Yellow-rumped Warbler, Forest Grove, Oregon on 23 March 2012 by Greg Gillson
Both the white-throated Myrtle form and yellow-throated Audubon's forms of Yellow-rumped Warbler are migrating through right now. Interestingly, the Myrtle Warblers are still in dull winter plumage, while most of the Audubon's Warblers are in bright breeding plumage--and the males are singing!
There have been rumors for a couple of years that these forms will be re-split. They hybridize where their ranges meet in western Canada. They were lumped back in 1983.
I have written a previous post on Yellow-rumped Warblers.