Should Conservation Cut-In Wind Speed Be Tailored to Site-Specific Conditions? Insights from Bat Activity Patterns at Windfarms in Northern Portugal

Wind energy stands as one of the most technologically mature renewable sources, playing a pivotal role in the mitigation of greenhouse gas emissions. However, wind farms and associated infrastructures increase collision risk for flying organisms. Implementing higher cut-in speeds is a proven mitigation strategy to significantly decrease wildlife mortality rates, particularly for bat species, by preventing turbine operation during low-wind periods of high activity. The suggested, non-standard, increased cut-in speed for wind turbines is generally 5.0 m/s. To test the effectiveness of cut-in speed increase, bat activity was monitored at three wind farms in northern Portugal (Gevancas, Azinheira and Dom João e Feirão), using ultrasonic acoustic detection, to characterize spatial and temporal activity patterns and assess the potential risk associated. Monitoring was carried out at fixed stations, at heights of 55m above ground level during seven consecutive nights per month, from march to October. Wind speed data were recorded concurrently using anemometers mounted on meteorological towers. Contradicting cut-in speed recommendations, the results show that 90% of bat activity occurred at wind speeds above the current mitigation thresholds (5.0 m/s.). Since turbine operation coincides with peak bat activity, it is imperative to implement site-specific mitigation strategies, such as optimized cut-in speeds, to minimize mortality risk.