I completed my second bat survey this Thursday, during a fortunately warm and dry evening at the Southern Cemetery, Manchester.
The survey was organised in order to collect evidence that could support a bid by local authorities to award the site nature reserve status, something that site managers have been working towards for some time. We were briefed to split up into 5 or so small groups/pairs and each travel to different sections of the site to make observations. The main focus of the survey was to determine the presence/absence of different bat species. Additional observations such as where the bats appeared to be arriving from, the presence of suitable trees for roosting and the presence of other mammalian species were also desirable.
Walking around with Steve Parker, a bat expert at the head of SLBG, I had a chance to learn what about this site would encourage bats. Mature trees were probably the most obvious feature. Generally speaking; trees’s greater than 80cm diameter at shoulder height, and more than 50 years old, begin to obtain features suitable to support bat roosts. Holes in tree trunks, hollow branches and thick, peeling bark are among some of the more important features. There are many such trees in the cemetery. Tree formation is also important. Bats are particularly attracted to defined tree lines such as is found in this site. These straight formations provide a means by which the bats can navigate as well as offering protection on one side, coupled with open space to hunt on the other.
A final bat friendly feature of this site was the presence of many native wildflowers, planted as part of the site management strategy. Such plants encourage a wide range of moths and insects which act as prey for bats.
For mine and Steve’s part of the survey, we identified both soprano and common pipistrelles, which, peculiarly were observed to be feeding together, a phenomenon that literature will say does not occur. The pipistrelles were identified with the aid of a heterodyne detector. Visually, the 2 species are impossible to tell apart in flight, both having identical body sizes. Their echolocations are the easiest way to distinguish the species. Again, both emit similar pulses, but at different frequencies. Tuning a heterodyne detector to around 45kHz will allow a crisp recitation of a common pip’s call, whereas that of the soprano will sound ‘tinny’. By tuning the detector to 55kHz, the opposite occurs and the call of soprano pipistrelles is heard with greater clarity. Whilst I was still struggling to determine between the calls, Steve could point out which of the 1 of the 4 bats we were watching was the soprano.
Rejoining the rest of the survey group at around 11pm gave me a chance to learn what others had witnessed. Overall findings were similar. All groups witnessed the two pip species at some point, one group heard a Noctule and another saw a fox cub.
Overall these results were generally as expected but nonetheless provide good support for the grant of nature reserve status. The presence of a Noctule was a bonus but not a complete surprise as roosts of this species are found at the neighbouring Chorlton Water Park and furthermore individuals of the species can travel over 12km to reach feeding sites.