San Francisco Bay

Ecology & Conservation

Importance to shorebirds
The San Francisco Bay Estuary is an important wintering area for shorebirds that breed in a variety of arctic and temperate habitats. For example, three of the most common winter species, Dunlin, Willet, and Marbled Godwit, nest respectively in northern Alaska, the Intermountain Great Basin, and in Prairie Grasslands. The region also is important during migration, particularly for arctic-breeding species such as the Whimbrel, Western Sandpiper, and Short-billed Dowitcher. Numbers of these shorebirds in the region swell during migration periods, which extend primarily from mid-March to mid-May in spring and from mid-June until November in autumn.

Species with important breeding populations in the region include the Snowy Plover, Killdeer, Black-necked Stilt, and American Avocet.

Historic loss and degradation of native wetlands and shorebirds' exploitation of human-created habitats undoubtedly have altered the abundance and distribution of shorebirds in the region.

Competition among agriculture, urban populations, and wildlife for a limited water supply and other resources may hamper wetland habitat restoration for all species.

Species that regularly use this site:
Common and scientific names of shorebird species in San Francisco Bay

The table below shows the percentage contribution of shorebirds counted in San Francisco Bay to the total recorded in wetlands for the entire Pacific coast of the contiguous United States (from Page et al. 1999), emphasizing the critical importance of the SF Bay for these species.

Threats
Shorebirds in the San Francisco Bay Estuary have experienced high levels of habitat loss, alteration, and degradation from agricultural and urban development over the past two centuries. Watershed run-off or point discharges have contaminated sediments or water at some inland and coastal locations. Mosquito abatement programs limit options for habitat management, especially the flooding of inland wetlands during summer.

The spread of exotic plants has reduced or threatens to reduce the extent of shorebird habitat. Spartina alterniflora has been introduced into San Francisco Bay from stock originating on the Atlantic coast of the US. This species grows at both lower and higher elevations in the intertidal zone than the native California cord grass (Spartina foliosa).

The ongoing introduction of many non-native invertebrates into the benthos of the Bay through ship ballast discharges and other human activities is regularly altering the composition of potential shorebird prey in an unpredictable manner. Other factors impacting, or potentially impacting, tidal flats and the invertebrates living in them include sea level rise, contaminants, oil spills, and proposed new ferry systems.

Nesting shorebirds in the region have experienced high rates of nest loss to introduced mammalian predators, especially the Red Fox (Vulpes vulpes), and to expanding populations of native predators, especially the Common Raven (Corvus corax).

Growing recreational use of beaches and wetlands appears to be causing increased disturbance of roosting and foraging shorebirds. The potential affects of climate change on shorebird populations, including changes in prey populations, and impacts to habitat quality, availability and extent, may be profound.

Management Priorities
The recent acquisition of more than 16,000 ha of salt ponds by state and federal wildlife agencies provides an unprecedented opportunity to restore large areas of contiguous tidal wetlands in South San Francisco Bay. Restoration of these complexes is now either underway (North Bay) or being planned (South Bay).  Over 70 wetland protection, restoration, and enhancement projects have been completed, totaling more than 70,000 acres with another 60 projects currently under development or in process.

Other priorities for conservation of shorebird populations in the San Francisco Bay are to:

• Increase breeding populations of the Snowy Plover as recommended in the draft USFWS Snowy Plover Recovery Plan.
• Increase or maintain breeding populations of the Black-necked Stilt, American Avocet, and Killdeer by restoring, enhancing, or creating nesting habitat.
• Increase migratory and wintering populations of all key shorebird species in the region using protection, restoration, enhancement, and management strategies as outlined in this document.

General habitat goals
Tidal Wetlands

• Restore tidal flats and marshes.
• Enhance tidal action in existing wetlands as needed.
• Reduce sedimentation from alteration of wetland watersheds.
• Prevent further wetland loss and fragmentation due to human infrastructure development.
• Minimize future introductions of non-native invertebrates and plants.
• Eliminate the exotic plant Spartina alterniflora from tidal flats.
• Restrict further development of tidal flats for oyster culture.
• Limit human disturbance to shorebirds in all seasons.

Managed Wetlands

• Improve the value of existing managed wetlands by expanding wetland management strategies that benefit shorebirds.
• Restore additional wetlands to support migrating, wintering, and breeding populations.
• Avoid further fragmentation and encroachment of wetlands by development.
• Retain and manage a sufficient amount of salt ponds and other shallow open water habitat to support shorebird populations.