It depends on what the turkey is in the mood to gobble back at and what part of the country you are hunting. Coyote howls work great out here in WA, crow calls don't seem to affect them at all, and a Barred Owl call works sometimes. I think almost any sudden loud noise can work on some days. I usually wait until daylight is just breaking to try a locator call, or I'll let the birds start the show themselves. Birds out here in WA will hit the ground anywhere from right at first light to sunrise, so you may be getting a gobbler that is on the ground to respond if you wait until you can see good. Then, that opens a whole other can of worms because he will be drawing hens to him too.