A new study has been conducted on dialect formation in birds:
Native North Island saddlebacks have developed such distinctive new songs in the past 50 years that it is not clear if birds on one island recognise what their neighbours are singing about, a Massey University study shows.
The phenomenon is an avian equivalent of the way human language develops regional accents and dialects as people migrate and settle in new locations, and provides fresh insights into how species evolve, says biology researcher Dr Kevin Parker, from the Institute of Natural Sciences at Albany.
I can’t find any published article but the press release is here.