Science foundation Chapter 5 Appendix 5.1: Case study shore birds: Western sandpipers (Calidris mauri) and American avocets (Recurvirostra Americana)

Western sandpipers (Calidris mauri) are small (22-35 g) sexually dimorphic sandpipers, with males typically smaller than females. Western sandpipers frequently occur in mixed species flocks along with other Calidris species, including least sandpipers (Calidris minutilla) and dunlin (Calidris alpina), in the San Francisco Bay Estuary (SFBE) and are the most abundant shorebird species found from fall to spring. Western sandpipers are one of the most common shorebird species in SFBE, the Pacific Flyway, and North America overall. The largest concentrations of western sandpipers, and of most shorebirds, are found in the South Bay where large expanses of mudflats are exposed at low tide and managed and/or salt ponds are available for high tide roosting and feeding habitat (Warnock et al 2002, Warnock and Takekawa 1995). In recent years, there is some evidence that there has been a shift in shorebird numbers towards the North Bay, perhaps as large salt pond restoration projects provide interim mud flat habitat during the evolution towards tidal marsh habitat (Pitkin and Wood, 2011).