This amazing video of a large flock of starlings making elaborate and intricate patterns in the sky above Denmark has been making the rounds on blogs and news sites lately:
Many of the bloggers pose the question: why do the birds do this? The answer actually lies in the physics of self-organizing systems.
Bird flocking is a well-known example of the self-organization phenomenon. No one bird is in charge, yet the flock as a whole organizes itself into beautiful patterns. Each bird takes note of its neighbor's position and direction of motion and adjusts accordingly, but nobody is the leader. No "head bird" tells the entire flock which way to go, yet they move as a unit.
Other videos of this phenomenon exist and it is sometimes the case that a predator is present. A hawk or other bird of prey could be present here as well, although it would be difficult to see it in such a large crowd of birds.
The predator's presence can explain what is causing the birds to fly around, rather than to sit quietly on the ground or in trees, but it cannot explain the intricate patterns that the starlings exhibit in their attempt to escape the predator. The theory of self-organizing systems is needed to understand the origin of these gorgeous patterns.
I have written about this phenomenon in earlier posts, since it applies to human behavior, too. Traffic and the movements of large crowds of pedestrians can be understood using this approach. It is not just birds who flock - people do, too!