Why Do Some Birds Bob Their Heads?

If you watch the birds at your feeding station you will see that some birds hop, hop, hop, and others prefer to walk around. Birds that hop take advantage of the pause between each jump to look around. Walking birds like the Mourning Doves, Robins, and Starlings, all move there head forward and back as they walk.

Based on an experiment done with doves walking on a conveyor-belt, it was discovered the head nodding is a way of fixing the eyes on their surroundings. Although the head is moving relative to the body, the eyes are steady relative to the world, so the bird can focus on food or distant predators. When the speed of the belt was adjusted so that the doves were stationary relative to their surroundings, they stopped nodding.