We are using naturally occurring stable isotopes of hydrogen (δ2H), nitrogen (δ2N),  carbon (δ13C), and sulfur (δ34S) to interpret the natal (hatch year) and molting (after hatch year) origin of mallards.  We are testing stable isotope values in flight feathers which are completely molted near nesting sites immediately following the breeding season.  We will assess the relative contribution of California and northern derived mallards to hunter harvest at two hunting areas in California (Sacramento National Wildlife Refuge and Conaway Ranch Duck Club) and determine if the proportion of harvested mallards that originate from California declines over the course of the hunting season as more northern migrants arrive during winter.  Additionally, we are assessing the prevalence of avian influenza infection between locally derived California mallards and those breeding at northern breeding grounds.

To complement the stable isotope approach, we also will complete a derivation of Pacific Flyway mallards using band recovery data and, specifically, the relative contribution of California mallards to the Pacific Flyway harvest as the proportion of California mallards within the Pacific Flyway has increased over time.