What makes a bird sing in the dark?

This morning I woke up at 4am and as I meandered around the place, having coffee and listening to the BBC, I heard a bird song coming from the big tree in my next door neighbour’s yard.  The bird is a Tui, I think, one of the truly beautiful native birds of New Zealand. But as it was still dark, rainy and gloomy, so was the bird heralding an unseen dawn?  I wonder.  I couldn’t even see a glimmer of light on the horizon.  The bird must have been hungry after a night bedded down in the tree, so was she singing a prayer for a good day, or just waking herself up in a good mood. Perhaps we could all take a leaf out of the bird’s book, and wake up singing. I am going to try it.