Distribution, movements and habitats of sage grouse Centrocercus urophasianus on the Upper Snake River Plain of Idaho: changes from the 1950s to the 1990s

The sage grouse Centrocercus urophasianus population level on the Upper Sna ke River Plain of Idaho has declined significantly over the past 40 years. We investigated migration patterns and seasonal ranges of these birds to co mpare to patterns from the 1950s and 1960s. Furthermore, we examined landsc ape changes that occurred between 1975 and 1992. Migration patterns have no t changed since the 1950s. The grouse currently migrate up to 125 km and us e an annual population range of at least 2,764 km(2). The major landscape c hange since 1975 that occurred in sage grouse habitat was a decline in the total amount of winter range. Between 1975 and 1992, 29,762 ha of sagebrush Artemisia spp. rangeland were converted to cropland, a 74% increase in cro pland. Regression analysis suggested a relationship between sagebrush habit at loss and grouse population decline (R-2 = 0.59, P = 0.002). Approximatel y 1,244 km(2) of privately-owned sagebrush on the study area could potentia lly be converted to cropland, which we predict would have serious negative implications for the sage grouse population.