Hey John,
Are the birds whacking themselves into the glass because they don't see it or do you get the same bird making repetitive whacks from a close distance because they see their reflection?
If the latter, good luck... I have had the same problem for a year or more. I tried taping a pic of an owl to the glass. Didn't do a thing.
I purchased an owl decoy and have had mediocre results. It works
for awhile if the owl is placed within a few feet of the window and you move it every couple days. After that, it's just something else for them to land on before making their window strike.
Mrs. Zoom had a Christmas decoration in the window for awhile. It was a 24" star with lights around the perimeter. That seemed to work as long as the lights were on all day.
In my case, it's also the same bird from day-to-day. I believe the best answer is 22 shotshell.