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9/25/2018 | 11:05 AM - 11:20 AM | Reduced Nest Success in Sage-Grouse is Associated with Increases in Raven Density and Occurrence in Nevada and California, USA | Eccles Conference Center Auditorium

Reduced Nest Success in Sage-Grouse is Associated with Increases in Raven Density and Occurrence in Nevada and California, USA

Anthropogenic subsidies often contribute to population increases in generalist predators. The common raven (corvus corax, hereafter, raven) is an ubiquitous predator within sagebrush ecosystems, and may contribute 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. We used >15,000 point count surveys to estimate raven density and probability of occurrence within Great Basin sagebrush ecosystems during 2007–2016, using distance sampling and Bayesian hierarchical occupancy models. We then linked raven density and occurrence along with other environmental covariates to variation in sage-grouse nest survival in Nevada and California using a Bayesian frailty modeling approach. Raven density commonly exceeded 0.40 ravens per km2 at study sites across the study area. Elevated raven densities were associated with reduced sage-grouse nest survival, even when accounting for local variation in sagebrush and perennial grass cover. Raven occurrence rates exceeded 80% on average and were typically greatest at lower elevations with open cover types, greener vegetation, and greater availability of anthropogenic resource subsidies (e.g., % agriculture and road density). Our results provide new empirical evidence that elevated raven density has adverse effects on sage-grouse reproductive success at broad spatial scales, and can diminish the fitness benefits associated with favorable vegetation structure within sagebrush ecosystems. These findings are preliminary and provided to meet the need for timely best science.

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Presenters/Authors

Peter Coates (), US Geological Survey, pcoates@usgs.gov;