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The Grasslands

Site Facts

Country, State, Province/Region:

United States, California

Relative Location:

Fresno and Merced Counties


-120.847W, 37.057N



Basis for Designation:

More than 100,000 shorebirds annually.


78,476 hectares (193,918 acres)


December 1992

Site Owner/Steward:

U.S. Fish and Wildlife, California Department of Game and Fish,  and Private Landowners

Site Partners:

California Waterfowl Associate, Ducks Unlimited, Inc., Sierra Club, National Audubon Society, Natural Resources Defense Council, Campaign to Save California Wetlands

Human Population within 100 km:



Outreach and Outdoor Recreation Planner
San Luis National Wildlife Refuge Complex
Los Banos, CA

General Manager
Grasslands Resource Conservation District
Los Banos, CA 

About Us

The Grasslands is one of the most important shorebird habitats in the western United States. California’s Central Valley hosts one of the largest wintering shorebird populations of any inland site in western North America. The Ramsar Convention on Wetlands has designated the Grasslands as a Wetland of International Importance, and it is the Grasslands Ecological Area of the San Joaquin Basin that comprises The Grasslands WHSRN Site of International Importance.

Wetlands in California’s Central Valley have declined from roughly 4,000,000 acres in the 1800s to just over 205,000 managed wetland acres as of 2006; about one-third of them are in the Grasslands. The site is dominated by intensively managed, seasonal and semi-permanent palustrine-emergent marsh, but also includes riparian wetlands, permanent marsh, alkali scrub, native grassland, and pastoral lands. All are managed under a mosaic of federal, state, and private ownerships.

Nearly 50% of all the shorebirds in California’s Central Valley are found in the Grasslands during mid-April, the peak of spring migration. According to Pacific Flyway Project censuses conducted by the Point Reyes Bird Observatory, the site seaonsally hosts: 

  • up to 200,000 shorebirds during the spring, predominantly Western Sandpipers, Long-billed Dowitchers, Dunlins, and Least Sandpipers;

  • some 14,000 shorebirds during the fall, mostly Long-billed Dowitchers, Least Sandpipers, Black-necked Stilts, and Least and Western Sandpipers; and

  • at least 60,000 shorebirds in winter, mainly Long-billed Dowitchers, Dunlins, Least Sandpipers, and Black-necked Stilts.

The Grasslands is also a critically important wintering area for Pacific Flyway waterfowl, with peak annual numbers of ducks and geese ranging from 800,000 to 1,000,000 during the last ten years. The site also supports 46 plant and animal species with federal or state endangered, threatened, or candidate status. 


Ecology & Conservation

The San Joaquin Basin is 80 miles long and covers 2,900 square miles. It extends from the Stanislaus River in the north, to the San Joaquin River in the south, and is bordered on the west by the California Aqueduct and on the east by the foothills of the Sierra Nevada. Major tributaries include the Chowchilla, Merced, and Tuolumne Rivers. Most private wetlands as well as several federal and state managed areas are located in the Grassland Resource Conservation District (GRCD) on the western side of the basin. 

Habitat Description:
Wetlands in The Grasslands include freshwater marshes dominated by aquatic and emergent vegetation; riparian woodlands and their various plant communities; and vernal pools that support a unique assemblage of plants and animals. Upland habitats include native grassland, alkali scrub, grain and hay crops, cornfields, and grazed or ungrazed pasture. 

Shorebird Highlights:
Common shorebird sightings in The Grasslands throughout the year include:

Year-round: Black-necked Stilts and Killdeer;
From autumn to spring: Greater Yellowlegs, Long-billed Curlews, Least Sandpipers, Dunlin, and Long-billed Dowitchers;
During cool, wet winter and spring: American Avocets and Black-bellied Plover; and
In the fall and winter: Lesser Yellowlegs and Wilson’s Snipe.  

Western Sandpipers are common, while Whimbrels and Short-billed Dowitchers are only occasionally seen during fall and spring migrations.  

Impacts and Disturbance:
Wetlands: more than 95% of the historic wetlands have been replaced or modified. Two-thirds of the remaining natural wetlands are in private ownership.
Riparian: over 90% of all riparian habitats in the valley have been lost. Of the more than 400 square-kilometers remaining, about 1% can be considered "intact."
Grasslands:  in most habitats, native taxa comprise less than 1% of the standing grassland crop.  
Marshlands: few freshwater marshlands are left; those that remain are generally degraded and heavily managed for duck production, water impoundments, or runoff and effluent storage.
Vernal Pools: an estimated 66% (or 2.8 million acres) of the valley's original vernal pools have been lost; the most intact pools exist on the higher terraces. The U.S. Fish and Wildilfe Service now has an ecosystem recovery plan for over 40 species that depend on these unique habitats. 

