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Nature Notebook – Great-horned Owl

Virginia, a great horned owl (Bubo virginianus), is Sarett’s newest raptor education ambassador. She sustained an injury to her eye that required its removal so she cannot survive in the wild. Raptors need their binocular vision to accurately strike their prey and maneuver through the forest while pursuing said prey.

With her limited vision, Virginia’s ability to rotate her head will be even more important. Most owls can turn their heads up to 270 degrees; great horned owls can only manage 180 degrees (still quite a feat).

New imaging technology has allowed scientists to determine how that flexion is possible without causing damage to blood vessels and, subsequently, the brain. The actual turning is possible because the owl’s bones are only connected by one socket. Humans have two. The owls’ vertebrae have very large hollow cavities through which a major artery passes. The extra space keeps the vessel from being squashed and allows it to move as the head twists.

The neck arteries swell to collect blood that can’t pass through a vessel that has closed off during the turning process. Backup arteries take over the job of supplying nutrients to the affected areas. To be sure oxygen and nutrients make it to the brain, many small connections (like the neighborhood streets used to avoid a traffic jam) facilitate uninterrupted flow between arteries.