Repeatable flight initiation distance is associated with nest-site characteristics in a colonial seabird

Behavioural responses are among the fastest ways for wild animals to respond and adapt to environmental change. In breeding birds, nest defence behaviour is particularly important, as it directly influences reproductive success. However, the variability of this behaviour, and its links to environmental conditions and fitness, remain poorly understood. Here, we investigate the repeatability of flight initiation distance (FID) - a proxy for nest defence behaviour - in Common gull (Larus canus) breeding pairs within a seabird colony. We assess how consistent differences in FID between gull pairs relate to nest-site characteristics and fitness-related traits. We find that FID is strongly repeatable at the pair level (R = 0.50), indicating consistent behavioural differences among breeding pairs. Moreover, pairs with shorter FID nest at higher elevations and in areas with higher conspecific density compared to pairs with longer FID. Finally, our results show that these different behavioural responses, linked to different nest-site contexts, do not lead to clear differences in terms of fitness outcomes, suggesting that breeding pairs with marked behavioural differences could achieve similar fitness by matching the environmental conditions of their nesting site with their behavioural responses to perceived risks.