It seems the songs are all learned, not instinctive, so regional variations do occur and yet, some are consistent even across the population of a continent.
NYT has an extended article about these songs, with audio examples you can play and try to guess the meaning of.
Can You Understand Bird? Test Your Recognition of Calls and Songs
It might sound like all chirps to you, but birds convey different messages, even across species.
Language has long been considered the exclusive provenance of humans.
But in the animal kingdom, birds, not primates, communicate with the level of vocal complexity and variability closest to ours. Ornithologists have made progress in understanding the rich variety of ways in which birds converse...
I was able to whistle one of the songs. The cat woke up out of a sound sleep and was very concerned.
