Wind energy generation has developed in Germany into by far the most important source of renewable energy production. Over 18,000 wind turbines with an installed capacity of over 19,000 MW are now in operation. The wind-rich offshore areas are seen as the best opportunity to increase the generation of wind energy. On the mainland, however, the expansion of wind energy is becoming increasingly more difficult, as most of the best sites are already taken and further extension of existing wind farms is restricted by the lack of wind in most of the inland regions, as well as planning restrictions for interests (protection of the environment, nature conservation and landscape). Therefore, „repowering“ provides a possibility to increase the production of electricity without simultaneously increasing the space required. „Repowering“ means that older, smaller and less powerful wind turbines are replaced by newer and more powerful ones. These new turbines are much higher than older ones - heights above 100m are now the norm.
The literature review of Hötker et al. (2005) (hereafter called the NABU-BfN report), which was funded by the German Agency for Nature Conservation (BfN), showed that wind turbines have only a relatively small disturbance effect on breeding birds, although many potentially sensitive species have not yet been analysed. Resting birds, in particular geese, ducks and waders responded sensitively to wind turbines and could be displaced from their resting areas. Wind turbines at certain sites, especially on bare mountain ridges and water bodies, are a collision risk for birds. In particular, birds of prey were affected, in Germany notably Red Kite and White-tailed Eagle. Bats were also killed by wind turbines, especially when these were located close to or within woodlands. The extent to which wind turbines have a harmful impact on the natural environment is mainly determined by their location. Practically the only effective means of avoiding damage was appropriate site selection.
The references used by Hötker et al. (2005) were generally studies which had been carried out on older, relatively small wind turbines. Although one could estimate a relationship between the size of wind turbines and the disturbance impact or collision risk for birds and bats, these relationships were not (with some exceptions) statistically significant. In order better to assess the impacts of the new generation of wind turbines on birds and bats, this report will analyse the more recent publications (up to summer 2006). The main emphasis was in particular the extent to which the danger for birds and bats caused by wind turbines is expected to change due to repowering. In this report, collisions of birds and bats and the displacement of birds by wind turbines have been considered as the potential impacts on these taxa. To our knowledge, no further essential studies about the displacement of bats and other mammals by wind turbines have been carried out recently (Bach & Rahmel, 2004) and therefore this aspect is not dealt with in this report.