The Western Sandpiper is the most numerous shorebird on the Pacific Coast of North America. It migrates along the Pacific Coast of North America each spring for breeding grounds in western Alaska and eastern Siberia, and returns in summer and early autumn to winter quarters from southern USA to Ecuador.

About 3 to 4 million western sandpipers are thought to exist in the world. The number of Western Sandpipers has declined in censuses made annually during the spring migration on the Fraser River delta, British Columbia. Several million sandpipers were estimated to use the delta in the early 1990s but by 2004 the number had dropped to about 500,000 individuals. One hypothesis for the census decline is that individual birds are staying for a shorter time and consequently are not counted on multiple days. The decline in the duration of stay coincides with an increase in sightings of Peregrine Falcons on the delta beginning in the mid 1980s.

Like many species of shorebirds, the western sandpiper’s habit of gathering in great numbers at a few sites makes them vulnerable to single events such as an oil spill. However, shorebirds are also impacted by the cumulative erosion of many sites from industrial development of the mudflats, contamination of food supplies, and human disturbance. Western Sandpipers make land fall at many industrialized mudflats including Humboldt and San Francisco bays and Salton Sea in California.

The western sandpiper is present in large numbers during spring migration in April and May when adults migrate north to breed, and during summer migration from late June to September when adults, followed by juveniles, migrate south for the winter. Each sandpiper stops for only a few days to rest and refuel. Western sandpipers feed on tiny marine invertebrates and biofilm in the organic layer of mudflats rich in organic matter.