Factors Affecting Nest Survival of Greater Sage‐Grouse in Northcentral Montana

Abstract

Abstract: We studied greater sage‐grouse (Centrocercus urophasianus) in northcentral Montana, USA, to examine the relationship between nest success and habitat conditions, environmental variables, and female sage‐grouse characteristics. During 2001‐2003, we radiomarked 243 female greater sage‐grouse, monitored 287 nests, and measured 426 vegetation plots at 4 sites in a 3,200‐km2 landscape. Nest survival varied with year, grass canopy cover, daily precipitation with a 1‐day lag effect, and nesting attempt. In all years, daily survival rate increased on the day of a rain event and decreased the next day. There was temporal variation in nest success both within and among years: success of early (first 28 d of nesting season) nests ranged from 0.238 (SE = 0.080) in 2001 to 0.316 (SE = 0.055) in 2003, whereas survival of late (last 28 d of nesting season) nests ranged from 0.276 (SE = 0.090) in 2001 to 0.418 (SE = 0.055) in 2003. Renests experienced higher survival than first nests. Grass cover was the only important model term that could be managed, but direction and magnitude of the grass effect varied. Site, shrub and forb canopy cover, and Robel pole reading were less useful predictors of nest success; however, temporal and spatial variation in these habitat covariates was low during our study. We note a marked difference between both values and interpretations of apparent nest success, which have been used almost exclusively in the past, and maximum‐likelihood estimates used in our study. Annual apparent nest success (0.46) was, on average, 53% higher than maximum‐likelihood estimates that incorporate individual, environmental, and habitat covariates. The difference between estimates was variable (range = +8% to +91%). Management of habitats for nesting sage‐grouse should focus on increasing grass cover to increase survival of first nests and contribute to favorable conditions for renesting, which should be less likely if survival of first nests increases.