To monitor the impact on birds following the construction of two offshore wind farms in the Belgian part of the North Sea, a twofold strategy was followed. Monthly ship-based seabird surveys allowed for a detailed displacement effect assessment, while radar research aimed at studying avoidance behaviour and barrier effects. Both methods provided input data for collision risk modelling in order to assess bird collision rates. Three years after the completion of the wind farm at the Bligh Bank, it showed that northern gannet, common guillemot and razorbill avoid the wind farm, while numbers of lesser black-backed and herring gull increased significantly. Collision risk modelling learned that gulls in particular are at risk of colliding with the turbine blades, with up to 2.4 bird strikes per turbine per year.