Singing Ice

It was mid December. In the distance, I heard what I thought was a flock of birds chirping. As I walked toward the lake, I realized it was the ice. The temperature had just dropped below freezing. There was already about a half inch of ice on the lake. I am not a physics or chemistry major, but I assume as the ice began to get cold and freeze again it began to expand pushing on itself. The sound was thousands of breaks occurring during this expansion.