Owls are famous for being able to turn their heads seemingly full circle. It turns out some owls can turn their necks an amazing 270 degrees whereas our necks turn a measly 180 or so — see if you can turn your chin along your shoulder on both sides.
However, it’s likely the cause for this amazing feat is that, unlike our eyes, theirs are set facing forward and don’t rotate. So rotating their head becomes a key skill. Biomechanically they are able to turn so far by having twice the neck vertebrae as we do. If each vertebrae turns a little then having more helps them twist much further than us.
And yet the real trick is turning your neck while maintaining blood supply to your head through the arteries that also run up your neck. Rotate too far and the arteries can twist, stretch or be impeded. Owls have evolved a number of nifty strategies to help them turn their necks while maintaining blood flow. These include having the large carotid arteries towards the centre where they twist less than ours do, which run up the sides of our vertebrae. They also have loads of space around the arteries that run up inside the vertebrae and an area that may pool with blood at the base of the skull to provide a kind of reservoir if flow gets restricted. And more. All kind of amazing.