Do you ever wish you had eyes in the back of your head? While most humans can only turn their heads 90 degrees in each direction, owls can turn theirs 270 degrees each way. This is more than any other vertebrate can turn its head, giving owls the highly sought after ability of being able to watch their own backs.
Owls have several adaptations that make this possible. First, they have twice as many vertebrae as humans, and their long necks create an S-shape. The upper region of their neck is responsible for a yaw movement, which is a rotation around the vertical axis and allows for owls’ impressive head-turning abilities. The lower region is responsible for a rolling movement, or rotation around the horizontal axis.
There are two parts of one’s field of view: the overall field one can see as they move their eyes and a binocular view, which is what can be seen with both eyes at once.
More importantly, owls only have one occipital bone ― the bone at the top of the spine, while humans have two. A common comparison between having one or two occipital bones is thinking of how much easier it is to pivot on one heel than two.
A 2013 Johns Hopkins University study illuminated another trait that gives owls the ability to turn their heads so far each way. If a human tried to turn their head much more than 90 degrees, not only would their vertebrae break but they would also likely die from a stroke due to tears in the arteries. Researchers found that owls’ vertebrae contain holes that essentially protect their arteries from breaking as they turn their heads. Between their singular occipital bone and protected arteries, owls are well-suited for 270-degree head turns.
Owls depend on their neck adaptations to make up for their lack of peripheral vision. There are two parts of one’s field of view: the overall field one can see as they move their eyes and a binocular view, which is what can be seen with both eyes at once. As such, the binocular view encompasses a smaller field. The field of view for humans is 180 degrees, of which 140 degrees are binocular. The field of view for owls is 110 degrees, of which 70 degrees are binocular. Despite their smaller range of peripheral vision, owls still manage to see quite a wide range — even behind their back!
Journal of Anatomy (2017). DOI: 10.1111/joa.12616