Last Friday on 29 November 2013,  a larger bird (unfamiliar to me, but larger than a American Robin, smaller than a dove, sleeker than a blue jay) crashed into my large window, but recovered to perch in a nearby tree.  At the exact same time two chickadees were feeding at my window feeder -- and surely heard the noise of the crash - froze in place for over a minute.  They looked like statues.  When a friend moved closer to that window, he saw their eyes move, but they were immobile.  I have bee watching chickadees at this feeder for almost 6 months now, and never have I seen them immobile.