Data from: Programmed and flexible: long-term Zugunruhe data highlight the many axes of variation in avian migratory behaviour

Studies of Zugunruhe – the ‘migratory restlessness’ behaviour of captive birds – have been integral to our understanding of animal migration, revealing an inherited propensity to migrate and an endogenous timing and navigation system. However, differences between Zugunruhe in captivity and migration in the wild call for more data, in particular on variation within and among taxa with diverse migration strategies. Here, we characterise Zugunruhe in a long-term dataset of activity profiles from stonechats (genus Saxicola) with diverse migratory phenotypes (976 migration periods from 414 birds), using a flexible and consistent quantitative approach based on changepoint analysis. For east African, Austrian, Irish, and Siberian stonechats and hybrids, we report key inter-population differences in the occurrence, timing, and intensity of Zugunruhe. In line with expectations, we found the highest Zugunruhe intensity in the longest-distance migrants, more variable patterns in short-distance migrants, and intermediate characteristics of hybrids relative to their parental groups. Inter-population differences imply high evolutionary lability of Zugunruhe timing within a robustly structured annual cycle. However, counter to theory, Irish partial migrants showed no segregation between migrant and resident individuals, and previously reported nocturnal restlessness was confirmed for resident African stonechats. Further features of nocturnal restlessness that did not align with migratory behaviour of stonechats were juvenile nocturnal restlessness even prior to postjuvenile moult, and protandry in spring, although stonechats winter in heterosexual pairs. Importantly, Zugunruhe of all populations declined with age, and the intensity of an individual bird's Zugunruhe was correlated with activity levels during other parts of the annual cycle. Our results confirm endogenous, population-specific migration programmes but also reveal apparent discrepancies between Zugunruhe and migration in the wild. We thus highlight both the continued potential of Zugunruhe study and the need for circumspect interpretation when using migratory restlessness to make inferences about migration in the wild.

对迁徙躁动（Zugunruhe）——圈养鸟类的“迁徙焦躁”行为——的研究，是我们理解动物迁徙的核心支撑，其揭示了动物迁徙的遗传倾向，以及内生性的时间调控与导航系统。然而，圈养环境下的迁徙躁动与野外迁徙行为之间存在差异，这要求我们获取更多数据，尤其是针对具备多样化迁徙策略的类群内部及类群间的变异特征。本研究采用基于变点分析（changepoint analysis）的灵活统一定量分析方法，对414只石鵖属（Saxicola）鸟类、涵盖976个迁徙周期的长期活动谱数据集展开分析，以刻画其迁徙躁动特征，这些石鵖拥有多样化的迁徙表型，涵盖东非、奥地利、爱尔兰、西伯利亚石鵖及其杂交个体。针对上述类群，我们报道了不同种群在迁徙躁动的发生、时序与强度上的关键差异：与预期相符，长距离迁徙种群的迁徙躁动强度最高，短距离迁徙种群的躁动模式更为多变，杂交个体的迁徙躁动特征则介于其亲本类群之间。种群间的差异表明，在结构稳定的年周期内，迁徙躁动的时序具有较高的进化可塑性。但与理论预期相悖的是，爱尔兰的部分迁徙种群并未表现出迁徙个体与留居个体间的行为分化；同时本研究证实了此前关于留居非洲石鵖存在夜间躁动的报道。此外，还有两项与石鵖迁徙行为不符的夜间躁动特征：其一，幼鸟甚至在幼后换羽前就出现了夜间躁动；其二，春季存在雄性优先迁徙（protandry）现象，尽管石鵖会以异性配对的形式越冬。值得注意的是，所有种群的迁徙躁动强度均随年龄增长而下降，且个体的迁徙躁动强度与其年周期内其他时段的活动水平呈显著相关。本研究结果既证实了迁徙躁动的内生性与种群特异性迁徙程序，也揭示了圈养迁徙躁动与野外迁徙行为之间存在明显差异。因此，我们既强调了迁徙躁动研究的持续价值，也指出了利用迁徙躁动推断野外迁徙行为时需谨慎解读。