Days turn darker and darker. Probably it’s just about 4 hours of daylight in the deepest part of winter. In some places not even that. Birds initiated their migration trip from Scandinavia via Berlin until they get to Extremadura.
They don´t run away from the cold, even if it would seem the actual reason. They want to leave the lack of light behind. The darkness. If it would be music it would sound like a trumpet, somehow far, like minimal electronic sounds. A lot of silence and certain noise.