Data from: Sex-specific difference in migration schedule as a precursor of protandry in a long-distance migratory bird

NOTE: An updated and larger version of this dataset is available. See https://doi.org/10.5441/001/1.4bt7365c. ABSTRACT: Protandry, the earlier arrival of males at the breeding grounds relative to females, is common in migratory birds. However, due to difficulties in following individual birds on migration, we still lack knowledge about the spatiotemporal origin of protandry during the annual cycle, impeding our understanding of the proximate drivers of this phenomenon. Here, we use full annual cycle tracking data of red-backed shrikes Lanius collurio to investigate the occurrence of sex-related differences in migratory pattern, which could be viewed as precursors (proximate causes) to protandry. We find protandry with males arriving an estimated 8.3 days (SE = 4.1) earlier at the breeding area than females. Furthermore, we find that, averaged across all departure and arrival events throughout the annual cycle, males migrate an estimated 5.3 days earlier than females during spring compared to 0.01 days in autumn. Event-wise estimates suggest that a divergence between male and female migratory schedules is initiated at departure from the main non-breeding area, thousands of kilometres from, and several months prior to arrival at the breeding area. Duration of migration, flight speed during migration and spatial locations of stationary sites were similar between sexes. Our results reveal that protandry might arise from sex-differential migratory schedules emerging at the departure from the main non-breeding area in southern Africa and retained throughout spring migration, supporting the view that sex-differential selection pressure operates during spring migration rather than autumn migration.

注意：本数据集存在更新且规模更大的版本，可通过https://doi.org/10.5441/001/1.4bt7365c查阅获取。摘要：雄性较雌性更早抵达繁殖地的现象（先雄现象，Protandry）在候鸟中极为普遍。但受限于难以追踪迁徙中的个体鸟类，目前学界对全年周期内先雄现象的时空起源仍缺乏系统认知，这也阻碍了我们对该现象近因驱动机制的理解。本研究借助红背伯劳（Lanius collurio）的全年周期追踪数据，探究其迁徙模式中的性别差异——这类差异可被视为先雄现象的前兆（即近因）。研究结果显示，雄性抵达繁殖地的时间较雌性早约8.3天（标准误SE=4.1）。进一步分析表明，综合全年所有迁徙出发与抵达事件来看，春季时雄性的迁徙启动时间较雌性早约5.3天，而秋季仅相差0.01天。按单次迁徙事件估算，雌雄迁徙日程的分化始于从主要非繁殖地出发阶段——该非繁殖地距离繁殖地数千公里，且早于抵达繁殖地数月之久。两性的迁徙时长、迁徙途中的飞行速度以及停歇地的空间位置均无显著差异。本研究结果揭示，先雄现象可能源于南非主要非繁殖地出发时产生的性别差异化迁徙日程，并在整个春季迁徙过程中持续存在，这支持了“性别差异化选择压力作用于春季迁徙而非秋季迁徙”的学术观点。