Many temperate birds invest considerable time and energy to travel the long distances between their breeding grounds and wintering areas. It has generally been assumed therefore that to minimize the energy cost of migration (and thus maximize fuel economy) birds ought to fly at speeds that maximize the distance travelled per unit of energy expended (termed the maximum range speed, Vmr). I tested this idea by comparing literature reports of flight speeds for 48 avian species on migration and comparing them to predictions of Vmr derived from three aerodynamic equations (Tucker, Pennycuick, and Greenewalt). No single equation made Vmr predictions that matched the full range of observed speeds. Species weighing 0.3 kg−3 kg (Greenewalt equation) and 0.1 kg−1 kg (Pennycuick equation) generally migrated at Vmr, but this represents only 42% (20/48) and 40% (19/48) of the total number surveyed, respectively. Deviations from Vmr outside these ranges varied systematically with mass. Lighter species almost always flew faster than Vmr, whereas heavier species showed the opposite trend. The latter group is likely constrained to fly below Vmr due to limits on metabolic performance imposed by mass-specific scaling effects. The Tucker equation almost always predicted Vmr values that were less than observed speeds.
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Clive V.J. Welhun (1994) studied this question.