The Cosumnes River is the only major river draining the western Sierra Nevada that remains entirely un-dammed and with a natural, snowmelt-fed flood regime. Managed by a consortium of non-profits and agencies, the Cosumnes currently (2009) protects over 45,000 acres of floodplain riparian woodland (both original and restored); grassland (including vernal pools); and freshwater wetland just south of Sacramento. Protected lands, including cooperative agricultural ventures and easements, extend from the confluence of the Cosumnes and the Mokelumne rivers (just west of I-5) then northeast to beyond I-99 to the town of Wilton east of Elk Grove.

Updated by Sacramento Audubon, November 2008

Ornithological Summary

The Cosumnes is a year-round magnet for birds, including many sensitive species that have long been extirpated from the most of the Central Valley. Numbers of Greater Sandhill Crane (a rare subspecies) wintering on the preserve alone average 1500 birds, a significant proportion of the state's population (J. Trochet, in litt., citing A. Engelis). Breeding raptors include Swainson's Hawk (3-5 pr.), White-tailed Kite (5-10 pr.) and Northern Harrier (at least 5 pr.). The preserve appears to also be important for summer (pre-migration) concentrations of raptors, which have included up to 100 Swainson's Hawks and 200 White-tailed Kites. Up to 25 American Bittern per year have been bred in the freshwater marshes, which have recently supported calling (and presumably breeding) Least Bittern and even the occasional Black Rail. The grassland toward the eastern portion of the preserve supports presumably-breeding Grasshopper Sparrow and Tricolored Blackbird, as well as a diverse community of wintering raptor such as Ferruginous Hawk and Burrowing, Short-eared and Long-eared owls. The agricultural lands north of the Preserve, particularly along Eschinger and Caroll Roads are important for Burrowing Owls (via email C. Conard). Large numbers of waterfowl utilize the preserve in winter, regularly exceeding 20,000 birds. Northbound shorebirds in spring regularly exceed 1000 birds, with 8500 recorded on one day in mid-April, 1998. Songbird migration is also well-documented here (in contrast to many Central Valley sites), with counts of up to 50 Willow Flycatchers utilizing the riparian forest edge. The riparian woodland, currently being augmented by restoration plots on former orchards and pastures, supports mainly the common obligate passerines, though a smattering of summer records for Yellow Warbler and Yellow-breasted Chat offer hope that the original riparian avifauna of the area can be restored. Ornithological monitoring has been ongoing at the Cosumnes since the late 1980s (PRBO, Sacramento Audubon, John Trochet).

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Conservation Issues

The importance of this IBA increases each year, as the surrounding area becomes dominated by office parks, corporate farms and vineyards. Cowbird parasitism remains a threat to the reproduction of songbirds within this IBA, as it is surrounded by dairies and pastureland, though no agency or group has committed to supporting a long-term trapping program (J. Trochet, pers. comm.). Although most of the lands within the preserve itself are secure, threats to the surrounding landscape could seriously impact its resources, including urban encroachment from the burgeoning suburbs of Sacramento on the north and Stockton on the south, which very realistically threaten to constrict the preserve to a narrow corridor from the Sierra foothills to the Sacramento River Delta. Agricultural run-off continues to pose a threat, especially given the proliferation of vineyards in the area (TNC 1998).

Ownership

Managed by a consortium of non-profits and agencies, the Cosumnes currently (2001) protects about 54,000 acres of floodplain riparian woodland. Listed below are the land owning partners found on
http://www.cosumnes.org/mission.htm.

Bureau of Land Management -- Folsom Field Office

California Department of Fish and Game

Ducks Unlimited, Inc.

California Department of Water Resources

Sacramento Co. Dept. of Regional Parks, Open Space, and Recreation

The Nature Conservancy

Wildlife Conservation Board

Habitat

The Cosumnes River is the only major river draining the western Sierra Nevada that remains entirely un-dammed and with a natural, snowmelt-fed flood regime. The Cosumnes currently (2001) protects about 15,000 acres of floodplain riparian woodland (both original and restored); grassland (including vernal pools); and freshwater wetland just south of Sacramento. The Cosumnes River Preserve protects one of the healthiest remaining valley oak riparian (streamside) communities.

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