This little guy seemed to be looking for bird eggs or hatchlings, but I don't think he had actually found anything to eat in the nest box. No parent bird was freaking out, and the front portion of the snake's body that was visible outside the box didn't appear to have any bulges. When I walked up close, he looked at me for a few seconds and then pulled his head back inside the box. His head was about 1 inch long.
I feel pretty confident this is a juvenile ratsnake, and the ID algorithm has suggested Gray Ratsnake (Pantherophis spiloides), but I don't know if there are any other similar-looking species in range.