Birdsong Radio, Live Dawn Chorus Bird Song Station
Scroll down to the "Live Dawn Chorus Birdsong Stream."

Metafilter identifies it as, "a 25 minute loop of birdsong recorded as a test pattern."

These tweets are a hoot. I'm going to let them chirp me to sleep. (Promos are a jarring interruption of the primeval forest, but they're whispered and brief.)

Later: A leap, but I ended up downloading a well-recommended mp3 of Thundering Rainstorm for 89 cents at Amazon.

I should have known I couldn't be chirped to sleep -- I want to know what they're saying.