This was a good year for this distinctive species. This is presumably the more northerly breeding nominate subspecies D. c. caerulescens. This has always been one of my favorite birds. Before I was old enough to own binoculars, these low foraging warblers sometimes gave me identifiable views which I carry in memory to this day.
Among the warblers, this is a unique species with no close relatives. Although it's plumage pattern and behavior suggest a relationship with the American Redstart, such a relationship is not supported by DNA evidence. Also the buzzy song of the Black-throated Blue seems closer to other species. Canon PowerShot S3 IS 12x