Livestock utilization and bird community composition in mixed-conifer forest and oak woodland in southern Oregon

We examined the degree to which bird community composition is associated with livestock grazing in the Cascade-Siskiyou National Monument in southern Oregon. We sampled riparian and adjacent upland areas along routes within mixed-conifer forests and oak woodlands. For each route, we generated a continuous measure (0-100%) of livestock grazing utilization and used this measure to group routes into low (0% to 40%) and high (>40%) grazing utilization classes. In 2003 and 2004, we conducted point counts along each route to quantify avian species richness and community composition. In mixed-conifer forest, species richness was significantly greater in upland areas and in areas with high grazing utilization; however, bird community composition differed only between upland and riparian areas and not between areas of low and high grazing utilization. In oak woodlands, bird community composition was significantly different between high and low utilization, but not between riparian and upland areas. Bird communities associated with high grazing utilization had significantly fewer shrub-nesting, foliage-gleaning, and long-distance migrant species than those associated with low grazing utilization. Our results suggest that grazing influences bird community composition in both riparian and upland areas of oak woodland vegetation. Reducing grazing in oak woodlands would likely lead to increases in the relative abundance of long-distance migrants, foliage gleaners, and shrub-nesting species in this habitat.