Abstract
In 2005 we started a two-year project investigating the collision risk of migrating birds in the Danish offshore wind farms Horns Rev, North, Sea, and Nysted, Baltic Sea. The project is financed by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety. Access to the offshore wind farms was granted by the Danish Energy companies Vattenfall (formerly ELSAM eng.) and DONG energy (formerly Energi E2). Data on migrating and other moving birds were obtained using vertical and horizontal radar in combination with visual and acoustic observations operating from an anchored vessel as a working platform. The anchoring positions were chosen along those sides of each wind farm area where birds following the main migration directions were expected to either approach the wind farm or to fly in a very close distance to it.
In 2005, 24 boat trips with 83 observation days, in 2006, 28 boat trips with 82 observation days were carried out. Study periods aimed to focus on migrating birds and thus covered the main migration periods between March and May in spring and September to November in autumn.
These investigations were set out to yield results in the direct vicinity of offshore wind farms in order to offer more insight into the potential risks of those recent developments in the offshore environment. The opportunity to work at the Danish offshore wind farm sites was unique; methods developed during the numerous offshore technical reports in the framework of the Environmental Impact Assessments (EIAs) in the German North Sea had to be adapted both with regard to visual observations, but more importantly with regard to remote techniques, in this case marine surveillance radar. Study design was deliberately chosen to place the observation platform (ship) in the direct vicinity of the wind farm; this way, data and results ought to be complementary to those of the Danish studies during baseline and operation phases; also, observation results can be allocated to areas inside and outside the wind farm and ought to allow the documentation of potential differences between these areas. Focus was to look at the potential barrier effects and collision risk of birds, while habitat loss was not addressed.
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