Yellow-rumped Warbler, Newport, Oregon on 2 October 2009 by Greg Gillson.
Now that fall is here and winter on the way, most neo-tropical migrants are either rushing south, or have done so already.
That includes the warblers. By mid-October only a few Common Yellowthroats can be scoured out of the marsh grasses. They'll be gone within days. Townsend's Warblers move out of the northern mountain pines to winter in lowlands in the Pacific NW, primarily west of the Cascades.
Right now, though, the Yellow-rumped Warblers are making their way south. Some will go to Mexico. Some will winter here in the Pacific NW. They will spend the winter in a location where insects remain in unfrozen areas. They also change their insectivorous diet to eat more fruit and berries.
In breeding plumage these are striking birds with blue-gray bodies with white wingbars and either white ("Myrtle" form) or yellow ("Audubon's" form) throats. In all plumages and in both forms, the tell-tale field mark is the obvious yellow rump patch.
The bird above is in a very dull non-breeding plumage. It is probably a first fall female Myrtle form of Yellow-rumped Warbler. I photographed it in an alder grove a couple of weeks ago on a trip to the coast.