Turbulence explains the accelerations of an eagle in natural flight

Although birds almost always navigate through atmospheric turbulence while flying, the role this turbulence plays is unclear. This holds especially for turbulent fluctuations with timescales similar to those of avian behaviors. We combine the measured accelerations of a golden eagle flying in the wild, its GPS coordinates, and wind speed data and find evidence that turbulence is the main contributor to the eagle's accelerations. We observe long tails in the probability distribution of accelerations similar to those observed for particles in turbulence. In an interval of timescales from about 1/2 and 10 seconds, we observe power-law acceleration spectra whose scaling and amplitude can be explained by a linear relationship between aerodynamic forces and turbulent wind velocity fluctuations. These timescales are comparable to those of turbulent structures both larger than the eagle's wingspan and smaller than atmospheric phenomena such as convection cells. The timescales are also comparable to those of typical flight behaviors, corresponding to between about 1 and 25 wingbeats. The dominance of turbulence's imprint on the bird's movements illustrates the need to refine our understanding of the interactions between turbulence and flight.