Head-bobbing in quail. A: Still images from a representative x-ray sequence of a quail during grounded running. During the hold phase the head is held in a fixed position relative to space, while the rest of the body continues to move forward. During the thrust phase the head is moved forward rapidly relative to the body. B: Coordination between head-bobbing and gait during a trial with vaulting mechanics as a means of minimizing vertical head displacement during locomotion. The trunk is subjected to specific rhythmic vertical displacements (fluctuations of E
) depending on the gait. We hypothesized that the onset of the thrust phase would occur around the event where the E
of the CoM
was at a minimum since the extension of the neck may function to reduce the vertical displacement of the head (eyes) and is thus potentially advantageous to vision. In this view, coordination between head-bobbing and gait during a trial with bouncing mechanics (C) would thus require a different timing of head-trunk coordination.