Anne Karpf's new book excerpted at the Guardian:
Apart from humans, birds' vocalisations are vastly more complex and precisely modulated than those of any other animal. Most remarkably, songbirds too learn from experience. Some songbirds even have 'dialects' - defined, localised, particular acoustic features that are culturally transmitted. And songbirds come to use their voices only if they're exposed to the communicative signals of adults of their species. Just as human infants who don't hear the human voice or speech don't develop normal vocal capacities of their own, so songbirds raised in isolation produce abnormal 'isolate' songs.