May 2015 On Sunday 10th May the barbastelle bat tracking team met in the Bovey Valley Woods. After two chilly weeks without much bat activity the weather had finally showed signs of warming a little. The group of volunteers, led by Andy Carr (PhD researcher at the University of Bristol) carried bundles of heavy equipment down into the valley to meet at the footbridge over the Becka Brook.
Gathering in an optimistic huddle the group were briefed on the task for the evening – trapping and tagging some female barbastelles for the radio tracking project. A series of nets were to be assembled along the valley in places where, it was calculated, that the bats may fly from their roosts and start to forage. Though it was still daylight, the moths were out and the midges were beginning to bite. All good reasons to be hoping for a successful night.
Great care is needed to avoid tangles in the mist nets; Dave joins two mist nets together
Two 6 metre wide mist nets were set up on aluminium poles to span the bottom of the woodland valley at a carefully selected narrow point. Great care was needed with these fine mesh nets as they can easily be tangled or damaged. Further along the valley another mist net was set up to catch the commuting bats on their way to their chosen foraging sites. A fourth mist nest was set up alongside a pool in the river; a possible place for the emerging bats to drop in for a drink.
Moving closer to the known roosting trees a harp trap was installed. This specialised piece of kit comprised a stainless steel frame with dozens of fine filaments stretched from top to bottom. It’s a smaller device than the mist nets but, when used with a lure, it can be very effective and kinder to the bats as it allows them to slide into a catching bag where they rest and relax! The chosen lure is an audio gadget which plays a selection of barbastelle calls to attract the local bats.
Now all the nets and traps were stretched across the crucial points of the valley the volunteers could feel the tension as they waited in expectation for sundown. Volunteers who were taking the opportunity to train as bat handlers were stationed at each mist net and waited, with the nest furled up to avoid snaring a passing bird, for the bats to emerge. All bat handlers have to protect themselves from a real but very small chance of catching rabies, and confirmed that they all had up-to-date vaccinations.
The final group would separate off to carry out an emergence survey on a cracked old oak tree which, in previous years, was a known roost tree. Sitting still with another collection of technological devices they waited for sleeping bats to wake and fly out of the roost. With bat detectors set at different frequencies (33MHz for the barbastelle) they got comfortable on a brash pile on the forest floor. Keeping a constant watch through a night vision scope (enhanced with an infra-red light) they would be able to see and hear any emerging barbastelles. As time went on the roost tree remained quiet. A few pipistrelles circled around as they foraged for insects nearby, but no barbastelles.
After an hour of patient study it was time to move back to the nets which were now lowered in anticipation of a catch. The night vision scopes now came into their own, as the group by the river pool reported a number of daubenton bats feeding over the river. In the green pool of light in the scope the daubentons could be seen skimming the river with a nimble display of acrobatic dining. These agile flyers were having a feast – but not getting caught in the mist net!
Moving back to the harp trap, the catching bag was checked but no bats had been caught. It was time to start the lure which began to play different barbastelle calls including social, foraging and distress signals.
With all this knowledge, experience, equipment and technology in the valley could we be beaten by a group of creatures no bigger than your front door key? The answer was yes. At 11pm any bats that were out that evening were slowing down and taking a rest. It was time for the volunteers to pack up and go to bed. No barbastelles tonight but the trappers will be out again tomorrow, and the next night to carrying on the trapping and tagging until there are enough bats for the study to get into full swing. This is the unpredictable nature of wildlife and, even though no barbastelles were tagged the volunteers had a good night in the deep dark woods of the Bovey Valley.
Words and images for the Barbastelle Tracking Diary are by Matt Parkins
The Bovey Valley barbastelle tracking project is managed by the Moor than meets the eye Landscape Partnership comprising Dartmoor National Park Authority, the Woodland Trust and Natural England.