After spreading across North America, West Nile virus (WNV) arrived in the Sacramento Valley of California in 2004 and began killing many corvids. To estimate the regional effect of WNV on corvids and other birds, we reinitiated a road survey along six routes totaling 203 km in the Sacramento Valley. We surveyed these transects 30 times in fall and winter from 1990 to 1995 and repeated the surveys each fall and winter from 2005 to 2008. By 2007–08, annual maximum counts of the Yellow-billed Magpie, American Crow, and Loggerhead Shrike had declined 83%, 63%, and 63%, respectively, from those of the 1990s. These species declined in riparian and rice-cultivation areas, most substantially outside Yolo County. The magpie declined 90% along our routes north of Yolo County, causing us concern for the viability of the species. After a lag, the crow began declining quickly in 2007. We recommend the Yellow-billed Magpie be given special status. Also, searches for Yellow-billed Magpies should be extended across the species' range to find locations with sizable numbers, and experimentally designed mosquito control should be considered in breeding areas, especially in areas of high densities of Culex mosquitoes.
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Vol. 111 • No. 2