A week or so ago, Zoe and I were sat in our living room when we were startled by a dull thud on the window. We both looked up to see this mark and a few small grey feathers floating downwards on the outside of the pane. I opened to window and looked out but there was no sign of a stunned bird on the ground below, so it must have managed to fly away.
I suspect that the unfortunate bird was a wood pigeon (Columba palumbus) which often feed on the lawns around our flats. The wingspan of the print was about 60cm.