Extended Data Fig. 2: Impact of ground effect on the line of feasible transition points.

We assessed the impact of ground effect by re-evaluating the powered dive phase (red) and unpowered glide phase (blue) with an aerodynamic model of ground effect³³ included for the same set of feasible parameter settings as we had identified previously without ground effect (black). Whereas the powered dive transitions smoothly into the unpowered glide for the original solutions without ground effect (black), the introduction of ground effect without any changes to the model parameters necessarily results in a small mismatch between the two flight phases. The extent of this mismatch is shown by the arrows plotting the change in position of the transition point predicted at the end of the powered dive (red arrows) and the start of the unpowered glide (blue arrows) for trajectories satisfying the take-off and landing constraints. The effect, shown here for the bird “Drogon”, is marginal; the enlarged inset shows the effect on transition points close to the ground at 12 m perch spacing for which the impact of ground effect is greatest.