Suisun Marsh Waterfowl and Wildlife Studies

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Suisun Marsh provides critical habitat for wintering and breeding waterbirds in California. USGS WERC collaborates with the California Department of Water Resources to examine trends in bird declines and to assess the habitat factors driving long-term survival of waterfowl, rails, and other birds in this important area.

Gadwall ducklings in nest

Gadwall ducklings in nest, Suisun Marsh, CA. (Credit: Sarah Peterson/USGS. Public domain.)


Suisun Marsh, California is the largest contiguous brackish water marsh in western North America, formed where the fresh water from the Sacramento-San Joaquin Delta joins up with the salt water from San Francisco Bay. The marsh provides habitat to thousands of migratory and resident waterfowl and water birds, along with many other plants and animals. The importance of the Suisun Marsh, California, as a waterfowl-use area is widely known and has a long history.

But as of 2014, waterfowl abundance was below the Central Valley Joint Venture’s population objective for 300,000 ducks wintering in Suisun Basin, and well below the nearly 370,000 waterfowl that typically wintered there during the 1950s.  Long-term population trends for dabbling ducks and geese are declining in Suisun Marsh, even after accounting for California-wide population trends, indicating that proportionately fewer dabbling ducks and geese are choosing to winter in Suisun Marsh than historically. Suisun Marsh also supports among the highest densities of breeding ducks in North America, and plays an important role in duck production within California.  

With more than 90 percent of California’s wetlands lost, Suisun Marsh represents one of the last remaining contiguous wetland habitats in the state. In order to understand and manage water bird populations and habitats in Suisun Marsh, the California Department of Water Resources has partnered with the USGS WERC and other collaborators to these address information needs.

USGS WERC’s research in Suisun Marsh focuses on waterfowl nesting and movement ecology, but covers many elements of the Suisun ecosystem. Learn more about each major research area below, and explore recent results, publications, multimedia, and news related to the Suisun Marsh Waterfowl project by clicking on each tab.


Click here or the image below to learn more in our Waterfowl Ecology Story Map

Screenshot of a website with a flock of flying ducks and the title Waterfowl Ecology in Suisun Marsh and the Pacific Flyway




Results that have been published so far from this project include the following:

  • [Nesting] Ducklings leave the nest in the early morning, suggesting predator avoidance                                                (Learn more - Publication - Download Research Spotlight)
  • [Movement] Ducks in Suisun Marsh use less space and travel shorter distances than expected                                                (Learn more - Publication - Download Research Spotlight)