Habitat relationships of great gray owl prey in meadows of the Sierra Nevada Mountains

The great gray owl (Strix nebulosa) has been a state endangered species in California since 1980 because of low population size. Annual productivity of the great gray owl in California is thought to be largely dependent on vole (Microtus spp.) and pocket gopher (Thomomys spp., hereafter gopher) abundance, yet the factors influencing these prey populations have not been thoroughly investigated. The abundance of voles and gophers has been influenced by vegetation and cattle grazing in other regions, and many meadows are grazed within the breeding range of the great gray owl in the Sierra Nevada Mountains of California. Therefore I evaluated the influence of vegetation and cattle grazing on great gray owl foraging habitat by quantifying vole abundance, gopher abundance, and vegetative conditions in grazed and ungrazed meadows during owl nestling and fledgling stages. I surveyed 17 grazed and 15 ungrazed meadow sites in 2010, and 19 grazed and 19 ungrazed meadow sites in 2011. I found that vole presence was positively associated with plant sward height and corn lily (Veratrum californicum) dominance; vole abundance was weakly negatively associated with cattle grazing. Gopher abundance was negatively associated with site wetness, and positively associated with stem density, the frequency of forb presence, cattle grazing, and the dominance of corn lily. When managing meadows for great gray owl conservation, cattle grazing and vegetation should be monitored to accommodate the habitat relationships of both voles and gophers. Management of owl prey may be most efficient by prioritizing wet meadow sites for voles since gophers were not likely to be abundant in wet sites, and vole abundance has been correlated with moist soils in other studies. Therefore particularly in areas with moist soils, I recommend maintaining plant sward height commensurate with the habitat relationships of voles found in this study.