An ecological cascade links climatic variability to avian irruptions and zoonotic salmonellosis outbreaks.

Salmonellosis is a common bacterial infection that can lead to severe illness and death in humans as well as domesticated and wild animals. In bird populations, salmonellosis outbreaks are temporally irregular but occur simultaneously across large spatial extents, frequently leading to widespread avian mortality with occasional spillover to humans. Here, we test the hypothesis that avian salmonellosis epidemics result from a cascade of ecological processes triggered by climate variability in coniferous forests. Building on well-evidenced ecological mechanisms, we find strong evidence for multiyear causal links between temperature cues that drive substantial "boom-bust" cycles in tree cone production across North America, the subsequent irruptions of seed-eating birds, and, finally, the eventual occurrence and severity of avian salmonellosis outbreaks in the United States. By using an integrated, multilevel Bayesian statistical model as a predictive tool to forecast future bird irruptions and disease outbreaks, we demonstrate that our methods can be employed as an early warning system for future epidemics, potentially mitigating outbreak severity among birds and lowering the risk of zoonotic spillover events by encouraging measures such as the temporary cessation of bird feeding ahead of high-risk periods.