I've called and shot them using both electronic callers and mouth calls. The mouth call is more work, obviously, and somewhat distracted me from the job at hand, but it got the job done.
A guy I bear hunted with would park his truck in thick cover near some young pines, roll down all his windows and play a crow calling cassette on his truck stereo. He would stand in the nearby pines to hide himself.
The pine tree trick works great. A cluster of pines about 10' tall are perfect. Crows can't see you until they're on top of you, and by then it's too late, if you're doing your part.
