Large numbers of migrant and resident shorebirds feed and roost along the open coast, bays, sloughs, and marshes of California. However, more than 70% of coastal wetlands in California have been degraded by diking, filling, pollution, and other human activities (Speth 1979). Elkhorn Slough is one of the largest remaining salt marshes in California available to migratory shorebirds using the Pacific Flyway. Identification and conservation of critical habitats are required for an understanding of shorebird ecology and effective management of our resources (Senner and Howe 1984).