Electromagnetic Radiation Effect on Foraging Bats - Recent Advances and Issues in Environmental Science - page 67

Immediately following sampling, the insect catch was transferred from the
collecting column into a 70% ethanol in water solution using a fi ne brush. Insects
were then counted using a dissecting microscope (×30). Any insects with wingspans
exceeding 20 mm were removed from the catch, as they would exceed the range of
insect sizes captured by the species recorded throughout the study [30]. Following
counting and sorting, the dry mass of insects was recorded by drying the samples in an
oven until a constant mass was achieved (21 hr).

Statistical Analysis
Differences in bat activity (bat counts and bat passes), bat foraging activity (FBRs) and
insect abundance between experimental and control trials were analyzed using paired
t tests. To account for multiple comparisons in paired t tests, we applied a manual
Bonferroni correction (P-values×number of comparisons). However, since the applica-
tion of the Bonferroni correction increases the risk of making more type II errors, that
is not recognizing a true effect as significant [31] we report both corrected P Bonferroni
and uncorrected P-values. The effect of distance from the radar antenna was analyzed
using one-way ANOVA. Analyses were carried out using Minitab version 14 [32].

Ethics Statement
The authors' work on bats is licensed by the statutory nature conservation organization
in Scotland (Scottish Natural Heritage).

RESULTS
Bat Activity
Experimental trials were carried out during 58 nights from July, 2007 till September,
2007 representing a total of 58 hr of recording data within the following parameters:
1. Rotating antennapulse length/pulse repetition rate (0.08 μs/2100 Hz)-20 hr
2. Fixed antennapulse length/pulse repetition rate (0.08 μs/2100 Hz)-20 hr
3. Fixed antennapulse length/pulse repetition rate (0.3 μs/1200 Hz)-18 hr
The maximum value (peak hold) of the electromagnetic fi eld strength within these
parameters is shown in Table 1. Field strength diminished slightly with increasing
distance from the antenna under all radar parameters. However, when the radar an-
tenna was fi xed to emit a unidirectional signal a fourfold increase in fi eld strength was
observed at all distances (Table 1).

Table 1. The maximum value (peak hold) of the electromagnetic field strength (v/m) at three distances
from the radar antenna.

Antenna
position

Pulse length
(μs)

Pulse Repeti-
tion rate (Hz)

Duty
Cycle (%)

EMF (v/m)
Peak hold
(10m)

EMF (v/m)
Peak hold
(20m)

EMF (v/m) Peak
hold (30m)

Rotating 0.08 2100 0.0168 5.58 5.11 3.79

Fixed 0.08 2100 0.0168 26.24 22.99 20.25

Fixed 0.3 1200 0.036 25.52 18.68 17.67

doi:1 0.1371 /journal.pone.0006246.t001