Flight in ground effect dramatically reduces aerodynamic costs in bats

Most flying animals, from insects to seabirds, perform flights close to ground or water when taking off or landing, drinking, and feeding or when traveling near water surfaces. When flying close to a surface within approximately one wingspan, the surface acts as an aerodynamic mirror, interrupting the downwash, resulting in increased pressure underneath the wing and suppression of wingtip vortex development. This aerodynamic interaction lowers the energy added to the air by the animal, reducing the cost of flying. Modeling suggests that flapping wings in ground effect can affect the expected power savings compared to gliding flight, either positively or negatively, depending on the wing motion. Although aerodynamic theory predicts substantial power reductions when animals fly in ground effect, quantitative measurements of savings are lacking. Here, we show, through wake-based power measurements, that Daubenton’s bats utilize 29% less aerodynamic power when flying in compared to out of g...