Andrew Biewener's group has long been fascinated by what keeps birds aloft. How birds transfer the power generated by their flight muscles to air and propel themselves along, without any buoyant support, is an intriguing question. Bret Tobalske and Tyson Hedrick wanted to know how birds that have similar builds but differ in weight change their wing beats as they accelerate. Heavier birds have to work harder to keep themselves off the ground, so Biewener's team expected that heavy birds would need to fly using a gait that generated more power until they reached a higher speed than a light bird. But to the Harvard group's surprise, when they compared flying birds with others that weighed half as much, both species switched gait at the same speed (p. 1389)!
As birds accelerate, they change gait, in much the same way as terrestrial animals. At low speeds, the birds...
