Skip to Navigation
 

San Francisco Bay

Site Facts

Country, State,
Province/Region:
USA, California

Relative Location:
Estuarine wetlands in the San Francisco and San Pablo Bays

Latitude/Longitude:
37º 28’ N, 122º 02’ W

Category:
Hemispheric Site

Basis for Designation:
Usage by more than 900,000 shorebirds annually

Size:
22,489 ha. (55,571 acres)

Joined:
1989

Site Owner/Steward:
Multiple landowners: U.S. Fish & Wildlife Service, California Department of Parks and Recreation, California Department of Fish and Game Lands, East Bay Regional District, Midpeninsula Regional Open Space District, City of Mountain View, National Audubon Society

Site Partners:
Point Reyes Bird Observatory, San Francisco Bay Joint Venture

Human Population within 100 km
About 8 million

Contact:

Catherine Hickey
Coordinator
Southern Pacific Shorebird Conservation
chickey@prbo.org

Beth Huning
Coordinator 
San Francisco Bay
Joint Venture
bhuning@sfbayjv.org

Description

San Francisco Bay is recognized as a Western Hemisphere Shorebird Reserve Network (WHSRN) Site of Hemispheric Importance for shorebirds – the highest possible ranking.

Snowy PloverSan Francisco Bay holds higher proportions of the total wintering and migrating shorebirds on the U.S. Pacific coast than any other wetland. For eleven species, the Bay holds over half of the individual shorebirds detected, during at least one season of the year (see Table). San Francisco Bay is also the northernmost regular breeding area of the American Avocet and Black-necked Stilt on the Pacific coast of North America. About 10% of the U.S. Pacific coast population of the Western Snowy Plover breeds in the salt ponds of the South Bay.

San Francisco Bay Overview
Nearly half of California’s fresh water runoff finds its way to the San Francisco Bay Estuary. Sierra snowmelt and foothills Range rainfall are captured by the Sacramento and San Joaquin rivers which meet with ocean tides entering through the Golden Gate. Once, the estuary sprawled over more than half-a-million acres of mudflats and salt marsh: the largest contiguous tidal marsh system on the Pacific Coast. San Francisco Bay wetlands have a long history of human alteration, including development of adjacent uplands and seasonal wetlands, dredging of tidal mudflats, and changes in salinity and tidal regime. Today more than 90% of the original wetlands have been lost to urban development; converted to agricultural fields or salt ponds; or degraded by pollution, exotic species introductions, and habitat destruction.

Despite the huge loss of natural habitat, the estuary’s remaining wetlands provide habitat for hundreds of thousands of shorebirds, waterfowl, and other water birds throughout the year.

Habitats in San Francisco Bay
Tidal flat is the primary foraging habitat of many of the region’s most abundant shorebirds, including the Black-bellied Plover, Semipalmated Plover, Willet, Long-billed Curlew, Marbled Godwit, Western Sandpiper, Least Sandpiper, Dunlin, and Short-billed Dowitcher. The main shorebird prey in the tidal flats are invertebrates, but many of these are introduced species that arrived through the release of ship ballast and other human actions.

Salt Pannes and Salt Ponds
Historically, about 645 ha of natural salt pannes, large open areas within the salt marsh vegetation, served as supra-tidal foraging and roosting sites for many shorebird species, and as nesting areas for plovers, stilts, and avocets. As the demand for salt rose in the mid-1800s, artificial salt ponds replaced the pannes.

American AvocetCurrently there are 13,943 ha of salt ponds in the estuary. The ponds vary in size, depth, salinity, and most importantly, invertebrate characteristics. Thus each type of pond varies in the vertebrate populations that are supported by the particular invertebrate assemblage found in that pond, resulting in the highest diversity of shorebird species of any other habitat in the Bay.

Though the habitat value of the once extensive vegetated marsh was lost when the ponds were formed, the ponds and levees within the salt complex became significant roosting and nesting sites for a wide variety of non marsh-dependent species, and the ponds themselves became important foraging areas for millions of shorebirds and other species of waterfowl, sea birds and other waterbirds.

