19.3 Wednesday, Jan. 4 The effects of posture and body mass on uneven terrain locomotion in Galliformes and Struthio camelus BIRN-JEFFERY, A.V.*; DALEY, M.A.; Royal Veterinary College, UK; Royal Veterinary College, UK email@example.com
Galliformes are a diverse group of ground dwelling birds, which are capable runners and span a 50-fold body size range (0.085-5kg). This order is ideal for investigating neuro-mechanical, stability and energy management mechanisms used over uneven terrain. In contrast, ostriches (Struthio) are the largest extant bipedal runners, and possess a straight legged posture typical of large animals. We hypothesise that postural changes associated with body size will alter the strategies used to run in uneven terrain. Small body mass combined with a crouched posture will allow robust stability using passive energy mechanisms, reducing reliance on feedback information. We collected kinetic and kinematic data as galliforms ran across six terrain conditions of varying ‘roughness’, using level terrain as control. Obstacles were of a single height; from 10-50% leg length (Lleg), spaced 2 strides apart. Similar data were collected from ostriches through an ontogenetic series, with only a 10% Lleg height obstacles. Ostriches were only capable of negotiating a 10% Lleg obstacle, and struggled with this height at 9 months old. In contrast, quails were capable of negotiating an obstacle of the same absolute size (8cm), which amounted to 80% Lleg. All birds appeared to anticipate the obstacle by increasing their centre of mass height before encountering the obstacle. Interestingly, smaller birds used a lower leg retraction velocity; one strategy for greater robustness in uneven terrain. Birds appear to optimise for safety over stability, as they allow changes in body motion and energy but minimise changes in ground reaction force. Understanding the mechanisms used by birds for robust locomotion in uneven terrain will allow replication of their remarkable performance in legged robots and prosthetics.