Breeding and Wintering Ecology of Waterfowl

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Western U.S. wetlands provide critical habitat for wintering and breeding waterfowl in California. WERC's Dr. Josh Ackerman is working toward collecting data to understand factors influencing duck nest success, to improve and restore breeding habitat for resident duck populations in California, and understand composition of predator communities. To learn more about how USGS WERC is implementing best management practices throughout California, click on the next tab.


Waterfowl Breeding Ecology

Predators are the primary cause of duck nest failure and can significantly limit recruitment, potentially below replacement levels for mallards and other waterfowl species.  Consequently, waterfowl research and management strategies have focused on understanding which factors influence nest success and ways of improving nest success.  Among the factors thought to influence nest success are the composition of the predator community, predator abundance, density of nesting cover, attributes of the landscape, hen age, hen behavior, availability of alternate prey, and nest density.  Despite advances in understanding factors influencing duck nest success in North America, it remains unclear which management strategies can be effectively implemented to benefit nesting ducks.

WERC duck nest in Suisun Marsh

(Credit: Josh Ackerman, USGS WERC. Public domain.)

Together with our partners, we are converting over 800 acres of upland habitat on the Grizzly Island Wildlife Area into 3 experimental habitats: native grasses, dense nesting cover, and control fields that are unmanipulated.  We will test whether nest density and reproductive success differs among upland habitat treatments.  We will then work with state, federal, and NGO agencies to implement the best management practice throughout California. 

Archiving California’s Breeding Duck Data

The U.S. Geological Survey is working together with California Waterfowl Association, University of California, Davis, and California Department of Fish and Wildlife to collect large datasets on the nesting ecology and management of dabbling ducks and associated upland nesting birds (Northern Harriers, Short-eared Owls, Ring-necked Pheasants, and American Bitterns) throughout the Central Valley of California on Federal Refuges, State Wildlife Areas, and private lands participating in state and federal habitat programs.  These data represent research and long-term monitoring from 1985 to present from many locations such as Grizzly Island Wildlife Area (Suisun Marsh), Conaway Ranch (Sacramento Valley), and many Central Valley locations and are comprised of over 24,000 nests and more than 25 years.  Together with our partners, USGS WERC is consolidating, organizing, electronically archiving, and entering these data into a relational nesting database that will provide the ability to easily access these long-term datasets on breeding ducks in California.

Migratory Linkages between Wintering and Breeding Waterfowl

California hunters annually harvest more than 300,000 mallards, the third most among states in the USA.  Based on band returns, it is thought that 60% to 80% of the mallards harvested in California originate from breeding grounds in California and Southern Oregon.  However, the contribution of locally raised mallards to hunter harvest is thought to have changed over time and remains unclear. We are combining analyses of banding data and stable isotopes to determine the proportion of mallards harvested in California that also originate from California wetlands.

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.