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Birmingham and Black Country Bat Group
Following the receipt of eight Echo Meter Touch 2 Pro bat detectors from the Wildlife Acoustics Scientific Product Grant in September, I have been working with volunteers to develop new methodology for surveying the use of linear features (canals and railways) by bats, looking for evidence of which bat species are using which types of feature to commute from their day roosts to their feeding grounds, and identifying important 'hop on' and 'hop off' points.
I designed the survey to utilise these detectors because they are full-spectrum, have an auto-ID feature, are user-friendly and would enable us to have GPS-tagged and time-stamped data. The idea was to spread out teams of recorders along a linear feature and (using both sound analysis and field observations) 'follow' the movement of individual bats as they passed each survey team.
The surveys have not been without their problems, and we have had to undergo a good deal of troubleshooting, but I'm now delighted to say that the kinks are ironed out and we're gathering some useful data. Initially, we had some discrepancies between auto time-stamps between the phones people were using, as the difference in time between any two phones could be out by up to 5 or 6 seconds. This was enough of a discrepancy to skew my data, and we had to find a workaround: I purchased four Lenovo Tab 7 Essential tablets to use with the detectors, and I manually calibrate them prior to the survey to within 0.5 seconds of the atomic clock. This works a treat and I will be purchasing more tablets for the remaining detectors soon.
But having accurate GPS and time-stamps on my sound files was useless unless I knew how long it would take for a bat to fly between survey points. Published results on bat flight speeds vary greatly between species and geographical area. The Bats and The Millennium project in Scotland measured the speed of Daubenton's bats along canals as having an average speed of 5.3 metres per second (MPS). Was this a good analog for my bats along this particular stretch of canal? I had no fancy equipment like lasers or radio tags to find out, so I decided to test it out in a rather old-school way...
I positioned six surveyors at 20m intervals along a straight stretch of canal, covering exactly 200m. Using Echo Meter Touch 2 Pro detectors, red LED torches, stopwatches and walkie talkies, we timed Daubenton's bats to ascertain their speed (4.9 mps, which was pleasingly close to the BATM study figures).
Using that speed, I was able to figure out how long it should take each bat to travel from each point along the canal to the next survey point, and as such I could look for a corresponding Auto-identified call in the next team's Kaleidoscope report.
It works. The green cells you can see in the spreadsheet above represent calls of a Daubenton's bat as it passed survey points Golf, Foxtrot and Echo — heading north (as anticipated) at almost exactly 4.9mps.
I really feel as though we have our equipment and methodology sorted out and hope to roll out this survey method as soon as bats wake up from hibernation in April! I've even got something in the pipeline to develop an R-script to automatically search for my correlated species calls from different survey points. Something to work on for the winter months...