Pigeons use tree structures as the leadership structure for flocking

Collective behaviors leading to various fascinating movement patterns are
believed to be the product of complex interplay among individuals.
Previous studies have identified two types of leadership structures in
pigeon flocks, i.e., hierarchical networks and reciprocal relationships.
However, both of these leadership structures are predicated based on data
analysis and lack substantial empirical evidence. Additionally, it is
difficult to delineate a direct correspondence between leadership
structures and trajectory data for pigeon flocks because birds cannot
report their leadership structure. Herein, we demonstrated that pigeons
adopt leadership relationships that can be characterized as tree
structures. In a tree structure, each follower follows its only leader
during collective flights, and the single top leader determines the entire
flock's flight direction. In the present study, we performed
experiments using student volunteers who could report leadership
relationships. We identified a one-to-one correspondence between
leadership structures and data characteristics and proposed a method for
determining the leadership structure based on trajectory data. This
strategy was used to analyze flight trajectory data from a pigeon flock
and elucidate the pigeons' leadership relationships. The developed
approach could effectively model the collective behavior of pigeon flocks,
thus accurately replicating findings from previous experimental studies.
The results of this study provide insights regarding the leadership
structure in pigeon flocks and have implications for artificial collective
systems, e.g., autonomous formation control of multiple unmanned aerial
vehicles or unmanned surface vehicles.