Songs are the language of birds. Some may have only one song, but others may have hundreds or even thousands. However, songs usually have only one of two meanings, said UMass ornithologist Donald E. Kroodsma, who focuses on wren songs. A brown thrasher can have 2,000 songs, but they all seem to mean the same thing. Of the 9,000 or so known species of birds in the world, about 4,000 are species of songbirds that learn their songs from adults of their own kind.
Most songbirds have regional dialects for the same reasons that humans have dialects.
However, it varies from species to species. Songbirds, like nearly all birds, will return to the same areas year after year to breed. And it is during the breeding season that most singing takes place. A slight deviation may begin in one bird's song. It may get passed down to younger birds or be picked up by other adults, and eventually it may become a prevalent song of that area.