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Sagebrush Steppe Restoration and Obligate Passerines
Steven T. Knick and Steven E. Hanser, USGS Forest and Rangeland Ecosystem Science Center, 970 Lusk Street, Boise, ID
Declining numbers of Greater Sage-Grouse (Centrocercus urophasianus) have focused management and conservation actions on restoring sagebrush habitats to maintain or enhance populations and their distribution. In addition to sage-grouse, other species of small passerine birds also depend on sagebrush and have been affected by the widespread loss and alteration of habitat. Brewer’s Sparrows (Spizella brewerii) have declined at an annual rate of >3%/year across their range. Sage Sparrows (Amphispiza belli) and Sage Thrashers (Oreoscoptes montanus) have experienced local population declines and are considered species of conservation concern in all states within their range. As a group, birds living in grass- and shrublands are declining faster than species in other habitats. Reversing these downward trajectories will be difficult because of the complexity of processes in shrubland ecosystems, time-lags in bird responses, and the magnitude and variety of stressors across large areas. In addition, the benefit to the suite of other bird species from restoring habitats based on requirements for sage-grouse remains unknown. For small passerines, the composition of sagebrush habitats and their arrangement in the landscape are important factors when selecting a breeding range. Different habitat requirements among species allow the wide variety of habitats across the sagebrush biome to be fully occupied. At larger spatial scales, sage-grouse use numerous habitat configurations within their home ranges. Consequently, the variety of habitats included under the sage-grouse umbrella potentially spans a large portion of the total gradient used by the smaller shrubland passerines. Although a single-species focus on sage-grouse might benefit the suite of other obligates, the full range of habitat variation is important in restoring sagebrush communities. If management focuses on only a narrow set of prescribed parameters to optimize sage-grouse populations, the umbrella contracts and benefits to other species are reduced.