Swarming bats

Last year I was invited along to a swarming survey with the South Lancashire Bat Group.

We met a little way from the site to condense into fewer cars, as parking was limited. It was my first time in the area so I allowed plenty of time and consequently got there early. Someone else pulled up shortly after, she said she hadn’t been sure she was in the right place until she spotted the soft toy bat I have hanging from my rear window screen.

The swarming site was a ten minute walk from the road, where tight hedges and a steep path give way to a fairly expansive, flat bottomed, quarry pit. We set up camp in the open, a few hundred metres from the rocky, overhung entrance to a long abandoned mine. Our camp consisted of a foldaway picnic table and repurposed T shaped pole, to hang processing bags from. Next, using telescopic poles, a mist net was rigged to cover most of the opening and the harp trap components were lugged the extra five minutes walk to be positioned some distance into a larger mine entrance.

Mist net setup

Mist net setup

Here’s some links to ol’ faithful for more info on mist nets and harp traps.

We sat around camp waiting for the action to start, occasionally running a high powered torch beam over the net from a distance, or wandering over to check either trap up close. The swarming activity started soon after sunset, but very few bats seemed to end up in the nets on their way out, most of the captures came later on. Bats caught in the net were painstakingly extricated, which sometimes required carefully snipping away the net fibres if the bat had struggled and become entangled. Bats caught in the harp trap were much easier to collect, and much more amusing to watch, truth be told. Being free within the pouch, they could scramble around and interact with each other. Captures were carefully placed in a cotton bag and then normally clipped onto a carabiner hung around the walkers neck – this leaves your hands free for balance or pocketing, and keeps the bats warmer, if you place them under a few of your layers.

Trying to untangle one of the first captures

Trying to untangle one of the first captures

Brown long-eared caught in a harp trap

Brown long-eared caught in a harp trap

Our guests were hung on the T bar by the table, ready for processing where the weight, forearm length, breeding condition, sex and species were assessed and recorded by a scribe. It wasn’t a particularly physical role so as the night wore on, it got quite cold. This meant a myriad of layers for me, and sometimes having to warm our captures up for some time before releasing them again. We had over a hundred total captures that night, with a variety of species and interesting, even ringed individuals. It was all fascinating and along with the other surveys that season, added to our understanding of swarming over all. I’ll dig out the project summary if I get the chance to provide a bit more detail on what we actually found.

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