It's really fascinating about the acorns. I never knew woodpeckers hid them like that. My family use to have a 40 year old pine tree planted in honor of the birth of my brother. The woodpeckers loved that thing and it was covered in holes just like the acorn tree. They would put holes in it and over time the sap leaked out and covered the entire trunk so you couldn't touch it without getting covered. I'd see them out the window all the time just pecking away it.
Most woodpeckers are interested in insects, so I think that sap helps attract bugs. These particular ones seem to like nuts also.