Salt Marsh
Shorebirds use salt marsh to a lesser degree than tidal flats, but under some tidal conditions, roosting birds do use this habitat. The larger non-vegetated channels in salt marsh are used as foraging habitat by the same species that feed on tidal flats. Some species, such as the Willet, Whimbrel, Long-billed Curlew, and Least Sandpiper, also forage on marsh plains with sparse or low vegetation. Species such as the Willet, Least Sandpiper, Dunlin, and Long-billed Dowitcher use salt marsh as diurnal and nocturnal roost sites, possibly to provide some protection from predators such as owls.

There currently are about 16,265 ha of tidal marsh in the San Francisco Bay, a 79% decline from historic levels. Tidal marsh has been lost primarily to the development of salt ponds, agriculture land, and urban areas.

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.

Black Necked StiltSpecies 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

Black-bellied Plover Pluvialis squatarola
American Golden-Plover Pluvialis dominica
Pacific Golden-Plover Pluvialis fulva
Snowy Plover Charadrius alexandrinus
Semipalmated Plover Charadrius semipalmatus
Killdeer Charadrius vociferus
Mountain Plover Charadrius montanus
Black Oystercatcher Haematopus bachmani
Black-necked Stilt Himantopus mexicanus
American Avocet Recurvirostra americana
Greater Yellowlegs Tringa melanoleuca
Lesser Yellowlegs Tringa flavipes
Solitary Sandpiper Tringa solitaria
Willet Catoptrophorus semipalmatus
Wandering Tattler Heteroscelus incanus
Spotted Sandpiper Actitis macularia
Whimbrel Numenius phaeopus
Long-billed Curlew Numenius americanus
Marbled Godwit Limosa fedoa
Ruddy Turnstone Arenaria interpres
Black Turnstone Arenaria melanocephala
Surfbird Aphriza virgata
Red Knot Calidris canutus
Sanderling Calidris alba
Semipalmated Sandpiper Calidris pusilla
Western Sandpiper Calidris mauri
Least Sandpiper Calidris minutilla
Baird's Sandpiper Calidris bairdii
Pectoral Sandpiper Calidris melanotos
Rock Sandpiper Calidris ptilocnemis
Dunlin Calidris alpina
Short-billed Dowitcher Limnodromus griseus
Long-billed Dowitcher Limnodromus scolopaceus
Wilson's Snipe Gallinago delicata
Wilson's Phalarope Phalaropus tricolor
Red-necked Phalarope Phalaropus lobatus
Red Phalarope Phalaropus fulicarius

 

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.

 

  SEASON
Species Fall Winter Spring
Black-bellied Plover 62 59 55
Semipalmated Plover 52 40 47
Black-necked Stilt 78 90 58
American Avocet 96 88 86
Greater Yellowlegs 41 41 26
Willet 69 58 57
Long-billed Curlew 66 49 46
Marbled Godwit 62 46 68
Red Knot 76 43 39
Western Sandpiper 59 68 54
Least Sandpiper 67 39 73
Dunlin - 38 24
Dowitcher, spp. 72 65 49



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.

Contact Us

San Francisco Bay Joint Venture:
Coordinator - Beth Huning, bhuning@sfbayjv.org

Assistant Coordinator - Sandy Scoggin, sscoggin@sfbayjv.org
Public Outreach Coordinator - Caroline Warner, cwarner@sfbayjv.org
San Francisco Bay Joint Venture
530 C Alameda del Prado #139
Novato, CA 94949
Phone: 415-883-3854
Fax: 415-883-3850

Catherine Hickey
Southern Pacific Shorebird Conservation Coordinator; Chair of the US Shorebird Conservation Council
PRBO Conservation Science
4990 Shoreline Highway One
Stinson Beach, CA 94970
Phone: 415-868-0371 ext 307
Fax: 415-868-8962
Web: www.prbo.org

Don Edwards San Francisco Bay National Wildlife Refuge Complex
P.O. Box 524
Newark, CA 94560
Phone: 510-792-0222
Email: sfbaynwrc@fws.gov
Web: www.fws.gov/desfbay/