Abstract
Altering speed and moving on a gradient can affect an animal’s posture and gait, which in turn can change the energetic requirements of terrestrial locomotion. Here, the energetic and kinematic effects of locomoting on an incline were investigated in the Indian peacock, Pavo cristatus. The mass-specific metabolic rate of the Indian peacock was elevated on an incline, but this change was not dependent on the angle ascended and the cost of lifting remained similar between the two inclines (+5 and +7°). Interestingly, the Indian peacock had the highest efficiency when compared to any other previously studied avian biped, despite the presence of a large train. Duty factors were higher for birds moving on an incline, but there was no difference between +5 and +7°. Our results highlight the importance of investigating kinematic responses during energetic studies, as these may enable explanation of what is driving the underlying metabolic differences when moving on inclines. Further investigations are required to elucidate the underlying mechanical processes occurring during incline movement.
Highlights
Locomotion is an integral part of every organism’s life, and requires a significant proportion of daily energy expenditure (Karasov, 1981; Pontzer & Wrangham, 2004)
The energetic cost of locomotion in the peacock is greater while moving on an incline gradient than on a level gradient, consistent with previous investigations in birds (Ellerby et al, 2003; Lees et al, 2013; Rubenson et al, 2006), reptiles (Farley & Emshwiller, 1996; Zani & Kram, 2008), mammals (Cohen, Robbins & Davitt, 1978; Eaton et al, 1995; Fancy & White, 1987) and some invertebrates (Full & Tullis, 1990; Tullis & Andrus, 2011)
The elevated metabolic cost associated with incline locomotion has been attributed to increases in muscle activity required to raise the centre of mass (CoM) against gravity, while accounting for the apparent reduction in elastic potential energy (Gabaldon, Nelson & Roberts, 2004; Roberts et al, 1997; Snyder & Farley, 2011)
Summary
Locomotion is an integral part of every organism’s life, and requires a significant proportion of daily energy expenditure (Karasov, 1981; Pontzer & Wrangham, 2004). Understanding how locomotor activity influences the daily energy budget of an animal is important as it can provide insights into adaptations that have evolved to alleviate the costs of moving around (Carrier, 1987; Webb, 1984). Increases in speed usually account for elevations in the energetic cost of terrestrial locomotion. This increase occurs as when speed increases, the force required to move the COM must be generated in less time, which is achieved by recruiting a higher volume of muscle and/or faster-acting muscle fibres (Ellerby et al, 2003; Full, 1987; Kram & Taylor, 1990; Taylor, Schmidt-Nielsen & Raab, 1970). Locomotion on an incline can increase metabolic rate when
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