head bobbing allows pigeons to momentarily fixate their gaze on various objects, giving the photoreceptors in their eyes enough time—about 20 milliseconds—to build a complete picture of the world around them.

And while it often appears as though the birds are moving their heads back and forth, there’s actually no backward movement at all. The bob is actually an illusion, scientists discovered in an experiment. The birds are simply moving their heads, allowing their vision to stabilize so their bodies can catch up, and then they’re on the move again.

This happens so quickly, it appears as though they’re using a constant bobbing motion.