Dance of the Birds

Sit in a train to some place far away. Play music on a device of your choice. Melodies; not some fast and insane numbers. Look out of the window. 

Acknowledge the greenery, cows, and other fauna. But focus on the sky. Watch out for birds (alone or in a flock) that are flying, gliding, soaring or zigzagging along. You will notice that their movements more or less coincide with the rhythm of the song or the interludes more often than not. 

The birds, however, are, mysteriously, unaware of their ability to choreograph to songs they have never heard in their lives. If a tree falls in the forest and no one hears it fall, did the tree make a sound?