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

Bernd-U Meyburg,Ugis Bergmanis,Christiane Meyburg,Kai Graszynski,Wouter M G Vansteelant,Torsten Langgemach,Arno Hinz,Ingo Börner

doi:10.1242/jeb.148932

Abstract

ABSTRACTThe 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.

Highlights

The advent of satellite telemetry and GPS tracking sparked a new age of discovery in animal ecology (Kays et al, 2015)
As Thorup et al (2010) argued: ‘how else could one account for the complex routes, such as those used by juvenile Eleonora’s falcons Falco eleonorae travelling to a restricted wintering range in Madagascar, in the absence of experienced elders (Gschweng et al, 2008)?’ besides cranes and geese, most social migrants do not travel in family groups, and so it remains unclear how long after dispersal it takes for naive juveniles to encounter elder conspecifics, what they do in the absence of elder guides and how social learning affects their survival
Translocated and native juvenile lesser spotted eagles (LSE) departing from Germany only managed to locate the southeastern flyway if they departed during the main migration period of native adults

Summary

Introduction

The advent of satellite telemetry and GPS tracking sparked a new age of discovery in animal ecology (Kays et al, 2015). Sometimes requiring accurate navigation toward crucial stop-over and staging sites, may be explained to some extent by relatively simple, genetically determined migration programs that involve one or more bouts of vector-based navigation (Berthold and Terrill, 1991; Mouritsen and Mouritsen, 2000), and some simple behavioural rules, such as aversion to crossing open water and other barriers (Erni et al, 2003; Hake et al, 2003; Kerlinger, 1985; Meyer et al, 2000; Thorup et al, 2003) Such simple mechanisms may be relevant for nocturnally migrating passerines and other solitary migrants. As Thorup et al (2010) argued: ‘how else could one account for the complex routes, such as those used by juvenile Eleonora’s falcons Falco eleonorae travelling to a restricted wintering range in Madagascar, in the absence of experienced elders (Gschweng et al, 2008)?’ besides cranes and geese, most social migrants do not travel in family groups, and so it remains unclear how long after dispersal it takes for naive juveniles to encounter elder conspecifics, what they do in the absence of elder guides and how social learning affects their survival

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