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.

研究目的：动物迁徙策略在季节性环境中权衡生存与繁殖的成本收益。了解动物迁徙的大范围生物地理格局，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，开展迁徙路线尺度的空间结构与季节动态评估，并探究环境物候如何指导长距离迁徙行为。
研究区域：欧洲与非洲。
时间范围：2009–2017年。
研究类群：鸟类。
方法：本研究整合了一套基于个体的数据集，涵盖55个欧洲繁殖种群的23种雀形目及近雀形目鸟类，总计追踪了564个个体在欧洲与撒哈拉以南非洲之间的迁徙过程。此外，我们利用遥感观测得到的初级生产力数据（归一化差异植被指数，Normalized Difference Vegetation Index, NDVI），估算了欧洲全境春季植被返青与秋季植被衰老的时间节点。首先，我们描述了个体繁殖地、越冬地与迁徙路线的地理关联模式；其次，我们检验了两条主要非洲-古北界迁徙路线上的迁徙时间，如何与中途及繁殖地的植被物候相匹配。
结果：尽管我们发现个体繁殖地与越冬地的经度呈显著正相关，但二者的纬度则呈显著负相关。秋季迁徙时间在东西两条迁徙路线上大致相近，且早于植被秋季衰老的时间。春季迁徙时间方面，东线迁徙路线较西线晚约两周，这与东欧春季植被返青更晚的现象相吻合。
主要结论：非洲-古北界陆禽的迁徙遵循沿经度平行的跳越迁徙（leap-frog migration）模式，迁徙种群会追踪春季植被返青，并在秋季植被衰老前离开越冬地。然而，当前持续的全球变化有可能打破迁徙时间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。