Suisun Marsh is the largest contiguous brackish water marsh remaining on the west coast of North America. Along with the Concord Marshes on the south side of Suisun Bay, Suisun Marsh ecologically links the Central Valley/Delta Area with the Pacific Coast. Encompassing 116,000 acres, the Suisun Marsh includes 52,000 acres of managed wetlands, 27,700 acres of upland grasses, 6,300 acres of tidal wetlands, and 30,000 acres of bays & sloughs. The Marsh is home to public waterfowl hunting areas and private duck clubs. The Marsh encompasses more than 10% of California's remaining natural wetlands and serves as the resting and feeding ground for thousands of waterfowl migrating on the Pacific Flyway. Despite a history of disturbance, Suisun Marsh remains a decidedly wild area, with abundant River Otter, an introduced herd of Tule Elk, several rare wetland plants and the federally endangered salt marsh harvest mouse. In addition, the Marsh provides essential habitat for more than 221 bird species, 45 animal species, 16 different reptilian and amphibian species, and more than 40 fish species (Interagency Ecological Program of California).

Politically, the Important Bird Area is a patchwork of 14,300 acres of state-owned parcels (known collectively as the Grizzly Island Complex), plus several thousand acres of agricultural lands and private duck clubs. A significant private parcel of wetlands and grassland, Rush Ranch, was acquired by the Solano Land Trust in 1988.

Ornithological Summary

An endemic race of Song Sparrow, Suisun Song Sparrow, has essentially its entire global population (c. 20,000-50,000 individuals) within the Important Bird Area, and it is believed to be the only area in the world where the Saltmarsh Common Yellowthroat, another Bay-Area endemic, is common (Nur et al. 1997). Suisun Bay is one of the few areas of California that supports more than 100,000 waterfowl during the winter, with ?dabbling ducks? (Green-winged Teal, Mallard, Northern Pintail, Northern Shoveler and American Wigeon) especially well represented. This is in contrast with the bay ducks (e.g. scaup) typical of San Francisco and San Pablo bays. Suisun is one of just three wintering areas for the rare ?Tule? race of the Greater White-fronted Goose (Small 1994). With its mix of freshwater and tidal marsh, nearly every wetland bird species in the region occurs here, often in exceptional numbers. The number of California Black Rails here and in the adjacent Carquinez Straits rivals that of San Pablo Bay just to the west, which holds about half the global population of the taxon (Evens and Nur, in press). Unlike coastal wetlands, just a handful of California Clapper Rails have been noted in the Important Bird Area, associated with tidal sloughs. Short-eared Owl winters in large numbers and many still breed, the only regular nesting locale along the coast of California. The diked wetlands support breeding colonies of Tricolored Blackbird, American White Pelican have recently begun summering in large numbers and may conceivably begin to breed. The hundreds of Great Egret breeding at Suisun represent an estimated 35% of the San Francisco Bay Area population (Kelly et al. 1993).

East of the tidal gates on Montezuma Slough the Montezuma Wetlands are being restored using dredged sediments. Sand cells in the project have attracted nesting Least Tern (25 nests) and Snowy Plover (5 nests) to the site.

Yellow Rail, an almost mythical marsh bird essentially extirpated in the state, was detected in February of 2002 (two birds), and may prove to be regular in winter (Robin Leong).

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Conservation Issues

From the Goals Project (1999), conservation efforts should focus on restoring and connecting tidal channels throughout the area, protecting vernal pools and other seasonal wetlands, enhancing natural transitions from tidal marsh to upland (e.g. grassland, woodland habitat in Portrero Hills), and maintaining open space for buffers around wetlands. This will rely on a combination of exotic species removal (the entire Important Bird Area is extensively invaded with Peppergrass and other exotics), dike reconfiguration, and land easements/acquisitions.

A proposed expansion of the Potrero Hills Landfill within the Susiun Marsh Secondary Management Area poses concern for impacts to species, water quality, and adjacent habitat.

As the upland areas surrounding Suisun Marsh become increasingly developed, their conservation will be of greater importance in the region for raptors (Golden Eagle has nested recently in the Portrero Hills north of Grizzly Isl.) and open-country species like Loggerhead Shrike.


Politically, the IBA is a patchwork of 14,300 acres of state-owned parcels (known collectively as the Grizzly Island Complex), plus several thousand acres of agricultural lands and private duck clubs. A significant private parcel of wetlands and grassland, Rush Ranch, has recently been acquired by the Solano Land Trust.


Covering about 84,000 acres northeast of San Francisco Bay, Suisun Marsh is the largest contiguous estuarine marsh in the U.S. The area is dominated by a vast, central block of diked wetlands, which consist of former tidal marsh separated by levees and alternately drained and filled with water (both fresh and brackish), surrounded by tidal marsh and the open waters of Grizzly and Suisun Bay. There is also a significant private parcel of wetlands and grassland.

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