SPATIALLY-EXPLICIT MODELING OF COMMON RAVEN DENSITY AND OCCURRENCE ACROSS SAGEBRUSH ECOSYSTEMS: IMPLICATIONS FOR GREATER SAGE-GROUSE REPRODUCTIVE SUCCESS

Shawn T. O'Neil; U.S. Geological Survey, Western Ecological Research Center; soneil@usgs.gov; Peter S. Coates, Brianne E. Brussee, David J. Delehanty, Pat Jackson, Kristy B. Howe, Lee Foster, Ann Moser

Anthropogenic subsidies often contribute to population increases in generalist predators. The common raven (Corvus corax) is a ubiquitous predator in sagebrush ecosystems and potentially contributes to reduced nest success and recruitment in greater sage-grouse (Centrocercus urophasianus). Ravens have expanded in distribution and abundance, in large part due to increased resource subsidies from human infrastructure and land-use activities. Yet, specific influential environmental covariates driving this expansion are still largely unknown. We quantified raven density and occurrence in Great Basin sagebrush ecosystems during 2007-2016, using >15,000 point-count surveys to estimate detection probability and account for imperfect detection. We used Bayesian hierarchical occupancy models to estimate probability of raven occurrence, conditional on natural and anthropogenic landscape covariates. Raven occurrence across all surveys was ~0.80, and raven density commonly exceeded 0.50 ravens per square kilometer. Raven occurrence was greatest at low elevations with open cover types and greener vegetation and was strongly associated with agriculture, road densities, landfills, and roadside rest areas. Raven detections also increased when livestock were present. Our results provide empirical evidence that anthropogenic subsidies drive widespread raven occurrence throughout the Great Basin, enabling better understanding of potential interactions between raven and sage-grouse populations across broad landscapes.

Ecology and Conservation of Birds II