Pigeons lock their eyes in place during flight.

Vision in most animals follows a fixate-and-saccade pattern.1,2 Birds fixate their viewing direction, then rapidly shift this gaze through head and eye movements. We used a head-mounted eye-tracking system in flying pigeons to relate eye to head movement and map eye position within the head. After take-off, the birds increased their pupil size and adopted a fixed and consistent eye position in their heads. In different visual environments, eye position returned to within 1° of a fixed position during flight. Pigeons thus "lock" their eyes in place by actively maintaining a near-consistent eye position within their head. When flying, the birds positioned their eyes close to the primary horizontal axes of their vestibular systems. Because visual neurons share a common reference frame with the vestibular system,3 a consistent flight gaze position may actively align vision with vestibular sensing and facilitate perception of self-motion.4.