Action Synopsis: Bat Conservation About Actions

Automatically reduce turbine blade rotation when bat activity is high

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Two studies evaluated the effects of automatically reducing turbine blade rotation when bat activity is high on bat populations. One study was in Germany, and one in the USA.



  • Survival (2 studies): Two replicated studies (one randomized, controlled and one paired sites study) in Germany and the USA found that automatically reducing the rotation speed of wind turbine blades when bat activity is predicted to be high resulted in fewer bat fatalities for all bat species combined and for five bat species.


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, paired sites study in 2012 at eight pairs of wind turbines in Germany (Behr et al 2016) found that using automated ‘bat-friendly’ operating systems that reduced turbine blade rotation speed resulted in fewer bat fatalities than at conventionally operated wind turbines. Total bat fatalities and average collision rates were lower at automated turbines (total 2 bat fatalities, 0.01 fatalities/turbine/night) than at conventionally operated turbines (total 21 bat fatalities, 0.06 fatalities/turbine/night). At automated turbines, predictive models identified periods of high fatality risk and low energy yield from bat activity and wind speed data. During these periods, rotor blades were moved parallel to the wind to reduce rotation speed according to a target bat fatality rate (0.012 fatalities/turbine/night). Conventionally operated turbines rotated freely. At each of eight sites, automated and conventional operating modes were alternated weekly between two paired turbines over 14 weeks in July–October 2012. Carcass searches were carried out daily. Carcass counts were corrected to account for searcher efficiency and removal by scavengers. If applied to all turbines, it was estimated that automated operation would result in annual energy losses of 2.1%.

    Study and other actions tested
  2. A replicated, randomized, controlled study in 2015 at a wind energy facility in an agricultural area of Wisconsin, USA (Hayes et al 2019) found that using automated ‘Smart Curtailment’ operating systems that reduced turbine blade rotation speed resulted in 74–91% fewer fatalities of five bat species compared to conventionally operated turbines. Total fatality estimates were lower at automated turbines than conventionally operated turbines for eastern red bats Lasiurus borealis (automated: 34 fatalities; conventional: 220 fatalities); hoary bats Lasiurus cinereus (automated: 11; conventional: 59); silver-haired bats Lasionycteris noctivagans (automated: 5; conventional: 55); big brown bats Eptesicus fuscus (automated: 8; conventional: 31); and little brown bats Myotis lucifugus (automated: 3; conventional: 35). Twenty turbines were randomly selected (10 operated by automated systems, 10 conventionally operated). At automated turbines, fatality risk was calculated by a predictive model using real-time bat activity and wind speed data every 10 minutes. If fatality risk was high (wind speed <8 m/s and >1 bat call detected in the previous 10 minutes), rotor blades were rotated out of the wind and slowed (to ≤1 rpm) for 30 minutes. Conventionally operated turbines were ‘feathered’ to rotate slowly below a cut-in speed of 3.5 m/s. Daily carcass searches were conducted along transects in  plots (80 x 80 m) centred on each of the 20 turbines in July–September 2015. Carcass counts were corrected to account for searcher efficiency and removal by scavengers. Electricity generation was reduced by 90 MWh/turbine at automated turbines during the study period.

    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.


Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Bat Conservation

This Action forms part of the Action Synopsis:

Bat Conservation
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust