BaTML used technology in an innovative
way through which directional information and activity could be measured
accurately. As far as we are aware no one used our methodology
anywhere else in relation to bat studies. We would like to acknowledge
the assistance provided by Peter Rigby and David Dodds in helping us acquire the correct specification of equipment.
In total 22 sites between Glasgow and Edinburgh were surveyed. The total length of the canal network roughly equals 110
km. Therefore on average we had a study location every 5 km across the
Central Belt of Scotland. All sites were surveyed to obtain basic
habitat information, of which some were looked at in more depth
with regards to bank side vegetation.
Standard Survey Model – Pipistrelle and Daubenton’s
We had 2 separate bat surveys running side-by-side
commencing 30 minutes after sunset. A survey lasted for 90mins, giving
us 180mins of data for each evening (the total of the 2 surveys added
together). All the information gathered was then replayed and analysed
later before various databases were populated with our results.
To survey for Daubenton’s bat we used 4 Heterodyne Bat Detectors linked via cabling to a central
4-track tape recorder. Each detector recorded on a
separate channel and each had its own level indicator. Therefore when a
bat flew past a detector its echolocation was recorded and the bat pass
could be timed. In other words we knew when a bat was on a particular part
of the canal. The detectors were set up in sequence allowing us to
measure time, speed and most importantly, direction. This directional
information allowed us to narrow down the likely location of any roosts.
In addition to this we were also able to say with a reasonable degree of
confidence how many bats were present in terms of minimum numbers. Most Daubenton’s bat passes were confirmed with a
visual sighting at the mid point using red torchlight.
To survey for pipistrelle species we used a Time Expansion Detector set up at the mid-point with
its own cabling running into a separate recording station. This method
allowed us to identify which type of pipistrelle bat
was present and also gave us a maximum number of bat passes per
species. In addition to recording the echolocation of these bats this
system also picked up their social calls, as well as the sounds made by
any other species of bat that passed by.
Radio Detector Survey Model
One of the key objectives of BaTML was to understand in much greater detail how the bats that use these canal corridors interact with their habitat. In order to have a healthy and sustainable bat population three basic features need to be present, namely:
- Roosts - a number and choice of suitable places (including Hibernacula) that will be used at different times of the year by different bats depending on species/sex.
- Foraging Areas where there is an abundance of insects for bats to feed upon.
- Commuting Corridors that connect the roost sites to foraging areas, thus allowing bats to navigate around their habitat at night.
With all of this in mind we developed a survey methodology that allowed us to do a number of things, including the following:
- Narrow down the location of roosts.
- Find the main foraging hotspots on the canal system.
- Discover at which points along the canal bats enter and/or leave the system.
- Find the important commuting corridors that connect to the canal habitat.
- Work out how many different populations of bats use the habitat.
The technology we used, developed by David Dodds, provided us with a number of radio frequency bat sensors (usually 8) which we located around an area of habitat. Once in place and as dusk loomed we listened for signs of bat activity coming from each of these sensors to our Receiving Station, which can be up to 2 kilometres away.
This methodology allowed us to quickly get a snapshot of what was happening in a particular area, from which we could do subsequent surveys to help complete the picture. The number of surveys for each location varied according to what we found, and a number of support methods were used to help complete the picture.