I watched Acorn Woodpeckers bring food to this nest cavity in a black oak multiple times. The young were squealing, which seems to be typical for this species (they don't sound much like the various other woodpecker young that I've heard). There was a moment of panic when a Cooper's Hawk flew into the area and chased after one of the adults, then perched near the granary tree (too bad I didn't have my spotting scope set up yet - damn!). But after a minute or so, it left and the woodpeckers carried on with the task of feeding the nestlings. I was interested to see them nesting in the same cavity as last year. I've included a picture of the nest tree. The nest cavity is near the top of the tree and is circled in white.