Electromagnetic Radiation Effect on Foraging Bats - Recent Advances and Issues in Environmental Science - page 68

The three automatic stations recorded a total of 102,810 bat counts during 58 hr
of recording (Table 2). No signifi cant difference was observed in the number of bat
counts recorded between automatic stations positioned at 10, 20, and 30 m from the
radar antenna (ANOVA, rotating antenna with pulse length 0.08 μs: P = 0.57; fi xed
antenna with pulse length 0.08 μs: P = 0.64; fi xed antenna with pulse length 0.3 μs P =
0.68) therefore all further tests were carried out on the average of these three values. A
further 53,731 bat passes were recorded with the frequency division detector (Table 2).
As expected, the majority of passes (84%) were attributed to the two cryptic pipistrelle
species: Pipistrellus pygmaeus and P. pipistrellus (51% and 33% respectively) which
are the most common and abundant bats in Scotland. A further 16% of bat passes were
attributed to Myotis daubentonii .

Table 2. Total numbers of bat counts, bat passes and feeding buzzes recorded within treatment and
control trials during 58 hr of recording.

Index of bat activity Rotating antenna (0.08

μ s/2100 Hz)

Fixed antenna (0.08
μ s/2100 Hz)

Fixed antenna (0.3
μs/1200 Hz)

Treatment Control Treatment Control Treatment Control

Bat passes 11160 11599 8065 9305 5367 8235

Feeding buzzes 3711 4015 2386 3300 1563 2720

Bat counts (10 m) 6052 6275 4998 5974 3241 5517

Bat counts (20 m) 6364 6820 5261 6183 3494 5525

Bat counts (30 m) 7066 7386 5744 6792 3879 6239

doi:1 0.1371 /journal.pone.0006246.t002

Total bat activity was invariably higher during the control trials when compared to
experimental trials (Table 2). However paired t tests carried out on all indices of bat
activity (bat counts, bat passes, FBRs) revealed no signifi cant difference in bat activity
between control and experimental trials when exposed to a short pulse length (0.08 μs)
radar signal from a rotating antenna (bat counts: t = 1.50; P = 0.151; P Bonferroni = 0.453;
Figure 2a. Bat passes: t = 1.89; P = 0.074; P Bonferroni = 0.222; Figure 3a. The FBR: t =
1.80; P = 0.088; P Bonferroni = 0.264; Figure 4a). Paired t tests carried out on all indices of
bat activity (bat counts, bat passes, FBRs) showed that bats were signifi cantly less ac-
tive during experimental trials than during control trials when exposed to a short pulse
length (0.08 μs) radar signal from a fi xed antenna (bat counts: t = 2.87; P = 0.010; P
Bonferroni = 0.030; Figure 2b. Bat passes: t = 2.54; P = 0.020; P Bonferroni = 0.060; Figure
3b. The FBR: t = 3.82; P = 0.001; P Bonferroni = 0.003; Figure 4b). However, following
Bonferroni correction the difference in the number of bat passes between experimental
and control trials was no longer signifi cant. Bats were also signifi cantly less active
during experimental trials than during control trials when exposed to a medium pulse
length (0.3 μs) radar signal from a fi xed antenna (bat counts: t = 3.95; P = 0.001; P
Bonferroni = 0.003; Figure 2c. Bat passes: t = 3.69; P = 0.002; P Bonferroni = 0.006; Figure 3c.
The FBR: t = 6.78; P<0.001; P Bonferroni = 0.003; Figure 4c). A summary of these results
is presented in Table 3.