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 intentional or unintentional feeding relationships formed between humans and wildlife can be understood as animals discovering new foraging methods in artificial environments, leading to behavioral changes. This study 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 sites (beach, shrimp ponds, and wharf) in Haizhou Bay, Lianyungang, Jiangsu Province, China. The results showed that black-headed gulls in the wharf exhibited significantly shorter FIDs, suggesting a higher tolerance of 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, where such "quasi-feeding" phenomena are absent, display longer FIDs, indicating a higher level of vigilance toward humans. This study further emphasizes that research on animal adaptability in the context of urbanization should be conducted at smaller geographical scales. Understanding the behavioral responses of birds to human activities can help develop scientific and rational conservation measures and promote harmonious coexistence between humans and nature.