But.. in my garden (or parks) the birds, which sing together, every year have different song and kind of imitate/answer each to other, repeating it, progresivel

But.. in my garden (or parks) the birds, which sing together, every year have different song and kind of imitate/answer each to other, repeating it, progresively trough months: two years ago they started really lame with some stupid phrase like.. someones doorbell and made it better with time, last year I enjoy the melody since the beginning. If it could be an evolving story, the words which stayed were created ad hoc, for invisible, recorded reasons - if in a competition, different birds complete the song in own (but sometimes similar) way. If it's a language, its the same kind as the music would have ( in the sense https://www.classicfm.com/music-news/study-proves-music-is-universal-language/ https://www.classicfm.com/music-news/study-proves-music-is-u... ;). Other thing: the song is not always the same - so it may communicate something.