In the middle of winter the robin may be the only bird singing in your garden, sometimes under a street lamp at night (sample note).
Both male and female robins hold their own territory through the winter, and song is how they keep it. The winter song is thinner and more wistful than the spring one.
Try Sound ID on a cold morning: robins sing from a low branch, close to you, which makes them one of the easiest first matches.