The ability of nocturnal birds of prey to rotate their heads almost completely without dying is only possible thanks to different adaptations of the bones and the vascular network. In the other vertebrates the torsion of the neck up to 270 ° would cause the interruption of the blood flow towards the brain.

Reserves of blood. One of the anatomical features that makes this hyperpolic movement possible is the presence of a complex system of blood vessels that forms a reserve of blood at the base of the neck, useful in the event of interruption of the flow. The arteries that reach the head are connected by small vessels, so as to guarantee the blood flow in the event that a path is interrupted. Finally, the owls have, in cavities in the vertebrae of the neck, air pockets that act as shock absorbers to protect the arteries. It is therefore an elaborate mechanical and pneumatic system, without which not even these animals could perform that head twist with impunity.