ICP Detail: Central Valley California

Central Valley / Coastal California Region 25*

The Coastal California Region extends from Bodega Bay south to northern Mexico and includes the important San Francisco and San Diego Bays. The Coast Mountain Range is also considered in this region as is the Central Valley and the Salton Sea. The most important waterfowl habitat in the region is the Central Valley where DU has an extensive program of habitat restoration, protection, and enhancement.

The Central Valley of California averages 64 km wide by 644 km long and consists of the two lesser valleys, the Sacramento in the north and the San Joaquin in the south. One of the largest freshwater deltas in the world is formed at the confluence of the Sacramento, San Joaquin, Mokelumne, and Cosumnes Rivers. These waters then flow through Suisun Bay (Marsh) into San Francisco Bay. Wetlands in the Central Valley historically have hosted some of the largest concentrations of wintering waterfowl in the world. Estimates from the 1800s place waterfowl numbers between twenty and 40 million birds. More recently, population objectives for the Central Valley have been stepped down from the North American Waterfowl Management Plan (NAWMP). These population objectives call for the Central Valley to sustain peak wintering populations of nearly six million ducks and one million geese. Up to 60% of all Pacific Flyway waterfowl rely on the Central Valley during some portion of the migration or wintering period. Nowhere in North America do so many waterfowl winter on such a small wetland base.

Prior to the Gold Rush period of the mid-1800s, an estimated 5 million acres of wetlands were present in the state (Heitmeyer et al. 1989). However, the loss and degradation of these habitats has been dramatic. More than 95% of the historic wetland area and over 90% of the riparian corridors in California have been destroyed or modified (Gilmer et al. 1982). Although habitat loss in the Central Valley has slowed or even been reversed in recent years, population growth and urbanization continue. Human populations in California are expected to nearly double by 2040. Much of this growth will occur in the Central Valley where human populations are projected to increase from 5.7 million to13.1 million over the same period.

Population increases in the Central Valley will result in significant land use changes, especially with respect to agriculture. It is estimated that nearly 800,000 acres of irrigated farmland will be converted to urban uses by 2040. For waterfowl, rice is by far the most important irrigated crop grown and loss of this habitat would have significant consequences for ducks and geese. However, a closer look at human population growth suggests that most of this growth will occur outside of today's rice growing regions. Of the nearly 500,000 acres of rice that is now grown in the Valley, less than 40,000 acres, or 8% of the total, is forecast to be lost by 2040.

The Sacramento and San Joaquin Valleys differ substantially in the amount and types of habitat provided for waterfowl. Riparian forests, semi-permanent tule marshes, and grasslands historically dominated the Sacramento Valley. Of the 1.5 million acres of wetlands that once existed in the Sacramento Valley, approximately 79,000 acres remain. Some 60% of the current wetlands are in private ownership and most are managed as duck clubs. Some of the most important areas of private duck clubs include the Willow Creek, Lurline, Butte Sinks, Colusa Trough, and District 10. Harvested rice fields provide winter foods and habitats for several species of waterbirds, especially if they are shallow flooded after harvest. Virtually all of the rice grown in the Central Valley occurs in the Sacramento Valley, with approximately 70% of this rice being flooded after harvest.

The San Joaquin Valley consists of the San Joaquin and Tulare drainage basins. Most of the San Joaquin Basin once consisted of seasonally flooded grasslands and vernal pools. Historically wetlands within the Tulare Basin were confined to Tulare, Kern, Goose, and Buena Vista lakes that covered some 625,000 acres. At present, there are 90,000 acres of wetland habitat in the San Joaquin Valley. Most of this habitat occurs in the Grasslands District, which is the largest contiguous block of wetlands in the Central Valley.

