Inter-annual and intra-seasonal patterns of abundance in a set of common waterbirds: a long term study in a Mediterranean wetland

"" Data on phenology and abundance of a set of common water-related birds were . collected in a remnant wetland of central Italy during six years, under a long-term management . project. In the study area, water level fluctuated following a seasonal pattern determined by climatic and anthropogenic factors (in particular, a local fish farming activity). We detected inter-annual and intra-seasonal changes in values of bird abundance. A high water level in wetland . channels and surrounding reed and rush beds, induced a higher availability of suitable habitats . for common ducks (mallard, teal, garganey), favouring an increase in the abundance of these . species. In particular, a significant correlation was found between water level and duck abun-. dance. On the contrary, the abundance of herons (little egret, grey heron, purple heron) increased . in association with a drop in water level. The latter was determined by both seasonal aridity and . fish farming activities in late spring. Such a decrease of water level implies a rise in fish density . and therefore its availability for herons. ""