Effect of winter water stress on the breeding bird assemblage of a remnant wetland in central Italy

Abstract

Summary . — We evaluated the effects of winter water stress on breeding bird communities and two assemblages of species (wet-reed species and open-habitat species) in a remnant coastal wetland of central Italy. Data were obtained by means of mapping method, on a five year-period (2001-2005), comprising a water stress year (2002). At community level, species richness, diversity index, evenness and consuming biomass showed the lowest values in the 2002 breeding season, but only the last parameter showed significant differences with the previous (2001) and subsequent (2003) years. In the paired years 2001-2002 and 2002-2003, species turnover was highest and percentage similarity index was lowest. Only considering the wet-reed assemblage, we observed that : species richness decreased in 2002 in comparison to other years ; the values of diversity index and consuming biomass changed significantly between that year and both previous (2001) and subsequent year (2003) ; ecological density (i. e. density in the suitable habitat) of these species was significantly lower in 2002 year compared to 2001. The significant decrease of the consuming biomass was due to the local disappearance of the species more strictly linked to water habitats and to the Phragmites reed-beds, with a higher mean body mass as compared to open-habitat species. No similar changes were observed for open-habitat species. Changes between years were more due to species turnover rather than abundance turnover. Wetland habitat conditions, i. e. linked to water level, were crucial to year-to-year variation in breeding bird species richness and density in the study area.