How does a bat count work?
Konstanze Mez: We try to locate the bats before they emerge. They can always be somewhere different under the bridge. First of all, I walk back and forth on the bridge with the detector and try to listen for some initial sounds. I use in-ear headphones to cut out ambient noise. When I hear something, I stop and lean over the parapet to get closer to the source of the sound.
Hans Gysin: The bat count uses a combination of sight and sound. At least two people are needed to do the count. One stands on the bank of the Reuss and one on the bridge. Both have an ultrasound detector in their hand. I also put recording devices in the flower boxes.
What makes bat-counting difficult?
Mez: Daubenton’s bats are not easy to spot with the naked eye. This species emerges very late in the evening when it’s almost dark and they are then very difficult to make out against the reflective surface of the water. The species cannot be determined by ultrasonic frequency alone. Bats have different calls, change frequency in mid-call and even avoid each other. The calls that the bat makes while hunting are very different from those it emits when it is unhurriedly making its way back to the roost.
Gysin: I can then analyse the data that has been recorded on my computer at home in my own time. This way we can be more confident of the results.
I have been asked in the past whether it’s a Geiger counter.Konstanze Mez
How many bats live under the Chapel Bridge?
Mez: We don’t know exactly. Even though a significant amount of research work has been carried out on the Daubenton’s bats living under the Chapel Bridge, we actually know very little. It’s more about establishing and proving the presence of the bats and so being able to protect them.
Gysin: We make certain to carry out a count both before and after the annual Lucerne Festival. Any proposed events in the vicinity of the Chapel Bridge are reviewed by the city authorities beforehand to ensure that they are bat-friendly. They don’t seem to be bothered by noise pollution from the bridge, but they are sensitive to light.
What fascinates you about this work?
Gysin: The devices are actually my hobby. I have more of a technical background… I’m an electrical engineer and have been involved in developing these types of ultrasound devices. It’s a way for me to give something back to nature.
Mez: I find watching the bats simply fascinating. I love the wait and then the thrill of making some small discovery. And I’d like to take away people’s fear of bats. These extraordinary animals are not scary, nor do they have anything to do with vampires. This means doing a lot of talking and explaining. We act as ambassadors between bats and people.