Data from: Three-dimensional 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
three-dimensional trajectories of ≈1 800 individual birds during a 30 min
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（Chimney swifts, Chaetura pelagica）是一类机动性极强的鸟类，以在秋季迁徙前及迁徙期间，以数百至数千只的规模集群夜栖于烟囱中而著称。黄昏时分，个体从栖息点周边区域大规模集结。随后整个鸟群会先呈现出有序且富有动态性的盘旋进场模式，再集体快速钻入狭小的出入口。我们在涵盖鸟群形成、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研究假说。具体而言，本研究探究了三个核心问题：一是雨燕是否采用基于拓扑距离（topological distance）（例如选取距离自身最近的n个邻居，不考量其物理间距）而非物理距离（physical distance）（例如选取x米范围内的邻居，不限定邻居数量）的局部互动规则来引导群体交互；二是烟囱入口区域的群体协作程度相较于鸟群其余区域是更高还是更低；三是典型亚群规模是保持恒定，还是会随鸟群密度发生变化。研究结果显示，烟囱雨燕群的群体结构基于物理距离的局部互动规则构建；亚群规模随鸟群密度提升而增大；且鸟群内部不同区域的协作程度存在差异，其中尤以烟囱入口区域的协作性最弱。