HANCOCK, J.A.*; BIKNEVICIUS, A.R.; STEVENS, N.J.; Ohio University, Athens; Ohio University, Athens; Ohio University, Athens: Head movements and terrestrial locomotion in tinamous (Eudromia elegans)

Since the first photographic analysis of the fore-aft movement of the head in birds by Dunlap and Mowrer (1930), it has been known that the movement consists of a thrust phase and a hold phase. During the thrust phase the velocity of the head is greater than the velocity of the body, extending the head in front of the body. During the hold phase the head is immobilized as the body moves forward, creating a delusive backward movement of the head. Head movement is commonly considered to be an optomotor response, in which the thrust phase uses motion parallax to generate depth perception and the hold phase functions to stabilize an image on the retina. Alternatively, some researchers argue that the visual aspects of head movement serve a secondary adaptive function and that the primary function is locomotor. Their argument is based on the findings that head movements are synchronized with body and leg movements at slow-moderate speeds and the hold phase is missing at higher speeds. Lacking are data coordinating head, body and limb movements across a range of walking and running speeds. In this study head movements (initiation of both thrust and hold phases) of tinamous (Eudromia elegans) are analyzed in relation to kinematic (times of touchdown and liftoff) and kinetic events (times of peak vertical force and maximum and minimum fore-aft forces) at a range of speeds. The frequency of head movements and the percentage of hold phase within the cycle are then related to speed and locomotor kinetics.