United States

Department of 

Agriculture

Forest Service

Northern 

Research Station

Research Note NRS-129

Effects of Acoustic 

Deterrents on Foraging Bats

Joshua B. Johnson

W. Mark Ford

Jane L. Rodrigue

John W. Edwards
Abstract

Signifi cant bat mortality events associated with wind energy 

expansion, particularly in the Appalachians, have highlighted the 

need for development of possible mitigation practices to reduce or 

prevent strike mortality. Other than increasing turbine cut-in speed, 

acoustic deterrents probably hold the greatest promise for reducing bat 

mortality. However, acoustic deterrent eff ectiveness and practicality 

has not been experimentally examined and is limited to site-specifi c 

case studies. Accordingly, we used a crossover experimental design 

with prior control period to show that bat activity was reduced 17.1 

percent by the deployment of ultrasonic deterrents placed around 

gauged watershed weir ponds on the Fernow Experimental Forest 

in West Virginia. We caution that while our results should not be 

extrapolated to the scope of a typical wind energy production facility, 

the results warrant further research on the use of acoustic deterrents to 

reduce bat fatalities.

KEY WORDS: acoustic, Anabat, bats, Fernow Experimental Forest, 

West Virginia, wind energy

Citation

Johnson, Joshua B.; Ford, W. Mark; Rodrigue, Jane L.; Edwards, 

John W. 2012. Eff ects of acoustic deterrents on foraging bats.

Res. Note NRS-129. Newtown Square, PA: U.S. Department of 

Agriculture, Forest Service, Northern Research Station. 5 p.

The Authors

JOSHUA B. JOHNSON is the wildlife biometrician with the 

Pennsylvania Game Commission, 2001 Elmerton Ave., Harrisburg, 

PA 17110. Ph: 717-525-0563, email: j-johnson3@juno.com.

W. MARK FORD is the unit leader of the U.S. Geological Survey, 

Virginia Cooperative Fish and Wildlife Research Unit located in 

Blacksburg, VA.

JANE L. RODRIGUE is an ecologist with the U.S. Forest Service, 

Northern Research Station in Princeton, WV.

JOHN W. EDWARDS is a professor in the Division of Forestry and 

Natural Resources at West Virginia University in Morgantown, WV.

Cover Photos

Top, northern long-eared myotis bat (Myotis septentrionalis), photo 

used with permission by Tim Carter, Ball State University; center, 

Anabat SD2 bat detector, photo by Jane Rodrigue, U.S. Forest 

Service; bottom, weir pond at the Fernow Experimental Forest, photo 

by Mary Beth Adams, U.S. Forest Service.
1

INTRODUCTION

Over the past decade, wind energy production capacity in 

the United States has increased by an order of magnitude. 

Wind energy potential is high throughout much of the 

Appalachians, and several production facilities are located 

along or near the Allegheny Front in West Virginia and 

Pennsylvania (Wiser and Bolinger 2011). Unfortunately, 

many of these sites have experienced unprecedented levels 

of bat mortality (Arnett et al. 2008). Several hypotheses 

have been forwarded regarding causes of bat mortality, 

such as an innate attraction to tall objects, an attraction 

to high insect concentrations around wind turbines, and 

attractive acoustical noise (Kunz et al. 2007). Mortalities 

are mostly comprised of long-distance migratory species 

(e.g., eastern red bat, Lasiurus borealis), and occur from 

July through September during the late summer and 

autumn migration periods (Arnett et al. 2008). Recent 

research has examined several of these hypotheses in an 

attempt to understand causes of bat mortality at wind 

energy facilities (Cryan and Barclay 2009). As a result, 

there have been many bat mortality mitigation measures 

proposed, including changing wind turbine siting criteria 

to avoid linear landscape features (Baerwald and Barclay 

2009), increasing wind turbine cut-in speeds (minimum 

wind speeds at which wind turbines generate energy; 

Baerwald et al. 2009), and placing acoustic deterrents on 

wind turbines (Szewczak and Arnett 2007).

Th ough some ex situ studies have shown evidence that 

acoustic deterrents are eff ective (Schaub et al. 2008), 

far fewer have concluded this in situ (e.g., Szewczak 

and Arnett 2007). Research indicates that bats avoid 

ambient noise when foraging, regardless of setting. Th is 

characteristic of bats may prove benefi cial in mitigating 

bat mortality at wind energy facilities. Acoustic deterrents 

emitting ultrasonic signals (12.5-112.5 kHz) in the 

hearing range of bats have been shown to aff ect bat 

foraging activity (Spanjer 2006), presumably through 

interference in prey detection (Schaub et al. 2008) 

and fl ight orientation (Mackey and Barclay 1989). 

