Top-down effects of raptor predation on northern bobwhite.

Understanding how predators affect prey species is a central endeavor in applied ecology. Game birds are a culturally and economically important group of birds throughout the world. Specifically, northern bobwhite (Colinus virginianus) is an imperiled game bird native to North America that has declined precipitously over the past 65 years. Concurrently, raptor populations increased substantially as a result of pesticide bans and legal protections. However, relationships between raptors and bobwhites are not well-understood because of limited long-term data. We analyzed long-term raptor survey and bobwhite survival datasets from 2008 to 2018 to determine if oscillations in raptor abundance affected bobwhite survival. We used a novel open multi-species dynamics hierarchical distance sampling model to estimate the abundance of raptors. We used a known-fate survival model to determine if variation in raptor abundance affected bobwhite survival. We had multiple working hypotheses regarding biological relationships between raptor abundance and bobwhite survival. Raptors affected bobwhites in every biological season but were more influential in the breeding season and late winter supporting the notion of bobwhite behavior and raptor migration were driving observed patterns. Our results suggest that even in areas with abundant habitat, predators exert top-down influences on vital rates suggesting similar or greater influences on populations under poor habitat conditions.