Is something I have always wondered. This article suggests that male chaffinches, at least develop different accents depending upon where they live. US scientists studied 723 male chaffinches in 12 different populations across Europe, the Azores and the Canaries. They found that the notes became more unpredictable they further they moved, with those birds in smaller island populations singing the same notes with a more structured pattern. I wonder then whether birds from different populations will soon be unable to understand each other.