Environmental Engineering Reference
In-Depth Information
Ahlén et al. [22] also reported anecdotal evidence that bats foraging offshore in
Sweden avoided an area around Utgrunden lighthouse where a powerful radar was in
permanent operation. However, although it has been demonstrated that large air traf-
fi c control and weather radars appear to exert an aversive response on foraging bats
[21], this has little practical application in preventing bats from colliding with turbine
blades. It is therefore necessary to establish whether a deterrent effect can be replicated
with a small, portable radar system. It is also possible that the electromagnetic radia-
tion from the radar may not be affecting bats directly but rather the insects upon which
they feed. Bat activity within an area is strongly correlated with insect density [23, 24]
therefore any reduction in insect density would result in a concurrent reduction in bat
activity. In order to provide an effi cient deterrent it is necessary to determine whether
any observed reduction in bat activity is a direct result of exposure to electromagnetic
radiation or an indirect result of a localized reduction in insect density.
Therefore the aims of the present study were to test the following hypotheses:
1. Bat activity will be reduced following exposure to a pulsed electromagnetic
signal from a small portable radar unit.
2. The abundance of aerial insects will be reduced following exposure to a pulsed
electromagnetic signal from a small portable radar unit.
MATERIALS AND METHODS
Study Sites and Sampling Protocol
In Britain, foraging bats are predominantly associated with areas where insect density
is high: broadleaved woodland, particularly woodland edge, linear vegetation (tree
lines and hedgerows) and riparian habitat. More open and intensively managed areas
are avoided. In order to assess the impact of radar on foraging bats it was important
to locate foraging sites with a high level of bat activity. Using existing knowledge
obtained from detailed radio telemetry projects [25] in conjunction with extensive
acoustic surveys, 20 foraging sites, with a high and consistent level of bat activity,
were selected. All foraging sites were located within a 100 km radius of Aberdeen
in northeast Scotland (latitude 57°23'N, longitude 02°45'W) and were separated by
a minimum straight-line distance of >1 km to ensure independence. Twelve of these
sites were located within riparian habitats (small ponds, rivers and streams) and the
remainder along the edge of woodland where the radar signal would not be attenuated
by any obstruction.
The radar used throughout the study was a Furuno FR--7062 X-band marine radar
(peak power 6 kW, beamwidth: horizontal −1.9°, vertical −22°, rotation 24 rpm, or 48
rpm) with a slotted waveguide array antenna (1.2 m) capable of transmitting at pulse
lengths of 0.08-0.8 μs depending on the range selected. At each site the radar antenna
was placed on a platform 2 m above ground level, such that the core area of bat activ-
ity was directly in line with the radar beam. At each foraging site a control (no radar
signal) and experimental trial (radar switched on) were carried out. Starting 45 min
after sunset, bat activity was recorded for a period of 30 min during each trial and the
order of trials were alternated between nights. To avoid pseudoreplication, recordings
were carried out only once at each of the 20 sites.
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