I spotted this Pygmy Nuthatch excavating a nest hole in the town of Beulah, CO last week. In the top pic the bird is seen with some of the tree material it was removing from the nest hole. If you enlarge that pic you can see the top of the inside of this tree cavity it is working on.
In the pic above here the Pygmy Nuthatch is seen inside the tree cavity it is excavating. It does not look like there is a lot of room in there yet so a lot more work to do.
I heard a number of Pygmy Nuthatches singing during this trip. SeEtta