Throughout their evolution seabirds have not had to contend with obstacles which extend into their flight space above the water surface. However, the recent introduction and expansion of the Offshore Wind sector has significantly increased the potential for collisions with turbines. Bird collision risk with Offshore Wind Farm (OWF) turbines is now a major consenting consideration for OWF projects. Therefore, the possibility of reducing those risks through a simple vision-based mitigation is highly desirable. It has the potential to help both governments and developers accelerate the growth of OWF to achieve renewable energy targets.
The report’s Appendix presents a review of the vision of birds. This is used to determine key elements for the design of vision based mitigation measures aimed at reducing the collision of marine birds with Offshore Wind Farms.
The review was prompted by the findings of May et al (2020) which tested a vision-based wind turbine mitigation measure. They reported a modelled 70% reduction in annual turbine-blade collision mortality rate in a suite of 19 bird species at a terrestrial location. The aim of the report is to extend this mitigation approach and increase its general applicability to a broader suite of bird species at sea, and to a wider range of viewing conditions.
The review explores key aspects of the vision, behaviour and ecology of marine birds which contribute to their collision risk under a range of natural viewing conditions. The same information is then employed to give insights into the requirements of mitigation measures.
The review concludes that there is a justifiable ecological basis to believe that the principle of increasing the internal visual contrast of turbines through blade marking should benefit seabirds. Although white-tailed eagle and seabird vision is comparable, it is important to consider differences in environments that influence relative collision risk. These include familiarity with areas where turbines are encountered, and factors which affect visibility at sea, especially light levels and weather conditions. As such, simple blade marking may not yield seabird collision reductions at rates recorded for white-tailed eagles at coastal wind farms. It is recommended that more complex markings of turbines should also be considered.
A mitigation measure is proposed which is neither site or species specific and can be employed generally in marine situations. The principle aim of the mitigation measure is to increase the conspicuousness of wind turbines across a wide range of natural viewing conditions such that a turbine can be detected by an approaching bird sufficiently early to allow change in their flight path and avoid collision.
The proposed mitigation requires modest changes to the appearance of wind turbines that can be implemented at the time of manufacture. These changes will increase the internal achromatic contrast of turbines and increase their contrast against a wide range of sky and sea conditions. The measures will allow birds with different flight speeds and visual acuities to detect turbines sufficiently early to allow alteration of flight direction and avoid collision.