Birds flying and pecking at my windows

For the past week I've had odd bird behavior at all the windows at the back of my house. I noticed one evening all these little marks on the windows. Then my son called me at work on Wednesday to say this bird keeps pecking at himself at the window. I caught a sparrow first thing this morning at the bottom of the patio door just pecking away. I had to wash all the windows and patio door today - that is how badly they were all marked up. Later today a Robin kept flying into one of our windows. We have lived here for years and never had this before.

I know they say birds might do this if your windows are clean and they can see themselves, but my windows weren't clean (until today) and this just seems a bit extreme especially since I caught two different types of birds doing it.