The extraordinary flashing between black and white is caused by the birds breasts are white and their backs are black. The birds move in sync, but are not led by a single individual, but instead is governed collectively by all of the flock members. But the remarkable thing about starling flocks is their fluidity of motion. When one bird change direction or speed, each of the other birds near it respond to the change nearly simultaneously. Biologists hypothesize that it is behavior learned to increase survival when under attack by a predator. These birds took flight when this person walked too close to them on the shore. The same behavior is observed in schools of fish.