Testing our detectors for the season

by Rowan Davis, BCT's Science Projects Officer

The bat survey season is well underway and the Science Team at Bat Conservation Trust (BCT) has sent out hundreds of bat detectors to citizen scientists and ecologists all over the country. In preparation for this we tested all of our AudioMoths for wear and tear, performance, and accuracy. We run a whole range of passive acoustic monitoring (PAM) programs here at BCT  including our citizen science programs like the British Bat Survey and NightWatch, as well as a series of other PAM projects like our National Bat Monitoring Programme's Woodland Survey, our work with Forestry England on rewilding (read more about this here) and the National Forest Inventory with Forest Research.   

To build a baseline of how our detectors work we partnered with the UCL and used their anechoic chamber, which is a room in which the walls, ceiling and floor are lined with a sound absorbent material to minimise reflections (read more about this room here). Setting up a suite of new AudioMoths, we played bat calls and digitally produced ultrasonic sweeps in this completely sound-absorbent room on campus. The strange wedges you can see in the photo stop any echoes by focussing in the sound waves into the triangular divets and then absorbing them into their material. The room itself is locked shut behind a huge metal door and is separated from the outside world by a raised floor, completely cut away from any sound. It was a ghostly experience and over time being in the room you could hear the thudding of the blood in your ears and the softest of breaths or movements in your body. This completely silent environment meant that we could collect precise measurements of how well our wonderful little detectors perform. We’ll be sending our audio files up through our sound classification system to see how our bat identifying algorithms fare, which will also give us interesting data on its accuracy too!

Due to the cost of using the chamber with its exacting setup, and how long this incredibly precise assessment takes, we tested the rest of our kit in a music studio. After building a repeatable methodology and travelling down into south London, AudioMoths in tow, we spent a couple of days in a drumming studio playing the same recorded sounds. After testing our hardware, we brought our data back to the office and have been uploading it to our classifier. Once we have our baseline data, we can test whether the detectors are getting old or damaged. This gives us a really good indication of what we can use next season and sets us up for building long-term monitoring of our beautiful and vital bat populations across the UK.

Bats at Haddon Hall

Claire Moran, a new Communications Officer at the Bat Conservation Trust, went to a bat watch at Haddon Hall, one of England's oldest houses. Organised by Steve Roe and the Derbyshire Bat Conservation Group, attendees got to spend time with hundreds of bats in an ancient chapel and walk along the River Wye using bat detectors and thermal cameras. In this blog she tells us what she saw.

Bats in the Hall

Hundreds of bats fly about a stained-glass window aglow with sunset. It’s an enchanting spectacle, and even the shower cap I'm given to protect my hair from bat wee doesn't make it any less magical.

I'm at Haddon Hall’s first bat watch event, where myself and a handful of people, are treated to a sight unfortunately rare in the UK: lots of bats. Certainly, I’ve never seen so many bats. In fact I don’t think I’ve even seen this many mammals together in real life that aren’t sheep or humans.  

Our watch starts in the chapel which is very old, parts of it date to the 12th century. I’m no historian, but you can feel the age in its rough walls, which are covered in colourful drawings of leaves and flowers, religious scenes and strange symbols. Bats take advantage of the craggy walls, clinging onto them briefly before dropping down into flight.  

Bats cling to the ancient walls of the chapel of Haddon Hall. 

 

When we enter the chapel at around 8pm, the number of bats flying above us is already impressive. As is their smell, sweet, musky and somehow familiar, mammalian – and their chattering squeaks. More bats join the swirls above our heads every minute.

Derbyshire Bat Conservation Group

Steve Roe from Derbyshire Bat Conservation Group (also BCT trustee and creator of our award-winning podcast) leads the night. Steve tells us the chapel’s bats are a maternity roost of common and soprano pipistrelles. Some are youngsters, just weened.  

 

Bats in the chapel at Haddon Hall. Steve Roe (BCT trustee and podcaster, Derbyshire Bat Conservation Group) talks. 

A great storyteller, Steve conjures up the world of bats, its wonder and vulnerability. And he sprinkles in some amazing facts, in one instance by literally sprinkling bat poo to show us how it glitters.  

 

At the end of his talk, the lights are turned off, the doors closed, and somehow even more bats take to the wing. Now they’re swooping to their exit point, a crack above the church door. A thermal camera shows us what the shadows conceal, as the bats consider leaving, think better of it, wheel away, and return. 

History at Haddon Hall

Haddon Hall is one of the oldest houses in the UK. Uniquely, it was left unoccupied for 200 years and so has not been subject to the sort of renovations other grand houses have undergone.

Approaching it through the Peak District you feel like you’re going back in time, as A-roads turn into country roads lined with stone walls or old hedgerows. Once on the grounds, the hall oozes character: part Lord of the Rings, part Dracula’s castle (in fact some famous fantasy films have been shot here, including The Princess Bride).

Haddon Hall is not as well-known as great houses like Chatsworth, or rewilding projects like Knepp, but it deserves to be. It has 187 hectares of parkland, woodland, river, water meadows, wetlands and former farmland. All sorts of mammals, insects, plants and fungi live here, and several species of bat forage, commute or roost on Haddon land. The Hall itself is a bat roost, and they often find bats behind tapestries.  

Bat detectors on the Wye River

With the sun about to disappear, we’re given bat detectors and led to the Wye, a river which winds through Haddon Hall’s ancient parkland. Clouds of white moths flutter up from the wild flowers and grasses, food for the bats. The air is sweet summer air full of pollen and warm earthy tones, fresh after the musk of the chapel.

In the dark the river looks spectral, it’s glassy surface full of shadows. Have I even seen a river at night before? I’m not sure I have. Holding my detector, I feel like a Ghostbuster. Alien sounds, clicks and clacks, faster and louder, announce bat after bat.

Steve tells us that noctules and Daubenton’s bats are flying over the water. I can see that some of these are bigger, and they move differently from the chapel’s bats snaking about above the water.  

Haddon Hall at sunset.

 

We stand awhile on a narrow stone bridge, which looks like goblins made it. It starts to rain, but it doesn’t dampen the wonder, as we use a thermal camera and see bats, otherwise invisible, among the trees lining the river.

After this our bat watch is over, and squinting our dark-adapted eyes, we make our way out of this enchanting place to go home.  

Spectacle and conservation 

It was both exhilarating and sobering to see so many bats at Haddon Hall. I was lucky to see such a spectacle, and it made me mad I was so lucky. Humans have so devastatingly quickly created a world where most people don’t know what a few hundred bats look like.  

Aside from ethical and practical problems stemming from and causing the biodiversity crisis, I think it makes us lonely to be without our fellow species. But places like Haddon act like beacons, they remind us that it wasn’t always this way, that enchantment used to be part of life, and there is lots we can do to bring the magic back.  

Images by Haddon Hall. Written by Claire Moran, Communications Officer at the Bat Conservation Trust.