dusty outline

Hi pauwen,

It's rotten isn't it when you see the pale outline of a bird that has hit the window and by the size of the wingspan it was a very big bird!!!!

You may already know this, so I don't know whether this is helpful to you but I have stickers on my larger windows as I had the same problem.  They are sillouettes of birds of prey or birds in flight - they adhere from the inside and help to ward off potential collisions.  Birds in your garden think there is another bird in their flight path so will fly away from it.  Other ways that can be useful are putting dominant objects on your window sill i.e. large potted plants, candles or even ornaments - the problem is to do with reflection, on clean windows birds outside find it hard to tell the difference and will fly straight at a window thinking that it has a clear flight path.  Sometime caused if they are being chased by a predatory bird or a sudden sound has spooked them.