Hmmm, I don’t know whether it was male or female then. There was no other object for me to compare it to, but I’m guessing it was around 15-16”. Are the females markings different? What should I look for the next time I see it? It’s come around twice in the last week.
1) The female Cooper's is the largest. If it looks real big, it's a female Cooper's.
2) The male sharp-shinned is real little (relatively). If it looks real little, it's a male sharp-shinned.
Now the problems: the male Cooper's is barely bigger than the female sharpie. And they look a lot alike. But here are some helpful ID tips:
Cooper's Hawks have rounded tail tips while sharpies have squared off tail tips. Also, Cooper's Hawks have big, prominent heads (the birder slang is blockhead), while sharpies have small heads with almost no neck (birder slang is pinhead).
Nevertheless, sometimes the ID can't be definitively made. On my survey form, one of the options is "Unknown Accipiter." Even expert birders will be forced to use that option occasionally.