Accordingly, we experimentally determined eff ects 

of acoustic deterrents on bat activity at water sources 

regularly used by bats. We hypothesized that bat activity 

would be reduced at water sources when acoustic 

deterrents were operating.

SITE DESCRIPTION

We conducted our research at the Fernow Experimental 

Forest (FEF) in Tucker County, WV (3900' N, 7967' 

W). Th e FEF is a 1,900-ha experimental forest managed 

by the U.S. Forest Service, Northern Research Station, 

and is located in the unglaciated Allegheny Mountains 

subsection of the Appalachian Plateau Physiographic 

Province (Kochenderfer et al. 2007). Elevations range 

from 530 to 1,100 m. Mean annual precipitation at 

FEF is 145.8 cm, ranging from 9.7 cm in October to 

14.4 cm in June. Mean annual temperature is 9.2 °C, 

ranging from -18.0 °C in January to 20.6 °C in July 

(Kochenderfer 2006). Vegetation at the FEF is a mosaic 

of second- and third-growth mixed-mesophytic and 

northern hardwood forest. Th e area has been managed 

by even-aged (patch clearcut) and uneven-aged (singletree selection) silviculture since the mid-20th century, 

or has been left undisturbed following initial harvesting 

from 1903 to 1911 (Schuler and Fajvan 1999). 

Approximately 5.5 km of dendritic intermittent and 

permanent streams incise the steep slopes and plateaulike ridgetops (Madarish et al. 2002). Portions of the 

western watersheds on the FEF have been devoted to 

forest hydrology research, and several gauged watersheds 

have small weir ponds (5 m x 5 m) that are used as water 

sources and foraging habitat by bats (Ford et al. 2005).

From spring through autumn, the bat community 

at FEF is comprised of northern long-eared myotis 

(Myotis septentrionalis), little brown myotis (Myotis 

lucifugus), big brown bats (Eptesicus fuscus), tri-colored 

bats (Perimyotis subfl avus), eastern red bats, silver-haired 

bats (Lasionycteris noctivagans), and hoary bats (Lasiurus 

cinereus) (Owen et al. 2004, Ford et al. 2005). A small 

number of endangered Indiana myotis (Myotis sodalis) 

and Virginia big-eared bats (Corynorhinus townsendii 

virginianus), primarily males that hibernate in Big 

Springs Cave in the central portion of the FEF also 

remain in the area during summer (Ford et al. 2002).

METHODS

In July 2009, we placed Anabat II (Titley Electronics, 

Ballina, Australia) broadband, frequency-division bat 

detectors at four weir ponds in the FEF. Potentially 

existing within home ranges of bats, the four weir 
2

ponds we studied were >100 m apart. At each site, we 

passively monitored for bat echolocation passes consisting 

of a series of search-phase or foraging echolocation 

pulses between 20-80 kHz (Murray et al. 2001). We 

calibrated each bat detector to 30 m standard detection 

distance and positioned detectors on weir dams with 

the microphones angled ~15° from horizontal over 

the weir ponds. Bat detectors were programmed to 

monitor from 1 hour prior to sunset to 1 hour after 

sunrise. Echolocation passes were recorded to Anabat 

CompactFlash storage Zero-Crossing Analysis Interface 

Modules (ZCAIM) and downloaded to a computer for 

analysis using Analook 4.8p software (Corben 2001). 

After fi ltering out extraneous noise, we used number 

of bat passes recorded as an index of bat activity. A bat 

pass was defi ned as a series of echolocation pulses or calls 

emitted by bats (Broders 2003). We did not attempt to 

identify the species of bat emitting each echolocation 

pass. Because bat activity can be infl uenced by nightly 

temperatures (Anthony et al. 1981), we recorded nightly 

minimum and daily maximum temperatures (°C) at each 

weir pond with StowAway®Tidbit® (Onset Computer 

Corp., Pocasset, MA) data loggers that recorded ambient 

temperature every minute.

We monitored the four weir ponds simultaneously for 

four consecutive nights (Period 1: 13-16 July) to establish 

baseline bat activity levels. Using a crossover experimental 

design, we then deployed ultrasonic pest deterrents 

(Model EX900-A, Black and Decker, New Britain, CT) 

at two randomly chosen weir ponds for three consecutive 

nights (Period 2: 18-20 July). Ultrasonic pest deterrents 

broadcasted a varying 26-74 kHz, 105 dB emission, 

and operated concurrently with Anabat II bat detectors. 

We used bat detectors to verify that these ultrasonic 

deterrents were audible around the entirety of each weir 

pond. On the following three consecutive nights (Period 

3: 21-23 July), we deployed ultrasonic deterrents at the 

other two weir ponds.

