Wind energy is a sector of the alternative energy industry that is growing worldwide. However, there are concerns regarding bat fatalities at wind turbines. This phenomenon is widespread and has received attention to warrant investigation into how and why these collisions occur. In this paper we characterize the ultrasonic acoustic field of a wind turbine in order to find out if the turbines emit ultrasound. We conducted this study at Serra dos Candeeiros near Lisbon, Portugal, where some bats have been found injured or dead beneath wind turbines . The measurements were divided into 3 different campaigns: 1) seven acquisitions at ground level in front of the nacelle, 2) five acquisitions around the turbine at ground level and 3) one acquisition inside the nacelle. The analysis of the results shows that the analysed wind turbine does not reveal any ultrasound noise source.