Background information and definitions
Bats rely on ultrasound to echolocate for foraging and navigation. Broadcasting ultrasonic sounds at the frequency range which bats use for echolocation may act as a deterrent by interfering with their ability to perceive echoes. Three studies in the USA found reduced bat activity at pond sites when ultrasonic deterrents were used (Szewczak & Arnett 2006, Szewczak & Arnett 2008, Johnson et al. 2012). For a similar intervention relating to roads, see ‘Threat: Transportation and service corridors – Deter bats from roads using ultrasound’.
Johnson J.B., Ford W.M., Rodrigue J.L. & Edwards J.W. (2012) Effects of acoustic deterrents on foraging bats. Research Note NRS-129. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station.
Szewczak J.M. & Arnett E. (2006) Preliminary field test results of an acoustic deterrent with the potential to reduce bat mortality from wind turbines. An investigative report submitted to the Bats and Wind Energy Cooperative. Bat Conservation International, Austin, Texas, USA.
Szewczak J.M. & Arnett E.B. (2008) Field test results of a potential acoustic deterrent to reduce bat mortality from wind turbines. An investigative report submitted to the Bats and Wind Energy Cooperative. Bat Conservation International, Austin, Texas, USA.
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. 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 h after sunset for 10 consecutive nights in August 2007 using thermal infrared imaging cameras.Study and other actions tested
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. Six bat species were identified during carcass searches (see original paper for data for individual species). 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. The deterrent emitted continuous ultrasonic broadband noise at 20–100 kHz, with a range of 5–10 m. 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.Study and other actions tested