Extending across the central and eastern floor of the Central Valley between 50 and 100 miles north of Sacramento, several National Wildlife Refuges, State Wildlife (Management) Areas and private sanctuaries anchor one of the most significant areas of wetlands habitat in the nation. Ownership of this area is divided into 24,000 acres of federal lands managed as the Sacramento NWR Complex (incl. Sacramento, Delevan, Colusa, Sutter, and Butte Sink NWRs and Llano Seco Ranch), 9000 acres of the state-managed Gray Lodge and Upper Butte Basin Wildlife Management Areas, and 850 acres at National Audubon Society's Paul L. Wattis Sanctuary. Hundreds of thousands of rice fields and private duck clubs in the area contribute substantially to the habitat within this large IBA. The Sacramento River NWR, also managed as the Sacramento NWR complex, is treated under the Sacramento River Upper IBA.
Updated October 2008
This IBA is a principle wintering area for Greater Sandhill Crane in the state, and nearly the entire global population of Tule Greater White-fronted Goose winters within the Sacramento Valley, among the 300,000 + White-fronts that regularly occur (BD). Between 5 and 25% of the state's population of Ross' Goose winters at Gray Lodge WMA alone. Tens of thousands of Tricolored Blackbirds breed here, making it one of the most critical areas in the state for this species. Flooded fields and drained impoundments make this IBA among the most important areas in the interior of the state for wintering and migrant shorebirds (DS). Many of the significant birds of this IBA are not evenly distributed, and are strongly dependent on local management practices at the individual units of the refuges. Flooded rice fields are found virtually throughout, which can host over a million waterfowl between November and March, with the number increasing through the winter as habitat in northeastern California freezes up. Each winter, the NWRs average 300,000 Northern Pintail, as well as 50,000+ Mallard, American Wigeon and Green-winged Teal (J. Kemper, in litt.). In summer, rice fields (on private lands surrounding the refuges) become attractive to wetlands breeders such as Black Tern, which are otherwise largely confined to the Modoc Plateau of northeastern California. Around half the state's nesting population of Black Tern was on wetlands of the Sacramento Valley (Shuford et al. 2001). Where watered throughout the summer, the freshwater marsh habitat throughout the IBA hosts nesting White-faced Ibis (especially at Colusa, Delevan and Sacramento NWRs), and represents some of best remaining breeding habitat in the Central Valley for both American and Least bitterns. Sutter NWR (see Gilmer et al. 1998) and Gray Lodge boast the best-developed riparian habitat, but recent events have decreased the value of Gray Lodge for several riparian-obligate breeders.
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Major concerns to the avifauna of this IBA include the proliferation of non-native plants and animal species, and the periodic outbreaks of communicable diseases (avian cholera, avian botulism), associated with high concentrations of species coming into contact with each other. Similar outbreaks have been documented at other large wetlands in the state with regular aggregations of several hundred thousand waterfowl (e.g. the Salton Sea). Grassland and riparian birds currently receive much less management attention relative to waterfowl within this IBA, and flooded fields (particularly rice fields) on private lands should be considered important wetland bird habitat (Shuford 1998a). Fires set for purposes of thinning stands of bulrushes and riparian scrub (to improve waterfowl habitat) remain an impediment locally to the development of riparian habitat, though several managers are making efforts to maintain riparian habitat in various levels of succession, particularly along watercourses. Finally, feral cats are now present throughout this IBA, and may represent a major threat to ground-dwelling birds (Gilmer et al. 1998).
Ownership of this area is divided into 24,000 acres of federal lands managed as the Sacramento NWR Complex (incl. Sacramento, Delevan, Colusa, Sutter, and Butte Sink NWRs and Llano Seco Ranch), 9000 acres of the state-managed Gray Lodge and Upper Butte Basin Wildlife Management Areas, and 850 acres at National Audubon Society?s Paul L. Wattis Sanctuary. Hundreds of thousands of rice fields and private duck clubs in the area contribute substantially to the habitat within this large IBA.
This IBA is one of the most significant areas of wetlands habitat in the nation. ). Sutter NWR (see Gilmer et al. 1998) and Gray Lodge boast the best developed riparian habitat.
"Wetlands: Emergent Herbaceous Wetlands: Other" refers to flooded rice fields