Important Bird Areas

Sacramento-San Joaquin Delta

California

The Sacramento-San Joaquin Delta is centered on the southwest arm of Sacramento County, roughly halfway between Sacramento and the East Bay cities of Antioch and Concord. This portion of the Sacramento-San Joaquin Delta, from Walnut Grove downstream to Oakley, was formerly a vast region of bulrush (tule) marsh with brackish water. The conversion of this area to agriculture in the late 1800s involved reclamation of these wetlands and the construction of levees along channels and draining the resulting islands of land for farming. These large blocks of farmland, many of which have sunk up to 25' below sea level, are alternately known as islands or tracts. Not to be confused with these islands are numerous small islets (up to several acres in size) within large river channels that are either natural remnants or mounds of dredge spoils left over from levee construction. These have since converted to or retained native riparian and tidal marsh vegetation, and are often the only such habitat for miles around. The best examples of in-stream islets are in San Joaquin Co., northwest of Stockton. Major tracts and islands with bird habitat include:
? Liberty/Ryer Islands, Solano Co. (Private)
? Sherman Island, Sacramento Co. (CA Department of Fish and Game (DFG) Lower Sherman Island Wildlife Area)
? Tyler Island, Sacramento Co. (Private)
? Webb Tract, Contra Costa Co. (Private)
? Holland/Palm Tracts, Contra Costa Co. (Private)
? Big Break/Iron House WTP, Contra Costa Co. (incl. Big Break Regional Shoreline, East Bay Regional Park District)
? Piper Slough, Contra Costa Co. (Private, with public boat access)
? Bouldin/Venice/Mandeville/Medford Islands and Empire/Ringe Tracts, San Joaquin and Contra Costa Co. (Private)
? Brack Tract/White Slough, San Joaquin Co. (DFG White Slough Wildlife Area.)
? Staten Island, San Joaquin Co. (The Nature Conservancy).

Updated February 2010

Ornithological Summary

The vast expanse of regularly-flooded agricultural lands enable the Delta to support a rich wintering bird community that includes Swainson's Hawk (breeding and wintering), Tundra Swan, Sandhill Crane and Short-eared Owl. Tens of thousands of shorebirds and hundreds of thousands of waterfowl occur in winter and migration. In San Joaquin Co., the Phil and Marilyn Isenberg Ecological Reserve, on Brack Tract and Staten Island, includes Blossom Slough, a series of ponds with a former peripheral canal now managed for wildlife. The Christmas Bird Count for this area regularly exceeds 150 species. According to local birder Waldo Holt (pers. comm.), the fields in this area are farmed in corn, and support between 55% and 75% of the state's Greater Sandhill Crane population (the remainder winter at the Cosumnes River Preserve and on the refuges of the Sacramento Valley, fide Thelander and Crabtree 1994). In Contra Costa Co., the rice fields of Webb Tract support tens of thousands of wintering geese (particularly Greater White-fronted), and hundreds of Sandhill Crane and White-faced Ibis. Holland and Palm tracts, just northeast of Brentwood, also host large numbers of geese and cranes, and wintering flocks of Tundra Swans and both Tricolored and Yellow-headed blackbirds; and nesting Short-eared Owl and Swainson's Hawk. North of here, the tips of Venice and Mandeville islands support shallow brackish marsh vegetation with high numbers of waterfowl, as well as breeding waders and the only Double-crested Cormorant colony in San Joaquin Co.

Significant concentrations of riparian species occur at Liberty Isl., Sherman Isl., and Piper Slough, supporting several pairs of Yellow-breasted Chat and Blue Grosbeak. Long-eared Owl was recently discovered roosting communally at the tip of Ryer Isl.. Big Break, including the Iron House Sanctuary (part of a water treatment facility) supports tidal marsh along the southern shoreline of the Stockton Deep Water Channel with a significant population of Black Rail, a species that probably also occurs in Salicornia habitat at Sherman Isl. (T. Manolis, pers. comm.). Elsewhere in the Delta, Black Rail occurs on most in-stream islands greater than 15 acres that support marsh vegetation elevated above the high tide and wave line. Piper Slough, up the channel to the northeast at the tip of Bethel Isl., is notable as one of the few known migrant traps in the Delta. A pair of Peregrine Falcons has nested for years on the Antioch Bridge.

Help us learn more about the birds at this IBA! Enter your birding data online at Calfornia eBird! (http://ebird.org/california/)

Conservation Issues

Many of the corn and rice harvest patterns within this IBA are currently ideal for supporting large numbers of sensitive bird species in winter, as is the presence of numerous private duck clubs that manage for waterfowl and open-country species. Though plans have been floated to create a "North Delta National Wildlife Refuge", only a fraction of this IBA is currently in public hands, which has led to widespread and ongoing destruction of its terrestrial and wetland habitats. The in-stream islands are being eroded away as channelization projects increase water speed through the Delta. Conversion of row crops (including grains) to vineyards continues apace with other parts of the Central Valley, with 1000 acres lost each year during the late 1990s within a three-mile radius of the Phil and Marilyn Isenberg Reserve (fide W. Holt). Since the tracts and islands are often lower than the surrounding landscape, breaks in levees leave deep reservoirs that are too deep to support wetland vegetation or, for that matter, rare anadramous fish habitat. Reservoir construction (to provide water to the expanding residential subdivisions from cities surrounding the Delta) remains popular and threatens open space locally, as does urbanization. For example, the 5000-acre Steward Tract was recently annexed to the City of Lathrop, and thousands of acres were added to Stockton during the 1990s.

Ownership

? Liberty/Ryer Islands, Solano Co. (Private)
? Sherman Island, Sacramento Co. (DFG ? ?Lower Sherman Island W.A.?)
? Tyler Island, Sacramento Co. (Private)
? Webb Tract, Contra Costa Co. (Private)
? Holland/Palm Tracts, Contra Costa Co. (Private)
? Big Break/Iron House WTP, Contra Costa Co. (incl. Big Break Regional Shoreline, East Bay
Regional Park District)
? Piper Slough, Contra Costa Co. (Private, with public boat access)
? Bouldin/Venice/Mandeville/Medford Islands and Empire/Ringe Tracts, San Joaquin and
Contra Costa Co. (Private)
? Brack Tract/White Slough, San Joaquin Co. (DFG ? ?White Slough W.A.?)
? Staten Island, San Joaquin Co. (The Nature Conservancy)

Habitat

This IBA is centered on the southwest arm of Sacramento County, roughly halfway between Sacramento and the East Bay cities of Antioch and Concord. This portion of the Sacramento Delta, from Walnut Grove downstream to Oakley, was formerly a vast region of bulrush (?tule?) marsh with brackish water. The conversion of this area to agriculture in the late 1800s involved ?reclamation? of these wetlands ? the construction of levees along channels and draining the resulting islands of land for farming. These large blocks of farmland, many of which have sunk up to 25? below sea level, are alternately known as ?islands? or ?tracts.? Not to be confused with these islands of agricultural are numerous small islets (up to several acres in size) within large river channels that are either natural remnants or mounds of dredge spoils left over from levee construction. These have since converted to or retained native riparian and tidal marsh vegetation, often the only such habitat for miles around.