1. Why Owls Must Turn Their Heads: Their Eyes Do Not Move
Humans can look to the side while keeping their face straight ahead. We move our eyeballs inside their sockets. Owls are different. According to a blog by a keeper at Kyoto City Zoo, an owl’s eyes are fixed in place by a ring of thin bone called the sclerotic ring. This means the eyes can hardly move [1].
Because the eyes are stuck, an owl must turn its entire head to see what it wants to look at. This need to move the head is the starting point for understanding why the neck rotates so far. However, the zoo’s description says the eyes "do not move at all." In this article, we have not verified this with academic papers, so it is safer to say the eyes "can hardly move."
2. Owl Neck Bones: 14 Vertebrae Instead of 7
The neck contains a stack of bones called cervical vertebrae. Most mammals, including humans, have seven of these bones. In a detailed study of the American Barn Owl, researchers counted 14 vertebrae, labeled C1 to C14 [2]. This is exactly double the number found in humans.
The Kyoto City Zoo blog also states that the Japanese Scops Owl has 14 neck bones, which is twice as many as humans [1]. However, the scientific count of 14 comes from the Barn Owl study. For the Japanese Scops Owl, we rely on the zoo’s description. More bones mean that even if each bone bends only a little, the total angle becomes very large. Note that the number of neck bones varies among bird species, so it is not true that "all birds have 14."
3. How Far Can an Owl Turn Its Head? The Observed 270-Degree Turn
A press release from Johns Hopkins University states that owls can turn their heads up to 270 degrees in either direction [3]. This is three-quarters of a full circle. It does not mean 270 degrees to the left plus 270 degrees to the right equals 270 degrees total.
A study on American Barn Owls used X-rays on living birds, forced rotation on dead birds, and CT scans to investigate rotations exceeding 270 degrees [4]. The researchers suggest that the upper neck twists like an axis, while the lower neck tilts sideways, combining these movements to achieve a large rotation.
However, another study argues that the movement of individual neck bones is not special for birds. Instead, it suggests that arranging the neck like a coil could allow a full 360-degree turn [5]. The 270-degree figure is what has been observed in living owls. The 360-degree figure is a theoretical possibility based on specimen posture, not a confirmed observation of a living owl turning fully. To be cautious, this article refers to the rotation as "about 270 degrees."
4. How Large Holes and Shortcuts Protect an Owl's Blood Vessels
In humans, twisting the neck strongly can stretch the inner lining of blood vessels. This can cause a tear, leading to a blood clot that travels to the brain and causes a stroke [7]. Owls have structures reported to protect their blood vessels.
A team from Johns Hopkins University reported four adaptations around the blood vessels [7]. First, the holes in the neck bones through which the vertebral artery passes are very large. The diameter of these holes is about ten times the diameter of the artery itself [6]. This was seen in 12 of the 14 neck vertebrae. Imagine putting a thin straw through a wide pipe. Even if you move the pipe, the straw does not get pinched. The blood vessels have similar extra space, though real blood vessels are softer than straws.
Second, this artery enters the neck at a higher position, at the 12th vertebra, whereas in other birds, it enters farther down the neck. Third, there are small connecting vessels that link two main blood vessels. Fourth, there is a contractile reservoir at the base of the head that stores blood [7]. The fourth point is described as keeping blood flowing to the brain while the head turns, but it is not known if this was fully verified by experiment.
5. How Researchers Studied the Owl's Neck
The report was led by Fabien de Cock Mercier, a medical illustrator who specializes in drawing bodies for medicine and biology. He led the team at Johns Hopkins University [7].
The team studied the bodies of 12 owls from three species. It is reported that these owls died of natural causes [6]. They injected a contrast agent visible in X-rays into the blood vessels and took images. Then they dissected the bodies, drew them, and scanned the drawings [3].
This work was featured in the February 1, 2013, issue of Science magazine. It won first place in the poster and graphics category of the National Science Foundation’s 2012 Visualization Challenge [7]. It is important to note that this was recognized for the power of its visual presentation, not as a result proven by a peer-reviewed research paper.
6. What Scientists Still Do Not Know About Owl Head Turning
Some points in this story are not fully settled. First, the rotation angle. 270 degrees is the value known from living individuals. 360 degrees is a view based on specimens. It has not been confirmed if a living owl actually turns its head 360 degrees. Second, blood flow. It is not known if the reservoir at the base of the head truly keeps sending blood to the brain while the neck is turning.
Despite these unknowns, it is believed that three factors combine to allow the owl’s large head rotation: eyes that are hard to move, many neck bones, and blood vessels with large holes and shortcuts.
7. An Activity: Use a Tube to Feel What Fixed Eyes Are Like
You can make a tube using a cardboard tube or rolled paper or by rolling paper and taping it. Hold it to one eye and close the other. Look straight ahead. If you move your eyeball, the view through the tube hardly changes. To see something to the side, you must turn your whole head and the tube.
This gives you a rough idea of why an owl with hard-to-move eyes needs to turn its head because its eyes are hard to move. However, human eyes do move even inside a tube, so this is not exactly like a real owl. Turn your head gently, and stop right away if you feel any pain. If you visit a zoo and see an owl, watch whether its eyes or its head move when it looks at something.