....and I had only cleaned that window this week!

It's like a glass rubbing, as opposed to a brass one!

That looks like a large bird. Pigeon? We have large windows in the main room and glass "rails" on the deck .....therefore have this problem also.

Very like it Shirley...quite beautiful really.
Klahanie, I think it must have been one of the doves who have a nest in the nearby Trachycarpus tree.

The bird can't have hurt itself much by barging into your window otherwise you would have found it outside below the window.

The first thing I do Balcony...it isn't the first time it has happened.

We have the same thing happen on our back windows. I think it's the way the sky reflects in them.