Common Raven Density and Greater Sage-Grouse Nesting Success in Southwest Wyoming: Potential Conservation and Management Implications (dissertation)
Jonathan B. Dinkins
Tags: sage-grouse, WLCI Related Publication
A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Wildlife Biology
"Declines in the distribution and abundance of greater sage-grouse ( Centrocercus urophasianus ; hereafter “sage - grouse” ) in western North America over the past century have been severe. The goal of my research was to increase the understanding of factors influencing where sage-grouse hens placed their nests, how common ravens ( Corvus corax : hereafter “raven” ) impacted sage-grouse nest success, and whether high raptor densities negatively impacted hen survival of sage-grouse. I compared raven and raptor densities at sage-grouse nest and brood locations to available habitat. I also assessed how sage-grouse positioned their nests and broods relative to proximity to man-made structures, forested and riparian habitat, and rough topography. While evaluating the effect of ravens on nest success of sage-grouse, I hypothesized that nest success of sage- grouse would be greater in areas where Wildlife Services lowered the density of ravens. Finally, I evaluated the effect of raptor densities, proximity to man-made structures and forested and riparian habitat, rough topography, and hen behavior on survival of sage- grouse hens.
Several studies on birds have shown that avoidance of predators and dangerous habitat can have dramatic effects on habitat use by prey species. Sage-grouse hens chose locations with lower raven and raptor densities, selected locations farther away from man-made structures and forested habitat, and used locations that were flatter. Depredation of sage-grouse nests can be an influential factor limiting their populations. I found that Wildlife Services decreased raven density, but I did not detect a direct improvement to sage-grouse nest success. However, sage-grouse nest success was 22% when ravens were seen near a sage-grouse nest and 41% when no raven was seen near a sage-grouse nest. Survival of adult female sage-grouse has been demonstrated to be the most important aspect of a sage-grouse’s life-cycle with respect to population growth. I found that sage-grouse hen survival was negatively related with golden eagle (Aquila chrysaetos) density when topography was flatter, proximity to man-made structures and forested habitat, and a hen’s nesting and brood-rearing status (i.e., whether the hen was incubating eggs for caring for chicks)."