Effects of wetland excavation on avian communities in eastern Washington

Despite having an arid climate, the Columbia River Basin of eastern Washington is one of the most important areas for breeding, migrating, and wintering wetland birds in the Pacific Northwest. Extensive farmland irrigation near the O'Sullivan Reservoir and other areas has raised water tables, resulting in closed canopies of emergent vegetation in what are now permanent, shallow wetlands. During 1994-95, we found that avian communities on vegetation-filled wetlands excavated to create open water had greater mean densities of dabbling and diving ducks (Anatidae), shorebirds, American coots (Fulica americana), and terns (Sterna spp.) than untreated control wetlands. Densities of yellow-beaded blackbirds (Xanthocephalus xanthocephalus) were greater on excavated wetlands. while the densities of red-winged blackbirds (Agelaius phoeniceus), Sera (Porzana carolina), and Virginia rails (Rallus limicola) were greater on unaltered sites. Densities of marsh wrens (Cistothorus palustris) and other passerines were similar among excavated and control wetlands. Zooplankton biomass was greater on altered wetlands and generally greater in older excavations. We suggest that managers may design constructed wetland basins to improve population management of diverse wetland bird species by creating an appropriate mix of wetland habitats at the landscape level.