Data from: Complex migration and breeding strategies in an elusive bird species illuminated by genetic and isotopic markers

Unlike the annual bi-directional movements of over 200 bird species within the Palaearctic–Afrotropical region, irregular movements such as irruptive migration with a low degree of philopatry are reported for a variety of species depending on highly seasonal and unpredictable resources. These flexible movements allow for itinerant breeding – consecutive breeding attempts in two or more geographically different regions during the same annual reproductive cycle. In order to illuminate migratory and breeding strategies of the erratic wetland species Baillon's crake Zapornia pusilla across the W-Palaearctic–Afrotropical region, we used a set of six DNA microsatellites as well as δ2Hf values of individuals sampled at one African and four European breeding sites. We investigated the degree of genetic population structure within and among different sites and assigned individuals’ feathers of unknown origin to their probable moulting (hence breeding) site using a likelihood approach. We found three genetic clusters, differentiating into one ‘European’ and two ‘African’ populations. Connectivity between the sampling sites was probable as genetic ‘African’ individuals were found in breeding conditions in Europe and vice versa. Likewise, assigned moulting locations based on δ2H isoscapes suggested trans-continental movements as well as moulting and possibly breeding by the same individual both in African and European breeding grounds. Both isotopic and genetic data reveal the Baillon's crake pursue a complex migration and breeding strategy, allowing as well for irruptive movements and itinerant breeding across the W-Palaearctic–Afrotropical region. However, a better knowledge about the species’ distribution as well as a more comprehensive data set, including samples from the southern and eastern boundaries of the distribution area would be necessary to improve the spatial resolution to the precision required to unambiguously infer migration directions and extent of exchange between African and European breeding grounds.与古北界-非洲热带界（Palaearctic–Afrotropical）内200余种鸟类每年进行的双向迁徙不同，诸多鸟类会因高度季节性且不可预测的资源状况，出现诸如低恋巢性（philopatry）的突发扩散迁徙（irruptive migration）这类不规则移动行为。这类灵活的移动模式支持漫游繁殖（itinerant breeding）——即在同一年度繁殖周期内，于两个及以上地理区域连续开展繁殖尝试。为阐明西古北界-非洲热带界（W-Palaearctic–Afrotropical）内行踪不定的湿地鸟类小田鸡（Baillon's crake，学名*Zapornia pusilla*）的迁徙与繁殖策略，本研究采用6个DNA微卫星（microsatellite）标记，结合对1个非洲繁殖位点与4个欧洲繁殖位点采样个体的氢稳定同位素δ²Hf值开展分析。本研究解析了不同繁殖位点内部及位点间的遗传种群结构程度，并通过似然法（likelihood approach）将未知来源的个体羽毛样本归属至其可能的换羽（即繁殖）位点。研究结果显示存在3个遗传簇，可划分为1个“欧洲种群”与2个“非洲种群”。由于在欧洲繁殖种群中检测到遗传特征为“非洲型”的个体，反之亦然，因此各采样位点间存在遗传连通性的可能性较高。同样，基于δ²H同位素等值线图（isoscape）推测的换羽位置表明，该物种存在跨大陆移动行为，且同一个体可同时在非洲与欧洲繁殖地完成换羽，甚至开展繁殖活动。同位素与遗传数据均表明，小田鸡在西古北界-非洲热带界范围内采取了复杂的迁徙与繁殖策略，其中涵盖突发扩散迁徙与漫游繁殖行为。不过，若要提升空间分辨率以达到明确推断迁徙方向及非洲与欧洲繁殖位点间基因交流程度所需的精度，还需要进一步明确该物种的分布范围，并采集分布区南部与东部边界的样本以构建更全面的数据集。