My mileage is all over the place and depends on a multitude of factors.
-How long I have to hunt that day: Before work hunts I'm not going to be walking near as far as an all-day hunt.
-Private vs public land: My public land spots around home typically require a bit more walking than my private land spots. I have a couple public spots that are 2+ miles one way. Average spot being ~0.75 miles. None of my private spots are more than a mile one way.
-Season timing: Early season I try to pick off the birds closer to roads/access before others get them or they get really pressured.
-Infrastructure: If the infrastructure allows me to "listen" to a lot of ground, I may do as much riding and listening/calling as walking.
-Species/Geographic Location: Some species/locations i'm more efficient covering ground by truck rather than pounding miles and miles on foot.
All the above considered... An "average" before work hunt would probably be 1.5-2 miles. An average day hunt ~5 miles. With some major outliers at both ends. An average day of hunting while traveling would be higher than my local days.