Those of us with more than just a little knowledge of North American birdlife will unhesitatingly identify this issue's quiz bird—at least generically—as a vireo. A small songbird with a uniformly deep, non-conical bill leaves no other choice except, perhaps, the Northern Beardless Tyrannulet (Camptostoma imberbe). A tyrannulet, however, would have a smaller, daintier bill than the bird shown here.
Let me add at this point (in an attempt to further confuse the issue) that although this is a black-and-white print, the color original reveals little more. In life, this bird was white below and gray above, with scarcely a trace of green or yellow.