Avian use of recently evolved riparian habitat on the lower Snake River, Washington

Since 1975 the U.S. Army Corps of Engineers has managed and irrigated 440 ha along the lower Snake River in Washington state, USA, as mitigation for 4 dams constructed 1962-1975. Avian use of irrigated Habitat Management Units (HMUs) was compared with that of non-irrigated sites and streams that entered the river, by conducting bird surveys at 25 sites in summer and autumn 1997 and in spring 1998. The HMUs were on bars or benches along the river and were intensively managed as well as irrigated. They were characterized by patches of planted trees and shrubs, and crops planted for wildlife, interspersed with upland grass/forb habitats; shoreline habitat included trees, shrubs and emergent palustrine vegetation. The non-irrigated sites were also along the river and had narrow strips of palustrine shrub-scrub and emergent palustrine vegetation, which was bordered by upland vegetation. Avian abundance, species richness, and species diversity were compared among habitats and seasons. An average of 169 birds and 33 species was detected at HMUs, with 120 birds and 28 species at non-irrigated sites, and 63 birds and 23 species along streams in all 3 seasons. There was an average of 29 species/site in summer, 31 in autumn, and 22 in spring. Species diversity, as measured by the Shannon-Wiener function, was higher in summer, indicating that large flocks of a few species were common in autumn and spring. These data demonstrated that the lower Snake River is an important stopover site for migrating birds. An average of 30 more bird species were detected than in a study conducted on the same area in 1974. The increase in species richness is attributed to the development of HMUs and to natural succession of palustrine vegetation since dam construction. Future potential changes in reservoir levels, such as breaching of dams, will undoubtedly affect bird communities along the lower Snake River in all seasons. However, the data demonstrated that habitat perturbations can be partially mitigated by habitat enhancement and management.Rocklage and Ratti "Avian use of recently evolved riparian habitat on the lower Snake River, Washington." Northwest Science. 2000; 74(4): 286-29