Approaching population thresholds in presence of uncertainty: Assessing displacement of seabirds from offshore wind farms

• A novel approach for assessing displacement impacts of offshore wind farms on seabirds is presented making best use of limited data
• A displacement matrix approach is linked with PBR analysis to increased confidence in assessment conclusions drawn
• A case example demonstrates the applicability of the methods described in practice

Assessment of the displacement impacts of offshore wind farms on seabirds is impeded by a lack of evidence regarding species-specific reactions to developed sites and the potential ecological consequences faced by displaced individuals. In this study, we present a method that makes best use of the currently limited understanding of displacement impacts. The combination of a matrix table displaying the full range of potential displacement and mortality levels together with seasonal potential biological removal (PBR) assessments provides a tool that increases confidence in the conclusions of impact assessments. If unrealistic displacement levels and/or mortality rates are required to equal or approach seasonal PBRs, this gives an indication of the likeliness of adverse impacts on the assessed population. This approach is demonstrated by assessing the displacement impacts of an offshore wind farm cluster in the German North Sea on the local common guillemot (Uria aalge) population.