In 2013 and 2016, we conducted a survey using marine radar off the coast of Choshi to clarify the reaction of seabirds to offshore wind turbines. In all the surveys, birds rarely flew within 100 m from the windmill, and the behavior of changing the flight direction near the windmill was recorded, suggesting that seabirds were avoiding the windmill. Comparing 2013 and 2016, 2016 tended to fly closer to the wind turbine. From the above results, it is considered that the effect of offshore wind turbines on seabirds is greater than that of bird strikes, such as avoiding wind turbines or not using the sea area. There is a bias and further investigation is needed to clarify the effects on seabirds.