Marine birds: Vision-based wind turbine collision mitigation

Abstract

Throughout their evolution seabirds have not had to contend with the collision risk posed by discrete objects that extend into their flight space above the water surface. However, the recent introduction of offshore wind turbines has significantly increased the potential for collisions. Bird collision risk with Offshore Wind Farm (OWF) turbines is now a major consenting consideration for OWF projects due to potential local population impacts on birds, especially those associated with protected sites. Therefore, the possibility of reducing those risks through a simple mitigation is highly desirable. Key elements for the design of vision-based mitigation measures aimed at reducing the collision of marine birds with wind turbines should be based upon knowledge of the vision of birds, not the vision of humans. May et al. (2020) tested a vision-based wind turbine mitigation measure and reported a modelled 70% reduction in annual turbine-blade collision mortality rate at a terrestrial location in a suite of 19 bird species. The aim of the present proposals is to extend this vision-based mitigation approach and increase its applicability to a broad suite of bird species considered vulnerable to collisions with wind turbines at sea. Key aspects of the vision, behaviour and ecology of marine birds which contribute to their collision risk under a range of natural viewing conditions are reviewed. The same information is then employed to give insights into the requirements of vision-based mitigation measures. We argue that the internal visual contrast of wind turbines should be increased using achromatic patterns applied to blades and pylons. These patterns should reduce the collision vulnerability of marine birds in general and should be effective under a range of visibility conditions determined by natural light levels and weather conditions. The measures should allow birds with different flight speeds and visual acuities to detect turbines sufficiently early to allow alteration of flight direction and avoid collision. The proposed mitigation requires changes to the appearance of wind turbines that can be implemented at the time of manufacture. They do not interfere with statutory requirements already required for the marking of turbines for the benefit of shipping and aircraft.