Are flying wildlife attracted to (or do they avoid) wind turbines?

Department of Energy award DE-EE0000523

       Flying bats are known to be seriously affected by wind turbines in several areas in North America and Europe. In addressing bat mortality at turbines it is critical to know what mortality events mean in the context of the conservation of the species involved, what proportion of the wildlife flying near the wind energy installation is actually affected, and what effect a certain amount of mortality has on the populations of the species involved.

       Many have addressed“risk” to flying wildlife, but have usually misused the term. In the case of flying wildlife we cannot currently estimate exposure and thus cannot evaluate risk nearby or at the population level. What animals are exposed? Are they all flying in the vicinity, only those whose flight paths take them through the rotor-swept-area of a turbine, or some intermediate group? This proposal seeks to put a scientific basis under the term “risk” for flying wildlife approaching wind turbines.

        The research community believes that bats are at special risk from wind turbines but does not know how that happens. If bats are attracted to turbines (conversely, birds may avoid turbines), the number of bats exposed is much higher than if they encounter turbines in the course of straight migratory flight.

       The situation is illustrated in the diagrams below. They show a wind turbine (blue object) from above and the side, with tracks of hypothetical bats approaching. They may encounter turbines in their flight path and subsequently court danger again and again by flying through the rotor-swept-zone repeatedly (left), or they sense the turbines and depart from normal flight to approach the turbines (middle), or both (right). Note that flying wildlife can approach, and avoid, turbines by changing direction, height, or both. Of course, it is also possible that migrants avoid turbines by turning away from them at night, which is an equally important possibility.

             From above (animals flying south) From the side (animals flying to right)

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      The Illinois Natural History Survey (INHS) operates the most capable research instrument in North American to apply to this problem. a tracking radar for studying flying wildlife. It can follow individual birds and bats accurately in three dimensions, at a distance, as they approach a wind turbine. Departures from a straight path, either turns or changes in height, can be measured accurately until the flying animal either flies near/into the turbine blades or continues past the turbine and into safety.

      Below is a track of a flying animal encountering a wind turbine (green symbol at lower right) at a facility near Casselman, Pennsylvania in 2009. The figure is a map of the flying animal’s path over the ground, with the radar where the axes cross. The track started over a kilometer away. As the creature flew north of the turbine, it gradually turned on a wavering course (indeed, looping at one point) and circled toward the turbine. As the animal approached the turbine it drew too close to the large metal object so that the radar could no longer continue to track it (lower right).

 

      The animal climbed until it started to turn, then descended sharply toward the base of the turbine.

 This radar “target” had wing beats on radar unlike those of songbirds–it was probably a bat.