That means he's in the mood for luuuuuuuuurve...
And it's the final confirmation that he's recovering very fast!
Chickens don't have the monopoly of dawn chorus -- pigeons do it too, as in the wild they start their morning activity at dawn. However, if that stops you from sleeping, you can fool him into thinking it's earlier by making his surroundings darker (with a curtain or some sort of cover, for example).
They can also burst into song when they hear a tune that they like. My daughter often got exhasperated when Hercules 'sang' along with the theme song of her favourite series and wouldn't let her hear the TV!