The object of all our effort.
It’s that time of year again when survey effort switches from the anti social dawn and dusk hours to the easier daytime, and we start to head underground to monitor swarming and hibernation sites.
Like Captain Ahab and his white whale, a somewhat smaller mammal has been keeping us searching for four years now since we first encountered a Lesser Horseshoe bat while out surveying caves in Bowland, Lancashire on Halloween (you couldn’t make it up).
The cave in question has a peak in temperature from mid October to mid November and our theory is the the bats use this to extend feeding opportunities a little bit longer as the nights get cold. And then they disappear possibly into inaccessible areas to hibernate.
From the DNA work we’ve done so far we know the Bowland bat seems to take a more basal position to current populations in North Wales and Somerset supporting our theory that we’re dealing with a remnant of the former northern range of the species rather than a recent arrival. Lessers survived in Yorkshire until 1944 in the Helmsley area so it’s not too hard to believe that an overlooked colony in a little surveyed area of ideal habitat survived unnoticed.
But the advances in our knowledge of the species here have come scattered amongst a whole load of survey effort (I don’t want to add up the hours) a bit like the return on a slot machine that makes them so addictive.
So we’re at that point again when an encounter will fill in another little gap of information, one step closer to understanding. Addictive, frustrating, time consuming and verging on an obsession but so so worth it, let’s face it if there wasn’t a challenge, if the answers came easily, it wouldn’t be half as much fun would it?…
Like a lot of licenced bat workers I also volunteer as a roost visitor for BCT/Natural England to help and advise householders where there may be issues or concerns to do with bats. For the most part this involves checking for the presence of bats and in most cases where there are bats, the species involved is one of the Pipistrelles.
So today’s visit came as a bit of a treat; firstly the 17th century farmhouse and it’s outhouses on the boundary of a known bat hotspot looked promising when considering roost potential. Sure enough a check of the roof void revealed distinctly Myotis like droppings, Natterer’s (Myotis nattereri) were high on my suspect list given the upland situation.
So down I pop to chat to the householder about the next step; a couple of Anabats left over the weekend to check for any bat activity before we come up with a plan of how bats can be accommodated in their re-roofing plans.
So we chat about the potential species involved and how they have requirements for different roosting conditions throughout the year. It’s at this point I’m asked “Would they use our tunnel?”
You have a tunnel?
You have a tunnel?
You have a tunnel with crevices...
And so I inspect the 100m+ drystone constructed tunnel beside the farmhouse which provides perfect humidity and temperature for hibernating bats and enough crevices to warrant another visit.
This job just got a lot more interesting.
Maglite XL50 LED Torch
Pro’s: Small, light, good light output.
Cons: Care needed to prevent accidentally turning it on when not it use.
LED torches offer two advantages for bat workers; one is improved battery life and the other is next to no heat emission. The Maglite XL50 runs on three AAA batteries and has three light settings cycleable via the push button switch at the back of the torch: high, low and strobe. High offers 104 lumens and a battery burn time of 8h45m; low reduces output to 25% giving a battery life of 36h. On low setting the torch offers plenty of focussed light to check all but the deepest crevices.
The torch is small and light enough to carry day to day although it’s easy for the rear mounted push button to get knocked when in pockets resulting in unecessary battery drain.
The XL50 is a great little survey torch.
Lascar USB2 temperature and Humidity Datalogger – £49.95 (at time of press)
Pro’s: Small, cheap and easily programmable.
Cons: Batteries need ordering (ebay is your friend here)
Lascar USB2 Datalogger
The Lascar USB2 datalogger is small, cheap and a very unobtrusive datalogger that’s perfect for recording conditions in bat roosts and hibernation sites. This datalogger is very suitable for monitoring crevices due to it’s size.
Lascar USB2 monitoring Temp/Rh in crevices used by Natterer's bats
Very easy to program with the supplied EasyLog USB software I tend to set them up to monitor at half hour intervals which means the battery lasts one year even in sub zero temperatures experienced during winter in exposed sites. Shorter intervals are possible but this obviously affects battery life.
With a netbook and a pocket of spare 1/2AA lithium batteries you can download and reset dataloggers in the field with ease.
Data downloads can be viewed either within EasyLog or imported into excel or similar spreadsheet programs.