Mebits,
".........I'm going to say that the coopers are too fast and thus it's a bad gambit to start a fight with them. No real risk of an unprovoked attack by a coopers, but if he turns on you, you can't get away........."
I think being bigger, and often in groups, or at least breeding pairs, the crow is too much bird for the smaller Coopers Hawk. Plus, the Coopers has more than enough smaller birds to feed on without having to tangle with the bigger crow.
Even the much larger Redtails try to avoid the Crows.
But, the Red tails will only put up with just so much from them. Ever see how a Red tail will flip upside down and claw at the underside of a Crow as the Crow dives past trying to get a hit on the Redtail ? The Red tail can flip upside down backwards just long enough to get a hit in on the Crow and while they are doing that, they keep going forward without loosing any speed. It's amazing to watch a Crow/Red Tail dog fight.
Paul.