Gait kinematic parameters plotted against walking speed (<i>U</i>) in winter (blue) and summer (red) acclimated birds.

<p>A) Duty factor decreased with <i>U</i>, but never dropped below 0.5 across the speed range tested, B) The relative durations of the stance (<i>l</i>_stance, circles) and swing (<i>l</i>_swing, squares) phases. <i>l</i>_swing remained relatively unchanged across the speed range and was slightly reduced in winter birds. <i>l</i>_stance decreased curvi-linearly and was less in winter birds C) Stride frequency increased linearly with <i>U</i> and was 0.51Hz faster across the speed range during winter D) Stride length similarly increased linearly with <i>U</i> and was reduced in winter birds.</p

Mass-specific metabolic power consumption during locomotion (<i>P</i>_met) plotted against walking speed (<i>U</i>) in winter (blue) and summer (red) acclimated birds.

<p>A) <i>P</i>_met increased linearly with <i>U</i> and was 31.05% higher in summer birds compared to winter birds, B) <i>P</i>_met values corrected for fat-free winter mass were not significantly different between the seasons, indicating a free cost of carrying the additional mass C) net <i>P</i>_met (calculated by subtracting resting metabolic rate values from <i>P</i>_met was significantly different between the seasons.</p