We determined if bat activity levels measured as the 

number of bat passes per night diff ered among weir 

ponds during Period 1. Because number of bat passes 

per night was count data, we modeled it as negative 

binomially-distributed data. We then compared bat 

activity between treatment weir ponds (when ultrasonic 

deterrents were operating) to non-treatment weir ponds. 

We determined if nightly minimum temperatures and 

daily maximum temperatures diff ered among pools 

during each Period. All analyses were conducted using 

the GLIMMIX procedure in SAS (SAS Institute Inc. 

2004).

RESULTS

Th roughout the study, we recorded 15,861 echolocation 

passes at the four weir ponds. On several nights, Anabat 

II bat detectors failed to record at one or two weir ponds. 

As a result, data are missing from two weir ponds on 

July 14 and one weir pond each on July 16, July 19, and 

July 23. Temperature loggers failed to record at one weir 

pond for the duration of the study. 

Baseline data collected during Period 1 indicated the 

mean number of nightly bat passes (±1 SE) among all 

weir ponds was 598.9±148.1, and that bat activity did 

not vary signifi cantly among weir ponds (F

3,8=1.14, 

P=0.391). Acoustic deterrents used during Period 2 and 

3 negatively aff ected bat activity (t=12.22, P<0.001). 

Mean number of nightly bat passes recorded at weir 

ponds where acoustic deterrents were deployed was 

signifi cantly lower (285.8±102.4) than at ponds on 

nights when acoustic deterrents were not deployed 

(344.7±112.8). Mean nightly temperature and mean 

daily maximum temperature were similar among weir 

ponds during all three measurement periods (Table 1).

DISCUSSION

As we hypothesized, our results support the supposition 

that bat foraging activity is reduced by ultrasonic noise 

(i.e., acoustic deterrents). Szewczak and Arnett (2007) 

also observed that ultrasonic noise deterred bats from 

foraging over water sources, but did not consider eff ects 

of weather on bat activity. We documented that weather 

played no signifi cant role in bat activity reductions. 

Bats are capable, to some extent, of adapting their 

echolocation processing to account for ultrasonic noise, 

such as echolocation calls of conspecifi cs (Chiu et al. 

2009). However, in natural settings, they typically avoid 

areas of ambient ultrasonic noise, such as at rapidly 

fl owing water (Mackey and Barclay 1989).
3

Considering the general agreement among in situ and ex 

situ research indicating bats avoid areas where ultrasonic 

noise is broadcast either naturally or artifi cially, there is 

a compelling argument for conducting fi eld experiments 

where ultrasonic deterrents are broadcasted at wind 

energy facilities (Kunz et al. 2007). At a wind energy 

facility in New York, Horn et al. (2008) documented 

mixed results regarding the eff ectiveness of ultrasonic 

deterrents at preventing bats from approaching wind 

turbines. However, they cautioned that their ultrasonic 

deterrents may not have been broadcasting at a suffi cient 

decibel level to aff ect bats outside the rotor-swept area. 

Because we experimented at small weir ponds, emissions 

from our ultrasonic deterrents encompassed entire pools, 

and thus consistently aff ected bat activity.

To be eff ective, emissions from ultrasonic deterrents 

placed on turbine towers or nacelles need to be at 

decibel levels suffi cient to reach beyond wind turbine 

blade lengths of ~40 m (Horn et al. 2008). Moreover, 

emissions need to randomly change in pulse duration 

and intensity to prevent bat habituation (Spanjer 2006). 

Ultrasonic deterrents also need to operate continuously, 

as we found bat activity increased following cessation of 

treatment. Further research examining the eff ectiveness 

of ultrasonic deterrents at reducing bat mortality at 

wind energy facilities holds promise and is warranted 

considering the results of our research that corroborate 

with fi ndings of numerous studies.

ACKNOWLEDGMENTS

Primary funding for our research was provided by Joint 

Venture Agreement 06-JV-11242300-140 of the U.S. 

Forest Service, Northern Research Station, and National 

Fire Plan with West Virginia University, Division of 

Forestry and Natural Resources.

Table 1.—Mean nightly minimum and mean daily maximum temperatures (°C) 

at three weir ponds on the Fernow Experimental Forest, West Virginia, 2009.

Perioda Temperature Mean SE F d.f. P

1 Mean nightly minimum 12.1 2.0 0.13 2,6 0.882

Mean daily maximum 24.4 0.9 0.01 2,6 0.993

2 Mean nightly minimum 12.4 0.5 0.01 1,4 0.923

Mean daily maximum 19.8 0.7 0.12 1,4 0.746

3 Mean nightly minimum 13.2 0.4 0.02 1,4 0.906

Mean daily maximum 21.0 0.5 1.22 1,4 0.330

a

Period 1=July 13-16, 2009; Period 2=July 18-20, 2009; Period 3=July 21-23, 2009.
4

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