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尚未明确。本研究依托异地放归（translocation）与卫星追踪技术，针对幼年小斑海雕（Lesser Spotted Eagle, LSE）（学名：Clanga pomarina）的迁徙定向行为展开调查。2004年至2016年间，研究人员人工繁育了85只第二孵出的幼雏（Abels），用于放归至种群数量持续衰减的德国小斑海雕种群中，其中50只个体从拉脱维亚异地放归至940公里外的德国境内。2009年，研究人员对12只异地放归幼鸟、8只本土幼鸟及9只本土成鸟进行卫星追踪，以探究无迁徙经验的个体如何习得战略性迁徙路线。本土幼鸟的启程时间与成鸟大致同步，8只幼鸟中有6只选择了地中海东侧的迁徙通道，而成鸟群体均使用该通道。与之形成鲜明对比的是，异地放归幼鸟的平均启程时间较本土小斑海雕早6天，其中5只个体向南飞行后死于地中海中部区域。据此，成功抵达非洲的异地放归幼鸟占比（4/12）低于本土幼鸟（7/8）。本研究得出结论：若幼年小斑海雕在启程时选择适宜时机，于出发时与具有迁徙经验的成鸟群体汇合，则其习得战略性东南迁徙通道的概率将大幅提升。目前尚无法解释异地放归幼鸟为何会提前启程。无论成因如何，截至当年年末，绝大多数幼鸟均已死亡——无论其是否为异地放归个体（放归组10/12死亡，本土组6/8死亡）。尽管异地放归幼鸟的存活个体数量极少，但这仍代表2009年德国小斑海雕种群的年度繁殖成效得到了显著提升。