We have revisited an old limestone mine, last surveyed in the late 1980's, with some success. The January survey there revealed one Natterer's, three Daubenton's, plus an unidentifiable bat's bum poking out of a crevice close to the entrance. It doesn't sound like much, but five bats is a fair result for almost three hours spent underground! (The bat pictured here is a Daubenton's Bat Myotis daubentonii)
Here in Scotland, most hibernating bats are found in old mines or caves, and they tend to be tucked into crevices and holes. For this reason, surveying for them is a slow and laborious business and it's likely that we only see a tiny proportion of the bats present. Nonetheless, it's important work, as we can compare results year-on-year and our findings are fed into the National Bat Monitoring Programme (NBMP).
I have never made any bones about the lack of joy that hibernaculum surveys bring me! The sites we currently visit are fairly civilised, with high roofs and not too much water or clay to wade through, but that's just the luck of the draw! Lulled into a false sense of security I recently agreed to take a small group of intrepid (more so than me) bat-workers to search for a couple of almost-forgotten mines, to see if they could be added to the Bat Group's survey programme.
The first site looked ok at first, though a low roof meant stooping (being 6 feet tall doesn't help!) Most of the floor was covered with about 12 inches of water and one by one we each experienced the joy of rapidly and unexpectedly descending twelve inches as the fine limestone silt undert he water acted like quicksand. Deciding that discretion was a good idea, we retreated and were lucky to leave the site with the same number of wellies we entered with!
The second site was even more entertaining, as recent heavy rain and a build-up of rubbish at the entrance meant that the water was within eighteen inches of the roof. I wasn't too keen on the colour of the water, either.
If you're interested in hibernaculum visits please ensure you work with your local bat group. Not only is it potentially dangerous to do this without appropriate equipment and experience, it requires a bat roost visitor's licence with a specific endorsement. Accidentally disturbing bats during hibernation is very easily done and can have a devastating effect on the bats.
National bat Monitoring Programme: http://www.bats.org.uk/nbmp/index.asp
My website: http://plecotus.co.uk/