Hi wychwood, I think It's because now that spring is in the air, it see's it's own reflection and thinks it's a rival male.
If you can reduce the refletion in some way, it may do the trick. Good Luck Tbird+
How about a picture of a bird of prey taped inside of the window or a plastic owl or somthing like that on the inside windowsill ,it may see this and fly straight off ,these type of things are used to scare pigeons away from rooftops so it may work in this case.
dont think the silhouetee of a bird of prey will work for your average crow- quite the opposite. If you see a bird of prey chances are its being mobbed- usually by a crow or two!
Hi wychwood put some frosted glass effect stuff on your windows ( sort of stuff that goes on with water ) reducing the reflection. Might just do the trick and if it doesn't work , not too much lost !