Climate and Other Human Causes of Spatial Variation in Mallard Mortality and Population Dynamics

Wildlife population dynamics change across time and space, but few studies use formal spatiotemporal statistical models to understand these patterns. The population distribution of mallards (Anas platyrhyncos) in the Prairie Pothole Region of central North America (PPR) has shifted dramatically over the past several decades as agricultural intensity and climate have changed. We examined spatiotemporal variation in survival, natural mortality, and harvest mortality rates for mallards in the PPR from 1974 to 2023 using intrinsic conditional autoregressive models in a Bayesian framework. There was substantial variation over time and space for all demographic rates, and relationships between mortality and habitat variables varied by age and sex cohort. Specifically, environmental relationships indicate that habitats with less agricultural activity and more wetlands decrease survival via increased natural mortality driven by reproductive risks. We also found a worrying trend: females exhibited declining survival probabilities since the late 1980s and early 1990s. Our analyses demonstrate major variation in survival rates of a well-studied organism across an environmental gradient, reveal subtle but critical differences relative to inference obtained from pooled data, and provide a clear roadmap to future research that can inform spatially explicit conservation and management goals.