I don't remember reading in literature about the song of the robin.
Now as the light creeps in earlier, I am beginning to pick out voices celebrating the new day. High in the holly outside our bedroom there is the bare branch of a rogue Ena Harkness rose, a favourite perch for the robin which lives in our garden. What a voice for one so small! Such a robust song, which falls in deliberate phrases. What does it mean, I wonder? Probably a chiding that we are not out digging worms!
The photo above is from a country diary article here, and you can hear the robin here.