When dawn breaks, they leave their daytime roosts and go out foraging. Bats often travel long distances to their hunting grounds on water bodies, along forest edges or in orchards. They regularly use the same flight corridors in the landscape going along hedges or other structures, including house facades, that they can detect with their echolocation ultrasound calls. But where exactly the animals fly is often not clear, although this would be important to know so that their flight paths can be protected – especially in places where many bats have to fly through confined spaces.
Until now, detecting such corridors has been complicated and is only possible with extensive use of bat detectors or radiotelemetry, in which individual animals are equipped with transmitters. A simulation model developed by WSL researchers in cooperation with partners and on behalf of the Swiss Federal Office for the Environment, FOEN, now simplifies the search. For the model, the researchers recorded the calls of two bat species while they were commuting to foraging areas from six different roosts each. By combining these with geodata on the areas, they were able to estimate how the animals move around in the landscape.
The model still has errors. “So far, we have not been able to include artificial light at night in our calculations because high-resolution data is, unfortunately, still not available for Switzerland,” explains project manager Martin Obrist. Bats avoid artificial light and shun street lamps, for example. In such cases, the model’s predicted routes may not correspond with the actual flight corridors observed by a bat expert or a local monitoring observer.
In a follow-up project, the light data for various locations will be collected and integrated into the model. In addition, WSL modelling specialist, Klaus Ecker, is calculating flight corridors for a further 200 bat roosts of four target species for bat protection in Switzerland. The resulting data will be evaluated by a team of specialists to decide what measures to recommend to the cantons and planning authorities. (Lisa Bose, Diagonal 1/19)