As I walked past some trees I heard a loud tapping. Thinking it was a woodpecker but with the tapping a bit "off", I was curious. For the life of me I couldn't see anything until suddenly a chickadee flew out of this cavity and perched above me as if to say "do you mind!!". Then back in it went and the tapping commenced again. He was excavating the cavity and at one point emerged with a beak full of sawdust which he deposited some distance away. Imagine the work that goes into excavating these holes? Clearing out a nest chamber one little beak full of wood scraps at a time.