I've seen it a lot. I've seen crows after owls and hawks. They make an awful racket. 34 years ago, opening day of my second deer season, I had it happen in a tree next to me. the crows were after a hawk. It went on for 15-20 minutes and it was driving me crazy so I shot a slug into the tree to scare them off. I have no way to prove it but a believe it makes deer nervous and they avoid the area till things quiet down.