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.