He would declare and could himself believe 
That the birds there in all the garden round 
From having heard the daylong voice of Eve 
Had added to their own an oversound, 
Her tone of meaning but without the words. 
Admittedly an eloquence so soft 
Could only have had an influence on birds 
When call or laughter carried it aloft. 
Be that as may be, she was in their song. 
Moreover her voice upon their voices crossed 
Had now persisted in the woods so long 
That probably it never would be lost. 
Never again would birds' song be the same. 
And to do that to birds was why she came.
Robert Frost
http://www.poemhunter.com/poem/never-again-would-bird-s-song-be-the-same/