Meeting Abstract

45.5  Sunday, Jan. 5 11:15  Scaling of avian bipedal locomotion: How does body size influence gait dynamics in level and uneven terrain? DALEY, MA*; BIRN-JEFFERY, AV; Royal Veterinary Colleg; University of California Riverside mdaley@rvc.ac.uk

Most studies on scaling of locomotion are based on steady movement over level terrain. It is well established that leg posture changes substantially with body size, such that small animals run with crouched legs, and large animals run with straighter legs. Yet, evidence is sparse and sometimes conflicting on whether scaling influences gait dynamics. For example, duty factor is often considered a key indicator of leg loading during locomotion; yet some studies suggest duty factor does not scale with body size, and others show weak support for a scaling effect. Here we re-visit the scaling of gait dynamics in striding bipeds using a recently collected dataset on ground birds spanning a 530-fold mass range from quail to ostrich. We test for scaling effects on duty factor, fore-aft impulse, and model-based parameters such as effective leg stiffness and damping ratio. We also explore the scaling of non-steady locomotion, using measures of fall risk and body stability. We found weak negative allometry in the scaling of duty factor with body size in both level and uneven terrain. However, the data are more suggestive of inter-specific variation rather than a strong scaling trend. Leg contact conditions and fore-aft impulses do exhibit substantial scaling effects. Overall, we find that larger species run with relatively steadier gait dynamics over both level and uneven terrain, indicated by smaller stride-to-stride variance in forward velocity. Larger species also use leg contact conditions indicative of minimising fluctuations in leg loading, which may reflect pressure among larger species to minimize injury risk. Small animals use leg contact conditions indicative of minimising fall risk in both level and uneven terrain.