Since owls can't move their eyes, does this put them in jeopardy from predators? asks Sanford Weinberg of Plainview.
Unlike our round eyes, swiveling in their sockets, owls have tubular eyes that are nearly immobile. But owls don't miss much, because they can swivel their heads like nobody's business. Owls are also usually perched at the top of their food chains. Most adults, from great horned to snowy, barred to barn, have no natural predators. Except, that is, for humans, who might (illegally) shoot, trap or poison them.
Baby owls are vulnerable, and are targets for other birds of prey, like hawks. Burrowing owls of all ages also have enemies. These small owls live underground in tunnels dug by animals like ground squirrels and prairie dogs. Foxes, badgers, coyotes, horned owls, hawks, cats and even dogs can prey on them.
Like a demon-possessed character in a horror film, an owl can effortlessly twirl its head around nearly full circle without injuring blood vessels in its neck and head. Researchers have long wondered how this is possible. Kinking arteries in the neck can cut blood flow to the brain. Arteries leading to the brain are fragile; quick head jerks can cause stretching tears in vessel linings. Clots can form, break off and travel into the brain, triggering a stroke.
But owls seem immune. In 2013, brain-imaging specialists at Johns Hopkins University teamed up with a medical illustrator to look at 12 owls in a new way. The owls had all died of natural causes, and the team injected dye into the birds' arteries, mimicking blood flow. CT scans looked at the owls' bones and blood vessels.
Like other birds, owls have extra vertebrae in their necks (14 to our seven), making the necks very flexible. Carotid arteries run near the center of the spine, rather than on the vulnerable sides of the neck. In owls, the researchers found, vertebral arteries passed through cavities in the bones that were 10 times wider than the arteries themselves. Surrounded by cushy air pockets, the blood vessels have room to move as the head turns.
As dye flowed through an owl's arteries, blood vessels at the base of its head expanded, creating tiny reservoirs. In a live owl, blood could collect there, feeding the brain as the neck twists. Researchers also found small vessels connecting the carotid with vertebral arteries, allowing blood to take the least impeded course as an owl's neck turns. All of these adaptations keep owls from keeling over during 270-degree head spins.