Figure 2

Kinematic parameters plotted against U for each gait - (a,b) l_stride against U; (c,d) ƒ_stride against U; (e,f) log₁₀ t_stance against log₁₀ U; and (g,h) log₁₀ t_swing against Log₁₀ U. The left panels (a,c,e,g) represent data points for the trials over all snow conditions. The right panels represent data points for ptarmigan exclusively moving over very hard surfaces to facilitate like-for like substrate comparisons between field and laboratory treadmill datasets. Walking, ground running and aerial running gaits are denoted by the red, white and blue circles, respectively. The lines of best fit describing the linear regression for wild ptarmigans are shown in black. The red lines represent the lines of best fit for the laboratory treadmill data. The vertical dashed line denotes the maximum sustainable speed recorded in the laboratory treadmill experiments⁷. To the right of the vertical line at 2.0 ms⁻¹, the red line becomes dashed to denote projected speed beyond that sustainable in the laboratory.