Many many years ago (ok, 1992) Dad wandered into my bedroom one evening and re tuned my radio from Radio One to...well, to birdsong!
He'd heard that they were testing the frequency that Classic FM was going to be broadcast on by playing (among other things) a recording of birdsong from someones countryside garden. I used to listen to it when I could, taping it when possible and then playing the tape at night as I went to sleep. I even had a kind of meditation that went with it (not that I thought of it as a meditation, it was just me daydreaming).
Then today I was watching Breakfast on BBC1 and they started playing the birdsong again.
The story about it is here.
I shall be listening as much as possible, just wish I had a way of taping it again.