Encompassing 3,200 square miles, the Santa Ana River Watershed is the largest drainage in coastal southern California.  Since 1997, the Santa Ana River Watershed Program has been working to reverse the negative effects of the large and growing human population living in this watershed.  We tested the theory that we could restore the natural functions of the river and its resources through control of destructive, invasive species, ensuing restoration of habitat, and wildlife management emphasizing rare and endangered species.  About half of the riparian woodland on the river had been replaced by giant reed, Arundo donax.  We are examining the feasibility of controlling 10,000 acres of weeds, replacing them with native cover through natural succession, and documenting increases in migratory songbirds.  Nearly 3,000 acres of giant reed have been removed and native riparian habitat has expanded into at least 60% of the reclaimed floodplain.  Migratory songbird populations including the endangered least Bell’s vireo, Vireo belli pusillus have greatly benefited with the increased habitat and our management efforts.  By 2004, the vireo population on the Santa Ana River at 837 territories had become the largest in existence and had grown to 992 territories by 2005.  The significance of these results is the scale of the restoration and recovery achieved without re-planting efforts.