This study describes the seabird community in Dutch North Sea waters where in the near-future two marine windfarms will we built (Q7 and Nearshore Windfarm; NSW). To document the current situation (“Tzero”), ship-based seabirds-at-sea counts were conducted during eight dedicated surveys, distributed over the year. The study area was considerably larger than the future windfarm areas. This made comparisons possible between bird densities within and outside the contours of the future sites, after correction for location (northing and depth). In this “before impact” situation, seabird densities at the future windfarm sites were mostly statistically similar to those in the immediate vicinity. Future (“Timpact”) studies will be conducted to asses if the impacted areas will have changed after the wind turbines have been put into place. Seabird presence is be highly variable in time and place as a result of migratory movements, weather conditions, seasonal and diurnal patterns. Apart from studying just the small future sites for windfarms, we also consulted existing longterm databases on seabird presence (aerial surveys) and passage (seawatching data) to enhance our understanding of existing variability. Seabird numbers in an area the size of a future windfarm may vary by at least an order of magnitude. This flaws direct comparisons of numbers present in a Tzero and a Timpact situation. Therefore, densities at the windfarm site should be compared to densities at sea in the immediate vicinity, measured simultaneously.