From what I've read, Coopers and Sarp Shinned are pretty hard to tell apart particularly because the larger female and smaller male blurs the size difference as a discriminator. Yesterday a Coopers (pretty sure) was chasing a sparrow through my front yard. Pretty amazing display of flying maneuverability! They both flew along the side of the house going around a bay window - I just happened to be standing at the window at the right time. Wish I'd had my camera, but honestly it was all too fast and close to track. LOL!!!