Spatial demographic drivers differ from temporal drivers in two dabbling duck populations

Spatial variation in demography is an important consideration for the conservation of many wildlife populations. Comparisons across populations can elucidate different selective pressures that give rise to variability in life history strategy, or simply highlight differences and similarities in demographic drivers to inform conservation actions. Many duck populations in the Intermountain West of North America remain largely unstudied despite extensive research and monitoring within their core breeding range across the Prairie Pothole Region (PPR) of the United States and Canada. Using an integrated population model (IPM)-transient life table response experiment (tLTRE) framework, we evaluated differences in demographic drivers between the core breeding populations of mallards (Anas platyrhynchos) and gadwall (Mareca strepera) and peripheral populations in north-central Colorado, USA. We identified the demographic pathways through which population growth varied for both species and populations, and compared the specific drivers contributing to differences in realized population growth annually. Population growth rates for both mallards (λ_CO = 0.99, σ_CO = 0.22, λ_PPR = 0.90, σ_PPR = 0.05) and gadwall (λ_CO = 0.95, σ_CO = 0.16, λ_PPR = 0.95, σ_PPR = 0.09) averaged <1 from 2018 to 2024 in both populations. Our tLTRE results indicated that contributions to the variance in population growth rates over time were driven primarily by fecundity for mallards in both populations, and by gadwall in Colorado, but that survival of both juvenile and adult birds contributed relatively more in the PPR than in Colorado. Among gadwall, the PPR population exhibited low survival and high fecundity, whereas North Park birds exhibited the opposite. Additionally, survival of hatch-year birds was the primary contributor to variation in PPR population growth rates. These results emphasize the need to consider spatial variation in demographic drivers and suggest potential differences in targeted conservation for dabbling ducks across their distribution.