Figure 2.

(a) Density curves of Δangle used by the birds along the tracks, separately for the searching and transit behavioural states. (b) Results of the generalized additive mixed effect wind model fitted to the transit portions of the tracks. The shaded areas represent the 95% confidence intervals. For visualization, the predicted effect of Δangle on ground speed was calculated for light and strong winds (the 25 and 75% quantiles of the wind speeds experienced by the birds, equal to 17 and 31 km h⁻¹, respectively). The Δangle predicted by the wind model to maximize the ground speed (50°) is similar to that maximally exploited by Desertas petrels during the transit state (60°). (Online version in colour.)