Owls cannot move their eyes and must turn their entire heads to see.

Owls have tubular eyes held firmly in place by sclerotic rings—bony structures found in the skulls of many birds and reptiles. Because these eyes are not spherical, they lack the muscles needed for independent movement within the socket. This evolutionary trade-off enables massive lenses and retinas that deliver exceptional low-light vision and depth perception for hunting.To overcome this lack of eye mobility, owls have evolved 14 cervical vertebrae—twice the number found in humans. This anatomical feature allows them to rotate their heads 270 degrees in either direction, a range critical for a predator that relies on both sight and sound to locate prey in complete darkness.A 2013 study by researchers at Johns Hopkins University School of Medicine used CT scans and angiography to reveal how owls survive such extreme neck twisting. The researchers discovered that owls have contractile blood reservoirs at the base of the head that pool blood to meet the brain's oxygen demands when the neck is turned. This mechanism prevents the stroke-like symptoms or vessel damage that would occur if a human attempted a similar movement.Additionally, the owl's vertebral arteries enter the neck at a higher point than in other birds, providing extra slack. The bony tunnels housing these arteries are approximately ten times larger than the vessels themselves. This extra space creates a protective cushion of air, ensuring the blood supply is never pinched or restricted during rapid, high-angle head movements.