Was it the nightingale or was it the lark?

The other night I heard something outside my window that had already caught my attention in London before: in the dead of the night you can hear songbirds chirping away!! I've never heard a single songbird chirp at night in the twenty-one years I'd lived in Austria! And then of all times in the middle of winter! And the strangest thing is that I hardly ever hear them during daytime... Strange habits, those insular birds, wouldn't even be surprised if they'd start to drink tea at five in the afternoon...^^