Electromagnetic Radiation Effect on Foraging Bats - Recent Advances and Issues in Environmental Science - page 66

be used to quantify foraging activity within a site. Foraging rate is expressed as the
ratio of terminal buzzes to bat passes; this feeding buzz ratio (FBR) provides a mea-
sure of foraging intensity per unit of fl ight activity [28]. The use of frequency division
detectors also allowed accurate species identifi cation at each site.
Figure 1. Sampling protocol of experimental trials carried out at 20 independent sites from July to
September, 2007. At each site bat activity was recorded for 1 hr at three distances from the radar
antenna (10, 20, 30 m) using three automatic bat recording stations orientated perpendicular to
the radar beam. A frequency division bat detector was positioned 20 m from the radar antenna to
provide further information on bat foraging activity during this period.
Insect Abundance
From July to September, 2008 aerial insects were sampled using two identical Pir-
bright-Miniature light-suction traps (PMLT) [29] equipped with 8 W UV light bulbs.
Each trap operated at 220 V transformed to 12 V to run from a car battery. At the base
of each trap was a water-filled collecting vessel containing 2-3 drops of detergent.
Most large insects were excluded by a large-mesh screen immediately above the fan
and below the light bulb. The traps were deployed at 16 of the 20 foraging sites de-
scribed above and were switched on for 1 hr prior to sunset. At each site the traps were
positioned approximately 40 m apart with their trap inlets 2 m above ground level. On
each sampling night the radar antenna was positioned on a platform 2 m above ground
level and 10 m from one of the traps such that the antenna was orientated directly to-
wards the trap inlet and fixed to produce a unidirectional signal. The second trap was
positioned perpendicular to the radar beam to prevent any potential exposure to elec-
tromagnetic radiation and left to function as a control. To avoid any potential bias the
selection of traps used as the control was alternated each night. The parameters of the
radar tested were identical to those described above (Pulse length/pulse repetition rate:
0.08 μs/2100 Hz; 0.3 μs/1200 Hz,) no test was carried out with the antenna rotating.