a) Seasonal variation in activity
Variation in acoustic activity during 2018 clearly shows species
differences in seasonal patterns (Figure 4 panels iii-vi). The acoustic
monitoring reveals that Daubenton’s bat swarms earlier than Natterer’s
bat. Bechstein’s bat had a much lower number of calls recorded
(as would be expected from trapping records, and its lower acoustic
amplitude; Barataud 2015), but is active across the Myotisswarming period. In the case of Brandt’s/whiskered bats, which cannot be
reliably separated by acoustic analysis, there are two main periods of
activity; early and late in the swarming season. The catch data (Figure
2) show that Brandt’s bat appears earlier in the season than whiskered
bat, suggesting that the earlier acoustic peak in Figure 1b panel iv, is
primarily composed of Brandt’s bats and the later peak is primarily
composed of whiskered bats. Figure 1b panel ii shows bimodal peaks of
calling activity in 2018 for Natterer’s bat. The pattern for other
species is less clear, possibly due to the lower counts involved.