Climbing performance of migrating birds as a basis for estimating limits for fuel-carrying capacity and muscle

Sustained climb rates and airspeeds in flapping flight were measured by radar tracking fifteen species of migrating birds ranging in body mass between 10 g and 10 kg. There was an inverse correlation between body size and climb rate: the lowest mean climb rate, 0.32 m s"', was observed in the mute swan and the highest mean value, 1.63ms"1, in the dunlin. Some dunlin flocks achieved sustained climb rates exceeding 2ms"1, up to 2.14ms"1. Assuming that the migrants expend maximum sustained power during their climbs, the climbing power can be used as a conservative estimate of the power margin. Estimates of climbing power for the species tracked by radar were used, in conjunction with aerodynamic theory, to calculate the amount of extra load the migrants should be able to carry if their power margin was used for load transportation rather than for climbing. Calculated ratios of total body mass with maximum load to lean body mass ranged between 1.28 and 2.75, showing an overall negative correlation with body size. There was a broad agreement with maximum fuel loads observed among free-living birds, indicating that the upper limits of fuel-carrying capacities and fligh