Chickadees build cavity nests in trees, often by adapting natural cavities or ones made by other birds, such as woodpeckers. Both parents work on clearing out the cavity, although it is the female who builds and provisions a deeply hidden nesting chamber within the cavity.
I watched the two parents fly back and forth to a cavity as they carried mouthfuls of woodchips to dump elsewhere. Presumably this is done so that a pile of chips below the tree would not betray the nest to predators.
This nest is going to be interesting to watch over the next two months as the couple raise their chicks.
A Black-capped Chickadee has dumped chips elsewhere and now returns to continue excavation.
After a short stint deep in the cavity, the chickadee emerges with a beak full of chips for disposal, and even spills some before flying off.