had one do the same thing a few years back, was only a Great Tit, it hit the window while I was there and scared the dickens out of me. I went out to see if it was OK and found it stunned on the ground, with a local cat just coming around the corner, all set to pounce

Am a huge cat fan but shooed it away, and picked up the bird, it was panting and obviously stunned but it sat on a branch when I placed it there. Kept an eye on it for a few minutes but I had to leave it