Data from: Orientation of native versus translocated juvenile Lesser Spotted Eagles (Clanga pomarina) on the first autumn migration

The ontogeny of migration routines used by wild birds remains unresolved. Here we investigated the migratory orientation of juvenile lesser spotted eagles (LSE) (Clanga pomarina) based on translocation and satellite tracking. Between 2004 and 2016, 85 second-hatched juveniles (Abels) were reared in captivity for release into the declining German population, including 50 birds that were translocated 940 km from Latvia. In 2009, we tracked 12 translocated juveniles, as well as 8 native juveniles and 9 native adults, to determine how inexperienced birds come to use strategic migration routes. Native juveniles departed around the same time as the adults and 6 of 8 used the eastern flyway around the Mediterranean, which was used by all adults. In contrast, translocated juveniles departed on average 6 days before native LSEs, and 5 traveled southward and died in the central Mediterranean region. Consequently fewer translocated juveniles (4/12) than native juveniles (7/8) reached Africa. We conclude that juvenile LSEs have a much better chance of learning the strategic southeastern flyway if they leave at an appropriate time to connect with experienced elders upon departure. It is not clear why translocated juveniles departed so early. Regardless, by the end of the year, most juveniles had perished, whether they were translocated (10/12) or not (6/8). The small number of surviving translocated juveniles thus still represents a significant increase in the annual productivity of the German LSE population in 2009.

野生鸟类迁徙行为的个体发育机制至今仍未阐明。本研究通过移地放飞与卫星追踪技术，探究了幼年小斑海雕（Lesser Spotted Eagle，LSE，学名*Clanga pomarina*）的迁徙定向行为。2004年至2016年间，研究人员人工繁育了85只第二孵出的幼雏（代号Abels），用于放归持续衰退的德国小斑海雕种群，其中50只个体从拉脱维亚移地放飞，放飞距离达940公里。2009年，我们对12只移地放飞的幼年个体、8只本土幼鸟以及9只本土成鸟开展卫星追踪，旨在探明无迁徙经验的个体如何习得战略性迁徙路径。本土幼鸟的出发时间与成鸟基本同步，8只个体中有6只选择了地中海东侧迁徙通道，而所有成鸟均使用该通道。与之形成鲜明对比的是，移地放飞的幼鸟平均比本土小斑海雕提前6天出发，其中5只个体向南飞行途中死于地中海中部海域。因此，最终成功抵达非洲的移地放飞幼鸟占比（4/12）低于本土幼鸟（7/8）。本研究得出结论：若幼年小斑海雕能在出发时选择恰当时机，与沿途具备迁徙经验的成鸟结伴，则其习得战略性东南迁徙通道的概率将大幅提升。目前仍无法阐明移地放飞幼鸟提前出发的原因。无论如何，截至当年年末，绝大多数幼鸟均已死亡——无论是移地放飞组（10/12）还是本土对照组（6/8）均未幸免。因此，即便存活的移地放飞幼鸟数量极少，其仍在2009年为德国小斑海雕种群的年度繁殖成功率带来了显著提升。