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

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 underexplored. A recent study found that urban birds were less tolerant of women than of men, a consistent observer gender specific pattern in five European countries. In light of this, 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. 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. Alternatively, 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. Our study contributed to filling the gap in understanding the effect of observer gender on avian escape behavior.