Restoration Potential: There is a high probability of sustaining thrashers wherever native sagebrush habitats are maintained with high shrub vigor, tall shrubs, horizontal shrub patchiness, and an open understory of bare ground and native bunchgrasses and forbs. However, sagebrush habitats can be very difficult to restore once invaded by cheatgrass and other noxious non-natives, leading to an escalation of fire frequency and fire intensity that permanently converts shrub-steppe to annual grassland. There are no simple prescriptions for eliminating cheatgrass, medusahead, and other noxious weeds. Restoration of native vegetation at severely degraded sites may be expensive and require long-term dedication that includes continuous weed control, control of disturbances, and repeated reseeding of sagebrush and native understory plants (see Paige and Ritter 1998).
Preserve Selection and Design Considerations: In Idaho, Knick and Rotenberry (1995) found the probability of occupancy increased with increasing homogeneity of the surrounding habitat within a 1-kilometer radius, and with greater percent sagebrush cover. Also, positively correlated with shrub patch size, and negatively correlated with disturbance.
Management Requirements: Will thrive where sagebrush habitat is maintained, with shrubs occurring in tall, clumped, and vigorous stands. Prefers tall shrubs for nesting or song perches and low percent grass cover to facilitate foraging on ground.
SAGEBRUSH CONTROL: Sensitive to sagebrush control; abundance declines with the loss of shrubs. In Wyoming, abundances lower on 22-year old herbicide-treated site (shrub cover approximately 15 percent) than on untreated site (shrub cover > 35 percent), and was not present on 9-year old burned site (shrub cover < 10 percent) (Kerley and Anderson 1995). Castrale (1982) found thrashers persisting in sagebrush islands with tall shrubs within a burned site (10.2 percent shrub cover in islands; max height = 59.0 centimeters), but found no territories within the burn itself (0.0 percent shrub cover), or within plowed (11.8 percent shrub cover; max height = 44.8 centimeters) or chained (5.8 percent shrub cover; max height = 41.4 centimeters) sites reseeded with grasses. In southern Oregon, densities declined following herbicidal spraying and removal of sagebrush and reseeding with crested wheatgrass, where sagebrush cover decreased from 19-24 percent to 4-12 percent (Wiens and Rotenberry 1985). In Idaho, crested wheatgrass seedings did not support sage thrashers (Reynolds and Trost 1980).
FIRE: Fire that kills and completely removes sagebrush cover over large areas would be detrimental. In Idaho, densities remained stable over three years following a prescribed burn that left 50 percent of the sagebrush in a mosaic pattern of burned and unburned sage (sagebrush cover was reduced from an average 21 percent to an average 12 percent) (Petersen and Best 1987).
GRAZING: Not likely affected where livestock grazing regime maintains native vegetation composition and densities. Reported responses to grazing are generally positive, particularly where grazing increases sagebrush cover. In Nevada, positive response to heavy grazing reported in greasewood and Nevada bluegrass habitats (Page et al. 1978, cited in Saab et al. 1995). Reynolds (1980, cited in Saab et al. 1995) reported a positive response to moderate grazing in big sage. In Idaho, Reynolds and Trost (1980) found more nests in sheep-grazed sagebrush with denser cover (14 nests; sage cover = 25 percent) than in ungrazed sagebrush (8 nests; sage cover = 17 percent). Nest success was slightly higher on a site grazed by sheep in spring (big sagebrush cover = 25 percent) than on an ungrazed site (big sagebrush cover = 22.5 percent; Reynolds and Rich 1978).
GRASS COVER: Abundance is negatively correlated with grass cover (Rotenberry and Wiens 1980). Not present in crested wheatgrass plantings (Reynolds and Trost 1980). Primarily a ground forager, foraging success may be reduced by continuous cover of crested wheatgrass, cheatgrass or other non-native grasses (Paige and Ritter 1998).
PESTICIDES: In southern Idaho shrub-steppe, aerial application of Malathion (applied at 585 grams per hectare ultra-low volume, in single-day applications in each of two successive years) reduced food base; nestling foot length was smaller on treated site although there were no observable direct effects on nestling survival (Howe et al. 1996).
Management Research Needs: Understanding of minimum patch sizes, fragmentation effects, spatial juxtaposition of habitat patches and other aspects of landscape ecology needed. Study of the effects of grazing and impact of predation in relation to habitat changes would be useful. Further study of direct and indirect impacts of herbicides and pesticides typically used in sagebrush shrub-steppe rangelands needed. Study of factors that may be differentially affecting sagebrush bird populations might shed light on why sage thrashers appear stable while Brewer's sparrows are widely decreasing (e.g., brood parasitism, effects on wintering grounds, productivity).
Biological Research Needs: Many aspects of biology and ecology are still unknown. Study of migration and wintering ecology and habitat relations needed. Further details needed on site fidelity, territory size, interspecific interactions, juvenile dispersal, diet and metabolism, social behavior in relation to breeding or wintering, life span and survivorship, and response to climatic changes on breeding or wintering sites.
