The majority of reports support model of eastward expansion from the Pacific Coast most probably using river systems as migratory pathways. In Figure 2, first detection data for this year was sorted into two groups and graphed. The coastal group includes all reports from the Oregon Coast and Puget Sound in Washington. The Inland Valley group represents most Willamette Valley records. From the available data, it is possible to speculate on the migration pathways for the early part of the migration.
Most birds start their migration along the coast.
The earliest arrivals, apparently continue up the coast and track east at Grays Harbor, Washington through the lowlands of the Chehalis River into Puget Sound. Some birds probably turn east at the Umpqua Valley in Oregon and begin working their way north, reaching Portland at about the same time that coastal route birds reach Puget Sound.