Barnacle geese were walked on a treadmill at speeds ranging from 0.25 to 1.25 ms(-1), which was their highest sustainable speed. No evidence for a gait change was found. The gait of a barnacle goose appears to conform to the classical pendulum mechanics based model of walking, with the kinetic energy of forward motion (horizontal kinetic energy, E(kh)) out-of-phase with the sum of the gravitational potential (E(p)), and vertical kinetic (E(kv)) energies of the centre of mass at all speeds. Why barnacle geese are unable to aerial run when other 'waddling' species do show an aerial phase (e.g., mallard ducks) is unclear. Presumably, however, it is likely to relate to the amount of lateral kinetic energy generated, which is a feature of 'waddling'. We predict that lateral kinetic energy generated by barnacle geese and other waddling species that cannot aerial run, is higher than in those that can. Due to competing selection pressures for swimming and flight, barnacle geese are mechanically and energetically inefficient walkers relative to more specialist cursorial birds. Their upper walking speed, however, appears to be limited by morphology (via kinematics) and not metabolic capacity (energetics).
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