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Bats and Windfarms
Radar as a method of
mitigation ?
*P.A. Racey & B. Nicholls
*School of Biological Sciences, University of Aberdeen, U.K.
Bats and RadarBats and Radar
1. Anecdote: No bats in vicinity of Aberdeen airport radar.
2. Pilot Project: Significantly fewer bats in vicinity of two Scottish airport
radars compared with sites matched for altitude and land use.
3. 2006 Project: To test hypothesis that bats avoid electromagnetic radiation
associated with radar installations.
Mitigation:
Birds: visual deterrents
Bats: Acoustic deterrents ???
Radar ?
Biological Effects of Biological Effects of
Electromagnetic Fields (EMF)Electromagnetic Fields (EMF)
1MHz – 300GHz: Thermal burden
Perception Aversion Thermal insult Death
Auditory microwave hypothesis: Thermal expansion
Thermoelastic wave sound pressure wave excitation of auditory neurones
Auditory response:
Humans: 13kHz
Cats: 38kHz
Rodents: 45kHz
Civil Air Traffic Control
(n=4)
Weather
(n=3)
Military Air Traffic Control
(n=3)
10 Radars: 300MHz 10 Radars: 300MHz –– 15GHz15GHz
Radar
a1
b1
c1
High
(>2v/m)
Medium
(<2v/m)
Control
(0 v/m)
Electromagnetic field
strength
Sampling protocol
c2
b2
a2 a3
b3
c3
10 radar sites, 9 samples in each: 3 high, 3 med,
3 low. Total = 90 samples, 30 in each group.
Sampled for bat activity, species and feeding
buzzes.
Three sites sampled contemporaneously
each night. Sites paired for: altitude,
latitude, landclass, habitat type,
connectivity and habitat structure.
Frequency division
transect: 30mins
Frequency division
transect: 30mins
Frequency division
transect: 30mins<200m 200 - 400m >400m
Results: high EMF vs control
Bat active minutes
(paired t test, n = 30, p<0.001)
Bat passes
(paired t test, n = 30, p<0.001)
-1.5
-1
-0.5
0
0.5
1
Civil ATC Military ATC Weatherlo
g (
hig
h E
MF
bat
acti
ve
min
ute
s +
1)
–lo
g (
con
tro
l b
at
act
ive
min
ute
s+1)
-2
-1.5
-1
-0.5
0
0.5
1
Civil ATC Military ATC Weather
log (
hig
h E
MF
bat
pa
sses
+1)
–lo
g (
con
tro
l b
at
pass
es+
1)
Results: Intermediate EMF vs control
-2
-1.5
-1
-0.5
0
0.5 Civil ATC Military ATC Weather
log (
med
ium
EM
F b
at
act
ive
min
ute
s +
1)
–lo
g (
con
tro
l b
at
act
ive
min
ute
s+1)
-2
-1.5
-1
-0.5
0
0.5
1
log (
med
ium
EM
F b
at
pass
es +
1)
–lo
g (
con
tro
l b
at
pass
es+
1)
Civil ATC Military ATC Weather
Bat active minutes
(paired t test, n = 30, p=0.004)
Bat passes
(paired t test, n = 30, p<0.001)\
ConclusionsConclusions
• Bat activity was reduced in habitats exposed to electromagnetic radiation.
• However without access to detailed specifications of individual radar units
(including operational times and operating frequency) it is difficult to quantify this relationship further.
Way ForwardWay Forward
• To more fully define the impact of radar on foraging bats, and ascertain its
value as a potential source of mitigation, field trials involving a mobile radar that can be introduced into areas of known bat activity are now required. If the parameters of an RF signal capable of inducing an aversive response in foraging bats could be characterised then this may offer a method of mitigating bat collisions with wind turbines.