How bats are affected by wind turbines

anglais. In this study a wind power park of five turbines, Gummaråsen, in the south west of Sweden have been investigated to find out if bats fly in the height of the rotor blades, what species are present and the abundance of bats, at the site. The result showed that no bats was flying close to the wind power turbine, at the height of the nacelle (machine housing) and rotor blades, but bats were present closer to the ground. On warm nights with no precipitation and low wind speed, bats were especially abundant at Gummaråsen. Bats are most abundant close to wind power turbines in late summer and early autumn, the conclusion of this study shows that bats were present at the site of Gummaråsen from September the 13th to October the 5th at ground level. At the height of the rotor blades no bats were detected from September the 12th to November the 21th. Further investigations performed earlier in the season, and investigations with automatic acoustic detectors, at each site, could give an additional picture of the bat abundance and species composition at Gummaråsen.

anglais. It is only recently that knowledge about negative impacts on bats by wind power has been realized. Bats seem to be attracted to hunt close to wind power turbines because of the insects that tend to gather at these sites. Bats are at risk of being injured or even killed by the moving blades of the turbines, either by a direct hit or by the fast change in air pressure around the moving turbine blades that can cause haemorrhage to the lungs, called barotrauma. The Swedish government has decided that in 2020 a much larger part of the power production than today will come from wind power. This means that 3000-4000 more wind power turbines will be constructed. Swedish law protects all bat species and when planning for wind power construction care must be taken of these species. On the European continent, research has shown that wind turbines placed at the coast and in forested areas kill more bats than those placed in agricultural landscapes. Distinct heights in the landscape is also places of high risk but that no investigations on how bats react to wind turbines placed on hills have been performed in Sweden, which has to be further examined before drawing conclusions on this matter. In this study I wanted to find out if bats fly at the height of the rotor blades at the site of Gummaråsen, in the Swedish province of Halland. If they did so, I wanted to investigate if bats got injured at this site. I could not find any published record of studies performed in Sweden, where an automatic ultrasound detector was put in the nacelle (machine housing) of a wind power turbine to detect bats at the height of the rotor blades. I wanted to find out if this was possible and if so, could it prove to be a good way to perform studies of bats at sites with wind power turbines? Some bat species are well adapted to flight in the open air, and are classified as “high risk” species, meaning that they are at risk of getting injured by the blades of the wind power turbines, since they share the same air space. Bats tend to hunt only at wind speeds below 6 m/s on nights with no or little precipitation and warm weather. Most often bats give birth to only one offspring a year and the species is therefore vulnerable to extensive killing. Bats use high frequency calls to detect their prey. When the sound of their screams hit something a sound picture of the surroundings is created based on the echoes of the calls. The frequencies of most bat species sounds are too high for the human ear to hear. An effective way of detecting bats is to use acoustic ultrasound detectors. These detectors translate high frequency sound of the bat call into audible frequencies. I placed an automatic ultrasound detector in the nacelle (machine housing) of a wind power turbine, to record sounds during two months in the autumn. I also conducted a field survey at ground level, using both an automatic ultrasound detector and a manual detector. To find out if bats were injured or killed at the site I searched the area around the turbines at dawn. No sounds from bats were recorded at the height of the rotor blades, even though the automatic ultrasound detector seemed to be working correctly, recording sounds made by other sources. At ground level, the far most common bat species was the pygmy pipistrelle (Pipistrellus pygmaeus). Only one recording was made of another bat species, a myotis spp. The pygmy pipistrelle is known to fly at the height of rotor blades and is classified as a high risk species. I also did not find any killed or injured bats at the sites. At the time of the investigation the wind speed only dropped below 6 m/s on very few occasions. Bats do not tend to hunt at higher wind speeds and wind power constructions are best placed where the wind speed is high. Therefore one conclusion that can be drawn from this study is that at the height of the rotor blades, Gummaråsen is a good place to create wind based power but not is not an optimal hunting ground for bats. Further investigations performed during the rest of the season, and investigations with automatic acoustic detectors at each site, could gain more information and an additional picture of the bat abundance and species composition at the site of Gummaråsen. Supervisor University of Lund: Prof. Anders Hedenström Supervisors Triventus Consulting: Malin Johansson and Stefan Johansson Master´s Degree Project in Biology, 30 credits Department of Biology, Lund University, Sölvegatan 35, SE-233 62 Lund