Assessing bird response patterns using flight initiation distance: evidence from multiple urban park surveys in Nanjing, China

Urban parks not only fulfill multiple functions within urban ecosystems but also serve as key sites for frequent interactions between wildlife and humans, thereby creating complex and dynamic symbiotic environments. As one of the most representative animal groups, birds’ behavioral patterns reflect both their adaptation to urban environments and the influence of urban habitats on wildlife spatial use. However, empirical studies on how environmental characteristics shape birds’ alert behavior remain limited. We used flight initiation distance (FID) as a quantitative behavioral indicator, assessing birds’ sensitivity to human approach in eight urban parks in Nanjing, China. The results showed that certain bird species exhibited relatively high tolerance and became dominant by continually adapting to human activities, whereas non-dominant species tended to avoid disturbances. Trees emerged as a critical factor affecting FID across species, particularly in areas with low vegetation cover. Compared with long-term stress, instantaneous disturbance exerted broader and more consistent impacts in parks across different urban development gradients. These findings highlight the notable potential of FID in urban ecological management and planning. Prioritizing the conservation of non-dominant species may help improve the ecological security of urban bird populations. Mitigating adverse impacts through optimized spatial zoning and enhanced vegetation conditions can further support this goal. This study offers valuable guidance for the conservation of bird diversity and the refinement of habitat design in urban parks.