Sitting in a room at the front of the house this afternoon, there was a loud thud from somewhere outside. I looked out of the window, couldn't see anything. I soon forgot about it.

Two hours later, my wife went into the lounge at the back of the house, where there are patio doors: large sheets of glass. On one was a white imprint of two rather large wings (with even some detail of feathers), either side of a denser white imprint where the bird's body must have hit the window. No sign of a dead bird outside, so it presumably survived.