If you see them hanging around a field in the AM or just before dark there is a good chance the area holds birds. Go in while it is still dark and try to listen for light hen yelps while they are all still in the trees. Try getting within 80yds of their location and wait until they start becoming a little more vocal..use light hen yelps and when a tom gobbles give a short, sweet cutting sound to excite the tom a little bit. Don't overcall though, always better not enough than too much. If you're not sure whether or not they are in the area you can always setup and call a little, wait 10-15 mins then call a little, and so on. The birds are always on the move and will most likely travel within hearing range eventually...may be a half hr or 2 hrs but if they are there somewhere just give it time.