Novel evaluation of raptor silhouettes and bird-collision prevention patterns through indoor flight tunnel testing and field verification

Bird collisions resulting from the increase of transparent structures associated with urbanization are recognized as a significant factor contributing to the decline of bird populations, and various strategies have been proposed to mitigate these incidents. However, scientific verification of the effectiveness of each pattern in preventing impacts on a global scale remains limited, with results differing across regions. We developed an indoor bird collision tunnel testing system that controls external variables to quantitatively evaluate the avoidance efficacy of 10 distinct samples using wild birds native to East Asian migratory routes. Initially, a comparative analysis of avoidance rates between a conventional raptor pattern and a modified raptor pattern where the raptor shape was inverted and affixed revealed no statistically significant differences. This finding suggests that birds do not perceive raptor silhouettes as genuine threats. Furthermore, brick-shaped sheets exhibited the highest avoidance rates, whereas dot patterns showed a wide range of avoidance rates depending on the experimental conditions. Avoidance rates did not differ significantly across the specific colors and shapes tested, with neither factor achieving statistical significance. Although pattern size did not produce statistically significant effects, avoidance rates tended to increase with larger dot size. Conversely, pattern spacing demonstrated a statistically significant inverse correlation with avoidance rates, whereby closer spacing resulted in increased avoidance. Products exhibiting avoidance rates above 70% in tunnel tests were considered effective, establishing a standardized threshold score of 70 for collision mitigation. Furthermore, the application of two types of samples (5×5 cm, silver, square, 8 mm; and 5×5 cm, white, square, 8 mm) that surpassed the baseline score on outdoor sound barriers resulted in a statistically significant reduction in bird collision frequency post-installation compared to pre-installation. This research experimentally reconfirms the limitations of raptor silhouettes and concurrently proposes effective patterns for mitigating bird collisions on the extensive transparent sound barriers commonly found in East Asia.