Bats in the mist

Working with local bat groups to learn more about these fabulous nocturnal creatures on our nature reserves.

As a long standing member of the Bedfordshire Bat Group I was keen to try to bring together WT volunteers and bat group members as a way to combine our resources and expertise to find out more about the bats in our area. Luckily I wasn’t the only one thinking along these lines as members of the Cambridgeshire Bat Group were eyeing up some of our reserves as good sites for more specialist bat trapping surveys. This led us to a meeting last winter with representatives from both these Bat Groups, Reserve Managers and M&R staff to discuss the best way forwards.

We discussed the merits of using trapping surveys as well as transects and static detectors. By trapping we are able to gather more information about species which more difficult to detect by call analysis such as Myotis bats whose calls are very similar to each other, and brown long-eared bats that call very quietly and so are often under recorded on detector surveys. Trapping can also give us useful information on our rarer bat species, such as Nathusius’ pipistrelle and barbastelle, including age, weight (a proxy for health) and breeding condition. Data collected this way can be fed in to the wider schemes such as the National Nathusius’ Project and so help their conservation on a much wider scale.

It was decided to work together at Brampton Wood in Cambridgeshire and Begwary Brook & Felmersham in Bedfordshire. At each site we arrange standard monthly transect surveys early in the season and trapping sessions slightly later in order to take advantage of the data collected on the transects. On each Bedfordshire reserve a single transect were carried out by Wildlife Trust volunteers whilst at Brampton volunteers from the Wildlife Trust and Cambridgeshire Bat Group combined forces to cover several transects on each visit. Unfortunately our recording bat detectors seemed cursed at Brampton this year meaning we were left with very little sonogram data but with Aidan’s expert knowledge of both the reserve and bats we managed to find some decent trapping areas.

Harp trap for bats set up in dusk — Harp trap for bats set up between two trees

The main method of trapping used were harp traps; these consist of a metal frame with two or three banks of vertical wires which the bat flies into and slides unhurt down the wires into a collecting bag where they can sit safe and sound before being taken out and processed. These are fairly small traps set in a gap between two trees used with an ultrasonic lure used to draw bats in.

We also used mist nets at Brampton Wood, the same thin nets that bird ringers use. These are passive traps being set across the rides that bats use as commuting routes. Bats fly into the net and removed by experienced bat workers. Bats caught were identified to species, sexed, aged and in most cases forearm length, weight and breeding condition was also recorded. All those handling bats were licence holders, or supervised by licence holders, to ensure the bats were unharmed by the whole process.

Nathusius' pipistrelle bat in the hand — Nathusius' pipistrelle at Begwary Brook by Gwen Hitchcock

Begwary Brook

We made it out to Begwary Brook on 2nd August; this is after the breeding season to ensure we didn’t keep any mothers from feeding young pups. We had already scouted out the areas during a previous visit so we quickly set up two harp traps. The first round of the checks yielded several bats including a male Nathusius’ pipistrelle, the first recorded at this site! This little fellow got lots of attention (it’s the first Nathusius I’ve seen in the hand) as well as a shiny new ring so if we, or any other bat groups, catch him again we can track his progress. Nathusius’ pipistrelles are migratory with individuals moving between UK and mainland Europe - the furthest from the UK being found in Latvia! We also caught a single Natterer’s bat and 10 soprano plus 4 common pipistrelles. A very good start to the trapping surveys!

Brampton Wood

The following week was rained off but we managed to visit Brampton Wood with the Cambridgeshire Bat Group on 14th August where we had 4 harp traps and two mist nets set up around the centre of the wood. In spite of the drops of rain before setting up the weather stayed dry right up until the cars were loaded to leave around 1:15am! During the evening we caught 20 bats: 12 soprano pipistrelles, 1 common pipistrelle, 1 noctule, 4 Daubenton’s, 1 whiskered and 1 barbastelle who sadly escaped the mist net by itself before we could get it out. Not a huge number of bats for the trapping effort but they came in a steady trickle allowing those learning to handle bats to get lots of practice and those new to trapping to get a good look at the process and of course the bats. Photos of the pipistrelle wing venation were also taken to be included in a research project looking at how often soprano pipistrelles have a wing with common pip venation and vice versa.

Soprano pipistrelles keeping dry in a harp trap

Felmersham

On the 18th August the Bedfordshire Bat Group came to Felmersham, the weather forecast wasn’t great but we were hoping we’d get a few hours of trapping in. We set up a couple of harp traps in fairly sheltered locations, it was too windy for the mist net to be of any use as the moving net is easier for the bats to spot! Unfortunately almost as soon as the traps were up a few drops began to fall. It’s only light we thought, it might go away… and anyway there were still bats flying into the traps. But sadly the rain got heavier so we decided to pack up the traps and release the bats who had found shelter in the harp trap holding bag. All in all 12 soprano pipistrelles were caught, they must have been as mad as the bat workers to go out in that weather! And the rain got even heavier as we loaded the equipment into Bob’s car and trudged back to our own. Unsurprisingly the following day consisted of drying out kit and clothes!

Back to Begwary Brook

We returned to Begwary Brook at the end of August for a second session and once again caught a male Nathusius’ pipistrelle! We know it’s a different bat because it didn’t have a ring one although we did give him one to fly off with. We also caught a noctule, our largest British bat, and 12 soprano pipistrelles, one of our smallest.

With such a successful start to partnership working more joint trapping sessions will hopefully be on forthcoming...