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.

Satellite tracking data of juvenile and adult eaglesLesser Spotted Eagles were tracked by means of GPS-enhanced satellite telemetry (Microwave Telemetry, Inc., Columbia, MD, USA) during their autumn migration until the end of the year in 2009. Migration data were obtained for 11 juvenile Lesser Spotted Eagles after they were translocated from Latvia to Germany as well as for 8 juveniles and 9 adults native to the German population. The file contains the columns 'Bird' containing the number of the tracking device, 'Origin' showing whether the bird originated from Latvia ('L') or Germany ('GE'), 'Age' indicating whether the bird was tagged as an adult or as a juvenile, and the columns 'Latitude', 'Longitude', 'Datetime'.Meyburg-etal-JEXBIO-Dryad.xlsx