Partly related, the book "Where poppies blow" is most likely (didn't read it) named after the Poem "In Flanders Fields" of which this is kind of a line.Or at least it reminds me of it so I'll share it:

     In Flanders fields the poppies blow
     Between the crosses, row on row,
     That mark our place; and in the sky
     The larks, still bravely singing, fly
     Scarce heard amid the guns below.

     We are the Dead. Short days ago
     We lived, felt dawn, saw sunset glow,
     Loved and were loved, and now we lie
     In Flanders fields.

     Take up our quarrel with the foe:
     To you from failing hands we throw
     The torch; be yours to hold it high.
     If ye break faith with us who die
     We shall not sleep, though poppies grow
     In Flanders fields.

EDIT: And actually the poem mentions the "larks" (birds) that were still singing. So the poem also confirms that birds could be heard.

Although they are indeed added to the audio afterwards.