Elegant-crested Tinamous Eudromia elegans do not synchronize head and leg movements during head-bobbing

Head-bobbing is the fore-aft movement of the head relative to the body during terrestrial locomotion in birds. It is considered to be a behaviour that helps to stabilize images on the retina during locomotion, yet some studies have suggested biomechanical links between the movements of the head and legs. This study analysed terrestrial locomotion and head-bobbing in the Elegant-crested Tinamou Eudromia elegans at a range of speeds by synchronously recording high-speed video and ground reaction forces in a laboratory setting. The results indicate that the timing of head and leg movements are dissociated from one another. Nonetheless, head and neck movements do affect stance duration, ground reaction forces and body pitch and, as a result, the movement of the centre of mass in head-bobbing birds. This study does not support the hypothesis that head-bobbing is itself constrained by terrestrial locomotion. Instead, it suggests that visual cues are the primary trigger for head-bobbing in birds, and locomotion is, in turn, constrained by a need for image stabilization and depth perception.