A RAPID ASSESSMENT FUNCTION TO ESTIMATE COMMON RAVEN POPULATION DENSITIES: IMPLICATIONS FOR TARGETED MANAGEMENT
|Brianne E Brussee; U.S.Geological Survey, Western Ecological Research Center; email@example.com; Peter S. Coates, Shawn T. O’Neil, Seth J. Dettenmaier, Pat J. Jackson, Kristy B. Howe, David J. Delehanty
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.