House building is in full swing. Despite an old nesting tree that is filled with holes, I guess there is a need for refreshing and enlarging some of the pre-used holes. A pair of BH Nuthatches took turns working on a hole taking small bits out. One would work for a while then they would trade off.
I suspect there is a network of holes. One would go in and then come out a hole on the other side and repeat the steps.