The head movement of birds is a mechanism for depth detection since they do not have binocular vision. By moving their heads back and forth, they can determine

The head movement of birds is a mechanism for depth detection since they do not have binocular vision. By moving their heads back and forth, they can determine distance based on the rate of size increase of an object. See for example: https://www.loc.gov/everyday-mysteries/zoology/item/why-do-pigeons-bob-their-heads-when-they-walk/ https://www.loc.gov/everyday-mysteries/zoology/item/why-do-p...