Tweets,
I have some information on Western Bluebirds on the west side of the hood canal that might help in this discussion. In some forest lands a couple of miles south of the Hood Canal Bridge in Jefferson Co. I have seen Western Bluebirds in December twice in the same area.
I was scouting for the Port Gamble cbc around the beginning of December 1998 and came accross a flock of about 15 bluebirds. While I did not get these birds on the cbc, the following year in the same area I did get them on the cbc. This time a flock of similar size. Out of curiousity I made a trip up into that area in spring (mid April) and did note Western Bluebirds in these areas.
While I do not know if these bluebirds are resident by these limited observations, it suggests that they individuals might be resident.

Scott Downes
downess at cwu.edu
Ellensburg WA