Shorebirds in The Grasslands also forage in evaporation and sewage ponds, which may expose them to concentrated contaminants like selenium, or increase the probability of disease transmission.

Threats to Habitat:
Loss of habitat quantity and quality from: urban encroachment, conversion to intensive agriculture and industry, water availability, pollution, alteration of hydrologic regimes, channelization, fires, invasive species, high (and rising) costs of operation and maintenance, opponents of waterfowl hunting (which supports wetland habitat), salinization, toxic runoff, and erosion from ecologically unsound agricultural and other practices. 

Water availability: this is the #1 concern in the area, and the federal Central Valley Project Improvement Act of 1992 does provide for a reliable water supply to some of The Grasslands. Ongoing risks to the supply and management of The Grasslands' water, as well as challenges to securing future supplies, include: increasing competition and costs to purchase limited water supplies, especially given California's growing population; delta export and pumping constraints; timing of water use on shared conveyance systems; increasing regulation of managed wetland water discharge and use; capacity limitations of existing water delivery systems; budget shortfalls that impact acquisition efforts and cost-share obligations; and unreliable groundwater supplies.  

Habitat Protection Measures:
More than 132,240 acres of The Grasslands (76%) is protected though federal and state ownership and by perpetual conservation easements on private lands. Federal, state, and private landowner organizations have identified critical areas to protect for wildlife and have developed biological justification documents for establishing agricultural buffer zones between The Grasslands and expanding urban areas. Strict protection and restoration of the last remnants of native communities is needed for all Central Valley habitats. Per its 2006 Implementation Plan, the Central Valley Joint Venture (CVJV) is committed to formulating and prioritizing activities to meet the habitat needs identified by various bird groups in the nine basins within the valley.  

Management Activities and Priorities:
Nearly 90% of The Grasslands' wetlands are intensively managed for wildlife on a seasonal basis. Seaonal wetlands, which provide the majority of foraging habitat for shorebirds, are flooded in the fall and drawn down between March and May; semi-permanent wetlands are flooded from early fall through early July; and permanent wetlands are flooded year-round. Per the CVJV's habitat assessment for the San Joaquin Basin, 66% of the managed seasonal wetlands and semi-permanent wetlands must provide foraging depths of < 10 cm to benefit shorebirds, especially during July - August.

Recognition as a WHSRN Site of International Importance for shorebirds, implementation of the Central Valley Project Improvement Act in 1993, and a long list of programs, acquisitions, investments, workshops, and other public and private efforts continue to improve wetland management in The Grasslands for all birds and other wildlife.

The Grasslands hosts a myriad of research projects by academic, federal, state, and nongovernmental organizations on a wide variety of subjects including wildlife, botany, ecology, contaminants, and management.  

Documents and References:
Central Valley Joint Venture 2006 Implementation Plan


Special Information

The San Luis National Wildlife Refuge Complex  

Merced National Wildlife Refuge  

San Joaquin River National Wildlife Refuge  

Great Grasslands State Park

Los Banos Wildlife Area  

Volta Wildlife Area

Grassland Environmental Education Center (GEECe)

"Grassland Explorer : The Grassland wetlands newsletter, produced by the Grassland Water District, located at 22759 S. Mercey Springs Rd. /
Los Banos, CA / 93635.  


Jack Sparks, Outreach and Outdoor Recreation Planner
San Luis National Wildlife Refuge Complex 
P.O. Box 2176 (947 W. Pacheco Blvd., Suite C)
Los Banos, CA 93635
Tel. 209-826-3508
Fax: 209-826-1445 

Ricardo Ortega, General Manager
Grassland Resource Conservation District 
22759 S. Mercey Springs Road
Los Banos, CA 93635
Tel. 209-826-5188
Fax 209-826-4984

Additional Resources


Anderson, D.G. 1956. A waterfowl nesting study on the Grasslands, Merced County, California. California Fish and Game, 42: 117-130.

Central Valley Joint Venture, 2006.  Central Valley Joint Venture Implementation Plan – Conserving Bird Habitat.  U.S. Fish and Wildlife Service, Sacramento, CA.

Connelly, D.P. 1979. Propagation of selected marsh plants in the San Joaquin Valley. California Department of Fish and Game, Wildlife Management Leaflet 15, Sacramento, 13 pp.

Connelly, D.P., and D. L. Chesemore. 1980. Food habits of pintails, Anas Acuta, wintering on seasonally flooded wetlands in the northern San Joaquin Valley, California. California Fish and Game, 66: 233-237.

