I've just had a pigeon (I think) fly into my study window, making a rather large bang, and then fly off again. It's the first time I've notice this large a bird do it, but there have been several instances of something sparrow like doing the same. At first I thought it was some kids throwing something at it, until I managed to actually see the bird flying off again afterwards.
Are their magnetic direction sensors adversely affected by all the technology in this room perhaps? :)