Flocking

Common Starling (Sturnus vulgaris). Gretna Green, Scotland. November.

Common Starling (Sturnus vulgaris). Gretna Green, Scotland. November.

Birds in a flock, like the Starlings above, sometimes move together as if connected by invisible threads. Scientists have found that a few simple rules can explain apparently complex flocking behavior.

The most famous flocking model, shown diagrammatically below, is known as Boids.

The three flocking rules from the /Boids model: 1) Separation; 2) Alignment; and 3) Cohesion.

The three flocking rules from the Boids model: 1) Separation; 2) Alignment; and 3) Cohesion.

This model requires each member of the flock to act based on visual cues as follows:

1) Separation : Give neighbors enough space to fly

2) Alignment: Steer in the same average direction as surrounding neighbors

3) Cohesion: Fly towards the average position of surrounding neighbors as long as rule 1 has been satisfied.

These rules have been used to generate life-like bird flocks in animated movies such as Batman Returns. Flocking does not need one overall leader — in contrast to the leader of a line of birds who are using upwash to save energy (see “Formation Flying”).

LEARN MORE ABOUT FLOCKING

KIDS QUESTION: In the museum exhibit, we asked: Why do birds flock together?

The answer is: For safety from predators
Birds form flocks for a number of reasons. They are always on the lookout for predators (such as raptors or coyotes) and a predator is much more likely to be spotted by many birds than by a solitary bird. Flying in a flock can also confuse an airborne attacker. On the ground, birds flock together where there is a source of food and sometimes to keep each other warm.