Flight initiation distance in waterbirds of two coastal wetlands with different protection regimes

Human activities can impact avian populations leading to impaired fitness. It is, therefore, important to monitor their response to direct disturbance. Flight initiation distance (FID) is considered a measure of tolerance to humans and can be affected by age and gregariousness, yet few systematic data are available across species in similar environments. We measured FID in eight species of waterbirds in two coastal lagoon environments with different protection regimes, taking into account age classes and whether individuals were grouped or alone. Species markedly differed in FID: average distance ranged between 50 (little egret, Egretta garzetta, singletons) and 188 m (spoonbill, Platalea leucorodia, flocks). Overall, adults were more cautious than immatures, likely due to learning and experience, while flocks flew up sooner than singletons likely due to the “many eyes” effect. In areas strictly protected, where only low and non-threatening human activities are allowed, birds flew at a shorter distance than in areas with a less strict regime of protection. Interestingly, large-sized species flew at longer distance than small-sized species. These findings have important implications for management to reduce disturbance to avian wildlife by human activities and to assess the effectiveness of protected areas.