Relationship between habitat changes and productivity of sage grouse at Hart Mountain National Antelope Refuge, Oregon

Graduation date: 1999Presentation date: 1998-11-23From 1987-1997, Oregon State University conducted studies at Hart Mountain National Antelope Refuge (HMNAR) to better understand the relationship between grouse productivity and key habitat components. Early studies indicated sage grouse habitat preference and reproductive success were related to particular forbs (including legumes and milky juice composites) and structural characters of native bunchgrasses. After early studies (1989-1991), climatic conditions and land-use practices changed at HMNAR. Livestock grazing was eliminated from HIVINAR in 1991 and during 1989-1997 there was an upward trend in crop year precipitation (total precipitation from 1 September - 30 June). Because of these changes a study was initiated to test the\ud relationships inferred from earlier studies. Two sample periods (1989-1991 and 1995-1997) were compared to determine the collective effect of increased crop year precipitation and reduced livestock grazing on key habitat components in 4 cover types and on sage grouse productivity measures. Habitat sampling during 1995-1997 indicated that spring and summer forb cover and residual grass cover increased in most cover types compared with 1989-1991. During the earlier studies at Hart Mountain, 65% of radio-marked hens initiated nests, 22% of nesting hens were successful, and 33% of successfully nesting hens recruited chicks into the 1 August population. During 1995-1997, 99% of radio-marked hens initiated nests, 37% of nesting hens were successful, and 39% of successfully nesting hens recruited chicks into the 1 August population. Increased nest initiation rates during 1995-1997 compared with 1989-1991 were concordant with increases in spring forb cover. Greater availability of spring forbs at Hart Mountain probably provided hens more opportunity to become physiologically prepared to attempt nesting. Nest success was greater during 1995-1997 compared with 1989-1991. Corresponding increases in nest success and residual grass cover were probably a result of a higher probability of hens initiating nests in cover that provided enhanced nest concealment. Brood success and summer forb availability were greater during 1995-1997 compared with 1989-1991. Increased forb availability probably allowed hens to remain in upland brood-rearing habitats longer (thereby providing a greater dispersion of broods) and reduced movements by hens with broods, which resulted in increased chick survival. This study confirmed the importance of spring forbs, residual bunchgrass, and summer forbs to sage grouse productivity, on a landscape scale and grouse population basis. I concluded these habitat components are key to sage grouse reproductive success