October 2010. Nine control turbines were left unaltered. Daily carcass searches were conducted along transects in plots (80 x 80 m) centred on each of the 36 turbines. Carcass counts were corrected for searcher efficiency and removal by scavengers.

    Study and other actions tested
  6. A replicated, randomized, controlled study in 2011 at a wind farm in an agricultural area of Indiana, USA (Good et al 2012; same site as Good et al 2011) found that increasing the wind speed at which turbines become operational (‘cut-in speed’), along with preventing turbine blades from turning at low wind speeds (‘feathering’), resulted in fewer bat fatalities compared to conventional turbines. Total bat fatalities were 59% and 75% lower (42 and 25 fatalities) when cut-in speeds were increased to 4.5 and 5.5 m/s respectively, and blades were feathered below these speeds, compared to conventional control turbines (105 fatalities). Differences in total fatalities between the two treatments were significant. Six bat species were found, although 80% of bat carcasses were eastern red bats Lasiurus borealis and hoary bats Lasiurus cinereus (see original report for data). Two treatments (cut-in speeds increased to 4.5 and 5.5 m/s and blades feathered below these speeds) were each assigned to a group of 42 turbines. Two control groups of nine and 42 turbines were left unaltered (blades rotated freely below cut-in speed of 3.5 m/s). Treatments were rotated between turbine groups nightly in July–October 2011. Carcass searches were conducted every 1–2 days along transects in circular plots (80-m radius) around each of the 135 turbines.

    Study and other actions tested
  7. A replicated, randomized, controlled study in 2011 at a wind farm on an island in Ontario, Canada (Stantec Consulting Ltd. 2012) 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 turbines with cut-in speeds increased to 4.5 m/s (2.7 bats/turbines) or 5.5 m/s (2.1 bats/turbine) than at conventional control turbines (5.3 bats/turbine). The differences were not tested for statistical significance. Four bat species were found (see original report for details). In July–September 2011, fourteen turbines were randomly assigned to each of two treatments (increased cut-in speed of 4.5 or 5.5 m/s from sunset to sunrise) or as controls (conventional cut-in speed of 4 m/s). Carcass searches were carried out twice weekly along transects within circular plots (50-m radius) around each of the 42 turbines. Carcass counts were corrected to account for searcher efficiency, removal by scavengers, and the percentage of plot areas searched.

    Study and other actions tested
  8. A replicated, randomized, controlled study in 2012 at a wind farm in a forested area of West Virginia, USA (Hein et al 2013; same site as Hein et al 2014) found that increasing the wind speed at which turbines become operational (‘cut-in speed’) for all or part of the night did not result in fewer bat fatalities than at conventional turbines. Overall, average nightly bat fatality rates did not differ significantly between turbines with the cut-in speed increased to 5 m/s for all or part of the night and conventional control turbines (data reported as statistical model results). The authors report that wind speeds of 3–5 m/s (i.e. when the treatments were in effect) only occurred for 17% of the time during the study. Six species were found across the site (see original report for details). Each of 12 turbines was randomly assigned to one of two treatments (cut-in speed increased to 5 m/s from sunset to sunrise or for the first 4 h after sunset) or as a control (conventional cut-in speed of 3 m/s). Treatments were rotated between turbines nightly over 75 nights in July–September 2012. All 12 turbines were prevented from turning (‘feathered’) below the cut-in speed. Daily carcass searches were conducted along transects in plots (126 x 120 m) centred on each of the 12 turbines.

    Study and other actions tested
  9. A before-and-after study in 2011–2012 at a wind energy facility in a forested area of Maryland, USA (Young et al 2013) found that increasing the speed at which turbines become operational (‘cut-in speed’), along with preventing turbine blades from turning at low wind speeds (‘feathering’), resulted in fewer bat fatalities than before the operational changes. Average bat fatality estimates were 62% lower after the cut-in speed was increased to 5 m/s and turbine blades were feathered below this speed (11 bats/turbine) compared to the previous year without operational changes (29 bats/turbine). The difference was not tested for statistical significance. Five bat species were found across the site (see original report for details). In July–October 2012, all of 28 turbines at the facility were operated with an increased cut-in speed of 5 m/s with blades feathered below this speed. Weekly carcass searches were conducted along transects in circular plots (40-m radius) around 14 of the 28 turbines. Data for before the operational changes (blades rotated freely below a cut-in speed of 4 m/s) were collected in a previous study in July–October 2011. Carcass counts in both years were corrected to account for searcher efficiency and removal by scavengers.

