samuel l crowe said:

I have a crazy bird!!!
There is a grayish colored bird that keeps banging into the window, he has
done this all summer three or four times a day he will bang into it every
few seconds for 15-20 minutes at a time, will light on the gutter for a rest
period and back at it again. He does this only on one window and only on the
same pane.

What would make a bird do such a crazy thing?

As the other responder said, he thinks his reflection is a rival and neither one
of them will back down. You are getting off easy if it is only one pane in one
window. I know someone who had a redwing blackbird that followed the sun
around her house banging on different windows at different times of the day.

I've also had birds banging away at the side mirrors on my car.
--
Pat in Plymouth MI

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)