If he has a field to fly down into, he will come off of the roost while it is still foggy and he can just see the ground. Looking down from above, they can see the ground through fog that looks dense to us looking horizontally.
One of the most memorable scenes that I have experienced is tracking the bird by his gobbles to a point right in front of me and then having him materialize from the fog in full strut. Awe inspiring!
FullChoke