Data from: African departure rather than migration speed determines variation in spring arrival in pied flycatchers

Properly timed spring migration enhances reproduction and survival. Climate change requires organisms to respond to changes such as advanced spring phenology. Pied flycatchers Ficedula hypoleuca have become a model species to study such phenological adaptations of long-distance migratory songbirds to climate change, but data on individuals’ time schedules outside the breeding season are still lacking.

Using light-level geolocators, we studied variation in migration schedules across the year in a pied flycatcher population in the Netherlands, which sheds light on the ability for individual adjustments in spring arrival timing to track environmental changes at their breeding grounds.

We show that variation in arrival dates to breeding sites in 2014 was caused by variation in departure date from sub-Saharan Africa and not by environmental conditions encountered en route. Spring migration duration was short for all individuals, on average 2 weeks. Males migrated ahead of females in spring, while migration schedules in autumn were flexibly adjusted according to breeding duties. Individuals were therefore not consistently early or late throughout the year.

In fast migrants like our Dutch pied flycatchers, advancement of arrival to climate change likely requires changes in spring departure dates. Adaptation for earlier arrival may be slowed down by harsh circumstances in winter, or years with high costs associated with early migration.

适时的春季迁徙可提升繁殖成功率与存活率。气候变化迫使生物应对春季物候提前等环境变化。斑姬鹟（Ficedula hypoleuca）已成为研究长距离迁徙鸣禽应对气候变化的物候适应性的模式物种，但目前仍缺乏繁殖季外个体迁徙时间安排的相关数据。
本研究利用光级地理定位器（light-level geolocator），对荷兰境内的一个斑姬鹟种群开展了全年迁徙节律变化的调查，该研究有助于阐明个体通过调整春季抵达繁殖地的时间以追踪其繁殖地环境变化的能力。
研究结果显示，2014年个体抵达繁殖地的时间差异源于其从撒哈拉以南非洲出发的时间差异，而非迁徙途中遭遇的环境条件。所有个体的春季迁徙时长均较短，平均仅为2周。春季迁徙中雄性早于雌性出发，而秋季迁徙节律则会根据繁殖任务灵活调整。因此，个体在全年的迁徙节奏并非始终保持早或晚的固定模式。
对于荷兰斑姬鹟这类快速迁徙物种而言，为应对气候变化而提前抵达繁殖地，大概率需要调整春季的出发时间。但冬季的恶劣环境，或是迁徙提前需承担高昂代价的年份，可能会延缓个体实现提前抵达的适应性演化。