Abundance of human-made food contribute to higher tolerance of human approaches in black-headed gulls

Food resources are key drivers of changes in animal behavior. The feeding relationships between humans and wildlife, intentionally or unintentionally, can be understood as a behavioral evolution that occurs as animals discover new ways of surviving in urban environments. This study was conducted in February 2024 in Haizhou Bay (34.933 N, 119.205 E), located in Haitou Town, Ganyu District, Lianyungang City, Jiangsu Province, along the central coast of China, bordering the Yellow Sea to the east.We focuses on the black-headed gull (Chroicocephalus ridibundus) to examine avian behavioral responses to human activities. We measured the flight initiation distance (FID) of black-headed gulls in three different areas (beach, shrimp ponds, and docks) in Haizhou Bay, Lianyungang, Jiangsu Province, China. The results showed that black-headed gulls in the dock area exhibited significantly shorter FIDs, suggesting a higher tolerance for human proximity. This tolerance is likely due to the incidental accumulation of oyster (family Ostreidae) shells by fishermen, which creates an association between humans and food resources, reducing their wariness of humans. In contrast, black-headed gulls in beach and shrimp pond areas, where such "quasi-feeding" phenomena are absent, display longer FIDs, indicating a higher level of vigilance toward humans. Our study suggests that food resources are essential in driving behavioral evolution in black-headed gulls. Also, this study highlights the importance of cognitive adaptation in animals' response to human activities, suggesting that behavioral flexibility is vital for animals to adapt to urbanization and respond effectively to human activities.