The chickadees are starting to excavate their nest cavities. This Chestnut-backed Chickadee was working on a dead snag right along the trail at Nestucca Bay NWR. Even though the birds choose soft dead wood on which to work, it seems a herculean task for a bird with such a diminutive bill to excavate a cavity large enough for nesting.
She can fit about half her body into the cavity so far. It takes about seven days to complete a nest.
Here she spits out a mouthful of wood chips. Larger chips are carried away from the nest site before being dropped. A big pile of wood chips at the base of the nest tree would alert predators to the location of the nest.
Ethical Birder 
I got to see a pair of Black-capped Chickadees working on a nest excavation a few weeks ago. Do they stay with that nest hole for the season or could they change their minds?
Given the amount of effort required to excavate a cavity, I imagine that the pair would stick with it, but I don’t have any hard data.