Data from: 3D trajectories and network analyses of group behaviour within Chimney Swift flocks during approaches to the roost

Chimney Swifts (Chaetura pelagica) are highly manoeuvrable birds notable for roosting overnight in chimneys, in groups of hundreds or thousands of birds, before and during their autumn migration. At dusk, birds gather in large numbers from surrounding areas near a roost site. The whole flock then employs an orderly, but dynamic, circling approach pattern before rapidly entering a small aperture en masse. We recorded the 3D trajectories of approximately 1800 individual birds during a 30 minute period encompassing flock formation, circling, and landing, and used these trajectories to test several hypotheses relating to flock or group behaviour. Specifically, we investigated whether the swifts use local interaction rules based on topological distance (e.g. the n nearest neighbours regardless of their distance) rather than physical distance (e.g. neighbours within x m, regardless of number) to guide interactions, whether the chimney entry zone is more or less cooperative than the surrounding flock, and whether the characteristic subgroup size is constant or varies with flock density. We found that the swift flock is structured around local rules based on physical distance, that subgroup size increases with density, and that there exist regions of the flock that are less cooperative than others, in particular the chimney entry zone.烟囱雨燕（Chaetura pelagica）是机动性极强的鸟类，以在秋季迁徙前及迁徙期间，集结数百乃至数千只个体在烟囱内过夜栖息而闻名。黄昏时分，鸟群会从栖息点周边区域大规模聚集，随后整体呈现出有序且兼具动态性的盘旋接近模式，最终集体快速钻入狭小的入口。本研究在涵盖鸟群形成、盘旋与降落的30分钟观测时段内，记录了约1800只个体的三维飞行轨迹，并基于这些轨迹验证了多项与鸟群或群体行为相关的假说。具体而言，本研究探讨了三个核心问题：其一，雨燕是否基于拓扑距离（例如仅关注最近的n个邻近个体，不考虑其物理间距）而非物理距离（例如间距在x米内的邻近个体，不考虑数量）制定局部互动规则以指导群体互动；其二，烟囱入口区域的群体协作性相较于周边鸟群更强还是更弱；其三，典型亚群规模是固定不变，还是会随鸟群密度发生变化。研究结果显示：烟囱雨燕的鸟群遵循基于物理距离的局部互动规则；亚群规模随鸟群密度提升而增大；鸟群内部存在协作性存在差异的区域，其中尤以烟囱入口区域的协作性最弱。