Action

Action Synopsis: Bat Conservation About Actions

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

How is the evidence assessed?
  • Effectiveness
    80%
  • Certainty
    70%
  • Harms
    0%

Source countries

Key messages

  • Four studies evaluated the effects of increasing the wind speed at which turbines become operational (‘cut-in speed’) on bat populations. One study was in Canada and three studies were in the USA.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (4 STUDIES)

  • Survival (4 studies): Three randomized, replicated, controlled studies (including one before-and-after study) in Canada and the USA, and one review in the USA found that bat fatalities were significantly reduced when the wind speed at which turbines became operational (‘cut-in speed’) was increased.

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 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. Total bat fatality rates were 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). Two bat species were identified during carcass searches (see original paper for data for individual species). 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.

    Study and other actions tested
  2. A randomized, replicated, 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 wind turbines become operational (‘cut-in speed’) resulted in fewer bat fatalities than at conventional wind turbines. Average bat fatalities were lower at turbines with increased cut-in speeds (5 m/s: 0.3–0.7 bats/turbine; 6.5 m/s: 0.5–0.6 bats/turbine) than at turbines with conventional cut-in speeds (3.5 m/s: 2 bats/turbine). In July–October 2008 and 2009, two treatments (cut-in speed increased to 5 m/s or 6m/s) and one control (cut-in speed of 3.5 m/s) were randomly assigned to three groups of four turbines for 25 nights/treatment. Daily carcass searches were conducted along transects in 120 x 126 m plots centred on each of 12 turbines. 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 review of 10 studies in 2006–2012 at wind energy facilities in Canada and the USA (Arnett et al. 2013) found that increasing the speed at which wind turbines become operational (‘cut-in speed’), or increasing the cut-in speed along with preventing rotor blades from turning at low wind speeds, resulted in fewer bat fatalities in all 10 studies. In eight studies, average bat fatalities were reduced by 47–82% when cut-in speeds were increased, and by 57–89% when rotor blades were also prevented from turning at low wind speeds, compared to conventionally operated turbines (see original report for more detailed results). Two studies found that bat fatalities were reduced by 20–38% at wind turbines when cut-in speeds were increased, but sample sizes were small and differences were either not statistically signficant or were not tested. In seven of 10 studies, cut-in speeds were increased to 4–6.9 m/s compared to the standard manufacturer’s cut-in speed (3–4 m/s). In three of 10 studies, turbine blades were also prevented from turning at low wind speeds by changing the angle of the blade parallel to the wind or turning the turbine out of the wind. Two of 10 studies reported estimated losses in power generation to be <1% of the total annual output. Three studies in this review have been summarised individually (Baerwald et al. 2009, Arnett et al. 2010, Martin et al. 2017).

    Study and other actions tested
  4. A randomized, replicated, controlled study in 2012–2013 at a wind farm 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 resulted in fewer bat fatalities than at turbines with conventional cut-in speeds. The total number of bat fatalities was 62% lower at wind turbines with increased cut-in speeds (average 0.5 bats/turbine) than at fully operational turbines (1.4 bats/turbine). At treatment turbines, cut-in wind speeds were increased to 6 m/s when temperatures were >9.5°C. Fully operational control turbines had a cut-in wind speed of 4 m/s. In each year, eight of 16 turbines were randomly assigned the treatment for 60 nights. Daily fatality searches were carried out in June–September 2012 and 2013. Rectangular study plots around each turbine were searched using transects spaced 6 m apart. 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
Please cite as:

Berthinussen, A., Richardson O.C. and Altringham J.D. (2019) Bat Conservation. Pages 67-140 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.

 

Where has this evidence come from?

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Bat Conservation

This Action forms part of the Action Synopsis:

Bat Conservation

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