I have heard the "dawn chorus" (Popular Electronics Magazine, December 1956, page 41) and it is quite remarkable!
However, I have never been able to accept the theory that a whistler bounces back and forth from one hemisphere of the Earth to the other following magnetic field lines. (Popular Electronics Magazine, December 1956, pages 39-40) Why the time delay of "a second or two"? Why the descending pitch?
Many years ago I was playing with a Jacob's ladder.
My father had a portable television operating nearby. I happened to observe a burst of interference on the television each time the arc broke - but always a split second after!
I wondered why and reasoned thusly: There exists a length of heated air in the arc - so hot it is radiating in the visible spectrum. What happens to that hot air when the arc breaks? (Could it be appearing on this page? No!) It cools, not instantly but over some period of time. As it cools it follows that it radiates at lower and lower frequencies. At some point the descending frequency passed through that of the TV channel my father was watching. Hence the delay before the burst of interference.
I had a very understanding father. He did not complain about the interference.
It further occured to me that the same must happen with a natural lighting bolt. After the discharge, the huge length of super-heated air begins to cool, also radiating at lower and lower frequencies. Eventually the radiated frequency passes through the audio spectrum and, with suitable apparatus, can be heard as a descending note a short time after the lighting bolt.
Presto! An explanation of the time delay and the descending pitch of the whistler. And one much more amenable, in my opinion, to Ockham's razor.