The use of the study area by swarming Myotis bats
The study area (encompassing multiple cave entrances) has recently been shown to be a swarming site for Myotis bats, as well as for lesser horseshoe bats Rhinolophus hipposideros (personal observations, Davison & Thomas 2017). Analysis of zero crossing echolocation files recorded at a nearby cave (“Hobbit Hole”) between 2015 and 2017, and analysed by visual inspection of the resulting sonograms, shows the considerable increase in Myotis bat activity in Spring and during the Autumn swarming season (Figure 1). The peak in the Spring is assumed to be when bats are emerging from hibernation in the caves. The timing of Autumn swarming at this cave (all Myotisspecies combined) varies slightly between the years, but in general lasts from late July until early October. In 2016 and 2017,Myotis activity during the Autumn swarming season exhibited a clear double-peak of activity, with a gap of 1-2 weeks between these peaks. In 2015, the swarming season started later and finished earlier than in the other two years, with less overall activity and a less evident double peak, with the primary peak in 2015 falling intermediate in date between the clear double peaks of the other two years.
Figure 1 : Seasonal variation in the activity of Myotisbats (all species combined) at “Hobbit Hole” cave in 2015-2017, measured as the number of zero-crossing files, and identified to genus level by visual inspection of the resulting sonograms.