Individual detachment–reintegration events in homing pigeon flocks and the dominance of directional adjustment in their kinematic features

Abstract

Individual detachment–reintegration processes offer a useful window into brief non-steady reorganization in collective flight, but whether such events can be identified objectively across flight trials remains unclear. Using high-resolution three-dimensional trajectory data from homing pigeon flocks, we first tested whether nearest-neighbour distance distributions contained a separable second spatial scale. Only in trials that passed this test did we define a trial-specific event threshold and extract validated events using temporal continuity screening and reintegration-stability verification. Of four homing-flight trials, only two satisfied the separability criterion, yielding 17 validated events. Within these events, directional adjustment provided a more consistent kinematic signature than speed difference: median lateral steering ratios Rsteer were 0.674 and 0.715, and median acceleration-direction deviation angles ∠aout were 93.27∘ and 90.15∘, whereas speed difference Δv showed no consistent unidirectional change across trials. Comparisons with matched non-event baselines and robustness analyses further indicated that event specificity was expressed primarily as enhanced directional adjustment.