Natal origins of Mallards harvested in the Atlantic Flyway of North America: implications for conservation and management

Appropriate management and conservation of migratory species requires knowledge of connectivity between natal or breeding sites and stopover or wintering sites. For game species, such as waterfowl, knowledge of source areas that produce juveniles, which are available for harvest in the autumn-winter, is of considerable interest. External markers have long been used in mark-recapture studies to identify breeding grounds of waterfowl. However, this approach is biased toward regions of marking effort and is logistically difficult in remote locations. Harvest management of Mallards (Anas platyrhynchos) in the U.S. portion of the Atlantic Flyway has assumed that the majority of harvested birds in the U.S. were produced there. We tested this assumption by inferring regions of natal origins of juvenile Mallards (n = 1254) harvested during the 2018–2019 and 2019–2020 hunting seasons in all states in the Atlantic Flyway using stable-hydrogen isotope analyses of breeding-ground grown feathers (δ²Hf). We created a species-specific feather isoscape and applied a Bayesian assignment approach to identify probable regions of origin. We determined 64% of our sample had δ²Hf consistent with origins in Canada versus the U.S. Our data suggested all states harvested Mallards that had origins from the U.S. and Canada throughout their entire hunting season. Our results contrast with long-term breeding population estimates which suggest the majority of breeding pairs of eastern Mallards occur in the U.S. We recommend further investigation into reasons for disparities in national natal origins of harvested Mallards.