Electromagnetic Radiation Effect on Foraging Bats - Recent Advances and Issues in Environmental Science - page 63

is clearly important, the rapid proliferation of wind turbines requires a more urgent
response. Research has to be focused on the underlying reasons behind these colli-
sions and potential methods of mitigation to prevent what is undoubtedly an increasing
threat to bat populations.
Attempts at mitigating bird collisions with wind turbines have typically in-
volved the application of visual stimuli to increase the conspicuousness of the turbine
blades [9, 10], but for bats, where audition is the primary sensory modality, this is
clearly not appropriate. The design of an acoustic deterrent for bats, as used to mitigate
cetacean entanglement in drift nets [11-13], is complicated by the intrinsic properties
of ultrasound, which attenuates rapidly in air [14]. Despite this inherent problem, a
recent study [15] revealed a signifi cant aversive response by big brown bats ( Eptesicus
fuscus ) following exposure to broadband white noise in a laboratory. However, when
an acoustic deterrent was deployed at a wind farm in New York State, USA, results
were more equivocal, and researchers concluded that the acoustic envelope of the de-
terrent system was probably not large enough to consistently deter the activity of bats
within the large volume of the rotor-swept zone [16].
A more promising solution is offered by curtailing the operations of wind turbines
during high-risk periods. A substantial portion of bat fatalities at operating wind farms
occurs during relatively low-wind conditions during the bat migration period [17].
Some curtailment of turbine operations during these conditions, and during this peri-
od, has been proposed as a possible means of reducing impacts to bats [17, 18]. Recent
results from studies in Canada [19] and North America [20] indicate that changing tur-
bine “cut-in speed” (i.e., the wind speed at which wind generated electricity enters the
power grid) from the customary 3.5-4.0 m/s, on modern turbines, to 5.5 m/s, resulted
in at least a 50% reduction in bat fatalities. This requires considerable cooperation on
behalf of the project operators as curtailing turbine operations, even on a limited basis,
clearly poses operational and economic restrictions resulting in some loss of revenue.
This method does however offer a promising solution, particularly in areas where it
has been proven that bat mortalities occur over a clearly defi ned and restricted time
period. It is not yet clear whether this method of mitigation will prove suffi ciently
feasible and effective at reducing impacts to bats at costs that are acceptable to com-
panies that operate wind energy facilities. Therefore, given the problems associated
with the existing proposed methods of mitigation it is essential to investigate all other
alternatives.
It has been suggested that the radio frequency (RF) radiation associated with radar
installations could potentially exert an aversive behavioral response in foraging bats
[21]. In 2006 Nicholls and Racey recorded bat activity along an electromagnetic gradi-
ent at 10 radar installations throughout Scotland. Their results revealed that bat activ-
ity and foraging effort per unit time were signifi cantly reduced in habitats exposed
to an electromagnetic fi eld (EMF) strength of greater than 2v/m when compared to
matched sites registering EMF levels of zero. Even at sites with lower levels of EMF
exposure (<2v/m), bat activity and foraging effort was signifi cantly reduced in com-
parison to control sites.