As far as I know, birds can't compose original songs. An individual nightingale can't suddenly go all Cole Porter on the other birds, and then do a little something 'in the manner of a shrike' etc. True, mockingbirds can patch together a string of sounds that it's imitated from those around him or her, including car alarms. But that's pure imitation. It may be that whales can compose new songs--I'm not sure. But humans are far, far freer to develop musical ideas in structured ways than any other animal. A simple cannon, a two part harmony, is beyond other animals. (well a cannon is beyond me too...). Again, some bird songs are beautiful, structured and have several, even many parts. They're to be admired. But they're not free to open into, explore, new musical terrain. Human's are.
Paul Weaver spruce 2014