风让鸟类飞行更省力

Winds make bird fl ights cheaper Many birds use atmospheric air currents to reduce the energy costs of flying Anders Hedenström The concept of cost of transport, introduced by physiologist Knut Schmidt-Nielsen, describes the energy that an animal spends to move a unit of mass over a unit of distance (1). It declines across all locomotion modes (swimming, running, flying) as body size increases. For the same body size, swimming is the most energy-efficient mode of transport. Because flying is fast, its cost is lower than that of running or walking, despite requiring a much higher metabolic rate. These relationships could explain the long-distance migrations of some fliers and swimmers, which are not seen in terrestrial runners. …