Are black-headed gulls (Chroicocephalus ridibundus) less tolerant of women than of men?

This study was conducted in Kunming City, and four historic tourism sites were chosen for field surveys: Daguan Park (25.0218° N, 102.6732° E), Haigeng East Wharf (24.9769° N, 102.6796° E), Haigeng Park (24.9604° N, 102.6599° E), and Haigeng Dam (24.9738° N, 102.6509° E). The average temperate of the study areas were about 4-17 ℃ (for more details, see Liu et al. 2025).The black-headed gull, belonging to the order Lariformes, family Laridae, is a bird species found worldwide. It breeds in the Palearctic region and migrates south to winter in India, Southeast Asia, and the Philippines (MacKinnon 2022). It is widely distributed in all provinces and regions of China and is one of the most common birds in inland and coastal areas (Zheng 2023). In Kunming City, black-headed gulls heavily rely on human food sources and most individuals forage in streets and squares and actively approach human feeders (Feng and Liang 2020).Flight initiation distance (FID) is an important behavioral metric for assessing an animal's fear level and evaluating the trade-offs in survival strategies under predation risk. Studies have shown that various characteristics of observers—such as clothing, behavior, and gaze direction—can influence avian FID, yet the effect of observer gender on FID remains poorly underexplored. A recent study found that urban birds were less tolerant of women than of men, a consistent observer sex-specific pattern in five European countries. This study investigated whether the FID of black-headed gulls (Chroicocephalus ridibundus) wintering in tourist areas of Kunming City, Yunnan, southwest China, differed in response to human observers of different genders. Our results revealed no significant difference in the FID measured by male and female observers. The coefficients of variation within both groups were relatively high, and the intra-class correlation coefficients showed significant inter‑observer variations. Our study suggests that due to long‑term exposure to large numbers of tourists with diverse behavioral patterns, the salience of observer gender cues may be attenuated for black-headed gulls. Meanwhile, differences among individual observers—potentially including uncontrolled subtle behaviors or appearance features—exert a greater influence on the birds' escape responses than does observer gender.