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Providing evidence to improve practice

Action: Prevent turbine blades from turning at low wind speeds to reduce bat fatalities Bat Conservation

Key messages

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  • Three studies evaluated the effects of preventing turbine blades from turning at low wind speeds on bat populations. Two studies were in Canada and one review was in the USA.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (3 STUDIES)

BEHAVIOUR (0 STUDIES)  

Supporting evidence from individual studies

1 

A replicated, controlled before-and-after study in 2005 at a wind farm in an agricultural area of Alberta, Canada (Brown & Hamilton 2006) found that preventing turbine blades from rotating at low wind speeds resulted in fewer bat fatalities than at conventional control turbines. The total number of bat carcasses recovered by searchers was lower at experimental turbines shut down at low wind speeds (64 bats, 40% of total) than at conventional control turbines (95 bats, 60% of total). The number of bat carcasses did not differ significantly between turbines before the experiment (‘experimental’ turbines: 157 bats, 49% of total; ‘control’ turbines: 164 bats, 51% of total). In August 2005, all of 39 turbines were operated using conventional methods. In September 2005, odd numbered turbines (20 of 39) were braked and locked to prevent them from turning at low wind speeds (<4 m/s). Nineteen control turbines were left unaltered. Carcass searches were conducted weekly along transects covering a 140 m2 area around each turbine in August–September 2005.

2 

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 preventing turbine blades from rotating at low wind speeds resulted in fewer bat fatalities than at conventional turbines. Total bat fatality rates were lower at experimental turbines with altered blade angles (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 19 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 of 14 turbines were operated using conventional methods. In 2007, six randomly chosen turbines were altered by changing the pitch angle of the rotor blades to prevent them from turning 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.

3 

A review of six studies in 2006–2011 at wind energy facilities in Canada and the USA (Arnett et al. 2013) found that preventing turbine blades from turning at low wind speeds, or preventing turbines blades from turning at low wind speeds along with increasing the wind speed at which turbines became operational (‘cut-in speed’) resulted in fewer bat fatalities in all six studies. Average bat fatalities were reduced by 23–57% when turbine blades were prevented from turning at low wind speeds, and by 57–89% when cut-in speeds were also increased, compared to conventionally operated turbines (see original report for more detailed results). In all six studies, turbine blades were prevented from turning at low wind speeds by changing the angle of turbine blades to be parallel to the wind. In three of the six studies, cut-in speeds were also increased (4–6.5 m/s) compared to the standard manufacturer’s cut-in speed (3–4 m/s). One study in this review has been summarised individually (Baerwald et al. 2009).

Referenced papers

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.