Perhaps people do not expect to see eastern bluebirds in Minnesota during the winter because that is what many of the field guides and experts tell them. Audubon, Sibley and Cornell all do not include Minnesota in the winter range of the eastern bluebird.
Cornell does state that in mild winters eastern bluebirds may be found further north but I do not know of many people who would consider this winter mild, it has been the worse we have seen in many years, and yet I photographed these bluebirds in Redwing, Minnesota on January 5th, 2009.
This is not an isolated incident either. I have participated in Christmas Bird Counts over the past couple of years and pretty much every count that I have worked on in the southeast suburbs of the Twin Cities we have had recorded eastern bluebirds. So I guess it is true that everyone makes mistakes, which is fortunate for those of us living in Minnesota who catch a glimpse of these colorful songbirds during the drab days of winter.