Chickadee Nest Excavation

A couple of hours ago I noticed a Black-capped Chickadee digging into the tree directly in front of my kitchen window. 

There are two chickadees out there and they appear to be taking turns excavating. 

I have read in Sibley's and online that the male and female will both work to excavate the nest cavity but then the female actually builds the nest.  It can take up to two weeks to complete.  I haven't noticed these guys working here before so they may have just begun. 

Looks like a lot of work!  I hope they don't change their minds and move to another tree.  It would be awesome to watch this family grow!