Orientation of native versus translocated juvenile lesser spotted eagles (Clanga pomarina) on the first autumn migration

Abstract

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 eight native juveniles and nine native adults, to determine how inexperienced birds come to use strategic migration routes. Native juveniles departed around the same time as the adults and six of eight 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 five travelled 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.

Accounting for differential migration strategies between age groups to monitor raptor population dynamics in the eastern Black Sea flyway

“…, Meyburg et al . ). Indeed, even though passage of juvenile Booted Eagle and Short‐toed Eagles started relatively late, most still passed during the peak and late migration period of non‐juveniles.…”

“…Another exception was Lesser Spotted Eagle, where both age groups had a very short but nevertheless strongly overlapping peak migration period. We consider that there is a strong selective advantage for juveniles in all large obligate soaring migrants to synchronize their first autumn migration with adult conspecifics, as this ought to facilitate social learning of safe traditional flyways via geographical bottlenecks (Mellone et al 2011, Oppel et al 2015, Meyburg et al 2017. Indeed, even though passage of juvenile Booted Eagle and Short-toed Eagles started relatively late, most still passed during the peak and late migration period of non-juveniles.…”

“…, Meyburg et al . ), juvenile counts may be indicative of breeding productivity and serve as an early‐warning system for impending population change (Bednarz et al . , Wright ).…”

“…For species that strongly depend on overland flyways for survival, i.e. the largest obligate soaring migrants (Oppel et al 2015, Meyburg et al 2017, juvenile counts may be indicative of breeding productivity and serve as an early-warning system for impending population change (Bednarz et al 1990, Wright 2016. In many other cases, however, juvenile long-distance migrants depart later and migrate slower and over a broader front than elder conspecifics (Kjell en 1992, Maransky & Bildstein 2001, Sergio et al 2014.…”

Dynamics of the energy seascape can explain intra-specific variations in sea-crossing behaviour of soaring birds

“…While first-year migrant birds generally suffer high mortality [34, 35] and juvenile soaring migrants are unlikely to survive long sea-crossings [36, 37], juvenile honey buzzards have high survival while migrating over the Mediterranean Sea [24]. Juvenile honey buzzards on their first autumn migration travel alone or in small flocks and are likely to have inferior soaring abilities compared to adults.…”