I think this is a Sharp-shinned Hawk although being not much of a birder... Anyone? This bird let me get right under its tree and circle completely around. When it finally left, it swooped down at me and shot off so fast that I couldn't see where it went! Too bad I was without my telephoto, making these pictures heavily cropped.
I'd earlier passed by this shot for posting. It was a bit fuzzy and I caught the bird just as it was leaving the frame--right after this shot is when it dove at me. Surprising what Photoshop's Smart Sharpen can accomplish...
I think this shot better than the others details some tail roundness but it's all relative and unknown to me. I'm tempted to call it Cooper's. Any further thoughts on this?
P.S. I noticed that the Comments widget has its own opinion on species! I'd used that name when first laying out the post, before very much research. Now it seems that it won't let go.
And the final word is that this is a male Cooper's Hawk, Accipiter cooperii. See the comments for details!