My kids call this a 'bird ballet'.
Whenever they see a flock of birds flying through the sky they all stop to watch the 'bird ballet'.
Today we were out and there was a gigantic bird ballet in the sky and, as usual, they all stopped to watch. Sarah piped in with "Well, you know that they are flying around together and landing all bunched together because they are trying to distribute their body heat and keep themselves warm." Imagine that.