Figure S1 from Simultaneous measurements of three-dimensional trajectories and wingbeat frequencies of birds in the field

Box plots of wingbeat frequency averaged over flapping modes after excluding rooks (that is, birds with mean wingbeat frequency<4 Hz). For each flock, we selected birds that are flying in low density regions defined by N3m < mean(N3m)-std(N3m), and that are flying in high density regions defined as N3m > mean(N3m) + std(N3m).