I used to give crows a lot of credit for brains. I've changed my mind, I give them a lot of credit for eyesight!
ALL the sounds that come on e-callers work, and when you see how they react to those sounds, how they sometimes hang around while being shot at, you will see it is eyesight! I recently bought a Primos Power Dogg and the crow sound on there works well too. I was at the end of a stand for coyotes one day recently and heard a crow off in the distance. I switched sounds to test the crow call and it worked like magic. Turned off the call and let them filter away, and called them right back, several times. I was 70 yards away with a .243, so they never saw me. Had I been near the call, I would have needed to be totally hidden.