The sophisticated song mechanism of birds leaves scientists speechless.
Nightingales can have a repertoire of 300 songs stored in their brains! They will often sing 70 songs before they repeat the repertoire again with perfect accuracy and pitch (and without a tuning fork!).
Some birds can perform antiphonal singing where two birds sing alternate notes in a song. This requires knowledge of the duet by both partners and split second timing in the execution of the duet.
Some say that birdsong is only required for communication and mating purposes but the complexity of their music goes way beyond any simple sounds that would satisfy these needs.
Since man-made music has an intelligent composer it's perfectly reasonable to conclude that equally complex birdsong has an intelligent, divine Composer, who created these birds for our enjoyment.