Admittedly, it’s not actually a very exciting bird, even for a birder, looking as it does rather like a drabber-than normal town pigeon. And due to poor light, streaky window glass and so on, it’s a rubbish photo:
But it’s a new species for the garden: Stock Dove, Columba oenas. I don’t really expect to see them in London, but I’ve noticed them getting a mention from time to time at Regent’s Park Birds, so I was slightly readier for it than I might have been. It’s possible that they pass through the garden occasionally and I usually assume they are normal pigeons; or perhaps they’re spreading into London; or perhaps it’s away from its normal wintering grounds because of the current cold snap. Who knows.