This report gives an overview of the current international knowledge about the impact of wind turbines on birds of prey, other breeding bird species, migrating birds and on bats. The different factors, which influence type and magnitude of impacts (site- and species-specificity, construction and operation), are considered. This is followed by a comprehensive overview of possible measures of avoidance and mitigation of impacts. The last part of the report gives more details for those species, which might be particularly affected by the future development of wind energy in Switzerland.
The extent of possible impacts is mainly determined by a combination of factors belonging to the occurring species and the respective location like the ecological and ethological context (e.g. territorial and courtship flights close to breeding sites), thermal upwinds for soaring species or differences during days and seasons. With regard to collision risk, birds of prey and other large species must be considered as especially affected since they collide more frequently in proportion to their population size and the number of casualties can lead more easily to population declines due to low reproduction rates. Macro siting (choose of location) and micro siting (optimization of wind farm layout) are regarded as the most important measures for minimization of impacts. Some species may be kept out of the danger zone by avoidance of attraction, by luring away or by deterrence. Temporal curtailment of turbine operation in periods of high flight activity is already common practice with regard to minimization of collision numbers of bats.
Management of impacts can only be successful on a case-by-case approach. Uncertainties in the impact prognosis may be handled by a more adaptive management. This would complement the established hierarchy of mitigation - avoid, minimise, compensate - with an accompanying monitoring in order to be able to modify certain mitigation measures depending on its outcome.