This Important Bird Area encompasses a large patch of grassland and constructed wetlands in one of the fastest-growing regions of California, on the outer ring of bedroom communities for the East San Francisco Bay Area that includes Oakley, Brentwood and Tracy. The "Byron Grasslands" (no formal name) lie in the ecotone between the eastern shoulder of the Diablo Range and the floor of the Central Valley, west of Byron Highway and south of Highway 160. Some of the best habitat here is centered on the Byron Airport. The non-profit Trust for Public Land acquired the 4000-acre "Cowell Ranch" property near Brentwood in 2002, but much of the grassland here remains in private hands. The Clifton Court Forebay is a 2000-acre water retention basin managed by the California Department of Water Resources at the southernmost portion of the current Sacramento Delta wetlands ecosystem.

This Important Bird Area encompasses a large patch of grassland and constructed wetlands in one of the fastest-growing regions of California, on the outer ring of bedroom communities for the East San Francisco Bay Area that includes Oakley, Brentwood and Tracy. The "Byron Grasslands" (no formal name) lie in the ecotone between the eastern shoulder of the Diablo Range and the floor of the Central Valley, west of Byron Highway and south of Highway 160. Some of the best habitat here is centered on the Byron Airport. The non-profit Trust for Public Land acquired the 4000-acre "Cowell Ranch" property near Brentwood in 2002, but much of the grassland here remains in private hands. The Clifton Court Forebay is a 2000-acre water retention basin managed by the California Department of Water Resources at the southernmost portion of the current Sacramento Delta wetlands ecosystem.

For IBA map, click here.

Updated December 2008

This region has become increasingly important for wintering raptors that cannot persist in intensively-farmed and/or developed areas of the southern Delta. Large numbers of waterfowl utilize the open water of the forebay during winter and migration (e.g. c. 3000 Tundra Swan on 2002 East Contra Costa County Christmas Bird Count), particularly for nighttime roosts. Short-eared Owl breeds in the wet grassland here (one of the few nesting areas left in the Central Valley), and Burrowing Owls utilize the raised, sandy spots here for nesting, having been eliminated from much of the valley floor. Lesser Nighthawk also breed in sandy, scrubby areas that have been extensively converted to agriculture elsewhere, and Swainson's Hawk nest in scattered clumps of trees (mainly planted Eucalyptus), about the closest they breed to the Bay Area.

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Although Clifton Court Forebay is fairly well protected, the grassland habitat within this Important Bird Area is being whittled away each year by housing tracts and associated road construction. Hopefully, the acquisition of Cowell Ranch can leverage additional conservation acquisitions in the region.