To build knowledge and experience with the construction and exploitation of offshore wind farms, a large research program was set up to study the economical, technological, social and ecological effects of a near shore wind farm in the coastal waters of the Dutch North Sea. The report at hand concerns the ecological effects, and deals with effects specifically on flying birds (Lot 6). It describes the 'reference situation', i.e. the situation prior to construction of the wind farm, and serves as a reference to which the situation during and after construction of the wind farm can be compared in the subsequent effect study. Effects of the future wind farm may range from avoidance behaviour to collision of birds with turbines. Only by determining the undisturbed flight patterns in the reference situation, can we assess the effects resulting from the presence of the wind farm in the future.