There are currently around 30,000 wind turbines in Germany – and the trend is rising. However, due to stricter distance rules to residential areas, the operators have to look for alternative building sites, which also include forest areas. According to a study, however, these wind turbines have a significant impact on the habitat of forest bats. Species that hunt below the treetops in particular feel disturbed by the turbines and keep a long distance from them.
In the course of the energy transition, in all likelihood mankind will not be able to avoid expanding wind energy. However, the question of possible locations for the plants has always been a source of discussion. In Germany, the legal minimum distance to housing estates is currently a matter for the federal states – in most federal states it is around 1,000 meters. This ensures that the wind farm operators are restricted in their choice of location and have to resort to alternative areas, which also include forest areas.
Disturbing effects beyond the rotor collisions examined
“Forests are sensitive ecosystems and valuable habitats for many rare and protected bat species,” explains senior author Christian Voigt from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin. Together with his colleague Julia Ellerbrok and other researchers, he investigated the extent to which bats living in forests are disturbed by wind turbines installed there. For this purpose, the scientists recorded bat activity in several Hessian forest areas around wind turbines over a period of several months. The bats were divided into three categories, depending on whether these species hunt in open areas, in the border area or in narrow surroundings, i.e. below the treetop. Scientists called the latter forest specialists.
“Wind turbines in forests can cause problems for bats in a number of ways. Bats that hunt for insects above the treetops can be killed directly at the turbines – by collision with rotor blades or simply by the considerable pressure differences that they cannot survive,” says Voigt. “Bats, which hunt in the vegetation under the treetops, lose part of their habitat due to the clearing.” This was also noticeable in the researchers’ measurements: “We found that these forest specialists are significantly less active in the vicinity of wind turbines , especially near turbines with large rotors, and in the high summer months,” explains Voigt.
“Wind turbines can cause problems”
To determine when the animals began to feel disturbed by the equipment, the team recorded acoustic activity using ultrasonic detectors at various distances from the machines. The scientists could not find any significant differences in bats hunting in open spaces or in peripheral areas. However, from the maximum measurement distance of 450 meters to a distance of 80 meters, the values measured by the forest specialists decreased by almost 50 percent. According to Voigt and his team, this is also due to the fact that species such as mouse-eared bats and long-eared bats need the narrow spaces and vertical heterogeneity under the treetops for their type of hunting and for protection. Areas cleared for wind turbines and the operation of the wind turbines disturb the fluttering animals.
“Forest specialists are therefore not typical victims, but their living space and their radius of activity are still clearly restricted within a radius of several hundred meters around the system,” explains Voigt. The scientists therefore recommend installing wind turbines in the open countryside rather than in forests. In particular, near-natural forests with a varied vegetation structure should be avoided as locations. If the rotors still have to be placed in forest areas due to a lack of alternatives, the researchers should at least take compensatory measures. This includes, for example, removing correspondingly large areas of forest from intensive forestry so that the loss of habitat for the forest bats caused by the operation of the wind turbines can be compensated for.
Source: Leibniz Institute for Zoo and Wildlife Research; Specialist article: Journal of Applied Ecology, doi: 10.1111/1365-2664.14249