Use and selection of nesting habitat by sage grouse in Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h128nj71f

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  • Sage grouse (Centrocercus urophasianus) populations in Oregon declined during the past 30 years as a result of impaired productivity. The western subspecies (C. u. phaios) was listed as a candidate for threatened and endangered status by the Department of the Interior in 1985 because of declines in Oregon and Washington and extirpation from British Columbia. Little information is available about habitats used for nesting in the range that encompasses the western subspecies. This study was conducted on two areas in southeastern Oregon: Hart Mountain National Antelope Refuge and Jackass Creek. Hart Mountain represented some of the best habitat in the state and Jackass Creek was typical of much of the remaining sage grouse range in Oregon. These areas had long term differences in sage grouse abundance, approximately 2.5 birds/km² at Hart Mountain and 1.5 bird/km² at Jackass Creek. The objectives of this study were to determine selection for cover types and habitat components within cover types used for nesting and to compare habitat use and selection between successful and unsuccessful nesting hens. Comparisons were made within and between study areas. Availability and selection of cover types differed between study areas. Sage grouse selected mountain big sagebrush (Artemisia tridentata vaseyana) stands at Hart Mountain and the mixed sagebrush cover type at Jackass Creek. Nest success was greater in cover types used selectively by hens. Habitat components were measured at 47 and 51 nest sites at Hart Mountain and Jackass Creek, respectively. At nests, sage grouse selected medium height shrubs (40-80 cm) with greater canopy cover than was present either adjacent to the nest or random locations. Grass cover was greater at nests than at random sites in cover types used selectively. Amount and type of grass cover were the only habitat components that differed between successful and unsuccessful nests. In mountain big sagebrush stands, 2 grass genera (Elymus, sp. and Festuca spp.) represented 81% of grass cover at successful nests and only 1% at unsuccessful nests. These genera were the tallest grasses occurring at either study area. Greater grass cover in association with tall grass at nest sites likely provided increased nest concealment from predators and resulted in greater nest success. The relationship between the grass component of habitat and sage grouse nesting success implies that removal of grass may negatively influence sage grouse productivity.
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