Birds can’t see windows – at least not at my house. As soon as the migrants arrive in spring the first of them bounces off the glass, leaving a little tuft of feathers.
Those feathers are a reminder to me to put up the window covering to protect the birds.
I have tried several ways of alerting the birds to the windows. The best are chicken wire or flagging tape twisted and secured across the window.
I recently read of people using the fruit and veggie stickers on the outside of the window. That would be messy to remove.
What doesn’t work are outlines of owls or other hunting birds and expensive peel-and-stick decals (unless you put them five cms or two inches apart).
Should a bird hit your window and be stunned, you can save its life. First throw a light towel or jacket over it. Reach underneath and pick it up gently. If it is not obviously dead, put it in a paper bag and roll the top closed. Put the bird in the bag in a dark quiet spot for about 30 minutes. Get the bag and go outside. Open the top of the bag. If the bird is alive it will be eager to fly away. If not, it is ready to be disposed of.
Thank you on behalf of the birds for protecting them from your windows.