Birds of the South
This bird looks like a hummingbird and according to a bird identification website, this is a Ruby-throated Hummingbird. We can't see it, but the bird is supposed to have a red spot under its mouth and white going down its front side. What was in the identification that we can see is the dark green tail and green back. You can't see it in the picture, but it hovered quite often and had rapid wing movements. Also, like the website described it.