Back in the day when I was surveying wooded tracts, if you got quiet you could hear them knock. The sound would carry surprisingly far. Usually I was beating through the brush and made a lot of noise, but there were a few times I could sit at the base of a tree and be quiet. I would see some as they got closer. They are actually bigger than you think they would be, and very handsome birds. You can see and hear a lot of things in the woods if you just sit still and shut up. Wish I had a camera those days…..