There really is nothing like watching behavior in the natural world. There were a pair of chickadees working quite efficiently excavating this tree. One would wait as the other disappeared down the cavity always bringing up a mouthful of wood chips. Usually , but not always they flew away with the wood chips to probably discourage evidence of the nest site from predators.
Then, as quick as can be the other would disappear down the hole to do the same. I'm still wondering though how they won't get flooded out in a good rain storm. I hope they have heard the term, "Location. location." when it comes to home buying!