Greg nailed it, at least for out west fox calling. If I go anywhere in southern Arizona that has rocky, cut up terrain and sand washes, a few minutes with any call that has fox vocals, fighting sounds, I can damn near be guaranteed a fox or foxes will show up. I seldom go calling for them, but the couple times a winter I go out specifically for fox, I leave wondering why I don't do more of it, beautiful animal and fun to call, lots of close action with fox.
