Broad-scale patterns of the Afro-Palearctic landbird migration

Aim: Animal migration strategies balance trade-offs between mortality and reproduction in seasonal environments. Knowledge of broad-scale biogeographical patterns of animal migration is important for understanding ecological drivers of migratory behaviours. Here we present a flyway-scale assessment of the spatial structure and seasonal dynamics of the Afro-Palearctic bird migration system and explore how phenology of the environment guides long-distance migration.
Location: Europe and Africa.
Time period: 2009–2017.
Major taxa studied: Birds.
Methods: We compiled an individual-based dataset comprising 23 passerine and near-passerine species of 55 European breeding populations where a total of 564 individuals were tracked migrating between Europe and sub-Saharan Africa. In addition, we used remote sensed observations on primary productivity (NDVI) to estimate the timing of vegetation green-up in spring and senescence in autumn across Europe. First, we described how individual breeding and non-breeding sites and the migratory flyways link geographically. Second, we examined how migration timing along the two major Afro-Palearctic flyways is tuned with vegetation phenology en route and at the breeding sites.
Results: While we found the longitudes of individual breeding and non-breeding sites to be strongly positively related, the latitudes of breeding and non-breeding sites were negatively related. In autumn, timing of migration was similar along the Western and the Eastern flyways and happened ahead of the autumnal senescence of vegetation. In spring, migration timing was approximately two weeks later along the Eastern flyway than on the Western flyway which coincided with the later spring green-up in Eastern Europe.
Main Conclusions: Migration of the Afro-Palearctic landbirds follows a longitudinally parallel leap-frog migration pattern where migrants track vegetation green-up in spring and depart before vegetation senescence in autumn. However, the ongoing global change have the potential to disrupt this spatiotemporal synchronization between migration timing and spring green-up with variable effects on different migrant populations.

研究目标：动物迁徙策略在季节性环境中权衡生存风险与繁殖收益。解析动物迁徙的大尺度生物地理格局，对于理解迁徙行为的生态驱动机制具有重要意义。本研究针对非洲-古北界（Afro-Palearctic）鸟类迁徙系统的空间结构与季节动态开展迁徙通道（flyway）尺度的评估，并探究环境物候如何调控长距离迁徙行为。
研究区域：欧洲与非洲。
研究时段：2009年—2017年。
研究类群：鸟类。
研究方法：本研究整合了一套个体水平数据集，涵盖欧洲55个繁殖种群的23种雀形目（passerine）与近雀形目鸟类，总计对564个个体完成了欧洲至撒哈拉以南非洲的迁徙轨迹追踪。此外，我们利用遥感观测得到的初级生产力数据——归一化差分植被指数（NDVI），估算了欧洲全域春季植被返青与秋季植被枯黄的时间节点。首先，我们刻画了单个繁殖、越冬位点与迁徙通道之间的地理关联模式；其次，我们分析了非洲-古北界两条主要迁徙通道上的迁徙时序，如何与迁徙途中及繁殖地的植被物候实现同步匹配。
研究结果：我们发现，单个繁殖位点与越冬位点的经度呈显著正相关，而纬度则呈显著负相关。秋季时，东西两条迁徙通道的迁徙时序基本一致，且均早于植被秋季枯黄期。春季时，东部迁徙通道的迁徙时序较西部通道晚约两周，这与东欧地区春季植被返青更晚的规律相吻合。
主要结论：非洲-古北界陆鸟的迁徙遵循沿经度平行的跳越迁徙（leap-frog migration）模式：春季迁徙时，鸟类追踪植被返青进程；秋季迁徙时，则在植被枯黄前启程。然而，当前持续的全球变化有可能打破迁徙时序与春季植被返青之间的时空同步性，进而对不同迁徙种群产生差异化影响。