Variable effects of blade black‐and‐white designs on detection of turbine rotation by birds

Abstract Wind turbines can negatively impact biodiversity, particularly through bird collisions with blades. A common mitigation measure involves the rapid, temporary curtailment of turbines using automatic detection systems, though their effectiveness remains unproven. A passive alternative is to modify turbine appearance to improve visual detection by birds. Several visual factors—motion blur, limited sensitivity to achromatic contrasts and difficulty in detecting rotating blades—may influence their detectability by different species and, therefore, collision risk. Enhancing turbine detectability, by applying black‐and‐white patterns to blades, offers a promising pathway to reduce collisions. However, painting blades on existing turbines is costly and the monitoring needed to assess this technique's effectiveness can take several years. We aimed at determining which pattern(s) would be most effective in improving the detection of blade rotation by birds. We used an experimental laboratory approach based on miniature wind turbines and operant conditioning, whereby captive‐bred birds (black kites Milvus migrans and domestic homing pigeons Columba livia ) were trained to respond to a positive visual stimulus with a food reward. The tests assessed the effect of four patterns—white blades, a black blade, striped blades and checkered blades—on the birds' detection of blade rotation. We observed an effect of (1) the pattern, (2) the rotation speed of the blades and (3) the achromatic contrast between the blades and their background on the detection of blade motion by birds. More than 50% of tested individuals could not distinguish between stationary and slowly rotating turbines (<5 rotations per minute). Striped and checkered patterns improved blade motion detection in black kites, whereas a checkered pattern reduced motion detection in pigeons. High variability in rotation detection was observed both between and within species. Synthesis and applications . Although no clear consensus emerged, striped patterns appeared to be the most promising for enhancing blade motion detection by several bird species. Field experiments are now required to validate these results in situ.