It is not unusual to shoot 10 crows at a spot if you use a Wildlifetech caller. The crows can't tell the difference between the caller and a real crow.
Often times I will call an owl into a tree usually a (Great Horned or Barred ow) and then call in the crows. The owl pays little attention to the crows and they flock around the owl but never fly within 5 feet of the owl.
As long as I call the owl on occassion, the owl will continur to answer the intruder even if I am shooting. The crows will leave, and when I play the crow in distress, the come back. Some will swarm the owl and others will land in surrounding trees which I try to dispatch with my 22 mag.
Since my caller has a remote control I try to stay 50 yards from the caller as not to scare the owl off and pick the crows off that land in surrounding trees.
The wildlifetech caller is quite a bit more expensive, but you get what you pay for. If a crow or an owl hears the call, they will come every time, unless you have shot at them a few times.
It works the same on coyotes, and most other perdators and many others. They will come if they hear the call, but will usually circle down wind and if they smell you, it's over.
Works extremely well on deer, bears, wolfs. elk, moose too.