The vast watershed of the Central Valley drains into the Sacramento-San Joaquin Delta at the confluence of the Sacramento, San Joaquin, Mokelumne, and Cosumnes rivers. The inland network of 700,000 acres of sloughs and islands form an inverted delta that is one of the 60 largest river deltas in the world (Heitmeyer et al. 1989); only the Yukon-Kuskokwim and Copper River deltas of Alaska are larger on the west coast of North America. Because of its unique geologic formation, the Delta is the largest inland delta, and its waters flow through the largest brackish estuary on the Pacific Coast. Recent estimates indicate that as little as 7,500 acres of wetlands and 29,000 acres of winter-flooded agriculture may exist in the eastern Delta. Suisun Marsh currently contains 38,375 acres of managed wetlands that provide important food resources for migrating and wintering waterfowl. However, recent proposals to restore tidal flow to up to 6,750 acres of these managed habitats may reduce the carrying capacity of Suisun Marsh. As a result, DU and its partners in the Central Valley will determine the effects of tidal restoration on waterfowl populations in the Suisun Marsh.

Millions of migrant and wintering waterfowl once used Suisun Marsh. Market hunting in the late 1800s suggests the size of estuary waterfowl populations where more than 182,000 green-winged teal were sold in San Francisco markets in the 1895-96 season (Grinnell et al. 1918). Estimates of wintering pintail populations in the recent past, including the Delta, vary from 200,000 to 1.4 million (Michny 1979). San Francisco and San Pablo Bays made up one of the largest contiguous tidal marsh systems on the Pacific Coast and included over 545,000 acres of tidal wetlands. The hydraulic mining in the Sierra-Nevada foothills, conversion of tidelands to agriculture in the late 1800s and early 1900s, and urban and industrial expansion have reduced the quality of this system (Nichols et al. 1986). Urban expansion has created large residential developments within and adjacent to wetland areas; industrial, military, and commercial developments; over 320 marinas; solid waste landfills; and substantial disturbance of wildlife. Critical coastal wetland habitats still exist in southern California and include, Morro Bay, Bolsa Chica, and San Diego Bay, however, urban encroachment is severe.

Another crucial factor related to conservation of water birds and aquatic habitat in the Central Valley is that of water itself. Agriculture accounts for 80% of water use, and projected demographic changes will result in dramatically increased tensions among agriculture, urban development and conservation interests. Even in an above-average water year like 1998-99, farmers in the San Joaquin Valley did not fully receive adequate water supplies. Congressional actions, such as 1992 passage of the Central Valley Project Improvement Act, have helped assure adequate water supplies for wildlife conservation in some areas (such as federal and state refuges), yet much remains to be done to secure adequate supplies of water quantities of suitable quality for wetlands conservation (especially private lands).

An additional factor related to water in the west is that of threatened and endangered anadromous fish. Almost all rivers and streams in northern California have large and small dams that halt successful salmon and steelhead spawning cycles. Alterations of streamside habitat and water availability at important times in the year further exacerbate the problems. Water diversions from streams and rivers for agricultural or wildlife conservation use can result in entrapment of fish onto upland areas, further compromising their population status. If solutions to such fish issues cannot be found, direct conflict in floodplain management strategies would certainly develop.

Importance to Waterfowl

Waterfowl concentrations are greatest in California during fall and winter when migrants from northern latitudes join locally breeding or produced birds (Bellrose 1980). The Central Valley winters nearly six million ducks and 1 million geese and swans when waterfowl populations are at NAWMP goals. This represents >60% of all waterfowl (excluding sea ducks) wintering in the Pacific Flyway. Of special importance, California winters >20% of all mallards, wigeon, green-winged teal, northern shovelers, canvasbacks, and ruddy ducks; >30% of all lesser snow geese and tundra swans; >50% of all northern pintails, white-fronted geese, and Ross' geese. Today, the San Francisco Bay is still an important staging and wintering area for waterfowl, especially diving ducks, in the Pacific Flyway. More ducks winter in San Francisco Bay than in the much larger Chesapeake Bay (SFEP 1992). Midwinter surveys during 1981-90 indicated that an average of 193,000 waterfowl were present on the open water and salt ponds of San Francisco Bay. During that time, the relative composition of waterfowl species in the Bay was scaup (35%), scoters (14%), shoveler (12%), ruddy duck (11%), canvasback (8%), other dabbling ducks (10%), and other ducks (10%). The most abundant diving ducks over the past 10 years have been scaup, surf scoter, ruddy duck, canvasback, and bufflehead - in that order (SFEP 1992).

