Fig. 6. The calculated fraction of vertical mechanical work done on the center of mass (COM) during locomotion across different inclines by the legs (A) and wings (B). At 60° chukars rarely use their wings, and the magnitude of the vertical component of the ground reaction force is sufficient to provide the motion in this plane. Over steeper inclines the vertical component of the GRF is no longer sufficient to provide the energy required of vertical motion, thus the difference must be attributed to the wings.