I hunted for years on heavily hunted public land in a heavily populated state without tagging one. I could always call birds in to within 100 yards or so, then they would just hang up. I got hooked on that alone, even though I never got one. Years later I started hunting Rio's on private property and now I can't seem to do anything to stop them from coming in. So I think it has to do with the bird and the pressure. Calling skill is also a factor, but in some places it is definitely harder than others to get that first bird.