Ooh, I like that. More sleuthing of the Hobbit tree. With a sort of Mt. Birdmore, of the forested set as the result. You have a keen eye, the owl jumped right out when I looked again. As did the others, though the owl was beyond obvious. (Sometimes we get too close to our own "art". ) Your Craftsbird [ O : ] theory holds BUCKETS of water. And I'm quite certain they must be Pileated woodpeckers (think Woody Woodpecker, only not on celluloid), and other lesser species, in joint effort. Pileated make square holes, and others round-ish. So a joint project, obviously.

Curious D here: Do you have Pileated in your neck of the sandy wood?