Conservation Programs

Ducks Unlimited's Valley CARE Program was initiated in the Central Valley in 1993 to comprehensively address wetland and waterfowl conservation issues in this important wintering and migration area. The program integrates several strategies including wetland restoration, enhancement, and protection; promotes wildlife friendly agriculture practices, especially post-harvest flooding of ricelands; and develops public policy and communication initiatives that address conservation needs in the Valley.

There have been substantial increases in waterfowl habitat within the Central Valley since the 1990s, and we've used the update of the ICP to report on some of these accomplishments. Since the early 1990s, DU and its partners have restored approximately 60,000 acres of wetland habitat. This represents half of the 120,000 acres wetland restoration objective identified in the ICP. In addition, over 56,800 acres of existing wetlands have received long-term protection. This equals 70% of the ICP's 84,000 acres wetland protection goal.

The ICP has also called for enhancement of 444,000 acres of agricultural habitat that was divided as follows; 1) enhancement of 332,000 acres of grain fields to help meet the food energy needs of migrating and wintering waterfowl, and 2) enhancement of 112,000 acres of upland habitat to ensure adequate nest success for breeding waterfowl. Although habitat programs for breeding waterfowl are just now gaining momentum in the Valley, over 353,000 acres of rice habitat is now flooded annually to provide food resources for wintering and migrating waterfowl. Finally, the ICP recommended securing reliable water supplies for all National Wildlife Refuges and State Wildlife Areas in the Central Valley, as well as for private wetlands in the Grasslands Resource Conservation District. This equals 506,000 acre-feet of annual water supplies. To date, over 70% of this objective has been achieved (363,000 acre-feet) as a result of passage of the Central Valley Project Improvement Act.

Ducks Unlimited has recently updated habitat objectives for the Central Valley in cooperation with its Central Valley Joint Venture partners. The purpose of this update was to clearly link waterfowl objectives for the Valley to the NAWMP, and to identify the landscape conditions needed to sustain waterfowl populations at NAWMP goals. A critical assumption of this update is that wetlands must provide a minimum of 50% of waterfowl food energy needs in each of the Valley's nine drainage basins, which serve as planning units. In some basins, agriculture accounts for over 70% of available waterfowl foods. Agricultural habitats will continue to be important in meeting the needs of waterfowl in the Central Valley. However, changing agricultural markets and increases in harvest efficiency are largely beyond the control of DU and its partners. Increasing the amount of wetland habitat for waterfowl can offset some of these unforeseen changes. Finally, the approach to establishing wetland enhancement objectives has been changed for this version of the ICP. Wetland enhancement typically involves periodic maintenance or improvement of water control structure, levees, and ditch networks used to manage wetlands. Interviews with resource professionals suggest that wetlands in the Valley should undergo some level of enhancement every ten to fifteen years. The ICP assumes that managed wetlands in the Central Valley need some form of enhancement an average of every twelve years. As a result, enhancement objectives are expressed on an annual basis and are perpetual. The annual enhancement objective in this version of the ICP assumes that wetland restoration objectives for the Valley are met.

Although most of DU's work in the Central Valley has focused on migrating and wintering waterfowl, there is a growing emphasis on meeting the needs of breeding waterfowl as well. For example mallard harvest in the Central Valley now exceeds that of pintails, and up to 75% of mallards shot in the Valley are produced there. As a result, DU and its partners have developed a plan to guide habitat efforts for breeding mallards. This includes identifying the types of habitat programs to be delivered, where these programs should be focused, and ongoing research to better understand what limits the size and success of breeding mallard populations in the Central Valley.


Ducks Unlimited, in cooperation with its partners in the CVJV, has recently updated habitat objectives for waterfowl in the Central Valley. These objectives are described below.

Specific to DU, the following goals have been adopted for the five-year planning horizon:



* Region 25 - NABCI Bird Conservation Region 32

Revised January 31, 2005 - Region 25

    Editing updates throughout

    Completely revised descriptions of Conservation Programs

    Completely revised Goals