Imagine you are in a movie theater watching an action film. Your head is fixed on the screen. How do you follow the action from one side of the screen to the other? Usually by moving your eyes. Actually, we humans have a high degree of eye movements that allows us to track objects and communicate signals to other human beings. Although, the degree of eye movement differs between bird species, it is overall more constrained than in humans.

How do birds solve the problem of tracking objects with eyes placed peripherally and limited eye movements? The solution to this evolutionary riddle is simple: moving the head!

While moving the head, birds can focus on two images at the same time (one per eye, as eyes are placed peripherally). However, to keep track of what is going on around its head, birds move their heads very quickly. How quickly?

Have a look at this video (requires Quick Time®). Even better: try to count the number of all head-movements this bird exhibits while pecking at seeds. The video lasts 1 min and 23 seconds, so you can calculate the rate of head movement per min.

Now, watch the video again, but now focus on how the bird moves its head right before going head-down. As you will see, one of its eyes focuses on the seeds on the ground by placing the head in a 90° angle in relation to the ground.

There are many things to study about head movements, as we do not know how they vary in species with different configuration of visual fields. Our research will address between-species variation in head movements.

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