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Reading The snow owl "Hedwig" has just looked her master Harry Potter in the face, now she turns her head - on and on, in the opposite direction and even further: Owls can turn their head in both directions by more than 270 degrees, "Actually, they would have to fall dead to the ground because they cut the blood supply to the brain, " says Philippe Gailloud of the Johns Hopkins University School of Medicine in Baltimore. But he and his colleagues have now found out why owls in their Halsverrenkungen yet the senses dwindle: The blood vessels in the neck of the birds therefore have more play than ours and additionally secure blood reservoirs the supply of the brain in extreme rotation. To unravel the mystery of the owls' spectacular flexibility, the researchers examined the heads and necks of twelve recently deceased birds. Using a CT scanner, they took three-dimensional images of the blood vessels and bones of these body parts. They also injected a liquid plastic into the arteries of the dead birds. He clarified the structures of the blood vessels when the researchers dissected them.

Safety systems ensure blood supply

The investigations revealed a clear difference to the neck anatomy of humans: The vertebral holes through which one of the carotid arteries from the body of the owl in the head, are significantly larger than the blood vessel itself. This leaves the vein space for movement, the researchers explain. In contrast, the human arteries fit snugly in the vertebral holes. In addition, owls still have special "safety arteries" in the neck, which allow emergency care, if it should actually pinch, the researchers report. In addition, Gailloud and his colleagues discovered bulges in blood vessels in the upper part of the neck, which presumably additionally serve as a blood reservoir in case of an extreme twisting of the head. "All of these protection systems are missing from humans, so extreme turns of the head, for example in accidents, are life-threatening for us, " says Gailloud.

The hypermobile neck has an important function for the owls in their way of life as Lauerjäger. In order not to scare prey animals such as mice, they must be quiet and unobtrusive, but still be able to monitor the largest possible area. Therefore, they sit motionless, only the head turns gently and silently. The rotation also compensates that the birds are unable to move their eyes independently of the head. At least as important, however, is the flexible alignment of the ear: In owls, the so-called veil - the ring-shaped feathers around the eyes - forms a kind of sound funnel that directs sound directly to the ear openings. By turning the head, owls can precisely align this sophisticated hearing system to noise sources. The combination of an extremely rotatable head with directional gaze and sensitive hearing allows owls to precisely locate both the finest twitching of a mouse's tail and the slightest rumbling on a crumb. display

Philippe Gailloud (Johns Hopkins University School of Medicine) et al .: Science, Acknowledgment in Issue 1 FEBRUARY 2013 VOL 339 © wissenschaft.de - Martin Vieweg

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