Chickadees

I love the little black capped Chickadees that come to my feeders.  They stay around all winter and happily sing away almost no matter how cold it is.  This winter, for some reason, I have had a number of occasions where a chickadee will flutter around one of the house windows, tapping and talking.  Not sure if they see their reflection, or maybe they are just so sick of winter, they want in where it's warm?  It's something I haven't seen them do before.