If there is an increased collision risk for certain so-called "wind energy sensitive bird species" in the course of the approval of wind energy plants, the effects can be reduced by means of suitable avoidance measures. The aim of the research and development project "Effectiveness of measures against bird collisions with wind turbines" commissioned by the BfN was to evaluate existing studies and literature to establish the state of knowledge and the gaps in knowledge regarding the effectiveness of such avoidance measures and, based on this, to underpin selected measures with a research concept for investigating their effectiveness.