Pattern in water-related birds reveals a shift in biomass between mature and mowed reedbeds: evidence from a coastal wetland

Abstract

In Mediterranean wetlands, Phragmites australis reed beds are often intensively managed through mowing. These practices may improve wetland heterogeneity with contrasting effects on many reed-bed related birds. Here, we analyzed the habitat selection of a guild of six water-related breeding birds in a patchy managed wetland, where reed-bed mowing was periodically carried out. We reported data about the habitat use and selection of species on five different habitat patches (non-managed mature and managed by mowing reed-beds, rush-beds, open waters, and ecotones), both considering species abundance and biomass. Moreover, we focused on differences between non-managed/mature reed-beds and managed (mowed) ones. As expected, all the species showed a significant difference in frequency of habitat use, both considering abundance and biomass. As expected, rails (Eurasian coot, Moorhen), Mallard and Little grebe selected open waters, Reed warbler selected reed beds and Cetti’s warbler selected ecotones. Detrended Correspondence Analysis (DCA) performed on abundance values confirmed the link among habitats and species. However, when performing DCA on biomasses, we showed a shift of the largest species toward mowed reed-beds. The direct comparisons between mature and managed (mowed) reed-beds, using the Abundance/Biomass comparisons, highlighted the difference in abundance and biomass when comparing these habitat patches: in mature reed-beds the biomass curve was located below the abundance one (high frequency in abundance of low biomass birds, as warblers), whilst in mowed reed-beds the biomass curve was located above the abundance one (comparable high frequency of large biomass species, such as ducks, rails and grebe). Although our data suggest reed-bed mowing may disadvantage small passerines, we observed this type of management may favor large body species, providing them a higher availability of shelters and breeding sites.