Fig. 2.
Observed obstacle negotiation strategy. Ground birds from bobwhite quail to ostrich use similar dynamics to negotiate obstacles, reflecting a consistent combination of vaulting onto the obstacle (step −1), some crouching on the obstacle (step 0) and energy exchange in the dismount, converting Ep to Ek (step +1). (A) Dynamics illustrated by velocity vectors (arrows), CoM position (balls) and leg posture (stick figures). (B) Ground reaction force (GRF). (C) Change in potential energy per step during obstacle negotiation. A and B show a grand mean across species for the aerial running data (walking and grounded running trials excluded from the average trajectories). In step 0, crouching accounts for 39±7% (mean ± s.d.) of the obstacle height across species. Peak forces remain within 0.35 body weights (BW) of level gait (B; grey shading indicates ±0.5BW). See supplementary material Tables S1–S6 for detailed statistics.