Blackie's Sublime Sub Song

It is only in the past couple of years that I have noticed birds singing extremely quietly with their beaks closed. The first was a robin, deep in a bush in my mother's garden. I was fascinated. 

Since then I've heard and seen at close quarters a robin in my own garden singing sotto voce, bill firmly closed but little throat heaving, inches from the end of my lens. Try as I might I couldn't find anything online about the phenomenon.

Thanks to a pair of recorders I met, I now know this is termed a sub song and was able to research it. How wonderful to have this lovely blackbird singing its barely audible version to me at lunchtime from the top of the Nissen hut. Blackbirds are usually quite flighty but this one seemed to be revelling in its music-making. Jazzy and I listened for ages.

Birds have to learn to sing and begin with a sub song which starts with just a jumble of notes and becomes more refined with practice. At this time of year the birds aren't competing for mates or territories so they can sing quietly to themselves, it seems just for the pleasure of doing it.