Expanding human enterprise across remote environments impacts many wildlife species, including sage-grouse (Centrocercus urophasianus), an indicator species whose decline is at the center of national conservation strategies and land use policies. Anthropogenic resources provide subsidies for generalist predators, potentially leading to cascading effects on sensitive prey species at lower trophic levels. In semi-arid western ecosystems, common ravens (Corvus corax) are expanding in distribution and abundance, and may be negatively affecting sage-grouse reproductive success at broad spatial scales. Ravens are a common predator of sage-grouse nests, and potentially prey on chicks as well. This research aimed to address the growing demand for information about potential interactions between subsidized predators (i.e. ravens) and species they prey upon. More specifically, our objectives were to disentangle natural and anthropogenic influences on raven occurrence at a landscape scale, and provide spatially explicit models and scientific products to help inform decisions regarding the management of ravens and conservation of sage-grouse. Using Bayesian hierarchical occupancy models, we mapped the broad-scale occurrence of common ravens as a function of natural and anthropogenic landscape covariates using more than 15,000 point count surveys performed during 2007-2016 within the Great Basin region, USA. In addition, we provide spatially explicit model-predicted surfaces that integrate anthropogenic and natural effects on raven occurrence with underlying information about breeding sage-grouse concentration areas. This approach meets several objectives with respect to the conservation and management of sage-grouse and ravens. First, we established landscape-level patterns of predicted raven occurrence across the Great Basin region. Second, we determined associations between anthropogenic and natural features, and the broad-scale occurrence of ravens. Third, we identified regions where A) high predicted raven occurrence overlapped with breeding sage-grouse concentration areas, and B) areas where raven occurrence was strongly influenced by anthropogenic (vs. natural) variables overlapping with breeding sage-grouse concentration areas. This approach can guide management decisions where subsidized predators overlap sensitive prey habitats. For example, management applications could focus on reducing raven access to anthropogenic subsidies in areas where elevated raven occurrence coincides with breeding sage-grouse concentration areas and appears to be largely driven by anthropogenic factors, while prioritizing habitat improvements for sage-grouse elsewhere. Our approach is applicable to other species where widespread survey data are available.
These data support the following publication: O'Neil, S.T., Coates, P.S., Brussee, B.E., Jackson, P.J., Howe, K.B., Moser, A.M., Foster, L.J., and Delehanty, D.J. 2018, Broad-scale occurrence of a subsidized avian predator: reducing impacts of ravens on sage-grouse and other sensitive prey. Journal of Applied Ecology