Ermacoff, N. 1968. Marsh and habitat management practices at the Mendota Wildlife Area. California Department of Fish and Game, Game Management Leaflet No. 12, 10 pp.

Fredrickson, L.H. and M. Laubhan. 1995. Land Use Impacts and Habitat Preservation in the Grasslands of Western Merced County, California. A report of the Grassland Water District, Los Banos, CA, 81 pp.

George, H.A. 1963. Planting alkali bulrush for waterfowl food. California Department of Fish and Game, Game Management Leaflet 9, Sacramento, 9 pp.

Kjelmyr, J., G. Page, W.D. Shuford, L.E. Stenzel. 1991. Shorebird Numbers in Wetlands of the Pacific Flyway: A Summary of Spring, Fall, Winter Counts in 1988, 1989, and 1990. 

Miller, A.W., and P.H. Arend. 1960. How to grow watergrass for ducks in California. California Department of Fish and Game, Game Management Leaflet No. 1, Sacramento, 16 pp.

Noss, R.F. 1994. Translating conservation principles to landscape design for the Grassland Water District. Report to Grassland Water District, Los Banos, CA, 27 pp.

Page, G.W., W.D. Shuford, J.E. Kjelmyr, and L.E. Stenzel. 1992. Shorebird Numbers In Wetlands of the Pacific Flyway: A Summary of Counts From April 1988 to January 1992. Point Reyes Bird Observatory. Stinson Beach, CA, 42 pp.

Page, G.W., W.D. Shuford, J.E. Kjelmyr. 1994. Results of the April, August, and November 1993 Shorebird Counts in the Wetlands of California’s Central Valley. Point Reyes Bird Observatory. Stinson Beach, CA, 11 pp.

Rathbun, G.B., N.J. Scott Jr., and T.G Murphy. 2002. Terrestrial habitat use by Pacific pond turtles in a Mediterranean climate.  The Southwestern Naturalist 47(2):225-235.

Reid, T. 1995. Grassland Water District Land Planning Guidance Study. A report to the Grassland Water District. Los Banos, CA, 29 pp.

Severson, D.J. 1987. Macroinvertebrate populations in seasonally flooded marshes of the San Joaquin Valley of California. M.S. Thesis, Humboldt State University, Arcata, CA, 113 pp.

Shuford, W.D., G.W. Page, J.E. Kjelmyr, and C.M. Hickey. 1994. Seasonal Abundance and Habitat Use of Shorebirds in California’s Central Valley, November 1993 to August 1994. Point Reyes Bird Observatory. Stinson Beach, CA, 17 pp.

U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service, California Department of Fish and Game, and Grasslands Resource Conservation District. 1998. An Interagency Coordinated Program for Wetland Water Use Planning: Central Valley, California. Sacramento, CA.

U.S. Bureau of Reclamation, 1989. Report on Refuge Water Supply Investigations. Central Valley Hydrologic Basin, California. U.S. Department of Interior, Mid Pacific Region. Sacramento, CA.

U.S. Fish and Wildlife Service. 2002. Birds of conservation concern 2002. Division of Migratory Bird Management, Arlington, Virginia. 99 pp. 

U.S. Fish and Wildlife Service. 2000. Central Valley wetlands water supply investigations: CVPIA 3406(d)(6)(A,B): a report to Congress: final report. U.S. Fish and Wildlife Service, Portland, OR.

U.S. Fish and Wildlife Service. 1978. Concept Plan for Waterfowl Wintering Habitat Preservation, Central Valley, California. U.S. Fish and Wildlife Service, Region 1, Portland, OR, 116 pp.

Fish and Wildlife Service. 1989. Wetlands of the California Central Valley: Status and

Trends - 1939 to Mid-1980s. Portland, Oregon, 28pp.

U.S. NABCI Committee. 2000. North American Bird Conservation Initiative: bird conservation region descriptions. U.S. Fish and Wildlife Service, Arlington, Virginia. 38 pp.

U.S. NABCI Committee. 2000. North American Bird Conservation Initiative: Bringing it all together. U.S. Fish and Wildlife Service, Arlington, Virginia.

Van Horne B. 1983. Density as a misleading indicator of habitat quality. J. Wildl. Manage. 47: 893–901.

Zeiner, D. C., and W. F. Laudenslayer, K. E. Mayer, and M. White, eds. California’s Wildlife: Volume II, Birds. California Statewide Wildlife Habitat Relationship System. State of California, The Resources Agency. Sacramento. 731 pp.