Kinematic constituents of the extreme head turn of Strix aluco estimated by means of CT-scanning.

To analyze extreme sideways turn of the head in owls, a total fresh specimen of Strix aluco was frozen in respective posture and CT-scanned. The maximum turn to one side was found to be 360°, provided that the head is drawn into the shoulders. 160° of this full turn are ensured by the neck axial rotation (this includes ~90° twist of the head relative to epistropheus and, posterior to it, less than 15° per every cervical joint), and the rest 200° are ensured by combination of dorsal and lateral flexion. The 15° limit is overcome in five joints in respect of dorsiflexion, and in six joints in respect of lateral flexion. So large a degree of lateral mobility is unusual among birds, and is appreciated as a crucial adaptation to extreme head turning.