A HUGE problem that I have noticed with friends and customers that I hunt with using locator calls is that they don't think about something very important. Once you start sounding off to locate birds, the birds are at the same time locating you. Do not stand in the middle of a wide open field and hit your crow call. I use a crow call often throughout the day and I act as if I am staring at a flock of birds 50 yards in front of me. Get up next to a tree, kneel down, do something other than wear your work clothes out there and stomp through the woods blowing your lungs out.
"Hunt" for the birds location, be stealthy, be cat-like and don't over do it with the crow call.
"Instruments of Mass Destruction"