Additive and interactive effects of wildfire and Corvus corax (Common Raven) density on Centrocercus urophasianus (Greater Sage-Grouse) nest site selection and survival

Abstract Habitat loss and fragmentation following wildfire and changes to predator communities are contributing to population declines of Centrocercus urophasianus (Greater Sage-Grouse; hereafter, sage-grouse) in North America. Specifically, large-scale wildfires and Corvus corax (Common Raven; hereafter raven) densities depress sage-grouse nest survival and influence nest site selection. However, little is known about the additive or multiplicative complexities of raven density on sage-grouse nests within wildfire-affected landscapes. We examined the effects of wildfire and raven density on sage-grouse nest site selection and nest survival using resource selection functions and Cox proportional hazards models, respectively. Nest site selection was positively associated with increasing cover of sagebrush, annual and perennial herbaceous plants, and closer proximity to leks and to areas burned within the last 10 yr. Nest site selection was negatively associated with increasing topographic ruggedness, road density, and closer proximity to agricultural areas and transmission lines. Raven density was not informative for nest site selection. Nest survival was positively associated with increasing shrub cover and later nest initiation dates, and negatively associated with increasing road density, northerly aspects, closer proximity to areas burned within the last 5 yr, and raven density. Our evaluation of high- and low-risk nesting habitat was primarily influenced by proximity to agricultural lands, roads, and transmission lines, each of which are known to support raven populations and fragment sage-grouse nesting habitat. Our derived nesting habitat risk surfaces indicated that certain study areas had larger amounts and more connected low-risk habitat compared to others, suggesting patch size and connectivity of nesting habitats may be important factors for nest survival. Additionally, mapping of risk surfaces for nesting habitat allows local management actions to target areas where nests are likely to occur, but survival rates are low, reducing ecological traps on the landscape.