Decades of anthropogenic development and associated subsidies within the western U.S. has contributed to common raven (Corvus corax, raven) populations that exceed pre-subsidy ecoregion-specific carrying capacities. Consequently, ravens are implicated in declines of species of conservation concern. The juvenile life-stage (0–10 yr) of the California endangered and federally threatened Mojave desert tortoise (Gopherus agassizii, tortoise) has been shown to be exceptionally susceptible to raven predation. Using 274 variable-radius point counts, a database of 724 nesting raven territories, and 77 tortoise decoy trials, we evaluated the viability of tortoise-raven relationships under variable measures of contact. Specifically, juvenile tortoise decoy “survival” was modeled as a function of raven density and distance to the nearest raven nest. Annual survival was derived by adjusting decoy exposure to reflect natural activity patterns. Our model predicted that tortoise populations exposed to raven densities >0.89 raven km^2, at distances <1.72 km from a raven nest exhibit unstable inter-generational population structure, as excess mortality outpaced natural survival and reproduction. These results demonstrate that estimates of raven density, distance to nearest previously active raven nest, and decoy “survival” rates can inform development of a tortoise-raven viable conflict threshold. These findings are preliminary, and are provided for timely science communication and are subject to change.

Common raven (Corvus corax; raven) populations are increasing and expanding across North America, affecting ranching and agriculture, human health, and sensitive species conservation. Therefore, managers need science-driven adaptive management plans for ravens that support multiple management goals. We developed the Science-based Management of Ravens Tool (SMaRT), a web-based application that guides managers through a tiered adaptive management framework to develop a customized plan for their area of interest and management objectives. Within the SMaRT interface, users can: (1) interact with pre-loaded maps of raven occurrence and density and define their areas of interest within the Great Basin to delineate proposed management sites; (2) enter site-level density estimates from distance sampling methods or estimate raven densities using a rapid assessment function or pre-existing density surface; (3) compare site-level density estimates to an ecological threshold; and (4) produce a tiered list of management options. The SMaRT supports decision-making by operationalizing scientific products for raven management and facilitates realization of diverse management goals addressing raven overabundance and expansion. We illustrate the use of the SMaRT using an example of greater sage-grouse (Centrocercus urophasianus) conservation efforts within the Great Basin. Findings are preliminary, are provided for timely science communication, and subject to change.

The western U.S. has experienced steady increases in common raven (Corvus corax) abundance over the previous 50 years. Raven population increases likely presage heightened impacts to the reproductive success of some sensitive prey species. For example, negative influences to nesting sage-grouse have been observed where raven density exceeded ~0.40 raven(s) km^2, a potential ecological threshold. Therefore, monitoring changing raven densities is crucial to inform adaptive management frameworks for sensitive species. However, obtaining reliable estimates of raven density can be data- and resource-intensive. We developed a rapid protocol to assess site-level density based on observed numbers of ravens per survey over a specified study site. Specifically, we used regression analysis to investigate the relationship between density estimates from robust distance sampling methods and ravens per survey, which revealed a strong correlation (R2 = 0.86). We used this estimated relationship to serve as a correction factor on the raven index, accounting for detection probability of ravens within sagebrush ecosystems, and bypassing the need to conduct distance-based methodologies in similar geographic regions. While the more robust distance sampling is preferred, this method provides a reliable approximation for informing management when faced with resource limitations. Findings are preliminary and provided for timely science communication.

Decades of scientific evidence reveal common raven (Corvus corax; raven) populations are increasing and expanding across their geographic range. Concomitant elevated predation rates in threatened and endangered avian species during nesting periods may hamper species recovery. We conducted an extensive literature review to identify knowledge gaps and synthesize environmental features which support raven population growth. Raven occurrence, demographic results, and resource use appeared 31, 21, and 17 times, respectively. We identified 13 explanatory covariates regularly used to explain variation in raven ecological processes, including vegetation, human settlement, recreation, and linear rights-of-way. We explored impacts of raven predation on nests and young of sensitive avian species using the “Raven Impact Index” (RII), a species-specific index that incorporates species demographic rates, abundance of ravens within each sensitive species’ breeding range, and the degree of overlap between raven and prey distributions. We found evidence of nest predation on 8 sensitive avian species, and suspected nest predation on 1 additional species. The RII varied among species, with greater sage-grouse (Centrocercus urophasianus) having the highest relative impact values, followed by snowy plover (Charadrius nivosus nivosus). Our species RII can help inform management decisions to mitigate the negative effects of raven predation of sensitive avian species.

Predation by subsidized common raven (Corvus corax; raven) populations is linked to population declines of several sensitive species. Ecosystem managers seek strategies for mitigating the adverse effects of raven predation where unsustainable predator-prey conflicts exist. We present three case studies examining how manipulating reproductive success of ravens influences demographic rates of two sensitive prey species. These studies examine impacts of removing raven nests or oiling raven eggs on nest survival of greater sage-grouse (Centrocercus urophasianus; sage-grouse) in Wyoming and the Great Basin as well as survival of juvenile Mojave desert tortoises (Gopherus agassizii; tortoise) in the Mojave Desert using tortoise decoys. Initial trial years from all three studies were consistent in finding improved vital rates associated with the application of strategies for reducing reproductive success of ravens. Raven nest removal resulted in increased nest survival of sage-grouse within treatment areas where predation by ravens was the primary cause of nest failure. Additionally, nest survival of sage-grouse and survival of juvenile tortoise decoys was higher following raven egg-oiling across six treatment areas. These findings inform raven reproduction management practices as important tools for conserving wildlife. Findings are preliminary and provided to meet the need for timely best science.