Bats depend on open bodies of water such as small ponds and lakes for foraging and drinking. Access to water is particularly important for survival in the increasingly hot and dry summers caused by climate change, the time when female bats are pregnant and rear their young. A scientific team from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) has now shown that access to drinking sites is hampered by wind turbines in agricultural landscapes: Many bat species avoid the turbines and water bodies located close to the turbines for several kilometres. These results have been published in the scientific journal “Biological Conservation”.
In order to counteract climate change, many countries are investing in the expansion of wind energy production in order to reduce greenhouse gases such as CO₂ through renewable electricity. However, the expansion of wind power production may also have negative consequences for wildlife and their habitats. This can potentially lead to some wildlife species being less able to cope with global warming. Prof Dr Christian Voigt and Dr Carolin Scholz from the Leibniz-IZW and Hannah Klein from the University of Potsdam showed in a scientific investigation of the acoustic activity of bats in agricultural landscapes that many bat species are displaced by wind turbines near smaller bodies of water. They analysed the spatial behaviour of bats belonging to the three functional guilds of open space foraging bats (that hunt above fields or the canopy of forests), narrow space foraging bats (that hunt in dense vegetations, for example below the forest canopy) and edge space foraging bats (that are specialised in foraging in transition zones such as forest edges). “We were able to clearly recognise that those bats which specialized to forage in the open space and in dense vegetation avoided water bodies when wind turbines were located near them”, says Voigt. “Only species of the guild of edge space foraging bats are apparently not driven away from the water sites by the wind turbines.”
The scientists placed acoustic detectors at a total of 59 small ponds that are permanently filled with water at distances of around 50 to 5,000 metres from wind turbines in northern Brandenburg, a federal state in Eastern Germany. Owing to its glacial history, the study area has more than a thousand of these small ponds, called kettle holes, kettle lakes or pothole lakes, which fulfil important ecological functions even in the intensively used agricultural landscape. “During the reproductive season in July, we measured the acoustic activity of bats at bodies of water at different distances from wind turbines. We paid attention to compare the data for similar conditions, such as a lack of rain and moderate winds”, explains Scholz. “In July, the lactation period of female bats slowly comes to an end and the young are weaned from the nursery roosts, which is an energetically strenuous phase for female bats. In addition, many waterholes dry up in midsummer, which is why the bats may be more dependent on small bodies of water that contain water all year round.”
The team identified a total of almost 8,400 calls of different bat species in the three bat guilds of open space hunters, narrow space hunters and edge spacer foragers. “With increasing proximity to wind turbines, the activity of open space foraging bats at water bodies decreased by 53 percent and the activity of bat species adapted to hunting in narrow vegetation decreased by 63 percent”, the authors summarise. The same picture was revealed when analysing the foraging behaviour that can be identified by the acoustic detectors: It decreased by 87 and 76 percent respectively as the distance to a wind turbine decreased from 5 kilometres to virtually zero.
“There is a certain tragedy in these results, because a measure to mitigate climate change has the unfortunate side effect that certain bats are less able to cope with hot and dry summers if they are displaced from their habitats by wind turbines”, says Voigt. “This emphasises once again how important it is to carefully consider the siting of wind turbines so as not to play off different objectives against each other. Habitats that are very important for species conservation should be given low priority or entirely excluded as sites for wind energy production.”
The bat species studied include the common pipistrelle (Pipistrellus pipistrellus), the soprano pipistrelle (Pipistrellus pygmaeus) and the western barbastelle (Barbastella barbastellus) as representatives of edge space foraging bats, species of the genera noctule bats (Nyctalus), house bats (Eptesicus) and vesper bats (Vespertilio) as representatives of open space foraging bats, and species of the genus mouse-eared bats (Myotis) and long-eared bats (Plecotus) as representatives of narrow space foraging bats.
Bats are protected species under German nature conservation law and EU law and should also be specially protected as migratory species. This protection is conflicting with the expansion of wind energy production, because there are a significant number of direct fatalities at the turbines and the habitats of bats are impaired in many ways. Voigt's team at the IZW has been conducting research into this “‘green-green conflict” between wind power expansion and bat conservation for many years.