Effect of spring water stress induced by fishery farming on two duck species Anas platyrhynchos L. and Anas crecca L. in a Mediterranean wetland

In a remnant wetland of Central Italy, we assessed the effect of water level changes induced by fishery farming activities (February–July) on the abundance of two duck species (mallard, Anas platyrhynchos and teal, A. crecca) during a two-years period: a “treatment” year (2004) when fishery farm activity was high and water level dropped, and a “control” year (2007) when it was inactive and water level increased. Abundance values of mallards and teals were significantly different in the two years, and showed a direct correlation with water level in both the species in 2004 but not in 2007. In both species, abundance was significantly lower in 2004, only in late spring (June–July), revealing their sensitivity to water stress. A higher water level in wetland in control year 2007 may favour teals and mallards in the study area, allowing respectively the permanent occurrence of the former (a locally wintering species) and a higher abundance of the latter (locally breeding and resident species). A higher water level in wetland channels with the flooding of the surrounding reed- and rush beds, may induce a larger area of suitable habitat, available for these duck species. These facts emphasized that water level changes due to human activities are key to year-to-year variation in duck abundance in Mediterranean wetland regions.