Biomechanics and Ecological Application of Escape Gaits by White-Tailed Deer, Mule Deer, and Their Hybrids

Abstract

White-tailed deer (Odocoileus virginianus) and mule deer (0. hemionus) traditionally prefer landscapes with distinct topographical features, but the basis for their preferences is not understood. Widespread changes in the distribution of white-tails and mule deer are occurring, and reports of hybridization have been received all along the north-south gradient of overlap. Two questions were posed to investigate these situations: (1) Do the escape gaits and behaviors of white-tails and mule deer account for the distinct habitat preferences of these species? (2) Are the locomotory and escape patterns of hybrids confused, possibly impairing their survival relative to purebred individuals? I used high-speed cinematography to film captive white-tails, mule deer, and hybrids as they travelled at fast speeds across flat ground and over obstacless. I adapted methods from the fields of human and equine biomechanics. Body points were digitized from film images of moving deer. A computer program was written to generate gait diagrams, calculate limb timing variables, generate stick-figures of each stride, calculate landing and takeoff angles of the limbs, and calculate angles of limb and vertebral flexion. F1 hybrids, when most alarmed, used a gait intermediate between the white-tail gallop and mule deer stott, but a gait that was unique to hybrids. Evaluation of the biomechanics and potential ecological application of hybrid gaits indicated the hybrid gaits are slow and mechanically inefficient. F1 hybrid also showed extreme “indecision” in their general behavioral response to the dog. It is predicted that hybrids would have difficulty in locations where they faced strong predator pressure or other challenging stimuli, such as tricky terrain. Gaits of individual three-quarter and seven-eights mule deer were more variable than those of individual Fls. Nevertheless, these backcrosses rarely reproduced the specialized mule deer gaits.