A while back I read that songbirds in England are now so crowded by people and cars and noise that they're starting to go deaf. This, of course, limits their ability to sing to attract mates, and presumably affects the quality of the songs. The astonishing, complex, recursive song of the blackbird comes to mind. In basic terms, the black bird sings a phrase lasting about 20 seconds. Then it repeats it with extra added phrasing so it's twice as long. Then it repeats that with even more additions, and so on - to produce an extraordinary and lengthy serenade. This may become a thing of distant memory. But we may never know, because we'll all be going deaf, too.