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.