Allot of guys here think the birds just quit gobbling ,and the dead ones do and the smart ones gobble less and less as day light gets longer. If you are in a good location there is no need to call more than once every half hour.
And a yelp is the very last call I ever try.[:-]Every run & gunner out there stops and yelps 7 times waits 20 seconds and is off spooking more birds.[]

If you get answered, your in the money ,and time is on your side.