The expanding development of offshore wind farms brings a growing concern about the human impact on seabirds. To assess this impact a better understanding of offshore bird abundance is needed. The aim of this study was to investigate offshore bird abundance in the breeding season and model the effect of predictable environmental factors. We used a bird radar, situated at the edge of a wind farm (52.427827°N, 4.185345°E), to record hourly aerial bird abundance at the North Sea near the Dutch coast between May 1st and July 15th in 2019 and 2020.The effect of sun position, week in the breeding season, and astronomic tide on hourly bird abundance was evaluated using generalized additive modelling. Sun position and week in the breeding season had a modest and statistically significant (p<0.001) effect on bird abundance, while astronomic tide did not. Predicted abundance was higher during the day than during the night, with highest abundance in the morning. Abundance increased throughout the breeding season until the end of June, but decreased again in July. In total the model explained 18.5% of deviance in bird abundance, indicating offshore bird abundance is partially dependent on predictable external factors. The high variability in bird abundance at scales ranging from hours up to weeks emphasizes the need for long term and continuous data which radar technology can provide. The findings of this study can help improve offshore bird density estimations and provide context on the temporal fluctuations in bird abundance for marine policy making.