Birds achieve high robustness in uneven terrain through active control of landing conditions

Abstract

SUMMARYWe understand little about how animals adjust locomotor behaviour to negotiate uneven terrain. The mechanical demands and constraints of such behaviours likely differ from uniform terrain locomotion. Here we investigated how common pheasants negotiate visible obstacles with heights from 10 to 50% of leg length. Our goal was to determine the neuro-mechanical strategies used to achieve robust stability, and address whether strategies vary with obstacle height. We found that control of landing conditions was crucial for minimising fluctuations in stance leg loading and work in uneven terrain. Variation in touchdown leg angle ( TD ) was correlated with the orientation of ground force during stance, and the angle between the leg and body velocity vector at touchdown ( TD ) was correlated with net limb work. Pheasants actively targeted obstacles to control body velocity and leg posture at touchdown to achieve nearly steady dynamics on the obstacle step. In the approach step to an obstacle, the birds produced net positive limb work to launch themselves upward. On the obstacle, body dynamics were similar to uniform terrain. Pheasants also increased swing leg retraction velocity during obstacle negotiation, which we suggest is an active strategy to minimise fluctuations in peak force and leg posture in uneven terrain. Thus, pheasants appear to achieve robustly stable locomotion through a combination of path planning using visual feedback and active adjustment of leg swing dynamics to control landing conditions. We suggest that strategies for robust stability are context specific, depending on the quality of sensory feedback available, especially visual input.

Preferred gait and walk–run transition speeds in ostriches measured using GPS-IMU sensors

“…However, we found higher stride-to-stride variance in energy phase with unsteady gait. This is consistent with previous findings that mechanical energy fluctuations vary considerably in unsteady gait, but ground reaction force magnitude remains consistent (BirnJeffery and Daley, 2012;Birn-Jeffery et al, 2014), constrained by the requirements to support body weight while avoiding injurious loads. Nonetheless, we found that gait identification based on displacement amplitude versus energy phase agreed for 83.5% of walking steps and 89.9% of running steps, using 90 deg threshold for gait distinction from energy phase.…”

Sensory feedback and coordinating asymmetrical landing in toads

“…Indeed, vision is used in a variety of animals to modulate limb kinematics and mechanics when adjusting to running over uneven ground [14,15] or stepping onto a sloped or raised surface [16]. Given this, we propose several questions that open directions for future work.…”

The effects of multiple obstacles on the locomotor behavior and performance of a terrestrial lizard

“…In all but one trial (Table 2), bipedal lizards also raised their hip height, a mechanism utilized by birds in anticipation of uneven terrain (Birn-Jeffery and Daley, 2012). Together with an increase in body angle and raising the hips, S. woodi depresses the tail to maintain a bipedal posture, and pitch the body COM forward and over the obstacle as it crosses it.…”

“…Uneven substrates directly affect the locomotion of animals by altering the transmission of locomotor forces (Tulli et al, 2012;Higham et al, 2001), influencing maneuverability and the ability to evade predators by sprinting. Furthermore, substrate unevenness requires adjustments in posture and velocity (Collins et al, 2013;Birn-Jeffery and Daley, 2012).…”