Migratory patterns of mallards in eastern North America as revealed from band‐recovery data

Abstract

AbstractMallard (Anas platyrhynchos) distributions have changed in North America over the last century because of altered habitat and the direct augmentation of eastern populations with captive‐bred game‐farm mallards in the early twentieth century. Geographical overlap between wild and game‐farm individuals has resulted in interbreeding, with North American mallard populations now ranging from largely wild to more feral and feral x wild hybrids. How changing genetic integrity of North America's mallards translates behaviorally remains unknown. We analyzed band‐recovery data from 1949–2019 to estimate emigration rates and geographic distributions of mallards to understand whether the admixed genetic heritage of mallards in North America's Mississippi and Atlantic flyways resulted in variable autumn distributions. We included American black ducks (Anas rubripes) as a flyway migratory comparative, and analyzed datasets partitioned by flyway and major international space (i.e., Canada vs. United States). We present results that correspond to the hypothesis that western mallard populations of the 1950s expanded eastward and were the precursor populations of mallards in the Canadian provinces of the Atlantic Flyway, while mallards of the Atlantic Flyway in the United States showed substantially differing patterns. Specifically, we estimate that since 1990, approximately 23% of banded mallards on the United States side of the Atlantic Flyway are annually recovered in the Mississippi Flyway as compared to about 5% of those banded in Canadian provinces of the Atlantic Flyway. Given that mallards from the United States side of the Atlantic Flyway are considered a feral × wild hybrid swarm, annual westward emigration of 23% of these mallards is concordant with increasing prevalence of game‐farm mallard molecular variation detected in the Great Lakes and mid‐continent mallard populations. Our results provide insight into potential means for the movement of game‐farm molecular variation from the Atlantic into the Mississippi Flyway, and suggest that the effect of these mallards on the genetic integrity and future adaptive capacity of mallard populations in the Mississippi Flyway requires attention and consideration in future management decisions.