Action: Deter bats from turbines using ultrasound 
Key messages
Read our guidance on Key messages before continuing- Two studies evaluated the effects of deterring bats from wind turbines using ultrasound on bat populations. The two studies were in the USA.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (1 STUDY)
- Survival (1 study): One randomized, replicated, controlled study with a before-and-after trial in the second year in the USA found mixed results. In the first year of the study, 21-51% fewer bats were killed at turbines with an ultrasonic deterrent fitted than at control turbines, but in the second year, from 2% more to 64% fewer bats were killed at turbines with ultrasonic deterrents fitted.
USAGE (1 STUDY)
- Behaviour change (1 study): One paired sites study in the USA found significantly fewer bats flying near one of two wind turbines with an ultrasonic deterrent compared to turbines without.
Supporting evidence from individual studies
A paired sites study in 2007 on a wind farm in an agricultural area of New York, USA (Horn et al 2008) found mixed effects on bat activity when an ultrasonic deterrent was used. Significantly fewer bats were observed over 10 consecutive nights at a turbine with an ultrasonic deterrent fitted (average 13 bat passes/night) than at a matched control turbine without a deterrent (average 24 bat passes/night). No significant difference was found in bat activity when this was repeated with a second matched pair (average 10 bat passes/night at both). The deterrent broadcast random pulses of broadband ultrasound from 20–80 kHz, with a range of up to 20 m. For both trials, bat activity was observed simultaneously at treatment and control turbines for 3.6 hours after sunset for 10 consecutive nights in August 2007 using thermal infrared imaging cameras.
A randomized, replicated, controlled study in 2009–2010, with a before-and-after trial in the second year, at a wind farm in a forested area of Pennsylvania, USA (Arnett et al 2013) found that an ultrasonic deterrent had mixed effects on bat mortality. In 2009, 21–51% fewer bats were killed per deterrent turbine (average 6 bats killed/turbine) than control turbine (average 9 bats killed/turbine). In the 2010 before-and-after trial, between 2% more and 64% fewer bats were killed at deterrent turbines than at control turbines when accounting for differences found between control and deterrent turbines in the ‘before’ trial. The deterrent emitted continuous ultrasonic broadband noise at 20–100 kHz, with a range of 5–10 m. In 2009 and 2010, 10 randomly selected wind turbines were fitted with deterrent devices, and 15 randomly selected turbines without the device were used as controls. In 2009, daily carcass searches were conducted in August–October. In 2010, the before-and-after trial was conducted with daily carcass searches in May–July before the deterrent was used, followed by daily searches in July–October with the deterrent active.
Referenced papers
- Horn J.W., Arnett E.B., Jensen M. & Kunz T.H. (2008) Testing the effectiveness of an experimental bat deterrent at the Maple Ridge Wind farm. Bat Conservation International report.
- Arnett E.B., Hein C.D., Schirmacher M.R., Huso M.M.P. & Szewczak J.M. (2013) Evaluating the effectiveness of an ultrasonic acoustic deterrent for reducing bat fatalities at wind turbines. PLoS ONE, 8, e65794