Contrasting effects of water stress on wetland-obligated birds in a semi-natural Mediterranean wetland

This study evaluated the effects of seasonal water level changes on two foraging guilds of water-related bird species in a remnant coastal wetland of central Italy. Data were obtained by point count method. During the seasonal water-level decrease in wetland channels, the Diversity Index and Species Richness of the entire assemblage dropped significantly between May and July. A significant decrease in the number of species was observed in the middle of May, attributed to decreasing water levels related to natural (climatic) and anthropogenic (local fish farming) causes, and the subsequent drying of surrounding marshes and meadows. A first phenological threshold was observed in May, when the water level decreased to 70 cm in channels. A high species turnover occurred in the entire assemblage during this period. The herbivorous-omnivorous species (Anatidae and Rallidae) and zoophagous species (Ardeidae and Podicipedidae) during the study period exhibited opposite trends in the diversity index values. The diversity index progressively decreased for the herbivorous-omnivorous species in the late spring, while increasing for the zoophagous species, due to a greater availability of food (increased fish density due to decreased water level). These contrasting results are a consequence of ecological and phenological (sedentary vs. migrants) traits of the species belonging to these guilds. These data represent useful information for elaborating management strategies focused on the water level regime in Mediterranean small wetlands in which fish-farming activities also occur.