The first thing we notice is how bright yellow this bird is, and we can go straight to looking at the wood-warblers. Remember that this photo was taken in spring so we are looking at a male bird in alternate plumage. We can rule out a large number of them, and just think about the species with brightly colored breasts and bellies, dark streaking, and tail spots: Magnolia, Cape May, Eastern Palm, Pine, Kirtland's, and Prairie. Pine Warbler and eastern Palm Warbler do not have black streaking that matches this individual so we can fairly quickly rule those out, leaving only these other four species.
If you clicked on the photo to enlarge you could see somewhat more clearly that the belly itself is pale, and so is much of the undertail coverts, but there is still some yellow-buff coloration posterior to the legs. Magnolia Warbler has bright white undertail coverts and broad black tips to the rectrices, therefore it is out. The dark streaking on Kirtland's Warbler really only extends down the sides of the breast and flanks, but this bird has streaking creeping down into the middle of the breast. Also, the dark tips to the rectrices extend completely around the tip of each rectrix isolating each individual spot unlike Kirtland's which has white extending all the way to the tips. So Kirtland's is out.
That leaves Prairie and Cape May Warblers. The dark tips and the streaking can also be used against Prairie Warbler. Additionally the pale gap in the yellow would be atypical for any Praire Warbler I've ever seen which tend to be fairly bright yellow all the way through the belly. Even the undertail coverts tend to be mostly yellowish. So I'm going with Cape May, which it is, but I knew the answer ahead of time. The lighting on the undertail really may not have been sufficient to be certain of an ID. Thanks for playing.
|A much more identifiable image of the Cape May Warbler. Presque Isle State Park, Erie, PA 5/2/13|