Breeding ecology of greater sage-grouse in southwestern Montana

Abstract

The greater sage-grouse (Centrocercus urophasianus; hereafter: sage-grouse) is an umbrella species that needs large intact tracts of sagebrush habitat with habitat requirements that represent the needs of many other species found in the sagebrush biome of the American West. Much of the information collected to date on sage-grouse is from low-elevation, homogenous, landscapes, leaving information gaps for topographically complex, high elevation locations within the sage-grouse range. In this dissertation, I assess the following aspects of the breeding ecology of sage-grouse: 1) how females select nest and brood sites based on sagebrush type, along with livestock grazing features and other biotic and abiotic characteristics; 2) the influence of female nest-site selection on nest-survival outcomes; 3) experimentally derived isotopic discrimination values in domesticated gallinaceous birds as an estimation method for nutrient allocation strategies in wild sage-grouse; and 4) the degree to which females allocated nutrients from winter habitats for formation of offspring by comparing females nesting in southwest vs. central Montana. Based on the research, I found evidence that: 1) sage-grouse avoid a high-elevation sagebrush type that is the most common type in my study region and instead select for intermediate- or low-elevation sagebrush types for both nesting and brood rearing, 2) sage-grouse broods selected sites away from low-lying mesic areas and near ridgelines on upper slopes with south-facing aspects and sites further from cattle paths, 3) nest survival was (a) higher for nests placed away from fence lines, (b) lower in areas with more cow pies and taller dead grass, and (c) higher in areas with increased living grass cover, and 4) females from southwest Montana and in the high-elevation sagebrush type primarily allocated nutrients from winter habitats, whereas females from central Montana and in the low-elevation sagebrush type primarily allocated nutrient sources from spring habitats for offspring formation. My findings highlight a unique breeding strategy for sage-grouse residing in high-elevation sagebrush landscapes. Results described herein will allow managers in southwest Montana, and other regions in the northern Rocky Mountains, to better manage sage-grouse and sage-grouse habitats.