    Study and other actions tested
  10. A replicated, randomized, controlled study in 2013 at a wind farm in a forested area of West Virginia, USA (Hein et al 2014; same site as Hein 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. Average bat fatality estimates were 54% and 76% lower when cut-in speeds were increased to 5 and 6.5 m/s respectively (0.5 and 0.3 bats/turbine/night) than at conventional control turbines (1.3 bats/turbine/night). The difference in fatality rates between the two treatments was not significant. Five bat species were found (see original report for data). Each of 12 turbines was randomly assigned to one of two treatments (cut-in speed increased to 5 or 6.5 m/s) or as a control (conventional cut-in speed of 3 m/s). Treatments were rotated between turbines nightly over 72 nights in July–September 2013. Turbines started/stopped operating when the average wind speed over 10 minutes (measured at a weather tower) was above or below the cut-in speed. All turbines were prevented from turning (‘feathered’) below the cut-in speed. Daily carcass searches were conducted along transects in plots (126 x 120 m) centred on each of the 12 turbines. Carcass counts were corrected to account for searcher efficiency, removal by scavengers, and unsearchable areas within plots.

    Study and other actions tested
  11. A replicated, randomized, controlled study in 2012–2013 at a wind farm in a forested area in Vermont USA (Martin et al 2017) found that increasing the wind speed at which turbines become operational (‘cut-in speed’) at temperatures above 9.5°C, along with preventing turbine blades from turning at low wind speeds (‘feathering’), resulted in fewer bat fatalities than at conventional turbines. The average number of bat fatalities was 62% lower at wind turbines when cut-in speeds were increased to 6 m/s at temperatures >9.5°C and the blades were feathered below this speed (0.5 bats/turbine) compared to conventional control turbines (1.4 bats/turbine). Three bat species were found (see original paper for details). In June–September 2012 and 2013, eight of 16 turbines were randomly assigned the treatment (cut-in speed increased to 6 m/s at temperatures >9.5°C and blades feathered below this speed) for a total of 60 nights. The other eight turbines were unaltered (cut-in speed of 4 m/s without feathering). Daily carcass searches were conducted along transects in rectangular plots (3,629–5,746 m2) centred on each of the 16 turbines. If applied to all turbines, it was estimated that the operational changes would result in annual energy losses of 1%.

    Study and other actions tested
  12. A study in 2013–2017 at a wind farm in an agricultural area of Indiana, USA (Stantec Consulting Services Inc. 2018) found that increasing the wind speed at which turbines become operational (‘cut-in speed’) resulted in fewer bat fatalities in both the spring and autumn migration periods. During spring, average bat fatality estimates were lower during one year in which the cut-in speed was increased to 5 m/s (0.3 bats/turbine) compared to three years in which the manufacturer’s cut-in speed was used (3.5 m/s; 0.7–1.4 bats/turbine). During autumn, average bat fatality estimates were lower during three years with an increased cut-in speed of 6.9 m/s (0.7–1.5 bats/turbine) compared to one year with a cut-in speed of 5 m/s (2.2. bats/turbine). The differences were not tested for statistical significance. Five bat species were found across the site (see original report for details). During spring (April–May), all of 125 turbines were operated at a cut-in speed of 5 m/s for one year (2016) and 3.5 m/s for four years (2013–2015, 2017). During autumn (August–October), all of 125 turbines were operated at a cut-in speed of 6.9 m/s for three years (2013–2015) and 5 m/s for one year (2017). Carcass searches were conducted 1–2 times/week along transects up to 80 m around each of the 125 turbines in April–May and August–October 2017. Data for 2013–2016 were collected during previous studies. All carcass counts were corrected for searcher efficiency, removal by scavengers, and unsearchable areas within plots.

    Study and other actions tested
Please cite as:

Berthinussen, A., Richardson O.C. and Altringham J.D. (2021) Bat Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

 

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