FLIGHT SPEEDS OF MIGRATING BIRDS - A TEST OF MAXIMUM RANGE SPEED PREDICTIONS FROM 3 AERODYNAMIC EQUATIONS

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 s peeds that maximize the distance travelled per unit of energy expended (termed the maximum range speed, V(mr)). I tested this idea by compar ing literature reports of flight speeds for 48 avian species on migrat ion and comparing them to predictions of V(mr) derived from three aero dynamic equations (Tucker, Pennycuick, and Greenewalt). No single equa tion made V(mr) predictions that matched the full range of observed sp eeds. Species weighing 0.3 kg-3 kg (Greenewalt equation) and 0.1 kg-1 kg (Pennycuick equation) generally migrated at V(mr), but this represe nts only 42% (20/48) and 40% (19/48) of the total number surveyed, res pectively. Deviations from V(mr) outside these ranges varied systemati cally with mass. Lighter species almost always flew faster than V(mr), whereas heavier species showed the opposite trend. The latter group i s likely constrained to fly below V(mr) due to limits on metabolic per formance imposed by mass-specific scaling effects. The Tucker equation almost always predicted V(mr) values that were less than observed spe eds.