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The marshes, floodplains, and riparian corridors (areas along streams and rivers) of the Bay-Delta are key wintering destinations for migratory waterbirds and serve as a crucial stopover on the Pacific Flyway (a major north-south route for birds, extending from Alaska to the tip of South America). The mosaic of wetland habitat types within the Bay-Delta is essential for the millions of shorebirds and waterfowl that return every year (more at Waterbird Ecology and Management). In fact, the Bay-Delta is designated as a “Site of Hemispheric Importance,” the highest ranking of habitat for migratory shorebirds.
Despite the regional and international importance of the Bay Delta along the Pacific Flyway, a variety of threats to waterbirds remain, including habitat loss, loss of preferred prey due to the invasion of non-native prey species, disturbance, industrial and agricultural run-off, and climate-induced changes to sea-level and salinity regimes.
USGS researchers are working to develop a solid scientific standard for assessing, monitoring, and restoring the health and habitat of birds such as (1) the surf scoter (Melanitta perspicillata), whose populations have declined 50 to 60 percent in the past 50 years; (2) the Federal and State endangered species Ridgway’s rail (Rallus obsoletus; formerly named California clapper rail), considered an indicator species for the health of tidal wetlands; and (3) birds nesting on Alcatraz Island in San Francisco Bay such as black-crowned night-heron (Nycticorax nycticorax) and snowy egret (Egretta thula). In Suisun Marsh and the Central Valley of California, scientists are studying ducks, such as mallard (Anas platyrhynchos), gadwall (Anas strepera), cinnamon teal (Anas cyanoptera), and northern pintail (Anas acuta), to better understand the habitat use of such birds within a diverse landscape mosaic, including natural and managed (water levels) habitats.
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