72 Microseasons of the Pacific Northwest

By the first days of July, the first wave of southbound shorebirds has already returned to Pacific Northwest estuaries — a phenomenon that surprises many observers who think of migration as strictly a spring event. These are mainly adult birds, disproportionately females, that nested early in the Arctic or subarctic or whose breeding attempts failed, and they waste no time beginning the 7,000-mile journey back toward South American wintering grounds. The vanguard species include Western Sandpipers (Calidris mauri), Short-billed Dowitchers (Limnodromus griseus), Least Sandpipers (Calidris minutilla), and Semipalmated Plovers (Charadrius semipalmatus), all arriving in nonbreeding or transitional plumage. Grays Harbor National Wildlife Refuge on the Washington coast is one of the four most important shorebird staging estuaries in North America. The refuge's Bowerman Basin unit, a 1,500-acre complex of salt marsh and intertidal mudflat, hosts tens of thousands of birds during this first southbound pulse. Birders watching the falling tide can observe sandpipers probing the soft sediment at extraordinary density — stitching patterns in the mud as they feed on amphipods, polychaete worms, and small mollusks. At Boundary Bay in British Columbia, the vast Tsawwassen tidal flats — accessible from the Delta shoreline — receive Western Sandpipers by the thousands alongside rarer Baird's Sandpipers (Calidris bairdii), Sharp-tailed Sandpipers (Calidris acuminata), and occasional Red Knots (Calidris canutus). On Puget Sound, Padilla Bay and the Nisqually National Wildlife Refuge estuary attract smaller but impressive concentrations. The key to finding these birds is timing: during a falling or low tide, mudflats are exposed and birds are pressed into visible feeding aggregations. At high tide they roost in tight flocks in marsh grass or open beaches. Unlike the spectacular spring staging at Grays Harbor (late April–May, when northbound birds pack the flats), the July return is quieter but sustained, with new arrivals trickling through for weeks. Juvenile birds, with their crisp, scaly upperparts, follow the adults by four to six weeks, providing a second wave of activity in late July through August.