Well, that's definitely a hawk alright! (calling upon my vast expertise)
I agree with everybody it's hard to ID with just a couple pictures. Those are really great pictures, by the way. Love 'em or hate 'em, you have to admit birds of prey are cool.
Question: How does it fly? Does it soar in, or fly swift with steady, pointed wings, or zigzag through the trees?
Looks like a youngster, whatever it is. That would also explain him dive-bombing and casing--an experienced adult would have nailed one of your birds on the first try. I don't think it's a merlin--doesn't look like a falcon. The shape sure looks like something of the accipiter clan, but immature coopers, sharp-shinned, and goshhawks all have yellow eyes. I'm guessing you have an immature red-tail.
There's some great BOP identification info here: http://www.mbr-pwrc.usgs.gov/Infocenter/infocenter.html#Accipitridae
None of which helps you in any way.
Good luck keeping your birds safe. Some falconer needs to come up with a breed of "guard birds" that can be trained to chase away other hawks. The Great Pyrenees Eagle, the Doberman Falcon, something like that.
Tom

I agree with everybody it's hard to ID with just a couple pictures. Those are really great pictures, by the way. Love 'em or hate 'em, you have to admit birds of prey are cool.
Question: How does it fly? Does it soar in, or fly swift with steady, pointed wings, or zigzag through the trees?
Looks like a youngster, whatever it is. That would also explain him dive-bombing and casing--an experienced adult would have nailed one of your birds on the first try. I don't think it's a merlin--doesn't look like a falcon. The shape sure looks like something of the accipiter clan, but immature coopers, sharp-shinned, and goshhawks all have yellow eyes. I'm guessing you have an immature red-tail.
There's some great BOP identification info here: http://www.mbr-pwrc.usgs.gov/Infocenter/infocenter.html#Accipitridae
None of which helps you in any way.

Tom