I actually participated in a group crow hunt for the first time in my life last year, and we had three set-ups within hearing distance of each other - about 80 acres N/S of each other and about 60 acres from E/W.
We had the crows doing a round-robin for about 3 hours. It seemed like they would play along for a while, until a few got knocked out of the sky at each location, then would lose interest and leave. About 15 to 20 minutes later a different group would come in and do the same. It was hilarious. So were the misses, but we all got at least one, and there were 6 or 8 of us - those of us who were experienced got more per.
I doubt that was normal behavior for them, and certainly if you did that every weekend they would learn pretty fast. It was a very cold day in February, and apparently they were hungry. As I recall it was either the last day of the season or it was the last Saturday of the season. Dave is probably right - it helped that there was distance between them, and everyone was calling a little differently - we were "moving around and changing things up" without moving around. It is pretty impressive when you fill half a square mile with crow calls and lots of hungry live crows. I am sure all the animals in the kingdom were pretty well wondering what was going on.
My typical experience with crows is that you better shoot straight, because you only get one crack at them. I had about 50 in the yard last weekend, and have been a little sick of them tearing things up (and waking me up), so I knocked one out of the tree. I didn't see any more of them the rest of the day. Of course I had other things going, and did not bother trying to call or anything...