The Grasslands Ecological Area is a 160,000-acre mosaic of Central Valley floor habitats located primarily within Merced County between I-5 and I-99 in the northern San Joaquin Valley, west of a line between Modesto and Fresno. It lies in the historic floodplain of the San Joaquin River, in an area historically prone to floods and poor farming soils. This vast network of freshwater marshes (permanent and seasonal), alkali grassland and riparian thickets is the result of decades of collaborative conservation agreements between private duck clubs, CA State Parks (Great Valley Grasslands), CA Department of Fish and Game(Volta, Los Banos, and North Grasslands wildlife areas), and the U.S. Fish and Wildlife Service (San Luis and Merced National Wildlife Refuges, Grasslands Wildlife Management Area). It is among the largest remaining areas of unplowed land on the floor of the Central Valley, and The Nature Conservancy (1998) has identified its Valley Sacaton Grassland (see Holland 1986) as the finest example of such habitat in the state.

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Updated February 2010

Ornithological Summary

This IBA is most notable for its abundance of native valley grassland and for its staggering concentrations of wintering waterfowl. It hosts a half-million individual ducks, geese, and swans each year between November and February, with Northern Pintail, Green-winged Teal, Northern Shoveler and Gadwall all having registered 100,000+ counts. It is also a major post-breeding dispersal area for American White Pelican (1000 counted on 20 August 1995; J. Fulton, in litt.). This IBA consistently hosts large numbers of breeding Tricolored Blackbirds, which average 5-10,000 breeding birds (RA), with over 60,000 typically wintering. Large numbers of wintering Sandhill Crane (high of 12,000+, including c. 25 Greater Sandhill Crane an average of over 10,000 Lesser Sandhill Crane) and Long-billed Curlew (up to 2000+) forage in its open pastures and fields, which host breeding colonies of Grasshopper Sparrow in the spring (RA). Winter roosts of White-faced Ibis were estimated at over 10,000 birds, making it the second-largest concentration of the species in winter in California, after the Imperial Valley (Shuford et al. 1996). It is a major stopover site for shorebirds moving through the Central Valley, with an average of 10,000 each fall, winter and spring, and over 200,000 counted during peaks (see Shuford et al. 1998), earning it a distinction as a Western Hemisphere Shorebird Reserve Site in addition to its recognition as a RAMSAR site. Several heron rookeries have developed here, with an average of 300 nests of Double-crested Cormorant, Great Blue Heron and Great Egret. Dozens of pairs of Swainson's Hawk breed, a significant percentage of the entire San Joaquin Valley population. The riparian bird community is best-developed along the San Joaquin River in the northwest section of the IBA, which supports breeding Yellow-breasted Chat, large numbers of Blue Grosbeak as well as the southernmost large population of the California-endemic Yellow-billed Magpie on the floor of the Central Valley (RA). Waterbird monitoring has been ongoing here for decades, and riparian songbird monitoring was initiated in the late 1990s, run in partnership with PRBO Conservation Science.

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Conservation Issues

Under the terms of the Central Valley Project Improvement Act (1992), a minimum flow of water must be maintained to the refuge and to private lands with easements for wildlife habitat. The GEA oversees 76 stream miles of existing or potential riparian habitat, and recent management plans have included the fencing of streambeds from cattle, the re-watering of ancient oxbows, and, remarkably, the de-authorization of portions of San Joaquin River flood control levees to restore the natural riparian ecology. Despite a vast network of easements and reserves within the GEA, the progression of land conversion, including urban sprawl along the Hwy. 152 corridor (e.g. Los Banos) and agricultural and industrial development region-wide, threatens the wildlife of this IBA. Non-native plants (incl. Yellow Star Thistle Centaurea solstitalis) remain a constant obstacle to conservation, but are being managed for by refuge staff. Giant Reed (Arundo donax) and perrenial pepperweed have established stands within the GEA. The conversion of native scrub habitats to grain crops (to attract game birds) has been an issue in the past, but current management seems sympathetic to the concerns of native wildlife. Interestingly, lack of grazing in portions of the IBA may become a possible threat to certain open-country species that thrive on the sparse, scrubby grassland maintained by cattle (TNC 1998). As an historical note, this IBA contains the infamous former Kesterson Reservoir, where thousands of water birds experienced acute selenium poisoning (including horrific birth defects and deformities) in the early 1980s due to improper storage of agricultural runoff. The site has since been cleaned up, filled in with soil, and absorbed into the GEA, and refuge managers are now keenly aware of the need to carefully manage runoff in and around the IBA.

Ownership

Collaborative conservation agreements are between private duck clubs, California State Parks, DFG (Volta and Los Banos wildlife areas), and the National Wildlife Refuge System (San Luis, Merced NWRs). The Nature Conservancy (1998) has identified its Valley Sacaton Grassland (see Holland 1986) as the finest example of such habitat in the state.

Habitat

The Grasslands Ecological Area is a 160,000-acre mosaic of Central Valley floor habitats. There is a vast network of freshwater marshes (permanent and seasonal), alkali grassland and riparian thickets. The GEA oversees 76 stream miles of existing or potential riparian habitat, and recent management plans have included the re-watering of ancient oxbows, and the de-authorization of portions of San Joaquin River flood control levees to restore the natural riparian ecology.

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