It's amazing how smart they are. When I got my 17hmr when I was 18 I took that gun to the barn every morning to try and pick off a crow or two in the pasture. I didn't really shoot crows anywhere else. After a summer of that I don't think you could get within 300 yards of a crow until the new crop came next year.
Crows are incredibly intelligent birds, there was a program on a nature show a few years back that was an hour long. It delved into the crow and its intelligence. If folks ever get a chance to watch that 1 hour documentary, it is very enlightening and well worth it.
Amongst other things, they showed that crows can convey information to their group and even describe things to the crows that have never seen such things. Why does the crow the off when you come out with a gun? ...... Because it recognizes the gun.