Sagebrush Bird Communities Differ with Varying Levels of Crested Wheatgrass Invasion

Abstract

Sagebrush communities, covering millions of hectares in the western United States, are among our most imperiled ecosystems. They are challenged by various anthropogenic stressors, including invasion by non-native grasses, which degrade habitat quality and alter ecosystem function. Sagebrush restoration efforts are being undertaken to improve habitat conditions to benefit a wide range of sagebrush-dependent species. Because birds are good indicators of habitat quality, monitoring avian metrics is an effective way to measure progress of sagebrush restoration. We compared avian community composition and individual species abundance among three sagebrush-steppe habitat types with varying degrees of invasion by non-native crested wheatgrass Agropyron cristatum at the Camas National Wildlife Refuge in eastern Idaho. Sagebrush-obligate birds, such as sage thrasher Oreoscoptes montanus and sagebrush sparrow Artemisiospiza nevadensis, were most abundant in sagebrush habitats with an understory of native grass. Community composition was similar between sagebrush habitats with native and non-native grasses, but quite different from bird communities occupying crested wheatgrass. HABPOPS, a conservation planning tool, predicts that restoration of crested wheatgrass sites to sagebrush in poor or fair condition will increase the density of sagebrush-obligate bird species. Taken together, these results suggest that restoration of crested wheatgrass near-monocultures back to sagebrush will improve habitat value for much of the bird community whether or not the understory can be converted to primarily native grasses, or a mix of natives and non-natives. Of the sagebrush bird species of concern, Brewer’s sparrow Spizella breweri occupied sagebrush habitats with native vs. non-native understory at similar abundances, and this species could serve as a metric of intermediate restoration success. However, sagebrush sparrow and sage thrasher, which were significant indicators of sagebrush with native grasses, will likely benefit most from full restoration of a native herbaceous understory. Grassland-obligate birds like horned lark Eremophila alpestris and grasshopper sparrow Ammodramus savannarum were most abundant at crested wheatgrass-dominated sites and may not benefit from restoration back to shrubland; managers should understand potential trade-offs.