Some of the tiny warblers are tricky to identify, but the Black-throated Blue Warbler is hard to confuse with the others I've seen so far. Even in the shadows when the blue is difficult to distinguish from the black, the white spot on each wing is a dead giveaway.

Most of the warblers I've seen I haven't seen for long; they flit from spot to spot before I can even aim the camera at them. This Black-throated Blue Warbler was a pleasant exception; it posed out in the sunlight just long enough for me to get a few shots I was happy with (and the usual zillion I deleted.)