Effects of Cattle Grazing on Passerine Birds Nesting in Riparian Habitat

Abstract

Nine transects, in areas with different histories of cattle grazing, were established along the Blitzen River in Oregon. Counts of birds and measurements of vegetation were made in the summers of 1981 and 1982. Increased frequency of grazing on an annual basis correlated significantly with decreases in bird abundance, shrub volume, and shrub heights. The longer the time since a transect was last grazed correlated significantly with increases in bird abundance, shrub volume, and shrub heights. Bird abundance increased significantly with increased shrub volume and taller shrub heights. Bird species richness decreased with increased grazing. Bird counts were 5 to 7 times higher on an area ungrazed since 1940 than on 2 areas grazed annually until 1980, and 11 to 13 times higher than on a transect severely disturbed by extensive grazing and dredging activities. Disturbances from camper activities also appeared to reduce bird populations.