Most birds migrate at night and may be at risk of colliding with artificial structures that protrude into the open airspace. Collision risk assessments concerning offshore windfarms have been routinely based on discontinuous observations from ships. Dedicated avian radar systems installed close to the operational offshore windfarm alpha ventus, however, allowed continuous quantification of migrating birds during day and night. Combined data collected by radar and various other optical and acoustical remote sensing techniques showed that nocturnal migrants get attracted to illuminated windfarms when visibility is low, occasionally leading to mass accumulations. On-going research will allow testing the severity of this impact and the effectiveness of possible mitigation measures.
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