Conducting the Dunsland bat survey
Dave Manifold uncovers the excitement of bat surveying in Dunsland Park
One Friday evening, towards the end of June 2017, just before dusk, a small team from the Brandis Corner Wildlife Group comprising of Chris Smith, Secretary Barrie Lewis, and local bat expert Helen Sinnett and myself gathered at the Dunsland car park. It was Helen who took the lead and provided some of the detector kit required. The idea was to try to find out what bat species are currently in residence at Dunsland, and just before we went out, Helen gave us a brief run-down of how the equipment worked and how to use it.
Barrie and I had done a reccie at the site a couple of weeks previously, just to fix in our minds eye where we would venture on the evening in question bearing in mind that we would be working as darkness fell, safety being all important. We earmarked several likely spots that would be ideal for our survey, the old coach house being the central reference point.
We set off walking down towards the bridge and excitedly located our fist bat which conveniently flew towards us through the tunnel of trees that cover the lane as it crosses the stream and exits with the pond on the left. The detectors pick up the frequency of the sound emitted by the bat that it uses to locate the insects that it preys on. You simply set the dial to say, 50 kHz and that might pick up the sound produced by the natterer’s bat or a brown long-eared bat that emits a sound at between 25-50 kHz, or the pipistrelles that register between 45 and 50 kHz and so on.
Helen brought along a tape recording of many of the bat sounds that we might come across and I have to say, they are quite fascinating. Most cannot be picked up by the human ear but when converted electronically, they come out as a series of clicks and rapid claps and slaps.
They are all quite complex and even an expert like Helen admitted that it is often difficult to distinguish some of the bats without the use of a computerised graph.
As darkness fell, we began to pick up more and more signals, sometimes the bats could be seen overhead, their signals getting stronger or weaker as they passed by.
Barrie, Chris and myself were enthralled, listening to our detectors clicking and clapping and squeaking in response to the bats echo location sounds. It was a truly wonderful experience and I would encourage anyone who gets the chance to give it a go. After a few days, Helen produced a very professional report detailing the events of the evening. It covered everything from time, date and weather conditions, humidity readings, and so on.
And finally, the information that we all wanted more than anything, bat species and numbers. Helen reported that she had identified 1 Whiskered bat, 2 Serotine, 2 Pipistrelle pipistrellus, 4 Pipistrelle pygmaeous, and 2 Daubentons bats. Ofcourse there may have been others of the same species and also some different species that we didn’t hear on this occasion but this is a start, we now know at least some of the bat species that inhabit Dunsland and the surrounding area.
Following on from that outing, on Tuesday 25th of July, Helen conducted a further bat survey, this time accompanied by just Barrie and myself. We followed a similar route and although we thought that weather conditions for the evening seemed better, it was calm and dry with plenty of flying insects, the bats seemed to be avoiding us.
We used our bat detectors to find a few bats that were feeding over the pond, and things then went quiet until we got up to where the house used to be. I was wandering around waving my detector in all directions when Helen, who was shining her torch through the gap in the huge coach-house doors, shouted that she could see a lesser horseshoe bat inside. Barrie then set his receiver to 110kHz and almost at once, he picked up the bats call, as its at the higher end of the scale, the lesser horseshoe makes a high pitched squeaking sound, unlike most of the others that emit a rapid slapping or clapping sound.
We were all thrilled at this find as we hadn’t detected the lesser horseshoes during the previous outing. Having set out at dusk around 9pm, we returned to the car park just before 11 o’clock and Helen’s report shows that this time 14 bats were detected and seen, 4 species were identified, these being; 4 Daubenton’s, 3 Pipistrelle, 6 Pygmaeous pipistrelle, and 1 Lesser horseshoe bat.
Helen has very kindly donated half a dozen bat boxes that we hope to put up within the grounds at Dunsland, they are made from a cement mix and, as you can imagine, are quite heavy. These particular boxes are called Schwegler boxes and once the bats find them, they should provide ideal summer roost sites for the local bats to use.
This report will provide the National Trust with useful information that they can use when they are planning any kind of work in Dunsland, be it in the woodland, the old buildings or the parkland and BCWG are surely indebted to Helen for providing us with a chance to see how a bat expert actually conducts a survey, and I for one found it to be a fascinating experience.
Dave Manifold, Dunsland Volunteer Community Ranger