The San Joaquin River NWR covers more than 6,500 acres at the confluence of the San Joaquin, Stanislaus and Tuolumne rivers. Together with 250-acre Caswell Memorial State Park, this IBA protects the most significant patch of lowland riparian woodland remaining in the San Joaquin Valley. Though other National Wildlife Refuges in the valley have only limited stringers of riparian thicket, this refuge features Christman Island, an 800-acre block of dense riparian jungle that has only recently (2001) been investigated by ornithologists (fide J. Gain), as well as an uncultivated floodplain dotted with enormous Valley Oaks. Christman Island has been selected to form the core of a 1300-acre riparian restoration project along the San Joaquin River (J. Hammond, PRBO, via email). Caswell, on the Stanislaus River just to the north, is relatively tiny by comparison, yet its Valley Oak riparian woodland represents one of the most intact and ecologically diverse riparian systems in the state (TNC 1998). Most of the refuge is maintained in agriculture (pastureland, corn, winter wheat), and is managed through the San Luis NWR Complex. Other important habitat areas include remnant wetlands along the San Joaquin River, bounded by Keyes and Carpenter roads (including the settling ponds of the Modesto Wastewater Treatment Plant (WTP) and adjacent alfalfa fields that are flooded in winter).

Updated by Stanislaus Audubon, September 2008

Ornithological Summary

San Joaquin River NWR owes its existence to the Aleutian Canada Goose, whose Recovery Plan identified it as a key management area, supporting nearly the entire global population in winter (USFWS 2003b). This flock is joined by several hundred Sandhill Crane, a handful of the scarce Tule race of the Greater White-fronted Goose, and by Cackling Canada Goose. The flooded fields in the area are notable for hosting large concentrations of wintering waterfowl, especially Northern Shoveler (c. 40,000), Ruddy Duck (20,000) and Gadwall (5000). About 30% of the world's Aleutian Canada Goose population that winters at the San Joaquin NWR roosts at night on the ponds at the Modesto WTP. Large numbers of shorebirds (mainly peeps, Dunlin and dowitchers) utilize these habitats during spring and fall migration (incl. the nearby Ceres WTP), and small numbers of Pacific Golden-Plover are now regular. A handful of Snowy Plover bred recently at Modesto WTP, one of their few Central Valley nesting sites north of the Tulare Lake Basin (fide J. Gains). The nearby fields flooded with treated effluent are appealing to large numbers of White-faced Ibis and Long-billed Curlew in winter, along with Short-eared Owl. During the summer, Northern Harrier breed in abundance in the alfalfa. Riparian birds eliminated elsewhere in the San Joaquin Valley, including California Thrasher and Yellow-breasted Chat, continue to maintain small numbers, particularly at Caswell, which was the site of a recent summer record of Yellow-billed Cuckoo, offering hope that a population of this species may persist somewhere between the northern Sacramento Valley and the South Fork Kern River in the southern Sierra. Several woodland species that probably occurred throughout Central Valley woodlands breed here, including Western Wood-Pewee and Hutton's Vireo (TNC 1998). The remnant gallery forest along the San Joaquin River throughout this IBA has great restoration potential, and supports numerous pairs of breeding Swainson's Hawk. Other sensitive wildlife here includes the Riparian Woodrat and the Riparian Brush Rabbit, the latter occurring nowhere else on earth.

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Conservation Issues

The main management concerns of this IBA involve its small size relative to the vast amounts of ecologically sterile agricultural lands just outside its borders. The NWR staff is currently working with local landowners to increase the aggregate amount of wildlife habitat in the region through easements in order to alleviate some of the pressure on public lands. A less direct but still major threat involves the continued degradation of habitat connectivity between this IBA and the Sierra via the Stanislaus and Tuolumne rivers, major valley waterways that are probably critical to maintain the richness of the natural community here. Disturbingly, The Nature Conservancy (1998) reports that the Army Corps of Engineers has been acquiring river frontage easements along the Stanislaus River corridor, giving it "exclusive right to do whatever it needs to reduce the threat of flooding on its easements, including vegetation clearing, rip-rapping, and levee patching." It is hoped that the Modesto WTP can be encouraged to manage for wildlife as well as for water quality, as other plants have done elsewhere in California (e.g. Arcata Marsh in Humboldt Co.; Hemet-San Jacinto WTP in Riverside Co.). Because so much of the land in the area is private, all of the habitat outside the boundaries of the refuges and the state park should be considered to be somewhat threatened.

Ownership

The San Joaquin River NWR covers 15,000 acres at the confluence of the San Joaquin, Stanislaus and Tuolumne rivers. Together with 250-acre Caswell Memorial State Park, this IBA protects the most significant patch of lowland riparian woodland remaining in the San Joaquin Valley.

Habitat

The San Joaquin River NWR covers 15,000 acres at the confluence of the San Joaquin, Stanislaus and Tuolumne rivers. Together with 250-acre Caswell Memorial State Park, this IBA protects the most significant patch of lowland riparian woodland remaining in the San Joaquin Valley. This refuge features Christman Island, an 800-acre block of dense riparian jungle as well as an uncultivated floodplain dotted with enormous Valley Oaks. Caswell, on the Stanislaus River just to the north, is relatively tiny by comparison, yet its Valley Oak riparian woodland represents ?one of the most intact and ecologically diverse riparian systems in the state? (TNC 1998). Most of the refuge is maintained in agriculture (pastureland, corn, winter wheat). Other important habitat areas include remnant wetlands and riparian habitat along the San Joaquin River, bounded by Keyes and Carpenter roads (including the settling ponds of the Modesto WTP and adjacent alfalfa fields that are flooded in winter).

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