This bird caused me a lot of trouble, as I could only get broken looks at it thru vegetation, and never did see the upperparts. It had to be a Yellow Warbler, evidently one of the darker 'amnicola' subspecies that migrates later than our local birds and breeds across much of Canada.

The look of a dark post-ocular line is just an artifact, not noticed in the field. A decent look at the tail finally convinced me that it was a Yellow Warbler, with the short tail with yellow spots.